IR-HARQ vs. Joint Channel-Network coding for Cooperative Wireless Communication

Transcription

1 Cyber Journals: ultdscplnary Journals n Scence and Technology, Journal of Selected Areas n Telecommuncatons (JSAT), August Edton, 2 IR-HARQ vs. Jont Channel-Network codng for Cooperatve Wreless Communcaton ohamed S. AbuZed, Yasmne A. Fahmy, agdy. S. El-Soudan Electroncs and Communcatons Department Faculty of Engneerng - Caro Unversty Abstract Wreless communcaton systems demand the use of many codng technques for data retransmsson between sendng and recevng end ponts to acheve the requred system capacty over varant channel condtons. Dfferent developed technques are ntroduced such as channel codng, network codng and jont codng to acheve ths target. As an mprovement for wreless communcaton systems, cooperatve wreless communcaton s llustrated to ncrease system throughput and enhance system capacty. Ths paper nvestgates dfferent data retransmsson schemes n cooperatve wreless communcaton systems scenaro. ore specfcally, two consdered technques are compared, Incremental redundancy Hybrd Automatc repeat Request (IR- HARQ) and jont Channel Network codng (-HARQ) from throughput and complexty perceptons. The system throughput s derved n both cases to compare the advantages and dsadvantages for each technque. Smulatons are conducted for dfferent number of end-pont recevers to confrm obtaned results persstence and trends. Both smulatons and theoretcal analyss confrm the advantages of the IR-HARQ over the - HARQ. Hgher throughput and better system capacty s ntroduced usng IR-HARQ when t s compared wth - HARQ, n addton to decreasng retransmsson complexty. Index Terms IR-HARQ, -HARQ, Jont Channel Network Codng, Throughput, Cooperatve Communcaton. T I. INTRODUCTION here are many dfferent schemes used for relable data retransmssons over nosy wreless channels. Tradtonally Automatc Repeat request (ARQ), where the data s retransmtted untl correctly receved and checked by Cyclc Redundancy Check (CRC) bts, s usually used. Forward Error Correcton (FEC) s another technque where a channel correctng code s used to correct erroneous data and prevent the need of retransmsson resultng n mprovng the channel throughput. Hybrd Automatc Repeat Request (HARQ) [][2] s a technque that merges the ARQ and FEC technques where user data and CRC bts are protected by an error correctng code to ncrease the probablty of successful transmsson. Another HARQ model s the ncremental redundancy HARQ (IR-HARQ) where the source data s encoded by a mother code and selected numbers of party bts are transmtted. If a retransmsson s requested, addtonal selected party bts are transmtted. At the recever, t combnes the old and new receved party bts to try recoverng the source data [2][3]. Fnally, Network Codng () [4] has been ntroduced as one of the promsng schemes used for effectve and relable data transmsson over wreless networks [4][5][6][7]. In, lost packets from dfferent recevers are combned, these packets are broadcasted at certan tme slots to dfferent recevers. At the recevng ends, each recever has the ablty to extract ts lost packets by performng modulo 2 addtons between the receved combned packets and earler successfully transmtted packets. Ths procedure s repeated tll all the recevers get all the source data packets [5]. In [6], jont channel network codng s ntroduced for sngle hop wreless network. In ths scheme, s used for combnng maxmum number of lost packets and channel codng technques are also used to protect packets aganst errors. It shows better performance when compared wth some other basc schemes lke (ARQ, HARQ, and tself) for 2 recevers. In ths paper, jont channel network codng s consdered and compared wth (IR-HARQ) for cooperatve wreless communcaton system for dfferent number of recevers. The system throughput s derved for general number of recevers under both schemes, -HARQ and IR-HARQ. The paper structure s as follows. In Secton II, the Cooperatve system model s ntroduced. In Secton III, analytcal and theoretcal dervatons are presented. In IV, smulaton results are revealed. Fnally n secton V, a concluson s ntroduced. II. COOPERATIVE ODEL Cooperatve communcaton ntroduces the broadcast advantage and space dversty for wreless transmsson. One of the most known cooperatve protocols s the Cooperatve- ARQ (C-ARQ) n [8]. There are some researches consder jont network channel codng for multuser model [9]. Hereby, the consdered cooperatve model conssts from a sngle source and cooperatng nodes. When the source transmts a packet to a certan recever Rx, all the - neghbors receve a copy. In C-ARQ, f Rx loses a packet, t requests a retransmsson from ts neghbor/cooperatve recevers. Any cooperator node that correctly receved ths packet earler can perform the retransmsson nstead of the source, so nearby recever acts as secondary source. In case 39

2 there s no node has the correct copy of the packet, Rx requests a retransmsson from the source tself [8]. In smlar manner, consder a cooperatve wreless communcaton system as shown n Fg., the source transmts data packets to dfferent recevers for the frst transmsson va wreless channels (hghlghted n sold), where there s an addtonal lnk between source and one of the recevers (R). If one or more recevers rather than R, after frst transmsson from source to all recevers, gets erroneous bts, frst t requests a packet retransmsson from R whch acts as a secondary source. Ths actually ntroduces cooperatve communcaton model. If t gets erroneous packet from the cooperatve recever R, t requests for a retransmsson from prmary source. -HARQ or IR-HARQ s used for lost packet retransmsson from secondary source to dfferent recevers. In the same context, assume the redundant lnk between source and R secondary source carres retransmssons to R usng IR-HARQ, where recevers feedback (ACK/NAK) are consdered error free. the CRC bts. In case of successve falures, the frst segment of redundancy bts s transmtted then the second, untl the last segment of redundancy bts. If the falure perssts, the transmtter repeats the process startng from the transmsson of the nformaton and CRC bts. Defne E( Y j) as the expected value of the total number of ndvdual retransmssons for CRC and party bts segments to reach j. Ths number s dvded nto E( Y j ) the expected value of the number of requred transmsson attempts of the N o bts to reach j o and E( Y j ) the expected value of the number of requred transmsson attempts to delver party bts segment number of length N to all recevers. The IR-HARQ throughput s then gven as follows: K K η IR HARQ = N L N E( Y j ) = o o Where E( Y j ) s gven as: E( Y j) E( Y j) L and E( Y j) E( Y j) L for for E( Y j) E( Y j) L L E( Y j) E( Y j) L L Fg. : Cooperatve Wreless Communcaton odel, Sngle Source and 4 Recevers III. ANALYTICAL DERIVATIONS Throughout ths paper, the throughput (or bandwdth effcency) s defned as the rato between the transmtted source nformaton bts and the total number of bts needed to correctly receve these nformaton bts. In ths secton, the throughput s derved for both cases IR-HARQ and - HARQ. Frst assume the IR-HARQ case where K nformaton bts are transmtted, N o K r s the number of the ntal K nformaton bts and r the CRC bts transmtted for the purpose of error detecton, N FEC s the number of FEC added party bts that are dvded nto L party segments. The transmsson begns wth transmttng the nformaton bts wth Next assume the jont channel network codng (-HARQ) as a retransmsson technque [6]. For the frst transmsson, packet s encoded by CRC error detectng code and then protected by FEC party check bts. At recevng ends, receved packets are decoded usng FEC decoder then pass through CRC decoder for error detecton. If data s not delvered successfully to all recevers, s ntroduced to combne maxmum possble combnatons of lost packets from dfferent recevers va modulo 2 addtons and retransmt these combned packets n certan tme slots. Hereby, combned packets are encoded wth CRC for error detecton and protected wth FEC party bts for error correcton. At recevng end, decodng operaton s appled to check whether there are lost packets or not. If there s at least one or more recever request for retransmsson, the combned packet s rebroadcasted to all recevers tll we get a successful transmsson. Table-I shows an example for -HARQ scheme wth four recevers where the lost packets are marked wth X. In case that more than one recever lost the same packet, ths packet s retransmtted ndvdually wthout combng t wth other lost packets. For example packets (2, 5) n Table-I are retransmtted ndvdually usng HARQ tll havng successful retransmsson for these packets to all recevers. After elmnatng packets that are retransmtted ndvdually, the remanng packets are combned va modulo 2 addtons, for example (4 3) as shown n Table I. t s 4

3 retransmtted n certan tme slots to all recevers. TABLE-I -HARQ LOST PACKETS EXAPLE P(Y = j) = P(Y j) P(Y j ) j j = P(Y = j) ( P ) ( P ) Then the expected number of the requred retransmsson attempts to delver source packets data successfully to dfferent recevers can be re-wrtten as: Each recever extracts ts lost packets by performng modulo 2 addtons between receved combned packets and earler successful receved packets found wthn the combnaton at the same recever. For example R extracts packet number 4 by performng modulo 2 addtons between combned packet wth earler successfully receved packets (,3) There are dfferent sets of lost packets combnatons accordng to the receved ACK/NAK feedback. 2 dfferent lost packets from 2 recevers are combned at least, and up to 4 dfferent packets combnaton from dfferent recevers. Remanng packets that don t have pars are retransmtted ndvdually to all recevers. Only one recever extracts ths packet and t s gnored by other recevers whch receved t earler n prevous transmssons. In the followng part, theoretcal dervatons are ntroduced for -HARQ throughput (bandwdth effcency). An analytcal expresson for -HARQ s obtaned as proved n [6], maxmum frame/packet error rates from dfferent recevers are consdered as a domnant rate. In the followng dervaton, frame error rates from all recevers are consdered n order to get more accurate expresson for throughput. Wthout loss of generalty, -HARQ throughput can be gven by η = K HARQ (K +r + N ) E(Y ) FEC Where E(Y ) s the expected number of the retransmsson attempts requred to delver source packets data successfully to dfferent recevers usng -HARQ. j Assume P s the packet error rate at recever R at transmsson attempt number j where j s the number of requred transmsson attempts to delver a packet successfully to all the recevers. Then we have Where E(Y = j)= j P(Y = j) j= E( Y j) ( ) ( ) j j j P, d P Pd d ( ) ( ) LL P P P P P P P j j j j j j j, d, l d l, d, l, m d l m d l d lm IV. SIULATION RESULTS In ths secton and for the purpose of smulaton we consder that same packets are transmtted to dfferent recevers n a broadcastng model. Recevers feedbacks (ACK/NAK) are consdered as error free. The transmtted packet s consdered as erroneous packet, f t ncludes at least one bt error. ATLAB s used to obtan dfferent system throughput at dfferent SNR that represents AWGN tme varant channels. Same FEC & CRC header sze are used for both -HARQ and IR-HARQ. For the consdered IR-HARQ, source data s encoded wth error detectng code (CRC) and FEC party bts are all ncluded n one segment. Frst transmsson s sent ncludng data and error detectng CRC bts. If t s receved successfully, the FEC party bts are not sent. If transmsson s not successful, FEC party bts are sent. Ths procedure s repeated tll delver all packets to all recevers. Hereby, Reed Solomon RS (27,23) s used for FEC and CRC-9 s used for error detecton. For -HARQ, Reed Solomon RS (27,23) for FEC and CRC-9 for error detecton are also used. If more than one recever lost the same packet, ths packet wll be retransmtted ndvdually wthout any combnaton to these recevers. Other lost packets from dfferent recevers are combned (usng odulo 2 addtons). At ths stage, there are dfferent numbers of packets combnatons that could be present accordng to lost packets herarchy. For example, n case of 4 recevers, up to 4 lost packets could be combned and retransmtted to dfferent recevng ends. ATLAB Smulatons are conducted for dfferent number of recevers, 2 and 4 recevers are consdered. Smulaton results reveal the obtaned throughput for varable number of recevers. Fgure 2 shows dfferent throughput for 2 and 4 recevers for IR-HARQ and -HARQ. 4

4 Throughput Throughput Throughput. IR-HARQ 4Rx IR-HARQ 2Rx -HARQ 4Rx -HARQ 2Rx Fg. 2: Throughput comparson wth dfferent number of recevers, =2, 4. -HARQ Sm. -HARQ Theor Fg. 3: -HARQ Smulaton Vs Theoretcal results, =4. IR-HARQ Sm. IR-HARQ Theor Fg. 4: IR-HARQ Smulaton Vs Theoretcal results, =4 As shown n Fg.2, IR-HARQ throughput s much better when compared wth jont channel network codng (- HARQ) for dfferent channel condtons and dfferent number of recevers. Also as number of recevers ncrease, system throughput s decreased accordngly. In order to confrm the theoretcal and the smulaton results, Fg. 3 and 4 llustrates a study for both theoretcal dervatons and smulaton results for 4 recevers for - HARQ and IR-HARQ respectvely. V. COLUSION In ths paper, IR-HARQ s proposed for cooperatve wreless communcaton system. It acheves hgher throughput and better bandwdth effcency when compared wth jont channel network codng scheme (-HARQ) for dfferent number of recevers. Both smulaton results and theoretcal proofs show IR-HARQ throughput advantages over - HARQ. In the same context, some challenges face the use of - HARQ, especally for large scale wreless communcaton systems as the complexty degree of the retransmsson schedulng ncreases. Ths accordngly extends transmsson tme and correspondng delays n packet recepton. Especally for lost packets combnng and retreval at dfferent recevers. Addng more enhancements for network codng, more complcated model should be ntroduced that mples combnng more numbers of lost packets before retransmsson. In ths case, the retreval mechansm complexty ncreases accordngly, whch mght add more delay at recevng ends to extract ts packets va odulo 2 addtons wth earler successful receved packets. REFEREES [] J. Clark Jr. and J. Can, Error-Correcton Codng for Dgtal Communcatons, New York: Plenum, 982. [2] E. Soljann, R. Lu, and P. Spasojevc, Hybrd ARQ wth random transmsson assgnments, n Proc. DIACS Workshop on Network Informaton Theory, Pscataway, NJ, ar. 23, pp [3] L. Bada,. Levorato, and. Zorz, A channel representaton method for the study of hybrd retransmsson-based error control, IEEE Trans. Commun., vol. 57, no. 7, pp , Jul. 29. [4] S Katt, D Katab, W Hu, H Rahul, and. edard, The mportance of beng opportunstc: Practcal network codng for wreless envronments, n Proc. 43rd Annual Allerton Conference on Communcaton, 25 [5] Dong Nguyen, Thnh Nguyen, and Bella Bose, Wreless broadcast usng network codng, n NetCod Workshop, Jan. 27 [6] T. Tran, T. Nguyen, and B. Bose. A jont network-channel codng technque for sngle-hop wreless networks. In Fourth Workshop on Network Codng, Theory, and Applcatons, Jan. 28. [7] Y. Wu, P. A. Chou, and S.-Y. Kung, Informaton exchange n wreless networks wth network codng and physcal-layer broadcast, n Techncal Report SR-TR-24-78, crosoft Research, Aug. 24. [8] J. orllo, J. Garca-Vdal, A Low Coordnaton Overhead C-ARQ Protocol wth Frame Combnng, 8th Annual IEEE Internatonal Symposum on Personal, Indoor and oble Rado Communcatons (IEEE PIRC 27), Athens, Greece, Sep. 27 [9] D. Duyck, D. Caprone,. oeneclaey, and J. J. Boutros, A fulldversty jont network-channel code constructon for cooperatve communcatons, n Proceedngs of the IEEE Internatonal Symposum on Personal, Indoor and oble Rado Communcatons (PIRC 9),

5 ohamed S. AbuZed receved the B.Sc. n Electroncs and Communcatons engneerng from Caro Unversty, Egypt n 26. He s currently a aster Degree student n Electroncs & Communcatons Department, Caro Unversty. Hs research nterests nclude wreless communcaton, Network Codng and jont channel network codng. (emal: moh_sayed_abuzed@yahoo.com) Yasmne A. Fahmy receved the B.Sc.,.Sc. and Ph.D. degrees n Communcaton and Electroncs engneerng from Caro Unversty, Egypt on 999, 2 and 25 respectvely. She s presently an assstant professor at the Electroncs and Communcatons Department, Faculty of Engneerng, Caro Unversty, Egypt. Her current feld of nterest ncludes wreless communcaton and channel codng technques. Snce 2, she has been wth the Center of Wreless Studes (CWS), Caro Unversty. (emal: yasfahmy@aucegypt.edu) agdy. S. El-Soudan receved the B.Sc. and.s. from Caro Unversty n 978 and 98 respectvely, and hs Doctorate d' Ingéneur from ENST, Pars, France n 983. He s a professor of communcaton at the Electroncs and Communcatons Department, Faculty of Engneerng. Caro Unversty, Egypt He s the Drector of the Natonal Telecommuncaton Insttute (NTI), nstry of Communcatons and Informaton Technology (CIT) of Egypt. Senor ember (S) of the Insttute of Electrcal and Electroncs Engneers (IEEE), Also member of the Consultaton Board for Electrcal Engneers, Egyptan Engneers Syndcate. He s co-founder of the Scentfc Socety of Telecom Engneers (SSTE) n 986, and member of the board of drectors snce that tme. SSTE s an NGO socety that cares about the Telecom sectors techncal problems and sklls of ts engneers as well the nfluence of Telecom on the socety. Hs man felds of research nclude channel codng (Error Correctng Technques), Securty systems (wth applcatons n Wreless Networks). The current research work also ncludes but not lmted to the Turbo and LDPC codes, Securty Systems (ncludng, dentfcaton schemes, ntruson detecton, Frewalls, wreless securty,..). ore than thrty papers have been publshed n specalzed techncal journals or presented at nternatonal conferences. (emal: elsoudan@yahoo.com) 43