Innovative research and development on OFDM transmission technologies for broadband wireless LANs

The prototype device of the world's first packet mode OFDM-based high-speed wireless LAN

Fig.1 The prototype device of the world's first packet mode OFDM-based high-speed wireless LAN

The prototype device of the world's first IEEE 802.11a compliant wireless LAN

Fig.2 The prototype device of the world's first IEEE 802.11a compliant wireless LAN

    In recent years, broadband wireless LAN systems have been getting a lot attention by being enhanced in their throughputs. A research group including Masahiro Morikura, Masato Mizoguchi and Takeshi Onizawa developed sophisticated packet mode transmission technologies for wireless LANs to realize a highly efficient broadband wireless communication system within a limited frequency bandwidth. For the first time in the world, they overcame the degradation due to multipath fading by applying an Orthogonal Frequency Division Multiplexing (OFDM) technology to wireless LANs that required packet mode operation. The OFDM scheme has higher frequency efficiency and more robustness against multipath fading in comparison to the conventional mainstream technologies such as spread spectrum CDMA techniques and several equalizers for a single carrier transmission. Their new technologies, by which the feasibility and effectiveness of OFDM broadband wireless LANs were clearly demonstrated, have contributed greatly to give direction to subsequent research on the broadband wireless transmission.

    OFDM transmission technologies had been conventionally used in the field of digital broadcasting in continuous mode. This research investigated packet mode OFDM demodulation techniques for wireless LANs, which demanded a highly difficult investigation in comparison to them in continuous mode operation, because the demodulator of wireless LANs required to receive signals in the packet-by-packet mode from any stations.

    Packet mode OFDM transmission requires its synchronization circuit to operate accurately within a very short period. The research group proposed a novel precise demodulation scheme which can receive packet signals without any previous information (i.e. packet-by-packet operation), and succeeded in establishing the world’s first broadband wireless LAN technologies using packet mode OFDM transmission not only on theoretical studies nor computer simulations but also on the development of the prototype wireless LAN system. They also proposed and made international standardization of the technologies, based on the results of their research and development. More detailed descriptions are as follows:
1) Early research on the demodulation techniques of the packet mode OFDM transmission
In order to demodulate packet signals whose arrival time the demodulator did not receive any previous notice, it was essential that a high speed symbol timing detection and a high precision automatic frequency control (AFC) should be developed. The proposed scheme which introduced two repetitive preamble signals realized packet-by-packet synchronization with high speed and precision. In addition, the technologies have been demonstrated with sufficient performance by the development of the prototype wireless LAN system, which includes the proposed adaptive channel estimation technique utilizing the correlation between adjacent subcarriers, and the proposed phase-tracking technique.
2) Proposal and standardization of packet mode OFDM transmission for wireless LANs
The developed wireless LAN using packet mode OFDM transmission was proposed to the IEEE 802.11 working group as a high rate wireless LAN specification. Then, the working group selected the technologies from among several competing proposals, and based on the proposal, the working group established the IEEE 802.11a standard which achieved 54 Mbit/s transmission using the 5GHz band. The developed technologies contributed significantly to some practical aspects. They have been adopted not only as the IEEE 802.11a standard but also as IEEE 802.11g, the prevailing 2.4GHz wireless LAN. In addition, they have contributed to give the direction to subsequent broadband wireless systems through the application of OFDM transmission. The systems include another high-speed wireless LAN, short-range wireless systems such as Ultra Wideband (UWB), Wireless Metropolitan Area Network (MAN) etc. This is because the results of the technologies demonstrated the superiority of the OFDM transmission over other technologies and encouraged their practical uses and further academic research.

    As described above, the research group including before-mentioned three persons carried out an innovative research and development project of wireless broadband transmission technologies, and made it widely available to users.

    For contribution of such an innovative project, the Institute of Electronics, Information and Communication Engineers gave Achievement Award to Masahiro Morikura, Masato Mizoguchi and Takeshi Onizawa in 2006.



Publications

[1] T. Onizawa, M. Mizoguchi, M. Morikura, and T. Tanaka、A Fast Synchronization Scheme of OFDM Signals for High-Rate Wireless LAN、1999、IEICE Trans. on Communications, Vol.E82-B, No.2, pp.455-463, Feb. 1999
[2] Masahiro Morikura and Hideaki Matsue、Trends of IEEE802.11 based Wireless LAN、2001、IEICE Trans. Commun. (Japanese Edition), J84-B, 11, pp.1918-1927 (2001-11)
[3] Masataka Iizuka, Masato Mizoguchi, and Masahiro Morikura、Development of IEEE 802.11a compliant high rate wireless LAN system、2001、NTT Technical Journal (Japanese Edition), vol.13, no.6, pp.83-87, 2001

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