Blind channel estimation in multi-rate CDMA systems

Abstract

Abstract-Multi-rate CDMA is a potentially attractive multiple access method for future broad-band multimedia wireless networks that must support integrated voice/data traffic. The primary impairment for such multi-rate systems is the multipath nature of radio channels that results in intra-user inter-chip interference (ICI) and multi-user interference (MUI) between different users' symbols. Explicit knowledge of the channel is typically needed for high performance detectors (such as coherent demodulation). In this work, we propose a subspace method for channel estimation in multi-rate CDMA systems. A unified signal model that applies to three multi-rate CDMA schemes proposed in the literature is developed. The computational complexity for multi-rate scenarios is large and variable-accordingly, a modified approach is devised that offers performance/complexity trade-offs. Performance analysis is conducted based on a close-form expression for the mean square error of the estimator, supported by simulation results that investigate the effectiveness of our method.

Parallel Interference Cancellation for Uplink Multirate Overlay CDMA Channels

“…Throughout the paper, we have assumed static frequency-nonselective channels. For wideband frequency-selective channels, sophisticated channel-estimation techniques [13] will be needed to construct the effective signature waveforms to replace the spreading codes. Some detailed investigations, such as suppression-filter selection for the W-CDMA system, may also benefit system performance.…”

“…Denote as an orthonormal basis of the interfering signature waveform matrix , then it follows that (12) for some . It is easy to see that (13) i.e., the projection of out-of-rate interference onto is itself. The observation indicates that can be extracted from , provided that an orthonormal basis of is obtained.…”

“…The received signal is processed over an interval which is the least common multiple of all the symbol periods, as in [13], to ensure wide-sense stationarity. Despite increased numerical complexity due to a larger observation vector size, the receiver design problem devolves into the familiar single-rate framework, but with equivalent multiple "fictitious" users corresponding to a physical user.…”

Bit error rate performance of Haar wavelet based scale‐code division multiple access (HW/S‐CDMA) over the asynchronous AWGN channel

“…Based on CDMA, there are mainly three schemes suggested for multirate communication: multi-code CDMA, multi-chip rate CDMA and multi-processing gain CDMA [1][2][3][4]. In multi-processing gain CDMA, different data rate users employ PN sequences of different lengths (different processing gains).…”

“…Although random codes are ideal in terms of autocorrelation and crosscorrelation properties, they are not practical since they also need to be transmitted together with the information symbols [11]. Therefore, to be practical we use deterministic PN sequences such as Gold and Kasami while many multirate CDMA systems [1][2][3][4] and wavelet based single-rate systems [7,8] generally work on random codes.…”