Multi-access Interference Research Articles

Packet throughput in slotted ALOHA DS/SSMA radio systems with random signature sequences

Packet throughput figures are obtained for direct sequence spread spectrum multiple access (DS/SSMA) slotted ALOHA radio systems where all users employ random signature sequences from bit-to-bit within all transmitted packets. These calculations use an improved Gaussian approximation technique which gives accurate bit error probabilities and also incorporates the effect of bit-to-bit error dependence within each packet in the multiaccess interference environment. Numerical results are given for packets which employ varying amounts of block error control, and a comparison is made with results obtained by other methods which ignore the effects of bit-to-bit error dependence within each packet in the multiaccess interference environment. Numerical results are given for packets which employ varying amount of block error control, and a comparison is made with results obtained by other methods which ignore the effects of bit-to-bit error and/or employ less-accurate Gaussian approximations to the probability of data bit error. Maximum throughput per unit bandwidth figures are calculated which compare favorably to similar figures for narrowband signaling techniques. >

Multiple hops/symbol fast frequency-hopping spread spectrum multiple access with coding for indoor radio

The paper is concerned with the bit error rate (BER) performance of multiple hops/ symbol fast-frequency-hopped spread-spectrum multiple-access (FFH-SSMA) systems operating through an indoor radio multipath Rayleigh fading channel. M-ary frequency-shift-keying (MFSK) modulation with noncoherent square-law envelope demodulation and Reed-Solomon (RS) coding is considered. Results obtained in this study show that an FFH-SSMA system is not sensitive to the changes in the number of paths. Employing RS coding with an increased number M of MFSK signals yields a significant improvement in BER performance. Assuming a given system bandwidth, using a single hop per symbol is the best solution when the multiaccess interference can be large. Using several hops per symbol is more advantageous when the multiaccess interference is small.

Application of an analytical model to evaluate storage structures

The File Design Analyzer is a software package which evaluates well-known data base storage structures and access methods in terms of secondary storage processing time and storage overhead required to service a set of user applications. It implements a first-order analytical model to specifically evaluate sequential, indexed sequential, direct access, and inverted multilist storage structures. Interaction with the package is available in conversational mode, enabling the experienced analyst to conduct on-line sensitivity analysis. The paper describes three extensions which converted an abstract conceptual model into a practical tool for evaluation of existing or proposed data base designs: batched transactions, multi-access interference due to shared secondary storage, and analysis of variable record size. A case study from a real system illustrates the potential of the File Design Analyzer to provide insight regarding the optimal choice of physical parameters within a specified storage structure and to effectively compare alternative storage structures for a particular set of applications.