Shoji Kaneko

BBU-RRH switching schemes for centralized RAN

Mobile data traffic has been increasing at a rapid pace over the past few years due to the rise of both smartphones and tablets. Small cell deployments are one of the most effective ways to increase system capacity by improving the spatial reuse of radio resources for the explosive increase in traffic loads. However, it leads to be a large cost impact for operators. Centralized RAN (C-RAN) has been proposed, which has the potential ability to reduce network costs due to reductions in civil work and/or electricity costs at local base station sites by centralizing baseband units to the center side. Moreover, C-RAN can be expected to further reduce network costs using baseband unit (BBU) pooling functions in which the centralized BBU resources can be dynamically allocated to remote radio heads (RRHs) depending on traffic load. This paper proposes semi-static and adaptive BBU-RRH switching schemes for C-RAN and evaluates their effectiveness through simulations. Under conditions of 100 RRHs, here, a RRH is comparable to a cell, and traffic distribution with a typical traffic profile in office (business) area, we confirmed that the number of BBUs can be reduced by 26% and 47% for semi-static and adaptive schemes, respectively, compared with conventional cell deployment.

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.

Predicting Radio Resource Availability in Cognitive Radio - an Experimental Examination

This paper presents a method for predicting radio resource availability in cognitive radio. In this paper, unlike a primary/secondary model, cognitive radio is defined as wireless communication technology in which each node communicates via an optimal wireless system based on recognition of radio resource availability in heterogeneous wireless communication systems. Therefore, it is important to be able to recognize such radio resource availability accurately. However, a cognitive radio node is unable to recognize the subsequent radio resource availability at the time of selecting the optimal wireless system. The authors focus on the prediction of radio resource availability to resolve the above issue. In this paper, the authors focus on IEEE802.11 and radio channel occupation time, which is calculated from packet length and the transmission rate, is used as radio resource availability. From the results of the examination, it would seem feasible that the auto-correlation coefficient (or partial auto-correlation coefficient) could be utilized as information on the reliability of the prediction value when an auto-regression model (AR model) is used for the prediction. Furthermore, by comparing n-step-ahead prediction for a time series calculated for a 1-second interval and 1-step-ahead prediction for a time series calculated for an n-second interval, it is shown that the accuracy of the prediction in both cases is almost identical when the information volume to calculate a prediction expression is the same. Therefore, either prediction approach can be selected depending on the cognitive radio system.

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.

Proposed relay method with P-MP structure of IEEE 802.16-2004

This paper presents a relay method with a P-MP (point to multipoint) structure by extending the IEEE 802.16-2004 standard in order to expand the coverage area (2004). In the proposed relay method, a RS (relay station) sends a polling message for the SSs (subscriber station) assigned to the former to forward uplink data in terms of the contention opportunities in the uplink subframe, and obtains a contention request period to communicate between the RS and these SSs. The feature of the proposed relay method is that it can be applied to TDD (time division duplex) and FDD (frequency division duplex), and both BS (base station) and RS operating at the same and at different carrier frequencies respectively. In this paper, we evaluated the basic characteristics of the proposed relay method in terms of throughput and delay time through computer simulations. We show that the introduction of the proposed relay method is effective in expanding the coverage area, and that the proposed relay method has an effect on the increase of the system throughput without affecting the delay time by adjusting the time interval parameter for BW requests of SSs assigned to the RS correctly

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.

Packet Switch and Its Impact on Dynamic Base Station Relocation in Mesh Networks Using Cognitive Radio

CR (Cognitive Radio) is a technology that can realize more intensive and efficient spectrum use through spatial and temporal utilization. In the context of mesh networks where each base station consists of heterogeneous multi-radio interfaces, packet switch in L2/L3 of each base station selects each radio interface and channel adaptively in order to take full advantage of all multiple heterogeneous interfaces. At first, this paper examines the achievable performance of the new packet switch schemes in mesh topology. Secondly, we investigate the potentiality of dynamic base station relocation approach in order to cope with the change of terminal traffic distribution, and show the impact of packet switch policy on dynamic base station relocation.

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.

Experimental Verification on the Prediction of the Trend in Radio Resource Availability in Cognitive Radio

This paper presents a prediction of the trend in radio resource availability in cognitive radio. In this paper, cognitive radio is defined as the wireless communication technology in which each node communicates via an optimal wireless system based on recognition of the radio resource availability in heterogeneous wireless communication systems. We focused on the prediction of the network allocation vector (NAV) value for radio resource availability in IEEE 802.11, which is one of the candidates for installation in a cognitive radio [1]. We verified the prediction of the future value of the trend in the NAV time series; based on an auto-regressive model (AR model) and using captured data within a real environment. Based on the results of the verification, we show that prediction based on the AR model with suitable parameters is applicable in comparison when the average of the last 10 samples is used as a predicted value and the case where prediction is not applied. Furthermore, it is possible to set up a long update interval for the regression coefficients.