Method and apparatus for wireless communications

Abstract

A communication system 20 uses TDMA techniques to distinguish intended recipients of a communication signal 26 from one another, and direct sequence spread spectrum (DSSS) techniques to encode and distinguish diverse parallel substreams 70 and 74 of each user's data stream. Parallel unspread substreams 70 are spread using cyclic variations of a common spreading code 38 . In one embodiment, the common spreading code 38 is chosen for low aperiodic autocorrelation sidelobes and a substantially flat spectral analysis. In another embodiment the common spreading code 38 is chosen for low periodic autocorrelation sidelobes and a substantially flat spectral analysis. In one embodiment, the use of cyclic variations of the spreading code 38 along with a cyclic prefix 114 enables the mathematical communicative matrix multiplication property, thereby permitting equalization for multipath to occur following or in conjunction with despreading.

1 . A method of operating a spread-spectrum-based communication system to efficiently utilize spectrum in the presence of multipath, comprising: 
 dividing a stream of data-conveying symbols into a plurality of unspread substreams at a transmitter;    generating a common spreading code at said transmitter;    spreading, at said transmitter, each of said unspread substreams using said common spreading code to form a plurality of spread substreams;    combining, at said transmitter, said plurality of spread substreams to form a composite signal;    wirelessly transmitting, from said transmitter, a communication signal formed from said composite signal;    receiving said communication signal at a receiver; and    despreading said communication signal at said receiver using a mismatched filter to generate a baseband signal wherein,    said spreading activity comprises temporally offsetting application of said common spreading code to said plurality of unspread substreams so that said spread substreams correspond to said unspread streams modulated by cyclic variations of said common code.    
     
     
         2 . A method of operating a spread-spectrum-based communication system as claimed in  claim 1  additionally comprising: 
 performing a first time-frequency domain transformation on said unspread substreams at said transmitter prior to said spreading activity; and    performing a second time-frequency domain transformation on said communication signal at said receiver prior to said despreading activity.    
     
     
         3 . A spread-spectrum-based communication system that efficiently utilizes spectrum in the presence of multipath, said communication system comprising: 
 a demultiplexer for dividing a stream of data-conveying symbols into a plurality of unspread substreams;    a spreading section coupled to said demultiplexer and configured to generate spread substreams from said plurality of unspread substreams, said spreading section being configured so that said spread substreams correspond to respective ones of said unspread substreams modulated by cyclic variations of a common spreading code;    a combining section coupled to said spreading section and configured to form a composite signal in response to said spread substreams;    a transmission section coupled to said combining section and configured to wirelessly transmit a communication signal formed from said composite signal;    a receiving section configured to receive said communication signal; and    a despreading section coupled to said receiving section, said despreading section being configured to generate a baseband signal in response to said communication signal wherein,    said communication system additionally comprises a first time-frequency domain transformation section coupled between said demultiplexer and said spreading section;    said communication system additionally comprises a second time-frequency domain transformation section coupled between said receiver and said despreading section; and    said despreading section comprises a frequency domain equalizer to compensate for multipath.    
     
     
         4 . A time division multiple access (TDMA), spread-spectrum-based communication system which efficiently utilizes spectrum in the presence of multipath, said communication system comprising: 
 a plurality of transmitters configured to wirelessly transmit TDMA communication signals which convey messages in adjacent radio coverage areas in accordance with a frequency reuse pattern substantially equal to one;    a plurality of receivers located in said adjacent radio coverage areas wherein each receiver is configured to detect ones of said messages intended for said each receiver by identifying time slots assigned to said each receiver;    wherein each of said transmitters comprises: 
 a demultiplexer for dividing a TDMA stream of data-conveying symbols into a plurality of unspread substreams;  
 a spreading section coupled to said demultiplexer and configured to generate spread substreams from said plurality of unspread substreams, said spreading section being configured so that said spread substreams correspond to respective ones of said unspread substreams modulated by cyclic variations of a common spreading code;  
 a combining section coupled to said spreading section and configured to form a composite signal in response to said spread substreams;  
   a transmission section coupled to said combining section and configured to transmit one of said TDMA communication signals formed from said composite signal; and    wherein each of said receivers comprises: 
 a receiving section configured to receive one of said TDMA communication signals; and  
 a despreading section coupled to said receiving section, said despreading section being configured to generate a baseband signal in response to said TDMA communication signal.