Packet Level STBC Combined with Hybrid ARQ for Multicast Communications in UMTS Networks

In this paper, the combination of packet level Space-Time Block Coding (STBC) with an adaptive Hybrid Automatic Repeat reQuest (HARQ) algorithm for efficient and reliable multicast transmission in UMTS networks is proposed. The aim of this paper is to provide a cross-layer design of packet-data transmissions in Multiple-Input Multiple-Output (MIMO) systems employing orthogonal STBC over Rayleigh fading channels. This work integrates physical layer design and Radio Link Control (RLC) layer HARQ, in an attempt to enhance the system performance in terms of delay and throughput. The proposed scheme combines temporal and spatial diversity in order to provide less attenuated replicas of the transmitted signal to the receiver and thus to mitigate the destructive effects of attenuation. Further, it exploits the channel autocorrelation in order to dynamically estimate the multicast users’ channel conditions and thus reduce the mean Service Data Unit (SDU) delay and increase the average SDU throughput. As stated in the results section, the proposed scheme outperforms other stand-alone HARQ algorithms presented in the literature so far, for multicast systems in both metrics examined, i.e., mean SDU delay and average SDU throughput. Key-Words: Packet STBC, Packet FEC, Hybrid ARQ, Multicast communications, UMTS