Hidekazu Shimodaira

Millimeter-Wave Evolution for 5G Cellular Networks

Triggered by the explosion of mobile traffic, 5G (5th Generation) cellular network requires evolution to increase the system rate 1000 times higher than the current systems in 10 years. Motivated by this common problem, there are several studies to integrate mm-wave access into current cellular networks as multi-band heterogeneous networks to exploit the ultra-wideband aspect of the mm-wave band. The authors of this paper have proposed comprehensive architecture of cellular networks with mm-wave access, where mm-wave small cell basestations and a conventional macro basestation are connected to Centralized-RAN (C-RAN) to effectively operate the system by enabling power efficient seamless handover as well as centralized resource control including dynamic cell structuring to match the limited coverage of mm-wave access with high traffic user locations via user-plane/control-plane splitting. In this paper, to prove the effectiveness of the proposed 5G cellular networks with mm-wave access, system level simulation is conducted by introducing an expected future traffic model, a measurement based mm-wave propagation model, and a centralized cell association algorithm by exploiting the C-RAN architecture. The numerical results show the effectiveness of the proposed network to realize 1000 times higher system rate than the current network in 10 years which is not achieved by the small cells using commonly considered 3.5 GHz band. Furthermore, the paper also gives latest status of mm-wave devices and regulations to show the feasibility of using mm-wave in the 5G systems.

Cloud cooperated heterogeneous cellular networks

This paper introduces a concept of cloud cooperated heterogeneous cellular network (C-HetNet) where small power pico base stations (BSs) overlaid on a macrocell are connected to cloud radio access network (C-RAN) to operate cooperatively with the macro BS. Since the macro BS assists operation of the pico BSs, it is easy to deploy multi-band HetNet where e.g. macro BS is operated at 2GHz band and pico BSs at 3GHz or 60GHz band to expand operation bandwidth. Moreover, cell structure of pico BSs are controlled dynamically to track hotspot users via beam steering and cooperative transmission among pico BSs. In this paper, several numerical simulations show effectiveness of the proposed architecture, where 1,000 times system rate than that of current single band cellular network is achieved by using the proposed architecture.

Outdoor millimeter-wave access for heterogeneous networks — Path loss and system performance

The millimeter-wave frequency bands, especially the license free band at 60 GHz, is a candidate for future broadband access links. Path loss measurements have been performed in a typical small cell access scenario. Path loss model parameters were derived for these results, including large and small scale effects. Using this model a system level analysis was performed to evaluate the performance of a heterogeneous network using millimeter-wave access links.

Dynamic cell activation and user association for green 5G heterogeneous cellular networks

The mobile traffic explosion predicted to be increased by 1000 times in the next 10 years has become a remarkable issue due to the proliferation of smart devices such as smart phones or tablets. Energy consumption of information processing is also becoming an economic issue for operators. It is a critical task to design the next generation cellular networks (5G) to be both spectral/energy efficient. This paper considers a future C-RAN based cloud cooperated HetNet which enables global resource optimization among smallcells. The architecture allows optimal user association for data offloading as well as dynamic ON/OFF of smallcell BSs in adaptation to daily data traffic. A joint optimization on both user association and dynamic ON/OFF scheme of BSs to maximizing the system rate over consumed energy of the network investigated in the paper reveals that without sacrificing the systems power resource, our proposed approach can effectively deactivate unnecessary BSs and attain the target 1000× system rate gain in the case of mm-wave smallcells.

Cell association method for multiband heterogeneous networks

In traditional heterogeneous cellular networks (Het-Net), base stations (BS) basically associate users based on received signal power. However, in the case of multiband HetNet, in which macro BSs and smallcell BSs use different frequency bands, this conventional cell association method is not effective because there is no interference between macro BSs and smallcell BSs. Additionally, there are huge differences in coverage and available bandwidth. These differences cause inefficient association which causes the imbalance between achievable rate and traffic demand. In order to overcome this problem, we propose a novel cell association method based on the combinatorial optimization. The proposed method considers achievable rates, traffic demands and the number of users belonging to each BSs simultaneously. Numerical simulation results show that the proposed association method achieves system rate gain twice as high as the conventional one.

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.

Investigation on millimeter-wave spectrum for 5G

Mobile traffic is increasing exponentially year by year and it will be over 1000 times higher than that of today in the near future. In order to tackle this matter, millimeter wave mobile access networks which can provide several GHz bandwidth attract international attention. This paper investigates the candidates of millimeter wave spectrum for 5G by referring to several ongoing 5G R&D projects and considering the spectrum allocation status of Japan, US, and EU. Consequently, five candidates are selected, (1) 31.8GHz-33.4GHz, (2) 45.5GHz-47.0GHz, (3) 47.2GHz-50.2GHz, (4) 55.78GHz-76.9GHz, and (5) 81.0GHz-86.0GHz. Additionally, for the evaluation of each band we develop path loss models for each candidate band by using an interpolation technique. Moreover, we compare the performance of the heterogeneous network (HetNet) system assuming new spectrum usage in terms of system rate and reveal that the system which has larger bandwidth can achieve the higher system rate regardless of large pathloss value, especially in high traffic case. This result shows that the system which can have large bandwidth will have the high priority for the future mobile wireless networks.

Cell discovery in 5G HetNets using location-based cell selection

Future heterogeneous networks (HetNets) are going to consist of cellular macro cell base stations (macro-BSs) and various types of small cell base stations (SC-BS), each operating in microwave and/or millimeter bands. Cell discovery of mm-wave SC-BSs is a challenging issue because of the limited communication range. In this paper, a location-based cell selection scheme that takes into account the effects of inaccuracy of the location estimation is introduced. The proposed scheme selects the SC-BSs according to the probability that they can reach the UE. This probability is dynamically calculated and updated during the search process to assure that at any step the SC-BS with highest detection probability is selected and assigned. The simulation results show a 30% reduction in the latency of the proposed cell discovery compared to the conventional scheme. Furthermore, even more than 70% reduction in latency is possible if the proposed algorithm is extended to simultaneously select three SC-BSs with maximum joint probability of detection.

Performance evaluation of interference mitigation techniques in the overlaying MmWave small cell network

In this paper we consider heterogeneous cellular network with a number of millimeter-wave (mmWave) small cells overlaying LTE macro cells. The impact of mutual interference in millimeter-wave band (57-64 GHz) is addressed and evaluated. We introduce several active interference cancellation techniques which are implemented at TX sides of mmWave small cell BSs equipped with adaptive antenna arrays. We started from the task of multi-stream intra-cell interference suppression in MU-MIMO mode by means of well-known Zero-Forcing (ZF) algorithm. Then more complex schemes involving coordinated multi-point (CoMP) operation of several neighboring BSs with Coordinated Scheduling (CS) and Coordinated Beamforming (CB) are investigated. Finally, performance evaluation and comprehensive comparative analysis are done by simulations for different mmWave small cell sizes and densification. Presented results allow to establish lower and upper bounds of interference impact and make reasonable selection of the suitable interference mitigation technique for mmWave overlaying network.

Diamond cellular network — Optimal combination of small power basestations and CoMP cellular networks-

In conventional studies on Coordinated Multi-Point (CoMP) cellular networks, dynamic clustering schemes have been introduced to achieve CoMP gain at all cell edges. However, such schemes increase complexity of the network drastically and are unfeasible in the current network topology. In this paper, small power basestations (BSs) are introduced instead of dynamic clustering to solve cluster edge problem in CoMP cellular networks. This new cell topology is called diamond cellular network since the created cell structure is similar with diamond pattern. We derive optimal locations of small power basestations and optimal resource allocation between the CoMP basestation and small power basestations for the diamond cellular network. By using the proposed architecture, more than 250% improvement of 5% outage throughput is achieved compared with conventional single cell networks.