Method and apparatus for reducing amplitude variations and interference in communication signals, such as in wireless communication signals employing inserted pilot symbols

Abstract

Several methods and corresponding apparatus reduce peak to average power in signals transmitted in a wireless communications system, particularly with respect to pilot symbols transmitted from a base station to several user stations. A large peak to average amplitude of inserted pilot symbols has been found to result from a common sign chip position that exists in orthogonal codes, such as Walsh codes. In a first embodiment, the Walsh codes are multiplied by a random value of ±1. Under a second embodiment, the common sign chip position is eliminated in each Walsh code. The user station then inserts the missing chip position to regain orthogonality. In a third embodiment, the base station transmits pilot symbols, on a separate pilot channel, in only symbol positions that user stations expect to find pilot symbols. Under a fourth embodiment, each Walsh code is randomly shifted.

What is claimed is:  
     
         1 . In a communication system having a base station and a plurality of user stations that exchange communication signals with the base station, a method for reducing transmission signal power of transmitted communication signals, the method comprising: 
 receiving channel data for transmission on a plurality of channels, wherein the channel data includes pilot symbol data;    combining orthogonal codes with the received channel data, wherein each orthogonal code has at least one common chip position, and wherein the common chip position has a same value for each orthogonal code; and    before transmitting the channel data combined with the orthogonal codes, altering the common chip position of at least one of the orthogonal codes to reduce a combined amplitude resulting from simultaneous transmission and addition of the common chip position for the plurality of channels.