Distance based dynamic adaptation of the air interface in TDMA

In a mobile radio environment, propagation and interference conditions experienced by a mobile are time-varying. The air interface is usually fixed and designed for the worst case. The paper proposes to dynamically select the air interface parameters from a set of predefined combinations known as transport modes. Modes are ordered according to their robustness towards channel errors. They correspond to the transmission of a variable net and/or gross bit rate leading to a possibly variable allocated resource. The proposed modes selection algorithm is based on the transmitter receiver distance separation. It results in a mode utilisation in concentric rings, a more robust mode being used at the cell border and a less robust mode at the cell center. The reasoning is that a mode should not be selected according to the channel quality experienced in the recent past due to the very rapid changing propagation and traffic load conditions particularly in a packet access system. The mode selection is performed with respect to the conditions that will be statistically encountered with a high probability, the statistics being gathered with respect to the mobile station -base station distance. The interworking of the algorithm with various power control strategies is studied. The adjustment of the rings' radii in order to achieve the best trade-off between the service quality, the cell capacity and the transmit power is addressed. Simulation results are finally presented.