Keiichi Mizutani

Acoustic communication in air using differential biphase shift keying with influence of impulse response and background noise

We describe short-range acoustic communication in air using differential biphase shift keying (DBPSK). In this system, a carrier recovery circuit is unnecessary, since the differential encoding is adopted, and the system configuration is simple. The acoustic transmission channel can be simply constructed of only a loudspeaker (SP) and a microphone (MIC). Acoustic communication in air has three problems that degrade the quality of communication. There are multipath fading by reflected waves, the influence of the impulse response of the SP and MIC and that of background noise. Even when multipath fading is disregarded, the performance is limited by the influence of the impulse response of the SP and MIC and that of the background noise. In this study, the performance limits are experimentally evaluated, and the design guidelines for the one-symbol time and signal-to-noise ratio are obtained for an acoustic DBPSK system. The period of a particularly intense influence of the impulse response of the acoustic system is 0.3 ms or more. If the one-symbol time is set at 0.8 ms, the communication quality becomes stable.

Some Initial Results and Observations from a Series of Trials within the Ofcom TV White Spaces Pilot

TV White Spaces (TVWS) technology allows wireless devices to opportunistically use locally-available TV channels enabled by a geolocation database. The UK regulator Ofcom has initiated a pilot of TVWS technology in the UK. This paper concerns a large- scale series of trials under that pilot. The purposes are to test aspects of white space technology, including the white space device and geolocation database interactions, the validity of the channel availability/powers calculations by the database and associated interference effects on primary services, and the performances of the white space devices, among others. An additional key purpose is to perform research investigations such as on aggregation of TVWS resources with conventional resources and also aggregation solely within TVWS, secondary coexistence issues and means to mitigate such issues, and primary coexistence issues under challenging deployment geometries, among others. This paper provides an update on the trials, giving an overview of their objectives and characteristics, some aspects that have been covered, and some early results and observations.

Experimental Study of Doppler Effect for Underwater Acoustic Communication Using Orthogonal Signal Division Multiplexing

This paper is about the underwater acoustic (UWA) communication using orthogonal signal division multiplexing (OSDM) in shallow water, whose environment is time spread and frequency spread. In this paper, the Doppler effect – Doppler shift and spread – for UWA communication using OSDM is mainly considered. The effects of Doppler shift and Doppler spread are evaluated in a test tank with a moving platform on a stable water surface and with a stable platform with a moving water surface, respectively. Doppler shift correction, which has been considered in simulation-based studies, is found to work effectively. In relation to the effect of Doppler spread, the experimental result well agrees with the simulation result. Through this study, it is confirmed that a smaller frame length is preferable because it enables the measurement of the UWA channel frequently so that it can keep up with channel changes.

Study of Doppler Shift Correction for Underwater Acoustic Communication Using Orthogonal Signal Division Multiplexing

In this study, we apply Doppler shift correction schemes for underwater acoustic (UWA) communication with orthogonal signal division multiplexing (OSDM) to achieve stable communication in underwater acoustic channels. Three Doppler correction schemes, which exploit the guard interval, are applied to UWA communication with OSDM and evaluated in simulations. Through a simulation in which only the Doppler effect is considered, we confirmed that by adapting schemes to UWA communication with OSDM, we can correct large Doppler shifts, which addresses the usual speed of vehicles and ships. Moreover, by considering both the Doppler effect and channel reverberation, we propose the best possible combination of Doppler correction schemes for UWA communication with OSDM. The results suggest that UWA communication with OSDM may lead to high-quality communication by considering channel reverberation and large Doppler shifts.

IEEE 802.11af Indoor Experiment in UK Ofcom TVWS Trial Pilot Program

This paper performs the worlds first IEEE 802.11af based Wireless Local Area Networks (WLAN) operating in TV White Space (TVWS) indoor experiment in the Ofcom TVWS pilot program of the UK. The prototype system consists of TVWS Database (WSDB), Registered Location Secure Server (RLSS), and two prototype hardware for an Access Point (AP) and a Station (STA). The developed WSDB qualified by Ofcom TVWS pilot program of the UK. The prototype hardware meets to the transmission spectrum regulation of the European Telecommunication Standards Institute (ETSI). By using the developed system, a trial indoor experiment performed in the building of the Kings College London (KCL), Denmark Hill Campus in London, UK. The prototype system and the experiment results show an effectiveness of the IEEE 802.11af and indicate the way to the practical application.

Field experiment of long-distance broadband communications in TV white space using IEEE 802.22 and IEEE 802.11af

A field experiment of TV White Space (TVWS) communications was conducted using developed systems following IEEE 802.22 and IEEE 802.11af standards and succeeded to have the world first throughput, distance, and application testing. The IEEE 802.22 system achieved throughput of 4.5 Mbps for uplink and 5.2 Mbps for downlink over 12.7 km. Also, feasibility of applications such as web browsing, video streaming and video talk was confirmed in multi-hop network where the IEEE 802.22 system was a backbone link and IEEE 802.11af was access area expansion. Furthermore, aggregating bandwidth of two discontinuous TV channels, throughput of 15.5 Mbps for downlink and 9.0 Mbps for uplink was achieved over 6.3 km.

Network Synchronization for Two-Way Multi-Hop Relay Networks with Block Modulation

This paper proposes novel time-efficient network synchronization schemes for TDD/TDMA based two-way multi-hop relay networks with block modulation. One of the proposed schemes is based on broadcast (BC) timing synchronization. Since this scheme causes network synchronization errors at each receiver, additional guard interval (GI) to compensate the error is introduced. The second proposed scheme is based on both of BC and multiple access (MA) timing synchronization. The additional GI is not required and the time-efficiency is improved because the transmit and receive timing at each node are adjusted to eliminate the network synchronization errors. The second proposed scheme achieves over 98.8% time-efficiency with arbitrary node arrangement, bandwidth, and number of hops when the number of symbols per frame is hundred.

Design and implementation of a Wi-Fi prototype system in TVWS based on IEEE 802.11 af

Driven by the progress of regulations of TVWS worldwide, IEEE 802.11 started a new Task Group af (TGaf) to pursue extension of traditional Wi-Fi to TV White Spaces (TVWS). Wi-Fi in TVWS offers longer distance and broader bandwidth; while maintaining the same user experience of traditional Wi-Fi systems. It is therefore regarded as one of most promising technologies to exploit the market derived from the new regulations of VHF/UHF bands. In this paper, we present the worlds first prototype system of Wi-Fi in TVWS based on the TGaf draft specification. The prototype system verifies the PHY and MAC design of TGaf and the database query protocols that is needed for TVWS operation but not in the scope of TGaf. It is demonstrated that, with sufficiently defined MAC protocol and PHY that meets sharp transmission spectrum mask, the developed prototype supports video streaming on single TV channel while well coexisting with primary TV services in the vicinity.

IEEE802.11af with partial subcarrier system for effective use of TV white spaces

Demand for wireless communication is increasing significantly, while the frequency availability for wireless communication is quite limited. Currently, various countries are prompting the use of TV white spaces. IEEE 802.11 WG (Working group) has started a TG (Task Group), namely IEEE 802.11af to develop the international standard for WLAN in TV white spaces. In order to increase maximum throughput, a channel aggregation mechanism is introduced in the draft standard of TGaf. In Japan, ISDB-T based area-one-segment broadcasting system (Area-one-seg) which is a digital TV broadcast service in the limited area have been permitted to do actual services in TV white spaces from April 2012. The operation of the IEEE 802.11af system shall not jeopardize the Area-one-seg system due to the common operating frequency band. If the Area-one-seg partially overlaps with the IEEE 802.11af in some frequency, the IEEE 802.11af cannot use the channel aggregation mechanism due to lack of channels. As a result, the throughput of the IEEE 802.11af deteriorates. In this paper, the physical layer of IEEE 802.11af D2.0 is introduced briefly, and a partial subcarrier system for the IEEE 802.11af is proposed to effective use of TV white spaces and increase throughput. The IEEE 802.11af systems effectively coexist with the Area-one-seg by using null subcarriers. Computer simulation shows up to 60 % throughput gain is achieved with the proposed mechanism.

Hardware Prototype for Two-Way Multi-Hop Relay Network with MIMO Network Coding

This paper develops the first prototype hardware for TDD/TDMA two-way multi-hop relay network with MIMO network coding. Since conventional wireless multi-hop relay networks have drawbacks of low data rate, TDD/TDMA two-way multi-hop relay networks have been studied as a solution to realize high data rate recently. In these networks, forward and backward streams are spatially multiplexed by using interference cancellation technology such as MIMO beamforming or MIMO network coding. In this prototype hardware, MIMO network coding and network synchronization scheme are implemented to realize such TDD/TDMA two-way multi-hop relay network in real environment. In the demonstrator using the prototype hardware, each transmitter and each receiver performs network coded broadcast (BC) and MIMO multiple access (MA) respectively. Performance of the demonstrator shows that the TDD/TDMA two-way multi-hop relay network with MIMO network coding can be realized.