Hybrid NOMA and ZF Pre-Coding Transmission for Multi-Cell VLC Networks

Abstract

Though visible-light communication (VLC) channels are contained by opaque boundaries, they present unique challenges in the development of multi-user/multi-cell scenarios. In this paper, two hybrid transmission schemes are proposed for managing multiple users in multi-cell VLC networks. The proposed schemes are based on using non-orthogonal multiple access (NOMA) in the network access points (APs), while applying zero-forcing (ZF) pre-coding to the cell edge users' signals, which are cooperatively broadcast from the APs. The proposed approach allows a reduction of the inter-cell interference affecting the cell-edge users thanks to ZF pre-coding, while dealing with inter-user interference for cell-center users via NOMA signaling. Considering different transmission scenarios, we show the improvement in the network total achievable data rate as well as fairness, as compared to conventional NOMA. For example, for a typical scenario considered, an improvement of up to 39% in total achievable rate and up to 112% in the network fairness is achieved. The proposed approach also presents a clear advantage over the conventional ZF pre-coding, for which the maximum number of users is constrained to the number of APs. INDEX TERMS Visible light communications, multiuser networks, non-orthogonal multiple access, pre-coding. 1. Note that, concerning the uplink, which could be realized using infrared transmission, carrier-sense MA with collision avoidance (CSMA/CA) protocol can be used, as suggested in [8].

Lights and Shadows: A Comprehensive Survey on Cooperative and Precoding Schemes to Overcome LOS Blockage and Interference in Indoor VLC

“…Thus, as pointed out previously, the backhaul is a key element for the management of a multi footprint scenario. It is worth remarking that this scenario is used in some pre-coding schemes, non-orthogonal multiple access (NOMA) proposals [ 48 , 105 ] and user-centric approaches [ 35 , 42 , 106 ].…”

Dimming-Aware Interference Mitigation for NOMA-Based Multi-Cell VLC Networks

“…We consider two performance metrics, i.e., the maximum achievable throughput and the Jain's fairness index (FI) [14]. This latter is a measure of the throughput homogeneity among users, which for a total number of N r users is defined as:…”

“…1(a), where APs are positioned at the center of the cells and the emitted optical power from each AP is set to P o = 1.584 W as in [14]. The considered heights of the APs and the Rxs are 2.5 and 0.85 m, [14] 36 Maximum signal current per LED chip [14] 100 mA LED conversion efficiency S [14] 0.44 W/A PD responsivity R [4] 0.4 A/W PD area A PD [14] 1 cm 2 Rx's FOV θ FOV [14] 62 deg. Refractive index of optical concentrator q [14] 1.5 BW B…”

On the Achievable Max-Min Rates of Cooperative Power-Domain NOMA Systems

“…The plot of the max-min rates for cooperative and noncooperative NOMA systems is shown in Fig. 6 for the twouser case, |h1| 2 |h3| 2 = 20, |h2| 2 |h3| 2 = 5, |h12| 2 |h2| 2 = 2, |h13| 2 |h3| 2 = 5, and σ 2 = 1, where it is assumed again, for theoretical benchmarking, that the free power constraint on the cooperation power at User1 and User2 will always satisfy the required optimal values of it as obtained before in (22)(23)(24)(25). The obtained results are similar to the two-user case where the cooperation, in general, is beneficial in the medium SNR range.…”

“…A similar work in [21] has considered the maximization of the minimum normalized rate for conventional NOMA in VLC networks where an approximation of the objective function was utilized to convexify the optimization problem. The maximization of the minimum rate of the cell-edge users in VLC networks in [22], using hybrid NOMA and linear zero-forcing (ZF) pre-coding schemes, was tackled by numerical convex optimization of the standard determinant maximization.…”