Jiaxin Zhang

Macro-assisted data-only carrier for 5G green cellular systems

As the commercial operation of 4G systems is speeding up worldwide to meet the increasingly explosive growth of mobile Internet in the 2020 era, a great many R&D efforts targeting the next generation wireless systems (5G) have been launched. With densely deployed small cells in a heterogeneous network, the excessive signaling overhead of conventional carrier design greatly degrades system performance. A new carrier designed for small cells in the next generation system will be highly beneficial toward a green communication network. In this article, we propose a macro-assisted data-only carrier for future 5G networks from a green prospective. With the help of macro base stations, control channel overhead, and cell-specific reference signals for small cells can be minimized to achieve a pure-data carrier. Under this architecture, key procedures are designed including small cell identification and access, synchronization, hand over, and small cell sleeping. Furthermore, to evaluate the potential of our proposed scheme, a complete system and link-level simulation platform according to the current 3GPP LTE standard is built. The simulation results show that our proposed systems, achieving significant performance enhancement of signaling overhead, can lead to more than 17 percent throughput improvement and 90 percent energy efficiency gain over the current LTE HetNet with on-off strategy implemented. The proposed scheme appears to be highly attractive as part of the future 5G green mobile networks.

Energy-Efficient Design in Heterogeneous Cellular Networks Based on Large-Scale User Behavior Constraints

Large-scale user behavior can be used as the guidance for deployment, configuration, and service control in heterogeneous cellular networks (HCNs). However, in wireless networks, large-scale user behavior (in terms of traffic fluctuation in spatial domain) follows inhomogeneous distribution, which brings enormous challenges to energy-efficient design of HCNs. In this paper, the heterogeneity of large-scale user behavior is quantitatively characterized and exploited to study the energy efficiency (EE) in HCNs. An optimization problem is formulated for energy-efficient two-tier deployment and configuration, where the base station (BS) density, BS transmit power, BS static power, and quality of service are taken into account. We present closed-form formulas that establish the quantitative relationship between large-scale user behavior and energy-efficient HCN configuration. These results can be used to determine BS density and BS transmit power with the objective of achieving optimal EE. Furthermore, we present three energy-efficient control strategies of micro BSs, including micro BS sleep control, coverage expansion control, and coverage shrinking control. Simulation results validate our theoretical analysis and demonstrate that the proposed control strategies can potentially lead to significant power savings.

Base stations from current mobile cellular networks: Measurement, spatial modeling and analysis

In heterogeneous cellular networks spatial characteristics of base stations (BSs) influence the system performance intensively. Existing models like two-dimensional hexagonal grid model or homogeneous spatial poisson point process (SPPP) are based on the assumption that BSs are ideal or uniformly distributed, but the aggregation behavior of users in hot spots has an important effect on the location of low power nodes (LPNs), so these models fail to characterize the distribution of BSs in the current mobile cellular networks. In this paper, firstly existing spatial models are analyzed. Then, based on real data from a mobile operator in one large city of China, a set of spatial models is proposed in three typical regions: dense urban, urban and suburban. For dense urban area, “Two Tiers Poisson Cluster Superimposed Process” is proposed to model the spatial characteristics of real-world BSs. Specifically, for urban and suburban area, conventional SPPP model still can be used. Finally, the fundamental relationship between user behavior and BS distribution is illustrated and summarized. Numerous results show that SPPP is only appropriate in the urban and suburban regions where users are not gathered together obviously. Principal parameters of these models are provided as reference for the theoretical analysis and computer simulation, which describe the complex spatial configuration more reasonably and reflect the current mobile cellular network performance more precisely.

Mobility enhancement and performance evaluation for 5G Ultra dense Networks

Future wireless network will address the explosive increase demand of high-data-rate video services as well as massive-access machine type communication (MTC) requests, so that increasing number of small cells are conceived to be densely deployed in hot spots, resulting in an Ultra-dense Network (UDN). As a main issue for the future network, UDN is a step further towards a low-cost, self-configuring and self-optimizing network, while also leading to high-frequent measurement, intolerable handover failure (HOF), as well as huge power consumption in both the terminal and access network. Thus, mobility enhancement in ultra-dense scenario has become a critical problem for the next generation wireless systems. To solve this problem, the split of control plane and user plane (C/U) has become one of the most promising way, as it allows more flexibility and better service control schemes. Inspired by this, a set of macro assisted small cell enhancement schemes is proposed contributing to a novel Data-only Carrier (DoC) system in our previous work. In this paper, for improving the handover (HO) performance, new mobility-enhanced schemes are designed and analyzed in detail in DoC network, taking into consideration of mobility, flexibility and various typical handover scenarios. Simulations are conducted by a system-level platform to illustrate the fundamental relationship between key handover parameters and mobility performance. Numerical results show that the gain of system HOF rises by 53.6% via optimizing and reconfiguring the handover parameters in DoC network. In addition, the DoC network has an excellent performance gain in UDN with 82% HO improvement and 44.34% energy efficiency promotion compared with the current LTE network, which may be a promising mobility enhancement strategy for future 5G networks.

An Approach for Spatial-Temporal Traffic Modeling in Mobile Cellular Networks

The volume and types of traffic data in mobile cellular networks have been increasing continuously. Meanwhile, traffic data change dynamically in several dimensions such as time and space. Thus, traffic modeling is essential for theoretical analysis and energy efficient design of future ultra-dense cellular networks. In this paper, the authors try to build a tractable and accurate model to describe the traffic variation pattern for a single base station in real cellular networks. Firstly a sinusoid superposition model is proposed for describing the temporal traffic variation of multiple base stations based on real data in a current cellular network. It shows that the mean traffic volume of many base stations in an area changes periodically and has three main frequency components. Then, lognormal distribution is verified for spatial modeling of real traffic data. The spatial traffic distributions at both spare time and busy time are analyzed. Moreover, the parameters of the model are presented in three typical regions: park, campus and central business district. Finally, an approach for combined spatial-temporal traffic modeling of single base station is proposed based on the temporal and spatial traffic distribution of multiple base stations. All the three models are evaluated through comparison with real data in current cellular networks. The results show that these models can accurately describe the variation pattern of real traffic data in cellular networks.

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

Edge aware cross-tier base station cooperation in heterogeneous wireless networks with non-uniformly-distributed nodes

This study investigates the cross-tier base station (BS) cooperation in non-uniform heterogeneous networks where the distribution of pico BSs (PBSs) is modelled as Neyman–Scott cluster process. The authors propose an edge aware cross-tier cooperation scheme to improve the performance of edge hotspot users that have weaker signal-to-interference-plus-noise ratio (SINR). Taking consideration of various user behaviours, non-hotspot users are only served by the nearest macro BS whilst the hotspot users with better SINR are only served by their serving PBSs. The edge hotspot users who suffer from high cross-tier interference operate in the cooperation mode. Stochastic geometry is utilised to derive the SINR and energy efficiency performance of the proposed scheme, which is compared with other classical schemes such as full cooperation (FC) and traditional non-cooperation scheme. Numerical results show that compared with the FC scheme, the proposed scheme can maximise the energy efficiency of the network by an optimal cooperation threshold, when SINR coverage is larger than a threshold. The authors also find that user behaviour have little effect on the tradeoff between SINR Coverage and energy efficiency, unless spatial aggregation coefficient is very small.

Information Caching Strategy for Cyber Social Computing Based Wireless Networks

Cyber social computing has brought great changes and potential intelligent technologies for wireless networks. Among these technologies, information caching strategies are promising approaches to achieving lower delay, higher throughput and energy efficiency (EE) of user equipment (UE) in 5G wireless networks, by deploying intelligent caching and computing at the mobile edge. However, the static information caching strategies ignore the relevance of traffic fluctuation among different base stations (BSs) and the variance of users’ interests. Thus in this paper, an information caching strategy for cyber social computing based wireless network is proposed, taking advantages of two layer social cyberspaces in both traffic correlation between BSs and the social relationship between UEs. In the first layer, a base station social network (BSSN) is constructed based on the social relationship between BSs, which is defined as social-tie factor (STF). In the second layer, the Indian Buffet Model (IBM) is used to describe the social influence of one UE to another. To reduce base station’s traffic load, users with similar social interest can share the contents they cached with each other. Therefore, device-to-device (D2D) communication is taken as the underlay to cellular networks in our proposed information caching strategy. By utilizing the social characteristic of BSSN, the very important BSs (VIBSs) with higher averages STF are selected. Then the normal small cells (NSCs) within the VIBS’s coverage are linked to the VIBSs only and the other unique small cells (USCs) will be routed back into the core network (CN) directly. Limited cache and backhaul capacity in the whole network are only shared by VIBSs and USCs. UEs will communicate with each other via D2D links only if they have i) similar interests, ii) enough encounter duration between users and iii) are adjacent with each other. Otherwise, the UE shall obtain the required contents via cellular networks. With the tool of stochastic geometry process, key performance indicators, e.g., coverage probability, network throughput power consumption, EE, delay and offloaded traffic are studied. Both the theoretical and numerical results show that the proposed information caching strategy for cyber social computing can achieve high coverage probability, throughput, EE and delay by optimizing STF threshold, VIBS coverage and D2D communication radius.

Mobility-Aware Coded Probabilistic Caching Scheme for MEC-Enabled Small Cell Networks

Caching on the edge has been recognized as an effective solution to tackle the backhaul constraint of network densification. However, most related works ignored user mobility in wireless networks, which is unreasonable under the background of network densification. For a more flexible and context-aware caching decision, the concept of caching on the edge can be extended to mobile edge computing (MEC) that enables computation and storage resources at mobile edge networks. With MEC servers deployed on base stations, a huge amount of collected radio access network context data can be analyzed and utilized to render a caching scheme adaptive to user’s context-aware information. In this regard, a novel mobility-aware coded probabilistic caching scheme is proposed for MEC-enabled small cell networks (SCNs). Different from previous mobility-aware caching schemes, user mobility and distributed storage are incorporated into a conventional probabilistic caching scheme, with the aim of throughput maximization. Based on stochastic geometry theory and a modified mobility model of discrete random jumps, the explicit expression of throughput is derived. Due to the complexity of the expression, two light-weight heuristic algorithms are provided to numerically obtain the optimal solutions. Moreover, a significant trade-off among the gains of mobility diversity, content diversity, and channel selection diversity is discussed, and we further numerically analyze how such a trade-off is influenced by user mobility, content popularity, and backhaul capacity, with some fundamental insights into the application of the proposed scheme in MEC-enabled SCNs. The superiority of our proposed scheme is demonstrated by the comparisons with the classical M most popular caching scheme and the conventional probabilistic caching scheme. Numerical results show that our proposed caching scheme achieves higher throughput than those of the other two, especially when users of intense mobility request contents, of which the popularity profile is not skewed, in MEC-enabled SCNs with poor backhaul capacity, indicating that the proposed caching scheme is a promising solution for network densification.

Energy Efficiency Analysis of Heterogeneous Cache-Enabled 5G Hyper Cellular Networks

The emerging 5G wireless networks will pose extreme requirements such as high throughput and low latency. Caching as a promising technology can effectively decrease latency and provide customized services based on group users behaviour (GUB). In this paper, we carry out the energy efficiency analysis in the cache-enabled hyper cellular networks (HCNs), where the macro cells and small cells (SCs) are deployed heterogeneously with the control and user plane (C/U) split. Benefiting from the assistance of macro cells, a novel access scheme is proposed according to both user interest and fairness of service, where the SCs can turn into semi- sleep mode. Expressions of coverage probability, throughput and energy efficiency (EE) are derived analytically as the functions of key parameters, including the cache ability, search radius and backhaul limitation. Numerical results show that the proposed scheme in HCNs can increase the network coverage probability by more than 200% compared with the single- tier networks. The network EE can be improved by 54% than the nearest access scheme, with larger research radius and higher SC cache capacity under lower traffic load. Our performance study provides insights into the efficient use of cache in the 5G software defined networking (SDN).