Chih-Lin I

New Paradigm of 5G Wireless Internet

5G network is anticipated to meet the challenging requirements of mobile traffic in the 2020s, which are characterized by super high data rate, low latency, high mobility, high energy efficiency, and high traffic density. This paper provides an overview of China Mobiles 5G vision and potential solutions. Targeting a paradigm shift to user-centric network operation from the traditional cell-centric operation, 5G radio access network (RAN) design considerations are presented, including RAN restructure, Turbo charged edge, core network (CN) and RAN function repartition, and network slice as a service. Adaptive multiple connections in the user-centric operation is further investigated, where the decoupled downlink and uplink, decoupled control and data, and adaptive multiple connections provide sufficient means to achieve a 5G network with “no more cells.” Software-defined air interface (SDAI) is presented under a unified framework, in which the frame structure, waveform, multiple access, duplex mode, and antenna configuration can be adaptively configured. New paradigm of 5G network featuring user-centric network (UCN) and SDAI is needed to meet the diverse yet extremely stringent requirements across the broad scope of 5G scenarios.

Sum rate optimization for MIMO non-orthogonal multiple access systems

Non-orthogonal multiple access (NOMA) is expected to be a promising technique for future wireless networks due to its superior spectral efficiency. In this paper, the sum rate optimization problem for multiple-input multiple-output (MIMO) NOMA systems is studied with the total transmit power constraint and the minimum rate constraint of weak user. We first derive a channel state information (CSI) condition in which MIMO NOMA systems can achieve full rate transmission, i.e. the transmission rate of the weak user equals to the channel capacity of weak user. Based on the CSI condition, we propose an optimal power allocation scheme for MIMO NOMA systems, which can achieve the capacity region of MIMO Broadcast channel as dirty paper coding. A low complexity suboptimal scheme is proposed as well for all CSI channel conditions. Numerical results show that the proposed NOMA schemes significantly outperform the traditional time division based single user MIMO scheme and the multi-user MIMO scheme.

Reference Signals Design for Hybrid Analog and Digital Beamforming

There are many issues regarding the implementation of digital beamforming (BF) structures in massive MIMO: calibration, complexity, and cost. In a practical massive MIMO deployment, hybrid digital and analog BF structures with active antennas can be an alternative choice. In this letter, an N (the number of transceivers) by M (the number of active antennas per transceiver) hybrid BF structure is investigated, where the analog BF (ABF) is performed per transceiver and digital BF (DBF) is performed across N transceivers. A hybrid BF scheme is proposed, where the same ABF is applied to each transceiver, on top of which a DBF is designed to maximize the gain in a certain direction around the ABFs main beam direction. The proposed hybrid BF design establishes an inherent connection between the DBF and the beam direction of hybrid BF. Therefore, beam domain reference signals (RSs) can be conveniently implemented via applying properly designed DBF on subcarriers within the coherent bandwidth. Simulation results are given to show the validity of the proposed scheme.

5G: rethink mobile communications for 2020+.

The 5G network is anticipated to meet the challenging requirements of mobile traffic in the 2020s, which are characterized by super high data rate, low latency, high mobility, high energy efficiency and high traffic density. This paper provides an overview of China Mobile’s 5G vision and potential solutions. Three key characteristics of 5G are analysed, i.e. super fast, soft and green. The main 5G R&D themes are further elaborated, which include five fundamental rethinkings of the traditional design methodologies. The 5G network design considerations are also discussed, with cloud radio access network, ultra-dense network, software defined network and network function virtualization examined as key potential solutions towards a green and soft 5G network. The paradigm shift to user-centric network operation from the traditional cell-centric operation is also investigated, where the decoupled downlink and uplink, control and data, and adaptive multiple connections provide sufficient means to achieve a user-centric 5G network with ‘no more cells’. The software defined air interface is investigated under a uniform framework and can adaptively adapt the parameters to well satisfy various requirements in different 5G scenarios.

Alternating beamforming methods for hybrid analog and digital MIMO transmission

Hybrid beamforming has drawn attention with the increasing concern on high frequency band communication and the appearance of flexible structures of base stations. This paper considers the practical transmitter structure that each antenna is only connected to a unique RF chain and optimizes the analog and digital beamforming matrices to maximize the achievable rate with transmit power constraint. Following alternating optimization principle, closed-form relationships between analog and digital precoders are obtained when both amplitude and phase or only phase can be adjusted to form analog beams. Simulation results demonstrate the advantage of our proposed methods over the existing beam steering method in terms of achievable rate with different scale antenna array. This reveals that the method can be applied to both low and high frequency band communications. When increasing the number of propagation paths, contrast to the traditional beam steering method, the performance of proposed methods becomes better while the complexity almost keeps at an acceptable constant level.

Theoretical study and performance evaluation of macro‐assisted data‐only carrier for next generation 5G system

Summary With the explosive growth of high-data rate multimedia services and machine-to-machine (M2M) type communications, numerous small cells will be densely deployed in future fifth generation wireless network, resulting in serious interference, intolerable delay, and huge handover failure. Massive access M2M services, with low-rate high-frequency requests, will also generate much signaling overhead costs and cause enormous waste of system resources. In the Third Generation Partnership Project, the split of control and user (C/U) planes is perceived as one of the most promising methods for small cell enhancement to address these challenges. In this article, a new C/U split architecture of data-only carrier (DoC) system is analyzed comprehensively from various aspects, such as overhead costs, coverage probability, spectral efficiency, and energy efficiency for the first time. Based on the model of stochastic geometry, the influences of density and power of small cell and cell range expansion factors are all taken into account to compare the DoC architecture with the baseline long-term evolution (LTE) system. Numerical results show that the DoC system can greatly reduce the overhead costs and help to achieve higher throughput gain and better coverage performance over the conventional LTE system. Copyright

Small data optimized radio access network signaling/control design

The fast adoption of smart phone triggers the migration of tremendous internet applications from desktop to mobile terminal, as well as various inherently mobile oriented applications. Among them, Instant Message (IM) represents a large portion of applications. Unlike over traditional wired network, IM brought a great trouble to the mobile network called “signaling storm” due to its small data dominated traffic profile. This paper conducts a comprehensive analysis on the signaling/control overhead of IM, compared with streaming oriented voice/video applications. It figures out that shift from connection oriented to connectionless can solve the problem. A new slim Radio Resource Control (RRC) state with corresponding slim signaling transfer procedures is proposed for the connectionless scheme. Numerical results show that great signaling/control saving can be achieved with our new design.

EE-SE relationship for large-scale antenna systems

In large-scale antenna systems (LSAS), both energy efficiency (EE) and spectral efficiency (SE) have been recognized as important metrics for future communication system design. This paper investigates the fundamental properties of the EE-SE relationship in LSAS. Both single-user and multi-user cases are studied and different channel state information (CSI) conditions are considered. Analysis and simulation results demonstrate that the slope of the EE-SE curve only depends on the circuit power and bandwidth when the SE approaches zero, and it depends on the number of data streams, when the SE approaches infinity. Reducing circuit power brings exponential EE increase with linear SE loss. The CSI and increasing the number of transmit antennas help to reduce the SE loss to keep the same EE in the single-user case. In the multi-user case, increasing the number of users will alleviate the speed of EE reduction with the increase of SE.

Fundamental properties of the EE-SE relationship

Energy efficiency (EE) has been recognized as another important metric as well as spectral efficiency (SE). This paper investigates the fundamental properties of the EE-SE relationship. The point-to-point MIMO transmission link is considered with different channel state information (CSI) conditions. Our analysis proves that the slope of EE-SE curves only depends on the circuit power and bandwidth when the SE approaches zero while it depends on the multiplexing gain when the SE approaches infinity. Reducing circuit power is helpful to improve EE in the low SE region while introducing more antennas benefits the EE in the high SE region. We also study the properties of EE-optimal points. It is found that reducing circuit power brings exponential EE increasing with linear SE loss at the EE-optimal points. More multiplexing gain will alleviate the speed of EE reduction with the increase of SE. More diversity gain brings a fixed EE gain.

The Big-Data-Driven Intelligent Wireless Network: Architecture, Use Cases, Solutions, and Future Trends

The concept of using big data (BD) for wireless communication network optimization is no longer new. However, previous work has primarily focused on long-term policies in the network, such as network planning and management. Apart from this, the source of the data collected for analysis/model training is mostly limited to the core network (CN). In this article, we introduce a novel data-driven intelligent radio access network (RAN) architecture that is hierarchical and distributed and operates in real time. We also identify the required data and respective workflows that facilitate intelligent network optimizations. It is our strong belief that the wireless BD (WBD) and machine-learning/artificial-intelligence (AI)-based methodology applies to all layers of the communication system. To demonstrate the superior performance gains of our proposed methodology, two use cases are analyzed with system-level simulations; one is the neural-network-aided optimization for Transmission Control Protocol (TCP), and the other is prediction-based proactive mobility management.