Increasing User Capacity by Interference Avoidance and Intentional Asynchrony in CDMA Systems

Hombs, B.; Lehnert, J.S.

doi:10.1109/tit.2008.917677

Cited by 2 publications

(4 citation statements)

References 17 publications

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“…where the noise vector is Gaussian with zero-mean and covariance matrix is given by (109) and is given by (27). The identity follows directly from (108).…”

Section: Appendix I Proof Of Theoremmentioning

confidence: 99%

“…There has also been a number of works in the study of symbol-asynchronous CDMA systems [23]- [27]. These works consider the case where each user is assigned a single pulse (a single signature sequence) in each symbol period which may ( [23], [24], [26]) or may not be ( [25], [27]) time-limited to each symbol period.…”

mentioning

confidence: 99%

“…These works consider the case where each user is assigned a single pulse (a single signature sequence) in each symbol period which may ( [23], [24], [26]) or may not be ( [25], [27]) time-limited to each symbol period. Rather than studying an explicit characterization of the entire capacity region, these works look at the degradation in the sum capacity due to asynchronity [23] or the asymptotic signal-to-interference ratio (SIR) at the detector output [24], [25] as well as some system-wide quantity such as the total squared asynchronous correlation [26] or the total number of users that may be supported at a given SIR [27].…”

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confidence: 99%

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Capacity Region of the Asynchronous Gaussian Vector Multiple-Access Channel

Chong

Motani

2013

IEEE Trans. Inform. Theory

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In this paper, we derive explicit expressions for the capacity region of the two-user symbol-asynchronous Gaussian vector multiple-access channel. Verdú considered the case where each user linearly modulates a fixed waveform in each symbol period, where the symbol periods for the users are not perfectly aligned at the receiver. He derived explicit capacity region expressions for the case where the transmitters have knowledge of the mutual offset and also for the case where the transmitters have no knowledge of the mutual offset. In this paper, we extend Verdú's results to allow each user to linearly modulate a set of orthonormal waveforms, instead of a single waveform, in each symbol period and with no restrictions imposed on the waveforms. We consider group power constraints, which include individual sum power constraints, as orthonormal waveforms assigned to each user may come from different frequency bands with different power constraints. Similar to the case where each user is allowed to linearly modulate only a single waveform, our results hold regardless of whether or not the transmitters are frame synchronous. In addition, we present some results that are necessary to numerically compute the capacity region expressions with general purpose convex optimization algorithms. Next, we simplify the capacity region expression when there are only individual sum power constraints and when the transmitters know the mutual offset. We also prove a sufficient condition for a similar simplification to hold when the transmitters have no knowledge of the mutual offset. Finally, we consider a specialized algorithm to numerically compute the simplified capacity region expression when the transmitters know the mutual offset.

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“…where the noise vector is Gaussian with zero-mean and covariance matrix is given by (109) and is given by (27). The identity follows directly from (108).…”

Section: Appendix I Proof Of Theoremmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Capacity Region of the Asynchronous Gaussian Vector Multiple-Access Channel

Chong

Motani

2013

IEEE Trans. Inform. Theory

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“…In [61] the number of users that can be supported at a given signal-to-interference ratio in asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems was examined. It was shown that for many chip waveforms the user capacity for asynchronous systems is larger than for optimally designed synchronous systems.…”

Section: Asynchrony In Cdma Systemsmentioning

confidence: 99%

Utilizing Spectrum Efficiently (USE)

Lehnert¹,

Shea²,

Shroff³

et al. 2011

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Increasing User Capacity by Interference Avoidance and Intentional Asynchrony in CDMA Systems

Cited by 2 publications

References 17 publications

Capacity Region of the Asynchronous Gaussian Vector Multiple-Access Channel

Capacity Region of the Asynchronous Gaussian Vector Multiple-Access Channel

Utilizing Spectrum Efficiently (USE)

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