Chapter 15. A Peek Ahead at 802.11n: MIMO-OFDM

802.11 task group N (TGn) has an interesting goal. Most IEEE task groups focus on increasing the peak throughput, making data fly as fast as possible during the time it is being transmitted. TGn’s goal is to achieve 100 Mbps net throughput, after subtracting all the overhead for protocol management features like preambles, interframe spacing, and acknowledgments. Although the goal is 100 Mbps net throughput, the final proposal seems certain to blow past that number, and offer many times that throughput in maximum configurations. There are two roads to 100 Mbps: improve the efficiency of the MAC, increase the peak data rate well beyond 100 Mbps—or both.

Six complete proposals were made to the group creating the eventual 802.11n, but support has coalesced around two main proposals, from groups named TGnSync and WWiSE (short for “World-Wide Spectrum Efficiency”). Both camps have chip-makers. Atheros, Agere, Marvell, and Intel are part of TGnSync; Airgo, Broadcom, Conexant, and Texas Instruments are the core of WWiSE. However, quite a few manufacturers of electronic devices that might use 802.11 (Cisco, Nokia, Nortel, Philips, Samsung, Sanyo, Sony, and Toshiba) have also become part of the effort, and they are disproportionately represented in TGnSync.

At a very high level, both proposals are similar, though they differ in the emphasis on increasing peak data rates versus improving efficiency. Each of them makes use of multiple-input/multiple-output ...

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