Hybrid LISA for Wideband Multiuser Millimeter Wave Communication Systems under Beam Squint

TL;DR

This paper jointly addresses user scheduling and precoder/combiner design in the downlink of a wideband millimeter-wave communications system and considers the orthogonal frequency-division multiplexing modulation to overcome the channel frequency selectivity.

Abstract

This work jointly addresses user scheduling and precoder/combiner design in the downlink of a wideband millimeter wave (mmWave) communications system. We consider Orthogonal Frequency Division Multiplexing (OFDM) modulation to overcome channel frequency selectivity and obtain a number of equivalent narrowband channels. Hence, the main challenge is that the analog preprocessing network is frequency flat and common to all the users at the transmitter side. Moreover, the effect of the signal bandwidth over the Uniform Linear Array (ULA) steering vectors has to be taken into account to design the hybrid precoders and combiners. The proposed algorithmic solution is based on Linear Successive Allocation (LISA), which greedily allocates streams to different users and computes the corresponding precoders and combiners. By taking into account the rank limitations imposed by the hardware at transmission and reception, the performance loss in terms of achievable sum rate for the hybrid approach is negligible. Numerical experiments show that the proposed method exhibits excellent performance with reasonable computational complexity.

Figures (8)

• Figure 1: Example of subbands and representation subcarriers for $L=15$ subcarriers and $L_s=3$ subbands
• Figure 2: Numerical results for $f_c=28$ GHz and bandwidths $B=800,3200$ MHz: Sum Rate vs SNR for $K=4$ users, $N=64$ transmit antennas, $R=16$ receive antennas, $L=32$ subcarriers and ${N_{\text{p},k}}=4$ propagation paths for each user. The number of RF chains are ${N_\text{RF}}=4$ and ${R_{\text{RF}}}=2$.
• Figure 3: Numerical results for carrier frequency $f_c=28$ GHz and signal bandwidth $B=400$ MHz: Sum Rate vs SNR for the relaxed interference constraint and different thresholds $\nu=\frac{1}{2},\frac{1}{10},\frac{1}{20},\frac{1}{50}$. $K=4$ users, $N=64$ transmit antennas, $R=16$ receive antennas, $L=32$ subcarriers and ${N_{\text{p},k}}=4$ propagation paths. The number of RF chains are ${N_\text{RF}}=8$ and ${R_{\text{RF}}}=2$.
• Figure 4: Numerical results for carrier frequency $f_c=28$ GHz and signal bandwidth $B=400$ MHz: Sum Rate vs SNR $K=4$ users, $N=64$ transmit antennas, $R=16$ receive antennas, $L=32$ subcarriers and ${N_{\text{p},k}}=4$ propagation paths for each user. The number of RF chains are ${N_\text{RF}}=8$ and ${R_{\text{RF}}}=2$.
• Figure 5: Sum Rate vs SNR considering $f_c=28$ GHz and $B=3200$ MHz. We use $L_s=3$ and $L_s=1$ subbands for $K=4$ users, $N=64$ transmit antennas, $R=16$ receive antennas, $L=32$ subcarriers and ${N_{\text{p},k}}=4$ propagation paths. The number of RF chains are ${N_\text{RF}}=4$ and ${R_{\text{RF}}}=2$.