Implications of random access collisions on physical layer performance of a hybrid TD/CDMA air interface with joint detection

The performance of a TD/CDMA air interface with joint detection is investigated under the assumptions that two or more users are colliding when sharing the same codes. This is a case that occurs in random access channels when terminals contend for the same spreading code in the same sub slot, following a CDMA/PRMA approach. The average BER over all the users (8) for different cases (colliding/non-colliding) is presented and the impact on the non-colliding ones is investigated. The above is investigated for the two cases that either all the 6 paths (ideal case) or only some of them-detected at the receiver-are correctly assigned to the colliding users. In the receiver a zero-forcing block linear equaliser algorithm is applied in the TD/CDMA system under consideration.