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Asynchronous CDMA systems with random spreading. Part I : fundamental limits

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dc.contributor.authorCottatellucci, L.
dc.contributor.authorMuller, R.R.
dc.contributor.authorDebbah, M.
dc.date.issued2010
dc.description.abstractSpectral efficiency for asynchronous code division multiple access (CDMA) with random spreading is calculated in the large system limit allowing for arbitrary chip waveforms and frequency-flat fading. Signal-to-interference and noise ratios (SINRs) for suboptimal receivers, such as the linear minimum mean square error (MMSE) detectors, are derived. The approach is general and optionally allows even for statistics obtained by undersampling the received signal. All performance measures are given as a function of the chip waveform and the delay distribution of the users in the large system limit. It turns out that synchronizing users on a chip level impairs performance for all chip waveforms with bandwidth greater than the Nyquist bandwidth, e.g., positive roll-off factors. For example, with the pulse shaping demanded in the UMTS standard, user synchronization reduces spectral efficiency up to 12% at 10 dB normalized signal-to-noise ratio. The benefits of asynchronism stem from the finding that the excess bandwidth of chip waveforms actually spans additional dimensions in signal space, if and only if the users are desynchronized at chip-level. The analysis of linear MMSE detectors shows that the limiting interference effects can be decoupled both in the user domain and in the frequency domain such that the concept of effective interference spectral density arises. This generalizes and refines Tse and Hanly's concept of effective interference. In Part II, the analysis is extended to any linear detector that admits a representation as multistage detector and guidelines for the design of low complexity multistage detectors with universal weights are provided.
dc.identifier.citationIEEE Transactions on Information Theory, 2010; 56(4):1477-1497
dc.identifier.doi10.1109/TIT.2010.2040890
dc.identifier.issn0018-9448
dc.identifier.issn1557-9654
dc.identifier.urihttps://hdl.handle.net/1959.8/94990
dc.language.isoen
dc.publisherIEEE
dc.rightsCopyright 2010 IEEE
dc.source.urihttps://doi.org/10.1109/TIT.2010.2040890
dc.subjectcode division multiple access
dc.subjectfading
dc.subjectleast mean squares methods
dc.subjectrandom sequences
dc.titleAsynchronous CDMA systems with random spreading. Part I : fundamental limits
dc.typeJournal article
pubs.publication-statusPublished
ror.fileinfo12143239620001831 13143235620001831 9915910598001831_53108835690001831.pdf
ror.mmsid9915910598001831

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