Range expansion and inter-cell interference coordination (ICIC) can improve the capacity and fairness of heterogeneous network (HetNet) deployments by off-loading macrocell users to low-power nodes. Due to difficulties in analytical treatment, current studies for range expansion and ICIC in HetNets rely mostly on simulations. In this letter, first, off-loading benefits of range expansion in HetNets are captured through cumulative distribution functions (CDFs) of the downlink signal to interference plus noise ratio (SINR) difference between the macrocell and strongest picocell signals. Then, these CDFs are used to investigate the system capacity and fairness as a continuous function of the range expansion bias, and benefits of using ICIC with range expansion are demonstrated through numerical results.

Capacity and Fairness Analysis of Heterogeneous Networks with Range Expansion and Interference Coordination

The Mobile and wireless communications Enablers for the Twenty-twenty Information Society (METIS) project is laying the foundations of Fifth Generation (5G) mobile and wireless communication system putting together the point of view of vendors, operators, vertical players, and academia. METIS envisions a 5G system concept that efficiently integrates new applications developed in the METIS horizontal topics and evolved versions of existing services and systems. This article provides a first view on the METIS system concept, highlights the main features including architecture, and addresses the challenges while discussing perspectives for the further research work.

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METIS research advances towards the 5G mobile and wireless system definition

To encourage data offloading in heterogeneous networks, range expansion techniques have been introduced in LTE-Advanced system. By adding a positive bias in cell selection process, more users can select picocells as their serving cells even the picocell is not of the strongest signal. Also, to protect offloaded users from severe macrocell interference, a specific subframe called almost blank subframe (ABS) is introduced. Since macrocell is kept silent during ABSs, the offloaded users can be allocated without strong macrocell interference within ABSs. It is noted that the offloaded user's average data rate highly depends on the amount of ABSs rather than the bias value because the scheduling opportunities of offloaded users are limited within ABSs. And from the user's point of view, the cell which is expected to give high data rate should be selected as a serving cell. In this paper, we propose a cell selection scheme based on expected user data rate which is a function of the ABS ratio. Simulation results show that the performance of our proposed cell selection scheme can improve average user rate and increase the number of offloaded users as the ABS ratio increases.

Cell selection for range expansion with almost blank subframe in heterogeneous networks

Heterogeneous networks (HetNets) with a topology of mixed macro-cells and low-power nodes (LPNs) form an important step of capacity enhancement for LTE and LTE-A. In this paper, we present an optimization framework for load balancing in LTE HetNets, by means of cell range assignment using cell-specific offset. For any given offset setting, the resulting cell load is effectively approached via the solution of a system of non-linear equations characterizing the load-coupling relation between cells. We present a computationally efficient bounding scheme to approximate the solution of the non-linear system and provide theoretical insights into the monotonicity and convergence of the scheme. The bounding scheme is embedded into an algorithm based on the principle of design of experiments (DOE) for cell offset optimization. Simulation results demonstrate the effectiveness of the optimization process for LTE load balancing with HetNet elements.

Load balancing in heterogeneous LTE: Range optimization via cell offset and load-coupling characterization

Multi-tier cellular networks are considered as an effective solution to enhance the coverage and data rate offered by cellular systems. In a multi-tier network, high power base stations (BSs) such as macro BSs are overlaid by lower power small cells such as femtocells and/or picocells. However, co-channel deployment of multiple tiers of BSs gives rise to the problem of cross-tier interference that significantly impacts the performance of wireless networks. Multicell cooperation techniques, such as coordinated multipoint (CoMP) transmission, have been proposed as a promising solution to mitigate the impact of the cross-tier interference in multi-tier networks. In this paper, we propose a novel scheme for Location-Aware Cross-Tier Cooperation (LA-CTC) between BSs in different tiers for downlink CoMP transmission in two-tier cellular networks. On one hand, the proposed scheme only uses CoMP transmission to enhance the performance of the users who suffer from high cross-tier interference due to the co-channel deployment of small cells such as picocells. On the other hand, users with good signal-to-interference-plus-noise ratio (SINR) conditions are served directly by a single BS from any of the two tiers. Thus, the data exchange between the cooperating BSs over the backhaul network can be reduced when compared to the traditional CoMP transmission scheme. We use tools from stochastic geometry to quantify the performance gains obtained by using the proposed scheme in terms of outage probability, achievable data rate, and load per BS. We compare the performance of the proposed scheme with that of other schemes in the literature such as the schemes which use cooperation to serve all users and schemes that use range expansion to offload users to the small cell tier.

Location-Aware Cross-Tier Coordinated Multipoint Transmission in Two-Tier Cellular Networks

Deploying Pico eNodeBs (PeNBs) throughout a Macro cell layout is a promising solution to enhance system capacity and user throughput. However, strong received power from Macro eNodeBs (MeNBs) makes the Pico cell areas narrow. This causes limited cell splitting gain. Cell Range Expansion (CRE), which allows a User Equipment (UE) to be served by a cell with weaker received power, is simple and typical one of alternative cell associations to enhance offloading but it causes downlink (DL) interference issue in not only data and also control channels (CCHs). In this paper, we investigate performance of CRE with various bias settings and show that a moderate bias setting is effective to enhance capacity and user throughput. With respect to the DL interference issue in CCHs, we propose to support coordination of Lightly Loaded CCH transmission Subframe (LLCS) in LTE-Advanced.

Pico Cell Range Expansion with Interference Mitigation toward LTE-Advanced Heterogeneous Networks

A radio communication system wherein a femto cell base station ( 100 a ) is located in a macro cell (MC 1 ) and a radio terminal ( 200 a ) is connected to the femto cell base station ( 100 a ) and wherein the femto cell base station ( 100 a ) or radio terminal ( 200 a ) controls, based on a propagation loss between the radio terminal ( 200 a ) and a macro cell base station ( 300 a ) existing in the neighborhood of the radio terminal ( 200 a ), the transmission power of a radio signal to be transmitted from the radio terminal ( 200 a ) to the femto cell base station ( 100 a ).

Radio communication system, small cell base station, radio terminal, transmission power control method, and allocation control method

An EMS (200) controls: a fuel cell unit (150) which comprises a cell stack (151B) which generates power by chemical reaction, and an auxiliary device; and a storage cell unit (140) which comprises a storage cell (141). The EMS (200) comprises: a control unit (230) which instructs the fuel cell unit (150) to enter one operation mode among a power generation mode and a temperature maintenance mode, said power generation mode being a mode wherein power generation is proactively carried out by the cell stack (151B), and said temperature preservation mode being a mode wherein control is performed such that power consumption by the auxiliary device is covered by power supplied from an external source and such that the temperature of a power generation unit is maintained within a prescribed temperature range. If, when charging the storage cell (141), the unit price of electricity from a grid falls below a prescribed value, the control unit (230) controls the fuel cell unit to operate in the temperature maintenance mode.

Control device, fuel cell system, and control method

A HEMS (100) for controlling a plurality of storage cells (10) provided to electric power consumers acquires information on the respective types and/or degradation levels of the plurality of storage cells (10). The HEMS (100) controls the charging and discharging of each of the plurality of storage cells (10) on the basis of the respective types and/or degradation levels of the plurality of storage cells (10).

Control device, control system, and storage cell control method

A HEMS 100 that controls a plurality of storage batteries 10 provided in a power consumer acquires information on type and/or deterioration level of each of the plurality of storage batteries. The HEMS 100 controls charge and discharge of each of the plurality of storage batteries 10 on the basis of the information on the type and/or the deterioration level of each of the plurality of storage batteries 10.

Hirotaka Sato

Papers

Pico Cell Range Expansion with Interference Mitigation toward LTE-Advanced Heterogeneous Networks

Radio communication system, small cell base station, radio terminal, transmission power control method, and allocation control method

Control device, fuel cell system, and control method

Control device, control system, and storage cell control method

Control apparatus, control system, and storage battery control method