TFRC-CR: An Equation-based Transport Protocol for Cognitive Radio Networks

Transcription

1 213 International onference on omputing, Networking and ommunication (IN) Workhop on omputing, Networking and ommunication -R: An Equation-baed Tranport Protocol for ognitive Radio Network Abdulla K. Al-Ali and Kauhik howdhury Department of Electrical and omputer Engineering Northeatern Univerity oton, MA {al-ali.a, Abtract Data delivery in a dynamically changing pectrum environment continue to remain an unolved problem, with exiting TP baed implementation falling hort owing to their inability to react wiftly to pectrum change. Thi paper propoe the firt equation-baed tranport protocol, baed on the TP Friendly Rate ontrol () protocol, which ue the recent F mandated pectrum databae information intead of relying on any intermediate node feedback. Not only doe thi approach maintain the trict end to end property required at thi layer of the protocol tack, but alo allow fine adjutment of the tranmiion rate through continuou adaptation. We explore intereting direction on how to limit repeated querie to the pectrum databae and yet allow the ource to control the rate effectively; when to re-tart the tranmiion; and how to interpret poible pectrum change in the intermediate node correctly without mitaking it for normal network congetion, among other. Our extenion to the n-2 imulator enable thorough teting of variou apect of our protocol adapted for cognitive radio, called a -R. We how through imulation an improvement of over 33% in the end to end throughput when compared with the claical. I. INTRODUTION ognitive radio (R) network enable opportunitic ue of available licened pectrum, and reduce the preure on the unlicened ISM band in the 2.4GHzand 5GHzrange. While the core function of pectrum ening, witching, and haring are now being better undertood given the rapid tride in thi area, work on higher layer of the protocol tack, uch a the tranport layer, i till in a nacent tage. There ha been extenive invetigation of window-baed TP protocol for auring congetion-free behavior in claical wirele network, given it widepread ue in the wired domain. y minor modification of the information contained in the feedback acknowledgment (AK) ent by the detination, uch a by falely advertiing a receive window of in Freeze TP [6] when an impending handoff i detected, the TP ource can be prevented from tranmitting. The ingle end-to-end connection can be plit into the wired (ender to bae tation or S, when uch an infratructure upport exit) and wirele (S to the wirele node) plane, a hown in WTP [7]. In Addition, ome protocol explore tuning the ender tranmiion rate through explicit notification (TP EFLN) [8] and via elective retranmiion of lot packet (TP SAK) [9]. While each of thee approache have merit, they were not originally deigned with the aim of licened or primary uer (PU) protection, udden large-cale bandwidth fluctuation, and periodic interruption caued by pectrum ening and channel witching. A recent approach called TP-RAHN addreed thee concern [1], though it relied on extenive feedback from the underlying layer of the protocol tack a well a the intermediate node that form the connected chain. Thi i undeirable a it violate the end-toend paradigm typically aumed for tranport layer protocol. Thi paper i aimed to open up freh dicuion on the deign of R-pecific protocol uing an equation-baed approach, wherein the concept of the congetion window in claical TP (and the elf-clocking via returning AK) i no longer followed. A notable example in thi area for wirele ad hoc network i ATP [4], which argue that the hort term unfairne of the SMA/A MA reult in an undeirable burty data flow. Thi problem i exacerbated in R network becaue node paue the tranmiion when they are engaged in ening or channel witching. Thi, in turn, reult in varying round-trip time etimate (in the cae of TP) and higher induced load rendering the elf-clocking nature ineffective. The frequency and reliance on the AK for window baed tranmiion alo lead to revere path performance impact on the forward DATA path. In TP, thi can amount to 1%-2% of the data tream rate [4]. The burty nature of TP i clearly demonetrated in Figure 1. In thi paper, we devie the firt equation baed tranport protocol uing exiting approach called a TP Friendly Rate ontrol () [2]. We name our modified deign a - R, whoe main feature are a follow: It allow the TP ource to integrate with a deignated pectrum databae, a mandated by the F in a recent ruling [5]. There i no feedback from any of the intermediate node, and neither i any information from an underlying layer i utilized. It enhance the peed of repone by ditinguihing between the effect of pectrum change and true congetion, by leveraging both the information from the pectrum databae and the periodic information ent by the detination through the uual AK. Hence, the tranmiion rate i almot never penalized unle the need i jutified and likewie, the coare jump in the rate can be much fater than that poible in traditional tranport protocol /13/$ IEEE 143

2 TALE I: Symbol ued by -R framework Symbol RT T avg RT T tddev I n I PU t t n t PU Decription Packet ize Average round-trip-time Round trip time tandard deviation Average AK inter-arrival during no PU activity Average AK inter-arrival during PU activity Time now Time lat AK received during no PU activity Time lat AK received during lat PU activity It intelligently poll the pectrum databae only when needed, by identifying a poible PU arrival event, i.e., it doe not conume the backend ytem reource ued for interacting with the databae. The databae may likely be a ingle point of failure and hence, it need to be protected from being overwhelmed in a practical ituation. The current regulation require databae polling at leat in 6 econd-interval, and our aim i to exceed that default value only when a critical need i detected. The ret of thi paper i organized a follow: The preliminary background of and the motivation for adapting it for R i decribed in Section II. In Section III, we decribe the propoed protocol -R in detail. Section IV give reult from our comprehenive imulation tudy, and finally, we conclude our paper in Section V with pointer to future reearch. Throughput (kbp) v TP throughput 18 TP Throughput 16 Throughput time (econd) Fig. 1: Throughput comparion between TP and in a 3-hop chain ad-hoc network II. AKGROUND AND MOTIVATION i a rate baed mechanim for congetion control in unicat traffic. We ue thi a the platform to build our protocol becaue it aim at providing a table throughput, a oppoed to the udden fluctuation caued by Additive Increae Multiplicative Decreae (AIMD) in TP, while maintaining a TP friendly rate. Given that i alo an end-toend protocol, deployment i only neceary at the ource and detination. To achieve reduced fluctuation, it calculate a parameter called the lo event rate (p) at the receiver by taking the reciprocal of the average weight in the lat (n) lo event ample where a ample i defined a the number of conecutive data packet received within a RTT before a packet lo happen., by default, average the lat 8 ample (n =8) which give an approximate naphot of how the traffic flow looked in the lat n RTT. p i then ent to the ender to be ued in the throughput equation that etimate TP average ending rate: X bp = 2 b p 3 b p R 3 +(t RT O (3 8 p ( p 2 )), (1) where X bp i TP average tranmit rate in byte per econd, i the packet ize in byte, R i the round-trip time in econd, p i the lo event rate between and 1., t RT O i TP retranmiion timeout value in econd, and b i the maximum number of packet acknowledged by a ingle TP AK. The goal of thi i to achieve a moother rate by avoiding udden abrupt rate fluctuation a i the cae in TP. uffer when deployed in ognitive Radio owing to the following reaon: (i) Low rate after PU exit: i not able to ue the maximum allocated bandwidth after a PU exit, due to weighing the lat lo rate which are recorded falely during PU activity, ii) Slow recovery: Afterthe PU exit, having mitaken the original interruption purely a a congetion event, tart polling the bandwidth connection over large interval of time, which can lead to ignificant delay in reuming the tranmiion, and iii) uffer overload and interference: initially end multiple packet during the PU activity a part of it regular rate control, cauing additional interference with the PU. Thee individual iue are decribed in further detail in the ret of thi ection. Low rate after PU exit: After a prolonged idle tate due to PU activity, the lat n lo event rate hould be neglected becaue they occurred in that tagnant tate. Thi caue to reume the throughput at a fale lo event rate p leading to le than optimal throughput. will recover after at leat n event lo rate have been recorded. Thi can take up to n Round-Trip-Time (RTT). Slow recovery: During PU Activity, nofeedback timer expire everal time which lead to reduction in the effective rate by half each time until the minimum rate of t mbi where i the packet ize and t mbi i et to 64 econd i reached. Thi mean that will poll the network once every 64 econd which can caue a delay of up to 64 econd for the network to reume activity after a PU exit. uffer overload and interference: During the PU activity, will initially continue the ongoing rate becaue it i unaware of the PU activity. Thi will lead to undeired packet being ent over the network leading to a bigger buffer queue at the MA layer of the node immediately before the affected area. Thee packet will retranmit until they timeout which caue additional undeired interference with the PU. 144

3 Normal AK Timeout Slow tart AK received Received a packet ondition not met PU Detected PU Exit ondition met No AK Received In average AK inter arrival PU Exit Reume Slow Start AK Received PU Exit & No AK Paued No AK Fig. 2: -R finite tate machine. PU detected tate Thi i an intermediate tate implemented a an additional meaure to verify that the lat AK timeout in the Normal tate wa in fact due to PU activity. On entering thi tate, the ource wait for a period I n for any incoming AK and continuouly poll the pectrum databae. If no ubequent AK are received, and the databae reveal that the PU i till preent, then the protocol tranition into the Paued tate. On the other hand, if an AK doe arrive in that time period, then the protocol return to the Normal tate a thi implie that the intermediate node are not affected by the PU activity. In uch a cae, the AK timer expiry wa due to random channel or congetion error. III. -R: AN EQUATION ASED TRANSPORT PROTOOL In thi ection, we decribe our propoed -R protocol and the modification done to claical. Our change in the protocol operation are aimed at (i) enuring that the connection reume the data tream immediately after the PU leave the affected traffic zone, (ii) triking a balance between polling the network too frequently by the ource that may caue interference with the PU, and converely, reacting too lowly to pectrum change, and (iii) finding the available bandwidth a oon a poible, after the PU vacate the pectrum. We preent an overview of our approach uing a finite tate machine diagram, a hown in Figure 2. The remainder of thi paper refer to the ymbol lited in Table I. A. Normal tate Thi i the default tate of -R, and the protocol return to thi tate whenever there i no expected pectrum outage. The repone during true congetion event and the reulting change i the tranmiion rate i identical to that of the claical. The protocol operation diverge, however, when a timeout event occur and no AK i received. To differentiate congetion from poible PU activity, the - R at the ource querie the F mandated pectrum databae to check if a PU uddenly appeared on any of the feaible channel. Note that the ource ha no knowledge of the location or the pecific channel ued by the node in the end to end connection. However, a udden arrival event of the PU (a indicated by the databae) and the timeout can be treated a correlated event, with a high probability. If thi condition i true, the protocol enter into the PU detected tate, and if not, the ituation i interpreted a a normal cae of network congetion. Additionally, the protocol continue to maintain an average AK inter-arrival time (denoted a I n ), and the tandard deviation of the round-trip time (denoted a RT T tddev ). Thee value are ued in the ubequent tate to influence the rate control mechanim.. Paued tate In thi tate, the PU i determined to be preent, and i aumed to be reponible for dirupting the continuou data tream a it ha occupied the pectrum. The challenge now i to identify when the tranmiion rate can revert back to a higher value, and thi i obtained by polling the connection bandwidth with an occaional packet. When a portion of the pectrum i occupied by a PU, the link layer algorithm on the node pair on the affected link may either paue the tranmiion altogether, or immediately try and identify an alternate pectrum for that link. Note that the ource ha no idea of which of thee option are actually elected, a no intermediate node feedback i allowed. Thu, by increaing the tranmiion rate too early, the ource rik added interference to the PU before it vacate the pectrum. Alo, by delaying the rate increae after a pectrum change, the ource i unable to efficiently ue the available bandwidth of the connection. y imply monitoring the pectrum databae (which can continue to how the PU a preent), the ource remain unaware of a local pectrum change. We have undertaken a ubtantial et of imulation and empirically identify the optimal polling rate a X bp = 6 RT T avg (Section II), i.e., the ource will poll the connection every 6 average RTT time whether or not the node have witched the channel. In comparion, reduce the rate after each AK timer expiry in half, until it reache a rate of 64, which end out a packet every 64 econd. Thi lead to low reaction to both the udden reduction in bandwidth when the PU tart affecting the traffic chain, and to the higher available bandwidth once the PU i out of the vicinity. If an AK i received in the Paued tate, the network retore the rate to the lat rate recorded in the Normal tate and enter the Reumed tate. -R perceive thi packet a an indication that the intermediate node have moved to a vacant pectrum and allow the rate to adapt accordingly. If no feedback packet are received during thi period, indicating that the node have not witched the pectrum, -R will enter the Slow tart tate immediately after the PU leave the pectrum. The PU exit time i known by the aforementioned pectrum databae. 145

4 D. Reumed tate -R enter thi tate when an AK i received while being in the Paued tate. The protocol interpret thi AK arrival a an indication that the intermediate node have witched to a vacant channel and allow for the rate to adapt accordingly by retoring it to the lat known rate in the Normal tate. The protocol tay in thi tate until the PU exit, at which time it enter the PU Exit tate. Notice that -R i not returning to the Normal tate yet becaue the AK that wa received in the Paued tate could be due to an intermediate node falely mi-detecting the PU preence. If the the node never mi-detect the PU preence, then the protocol will never enter thi tate becaue it will remain in the Paued tate. The protocol enter the PU Exit tate when the current active PU exit the vicinity. Thi time i cheduled baed on the query reult from the integrated F databae which i known at the ender. The average AK inter-arrival time I PU i calculated during thi time period for ue in the next tate. E. PU Exit tate In the PU Exit tate, the goal i to determine whether a low-tart i required or not. -R low-tart if the rate at the time of the PU exit i relatively low in comparion to the rate recorded during the lat Normal tate. In other word, the AK received during the Paued tate wa a reult of a ening error and a low-tart to probe for new bandwidth i required. Otherwie, the protocol quietly return to the Normal tate becaue the intermediate node have found a vacant pectrum and reumed tranmiion. The deciion whether to low-tart i made baed on the reult obtained in Algorithm 1. Algorithm 1 : i low tart required let I n be the average inter-arrival of AK at the ender in the Normal tate. let I PU be the the average inter-arrival of AKS at the ender during the Paued tate. let t be the time now. let t PU time lat AK received during Paued tate. 1: if I PU > (2 I n ) OR t t PU > (3 I n ) then 2: return true 3: ele 4: return fale 5: end if In ummary, Algorithm 1 check if one of the following i true, baed on empirical obervation: ae I: If the average inter-arrival of AK during the Paued tate i larger than twice the average inter-arrival of AK during Normal tate. ae II: If the time elaped ince the lat AK received during an ongoing PU activity i larger than 3 time the average inter-arrival of AK during Normal tate. F. Slow tart tate -R enter Slow-tart if the rate during Reumed tate wa low according to Algorithm 1 or if the previou tate wa the Paued tate, i.e., no AK were received in Paued tate. Slow-tart i ued to quickly probe the new vacant pectrum for the maximum available bandwidth. -R low-tart by reetting the weight and variable of. Thi i done by having the ource flag the next packet a a low-tart requet packet (SSREQ). When the detination receive thi packet, it reet it own lo rate p calculation (ee Section II) and end back a low-tart acknowledgement packet (SSAK) immediately. During low tart, the nofeedback timer i et to RT T avg +4 RT T tddev. We ue thi a a more accurate reult than default tatic 2 packetize 3. Once the SSAK packet i received at the ource, -R return back to the Normal tate, thu completing the cycle. IV. PERFORMANE EVALUATION We imulate -R over a multihop chain in n2 a depicted in Figure 5. In our imulation, we ue the ognitive Radio Ad-Hoc Network (RAHN) framework built by [3] and place four node in a traight line. In thi framework, the node do not end TS to RTS requet if they ene any PU activity. Thi lead to packet being queued at the node immediately before the PU region and eventually dropped due to retrie or timeout. We et our ening period to.1 econd and tranmiion period to 3. econd [1]. The bandwidth of the channel at each hop i et to 2 Mbp. The node in thi imulation do not witch to another pectrum when PU i detected; they wait until the PU exit the pectrum to tart tranmitting again. All enor node pick from 1 available pectrum band at random at the beginning of the imulation. Each node will have two different interface: one for receiving packet and one for ending. We vary the type of PU activity from an exponentially ditributed on and off time with mean (2 ec) and (1 ec) repectively, which we name hort burt. Similarly, a PU on time of 1 ec i deigned to imulate long PU activity event PU Region Fig. 5: 3-Hop chain and PU region The imulation compare with -R regarding the following metric: (i) throughput over time, (ii) interference percentage with the PU, (iii) total data received by the receiver over the ame period of time, (iv) the goodput of the data tream, and (v) the queue length of the affected node. A. Throughput over time Figure 3 and 4 compare with -R in term of throughput at the receiver for long and hort activity duration of the PU, repectively. The imulation wa run for for

5 kbp A v R Throughput R time (econd) Fig. 3: Throughput (kbp) v Time for 3-hop (long PU activity) kbp A v R Throughput R time (econd) Fig. 4: Throughput (kbp) v Time for 3-hop (hort burt) Interference % (Tx during PU/Total PU activity) Interference with the PU Long PU activity -R Short PU burt M Total tranferred data Long PU activity -R Short PU burt Goodput % Goodput comparion Long PU activity -R Short PU burt (a) (b) (c) Fig. 6: The interference, total data tranmitted and goodput comparion are provided in (a), (b) and (c), repectively. econd, and the region of interet are denoted with letter A, and. The area in gray repreent the PU active region. 1) Region A: In thi region, -R i in the Normal tate. We can oberve that the protocol throughput matche that of. Intereting to note that in Figure 4, although the PU wa affecting the traffic tream, -R could not detect it becaue it did not encounter a nofeedback timer expiry during thee hort PU activity period. 2) Region : Area indicated by indicate that -R goe into low-tart immediately after the PU exit the vicinity. We notice here that i unaware of PU activity, and due to the reduction in rate during the PU activity period, the data flow reume later. The longer the PU activity, the lower the rate, and hence, the later the protocol reume. Thi i clearly indicated by Figure 3. 3) Region : In thi area, the PU i active but we notice the pike in throughput during thi period. The pike occur more frequently at the beginning of the PU activity region due to the long time it take to reduce the rate (i.e. with every AK timer expiry, it reduce the rate by half). Thi low reaction to the link diconnection caued by the PU caue undeirable interference. In thee area, -R reduce the rate to 6 RT T avg until an AK i received. Thi lead to le interference a will be hown in the next ection. 147

6 . Interference with the PU The immediate reduction in rate when -R encounter the firt AK timer expiry lead to le interference with the PU. For example, with I n of 1.2 ec, a rate of 3 bp in the Normal tate, and a nofeedback timer et at 2 econd, -R will reduce the rate to bp in 2 ec. In comparion, the ame rate will be reached by after 5.8 econd leading to an exce of retranmiion attempt during that time period. We calculate the interference to be the total time it take to tranmit RTS, TS, AK and DATA packet divided by the total PU on period. 6a how the lower interference of -R in both the hort burt and the long PU activity imulation run.. Total data received Due to the fact that fail to reume the data tream immediately after a PU exit or to ue low-tart to probe for the new network bandwidth, -R i able to tranmit more data in the 3 econd of the imulation with both type of PU activity. Thi can be een in Figure 6b. In the hort burt cenario, the amount of increae i 33%. D. Goodput total data packet received We calculate the goodput a total data packet ent.we can infer from Figure 6c that and -R have very imilar goodput, however, -R ha lightly higher percentage due to it being able to low down fater during the Paued tate (read: when PU i active), and by doing that, it avoid the exce wated packet that occur in. E. Queue length When the affected node detect PU activity, they halt any tranmiion that i cheduled at the MA layer. Thi caue the queue to build up on the node immediately before the PU active region or node 3 in our topology. Figure 7a how the queue length at that node. We note that there in no exceive build up on the queue and the increae in queue length are proportional to the ending rate at that time a hown in Figure 7b. When the PU enter the vicinity at time 6ec, -R queue length are at mot 1 packet higher than even though the throughput i double that of. V. ONLUSION We preented an equation-driven TP protocol that i geared to meet the demand of R network, which alo accommodate ome of the latet development in thi pace, uch a pectrum databae acce. Our olution -R i demontrated to perform ignificantly better than it claical counter, with repect to both PU protection and tranmiion efficiency in a dynamically changing pectrum environment. Different from the few exiting work at the tranport layer for R, our protocol doe not aume any cro-layer feedback or other input from intermediate node. Our future work i aimed at changing the baic rate control equation baed on different pectrum-related event. Queue length Throughput (kbp) v -R Queue Length 9 Queue length 8 -R Queue length time (econd) (a) v -R throughput time (econd) (b) Throughput -R Throughput Fig. 7: (a) Queue length of and -R at node 3 and (b) the correponding throughput of the network VI. AKNOWLEDGMENT The leading author would like to thank Qatar Univerity for the PhD cholarhip upport. REFERENES [1] K. R. howdhury, M. Di Felice and I. F. Akyildiz. TP-RAHN: a tranport protocol for cognitive radio ad-hoc network. In INFOOM 29, IEEE, page , April 29. [2] S. Floyd, M. Handley, J. Padhye, and J. Widmer, Equation-baed congetion control for unicat application, In Proc. of AM SIGOMM, Aug. 2. [3] Marco Di Felice, Kauhik Roy howdhury, and Luciano ononi, Modeling and performance evaluation of tranmiion control protocol over cognitive radio ad hoc network, in Proc. of AM MSWiM, 29. [4] Karthikeyan Sundarean, Vaidyanathan Anantharaman, Hung-Yun Hieh, and Raghupathy Sivakumar, ATP: A reliable tranport protocol for ad hoc network, in IEEE Tran. Mob. omput., 4(6):58863, 25. [5] F, Second Memorandum Opinion and Order, ET Docket No , September 21. [6] T. Goff et al., Freeze-TP: A True End-to-End TP Enhancement, in Proc. IEEE INFOOM, 2. [7] P. Sinha, T. Nandagopal, N. Venkitaraman, R. Sivakumar, and V. harghavan. WTP: A reliable tranport protocol for wirele wide-area network, in Wirele Network, 8(2-3):31-316, 22 [8] G. Holland and N. H. Vaidya, Analyi of TP Performance over Mobile Ad Hoc Network. in Proc. of AM MOIOM, pp , Seattle, WA, Aug [9] M. Mathi, J. Mahdavi, S. Floyd and A. Romanow, TP elective acknowledgment option, RF 218 (October 1996). [1] W. Y. Lee and I. F. Akyildiz, Optimal Spectrum Sening Framework for ognitive Radio Network, IEEE Tran. on Wirele omm., vol. 7, no. 1, Oct