In this paper we propose priority backoff algorithm for random access procedure setting different re-access probability to users depending on their different group priority grades, different user priority grades and different number of collisions in TD-LTE trunking system. Its objective is to make these groups or users with high priority have lower collision rate and access time delay than those with low priority, and make these users with high collisions number have slightly higher access probability than those with low collisions number in the same grade. In order to make further performance optimization, we also improve the power control policy in PUSCH for sending the random access message according to users' different priority grades. Simulations will validate the analytical result.

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