2-dimensional (2D) block spread direct sequence-code division multiple access (DS-CDMA) allows uplink mutli- rate/mutli-connection transmissions without causing a serious multi-access interference (MAI) in the presence of a frequency- selective fading channel. However, in a cellular system, the inter- cell interference remains. The site selection diversity (SSD) can be used to reduce the inter-cell interference and increase the uplink capacity. Furthermore, transmit power control (TPC) is necessary to combat the near-far problem. In this paper, we discuss the impact of SSD and TPC on the uplink capacity of 2D block spread DS-CDMA and compare it with those of conventional DS-CDMA and ID block spread DS-CDMA.

2D block spread direct sequence-code division multiple access (DS-CDMA) allows multi-rate/multi-connection without causing downlink multi-access interference (MAI) in the presence of a frequency-selective fading channel. However, in a cellular system, the inter-cell interference remains. The site selection diversity transmission (SSDT) can be used to reduce the inter-cell interference and increase the downlink capacity. In this paper, we show that if adaptive power allocation is applied, where the BS allocates different power levels to different users according to their channel conditions, 2D block spread DS-CDMA with SSDT provides larger downlink capacity than the conventional DS-CDMA with SSDT.

The multiple-access interference (MAI) limits the performance of the DS-CDMA uplink transmission. 2 dimensional (2D) spread/chip-interleaved DS-CDMA is an MAI-free system, where single-user coherent frequency- domain equalization (FDE) can be used instead of complicated multiuser detection (MUD). However, coherent FDE needs channel estimation. Pilot-assisted channel estimation is not reliable in a fast fading environment. In this paper, we apply joint frequency- domain differential detection and equalization (FDDDE) that requires no channel estimation to 2D spread/chip- interleaved DS-CDMA in a multiuser/multipath environment. The filter coefficient used in FDDDE is updated by estimating the normalized Doppler frequency. Computer simulation results show that 2D spread/chip- interleaved DS-CDMA using FDDDE is robust against fast fading.

Chip interleaving technique has been proposed for DS-CDMA to eliminate the multiple-access interference (MAI). In this paper, we develop this technique to provide the single- or multicarrier CDMA with flexible low-to-high bit rate transmission by jointly using 2-dimensional (2D) OVSF spreading and chip interleaving for quasi-synchronous uplink transmissions in time- and frequency-selective fading channels. Through appropriate design of 2D spreading code assignment, not only the maximum time- and frequency-domain diversity can be achieved but also users are equipped with multi-rate services. The complexity of receivers is greatly reduced since single-user frequency-domain equalization (FDE) based on the MMSE criterion can be applied for signal detection. Computer simulation results show that the multi-rate transmission is possible for the 2D OVSF spread/chip-interleaved CDMA uplink and the bit error rate (BER) performance with turbo coding is very robust against Doppler spread

It has been revealed that direct sequence code-division multiple access (DS-CDMA) can achieve a good bit-error rate (BER) performance, comparable to multicarrier CDMA (MC-CDMA), by using coherent frequency-domain equalization (FDE) instead of coherent Rake combining. However, coherent FDE requires accurate channel estimation. Pilot-assisted channel estimation is a practical solution, but its accuracy is sensitive to the Doppler spread. In this paper, a frequency-domain differential encoding and detection scheme is proposed for a DS-CDMA mobile radio. Joint frequency-domain differential detection and equalization (FDDDE) based on minimum mean-square error (MMSE) criterion is presented, where a simple decision feedback filter is used to provide a reliable reference signal for MMSE-FDDDE. Also presented is an approximate BER analysis. It is confirmed by both approximate BER analysis and computer simulation that MMSE-FDDDE provides good BER performance close to the coherent MMSE-FDE and shows high robustness against the Doppler spread; it outperforms coherent MMSE-FDE for large Doppler spreads. The proposed MMSE-FDDDE can also be applied to MC-CDMA. A performance comparison between uncoded DS- and MC-CDMA shows that DS-CDMA with MMSE-FDDDE achieves better BER performance than MC-CDMA with MMSE-FDDDE for small spreading factors.