Masataka Iizuka

Novel multiple access protocol for voice over IP in wireless LAN

VoIP (voice over IP) is one of the real time applications which demand that wireless LAN systems achieve severe quality requirements in terms of delay time, jitter and packet loss. However, it is difficult for CSMA/CA (carrier sense multiple access with collision avoidance) to achieve the service quality demanded by VoIP if voice and data traffic coexist, so some form of priority control is needed. This paper proposes a novel multiple access protocol that allows wireless LANs based on autonomous distributed control to satisfy the VoIP requirements. This new protocol suits both VoIP and data traffic and executes priority control dynamically according to whether the VoIP packet collides with a data packet or another VoIP packet. The results of a theoretical analysis and computer simulations indicate its excellent performance. This proposed protocol reduces the delay time of VoIP packets by 54 to 70% compared with conventional CSMA/CA, even if the traffic load increases, provided that the packet loss probability is less than 3%.

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.

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.

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.

Wireless bridging and routing method employing a novel frame transfer protocol with shortcut

This paper presents a new wireless bridging and routing method for ad-hoc networks comprised of wireless bridges and/or wireless routers that comply with IEEE 802.11, a global standard for wireless LAN systems. This wireless bridging and routing method uses a novel frame transfer protocol with shortcut (FRASH) that we developed; that users can establish flexible and high speed ad-hoc wireless LANs easily at their offices and houses. This paper clarifies that the proposed bridging and routing method achieves higher throughput and less forwarding delay than the conventional transparent bridging protocol (TBP) by computer simulations, theoretical analysis, and experiments using a prototype wireless bridge and router device (WBR).

Design of common access channels for TDMA-TDD microcell communications systems

This paper describes a detailed design of common access channels in the down link which are constructed with two transmission frames, multi-frame and super-frame, on a dedicated control carrier frequency in TDMA-TDD systems. The co-channel interference between TDMA-TDD bursts is discussed as the first consideration in the design of multi-frame. For the super-frame design, the average connection delay in a call control sequence is evaluated for the various period of super-frame as a function of offered traffic. A method of designing the optimum common access channels transmission frames is proposed.<<ETX>>

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.

Proposal of wireless traffic control schemes for wireless LANs

This paper proposes two traffic control schemes to support the communication quality of multimedia streaming services such as VoIP and audio/video over IEEE 802.11 wireless LAN systems. The main features of the proposed scheme are bandwidth control for each flow of the multimedia streaming service and load balancing between access points (APs) of the wireless LAN by using information of data link, network and transport layers. The proposed schemes are implemented on a Linux machine which is called the wireless traffic controller (WTC). The WTC connects a high capacity backbone network and an access network to which the APs are attached. We evaluated the performance of the proposed WTC and confirmed that the communication quality of the multimedia streaming would be greatly improved by using this technique.

Enhanced capture effect for slotted ALOHA employing transmission power control corresponding to offered traffic

This paper presents a novel slotted ALOHA that has an enhanced capture effect even if heavy traffic is offered. Capture event success probability is improved by controlling the probability of high power transmission permission. This makes it possible to capture the other packets if only one station increases its transmission power. This control method is the key issue of this paper since the capture effect is one of the most promising ways to achieve high throughput without interference (collision) detection/carrier sense. We modified the conventional slotted ALOHA to yield a practical and useful packet transmission scheme. This modified slotted ALOHA has a finite buffer that stores backlog packets. Heavy traffic may cause buffer overflow which implies packet loss. When a station of a wireless LAN or another data terminal intends to send a packet, its transmission power is controlled by the number of stations in an area that covers the same cell shaped by an access point. As a result, only one of the packets can be successfully sent by capturing the other packets. This capture effect is improved significantly by the proposed scheme. This modified and enhanced slotted ALOHA achieves the maximum throughput of 0.74, which is higher than the 0.47 achieved by transmission power control in a previous paper. This is double the throughput of the original slotted ALOHA.

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.