Analysis into Timing Advance Issue in CoMP Systems

Coordinated Multi-Point transmission / reception (CoMP) has been adopted in LTE-Advanced to improve system performance, especially user equipment (UE) at the cell edge. The conventional timing advance (TA) design is not suitable since a UE can be served by multiple geographically distributed access points (AP). TA issue´s impact is investigated in great detail. Simulation results validates that the conventional design limits performance improvement. Two ways can be taken to solve the issue: (1) to adopt extended cyclic prefix (CP); (2) to adjust TA based on the nearest AP. Both ways increase the number of UEs that can use CoMP, but the extended CP incurs a large overhead that lowers throughput. The latter scheme can bring 15% throughput improvement over a non-CoMP system, and is recommended to be adopted in the CoMP system.