On the impact of soft decision functions on the performance of multistage parallel interference cancelers for CDMA systems

Irmer, Ralf; Nahler, A.; Fettweis, Gerhard

doi:10.1109/vetecs.2001.944640

Cited by 17 publications

(6 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is subtracted from the output of the time-domain combiner, given by (7) where the superscript of stands for the th stage, and is the soft data decision. The resultant signals are then combined in frequency-domain with the MMSE technique.…”

Section: Receivermentioning

confidence: 99%

“…However, when the tentative decisions are wrong, the MCI will be increased considerably from error propagation, actually doubled for binary phase-shift keying (BPSK) modulation. In order to improve the system performance with hard decisions, a soft-decision function [7] should be used to regenerate MCI. The soft MCI cancellation approach is more complex, but it can provide better performance over the hard one by alleviating the effect of error propagation.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Downlink transmission of broadband OFCDM systems-part IV: soft decision

Zhou¹,

Wang

2006

IEEE J. Select. Areas Commun.

View full text Add to dashboard Cite

In this paper, the performance of turbo-coded orthogonal frequency and code-division multiplexing (OFCDM) systems is investigated with soft multicode interference (MCI) cancellation and minimum mean-square error (MMSE) detection for downlink transmission in future high-speed wireless communications. To regenerate the soft interference signal, the conventional turbo decoding algorithm must be modified to provide log-likelihood ratio (LLR) values for all coded bits. Based on the LLR outputs of turbo decoder, two soft-decision functions are proposed, called LLR-soft-decision and Gaussian-soft-decision functions. The Gaussian assumptions used for deriving these two soft functions are verified by simulation results, and simple methods are proposed to estimate parameters used in the soft functions in practical systems. By means of computer simulations, the performance of soft MCI cancellation is studied extensively and compared with that of hard ones. It is shown that in a highly frequency-selective channel, soft MCI cancellation and MMSE detection can significantly improve the performance of turbo-coded OFCDM systems. Two iterations in turbo decoding are sufficient for both hard and soft-decision functions. The proposed soft-decision functions outperform the hard-decison function with various channel conditions and system parameters, such as the channel correlation, the quality of channel estimation, the number of iterations in turbo decoding and the frequency-domain spreading factor ( ). Furthermore, the Gaussian-soft-decision function provides better performance than the LLR-soft-decision function. Finally, although frequency diversity gain is saturated for large channel correlation when is large as in [6], the gain increases further with increasing for small channel correlation even when is large.Index Terms-Fading channel, interference cancellation, minimum mean-square error (MMSE) detection, orthogonal frequency-division multiplexing (OFDM), packet-error rate (PER), soft-decision function, two-dimensional (2-D) spreading.

show abstract

Section: Receivermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Downlink transmission of broadband OFCDM systems-part IV: soft decision

Zhou¹,

Wang

2006

IEEE J. Select. Areas Commun.

View full text Add to dashboard Cite

show abstract

“…These effective codes might be used in place of the unknown actual codes, since the actual symbol estimates and their powers are not necessary as long as the pseudo-symbols are treated linearly in interference cancellation. However, knowing or detecting the actual codes is an opportunity for exploiting hard or hyperbolic-tangent non-linearities (or even channel decoding and encoding) to refine their symbol estimates [10,17].…”

Section: Introductionmentioning

confidence: 99%

Downlink WCDMA receivers based on combined chip and symbol level equalisation

Bastug

Slock

2005

Trans Emerging Tel Tech

View full text Add to dashboard Cite

SUMMARYIn this paper, we consider iterative receiver techniques for the downlink in WCDMA systems (UMTS FDD mode). We start from the linear minimum mean square error (MMSE) receiver (at symbol level), which is time varying and hence too complex to implement. By applying polynomial expansion (PE) to the LMMSE receiver, an iterative solution is obtained in which the complexity per iteration becomes comparable to twice that of the Rake receiver. Our one contribution is to replace the channel matched filter by a channel equaliser within this PE to accelerate the convergence of the iterations. We also investigate various scenarios for the introduction of non-linearities in the PE scheme that are particularly applicable to the multicode case of the high speed downlink packet access (HSDPA) mode since it is well known that non-linearities in the PE scheme lead, in fact, to the parallel interference canceler (PIC).

show abstract

“…Pseudocodes might be used in place of the unknown actual codes since the actual symbol estimates and their powers are not necessary as long as the pseudo-symbols are treated linearly in interference cancellation. However, knowing or detecting the actual codes is an opportunity for exploiting hard or hyperbolic-tangent nonlinearities or even channel decoding and encoding to refine their symbol estimates [11], [12]. In the latter case, one can pass between the symbol blocks of known codes and their pseudo-equivalents at SF-256 by properly dimensioned FWHTs.…”

mentioning

confidence: 99%

Optimization Combined Chip and Symbol Level Equalization for Downlink WCDMA Reception

Bastug

Slock

2006

2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications

View full text Add to dashboard Cite

We consider iterative WCDMA receiver techniques for the UMTS FDD downlink. The popular LMMSE chip equalizer-correlator receiver does not exploit subspaces in partially loaded systems. This is in contrast to the symbol level LMMSE receiver, which is time-varying though, due to the scrambler, and hence too complex to implement. A compromise can be found by performing symbol level Multi-Stage Wiener Filtering (MSWF), which is an iterative solution in which the complexity per iteration becomes comparable to twice that of the RAKE receiver. Since the MSWF works best when the input is white, better performance is obtained if the RAKE in each MSWF stage gets replaced by a chip equalizer-correlator. One of the main contributions here is to point out that the chip equalizer benefits from a separate optimization in every stage. This is shown through a mix of analysis and simulation results.

show abstract

On the impact of soft decision functions on the performance of multistage parallel interference cancelers for CDMA systems

Cited by 17 publications

References 13 publications

Downlink transmission of broadband OFCDM systems-part IV: soft decision

Downlink transmission of broadband OFCDM systems-part IV: soft decision

Downlink WCDMA receivers based on combined chip and symbol level equalisation

Optimization Combined Chip and Symbol Level Equalization for Downlink WCDMA Reception

Contact Info

Product

Resources

About