Satoru Aikawa

256 QAM Modem for Multicarrier 400 Mbit/s Digital Radio

This paper describes the performance of a 256 QAM modem with 400 Mbit / s transmission capacity. A variety of novel techniques are introduced as ways to achieve good performance. Key techniques include 1) an accurate 256 QAM modulator employing a new monolithic multiplier IC, 2) a carrier recovery circuit which satisfies such requirements: good phase jitter performance and no false lock phenomenon, 3) a highly stable high-level decision circuit, and 4) a forward error correcting code. As an overall modem performance, BER characteristics and signatures are presented. The equivalent CNR degradations of 1 dB(at BER of 10-4) and 2 dB (at BER of 10-9)are obtained using a single Lee-error correcting code and a seven-tap baseband transversal equalizer. The residual bit errors are decreased below the order of 10-10. The performance of a 256 QAM multicarrier modem has given prospect for the development of 400 Mbit/s digital microwave radio system.

Cell discard and TDMA synchronization using FEC in wireless ATM systems

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.

256-QAM subcarrier transmission for broadband distribution networks

Broadband distribution networks are presented combining digital microwave radio with optics using subcarrier multiplexing (SCM) transmission. In the first implementation of a high-capacity transmission, the authors present the prospect of fiber-optic transmission of microwave 256 quadrature amplitude modulation (QAM) signals at 10-Mb/s and 50-Mb/s transmission rates. Bit error rate (BER) performance results are shown as a function of received optical power and optical modulation index. It is shown that the results of theoretical BER performance calculations are in agreement with that of preliminary experiments for two types of 256-QAM signals. Error correction coding using a BCH code is very effective in improving the system performance. Finally, the choice of the total optical modulation index for multichannel transmission is discussed.<<ETX>>

Fast Algorithm for Decision Feedback Equalization in Multiple Input Multiple Output Channel

In this paper, we propose a new algorithm for zero-forcing decision feedback equalization (ZF-DFE) in multiple input multiple output flat Rayleigh fading channel. The basic idea is to separates the layer ordering and the filter construction operations, thus making both operations tractable and efficient. The new layer ordering strategy approximates the optimal ordering rule (VBLAST) from a geometrical perspective, and the filters in proposed ZF-DFE are constructed using a matrix Cholesky decomposition aided QR decomposition. Compared to the conventional ZF-DFE detectors utilizing optimal and suboptimal ordering rules (SQRD), the proposal is complexity efficient. Additionally, the bit error rate performance of the new algorithm significantly approximates that of the optimal ordering ZF-DFE. Thus a practical signal detection scheme for the vector channel is found

Advanced techniques for super multi-carrier digital microwave radio with trellis-coded 256 QAM modulation

The latest techniques for realization of an outage-free digital microwave radio (DMR) are presented. Three major techniques, trellis-coded 256 QAM (quadrature amplitude modulation) modulation, super multicarrier transmission, and microwave signal processing (MSP), are described. The BER (bit error rate) and signature characteristics of the trellis-coded 256 QAM system are simulated, and its validity as a fading countermeasure is indicated. The Viterbi-decoder LSI and effect of phase error on the TCM modem are also presented. An experiment using a 4, 8, 40-carrier 256 QAM modem showed an overall outage improvement factor of nearly 500 times due to a 40-carrier system. Lastly, the microwave signal processing technique, including IF stage (carrier) signals for DMR systems, is presented. An all-digital 256 QAM modulator was constructed and showed superior performance with no adjustment.<<ETX>>

Performance of trellis coded 256 QAM super-multicarrier modem using VLSI's for SDH interface outage-free digital microwave radio

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 VLSIs 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/sup /spl minus/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. >

A Simple and Feasible Decision-Feedback Channel Tracking Scheme for MIMO-OFDM Systems

This paper proposes a simple and feasible decision-feedback channel tracking scheme for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems designed for wireless local area networks (LANs). In the proposed scheme, the channel state matrix for each subcarrier is tentatively estimated from a replica matrix of the transmitted signals. The estimated channel matrices, each derived at a different timing, are combined, and the previously estimated channel matrices are replaced with the latest ones. Unlike conventional channel tracking schemes based on a Kalman filter, the proposed scheme needs no statistical information about a MIMO channel, which makes the receiver structure quite simple. The packet error rate (PER) performances for the proposed scheme are evaluated on computer simulations. When there are three transmit and receive antennas, the subcarrier modulation scheme is 64 QAM, and the coding rate is 3/4, the proposed scheme keeps the SNR degradation at PER of le-2 less than 0.1 dB when the velocity of receiver is 3 km/h in an indoor office environment at 5 GHz band. In addition, compared to the conventional channel tracking scheme based on known pilot symbols, the proposed scheme improves throughput performance by 13.8% because it does not need pilot symbols. These results demonstrate that the proposed channel tracking scheme is simple and feasible for implementation in MIMO-OFDM systems based on wireless LANs.

MMSE Criterion Fast Decision Feedback Equalization Algorithm for Spatial Multiplexing Systems

Recent studies indicate that spatial multiplexing (SM) scheme has enormous potential for increasing the capacity of MIMO channels in rich scattering environments. In this paper, we present a new MMSE decision feedback equalization algorithm for signal detection in SM systems. The new algorithm separates the order search and the filter generation to avoid recursive ordering operations. Compared to the earlier MMSE-DFE detectors with optimal and suboptimal ordering rules, the new algorithm is less complex and achieves a bit error rate performance that closely approximates that of the standard BLAST algorithm.

A Multi-channel infrastructure based on DCF access mechanism for Wireless LAN Mesh Networks compliant with IEEE 802.11

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

A smart multiple sector antennas control technique for a high-speed ATM wireless access system using 25-GHz band

This paper proposes a smart antenna control technique for an ATM wireless access system (AWA) that offers broadband mobile services. Although the quasi-millimeter band is a promising frequency band for the AWA system, which needs wide frequency spectrum, it suffers from heavy shadowing and multipath fading. The AWA system will employ sector-type B-CS/B-RM antennas to combat both problems. Space and site diversity using sector antennas at multiple sites can be achieved by smart antenna control. This technique is useful for reducing the deterioration caused by shadowing and multipath fading. This paper conducts experiments on a prototype AWA system to confirm that the proposed antenna control technique is realistic and effective.