A Novel Interference-Avoidance Code Reassignment for Downlink Two-Dimensional-Spread MC-DS-CDMA Systems With Power Control

In the 2-D time-and frequency-domain spread multicarrier direct-sequenced code-division multiple-access (MC-DS-CDMA) system, maintaining a good code tree structure is the key to controlling the interference level. However, as users come and go, the code tree structure will be fragmented and steeped in a high level of interference. In this situation, an active call may be dropped for not being able to reach a predefined signal quality. To solve this call-dropping problem, we propose a novel code-reassignment strategy to reallocate a low-interferenced code to the could-be-dropped call. This way, not only can this possible call-dropping event be evaded, but also, a low-interferenced 2-D code tree structure can be maintained. The simulation results show that the proposed code-reassignment method can efficiently alleviate the call-dropping problem and boost the call-survival rate simultaneously. It is believed that the proposed scheme fills up an important missing link of the dynamic call-resource management for the 2-D-spread MC-DS-CDMA system.