Optimization of code rate and spreading factor for direct-sequence CDMA systems

Bickel, M.; Granzow, W.; Schramm, Peter

doi:10.1109/isssta.1996.563194

Cited by 14 publications

(6 citation statements)

References 4 publications

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“…For example, in [1], [2], the author concluded that spread-spectrum multiple-access communication system approaches its ultimate potential only with the use of very low rate forward error control code with consequently large bandwidth expansion. Similar conclusions have been also made in [3] assuming coherent detection and in [4] that very low rate encoder with short spreading sequences should be used in terms of capacity and cutoff rates. Thus, IDMA may be seen as a special case of CDMA with spreading gain of one using very low rate codes.…”

Section: Nterleave Division Multiple Access (Idma)supporting

confidence: 71%

IDMA vs. CDMA: Analysis and Comparison of Two Multiple Access Schemes

Kusume

Bauch

Utschick

2012

IEEE Trans. Wireless Commun.

123

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This article presents comprehensive comparisons of interleave division multiple access (IDMA) and direct sequence code division multiple access (DS-CDMA) in terms of performance and complexity assuming iterative multiuser detection. IDMA can be seen as a special case of DS-CDMA with spreading gain of one using very low rate code and user-specific interleavers for user separation. We focus on three suboptimum linear detectors: minimum mean square error (MMSE), rake (or matched filter), and soft-rake detectors from practical concerns. We analytically prove that the three detectors are equivalent for asynchronous users of IDMA on frequency flat channels for complex modulation alphabets. Such equivalence has been shown only for binary phase shift keying (BPSK) in the literature. The equivalence guarantees the MMSE solution for IDMA without computationally expensive matrix inversions or matrix-vector multiplications. This is generally not the case for DS-CDMA since DS-CDMA is sensitive to user asynchronism. We also discuss complexity aspects when the MMSE detector is used where we focus on essential differences in complexity between IDMA and DS-CDMA, instead of discussing particular complexity reduction techniques. Computer simulations are performed in various scenarios and the performance is analyzed by bit error rate simulations as well as by extrinsic information transfer (EXIT) charts. The analysis reveals the advantages of IDMA over DS-CDMA in terms of performance and complexity under practical considerations, particularly in highly user loaded scenarios.Index Terms-Interleave division multiple access (IDMA), direct sequence code division multiple access (DS-CDMA), multiuser detection, iterative detection and decoding.

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Section: Nterleave Division Multiple Access (Idma)supporting

confidence: 71%

IDMA vs. CDMA: Analysis and Comparison of Two Multiple Access Schemes

Kusume

Bauch

Utschick

2012

IEEE Trans. Wireless Commun.

123

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“…Considering conventional decision feedback with equal powers we get the average capacity by averaging (22) with respect to Spectral efficiency of the MMSE detector has been examined with the help of Monte Carlo methods in [36]. The later analytical result (24) is due to [6] and [7].…”

Section: A Results For Other Detectorsmentioning

confidence: 99%

“…Spectral efficiency of conventional CDMA has been extensively studied in the literature [19]- [23], [14], [24], [3], [6], [4], [7]. However, these references are either asymptotic in the number of users, or based on approximations and/or Monte Carlo simulations.…”

Section: Conventional Matched-filteringmentioning

confidence: 99%

Multiuser receivers for randomly spread signals: fundamental limits with and without decision-feedback

Müller

2001

IEEE Trans. Inform. Theory

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Synchronous code-division multiple-access (CDMA) communication systems with randomly chosen spreading sequences and capacity-achieving forward error correction coding are analyzed in terms of spectral efficiency. Emphasis is on the penalties paid by applying single-user coding in conjunction with suboptimal multiuser receivers as opposed to optimal joint decoding which involves complexity that is exponential in the number of users times the codeword length.The conventional, the decorrelating, and the (re-encoded) decorrelating decision-feedback detectors are analyzed in the nonasymptotic case for spherical random sequences. The re-encoded minimum mean-squared error (MMSE) decision-feedback receiver achieving the same performance as joint multiuser decoding for equal power users is shown to be suboptimal in the case of equal rates.

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“…(1)) and a negligible spreading gain with respect to the number of users. This conclusion was known to hold for the single-user matched filter [41] (although it may not extend to noncoherent demodulation models [52]). Note, however, that the behavior of optimum processing and the conventional single-user matched filter at are quite different: the optimal spectral efficiency grows without bound with , whereas the matched-filter efficiency approaches 0.72 bit/chip monotonically as .…”

Section: ) Optimum Coding-spreading Tradeoffmentioning

confidence: 98%

Spectral efficiency of CDMA with random spreading

Verdú

Shamai

1999

IEEE Trans. Inform. Theory

823

815

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Abstract-The CDMA channel with randomly and independently chosen spreading sequences accurately models the situation where pseudonoise sequences span many symbol periods. Furthermore, its analysis provides a comparison baseline for CDMA channels with deterministic signature waveforms spanning one symbol period. We analyze the spectral efficiency (total capacity per chip) as a function of the number of users, spreading gain, and signal-to-noise ratio, and we quantify the loss in efficiency relative to an optimally chosen set of signature sequences and relative to multiaccess with no spreading. White Gaussian background noise and equal-power synchronous users are assumed. The following receivers are analyzed: a) optimal joint processing, b) single-user matched filtering, c) decorrelation, and d) MMSE linear processing.

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Optimization of code rate and spreading factor for direct-sequence CDMA systems

Cited by 14 publications

References 4 publications

IDMA vs. CDMA: Analysis and Comparison of Two Multiple Access Schemes

IDMA vs. CDMA: Analysis and Comparison of Two Multiple Access Schemes

Multiuser receivers for randomly spread signals: fundamental limits with and without decision-feedback

Spectral efficiency of CDMA with random spreading

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