A Cross-Layer Framework of QoS Routing and Distributed Scheduling for Mesh Networks

Transcription

1 A Coss-Laye Famewok of QoS Routing and Distibuted Scheduling fo Mesh Netwoks Chi Haold Liu, Athanasios Gkelias, and Kin K. Leung Depatment of Electical and Electonic Engineeing, Impeial College London Exhibition Road, London, SW7 2BT, United Kingdom {chiliu, a.gkelias, Abstact Coss-laye outing and scheduling algoithms design fo wieless backhaul mesh netwok has attacted much eseach inteest ecently. The netwok is expected to suppot vaious types of applications with diffeent quality of sevice (QoS) equiements fom both outing and scheduling pespectives. Existing woks do not efficiently integate these QoS constaints in oute discovey and maintenance phases and ovelook the inteaction between medium access contol (MAC) and outing algoithms. In this wok, we popose a novel cosslaye famewok of QoS outing and distibuted oppotunistic scheduling fo wieless mesh netwok, which povides esouce esevation fo QoS flows. Studies with diffeent scheduling algoithms and outing potocols have shown that ou algoithm successfully guaantees vaious QoS equiements and achieves highe netwok thoughput when compaed with othe standad techniques. INTERNET Wieless oute Cellula Netwok Wied connection Rual/emote aea Wieless Mesh Backhaul Hot spot (Wi-Fi) I. INTRODUCTION Wieless mesh netwoks (WMNs) is a elatively new and pomising key technology fo next geneation wieless netwoking that have ecently attacted both the academic and industial inteest. Mesh netwoks ae expected gadually to patially substitute the wied netwok infastuctue functionality by being able to povide a cheap, quick and efficient solution fo wieless data netwoking in uban, sububan and even ual envionments. Thei populaity comes fom the fact that they ae self-oganized, self-configuable and easily adaptable to diffeent taffic equiements and netwok changes. Mesh netwoks ae composed of static wieless nodes/mesh outes (WMR) that have ample enegy supply. Each node opeates not only as an conventional access point (AP)/Intenet gateway (IGW) to the intenet but also as a wieless oute (Fig. 1) able to elay packets fom othe nodes without diect access to thei destinations [1]. The destination can be an intenet gateway o a mobile use seved by anothe AP in the same mesh netwok. WMNs must meet a numbe of technical equiements, such as poviding high capacity wieless links and lage enough communication ange to ensue netwok connectivity to IGWs, while at the same time must guaantee that the multiple and stict quality-of-sevice (QoS) applications constaints ae satisfied. Unfotunately, most of the cuent wok on wieless ad hoc netwok potocol analysis and design is mainly based on a layeed appoach. This layeed achitectue by poviding modulaity and tanspaency between the layes, led to the obust scalable potocols in the Intenet and it has become Fig. 1. Typical wieless mesh netwok scenaio. the de facto achitectue fo wieless systems. Howeve, in wieless mesh netwoks the spatial euse of the spectal fequency and the boadcast, unstable and eo pone natue of the channel, make the layeed appoach suboptimum fo the oveall system pefomance. Fo instance, a bad esouce scheduling in MAC laye can lead to intefeence that affects the pefomance of the PHY laye due to educed Signalto-Intefeence-plus-Noise-Ratio (SINR). Local capacity optimization with oppotunistic scheduling techniques that exploit the multi-use divesity may incease the oveall outgoing thoughput of the tansceives but they can also geneate new bottlenecks in seveal outes in the netwok. This is why coss-laye design fo impoving the netwok pefomance has been a focus of much ecent wok. In a cosslaye paadigm, the joint optimization of contol ove two o moe layes can yield significantly impoved pefomance. Caution needs to be execised, though, since coss-laye design has the potential to destoy the modulaity and make the oveall system fagile. Othe impotance challenges that have to be taken into account duing the design of coss-layeed solution fo WMNs is the diffeent opeation time-scales between coding, scheduling and outing algoithms; especially in the case that system pefomance pedictions in diffeent layes have to be pefomed. Moeove, since WMNs have to suppot a wide vaiety of applications and sevices, thee ae multi-constained QoS equiements that have to be jointly

2 satisfied by the coss-laye appoach. Fo instance, additive (i.e., cost, delay, jitte), multiplicative (i.e., packet-eo-ate and path beak pobability) and concave (i.e., thoughput) metics have to be jointly taken into account which has been poven to be NP-complete [13]. In this wok we pesent a heuistic low-complexity coss-laye famewok that attempts to tackle the afoementioned challenges and povide multiconstained QoS suppot to any WMNs. Related Wok: The well-known Ad hoc on-demand distance vecto (AODV) [11] potocol, a eactive appoach fo oute discovey and maintenance that finds the outes with minimum numbe of hops fom souce to destination in ad-hoc netwoks, is not suitable fo high thoughput and delay-sensitive applications. An extension of AODV, QoS- AODV [15], povides QoS povisioning in tems of both bandwidth and delay. Howeve, it ovelooks the packet queuing delay but only the packet pocessing time was consideed in Node Tavesal Time. This inaccuate estimation may esult in much highe end-to-end (ETE) packet delay than expected when high taffic load is consideed. Anothe bandwidth outing (BR) potocol [8], and a simila on-demand QoS outing (OQR) potocol [7] wee poposed to calculate the available bandwidth in tems of slot fo QoS flows. Howeve, packet delay is clealy not consideed. Futhemoe, because slots ae pe-detemined befoe taffic flows ae scheduled, it fails to exploit the scheduling oppotunistic gain in fast-fading channels. In othe wods, the eseved time slots may deteioate packet tansmission quality due to bad instantaneous channel conditions. On the othe hand, scheduling fo wieless mesh netwoks has dawn a lot of eseach attention ecently. Due to the fact in [2] and [12] that finding a pefect match with the highest netwok thoughput is NP-complete ([1], [3]) fo centalized scheduling algoithms, vaious distibuted scheduling algoithms wee poposed. Recently, [4] and [5] poposed a distibuted oppotunistic scheduling algoithm fo backhaul netwoks, which povides multi-use divesity gain in the wieless envionments, enfoces esouce allocation in the long un and maintains stong tempoal coelation fo intefeence, without which channel quality and intefeence cannot be tacked and pedicted with easonable accuacy. In this pape, we popose a novel coss-laye famewok that combines a QoS outing scheme with a distibuted oppotunistic scheduling algoithm fo wieless mesh netwoks. Ou contibution is theefold: (1) we povide a unified appoach to integate multiple QoS constaints in a sole utility function, (2) we exploit the multiuse divesity gain and multiple antenna diective gain, (3) we successfully combine thee diffeent layes (i.e., netwok, MAC and PHY). Moe specifically, this wok is an extension of the integated QoS outing (IQoSR) potocol pesented in [9]. The actual inteface between the scheduling and outing schemes is defined and a novel utility function is used to link the and-to-end and long tem outing demands with the shot tem and localized scheduling decisions of the oppotunistic scheduling scheme [5] unde consideation. Diectional antenna tansmissions with adaptive modulation schemes have been consideed in the physical laye while channel pediction in diffeent time-scales is included to assist and guide the optimum opeation of the ovelying layes and algoithms. Extensive simulation esults show that ou algoithms can successfully guaantee multi-constained QoS while at the same time achieving bette netwok pefomance compaed with othe standad techniques. Moeove, the impact of the esouce esevation weight facto β, defined in [9] and its effect on the QoS outage pobability and blocking pobability of new flows is investigated and analyzed. The est of the pape is oganized as follows. In Section II, the system model and the algoithm desciption ae intoduced. Section III povides a thoough desciption of the cosslaye famewok and the inteface between scheduling and outing schemes. Numeical esults and a detailed pefomance analysis ae given in Section IV. Finally conclusions ae dawn in Section V. II. SYSTEM MODEL &ALGORITHM DESCRIPTION Conside a wieless mesh netwok compises a set of n numbe of WMRs, denoted as V R = {v =1, 2,...,n } and a set of n g numbe of IGWs denoted as V G = {v g g = 1, 2,...,n g }. Each WMR independently geneates data sessions. Each QoS flow with flow index q has to fulfil a set of QoS constaints that includes ETE packet delay Dq, thoughput Tq and packet-eo-ate (PER) Eq. We denote this set as (Dq,T q,eq ). A oute Ω k st fom a souce WMR with index s to a destination IGW indexed t within the oute set Ω st is concatenated by a set of links {(v i,v j )}, fo all v i,v j V R VG. Theefoe, we could fomally expess the oute fom s to t as (1), whee total m candidate outes exist. In the following discussions, we use tem session and flow fo the taffic input, (v i,v j ) and (i, j) fo the link between v i and v j intechangeably. Ω k st = {(v i,v j ) v i,v j V R VG,k =1, 2,...,m} (1) A. QoS Pefomance Metic As it has been mentioned above the poblem of poviding optimum outes that guaantee multiple QoS constaints has been poven to be NP-complete [13]. Theefoe, in ode to ovecome this difficulty we define a new utility function based on the dissatisfaction atio R that expeienced by each QoS metic. Moe specifically, we define the atio R fo each of the QoS equiement as follows: 1) R D k : ETE packet delay dissatisfaction atio fo oute Ωk st is defined as the actual delay measuement, (i,j) Ω D a k st ij, ove the QoS delay equiement Dq,i.e., R D (i,j) Ω D a k (q) = k st ij (1 β D )Dq. (2) 2) R T k : Thoughput dissatisfaction atio is fomulated as the atio between the thoughput equiement Tq and actual bottleneck link thoughput, min (i,j) Ω k st Tij a, the minimum of

3 TABLE I QOS FLOWS WITH RELATED RESOURCE RESERVATION FACTORS voice-ove-ip Inteactive-video Boadband Data I D,β D 1, changeable 1, changeable, I T,β T 1, changeable 1, changeable 1, changeable I E,β E, 1, changeable 1, changeable all one-hop thoughputs along oute Ω k st, i.e., R T k (q) = (1 + β T )Tq min (i,j) Ω k st Tij a (3) 3) R E k : PER dissatisfaction atio is defined as the multiplication of all one-hop eo ate, 1 (i,j) Ω E st(1 a k ij ), ove PER equiement Eq since this is a multiplicative constain, i.e., R E k (q) = 1 (i,j) Ω (1 E a k st ij ) (1 β E )Eq (4) A esouce esevation magin facto has been intoduced as β D, β T and β E fo delay, thoughput and PER espectively. In othe wods β i epesent the additional esouces that we eseve beyond the QoS equiements in ode to povide a safe guad fo impefect esouce estimations and system fluctuations. The impact of β i on the QoS outage pobability and new sessions blockage pobability is given in section???. Since a session has to fulfil the set of QoS equiements, a souce-to-gateway oute will be feasible if and only if all defined atios ae less than one (R D k (q), RT k (q), RE k (q)) 1. Howeve, some constaints may not be citical in some applications (fo instance, boadband data sevices ae not sensitive in delay). In ode to efficiently cope with this issue we intoduce the indication function I p, whee p = D, T, E, expessed as { 1 if paamete p is citical in QoS flow q I p = (5) othewise An example of the esouce esevation magin factos and indication functions chosen fo thee types of QoS flows in the netwok, namely, voice-ove-ip, inteactive-video and boadband data sevices espectively, is demonstated in Table I. Ou multi-constain pefomance index in oute Ω k st can be fomulated as U k = max[i D R D k (q), I T R T k (q), I E R E k (q)] (6) and the poposed multi-objective function in ode to take an optimum heuistic decision is given by S = min [U k ] (7) Ω k st Ωst III. CROSS-LAYER FRAMEWORK This section povides a thoough desciption of the inteactions and intefaces between diffeent layes and the layeed paamete and functionalities that have been taken into account in ou poposed famewok. PHY Laye: The Jake s Model [6] is used fo the wieless channel epesentation while the equied PER is deived based on SINR cuves fo the used adaptive modulation and coding scheme. Each WMR is equipped with diectional antennas while accuate positioning is assumed. At given time t, the eceiving SINR γ ij fo the tansmitteeceive pai (v i,v j ) is given by (8), γ ij = P ij C ij d α ij k P kjc kj d α kj + N whee P ij, C ij and d α ij ae tansmission powe, channel gain (the antenna gain has been also included hee) and path loss between link (v i,v j ) espectively. Typical value fo path loss exponential facto is 3.5. N is the single-sided powe spectum density fo additive white Gaussian noise. In ode to educe the intefeence to adjacent concuent tansmissions and incease the fequency euse and channel capacity, the WMRs ae equipped with diectional antennas. Futhemoe, half duplex is assumed and powe contol is not consideed in this phase, i.e., all the nodes have the same fixed tansmission powe. Medium Access Contol: In ode to exploit the multiuse divesity gain, the distibuted oppotunistic popotional fai schedule poposed in [4][5] is consideed in ou cosslaye famewok. This scheduling scheme has been poven not only to achieve a netwok thoughput impovement but at the same time to allow fo moe accuate channel pedictions by poviding high level of tempoal coelation of intefeence. This popety is of paamount impotance fo the long tem pediction of channel quality equied fo the optimum pefomance of the outing algoithm as it will be descibed in the following. Howeve, the oppotunistic natue of this scheme comes with the inheent difficulty to guaantee the equied QoS pefomance in a long un. This is because oppotunistic appoaches usually intoduce moe fluctuating instantaneous pefomance at individual nodes. In ode to ovecome this a utility function (o scheduling metic) that compises both outing and scheduling paametes is used. In that way not only it achieves oppotunistic gain but also suppots quality of sevice as committed by the outing algoithm in use. The outing algoithm estimates the outing demand fo the session q in a cetain futue (e.g., fo the whole duation of a data session) and passes the scheduling the thoughput allocation taget a q ij fo the link (i, j). Fo instance, the outing algoithm may ask fo a q ij =(1+β T ) Tq amount of bandwidth esouces to be eseved on the link (i, j). The scheduling scheme at node i will geneate the thoughput allocation taget vecto a i =(a i1,a i2,..., a il ) with the demands of all l incoming and outgoing links and activate the appopiate link fo tansmission-eception each time based on the following utility function, ρ ij (8) U ij = a q ij (9) C ij whee ρ ij and C ij ae the instantaneous thoughput and channel capacity in the long un espectively. [5] poves that, fom a MAC pespective, by choosing the poposed link utility

4 TABLE II SIMULATION PARAMETERS Paamete Value Paamete Value Channel Model Jakes Model Path Loss Coeff. 2-4 Antenna Patten Side lobe: -25dB AMC MPSK Main lobe: 3 MQAM Dopple Feq. 1-25Hz System Bandwidth 5MHz Slot Duation 8us Slots pe Fame 1 Fame Duation 8ms Packet Length 512 bytes WMR 15 IGW 1 Netwok Size 3 miles Tx Range 1.5 miles Taffic Aival Poisson metic (9) the schedule guaantees the popotional taget QoS thoughput as well as fainess among links. Howeve, in this pape it is not clea how the localized and shot tem scheduling decisions can affect the long tem outing pefomance and guaantee the multiple QoS equiements. Pefomance paametes pediction: The pefomance of the poposed famewok highly depends on the accuate estimation of multiple system paametes equied fo the optimum outing decision. Fo this eason, each node keeps a table with measuement of pevious tansmissions fom all its neighbos. The measued paametes include link thoughput, Signal-to- Intefeence-plus-Noise-Ratio (SINR) and queuing delay. The thoughput statistics ae passed to the scheduling scheme fo the estimation of the long un channel capacity C ij. The SINR statistics fo each link (i, j) and the queuing delay statistics in each node ae used to estimate the expected PER and ETE packet delay, espectively, fo the outing decisions. IV. NUMERICAL RESULTS To access the coss-laye famewok pefomance a slotted, time-diven simulation platfom has been developed. A numbe of WMRs and IGWs ae andomly and independently deployed on a ectangula two-dimensional space. Sessions ae geneated accoding to a Poisson pocess. Each session has to fulfil thee QoS constaints, i.e., ETE packet delay, thoughput and end-to-end PER. Retansmission scheme is assumed in case of packet failue. The simulato includes the PHY, MAC and Netwok afoementioned algoithms as they have been descibed in the pevious sessions. The simulation paametes ae summaized in Table II. Fo compaison puposes, the well known Round Robin (RR) schedule [14] and the AODV outing potocol ae used as benchmaks and fou diffeent combinations ae consideed as they summaized in Table III. This gives as the oppotunity to investigate sepaately the impact of schedule and outing algoithm on the pefomance of ou system. The pefomance of the poposed coss-laye famewok is investigated in tems of Gateway Thoughput (Fig. 2a) and pobability of successful end-to-end packet eception as a function of the packet inte-aival time. The pobability of success is defined as the atio of the packets that aive at the gateway and have fulfilled the Delay QoS equiements TABLE III FOUR COMPARISONS MAC Scheduling Routing Coss-Laye Tem 1 Round Robin AODV 2 Round Robin IQoSR 3 Distibuted Oppotunistic AODV 4 Distibuted Oppotunistic IQoSR (Fig. 2b), denoted as PD S, and the PER QoS equiements (Fig. 2c), denoted as PPER S, thoughout the whole oute. Fig. 2a shows that the oppotunistic schedule consideed in ou famewok can guaantee hight thoughput even fo small inte-aival ate when the offeed netwok taffic is getting high. On the othe hand, the RR scheme povides a constant thoughput since the channel esouces ae eseved (on MAC level) independently of the offeed taffic. The combination of oppotunistic scheduling and ou poposed outing scheme gives by fa the best oveall pefomance. Fig. 2b highlights the fact that ou poposed famewok can also satisfy the packet delay QoS equiements while at the same time guaantees high thoughput ate at the gateway side. It is inteesting to note that the outage pobability is less than.1 even fo high taffic conditions. Howeve, the PER pobability is much wost compaed to the thee othe cases as it can be seen fom Fig. 2c. Nevetheless, the dominant effect fo the end-to-end packet delay is the queuing delay in each node s buffe and that gives to ou famewok bette oveall delay pefomance. Fig. 3 depicts the outage pobability of QoS pe session as a function of the esouce esevation weight facto β. This is defined as the pobability of any of the QoS equiements of a session to fail duing the life time of the given session. In othe wods, it gives the pobability of U k (q) > 1. Fo simplicity we assumed the same β fo each QoS metic, i.e., β D = β T = β E = β and the inte-aival time of new flows is set to 6ms. It is impotant to notice that even fo β =(i.e., we do not eseve any additional esouces) ou poposed distibuted QoS outing algoithm integated with the oppotunistic schedule can guaantee the all the QoS of the undelying application fo 88% of the time compae to 78% if ound obin is used fo scheduling. Geneally it can be seen that the used utility function (9) fo the oppotunistic schedule can guaantee aound 1% lowe outage pobability than the ound obin independent of the additional esouces equested by the oute. By inceasing the esouce esevation weight facto we can educe the outage to less than 5% (i.e., fo β >.3), howeve this means that moe esouces ae eseved pe session affecting in this way the admission ate of new incoming flows. This tade-off becomes cleae in Fig. 4 whee the effect of β on the blocking pobability of new incoming sessions is demonstated. It can be seen that a less than 5% outage pobability fo existing flows comes with the cost of moe than 25% blocking pobability fo new flows. Nevetheless, by using the poposed utility function (9) togethe with ou multiconstain QoS outing scheme, we can achieve 1% blocking pobability compae to the case whee ound obin is used.

5 Gateway Thoughput (Mbps) P S D Inte-aival time fo all new flows (ms) Inte-aival time fo all new flows (ms) Inte-aival time fo all new flows (ms) (a) (b) (c) P S PER Fig. 2. The effect of netwok taffic on (a) Netwok Thoughput, pobability of successful end-to-end packet eception in tems of (b) Packet Delay and (c) PER. Fig. 4. QoS Outage Pobability Resouce esevation weight facto Fig. 3. QoS outage pobability fo existing sessions. New Session Blocking Pobability Resouce esevation weight facto Aveage blocking pobability fo new incoming sessions. V. CONCLUSIONS In this pape, a novel coss-laye QoS outing and distibuted oppotunistic scheduling famewok fo wieless mesh netwoks has been poposed to povide multiple QoS guaantees by esouce esevation and allocation schemes. Extensive simulation esults shows that by caeful consideation of the esouce esevation weight facto β, ou poposed famewok achieves highe netwok pefomance gain and bette QoS guaantees in compaison to othe benchmak potocols. Moeove, the poposed integated QoS pefomance metic can be easily extended to othe metics like delay jitte o use-defined utilities, and used fo multi-path outing. Futue eseach will include investigation of the joint QoS outing and scheduling optimization poblem using diectional antennas and MIMO techniques in the PHY laye. ACKNOWLEDGMENT This eseach is financially suppoted by the EU IST FP6 MEMBRANE poject (contact numbe: 2731). REFERENCES [1] I. F. Akyildiz and X. Wang, A suvey on wieless mesh netwoks, IEEE Communications Magazine, vol. 43(9), pp. S23 S3, Sept. 25. [2] L. Chen, S. H. Low, J. C. Doyle, and M. Chiang, Coss-laye congestion contol, outing and scheduling design in ad hoc wieless netwoks, in Poceedings of IEEE INFOCOM 26, Bacelona, Spain, 26. [3] M.R.Gaey,Computes and intactability: a guide to the theoy of NP-completeness. W. H. Feeman, [4] Y. Hou and K. K. Leung, Famewok of oppotunistic allocation of wieless esouces, in Poceedings of PacRim 27, Victoia, B.C., Canada, Aug. 27. [5], A novel distibuted scheduling algoithm fo mesh netwoks, in Poceedings of IEEE Globecom 27, U.S.A., 27. [6] W.C.Jakes,Micowave Mobile Communications, New Yok. Wiley, [7] C. R. Lin, On-demand qos outing in multihop mobile netwoks, in Poceedings of IEEE INFOCOM 21, vol. 3, Ap. 21, pp [8] C. R. Lin and J. Liu, Qos outing in ad hoc wieless netwoks, IEEE JSAC, vol. 17(8), pp , [9] C. H. Liu, K. K. Leung, and A. Gkelias, A novel coss-laye qos outing algoithm fo wieless mesh netwok, in ICOIN 8, Busan, Koea, Submitted fo publication. [1] L. Lovasz, Matching theoy. Noth-Holland, [11] C. Pekins and E. Roye, Ad-hoc on-demand distance vecto outing, in Poceedings of WMCSA 99, San Jose, CA, USA, 1999, pp [12] S. Ramanathan, Scheduling algoithms fo multihop adio netwoks, IEEE/ACM Tansactions on Netwoking, vol. 1(2), pp , Sept [13] Z. Wang and J. Cowcoft, Quality-of-sevice outing fo suppoting multimedia applications, IEEE JSAC, vol. 14(7), pp , Sept [14] X. Yuan and Z. Duan, F: a popotional and wost-case fai ound obin schedule, in Poceedings of IEEE INFOCOM 25, vol. 2, U.S.A., 25, pp [15] Y. Zhang and T. Gullive, Quality of sevice fo ad hoc on-demand distance vecto outing, in Poceedings of WiMob 25, vol. 3, Aug. 25, pp