A New Decoding Scheme for Errorless Codes for Overloaded CDMA With Active User Detection

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Executive Summary

In a binary CDMA system, each user is assigned a binary signature vector. At each symbol interval, each user multiplies its symbol (which is +1 or -1) by its signature and sends it through the channel. At the receiver end, the summation of the transmitted vectors embedded in noise is received (the noise almost always is assumed to be AWGN). In under- or fully-loaded CDMA systems (where the number of users is lower than or equal to the spreading factor), it is easy to show that the optimum signature codes are Hadamard codes which are mutually orthogonal. The optimum receiver in this case is a simple correlator.

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