Showing papers by "Qualcomm published in 1987"

Spread spectrum multiple access communication using satellite or terrestrial repeaters

Abstract: A multiple access, spread spectrum communication system and method for providing high capacity communications to, from, or between a plurality of system users, using code-division-spread-spectrum communication signals. The communication system uses means for providing marginal isolation between user communication signals. The marginal isolation is provided by generating simultaneous multiple steerable beams; using an omni-directional antenna with polarization enhancement; using power control devices to adjust the output power for user generated communication signals either in response to their input activity level, or in accordance with a minimum allowable power for maintaining a communication link. The communication system can also employ a means for transmitting a predetermined pilot chip sequence contiguous with the code-division-spread-spectrum communication signals. In further embodiments the communication system employs a plurality of user terminals linked to each other or to other services through one or more terrestrial or satellite repeaters. Multiple satellite repeaters are operable in a new communication mode to obtain further gains in signal isolation.

On the performance evaluation of trellis codes

Abstract: Generating function techniques for analyzing the error event and the bit-error probabilities for trellis codes are considered. The conventional state diagram approach for linear codes where the number of states is equal to the number of trellis states cannot be applied directly to arbitrary trellis codes, and instead, a state diagram where the number of states is equal to the square of the number of trellis states must be used. It is shown that for an interesting class of trellis codes a modified generating function can be defined for which the number of states {\em is equal to} the number of trellis states. The class of codes considered includes trellis codes of rate R=(n-1)/n based upon set partitioning whenever the first partition breaks the signal constellation into two subsets which have the same "configuration matrix," i.e., the same ordered set of mutual distances. The complexity of calculating this modified generating function is the same as for the ordinary generating function of a convolutional code with the same number of trellis states. Bounds on the performance of some interesting codes are given based upon this method.

Optimal Performance of Coded Interleaved PSK Modulation in Slowly Varying Rician Fading

Abstract: It is shown that in direct line-of-sight communications multiple reflections which give rise to Rician amplitude fading statistics need not degrade performance (compared to the case of specular component only), provided the fading is slow compared to several bit times and sufficient interleaving with powerful low rate coding is employed. Theoretical bounds as well as simulation results with practical codes are presented to support this conclusion.