The performance of single burst-error-correcting (BEC) codes used over bursty channels is evaluated. The channel is represented by the Gilbert-Elliott (1960, 1963) model, which has been used by numerous authors to evaluate the performance of random-error-correcting (REC) codes over bursty channels. Recursive expressions are derived, which are used in evaluating the probability of a codeword error. These expressions and an approximate closed-form expression are applied to the performance of a single (23,12) BEC code.

This paper presents a concept under development, that of dynamically coloring the spectrum of a pseudorandom spreading code in order to aid slow rate data communication in a very poor channel. The method seems to hold promise for some difficult industrial communications problems, especially for wireless random access communications in time varying noisy channels that are difficult to effectively model and are resistant to conventional approaches.

The performance of a countermeasure technique in the presence of the optimal follower multitone jammer is evaluated for frequency-hopped spread spectrum (FHSS) communications. It is shown that, with a certain probability, the optimal jammer will have dual tones in a frequency channel.

A method for optical signaling is investigated that allows multiple transmitters to simultaneously use the same noncoherent receiving aperture. The signaling is based on the properties of laser speckle interference patterns. Capacity for an interference limited system is explored for a correlation receiver based on random coding. A synchronization scheme is presented that allows a practical implementation of the proposed optical multiple access system.>

A countermeasure technique to a follower tone-jammer is evaluated for frequency-hopped spread spectrum communications. This technique utilizes randomized decisions by the transmitter and the receiver to lure the jammer into helping the communicator's performance part of the time. It is shown that the proposed technique reduces the bit error rate of the system.>

We present three unconventional approaches to keying variable management. The first approach is based on using a public key cryptosystem (PKC) that is breakable in short, but on average less, time than it takes to set up an ultrawide bandwidth modem that is then used to transport a keying variable for a classical cryptosystem. The second concept proposes using the characteristics of an urban UHF radio channel, determined by mutual sounding, as the cryptovariable. The third concept encourages research into ill-conditioned problems as potentially fruitful ground for PKCs not based on finite field arithmetic.>

Decoding that uses soft-decision information but with multiple low-complexity decoders are investigated. These decoders correct only errors and erasures. The structure of the receiver consists of a bank of z demodulators followed by errors- and erasures-correcting decoders operating in parallel. Each demodulator has a threshold for determining when to erase a given symbol. We assign a cost f(/spl theta/) to the noise for causing an erasure when the receiver uses a particular threshold /spl theta/ and a (larger) cost f(/spl theta.>

We evaluate the down-link (base-to-mobile) capacity of a frequency-hopped TDMA system using a theoretical development of outage probability. Expressions for outage probability are provided considering voice activity, antenna diversity and Reed-Solomon coding. The system capacity is evaluated with and without power control. Down-link capacity is compared with up-link capacity. The effect of increasing system bandwidth on capacity is analyzed. Finally, the issue of calculating capacity under the assumption of connecting mobiles to the closest base station instead of the strongest base station is examined.>

A countermeasure to a partial-band follower jammer is proposed for frequency-hopped spread-spectrum communications. This technique randomizes the transmission technique used by the transmitter (and receiver). Either the information is carried by M tones which are transmitted in a frequency slot, or by M frequency slots which contain signal energy. As a counter-countermeasures, the jammer randomizes between jamming the same frequency slot being used by the communicator, or jamming a subset of the slots not being used by the communicator. The performance for randomized strategies for the communicator and jammer is investigated. It is shown that the proposed technique enhances the system's performance.>

The correcting properties of concatenated codes with parallel decoding over an additive channel are investigated. The ith inner decoder's output is a codeword if the Euclidean distance between the received vector and some codeword is less than Delta /sub i/ and an erasure otherwise. The outer decoders correct errors and erasures. The error-correcting capability, which is taken to be the minimum length of any noise vector that can cause an error, is obtained for a bank of z inner and outer decoders as a function of the thresholds used. The set of thresholds that maximize the error-correcting capability is also found. It is shown that for a small number of branches, the error-correcting capability is nearly as large as any decoder.>