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Electronic Design

Advanced 802.11 Chip Sets Push Wi-Fi Into The Video Home

Millions of homes already have wireless networks that generally do a superior job delivering broadband connections to PCs and laptops. But those networks may need to be replaced or at least upgraded when consumers begin to adopt new Internet Protocol video and attempt to distribute video throughout the home from any source.

The main contender is the forthcoming upgrade to the versatile 802.11 wireless local-area network (WLAN) standard. The IEEE Standards Task Group is developing a high-speed version known as 11n. A draft version is now available, and a final version is expected in March 2008.

Meanwhile, chip vendors and equipment manufacturers are offering pre-n or draft-n products that mostly comply with the expected final 11n standard, though some variations are likely to occur. Most manufacturers say draft-n versions will be compatible and/or upgradeable. The Wi-Fi Alliance is even beginning to certify the interoperability of draft-n products.

In addition to providing the extra high speed that 11n promises, some chip vendors are offering products that go beyond the standard to improve range, quality of service (QoS), and speed, such as new chip sets from Metalink Ltd. and Raylink Technology.

Metalink's second-generation draft-11n chip set, WLANPlus, comprises the MtW8151 RF IC and the MtW8171 baseband IC (see the figure).

The 8151 is a complete RF multiple-input/multiple-output (MIMO) front end with three receivers and two transmitters (2x3). It operates in the 2.4- and 5-GHz unlicensed Wi-Fi bands. It's compatible with 802.11n draft standards, but it's also fully backward compatible with 802.11a/b/g. And, this new physical-layer (PHY) chip features a Near Maximum Likelihood (NML) slicer that effectively doubles the coverage area.

The 8171 is a full implementation of an integrated lower and upper media-access controller (MAC) that dramatically reduces the required processing power and memory allocation from the host application processor. This greatly simplifies the integration with consumer electronic devices and helps reduce the total cost.

Another range-extending feature is its low-density parity check (LDPC) forward error correction (FEC), which provides advanced coding gain. It also supports the channel bonding specification with both 20- and 40-MHz channels. Furthermore, its QoS capability makes it fully compatible with the IEEE's 802.11e QoS standard, which is critical for both high-quality voice and video services.

The 8171 implements other QoS mechanisms as well, such as Enhanced Distribution Channel Access (EDCA) with Admission Control and Fast Link Adaption (FLA). The Dynamic Link Adaption features save 50% on airtime and increase network efficiency. Host bus interfaces include CardBus, mPCI, and PCI 2.3.

As for security, the chip set supports the IEEE 802.11i standard as well as all the usual WLAN security modes, such as 64/128-bit WEP, AES, TKIP, WPA, and WPA2. The set also delivers multiple HDTV streams to any location within a radius of 100 ft while maintaining full QoS performance at a data rate to 300 Mbits/s.

WLANPlus exceeds the de facto HDTV802.11n streaming critical requirement for delivering 60-Mbit/s effective throughput to a distance of 60 ft at 5 GHz. This capability will support the multiroom networking of multiple HD video streams. Expected applications include laptops, digital media adapters (DMA), HDTV sets, DVRs, and residential gateways.

Metalink has reference designs for a mini PCI card (type111B), CardBus, and residential gateway. Production is expected by mid-2007 with volume expected in the second and third quarters. Check with Metalink for volume pricing.

According to Ralink, its two-chip RT2800 draft-n compliant 802.11n Wi-Fi chip set has the longest range of any draft-n product. It doubles the range of Wi-Fi systems and eliminates reception shadows in homes, offices, and city-wide mesh networks. The long-range reception is made possible by patented low-noise circuitry that pinpoints and recovers the high-speed data stream.

In recent outdoor tests, Ralink achieved a 700-m range at 14 Mbits/s while competitive devices could only reach a maximum of 350 ft. The chip set supports a raw data rate to 300 Mbits/s with a solid throughput without protocol overhead of 180 Mbits/s. This is enough to ensure the streaming of three channels of HDTV and to keep up with the 100-Mbit/s capability of the newer VDSL lines that potentially will supply the video.

The RT2800 chip set is flexible and can be used in desktop computers, laptops, printers, network storage systems, media servers, projectors, TV set-top boxes, and home routers/gateways. With its range greater than most competitors, it suits large homes as well as the wireless mesh networks that have been sprouting up all around the country.

Both versions of the silicon-germanium RF chip use the standard 2x3 (Tx-Rx) MIMO format with two transmitters and three receivers. The RT2850 version covers the 2.4- and 5-GHz bands, but the RT2820 only covers the 2.4-GHz band.

All three versions of the baseband and MAC chip meet the draft-n specs and are backward-compatible with 802.11a/b/g. The difference is in the interfaces. The RT2890 has MiniCard and PCI Express interfaces. The RT2870 has a USB 2.0 interface. The RT2860 has PCI, MiniPCI, and CardBus (PCMCIA) interfaces.

The USB 2.0 chip's internal patented 2x2 antenna makes the chip set ideal for dongles and other small packages. The USB 2.0 version is the first solution to offer its driver in optional on-board flash memory instead of on a CD-ROM. This gives the end user a true plug-and-play product because the driver is uploaded into the computer through the USB connector. The Linux driver source code is available.

The baseband chip includes security (802.11i, WEP, TKIP, AES, WPA, and WPA2) and QoS (802.11e) accelerators. Other 11n features supported include short GI, green field, spatial expansion, reverse data grant, and Fast Link Adaption. It also accommodates 20- and 40-MHz channels. The chip set is designed so any variations with the final 11n standard can be corrected with a software upgrade.

The chip set's low power consumption helps extend the battery life of notebooks and other portable Wi-Fi-powered products. The chips automatically power down any circuitry that isn't being used. The entire chip set operates from a 3.3-V supply and consumes only 480 mA under MCS15 (modulation coding scheme), IPG (interpacket gap) = 50 ┬Ás and 40 MHz during transmit. It draws only 400 mA during receive under the same conditions.

Chip set prices start at $20 in volumes of 1000. Samples are available now. Production is slated for later in 2007.
Metalink Ltd.
Ralink Technologies

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