Achievement Award

Research on Multiple-Input Multiple-Output (MIMO) Technology in High Speed Wireless LAN and its Practical Implementation

Tsuguhide AOKI, Tomoko ADACHI, Namekata MINORU

  Being equipped as a standard feature on smartphones and tablets, wireless LAN has achieved a firm winning position as a widely used communication tool for consumers. In the 1990fs, IEEE standardized a wireless LAN standard called 802.11 and its amendment, 802.11b. It is true that these standards triggered the spread of wireless LAN, but for the further acceleration, MIMO was recognized as a promising technology. By using multiple antennas to transmit wireless packets in parallel, MIMO can achieve high data rates proportional to the degree of parallelism. However, there were fundamental issues to achieving high-speed wireless LAN through MIMO technology. The awardees developed the worldfs first technology solving issues to realize the practical use of MIMO for high-speed wireless LAN.
  In MIMO transmission, when pilot signals, which compensate for the oscillator gap between the transmitter and the receiver, are transmitted in multiple antennas as the same way with the one-antenna case, the signal correlation between the antennas becomes high and disturbs proper compensation. This will result in causing areas where radio waves are canceled, and signals wonft be able to cover the overall area. The awardees solved the issue by systematically shifting the phase of pilot signals according to frequency as in Fig.1 (a). As a result, the area coverage of 16% with the conventional approach becomes almost 100% with the new approach. By this technology, MIMO became applicable to wireless LAN to accelerate its data rate.
  On the other hand, by a conditional frame exchange, the actual speed plateaus as data rate increases. See the blue curve in Fig.2. This is due to overheads such as packet headers, inter-frame space, and time to transmit the acknowledgment frame. By aggregating multiple frames into one physical packet, the awardees decreased the overhead of transmitting frames. In addition, by transmitting reception statuses as an acknowledgment frame when receiving an aggregated frame, the frame to request an acknowledgement frame was omitted. This resulted in also easing the management load of reception status. Eliminating fragmentation, which is the opposite processing to frame aggregation, further eased the implementation load and cut down the length of the reception status. The combination of these techniques has made the frame exchange efficient and has realized an actual speed in excess of 100 Mbps. See Fig.1 (b) and the red curve in Fig.2.
  These technologies have been adopted in the world standards of wireless LAN, IEEE 802.11n@and IEEE 802.11ac. They have also been adopted in the next generation wireless LAN standard, IEEE 802.11ax, which is on-going. The awardees have also developed other technologies such as preamble signals to coexist with legacy stations and techniques to limit subscribing stations to keep high efficiency and they are also adopted in these standards.
  The awardees have contributed to the commercialization of a wireless LAN baseband LSI, a wireless LAN one-chip LSI with analogue function, and a wireless LAN mounted SD memory card, which are compatible with IEEE 802.11n and IEEE 802.11ac. An LSI compatible to the 802.11ax draft standard has been further developed and was presented as a worldfs first 802.11ax compatible LSI at ISSCC 2018 on Feb. 2018, with one of the awardees as a co-author.
  According to investigation reports, 2.5 billion devices have been equipped with high-speed wireless LAN standards in 2015 and the number is forecasted to grow to the order of 3.3 billion in 2020. This technology greatly contributes to the acceleration of the use of wireless LAN in offices and homes, and further to the propagation of public wireless LAN. From now on, it is highly expected that this technology will open out to IoT and other new areas. With regard to high-speed wireless LAN, the awardees have already received several awards such as IEEJ*1 Technical Development Award (2014), the Young Scientistsf Prize of the Commendation for Science and Technology by the Minister of MEXT*2 (2015), and the Ichimura Prize in Industry for Distinguished Achievement (2016). The awardeesf contributions are prominent, and they are strongly recommended for the Achievement Award of IEICE.
  *1: The Institute of Electrical Engineers of Japan
  *2: Ministry of Education, Culture, Sports, Science and Technology
Fig.1 This MIMO Technology
Fig. 1 This MIMO Technology
Fig.2 Effect ofthis Technology
Fig. 2 Effect ofthis Technology

References

  1. Tsuguhide Aoki, Yoshimasa Egashira, Daisuke Takeda, gPreamble Structure for MIMO-OFDM WLAN Systems Based on IEEE 802.11a,h PIMRC2006, Sept. 2006.
  2. Tsuguhide Aoki, Yoshimasa Egashira, Daisuke Takeda,h Preamble Structure for IEEE 802.11n Wireless LAN System,h IEICE Trans. Comm., Vol.E92-B, No.10, pp.3219-3227, Oct. 2009.
  3. Tsuguhide Aoki, Tomoko Adachi, MIMO pilot signals and selective repeat scheme for high throughput wireless LANs,h WECC2015, Dec. 2015.
  4. (4) Tsuguhide Aoki, Magnus Sandell, gAnalysis of pilots for residual frequency offset estimation in MIMO OFDM systems,h IEEE Trans. Wireless Comm., VOL. 8, NO. 3, March 2009.
  5. Tetsu Nakajima, Yoriko Utsunomiya, Yasuyuki Nishibayashi, Tomoya Tandai, Tomoko Adachi, Masahiro Takagi, gCompressed Block Ack, an efficient selective repeat mechanism for IEEE802.11n,h PIMRC2005, Sept. 2005.
  6. Tetsu Nakajima, Toshihisa Nabetani, Yoriko Utsunomiya, Tomoko Adachi, Masahiro Takagi, gA Simple and Efficient Selective Repeat Scheme for High Throughput WLAN, IEEE802.11n,h VTC 2007-Spring, 2007.
  7. Tomoko Adachi, [Tutorial Session] gThe Latest Technology Treand in IEEE802.11 Wireless LAN,h IEICE General Conference, March 2009.
  8. Tomoko Adachi, gWork Front in Standardization 15th IEEE802.11n,h ITE Journal Vol. 65, No.7, 2011
  9. IEEE Std 802.11nTM-2009: Enhancements for Higher Throughput (Amendment 5)
  10. S. Kawai, et al., gAn 802.11ax 4~4 Spectrum-Efficient WLAN AP Transceiver SoC Supporting 1024QAM with Frequency-Dependent IQ Calibration and Integrated Interference Analyzer,h ISSCC 2018, Feb. 2018.
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