802.11n in Handsets

802.11n will be finally approved at the end of this year, and it is huge for voice over WiFi (News - Alert).

Compared to 802.11g or 802.11a it can quadruple effective throughput (to 100 Mbps), improve rate at range and improve battery life. This is with a single antenna, since MIMO is unsuitable for handsets.

Recent 802.11g chips for phones have made great strides in power efficiency. First, 802.11e contains a feature called WMM Power Save; this greatly increases battery life. Second, the chip industry has been making great strides in power management in every kind of chip. These improvements come from several sources, but the most significant one is partitioning the chip into numerous blocks, and keeping the blocks that are not in use powered down. The trick is to switch on each part just before it is needed, then to switch it off again immediately. 802.11n chips deliver these benefits, plus they greatly improve rate at range. Faster transmissions mean that the chip spends less time powered up. Even though the 11n protocol is compute intensive and burns a lot of power when it is running, the faster transmission speed means that each bit sent or received uses less battery than an 802.11g bit. With these new chips, talk-time on WiFi is better than on cellular connections.

The 100 Mbps of effective throughput with a single antenna is also worth explaining. Changes to the protocol bump the nominal transmission speed from 54 to 72 Mbps. Other changes reduce the overhead from 50 percent to 30 percent, resulting in an increase of effective throughput from 25 Mbps to 50 Mbps. There is also a new mode that increases the single-channel bandwidth from 20 MHz to 40 MHz, doubling the throughput by using two adjacent 802.11 channels simultaneously. Maximum 802.11 throughput figures are rarely achieved in the real world; the transmission rate falls rapidly with increasing distance and other impairments. 802.11n has several features to keep transmission speeds high even at a distance. The one to look for is STBC (Space Time Block Coding), which yields some of the benefits of MIMO on a single antenna.

No phone contains 802.11n yet, but it is imminent; four vendors (Broadcom, TI, CSR and Redpine) have 802.11n chips for handsets either sampling or already in production. IT

Michael Stanford (News - Alert) has been an entrepreneur and strategist in Voice-over-IP for over a decade. Visit his blog at www.wirevolution.com.

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