Adaptive Interference Suppression for the Downlink of a Direct Sequence CDMA System with Long Spreading Sequences

Frank, C.D.; Visotsky, Eugene; Madhow, Upamanyu

doi:10.1007/0-306-47322-4_17

Cited by 35 publications

(44 citation statements)

References 12 publications

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“…BRR shows a comparable performance at low and medium SNR since it has a reasonably accurate channel estimate, and the correlation with the spreading code ( ) averages out the other users interference effectively in less-severe multiaccess interference environments. We also observe that the theoretical BER calculations (14) and (15) are close to the performance obtained via Monte Carlo runs, indicating that the assumptions made in Section VI-A are accurate. As benchmarks, we show the performance of receivers with knowledge of the true channel.…”

Section: B Mse and Cramér-rao Boundsupporting

confidence: 68%

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Blind decorrelating rake receivers for long-code WCDMA

Tong

Veen

Dewilde

et al. 2003

IEEE Trans. Signal Process.

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Abstract-The problem of blind and semiblind channel estimation and symbol detection is considered for long-code wideband code division multiple access (CDMA) systems, including systems with multirate and multicode transmissions. A decorrelating matched filter, implemented efficiently in state-space, eliminates multiaccess interference and produces a bank of vector processes. Each vector process spans a one-dimensional (1-D) subspace from which channel parameters and data symbols of one user are estimated jointly by least squares. A new identifiability condition is established, which suggests that channels unidentifiable in short-code CDMA systems are almost surely identifiable when aperiodic spreading codes are used. The decorrelating matched filter is implemented efficiently based on time-varying state-space realizations that exploit the structure of sparsity of the code matrix. The mean square error of the estimated channel is compared to the Cramér-Rao bound, and a bit error rate (BER) expression for the proposed algorithm is presented.Index Terms-Aperiodic spreading sequences/codes, blind and semiblind multiuser detection, channel estimation, decorrelating matched filter/RAKE receiver, fast algorithms, identifiability conditions, long-code wideband CDMA.

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Section: B Mse and Cramér-rao Boundsupporting

confidence: 68%

“…Other related approaches include the use of chip-level equalization. See, for example, [13], [14], and references therein.…”

Section: B Related Workmentioning

confidence: 99%

Blind decorrelating rake receivers for long-code WCDMA

Tong

Veen

Dewilde

et al. 2003

IEEE Trans. Signal Process.

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“…This idea can also be applied in the multipath channel case but since users within a cell are no longer orthogonal there will be some loss of optimality. Note that even if the orthogonality between the users within a particular cell is restored using the equalization techniques described in [3], [4], [5], [6], [7], [8], [9], [10], [11], the resulting matched filter bank outputs will contain noise terms that are correlated across the users.…”

Section: Reduced Complexity Optimum Detectionmentioning

confidence: 99%

Multiuser Detection for Out-of-Cell Cochannel Interference Mitigation in the IS-95 Downlink

Brown¹,

Poor²,

Verdú³

et al. 2002

Information Technology: Transmission, Processing and Storage

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This paper considers the application of multiuser detection techniques to improve the quality of downlink reception in a multi-cell IS-95 digital cellular communication system. In order to understand the relative performance of suboptimum multiuser detectors including the matched filter detector, optimum multiuser detection in the context of the IS-95 downlink is first considered. A reduced complexity optimum detector that takes advantage of the structural properties of the IS-95 downlink and exhibits exponentially lower complexity than the brute-force optimum detector is developed. The Group Parallel Interference Cancellation (GPIC) detector, a suboptimum, low-complexity multiuser detector that also exploits the structure of the IS-95 downlink is then developed. Simulation evidence is presented that suggests that the performance of the GPIC detector may be near-optimum in several cases. The GPIC detector is also tested on a snapshot of on-air data measured with an omnidirectional antenna in an active IS-95 system and is shown to be effective for extracting weak downlink transmissions from strong out-of-cell cochannel interference. The results of this paper suggest that the GPIC detector offers the most performance gain in scenarios where weak downlink signals are corrupted by strong out-of-cell cochannel interference.

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“…In [1], we presented another receiver approach which is based on channel equalization. This approach was introduced independently in [2] and [3]. Whereas the RAKE approach focuses on the noise (and intercell interference), the equalizer approach focuses on the intracell interference.…”

Section: Introductionmentioning

confidence: 99%

A RAKE receiver with intracell interference cancellation for a DS-CDMA synchronous downlink with orthogonal codes

Lenardi

Slock²

VTC2000-Spring. 2000 IEEE 51st Vehicular Technology Conference Proceedings (Cat. No.00CH37026)

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-The conventional receiver for DS-CDMA communications is the RAKE receiver. The RAKE receiver is a matched filter, matched to the operations of spreading, pulse shape filtering and channel filtering. Such a matched filter maximizes the Signal-to-Interference-plus-Noise Ratio (SINR) at its output if the interference plus noise is white. This may be approximately the case if user-dependent scrambling (aperiodic spreading) is used. This is one option for the uplink in 3rd generation systems. However, this is not the case in the synchronous downlink with cell-dependent scrambling, orthogonal codes and a common channel. In this paper we propose a restricted class of linear receivers for the downlink, exhibiting a limited or no complexity increase with respect to the RAKE receiver. The linear receivers in this class have the same structure as a RAKE receiver, but the channel matched filter gets replaced by an equalizer filter that is designed to maximize the SINR at the output of the receiver. The complexity of the equalizer filter is variable and can possibly be taken to be as low as in the RAKE receiver (same structure as the channel matched filter), while its adaptation guarantees improved performance with respect to (w.r.t.) the RAKE receiver. Various adaptation strategies are considered and compared in simulations.

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Adaptive Interference Suppression for the Downlink of a Direct Sequence CDMA System with Long Spreading Sequences

Cited by 35 publications

References 12 publications

Blind decorrelating rake receivers for long-code WCDMA

Blind decorrelating rake receivers for long-code WCDMA

Multiuser Detection for Out-of-Cell Cochannel Interference Mitigation in the IS-95 Downlink

A RAKE receiver with intracell interference cancellation for a DS-CDMA synchronous downlink with orthogonal codes

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