Masahiro Umehira

Forward error correction schemes for wireless ATM systems

Wireless asynchronous transfer mode (ATM) systems have been proposed for future broadband multimedia personal communication. Forward error correction (FEC) is often used to improve the bit error rate (BER) performance of wireless transmission systems. The ATM employs header error control (HEC) to protect the ATM cell header from bit errors. Since ATM specifications have been developed for high-quality optical fiber transmission systems, the HEC has single-bit error correction capabilities. However, wireless ATM requires a more powerful FEC scheme to improve the BER performance resulting in a reduction in the transmission power and antenna size. This concatenation of wireless FEC and HEC of the ATM may affect the cell loss performance. This paper proposes an FEC scheme suitable for wireless ATM and analyzes the performance the proposed FEC scheme.

A new frequency-domain link adaptation scheme for broadband OFDM systems

This paper proposes an OFDM-oriented link adaptation scheme with new frequency-domain-based link quality estimation functions. System throughput of an OFDM system can be enhanced by using link adaptation; the best set of modulation scheme and FEC coding rate is dynamically selected to achieve the target packet error rate (PER) before ARQ. An important practical issue in applying link adaptation is how to estimate the link quality precisely. Link quality is well assessed by carrier/noise ratio (CNR) and the delay spread. Two link quality estimation functions are introduced; one examines the correlation between subcarriers while the another considers CNR. Both are simple to implement in combination with the frequency-domain initial equalizer. Simulation results verify that the proposed link adaptation scheme is effective in improving system throughput in a practical manner.

A high performance frequency and timing synchronization technique for OFDM

In this paper, we propose a new signal-repetition-based frequency and timing synchronization technique for a burst OFDM modem in the severe fading environments typical of broadband wireless communication systems. The repeated synchronization signals are added at the beginning of the radio packets for synchronization agility. The proposed technique employs a weighting function for correlation calculation based on the identical signal repetition approach. The computer simulation results show that the proposed technique significantly improves carrier frequency offset estimation and timing detection performance compared to the conventional scheme without the weighting function.

Concept and Feasibility Study of Wide Area Ubiquitous Network for Sensors and Actuators

The wide area ubiquitous network (WAUN), which is used for transmitting and receiving information for sensors and actuators, is proposed and the feasibility study of a new wireless network for the WAUN is described. The WAUN is designed to satisfy the requirements of many new applications using sensors and actuators, which are wirelessly connected to the IP network. One of the basic requirements for the wireless system of the WAUN is wide coverage larger than several km with low wireless terminal output power of 10 mW To meet this requirement, an experimental wireless system, which uses a powerful FEC and the diversity technique, for use in WAUNs is designed, and its feasibility is evaluated by field experiments. The experimental results demonstrate the feasibility of the WAUN. That is, the 10 mW transmission power wireless terminal communicates with the access point (base station) 5 km away

Wireless and IP integrated system architectures for broadband mobile multimedia services

This paper discusses wireless and IP integrated system architectures for broadband mobile multimedia services. Possible wireless IP network architectures are given and discussed, taking mobility support into account. This paper also proposes a new ATM-based wireless IP network architecture with handover capability for broadband mobile multimedia services.

PRIME ARQ: a novel ARQ scheme for high-speed wireless ATM-design, implementation and performance evaluation

Error control for high-speed wireless ATM (WATM) operating at 20 Mbps or higher is an important research topic. Automatic repeat request (ARQ) for WATM is required to achieve high throughput as well as high transmission quality, i.e., low CLR (cell loss ratio). Selective repeat (SR) and go-back-N (GBN) are typical ARQ schemes. Though SR-ARQ is superior to GBN-ARQ in terms of throughput performance, the implementation complexity of SR-ARQs control procedures prohibits its application to high-speed wireless systems. GBN-ARQ, on the other hand, cannot avoid serious throughput degradation due to fairly high BER caused by multipath fading and shadowing. To solve this problem, this paper proposes a novel ARQ scheme named PRIME-ARQ (partial selective repeat superimposed on GBN-ARQ) for TDMA-based WATM. PRIME-ARQ achieves high throughput performance, almost equal to selective repeat ARQ, with a simple algorithm resulting in reduced implementation complexity for high speed operation. This paper describes the design, implementation, and performance of the proposed PRIME-ARQ. In addition, it shows the experimental results using a PRIME-ARQ processor.

SDM-COFDM scheme using feed-forward inter-channel interference canceller for broadband mobile communications

This paper proposes space division multiplexed coded orthogonal frequency division multiplexing (SDM-COFDM) scheme using inter-channel interference canceller for multi-input multi-output (MIMO) channels. It reduces the degradation due to inter-channel interference in SDM transmission with a feed-forward canceller multiplying the received symbols by the estimated propagation inverse matrix for each OFDM subcarrier. Moreover, the proposed likelihood-weighting scheme, which is based on each subcarriers signal-to-noise power ratio (SNR), enhances the error correction performance or soft decision Viterbi decoding. Computer simulation shows that the SDM-COFDM scheme achieves more than 100 Mbit/s per 20 MHz in frequency selective fading environments with the same carrier-to-noise ratio (CNR) as the single channel COFDM.

Error correction and error detection techniques for wireless ATM systems

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.

A proposal of an ATM wireless access system for tetherless multimedia services

This paper proposes an ATM wireless access system for tetherless multimedia services. The proposed system is intended to provide ATM-based high-speed transmission capability for tetherless multimedia services by wireless media in private LAN/WAN environments as well as public environments. To enable high-speed transmission, this paper proposes the utilization of the SHF band taking advantage of its wide frequency spectrum availability. However, the propagation feature of the SHF band limits the wireless terminal mobility in the proposed system compared with current cellular phone systems. This paper discusses the concept and system architecture of the proposed ATM wireless access system, including its ATM transport based on ATM/TDMA conversion using a time stamp scheme.

A TDMA satellite communication system for ISDN services

The authors propose a TDMA (time-division multiple-access) satellite communication system suitable for both basic and primary ISDN services in addition to B-channel transmission lines among ISDN switches. To provide these services economically and efficiently, the proposed system uses an offset quadrature phase-shift keying (QPSK) burst model coupled with high-coding gain and rate-forward-error correction, demand assignment technology for each data burst, and a transmission and reception transponder (carrier) hopping scheme. To realize cost-effective transmission and subscriber lines and to increase the reliability of TDMA terminals, the major functions of TDMA terminals have been implemented in large-scale integrated circuits (LSICs), monolithic ICs (MICs) and hybrid ICs (HICs). The experimental results show narrow spectrum transmission with little bit error probability degradation for the offset QPSK burst modem and perfect operation of demand assignment and carrier hopping capability of the system. >