Low-Complexity Multiuser Receiver for Massive Hybrid Array mmWave Communications

Abstract

In this paper, we study the low complexity reception of multiuser signals in uplink millimeter wave (mmWave) communications using a partially connected hybrid antenna array. Exploiting the mmWave channel property, we propose a lowcomplexity user-directed multiuser receiver with three novel schemes for allocating subarrays to users. This receiver only requires the knowledge of angles-of-arrival (AoAs) for dominating paths and a small amount of equivalent channel information instead of perfect channel state information. For comparison, we also derive a successive interference cancellation-based solution as a performance benchmark. We design two types of reference signals with the channel estimation method to enable efficient and simple estimation for AoA and equivalent baseband channel. Also, we provide analytical results for the performance of the AoA estimation, using the lower bounds of mean square errors in line-of-sight dominated mmWave channels. The simulation results validate that the proposed channel estimation method is effective when employed in combination with a zero-forcing equalizer.

Achieving the performance of the MMSE receiver with the maximum ratio combiner

“…for the sub6-GHz band W r RF j j w BB j ji [s], for the mmWave band, (5) where w BB j ji [s] denotes the N r × 1 digital BB combiner [18,[20][21][22].…”

“…Hence, is equivalent to where denotes the digital BB combiner [18, 20–22].…”

Performance Improvement for Multi-User Millimeter-Wave Massive MIMO Systems

“…, K , j = k, where ρ k and ρ j represent the transmission power of the k th and j th UEs, respectively. Finally, N u ∈ C N r ×N s is the vector of i.i.d CN 0, σ 2 N u noise at the u th RF chain of the BS [15], [26].…”

“…According to [15], [26], the sum spectral efficiency of a partially-connected hybrid array depends on the correlation of the channels between the different subarrays, the accuracy of the mmWave channel estimation, and the SINR of the received signal.…”

“…For NR systems, the modulation scheme used for the demodulation reference signals (DMRS), commonly known as pilots, is the quadrature phase-shift keying (QPSK), which requires a minimum SNR of 10 dB. However, in the mmWave band, the SNR required for channel estimation is small due to high path loss [26], [31]. So, to tackle the orthogonality disadvantage, we propose to use a new pilot mapping capable of mitigating the inter-user interference effects.…”