Abstract
In this study, we investigated the nonorthogonal multiple access (NOMA) for visible light communication (VLC) Internet of Things (IoT) networks and provided a promising system design for 5G and beyond 5G applications. Specifically, we studied the capacity region of a practical uplink NOMA for multiple IoT devices with discrete and continuous inputs, respectively. For discrete inputs, we proposed an entropy approximation method to approach the channel capacity and obtain the discrete inner and outer bounds. For the continuous inputs, we derived the inner and outer bounds in closed forms. Based on these results, we further investigated the optimal receiver beamforming design for the multiple access channel (MAC) of VLC IoT networks to maximize the minimum uplink rate under receiver power constraints. By exploiting the structure of the achievable rate expressions, we showed that the optimal beamformers are the generalized eigenvectors corresponding to the largest generalized eigenvalues. Numerical results show the tightness of the proposed capacity regions and the superiority of the proposed beamformers for VLC IoT networks.
Highlights
As the wireless data traffic exponentially increased in 5G, traditional radio frequency- (RF-) based Internet of Things (IoT) network suffers from a limited data rate and network capacity due to the shortage of RF spectra and massive IoT devices
To the best of our knowledge, the proposed inner and outer bounds are the first theoretical bounds of the channel capacity region for uplink nonorthogonal multiple access (NOMA) of visible light communication (VLC) IoT networks (iii) based on the obtained results of NOMA, we further studied the optimal receiver beamforming design for VLC IoT
Let φ ≜ A2/ε denote the amplitude-tovariance ratio, and define SNR as ≜ ε/σ2. Both the uniform inner and outer bounds of the capacity region of multiple access channel (MAC) NOMA of VLC IoT networks are presented for comparison, where the input signals follow a uniform distribution [36,37,38]
Summary
As the wireless data traffic exponentially increased in 5G, traditional radio frequency- (RF-) based Internet of Things (IoT) network suffers from a limited data rate and network capacity due to the shortage of RF spectra and massive IoT devices. With its vast unlicensed bandwidth, visible light communication (VLC) is a promising complementary solution to meet the growing wireless traffic demands for IoT networks [1, 2]. Traditional IoT networks have generally utilized orthogonal multiple access (OMA) techniques such as frequency division multiple access (FDMA) and time division multiple access (TDMA). The nonorthogonal multiple access (NOMA) technique exploits the power domain for multiple access and is able to serve multiple users at the same time frequency-code resource [8,9,10], which has recently been included into the 3GPP long-term evolution advanced standard [11,12,13] and is widely recognized as a promising candidate for the MAC scheme in 5G-enabled IoT applications
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