In this paper, convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) employing the zero-correlation-zone (ZCZ) code generated from the Chu sequence is proposed as a novel multi-access scheme for fast fading multipath channels. Analysis results demonstrate that the system remains approximately multiuser interference (MUI)-free even when the system is heavily loaded and subject to severe Doppler spreads. An effective channel estimation method based on B-spline approximation is also proposed. Simulation results show, in combination with the Probabilistic Data Association (PDA) equalization, the system significantly outperforms the DS-CDMA system employing Linear Minimum Mean Squared Error (LMMSE) chip-wise equalization and polynomial interpolation-based channel estimation from medium to high user population.

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) enables multiuser interference-free (MUI-free) transmission over multipath downlink channels with the use of zero correlation zone (ZCZ) codes. However, MUI-free transmission is guaranteed only when the data length D, channel delay L, and ZCZ length Z satisfy Z+1 ≥ D + L. In this paper, we consider the situation that MUI-free transmission is not realized inevitably because of excessive multipath delays or deliberately because of the necessity to get a higher bandwidth efficiency, clarify the structure of MUI in the CS-CDMA/CP system employing M-ZCZ codes, and propose iterative partial multiuser detection (IPMUD). The detection is implemented at symbol-level (after despreading) and the number of users jointly considered can be adjusted flexibly to offer a tradeoff between system performance and receiver complexity. The performance of the proposed scheme is verified numerically by density evolution approach and BER simulations. The CS-CDMA/CP system with IPMUD is shown to be much less complex than the DS-CDMA system with Wang and Poor's turbo MUD receiver and to be less complex and better, in terms of bit error rate (BER) performance, than the DS-CDMA system with iterative chip-wise equalization receivers.

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) enables multiuser interference-free (MUI-free) transmission over multipath downlink channels with the use of zero correlation zone (ZCZ) codes. However, MUI-free transmission is guaranteed only when the data length D, channel delay L, and ZCZ length Z satisfy Z + 1 ges D + L, and the user population is constraint to be K les [N/(Z+1)], where N is the code length. In this paper, for the purpose of allowing higher bandwidth efficiency for more active users, we propose an iterative partial multiuser detector for CS-CDMA/CP with M-ZCZ code to allow Z + 1 < D + L. Because the detector is implemented in the symbol-level (after despreading) and only a partion of users are jointly considered, its receiver complexity is expected to be acceptable for a mobile terminal. Comparison with the DS-CDMA system employing chip-equalization receiver shows that the CS-CDMA/CP system employing the proposed receiver offers a better tradeoff between the performance and receiver complexity, which indicates its potential application in future wireless communications.

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.

This paper studies the impact of fast fading on the performance of coded convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) combined with iterative detection, which was originally proposed for multiuser interference-free (MUI-free) downlink transmission over a quasi-static multipath fading channel. We show that the CS-CDMA/CP system in conjunction with a single pilot, with zero-correlation-zone code from an M-sequence (M-ZCZ), and with iterative detection works also well for fast fading, and the impacts of Doppler spreads can be made negligible without bandwidth efficiency loss by the employment of excess channel spread configuration and iterative partial multiuser detection. We compare the proposed system and the standard W-CDMA system for downlink transmission by simulation and show that both systems enjoy time-diversity effects of fast fading and that, although the W-CDMA system performs better for a small number of users, the CS-CDMA/CP system performs much better for the number of users from moderate to as large as processing gain.