Transmit power and window control to reduce inter-user interference in CDMA cellular packet systems

A novel interference reduction method, transmit power and window control (TPWC), is proposed to enhance the system capacity in the downlink of CDMA cellular packet systems. TPWC measures the propagation conditions such as the required instantaneous transmit power between a base station (BS) and a mobile station (MS). Then, TPWC sends packets only during a transmit time-window, in which the packets can be sent with less power than a predetermined threshold. TPWC reduces the average transmit power at the cost of an extra transmission delay at the BS. Computer simulations show that, in a two-path Rayleigh fading environment with maximum Doppler frequency of 80 Hz, TPWC enhances the system capacity by 1.8-fold in a CDMA cellular packet system when each MS has a load of 0.5 and a 90% delay allowance of 5 ms. In order to confirm the implementation feasibility and to evaluate the performance of TPWC, an experimental TPWC processor is developed and its performance is measured.