A mobile communication system uses a multiple-input-multiple-output (MIMO) technology with an orthogonal frequency division multiplexing access (OFDMA) scheme. Multiuser diversity, multiantenna diversity, and power control since the first ranging attempt are exploited in the initial ranging process. At network entry, an initial ranging method selects from multiple ranging signal designs to accomplish the initial ranging process. In one embodiment, three classes of ranging signal designs may be selected for use in generating ranging codes. The information on the ranging signal design to be used, which is selected by the base station based on the cell size of the communication system (i.e., the radio coverage area of the base station), is broadcast from the BS. The ranging signal designs are directly applicable to single-antenna systems, and they are applied to MIMO systems by using appropriate mapping across transmit antennas based on the adopted MIMO ranging transmission scheme. In a mobile communication system using MIMO technology with the OFDMA scheme, the ranging user selects from multiple ranging transmission schemes of different levels of computation complexity, power consumption and performance. In one example, optimum eigenmode and suboptimum eigenmode transmission schemes provide the best performance at high computational complexity and high power consumption. A simpler single-antenna selection transmission scheme provides significantly reduces computational complexity and achieves power saving at a marginal degradation in system performance.