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.

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.

In this paper, a coded convolutional spreading codedivision multiaccess with cyclic prefix (CS-CDMA/CP) system in conjunction with iterative receivers is proposed for synchronous downlink transmission over frequency selective fading channels and its performance is compared with the uncoded CS-CDMA/CP employing maximum-likelihood sequence estimation (MLSE) receiver as well as with the conventional coded direct sequence CDMA (DS-CDMA) employing (maximal ratio combining-) MRC-RAKE. Contrary to the uncoded CSCDMA/ CP system which suffers from performance degradation at low signal-to-noise power ratios (SNRs), it is demonstrated that the proposed scheme can attain almost the full path diversity gain over all SNRs with single-user complexity. Compared with the coded DS-CDMA system with single-user receivers, the proposed system is free from multiuser interference (MUI) whenever the multipath delay of the channel does not exceed the designed maximum delay. It is also demonstrated, moreover, that the proposed system shows a robust performance even if the channel length exceed the designed maximum delay slightly. Because of the subblock structure of CS-CDMA/CP, the proposed system can utilize time-diversity effects, when the channel subjects fast fading, and this greatly improves the resultant performance. Finally, it is shown that the receiver complexity of the proposed system is compared quite favorably with the iterative multiuser receivers for coded DS-CDMA systems of comparable performance.

We propose a transmit diversity CDMA scheme which is a combination of convolutional spreading (CS) and space-time spreading (STS) over multiple-input single-output (MISO) multipath Rayleigh fading channels. With our scheme, multiuser detection over an MISO multipath channel is transformed to single-user detection over a single-input single-output (SISO) multipath channel as the scheme by Petre et al. Because of its simple configuration, it is immediate to see that our scheme realizes full transmit- and path-diversity for two transmit antennas. We extend the system to four transmit antennas employing quasi-orthogonal construction and show a necessary and sufficient condition for full transmit- and path-diversity to be realized. The proposed scheme requires less hardware complexity and less latency than the one by Petre et al.

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) enables multiuser interference-free (MUI-free) transmission over multipath channels with the use of zero correlation zone (ZCZ) codes. In our previous work, we proposed application of a class of binary ZCZ codes generated from an M- sequence, the M-ZCZ code, which has larger user capacity than known binary ZCZ codes and high robustness against transmitter nonlinearity. CS-CDMA/CP guarantees MUI-free transmission only when the data length D, multipath channel length L, and the ZCZ length Z satisfy Z ges D + L - 1, and, for a long spread multipath channel of length Le> L, CS-CDMA/CP suffers from MUI. In this paper we discuss the effect of MUI over the CS-CDMA/CP system employing an M-ZCZ code and propose MUI cancellation schemes for channels with excess spreads, D + Le- 1 > Z. Some simulation results show that the proposed schemes show good BER performance and, more importantly, allows increased user population, compared to the fully MUI- free case with a graceful performance degradation.

We propose a transmit diversity CDMA scheme which is a combination of convolutional spreading (CS) and space-time block coding over multiple input single output (MISO) multipath Rayleigh fading channels. Using orthogonal space-time block coded CS, we can reduce the communication problem over the multiple-input and multiuser channel to relatively simple communication problem over a single-antenna and single-user system. Similar to the scheme in [5], full transmit diversity gain is achieved, and path diversity gain is achieved as well. For quasiorthogonal space-time block coded CS, we also show that signal-constellation rotation is adopted [16] to achieved the full transmit diversity and path diversity gain.

For synchronous downlink direct-sequence code-division multiple access (DS-CDMA), we introduce a cyclic-prefix (CP)-based convolutional spreading CDMA (CS-CDMA/CP) scheme employing zero correlation zone (ZCZ) codes, which gives a class of multiuser interference (MUI)-free CDMA schemes, including Suehiro's CDMA and block spreading (BS) CDMA as special cases. We show that CS-CDMA/CP employing appropriately selected binary and ternary ZCZ codes have good user capacity, peak-to-average power ratio (PAPR), and transmission power loss, compared with previously proposed BS-CDMA schemes. By simulation, we show the effect of PAPR to its bit-error rate (BER) performance when nonlinear amplifiers are used, and also compare its BER performance with the conventional DS-CDMA scheme employing a RAKE receiver

In synchronous DS-CDMA systems the multi-user interference (MUI) caused by multipath propagation degrades the system performance. To overcome this, MUI-free schemes, such as Suehiro's CDMA in N. Suehori (1994) and H.H. Chen et al. (2001) and CIBS-CDMA in S. Zhou et al. (2002) are introduced. In this paper a new class of cyclic prefix (CP) based convolutional spreading CDMA (CS-CDMA/CP) scheme employing zero correlation zone (ZCZ) codes [P.Z. Fan et al., May 1999] is proposed. We show that above two MUI-free schemes are special cases of CS-CDMA/CP and they only difference comes from the particular employed ZCZ code. A comparison in terms of PAPR and transmission power loss for the CS-CDMA schemes is given. We consider a pilot aided downlink CS-CDMA/CP employing equalizers, and compare its performance with the conventional DS-CDMA system employing RAKE receivers via simulation. Our simulation results show that, CS-CDMA/CP performs better than DS-CDMA when system has many users.