The Study On TA Estimation Algorithm For VAMOS

Voice service over Adaptive Multi-user Channels on One Slot (VAMOS) is introduced tosignificantly increase the network capacity of Global System for Mobile Communications (GSM).The technology reuses two or more users to one slot. So, GSM network capacity can besignificantlyincreasedforaspecifictransceiverhardwareandpossiblespectrum resources. Inorderto guarantee the performance of equalizer and the accuracyof channel estimation, the accurate startpositionoftheBurst are neededinthe receiver.Therefore,inthe receiver weneed to estimateTimeAdvance(TA),whoseveracitydirectlyrelatestotheperformanceofthewholesystem.In this paper,the TAestimation algorithms suitable for VAMOS system arestudied referring tothe existing TA estimation algorithm of GSM/EDGE.In this paper, a TA estimation method suitable for downlink of VAMOS system is proposedfirstly. In downlink, the BTS sends messages to the two paired users synchronously. So, the mobilephone only needs to demodulate the signal send to itself from the received mixed signal in thereceiver. In orderto reducethe influenceofthe Co-Channel Interference,the InterferenceRejectionCombining is introduced after the traditional TA estimation method. Then, a more accurate TAsearchmethodisintroducedtoimprovetheperformanceofchannelestimationanddemodulation.Secondly, aTAestimationmethodsuitableforuplinkofVAMOSsystemisproposed.Inuplink,thetwopaired users oftensendtheirsignals asynchronously. Inotherwords, there exists atime gapbetween their signals. In view of this situation, the paper proposes estimation of the asynchronousinformation in the base of above TA estimation method suitable for downlink. Through this way,theperformanceoftheuplinkreceivercanbeimprovedsignificantly.