The most favorable impulsive interference for ternary CDMA

Ternary Code Division Multiple Access (CDMA) with a variable number of non-zero chips per symbol allows to control the transmission impulsiveness, ranging from nonimpulsive signaling (with all chips being non-zero) to a fully impulsive signal (with only one chip per symbol being nonzero). The former corresponds to conventional CDMA while the latter to Impulse-Radio (IR). Recent work showed that the fully impulsive signal maximizes the Average Signal to Interference Ratio (ASIR) in asynchronous multiple user environment. We extend this result to information measures, and show that by adapting the impulsiveness figure (i.e., the number of non zero chips) to the channel conditions, the system can create a favorable interference environment for the other users. In particular, fully impulsive signaling maximizes the Shannon capacity of each user (treating interference from other users as noise). On the other hand, at transmission rates strictly below capacity, less impulsive signaling is better in terms of decoding error probability.