This paper considers the application of multiple-input multiple-output (MIMO) techniques to non-orthogonal multiple access (NOMA) systems. A new design of precoding and detection matrices for MIMO-NOMA is proposed and its performance is analyzed for the case with a fixed set of power allocation coefficients. To further improve the performance gap between MIMO-NOMA and conventional orthogonal multiple access schemes, user pairing is applied to NOMA and its impact on the system performance is characterized. More sophisticated choices of power allocation coefficients are also proposed to meet various quality of service requirements. Finally computer simulation results are provided to facilitate the performance evaluation of MIMO-NOMA and also demonstrate the accuracy of the developed analytical results.

sion multiple access aimed at third-generation mobile communications systems is reviewed. W-CDMA is designed t o flexibly offer wideband services which cannot be provided by present cellular systems, with various data rates as high as 2 Mb/s. The important concept of W-CDMA is the introduction of intercell asynchronous operation and t h e pilot channel associated w i t h individual data channels. Intercell asynchronous operation facilitates continuous system deployment from outdoors t o indoors. Other technical features of W-CDMA include fast cell search under intercell asynchronous operation, fast transmit power control, coherent spreading code tracking, a coherent Rake receiver, orthogonal multispreading factor forward link, and variable-rate transmission w i t h blind rate detection. The introduction o f the data-channel-associated pilot channel allows W-CDMA t o support interference cancellation and adaptive antenna array techniques that can significantly increase the link capacity and coverage. This article presents radio link performance evaluated by computer simulation. Field experiment radio link performance results are also presented. ecently, mobile communications services are pen-R etrating into our society at an explosive growth rate. All of the current second-generation cellular communications systems (e.g., PDCIGSMIIS54 and IS95) have adopted digital technology. However, the major services they provide are limited to basic services, such as voice, facsimile, and low-bit-rate (far less than 64 kb/s) data. We are now approaching the 21st century, when demands for a variety of wideband services such as high-speed Internet access and videolhigh-quality image transmission, will continue to increase. The third-generation mobile communication systems, called International Mobile Telecommunications-2000 (IMT-2000) in the International Telecommunication Union (ITU) [l], must be designed to support wideband services at data rates as high as 2 Mbis, with the same quality as fixed networks. Direct sequence code-division multiple access (DS-CDMA) technology [a] is attractive for wireless access because of its numerous advantages over time-division multiple access (TDMA) and frequency-division multiple access (FDMA), including soft handoff (or site diversity), exploitation of multipath fading through Rake combining, and direct capacity increase by the use of cell sectorization. However, the current IS-95 is based on narrowband DS-CDMA technology optimized for basic services. To realize true IMT-2000 systems, a new wideband wireless access technology incorporating as many recent technology developments as possible is necessary. The most promising candidate, wideband DS-CDMA (W-CDMA), is being developed throughout the world [3, 41. In January 1998, the European Telecommunications Standards Institute (ETSI) decided to adopt W-CDMA technology for frequency-division duplex (FDD) bands. In Japan, the Association of Radio Industries and Businesses (ARIB), the standardization body of the radio sector, is now developing a...

Millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) has been regarded to be an emerging solution for the next generation of communications, in which hybrid analog and digital precoding is an important method for reducing the hardware complexity and energy consumption associated with mixed signal components. However, the fundamental limitations of the existing hybrid precoding schemes is that they have high computational complexity and fail to fully exploit the spatial information. To overcome these limitations, this paper proposes a deep-learning-enabled mmWave massive MIMO framework for effective hybrid precoding, in which each selection of the precoders for obtaining the optimized decoder is regarded as a mapping relation in the deep neural network (DNN). Specifically, the hybrid precoder is selected through training based on the DNN for optimizing precoding process of the mmWave massive MIMO. Additionally, we present extensive simulation results to validate the excellent performance of the proposed scheme. The results exhibit that the DNN-based approach is capable of minimizing the bit error ratio (BER) and enhancing spectrum efficiency of the mmWave massive MIMO, which achieves better performance in hybrid precoding compared with conventional schemes while substantially reducing the required computational complexity.Index Terms-Millimeter wave (mmWave), massive multipleinput multiple-output (MIMO), deep learning, hybrid precoding.

The innovations of sixth generation wireless communication (6G) as compared to fifth generation (5G) are considered in this paper based on the analysis of related works. With the aim of improving multiple communication targets in each service, five 6G core services are identified for different target requirements. Two centricities and eight key performance indices (KPIs) are detailed to describe these services, and enabling technologies are discussed to satisfy the KPIs. A 6G architecture is proposed as an integrated system of the enabling technologies, and is then illustrated using four typical application scenarios. Potential challenges for development of 6G technology is then discussed and possible solutions are proposed. Finally, opportunities for exploring 6G are analyzed in order to guide future research. RELATED WORKSCommercial approvals have been officially declared for the deployment of fifth generation (5G) wireless systems in numerous countries, with 5G enabled smart phones and infrastructures already appearing in the market. However, prior to the recently emerging commercial applications of 5G, research exploring future wireless systems has already extended to the concept of beyond 5G (B5G). Furthermore, since 2018, scholars have begun to focus on the concept of 6G and its applications [1]. B.

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The new demands for high-reliability and ultra-high capacity wireless communication have led to extensive research into 5G communications. However, the current communication systems, which were designed on the basis of conventional communication theories, significantly restrict further performance improvements and lead to severe limitations. Recently, the emerging deep learning techniques have been recognized as a promising tool for handling the complicated communication systems, and their potential for optimizing wireless communications has been demonstrated. In this article, we first review the development of deep learning solutions for 5G communication, and then propose efficient schemes for deep learning-based 5G scenarios. Specifically, the key ideas for several important deep learningbased communication methods are presented along with the research opportunities and challenges.In particular, novel communication frameworks of non-orthogonal multiple access (NOMA), massive 2 multiple-input multiple-output (MIMO), and millimeter wave (mmWave) are investigated, and their superior performances are demonstrated. We vision that the appealing deep learning-based wireless physical layer frameworks will bring a new direction in communication theories and that this work will move us forward along this road.

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An experimental investigation is reported of the crosscorrelation of 900 MHz signals received by two spatially separated antennas at a base station. The investigation embraced vertical, horizontal and combined horizontal and vertical separation of the antennas, for transmission from test routes 1.3 km from the base station. It was found that a crosscorrelation <0.7 (i.e. when diversity improvement becomes significant) can best be achieved using vertical separation of the antennas of between 11 X and 13 X, for the 1.3 km cell radius. At 900 MHz such an antenna separation is easily obtained and, in addition, the roof space required is small. Moreover, the crosscorrelation using vertically spaced antennas is independent of the incoming arrival angle (unlike horizontally spaced antennas), and hence low correlation can be achieved while maintaining omnidirectional coverage. List of principal symbolsd' d H dy p ID ft 7s L m 2 N p(z) r v = R(t) = r(t) = T = {z}* = <2> = a = oc H = a,-= oc v = A = 4>i = Penv =