Yoji Kishi

A Cell-Planning Model for HetNet with CRE and TDM-ICIC in LTE-Advanced

Heterogeneous Network (HetNet) in 3GPP is a technique to increase network capacity. In order to further increase network capacity, Cell Range Expansion (CRE) and Time Domain Multiplexing Inter-Cell Interference Coordination (TDM-ICIC) have been discussed for LTE-Advanced. Since the parameter values for CRE and TDM-ICIC have a huge effect on network capacity expansion, in this paper, a cell-planning model for the downlink in HetNet with CRE and TDM-ICIC is presented in order to find the minimum number of installed pico BSs under the constraint of covering all user data traffic. The constraint condition is formulated by using an overload indicator for the cases of between normal subframes and muted subframes, because different interference sources are considered for these subframes by adopting TDM-ICIC. The appropriate parameter values of not only CRE and TDM-ICIC but also the location, transmission power, and antenna tilt for each pico BS are determined. Cell planning is conducted for traffic distribution generated by reference to realistic traffic distribution by a greedy algorithm based on the proposed cell-planning model. The result shows that the solution algorithm finds a good approximate solution which covers all data traffic by installing one pico BS with CRE bias value = 8 dB and setting the muted subframe ratio = 0.2.

Fractional Base Station Cooperation Cellular Network

In modern cellular systems, high-rate communication is performed using MIMO transmission by a Single Base Station (BS). This method is able to improve the transmission rate when the user is at the cell-inner. However the rate severely degrades when the user is located at cell-edge. Base Station Cooperation (BSC) MIMO is solve the cell-edge problem. BSC MIMO can improve capacity at the cell-edge than FFR or TAA cancellation, however, it has minimal impact on cell-inner users and increases complexity of the network. In this paper, Fractional Base Station Cooperation Cellular Network (FBSC-CN) is proposed in which a combination of Single BS MIMO and BSC Multiuser (MU) MIMO is performed in order to achieve gains both at the cell-inner and cell-edge with limited complexity. Furthermore, by cooperating with each BS autonomously and distributedly, cooperative BSs are able to select the most suitable transmission schemes to the users accordingly.

A proposal of millimeter-wave multi-hop mesh wireless network architecture with adaptive network control features for broadband fixed wireless access

This paper proposed new system architecture and its features for multi-hop mesh wireless networks using millimeter-wave bands for broadband fixed wireless access (BFWA) systems. Adopting the adaptive control of network resources such as communications routes, wireless links and radio channels, the proposed system aimed to overcome the difficulty in the deployment of millimeter-wave broadband wireless access systems. The wireless node architecture and two possible approaches are also discussed for the adaptive control in the proposed mesh wireless network. The quantitative evaluation on the overall performance is performed for the proposed adaptive network control together with the studies on the algorithms for each of the communications routing, the wireless link configuration, and the radio channel controls.

Novel WLAN Coverage Area Estimation Leveraging Transition of Cellular Signal Using Multi-Mode Mobile Terminal for Heterogeneous Networks

It is necessary to select an appropriate access network out of the several available as well as perform vertical handover, which can be considered to be one of the key features of IMT-Advanced. We now have a dual-mode mobile terminal (MT) which can connect to both wireless LAN (WLAN) and cellular NWs, featuring a high transmission rate and wide coverage area, respectively. Before selecting and switching access NWs, it must detect the coverage areas of the access NWs that are candidates for connection. Since the MT is generally battery powered, it is a mandatory requirement to detect NWs without consuming too much power. Thus, the authors consider the possibility of controlling WLAN interface (I/F) activation solely by monitoring the transition of the signal quality of a cellular system. From some preliminary experiments and based on previous literature, it has been shown that the signal quality tends to rapidly degrade and then become more stable when moving into an indoor space, which is a different signal transition than that under fading circumstances. From the findings, in this paper, the authors introduce a radically new WLAN area estimation approach for such dual-mode MT leveraging the transition. The transition is used for the estimation of the movement from an outdoor cellular area into an indoor space, where the WLAN areas are expected. The MT activates the WLAN I/F only when it is deduced that the user is about to walk indoors. Furthermore, the authors introduce a method of ascertaining the deduction by leveraging the GPS signal. Thus, the proposed approach adopts a completely different concept from existing ones which require changes to existing NWs or keeping the WLAN I/F active for WLAN area detection. Experimental results and analysis show that the proposed approach has huge potential for reducing the amount of power consumed in detecting the coverage area compared to continuous or periodic search of the WLAN area while keeping the I/F active.

Impact of base station cooperation on cell planning

Base station cooperation (BSC) has been identified as a key radio access technology for next-generation cellular networks such as LTE-Advanced. BSC impacts cell planning, which is the methodical selection of base station (BS) sites, and BS equipment configuration for cost-effective cellular networks. In this paper, the impact of BSC on cell plan parameters (coverage, traffic, handover, and cost), as well as additional cell planning steps required for BSC are discussed. Results show that BSC maximizes its gains over noncooperation (NC) in a network wherein interference from cooperating BSs is the main limitation. Locations exist where NC may produce higher throughputs, therefore dynamic or semistatic switching between BSC and NC, called fractional BSC, is recommended. Because of interference from noncooperating BSs, the gains of BSC over NC are upper bounded, and diminishes at greater intersite distances because of noise. This encourages smaller cell sizes, higher transmit powers, and dynamic clustering of cooperative BSs.

Shared Remote Radio Head architecture to realize semi-dynamic clustering in CoMP cellular networks

In conventional cellular systems, transmission rate degrades at cell-edge because of inter-cell interference and pathloss. This problem is called “cell-edge problem”. To solve this problem, Coordinated Multi-Point (CoMP) technique has been proposed recently. CoMP can convert inter-cell interference signals from neighbor base stations (BSs) to desired signals. However, CoMP requires accurate synchronization among cooperative BSs as well as Channel State Information (CSI) between target user and all cooperative BSs. For practical realization of CoMP, new BS architecture in which a BS unit is connected to multiple Remote Radio Heads (RRHs) located apart through optical fiber has been proposed. Even using this architecture, however, CoMP can only be realized within the predefined connected RRHs (CoMP cluster). Therefore, cluster-edge users cannot experience throughput improvement by means of CoMP. This paper proposes a novel BS architecture called shared RRH network, in which each RRH is additionally connected to multiple BS units. As flexible clustering is made possible by this architecture, semi-dynamic clustering using geometrically overlapped cluster patterns allocated with orthogonal resources can be achieved which alleviates the cluster-edge problem. Simulation with parameters based on the 3GPP is setup for performance evaluation of the proposed system. Numerical results show that semi-dynamic CoMP using shared RRHs can significantly improve the system performance both at cell-inner and cell-edge compared with the conventional RRH systems, which confirms the effectiveness of the proposed network.

Optimization of picocell locations and its parameters in heterogeneous networks with hotspots

This work analyzes the optimal pico base station (BS) deployment in heterogeneous cellular networks (HetNet) with hotspots. Most of conventional works for HetNet focused on interference coordination and effective cell association methods, however, the problem of pico BS deployment (cell planning) for HetNet with hotspots has not been analyzed so much. In this paper, we extend the previously proposed optimization problem in terms of network parameters (spectrum splitting ratio and SINR bias value) to the optimal pico BS locations to maximize the system rate. Furthermore, the average user and outage user rates are evaluated numerically to show the effectiveness of the proposed optimization method. Numerical results show that the optimized pico BS locations can improve both the average and outage user rates in HetNet with hotspots.

MIMO capacity estimation based on single and dual-polarization MIMO channel measurements

Multiple-Input Multiple-Output (MIMO) wireless system is one of the most promising technologies for providing a large transmission capacity without expanding the frequency band in cellular mobile systems. This paper focuses on 2×2 MIMO capacity estimation through propagation measurements at 2GHz band. The authors conducted the measurement campaign in two regions in Fujimino (Saitama prefecture) and Yokohama (Kanagawa prefecture) Japan. The former is a typical residential area and the latter is an urban area. The paper compares MIMO spatial multiplexing efficiency in terms of the eigenvalue ratio between the single and orthogonal dual-polarization antenna configurations. The eigenvalue ratio is characterized by two parameters. One is cross-polarization discrimination (XPD) and the other is the normalized received signal strength indicator (RSSI), which represents the difference from the RSSI when free space propagation is assumed. It is verified that the MIMO capacity of the dual-polarization can be estimated from just the SNR because the dependency of the eigenvalue ratio on the propagation environment is small. In contrast, that of the single-polarization needs to consider both the eigenvalue ratio and the SNR because the eigenvalue ratios change significantly due to the propagation environment.

An adaptive load balancing in multi-hop mesh networks for broadband fixed wireless access systems

Broadband fixed wireless access (BFWA) systems with multi-hop mesh topologies operating at millimeter-wave bands have attracted considerable attention as a promising technology for high capacity access infrastructures. The primary advantage of the mesh network is an improvement of capacity by means of traffic engineering throughout the network. This work discusses an adaptive load balancing method that enables us to maximize the capacity for the mesh BFWA networks by transferring traffic using multiple routes. Considering wireless link qualities, the adaptive traffic load balancing method attempts to equalize each wireless links utilization. The proposed method implements flow-based traffic load balancing in order to avoid deteriorating the performance of TCP communications. The performance of the proposed adaptive traffic load balancing method is evaluated on experimental mesh network environments.

A study on the autonomous network synchronization scheme for mesh wireless network

In a mesh wireless network system that consists of plural wireless nodes, it is important that all wireless nodes share the same time. For example, in a TDD wireless system, the frequency resources utilization over the network can be improved by acquiring TDD frame synchronization. This paper proposes a novel scheme that autonomously realizes the synchronization in a whole wireless network without centralized control. The proposed scheme just needs information from adjacent wireless nodes and other mechanisms are not necessary. In addition, this scheme maintains synchronization in the link connected-area, if the network topology changes or node failure occurs in a local area. The proposed scheme responds flexibly to changing the network topology. The scheme is applicable in the case where many nodes join in and out frequently in the network, such as in nomadic wireless access. This paper discusses the procedures of the proposed synchronization scheme and presents examples of establishment network-wide synchronization and recovery from link failure.