Results 1  10
of
31
Spectral Efficiency of CDMA with Random Spreading
 IEEE TRANS. INFORM. THEORY
, 1999
"... 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 per ..."
Abstract

Cited by 313 (23 self)
 Add to MetaCart
(Show Context)
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 signaltonoise 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 equalpower synchronous users are assumed. The following receivers are analyzed: a) optimal joint processing, b) singleuser matched filtering, c) decorrelation, and d) MMSE linear processing.
Large System Performance of Linear Multiuser Receivers in Multipath Fading Channels
 IEEE Trans. Inform. Theory
, 2000
"... A linear multiuser receiver for a particular user in a codedivision multipleaccess (CDMA) network gains potential benefits from knowledge of the channels of all users in the system. In fast multipath fading environments we cannot assume that the channel estimates are perfect and the inevitable cha ..."
Abstract

Cited by 102 (6 self)
 Add to MetaCart
A linear multiuser receiver for a particular user in a codedivision multipleaccess (CDMA) network gains potential benefits from knowledge of the channels of all users in the system. In fast multipath fading environments we cannot assume that the channel estimates are perfect and the inevitable channel estimation errors will limit this potential gain. In this paper, we study the impact of channel estimation errors on the performance of linear multiuser receivers, as well as the channel estimation problem itself. Of particular interest are the scalability properties of the channel and data estimation algorithms: what happens to the performance as the system bandwidth and the number of users (and hence channels to estimate) grows? Our main results involve asymptotic expressions for the signaltointerference ratio of linear multiuser receivers in the limit of large processing gain, with the number of users divided by the processing gain held constant. We employ a random model for the spreading sequences and the limiting signaltointerference ratio expressions are independent of the actual signature sequences, depending only on the system loading and the channel statistics: background noise power, energy profile of resolvable multipaths, and channel coherence time. The effect of channel uncertainty on the performance of multiuser receivers is succinctly captured by the notion of effective interference.
Linear Multiuser Receivers in Random Environments
 IEEE Trans. Inform. Theory
, 2000
"... We study the signaltointerference (SIR) performance of linear multiuser receivers in random environments, where signals from the users arrive in "random directions." Such random environment may arise in a DSCDMA system with random signature sequences, or in a system with antenna diversi ..."
Abstract

Cited by 70 (2 self)
 Add to MetaCart
(Show Context)
We study the signaltointerference (SIR) performance of linear multiuser receivers in random environments, where signals from the users arrive in "random directions." Such random environment may arise in a DSCDMA system with random signature sequences, or in a system with antenna diversity where the randomness is due to channel fading. Assuming that such random directions can be tracked by the receiver, the resulting SIR performance is a function of the directions and therefore also random. We study the asymptotic distribution of this random performance in the regime where both the number of users and the number of degrees of freedom in the system are large, but keeping their ratio fixed. Our results show that for both the decorrelator and the minimum meansquare error (MMSE) receiver, the variance of the SIR distribution decreases like 1 , and the SIR distribution is asymptotically Gaussian. We compute closedform expressions for the asymptotic means and variances for both receivers. Simulation results are presented to verify the accuracy of the asymptotic results for finitesized systems.
Design and Analysis of LowComplexity Interference Mitigation on Vector Channels
, 2001
"... Linear multiuser detectors for vector channels with crosstalk are approximated by weighted matrix polynomials. The weight optimization problem is overcome using convergence results from random matrix theory. The results are also extended to receivers with subsequent successive decoding. ..."
Abstract

Cited by 41 (14 self)
 Add to MetaCart
Linear multiuser detectors for vector channels with crosstalk are approximated by weighted matrix polynomials. The weight optimization problem is overcome using convergence results from random matrix theory. The results are also extended to receivers with subsequent successive decoding.
On the distribution of SINR for the MMSE MIMO receiver and performance analysis
 IEEE Trans. Inform. Theory
, 2006
"... Abstract — This paper studies the statistical distribution of the signaltointerferenceplusnoise ratio (SINR) for the minimum mean square error (MMSE) receiver in multipleinputmultipleoutput (MIMO) wireless communications. The channel model is assumed to be (transmit) correlated Rayleigh flatf ..."
Abstract

Cited by 33 (6 self)
 Add to MetaCart
(Show Context)
Abstract — This paper studies the statistical distribution of the signaltointerferenceplusnoise ratio (SINR) for the minimum mean square error (MMSE) receiver in multipleinputmultipleoutput (MIMO) wireless communications. The channel model is assumed to be (transmit) correlated Rayleigh flatfading with unequal powers. The SINR can be decomposed into two independent random variables: SINR = SINR ZF + T, where SINR ZF corresponds to the SINR for a zeroforcing (ZF) receiver and has an exact Gamma distribution. This paper focuses on characterizing the statistical properties of T using the results from random matrix theory. First three asymptotic moments of T are derived for uncorrelated channels and channels with equicorrelations. For general correlated channels, some limiting upperbounds for the first three moments are also provided. For uncorrelated channels and correlated channels satisfying certain conditions, it is proved that T converges to a Normal random variable. A Gamma distribution and a generalized Gamma distribution are proposed as approximations to the finite sample distribution of T. Simulations suggest that these approximate distributions can be used to accurately estimate the probability of errors even for very small dimensions (e.g., 2 transmit antennas). Index Terms — Multipleinputmultipleoutput system, minimum mean square error receiver, signaltointerferenceplusnoise ratio, channel correlation, random matrix, asymptotic distributions, Gamma approximation, error probability. I.
MMSE Analysis of Certain Large Isometric Random Precoded Systems
 IEEE Transactions on Information Theory, Volume: 49 Issue: 5, Page(s): 1293 1311
, 2001
"... Linear Precoding consists in multiplying by a N K matrix a Kdimensional vector obtained by serial to parallel conversion of a symbol sequence to be transmitted. In this paper, we analyse the performance of MMSE receivers for certain large random isometric precoded systems on fading channels. Using ..."
Abstract

Cited by 24 (11 self)
 Add to MetaCart
Linear Precoding consists in multiplying by a N K matrix a Kdimensional vector obtained by serial to parallel conversion of a symbol sequence to be transmitted. In this paper, we analyse the performance of MMSE receivers for certain large random isometric precoded systems on fading channels. Using new tools, borrowed from the socalled Free Probability Theory, it can be shown that the Signal to Interference plus Noise Ratio at the equalizer output converges almost surely to a deterministic value depending on the probability distribution of the channel coefficients when N 1. These asymptotic results are used to optimally balance the redundancy introduced between Linear Precoding and classical Convolutional Coding, while preserving a simple MMSE equalization scheme at the receiver.
Optimum Asymptotic Multiuser Efficiency of Randomly Spread CDMA
, 2000
"... This paper analyzes the high SNR performance of optimum multiuser detectors for synchronous directsequence spread spectrum with random spreading in an additive white Gaussian noise channel. Under very general conditions on the received powers, we show that the asymptotic efficiency of a Kuser syst ..."
Abstract

Cited by 19 (2 self)
 Add to MetaCart
This paper analyzes the high SNR performance of optimum multiuser detectors for synchronous directsequence spread spectrum with random spreading in an additive white Gaussian noise channel. Under very general conditions on the received powers, we show that the asymptotic efficiency of a Kuser system with spreading gain N converges to 1 almost surely as K ! 1, and K=N is kept equal to an arbitrary nonzero constant. Therefore, the asymptotic behavior of the minimum biterrorrate is equivalent to that of a singleuser system. Keywords: Multiuser Detection, Asymptotic Efficiency, CDMA, Spread Spectrum, Optimum Multiuser Detection. David Tse is with the Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, dtse@eecs.berkeley.edu. Sergio Verd'u is with the Department of Electrical Engineering, Princeton University, verdu@princeton.edu 2 I Introduction This paper is concerned with the analysis of the capabilities of optimum multiuser detection...
On the Average Near–Far Resistance for MMSE Detection of Direct Sequence CDMA Signals with Random Spreading
, 1999
"... The performance of a near–farresistant, finitecomplexity, minimum mean squared error (MMSE) linear detector for demodulating direct sequence (DS) codedivision multiple access (CDMA) signals is studied, assuming that the users are assigned random signature sequences. We obtain tight upper and lowe ..."
Abstract

Cited by 18 (1 self)
 Add to MetaCart
The performance of a near–farresistant, finitecomplexity, minimum mean squared error (MMSE) linear detector for demodulating direct sequence (DS) codedivision multiple access (CDMA) signals is studied, assuming that the users are assigned random signature sequences. We obtain tight upper and lower bounds on the expected near–far resistance of the MMSE detector, averaged over signature sequences and delays, as a function of the processing gain and the number of users. Since the MMSE detector is optimally near–farresistant, these bounds apply to any multiuser detector that uses the same observation interval and sampling rate. The lower bound on near–far resistance implies that, even without power control, linear multiuser detection provides near–farresistant performance for a number of users that grows linearly with the processing gain.
Capacity Of Cellular CDMA Systems Applying Interference Cancellation And Channel Coding
 In Proc. of Communication Theory Mini Conference (CTMC) at IEEE Globecom
, 1997
"... Capacity of cellular CDMA applying interference cancellation is calculated for the uplink (reverse link) in the presence of AWGN. Both conventional demodulation and decorrelation are investigated as preprocessing unit to interference cancellation. Taking into account the path loss in a cellular syst ..."
Abstract

Cited by 13 (5 self)
 Add to MetaCart
(Show Context)
Capacity of cellular CDMA applying interference cancellation is calculated for the uplink (reverse link) in the presence of AWGN. Both conventional demodulation and decorrelation are investigated as preprocessing unit to interference cancellation. Taking into account the path loss in a cellular system, CDMA applying interference cancellation shows a substantial difference in power efficiency, whether receive or transmit power is considered. This is in contrast to orthogonal multipleaccess techniques, like TDMA and FDMA. If the comparison is based on transmit power, which is more reasonable, CDMA outperforms orthogonal multipleaccess schemes. 1. INTRODUCTION Codedivision multipleaccess (CDMA) is a promising multiple access technique for future mobile communication systems. Its main advantages are firstly a wideband transmitter signal reducing the adverse effects of frequencyselective fading, and secondly the fact, that in cellular systems the same carrier frequency may be ...
Performance of Linear Multiuser Receivers in Random Environments
, 1998
"... We study the SIR performance of linear multiuser receivers in random environments, where signals from the users arrive in "random directions". Such random environment may arise in a DSCDMA system with random signature sequences, or in a system with antenna diversity where the randomness i ..."
Abstract

Cited by 12 (2 self)
 Add to MetaCart
We study the SIR performance of linear multiuser receivers in random environments, where signals from the users arrive in "random directions". Such random environment may arise in a DSCDMA system with random signature sequences, or in a system with antenna diversity where the randomness is due to channel fading. Assuming that such random directions can be tracked by the receiver, the resulting SIR performance is a function of the directions and therefore also random. We study the asymptotic distribution of this random performance in the regime where both the number of users M and the number of degrees of freedom L in the system are large, but keeping their ratio fixed. Our results show that for both the decorrelator and the MMSE receiver, the variance of the SIR distribution decreases like 1=L, and the SIR distribution is asymptotically Gaussian. We compute closedform expressions for the asymptotic means and variances for both receivers. Simulation results are presented to verify the...