Abstract
Conventional vector perturbation (VP) is not directly applicable to adaptive modulation, whereas other existing algorithms are suboptimal due to the reduced search dimension of perturbation vectors. In this paper, by applying a simple transformation to the conventional VP operation, the search dimension for the proposed joint VP is made equal to that of conventional VP, and therefore, the performance advantages of VP still hold in this scenario. Furthermore, to reduce the computational complexity, a joint constructive VP scheme is introduced by exploiting constructive interference to simplify the VP operation. By doing so, the sophisticated search for perturbation vectors is partially replaced by a quadratic programming problem, therefore saving significant computational complexity. Our analysis and results show that the proposed scheme offers an improved performance-complexity tradeoff compared with conventional VP approaches by means of the measurement in energy efficiency.
Highlights
I N recent multiple-input-multiple-output (MIMO) communication systems, precoding techniques have been widely studied and simple forms of precoding have appeared in communication standards [1][2]
One drawback of conventional vector perturbation (VP) scheme is that it does not apply to scenarios where multiple modulation types are employed by different users due to the fact that the modulo base τ = 2|C|max + ∆ is modulation dependent, where |C|max is the absolute value of the constellation symbol with the maximum magnitude and ∆ denotes the minimum Euclidean distance between constellation points
For reasons of clarity we summarize the contributions of the paper as: 1) We propose a reduced complexity two-stage VP scheme for adaptive modulation scenarios
Summary
I N recent multiple-input-multiple-output (MIMO) communication systems, precoding techniques have been widely studied and simple forms of precoding have appeared in communication standards [1][2]. Non-linear vector perturbation (VP) based precoding in [4][7] improves the performance of linear channel inversion precoding schemes. Scheme is introduced in [9] and a user-grouping VP (UGVP) is proposed to improve the performance of BDVP Both BD-VP and UG-VP are suboptimal to conventional VP due to the reduced search dimensions. By scaling the constellation of different modulation types and the corresponding channel matrix, the modulo base τ is made common for all modulation types, and a full dimension search for the perturbation vectors could be performed. The search for the perturbation vectors is exclusively limited for users applying QAM modulation while in the second stage, the constructive VP [11] is performed for users applying PSK modulation where the search space is limited to the areas that are constructive to the transmit symbols.
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