Yuuta Nakaya

Dynamic Data Forwarding in Wireless Mesh Networks

Unreliable wireless links can cause frequent link (and route) failures, creating a major challenge for routing protocols who need to constantly repair routes and find alternate paths. In this paper we propose DADR (Distributed Autonomous Depth-first Routing), a new distributed distance-vector routing protocol designed to adapt quickly to changing link conditions while minimizing network control overhead. In our algorithm, when a link fails, data packets are rerouted through an alternate next hop, and the information about the failed link is propagated with the data packet; therefore, routes are updated dynamically and with little overhead. We have implemented DADR on several link-layer technologies and deployed it in different applications, including AMI deployments in Japan; all implementations resulted in reliable networks that were easy to set up, maintain, and resilient to changing conditions.

MIMO receiver using an RF-adaptive array antenna with a novel control method

An RF-adaptive array antenna (RF-AAA) is useful for improving the signal-to-interference plus noise ratio (SINR) on each branch in a multiple-input multiple-output (MIMO) receiver. A weight-control method for the RF-AAA, however, has been a major challenge towards its practical use because only one output signal can be observed at the RF-AAA. In this paper, we propose a novel control method that can estimate each channel impulse response (CIR) for each antenna element and calculate optimum weights for the RF-AAA, the same principle as that of the digital-processing type AAA. The proposed control method is implemented with a frame format based on the IEEE 802.11a standard. Bit error rate performance shows that the proposed control method estimates the CIR and calculates the global optimum weights to maximize the output SINR. Consequently, the RF-AAA suppresses the interference and provides a BER close to that without interference.

A Receive Antenna Selection for MIMO-OFDM System

The combination of multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) technologies gives wireless communications systems the advantages of lower bit error rate (BER) and higher data rate in frequency-selective fading environments. However, the main drawback of the MIMO-OFDM systems is the increase of complexity, and thus cost. In this paper, we propose an antenna selection method for a MIMO-OFDM receiver. The proposed method selects a proper combination of polarization antenna elements at receive antenna branches to achieve lower BER performance. Using the channel impulse responses measured in an indoor environment, numerical results show that the proposed selection method works effectively for the realistic channel and promises a great deal of decrease in computational complexity

Incorporation of RF-adaptive array antenna into MIMO receivers

We propose the incorporation of an RF-adaptive array antenna (RF-AAA) into each receive branch on multiple-input multiple output (MIMO) systems. The RF-AAA consists of multiple antenna elements where a variable-gained low-noise amplifier (VG-LNA) and a 360/spl deg/- continuously adjustable phase shifter are inserted in each antenna element and an adder for the array output is connected into the RF front-end of each receive branch. The phase shifters are adaptively controlled to increase the total channel capacity of MIMO systems. Computer simulations showed that the capacity of a 2-element-receive-RF-AAA incorporated 2 /spl times/ 2 MIMO system is higher than that of a conventional 3 /spl times/ 3 MIMO system (without RF-AAA) under average transmit power constraints.

A Receiver Side Antenna Selection Method for MIMO-OFDM System

This paper proposes an antenna selection method for a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) receiver. The proposed method selects a proper combination of polarization antenna elements at receive antenna branches to achieve lower bit error rate (BER) performance. Using the channel impulse responses measured in an indoor environment, numerical results show that the proposed selection method works effectively for the realistic channel and promises a great deal of decrease in computational complexity.

An Adaptive Beamforming Method for Phased Array Antenna with MEMS Phase Shifters

Adaptive array antennas, which control their own patterns by means of feed-back or feed-forward control, are effective tools for gain enhancement and interference suppression. However, when applying them to mobile terminals, the problems of hardware complexity and power consumption need to be taken into consideration. One solution is the use of analog device-based adaptive array antennas, such as Reactively Steered Adaptive Array (RESAA) antennas and phased array antennas, which have the attractive characteristics of low cost and power consumption. In this paper, we propose an adaptive beamforming method based on a one-dimension search algorithm for phased array antennas with Micro Electro Mechanical Systems (MEMS) phase shifters, taking into consideration their slow operating speed due to mechanical structure of the devices. Furthermore, a smoothing processing is introduced to prevent the effect of noise and a multi-resolution alogrithm is proposed to help the system form beams more quickly and stably. Numerical results based on the IEEE 802.11 a Wireless Local Area Network (WLAN) standard show that the proposed method has good interference suppression and gain enhancement capabilities in multipath fading channels.

An RF-adaptive array antenna incorporated in a MIMO receiver under interference

In this paper, incorporation of an RF-adaptive array antenna (RF-AAA) is proposed on each receive branch in a multiple-input multiple-output (MIMO) receiver to achieve interference suppression. A criterion is shown for maximizing the output signal-to-interference-plus-noise ratio (SINR) in the RF-AAA with amplitude and phase adjusts. The performance is roughly evaluated with no amplitude adjust and a four-bit phase shift. Computer simulation verifies that the RF-AAA improves the capacity of the MIMO system and the bit-error rate (BER) performance of its receiver by suppressing interference, as the number of RF-AAA elements increases. However, diversity gain is not obtained as the number of RF-AAA elements increases, and the impact of interference suppression is seriously degraded as the angular spread of the interference increases.

Proposal of Receive Antenna Selection Methods for MIMO-OFDM System

The combination of Multiple-Input Multiple-Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) technologies gives wireless communications systems the advantages of lower bit error rate (BER) and higher data rate in frequency-selective fading environments. However, the main drawbacks of MIMO systems are their high complexity and high cost. Therefore, antenna selection in MIMO systems has been shown to be an effective way to overcome the drawbacks. In this paper, we propose two receive antenna selection methods for a MIMO-OFDM system with radio frequency (RF) switches and polarization antenna elements at the receiver side, taking into consideration low computational complexity. The first method selects a set of polarization antenna elements which gives lower correlation between received signals and larger received signal power, thus achieves a lower BER with low computational complexity. The second method first selects a set of polarization antenna elements based on the criterion of the first method and another set of polarization antenna elements based on the criterion of minimizing the correlation between the received signals; it then calculates the signal-to-interference-plus-noise power ratio (SINR) of the two sets and selects a set with larger SINR. As a result, the second method achieves a better BER than the first one but it also requires higher computational complexity than the first one. We use the measured channel data to evaluate the performance of the two methods and show that they work effectively for the realistic channel.

A Receive Antenna Directivity Diversity Method for MIMO-OFDM

Receive antenna selection diverrsity in MIMO-OFDM transmission is attractive because it can achieve better BER performance due to higher diversity gain obtained, keeping the cost and energy consumption low. However, how to select a suitable set of receive antenna elements is a key issue, with low computational and hardware complexity. In this paper, we propose an receive antenna directivity diversity method for a MIMO-OFDM system with RF-MEMS switches. We discuss the BER performance of the proposed method as well as conventional methods by computer simulations with the measured channel data in a 5 GHz frequency band.

Performance Evaluation of an Antenna Selection MIMO System with RF Switches in Mobile Terminals

Performance of a multiple input/multiple output (MIMO) system is largely degraded when it is equipped in mobile terminals or placed near a human body because radio waves are absorbed or shielded by the human body. This paper evaluates an antenna selection-based MIMO system under environments near human body. Each MIMO antenna branch at the receiver of the proposed MIMO system is equipped with several antennas, which have different characteristics such as polarizations and directional patterns, and the receiver selects one of them by radio frequency (RF) switches. A 2times2 MIMO propagation measurement at an indoor environment with the proposed antenna is conducted, and channel capacities and bit error rates (BERs) are evaluated by computer simulations with the measured channel data. From the results, the channel capacity is improved by more than 1.5 bit/sec/Hz when the proposed antenna is used near a human body. In addition, from the BER simulations that assume OFDM transmission IEEE802.11n, it is found that the received power is improved by more than 5 dB at cumulative distribution function (CDF) value of 0.5.