In this letter, we propose an efficient algorithm which reduces the complexity of conventional vector perturbation schemes by searching the real and imaginary components of a perturbation vector individually. To minimize a performance loss induced from the decoupled joint search, we apply diagonal precoding at the transmitter whose parameters are iteratively optimized to maximize the chordal distance between subspaces spanned by the real and imaginary components. We also propose a simple non-iterative method with a slight performance loss which can achieve a significant complexity reduction compared to the conventional vector perturbation schemes.

In this paper, we propose a new vector perturbation scheme which reduces the complexity associated with finding perturbation vectors by searching for the real and imaginary components individually. To minimize a performance loss induced from decoupling joint search, we apply diagonal preceding at the transmitter whose phase angles are iteratively optimized according to the criterion of maximizing the chordal distance between subspaces spanned by the real and imaginary components. Since our main objective is to reduce the system cost, we also propose a simple non-iterative method of finding phase angles with slight performance loss. Simulation results show that the proposed decoupled vector perturbation reduces the average number of search candidate by 56% in comparison to the original vector perturbation in 4-by-4 system. It is also noted that the simple choice of phase angles provides the performance almost identical to that of the iteratively optimized angles. Moreover, we develope a receive antenna combining method for the vector perturbation systems with multiple-antenna receivers. The proposed algorithm designs receive combiners based on the criterion of optimizing the performance metric via a block-coordinate ascent approach.

In this letter, we present an improved precoding technique which reduces a modulo loss in vector perturbation with low complexity. Instead of searching perturbation vectors in the infinite lattice, the proposed scheme restricts the search range by utilizing the distribution of the perturbation vector depending on transmitted data. As a result, we can achieve significant complexity savings at the transmitter while providing better performance compared to the original vector perturbation.

In this paper, we present an improved precoding technique which reduces a modulo loss in vector perturbation (VP) with low complexity for the downlink of a multiuser multiple-input multiple-output (MIMO) system. At low SNR regime, the VP suffers from the modulo loss due to the increased number of nearest neighbors. For the original VP, the sphere encoder searches perturbation vectors in the infinite lattice. In contrast, the proposed scheme restricts the search range utilizing the distribution of the perturbation vector depending on transmitted data. As a result, we can achieve significant complexity savings at the transmitter and the receiver while providing better performance compared to the conventional sphere encoder. Simulation results show that the proposed scheme provides a 0.2 dB gain over the conventional VP at a bit error rate (BER) of 10-3for the case of four transmit antennas and four users with 4QAM. Also, the proposed scheme reduces the maximum number of candidate search by 95% in comparison to the original VP.