Zhenxue He
email: hezhenxue@buaa.edu.cn

Guangjun Qin

Limin Xiao
email: xiaolm@buaa.edu.cn

Fei Gu

Zhisheng Huo

Li Ruan

Haitao Wang

Longbing Zhang

Jianbin Liu

Shaobo Liu

Xiang Wang

An Efficient Polarity Optimization Approach for Fixed Polarity Reed-Muller Logic Circuits Based on Novel Binary Differential Evolution Algorithm

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Traditional IC design based on the Boolean logic is facing serious power, area and delay challenges. Plenty of studies (e.g., [START_REF] He | A Power and Area Optimization Approach for Mixed Polarity Reed-Muller Expressions for Incompletely Specified Boolean Functions[END_REF][START_REF] Ma | Power Optimization Technique Based on Duallogic Diagram Expression at Gate Level[END_REF][START_REF] He | An Efficient and Fast Polarity Optimization Approach for Mixed Polarity Reed-Muller Logic Circuits[END_REF][START_REF] Rahaman | Secure Testable S-box Architecture for Cryptographic Hardware Implementation[END_REF]) demonstrate that compared with the circuits implemented by Boolean logic, the circuits implemented by RM logic are capable of achieving lower power and area. However, the existing polarity optimization approaches, which are based on GA or its variants, have a low convergence speed or are easily trapped into the local optimal solution [START_REF] Wang | Area and Power Optimization of ISFPRM Circuits Based on PSGA Algorithm[END_REF][START_REF] He | EMA-FPRMs: An efficient minimization algorithm for fixed polarity Reed-Muller expressions[END_REF].

In this paper, we propose a binary version of the Differential Evolution (DE) algorithm according to the polarity characteristic of FPRM logic circuits, called Novel Binary Differential Evolution algorithm (NBDE), to find the optimal solution in binary optimization space. Moreover, based on the NBDE, we propose an Efficient Polarity Optimization Approach (EPOA) for FPRM logic circuits, which uses the NBDE to search the best polarity.

An Efficient Polarity Optimization Approach for FPRM Logic Circuits

To enhance the global convergence ability, we introduce the elitism strategy to the NBDE. In addition, we propose a binary random mutation operator to increase the population diversity and improve the global searching ability.

Population Initialization

Firstly, a random number r is generated in [0,1]. Then, the j -th element of i -th

individual ij
x is set to 1 (which represents polarity 1) if r is less than 1/2; otherwise, ij x is set to 0 (which represents polarity 0).

Mutation Operator

To avoid the premature convergence and increase the population diversity, we propose a binary random mutation operator, which is represented as follows: , , ,

j best j x i j r j r j i j x best j r j r j x x x rand v x x x rand                 (1) 2, 3, , , 2, 3, ( 1) , 0.5 ( 1) , 0.5 i
where ,

i j v represents the j -th element of mutation vector i v . 2, 3 {1, 2,..., } r r NP  and 2 3 r r i   . best
x is the optimal individual in current population, and rand is a random number in [0,1].

Since the polarity of FPRM expression is taken as 0 or 1, the absolute value of difference vector is only 0 or 1 and the mutated variable is still 0-1 variable. Therefore, the mutation operator satisfies the closure. Moreover, whether one dimension variable can be mutated or not depends on the difference vector. Specifically, the ,

Experiments Results

The EPOA has been implemented in C and compiled by the GNU C complier. The results were obtained by using a PC with Intel Core i7 3.40GHz with 4G RAM under Linux. In this paper, we set the logic minimization as the polarity optimization goal to validate the effectiveness of the EPOA. We compared the EPOA with the GA based Polarity Optimization approach (GAPO) [START_REF] Sun | Ternary FPRM Circuit Area Optimization Based on Genetic Algorithm[END_REF] and Whole Annealing GA based Polarity Optimization approach (WAGAPO) [START_REF] Yang | Optimization of Mixed Polarity Reed-Muller Functions Based on Whole Annealing Genetic Algorithm[END_REF] on 24 randomly selected MCNC benchmark circuits. Moreover, we ran the GAPO, WAGAPO and EPOA 10 times on each circuit to reduce the impact of randomness on the results. The population size is set to 100, and termination criterion is that there is no improvement on the optimal solution in population over 10 iterations.

The comparison of GAPO, WAGAPO and EPOA on the average number of iterations and run time (in CPU seconds) over 10 independent run are listed in Table 1. Columns 9 and 10 denote the percentage of the number of iterations and run time saved by EPOA compared to GAPO. Columns 11 and 12 denote the percentage of the number of iterations and run time saved by EPOA compared to WAGAPO. Compared with the GAPO, the greatest improvement in the number of iterations and run time, which were made by EPOA, are 92.86% and 98.09%, respectively. Moreover, compared with the WAGAPO, the greatest improvement in the number of iterations and run time, which were made by EPOA, are 83.33% and 96.22%, respectively.

Conclusion

In this paper, we propose a novel binary DE algorithm, called NBDE, which can solve the binary-encoded combination optimization problem. Additionally, based on the NBDE, we propose a polarity optimization approach, called EPOA, which uses the NBDE to search the best polarity of FPRM logic circuits. The experimental results over MCNC benchmark circuits show that the EPOA performs better than, or at least comparable to, the existing GA or its variants based polarity optimization approaches in terms of solution accuracy and convergence speed.

  could increase the population diversity, improve the global searching ability and prevent the algorithm trapping into the local optimal solution. In addition, the probability of 2, r jx is equal to 3, r jx is increasing along with the population evolution. The ,

Table 1 .

 1 Comparison of GAPO, WAGAPO and EPOA on the average number of iterations and run time

				GAPO	WAGAPO		EPOA	Save1(%)	Save2(%)
	Name	Input
			iter time(s) iter time(s) iter time(s)	iter	time(s)	iter	time(s)
	b3	3	1	0.20	1	0.18	1	0.03	0.00	85.00	0.00	83.33
	xor3	3	1	0.19	1	0.18	1	0.05	0.00	73.68	0.00	72.22
	bw	5	6	0.96	3	0.42	1	0.06	83.33	93.75	66.67	85.71
	xor5	5	8	0.82	4	0.57	1	0.05	87.50	93.90	75.00	91.23
	m1	6	12	1.18	4	0.61	1	0.06	91.67	94.92	75.00	90.16
	Z5xp1	7	12	1.22	5	0.63	1	0.06	91.67	95.08	80.00	90.48
	lin	7	14	7.34	6	3.70	1	0.14	92.86	98.09	83.33	96.22
	ex5	8	15	2.85	8	1.44	2	0.37	86.67	87.02	75.00	74.31
	m3	8	14	2.21	6	1.28	3	0.55	78.57	75.11	50.00	57.03
	rd84	8	22	14.92	7	5.62	4	0.62	81.82	95.84	42.86	88.97
	1020	10	24	23.03	9	7.76	6	4.60	75.00	80.03	33.33	40.72
	ex1010	10	20	15.78	12	6.14	7	4.81	65.00	69.52	41.67	21.66
	br1	12	31	17.02	16	9.37	8	3.44	74.19	79.79	50.00	63.29
	14_4color	14	55	30.08	23	15.26	10	7.05	81.82	76.56	56.52	53.80
	table3	14	70	37.40	27	18.70	18	11.62	74.29	68.93	33.33	37.86
	dk48	15	62	36.32	26	16.43	20	9.59	67.74	73.60	23.08	41.63
	alcom	16	69	67.85	31	34.41	23	17.53	66.67	74.16	25.81	49.06
	table5	17	81	84.99	52	52.90	31	22.42	61.73	73.62	40.38	57.62
	src1	18	73	173.55	37	139.34	29	54.63	60.27	68.52	21.62	60.79
	in2	19	84	158.64	41	127.88	33	32.26	60.71	79.66	19.51	74.77
	mark1	20	127 240.91	40	195.61	30	60.75	76.38	74.78	25.00	68.94
	mux	21	95	226.33	34	174.26	27	68.90	71.58	69.56	20.59	60.46
	duke2	22	116 262.72	45	223.15	34	75.18	70.69	71.38	24.44	66.31
	cordic	23	145 318.05	67	257.18	42	95.84	71.03	69.87	37.31	62.73

Acknowledgments. This work is supported by the National Natural Science Foundation of China (Nos. 61370059 and 61232009), Beijing Natural Science Foundation (No. 4152030), Fundamental Research Funds for the Central Universities (YWF-14-JSJXY-14) , the fund of the State Key Laboratory of Computer Architecture (CARCH201507), the State Administration of Science Technology and Industry for National Defense, the major projects of high resolution earth observation system (Y20A-E03), and the fund of the State Key Laboratory of Software Development Environment (SKLSDE-2016ZX-15).


Baolin Sun
email: blsun@163.com

Gui Chao
email: gui_chao@126.com

Ying Song

Hua Chen

Adaptive Length Sliding Window-based Network Coding for Energy Efficient Algorithm in MANETs 1

Keywords: MANET, sliding window, network coding, energy efficient

A key problem in network coding (NC) lies in the complexity and energy consumption associated with the packet decoding processes, which hinder its application in mobile ad hoc networks (MANETs). Sliding-window Network Coding is a variation of NC that is an addition to TCP/IP and improves the throughput of TCP on MANETs. In this paper, we propose an Adaptive Length Sliding Window-based Network Coding for Energy Efficient algorithm in MANETs (ALSW-NCEE). The performance of this ALSW-NCEE is studied using NS2 and evaluated in terms of the network throughput, encoding overhead, energy consumption, and energy efficiency when packet is transmitted. The simulations result shows that the ALSW-NCEE with our proposition can significantly improve the network throughput and achieves higher diversity order.

Introduction

Due to the rapid growth of mobile devices such as laptops and smartphones, wireless data traffic has significantly increased, driving the many efforts to increase wireless bandwidth [START_REF] Sun | A Novel Network Coding and Multi-path Routing Approach for Wireless Sensor Network[END_REF][START_REF] Sun | Network Coding-Based Priority-Packet Scheduler Multi-path Routing in MANET using Fuzzy Controllers[END_REF][START_REF] Ahlswede | Network information flow[END_REF][START_REF] Guang | On random linear network coding for butterfly network[END_REF][START_REF] Ho | A Random Linear Network Coding Approach to Multicast[END_REF]. Recently, wide attention has focused on a novel paradigm called network coding (NC) to maximize the link utilization of a given wireless bandwidth.

Energy efficient technique has been widely acknowledged as a promising diversity technique to combat wireless fading [START_REF] Sun | A Novel Network Coding and Multi-path Routing Approach for Wireless Sensor Network[END_REF][START_REF] Sun | Network Coding-Based Priority-Packet Scheduler Multi-path Routing in MANET using Fuzzy Controllers[END_REF][START_REF] Ahlswede | Network information flow[END_REF][START_REF] Guang | On random linear network coding for butterfly network[END_REF][START_REF] Ho | A Random Linear Network Coding Approach to Multicast[END_REF]. Two research areas are exploring this approach: energy efficient and network coding by a neighbor node. Network coding (NC) is an area that has emerged in 2000 [START_REF] Ahlswede | Network information flow[END_REF], and has since then attracted an increasing interest, as it promises to have a significant impact on both the theory and practice of networks. NC provides some benefits in terms of performance efficiency and throughput in dynamic environments such as mobile ad hoc network (MANET). Suppose a source node sends a set of data packets, grouped into what are referred to as generations, to several destination nodes. Network coding allows the intermediate nodes to combine the different data packets of the same generation.

The advantages of NC come however at the price of additional computational complexity, mainly due to the packet encoding and decoding process. In [START_REF] Guang | On random linear network coding for butterfly network[END_REF], Guang et al. study the performance of random linear network coding (RLNC) for the wellknown butterfly network by analyzing some failure probabilities. Ho et al. [START_REF] Ho | A Random Linear Network Coding Approach to Multicast[END_REF] present a distributed RLNC algorithm for transmission and compression of information in general multisource multicast networks. The authors show that the RLNC can take advantage of redundant network capacity for improved success probability and robustness. Papanikos et al. [START_REF] Papanikos | Deterministic Broadcasting and Random Linear Network Coding in Mobile Ad Hoc Networks[END_REF] focus on the problem of multiple sources broadcasting in MANETs. The authors propose a connected dominating set-based algorithm that works in synergy with RLNC on the "packet generation level".

How to improve the energy efficient is an important issue for packet transmission in MANETs. This paper proposes an Adaptive Length Sliding Window-based Network Coding for Energy Efficient algorithm in MANETs (ALSW-NCEE). We apply network coding over GF(2 q ) on symbols rather than on packets to fully exploit the advantages of network coding including adaptive length sliding window, energy efficient. The main contribution of this work is summarized as:

1) We present an efficient approach to construct adaptive length sliding window and network coding coefficients in a pseudo-random manner on each user. We provide a thorough description of adaptive length sliding window, network coding, and energy efficient in MANETs (ALSW-NCEE), a novel class of network codes.

2) Second, an analytical model of ALSW-NCEE decoding complexity is derived allowing to matching the decoding computational cost to the capacity of the mobile node.

3) The performance of the ALSW-NCEE is studied using NS2 and experimentation to assess the encoding efficiency of ALSW-NCEE enabled mobile node. The ALSW-NCEE is shown to achieve significant performance gain.

The rest of the paper is organized as follows. Section 2 discusses the some related work. Section 3 describes models of sliding encoding window model in MANETs. Some simulating results are provided in section 4. Finally, the paper concludes in section 5.

Related Works

In this section, we overview the existing literature on lower complexity NC and energy efficient for MANETs. In its best known algorithm, NC is defined over finite fields such as GF(2 q ), as the size of the field to ensure the node receives the packet has the very high decoding ability.

In MANET, network coding in higher finite field has been proved with solid performance improvement over binary codes. A key problem in network coding (NC) lies in the complexity and energy consumption associated with the packet decoding processes, which hinder its application in mobile environments. Energy efficiency directly affects battery life and thus is a critical design parameter for MANETs. Ap-plying network coding for wireless applications in general has also been proposed and investigated in the more recent literature. Keller et al. [START_REF] Keller | SenseCode: Network Coding for Reliable Sensor Networks[END_REF] present SenseCode, a new collection protocol for sensor networks, which leverages network coding to balance energy efficiency and end-to-end packet error rate. Fiandrotti et al. [START_REF] Fiandrotti | Band Codes for Energy-Efficient Network Coding With Application to P2P Mobile Streaming[END_REF] propose a band codes algorithm, a novel class of network codes specifically designed to preserve the packet degree distribution during packet encoding, recombination and decoding. Seferoglu et al. [START_REF] Seferoglu | Network Coding-Aware Queue Management for TCP Flows Over Coded Wireless Networks[END_REF] propose a network coding aware queue management scheme (NCAQM) that is implemented at intermediate network coding nodes and bridges the gap between network coding and TCP rate control. The NCAQM scheme is grounded on the network utility maximization framework, stores coded packets at intermediate nodes, and drops packets at intermediate nodes. Hong et al. [START_REF] Hong | Short Message Noisy Network Coding With Sliding-Window Decoding for Half-Duplex Multihop Relay Networks[END_REF] present a cooperative relaying strategy for half-duplex multihop relay networks. The author propose a short message noisy network coding with sliding-window decoding (SNNC-SW), the SNNC-SW has a better rate-scaling, lower decoding complexity and delay. Lee et al. [START_REF] Lee | Multi-way relay system with network coding in multi-spot beam satellite networks[END_REF] focus on multiparty video conferencing via a satellite. The author proposed protocol uses the multicasting routing information and number of video frame packets to generate coded packets. The proposed protocol ensures the reliable transmission of multicasting packet for mobile users using the decoding error rate for the random linear network coding batch.

Although some network coding algorithms are proposed to improve network performance, most of these approaches do not consider mobile energy efficient scenario. In this paper, we focus primarily on the mobile packet network problem of MANETs. We take into account maximizing network throughput, consider minimizing decoding delay. By constructing the appropriate network coding structure, we can achieve the higher energy efficient.

Qin et al. [START_REF] Qin | An energy-saving scheme for wireless sensor networks based on network coding and duty-cycle[END_REF] proposed an energy-saving scheme for wireless sensor networks based on network coding and duty-cycle (NCDES). The scheme determines the node's status based on the ID information which embedded in data information. When combining network coding and duty-cycle in wireless sensor networks, it will reduce transmission coding coefficients and retransmissions. Jiang et al. [START_REF] Jiang | Network coding-based energy-efficient multicast routing algorithm for multi-hop wireless networks[END_REF] proposes an energy-efficient multicast routing approach to achieve the data forwarding in the multi-hop wireless network. Analysis of the multi-hop networks energy metric and energy efficiency metric. Then the corresponding models are given network coding is used to improve network throughput. Antonopoulos et al. [START_REF] Antonopoulos | Analogue network coding-aided game theoretic medium access control protocol for energy-efficient data dissemination[END_REF] propose an ANC-aided game theoretic energy-efficient layout (ANGEL) for data dissemination in wireless networks. Júnior et al. [START_REF] Júnior | CodeDrip: Improving data dissemination for wireless sensor networks with network coding[END_REF] propose a show-case that applying Network Coding to data dissemination for Wireless Sensor Networks provides benefits even for small values (CodeDrip). CodeDrip is a data dissemination protocol with network coding capability. CodeDrip utilizes network coding to improve energy efficiency, reliability, and speed of dissemination. Qu et al. [START_REF] Qu | Opportunistic network coding for secondary users in cognitive radio networks[END_REF] develop an efficient network coding strategy for secondary users while considering the uncertain idle durations in cognitive radio networks. The authors propose a coding parameter selection algorithm for systematic network coding by considering the complicated correlation among the receptions at different receivers. Nawaz et al. [START_REF] Nawaz | GREEN protocol: gradient based energy efficient routing with network coding capacity[END_REF] proposes a gradient based energy efficient with network coding routing protocol (GREEN). The GREEN algorithm improves the lifetime of industrial wireless sensor network. Energy efficiency increases as more data is routed towards the sink with less number of transmissions.

Adaptive Length Sliding Window

We now focus to the adaptive length sliding window and the random network coding approaches. When using this approach, not all packets need to be coded together in a generation, only the code group operating in the same window.

Network Model

The network model is represented as G=(V, E) where V represents the set of nodes in the network and E denotes the set of directed edges. Each link e=(i, j)∈E means that node i can transmit to node j. We assume links are symmetric that if (i, j)∈E; (j, i) ∈E as well. Whether two links interfere with each other depends on the interference model adopted.

Adaptive Length Sliding Window

The conventional sliding window algorithm using a fixed window length, the computational complexity of the algorithm can increase the additional and proportional to the length of the sliding window. In order to effectively improve the performance of sliding window, we proposed an adaptive length sliding window algorithm using a network coding length. Adaptive length sliding window algorithm of the general structure and process the same as the traditional sliding window algorithm, just in the process according to the performance of adaptive window to resize the sliding window. The adaptive length sliding window of algorithm will be adaptive set the length of each sliding window, which can avoid the length of the sliding window is too big or too small. Fig. 1 illustrates the conceptual structure of the proposed adaptive length sliding window algorithm with a sliding window length of w information bits and a frame length of N information bits, assumed to be an integer multiple of w. Let us define the i-th (1≤i≤N/w) forward recursion and the i-th backward recursion computation as the forward metric and backward recursion computation computed from the beginning of the (i-1)-th sliding window to the beginning of the i-th sliding window, respectively. In the conventional sliding window algorithm, the length of the sliding window is fixed for all encoding windows, decoding windows and all decoder iterations. However, in the proposed adaptive length sliding window algorithm, the length of the sliding window is adaptively varied for each encoding windows, decoding window and each iteration depending on the reliability information obtained from the backward recursion.

We define the following formula to aggregate the most recent received packet R i , given the packet R i is the i-th packet in current sliding window W i .

… … R1

1st sliding window 2nd sliding window ist sliding window

N/wth sliding window f(1) R2 f(2) Ri f(i) RN/w f(N/w) R i = α•f(i) + (1-α) •R i-1 , and
f(i) = k•i + C (1) W i = β• W i-2 + (1-β) •W i-1
(2) where α, β(0≤α, β<1) is the weight assigned to the predictive sliding window value of latest received packet in window W i . f(i) is the linear regression function on packets. When the behavior of a service changes, current sliding window value R i will be updated in a new sliding window, therefore current sliding window may be updated as the new sliding window.

Network Coding Operation

The network coding process consists of randomly combining source symbols by using coefficients randomly selected within a finite field GF(2 q ). Let x 1 , x 2 , …, x n denote the source packets associated with the nodes. Linear network coding allows inter-mediate nodes to combine incoming packets (symbols). Each packet contains a linear combination of the source packets, as described by a vector of coefficients with respect to the source symbols called coding vector, which is sent appended to the packet.

The coding vector can be used by network nodes to decode the data, or further encode it. Encoding can be performed recursively, namely, with already encoded packets. Consider a node that has received and stored a set (a 1 , X 1 ), (a 2 , X 2 ), …, (a m , X m ), where X i denotes the information symbols and a i the appended coding vector to packet. This node may generate a new encoded packet (a ' , X ' ) by picking a set of coefficients e=(e 1 , e 2 , …, e m ) and computing the linear combination X ' = 1 m j j j e X = ∑ . The corresponding coding vector a ' is not simply equal to e, since the coefficients are with respect to the original packets x 1 , x 2 , …, x n ; in contrast, straightforward algebra shows that it is given by ' . This operation may be repeated at several nodes in the network. The node has received m the corresponding linear combinations of the source symbols. Each node v collects the coding vectors for the packets it receives (or generates) in a decoding matrix G v . To transmit, the node generates a linear combination whose coding vector lies in the vector space of its decoding matrix. Once a node receives linearly independent combinations, or equivalently, a basis of the n-dimensional space, it is able to decode and retrieve the information of the n sources. Decoding amounts to solving a system of linear equations with complexity bounded as O(n 3 ).

Assigning Probabilities to Sliding Windows

Once the window boundaries have been set around each position of each of the result sets that are to be fused, the next stage in the fusion process is to assign a probability score to each position based on those positions contained in the window surrounding it. P(d p , w|s), the probability of relevance of packet d in position p using a window size of w packets either side of p, given that it has been returned by input system s is given by

The use of the sliding window results in a smoother decrease in the probabilities later in the result set, when compared with using probabilities based on data available at each position alone.

Energy efficiency

Focusing on the energy aspect of the problem, we have chosen the utility function so as to quantify the lifetime of the nodes. The energy efficiency (η EE ) is evaluated as the expected number of successfully transmitted information bits L divided by the total consumed energy E tot in the MANET, i.e., EE (bits) = (Joule)

tot L E η (4)
where L is the total amount of useful data delivered and E tot denotes the total energy consumed.

In MANETs, as long as the mobile nodes are deployed in the transmission range of the transmitting nodes, they receive these packets for free even if these packets do not belong to their duties. Having analyzed the ALSW-NCEE's performance, we are able to derive a closed-form formula that describes the average energy consumption in the network

E tot = E NC + E min + E EC + E SW ( 5
) where E NC represent the average energy consumption during the network coding and the initial transmission from the source node, E min denotes the energy waste in a perfect scheduled cooperative phase, E EC is the energy consumed during the contention phase, and E SW is the sliding encoding window during the sliding energy consumption.

The energy consumed in transmitting and receiving a packet is denoted by P T , P R , respectively. Furthermore, the relationship between energy and power is given by E=P•t, where the terms ε, P and t represent the energy, the power and the time, respectively. We recall that the network consists of a source node, a destination node and a set of n intermediate nodes (code node and sliding node). Therefore, considering the network topology, we have:

E NCS =P T •T A +(n+1) • P R •T A (6
) where E NCS represents the average energy required to transmit a NC packet during the contention phase among all the intermediate nodes. Computing the energy consumed during the sliding encoding window phase constitutes one of the most challenging parts in this analytical model. Let us start by defining that:

E NC = E r • E NCS (7)
With coding, packets are delivered to the application in a packet-by-packet manner. For every coding packet, the receiver node needs to receive B independent coded packets in order to decode and recover the original coding packet. Let N i denote the number of transmitted coded packets until the receiver decodes coding block i. p is the packet loss rate. The probability that the receiver receives exactly B coded packets Simulation Experiments

In this section, we evaluate and compare the performance of the proposed ALSW-NCEE algorithm for MANETs with SenseCode algorithm [START_REF] Keller | SenseCode: Network Coding for Reliable Sensor Networks[END_REF] and ANGEL algorithm [START_REF] Antonopoulos | Analogue network coding-aided game theoretic medium access control protocol for energy-efficient data dissemination[END_REF]. We implemented the code by integrating the Network Simulator NS-2 [START_REF]The Network Simulator -NS-2[END_REF] to perform the simulations for the MANETs with adaptive length sliding window network coding with energy efficient algorithm.

Simulation Scenario

We evaluate ALSW-NCEE in a wireless packets scenario where one source distributes a packet sequence to receiver nodes. Nodes are randomly and uniformly located over a 1000m × 1000m area, with a node transmission range of 250 m [START_REF] Waxman | Routing of Multipoint Connections[END_REF]. Node mobility follows the random waypoint model. The generation distributed by the source is called seeding position within the wireless packets stream. The results of the simulation are positive with respect to performance. The corresponding simulation parameters are summarized in Table 1.

Simulation Results

In this section, we evaluate and compare the performance of the proposed ALSW-NCEE algorithm for MANETs with SenseCode algorithm [START_REF] Keller | SenseCode: Network Coding for Reliable Sensor Networks[END_REF] and ANGEL algorithm [START_REF] Antonopoulos | Analogue network coding-aided game theoretic medium access control protocol for energy-efficient data dissemination[END_REF].

In Fig. 2, we compare the average network throughput of ALSW-NCEE with those of SenseCode and ANGEL under node's mobility speed for three algorithms. From the Fig. 2 we can see that when the node's mobility speed increases, SenseCode and ANGEL average network throughput is lower than that of ALSW-NCEE. Therefore we emphasize that the main aim of these algorithms is to avoid any source of energy consumption that rise due to bad wireless links, hence, ALSW-NCEE has an advantage in transmission, than consuming energy by limiting the transmitted packets, and its utilization to adaptive length sliding window network coding algorithms allows for reliable transmission and less energy due to decreased re-transmissions encountered. In Fig. 3, we test the ALSW-NCEE performance in encoding overhead. We plot the encoding overhead versus node's mobility speed for three algorithms. The encoding overhead increases as the packets transmission increases because the node's mobility speed increases. ALSW-NCEE reduces the encoding overhead the best. Fig. 3 shows the encoding overhead of ALSW-NCEE, SenseCode and ANGEL, which use the adaptive length sliding window network coding and energy efficient that minimize the encoding overhead. As the node's movement speed is increased, the distance between the nodes is changing, the energy consumption of the nodes increases. Observe in Fig. 4 that ALSW-NCEE significantly improves the energy consumption of the nodes, hence reducing the frequency of path update events. The energy consumption of ALSW-NCEE is lower than that of SenseCode and ANGEL, especially when the node's movement speed changes from 0 to 20.

Conclusion

In this paper, we discuss adaptive length sliding window network coding and energy efficient problem, which may deal with the sliding window network coding model for researching in wireless networks. by solving a set of linear equations. The performance of the ALSW-NCEE is studied using NS2 and experimentation to assess the network throughput, encoding overhead, energy consumption, energy efficiency of ALSW-NCEE enabled mobile node. The ALSW-NCEE is shown to achieve significant performance gain.

Fig. 1 .

 1 Fig. 1. Depiction of the proposed adaptive length sliding window algorithm.

,

Fig. 2 .

 2 Fig. 2. Network throughput vs. Node's mobility speed (m/s).

Fig. 3 .

 3 Fig. 3. Encoding overhead with Node's movement speed (m/s).

Fig. 4 .

 4 Fig. 4. Energy consumption with Node's movement speed (m/s).

Fig. 5

 5 Fig.5illustrates the energy efficiency versus the node's movement speed with various traffic communication scenarios. The energy efficiency presents the network throughput by multipath receivers versus the number of network coding data packets supposed to be received. The proposed ALSW-NCEE scheme has the better energy efficiency than that of SenseCode and ANGEL algorithm.

Fig. 5 .

 5 Fig. 5. Energy efficiency with Node's movement speed (m/s).

  It presents an Adaptive Length Sliding Windowbased Network Coding for Energy Efficient algorithm in MANETs (ALSW-NCEE).We provide a thorough description of adaptive length sliding window, network coding, and energy efficient in MANETs. When the destination node receives enough original and coded packets from two transmission phases, it retrieves all the packets Node's movement speed (m/s) Energy consumption (nj)

Table 1 .

 1 Simulation Parameters

	Number of nodes	100
	Network area	1000m × 1000 m
	Transmission range	250 m
	Simulation time	600 seconds
	Transmission range	250 m
	Beacon period	100 ms
	Communication model	Constant Bit Rate (CBR)
	Message size (b msg )	512 bytes/packet
	E elec	50 nj/bit
	E start	2500 nj/packet
	Max sending power	100 mW
	Receive power	56 mW
	Examined routing proto-col	SenseCode[7], ANGEL[14]

* This work is supported by The National Natural Science Foundation of China (No. 61572012).

after the n-th packet transmission by the sender for coding packet i is given by a negative binomial distribution, i.e., 1 { } (1 ) , 1

which is the probability that B-1 packets out of the first n-1 transmissions are received successfully and the last transmission is a success too. Recall that, for the moment, we are assuming all coded packets are independent following the mechanism described earlier. Therefore, we obtain that,


Jianhui Lv
email: lvjianhui2012@163.com

Xingwei Wang
email: wangxw@mail.neu.edu.cn

Min Huang
email: mhuang@mail.neu.edu.cn

ACO-inspired ICN Routing Scheme with Density-based Spatial Clustering

This paper proposes a new Ant Colony Optimization (ACO)-inspired Information-Centric Networking (ICN) routing scheme with Density-based Spatial Clustering (DSC). At first, the content concentration model is established with network load to address interest routing; in particular, we investigate the failed situation of content retrieval. Then, the dot product method is used to compute similarity relation between two routers, which is considered as clustering reference attribute. In addition, DSC is exploited to detect core nodes which are used to cache contents during the data routing process. Finally, the proposed scheme is simulated over Mini-NDN, and the results show that it has better performance than the benchmark scheme.

Introduction

In recent years, Ant Colony Optimization (ACO)-inspired solutions have been proposed to address Information-Centric Networking (ICN) routing issue [START_REF] Shanbhag | SoCCeR: services over content-centric routing[END_REF][START_REF] Lv | ACO-inspired Information-Centric Networking routing mechanism[END_REF][START_REF] Lv | Ant colony optimization inspired ICN routing with content concentration and similarity relation[END_REF]. In ACO-inspired ICN solution which relies on Named Data Networking (NDN) architecture, Interest packet and Data packet are regarded as Interest ant (Iant) and Data ant (Dant) respectively. Lv et al. [START_REF] Lv | Ant colony optimization inspired ICN routing with content concentration and similarity relation[END_REF] considered user interest request and established similarity relation between two routers by the cached contents, i.e., ACO-inspired ICN Routing with Content concentration and Similarity relation (AIRCS). During the Iant routing process, similarity relation was regarded as a significant inspired factor to conduct the forwarding of Iant. This paper improves AIRCS based on Density-based Spatial Clustering (DSC), and the major contributions are summarized as follows. (i) The dot product method is used to compute similarity relation between two routers, in order to save more computation time. (ii) For the failed Iant, the corresponding updating strategy of content concentration (pheromone) is different from that of the successful Iant, and the updating process considers network load. (iii) DSC based on similarity relation is used to find core routers, in order to cache the multiple content during the Dant routing process.

2 The Proposed AIRD Scheme

Content concentration design

The computation of content concentration regarding the edge between routers R i and R j (denoted by e i,j ) is the fundamental task. Let T i,j (t, I) denote the total content concentration over e i,j at time t after I(∈ N) iterations,

T i,j (t, I) = (1 -ρ) • T i,j (t, I -1) + cc i,j (t, I), (1)
where ρ is a volatilization coefficient of content concentration, 1 -ρ is a residual factor of content concentration, and 0 < ρ < 1 prevents the infinite accumulation of content concentration. In addition, cc i,j (t, I) denotes the content concentration over e i,j by some of m (∈ N) Iants after the I -th iteration, and it is defined as follows.

cc i,j (t, I) = m λ=1 τ λ i,j (t, I) • x λ , (2)
where x λ ∈ {0, 1}. Let ia λ denote arbitrary Iant, here λ ∈ {1, 2, • • • , m}: if ia λ traverses e i,j , x λ = 1; otherwise, x λ = 0. In addition, τ λ i,j (t, I) denotes the content concentration over e i,j left by ia λ after the I -th iteration. When ia λ finds the content within one iteration, τ λ i,j (t, I) is defined as follows.

τ λ i,j (t, I) = cos(1 -e -pconj ) hop j • L λ • I . ( 3
)
where pcon j is the times which R j provides the content, hop j is the hop count between interest requester and R j , and L λ is the total distance traversed by ia λ within one iteration. In addition, cos(1 -e -pconj ) is a decreasing function regarding pcon j , and its function is to reduce and balance node load with large pcon j .

When ia λ cannot find the content within one iteration, τ λ i,j (t, I) is defined as follows.

τ λ i,j (t, I) = γ • hop -σ j L λ . (4)
Among them, σ reflects the importance of Iant to the whole network during the process of updating content concentration; γ is a regulatory factor to avoid the situation where hop -σ j /L λ becomes too large or small.

Similarity relation computation

Suppose that R i consists of h i types of contents and each one is regarded as a class of user interests, then

R i ∼ int(i) 1 , int(i) 2 , • • • , int(i) hi , (5)
where int(i) l is one type of contents, 1 ≤ l ≤ h i . Suppose that int(i) l is quantified as int(i) l which equals to l, and that int(i) l corresponds to N (i) l content items, then

R i := N (i) 1 , 2 • N (i) 2 , • • • , h i • N (i) hi , (6)
Assume that R i and R j have p same types of contents, when R i and R j are adjacent, then

r i,j = 1 M • max{hi,hj } l=1 l • N (i) l • l • N (j) l = l 2 M p l=1 N (i) l • N (j) l , (7)
M = max ∀i,j p l=1 N (i) l • N (j) l , (8)
where r i,j is the similarity relation between R i and R j . Especially when R i and R j are not adjacent, r i,j = 0.

DSC-based core detection

In this paper, the DSC-based method is used to determine core routers, and similarity relation between two routers is used as clustering reference attribute. Let N ε (R i ) denote the number of routers with a neighbourhood, and it is defined as follows.

N ε (R i ) = {R j ∈ D|mr i,j ≥ eps}. (9)
Among them, D is the ε neighbourhood regarding R i ; mr i,j is the clustering metric between R i and R j ; eps is a threshold. the uniform distribution; instead, AIRCS considers the content as an entire object, which leads to serious load in terms of some links. Fig. 3 shows execution time for AIRCS and AIRD. We can observe that execution time of AIRD is always smaller than that of AIRCS, and two reasons are as follows. (i) AIRD uses dot product method to compute similarity relation, which can save much more computation time than the using of absolute subtrahend method in AIRCS. (ii) AIRD designs and updates content concentration based on discrete model rather than continuous model, which decreases much more than AIRCS.

Conclusions

This paper extends and deepens the previous research on ACO-inspired ICN routing scheme, and the contributions are triple, i.e., (i) computing similarity relation based on dot product method, (ii) processing the successful packets and failed packets when the content concentration is updated and (iii) detecting core routers to cache the content during the Dant routing process. Then, the performance is evaluated, and the simulation results have shown that the proposed AIRD is more efficient and effective than the previous work.

Fig. 1 .

 1 Fig. 1. Routing success rate.

Fig. 2 .

 2 Fig. 2. Load balance degree.

Fig. 3 .

 3 Fig. 3. Execution time.

Acknowledgments

This work is supported by National Natural Science Foundation of China (Grant No. 61572123) and National Science Foundation for Distinguished Young Scholars of China (Grant No. 71325002).

If R i and R j are adjacent, mr i,j = r i,j . If R i is connected to R j according to k routers, denoted by R c1 , R c2 , • • • , R ck respectively, we have

which indicates that mr i,j is computed by indirect method among k + 2 routers. Then, the definition about core router is shown as follows.

Definition 1 (Core router):

where ξ is a positive constant.

Routing decision

The routing decision consists of two parts, i.e., ACO-based Iant routing and DSC-based Dant routing. The first one is same to that in [START_REF] Lv | Ant colony optimization inspired ICN routing with content concentration and similarity relation[END_REF] and [START_REF] Lv | ACO-inspired ICN routing mechanism with mobility support[END_REF]. If the number of iterations reaches the maximum, the Iant routing is finished and the Dant routing starts, as follows.

At first, content provider generates some Dants. Let Dn denote the number of Dants, and it is defined as follows.

where Sc is the content size, o is a positive integer, B is the unit of byte, and the operator of ceiling guarantees that Dn is a positive integer. Dn Dants are denoted by Dant(1), Dant(2),

Secondly, for one of Dn Dants, it carries the corresponding content from content provider to interest requester along the path which provides the closest content copy for interest requester. When arriving at R i , it first checks whether R i is a core router. If yes, two cases emerge: (i) when Content Store (CS) is not full, the carried content is cached to R i ; or (ii) when CS is full, a replacement strategy is used and then the carried content is cached to R i . Otherwise, it checks Pending Interest Table (PIT) directly to find an appropriate interface in order to forward itself.

Finally, interest requester checks whether the generated Dn Dants have been received. If yes, their carried contents are recombined in the order of Dant(1), Dant(2), • • • , Dant(Dn). Otherwise, interest requester waits until all Dants arrive.

Simulation results

The proposed ACO-inspired ICN Routing scheme with DSC (AIRD) is simulated over Mini-NDN, and Deltacom topology with 97 nodes and 124 edges [START_REF] Lv | ACO-inspired ICN routing mechanism with mobility support[END_REF] is selected to do the performance evaluation by sending 1000 interest requests based on 100 times simulation. α = β = σ = 1, η = m = 10, ρ = eps = 0.5, γ = 2, ξ = 3 and o = 8. Fig. 1 shows routing success rate for AIRCS and AIRD. We can observe that routing success rate of AIRD mainly concentrates on 96% and 97%, whilst that of AIRCS mainly concentrates on 93% and 94%. The emergence of these abnormal results is suffered from the congestion of interest requests, which causes the instability of system. Besides, the data selection has a certain randomness. From the global perspective, AIRD has higher routing success rate than AIRCS, and two reasons are as follows. (i) AIRD handles the failed Iants besides the successful Iants and conducts them to gather around the closest content copy, which increases retrieval probability. (ii) AIRD uses DSC to find core routers to cache the content during the Dant routing process, which guarantees content retrieval, especially for the similar and even same interest requests.

Fig. 2 shows load balance degree for AIRCS and AIRD. We can observe that load balance degree of AIRD is always lower than that of AIRCS, which means that AIRD is much more stable than AIRCS. Two reasons are as follows. (i) In the Iant routing stage, AIRD considers network load when updating content concentration. (ii) in the Dant routing stage, AIRD considers the fine granularity of content to divide the content into some pieces which are


Bingyu Zhou
email: zhouby@buaa.edu.cn

Guangjun Qin

Limin Xiao
email: xiaolm@buaa.edu.cn

Zhisheng Huo

Bing Wei

Jiulong Chang

Nan Zhou

Li Ruan

Haitao Wang

Zipeng Wei

Balancing Global and Local Fairness Allocation Model in Heterogeneous Data center

Aiming at the problem that the bandwidth allocation method in heterogeneous data center can't take into account the global and local fairness, we propose an allocation method called GLA that satisfies fair attributes and can improve the utilization of system resources by nearly 20% when the number of clients are more than six contrasting with the existing methods. The algorithm is also protable and scalable that can adapt to most of systems.

Introduction

The existing methods of bandwidth allocation [START_REF] Gutman | Fair allocation without trade[END_REF][START_REF] Yusuke | A Bandwidth Reallocation Scheme to Improve Fairness and Link Utilization in Data Center Networks[END_REF] in the heterogeneous data center such as DRF, DRFH(e.g., [START_REF] Ghodsi | Dominant resource fairness: Fair allocation of multiple resource types[END_REF][START_REF] Dolev | No justied complaints: On fair sharing of multiple resources[END_REF][START_REF] Parkes | Beyond dominant resource fairness: Extensions, limitations,and indivisibilities[END_REF]), BAA [START_REF] Wang | Balancing fairness and efficiency in tiered storage systems with bottleneck-aware allocation[END_REF][START_REF] Wang | Brief Announcement: Fairness-Efficiency Tradeoffs in Tiered Storage Allocation[END_REF] and UAF [START_REF] Huo | Hybrid Storage Throughput Allocation Among Multiple Clients in Heterogeneous Data Center[END_REF] have a poor performance for that the utilization only can up to 70% in the best situation and the usage of resource is unbalanced. Through contrasting the distribution result among above methods, we found the situation that the allocation in the entire data center meet the fairness but on each server is unfair or the global allocation shows unfairness and the total throughput is at a low level for applying fair allocation algorithm on each server. These methods are restricted to fair policies and the efficiency of global and local, so we must balance the allocation of global and local to enhance the utilization rate. The allocation model called Balancing Global and Local Fairness Allocation(GLA) we proposed in the paper can solve this problem. It includes global allocation strategy and local allocation strategy., meanwhile setting the global parameters to coordinate the consistency of the two strategies.

In the second part, we introduce the GLA model and implementation architecture. The performance evaluation results will be described in Section 3. In the end, we will conclude our work.

GLA Allocation Model and Scheduling Architecture

The functions of GLA model are shown as follows:

Maximize            S j k l h jls D i k l m ild jl il x x 1 1 1 1 )) ( ( ) ) ( ( (3.1)                     ) ( 1 ) ( 1 1 1 S i or D i h k l il il k l il   (3.2)                                l l sl S j C C D i m h ild dl S j h m C C D i ild S j D i V l C x C x dl sl il il jl jl dl sl , , ) ( ) (   (3.3)                   l l il il ild jls h m jls ild n C jls n C ild S j D i m h x x x x x x jl jl sl dl , , , (3.4)
                          S j D i x x x x i i j j m h k l ild k l jls h m k l jls k l ild , 1 1 1 1 (3.5)                                    k l jls k l ils h m k l jls h m k l ils k l jld k l ild m h k l jld m h k l ild x x then x x if S j i x x then x x if D j i j j i i j j i i 1 1 1 1 1 1 1 1 , , , , , , (3.6)
The scheduling architecture of the heterogeneous data center has two layers(Fig. 1), GLA is deployed in the second layer. The first layer scheduler assigns the requests of clients to the corresponding server in terms of the original weight, the second tier calculate the bandwidth allocated to each client based on the GLA algorithm. Different form other algorithm, the global parameters produced by GLA will be send to the first layer to assist the next allocation. The algorithm obeys the principle of conservation. The throughput of allocation subjects to the limitations that are presented into progressive from local to the whole.

Conclusion

In this paper,we focus on the problem that the existing allocation methods can't balance global and local fairness, and propose a bandwidth allocation algorithm called GLA. Through experiments, we exhibit that GLA is fairness and improve the throughput of heterogeneous data center for 19.8% when the number of clients are more than six. GLA is more suitable for large-scale clients.

Fig. 1 ..Fig. 2 .Fig. 3 .

 123 Fig. 1. The scheduling architecture of heterogeneous data center

Acknowledgments. This work is supported by the National Natural Science Foundation of China under Grant No. 61370059 and No. 61232009, Beijing Natural Science Foundation under Grant No. 4152030, the fund of the State Key laboratory of Software Development Environment under Grant No. SKLSDE-2016ZX-13, the State Administration of Science Technology and Industry for National Defense, the major projects of high resolution earth observation system under Grant No. Y20A-E03.


Katarina Drža Jić
email: katarina.p.drzajic@apeiron-edu.eu

Frank Vega
email: vega.frank@gmail.com

Working Conditions as a Factor of Productivity in SMEs

Keywords: SMEs, working conditions, jobs, investment, current standards JEL: J24, J30

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Introduction

The quality of jobs in small and medium-sized enterprises (SMEs), particularly in developing countries, is often poor [START_REF] Bell | The World Bank: Small and medium enterprises (smes) finance[END_REF]. However, SMEs play a major role in most emerging economies, since recent studies have shown SMEs contribute up to 60% of total employment and up to 40% of national income(GDP) [START_REF] Bell | The World Bank: Small and medium enterprises (smes) finance[END_REF]. Small business owners and managers often view the obligation to apply better working conditions to their workers as a burden in terms of financing and administration [START_REF] Atkinson | You try to be a fair employer": Regulation and employment relationships in medium-sized firms[END_REF]. As workers in SMEs make up for the majority of the global workforce (International Labour Office/Organization (ILO), 2012), the impact of these barriers on economic productivity and working conditions is crucial for encompassing a global dialogue on universal coverage, economic growth and development.

The effects of psychological, social, cognitive, and emotional factors on the economic decisions of individuals and institutions and the consequences for market prices, returns, and resource allocation have been deeply studied since the Adam Smith's pioneer work [START_REF] Nava Ashraf | Adam smith, behavioral economist[END_REF]. Even famous and diverse approaches, such as the mathematical work of John Nash (Nobel Memorial Prize in Economic Sciences and the Abel Prize) (John [START_REF] Nash | Non-cooperative games[END_REF] or the recent biological studies on animals (Raymond C. [START_REF] Battalio | Income-leisure tradeoffs of animal workers[END_REF], have shown this is the main point in the economical development and growth.

Social protection, wages, working hours, work organization and arrangements to adapt working standards to the demands of life outside work are core elements which are directly related to this topic [START_REF] Tom | A behavioral framework for securities risk[END_REF]. It is a true fact in all countries of the world, the workers in SMEs are probably the most susceptible and most affected by adverse working: low payment, lack of employment security, long working hours, unstable workplaces, lack of social protection and no consideration for a work-life balance [START_REF] Fagan | In search of good quality part-time employment[END_REF]. Can productivity in SMEs be increased by investing in working conditions? Recent studies have shown better working conditions can improve the performance of SMEs [START_REF] Croucher | Can better working conditions improve the performance of smes[END_REF]. The research discusses some evidence which prove how good practices can have a positive impact in economic enterprise-level outcomes [START_REF] Croucher | Can better working conditions improve the performance of smes[END_REF].

Nowadays, productive employees are connected with capable entrepreneurs that guarantee better working conditions and pay higher wages [START_REF] Walter | Chapter 33 firm size and wages[END_REF]. The fact is that big enterprises pay efficient wages to prevent shirking [START_REF] Walter | Chapter 33 firm size and wages[END_REF]. They are capable of doing that by making a balance between the actual wages and the costs of the company [START_REF] Walter | Chapter 33 firm size and wages[END_REF]. SMEs need strategies to fulfill their job vacancies and avoid the negligence of worker responsibilities in order to be more competitive and keep the economic growth in the future. This study represents the results (based on a suggested core criteria) in evaluating the current state of knowledge on the relationship between good practices relating to working conditions with feasible and positive outcomes in SMEs based on international references.

Core Methodology

A well-recognized Jobs Rated Methodology was developed with the data provided from the Bureau of Labor Statistics (BLS), a division of the U.S. Department of Labor, to measure what the riskiest or most profitable jobs in that country were (CareerCast.com, 2017). The core criteria is based on general categories that are inherent to every job: environment, income, outlook, and stress (CareerCast.com, 2017). We have discussed three core criteria: Environment, Benefits for Women and Diversity. These factors have experienced a certain boom since they have become very popular within the work force in the recent years (Fortune Magazine, 2017). Our methodology will focus on two aspects of each criteria: presenting innovations by large companies in terms of working conditions and suggesting practical strategies for SMEs regarding these subjects.

Environment

Quotes: "Employees who are felt part of positive workplaces are people who are excited to be part of a larger purpose on SME's goals" (European Commission, 2013).

Positive aspects in the work environment are essential for workers' mental and physical wellbeing [START_REF] Hemström | [END_REF]. Frequently, these aspects are focused on social security, including social and health protection as the key areas. Some ranking systems used to evaluate a job's environment, consider and measure the physical work environment as one of the basic components (CareerCast.com, 2017). However, we have studied some other good working conditions on this subject based on emotional environments since the Technological Advances have created more intellectually demanding jobs (theguardian.com, 2015). Nowadays, the following aspects have risen the companies values in the global market and are viewed as important by the work force (Fortune Magazine, 2017).

Transparent and Open Communication

This aspect addresses the employees' need to feel that they belong in the organization. Psychologically, work becomes meaningful for them because they know how their contribution affects the organization which are affiliated with (Karen K. [START_REF] Myers | Millennials in the Workplace: A Communication Perspective on Millennials' Organizational Relationships and Performance[END_REF]. It is essential for staff to discuss the organization's mission and values (Karen K. [START_REF] Myers | Millennials in the Workplace: A Communication Perspective on Millennials' Organizational Relationships and Performance[END_REF]. This is summarized in exact explaining, from time to time, the current situation of the company during retreats, successful outcomes or even informing on the stock values. This frequent open discussions could get people involved and allow them to share their views and perspectives while the management can give their own perspectives on how to fulfill the organization's goal and mission (Karen K. [START_REF] Myers | Millennials in the Workplace: A Communication Perspective on Millennials' Organizational Relationships and Performance[END_REF].

Large company strategies. The airline industry is often criticized for rude employees and poor customer service, but Southwest Airlines overcame those trends (business.com, 2017). Customers loyal to Southwest often point to happy and friendly employees who try hard to help (Entrepreneur, 2015). Southwest has been operating for more than 40 years (business.com, 2017). During all that time, the company has managed to communicate its goals and vision to employees in a way that makes them a part of a unified team (Entrepreneur, 2015). Southwest also gives employees the "permission" to go that extra mile to make customers happy, empowering them to do what they need to do to meet that vision (Entrepreneur, 2015).

SMEs strategies.

Recent research in the UK looked at how well businesses communicate staff benefits (European Cleaning Journal, 2014). It found an SME with 250 employees that offers good benefits but fails to communicate them. It spends 302,000 euros a year more on staff turnover and sickness absence than those that have comparable employee benefit packages, but also have good internal communication processes (European Cleaning Journal, 2014). Some SMEs strategies are suggested to face this problem:

Open door policy Encourage an open door policy for all managers so they are more approachable. Organize the employee workplaces (desks, offices, etc) on different floors inside the company providing a diverse environments and therefore promoting more interpersonal communication. Use separate offices for meetings only.

Crisis communications tools Help you deal with emergency communications or to share information on important priorities. Consider technological approaches such as video conference calls or traditional ones such as small group meetings to encourage the employees in face-to-face communication. Suggestion boxes are also a good option in critical or daily situations in the company, because they enable the employees to raise their concerns and issues anonymously and can prevent employees' shirking or quitting if the company is uncapable to manage the appeals.

Technological and traditional tools Company newsletter is an ideal medium for providing employees with information: including client testimonials, employee success stories and updates on company news, events and strategies. In the same way, create an intranet site to put important information online and update it regularly. Finally, use modern resources on the web such as encyclopedias, shared documents repositories and social medias like forums or chats.

It is optional to use internet or not for this purpose. On the one hand, the development of intranet web sites and multimedia infrastructure could be expensive, but can guarantee some interests for the company such as the security settings and secrecy of confidential issues. On the other hand, companies, using wider internet conditions, engage more work force since younger staff become increasingly switched on to sites like Facebook. At the same time, the traditional and still powerful tools such as posters in areas of high visibility within an office, factory or workplace, can make a useful impact.

Work-Life Balance

When employees fulfill their various needs and goals in life, such as those of family, spiritual pursuits and self-growth, then they can feel more confident and perform their best at work (American Psychological Association, 2010). On the one hand, hiring and expecting the best from employees can easily become a stressor if an enterprise does not allow for good work-life balance. On the other hand, the work-life balance can promote creativity and thinking out-of-thebox. According to many researchers studying the field of employees' family needs, they agree this is one the most important issue that a working organization faces (United States Department of Labor: Bureau of Labor Statistics, 2017b). In addition, dealing with healthcare and recognition for hard work are also main points in work-life expectations (American Psychological Association, 2010).

Large company strategies. Google has been recognized for years as the best company providing many of the recent perks in work-life balance (Fortune Magazine, 2017). Just to mention a few of them, Google offers free meals, employee trips and parties, financial bonuses, gym, hairdresser and laundry services (Fortune Magazine, 2017). At the same time, Google is not only famous for luxurious perks, but it also takes a rigorous analytical approach to moral ethics (Fortune Magazine, 2017). Besides, Google boosted its parental leave policies and this has directly impacted its productivity (Fortune Magazine, 2017). Google's employees are known to be driven, talented and among the best (Business Insider, 2014).

SMEs strategies. Results from working arrangements in SMEs have proved that the flexibility in this sector is vital. For instance in countries with emerging economies, such as Ireland, it has been estimated that 53% of SMEs operate one or more family friendly work arrangements, although the overall number of employees involved with such measures remains low [START_REF] Fisher | Investing in People: Family-Friendly Working Arrangements in Small and Medium-sized Enterprises in Ireland[END_REF]. Some SMEs strategies are suggested to face this problem:

Entertainment policy Participating in hobbies provides a variety of benefits that extend into the workplace such as developing new skills, new thought processes and really challenges them to learn something new and develop the employee skill set (Fast Company, 2015). Arrange cultural activities (such as music concerts), playing team sports and providing indoor or outdoor colleague meetings such as parties or trips to enjoy the nature, camping, fishing or simply going to the beach. But mostly, try to involve the employees directly just by making them protagonists and possible organizers on these activities.

Physical activity Employee sickness and absence is a great expense for business. For example, 175 million working days were lost to illness in 2006 and 3 percent of people were off work due to illness frequently (Wayne N. [START_REF] Burton | The association of health status, worksite fitness centre participation and two measures of productivity[END_REF]. Promote informal exercise classes for the employees inside the employees' workplace through inexpensive alternatives such as lunchtime walks or 5 minute of instant recess with dynamic aerobic sessions. Employees who exercise for at least 30 minutes a day, three times a week are 15 percent more likely to have better job performance (Ray M. [START_REF] Merrill | Self-rated job performance and absenteeism according to employee engagement, health behaviors, and physical health[END_REF]. Recent studies based on 618 employees from five SMEs diverse companies prove the exercise practices across these companies effectively improved employees' health, performance and productivity (Ray M. [START_REF] Merrill | A small business worksite wellness model for improving health behaviors[END_REF].

Emotional and subjective support Psychological theory suggests that rewards are a positive reinforcement that can motivate employees to reach their full potential (Kelly [START_REF] Burton | A study of motivation: How to get your employees moving[END_REF]. This is usually used in organizational behavior management by rewarding employees who make effort in their work [START_REF] Burton | A study of motivation: How to get your employees moving[END_REF]. In this way, SMEs cannot compete with large companies as the same level, but the reward here does not have to be monetary in nature [START_REF] Burton | A study of motivation: How to get your employees moving[END_REF]. Rewarding employees sometimes even with a simple verbal recognition by the supervisor will give them more motivation (Kelly [START_REF] Burton | A study of motivation: How to get your employees moving[END_REF]. Apart from having a system of monetary rewards, daily interaction can also be a good means of recognizing efforts. Make these in a specific and personal way for the employee to feel that what they do is being taken seriously and appreciated (Kelly [START_REF] Burton | A study of motivation: How to get your employees moving[END_REF]. Organize and invest in teamwork relationships: one of which could be peer-to-peer recognition and reward. Recent researches, taken from over 200,000 employee responses and more than 500 organizations, found that peer relationships are the first factor in employees choosing to go the extra mile (TINYpulse, 2014).

Benefits for Women

Quotes: "There is almost universal interest among SME employers in finding out more about the arrangements and in being advised as to what other employer organizations are doing in this context" [START_REF] Fisher | Investing in People: Family-Friendly Working Arrangements in Small and Medium-sized Enterprises in Ireland[END_REF].

SME employers have arrangements applying to female staff to help with childcare [START_REF] Fisher | Investing in People: Family-Friendly Working Arrangements in Small and Medium-sized Enterprises in Ireland[END_REF]. These arrangements predominate in those companies with a predominantly female workforce [START_REF] Fisher | Investing in People: Family-Friendly Working Arrangements in Small and Medium-sized Enterprises in Ireland[END_REF]. Likewise, very few SMEs have either established formal policies for their staff or have undertaken any formal evaluation of their operation: this subject is not the exception [START_REF] Fisher | Investing in People: Family-Friendly Working Arrangements in Small and Medium-sized Enterprises in Ireland[END_REF]. Increasing women education contributes to higher economic growth (OECD, 2012). The increased women education has produced 50% of the economic growth according to the Organization for Economic Co-operation and Development (OECD) over the past 50 years (OECD, 2012). However, there are still factors that directly and negatively impacts women's participation in the labor force. For example, in the year 2014, the countries in the European Union had the 25% of women being absent from work due to childcare and other family and personal responsibilities, versus only 3% of men [START_REF] Eurostat | Labour market statistics[END_REF]. In this way, efforts to promote gender equality often focus disproportionately on working mothers (Fortune Magazine, 2017). However, parents with young children represent only a portion of the female workforce in developed countries like the US (Fortune Magazine, 2017). For that reason, we propose some other progress steps which have risen the income and prestige of well-known companies and have motivated their work force (Fortune Magazine, 2017).

Women (like men)

Recent research found that women employees who said they were treated as full team members regardless of position were five times more likely to plan long-term career at their jobs, compared to colleagues who didn't feel this way (Fortune Magazine, 2017). In a US survey, women who said they made a difference at their company were 27 times more likely to progress in their workplace (Fortune Magazine, 2017). Women's management and senior positions have considerably increased in developed countries in recent years such as Canada (Statistics Canada, 2017) and Australia (Workplace Gender Equality Agency, 2016). It is a fact that very competitive economies have invested in professional development and managing positions for women. For instance, in 2016 around 40% of managers were women according to the Bureau of Labor Statistics from US (United States Department of Labor: Bureau of Labor Statistics, 2017a).

Large company strategies. Nowadays, large companies have been focusing on important investments for professional development for women in their working teams. It is not a coincidence that a recognized survey in 2017 shown us the No. 1 company on the list of 100 best workplaces for women from US was Texas Health Resources (Fortune Magazine, 2017). The company helps employees built their academic credentials from the General Educational Development (GED) through graduate coursework (Fortune Magazine, 2017). This programs places a particular emphasis on the specializations for licensed nurses (Fortune Magazine, 2017). These include a one-year residency and mentorship support for new graduates, as well as a flexible career program for mid-career nurses who can continue their patient care while learning new skills (Fortune Magazine, 2017).

SMEs strategies. Gender equality in SMEs is a moral and economic imperative and affects both women and men (Anne [START_REF] Marie | Who takes the credit? gender, power, and control over loan use in rural credit programs in bangladesh[END_REF]. The improvements in women's working conditions require considerable commitment by development workers and a willingness to cope with the sometimes violent and disruptive consequences of challenging gender privilege (Anne [START_REF] Marie | Who takes the credit? gender, power, and control over loan use in rural credit programs in bangladesh[END_REF]. SMEs need a strong commitment to understanding of the constraints that women often have to overcome, due to the different traditional structural and social expectations and responsibilities of women and men [START_REF] Syed Zamberi | Strengthening access to finance for women-owned smes in developing countries. Equality, Diversity and Inclusion[END_REF]. Some SMEs strategies are suggested to concrete actions in order to translate commitments into reality.

Safe and comfortable workplace Make workplaces safe and free from violence and sexual harassment through policies that guarantee confidential complaints with direct and clear warnings about the moral positions of the company regarding this subject exposing the possible consequences from its violation. Emphasize workplace hygiene, since clean work space is a powerful psychological factor especially for women (Darby E. [START_REF] Saxbe | No place like home: home tours correlate with daily patterns of mood and cortisol[END_REF]. Involve pregnant and mother of young children in alternative activities inside the workplace gathering them together in motivational meetings, since depression is common in pregnancy and some months in the first postpartum year (Norma I [START_REF] Gavin | Perinatal depression: a systematic review of prevalence and incidence[END_REF].

Empowering jobs Connect women's work to the overall mission on endorsing promotions, making them feel part of the company's success. Support older and young women employees: visible patterns regarding professional and experienced women can help the younger ones to remain in the workplace longer. Promote well-paid jobs for women in realistic analysis of their talent and proficiency. At the same time, involve professionals women in the discussion and participation in panels, conferences and training at the enterprise. Since women are very good communicators [START_REF] Labov | A sociolinguistic perspective on sociophonetic research[END_REF], involve experienced and talent proven women inside the directive board.

Unveil the myths Change the employees' minds on policies and open announcement of women support by the organization. Promote this indoors and outdoors. Inform the investors how good quality conditions for women enforce economic productivity, since it produces better performance for all employees in a long term (Fortune Magazine, 2017). Emphasizing this is also valid for SMEs, exhibit how these policies have been main points in current economic growth in developing countries, where SMEs play a vital role (Pierre-Richard [START_REF] Agenor | Gender equality and economic growth in brazil: a long-run analysis[END_REF]. Put poster in public places regarding positive examples of intellectuals and businessmen supporting female workforce (Financial Times, 2015). Work on effective advertisement from the higher directives promoting talented women as an economical imperative for the organization (Nissan Motor Corporation: Global Newsroom, 2017).

Diversity

Quotes: "Reality is that world today is more diverse than it was 20 or even 10 years ago, making diversity policies more necessary than ever before for all companies, regardless of their size" (European Commission, 2016).

Nowadays, ethnic diversity management integration constitutes a major challenge (European Commission, 2016). Even post-graduate certificate or degree programs in management careers have started to focus some of their programs specifically on diversity and inclusion in business organization (Tufts University, 2017). Ethnic diversity has presented a growing presence in modern sectors such as IT, pharmacy and the media (Fortune Magazine, 2017). It is a fact that professional and qualified migrants represent a considerable economic contributions for local or regional economies [START_REF] Nathan | The wider economic impacts of high-skilled migrants: a survey of the literature[END_REF]. Those migrants who later form foreign-owned businesses are notably changing globally economies (Laura [START_REF] Alfaro | How does foreign direct investment promote economic growth? Exploring the effects of financial markets on linkages[END_REF]. Although these current tangible advantages can determine the economical growth of developing countries, the ethnic origin is still the most common form of discrimination in regions such as Europe (Eurobarometer, 2007). Nevertheless, recent news reveal China has set up a 10 billion euro (US$11.15 billion) investment fund to finance projects in Central and Eastern Europe (Asia Times, 2016). It is vital then for SMEs to address the diversity management which confronts these challenging circumstances and enables beneficial opportunities supporting their economical growing.

Large company strategies. The PricewaterhouseCoopers (PwC) is a company which consists of audit, tax and advisory businesses. The company's global revenues were $37.7 billion in gross in 2016 (PwC, 2017). The company was recognized by The European Diversity Awards as the "Most Inclusive Employer of the Year" in 2015 (European Diversity Awards, 2015). The company's policy was based on promoting dialogues, respect and tolerance about the inclusion inside and outside the company (European Diversity Awards, 2015). This has attracted the working force, assuring the productivity and income, since they guarantee a respectful work environment (European Diversity Awards, 2015). This good example of success joined with the diversity has gained followers among CEOs and Chairmen around the world (Richard J. [START_REF] Kramer | Goodyear corporate[END_REF].

SMEs strategies. Since the future point to this direction, there are many initiatives in promoting diversity in SMEs (Up2Europe, 2016). However, we need to go further since there is still tension about this topic in SMEs (Sara [START_REF] Carter | Diversity and smes: Existing evidence and policy tensions: Erc white paper no[END_REF]. In July 2017, a report by Aldermore found that 26% of SMEs have no plans to make workforce diversity a priority for their organization in the next 12 months inside the UK [START_REF] Aldermore | Sme future attitudes[END_REF]. We propose some aspects for SMEs which can help to build diversity into their organizations without causing significant costs.

Team integration Facilitate the adaptation to the culture of the employer's country through dynamic interchanges between foreigners and native employees. Utilize the English as the principal language for the foreign beginners within the first months inside the organization. Involve foreign individuals from the enterprise as mentors for juniors and native employees. Empower foreign or non-white employees to have the chance for applying to management positions after proven experience and high skilled values.

Recruitment operation Provide interviews in English for foreign applicants. Use a range of recruitment channels with different languages such as using simple online web sites which clearly expose the reference to the skills needed. Use psychological alternatives so that a nonnative applicant may feel comfortable during the interview sessions. For instance, start with short introductions asking about the homeland and point out the positive aspects of its culture even if these were covered in the curriculum. Furthermore, provide indispensable employment requirements such as visa appliance or health insurance.

Respect and tolerance policies Researches stress that, while discourses on ethnicity and nationality are shown as "fluid" by some SMEs, there is indeed tension and conflicts associated with such diversity (Helen [START_REF] Kopnina | Cultural hybrids or ethnic fundamentalists? discourses on ethnicity in singaporean smes[END_REF]. In this way, avoid as much as possible the judgement or segregation in case of employees inside the company whose efforts have promoted diverse workplaces (The British Psychological Society, 2017). Enable open intercommunication between employees with diverse ethnical and religious cultures. Proceed to take steps forwards against work harassment in case of denouncement.

Conclusion

In this paper, we have introduced the core criteria to analyze working conditions as a factor of understanding the SMEs resources and capabilities in this context. We have studied the current strategies that have been developed by the large companies in contrast with SMEs and suggested good tactics for SMEs to counteract and guarantee the enterprise survival. Our starting and ending point was always focused on our proposed criteria which is a compendium of different well-recognized methodologies. Simultaneously, we have shown how these popular metrics have positively impacted in some case studies in order to illustrate the claim:

Nowadays, work force demands better working conditions regarding Environment, Benefits for Women and Diversity and emerging economies are moving in that direction. The evolution of SMEs in these circumstances does not have a sole purpose of filling job vacancies, but also the guarantee of longer survival, economic growth and remaining competitive.