Abstract
Hybrid precoding and combining is a key technique to provide an appropriate antenna gain in millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems. In wideband mmWave channels, the analog precoder and combiner is designed in the time domain and remain unchanged over the whole bandwidth. In contrast, digital precoders and combiners are optimized on a per-subcarrier basis which makes the resultant problem very difficult. To solve this problem, we combine the well-known turbo-equalizer with the tabu-search (TS)-algorithm developed in artificial intelligence and propose TS-based joint hybrid precoding and combining scheme to intelligently search the near-optimum pair of hybrid precoder and combiner. Specifically, our scheme consists of two key steps. At first, a base station (BS) and a mobile station (MS) develop the turbo-like (TL)-joint search by using the idea of iterative information exchange between them. Then, to find out the near-optimum pair of hybrid precoder and combiner in each iteration of the TL-joint search, the TS-algorithm is employed. Simulation results are shown to verify the significant sum-rate performance of the proposed solution with low-complexity compared to some existing solutions.
Highlights
D UE to the continuous growth in data-rate requirements of the current cellular networks, new spectrum resources are needed to explore [1]
Different from conventional TL-like scheme [22] where the TLsearch starts by selecting a random initial solution from the predefined codebook, we propose an initialization procedure based on eigenvalue decomposition (EVD) of the effective channel to obtain the initial hybrid precoder and combiner
PROBLEM FORMULATION Based on the above system and channel models, we present the codebook based hybrid precoding which is commonly used in mmWave massive MIMO systems
Summary
D UE to the continuous growth in data-rate requirements of the current cellular networks, new spectrum resources are needed to explore [1]. The other part is the large-size analog precoder implemented by using the phase shifters or switches to increase the antenna gain [12] In this way, hybrid precoding is capable to inherit the sum-rate performance close to the fully-digital precoding and significantly reduce the number of required RF chains [4]. The network of phase-shifters is used to implement the analog precoder and it needs to be designed by considering the entire wideband [18] This distinct feature of hybrid precoding for wideband mmWave channels makes it more challenging compared to the conventional fully-digital precoding [19]. The authors in [20] focus on the spectral efficiency maximization for wideband mmWave systems They provide the codebook design guidelines at first for wideband mmWave channels and propose the gram-Schmidtorthogonalization algorithm to solve the hybrid precoding problem.
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