Adaptive receiver structures for asynchronous CDMA systems

Rapajic, P.B.; Vucetic, Branka

doi:10.1109/49.286675

Cited by 371 publications

(138 citation statements)

References 23 publications

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“…Thus, the pseudoinverse solution defines the optimal FIR decorrelating detector (12) where mbc denotes "middle block column of." It should be noted that the above detector is the optimal FIR decorrelator in the sense that it minimizes the least squares error in the solution of (11). However, there is no guarantee that the detector would yield lower bit-error probability than the truncated decorrelating detector…”

Section: B Linear Multiuser Detectorsmentioning

confidence: 99%

“…10 In the second column, for example, R > 2 (1) = R >(n0P+1) (1); R 2 (0) = R (n0P +1) (0); R 3 (1) = R (n0P +2) (1); etc. 11 The analysis we perform also applies to systems with time-invariant signature waveforms since the time-invariant case can be viewed as a special case of a system with time-variant signature waveforms. most of the numerical examples, but still the detectors were stable in all cases.…”

Section: Stability Of Detectorsmentioning

confidence: 99%

“…To generalize the decorrelating detector we should find a zero-forcing detector, satisfying (11) which does not have a unique solution. A unique detector can be found by selecting the pseudoinverse (i.e., Moore-Penrose generalized inverse), which yields the best least squares solution to (11). Since is positive definite, has full rank with more columns than rows.…”

Section: B Linear Multiuser Detectorsmentioning

confidence: 99%

See 2 more Smart Citations

Finite memory-length linear multiuser detection for asynchronous CDMA communications

Juntti

Aazhang

1997

IEEE Trans. Commun.

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Abstract-Decorrelating, linear, minimum mean-squared error (LMMSE), and noise-whitening multiuser detectors for code-division multiple-access systems (CDMA) are ideally infinite memory-length (referred to as IIR) detectors. To obtain practical detectors, which have low implementation complexity and are suitable for CDMA systems with time-variant system parameters (e.g., the number of users, the delays of users, and the signature waveforms), linear finite-memory-length (referred to as FIR) multiuser detectors are studied in this paper. They are obtained by truncating the IIR detectors or by finding optimal FIR detectors. The signature waveforms are not restricted to be timeinvariant (periodic over symbol interval). Thus, linear multiuser detection is generalized to systems with spreading sequences longer than the symbol interval. Conditions for the stability of the truncated detectors are discussed. Stable truncated detectors are shown to be near-far resistant if the received powers are upper bounded, and if the memory length is large enough (but finite). Numerical examples demonstrate that moderate memory lengths are sufficient to obtain the performance of the IIR detectors even with a severe near-far problem.

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Section: B Linear Multiuser Detectorsmentioning

confidence: 99%

Section: Stability Of Detectorsmentioning

confidence: 99%

Section: B Linear Multiuser Detectorsmentioning

confidence: 99%

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Finite memory-length linear multiuser detection for asynchronous CDMA communications

Juntti

Aazhang

1997

IEEE Trans. Commun.

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“…In [15] and [25], several iterative methods for general adaptive filter and equalizer applications are discussed in detail. Specific algorithms applicable for CDMA systems are developed in [26]- [29]. Most of these algorithms are based on the method of gradient descent or the method of least squares.…”

Section: B Performance Comparisonsmentioning

confidence: 99%

Real-time algorithms and architectures for multiuser channel estimation and detection in wireless base-station receivers

Rajagopal

Bhashyam

Cavallaro

et al. 2002

IEEE Trans. Wireless Commun.

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Abstract-This paper presents algorithms and architecture designs that can meet real-time requirements of multiuser channel estimation and detection in future code-division multiple-access-based wireless base-station receivers. Sophisticated algorithms proposed to implement multiuser channel estimation and detection make their real-time implementation difficult on current digital signal processor-based receivers. A maximum-likelihood based multiuser channel estimation scheme requiring matrix inversions is redesigned from an implementation perspective for a reduced complexity, iterative scheme with a simple fixed-point very large scale integration (VLSI) architecture. A reduced-complexity, bit-streaming multiuser detection algorithm that avoids the need for multishot detection is also developed for a simple, pipelined VLSI architecture. Thus, we develop real-time solutions for multiuser channel estimation and detection for third-generation wireless systems by: 1) designing the algorithms from a fixed-point implementation perspective, without significant loss in error rate performance; 2) task partitioning; and 3) designing bit-streaming fixed-point VLSI architectures that explore pipelining, parallelism, and bit-level computations to achieve real-time with minimum area overhead.

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“…As we will see, the overall system proposed in this paper is optimally matched to the fast fading channel and can deliver improved performance compared to the scheme presented in [10]. Overlapping signature sequences have also been studied in [12] for other advantageous system characteristics, such as increased resistance to impulse noise and increased number of available signature sequences.…”

mentioning

confidence: 99%

Time-selective signaling and reception for communication over multipath fading channels

Bhashyam

Sayeed

Aazhang

2000

IEEE Trans. Commun.

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Abstract-The mobile wireless channel affords inherent diversity to combat the effects of fading. Existing code-division multiple-access systems, by virtue of spread-spectrum signaling and RAKE reception, exploit only part of the channel diversity via multipath combination. Moreover, their performance degrades under fast fading commonly encountered in mobile scenarios. In this paper, we develop new signaling and reception techniques that maximally exploit channel diversity via joint multipath-Doppler processing. Our approach is based on a canonical representation of the wireless channel, which leads to a time-frequency generalization of the RAKE receiver for diversity processing. Our signaling scheme facilitates joint multipath-Doppler diversity by spreading the symbol waveform beyond the intersymbol duration to make the channel time-selective. A variety of detection schemes are developed to account for the intersymbol interference (ISI) due to overlapping symbols. However, our results indicate that the effects of ISI are virtually negligible due to the excellent correlation properties of the pseudorandom codes. Performance analysis also shows that relatively small Doppler spreads can yield significant diversity gains. The inherently higher level of diversity achieved by time-selective signaling brings the fading channel closer to an additive white Gaussian noise channel, thereby facilitating the use of powerful existing coding techniques for Gaussian channels.

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Adaptive receiver structures for asynchronous CDMA systems

Cited by 371 publications

References 23 publications

Finite memory-length linear multiuser detection for asynchronous CDMA communications

Finite memory-length linear multiuser detection for asynchronous CDMA communications

Real-time algorithms and architectures for multiuser channel estimation and detection in wireless base-station receivers

Time-selective signaling and reception for communication over multipath fading channels

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