Luby Transform Coding Aided Iterative Detection for Downlink SDMA Systems

A Luby Transform (LT) coded downlink Spatial Division Multiple Access (SDMA) system using iterative detection is proposed, which invokes a low-complexity near-Maximum-Likelihood (ML) Sphere Decoder (SD). The Ethernet-based Internet section of the transmission chain inflicts random packet erasures, which is modelled by the Binary Erasure Channel (BE), while the wireless downlink imposes both fading and noise. A novel Log-Likelihood Ratio based packet reliability meric is used for identifying the channel-decoded packets, which are likely to be error-infested. Packets having residual errors must not be passed on to the LT decoder for the sake of avoiding LT-decoding-induced error propagation. The proposed scheme is capable of maintaining an infinitesimally low packet error ratio in the downlink of the wireless Internet for Eb/N0 values in excess of about 3dB.