On the network performance of UTRA-like TDD and FDD CDMA systems using adaptive modulation and adaptive beamforming

摘要

In this distribution we characterise the capacity of an adaptive modulation assisted, beam-steering aided TDD/CDMA system. In TDD/CDMA the mobiles suffer from interference inflicted by the other mobile stations (MSs) both in the reference cell the MS is roaming in (intracell interference) as well as due to those in the neighbouring cells (intercell interference). Furthermore, in contrast to FDD/CMDA, where the base stations (BSs) transmit in an orthogonal frequency band, in TDD/CDMA there is additional interference imposed by other BSs of the adjacent cells, since all time-slots can be used in both the uplink and downlink. In return for this disadvantage, TDD/CDMA guarantees the flexible utilization of all the available bandwidth, which meets the demand for the support of asymmetric uplink and downlink services, such as high data rate file download in mobile Internet services, etc. In wireless systems the link quality fluctuates due to either fading- and dispersion-induced channel impairments or as a consequence of the time-variant co-channel interference imposed by the teletraffic fluctuations due to the varying number of users supported. Due to these impairments conventional wireless systems often drop the call. By contrast, a particular advantage of employing adaptive modulation is that the transceiver is capable of automatically reconfiguring itself in a more error-resilient transmission mode, instead of dropping the call. This contribution studies the achievable network performance by simulation and compares it to that of the FDD/UTRA system.