Ranging code collision probability in OFDMA based BWA network

For uplink time synchronization and power adjustment, ranging process has been suggested for OFDMA (orthogonal frequency division multiple access) based BWA (broadband wireless access) networks like IEEE 802.16. The CDMA (code division multiple access) type code transmission in contention based ranging channel has been provisioned to send the ranging request by an SS (subscriber station) to BS (base station). In contention based ranging channel, ranging code suffers with collision if same code is transmitted by two or more than two subscriber stations in a same frame. However, the number of available ranging codes, the applied contention resolution scheme, and the number of SSs in the network determine the collision probability of the transmitted request code in an any arbitrary time frame. Since the analysis of the collision probability of the transmitted ranging codes in the ranging channel is one of an important issues in OFDMA based BWA network when modeling or configuring the network parameters, in this paper, we have mathematically analyzed that issue. A analytical model along with simulation results has been presented to analyze the ranging code collision probability in terms of number of users, varying the number of ranging codes and contention window size.