Benoît Escrig
email: escrig@enseeiht.fr

Outage Probability of an Optimal Cooperative MAC Protocol in Nakagami-m Channels

A new cooperative access protocol is presented in the context of IEEE 802.11-based fixed ad hoc networks. The protocol achieves optimal diversity-multiplexing tradeoff thanks to two known functionalities: on-demand cooperation and selection of the best relay. The on-demand approach allows maximization of the spatial multiplexing gain. The selection of the best relay allows maximization of the spatial diversity order. The main contribution of this paper consists in the design of a proactive mechanism in order to select the best relay. The mechanism is centralized at the destination terminal. Destination terminals maintain lists of relays for all possible source terminals by overhearing ongoing transmissions. So when cooperation is needed, a destination terminal just picks the best relay for a specific source terminal in the corresponding table. Hence, collision among relay candidates is now avoided. Moreover, only terminals that can improve the direct transmission are selected. This guarantees the usefulness of relaying. This study focusses on Nakagami-m wireless channel models in order to encompass a wide variety of fading models.

I. INTRODUCTION

Cooperative communications offer an efficient means to make wireless communications more robust to link failures since they provide more optimization opportunities than a simple retransmission mechanism. Spatial diversity is the main property obtained with cooperative communications since one or several relay terminals are helping the transmission between a source terminal S and a destination terminal D (see Fig. 3). However, this property comes at the price of additional bandwidth (and energy) consumption needed for both relay selection and relay transmission 1 . Bandwidth can be expressed in time slots, frequency bands, spreading codes or space time codes. In this context, cooperation techniques are usually compared using the Diversity-Multiplexing Tradeoff (DMT) [START_REF] Zheng | Diversity and multiplexing: A fundamental tradeoff in multiple antenna channels[END_REF]- [START_REF] Hunter | Diversity through coded cooperation[END_REF]. The DMT analysis of a transmission scheme yields the diversity gain d(r) achievable for a multiplexing gain r (see Fig. 1). A transmission scheme is said to have a spatial multiplexing gain r and a diversity gain d(r) if the spectral efficiency R scales like r log 2 SN R, and the outage probability decays like 1/SN R d (r) , where SN R denotes the effective signal to noise ratio at the receiver. A protocol achieves an optimal DMT curve when it maximizes both the diversity gain d(r) and the multiplexing gain r, i.e. when the protocol achieves a target outage probability with both the lowest transmitted power and the lowest bandwidth consumption.

When a single relay terminal is involved in a cooperation scenario, an optimal DMT curve can be obtained using ondemand relaying [START_REF] Laneman | Cooperative diversity in wireless networks: efficient protocols and outage behavior[END_REF]. In an on-demand relaying scenario, the relay terminal is transmitting only when the destination terminal asks for cooperation. In [START_REF] Azarian | On the achievable diversity-multiplexing tradeoff in half-duplex cooperative channels[END_REF], other optimal DMT curves have been established when no feedback to the transmitting terminal is allowed. The optimal DMT curve is given by d(r) = 2(1r) for 0 ≤ r ≤ 1 (see Fig. 1). Even if the DMT Fig. 1. DMT curves of a direct transmission and three cooperative protocols involving one relay terminal: fixed amplify-and-forward (AF), selective decode-and-forward (DF), and on-demand relaying [START_REF] Laneman | Cooperative diversity in wireless networks: efficient protocols and outage behavior[END_REF].

curve is optimal, the diversity is limited to a value of two. To increase the diversity gain, several relay terminals should be considered.

When (N -1) relay terminals are involved in a cooperative scenario, a diversity order of N can be achieved (see Fig. 2). When a repetition scheme is implemented at the relay terminals, relay terminals are just repeating the source message. So the multiplexing gain is limited to the value of 1/N . The DMT curve is: d(r) = N (1 -Nr) for 0 ≤ r ≤ 1/N . The value of r can be increased to 1/2 using space-time coding (STC) [START_REF] Laneman | Distributed spacetime-coded protocols for exploiting cooperative diversity in wireless networks[END_REF]. The DMT curve is then: d(r) = N (1 -2r) for 0 ≤ r ≤ 1/2. An alternative solution has been proposed in [START_REF] Bletsas | A simple cooperative diversity method based on network path selection[END_REF]. The solution is based on the selection of the best relay terminal among the set of (N -1) relay candidates. When only the best relay terminal is transmitting the source message, the DMT curve is the same as the previous one and less resources are needed to implement the cooperation scheme (allocating space-time codes to the relay terminals). However, even if the spatial diversity order is N , the spatial multiplexing gain r is still limited to the value of 1/2. An optimal DMT curve can be achieved by implementing both ondemand relaying and the selection of the best relay terminal: d(r) = N (1r) for 0 ≤ r ≤ 1. This optimal DMT curve can be achieved using either a fixed Amplify-and-Fig. 2. DMT curves of protocols using (N -1) relay terminals: the fixed AF protocol using a repetition scheme at the relay terminals (Repetition) [START_REF] Laneman | Cooperative diversity in wireless networks: efficient protocols and outage behavior[END_REF], the fixed AF protocol implementing space-time coding (STC) [START_REF] Laneman | Distributed spacetime-coded protocols for exploiting cooperative diversity in wireless networks[END_REF], the AF protocol based on the selection of the best relay terminal (Selection of the Best Relay Terminal) [START_REF] Bletsas | A simple cooperative diversity method based on network path selection[END_REF], and the optimal DMT curve (Optimal DMT Curve) [START_REF] Bletsas | Opportunistic cooperative diversity with feedback and cheap radios[END_REF], [START_REF] Escrig | On-Demand Cooperation MAC Protocols with Optimal Diversity-Multiplexing Tradeoff[END_REF].

Forward (AF) transmission scheme [START_REF] Bletsas | Opportunistic cooperative diversity with feedback and cheap radios[END_REF], [START_REF] Escrig | Optimal Cooperative MAC Protocol for IEEE 802.11-based Mesh Networks[END_REF] or a selective Decode-and-Forward (DF) transmission scheme [START_REF] Escrig | On-Demand Cooperation MAC Protocols with Optimal Diversity-Multiplexing Tradeoff[END_REF], [START_REF]DMT Optimal On-Demand Relaying for Mesh Networks[END_REF]. In the proposed protocols, cooperation is activated when the destination terminal fails in decoding the source message. A selection of the best relay is then undertaken. Once selected, the best relay forwards the source message to the destination terminal. The selection of the best relay terminal is the weak point of these optimal protocols since the selection process is a distributed mechanism. Indeed, the selection consists of two steps. During the first step, several terminals may select themselves as best relay terminals. This self selection is based on channel metrics between the relay and both end terminals. Then, during a second step, the relay terminals try and signal their presence to other terminals [START_REF] Bletsas | A simple cooperative diversity method based on network path selection[END_REF], [START_REF] Chou | Cooperative mac protocol with automatic relay selection in distributed wireless networks[END_REF]. Since there is no coordination among the relay candidates, collisions among relay terminals are not avoided. Collisionfree selection algorithms have been proposed in the context of fixed ad-hoc networks [START_REF] Azgin | Cooperative mac and routing protocols for wireless ad hoc networks[END_REF]. However, these algorithms have not been designed with the purpose of optimizing both the DMT of the cooperative protocol and the signaling needed to select the relays. A last limitation should be pointed out. In previous approaches, a terminal is always selected as best relay terminal, even if this terminal cannot improve the direct transmission between the source terminal S and the destination terminal D. Cooperative protocol designs should take this limitation into account. In other words, the relevance and the efficiency of cooperation schemes should be guaranteed.

In order to tackle these issues, we propose a new cooperative MAC (Medium Access Control) protocol. We call this protocol OXIDE: an On-demand Cooperation with a Selection of relays Initiated by the Destination Equipment. The main contribution of this paper consists in the design of a proactive mechanism in order to select the best relay. In our proposed protocol, each destination terminal maintains a table of potential relay terminals that can assist in its decoding by overhearing ongoing transmissions [START_REF] Liu | Coopmac: A cooperative mac for wireless lans[END_REF]. Each destination terminal maintains a table for each source terminal. When a source terminal sends a message, all the terminals in the range of the source terminal store the data frame and wait for an acknowledgment from the destination terminal. When the destination succeeds in decoding the source message, it transmits a positive acknowledgment and all the terminals in the range of the source terminal discard the source message. When the destination terminal fails in decoding the source message, it looks for a potential relay terminal in the table associated with the source terminal. When a relay terminal is successfully found, the destination terminal sends a negative acknowledgment for the source message with the address of the selected relay in a specific field. All the terminals in the range of the source terminal discard the source message except the selected terminal that retransmits the source message. When there are no relay available, or when the negative acknowledgment is not successfully decoded by the selected relay, the source terminal retransmits its message. This protocol guarantees efficient cooperation. Indeed, destination terminals use the negative acknowledgment frame only when they find terminals that can improve their transmissions. The selection mechanism is centralized at destination terminals. So collision among relay candidates is now avoided [START_REF] Bletsas | A simple cooperative diversity method based on network path selection[END_REF], [START_REF] Bletsas | Opportunistic cooperative diversity with feedback and cheap radios[END_REF], [START_REF] Chou | Cooperative mac protocol with automatic relay selection in distributed wireless networks[END_REF]. In particular, the problem of hidden groups of relays is avoided. The proposed protocol is optimal in terms of the DMT criterion since it implements the two basic functionalities: on-demand cooperation and selection of a best relay terminal. Moreover, the protocol relies on a selective DF transmission scheme since this scheme is more efficient than the fixed AF scheme in terms of outage probability [START_REF] Bletsas | Opportunistic cooperative diversity with feedback and cheap radios[END_REF], [START_REF] Escrig | On-Demand Cooperation MAC Protocols with Optimal Diversity-Multiplexing Tradeoff[END_REF], [START_REF]DMT Optimal On-Demand Relaying for Mesh Networks[END_REF]. The protocol recommends also that the destination terminal discards the source message when D fails in decoding the data transmitted by S. Hence, the destination terminal does not need to allocate resources to the signal/frame combination.

Finally, we consider Nakagami-m fading channels in order to encompass a variety of fading models followed in the literature. Classical Rayleigh fading model corresponds to the case m = 1 while the Rice fading model corresponds to the case m = (κ+1) 2 /(2κ+1) > 1, where κ is the Ricean factor.

This new MAC protocol relies on the IEEE 802.11 standard. Though restricted to the context of fixed ad hoc networks in this paper, this protocol can also be applied to other wireless architectures such as broadcast wireless systems. We believe that our proposal can benefit the delivery of broadband services in several contexts since it provides an efficient transmission scheme in terms of both bandwidth and energy consumption.

The cooperative MAC protocol is described in details in section II. In section III, we show that this new protocol provides an optimal performance in terms of DMT. Simulation results are presented in section IV and we conclude in section V.

II. ON-DEMAND RELAYING WITH SELECTION OF THE BEST RELAY TERMINAL

A. System model

We consider a slow Nakagami -m fading channel model. Our analysis focuses on the case of slow fading, to capture scenarios in which delay constraints are on the order of the channel coherence time. Coherence time is actually a statistical measure of the time duration over which the channel response is essentially invariant. If the inverse frequency band of the transmitted signal is greater than the coherence time, then the channel will change during the transmission of the message, thus causing distortion at the receiver. A half duplex constraint is imposed across each relay terminal, i.e. it cannot transmit and listen simultaneously. Moreover, transmissions are multiplexed in time, they use the same frequency band. Let h ij be the channel gain between a transmitting terminal i and a receiving terminal j. We consider scenarios in which each fading coefficient h ij is accurately measured by the receiver j, but not known to the transmitter i. We also assume that the channel gain h ij is identical to the channel gain h ji . This assumption is relevant since both channels are using the same frequency band. Statistically, the channel gain h ij between any two pair of terminals i and j is such that |h ji | is distributed according to a Nakagami-m distribution. In particular, the ran-

dom variable |h ij | 2 is gamma distributed with scale parameter θ ij (θ ij > 0) and shape parameter κ ij (κ ij > 0). So, the probability density function f |hij | 2 (x; κ ij , θ ij ) of the random variable |h ij | 2 is f |hij | 2 (x; κ ij , θ ij ) = x κij -1 θ κij ij Γ(κ ij ) exp(- x θ ij )
where Γ(y) denotes the complete gamma function

Γ(y) = ∞ 0 t y-1 exp(-t)dt
Let P be the power transmitted by each terminal and σ2 w be the variance of the Additive White Gaussian Noise (AWGN) in the wireless channel. We define SN R = P/σ 2 w to be the effective signal-to-noise ratio.

We also restrict our study to a single source-destination pair. We assume that there are (N -1) terminals situated in the range of both the source and the destination terminals (see Fig. 3).

B. Protocol Description

We model the protocol by four main tasks: activation of the cooperative transmission mode, collection of cooperation information (CoI), relay selection, and notification of the terminals [START_REF] Escrig | A framework for cooperative communications at the system level[END_REF]. In the following, we review these four tasks.

1) Cooperation Mode Activation:

We assume that all the terminals in the network are implementing the new cooperative MAC protocol. The inter-operability issue will be addressed in future work. We also assume that the cooperation functionality has been turned on. When the source terminal S sends its message, each terminal in the range of S can overhear the transmission. This event triggers the storage of the source message at the relay candidates.

2) CoI Collection: Each terminal maintains a table of terminals, referred to as the Relay-Table . The stored terminals can be used as relays when cooperation is needed. One Relay-Table is maintained for each possible source address. The maintenance of a Relay-Table involves two tasks [START_REF] Liu | Coopmac: A cooperative mac for wireless lans[END_REF]: creation and updating. The two tasks are done by overhearing all ongoing transmissions. This assumes that there is always information to be sent between the terminals. This assumption is consistent since signaling packets must be transmitted repeatedly in order to create and update routes between the terminals. As soon as terminal D overhears a transmission between terminal S and terminal T, terminal T is considered as a potential relay for the transmission between S and D. Hence, whenever terminal T sends a message, terminal D stores the channel state information (CSI) related to the channel between T and D. This CSI can be a channel metric such as SN R|h T D | 2 , where h T D is the channel gain between terminal T and terminal D, and SN R is the signal to noise ratio at the receiver. Since all the terminals use the same frequency band for transmission and reception, the channel between any two terminals is symmetric. So, we assume that h T D equals h DT . The fields contained in the Relay-Table are shown in Fig. 4. Entries are ordered by the timestamp values, based on the last time a frame from that terminal is overheard. The first column in Fig. 4, namely the ID field, stores the MAC address of a potential relay terminal T learned from the data frames transmitted by terminal T. The Time field stores the time of the last frame transmission heard from terminal T. The CSI field stores the channel metric SN R|h T D | 2 from terminal T to the destination terminal. The last field in the table, NbFailures tracks the number of sequential failures associated with the particular terminal T. When this number exceeds a predefined threshold value 2 , the corresponding entry is removed from the Relay-Table . The value of NbFailures is incremented after every failed transmission attempt through terminal T, and this value is reset to zero after a successful transmission through terminal T. Each of these entries is updated to reflect the current channel conditions and status.

I T D > R 2
where I T D denotes the mutual information of cooperation transmission through the channel between T and D and R denotes the spectral efficiency of the direct transmission between S and D. Note that D can compute the spectral efficiency R by knowing the frequency band of the transmission, the duration field in the data frame, and other physical layer parameters, such as the modulation type. Thus, only terminals that can improve a transmission will be selected as relay terminals in a Relay-Table . When selective DF is considered, the mutual information of the cooperative transmission, I T D , is defined as

I T D = 1 2 log 2 (1 + SN R|h T D | 2 )
This expression differs from the one that is usually given

1 2 log 2 (1 + SN R|h SD | 2 + SN R|h T D | 2 )
This is due to the fact that the destination terminal discards the source message in case of a decoding failure. Note that the 1/2 factor comes from the fact that cooperation uses twice the bandwidth. When the Relay-Table has more than one entry, terminal D select the terminal that maximizes the mutual information of the cooperative transmission I T D . Let's denotes this terminal, terminal B (B for Best terminal). 4) Relay Notification: Terminal D notifies the result of the relay selection by sending a negative acknowledgment on the data frame transmitted by terminal S, denoted CFC frame for Claim For Cooperation following [START_REF] Alonso-Zarate | Performance evaluation of a cooperative scheme for wireless networks[END_REF], [START_REF] Gomez | Cooperation on demand protocols for wireless networks[END_REF]. The CFC frame includes the MAC address of terminal B. When terminal B has successfully decoded both the source message and the negative acknowledgment frame from the destination terminal, it retransmits the source message it overheard. When terminal terminal B fails in decoding either the source message or the negative acknowledgment, terminal B remains silent (selective DF forwarding scheme) and S re-transmits its data frame. Note that an extra time-slot is added to the waiting time of terminal S in order to avoid collision between its retransmission and the forwarding of terminal B3 . This time slot equals a SIFS (Short Interframe Space). When D succeeds in decoding the data frame transmitted by either B or S, D sends a positive ACK frame (see Fig. 5). Otherwise, D remains silent and the timeout at the source terminal triggers another retransmission. When the CFC frame is lost, the protocol implements a classical error recovery mechanism. Terminals that have stored the source message, wait for either a positive ACK frame or a CFC frame. If any of these two frames is not received within a given time-slot, the source message is discarded. Terminals that just receive either a positive ACK frame or a CFC frame ignore the signaling frame.

5) Comments on the Protocol Design:

We give here some additional comments on the protocol design:

• RTS/CTS optional access method: Several cooperative MAC protocols rely on the exchange of modified Request-to-Send (RTS) and Clear-to-Send (CTS) signaling frames [START_REF] Chou | Cooperative mac protocol with automatic relay selection in distributed wireless networks[END_REF], [START_REF] Azgin | Cooperative mac and routing protocols for wireless ad hoc networks[END_REF], [START_REF] Liu | Coopmac: A cooperative mac for wireless lans[END_REF]. If CTS frames transmitted by the destination terminal D can be modified, we can infer that channel state information is available at the transmitter. Hence, the source can actually choose not to transmit when it cannot support a given spectral efficiency R. This gives rise to new cooperative protocols, the study of which is left for future work. • NAV modification: The Network Allocation Vector (NAV) values at each terminal should be increased according to the new frame scheduling. In particular, an additional time-slot should be considered when terminal D transmits its CFC frame and waits for a response from either the best relay B or the source terminal S. This should avoid unnecessary soundings by neighboring terminals. • The negative acknowledgement approach: the negative acknowledgment approach assumes that the CRC (Cyclic Redundancy Check) of the source message is wrong whereas the destination address is correct. We guarantee the detection of this case by appending an additional CRC to the control field of the source message. This additional CRC is only dedicated to the detection of erroneous destination addresses. • Error recovery mechanism: A timeout is used at the source terminal to avoid blocking states. In particular, as soon as a frame is missing or when the set of relay is empty, the protocol returns to its starting point according to a given timeout.

C. Transmission Algorithm

The flow charts at the source terminal S, the destination terminal D, and a potential relay terminal T are depicted in Fig. 6 to 8.

1) Source Terminal S:

• S waits for data to send. As soon as S has data to send, S enters the subsequent step. • S sends the data frame and triggers a timeout.

• When no acknowledgment frame (positive or negative) has been successfully received by S before the timeout, S goes to the previous step. Otherwise, S proceeds to the next step. • S tests whether it has received a positive acknowledgment frame ACK or a negative acknowledgment frame CFC.

-When S receives an ACK frame, it goes back to the first step. -When S receives a CFC frame, it adjusts its timer according to a new timeout in order to take into account the transmission of the best relay. Then, S waits for a positive acknowledgment frame ACK from D.

• When S successfully receives a positive acknowledgment frame ACK from D, it proceeds to the first step. Otherwise, it retransmits the data frame.

2) Destination Terminal D:

• A flag bit F is defined and set to 0.

-When set to 0, the flag indicates that D is waiting a data frame from a source terminal. -When set to 1, the flag indicates that D waits for the same data frame transmitted by the best relay terminal.

• Whenever D receives a data frame from a source terminal S, it checks the CRC. • When the data frame passes the CRC check, the flag F is set to 0 and the data frame is sent to upper layers. Otherwise, the flag F is checked.

-When the flag is 1, a CFC frame has already been sent. So, D remains silent and waits for a retransmission of the data frame. -When the flag is 0, D checks the additional CRC on the destination address field. When the additional CRC is correct, D sends a negative acknowledgment frame CFC. Otherwise, D remains silent and goes back to a waiting state.

3) Potential Relay T:

• Whenever T successfully overhears and decodes a data frame from a terminal S, it stores the data frame and waits for an acknowledgment frame from D. • As soon as T successfully decodes an acknowledgment frame from D before a timeout, it checks whether it received a positive acknowledgment frame ACK or a negative acknowledgment frame CFC. Otherwise, it discards the data frame and goes back to a waiting state.

-When T receives an ACK frame, it discards the data frame from S and goes back to a waiting state. -When T receives a CFC frame, it sends the data frame from S, then discards the data frame and goes back to a waiting state.

III. PERFORMANCE ANALYSIS OF THE OXIDE PROTOCOL

A. DMT Analysis of the Cooperative Protocol

In this section, we study the DMT curve of the OXIDE protocol. We characterize our channel models using the system

y SD (n) = h SD x(n) + w SD (n) y SB (n) = h SB x(n) + w SB (n)
for n = 1, 2, ..., T M /2, where T M denotes the duration of time-slots reserved for each message. When terminal D succeeds in decoding the data frame from S, no signal is transmitted by the best relay terminal B. Otherwise, the best relay terminal sends a new signal using a selective DF scheme, i.e. if and only if it has been able to decode the source message. So we consider that the estimation of signal x(n), denoted x(n), is error free. Hence, during the second time slot, D is receiving a signal from B

y BD (n) = h BD x(n) + w BD (n), if I SB > R 0, if I SB ≤ R
for n = T M /2 + 1, ..., T M , where the mutual information I SB is given by

I SB = log 2 (1 + SN R|h SB | 2 )
The noise w ij (n) between transmitting terminal i and receiving terminal j are all assumed to be i.i.d. circularly symmetric complex Gaussian with zero mean and variance σ 2 w . Symbols transmitted by the source terminal S are denoted x(n). For simplicity, we impose the same power constraint at both the source and the relay: E[|x(n)| 2 ] ≤ P . We assume that the source and the relay each transmit orthogonally on half of the time-slots. We also consider that a perfect synchronization is provided at the block, carrier, and symbol level.

We define the diversity gain d OXIDE (r) of the OXIDE protocol by

d OXIDE (r) = lim SNR→∞ - log[p out OXIDE (SN R, r)] log(SN R)
The probability p out OXIDE (SN R, r) is the outage probability for a signal to noise ratio SN R and a spatial multiplexing gain r defined by

r = lim SNR→∞ R log 2 (SN R)
where R is the spectral efficiency of the direct transmission (in b/s/Hz). For high SN R values, we use

R = r log 2 SN R (1)
The event that the relay has successfully decoded the data transmitted by S with a spectral efficiency R is equivalent to the event that the mutual information of the channel between S and the best relay B, I SB , lies above the spectral efficiency R [START_REF] Laneman | Distributed spacetime-coded protocols for exploiting cooperative diversity in wireless networks[END_REF], [START_REF] Bletsas | A simple cooperative diversity method based on network path selection[END_REF]. When (N -1) terminals are available, the OXIDE protocol is in outage if all the (N -1) relay candidates fail in improving the direct transmission

p out OXIDE (SN R, r) = Pr[I SD ≤ R] (2) × Pr[ N -1 i=1 (I (i) OXIDE ≤ R 2 )|I SD ≤ R]
where

I (i)
OXIDE is the mutual information of the relayed transmission using selective DF cooperation scheme at terminal R i and implementing frame dropping at the destination terminal (the source message is discarded at the destination terminal when cooperation is needed)

I (i) OXIDE = 1 2 log 2 (1 + SN R|h SD | 2 ), if I SRi ≤ R 1 2 log 2 (1 + SN R|h RiD | 2 ), if I SRi > R
where the mutual information I SRi is defined by

I SRi = log 2 (1 + SN R|h SRi | 2 )
and the mutual information I SD is defined by

I SD = log 2 (1 + SN R|h SD | 2 )
The probability p out OXIDE (SN R, r) can be expressed as the sum of 2 (N -1) terms

p out OXIDE (SN R, r) = 2 (N -1) j=1 P j
where P j is given by

P j = P E j N -1 i=1 Pr[ (i) j ] (3)
where

P E j = Pr[I D ≤ R] × Pr{ N -1 i=1 [I (i) OXIDE ≤ R 2 |( (i) j , I SD ≤ R)]}
The event (i) j equals the event I SRi ≤ R or I SRi > R according to the value of index j, 1 ≤ j ≤ 2 (N -1) . The probability P j in (3) is constituted with N components. The first component P E j is the probability denoted in (2) where each value of

I (i)
OXIDE is conditioned to the value of I SRi . The (N -1) last terms in the product exhibit the probabilities that the I SRi are above or beyond the threshold R, for 1 ≤ i ≤ (N -1). We assume that there are N j passive relay terminals such that k j = [I SR k ≤ R] in P j . We define the set K j such that

K j = {k/ (k) j = [I SR k ≤ R], 1 ≤ k ≤ (N -1)}
with cardinality |K j | = N j . Thus, there are (N -1) -N j active relay terminals such that

(l) j = [I SR l > R] in P j . We define the set L j such that L j = {l/ (l) j = [I SR l > R], 1 ≤ l ≤ (N -1)} with cardinality |L j | = (N -1) -N j . Note also that 0 ≤ N j ≤ (N -1)
. So, we have that

P E j = Pr[I D ≤ R] × Pr{ k∈Kj [I (k) OXIDE ≤ R 2 |( (k) j , I SD ≤ R)], l∈Lj [I (l) OXIDE ≤ R 2 |( (l) j , I SD ≤ R)]} (4)
For the N j passive relay terminals, we have that

I (k) OXIDE ≤ R 2 | (k) j ⇐⇒ I (k) OXIDE ≤ R 2 |I SR k ≤ R ⇐⇒ I SD ≤ R So, we have that Pr[(I (k) OXIDE ≤ R 2 | (k) j )|I SD ≤ R] = 1
Moreover, we have that Pr[

(k) j ] = Pr[I SR k ≤ R] = Pr[log 2 (1 + SN R|h SR k | 2 ) ≤ R]
For the (N -1) -N j active relay terminals, we have that

I (l) OXIDE ≤ R 2 | (l) j ⇐⇒ I (l) OXIDE ≤ R 2 |I SR l > R ⇐⇒ log 2 (1 + SN R|h R l D | 2 ) ≤ R 2 and
Pr[

(l) j ] = Pr[I SR l > R]
For high SN R values, we have a simpler expression for ( 4)

P E j = Pr[log 2 (1 + SN R|h SD | 2 ) ≤ R] × Pr{ l∈Lj [log 2 (1 + SN R|h R l D | 2 ) ≤ R]}
The |h R l D | 2 random variables being mutually independent, we have that

P E j = Pr[|h SD | 2 ≤ SN R r-1 ] × l∈Lj Pr[|h R l D | 2 ≤ SN R r-1 ]
using (1) The random variables |h SR k | 2 and |h R l D | 2 being mutually independent, we have that

N -1 i=1 Pr[ (i) j ] ≤ k∈Kj Pr[|h SR k | 2 ≤ SN R r-1 ] (5)
So, using (5), we have that

P j ≤ Pr[|h SD | 2 ≤ SN R r-1 ] × l∈L Pr[|h R l D | 2 ≤ SN R r-1 ] (6)
× k∈K Pr[|h SR k | 2 ≤ SN R r-1 ]
The random variables

|h SD | 2 , |h R l D | 2 for l ∈ L j , and |h SR k | 2
for k ∈ K j are all gamma distributed variables. Let |h| 2 be one of these random variables, with shape parameter κ. From Lemma 2 in [START_REF] Bletsas | Opportunistic cooperative diversity with feedback and cheap radios[END_REF], we have that

lim SNR→∞ log{Pr[|h| 2 ≤ SN R r-1 ]} log(SN R) = κ(r -1) (7)
So, using ( 7) in ( 6), we have that 1) , where κ ij is the shape parameter or the random variable |h ij | 2 , where i (resp. j) denotes the transmitting (resp. receiving) terminal. For 1 ≤ i ≤ (N -1), we define κ i = min{κ SRi , κ RiD }. So, we have that

lim SNR→∞ log[P j ] log(SN R) = (κ SD + k∈Kj κ SR k + l∈Lj κ R l D )(r -1) for every j, 1 ≤ j ≤ 2 (N -
lim SNR→∞ log[P j ] log(SN R) ≥ (κ SD + N -1 i=1 κ i )(r -1)
So, we have that

lim SNR→∞ - log[p out OXIDE (SN R, r)] log(SN R) ≥ (κ SD + N -1 i=1 κ i )(1 -r)
Hence, the diversity curve d OXIDE (r), i.e. the DMT of the OXIDE protocol, is lowerbounded by the following expression

d OXIDE (r) ≥ (κ SD + N -1 i=1 κ i )(1 -r) (8)
For the special case of Rayleigh fading, i.e κ SD = κ i = 1 for 1 ≤ i ≤ (N -1), we have that

d OXIDE (r) = N (1 -r)
So, when there are (N -1) potential relay terminals, the Fig. 9. DMT curve of three protocols : the OXIDE protocol, the direct transmission, and the on-demand cooperation with one relay terminal [START_REF] Laneman | Cooperative diversity in wireless networks: efficient protocols and outage behavior[END_REF]. For the special case of Rayleigh fading,

κ SD + N -1 i=1 κ i = N .
OXIDE protocol achieves the optimal DMT curve reaching the two extremes points d(0) = N and d(1) = 0 (see Fig. 2). Note that the only information provided by the DMT curve is that the data rate of the overall transmission scales like a direct transmission, even in presence of a cooperative relaying.

In particular, the overheard induced by the additional signaling frames (CFC, etc) does not appear in [START_REF] Bletsas | A simple cooperative diversity method based on network path selection[END_REF] because the DMT analysis is just providing a rough estimate of the achieved multiplexing gain r, not a precise value. In particular, the spatial multiplexing gain scales like 1. This results is consistent with the one obtained with other on-demand cooperation techniques [START_REF] Laneman | Cooperative diversity in wireless networks: efficient protocols and outage behavior[END_REF].

B. Spectral Efficiency Analysis

We have studied the performance of the proposed protocol in terms of outage probability. We have shown that the OXIDE protocol achieves optimal performance in terms of DMT. We now compute the spectral efficiency of the OXIDE protocol and compare it to one of other existing protocols. The spectral efficiency of the protocol is the ratio between the data rate and the bandwidth used by the protocol in order to achieve the data rate. Let R denote the spectral efficiency of the direct transmission between terminals S and D. The effective spectral efficiency of the OXIDE protocol is R

R = R × Pr[I SD > R] + R 2 × Pr[I SD ≤ R] ( 9
)
where the mutual information of the direct transmission, I SD , is defined in (3). Equation ( 9) follows from the fact that the OXIDE protocol operates at spectral efficiency R when the direct transmission is successful, and operates at spectral efficiency R/2 when a cooperative transmission is needed [START_REF] Laneman | Cooperative diversity in wireless networks: efficient protocols and outage behavior[END_REF].

Using the expression of I SD , we have that

Pr[I SD ≤ R] = Pr[log 2 (1 + SN R|h SD | 2 ) ≤ R] = Pr[|h SD | 2 ≤ 2 R -1 SN R ]
For Nakagami-m fading with m = 1 (Rayleigh fading), |h SD | 2 is exponentially distributed with parameter σ 2 . So, we have that

Pr[I SD ≤ R] = 1 -exp(- 1 σ 2 2 R -1 SN R )
Using the above expression in (9), we have that

R = R 2 [1 + exp(- 1 σ 2 2 R -1 SN R )]
So the effective spectral efficiency R of the OXIDE protocol tends toward R when the effective signal-to-boise ratio SN R tends towards infinity. Fig. 11 shows several curves of R as a function of the signal-to-noise ratio SN R for a given spectral efficiency (R = 1) and several values of parameter σ 2 . We note that a given spectral efficiency R can arise from several possible spectral efficiency R, depending upon the value of the signal-to-noise ratio SN R. In that case, the lowest spectral efficiency R should be considered (see Fig. 10).

IV. SIMULATION RESULTS

For simulation purposes, we consider a single sourcedestination pair. We assume that there are (N -1) terminals available for cooperation in the range of both source and destination terminals, i.e. they all implement the cooperation functionality. We assume slow fading Nakagami-m channels with m = 1 (Rayleigh fading) between each pair of terminals, with equal variance: σ 2 = 1. The channel gains are assumed to be known at the receiver side. Each channel gain has a constant value during the transmission of a frame and this value may change from one frame to another. Fig. 12 shows the simulation results for several values of the signal-to-noise ratio SN R and for several values of N , the number of transmitting terminals. Each simulation has been run until a hundred of outage events occurred. For large SN R values, the slopes of the curves indicate that the spatial diversity order of the transmission scheme increases with the number of relays. Moreover, the slope of each curve equals the number of transmitting terminals: N . So, it can be deduced from Fig. 12 that the OXIDE protocol achieves full diversity order. This result is consistent with the expression of the DMT curve in [START_REF] Bletsas | Opportunistic cooperative diversity with feedback and cheap radios[END_REF]. Note that when a target outage probability is set to 3.10 -2 , a 10 dB margin is achieved on the received SN R by the cooperative scheme with 3 relays compared to the direct transmission. This margin reduces to 7 dB when a one-relay cooperation scheme is considered.

We now compare the outage probability of four transmission schemes: the direct transmission (D), the on-demand AF relaying with one relay (OAF) [START_REF] Laneman | Cooperative diversity in wireless networks: efficient protocols and outage behavior[END_REF], the on-demand AF relaying with non collision-free selection of relays (OABF) [START_REF] Bletsas | Opportunistic cooperative diversity with feedback and cheap radios[END_REF], and the OXIDE protocol. The OAF protocol implements on-demand relaying with one single relay terminal. The diversity order of this transmission scheme should be 2. The OABF implements also on-demand relaying. Moreover, this protocols implements a non collision-free selection of the best relay terminal. This protocol should achieve a full diversity order, i.e. a diversity order of N , the number of transmitting terminals. We assume slow fading Nakagami-m channels between each pair of terminals, with equal variance: σ 2 = 1. The channel gains are assumed to be known at the receiver. To ensure fair comparison, the OAFB and the OXIDE protocols use the same number of relay candidates (N -1). As Fig. 13 indicates, all the presented protocols achieve full diversity. the direct transmission achieves a full diversity order or 1 since there is only one transmitter. The OAF protocols achieves a diversity order of 2 because there are exactly two transmitting terminals: the source and the relay. The OAFB and the OXIDE protocols achieve full spatial diversity of order N , the number of cooperative terminals, for sufficiently large SN R. In other words, the outage probability of these protocols scales like 1/SN R N where N is the number of transmitting terminals. Moreover, the new OXIDE protocol achieves a better outage probability because it uses a selective DF transmission scheme instead of a fixed AF one.

V. CONCLUSION

A new cooperative MAC protocol, the OXIDE protocol, has been proposed in the context of IEEE 802.11-based fixed ad hoc networks. This protocol implements an on-demand cooperative transmission between a source terminal S and a destination terminal D. When the destination terminal fails in decoding the source message, the destination terminals asks for cooperation using a signaling frame. The frame includes the MAC address of the best relay that can help the transmission between S and D. Indeed, each destination terminal maintains a table of potential relays, the Relay- about terminal T is gathered by terminal D in two steps: overhearing transmissions between S and T, and receiving frames from T. Hence, when cooperation is needed and the Relay-Table related to S is not empty, a relay is successfully found in the cooperation table. The MAC address of the relay is included in the signaling frame asking for cooperation. When the best relay has successfully received the source message, it retransmits the data toward D according to a selective DF scheme. The main contribution of this paper consists in the implementation of a DMT optimal MAC protocol using a collision-free mechanism to select the best relay. Moreover, only terminals that can improve transmissions between S and D are considered. This property guarantees efficient and useful cooperation. Hence, when (N -1) terminals are situated in the range of both a source terminal S and a destination terminal D, a spatial diversity gain of N is provided while a spatial multiplexing gain of one is achieved. Thus, the protocol implements a DMT optimal transmission scheme.

The impact and the performance of cooperative transmissions have been evaluated at the level of a single link between a source terminal and a destination terminal. The impact of cooperative communications should now be assessed at the network level. Indeed, as cooperative communications involve more then two terminals (the source terminal and the destination terminal), the contention area is increased when one or several terminals must forward the source message. So the overall throughput of the network may be affected by the implementation of the OXIDE protocol. A detailed analysis of this point is currently in progress. Moreover, the traffic load generated by cooperative transmissions at a relay terminal depends on the actual position of the terminal. When a terminal is often relaying because it has a central location in the network, energy consumption and billing issues must then be addressed. These issues ask for cross-layer designs, the study of which is left for future work.

Fig. 3 .

 3 Fig. 3. Cooperation scenario with four relay candidates: (N -1) = 4.

Fig. 4 .

 4 Fig. 4. Format of the Relay-Table for terminal D.

3 )

 3 Relay Selection Algorithm: When terminal D succeeds in decoding the data frame, terminal D sends a positive acknowledgment frame (ACK). Otherwise, D discards the data frame. This allows processing optimization at the destination terminal without sacrificing the optimality of the DMT. Terminal D searches for a relay terminal in the Relay-

Fig. 5 .

 5 Fig. 5. Frame exchange sequence in the OXIDE protocol using the basic IEEE 802.11 access method (S is the source terminal, D is the destination terminal, B is the best relay terminal, and T is a relay candidate). The top figure represents the case when D succeeds in decoding the data frame from S. The middle figure represents the case when D asks for cooperation and B is relaying. The bottom figure represents the case when the cooperation fails and S must retransmit its frame.

Fig. 6 .

 6 Fig. 6. Flow chart at the source terminal S.

Fig. 7 .

 7 Fig. 7. Flow chart at the source terminal D.

Fig. 8 .

 8 Fig.8. Flow chart at a potential relay R.

Fig. 10 .

 10 Fig. 10. Effective Spectral Efficiency R of the OXIDE protocol vs Spectral Efficiency R for several values of the signal-to-noise ratio SNR.

Fig. 11 .

 11 Fig. 11. Effective Spectral Efficiency R of the OXIDE protocol vs Signal to Noise Ratio SNR (R = 1).

Fig. 12 .

 12 Fig. 12. Outage performance of direct transmission (0 relay) and cooperative transmissions using the OXIDE protocol (1, 2, and 3 relays).

Fig. 13 .

 13 Fig. 13. Outage performance of noncooperative and cooperative protocols (N = 4): direct transmission (D), on-demand AF relaying with one relay (OAF), on-demand AF relaying with selection of the best relay terminal (OAFB), and OXIDE protocol (OXIDE).

  Table dedicated to terminal S. In order to select useful relay terminals, a terminal D should select a terminal T in its Relay-Table if terminal T satisfies

  Table, one table for each source address. The maintenance of a Relay-Table is done by overhearing ongoing transmissions. In particular, information

Throughout this paper, we use bandwidth as a general term for resource in a communication network.

The recommended value in[START_REF] Liu | Coopmac: A cooperative mac for wireless lans[END_REF] is

Note that the source terminal does not need to overhear the CFC frame from D. Its retransmission is triggered by a given timeout.


Odile Blanchard

The Bush Administration's Climate Proposal: Rhetoric and Reality?

In February 2002, nearly a year after rejecting the Kyoto Protocol, President Bush unveiled his long-awaited "Global Climate Change Initiatives". A year further on, the proposal has acquired enough content and clarity to sort through the context, rhetoric and reality, which is

The Bush Administration's wait-and-see climate proposal

The Bush Administration's climate policy can be looked at in a few ways: a timeline that chronicles the climate-related public statements of Candidate-turned-President G.W. Bush and his officials (sub-section 1.2) and an analysis of key principles (subsection 1.3). Sub-section 1.1 sets the stage with a brief review from Rio through 1999.

A Decade Prelude-An Internationally Engaged United States

Domestically U.S. climate policy has been fairly timid for a decade. The issue of binding targets to reduce greenhouse gas emissions has constantly been sensitive. The UNFCCC, adopted at the Earth Summit in 1992, lacked binding targets because the United States, under the first Bush Administration (1989-92), conditioned its treaty signature on it. After taking office in 1993, the Clinton Administration implemented the Climate Change Action Plan (CCAP) voluntary measures to curb the country's greenhouse gas emissions. At the time of the first Conference of the Parties to the UNFCCC, in 1995, the United States accepted the "Berlin Mandate" aimed to negotiate binding targets and timetables for industrialized Parties (so called "Annex I" Parties).

In 1997-98, momentum toward binding targets was halting. With a 95-0 vote in July 1997, the Senate passed the infamous "Byrd-Hagel" Resolution, which held a few main messages: the United States should not accept any new emission limitation commitment unless developing countries also accept "specific scheduled commitments" nor should it accept any commitment that would harm the U.S. economy. 3 Despite this resolution and without any developing country commitments, the United States agreed to take on a binding target in the Kyoto Protocol, in December 1997, 4 after the Clinton Administration had obtained so-called international, market-based 'flexibility' instruments that could help countries meet the targets more cost-effectively. 5 Although the United States signed the Protocol in November, 1998, the Clinton Administration knew better than to send to the Senate for ratification what would not pass: the Byrd-Hagel Resolution cast a foreboding shadow.

The slow build-up of the Bush Administration's climate proposal

The early announcement of candidate George Bush to reduce CO 2 emissions shifted to the rejection of the Kyoto Protocol in March 2001, shortly after his Presidential election. During spring and fall 2001, the Bush Administration clarified the principles of its orientation in the climate field on the basis of various reports. Finally the alternative solutions advocated to address climate change were announced in February 2002, as the "Global Climate Change Policy". Since then, no major declaration nor decision regarding climate change has profoundly changed the course of action of the Bush Administration.

Luring announcements:

September, 2000: running for the U.S. Presidency, candidate G.W. Bush announces his intention to set mandatory reduction targets for CO 2 emissions from power plants (Bush, 2000).

February 27, March 4, 2001: Environmental Protection Agency Administrator Christie Todd Whitman states that the Bush Administration recognizes the climate change challenge and supports the Kyoto Protocol (Whitman, 2001a and b) Stepping back: rejecting the Kyoto Protocol March 13, 2001: President Bush rejects the Kyoto Protocol in a letter to four senators (Bush, 2001a). About six weeks after inauguration, P George Bush (junior) repudiated the Kyoto Protocol. In a letter of 13 March, 2001, President Bush made climate policy crystal clear, flipped on a campaign pledge to regulate power plant carbon emissions, contradicted many previous official statements of his Environmental Protection Agency Administrator, Christine Todd Whitman, and declared U.S. opposition to the Kyoto Protocol. He wrote that the Kyoto Protocol "exempts 80 percent of the world, (…), from compliance" and that it "would cause serious harm to the U.S. economy"; especially given the current scientific and technical uncertainties (Bush, 2001a). From that date, the Bush Administration position on climate change policy has been slowly refined.

March 13-31, 2001: the Bush Administration confirms in various meetings that the Kyoto Protocol is dead, and that priority is the strength of the American economy (White House, 2001 a and b ; WWF, 2001).

May, 2001 : The Bush Administration releases the National Energy Policy, enhancing the need for increasing energy supply and energy security (National Energy Policy Development Group, 2001).

June 6, 2001 : upon the Bush Administration request, the National Academy of Sciences issues a review of the state of the climate change science (NAS, 2001) to counterbalance the results brought by the Intergovernmental Panel on Climate Change (IPCC, 2001). The NAS report backfires on the Bush Administration as its conclusions are overall consistent with those of IPCC.

June 11, 2001: The Environmental Protection Agency releases a Cabinet-level review of the U.S. climate policy (EPA, 2001). The report reviews the current voluntary initiatives, which were launched under former President Clinton.

Setting the guiding principles :

June 11, 2001 : President Bush draws on the released NAS report and the Cabinetlevel review to discuss climate change (Bush, 2001b). He justifies the rejection of the Kyoto Protocol, "which was fatally flawed in fundamental ways": it exempts developing countries from emission reduction requirements ; it bears the risk of harming the United States and global economies ; and meeting the target depends on other countries, should the United States adopt the Kyoto Protocol. He reaffirms the U.S. commitment to the UNFCCC. He announces three initiatives to advance climate change science, encourage technological progress and enhance international cooperation in the climate change field. He calls for an approach that should be flexible, economy-friendly, market-based and global.

July 13, 2001 : President Bush reports the first set of actions taken by his Administration to implement the three initiatives previously announced (Bush, 2001c).

July 16-27, 2001: at the Conference of the Parties to the UNFCCC -6.5, the United States acts as a Party to the UNFCCC, and as observer for the negotiations related to the Kyoto Protocol. The Under Secretary of State for Global Affairs Paula J. Dobriansky leads the U.S. delegation. She reiterates why the United States will not ratify the Kyoto Protocol, refers to the UNFCCC to pledge for international cooperation on climate change issues, and reviews the Bush Administration's new set of initiatives (Dobriansky, 2001a and b).

Fall 2001: Harlon L. Watson -Senior Climate Negotiator and Special Representative, from the U.S. Department of State-reiterates in various arenas the principles previously set by President Bush (Watson, 2001a and b). At COP 7 in Marrakech, Paula J. Dobriansky again recalls the U.S. commitment to the UNFCCC along with the rejection of the Kyoto Protocol. She insists that the United States will not block other countries from moving towards the Kyoto Protocol.6 She underscores the need for economic development and poverty alleviation to address environmental protection. 7 Glenn Hubbard, Chairman of the Council of Economic Advisers, develops the Bush Administration's policy, mainly from an economic perspective. Starting from the existing uncertainties of climate science, he rejects the Kyoto Protocol for its lack of long-term goal, scientifically unsound and binding targets, likely costly reductions, and lack of participation of developing countries. He criticizes the Bonn Accords which sound to him better in theory than in practice. Instead, in addition to advancing science and technology research and coupled to developing international partnerships, he advocates a gradualist, flexible approach, like linking greenhouse gas emission growth to a percentage of economic growth, as well as voluntary commitments to reporting emissions and trading. 8 February 5 , 2002: the Annual Report of the Council of Economic Advisers is released. The portion dealing with the U.S. climate policy contains the same elements as those previously developed by Glenn Hubbard. In addition, flexibility acquires multiple dimensions : emissions must be reduced over time, according to short-and long-term opportunities ; all greenhouse gases (including black soot and tropospheric ozone), all sources, all sinks, all countries must be taken into account. The report advocates modesty and time in the design of a climate policy. It stresses that an international emission permit market currently constitutes an impractical solution due to the lack of appropriate institutions (CAE, 2002).

Proposing an 'Intensity' solution :

February 14, 2002 : President Bush presents his Administration's climate policy (Bush, 2002 ; White House, 2002), which calls for a reduction of 18 percent of the greenhouse gas (GHG) intensity over the next ten years. Unlike a fixed target that limits absolute emissions, this intensity target limits GHG emissions as a ratio of the gross domestic product (GDP). The proposal allows for a review by 2012 in order to determine whether the target has been met. Voluntarism is proposed as the way to achieve the target. It is called for the improvement of the current standards for reporting emissions reductions and for transferable credits for companies that undertake real reductions. Still, if the goal is not met by 2012, additional measures including market-based programs are suggested. Budget credits are announced for climate technology initiatives and climate science research. In the international field, President Bush reaffirms the U.S. commitment to the UNFCCC, and the noninterference of the United States towards other states that may choose to ratify the Kyoto Protocol. He praises the greenhouse gas intensity approach for developing countries, and announces (minor) budget allocation proposals for assisting them in various climate-related areas. Reaffirming the policy advocated June, 2002 : the EPA sends the U.S. Climate Action Report 2002 to the Secretariat of the Climate Convention. This Third National Communication to the UNFCCC is the first official document, under the Bush Administration, that recognizes that global warming over the last decades is likely mostly due to human activities. The report does not recommend reducing greenhouse gas emissions. Rather, it recommends adapting to climate changes. Still President Bush tunes down the report conclusions, qualifying the report as "put out by the bureaucracy". Similarly, EPA Administrator Christie Todd Whitman distances herself from the report, stating that she was not briefed before the report was published.

Implementing the proposal

Legislatively, the Bush Administration's proposal has only very partially been turned into bills introduced to Congress. 16 But none of the bills reached the President's desk for signature. As the 107 th Congress was almost evenly divided between the Republican led-House of Representatives and the Democrat-led Senate, bills from either Party did not get enough support to be enacted. The core measure of the proposal, namely the emissions intensity target, has not been included in any bill: as it is a voluntary target, it does not need to be enacted.

Key principles underlying the proposal

While rejecting the Kyoto Protocol at least for the years of the Bush presidency, the Administration has yet regularly reaffirmed the United States' commitment to the UNFCCC. Key principles shaping the U.S. climate proposal, coupled to this commitment, include the need for addressing the climate change challenge globally, considering scientific uncertainties, allowing for time, gradualism, economic growth primacy, flexibility, and voluntarism.

Because climate change is a global problem, solutions must be global regarding greenhouse gas sources, sinks, and the countries involved. International cooperation is essential. The U.S. climate policy must be based on sound science, which in the Administration's sense means 'not like the arbitrarily defined Kyoto Protocol targets'. For that matter, the need for more research is emphasized to reduce scientific uncertainties related to global warming magnitude and impacts. Time is called for, both to improve climate change science knowledge and to implement technologies that will be more cost effective. Therefore the solution advocated must be gradual.

In addition, the climate policy should not harm the U.S. economy, that is, it should not jeopardize economic growth and jobs. The target set by the Bush Administration to reduce the GHG emission intensity (the ratio of GHG emissions to the GDP) by 18 percent over the ten-year period 2002-2012 is meant to meet these goals. As President Bush puts it, the reduction target in the GHG emission intensity constitutes a "path to 14 Source : Reuters, October 24, 2002. Online at : http://www.planetark.org/dailynewsstory.cfm/newsid/18329/story.htm 15 Source : http://www.state.gov/g/oes/rls/rm/2002/14758.htm 16 Inter alia, the Climate Change Risk Management Act (S.1294), the International Carbon Conservation Act (S.769), and the Carbon Sequestration Investment Tax Credit Act (S.765), introduced by Republican senators, include provisions close to some of the Bush Administration's proposal.

slow the growth of [the] greenhouse gas emissions and, as science justifies, to stop and then reverse the growth of [U.S.] emissions" (Bush, 2002).

As for the heralded flexibility and cost-effectiveness that market mechanisms provide, the Bush Administration's position seems a bit curious. It advocates the 'power of markets' generally as well as the Clear Skies Initiative, in which electric utilities would have fixed targets or caps on three pollutants (i.e., sulphur dioxide, nitrogen oxides and mercury) and could trade the rights to emit amongst themselves, 17 but not greenhouse gas emissions trading specifically. President Bush's February 2002 speech is clear in this respect. Two different environmental issues are considered: domestic air pollution stemming from U.S. power plants and global climate change. For the former, President Bush calls for, and praises the merits of, a market-based cap and trade approach to reach the mandatory goals. By contrast, the approach selected for climate change is voluntary and does not refer to permit trading. He merely announces that transferable credits will be issued to companies that can show real reductions. The 2002 CEA annual report holds the key to understanding the paradoxical treatment on market mechanisms: the worldwide feature of the greenhouse gas permit system entails "enormous institutional and logistical obstacles". As a result, it "would be dangerous to make any serious U.S. policy or commitment dependent on newly designed and untried international institutions". 18 Internationally, the Bush Administration's position has shifted regarding developing countries' commitment to reduce GHG emissions. In March 2001, President Bush announced that the United States will not ratify the Kyoto Protocol because, among other things, the Protocol exempts eighty percent of the world from emission limitation commitments. In February 2002, the Administration no more calls for any commitment from developing countries as a trade-off to its own action. Instead it praises the emissions intensity approach for developing countries. Flipping on his previous requirement, President Bush states that "it would be unfair -indeed counterproductive-to condemn developing nations to slow growth or no growth by insisting that they take on impractical and unrealistic greenhouse gas targets". 19 All the above mentioned key features of the proposal reflect a wait-and-see approach. The only somewhat pro-active measures may be in the technological field. Cuttingedge actions to reduce greenhouse gas emissions are not on the current Administration's agenda. According to the Administration, serious actions, that still need to be defined, could be taken on after 2012, if necessary. But by that time, the incumbent President will no more be in office.

The driving forces behind the climate proposal

A few driving forces explain the main features of the Bush Administration's climate proposal. Some are mainly related to short-term events (sub-section 2.1), while others are more profoundly rooted (sub-section 2.2). 17 See for example his June 11, 2001 address and his 13 July, 2001 statement, for general advocacy of market mechanisms ; see (Bush, 2002) for the Clear Skies Initiative. 18 Source: chapter 6 of the Annual report of the CEA 19 Source : (Bush, 2002).

Short term factors

Regarding short term factors, the main concerns of the Bush Administration in the first half of 2001 are the slowdown of the U.S. economy and energy security: the vigorous economic expansion of the four previous years sounds over for 2001; 20 in the energy field, the United States faces the electricity crisis in California, 21 overall increasing demand, and an increasing dependence of foreign energy supply. Needless to say that these concerns have been strongly reinforced in the aftermath of the September 11 attacks.

The reduction of the greenhouse gas emissions intensity announced in February, 2002 is the Bush Administration's way to address the concern for economic growth, as opposed to the Kyoto Protocol, which, according to the Administration, "would have cost [the] economy up to $400 billion and [lead to the loss of] 4.9 million jobs". [START_REF]President's Bush speech of February 14[END_REF] A Kyoto-type 'fixed target' caps the allowable emission level, regardless of economic growth. Such a fixed target is obviously more stringent and costly in absolute terms when the GDP growth is high, compared to a low-economic growth scenario. 23 Instead, a "dynamic" emissions intensity target, like the one proposed by the Bush Administration, adjusts the allowable emission level to the GDP changes. A dynamic target therefore reduces the cost uncertainty. Furthermore, the target adopted by the Bush Administration is quantitatively more lenient than the preceding Administration agreed to at Kyoto. Whereas the Kyoto Protocol would have required a seven percent emissions reduction by 2008-2012 relative to a 1990 baseline, the newly proposed target will most likely induce emissions to grow substantially from 2002 to 2012 (see sub-section 3.2).

The National Energy Plan released in May 2001 is the domestic response to what the Bush Administration calls the "energy crisis". 24 It encourages expanding domestic coal supply, domestic oil drilling and nuclear power to secure domestic supply. Although the National Energy Plan also calls for the promotion of energy efficiency and conservation, and proposes a few tax credits for alternative, renewable, and cleaner forms of energy, the whole package of suggested actions obviously does not aim to reduce greenhouse gas emissions, nor will it in fact. [START_REF]For an in-depth analysis of the National Energy Policy, see[END_REF] But the Plan has also to do with other factors more deeply rooted, than merely the "energy crisis".

In fact, the Bush Administration's climate proposal and its current status may be further explained by the governance pattern of the U.S. economy, namely the constitutional framework, the weight of interest groups in policy-making, the historical reticence for government intervention, the U.S. unilateralism, and the overall trust in technology (Lee, 2001).

Thus far, the Bush Administration's proposal has not been enacted, even in partial Acts, for institutional purposes. To become an Act, any domestic climate policy requires close cooperation, first between several executive agencies that may have conflicting views (the Environmental Protection Agency (EPA) as well as the Departments of Energy, State, Agriculture, and Commerce), 26 and secondly within Congress. Any bill introduced in either house of Congress (the Senate and the House of Representatives) has to go through several committees and amendments before being sequentially adopted by both branches, and signed into an Act by the President (unless over-ridden by super-majorities). During the 107 th Congress, the Republicans held the majority in the House of Representatives, whereas the Democrats controlled the Senate. Consequently, political posturing and ideological contrasts thwarted agreement. 27 Among interest groups, the energy industry is the most powerful to influence the design of the Bush Administration's energy policy, and in the background climate policy. Reports from various environmental non-governmental organizations (NGOs) point to the strong link between the energy industry and the White House energy task force. 28 Furthermore, the official support of the United States for Dr Pachauri in the run-up to IPCC chairman election may have been induced by the recommendations of some energy lobbyists, including ExxonMobil. 29 The energy lobby can take well-earned credit for the voluntary (instead of mandatory) measures advocated by President Bush and his Administration to address the climate issue. Still, such a policy is also the evidence of the historical reluctance of the U.S. corporations and citizens to governmental intervention. In the oil and car manufacturing sectors, the ever-postponed tightening of Corporate Average Fuel 26 Conflicting views between executive agencies may be illustrated in the field of greenhouse gas inventory and reporting. The EPA currently proposes to use the "GHG Protocol" (Rangathan et al, 2001) for companies to register their greenhouse gases corporate wide, whereas the Department of Energy has launched a long-lasting consultation to revise existing section 1605 (b) of the 1992 Energy Policy Act. See sub-section 3.2. 27 The "Energy bill" is an illustration of the deadlock that occurred in the 107 th Congress. The H.R.4 Energy bill passed the House of Representatives in August 2001. After intense debates and amendments, the Senate passed its own Energy bill S. 517 in April 2002. But both bills differed so widely that they could not be reconciled before Congress recessed for the elections in fall 2002. See (NRDC, 2002). 28 See for example World Watch, vol 14, # 4, July/August 2001 (The article highlights that 50 out of the 63 members of the advisory team for the National Energy Plan come from the energy industry) ; see also : NRDC "Heavily Censored Energy Department Papers Show Industry is the Real Author of Administration's Energy Task Force Report" , available at : http://www.nrdc.org/media/pressreleases/020327.asp 29 A year ago, Exxon Mobil suggested to the Bush Administration that IPCC chairman Robert Watson be replaced (Dr R. Watson is an advocate of immediate actions against climate change.). See: NRDC "Confidential Papers Show Exxon Hand in White House Move to Oust Top Scientist from International Global Warming Panel", available at: http://www.nrdc.org/media/pressreleases/020403.asp. Economy (CAFE) standards of road vehicles as well as the low gasoline prices (due to relatively low petrol taxes) illustrate both strong interest-group pressure and minimal governmental interference. In this latter case, the interest groups do not only involve the oil industry and the car manufacturers but also all the U.S. citizens, for which the car is a cultural symbol of freedom.

"What goes on inside the state is critical in understanding foreign policy" (Harris, 1998, p.40). Decisions at the federal level on climate change issues are made according to what best serves the United States' interests, or even the interests of who are in power. Powerful business and individual interests influencing the Bush Administration differ from the pluralist interests (including environmental NGOs) that were shaping the Clinton Administration's climate policymakers. The former may be considered close to those of the G. H. W. Bush Administration in the early nineties. Still the overall context has changed. The United States clearly held leadership in the climate negotiations for several years during the nineties, 30 because climate change was perceived at that time as an important environmental threat to national interests (Harris, 2001). The rejection of the Kyoto Protocol and the current Administration's go-it-alone climate proposal mainly reflect the primacy of U.S. economic and energy security.

The last driving force of the Bush climate proposal is technological optimism. The United States has favored research and technology innovation for decades. On balance, this strategy has paid handsome dividends. The steadfast confidence that technology can tackle any problem may be reflected in the Bush Administration's calling for time in order to drive market-based innovations and science-based actions. The underlying assumption may be that, should climate change prove to be a serious threat (for which the Bush Administration still requires further evidence), the new technologies will probably 'solve' the problem more cheaply and more quickly than the current technologies. Thus, the Bush climate plan announces funds for research and development programs, such as the Freedom Cooperative Automotive Research (CAR) 31 for fuel cell-powered cars, as well as for investments in renewable energies and carbon sequestration. The National Hydrogen Energy Roadmap released by the Department of Energy in November 2002 is also part of this research effort to reduce dependence on foreign oil and to meet the future need for carbon-free energy. 32

The Bush Administration's rhetoric

The main purported flaws attributed by the Bush Administration to the Kyoto Protocol are qualified in sub-section 3.1, while the own flaws of the Bush Administration's proposal are examined in sub-section 3.2.

Examining the flaws of the Kyoto Protocol

30 For example, the Climate Convention did not commit Annex I countries to binding targets due to the U.S. refusal to accept any. Similarly, various flexibility mechanisms were embedded in the Kyoto Protocol on U.S. proposal. 31 See : http://www.energy.gov/HQPress/releases02/janpr/pr02001.htm. The Freedom CAR actually replaces the eight-year old Partnership for a New Generation of Vehicles (PNGV), which aimed at producing affordable high-mileage gas-burning cars by 2004. 32 Online at : http://www.eren.doe.gov/hydrogenandfuelcells/pdfs/national_h2_roadmap.pdf Soon after the January 2001 inauguration, President Bush rejected the Kyoto Protocol, citing three main reasons : the agreement did not commit the developing countries to emissions reduction ; the commitment could harm the U.S. economy ; and the United States would depend on other countries to meet its assigned target. These arguments merit closer examination.

Regarding developing countries' lack of participation in the global effort, various authors (Reid et al.; Biagini 2000; Baumert et al, 2001; Muller, 2001; Chandler et al., 2002) show that many developing countries are already limiting their greenhouse gas emissions, even without binding commitments to do so. In taking actions to meet their development needs, secure energy supply, improve local air quality, these countries simultaneously get ancillary benefits in the form of mitigation of their greenhouse gas emissions.

The risk of harming the U.S. economy is estimated by the Bush Administration at a cost of (1996 $ constant price) 400 billion and a loss of 4.9 million jobs by 2010. These figures stem from a synthesis report completed by the now deactivated Global Climate Coalition (GCC, 2000), an industry-lobby group. These statistics occupy the upper ranges found in the report and crucially depend on the assumption that the United States achieves its Kyoto target domestically. When international emission trading is considered, the report's estimated costs to the U.S. economy and employment fall by a factor of two to four. Moreover, other studies do not corroborate the same results. In the Energy Modelling Forum (EMF) studies, the range of GDP costs for the United States is between 0.42 and 1.78 percent of the GDP in 2010 (Weyant & al, 1999), compared to the 3.2 percent-equivalent loss of $ 400 billion assessed by the GCC. Evaluating the EMF and other models, Barker et al conclude that "the macroeconomic costs of greenhouse gas mitigation [under the Kyoto Protocol] is likely to be insignificant in the United States […], provided that the policies are expected, long-term and well-designed" (Barker & al, 2001, p.13).

Still, no concrete action to achieve the U.S. target inscribed in the Kyoto Protocol was implemented by 2001, more than three years after the release of the Protocol. The cost of reaching the target over the commitment period (2008-2012) was increasing as mitigation actions were put off. Had the United States ratified the Kyoto Protocol at that time, using the flexibility mechanisms of the treaty, particularly emissions trading, would have become essential to reduce those costs. The dependence on other countries to comply with the target would have been real. Ironically, this dependence is considered as a major obstacle to ratify the Kyoto Protocol by the current Administration, whereas the previous (Clinton) Administration had envisioned it as a major means to meet the Protocol target.

Flaws in the Bush Administration's proposal

The climate proposal of the Bush Administration bears its own flaws: it can hardly be considered as complying with the spirit of the UNFCCC; the proposal follows a different path in which the economic and energy security takes the leading roles. Climate mitigation and GHG emission reductions are hardly written into the script, given bit parts in largely voluntary performances. Yet they may play the starring roles in the next sequels. In short, there is some difficulty in reconciling the rhetoric with reality.

The Bush Administration has reiterated the U.S. commitment to the UNFCCC. But it seems hard to assert that the Bush Administration's proposal meets the principle that "the developed country Parties should take the lead in combating climate change and the adverse effects thereof", which is part of Article 3.1 of the UNFCCC. Neither is it clear that the proposal addresses the ultimate goal of the Convention, which is to stabilize "greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system" (Article 2, UNFCCC 1992).

In fact, the Administration's goal to cut the U.S. greenhouse gas intensity by 18 percent over the next ten years is little more than rhetoric-or, as noted economist Paul Krugman wryly, an "ersatz climate policy". 33 The emission intensity goal set by the Bush Administration is amazingly similar to the trend observed in the 1990s when, other than ineffective voluntary programs, no climate mitigation actions were implemented. After declining by 23 percent in the 1980s, the U.S. greenhouse gas emission intensity decreased by 17 percent over the last decade, mainly as a result of combined effects of energy efficiency improvements and structural changes of the economy, such as transitioning from energy-intensive industries towards information and service activities. The Bush Administration's goal is thus merely the continuation of the past trend. Not coincidentally, it strongly resembles the business-as-usual ("reference") projection built up by the Administration for 2002-2012 (figure 1).

Reference case

In addition, the Bush Administration's call for an -apparent-effort to decrease the emissions intensity obliterates a substantial growth of U.S. greenhouse gas emissions over the next coming decade, at a pace comparable to that of the last decade. The rhetoric relies on the fact that the greenhouse gas intensity is a ratio: it may therefore decrease even though both its numerator and denominator increase. The Administration expects the denominator of the greenhouse gas intensity ratio, namely the U.S. GDP, to increase by 38 percent between 2002 and 2012 on a business-asusual trend. 34 Reaching the target of an 18 percent decrease of the greenhouse gas intensity over the same period entails that the numerator of the ratio, namely greenhouse gas emissions, is expected to grow at a slower pace than the denominator, namely by 14 percent.

This 14 percent expected growth rate of greenhouse gas emissions to meet the emission intensity target is actually the emission increase that occurred over the last decade. It stands only five percentage points below the projected 19 percent increase of the business-as-usual ("reference") case (figure 2). As has been extensively noted, 35 To meet the target, the Bush Administration calls for voluntary actions from companies to inventory, report and reduce their emissions. Indeed, voluntary measures have not yielded substantial results in the past, in terms of overall emission reductions. 37 The emission intensity approach, adopted domestically and advocated by the Administration for the developing countries, may be appealing for the latter because it reduces economic uncertainties embedded in fixed emission reduction targets (Baumert & al, 1999). It is an option often mentioned when tackling the question of the developing countries' participation in the second commitment period within the Kyoto Protocol framework (Baumert et al, 2002). However, for now, developing countries refuse to consider any future emission limitation agreement, arguingcorrectly, as witnessed in the 1995 Berlin Mandate-that the industrialized nations, especially the United States, should first take the lead in reducing their emissions. The Bush Administration's unilateralist approach may induce a stalemate in upcoming negotiations. Consider too efforts by civil society and corporate America. Universities, religious groups, and non governmental organizations are leading the charge from the bottom up. 45 In addition, corporations are increasingly taking steps to limit their greenhouse emissions as well as publicly pledging to do so. 46 The latest initiative in this respect is the cap-and-trade program coordinated through the Chicago Climate Exchange, which was officially launched on January 16, 2003. 47 Under this program, major companies in various sectors have made a binding promise-a private contract (in common law) but voluntary in that there is no public law mandate-to reduce their greenhouse gas emissions by four percent by 2006, relative to their 1998-2001 baseline. 48 Depending on their reduction costs, the companies participating in the climate exchange will be able to trade emission quotas and credits to reach their emission reduction target.

Near

On the international stage, contrary to many experts' expectations, the Kyoto Protocol is not dead despite its rejection by the United States. Only a few nations (e.g., Australia and Saudi Arabia) have overtly welcomed the U.S. approach and rejected the Kyoto Protocol. The entry into force of the Kyoto Protocol depends on two conditions: 55% of the Parties to the agreement must have ratified it ; the 1990 emissions of the Annex B Parties (industrialized countries) that have ratified must represent 55 % of the 1990 total Annex B emissions. The first condition is currently met, whereas the second one depends on the ratification by Russia.

Conclusion

A year after rejecting the Kyoto Protocol, President Bush advanced a climate proposal that failed to entail credible climate change mitigation: the 18 percent emission intensity reduction target amounts to a substantial increase in actual emissions over the next decade and hardly veers from the business-as-usual path. The actions proposed to meet the target are voluntary and are not to be reviewed before 2012. The proposal, on balance, contains more rhetoric than reality. It delays substantive mitigation programs, at least, beyond Bush Administration's current mandate.

This wait-and-see policy reflects some fundamental aspects of the U.S. governance of its economy, such as the pressure of specific interest groups (especially the energy and extractive-resource lobbies), the unilateralism of the country, the reluctance to governmental intervention, and the trust in technology to drive U.S. economic growth. Moreover the Republican Party, generally not keen on climate actions, presently controls the White House and both branches of the new 108 th Congress. The chairs of the Senate Environment and Public Works Committee and the Energy and Natural Resources Committee have recently shifted to two senators known to support the energy sector much more than environmental issues.

While much of the world perceives the threat of global climate change, much of the Bush Administration and Congress disagree over the threat's severity. So the question is if and when federal politicians feel the heat, so to speak, to implement substantive GHG emission mitigation policies. Considering the current unilateralist approach adopted by the United States, international pressure may not contribute much to driving them to decide on mitigation actions. If the emerging domestic pressure from states, corporations and civil society becomes a groundswell, the federal government may take the reins. Political entrepreneurs in Congress and maybe even within the Administration may seize the opportunity of steering the powerful current where the grassroots and the corporate cooperate.

When threat is not seen as immanent, this force may be painfully slow to build, but it is sustainable when it matures-not a whimsical fad but a secular trend. When the threat is confronted-from public outrage or a summer drought causing catastrophic crop losses-, the U.S. may be nimble. In the words of historian Stephen Ambrose, "[The United States] is a country that can change faster and quicker in the right direction than anybody else in the world."51 French politician and writer Françoise Giroud did not agree more when she pointed that "there is a strength in the United States that we in Europe constantly tend to underestimate.

  October, 2002 : at the eighth Conference of the Parties in Delhi, Harlan Watson -Senior Climate Negotiator and Special Representative-reiterates that the United States will not ratify the Kyoto Protocol, 14 and that economic growth, research and technology developments are the keys to climate change issues. He invites developing countries to share the U.S. approach giving priority to economic growth. 15 December, 2002 : over one thousand climate experts meet in Washington DC at the Climate Change Science Program Planning Workshop, sponsored by thirteen U.S. government agencies. The workshop aims to jump-start the public review of a draft version of the Strategic Plan for climate change and climate change studies. The Strategic plan represents the research strategy of the Bush Administration to reduce the scientific uncertainties surrounding climate change.

Figure

  Figure 1 : U.S. GHG intensity changes: is past prologue? US GHG intensity (tC/2001$)

  it is in no way what can be called an "ambitious" initiative to slow global climate change. If the United States were to comply by 2012 with the 7 percent emission reduction target of the Kyoto Protocol relative to 1990, the emissions intensity would have to decrease by 41 percent between 2002 and 2012. 36

Figure 2 :

 2 Figure 2: the past and future upward-trend of U.S. absolute emissions GHG emissions (MtC)

" 52 Bibliography

 52 Barker T., and P. Ekins 2001. "How high are the costs of Kyoto for the U.S. economy?". Tyndall Centre Working Paper Number 4, July 4.

  April, 2002 : the removal of one IPCC Chairman and the elevation of a successor occurs at the junction where climate policy meets climate politics. On April 19, 2002, Dr. Rajendra Pachauri, head of the Indian environmental policy group Tata Enery Research Institute (TERI), is elected to the post of IPCC Chairman. He replaces former World Bank and White House scientific advisor for the Environment Dr. Robert Watson, who held the IPCC chairman position since 1996. The United States pushed hard for both Robert Watson's ouster and Pachauri's election. The United States supported the latter most likely because it perceived that Robert Watson advocated 'early action' on climate change a bit too forcefully. 13

	February 20, 2002 : the Environmental Protection Agency (EPA) launches the
	Climate Leaders program. Each U.S. based company that voluntarily joins the
	program commits to fulfilling a corporate-wide greenhouse gas inventory and to
	working with EPA to set a corporate emission reduction target. 9
	Spring 2002 : President Bush's Administration pursues or engages talks with some
	countries. Australia, which supports the Bush Administration's climate proposal,
	signs a bilateral Climate Action Partnership with the United States. 10 High-level
	consultations are organized with Japan, Canada, the European Union. 11 Regarding
	developing countries, Harlon Watson has various high-level talks with India and
	China. 12

  Furthermore the reporting registration program proposed by the Bush Administration relies on the Department of Energy's "Voluntary Greenhouse Gas Emissions Reporting" Program mandated by Section 1605(b) of the 1992 Energy Policy Act. The current program under Section 1605 (b) is known to contain various pitfalls that hinder its use to report real emission reductions(NRDC, 2001b).38 Various executive agencies jointly proposed improvements to this program in July 2002, based on previously solicited public comments. Public workshops were recently convened to discuss the proposed improvements. Further public comments on revised versions of the program will be solicited during 2003. The final version should be released in January 2004. This long administrative procedure may well illustrate the tendency of the Bush Administration to delay any real mitigation effort. EPA's Climate Leaders Charter sounds more promising: to conduct greenhouse gas inventories, it proposes to use the high quality Greenhouse Gas Protocol(Ranganathan & al, 2001) developed by the World Resources Institute (WRI) and the World Business Council for Sustainable Developments (WBCSD). But the Climate Leaders program has attracted only around thirty partners to date.39 Likewise, the actions announced in the climate science research field sound like delaying climate change mitigation actions still further. Substantial research has already been carried out in the United States and internationally for a decade, and has clearly come to the conclusion that mitigation actions are urgently needed.40 Still the Bush Administration launched a Strategic Plan for climate change and climate change studies, in December 2002 (see sub-section 1.1). The public review of a draft version of this Plan is due in April 2003. The Strategic plan represents the research strategy of the Bush Administration for the next two to five years, to better understand the climate system and the role of human activities on climate change. It aims to provide more scientific information to define a "clearly articulated regulatory policy that's practical, affordable and doesn't put the economy at risk".41 In effect, this means that the Bush Administration will probably not propose, barring a public groundswell or a summer drought, any substantive mitigation measures before the research results are released.The Administration's strategy on how developing countries need to become partners in the global efforts to prevent climate change has shifted: the call that developing countries should take on binding emission limitation commitments has been silenced. In so doing, the Bush Administration implicitly recognizes the common but differentiated responsibilities and capabilities of the Parties, called for in a paragraph of Article 3.1 of the Climate Convention. But this ad hoc compliance merely reflects the unilateralist approach of the United States. Harlan Watson, Senior Climate Negotiator and Special Representative from the U.S. Department of State, has reaffirmed that the United States will not return to international negotiations for the next review of greenhouse gas reductions (due in 2005).42

-term prospects for climate mitigation actions in the United States

  Climate change is a global environmental threat that requires global actions. With the possible exception of future technologies, the Bush Administration's climate proposal would hardly constitute the meaningful U.S. participation, however reasonably defined, in the climate mitigation challenge that Democratic and Republican politicians have called from the developing world. No ambitious emission reduction target may be expected to be taken on at the Federal level by the present Administration, although the United States presently emits almost 25 percent of the world greenhouse gases with four percent of the world population. How can the potential deadlock due to U.S. passive attitude towards climate mitigation actions be overcome ? Encouraging signs are on the horizon.Congressional activity around climate change issues has considerably increased over the last Congress sessions.43 The bipartisan bill S.139 introduced in January 2003 in the Senate by Democrat Lieberman and Republican McCain aims to provide tradeable greenhouse gas allowances economy wide to limit greenhouse gas emissions. This bill and others reflect the growing domestic concern to address climate change more aggressively than through the approach adopted by the Bush Administration. All these domestic changes may contribute in the near future to claim for a more stringent federal policy, although the Bush Administration is led by anti-climate forces from the energy sector.Despite the absence of any ambitious climate policy at the federal level, numerous emission limitation actions are carried out at the subnational level-individual states and municipalities. Consider states with legislation to reduce their greenhouse gas emissions in effect or in the regulatory pipeline.44 For instance, New Jersey has set a reduction target of 3.5 percent below 1990 level by 2005 ; Oregon has established a drastic standard for CO 2 emissions from new power plants ; fifteen states have imposed their Renewable Portfolio Standard to boost the electricity produced from renewable resources ; California passed a law to set by 2005 maximum but economically feasible emission standards for passenger vehicles sold in the state.

  49 Sixty-six additional ratifications were registered by the UNFCCC Secretariat betweenMarch, 2001 and December, 2002, including those of China, New Zealand and Canada. The total number of ratifications has reached over one hundred. With the United States out of the agreement, the entry into force of the Kyoto Protocol is presently pending upon Russia.50 Still at the international level, the European Union's Council of Environment Ministers adopted in December 2002 an emissions trading Directive. Some countries are obviously moving ahead toward climate protection. U.S. based companies operating in foreign countries that have ratified the Kyoto Protocol may push hard the U.S. government to take on domestic measures for competitive purposes.To be sure, the United States probably will not rally around the Kyoto Protocol for the foreseeable, if ever. Whatever the alternative framework the United States may implement, substantive mitigation actions are urgently needed, for several reasons. The United States is the largest greenhouse gas emitter in the world, and it is among the richest countries, per capita, too. So proportionate responsibility for emissions and capacity to respond are both present. Developing countries will not move forward into further mitigation actions, as long as the United States does not do so. Should the United States move forward into enhanced climate mitigation actions, it would most likely be when the federal government builds on the ongoing efforts of states and municipalities as well as civil society and corporate America. Soon, the world may well end up with two climate protection regimes -the Kyoto Protocol and a U.S.dominated plurilateral affiliation, which some countries like Australia may rally-. Various experts have explored how both systems could simultaneously operate for some time (Bodansky (2002),Baron et al. (2002)).45 See for example(Grist Magazine, 2002) 46 See for example(Pew Center, 2002).47 For further information, visit: http://www.chicagoclimatex.com/html/about.html 48 Exchange participants include the city of Chicago, DuPont, Ford Motor, Motorola, Manitoba Hydro, STMicroelectronics, and Stora Enso North America, a division of a Finnish paper maker.49 Australia officially rejected the Kyoto Protocol in July, 2002. See : "Australia Shuns Kyoto Protocol ; World's biggest coal exporter Australia dumps Kyoto", Planetark.org, June 6, 2002. Available online at: http://www.heatisonline.org/news.cfm 50

The author is grateful to James Perkaus, research fellow at the World Resources Institute, for his insightful comments. This research was partially funded by Institut Français de l'Energie.

The United States signed the UNFCCC inJune, 1992 and ratified it in October, 1992.

The Senate Resolution SR-98 is often referred to as the "Byrd-Hagel" Resolution from the names of the co-sponsors Democrat Robert Byrd and Republican Chuck Hagel.

The Kyoto Protocol target agreed by the United States at the third Conference of the Parties is to reduce the country's GHG emissions by 7 % relatively to 1990 levels by the five-year period 2008-2012.

 5 The flexibility mechanisms of the Kyoto Protocol include international emissions trading, the Clean Development Mechanism, Joint Implementation, and carbon sinks.

Source : http://www.state.gov/g/rls/rm/2001/5969.htm

Sources : Seventh Session of the Conference of the Parties, November 7, 2001 http://www.state.gov/g/rls/rm/2001/5969.htm ; Closing statement of the Seventh Session of the Conference of the Parties, November 9, 2001 http://www.state.gov/g/oes/rls/rm/6050.htm.

Sources: Glenn Hubbard's speeches at the Pew Center Conference on the Timing of Climate Change Policies, October 11-12, 2001 and at the Global Change Forum of the Massachusetts Institute of Technology , October 17-19, 2001.

Source : The New York Times, February 15, 2002.

This growth rate is that of the "Reference case". Source: Addendum to the Global Climate Change Policy Book, available at: http://www.whitehouse.gov/news/releases/2002/02/addendum.pdf

In addition to numerous NGOs press releases, see for example[START_REF] Viguier | The Bush Climate Change Policy: A Preliminary Evaluation[END_REF][START_REF] Moor (de) | Evaluating the Bush Climate Change Initiative[END_REF] for in-depth analyses.

Assuming the GDP growth of the "reference case" (+38 %) and domestic emission reductions (no permit trading).

See for example[START_REF] Gardiner | The Effectiveness of Voluntary Programs and Next Steps in Climate Change Policy[END_REF]

For example, emission reductions may be reported on a project-by-project basis, or from one set of activities, not at the corporate level. Therefore emission reductions of a company reported under current section 1605 (b) may be offset by emission increases that were not reported because they were undertaken by the company in other projects or activities.

For more information on EPA's Climate Leaders Partnership, visit: http://www.epa.gov/climateleaders/

See for example(National Assessment Synthesis Team, 2000), (National Academy ofScience, 2001), and (IPCC, 2001).

Citation : John Marburger, the White House science and technology adviser, cited in the Washington Post, December 4, 2002, p. A08.

Source : The Guardian, May 14, 2002, available at : http://www.guardian.co.uk/Archive/Article/0,4273,4412866,00.html

The number of climate change-related bills, resolutions, and amendments introduced into Congress increased from seven in the 105 th Congress, to twenty-five in the 106 th Congress and eighty-five in the 107 th Congress. See(Pew Center, 2002).

See for example[START_REF] Rabe | Greenhouse and Statehouse: the Evolving State Government Role in Climate Change[END_REF].

Source : Online NewsHour: Conversation with Stephen Ambrose, July 30, 2002 http://www.pbs.org/newshour/conversation/july-dec02/ambrose_7-30.html

Quoted in the obituary released by The Economist,January 25 th , 2003.

precisely what this paper attempts to do. This paper examines the Bush Administration's proposal and subsequent actions in terms of the United Nations Framework Convention on Climate Change (UNFCCC), which the United States flaws" the Bush Administration attributed to the Kyoto Protocol.