Abstract
Internet of Things (IoT) is an emerging network that aims to connect massive devices for exchanging information with each other. There have been various IoT access techniques, such as RFID, Blue Tooth, WiFi, LoRa and cellular IoT, in which cellular IoT has advantages in wide coverage and the economical reuse of exsiting cellular infrastructure. However, cellular base station (BS) consumes most of the energy in wireless communication networks. Therefore, improving the energy efficiency (EE) of the BS is of great importance to make cellular IoT green. In this paper, we propose a novel orbital angular momentum (OAM)-based concentric spatial division multiplexing (CSDM) downlink transmission scheme for cellular IoT terminals. Specifically, the hybrid radio frequency (RF) and baseband CSDM scheme exploits analog OAM beamforming to generate concentric annular beams for covering cell-center, cell-mediate and cell-edge groups of users, and digital space-frequency vector perturbation (SFVP) precoding and orthogonal frequency division multiple access (OFDMA) to mitigate inter- and intra-group interferences. Mathematical analysis and numerical simulations validate that the IoT BS with the proposed CSDM-SFVP scheme has better bit error rate (BER) and EE performance than traditional massive multiple-input multiple-output (MIMO) BS with full-baseband zero-forcing (FBZF) precoding in a IoT cell.
Highlights
The fifth generation (5G) New Radio (NR) networks will support three generic types of connectivity: extended mobile broadband, ultra-reliable low-latency communication (URLLC) and massive machine-type communication [1]. eMBB is a natural evolution of long term evolution (LTE) to further increase the user data rates and network spectral efficiency (SE), which is mainly for humantype traffic, such as high data-rate wireless broadband access, ultrahigh-quality video streaming, virtual reality (VR) and augmented reality (AR)
The bit error rate (BER) of FAB is much higher than other schemes owing to the remaining inter-group interferences (IRGIs), which verifies that the cancellation of IRGIs is of great importance to improve the BER performance
Compared with concentric spatial division multiplexing (CSDM)-ZF, CSDM-space-frequency vector perturbation (SFVP) obtains better BER performance because it turns the IRGIs into the collectable diversity
Summary
The fifth generation (5G) New Radio (NR) networks will support three generic types of connectivity: extended mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC) and massive machine-type communication (mMTC) [1]. eMBB is a natural evolution of long term evolution (LTE) to further increase the user data rates and network spectral efficiency (SE), which is mainly for humantype traffic, such as high data-rate wireless broadband access, ultrahigh-quality video streaming, virtual reality (VR) and augmented reality (AR). On one hand, different power could be allocated to the users in different rings to ensure all the users in a macrocell to obtain near the same received signal power and achieving the fairness between CEUs, CMUs and CCUs, on the other hand, multiple OAM beams with much fewer RF chains serve massive devices within the same time-frequency resources improving the EE performance of the BS. E and CZn represent expectation and the set of n × 1 vectors in complex integer field, respectively
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