相河 聡

The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promising architecture for achieving a ubiquitous wireless Internet access in the future. However, the current IEEE 802.11 protocol is aimed at single access point (AP) environments and many problems related to the wireless meshed interconnection of APs and Mobile Terminals (MTs) remain to be solved. Some proposed solutions to build Such mesh architectures are based on single-channel ad-hoc oriented schemes in which IEEE 802.11 protocol has been modified. The main problem with this type of schemes, however, lies in the very low performance of the single-channel architecture itself. The task group S of IEEE 802.11 is currently working out standards for IEEE 802.11 -compliant mesh architectures in a number of usage scenarios including residential, office and campus/community/public access network but a lot of work remains to be done since the group was established just on last year. In this paper we propose a new multi-channel mesh architecture for hot zones which works using a Distributed Coordination Function (DCF)-based technique for interconnecting APs. A major advantage of our proposed scheme is that, putting routing issues aside, it introduces no change into the MAC protocol of IEEE 802.11. Our simulations results obtained in OPNET show a good performance of our proposed scheme in terms of throughput and delay. We also show interesting results related with the size of packets and the mesh architecture itself that could lead to further research in the future.

This paper proposes a new synchronization scheme for packet mode orthogonal frequency division multiplexing (OFDM) signals employing space division multiplexing (SDM); it targets IEEE 802.11 TGn wireless LANs that offer over 100 Mbit/s. In addition, this paper shows the packet format of OFDM-SDM signals that ensures backward compatibility with IEEE 802.11a. The proposed synchronization scheme has simple open-loop construction and consists of automatic frequency control (AFC), symbol timing detection, channel estimation and phase tracking, The AFC and symbol timing detection are carried out in the time-domain. After OFDM demodulation, the proposed scheme processes channel estimation and phase tracking in the frequency-domain. Considering all the above synchronization tasks, we evaluate the packet error rate (PER) performance using the TGn-defined multi-input multi-output (MIMO) channel model. The proposed scheme shows superior performance; it suppress the required E(b)/N(0) degradation to within 0.4 dB (0.3 dB) with 64 byte (1000 byte) packets compared to the performance achieved if only channel estimation is considered; the RMS delay spread = 50ns.

This paper considers a wireless LAN system operated in a multiple-cell environment with universal frequency reuse. A key technical goal is to increase cell-capacity within a cell. A very high-rate wireless LAN system, maximum data rates of over 100Mbit/s, is proposed that offers an expanded signal-bandwidth compared to that specified in IEEE802.11a. The system employs OFDM and MC/CDMA signals in packet mode. It falls back from OFDM signals with low subcarrier modulation orders to MC/CDMA signals. A link level performance comparison shows that OFDM has superior performance to MC/CDMA at over 32 Mbit/s. Under 16 Mbit/s, however, MC/CDMA can establish wireless link connections unlike OFDM. Thus the fallback technique, which is triggered by the CIR environment, should select OFDM if the data rate exceeds 32 Mbit/s. It should fallback to MC/CDMA if the rate is less than 16 Mbit/s. We also evaluate the proposed scheme in a multiple-cell environment with universal frequency reuse, where the severe co-channel (other-cell) interference is present. We derive a cell capacity criterion for wireless LAN systems, and show that the proposed scheme offers a 2.2 times larger available transmission distance than the OFDM-only scheme. In addition, it is found that the proposed scheme offers a 1.3 times improvement in cell capacity compared to the MC/CDMA-only scheme, even if all other-cell interference is considered.

This paper proposes a new scheme that can evaluate the cell throughput performance of wireless local area network (LAN) systems, which use carrier sense multiple access/collision avoidance (CSMA/CA) and multiple transmission bit-rates (multi-rate). We extend the interference model of the conventional scheme in order to deal with interference more accurately in multi-cell environments. Unlike the conventional scheme, the proposed scheme is able to handle multi-rate systems. We use the proposed scheme to evaluate the IEEE 802.11a system and systems whose signal-bandwidth is expanded from that of the IEEE 802.11a system. We find that a system with 35(75) MHz signal-bandwidth achieves about 1.3(1.25) times higher cell throughput than the IEEE 802.11a system. Furthermore, the system with 35(75) MHz signal-bandwidth is also shown to have the potential to achieve up to 1.5(1.8) times higher cell throughput performance than the IEEE 802.11a system if the transmission efficiency on the media access control (MAC) layer is assumed to be ideal. It is concluded that the proposed scheme confirms that the approach to expand the signal bandwidth of the IEEE 802.11a system is effective to improve the cell throughput performance. This result is virtually impossible to derive with the conventional scheme.

The key technologies that materialize the ubiquitous service are core network, wireless access and terminal/application. Especially, system design of wireless access placed in the middle of network and terminal is important. By make combining the characteristics wireless terminal portability and broadband optical fiber the realization of the ubiquitous service becomes possible. This paper describes about the introduction and future activity of present condition technology about the wireless access that turned it to the ubiquitous service in this paper.<br>This paper expresses the technology activity of 3 fields that are (1) Wireless LAN (2) NWA : Nomadic Wireless Access (3) FWA : Fixed Wireless Access. Furthermore we express about the subject of the future direction nature and wireless access technology of the ubiquitous service based on existing research progress and activity.

This paper evaluates a novel media access control (MAC) method with multiple frame transmission that increases the throughput performance of high speed wireless local area network (LAN) systems. The current MAC protocol has two problems when used in high speed wireless LAN systems: poor efficiency and the failure to match for a multirate mechanism. The frame bursting method solves these problems by allowing multiple frames to be transmitted within one media access period. In this paper, the performance evaluations of the frame bursting method are performed by computer simulation. The results demonstrate that the frame bursting method can achieve higher system throughput, 10 Mbit/s, than the system throughput performance of conventional systems. Moreover, the results shows that the frame bursting method works well in the wireless LAN systems that employ the multirate mechanism and can achieve higher throughput performance.

This paper proposes a new scheme that can evaluate the cell throughput performance of wireless local area network (LAN) systems that use the carrier sense multiple access/collision avoidance (CSMA/CA) and multiple transmission bit-rate (multi-rate) techniques. We use the proposed scheme to evaluate the IEEE 802.11a system and systems whose signal-bandwidth is expanded from that of the IEEE 802.11a system. We find that a system with 35(75) MHz signal-bandwidth achieves about 1.3(1.25) times higher cell throughput than the IEEE 802.11a system. Furthermore, the system with 35(75) MHz signal-bandwidth is also shown to have the potential to achieve up to 1.5(1.8) times higher cell throughput performance than the IEEE 802.11a system if the transmission efficiency on the media access control (MAC) layer is improved. The proposed scheme confirms that the approach of expanding the signal bandwidth of the IEEE 802.11a system is effective in improving the cell throughput performance. This result is virtually impossible to derive with the conventional scheme.

A method is proposed to segregate channels used by each base station in both time and frequency in the case of a high-speed wireless access system. By means of this method, many base stations can be established in a highspeed wireless access system in which the number of frequency channels is reduced as the bandwidth per wave becomes wider. Further, the frequency-use efficiency is improved in the entire system. In this paper, the timing and frequency-based channel segregation method is proposed. The base station channel segregation algorithm in which this method is applied to a specific system is presented. By means of computer simulation, the possibility of achieving base station segregation is evaluated. It is shown that the proposed method is effective in a high-speed wireless access system. Experiments using test apparatus show the correct operation of the system. (C) 2002 Scripta Technica, Electron Comm Jpn.

高速ワイヤレスアクセスシステムにおいて,各基地局が使用するチャネルを時間・周波数の両面ですみ分ける方法を提案する.これにより,1波当りの帯域が広いためシステム全体で使用できる周波数チャネル数が少なくなる高速ワイヤレスアクセスシステムにおいて,多くの基地局を配置することが可能となる.更に,システム全体として周波数利用効率を向上できる.本論文では時間・周波数チャネルすみ分け方式を提案し,具体的なシステムに適用した場合の基地局チャネルすみ分けアルゴリズムを示す.また,計算機シミュレーションにより基地局すみ分け可能確率等による評価を行い,提案方式が高速ワイヤレスアクセスシステムにおいて有効であることを示す.更に,試作機を用いた実験より,本方式の正常動作を確認した結果を示す.

This paper describes the design and implementation of a prototype ATM Wireless Access (AWA) system that provides high speed ATM transport capability for tetherless multimedia services. The prototype AWA uses the 25 GHz band for experimental purpose because of its support of high speed transmission. This paper describes the design concept of the prototype AWA as well as key technologies that allow it to achieve high speed and high quality ATM-based transmission. (C) 1999 Elsevier Science B.V. All rights reserved.

The ATM Wireless Access (AWA) prototype employs TDMA-TDD (Time Division Multiple Access-Time Division Duplex) to flexibly support user de-mand. It also employs sector/space diversity to combat shadowing and multipath fading. The frame format, access-, control-, and user-channel functions, frame synchronization, and forward error correction are presented. The diversity/sector antenna configuration and the control schemes are also described.

This paper presents experimental results obtained in indoor broad-band transmission experiments using a QPSK-100 Mbps modem in the 37GHz band. Transmission performance is measured at many antenna locations in an office. The zone coverage, defined poitns where as the BER was less than 10^<-7>, was derived in order to evaluate the possibility of high-speed transmission. It was found that adjusting the receiving antenna position a few centimeters greatly improves the zone coverage in utilizing millimeter waves. This result indicates the effectiveness in improving zone coverage of space diversity reception with an antenna spacing of several centimeters. Experimental results obtained show that zone coverage of up to 70% in the measured range is achieved by space diversity reception. Thus, the feasibility of 100Mbps indoor wireless transmission, conventionally thought to be impossible, is experimentally confirmed.

Error correction and error detection techniques are often used in wireless transmission systems. The Asynchronous Transfer Mode (ATM) employs Header Error Control (HEC). Since ATM specifications have been developed for high-quality optical fiber transmission systems, HEC has single-bit error correction and multiple-bit error detection capabilities. When HEC detects multiple-bit error, the cell is discarded. However, wireless ATM requires a more powerful Forward Error Correction (FEC) scheme to improve the Bit Error Rate (BER) performance resulting in a reduction in the transmission power and antenna size. This concatenation of wireless FEC and HEC of the ATM may effect cell loss performance. This paper proposes error correction and error detection techniques suitable for wireless ATM and analyzes the performance of the proposed schemes.

The asynchronous transfer mode (ATM) employs header-error control (HEC) to protect the ATM cell header from bit error and/or avoid the misforwarding of ATM cells, However, wireless ATM systems require a more powerful forward-error correction (FEC) scheme to offer acceptable bit-error rate (BER) performance, This paper proposes the utilization of FEC, which makes it possible to discard ATM cells more reliably, Time-division multiple access (TDMA) is very suitable for wireless ATM systems, In the TDMA scheme, synchronization is very important, This paper also proposes to combine FEC with unique word (UW) detection for improving TDMA synchronization characteristics.

マルチパスとシャドーイングが発生する屋内におけるリアルタイム無線通信システムについて,シャドーイングによる瞬断を防止するためのアンテナダイバーシチ方式を提案し,更に,屋内伝搬のシミュレーションからその効果の可能性を示した.

This paper considers the modem which has the features of high precision, high‐level functions, adjustment‐free operation, and low cost, to provide high‐capacity transmission and to cope flexibly with various radio communication systems. A fully digitized modem is investigated, in which the digital signal processing techniques are applied up to the IF band. This paper shows the effects of the quantization level, the aperture effect and the clock jitter, which are the major deteriorating factors of digital signal processing (DSP), on the multilevel modem. an analysis method based on the equivalent C/N degradation is proposed, and fixed degradation of the modulation/demodulation systems is calculated quantitatively. It is verified as a result that when the method is applied to the devices on the market, the fixed degradation is approximately 2 dB in 256 QAM, which is nearly the same as in the modem with the conventional configuration. It is seen also that the effect of the degrading factors depends on the number of levels. When the number of levels is small, the quantization level has the dominant effect, and when the number of levels is large, the aperture effect, as a factor for the waveform distortion, is the dominant effect. Finally, a fully digital modem is constructed experimentally. As a result of the performance evaluation, the validity of the analysis method is verified by experiment. Copyright © 1995 Wiley Subscription Services, Inc., A Wiley Company

This paper describes the performance of an outage free SDH (Synchronous Digital Hierarchy) interface 256 QAM modem. An outage free DMR (Digital Microwave Radio) is achieved by a high coding gain trellis coded SPORT QAM and Super Multicarrier modem. A new frame format and its associated circuits connect the outage free modem to the SDH interface. The newly designed VLSI's are key devices for developing the modem. As an overall modem performance, BER(Bit Error Rate) characteristics and equipment signatures are presented. A coding gain of 4.7dB(at a BER of 10(-4) ) is obtained using SPORT 256 QAM and Viterbi decoding. This coding gain is realized by trellis coding as well as by increasing of transmission rate. Roll-off factor is decreased to maintain the same frequency occupation and modulation level as ordinary SDH 256 QAM modem.

Recently, degradation due to radar interference has been reported in high‐frequency efficiency microwave radio systems. However, there has been no solution to this problem. This paper proposes a bit interleaving technique as a radar interference canceller and presents a designing method and its performance in digital microwave radio systems. First, the characteristics of radar interference are described. Next, the bit interleaving technique is proposed as an interference canceller for maritime radar, whose source is difficult to determine. Next, the method of designing the bit interleaving on a channel with burst errors and random errors is described. Finally, the effectiveness of the canceller is shown by the experimental results obtained using a prototype. The results show that bit interleaves can correct errors due to radar interference. Copyright © 1994 Wiley Periodicals, Inc., A Wiley Company

ディジタルマイクロ波無線通信においては近年の高品質化に伴いレーダ干渉による品質劣化が浮かび上がっている.しかし今までこれを解決する補償装置はなかった.本論文では,新たにレーダ干渉補償装置としてのビットインタリーブの適用を提案し,その効果を理論的に明らかにすると共にその設計法と特性を示した.まず,レーダ干渉波の特性について述べた.更に干渉源の探索が困難な不特定多数の船舶レーダからの干渉による誤りについても訂正できるビットインタリーブの適用を提案した.次にバースト誤りとランダム誤りが同時に発生する無線伝搬路におけるビットインタリーブの理論的特性からビットインタリーブおよび誤り訂正符号の設計法について検討した.更に試作機による実験的検討結果から本装置の有効性を示した.結果として,船舶用レーダなど不特定多数のレーダ干渉源に対してもビットインタリーブによって完全に誤りを訂正できることを明らかにした.

With the advent of the radio relay system and multilevel modulation, the multicarrier system and variable capacity transmission system are proposed to realize excellent performance in the fading channel. Accordingly, it is desired to realize a highly functioned MODEM which can cope with those systems in a flexible way. On the other hand, intensive studies have been made on digital signal processing in the modulation and demodulation in the field of data modem. However, these methods consider the low‐rate system of less than 100 Kbaud and are difficult to apply directly to the system where the transmission rate of 10 Mbaud or above is required. For the foregoing reasons, this paper considers the realization of the all‐digital modulator which can realize the high‐capacity transmission of over 10 Mbaud for the multilevel modulation system, such as 256 QAM. This paper discusses the design of the digital filter with excellent intersymbol interference. The condition for the carrier frequency for a given clock rate is presented. Then a variable multilevel modulator with a simple correction circuit is proposed which can be applied to the variable‐capacity transmission system. Finally, the proposed circuit is constructed and it is confirmed that an excellent modulation performance is obtained without adjustment in various multilevel modulation systems. Copyright © 1993 Wiley Periodicals, Inc., A Wiley Company

Multilevel trellis-coded QAM VLSI's were designed and developed. These VLSI's realize a coding gain of 7.9 dB with SPORT-256QAM. The VLSI's contain an encoder, mapper, and decoder for trellis-coded 16, 32, 64, 128, and 256QAM utilizing general mapping. Using small-size and low-power path memory, 150K gates are achieved using two chips with die sizes of 8 x 11 and 14 x 14 mm2. The VLSI's achieve a maximum data throughput rate of 17 MBd (guaranteed), 30 MBd (typical), and dissipate only 1 W at a data rate of 17 MBd. The VLSI's also contain a phase ambiguity rejection circuit for a recovered carrier and error pulse generator. The devices are designed with a BiCMOS 0.8-mu-m process rule. The experimental result of bit-error-rate (BER) performance is presented. The developed VLSI's are effective for outage-free digital microwave radio systems.

Various types of robust technology for upgrading circuit quality of digital radio systems, higher than 10 times conventional ratings, are being developed. This paper will report on the prototype modem developed for use with trellis-coded modulation and super multi-carrier transmissions, and the excellent characteristics that were obtained. This device has speed conversion, frame conversion signal processing functions to satisfy compatibility requirements with existing SDH systems. Also not only to achieve robustness, the modem was designed to achieve miniaturization through integrating the trellis-coded section, roll-off waveform reshaping filter, transversal equalizer, and the signal processing section onto a submicron LSI. High functional and economy were both achieved. Also, complete digitization technology was developed for the modem. The prospects of obtaining non-adjustment of the modem will also be reported. Furthermore, together with trellis-coded modulation with powerful coded gain, a highly tolerable carrier recovery circuit was proposed and realized. This circuit enables elimination of instability in the required carrier phase when there is an absolute synchronous detection wave and makes possible stable modulation operations even with a low CNR. As a result, the prospects of achieving a robust microwave system which has a circuit outage rate of under 1/10 of the conventional rate was obtained.