Abstract
A downlink adaptive distributed precoding scheme is proposed for coordinated multi-point (CoMP) transmission systems. The serving base station (BS) obtains the optimal precoding vector via user feedback. Meanwhile, the precoding vector of each coordinated BS is determined by adaptive gradient iteration according to the perturbation vector and the adjustment factor based on the vector perturbation method. In each transmission frame, the CoMP user feeds the precoding matrix index back to the serving BS, and feeds back the adjustment factor index to the coordinated BSs, which can reduce the uplink feedback overhead. The selected adjustment factor for each coordinated BS is obtained via the precoding vector of the coordinated BS used in the previous frame and the preferred precoding vector of the serving BS in this frame. The proposed scheme takes advantage of the spatial non-correlation and temporal correlation of the distributed MIMO channel. The design of the adjustment factor set is given and the channel feedback delay is considered. The system performance of the proposed scheme is verified with and without feedback delay respectively and the system feedback overhead is analyzed. Simulation results show that the proposed scheme has a good trade-off between system performance and the system control information overhead on feedback.
Highlights
Coordinated multi-point (CoMP) transmission/reception is considered as one of the key potential technologies for LTE-Advanced [1]
Each coordinated base station (BS) adjusts the precoding vector based on the precoding vector used in the previous frame and the adjustment factor fed back by the user
The feedback overhead is reduced, since the user does not need to feed back the precoding matrix index (PMI) for coordinated BSs
Summary
Coordinated multi-point (CoMP) transmission/reception is considered as one of the key potential technologies for LTE-Advanced [1]. In [4,5,6,7], feedback-assisted distributed beamforming with phase perturbation in wireless sensor networks was considered: each transmitter adjusted its phase randomly at each iteration and the receiver broadcasted one bit of feedback per iteration indicating whether its net SNR was better or worse than before. This article proposes a vector perturbation-based adaptive distributed precoding (ADP) scheme for downlink CoMP joint processing which serves the user by one serving BS and several coordinated BSs. The proposed ADP can achieve better system performance than MBSFN and it will reduce the feedback overhead compared with WLP. The precoding vector for each coordinated BS is given as follows Both the user and the coordinated BSs have knowledge of the perturbation vector set and the adjustment factor set. Hltl is the channel matrix of the serving BS multiplied by its precoding vector and Hktk(k ≠ 1) is the channel matrix of kth coordinated BS multiplying its precoding vector
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