Subspace-based Channel Estimation Algorithm Research Articles

Performance Analysis of Subspace Based Downlink Channel Estimation for W-CDMA Systems Using Chaotic Codes

This paper presents blind channel estimation for downlink W-CDMA system that employs chaotic codes and Walsh codes for spreading information bits of the multiple users. In a W-CDMA system, while transmitting over multipath channels, both intersymbol interference (ISI) as a result of Inter Chip Interference and multiple access interference (MAI) cannot be easily eliminated. Although it is possible to design multiuser detectors that suppress MAI and ISI, these detectors often require explicit knowledge of at least the desired users' signature waveform. Earlier work focused on a subspace based channel estimation algorithm for asynchronous CDMA systems to estimate the multiple users' symbols, where only AWGN channel was considered. In our work, we study a similar subspace-based signature waveform estimation algorithm for downlink W-CDMA systems, which use chaotic codes instead of pseudo random codes, that provide estimates of the multiuser channel by exploiting structural information of the data output at the base station. In particular, we show that the subspace of the (data+noise) matrix contains sufficient information for unique determination of channels, and hence, the signature waveforms and signal constellation. We consider Rayleigh and Rician fading channel model to quantify the multipath channel effects. Performance measures like bit error rate and root mean square error are plotted for both chaotic codes and Walsh codes under Rayleigh and Rician fading channels.

Subspace based downlink channel estimation for W-CDMA systems

Wideband code division multiple access (W-CDMA) is a third generation (3G) mobile wireless technology that promises much higher data speeds for mobile and portable wireless devices than those which are commonly offered in todayʼs market. In W-CDMA systems transmitting over multipath channels, both Inter Symbol Interference (ISI) as a result of Inter Chip Interference (ICI) and Multiple Access Interference (MAI) cannot be easily eliminated. Although it is possible to design multiuser detectors that suppress MAI and ISI, these detectors often require explicit knowledge of at least the desired usersʼ signature waveform. Torlak and Xu (1997) [1] proposed a subspace based channel estimation algorithm for Asynchronous CDMA (A-CDMA) systems to estimate the multiple usersʼ symbols. In our work, we study a similar subspace based channel estimation scheme for downlink W-CDMA systems that provide estimates of the subchannels of multiple users by exploiting the structural information of the data output. In particular, we show that the subspace of the (data + noise) matrix contains sufficient information for unique determination of channels, and hence, the signature waveforms and signal constellation. Performance measures like Bit Error Rate (BER) and Root Mean Square Error (RMSE) are plotted for Rayleigh and Rician fading channels.

Semiblind Channel Estimation for IFDMA in Case of Channels with Large Delay Spreads

Discrete Fourier Transform- (DFT-) precoded Orthogonal Frequency Division Multiple Access (OFDMA) with interleaved subcarrier allocation per user is considered which is denoted as Interleaved Frequency Division Multiple Access (IFDMA). For IFDMA, the received signal exhibits a cyclostationarity with the parameter which defines the number of allocated subcarriers per user. In previous works, we have shown that this cyclostationarity can be exploited for the application of subspace-based semiblind channel estimation to IFDMA. Nevertheless, the formerly proposed algorithm is restricted to channels with small delay spreads, meaning that the number of channel delay taps needs to be smaller than . In this paper, we introduce a new semiblind subspace-based channel estimation algorithm which identifies a subspace of the received signal that is spanned by the elements of the so-called cyclic channel impulse response. By doing so, the number of elements to be estimated is reduced and the proposed algorithm is able to cope with channels with large delay spreads.

Improved subspace-based channel estimation algorithm for DS∕CDMA systems exploiting pulse-shaping information

An improved subspace-based channel estimation algorithm for DS/CDMA system is presented. The proposed algorithm is based on the Torlak/Xu algorithm for asynchronous DS/CDMA systems. The aim is to incorporate knowledge of the pulse-shaping filter into the Torlak/Xu subspace algorithm with the objective of reducing the variance of the channel estimates. The improved algorithm is developed from a system model of a DS/CDMA system where the output is oversampled with respect to the chip rate. By oversampling the received signal, knowledge of the pulse-shaping filter is incorporated into the proposed channel estimation algorithm. It is shown that the variance of the channel estimate for the proposed subspace algorithm is less than the Torlak/Xu algorithm that does not exploit pulse-shaping filter information. A mathematical expression of the mean square error of estimation for the improved algorithm is also derived. It is shown that the analytical expression provides a good approximation of the actual mean square error for high SNR signals.

On Blind Timing Acquisition and Channel Estimation for Wideband Multiuser DS-CDMA Systems

The problems of blind timing acquisition and channel estimation for DS-CDMA signals in multipath fading channels are investigated. Using only the spreading code of the desired user, methods based on QR decompositions are proposed. These methods perform comparably or even better than subspace based methods with an order lower complexity. Furthermore, the methods exhibit significantly more robustness to channel order mismatch. Based on the acquired timing information, channel estimation algorithms are also developed which are competitive with the previously proposed subspace based channel estimation algorithms. In addition, a channel order estimation algorithm is proposed for the scenario where the order is unknown. Performance of the proposed algorithms is evaluated through simulation and comparison to asymptotic Cramer-Rao bounds.