Performance Analysis of Oversaturated Collaboratively Coded Group Orthogonal CDMA in AWGN Channel

Oversaturated synchronous CDMA system based on the collaborative coding of group orthogonal signatures, where the data bits of group of L + s users are jointly one-to-one mapped onto 2^L+S L-dimensional signal vectors, is analyzed. Instead of unique signature per each user, the L-dimensional signature subspace is used to transmit the bits of L + s users (s > 0). All signature subspaces are orthogonal to each other which simplifies the optimal receiver structure. With the signal space dimension N, the number of users is K = N(1 + s/L). Preferable modulation mappings are proposed and their BER performance in the AWGN channel is compared to group orthogonal oversaturated system employing unique signatures for each user and to the conventional non-oversaturated orthogonal signaling. Simulation results confirm the predictable gain of collaboratively encoded group orthogonal CDMA against to one exploiting individual signature per user