Managing the Degree of Impulsiveness of Other Cell Interference

We develop mechanisms for reducing the effect of interference between un-synchronized users by means of controlling the degree of impulsiveness of their interference signals. Our analysis assumes spread-spectrum multiple-access in the form of ternary (0,+1,-1) CDMA signaling. The interference statistics of this signaling and in particular its degree of impulsiveness, can be parameterized while keeping the desired de-spread signal fixed. We find the pairs of random spreading patterns of interferer and user which minimize the bit error rate (BER) at the user, as a function of the signal/interference-to-noise ratio matrix. At low SINRs high degree of impulsiveness (single active chip per spreading sequence) minimizes the BER, while at high SINRs low degree of impulsiveness is better. We then extend our analysis to coded systems with channel state information at the receiver, and show that the same spreading pairs maximize the exponential effective SNR mapping (EESM) criterion at the decoder. Finally, we propose distributed protocols which try to approach the optimal operation points (i.e., pairs of spreading patterns) in the lack of central coordination.