Approach to MAI cancellation for micro-satellite clusters

With the development of micro-satellite technology, traditional monolithic satellites can be replaced by micro-satellite clusters to achieve high flexibility and dynamic reconfiguration capability. For satellite clusters based on the frequency division-code division multiple access (FD-CDMA) communication system, the inter-satellite ranging precision is usually constrained due to the influence of multi-address interference (MAI). The multi-user detection (MUD) is a solution to MAI, which can be divided into two categories: the linear detector (LD) and the non-linear detector (NLD). The general idea of the LD is aiming to make a better decision during the symbol decision process by using the information of all channels. However, it is not beneficial for the signal phase tracking precision. Instead, the principle of the NLD is to rebuild the interference signal and cancel it from the original one, which can improve the ranging performance at the expense of considerable delays. In order to enable simultaneous ranging and communication and reduce multi-node ranging performance degradation, this paper proposes an NLD scheme based on a delay locked loop (DLL), which simplifies the receiver structure and introduces no delay in the decision process. This scheme utilizes the information obtained from the interference channel to reconstruct the interference signal and then cancels it from the original delayed signal. Therefore, the DLL input signal-to-interference ratio (SIR) of the desired channel can be significantly improved. The experimental results show that with the proposed scheme, the standard deviation of the tracking steady error is decreased from 5.59 cm to 3.97 cm for SIR = 5 dB, and 13.53 cm to 5.77 cm for SIR = -5 dB, respectively.