Novel hybrid precoder based on SVD for downlink mmWave massive MU-MIMO systems

Abstract

We propose four hybrid combiner/precoder for downlink mmWave massive MU-MIMO systems.The design of a hybrid combiner/precoder is divided in two parts, analog and digital. The system baseband model shows that the signal processed by the mobile station can be interpreted as a received signal in the presence of colored Gaussian noise, therefore, since the digital part of the combiner and precoder do not have constraints for their generation, their designs can be based on any traditional signal processing that takes into account this kind of noise. To the best of our knowledge, this was not considered by previous works. A more realistic and appropriate design is described in this paper.Also, the approaches adopted in the literature for the designing of the combiner'/precoder' analog parts do not try to avoid or even reduce the inter user/symbol interference, they concentrate on increasing the signal-to-noise ratio (SNR). We propose a simple solution that decreases the interference while maintaining large SNR. In addition, one of the proposed hybrid combiners reaches the maximum value of our objective function according with the Hadamard's inequality. Numerical results illustrate the BER performance improvements resulting from our proposals. In addition, a simple detection approach can be used for data estimation without significant performance loss. Index TermsMassive MIMO, hybrid precoding, hybrid combining, millimeter wave (mmWave), RF chain number limitations, multiuser.

Approximate expressions for BER performance in downlink mmWave MU‐MIMO hybrid systems with different data detection approaches

“…An option to reach this is by taking into account that the ideal equivalent baseband channel is a diagonal matrix with large entries values. In a previous work [9], we presented a methodology to obtain an approximation to this desired result through SVD techniques and a derivation of the low‐dimensional MMSE linear precoder to be used as . The proposed design has shown a superior BER performance when compared with different hybrid designs described in the literature.…”

“…The proposed design has shown a superior BER performance when compared with different hybrid designs described in the literature. In addition, a similar work was described in [14], where the analogue design proposed in [9] followed by an all digital ZFs was tested as a hybrid precoder.…”

“…A large number of HB designs have been proposed with different approaches. This paper considers a HB design made by two stages, where the first stage performs the analogue part of the beamforming that maximises the effective channel gain, and the second stage applies a low‐dimensional baseband precoder to manage the inter user/symbol interference [6–11].…”

“…The remainder of this paper is organised as follows: Sections 2 and 3 describe the system model and channel model, respectively; in Section 4, some expressions to obtain an upper bound of the BER performance via semi‐analytic are derived; Section 5 presents our proposed methodology to estimate an approximation of the BER performance considering different data detectors. Section 6 presents two options for the realisation of the hybrid precoder, which have been proposed in [9, 14] showing a superior BER performance when compared with others. In Section 7, numerical results obtained via simulation and through proposed expressions are compared; and finally, in Section 8, appropriate conclusions wrap up this paper.…”

On Hybrid Beamforming Design for Downlink Mmwave Massive Mu-Mimo Systems

“…Many hybrid beamforming designs have been proposed for the last years, e.g., [21,24,29,39]. However, to the best of our knowledge, there are no works presenting exact closed forms expressions for the BER performance in mmWave system.…”