Wireless Systems Design

Chip Set Rejects One-Channel Approach

This Switching Engine Promises Multi-Channel And Multiband Support For IEEE 802.11b/g/a Access Points.

As Wi-Fi products continue their remarkable growth rate, so too will the potential for airway congestion. The wireless networks in the enterprise environment and commercial "hot spots" will be particularly susceptible. After all, they have a greater density of users than the home WLAN community. As more users connect from their mobile laptops, PDAs, and soft phones to the nearest access point, response times will increase. Bandwidths will decrease, leaving customers with a longer wait for less data.

The real problem with bandwidth and response time stems from the fact that the 802.11 technology was designed to provide shared—rather than dedicated—bandwidth. IEEE 802.11b access points have three non-overlapping RF channels (whereas 802.11a products have eight). Yet every 802.11b access point is set to send and receive over only one of the available channels. The other channels are simply ignored. As more users connect to a given access point, they must take turns using that one channel. A single high-use user can effectively dominate the available bandwidth, forcing others to wait.

To address this looming problem, Engim has recently introduced a wireless-local-area-network switching chip set. The EN-3000 Multi-Channel WLAN switching engine delivers significantly higher bandwidth capabilities by simultaneously using all of the available 802.11 channels from a single access point.

The company's EN-3000 family of chips supports the IEEE 802.11b (11 Mbps over 2.4 GHz), 802.11a (54 Mbps over 5 GHz), and 802.11g (54 Mbps over 2.4 GHz) standards. The chip set' s DSP-based front end analyzes the available RF spectrum from all channels, thereby enabling multiband (b, a, or g) and multi-channel support. Consequently, the chip set can process three channels of 802.11b/g for a maximum throughput of 3 × 11 Mbps (33 Mbps). Or it can process three 802.11g or 802.11a channels for a maximum throughput of 3 × 54 Mbps (162 Mbps).

The EN-3000 chip set consists of a wideband RF front end supporting 2.4 or 5 GHz, an analog baseband, and a digital baseband/medium access controller (MAC). A complete Engim-based access point would contain at least one chip from each of the radio-frequency, analog, and digital basebands (see figure).

In the RF section, two chips are required to cover the needed spectrum. The EN-3200 is a 2.4-GHz wideband RF front-end chip that is intended for 802.11b/g WLAN applications. Using direct-conversion technology for the IF band, this transceiver supports three simultaneous channels for 802.11b/g.

The EN-3500 is the corresponding transceiver for 5-GHz 802.11a usage. The 5-GHz band spans from 5.15 to 5.825 GHz with eight channels that cover 300 MHz of spectrum. Within that band, the front end can be tuned to capture any three of the eight channels.

The EN-3100 chip provides analog baseband processing. It includes a 12-b analog-to-digital converter and two IQ, 10-b digital-to-analog converters.

The final component in the EN-3000 chip-set family is a tri-channel digital baseband processor and MAC chip called the EN-3300. This multi-channel, multi-standard device includes a triple-speed programmable MAC. The three 802.11a/b/g-compliant digital basebands and modems can achieve a peak data rate of 162 Mbps.

This WLAN chip set is controlled via a multi-threading software MAC running on an integrated RISC core. It can be bypassed altogether for custom third-party MAC designs.

In addition to the chip-set hardware, the EN-3000 comes with a basic software interface. Development partners can use this interface to control and manage access points. Development kits for the EN-3000 chip-set family are now available. The company anticipates that the EN-3000 chip set will come in at just under $100.

Engim, Inc.
40 Nagog Park, Acton, MA 01720; (978) 206-3400, FAX: (978) 929-9779, www.engim.com.

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