Block Spread CDMA Research Articles

Iterative Successive Interference Cancellation for Quasi-Synchronous Block Spread CDMA Based on the Orders of the Times of Arrival

Recently, a block spreading code division multiple access (BS-CDMA) technique was presented, whereby user-specific precoding along with orthogonal spreading codes is used to achieve multiuser interference- (MUI-) free reception when all users arrive at the base station simultaneously. In practice, however, imperfect synchronization destroys the orthogonality among users, and MUI occurs. To mitigate the MUI in BS-CDMA due to quasisynchronous reception, this paper proposes an iterative successive interference cancellation (SIC) receiver, where cancellation of interfering signals is ordered according to the times of arrival (TOA) of the signals from different users. The ordering criterion is justified through analysis and simulation on the average signal-to interference-plus-noise ratio (SINR) of different users, where it is shown that in a quasisynchronous BS-CDMA system, ordering with regard to increasing TOA is equivalent to ordering with respect to decreasing average SINR, when practical channels such as the exponentially decaying channel is considered. The proposed SIC receiver is shown to achieve a performance close to a system with synchronous reception for only two iterations. In addition, an algorithm to determine the detection order of different blocks is proposed such that parallel detection of the signals from different users with reduced latency can be achieved.

Estimation of CSI for LST BS-CDMA systems using special sequences with pre-defined spectral nulls

Layered space-time block spread CDMA (LST BSCDMA) has been previously proposed as an alternative to conventional CDMA systems for high-rate mobile communications. This paper proposes two approaches to obtain channel state information (CSI) for LST BS-CDMA system. The basic approach suffers from high computational complexity and poor performance in systems with high order of transmitter diversity due to inter-layer interference (ILI). The second approach reduces computation complexity and eliminates ILI, making it suitable for systems with higher order of transmitter diversity. The detailed simulation studies show that the highly accurate CSI obtained using the improved technique leads to considerable superior performance.

Generalized precoded block-spread CDMA

A novel block-spread code-division multiple access (BS-CDMA) framework is presented whereby user-specific, channel-independent precoding is employed along with special spreading codes to ensure multi-user interference free reception with maximum user load. This framework is presented in a general form, from which other BS-CDMA techniques can be derived. Finally, it is shown that specific precoder and spreading code designs facilitate low-complexity frequency-domain equalization at the receiver.

Novel interference cancellation methods for BS-CDMA in uplink broadband mobile communication systems

A single-carrier block-spread CDMA (BS-CDMA) system was proposed to offer multi-user interference (MUI) robustness and complexity reduction. However, perfect MUI elimination in BS-CDMA requires channels to be stationary within the block spreading duration which is not always applicable in high-rate mobile communication system. This letter proposes two novel interference cancellation methods to reduce the MUI arising from such scenario by using mobility condition to determine the detection ordering. Simulation results show that the proposed techniques offer significant performance improvement in a realistic multi-user multi-path environment.

Frequency‐domain equalisation for block CDMA transmission

AbstractIn next generation wireless network, significantly higher rate data services of close to 1 Gpbs are expected. The wireless channels for such a broadband data transmission become severe frequency‐selective. Frequency‐domain equalisation (FDE) technique may play an important role for broadband data transmission using multi‐carrier (MC)‐ and direct‐sequence code division multiple access (DS‐CDMA). The performance can be further improved by the use of multi‐input/multi‐output (MIMO) antenna diversity technique. The downlink performance is significantly improved with FDE. However, the uplink performance is limited by the multiple access interference (MAI). To remove the MAI while gaining the frequency diversity effect through the use of FDE, two‐dimensional (2D) block spread CDMA can be used. Recently, particular attention has been paid to MIMO space division multiplexing (SDM) to significantly increase the throughput without expanding the signal bandwidth. In this paper, we present a comprehensive performance comparison of MC‐ and DS‐CDMA using FDE. Copyright © 2008 John Wiley & Sons, Ltd.

MIMO Block Spread CDMA Systems for Broadband Wireless Communications

This paper studies two MIMO architectures for single-carrier CDMA system employing block spreading, namely Layered Space-Time Block Spread CDMA (LST BS-CDMA) and Space-Time Coded Block Spread CDMA (STC BS-CDMA). It is shown that under low mobility conditions, the proposed systems are virtually free from Multiple User Interference (MUI) and the block processing technique used leads to considerable reduction in the overall processing complexity. Extensive simulation was performed to study the impact of the spreading factor and Doppler frequency on the proposed systems. A new parameter called channel coherence ratio (CCR) is introduced as a key parameter in determining the performance of MIMO BS-CDMA.

Layered space-time architecture for MIMO block spread CDMA systems

In this paper, single-carrier block spread CDMA for multiple-input-multiple-output (MIMO) systems is proposed. With block spreading and despreading, multiple-user intererence free (MUI-free) transmission with reduced processing complexity is achieved. Layered space-time transmission (LST) is employed to enhance the data rak. of the proposed system. The proposed system is studied extensively under different channel conditions and its performance is compared against conventional single-carrier and multicarrier CDMA systems