A new performance bound for non-orthogonal space-time spreading CDMA systems over MIMO Rayleigh fading channels

Verdu¿ introduced the notion of indecomposable error vectors (IEVs) and showed that the union bound including IEVs only gives a quite tight bit error rate (BER) upper bound for multiuser detection over an AWGN channel. There have been some efforts to strengthen the notion of IEVs to make them applicable to fading channels, but those efforts only led to bounds still loose at low signal-to-noise power ratios (SNRs). In this paper, we propose a new union bound based on the notion of IEVs and apply it to a space-time spreading (STS) code-division multiple access (CDMA) system over an MIMO Rayleigh fading channel. We calculate a BER upper bound for the ML receiver in a downlink space-time CDMA system and show that the upper bound is tighter than the previously known union bound based on the conventional strengthening of the IEV property and than the well-known limit-before-averaging (LBA) bound more than one transmit antennas.