High Utility Video Surveillance System on Public Transport using WiMAX technology

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1 Edth Cowan Unversty Research Onlne ECU Publcatons Pre Hgh Utlty Vdeo Survellance System on Publc Transport usng WMAX technology Iftekhar Ahmad Edth Cowan Unversty Daryoush Habb Edth Cowan Unversty /WCNC Ths artcle was orgnally publshed as: Ahmad, I., & Habb, D. (2010). Hgh Utlty Vdeo Survellance System on Publc Transport usng WMAX technology. Proceedngs of IEEE Wreless Communcatons and Networkng Conference. (pp. 1-5.). Sydney, Australa. IEEE. Orgnal artcle avalable here 2010 IEEE. Personal use of ths materal s permtted. Permsson from IEEE must be obtaned for all other uses, n any current or future meda, ncludng reprntng/republshng ths materal for advertsng or promotonal purposes, creatng new collectve works, for resale or redstrbuton to servers or lsts, or reuse of any copyrghted component of ths work n other works. Ths Conference Proceedng s posted at Research Onlne.

2 Hgh Utlty Vdeo Survellance System on Publc Transport usng WMAX Technology Iftekhar Ahmad and Daryoush Habb Centre for Communcatons Engneerng Research Edth Cowan Unversty, Abstract Vdeo survellance on publc transport s a useful tool to fght aganst ant-socal behavour lke vandalsm, harassment, grafft and terrorsm. Real-tme vdeo survellance on movng publc transport faces serous technologcal challenges manly due to lmted throughput offered by exstng communcaton technologes at hgh vehcular speeds. Success of real-tme vdeo survellance on publc transport heavly depends on future communcaton technologes lke WMAX. WMAX has emerged as an exctng technology wth promses to offer hgh throughput and mproved qualty of servces (QoS), key requrements for vdeo survellance on publc transport. WMAX however, offers lmted throughput at hgh vehcular speeds manly because of multpath fadng that causes hgh bt error rate at the recever at vehcular speeds. In our prevous works, we showed that t s possble to estmate the bt error rate at the recever end at varous vehcular speeds n WMAX and accordngly, some proactve measures can be adopted to mprove the throughput to some extents. Overall throughput however, may stll be nsuffcent to support the streamng vdeo data from all the cameras mounted on a publc transport at hgh vehcular speeds. In ths paper, we propose a new scheme that estmates utlty for dfferent cameras and puts some low utlty cameras offlne and thereby mantans hgh utlty of the vdeo survellance system when the throughput at hgh vehcular speeds become nsuffcent. Smulaton results confrm the effectveness of the proposed scheme. Keywords: Vdeo survellance, vehcular speeds, wreless communcaton, fadng. I. INTRODUCTION The upward trend of fuel cost and an ncrease n envronment awareness motvate more and more people to leave ther prvate transports at home and use publc transport nstead. It s hghly lkely that there wll be a sgnfcant rse n publc transport users n near future. Passengers safety and securty s an ssue of supreme nterest to all transport authortes and lve vdeo survellance on publc transport can be a powerful tool to the transport authortes to ensure passengers safety and securty. Real-tme vdeo survellance has long been used n statonary envronments lke arports, bus and tran statons wth great success to fght aganst odd events. Vdeo survellance systems on movng publc transports however, are stll non real-tme. A real-tme vdeo survellance system on movng vehcles encounters serous technologcal challenges manly due to the lmted throughput offered by the exstng communcaton technologes at hgh vehcular speeds. In a centrally montored vdeo survellance system, realtme vdeo data from multple vdeo cameras mounted on a moble transport needs to be uploaded to the base statons (BS) that are connected to a hgh speed wde area network (WAN). BSs then forward the vdeo data to a central control room where the securty experts montor and nterpret the vdeo contents. For a real-tme vdeo survellance system on a movng publc transport, wreless communcaton s the most sutable technology that has so far been dctated by the IEEE standards. Almost all moble vdeo cameras (e.g., vdeocomm RT moble systems [1]) avalable n the market place adhere to the IEEE [2-4] standards wth a promse to delver a data rate up to 64 Mbps for a near deal communcaton envronment where the nodes are fxed. Throughput starts to decrease exponentally wth the ncrease n speed and moblty of nodes [5]. Other vdeo survellance technologes reported n the lterature, are ether for statc envronment [6-8] (e.g., ntellgent analyss of CCTV coverage at tran statons/arports) or for very low moblty envronment [9] (e.g., robot vson n underground mnng). To the best our knowledge, there s no sutable technology that can be readly adopted to facltate vdeo transmssons from a vehcle movng at hgh vehcular speeds. Success of real-tme vdeo survellance system therefore largely depends on future wreless technologes lke WMAX. The IEEE , also known as WMAX [10-13], has emerged as an exctng wreless technology wth a promse to delver long range coverage, hgh moblty /10/$ IEEE

3 support, and hgher throughput. Ths holds true manly for statc envronments and performance of WMAX technology s not yet proven n scenaros where the nodes are not fxed and free move at vehcular speeds. Recent studes suggest that whle WMAX has the potental to delver a data rate up to 75 Mbps for fxed wreless communcatons, throughput fals drastcally for moble wreless communcaton, often reachng a data rate less than 1 Mbps when the moble nodes travel at about 100 km/hr. Many objects surroundng the transmtter and the recever, act as reflectors of the orgnal rado sgnal, whch create multple paths that the orgnal sgnal can traverse, causng the recever to experence the overlappng of multple copes of the transmtted sgnal, each traversng a dfferent path and havng dfferences n attenuaton, delay and phase shft. Such overlappng of sgnals causes nterference, ether amplfyng or attenuatng the sgnal power receved at the recever, known as the fadng problem. Multpath fadng s the man reason for low throughput at hgh vehcular speeds, even n WMAX, especally when the carrer frequency s n the lower range [3]. In our prevous work [15], we showed that t s possble to estmate the bt error rate at the recever end n WMAX for varous vehcular speeds of the transmtter node. Based on the estmated bt error probablty, we proposed a proactve error correcton scheme that mproves the throughput at varous vehcular speeds. The mproved throughput however, may not be suffcent to accommodate the streamng vdeo data from all the cameras mounted on a publc transport movng at hgh vehcular speeds. A crucal requrement for a vdeo survellance system s that vdeo qualty (hence data rate) must not fall below a certan lmt as the contents must be percevable to the securty experts. In the standard system, when the effectve throughput drops sharply, data rate for all the cameras drops equally and the utlty of the whole vdeo survellance system drops sgnfcantly. In ths paper, we propose a scheme that estmates the utlty of dfferent cameras mounted on a publc transport and, based on the estmated utlty, decdes whch camera(s) to put offlne so that overall utlty of the whole vdeo survellance system mproves. II. THROUGHPUT IN THE IEEE E AT HIGH VEHICULAR SPEEDS The e standard ncludes the ar nterfaces for fxed and moble broadband wreless access. The standard contans the specfcatons n relaton to the convergence sublayer (CS), medum access control (MAC) layer, and physcal layer (PHY) [10]. Snce the e s for moble wreless networks, t nherts some of the hstorcal problems evdent n moble wreless communcatons. Rado sgnal propagaton can experence fast and slow fadng. Slow fadng s normally caused by shadowng, and s consdered as a slow varaton n the mean envelop over a dstance and can be assumed to be relatvely unchanged over tme and absorbed nto the average symbol energy at the recever [11]. Fast fadng s normally caused by multpath sgnal propagatons, and vares drastcally n response to the moblty and speed of the moble statons. For fast fadng, Raylegh fadng [11][12] has proven to be an excellent model that can emulate the error n rado sgnal when there are many objects n the envronment scatterng the rado sgnal before the recever receves the sgnal. In [15], we showed a scheme to estmate the bt error probablty at varous vehcular speeds n WMAX technology. Based on the estmated bt error rate, we presented a proactve forward error correcton (FEC) mechansm that mproves throughput at varous vehcular speeds. The error correcton scheme takes the estmated bt error rate nto consderaton and computes a code sze C, strong enough to recover the lost nformaton at the receved end and thereby, savng the packet from beng declared as corrupted. Ths mproves the throughput at the cost of some extra party bts added to each packet. At hgh vehcular speeds, the code sze becomes sgnfcantly large causng effectve throughput to drop sharply. When the overall effectve throughput becomes small, the vdeo qualty of the transmtted vdeo becomes unacceptably poor and some measures need to be taken to mantan the utlty of the vdeo survellance system. In the followng, we propose a scheme that estmates the utlty of varous vdeo cameras and decdes when and whch camera(s) to put Central Control Room Fgure 1: Smulaton scenaro of a real-tme vdeo survellance system on a publc tran.

4 offlne, when the estmated effectve throughput becomes nsuffcent to support the streamng vdeo data transmsson from all cameras. III. PROPOSED SCHEME TO MAINTAIN HIGH UTILITY OF LIVE VIDEO SURVEILLANCE APPLICATION ON PUBLIC TRANSPORT As shown n Fgure 1, lve vdeo data needs to be uploaded at vehcular speeds for a real-tme vdeo survellance applcaton on publc transport. The man challenge here s to acheve suffcent throughput to support multple vdeo streamng from dfferent cameras nstalled n the tran. WMAX medum access control (MAC) has the scheduler to mantan QoS of vdeo streams as long as the throughput remans satsfactory. One of the key requrements for survellance vdeo s that the receved vdeo data rate must not fall below a certan lmt where the securty experts/ automated software can not nterpret the nformaton contents of the survellance envronment because of the poor vdeo qualty. As such, the utlty for a streamng vdeo decreases dramatcally f the transmsson rate s not mantaned above a certan lmt. In consultaton wth the commonwealth securty experts, we propose a utlty functon for CCTV camera n publc transport as: d β ( 1) D (1) U ( ) e f d d = b μ f d<b Here, U stands for the utlty of streamng vdeo from - th camera, d s the current rate of receved vdeo sent from -th camera source, b s the mnmum acceptable vdeo data rate, D s the desred transmsson rate (bandwdth demand), μ s the nsgnfcant utlty for poor qualty vdeo (μ = 0 n Fg. 2), and β s used to select the prorty of the -th camera based on ts locaton. The utlty model s depcted n Fgure 2 and t s evdent that utlty of streamng vdeo decreases wth decreasng receved data rate and the utlty becomes nsgnfcant beyond a certan transmsson rate (50% of the bandwdth demand n ths case). In cases where the average receved vdeo data rate falls below the acceptable level, we propose to stop lve feedng from one or more cameras and store the data nto the storage devce nstalled at the tran that can be uploaded once the stuaton mproves and the avalable throughput permts. A data packet of sze K has overhead n the form of a header h and RS code C at a speed v, and the overhead q per data bt can be expressed as: q= ( h+ C)/ K (2) Utlty If q per bt can be estmated at varous vehcular speeds at the moble node, ths can assst to estmate the effectve data transmsson rate W * (W * = W - qw where W s the maxmum data rate n bps supported by the system) at dfferent speeds. Based on the estmated effectve data transmsson rate, a decson can be made at the transmtter end whether the avalable bandwdth wll be able to support all the streamng vdeos at acceptable vdeo qualty. If b stands for the mnmum bandwdth demand for streamng vdeo from -th camera, then the overall mnmum bandwdth demand B mn s gven by (3) B mn = j b =1 and f W * < B mn then the moble node needs to stop lve feedng from one or more cameras untl W * B mn condton s satsfed. The overall algorthm of the proposed soluton can be summarzed as: Procedure lve_feedng_status_check (v, K) begn C r = compute_fec_code_sze (v, K) [15] q = (h+c r ) / K W * = W qw B Fgure 2: Utlty of streamng vdeo at varous receved data rate. mn = j b =1 Whle (W * < B mn ) β =1 β =3 β =5 Receved data rate : bandwdth requrement { Stop lve feedng from camera where camera

5 has the lowest utlty return U and store the data offlne. B mn = B mn - b } end lve_feedng_status_check (v, K). IV. SIMULATION RESULTS The smulaton s conducted for a centralzed real-tme vdeo survellance system n a tran (Fgure 2) usng the WMAX technology. The tran s equpped wth 3 vdeo cameras (one at front, one at rear and one at the mddle); each of them sendng vdeo data at a rate of 512 Kbps to the base statons. The maxmum data rate capacty of the wreless channel s 2 Mbps and carrer frequency s 2.6 GHz, number of sub-carrers s 2048 and the modulaton style s QPSK. For the smulaton scenaro, the tran moves from a stop and gradually ncreases ts speed, reachng a speed of 40 km/hr at 20 sec and a top speed of 70km/hr at around 60 sec tme. The tran contnues to cruse at that speed for sometme before the tran starts to slow down at 110 sec. The tran contnues to slow down and fnally stops at the next staton at 180sec. The whole scenaro was smulated n Network Smulator 2 (NS-2) [14], a wdely used smulator for networkng research. We montored the overall throughput and actual vdeo data receved by the base staton whle the tran was movng. The overall throughput contans bts representng headers and protocols related packets whle the vdeo data s the actual nformaton contents transferred across the wreless channel. Fgure 3 shows the receved throughput at varous vehcular speeds. Whle packets wth larger data sze (256 bytes) offer lower overheads and hence carres extra data bts at low vehcular speeds, packet corrupton rate ncreases sharply at hgh vehcular speeds for larger packets because the probablty of contanng corrupted bt(s) s hgher n a large packet compared to a small packet. Smaller data packets perform effcently compared to larger packets at hgh vehcular speeds. However, extra overheads lmt the performance of smaller packets at low vehcular speeds. Fgure 4 shows the comparson of receved vdeo data rate at the recever end n standard (.e., wthout bt error estmaton and FEC) and our prevously proposed proactve FEC (PFEC) scheme. It s evdent that PFEC scheme acheves mproved effectve throughput compared to the standard scheme at varous vehcular speeds. At hgh vehcular speeds however, the effectve throughput becomes nsuffcent to support the Receved bts/sec Receved Vdeo Data bts/sec Avg. Utlty/camera Standard 256 Bytes Standard 64 Bytes Speed (km/hr) Fgure 3: Throughput at varous vehcular speeds Fgure 4: Receved vdeo data at dfferent smulaton tme on a publc tran. Proposed Soluton PFEC Standard 256 bytes Tme(sec) Standard Scheme Speed (km/hr) Fgure 5: Average utlty per camera n the proposed and standard schemes.

6 streamng vdeo data from all cameras, and ths s when our proposed scheme n ths paper comes nto rescue. We montored the average utlty per camera of the vdeo survellance system n a publc tran. The utlty for vdeo transmsson rate below half of the bandwdth demand s consdered to be nsgnfcant (0.05 n ths case). The proposed lve_feedng_status_check algorthm estmates the effectve transmsson rate at the transmtter end at varous vehcular speeds and makes a decson whether to put one or multple camera(s) offlne. Utlty for each offlne camera s assumed to be 0.2 and all cameras are assumed to have the same prorty (β=1). The result as reported n Fgure 5, s the actual utlty (.e., measured aganst actual receved data rate) measured at the recever end. As evdent n the Fgure, whle the proposed soluton yelds better utlty compared to standard approach, the dfference s not sgnfcant n terms of average utlty per camera at low vehcular speeds (<30 km/hr). However, when the speed ncreases, the proposed soluton acheves sgnfcantly hgher utlty gan compared to standard approach. Ths s because the lve_feedng_status_check algorthm asssts the WMAX MAC to make a decson whether to put camera(s) offlne based on the estmated vdeo transmsson rate and utlty from varous camera sourcers. V. CONCLUSION Although WMAX s a promsng technology for fxed wreless MAN, t s performance s stll not good enough for hgh bandwdth demandng applcatons lke vdeo survellance system when the node moves at vehcular speeds. Mutpath fadng at hgh speed that causes hgh bt error rate at the recever end s a major reason for low throughput at hgh speed, especally for low frequency carrer. In our prevous work, we showed that proactve measures can be adopted once the bt error rate at varous vehcular speeds can be estmated. Proactve measures may stll prove nsuffcent at hgh vehcular speeds to accommodate the bandwdth demand for the streamng vdeo data from all the cameras mounted on a publc transport. In ths paper, we propose a model that estmates the utlty for varous cameras and puts low utlty camera(s) offlne, f requred, so that the overall utlty of the vdeo survellance system remans satsfactory. Smulaton results confrm that our proposed scheme comfortably acheves better utlty compared to standard schemes. VI. REFERENCE [1] IEEE Standard Department, Wreless LAN Medum Access Control (MAC) and Physcal Layer (PHY) Specfcatons, IEEE standard , [2] C. Eklund, R. B. Marks, K. L. Stanwood and S. Wang, IEEE Standard : a techncal overvew of the WrelessMAN ar nterface for broadband wreless access, IEEE Communcatons Magazne, pp , June [3] IEEE e Task Group (Moble WrelessMAN ), 16/tge/, last accessed Aprl [4] IEEE P802.16e/D4, Draft IEEE standard for local and metropoltan area networks part 16: ar nterface for fxed and moble broadband wreless access systems, August, [5] X. L, P. Y. Kong, and K. C. Chua, Performance n IEEE based ad-hoc networks wth multple wreless lossy lnks, IEEE Transactons on Moble Computng, Vol. 6, No. 12, pp , [6] J. P. Makela, T. Brasy, and K. Pahlavan, Analyss of moblty n adaptve data rate wreless communcatons, Proc. IEEE Mltary Communcaton Conference, MILCOM 2006, pp. 1-6, [7] S. Aramvth, C.W. Ln, S. Roy, and M.T. Sun, Wreless vdeo transport usng condtonal retransmsson and low-delay nterleavng, IEEE Trans. Crcuts Syst. Vdeo Technol., vol. 12, pp , June [8] C. M. Chen, C. W. Ln, H. C. We and Y. C. Chen, Robust vdeo stramng over wreless LANs usng multple descrpton transcodng and protxed retransmsson, Journal of Vsual Communcaton and Image Presentaton, pp , [9] C. X. Wang, and W. Xu, Packet-level error models for dgtal wreless channels, IEEE Internatonal Conference on Communcatons, ICC 2005, pp , [10] T. Kwon; H. Lee; S. Cho; J. Km, D. Cho, S. Cho, S. Yun, W. Park, K. Km, Desgn and mplementaton of a smulator based on a cross-layer protocol between MAC and PHY layers n a WBro Compatble IEEE e OFDMA system, IEEE Communcatons Magazne, vol 43, no 12, pg , [11] G. L. Stuber, Prncples of Moble Communcaton, 2nd Edton, Boston, MA, Kluwer Acdemc Publsher, [12] W. C. Jakes, Mcrowave Moble Communcatons, Pscataway, NJ, IEEE Press, [13] H. Lee T. Kwon D. Cho, Extended-rtPS Algorthm for VoIP Servces n IEEE systems, IEEE Internatonal Conference on Communcatons (ICC), pp , [14] Network Smulator 2, last accessed November, [15] I. Ahmad and D. Habb, A Proactve Forward Error Control Scheme for Moble WMAX Communcaton, Proc. 9th IEEE Internatonal Conference on Communcaton Systems (ICCS), pp , 2008.