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In CDMA 2000 we use 64 bit walsh code because of its standard as well as to encrypt the data so that of security point of view
Posted by HamidAliKhan
The present invention relates to the art of wireless telecommunication networks. It finds particular application in conjunction with third generation (3G) wireless systems using code division multiple access (CDMA) technology, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
Walsh codes, spreading codes, channelization codes and the like are generally known in the art of wireless telecommunication networks. In particular, Walsh codes and/or Walsh functions are based on the Walsh-Hadamard matrices. However, for simplicity herein, the terms Walsh code and/or Walsh function are used to refer generally to any similarly employed spreading codes/functions, channelization codes/functions, etc. In CDMA, Walsh functions are used in a forward direction to organize network traffic over an air interface into different channels that can be isolated and decoded by target mobiles, e.g., wireless telephones, wireless personal digital assistants (PDAs) or other wireless devices. The forward or downlink direction refers to a transmitting direction from a base station to a mobile station.
At any given time for the same sector/carrier within a given cell site of a wireless telecommunications network, all the Walsh codes in use have to be mutually orthogonal with each other in order to properly organize the network traffic without dropped calls, interference or cross-talk between the different channels. This restriction was not particularly problematic for second generation wireless systems using CDMA. Second generation wireless generally encompasses the so called digital personal communications service (PCS). In any event, 2nd generation systems using CDMA only employ Walsh codes of a single size or bit length and all the codes used are guaranteed to be orthogonal to one another. For example, 64 Walsh codes each 64 bits in length are used in the typical implementation of 2nd generation systems.
As opposed to the 2nd generation, 3G wireless systems employing CDMA use Walsh codes of varying sizes or bit lengths. For example, traffic such as voice calls typically continue to use 64-bit Walsh codes. However, in 3G, some voice calls or traffic may use 128-bit Walsh codes. Similarly, for high-speed data traffic (e.g., wireless Internet access), 3G wireless makes available a variety of Walsh codes with shorter lengths, e.g., 32, 16, 8 and 4 bit lengths. Accordingly, unlike the 2nd generation which uses uniformly sized Walsh codes, Walsh code allocation in 3G CDMA wireless is not trivial. Walsh code allocation refers to the selection and/or assignment of Walsh codes for the different channels of cell traffic. Generally, it is preferable to employ shorter bit length Walsh codes for higher speed traffic.
Posted by GLADIATOR
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