Kazuki Maruta

A novel application of Massive MIMO: Massive Antenna Systems for Wireless Entrance (MAS-WE)

This paper proposes a practical application of Massive MIMO technology, Massive Antenna Systems for Wireless Entrance (MAS-WE), and its related inter-user interference (IUI) cancellation and scheduling techniques. MAS-WE, on which the entrance base station (EBS) employs a large number of antennas, can effectively provide high capacity wireless entrance links to a large number of Wi-Fi access points (APs) distributed in wide coverage area. The proposed techniques have been ultimately simplified to be less impact for their practical implementation in order to spatially multiplex more than 16 signal streams with around 100 antenna elements at EBS side. SIR performance was evaluated by system level simulation considering imperfect channel state information (CSI) and the results showed that the proposed MAS-WE with simplified techniques can achieve high spectral efficiency with high level space division multiplexing.

Application of directional antenna to wireless multihop network enabled by IPT forwarding

Intermittent periodic transmit (IPT forwarding) is known as a packet forwarding scheme that achieves highly efficient packet relays in wireless multihop networks. In the method, a source node sends source packets intermittently and periodically with some transmit period, by which co-transmission space of forwarding packets, that is defined as space between multihop nodes in packet transmission, can be controlled in accordance with the given transmit period. If the transmit period is greater than a certain limit, packet collisions due to interference are eliminated and thus packet forwarding is maximized in its efficiency. In order to compensate for broadband traffic, improvement of relay efficiency is highly expected. To this end, we consider an application of directional antenna to wireless multihop networks enabled by IPT forwarding for further improvement of relay efficiency. Upon addressing a key issue caused by the application of directional antenna, we propose a new directional MAC protocol which consists of an IPT forwarding based packet forwarding and a routing. Simulation results ensure that the proposed directional MAC achieves higher throughput and lower packet loss rate compared with a conventional packet forwarding with omni-directional antennas.

Experimental investigation of space division multiplexing on Massive Antenna Systems

This paper experimentally verifies the potential of higher order space division multiplexing for multiuser massive MIMO in line-of-sight (LOS) channels. We previously proposed an inter-user interference (IUI) cancellation scheme and simplified user scheduling method on Massive Antenna Systems for Wireless Entrance (MAS-WE). In order to verify the effectiveness of the proposed techniques, channel state information (CSI) for a 1×32 SIMO channel is measured in a real propagation environment with simplified test equipment. System level simulations using the measured CSI confirm that enlarging the angular gap between users reduces spatial correlation, and that the IUI cancellation proposal is effective under this condition. The degradation in SIR compared to ideal LOS channel model case is insignificant.

Inter-cluster interference canceller for multiuser MIMO distributed antenna systems

We propose a co-channel inter-cluster interference canceller for distributed antenna systems (DAS) that utilize the multiuser Multiple Input Multiple Output (MU-MIMO) technique in the downlink. We first define the cluster as a virtual cell that consists of a few remote antennas and subscriber stations which communicate cooperatively by MU-MIMO. Multiuser beamforming is applied to each cluster, so the proposed method can decrease the computational complexity of spatial division multiplexing processes compared to MIMO systems with large number of antennas. Though clustering causes co-channel inter-cluster interference, it can be cancelled simply by linear processing of the downlink transmission signals. Computer simulations show that the proposed method enables denser cluster configurations. The method contributes to the practical realization of distributed antenna systems through its effective frequency reuse.

Iterative Inter-Cluster Interference Cancellation for Cooperative Base Station Systems

This paper proposes an iterative inter-cluster interference (ICI) cancellation method for cooperative base station systems on the downlink/uplink. System level simulations were conducted with the parameter sets of cluster size and iteration order. The result showed that even in the imperfect CSI case, the spectral efficiency performance of the proposed method with the optimum parameter set is comparable to that of cooperative transmission/reception via MU-MIMO which can completely remove inter-cell interference. In addition, since the proposed method can be practiced in a simple manner, it also has a remarkable advantage to reduce computational complexity. It is a practical way to realize the nationwide wireless systems.

Utilization comparison of small-cell accommodation with PON-based mobile fronthaul

The network between the baseband units (BBUs) and the remote radio heads (RRHs) in a centralized radio access network (C-RAN) architecture is called the mobile fronthaul (MFH). A passive optical network (PON) is expected to reduce the deployment cost of MFH by sharing the optical fibers. Using system-level simulation results as a basis, we report that MFH downlink utilization can be improved with PON, regardless of the functional splitting point between BBUs and RRHs. We then clarify the application range of PON-based architectures, which represents the number of small cells that a PON system can accommodate with a certain amount of user equipment and certain data rates.

Inter-user interference suppression in time varying channel with null-space expansion for multiuser massive MIMO

This paper proposes a novel Inter-User Interference (IUI) suppression scheme in time varying channels with null-space expansion for multiuser massive MIMO systems. The channel time variation deteriorates the accuracy of the channel state information at the transmitter (CSIT) and causes IUI on multiuser MIMO downlink transmission. In massive MIMO, the degrees of freedom (DoFs) of the base station antenna array are generally used to obtain the beamforming gain and capacity enhancement. The proposed null-space expansion scheme exploits the excess DoFs to perform additional null-steering, which extend the null-space dimension and thus suppress the IUI caused by the time varying channel. Computer simulations show that the proposed scheme has superior IUI suppression performance to existing channel prediction scheme; our scheme can improve the SIR by over 50dB.

First Eigenmode Transmission by High Efficient CSI Estimation for Multiuser Massive MIMO Using Millimeter Wave Bands.

Drastic improvements in transmission rate and system capacity are required towards 5th generation mobile communications (5G). One promising approach, utilizing the millimeter wave band for its rich spectrum resources, suffers area coverage shortfalls due to its large propagation loss. Fortunately, massive multiple-input multiple-output (MIMO) can offset this shortfall as well as offer high order spatial multiplexing gain. Multiuser MIMO is also effective in further enhancing system capacity by multiplexing spatially de-correlated users. However, the transmission performance of multiuser MIMO is strongly degraded by channel time variation, which causes inter-user interference since null steering must be performed at the transmitter. This paper first addresses the effectiveness of multiuser massive MIMO transmission that exploits the first eigenmode for each user. In Line-of-Sight (LoS) dominant channel environments, the first eigenmode is chiefly formed by the LoS component, which is highly correlated with user movement. Therefore, the first eigenmode provided by a large antenna array can improve the robustness against the channel time variation. In addition, we propose a simplified beamforming scheme based on high efficient channel state information (CSI) estimation that extracts the LoS component. We also show that this approximate beamforming can achieve throughput performance comparable to that of the rigorous first eigenmode transmission. Our proposed multiuser massive MIMO scheme can open the door for practical millimeter wave communication with enhanced system capacity.

Wired and Wireless Network Cooperation for Wide-Area Quick Disaster Recovery

It is a significant challenge for telecommunication network operators to immediately restore communication services in the disaster area. To quickly recover telecommunication services in the affected area, this paper proposes a wired and wireless network cooperation system. When the wired communication for leaf nodes of optical tree networks is disrupted, surviving leaf nodes relay packets to and from these nodes via wireless bypass routes. The advantages of the proposed method are promptness and high-throughput, which is achieved with single-hop wireless bypass routes backhauled by wired networks. The optimal routes for wireless links are calculated to maximize the expected throughput by solving a binary integer programming problem. The proposed system is cost effective, because it can be deployed with minimum additional functions for leaf nodes of optical networks. To overcome the limitation of the proposed approach that the distribution of leaf nodes is determined by the demand distribution, additional recovery nodes can be deployed to improve the expected throughput. The numerical simulations including a medium access control level simulation conducting carrier sense multiple access with collision avoidance behavior showed that the proposed method can achieve a higher throughput than an existing bypass routing method, irrespective of the topology of the wired networks.

Highly Efficient Multi Channel Packet Forwarding with Round Robin Intermittent Periodic Transmit for Multihop Wireless Backhaul Networks

Round Robin based Intermittent Periodic Transmit (RR-IPT) has been proposed which achieves highly efficient multi-hop relays in multi-hop wireless backhaul networks (MWBN) where relay nodes are 2-dimensionally deployed. This paper newly investigates multi-channel packet scheduling and forwarding scheme for RR-IPT. Downlink traffic is forwarded by RR-IPT via one of the channels, while uplink traffic and part of downlink are accommodated in the other channel. By comparing IPT and carrier sense multiple access with collision avoidance (CSMA/CA) for uplink/downlink packet forwarding channel, IPT is more effective in reducing packet loss rate whereas CSMA/CA is better in terms of system throughput and packet delay improvement.