Research Article Adapted Packet Scheduling Algorithm for Robust Real-time Multimedia

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1 Research Journal of Appled Scences, Engneerng and Technology 3(3): , 206 DOI:0.9026/raset ISSN: ; e-issn: Maxwell Scentfc Publcaton Corp. Submtted: November 27, 205 Accepted: March, 206 Publshed: August 05, 206 Research Artcle Adapted Packet Schedulng Algorthm for Robust Real-tme Multmeda Huda Adbah Mohd Raml, Ahmad Fadzl Ismal, Farah Nada Mohd Isa and Asha Hassan Abdalla Hashm Department of Electrcal and Computer Engneerng, Internatonal Islamc Unverst Malaysa (IIUM), Kuala Lumpur, Malaysa Abstract: Ths study ams to provde a good real-tme multmeda performance under the presence of moble cellular channel mparments by proposng a novel packet schedulng algorthm that adapts the well-known snglecarrer Maxmum Largest Weghted Delay Frst (M-LWDF) algorthm nto the mult-carrer downlnk Long-Term Evoluton-Advanced (LTE-A). The proposed algorthm prortzes packets that requre retransmsson as compared to new packets. Packet schedulng of new packets s performed per moble cellular channel bass. Smulaton results demonstrate the effcacy of the proposed algorthm where t s capable n provdng good real-tme multmeda experence for more users and s more robust towards the mpact of moble cellular channel mparments as compared to a benchmark algorthm. Keywords: Channel qualty nformaton, hybrd automatc repeat request, long term evoluton-advanced, moble cellular channel mparments, orthogonal frequency dvson multple access, qualty of servce INTRODUCTION Long Term Evoluton-Advanced (LTE-A) s an emergng moble cellular technology standardzed by the Thrd Generaton Partnershp Proect (3GPP) organzaton n ts attempt to meet the Internatonal Moble Telecommuncatons Advanced (IMT- Advanced) requrements. The LTE-A s expected to support 00 Mbps peak data rates for hghly moble users and Gbps peak data rates for low moblty users. A hgh peak data rate n LTE-A s ratonalzed va carrer aggregaton. Carrer aggregaton s a method that aggregates two or more Component Carrers (CCs) of the same or dfferent frequency spectrums. LTE-A has a smplfed archtecture that contans only enhanced Node B (enodeb) at the Evolved Unversal Terrestral Rado Access Network (E-UTRAN). The enodeb connects users to the core network and performs all Rado Resource Management (RRM) functons. The LTE-A uses Orthogonal Frequency Dvson Multple Access (OFDMA) and Sngle-Carrer Frequency Dvson Multple Access (S-CFDMA) for downlnk and uplnk transmssons, respectvely. The S- CFDMA wll not be dscussed any further as ths study focuses on the downlnk. The mnmum transmsson unt n the downlnk LTE-A that s beng used for (re)transmsson of packets to users n each CC are known as Resource Blocks (RBs). An RB has 2 subcarrers each of 5 khz bandwdthn the frequency doman. In the tme doman, an RB extends to ms duraton. The advancement of moble cellular technologes has accelerated demand for real-tme and non real-tme multmeda applcatons. These applcatons have dverse QoS requrements where real-tme packets are more senstve to delays whereas the non real-tme packets are more senstve to packet loss. It should be noted that packets are dscarded and consdered as lost packets f the packets do not arrve at the user s end wthn the end-to-end delay threshold (Poudyal et al., 20). The LTE-A delvers real-tme and non real-tme multmeda packets usng packet-swtchng technology. As such, packet schedulng, whch s another RRM functon, s of paramount mportance n ths system. However, provdng Qualty of Servce (QoS) of multmeda applcatons comparable to fxed lne s challengng because of the nature of moble cellular channels that are subect to varous mparments ncludng mperfect Channel Qualty Informaton (CQI) report and adequate CQI reportng rate as well as expensve moble cellular channels. Packet schedulng has been an nterestng area of research and abundant research studes attempted to optmze throughput of moble cellular technologes wthout degradng the QoS of multmeda performance (Andrews et al., 200; Cheng et al., 203; Cho et al., Correspondng Author: Huda Adbah Mohd Raml, Department of Electrcal and Computer Engneerng, Internatonal Islamc Unverst Malaysa (IIUM), Kuala Lumpur, Malaysa, Tel.: , Ths work s lcensed under a Creatve Commons Attrbuton 4.0 Internatonal Lcense (URL: 25

2 204; Jalal et al., 2000; Lu et al., 200; Mao et al., 204; Mnf et al., 204; Pokharyal et al., 2007a, 2007b; Raml, 204; Raml et al., 20; Sandrasegaran et al., 200; Torabzadeh and Ab, 200; Tsybakov, 2002; Yafeng and Hongwen, 2003; Yuanye et al., 200). However maorty of these studes mostly focus on ether delay-tolerant non real-tme multmeda applcatons (Cho et al., 204; Lu et al., 200; Pokharyal et al., 2007b; Twana et al., 204; Yafeng and Hongwen, 2003; Yuanye et al., 200) or the legacy sngle-carrer moble cellular technologes (Andrews et al., 200; Jalal et al., 2000; Tsybakov, 2002) and made a common assumpton that the moble cellular channels are free from any mparments (Andrews et al., 200; Raml, 204; Raml et al., 20; Rndzevcus et al., 2008; Sandrasegaran et al., 200). Note that the legacy sngle-carrer moble cellular technology contans only one CC and transmsson of packets to a user n each schedulng nterval utlzes all of the avalable bandwdth whch s n contrast to multcarrer downlnk LTE-A where packet schedulng s performed n each CC and accounts both tme and frequency domans. Snce delay-senstve real-tme multmeda applcatons are gettng ncreasng demand among moble cellular users and a large porton of moble cellular resources has to be allocated to support realtme multmeda (re) transmsson, ths study proposes a novel packet schedulng algorthm that adapts a wellknown sngle-carrer packet schedulng algorthm nto mult-carrer downlnk LTE-A takng moble cellular channels mparments nto consderaton. It should be noted that transmtted packets may be receved n error at a user end due to varous mparments and correctly receved packets n sub-sequent ntervals cannot be delvered to applcaton layer untl the erroneously receved packets are retransmt and decode correctly at the user s end. Therefore, packets that requre retransmsson (retransmttng packets) need to be gven a hgher prorty as compared to packets of frst transmsson (new packets) to avod these packets from beng dscarded for delay volaton and hence mnmzng the Packet Loss Rato (PLR). The remander of ths study s organzed as follows: Secton materals and methods provdes a detaled descrpton of the adapted well-known snglecarrer packet schedulng algorthm as well as dscussed the envronments of smulaton. Results obtaned va smulaton are dscussed n detaled n secton results and dscusson and fnally, concluson secton concludes the paper. MATERIALS AND METHODS Res. J. Appl. Sc. Eng. Technol., 3(3): , Adapted well-known sngle-carrer packet schedulng algorthms: Ths study adapts the wellknown sngle-carrer Maxmum-Largest Weghted Delay Frst (M-LWDF) (Andrews et al., 200) algorthm nto the downlnk LTE-A. The aforementoned algorthm shows an excellent performance for provdng good real-tme multmeda experence n the legacy sngle-carrer moble cellular technologes. In each schedulng nterval, the M-LWDF selects new packets of a user accordng to () and allocates all of the avalable bandwdth for transmsson of new packets to the selected user: r µ = a * W * R a (logδ ) = T R = R ( t ) I * * r t + c tc () (2) (3) where, µ (t) s the prorty of user at schedulng nterval t, a s the QoS requrement of user, W (t) s the delay of the Head-of-Lne (HOL) packet of user at schedulng nterval t, r (t) s the nstantaneous data rate (across the whole bandwdth) of user at schedulng nterval t, R (t) s the average throughput of user at schedulng nterval t, δ s the applcaton-dependent PLR threshold of user, T s the applcaton-dependent buffer delay threshold of user, I (t) s the ndcator functon of the event that packets of user are selected for transmsson at schedulng nterval t and t c s a tme constant. Note that the HOL packet of a user s the packet that has resded the longest n ts buffer at the base staton whle the buffer delay threshold s defned as the maxmum allowable watng tme of a packet at the base staton buffer. The present state of the M-LWDF algorthm may not be suted for mplementaton n mult-carrer downlnk LTE-A because t does not account for the stuaton where multple CCs are avalable and schedulng s performed n both tme and frequency domans. Addtonally, the ndcated algorthm assumed that all transmtted packets are correctly receved at users end and hence retransmttng packets are not avalable. In our attempt to address the stated stuaton, the M-LWDF s adapted such that packet schedulng s performed n more than one CCs and accounts both tme and frequency domans. Moreover, the adapted M- LWDF consders the stuaton where the downlnk LTE-A contans both new and retransmttng packets. It should be noted that the adapted M-LWDF s developed under the constrant that retransmttng packets of a user have to use the same number of RBs and smlar Modulaton and Codng Scheme (MCS) as n the frst transmsson. MCS s determned based on the CQI reported by the user. Addtonally, t s assumed n ths

3 Res. J. Appl. Sc. Eng. Technol., 3(3): , 206 Fg. : Flowchart of the adapted-m algorthm study that a user can ether receve new packets or randomly sorted n ths algorthm as t s not necessary retransmsson packets (not both) n each schedulng to prortze a user wth good channel qualty for nterval. Detaled descrpton of ths adapted M-LWDF packets retransmsson gven that retransmttng packets algorthm, referred to as Adapted-M, s gven next. are more lkely to be correctly decoded at user s end The Adapted-M proposed n ths study s dvded compared to packets of the frst transmsson. Ths s nto fve steps (Fg. ). Step untl Step 4 of the due to the combnng gan of multple retransmssons. Adapted-M s responsble to schedule retransmttng Step 3 checks f Tot_RB req s more than the packets whereas Step 5 s only executed f there are maxmum avalable number of RBs n the lst of remanng RBs after completon of Step 4. When avalable RBs. If yes, t ndcates that RBs n the CC are compared wth new packets, the Adapted-M prortzes nsuffcent for packets retransmsson. Therefore a user retransmttng packets whch are more urgent. Ths s at the lowest prorty s excluded from packets because t s hghly lkely that retransmttng packets retransmsson and the lst of retransmttng users and wll be dscarded for delay volaton. In each schedulng Tot_RB req are updated. Step 3 repeats untl Tot_RB req <= nterval and on each CC, Step begns by determnng the maxmum avalable number of RBs n the lst of the type of each user packets that needs to be avalable RBs. Step 4 s responsble to randomly assgn (re)transmt. If a user has retransmttng packets, then the requred number of RBs and retransmt packets to Step ncludes the user nto retransmttng user lst, all users n the lst usng the same MCS as n the frst computes ts requred number of RBs (RB req ) whch s transmsson. It was shown n Raml et al. (203) that based on frst transmsson (see Step 5) and update total random assgnment of RBs for packets retransmsson number of RBs requred for retransmsson (Tot_RB req ) led to throughput mprovement. The RBs that have n the CC. Step s repeated untl all retransmttng been used for packets retransmsson are removed from users have been determned. Thereafter, all users n the the lst of avalable RBs and the buffers of all users n retransmttng user lst are sorted accordng to a random the lst of retransmttng user are updated after prorty n descendng order n Step 2. A user s completon of Step 4. 27

4 Res. J. Appl. Sc. Eng. Technol., 3(3): , 206 Table : Smulaton parameters Parameters Values Type of CA Inter-band Non-Contguous CA Number of CCs 2 Bandwdth 3 MHz each Carrer Frequences 2 GHz and 900 MHz Number of RBs 5 RBs each enb Transmt Power 43.0 dbm Rado Propagaton Path loss: Hata model for an urban envronment Shadow fadng: a Gaussan log-normal dstrbuton Mult-path fadng: Frequency-flat Raylegh fadng Channel Qualty Reportng Error-free HARQ Type Type II HARQ wth Chase Combnng HARQ Feedback Error-free wth 4 ms delay Maxmum Number of Retransmsson 3 Step 5 s executed f remanng RBs are avalable after completon of Step 4. Ths step s responsble to select new packets for transmsson where users who are not n the retransmttng user lst are consdered. At each schedulng nterval, on each CC and on each RB, Step 5 chooses new packets for transmsson to a user that maxmzes (4). Thereafter, the packets of the selected user are transmtted on the RB and the user buffer s updated. Addtonally, Step 5 updates the lst of avalable RBs. Step 5 of the Adapted-M algorthm completes after all nformaton regardng frst transmsson of the new packets are stored. Ths nformaton s needed n sub-sequent schedulng ntervals f the packets are erroneously receved and requre retransmsson. Step 5 s repeated untl the lst avalable RBs become empty: µ R,, k,, k = a * W * = CCmax r = R (4) (5) where, µ,,k (t) s the prorty of user on CC on RB k at schedulng nterval t, a s the QoS requrement of user (as defned n (2)), W (t) s the delay of the HOL packet of user at schedulng nterval t, r,,k (t) s the nstantaneous data rate of user on CC on RB k at schedulng nterval t, R, (t) s the average throughput of user on CC at schedulng nterval t, rtot, (t) s the total data rate of user on CC at schedulng nterval t, I, (t) s the ndcator functon of the event that packets of user are selected for transmsson on CC at schedulng nterval t, CC max s the maxmum avalable number of CCs and t c s a tme constant. Smulaton envronment: Ths performance evaluaton uses PLR and mean user throughput metrcs. Each metrc s descrbed as followng:, = R, ( t ) I, * * rtot, t c tc ( ), + t PLR N T = t= = N T = t= pdscard psze mean user throughput = N T = t= where, pdscard (t) s the total sze of dscarded packets (n bts) of user at tme t, psze (t) s the total sze of all packets (n bts) arrve nto the enb buffer of user at tme t, prx (t) s the total sze of correctly-receved packets (n bts) of user at tme t, N sthe total number of users and T s the total smulaton tme. The performance evaluaton was conducted wthn a mcro-cell of 250m radus. It s assumed that all users move at 60 km/h and run vdeo applcaton wth average data rates of 52 kbps. It should be noted that vdeo streamng s one of real-tme multmeda applcaton. The buffer delay threshold s set to 00 ms 3GPP acceptable threshold. The PLR threshold s capped at 0-3 threshold (3GPP, 2009). Ths PLR threshold s consdered as the maxmum threshold where the QoS requrement of the vdeo streamng s satsfed (.e., vdeo users to experence good streamng experence). Moreover, to allow a user to run 2 mn vdeo streamng sesson wthout ts buffer runnng dry (f the sze of de-tter buffer s assumed to be 0 s when a user starts ts sesson), the mnmum user throughput s assumed to be mantaned above 469 kbps. Other parameters used n ths performance evaluaton are summarzed n Table (Raml and Sandrasegaran, 203). RESULTS AND DISCUSSION The performance of the Adapted-M algorthm s evaluated and compared wth another adapted M- LWDF algorthm (Raml and Rezman, 205) (referred to as Benchmark algorthm hereafter). Ths algorthm was consdered as the well-known M-LWDF algorthm developed n Andrews et al. (200) does not account the stuaton where () multple CCs are avalable and schedulng s performed n both tme and frequency domans and () retransmttng packets are not avalable. The Benchmark algorthm contans four steps. When compared wth the Adapted-M algorthm that prortzes retransmttng users, the Benchmark algorthm gves equal opportunty to users wth new and retransmsson packets. In each schedulng nterval (6) and on each CC, Step of the Benchmark algorthm 28 N T prx (7)

5 Res. J. Appl. Sc. Eng. Technol., 3(3): , 206 Fg. 2: PLR vs. system capacty Table 2: Maxmum system capactes to satsfy good real-tme multmeda experence Packet schedulng algorthm Maxmum system capactes Percentage of mprovement n Adapted-M over Benchmark (%) Benchmark Adapted-M 36 begns by determnng the type of each user packets that needs to be (re)transmt. If a user has retransmttng packets; then, ths step computes the number of RBs requred (RBreq) by the user. The user wll only be ncluded nto actve user lst f ts RBreq s less than the lst of avalable RBs n the CC. A user wth new packets to be transmtted wll automatcally be ncluded nto actve user lst n Step. Thereafter, Step 2 selects a user (from the actve user lst) that maxmzes (8): µ avg _ r, = a * W * = CCmax avg _ r = R,, k= RBmax, = * r,, k RBmax k= (8) (9) the best channel qualty wll be selected and new packets wll be transmtted to the user on the selected RB. Subsequently, the user buffer at the enodeb s updated and the selected RB s removed from the lst of avalable RBs. Step 4 s repeated untl the user does not have any new packets n ts buffer or the lst of avalable RBs becomes empty. The nformaton regardng the frst transmsson of the packets are stored at the end of Step 4. If the lst of avalable RBs n the CC and the actve user lst are not empty after completon of Step 3 or Step 4 then Step 2 wll agan be repeated. The PLR performances of the Adapted-M and Benchmark algorthms wth ncreasng system capacty are llustrated n Fg. 2. The CQI delay s set at ms duraton n ths performance evaluaton. Wth ncreasng system capacty, more packets wll be dscarded for delay volatons as there are nsuffcent RBs avalable n each CC to schedule all the packets. Ths leads to PLR degradaton wth ncreasng system capacty. If a good real-tme multmeda experence s to be satsfed, then t can be observed n Table 2 that the Adapted-M has approxmately 63.6% system capacty mprovement over the Benchmark algorthm. Smlarly, f the mnmum mean user throughput requrement s to be satsfed at 469 kbps, then t s llustrated n Fg. 3 and Table 3 that the Adapted-M s capable to support more than 36 users as compared to the Benchmark algorthm that can only support up to 28 users. Fgure 4 and 5 show the PLR and mean user throughput performances of both algorthms wth ncreasng CQI delay. These performance evaluatons were conducted to show the robustness of the proposed algorthm n mnmzng the detrmental effect due to where, µ, (t) s the prorty of user on CC at schedulng nterval t, a s the QoS requrement of user (as defned n (2)), W (t) s the delay of the HOL packet of user at schedulng nterval t, avg_r, (t) s the average data rate of user on CC at schedulng nterval t, R, (t) s the average throughput of user on CC at schedulng nterval t, r,,k (t) s the nstantaneous data rate of user on CC on RB k at schedulng nterval t, CC max s the maxmum avalable number of CCs and RB max s the maxmum avalable number of RBs. If a user wth retransmttng packets s selected, Step 3 wll randomly assgn RB req and retransmts the packets to the user usng the same MCS as n the frst transmsson. The lst of avalable RBs n the CC and the user buffer are then updated after completon of ths step. Step 4 wll only be executed f a user wth new packets s selected n Step 2. In ths step, an RB wth moble cellular channel mparments, generally and due 29

6 Res. J. Appl. Sc. Eng. Technol., 3(3): , 206 Table 3: Maxmum system capactes to satsfy mean user throughput at 469 kbps Packet schedulng algorthm Maxmum system capactes Benchmark >36 Adapted-M 28 Table 4: Maxmum tolerable CQI delays to satsfy good real-tme multmeda experence Packet schedulng algorthm Maxmum CQI delay Percentage of mprovement n Adapted-M over Benchmark (%) Benchmark Adapted-M 26 Fg. 3: Mean user throughput vs. system capacty Fg. 4: PLR vs CQI delay Fg. 5: Mean user throughput vs. CQI delay 220

7 to outdated CQI report, specfcally. It can be observed n Fg. 4 that the PLR degrades wth ncreasng CQI delay. Ths s because the CQI that s beng used to determne the MCS for the packets before they were (re) transmtted are not up-to-date as the moble cellular channels vary rapdly due to user speed whch s at 60 km/h n ths performance evaluaton. The packets that arrve n error at the users end may need to be retransmtted. However, gven the strct delay of the real-tme multmeda, maorty of the packets are dscarded for delay volatons and some due to exceedng maxmum number of retransmssons. It s demonstrated n Table 4 that the Adapted-M algorthm s more robust as compared to the Benchmark algorthm where f a good real-tme multmeda experence s to be satsfed at 0-3, then the maxmum tolerable CQI delay n Adapted-M can be as hgh as 26 ms but lmted to 7 ms n the Benchmark algorthm. Addtonally, though a slght degradaton n terms of mean user throughput s acheved n Benchmark over the Adapted-M, the algorthm cannot provde a good real-tme multmeda experence when CQI delay s above 7 ms. The sgnfcant achevements of the Adapted-M over Benchmark algorthm can be explaned as follows. () The Adapted-M chooses packets of a user for transmsson per RB bass. After the packets have been transmtted to the selected user, ts buffer status s updated. Ths allows the algorthm to always schedule the most urgent packets on each RB. Addtonally, gven that decson s made per RB bass, ths allows the Adapted-M algorthm to explot mult-user dversty on each RB and on each CC. On the other hand, the Benchmark algorthm selects a user frst before assgnng RBs to the selected user for packets transmsson. There s hghly lkely some packets transmtted to the selected user are not urgent packets, gven that buffer status s not updated n each RB. Ths leads to these packets beng dscarded n subsequent schedulng ntervals for delay volatons and hence degradng the Benchmarks performances, () snce the Adapted-M prortzes retransmsson as compared to new packets, ths allows the algorthm to further optmze the real-tme multmeda performance as maorty of retransmttng packets have resded longer at the enodeb hghly lkely to be dscarded for delay volaton. CONCLUSION Res. J. Appl. Sc. Eng. Technol., 3(3): , 206 To mnmze detrmental effects due to moble cellular channel mparments on the QoS of real-tme multmeda applcatons, ths study proposes a novel packet schedulng algorthm called Adapted-M. Ths algorthm adapts the well-known sngle-carrer M- LWDF so as to allow the M-LWDF algorthm to perform packet schedulng n the mult-carrer downlnk LTE-A and takng the mpacts of moble cellular channel mparments nto consderaton. When compared to new packets, ths algorthm prortzes 22 packets that requre retransmsson. Smulaton results demonstrate that the Adapted-M s effcent n provdng good real-tme multmeda experence for 63.6 % more users and can tolerate up to 52.9% outdated CQI (CQI delay) over the Benchmark algorthm. Future studes wll nvestgate the mpacts of other moble cellular channel mparments on the proposed algorthm when supportng real-tme and non real-tme multmeda applcatons. ACKNOWLEDGMENT Ths research was funded by a grant (No. FRGS ) from the Kementeran Penddkan Malaysa. REFERENCES Andrews, M., K. Kumaran, K. Ramanan, A. Stolyar, P. Whtng and R. Vayakumar, 200. Provdng qualty of servce over a shared wreless lnk. IEEE Commun. Mag., 39(2): Cheng, X., G. Gupta and P. Mahopatra, 203. Jont carrer aggregaton and packet schedulng n LTEadvanced networks. Proceedng of IEEE Internatonal Conference on Sensng, Communcatons and Networkng (SECON). New Orleans, LA, pp: Cho, J., E. Seo and J. Jeong, 204. A hybrd web browser archtecture for moble devces. Adv. Electr. Comput. En., 4(3): 3-4. Jalal, A., R. Padovan and R. Panka, Data throughput of CDMA-HDR a hgh effcency-hgh data rate personal communcaton wreless system. Proceedng of the IEEE 5st Vehcular Technology Conference. Tokyo, Japan, pp: Lu, X., H. Zhu and J. Wang, 200. Adaptve resource allocaton wth packet retransmssons n OFDMA systems. Proceedng of the IEEE Internatonal Conference on Communcatons (ICC, 200). Cape Town, South Afrca, pp: -5. Mao, W., G. Mn, Y. Jang, X. Jn and H. Wang, 204. QoS-aware resource allocaton for LTE-A systems wth carrer aggregaton. Proceedng of the IEEE Wreless Communcatons and Networkng Conference (WCNC, 204). Istanbul, pp: Mnf, K., A. Masmoud and L. Kamoun, 204. Adaptve effcent downlnk packet schedulng algorthm n LTE-advanced system. Proceedng of the Internatonal Symposum on Networks, Computers and Communcatons. Hammamet, pp: -5. Pokharyal, A., G. Monghal, K.I. Pedersen, P.E. Mogensen, I.Z. Kovacs, C. Rosa and T.E. Koldng, 2007a. Frequency doman packet schedulng under fractonal load for the UTRAN LTE downlnk. Proceedng of the IEEE 65th Vehcular Technology Conference. Dubln, pp:

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