Interference cancellation and avoidance for secondary users co-existing with TDD-based primary systems

This paper proposes a new interference cancellation/avoidance scheme for secondary spectrum usage, which takes advantage of the features of Time Division Duplex (TDD) based primary systems. We focus on the co-existence between the heterogeneous systems, where the primary and the secondary are using the same spectrum simultaneously. The secondary systems have to accurately find the possible interference from/to the primary systems for discreet and efficient secondary transmission. In order to judge the arrival of interference from/to the primary system, the secondary access point (AP) compares the difference in power between the up and downlink signals in TDD-based primary systems. This scheme enables the secondary AP to know the level of interference from the primary systems that arrives at the AP without employing complex signal detection. The proposed scheme also determines the level of interference induced to the primary system by measuring the difference in power. To cancel and avoid interference in the proposed scheme, we introduce an adaptive array at only the AP that creates a null toward the interference with a higher power level between the up and downlink signals. Moreover, new algorithms by using scheduling information of the multiple primary nodes are introduced in the proposed method, in order to enhance the transmission quality of a secondary mobile station (MS) while maintaining a simple control scheme for the MS. Finally, we verify the effectiveness of the proposed method based on computer simulations.