Uncorrelated PN sequences generator for spreading codes in CDMA systems

In a CDMA system each user modulates his data signal (typically with few kbits/s) onto a wideband spreading waveform. The target receiver correlates its input with the same spreading function, suitably synchronised, to recover the signal. For this, each transmit-receive pair employs a unique spreading code, that must be uncorrelated with the codes used by other transmit-receive pairs. In this way transmission from unwanted users and also any interference (including the intermodulation products) are rejected by the despreading process in the receiver, and may be modelled as Gaussian noise. A nonlinear pseudonoise (PN) generator is proposed that can produce a great number of uncorrelated random sequences with good auto- and cross-correlation properties. Each of these shows a very good behaviour, as is expected for this type of sequence, that is, a high unpredictability and very good statistical properties. Moreover, it shows itself to be advantageous for high speed generation of PN codes, with low cost, low power consumption, small volume and simplicity of implementation, and exhibits a structural parallelism useful for VLSI implementations. All these features makes it potentially suitable for the generation of independent spreading pseudorandom codes in CDMA systems