1-bit Massive MU-MIMO Precoding in VLSI

Abstract

Massive multiuser (MU) multiple-input multipleoutput (MIMO) will be a core technology in fifth-generation (5G) wireless systems as it offers significant improvements in spectral efficiency compared to existing multi-antenna technologies. The presence of hundreds of antenna elements at the base station (BS), however, results in excessively high hardware costs and power consumption, and requires high interconnect throughput between the baseband-processing unit and the radio unit. Massive MU-MIMO that uses low-resolution analog-to-digital and digital-toanalog converters (DACs) has the potential to address all these issues. In this paper, we focus on downlink precoding for massive MU-MIMO systems with 1-bit DACs at the BS. The objective is to design precoders that simultaneously mitigate multi-user interference (MUI) and quantization artifacts. We propose two nonlinear 1-bit precoding algorithms and corresponding verylarge scale integration (VLSI) designs. Our algorithms rely on biconvex relaxation, which enables the design of efficient 1-bit precoding algorithms that achieve superior error-rate performance compared to that of linear precoding algorithms followed by quantization. To showcase the efficacy of our algorithms, we design VLSI architectures that enable efficient 1-bit precoding for massive MU-MIMO systems in which hundreds of antennas serve tens of user equipments. We present corresponding fieldprogrammable gate array (FPGA) reference implementations to demonstrate that 1-bit precoding enables reliable and high-rate downlink data transmission in practical systems.

Timing and Frequency Synchronization for 1-bit Massive MU-MIMO-OFDM Downlink

“…By doing so, ISI-free communication is achieved if the residual STO is −G/2 + L − 1 ≤ ∆τ u ≤ G/2. The rotations incurred by the shift in the DFT window are compensated for in (6) by multiplying the kth subcarrier by e jπGk/N .…”

“…To avoid ISI from adjacent OFDM symbols, the DFT window in (6) should only contain samples from the ith OFDM symbol. However, when ∆τ u < −G/2, the DFT window includes also samples from the (i − 1)th OFDM symbol, whereas when ∆τ u > G/2 the DFT window includes also samples from the (i + 1)th OFDM symbol.…”

Near-Optimal Interference Exploitation 1-Bit Massive MIMO Precoding Via Partial Branch-and-Bound

“…Based on that card (S) = 2K, we obtain that Wp is full-rank. According to the linear algebra theory [28], given a full-rank coefficient matrix Wp, a non-zero solution to (19) does not exist and there is only a trivial solution, i.e.,…”

Neural-Network Optimized 1-bit Precoding for Massive MU-MIMO

“…In this paper, we propose to use neural-network optimization tools to tune the algorithm parameters of the nonlinear biConvex 1-bit PrecOding (C2PO) algorithm proposed in [13]. Specifically, we unfold the C2PO iterations and use backpropagation for parameter tuning.…”

“…In contrast, sophisticated nonlinear precoders [7]- [16] achieve superior BER performance (especially in the extreme case where a pair of 1-bit DACs per RF chain is used), at the cost of a higher complexity. Existing nonlinear precoding algorithms require manual parameter tuning to optimize the BER performance [13]. Parameter tuning is time-consuming and may yield suboptimal results in realistic systems with vastly changing propagation conditions.…”