MMSEC-RAKE receivers with resolution reduction of the diversity branches: analysis, simulation, and applications

Abstract

In channels where the delay spread is smaller than the chip interval (e.g., an IS-95 system operating in indoor environments), spread-spectrum signals do not give rise to path diversity. In this situation, maximal-ratio combiner (MRC) RAKE receivers with resolution reduction (RR) of the diversity receiver branches may be used by the mobile stations to provide diversity gain, significantly improving system performance. A new resolution reduction technique based on the use of a minimum mean-square-error diversity combiner (MMSEC) is proposed in this work. We show that, under very general assumptions, this new method of RR is optimal. A detailed study of the performance of a dual-branch MMSEC-RAKE receiver with RR in a typical indoor office environment is presented. In order to allow a simple practical implementation, a suboptimal structure of the MMSEC is also proposed. Numerical results show that this new receiver scheme provides a 1.2-dB improvement over the previously proposed RR technique based on MRC, and a 4.9-dB improvement over conventional MRC-RAKE receiver without RR, at a frame-error rate of 0.01 for the downlink of the IS-95 system in a typical indoor office environment.

Robust Interactive Video Transmission in MC-CDMA Cellular Networks over Slow Fading Channels

“…Since the rate variation of the channel is small, we assume ideal coherent demodulation at the RAKE receiver [36]. Throughout this work, we assume Rayleigh fading and adopt the Gaussian approximation for the interference-plus noise component [35], [37]. The Rayleigh channel is simulated using Jakes' model [38].…”

Multiple finger expansion for blind interference canceller in the presence of subchip-spaced multipath components

“…We can see that the MFE-OMF with suboptimum diversity combining performs worse than the theoretical bound. This gap can be narrowed by using optimum techniques in [33] and [34] at the expense of additional computational complexity. It can also be seen that as f D increases the average BER becomes larger.…”

“…Hence, we are able to coherently combine the outputs from MFE-OMF in a suboptimum manner. Although this suboptimum method suffers a performance loss due to the correlation between the outputs from MFE-OMF, it is simpler and practical compared to other optimum techniques [33], [34]. …”

“…Nevertheless, improved performance can be obtained by using other optimum combining techniques to whiten the signals at the output of MFE-OMF [33], [34]. However, these techniques are impractical since they are only optimal if the correlation matrix is completely known to the receiver and computational intensive operations are required.…”

Performance evaluation of rake receiver of DS-CDMA under AWGN environments

“…The demodulated data, after being time aligned to compensate for the different, possibly time-varying time delays of the multipath components, are combined for a final decision or fed into a channel decoder [7]. Several schemes have been proposed in recent years in the direction of the RAKE receiver [8]- [15]. The linear minimum meansquare error (MMSE) multiuser receiver can be obtained directly by solving a Wiener estimation problem, if probing data are available [16].…”