Motorola Corporation

Marc David Brack

Scott David Blanchard

Kenneth Solomon Wreschner

Terry Winningham

Douglas Paul Dobson

The present invention describes a communications system that utilizes frequency division multiple access (FDMA), code division multiple access (CDMA), and time division multiple access (TDMA) techniques for providing efficient use of frequency spectrum while supporting a large number of transmitters/users (2-6). Many users of the communications system share a common frequency band, but each transmit their respective message bursts (50) at different and specific times via a TDMA technique. To facilitate synchronization of the TDMA technique, each transmitter of the system is synchronized to a common timing reference (1) thereby abating the need to maintain synchronization between the transmitters (2-6) and receivers (8-12) of the system. Each TDMA message is then transmitted via a spread spectrum technique by multiplying (82) the message burst to be transmitted by a pseudo-random sequence of ones and zeroes (84) and transmitting such spread spectrum message burst for reception by one or more receivers within the system.

System and method for multiple access short message communications

An asynchronous communications receiver rapidly despreads and demodulating a short, low duty cycle CDMA burst signal. The receiver includes a multichannel despreader (20) for generating a plurality of despread signals (21) corresponding to timing offsets of a spreading code. The plurality of despread signals are respectively supplied to a plurality of demodulators (22) for demodulating each despread signal and for respectively generating a plurality of soft decisions for each demodulated bit values whereby each soft decision is proportional to the quality of the received signal. The plurality of soft decisions are supplied to both a first input of a plurality of multipliers (23) and to a plurality of inputs of a selector (28). The selector processes the soft decisions from each of the demodulators and generates a message indicator (29) when a message is present. The selector also generates a plurality of weights (W1-WN) corresponding to each of the plurality of soft decisions and applies these weights to a second input of the plurality of multipliers. The multipliers multiply the soft decision by its respective weight as supplied from the selector to generate output scaled signals. Finally, a combiner (30) sums the scaled signals to provide an output bit value for applying to a message extractor (32) which generates the actual received digital message.

Apparatus for despreading and demodulating a burst CDMA signal

A receiver performs rapid adaptive interference canceling for use in despreading multiple CDMA channels sharing the same RF front end. The receiver includes a buffer (22) for providing for overlapping time samples and rate adaptation, a windowing function (24) for improving interference rejection capability and a FFT (26) for calculating the input power spectrum. The receiver further includes a circuit (28, 30) to whiten the input power spectrum. The whitened power spectrum is multiplied (32) against the frequency domain version of different spreading sequences and the inverse FFT (40) of the product is performed. The output of this inverse FFT is buffered (44) to provide multiple despread output channels, with a plurality of code phases for further processing.

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Chandler, AZ, United States of America

Marc David Brack