The authors consider the use of a multiple-beam adaptive array (MBAA) in a packet radio system. In an MBAA, a given set of antenna elements is used to form several antenna patterns simultaneously. When it is used in a packet radio system, an MBAA can successfully receive two or more overlapping packets at the same time. Each beam captures a different packet by automatically pointing its pattern toward one packet while nulling other, contending packets. It is shown how an MBAA can be integrated into a single-hop slotted ALOHA packet radio system, and the resulting throughput is analyzed for both finite- and infinite-user populations.>

The statistical performance of using ESPRIT to estimate both the arrival directions and the polarizations of incoming plane waves with a uniform linear array of crossed dipoles is studied. Compact formulae for the mean-squared errors of both direction and polarization estimates are provided for both the case of large data samples and the case of high signal-to-noise ratio. Numerical results are presented to compare the theoretical analysis and the Monte-Carlo simulation results.>

The use of an adaptive antenna array as a means of improving the performance of a slotted ALOHA packet radio network is presented. An adaptive array creates a strong capture effect at a packet radio terminal by automatically steering the receiver antenna pattern toward one packet and nulling other contending packets in a slot. A special code preamble and randomized arrival times within each slot allow the adaptive array to lock onto one packet in each slot. The throughput and delay performance of a network with an adaptive array are computed by applying the standard Markov chain analysis of slotted ALOHA. It is shown that throughput levels comparable to carrier sense multiple access (CSMA) are attainable with an adaptive array without the need for stations to be able to hear each other. The performance depends primarily on the number of adaptive array nulls, the array resolution, and the length of the randomization interval within each slot.>

A new technique is presented for reference signal generation in adaptive arrays, and it is shown how it can be used in a binary FSK communication system. This method consists of encoding the message bit stream at the transmitter to convert it to a first-order Markov source with a transition probability of p>1/2. Then, in the receiver, each detected bit is used to predict the next bit, and the predicted bits are used to generate a reference signal. The performance of an FSK system based on this concept is analyzed, and an experimental system is described. This experimental system demonstrated that the reference signal generation concept is feasible and showed that this technique could be used to protect an FSK communication system from a CW interference signal.>

This paper describes the performance of an adaptive array when used with narrow-band BPSK communication signals; A previous paper [11] described the performance of an adaptive array with a standard BPSK signal when the array bandwidth is several times the signal bandwidth. These earlier results are extended to the case where the array bandwidth is as small as possible, equal to the desired signal symbol rate. To realize such a bandwidth reduction, it is necessary to reshape the BPSK signaling waveform before transmission to prevent intersymbol interference. This is done by passing the BPSK signal through a pulseshaping filter at the transmitter. The performance of the optimal detector for the narrow-band BPSK signal is determined when this detector operates behind an adaptive array that is subjected to CW interference. The bit error probability is obtained as a function of the desired signal and interference powers and arrival angles as well as the array bandwidth.