A joint power control and interference avoidance code assignment strategy for downlink MC-DS-CDMA with 2D spreading

Maintaining the quality-of-service (QoS) requirement by transmission power adjustment while eliminating interference is an important but difficult task in the downlink multicarrier direct-sequence code division multiple access (MC-DSCDMA) systems with two-dimensional (2D) spreading. To achieve this goal, we integrate the power control (PC) mechanism and the interference avoidance code assignment strategy. This joint policy is to firstly eliminate interference via an interference avoidance (IA) code assignment strategy and then maintain the QoS via a power control mechanism. To facilitate the code assignment strategy, a new PC-based multiple access interference (MAI) coefficient is defined through performance analysis. Thanks to the help of the PC-based MAI coefficient, we can evaluate each candidate code by quantitatively predicting the amount of interference produced by a possible code assignment event. With this interference pre-evaluation, the PC mechanism can not only maintain the QoS with less transmission power but also eliminate extra MAI in the system. The simulation results show that the proposed joint scheme can maintain a predefined signal quality and significantly improve the call admission rate while largely reducing the power consumption. The contribution of this paper fills up the missing link between the power control and code assignment in the 2D-spread MC-DS-CDMA systems.