Spectral and energy efficiency of line-of-sight OAM-MIMO communication systems

Not only high spectral efficiency (SE) but also high energy efficiency (EE) are required for future wireless communication systems. Radio orbital angular momentum (OAM) provides a new perspective of mode multiplexing to improve SE. However, there are few studies on the EE performance of OAM mode multiplexing. In this paper, we investigate the SE and EE of a misaligned uniform concentric circle array (UCCA)-based multi-carrier multimode OAM and multiple-input multiple-output (MCMM-OAM-MIMO) system in the line-of-sight (LoS) channel, in which two transceiver architectures implemented by radio frequency (RF) analog synthesis and baseband digital synthesis are considered. The distance and angle of arrival (AoA) estimation are utilized for channel estimation and signal detection, whose training overhead is much less than that of traditional MIMO systems. Simulation results validate that the UCCA-based MCMM-OAM-MI-MO system is superior to conventional MIMO-OFDM system in the EE and SE performances

Energy Efficient Resource Allocation for UCA-Based OAM-MIMO System

The combination of orbital angular momentum (OAM) and multi-input multi-output (MIMO) is identified as an effective solution to improve energy efficiency (EE) in the next-generation wireless communication. According to the orthogonality of OAM, we adopt uniform circular array (UCA) to establish the transmitter and receiver of the OAM-MIMO system in this paper. Our goal is to maximize the EE of the system whilst satisfying the maximum total transmit power and the minimum capacity requirement of each mode. Due to the inter-interference of different UCA at the same mode, the optimization problem involving the power allocation of modes is non-convex, thus is difficult to solve directly. To tackle this problem, the optimization problem is transformed into two sub-problems by using the fractional programming. Then we develop a dual-layer iteration algorithm where the nonconvex power allocation problem is transformed into a convex problem by exploiting the the first-order Taylor approximation in the inner layer, and the dichotomy is used to update EE in the outer layer. Simulation results confirm the effectiveness of the proposed solution, and demonstrate the superiority of the OAM-MIMO system over the conventional MIMO system from the perspective of EE

Energy Efficiency Optimization for PSOAM Mode-Groups based MIMO-NOMA Systems

Plane spiral orbital angular momentum (PSOAM) mode-groups (MGs) and multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) serve as two emerging techniques for achieving high spectral efficiency (SE) in the next-generation networks. In this paper, a PSOAM MGs based multi-user MIMO-NOMA system is studied, where the base station transmits data to users by utilizing the generated PSOAM beams. For such scenario, the interference between users in different PSOAM mode groups can be avoided, which leads to a significant performance enhancement. We aim to maximize the energy efficiency (EE) of the system subject to the constraints of the total transmission power and the minimum data rate. This designed optimization problem is non-convex owing to the interference among users, and hence is quite difficult to tackle directly. To solve this issue, we develop a dual layer resource allocation algorithm where the bisection method is exploited in the outer layer to obtain the optimal EE and a resource distributed iterative algorithm is exploited in the inner layer to optimize the transmit power. Besides, an alternative resource allocation algorithm with Deep Belief Networks (DBN) is proposed to cope with the requirement for low computational complexity. Simulation results verify the theoretical findings and demonstrate the proposed algorithms on the PSOAM MGs based MIMO-NOMA system can obtain a better performance comparing to the conventional MIMO-NOMA system in terms of EE

Novel Insights into Orbital Angular Momentum Beams: From Fundamentals, Devices to Applications

It is well-known by now that the angular momentum carried by elementary particles can be categorized as spin angular momentum (SAM) and orbital angular momentum (OAM). In the early 1900s, Poynting recognized that a particle, such as a photon, can carry SAM, which has only two possible states, i.e., clockwise and anticlockwise circular polarization states. However, only fairly recently, in 1992, Allen et al. discovered that photons with helical phase fronts can carry OAM, which has infinite orthogonal states. In the past two decades, the OAM-carrying beam, due to its unique features, has gained increasing interest from many different research communities, including physics, chemistry, and engineering. Its twisted phase front and intensity distribution have enabled a variety of applications, such as micromanipulation, laser beam machining, nonlinear matter interactions, imaging, sensing, quantum cryptography and classical communications. This book aims to explore novel insights of OAM beams. It focuses on state-of-the-art advances in fundamental theories, devices and applications, as well as future perspectives of OAM beams

Millimeter-wave multiplexed wideband wireless link using rectangular-coordinate orthogonal multiplexing (ROM) antennas

This paper is the first demonstration of multiplexed wideband data transmission in the millimeter-wave range using rectangular-coordinate orthogonal multiplexing (ROM) antennas. This spatial wireless multiplex communication method can be applied at several hundred GHz for further improvements in the data rate because much wider bandwidth is available and this multiplexing method does not require any signal processing. The multiplexing is achieved through the spatial eigenmodes of a novel antenna based on a rectangular coordinate system and magic-T which eliminates the need for computational signal processing efforts. The aperture distributions of these spatial eigenmodes are designed to have different polarities to avoid crosstalk and operate over a wide bandwidth range. We demonstrate their performance with four eigenmodes, achieving crosstalk between modes below -37.8 dB over a 14.6% relative bandwidth (57-66 GHz). We have introduced these antennas on a photonics-enabled real-time wireless data transmission, transmitting over two channels simultaneously, without any signal processing at the transmitter (multiplex) or the receiver (demultiplex). The two multiplexed channels show a total data rate up to 9.0 Gbps at most (5.875 Gbps and 3.125 Gbps for each channel) limited by the bandwidth of the low noise amplifiers at the receiver. The measured bit error rate (BER) is below the forward error correction (FEC) limit.This work was supported in part by SEI Group CSR Foundation and the Murata Science Foundation

ループアンテナアレイを用いたOAM 多重通信の給電点方位制御及び信号処理による高性能化

　近年，多様な無線システムが通信容量を向上させるために帯域幅の拡大を図っている．しかし，利用できる周波数帯域には制限があるため，シャノン・ハートレーの定理に添った形で指数関数的に電力を消費することで周波数利用効率を向上させている．一方，OAM多重通信は電磁界の軌道角運動量(OAM: Orbital Angular Momentum)を活用することで，伝送容量倍の電力で同じ多重化が可能となるため，通信多重化の新たな次元を提供するものとして近年注目されている．OAMは空間の対称性から整数値mに限られ，それらのモードは互いに直交していることから，複数のモードのOAM波を同一空間，同一周波数に用いても，単一モードのOAM波を放射するアンテナを用いることでモードが同じアンテナ間のみで通信が成立する．　ここでは，概ね単一モードのOAM波を放射する円形ループアンテナの給電点方位を制御することで，干渉波を抑制できることを示した．また，近距離通信において，受信アレイを反転させることで隣接ループからの干渉波を抑制できることを数式によって示した．5GHz帯において，給電点方位がすべて同一である場合に比べて，給電点方位DEG-Aを用いた近距離OAM多重通信では9.2dB改善し23.6dB，給電点方位DEG-Bを用いた遠距離OAM多重通信では2.7dB改善し13.5dBの通過アイソレーションを得た．　また，遠距離OAM多重通信の性能を向上させるために，回折を抑制する目的で高周波数化し，12GHz帯OAM多重通信を行った．また，パラボロイドからのアレイ位置の最適化，電流分布への影響を抑制するための垂直バランを用いて伝送距離90cmの実測を行い，17.6dBの通過アイソレーションを得た．　固定体間Line-of-Sight(LoS)環境では伝達関数が一意に定まるため，測定で得られた伝達関数を用いて周波数領域での等価を行った．2×2の5GHz帯近距離OAM多重通信の実測において，EVMが8.9%，7.4%から1.5%，2.0%に改善した．実測の結果に数値計算においてノイズを加えることで，信号処理を行ったBER特性が64QAMでの理論値に沿ったものになった．電気通信大学201