Abstract. This paper is motivated by the need for fundamental understanding of ultimate limits of bandwidth efficient delivery of higher bit-rates in digital wireless communications and to also begin to look into how these limits might be approached. We examine exploitation of multi-element array (MEA) technology, that is processing the spatial dimension (not just the time dimension) to improve wireless capacities in certain applications. Specifically, we present some basic information theory results that promise great advantages of using MEAs in wireless LANs and building to building wireless communication links. We explore the important case when the channel characteristic is not available at the transmitter but the receiver knows (tracks) the characteristic which is subject to Rayleigh fading. Fixing the overall transmitted power, we express the capacity offered by MEA technology and we see how the capacity scales with increasing SNR for a large but practical number, n, of antenna elements at both transmitter and receiver. We investigate the case of independent Rayleigh faded paths between antenna elements and find that with high probability extraordinary capacity is available. Compared to the baseline n = 1 case, which by Shannon’s classical formula scales as one more bit/cycle for every 3 dB of signal-to-noise ratio (SNR) increase, remarkably with MEAs, the scaling is almost like n more bits/cycle for each 3 dB increase in SNR. To illustrate how great this capacity is, even for small n, take the cases n = 2, 4 and 16 at an average received SNR of 21 dB. For over 99%

Abstract — A linear receiver for direct-sequence spreadspectrum multiple-access communication systems under the aperiodic random sequence model is considered. The receiver consists of the conventional matched filter followed by a tapped delay line with the provision of incorporating the use of antenna arrays. It has the ability of suppressing multipleaccess interference (MAI) and narrowband interference in some weighted proportions, as well as combining multipath components without explicit estimation of any channel conditions. Under some specific simplified channel models, the receiver reduces to the minimum variance distortionless response beamformer, the RAKE receiver, a notch filter, or an MAI suppressor. The interference rejection capability is made possible through a suitable choice of weights in the tapped delay line. The optimal weights can be obtained by straightforward but computationally complex eigenanalysis. In order to reduce the computational complexity, a simple blind adaptive algorithm is also developed. Index Terms—Adaptive signal detection, antenna arrays, codedivision multiaccess, interference suppression, pseudonoise-coded communication. I.

Abstract—Beamforming problem is studied in wireless networks where both transmitters and receivers have linear adaptive antenna arrays. Algorithms are proposed that find antenna array weight vectors at both transmitters and receivers as well as the transmitter powers with one of the following two objectives: 1) to maximize the minimum signal-to-interference-and-noise ratio (SINR) over all receivers and 2) to minimize the sum of the total transmitted power satisfying the SINR requirements at all links. Numerical study is performed to compare the network capacity and the power consumption among systems having different number of antenna array elements in a code division multiple access network. Index Terms—Adaptive antenna arrays, adaptive beamforming, joint transmit and receive beamforming, power control. I.

Recent work on Direct-Sequence (DS) Code Division Multiple Access (CDMA) has shown that blind adaptive interference suppression techniques can be used for reliable demodulation, provided that the timing of the desired signal is known. The blind demodulator has since been used as a building block for a scheme for joint timing acquisition and demodulation. In this paper, we consider a blind adaptive demodulator that uses spatial diversity in the form of an antenna array in addition to the inherent time diversity of the DS signals exploited in previous work. Our results show that, as expected, the use of an antenna array leads to a substantial increase in system capacity, but that the convergence of an adaptive implementation using a stochastic gradient algorithm may be too slow for many applications. On the other hand, the large number of taps in the space-time filter imply that a faster least squares implementation is quite complex. Our results therefore point out the need for...

A taxonomy of space-time signal processing is addressed in terms of architectural and algorithmic classification, and the influence of the propagation channel on the space-time processing. The architecture is classified according to link structure, channel reuse and multiple access scheme. Algorithms are classified into channel estimation methods, TDMA and CDMA receive algorithms and space-time transmit algorithms. Finally, the effects of Doppler spread, delay spread and angle spread on space-time processing is adressed.

Antenna array beamforming and power control have been studied separately to increase the capacity in wireless communication networks. Recently, the two were considered jointly in a system with power control capabilities which uses antenna array at the receiver only or the transmitter only. In this paper we formulate and study the joint beamforming and power control problem in a system with antenna arrays both at the transmitter and the receiver. Two algorithms are proposed for the joint problem. The capacity of the system that has beamforming capabilities at both sides is compared with the system that has one side beamforming capabilities only. The increase in the network capacity is evaluated through a numerical study. 1

In this paper, we consider the problem of blind estimation of the directions of arrival (DOA's) of users' paths in a multipath DS/CDMA channel. Making use of the signal that is sampled at multiple antenna elements and using a subspace based MUSIC-like technique, we show the possibility of DOA estimation using two search methods. The first provides path delays and DOAs simultaneously, and the second provides only DOAs. Knowledge of the chip waveform is used in the first method. It is seen that the two methods exhibit good estimation accuracy, besides being extremely near-far resistant.