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.