Application of the VLC Parallel Transmission Technique to Motion Vector Transmission (Special Section on Spread Spectrum Techniques and Applications)

SUMMARY Recentlyportablecomputersandmobilecom-munications have been developed rapidly. Along with the de-velopments of mobile computing environment, the demands oftransmitting images over wireless channels are growing. How-ever, high efficiency image coding techniques are not designedfor the wireless communication channels. The use of variablelengthcodes(VLCs)inthosecodingtechniquesmakesareceiverhard to synchronize with the codewords on the noisy channel.On the other hand, a variable length code transmission tech-nique utilizing multicode CDM (Code Division Multiplex) hasbeen proposed. In this paper, the multicode CDM techniqueisappliedtowirelesstransmissionofimagescompressedbytheH.263algorithm. Especially,theproposedtechniqueisemployedfor motion vector transmission. In consequence, the proposedtransmissiontechniquereducestherequired E b /N 0 ascomparedwiththeconventionaltransmissiontechnique. key words: multicode, H.263, video image, spread spectrum,variable length code 1. IntroductionInrecentyears,imagetransmissionthroughtheInter-netortelephonelineshasbecomemorepopular. Duetothewideuseofmobilephonesandportablecomput-ers,thedemandsofwirelessimagetransmissionarealsogrowing.Alongwiththesedevelopments,researchesonimagetransmissionoverwirelesschannelshavebeencarriedout[1],[2].High efficient image coding techniques such asMPEGseriesandH.serieshavebeenstandardizedin-ternationally.However,thereisnotyetaneffectivecod-ingtechniquespecializedforaspecificwirelesscommu-nicationsystem.Oneoftheproblemsislossofsynchro-nizationduetobitinversioncausedbychannelnoise.Theuseofvariablelengthcodes(VLCs)makesthere-ceiverhardtosynchronizewiththecodewordsonthenoisychannelasthelengthofthecodewordisnotfixed.IthasbeenconsideredthatCodeDivisionMul-tipleAccess(CDMA)usingSpreadSpectrummodu-lationwouldbethestandardforthenextgenerationwirelesscellularsystems. ThecapacityoftheCDMA