In view of the frequent and complex changes of GNSS visible satellite constellation in attitude determination system, an improved attitude signal simulation algorithm for high dynamic satellite signal simulator is proposed. Based on Software Radio architecture, elevation calculation in the antenna coordinate system and channel state control logic under the condition of carrier attitude changes are introduced into the algorithm to implement synchronous scheduling of visible satellite constellation and attitude signal simulation. This work guarantees the simulator to run constantly and stably for a long time with the advantages of high precision and low complexity. Compared with synchronous positioning results from the receiver, the simulation results show that not only can the output signals of the simulator accurately reflect the carrier's attitude characteristics, but also no step error is generated and the positioning precision is not influenced when visible satellite constellation changes.

The traditional selection cooperation scheme selects the relay with best instantaneous receive signal-to-noise ratio to forward the message and achieves good outage performance, which may however cause poor fairness among relays. In this letter, we propose two practical selection cooperation schemes in Decode-and-Forward (DF) fashion to improve the fairness of relay selection. Numerical results suggest that both of the proposed schemes can achieve fairness close to the strict fairness scheme without outage performance deterioration. It is also validated that these schemes have lower complexities than traditional ones and therefore are practical for real networks.