Abstract:

The scenario that multiple cell-edge mobile stations (MS) all without direct-links to the base station (BS) but have confidential messages in the uplink in the presence of untrusted relay (UR) cooperation was considered.In order to implement the secure communication between BS and multiple MS，destination-based jamming (DBJ) scheme was adopted.With the assumption that all MS had fixed transmit power，the joint UR and BS power control which aims at maximizing system sum secrecy rate was discussed.For this problem，analysis indicated that it was equivalent to joint access control and power allocation problem thus its NP-hard.Through problem relaxation，a suboptimal MS access control and alternatively power allocation algorithm was provided.This algorithm is proved to have polynomial complexity and can converge to at least a suboptimal solution for original problem.Simulation results show that compared with the benchmark algorithms，the proposed suboptimal algorithm is better in the achievable secrecy rate performance.

Key words: OFDMA, untrusted relay, power control, information-theoretic security