M Van Der Wal

Devos

Keywords: grammaticalization, motion verb, deixis, directionals, demonstrative

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The directional clitics in Western Kabyle have the form =dd or =n if preceded by a vowel, and the form =idd or =in if preceded by a consonant.

If the clause contains a mood (negative or potential) particle, or a relative marker, or a temporal conjunction, the directional clitic, together with all the personal clitics (dative and absolutive), are cliticized to that particle/marker:

(1) ur=as=t=idd j-fki ara NEG=DAT3SG=ABSV3SG.M=PROX SBJ3SG.M-give\NEGPFV POSTNEG 'He didn't give it to her/him' (Western Kabyle)

If the clause does not contain any of those markers, then the directional clitic, together with all the personal clitics (dative and absolutive), are cliticized to the verb:

(2) j-fka=jas=t=idd SBJ3SG.M-give\PFV =DAT3SG=ABSV3SG.M=PROX 'He gave it to her/him' (Western Kabyle)

This situation holds for the majority of Berber languages 1 , except those where the system of directionals is disappearing such as Siwi: in that case the clitic tends to remain attached to the verb and no longer climbs to the head of the clause:

(3) ga t-us-!d POT SBJ3F.SG-arrive\AOR-PROX 'She will come' (Siwi, Laoust 1931 :136) (interlinear glosses mine)

Traditional presentation

The usual presentation of the system is the following: Berber has two morphemes that attach to verbs (or to mood-negation-relativization particles): one that indicates movement towards the speaker (=dd), and one that indicates movement away from the speaker (=n)

Thus, examples such as ( 4) and (4') are given:

(4) i-"u#=dd The first problem with that presentation is that the opposition is not binary but ternary:

verbs often appear without an extension (=dd / =n / Ø). Moreover, the distal clitic is by far less frequent (0,1% of the clauses, as opposed to 23% (in narratives) and 36% (in conversation) for the proximal clitic in my Western Kabyle spoken corpus). Furthermore, many verbs bearing those extensions are not motion verbs. Several authors have pointed at those facts in various publications: [START_REF] Marcy | Fonctions originales dans les parlers berbères des pronoms démonstratifs relatifs îd/în[END_REF], [START_REF] Galand | Une opposition perdue: note sur la particule d'approche dans un parler kabyle des Bibans[END_REF], [START_REF] Bentolila | Les modalités d'orientation du procès en berbère (parler des Aït Seghrouchen d'Oum Jeniba)[END_REF], Aït [START_REF] Ahmed | Un particularisme de Tamazight: les modalités "d" et[END_REF], [START_REF] Mettouchi | La Particule D en berbère (kabyle) : transcatégorialité des marqueurs énonciatifs[END_REF], El [START_REF] Mountassir | Langage et espace: les particules d'orientation -d / -nn en berbère (tachelhit)[END_REF], [START_REF] Aoumer | Sémantique verbale, deixis et 'orientation' en berbère (parler kabyle des Iâamranen)[END_REF][START_REF] Aoumer | Une opposition perdue -la particule dite 'd'approche' ou la deixis verbale dans un parler kabyle de Bejaïa[END_REF].

Therefore, one has to study the situation in much more detail, in order to account for such examples as the following:

(5) ur=dd zwi$-% alamma t-kks=dd

The distal verbal clitic =(i)n

This clitic, which appears in 0,1% of the clauses in my corpus, is always used in interactive contexts involving situations where an action is viewed from the perspective of the addressee.

(6) i-nna=jas lli='=in We propose that its function is to indicate that the process is construed relative to the deictic center of the addressee (direct or reported, as in example 4 where the speaker's grandmother is about to address the teacher to ask him to let the speaker (then a little girl) come with her to graze the sheep). Distance is not at play, since in (8), A)mar is holding the donkey, and in (6) the door is in front of the speaker. Viewpoint is more important: the speaker could have used a proximal clitic in examples ( 6) and ( 8), thus making the command more peremptory. The use of the distal clitic subordinates the speaker's viewpoint to the addresse's. The same holds for ( 7), where the verb could have been used without a directional clitic. Movement towards the adressee is a possible interpretation, but it cannot be considered as a core function since most examples involve no movement, and no distance towards the addressee.

The proximal verbal clitic =(i)dd

As opposed to the distal clitic, 23% of the clauses in narratives, and up to 36% in conversation, have the proximal marker cliticized to the verb or to the clause-initial moodrelative-temporal marker.

What are its functions?

Motion verbs

In Western Kabyle, motion verbs are generally underspecified for directionality. We present below the most frequent motion verbs in our corpus. With =dd, the process is considered as having a goal, the endpoint is underlined, the process is viewed from that endpoint.

Without =dd, the process is described without viewpoint, the endpoint is simply locative. Example ( 16) is viewed neutrally, with a narrative viewpoint, the locative complement expresses the endpoint of the process. In example ( 17), the process is viewed through a deictic center identified with the locative complement, which is interpreted by default as a starting point.

Change of state verbs

Other verbs having an inherent endpoint or implying a change of state are used with =dd more often than average : (kks, 'take off, away', 66%; af, 'find' 63%; etc.)

For kks compare example (5) with example ( 18), the attainment of the endpoint was underlined in (5) with =dd, whereas in (18) there is no zooming effect on the attainment, just a narrative description of the action:

( The first proximal clitic is clearly speaker-oriented (polemical, a more modal perspective), whereas the second one represents the perspective of the speaker, but from the processcompletion point of view (a more aspectual perspective).

OTHER BERBER SYSTEMS

Berber languages are varied and cover a large area, from the Mediterranean to Burkina Faso, and from the Atlantic to the oasis of Siwa in Egypt.

Not all Berber languages have a full system of directional clitics: some languages have lost the distal marker (Chaouia (Penchoen 1973 :57) ; Eastern Kabyle [START_REF] Galand | Une opposition perdue: note sur la particule d'approche dans un parler kabyle des Bibans[END_REF] Those verbs are also frequently associated with directional clitics in Berber languages in which the system is still very pervasive, such as Ghadamsi, Western Kabyle, Tamashek...

In Ghadamsi, the respective frequencies of the proximal and the distal are similar (Lanfry 1973 : 227), which is exceptional in Berber, where the distal is generally much rarer than the proximal (Basset 1952 :36). The values proposed for the proximal by Lanfry (1973 : 47) are: proximity ; the fact that the situation concerns the speaker, or that the action is close to the speaker or the protagonist whose viewpoint is adopted.

The verbs most frequently used with the proximal clitic are: tef ('enter'), rr ('give back, turn into'), kri ('move back'), s ('arrive'), among others (Lanfry 1973 :47).

The values proposed for the distal by Lanfry (1973: 225) are: distance; the fact that the situation concerns a place, a person, a situation that are spatially distant. It can also refer to a meeting, a causality that are going to manifest themselves regarding a third person, who can be absent or distant, or even present.

The verbs most frequently used with the proximal clitic are : ig ('put'), w ('arrive'), s ('reach'), among others (Lanfry 1973 :225-227).

(32) i-tkel=t i-g er-t=in SBJ3SG.M-take\PFV=OBJ3SG.M SBJ3SG.M-throw\PFV=OBJ3SG.M=DIST 'He took it and threw it" (Ghadamsi, Lanfry 1973:225; interlinear glosses mine)

In Tamashek, Heath (2005 :595) notes that both the 'centripetal' and 'centrifugal' clitics are used, but the latter is "less common than the centripetal in texts" (2005:301). According to Heath (2005:598), the centripetal "specifies direction of movement (whether completed or not) toward the deictic center, usually the speaker's 'here' but sometimes another deictic center within a narrative. [...] With non-motion verbs, the clitic suggests that the action was directed toward 'here' in some way, or that it was accompanied by motion toward here".

The centrifugal clitic "indicates direction toward a nonproximate location with motion verbs ('run away'), fixed nonproximate location with statives ('sit way over there'), and motion away from the deictic center in combination with activity verbs ('go away chewing')" (Heath 2005:601). involve spatiality more centrally than those in which only the proximal is retained (Eastern Kabyle, Chaouia), or in which the distal is much rarer than the proximal (Western Kabyle).

c) in the latter languages, viewpoint of the speaker (or the addresse when there is a distal) is prevalent over movement towards the location of the speaker or away from him.

d) in languages where both clitics are used (Ghadamsi and Tamashek), the system of nominal deictics is also very rich and complex, involving fine-grained spatial distinctions.

e) in languages that have almost completely lost the system of directionals, such as Siwi, the clitics are retained on punctual verbs which semantically involve transition or endpoint ('take', 'arrive').

Grammaticalization hypotheses

The question is now whether the survey of the various systems of directionals thoughout the Berber languages can help us decide how the system was grammaticalized.

In the whole Berber area, the directionals are variants of =dd and =n. They are all encliticized to the verb or the mood-aspect-negation-relativization head of the clause. A common origin for each clitic is therefore very probable.

The first hypothesis is that those directionals were grammaticalized from motion verbs.

There are elements in favor and elements against this hypothesis. The second hypothesis is that those directionals were grammaticalized from demonstratives. Here again, this hypothesis is supported by some facts, and undermined by others.

Grammaticalization from verbs

The most likely candidate for the grammaticalization of =dd is verb ddu, meaning 'move', with a strong comitative component, and no marked directionality (although often translated 'go' in glossaries/dictionaries). It appears synchronically as ddu in Western Kabyle ('accompany', 'go with'), ddu in Eastern Kabyle ('walk'), idaw in Tamashek ('to accompany', 'be with'; 'be married to'), ddiw in Wargli ('to accompany', 'go with', walk'). This verb does not appear however in the glossaries of Mzab Berber or Ghadamsi.

One argument in favor of ddu is phonological: in most Berber varieties where it appears, it has a geminated root consonant, just like the proximal marker. Moreover, it belongs to the semantic domain of motion, which is a frequent source for ventive extensions [START_REF] Frajzyngier | Ventive and Centrifugal in Chadic[END_REF][START_REF] Heine | World Lexicon of Grammaticalization[END_REF]. It has been grammaticalized in Shilha as near-future clitic,

which shows that it has potential for grammaticalization. In exemple (37) the verb still has its full meaning but is employed metaphorically:

(37) i-dda ad i-hmu SBJ3SG.M-move\PFV POT SBJ3SG.M-be_warm\AOR
'It is about to warm up' (Shilha)

In example ( 38) the verb has undergone morphological and phonetic reduction (loss of the personal affix, fusion of the verb and the following particle), it is fully grammaticalized:

(38) ddad ihmu This scenario would have to be replicated for the other member of the directional system, clitic =n. In this case, the most likely candidate would be verb ini 'say' (attested in almost all Berber languages that have not replaced it with a borrowing of Arabic origin), which is not a movement verb. It has been grammaticalized as a conjunction meaning 'or' in Wargli for instance (Delheure 1987:208). However, the link with the distal/addressee-oriented meanings the clitic has in synchrony is rather difficult to establish. And [START_REF] Heine | World Lexicon of Grammaticalization[END_REF] do not provide those meanings as usual grammaticalized meanings for verbs of saying. There is no external evidence for his hypothesis, and no attested grammaticalization of a verb 'say' in Berber other than for a conjunction.

Grammaticalization of demonstratives

The marker n is part of the demonstrative system of all Berber languages, with a distal meaning: argaz-an ('that man', Shilha), argaz-n ('that man', Wargli), w ggid-enn ('that man', Ghadamsi), aeháls-én ('that man', Tamashek), etc.

Similarly, marker d is part of the demonstrative system of a lot of Berber languages, with a proximal meaning: argaz-ad ('this man', Shilha), w ggid-det ('this (very close) man', Ghadamsi), aeháls-dí ('this man' (near-distant), Tamashek), etc.

It is also the basis of series of locative demonstratives, proximal and distal (da, dagi, 'here' (Kabyle); din, dinna, 'there' (Kabyle); dihá, 'here' (Tamashek), dihén, 'there' (Tamashek) etc.).

The potential particle ad (<-a+d), which indicates the process as potential but tending towards realization (future, conditional, tendencial etc.) is also based on locative d in most

Berber languages. The origin of the equative-locative copula d is most probably deictic as well.

Therefore, another grammaticalization hypothesis would be that the system of nominal demonstratives has been grammaticalized on verbs by analogy. This hypothesis is supported by external evidence, since there are languages where demonstratives have grammaticalized as directional verbal extensions (Papago, Mojave and Inuktikut are cited by Diessel (1999: 142), Bourdin (2002: 186) also mentions this fact.

However, it is not the most frequently used proximal suffixes (vocalic -a, -í, or -depending on Berber languages) that have been grammaticalized as a proximal extension on verbs, but the deictic locative d, whereas it is the distal demonstrative which has been grammaticalized as a distal extension on verbs. The nominal and the verbal systems are not completely parallel, except for some Berber languages such as Shilha [START_REF] Galand | Une opposition perdue: note sur la particule d'approche dans un parler kabyle des Bibans[END_REF] 3 This man (prox) argaz-a-d

3 That man (dist) argaz-a-nn 3 He arrived (here) juska-d 3 He arrived (there, where I no longer am) juska-nn 3

One argument that could be presented against this grammaticalization is the fact that the proximal clitic is generally geminated, whereas the deictic locative d is a single consonantal root. However, the fact that directionals form a system where it is very hard to ignore the link between distal clitic on verbs and distal suffix on nouns tends to give weight to the demonstrative hypothesis.

A grammaticalization network ?

Given that both hypotheses have their strengths and weaknesses, it may be the case that the grammaticalization of the pair =n/=dd from demonstratives was reinforced by the presence of verb ddu in the lexicon: indeed if the grammaticalization had occured purely by analogy with the system of nominal demonstratives, the pair would have been =a (or =i or =u) / =n. As was shown in part 1.3., d is not the mirror-image of n in the system of demonstratives.

A possibility is that the first reason d was promoted was because d is a locative basis in many Berber languages, and a deictic one in some; and the reason it was geminated was because it is reminiscent of ddu. This hypothesis implies that grammaticalization is not necessarily linear along a single path, but can also depend on a network of related markers, such as equative-existential copula d, grammaticalized from demonstrative d, and comitative preposition d, probably grammaticalized from verb ddu. A complex interplay of analogies links together all those markers, and the fact that Berber languages have a root and pattern morphology facilitates the mapping of those markers at the abstract level of the root. Thus, proximal clitic =dd would be the outcome of a complex grammaticalization process with a main source, the locative demonstrative d, and peripheral reinforcements: verb ddu, equative-locative copula d, comitative preposition d. The resulting semantics revolves around the notion of closeness to a deictic center or a (human) landmark.

Conclusion

Given the arguments developed in this paper, demonstratives are the most likely candidates as sources of the grammaticalization of the 'directionals' of Berber. If one considers that the semantics or original function of the source of grammaticalization motivates to a certain extent the target of grammaticalization, this would explain the fact that directionals are not limited to motion verbs in Berber, but are used for all sorts of verbs, and clauses (negative, irrealis etc.). It would also explain the variety of values they carry: spatial, aspectual, modal... Demonstratives, by integrating all dimensions of the speech situation, the hic et nunc as well as the speaker and the addressee, have a potentially broader scope than motion verbs, thus giving rise to more varied contextual interpretations.

Motion verbs themselves are seldom grammaticalized in Berber: the near-future auxiliary of Shilha (based on ddu, 'move with'), and the tendency of "u# ('leave') to act as an abstract V1 in sequences, are the only documented cases. Position and change of position verbs such as kkr 'stand, stand up', and qqim, 'stay', tend to grammaticalize more easily.

  't marry until Fatima manages to take the bread from the shelf' (Western Kabyle)

  , Aoumer 2008 and 2011)), although the proximal is extensively used. Others such as Siwi (Laoust 1931: 135-136) only have vestigial uses of those clitics, which now belong to the verb root, and do not undergo clitic climbing anymore. The verbs mentioned by Laoust are an (take), ad (take), and usd (come): (31) a/-n-0&t take\IMP.AOR-DIST-SBJ2PL "take!" (Siwi, Laoust 1931:136; interlinear glosses mine)

  that (is) a thing (=custom), get rid of it !'(Tamashek, Heath 2005:601) (34) i-k2a-\hín sit.PERFP-1SG-\CENTRIF 'I stayed there (i.e. didn't come)'(Tamashek, Heath 2005:600) working.' (=He was working as he came')(Tamashek, Heath 2005:599) This survey of the various systems in some Berber languages calls for the following conclusions: a) the system of 'directionals' originally involved both a proximal and a distal clitics, since both appear in several Berber languages in various geographical areas; b) the systems where both clitics are still quite frequently used (Ghadamsi and Tamashek)

'

  going to warm up'. (Shilha) However, there are arguments against ddu as a candidate for grammaticalization into the proximal clitic: first, the proximal clitic is postverbal (or enclitic to heads), which makes it a V2 if we think in terms of V1-V2 sequences. The problem is that V1-V2 verb sequences in Berber have V1 typically more abstract and functional and V2 typically more 'lexical'. V1 is more likely than V2 to grammaticalize, as is shown by all the cases of grammaticalization of V1 into auxiliaries or particles in various Berber languages. No instance of V2 grammaticalization has ever been noted so far.A solution to this counterargument would be to postulate that grammaticalization started in the 'clitic climbing' position (i.e. in irrealis, negative and relative clause), and only then extended to postverbal position (other types of clauses and moods). Following this hypothesis, verb ddu might have appeared as a reinforcement of a second verb: -move\AOR SBJ3SG.M-arrive\AOR 'He will arrive here' (lit. 'he will move arrive') Then the full verb would have undergone phonetic reduction and cliticized to the dative and absolutive pronouns in this position appear after the verb when there are no mood-negation-relative markers, it would be possible to postulate that from He will give it to her' the proximal particle could move to postverbal position together with all the other clitics:(42) j-&fka=jas=t=idd SBJ3SG.M-give\PFV=DAT3SG=ABSV3SG.M=PROX 'He gave it to her' thus making this position available for this marker, even when there are no

  When she arrived there, Amina, she found it was the Mountain Cat who inhabited it, the house. Some verbs have no inherent endpoint, are not motion or position verbs and are nevertheless associated with =dd (ex. ini, 23% of occurrences in conversation, 15% in narratives bear the proximal clitic) The semantics and aktionsart of the verb are important, since motion verbs and processes involving an inherent endpoint (or one represented by a locative complement or an object) are very often associated with the proximal clitic. Dative pronouns as recipients are often associated with the proximal or distal clitic. The conjunction heading the clause also plays a role: mi 'when' is strongly associated with =dd : 60% of temporal clauses beginning with mi contain the proximal clitic, regardless of verb type (the same thing holds with aramma 'until'); in this case, =dd focusses on the completion of the process on which the main clause depends (the scope is larger than the verb itself):With verbs of motion, the proximal clitic tends to focus on the endpoint of the movement, which is by default the speaker's deictic center, or a previously mentioned deictic center. If there is a locative complement, it is construed as the endpoint of the movement, and the process is viewed from that endpoint. If the verb is not a motion verb, =dd underlines the present relevance of the process, or its result, or impact on the speaker or another deictic source. If the verb is a verb of saying in the first/second person and/or bears a dative pronoun, =dd underlines the relevance of the process on the speech situation, and the viewpoint of the speaker or another deictic source. When cliticized to a particle or clause marker, =dd may underline the completion or relevance of the process in relation to the speech situation or to another clause.

	n&%	ad=dd		ff%-&%		//
	(Western Kabyle) or POT=PROX	exit\AOR-SBJ1SG //
	'The woman told her husband: "I told you, I won't accept anything else than their being eaten,
	(20) i-nna=jas either they quit the house, or I will go!"' (Western Kabyle) lli=*=in
	SBJ3SG.M-say\PFV=DAT3SG Without =dd the process refers to the fact of uttering something: open\AOR(IMP2SG)=ABS3SG.F=DIST In sum, the proximal clitic subsumes the following subfunctions: direction towards a deictic
	d 1.2.5. Interpretation factors in&bgi n center (different from direction towards the addressee), standpoint of the speaker, or of a "bbi / imi=*=idd t-lli
	COP (24) ss&n-%=tnt guest\ABS.SG.M // reported speaker, zooming effects, viewpoint shifts, current relevance, polemical, GEN god / when-ABS3SG.F=PROX SBJ3SG.F-open\PFV nni-%=am
	Amina / know\PFV-SBJ1SG=ABS3PL.F // t-ufa=dd presuppositional, counter-expectative stance, goal, resultative (change-of-state), benefactive. d baba-s // say\PFV-SBJ1SG=DAT2SG.F
	amina/ ju% We therefore propose the general function 'Viewpoint of the (direct or reported) speaker (or SBJ3SG.F-find\PFV=PROX COP father-KIN3SG // s&**i //
	SBJ3SG.M-take\PFV protagonist)' for the proximal clitic in Western Kabyle, the distal clitic expressing the grandmother\SG //
	'I know them (my grandfather's wives), I told you he married my grandmother, …' (Western addressee's viewpoint.
	Kabyle) This function allows the interpretation of examples such as (5), reproduced here as (30)
	Or being named X or Y: (30) ur=dd zwi$-%			alamma	t-kks=dd
	NEG=PROX	marry\NEGPFV-SBJ1SG	until	SBJ3SG.F-take\PFV=PROX
	(21) (25) (28) mi=dd j&-,,a qqar-n=as Fatima a%rum / SBJ3SG.M-eat\PFV / j&-qqim say\IPFV-SBJ3PL.M=DAT3SG t-#&d&" aj&n j&-qqim j&-swa jamina // g ud&kkan / SBJ3SG.M-drink\PFV / / amina // ad n-()&l tim&s 'Her name is Amina.' (Western Kabyle) when=PROX SBJ3SG.F-be_present\PFV Fatima bread:ABS	tm&ddit evening\ANN.SG.F / /
	With =dd the process refers to:
	a) Answering
	(26) az&kka		ad=dd		t-qq°&l	t&m--ut-nni /
	tomorrow		POT=PROX		SBJ3SG.F-come_anew\AOR	woman\ANN-CNS /
	18) ad=as	ad=as	t-ini	j-&kks			ma	lq&( t-nna-mt=as	m&skint /
	POT=DAT3SG (22) t&-qqim=dd SBJ3SG.F-stay\PFV=PROX SBJ3SG.M-take\AOR fa-ima fa-ima POT=DAT3SG SBJ3SG.F-say\AOR if i baba-tk°nt // ad=as (29) ma j&-b%a a%rum DAT father-KIN2PL.F // if SBJ3SG.M-want\PFV bread\ABS.SG.M / clothes\ABS.COLL tu#"i(t-nni // clever-CNS // SBJ2-say\PFV-SBJ2PL.F=DAT3SG poor\SG.F / ini-nt / / POT=DAT3SG say\AOR-SBJ3PL.F / n-nna=jas / j&-nna=ja%=dd akka // 'If he wants bread,
	SBJ1Pl-say\PFV=DAT3SG /	SBJ3SG.M-say\PFV=DAT1PL=PROX	thus //
	'On the following day the woman would return, she would ask them if they had asked their ad i-"u# ad j-a% i t#anu* //
	movement: father (about his marrying her). The girls would tell her "we asked him, and he answered this POT SBJ3SG.M-go\AOR POT SBJ3SG.M-take\AOR LOC shop\ANN.SG.F //
	(19) imi and that". (Western Kabyle) t-ww&+ he will go and buy it at the shop'. (Western Kabyle) a Amina	ar dinna /
	when (23)	SBJ3SG.F-arrive\PFV t-.&+r=as=idd	/	VOC	amina	to there /
	t-ufa SBJ3SG.F talk\PFV=DAT3SG=PROX / d am(i( b) Saying something relevant to the speaker:	n	w&drar	//
	SBJ3SG.F-find\PFV t-ss&bla)=it (27) t&-nna=jas	COP	cat\ABS.SG.M /	GEN lqa)a nni-%=ak=idd mountain\ANN.SG.M // / /
	i=t SBJ3SG.F-be_swallowed\CAUS.IPFV=ABS3SG.m i-zd&%-n / SBJ3SG.F-say\PFV=DAT3SG / say\PFV-SBJ1SG=DAT2SG.M=PROX / ground\ANN /
	aramma #a(a	tu,,in	i=dd	ara			j&-qqim **w-&,,-nt	//	akka //
	until only eating	REL.REAL=PROX REL.IRR		SBJ3SG.M-stay\PFV PASS-eat\AOR-SBJ3PL.F // thus //
	ad	ff%-&nt			g		w&xxam	/
	POT	exit\AOR-SBJ3PL.F	LOC		house\ANN.SG.M /

'He would take off her clothes, poor girl.' (Kabyle)

For af, the most frequent difference in meaning is: a description of the object/situation found, when the verb is used without =dd, ex.19) vs. indication that the object/situation found is unexpected (with =dd, ex.20) REL.REAL=ABS3SG.M RELSBJ.POS-dwell\PFV-RELSBJ.POS / w&xxam-nni // house\ANN.SG-CNS // ''He said open the door, I'm a beggar. When she opened the door, Amina, she realized it was her father.' (Western Kabyle) 1.2.3. Position verb qqim Position verbs and not only motion verbs can be used with =dd. Without =dd, the verb qqim, 'stay' refers to static position of the subject in some place: SBJ3SG.M-stay\PFV what SBJ3SG.M-stay\PFV / 'He ate, he drank, he stayed for a while.' (Western Kabyle)

With =dd, the effect is to underline the fact that motion was assumed, and that contrary to expectations, the subject remained in its original place, 'There remained Clever Fatima.' (Western Kabyle)

Or that there was movement and that position denoted by qqim is the endpoint of that 'She talked to him, the ground was swallowing him, until he remained thus.' (Western Kabyle)

1.2.4. Verb of saying ini

POT SBJ1PL-light\AOR fire\ABS.SG.F 'When the evening came, we would light a fire' (Western Kabyle) Ma 'if' on the contrary, almost never appears with =dd, and if it does, the focus is on the verb's interpretation (endpoint of a motion verb for instance): LOC shelf:ANN 'I won't marry until Fatima manages to take the bread from the shelf' (Western Kabyle)


Najett Neji

Raul De Lacerda

Felipe Nyland
email: nyland@gmail.com

Lionel Pichon
email: lionel.pichon@supelec.fr

Electromagnetic compatibility: new trends for new standards

Interference between radio systems may occur if they share the same environment and use close frequencies at the same time. To ensure their successful coexistence, the Electromagnetic Compatibility (EMC) established rules and regulations within standardisation bodies and aims to protect these systems from harmful interference. Nowadays, with the proliferation of wireless communications and digital technologies, in addition to electronics evolution inside radio terminals, some additional parameters and new techniques are needed to represent more accurately the interference environment and guarantee radio systems coexistence. In this work, we provide an overview of the main standards related to EMC approaches and measurement techniques currently in use, and we show the benefits of considering time-domain parameters in the EMC analysis.

I. INTRODUCTION

The Electromagnetic Compatibility (EMC) determines necessary conditions to protect systems against harmful interference and undesired radiations. Systems and equipments should operate correctly in their environment and they must not cause harmful interference on other equipments.

To evaluate EMC, current standards are mainly focused on frequency-domain approaches that deal with worst-case situations where interference is assumed to be permanent. However, due to the advancement of technologies which includes the size of electronic components, wireless communication technologies are nowadays widespread around the world. As a consequence, radio coexistence is becoming hard to guarantee considering that spectrum is a limited resource. For this reason, it is necessary to evolve the standards to enable higher data rates, better spectral efficiency and intelligent frequency usage.

Hence, we emphasize in this paper that considering additional parameters in the theoretical studies'framework and employing other measurement techniques could improve EMC results. We propose to include these new aspects into current EMC standards.

The paper is organized as follows. First, in section II, we describe the state-of-the-art in EMC analysis approaches and measurement techniques. Then, in section III, we emphasize the influence of time-domain parameters on the EMC through a simple study case (some calculus have been developed in our previous work [START_REF] Neji | Electromagnetic compatibility from a time-frequency perspective[END_REF]). Finally, in section IV, we summarize the conclusions of the study.

II. STATE-OF-THE-ART: EXISTING EMC STANDARDS FOR TELECOMMUNICATION SYSTEMS

Regarding telecommunications and information systems, there are standards in charge of establishing guidelines to keep equipment working within the EMC requirements. This means that they can coexist with other systems, without causing any interference or degradation in their functioning or causing losses in the quality of transmitted signals.

Besides the fast progress in technologies and electronic devices, the number of messages that need to be transferred is increasingly occupying the spectrum of frequencies. The various ways of conveying these signals (Wi-Fi, WiMAX, Bluetooth, LTE, etc.) compete for limited spectrum. This limitation led to a search for effective solutions that allow them to occupy a lower frequency bandwidth to transmit the same amount of information meeting the necessary conditions for their functioning.

To study the EMC, we represent two radio systems, system 1 and system 2, operating in the same environment. Interference between these systems may occur if they transmit at the same time using overlapping frequency bands. We illustrate in Fig. 1 the EMC scenario where the victim receiver (receiver of system 1) gets an interfering signal from the interferer (transmitter of system 2). If the interference level I is lower than the thermal noise level N (both computed at the victim receiver input), the compatibility is guaranteed. For all the other cases, to ensure successful coexistence, current EMC standards usually specify a frequency and/or spatial separation in order to respect the required receiver performance for given signal level and quality of service.

This approach, called herein frequency-domain analysis, is based on five successive steps:

• Interference scenario identification, • Interferer characterization, • Victim receiver characterization,
• Interference path and victim path parameters determination, • Link budget calculation. We summarize in Fig. 2 the main parameters that should be considered in the EMC study.

The International Telecommunications Union, more particularly its Radio-communications sector (ITU-R), specify these parameters. To protect other systems operating in adjacent frequency bands, [START_REF]Unwanted emissions in the out-of-band domain[END_REF] and [3] provide spectral density limitations for out-of-band and spurious radiations, respectively. In addition, [START_REF]Selectivity of receivers[END_REF] specifies receivers selectivity and [START_REF]Noise and Sensitivity of receivers[END_REF] their sensitivity and noise level. Antenna radiation patterns and maximal gains in certain frequency bands are also provided in the ITU recommandation 1336. Moreover, some ITU-R recommendations propose different propagation models to be used according to the interference scenario and frequency range, for example [START_REF]Calculation of free space attenuation[END_REF].

The ITU-R applies frequency-domain analysis with the previously mentioned parameters, to spectrum sharing studies (also named coordination studies) between radio systems (e.g. [START_REF]Frequency Sharing Between Systems in the Fixed-Satellite Service and Radio-Relay Systems in the Same Frequency Bands[END_REF]). This methodology was also used in spectrum sharing studies within some European standardization bodies such as the Electronic Communications Committee (ECC) and the Conférence Européenne des administrations des Postes et Télécommunications (CEPT) (see [START_REF]Report from CEPT to the European Commission in response to task 3 of the Mandate to CEPT on the 900/1800 MHz bands[END_REF] for example).

Most of these studies are based on Monte-Carlo simulations, using the (Spectrum Engineering Advanced Monte-Carlo Tool (SEAMCAT)) [START_REF]ECO : European Communication Office, Spectrum Engineering Advanced Monte-Carlo Tool : SEAMCAT Handbook[END_REF] software. The interference is evaluated in terms of probability that the Signal to Interference plus Noise Ratio (SINR) becomes lower than a specified minimum threshold by the user, and based on input physical layer parameters.

In conventional EMC testing, the interfering field strength at the victim receiver is required to be less than the regulatory levels recommended by the ITU. Hence, the radio spectrum has been divided into distinct frequency bands, usually with exclusive access.

However, spectrum resources become scarce as digital systems are being deployed to provide various services requiring higher data rates. Consequently, the ITU has kept some bands for unlicensed use to allow the development of new technologies. Systems operating in these bands are foreseen to use simultaneously the same or nearby frequency bands (case of Industrial, Scientific, Medical (ISM) bands). The frequency allocation is also changing with the emergence of digital systems (case of white spaces in the broadcast television spectrum). The radio environment is becoming complex also because of electronics evolution within radio devices (converged wireless communication devices). In addition, decentralized wireless networks (also named ad-hoc networks) are being widely developed and use complex technologies. These networks are increasing and use cognitive radios (CR) which are smart radios able to adapt their technologies depending on the user demand, the traffic load and propagation conditions.

Under these complex environments, radio systems are likely to suffer from interference and this is critical for their coexistence. Consequently, the ITU also recommends to refine the compatibility criteria based on link budget considerations for systems allocated in adjacent or nearby bands [START_REF]Compatibility analysis between a passive service and an active service allocated in adjacent and nearby bands[END_REF] or at the same frequency [START_REF]An additional methodology for the evaluation of the effect of interference between radiocommunication networks operating in a shared frequency band[END_REF]. One other proposed solution by the is to limit transmit power spectral densities of systems operating in the ISM bands. Interference mitigation techniques are also mentioned in the literature, such as frequency hopping, Listen Before Talk [START_REF] Zhao | Spectrum opportunity detection: How good is listen-before-talk?[END_REF] and Dynamic Frequency Selection [START_REF]Use of the band 5 725-5 875 MHz for broadband fixed wireless access (BFWA)[END_REF]. These techniques use additional time-domain parameters but they are applied to specific spectrum sharing studies.

In addition, we still have a set of standards that cover all the electronic systems that are not intentional emission sources, as example, Comité International Spécial des Perturbations Radioélectriques CISPR 11 (for industrial, scientific, and medical apparatus) [START_REF]Cispr11 ed. 5.1, industrial, scientific and medical equipment -radiofrequency disturbance characteristics -limits and methods of measurement[END_REF] and CISPR 22 (for Information Technology (IT) equipment) [START_REF]information technology equipment -radio distrubance characteristics -limits and methods of measurement[END_REF]. These standards specify the tests to be performed, electromagnetic fields limits to be respected, and check if the equipment under these regulations are compatible. In addition, CISPR-16-1-1 [START_REF]Radio disturbance and immunity measuring apparatus -measuring apparatus[END_REF] determines the allowed equipment that can be used to perform these measurements.

Many electronic components can be very vulnerable to radio frequency pollution due to repetitive digital signals that have harmonics reaching the GHz range. This non-intentional energy can be either radiated or conducted.

The CISPR standards establish that the issue of measuring the emitted field by an Equipment Under Test (EUT) should preferably be done under two conditions. At first, EUT and the measurement system are inserted into an Open Area Test Site (OATS), free from any external Electromagnetic Interference (EMI). At second, tests could be performed inside "semi" anechoic chambers. In both settings, a calibrated antenna located at 3 and at 10 meters away from EUT, is connected to an EMI Test Receiver. It measures the emission of electromagnetic fields throughout the established frequency range (between 9 kHz and 6 GHz).

These tests usually take a long time to be concluded, because they are performed completely in the frequency domain. However, many recent works have questioned the guidelines imposed by CISPR. Problems involving standardization [START_REF] Ianoz | Standardisation problems related to conducted limits for power line communication equipment[END_REF], chamber validation techniques [START_REF] Wiles | The impact of recent changes to cispr standards on emc anechoic chambers[END_REF], laboratory correlation studies [START_REF] Toh | Electromagnetic interference laboratory correlation study and margin determination[END_REF] and correlations between measurements at 3 and 10 meters [START_REF] Garn | Problems with radiated-emission testing at 3 m distance according to cispr 11 and cispr 22[END_REF] have been addressed. The correlations between measurements at 3 and 10 meters are based on Maxwell equations and assume three conditions: a point source, a free-space environment, and a far-field environment. However, these conditions are not always necessarily satisfied. First, the majority of tested electronic products in EMC laboratories are distributed sources (they have a width, a height, and a length). Moreover, most measurements are not made in the farfield environment. Since near-field effects depend on effective size of source, effective size of the observer and the distance between source and observer, the antennas coupling would be very complex to model, mainly in low frequencies.

Many studies have also suggested new enhancements to improve the results in accordance with reality. Projects of better EMI receivers covering larger frequency ranges [START_REF] Festa | A novel approach to the design of a fully cisprcompliant emc/emi receiver 10 hz â Ȃ Ş 6 ghz[END_REF] and joint time-frequency analysis [START_REF] Pan | Emi failure analysis techniques: Ii. joint time-frequency analysis[END_REF] were recently presented.

As far as EMI susceptibility is concerned, the International Electrotechnical Commission IEC 61.000-4-3 Standard [23] gives specified field levels subjected to the type of used EUT. The susceptibility tests are performed by sweeping single continuous wave signals through the test-frequency range. However, signals in the real RF environment are rather wideband signals having random variations in amplitude, frequency, and timing (for example Orthogonal Frequency Division Multiplexing (OFDM) signals). Hence, the coupling of EM fields is complex and it is difficult to predict EUT performance only based on a single test result.

III. TIME-FREQUENCY APPROACH FOR EMC

CALCULATION Current EMC analysis in the frequency domain deals with worst case scenarios, where the interferer is assumed to transmit continuously and the victim receiver is likely to intercept signals continuously. In some cases where the interference is still high, one common solution is to move the interferer away from the victim receiver and/or to change their relative orientation.

As the radio environment is becoming complex, EMI compliance is hard to guarantee and additional parameters are needed to represent more accurately the propagation environment. Time-domain parameters are interesting because the information within digital systems is transmitted through pulsed signals.

In this section, we propose to study the influence of the channel-occupation-rate parameter ( percentage of time of effective transmission by a system) on the coexistence between radio systems sharing the same spectrum. Let us take again the example shown in Fig. 1 where system 1 is the victim system and system 2 is the interfering system.

We call the respectively bandwidths of victim and interfering systems by B 1 and B 2 and their center frequencies by F 1 and F 2 . In addition, we denote the total power of victim and interference signals at the victim's receiver by P 1 and P 2 . Moreover, H 1 ( f ) and H 2 ( f ) are respectively the reception filter of system 1 and the transmission mask of system 2. We also define the receptively channel occupation rates of both signals by R 1 and R 2 . Finally, we suppose that both signals are independent.

Let us first compute the SINR before taking into account the channel occupation rates. The general expression of the SINR is :

SINR = S N + I = 1 ( N S ) + ( I S ) = 1 ( 1 SNR ) + ( 1 SIR ) , (1)
being SNR the ratio S N and SIR the ratio S I . S and I are the powers received by the victim from the victim transmitter and the interferer, respectively, both computed in the victim system bandwidth:

S = B 1 P 1 B 1 • H 1 ( f ) d f (2)
and

I = +∞ -∞ P 2 B 2 • H 1 ( f ) • H 2 ( f ) d f . (3)
In addition, N is the noise level in the victim system bandwidth, related to the Boltzmann constant k and the temperature T (in K) by :

N = k • T • B 1 . (4)
Consequently, we have:

SINR = B 1 P 1 B 1 • H 1 ( f ) d f ( +∞ -∞ P 2 B 2 • H 1 ( f ) • H 2 ( f ) d f ) + (kT B 1 ) (5)
For the victim system performance evaluation, we use the famous theorem of Shannon [START_REF] Shannon | Communication in the presence of noise[END_REF] which provides the error-free capacity under gaussian noise interference. We assume from now on that interference plus noise could be modeled as a white gaussian noise. Theorem 3.1: (Shannon-Hartley Theorem [START_REF] Shannon | Communication in the presence of noise[END_REF]) The errorfree capacity (bits/second) that can be transmitted over a additive white gaussian channel is

D max = B • log 2 (1 + SNR). (6)
In our case, we call C (in bits/channel access) the capacity of the victim system in the presence of noise and interference. Three cases are possible :

• Capacity C without taking into account the channel occupation rates; • Capacity C based on the average SINR ( SINR);

• Average capacity C based on the instantaneous SINR (SINR(t)). In the first case, the capacity of the victim system is:

C = R 1 • log 2 (1 + SINR) (7)
which means that:

C = R 1 log 2 1 + B 1 P 1 B 1 H 1 ( f ) d f +∞ -∞ P 2 B 2 H 1 ( f )H 2 ( f ) d f + kT B 1 (8)
In the second case, the capacity of the victim system is computed based on SINR (calculus are developed in [START_REF] Neji | Electromagnetic compatibility from a time-frequency perspective[END_REF]) and its final expression is:

C = R 1 log 2 1 + R 1 B 1 P 1 B 1 • H 1 ( f ) d f R 2 ∞ -∞ P 2 B 2 H 1 ( f )H 2 ( f ) d f + R 1 kT B 1 (9)
In the third case, the average capacity of the victim system in the presence of the interferer considering SINR(t) (also see [START_REF] Neji | Electromagnetic compatibility from a time-frequency perspective[END_REF]) is given by:

C = R 1 • (1 -R 2 ) • log 2 1 + B 1 P 1 B 1 • H 1 ( f ) d f kT B 1 +R 1 • R 2 • log 2 1 + B 1 P 1 B 1 • H 1 ( f ) d f +∞ -∞ P 2 B 2 H 1 ( f )H 2 ( f ) d f + kT B 1 , (10)
We now compute the three capacities C, C and C with respect to the ratio of system powers P 1 P 2 . To simplify the study, we assumed that both system masks (H 1 ( f ) and H 2 ( f )) are ideal, i.e. that they are expressed by :

H 1 ( f ) =    1 F 1 -B 1 2 ≤ f ≤ F 1 + B 1 2 0 otherwise (11)
and

H 2 ( f ) =    1 F 2 -B 2 2 ≤ f ≤ F 2 + B 2 2 0 otherwise (12)
We also consider that system 1 and system 2 use overlapping frequency bands, which means that the frequency offset between them δ (given by F 2 -F 1 ) verifies

- B 1 + B 2 2 ≤ δ ≤ B 1 + B 2 2 . ( 13
)
We finally assume that B 1 ≤ B 2 , which means that the interfering signal occupies a larger bandwidth than the victim system. Under these conditions, the expressions of the three capacities are given by (calculus are developed in [START_REF] Neji | Electromagnetic compatibility from a time-frequency perspective[END_REF]):

,R 1 =1,R 2 =1 C',R 1 =1,R 2 =1 C'',R 1 =1,R 2 =1 C',R 1 =1,R 2 =0.5 C'',R 1 =1,R 2 =0.5
C = R 1 log 2 1 + 1 SNR + P 2 P 1 B 1 + B 2 -2δ 2B 2 -1 , (14)
C = R 1 log 2 1 + 1 SNR + R 2 R 1 P 2 P 1 B 1 + B 2 -2δ 2B 2 -1 , (15)
C = R 1 (1 -R 2 ) log 2 (1 + SNR) + R 1 R 2 log 2 1 + 1 SNR + P 2 P 1 B 1 + B 2 -2δ 2B 2 -1 . (16)
For the simulation results, we consider P 1 P 2 values between -20dB and 10dB and we set the SNR to 20dB. We investigate R 1 = 1 (continuous transmission by the victim) and two values of the channel occupation rate by the interferer: R 2 = 1 (continuous interference) and R 2 = 0.5 (half-time interference). Finally, for the results presented in this paper, we assume that B 2 B 1 = 2 and we take two values of systems center frequencies offset (δ = 0 and δ = B 1 +B 2 4 ). We notice from Fig. 3 and Fig. 4 that when both systems transmit continuously, the capacities C, C and C are identical. When the average or instantaneous SINR is considered, the victim system capacity increases for both studied values of systems frequency offset. We also notice that the higher is the power ratio P 1 P 2 , the higher is the capacity gain with average SINR, whereas the capacity gain with instantaneous SINR is the more significant for low values of P 1 P 2 . We can see in this simple example that the victim system performance increases significantly when channel occupation rates of both systems are considered. By taking into account the instantaneous SINR in the coexistence analysis, the result becomes more realistic. As a result, frequency sharing studies Interfered system Capacity (Bits/Channel Access)

Ratio of systems powers P1/P2 C,R 1 =1,R 2 =1 C',R 1 =1,R 2 =1 C'',R 1 =1,R 2 =1 C',R 1 =1,R 2 =0.5 C'',R 1 =1,R 2 =0.5
Fig. 4. : Channel capacity in the presence of co-channel interference and noise with respect to the ratio

P 1 P 2 , for SNR = 20 dB, B 2 B 1 = 2 and δ = B 1 +B 2 4 .
could be more precise and systems could be more accurately characterized.

We recall herein that we made approximations on the propagation environment to get simple SINR expressions using the channel occupation rates of both systems. We also studied the case where interfering transmission mask and victim reception filter are ideal and we considered that their antennas are isotropic. More results can be easily obtained using realistic masks/filters and antennas radiation patterns in our study case. To get more accurate results, additional parameters should be taken into account such as the Inter-Symbol Interference and multi-path phenomena.

IV. CONCLUSION

In this paper, we summarized trends of technological advances and their consequences on EMC analysis. The difficulties and problems that go against current EMC standards were also discussed.

In addition, we showed the importance of time-domain considerations to improve the spectrum sharing between radio systems. Current EMC frequency domain analysis provides worstcase results (the involved systems are assumed to transmit continuously), whereas the time-frequency approach seems to be more accurate. It takes into account time-frequency aspects and technology properties. Through a simple study case, we emphasized the benefits of using time-domain parameters in the EMC study.

For instance, the growing technological advancement brings increasing challenges to the agencies in charge of designing EMC standards. It demands a increasingly faster response and more frequent updates to ensure that the electromagnetic compatibility is guaranteed. This work can be considered as an openess to new methods of measurements and simulations under more realistic conditions, according to these new technological realities.

Fig. 1 .

 1 Fig. 1. EMC System model: transmitter, interferer and victim.

Fig. 2 .

 2 Fig. 2. Parameters for EMC study.

Fig. 3 . 1 P 2 , 2 B 1 = 2

 312212 Fig. 3. : Channel capacity in the presence of co-channel interference and noise with respect to the ratio P 1 P 2 , for SNR = 20 dB, B 2 B 1 = 2 and δ = 0.


Najett Neji

Raul De Lacerda

Alain Azoulay

Thierry Letertre
email: thierry.letertre@supelec.fr

Olivier Outtier
email: olivier.outtier@aviation-civile.gouv.fr

Coexistence between the future aeronautical system for continental communication L-DACS and the Distance Measuring Equipment DME

In the last decade, the aeronautical authorities expressed their need to develop a new system for aeronautical radiocommunications. The L-band Digital Aeronautical Communication System (L-DACS) is the part of the future system that will be operating in a part of the aeronautical L-band (960-1164 M Hz), already occupied by a large number of radio-frequency legacy systems. This paper aims at studying the L-DACS impact on a legacy system, the Distance Measuring Equipment (DME), under two critical situations. Such topics are fundamental in aeronautics, as any communication or radionavigation dysfunction may endanger flight and passengers security. Some obtained results will be used for the L-DACS standardization and its specifications finalization. For the first scenario (air-to-air scenario), we propose a deterministic algorithm to compute the interference level in the frequency domain. Since this seems to be insufficient for the second scenario (co-site scenario), we develop a time-frequency approach to analyze the interference using an aeronautical RFC test-bed that we implemented at Supelec.

I. INTRODUCTION

In the beginning of the 21th century, international aeronautical authorities expressed their need to develop a new infrastructure for aeronautical radiocommunications, because the air-traffic is increasing (see Fig. 1) and that current communication systems in the aeronautical VHF-band (118 -136 M Hz) between pilots and air-controllers are reaching their capacity limits. [START_REF] Hakegard | Spectral Efficient COMmunications for future Aeronautical Services (SECOMAS)[END_REF] The L-band Digital Aeronautical Communication System (L-DACS) is the part of the future infrastructure that will be in charge of continental radiocommunication and it is expected to operate in a part of the aeronautical L-band (960 -1164 M Hz), already occupied by a large number of radio-frequency legacy systems (see Fig. 2). Among them, one of the most important systems is the Distance Measuring Equipment (DME), which permanently evaluates the slant distance between the aircraft and ground beacons, and which uses most of the 960 -1164 M Hz spectrum.

Consequently, it is essential to consider its radio-frequency compatibility (RFC) for the development of the future L-DACS system. Through RFC, the coexistence between L-DACS and legacy systems can be evaluated, both in ground and airborne environments. L-DACS and a legacy system are considered compatible from a RFC perspective, if L-DACS can operate correctly (with respect to its expected quality of service) in the presence of the legacy system without generating harmful interference, and vice versa. To evaluate the RFC, it is essential ti study many interference scenarios, most of them are emphasized in Fig. 3. For the moment, two candidate technologies have been preselected and they are named L-DACS1 and L-DACS2, respectively. In this paper, we particularly focus on the L-DACS1/2 effect on the performance of a DME on-board receiver. To this end, we identified two among the most critical interference scenarios from the RFC viewpoint. Under the first scenario called the air-to-air scenario, L-DACS and DME are airborne equipment onboard of distinct aircrafts whereas for the second scenario, named the co-site scenario, both airborne devices are placed in the same aircraft.

The paper is organized as follows. In Section II, we give better insights on the L-DACS system and development status, and we present the DME system. In Sections III and IV, we analyze L-DACS impact on DME under the air-to-air scenario and co-site scenario, respectively. For both cases, we describe our methodology and emphasize the main results. Finally, in Section V, we summarize the paper contributions and we provide some perspectives for further research works.

II. L-DACS AND DME SYSTEMS PRESENTATION

Since their standardization, aeronautical communications are essentially analogical, and they are performed in the aeronautical VHF band (118 -136 M Hz). On the other hand, according to the aeronautical authorities forecasts, the aerial traffic is expected to grow continually. Consequently, a congestion phenomenon is likely to happen in the few coming years in regions of the world with the highest traffic load.

In this context, the International Civil Aviation Organization (ICAO) launched in 2004 a Euro-American initiative to develop a future infrastructure for aeronautical communications (FCI). The FCI development started under a cooperative research program named Action-Plan 17 (AP17) [START_REF]Action Plan 17 : Future Communication Study -Terms of reference[END_REF] and involves research teams, industrial partners and aeronautical authorities from many countries in the world. The first step of the FCI development activities was to determine the most promising technologies to fulfill the new aeronautical requirements expressed in the report [START_REF]Communications Operating Concept and Requirements for the Future Radio System[END_REF]. According to the first assessment results published in 2007 [START_REF] Schnell | Future Communications Infrastructure -Step 2: Technology Assessment Results -version 1.0[END_REF], [START_REF] Gilbert | FCS Phase II -Identification of Technologies for Provision of Future Aeronautical Communications[END_REF], the infrastructure comprises many technologies depending on the flight phase. Among these technologies, the L-band Digital Aeronautical Communication System (L-DACS) was identified to be in charge of the continental communications. It is expected to operate in a part of the aeronautical L-Band (960 -1164 M Hz) [START_REF]World Radiocommunication Conference (WRC-12) -Plenary Meeting -European Common Proposals for the Work of the Conference -Part 4 -Agenda Item 1.4[END_REF]. The L-band is potentially large but its spectrum occupation is dense, not only by diverse aeronautical systems but also by mobile telephony and satellite navigation systems as it is shown in Fig. 2. Therefore, it is important to address the L-DACS coexistence with all these systems in both airborne and ground environments.

For the moment, two technologies have been identified as potential candidates to support L-DACS and they are named L-DACS1 [START_REF]European Organization for the Safety of Air Navigation[END_REF], [START_REF]L-DACS1 System Definition Proposal: Delivrable D3 : Design Specifications for L-DACS1 Prototype[END_REF] and L-DACS2 [START_REF]L-DACS2 System Definition Proposal: Delivrable D2[END_REF], [START_REF]L-DACS2 Transmitter and Receiver prototype equipment specifications : Deliverable D3[END_REF] . L-DACS1 is similar to the IEEE 802. [START_REF]Radio Navigation Aids[END_REF] wireless system and is based on Frequency-Duplex Division (FDD) technique, where the ground station and the airborne equipment transmit Fig. 4. The applied process for L-DACS candidate selection (from [START_REF]European Organization for the Safety of Air Navigation[END_REF] and [START_REF]L-DACS2 System Definition Proposal: Delivrable D2[END_REF].

simultaneously using distinct frequency bands. However, the L-DACS2 is similar to the GSM standard and is based on Time-Duplex Division (TDD) technique, where the ground station and the airborne equipment transmit using the same carrier frequency during distinct time intervals. We summarize in Table ?? main system parameters of both candidates. L-DACS1/2 systems development is now a part of two research programs (SESAR [START_REF]SESAR Definition Phase -Delivrable D6 -Work Programme for 2008 -2013[END_REF] in Europe and NextGen [START_REF]Concept of Operations for the Next Generation Air Transportation System[END_REF] in the USA, additionally to parallel activities in Japan [START_REF] Nagaoka | Long-term Vision of ENRI's Research and Development[END_REF]) and three main tasks have been identified: systems specifications, prototypes development and performance evaluation through operational scenarios and interference scenarios. These tasks are shown in Fig. 4.

In this paper, we are interested in the third task and we aim to analyze the L-DACS1/2 impact on an L-band legacy system, the Distance Measuring Equipment (DME).

The DME [START_REF]Radio Navigation Aids[END_REF] is a radio navigation system that is nowadays used in all airplanes to measure permanently the slant distance between an airplane and ground beacons. It operates in the 960-1215 M Hz frequency band and has been used for near a century. The frequency channel used by the airplane and the one employed by the ground beacon are separated by 63 MHz. The DME communication is based on three steps. It starts on the airborne equipment (named the interrogator) which sends a stream of Gaussian-shaped pulse pairs to the ground station (called the transponder). The latter sends back the received signal to the interrogator with a certain delay, and finally, by measuring the time interval between sent and received streams, the interrogator determines its distance to the transponder.

According to its specifications, the DME transmitted signal consists of a maximum of 150 random pulse pairs per second. In each pair, the peaks of the two gaussian pulses are separated by at least 12 µs depending on the DME mode of operation. A DME shape is given in Fig.

III. AIR-TO-AIR INTERFERENCE SCENARIO ANALYSIS

Under the air-to-air scenario, L-DACS and DME systems are onboard distinct aircrafts. This scenario is critical because the victim receiver is likely to intercept signals from many interferers (this is due to its high radio visibility). Moreover, this scenario seems useful for both the aeronautical network dimensioning and frequency/distance planning.

We evaluated the L-DACS1/2 interference effect based on a frequency-domain analysis and using a specific algorithm to compute the interference level in the worst case. Under this situation, the victim receiver is likely to get the maximum interference level. In addition, we considered the case of co-channel interference, where the interferer and the victim receiver use overlapping frequency bands. Finally, we assumed a free-space propagation model. We defined a deterministic approach, different from existing methodologies dealing with L-DACS interference, taking into account the imposed vertical and horizontal aircrafts separations by aeronautical authorities (see Fig. 6).

To model the aeronautical environment, we used L-DACS antennas characteristics (which are typical L-band antennas, omnidirectional in azimuthal direction and slightly directive in vertical direction to place interferers in a bi-dimensional grid. The methodology assumes at maximum two airplanes per flight level and is based on three steps. In the first step, we identify the strongest one/two interferer(s) for each flight level independently. In the second step, we select the positions of the K identified airplanes generating the highest cumulative interference power at the victim receiver. In the last step, we allocate to each interferer a frequency channel such as the interference level remains the highest.

In previous publications [START_REF]Radioelectric Compatibility of the Future Aeronautical Communication System[END_REF] and [START_REF]Minimal Operational Performance Requirements for Distance Measuring Equipment Interrogator (DME/P and DME/N) operating within the Radio Frequency Range 960 to 1215 MHz (Airborne Equipment)[END_REF], we applied this approach to an ideal victim receiver. In this paper, we analyze the L-DACS interference considering a DME receiver.

From their specifications, L-DACS1 uses a 0.5 M Hz bandwidth for transmission/reception and its airborne transmission power is 16 dBW (46 dBm); and L-DACS2 uses a 0.2 M Hz bandwidth for transmission/reception and its airborne transmission power is 17 dBW (47 dBm). The DME uses a 1 M Hz bandwidth and for the DME receiver, the computed maximum acceptable interference spectral density is -129 dBW/M Hz (-99 dBm/M Hz). It should be noticed that aeronautical safety margins have to be added to obtain the operational acceptable threshold.

Based on these information, we considered K = 2 L-DACS interferers around the DME victim receiver. Three cases may occur: both interferers are in-band, or only one of them is in-band or both of them are out-of-band. We computed the cumulative interference spectral density in the three situations and the results are summarized in Fig. 7 and Fig. 8. In these figures, we present the total interference spectral density I d at the DME receiver, with respect to vertical separation between the strongest L-DACS interferer and the DME receiver altitudes.

From these results, we can see that as expected by classical frequency sharing studies, it is necessary to have no in-band L-DACS1/2 interferers in order to avoid harmful interference. We also notice that interference is principally due to the first identified L-DACS interferer (which is the strongest interferer). Moreover, for both L-DACS candidates, we obtained a precise estimation of the interference level using our deterministic approach.

IV. CO-SITE INTERFERENCE SCENARIO ANALYSIS

For the second identified interference scenario, called the co-site scenario, both the interferer and the victim receiver are on-board the same aircraft. This scenario is considered as the most critical from a RFC viewpoint because of equipment proximity. From now on, we precisely focus on one of the L-DACS candidates on the DME performance and we chose to investigate L-DACS2.

The frequency-domain analysis seems insufficient for this case. In fact, the interference level P DME received by the DME interrogator is given by equation (1):

P DME (dBW ) = P LDACS2 (dBW ) -L LDACS2 (dB) -C A (dB) -L DME (dB) + M dB (dB), (1)
where P LDACS2 (in dBW ) is the L-DACS2 output power, L LDACS2 and L DME (in dB) are cable losses at the L-DACS2 transmitter and the DME interrogator, respectively, and C A (in dB) is the coupling between their antennas. M dB (in dB) is the attenuation obtained by the superposition between the L-DACS2 transmit mask and the DME blocking mask. Now, using system characteristics given in [START_REF]L-DACS2 System Definition Proposal: Delivrable D2[END_REF], we have P LDACS2 = 17 dBW and L LDACS2 = 3 dB. In according to [START_REF] Neji | Interference analysis for the future aeronautical communication system[END_REF], C A = 20 dB. Moreover, at 1 M Hz offset relatively to its center frequency, the L-DACS2 maximum mask attenuation is 80 dB (see [START_REF]Protection criterion for the aeronautical radionavigation service with respect to aggregate emissions from space stations in the radionavigationsatellite service in the band 1 164-1 215 MHz[END_REF]). Hence, if L-DACS2 and DME frequencies separated by 1 M Hz, M dB = -80 dB. If we assume that L DME = 2 dB, we obtain P DME = -88 dBW . Knowing that the DME bandpass is equal to 1 M Hz, the interference density is I DME = -88 dBW/M Hz at the DME receiver interrogator input. However, as mentioned in [START_REF] Neji | Effect of the aeronautical L-DACS2 radio-frequency signals on the DME system performance[END_REF], the maximum acceptable interference level by the DME interrogator is I max = -129 dBW/M Hz (before taking into account aeronautical margins).

Thus, to study this scenario, we consider a different methodology, named time-domain approach, considering system dynamics and technology properties. Let us first describe the interference process in this case (see Fig. 9).

The L-DACS interference is added to the DME signal sent by the transponder to the interrogator (the reply signal, which is a replica of the interrogation signal). In this situation, collision between L-DACS and DME signals may occur. Due to this phenomenon, some Gaussian-pulse pairs may be lost at the DME airborne receiver. Let us call R (in %) the rate of correctly received DME pairs, compared to the total number of sent pairs in the interrogation signal. If R becomes lower than a certain threshold Rmin after a precise time delay (called the maximum synchronization time), the synchronization between the DME interrogator and the DME ground beacon is considered lost.

In this paper, we implement the scenario considering an L-DACS2 interferer (TDD system), through specific test-beds with an L-DACS2 signal generator and DME commercial equipment. Our criterion of analysis is the DME synchronization state (binary information), which can be easily detected by observing the DME interrogator screen during the maximum synchronization time (see Fig. 10). The synchronization state is 1 if the distance is displayed with acceptable precision (referring to DME interrogator specifications) before the maximum synchronization time expires, and 0 else.

In the previous papers [START_REF]How the aeronautical L-DACS2 radio-frequency signals modulation affects the DME system performance[END_REF] and [24], we presented the obtained measurement results for the conducted mode, where L-DACS unwanted signals are propagated through cables, connectors and electronic devices. In this work, we are more focused on laboratory measurements in the radiated mode, where unwanted signals are radiated by the L-DACS2 antenna and captured by the DME antenna. For this mode, we first enumerate the used material, then we describe the experimental setup and we detail the followed protocol. For the experimental material (see Fig. 11), we associate an antenna to the L-DACS2 transmitter, an antenna to the DME interrogator and an antenna to DME transponder. In addition to the L-DACS2 signal generator (Agilent E4438C ESG), the DME used commercial interrogator (Bendix King KN62A) and the DME commercial transponder (Aeroflex IFR6000 Ramp test), the test-bed comprises:

• Two identical commercial aeronautical antennas manufactured by "Comant" and associated to the DME inter-(antenna 1) and the L-DACS2 generator (antenna 2),

• A specific antenna provided with the Aeroflex IFR6000 pack and associated to the DME transponder (antenna 3), • A network/spectrum analyzer manufactured by "Rohde and Schwarz" (ZVL type) to measure signals at antenna ports of the different devices. In Fig. 11, black-colored arrows indicate the power circulation starting from the DME interrogator and green-colored arrows show outputs to spectrum analyzers. We also precise the minimum and maximum output powers P s and maximum input power P e of our equipments as well as the minimum and maximum input power of our spectrum analyzers. We implemented this diagram with commercial equipments and antennas at the planar anechoic chamber at Suplec (see Fig. 12).

To perform the measurements, we proposed the following experimental protocol, based on the reference document [START_REF] Neji | Interference analysis for the future aeronautical communication system[END_REF], and composed by 11 steps 1 :

1-Verify the link budget before beginning measurements. 1 For a fixed power in step 7, repeat steps 8 to 11 until the DME synchronization state changes. Then, increase the power and follow the same procedure. 2-Switch on the DME interrogator's alimentation.

3-Turn on the DME interrogator and set its VOR frequency (based on tables from [START_REF] Neji | Interference analysis for the future aeronautical communication system[END_REF], this selected VOR frequency will determine a specific DME channel and consequently both interrogator and transponder center frequencies). 7-Set the L-DACS2 maximum power (depending on the target SIR value), its modulation and set its center frequency.

8-Increase the L-DACS2 channel occupation rate. 9-Run the test. 10-Count a certain time delay (corresponding to the maximum synchronization time) and observe the DME synchronization state. For each measure, we verify both stability and precision criteria. We considered that a measure is stable if the same DME synchronization state is obtained after two consecutive tests under the same conditions.

11-Stop the test.

We also assumed in-band interference and out-of-band interference. For the experimental protocol, we considered 2 seconds for the maximal synchronization time, and S min + 3 dB for the useful signal power at the DME victim receiver, being S min (in dB) the tested DME equipment sensitivity (both values are based on the DME specifications). Finally, we selected the DME channel 17X, which corresponds to the carrier frequency F c = 978 M Hz for the transponder (this corresponds to the lowest operational frequency for the investigated DME device). Under these assumptions, we analyze the impact of the L-DACS2 channel occupation rate, which is the percentage of time of effective L-DACS2 transmission, on the DME performance. We summarize the obtained results in Fig. 13, where the maximum acceptable L-DACS2 channel occupation rate is shown with respect to the frequency separation between L-DACS2 and DME transponder signal carriers, for different values of the Signal to Interference Ratio (SIR) at the DME airborne receiver.

We can see that under this scenario and with the specific tested equipment, the DME synchronization is successful in the presence of the L-DACS2 interferer if its channel occupation rate remains lower than 72 % for SIR higher than -40 dB and this also occurs in the co-channel mode (L-DACS2 and DME use overlapping channels). Hence, based on our proposed approach, implemented test bed and available DME commercial equipment at Supelec, L-DACS2 would not cause harmful interference on the DME system. We prove herein that while time-domain parameters are considered, satisfying results in terms of RFC can be obtained. In fact, according to existing RFC studies, in the co-channel mode, these systems cannot coexist.

V. CONCLUSION In this paper, we studied the L-DACS interference impact on the DME receiver performance under some critical scenario from the RFC viewpoint (air-to-air scenario and co-site scenario). To analyze the first scenario, we proposed a deterministic frequency-domain methodology which is different from existing approaches mentioned in frequency sharing studies involving L-DACS, and which gives a good estimation of the interference level at the victim receiver. For the second scenario we developed a time-frequency approach, which takes into account system dynamics and which provides more realistic evaluation to the actual interference level. More particularly, for the co-site scenario, we proved that under this new methodology and using a specific laboratory setup to emulate the interference environment, L-DACS2 would not cause harmful interference on the DME interrogator, whereas in classical studies, this was not expected to happen. For further work, these results should be confirmed by additional tests with other commercial DME devices using other metrics to analyze their performance. To complete the analysis, it is also important to study the DME effect on the L-DACS2 performance using the time-frequency approach, then to extend it to other interference scenarios, in order to evaluate the interference more precisely than under classical RFC methodologies. We finally suggest generalizing the proposed time-frequency approach to analyze the RFC between any two radio-frequency systems, taking into account additional parameters related to system dynamics and their technology properties.

Fig. 1 .

 1 Fig. 1. Air traffic forecast in Europe for 2012 (from [2]).

Fig. 2 .

 2 Fig. 2. The L-Band spectral occupancy (adapted from [3])

Fig. 3 .

 3 Fig. 3. Main interference scenarios to be studied for the RFC.

  Fig. 5. The structure of a DME pulse pair

Fig. 7 .

 7 Fig. 7. Total interference spectral density at the DME victim receiver, by two L-DACS1 transmitters (for 2, 1 and 0 in-band interferers).

Fig. 8 .

 8 Fig. 8. Total interference spectral density at the DME victim receiver, by two L-DACS2 transmitters (for 2, 1 and 0 in-band interferers).

Fig. 9 .

 9 Fig. 9. RFC system model: DME transmitter, L-DACS2 interferer and DME victim.

Fig. 10 .

 10 Fig. 10. Displayed information by the synchronized DME interrogator.

Fig. 11 .

 11 Fig. 11. Schematic diagram for RFC measurements in the radiated mode.

Fig. 12 .

 12 Fig. 12. Implemented aeronautical RFC test-bed in the radiated mode.

4 -

 4 Check L-DACS2 and DME equipments' good functioning through preliminary tests. 5-Generate the L-DACS2 time-domain radio-frequency (RF) signal. 6-Activate the L-DACS2 generator "local" mode.

Fig. 13 .

 13 Fig.[START_REF]SESAR Definition Phase -Delivrable D6 -Work Programme for 2008 -2013[END_REF]. DME receiver performance measurement in presence of L-DACS2 interference, with respect to the frequency offset between useful and interfering transmitters.