Analysis of random access channel in UTRA-TDD on AWGN channel

The Random Access Channel (RACH) in UTRA-TDD systems is an uplink contention-based transport channel that is mainly used to carry control information from mobile stations to base stations. In this paper, we study the performance of RACH on an additive white Gaussian noise (AWGN) channel whereby successful transmission of a burst requires the spreading code chosen to be collision-free and the burst is error-free after convolutional decoding. Based on this model, the code-collision probability, the data bit error probability and the RACH channel capacity are derived. The random retransmission delay mechanism is not specified in UTRA-TDD. We therefore choose an access mechanism with binary exponential backoff delay procedure similar to that in IEEE 802.11. Based on that mechanism, the blocking probability and the first two moments of the delay are also derived. Compared with the mean, the standard deviation is found to be very high. Index Terms — Time division multiple access, code division multiple access, UTRA-TDD, random access channel, binary exponential backoff delay.