Wireless Systems Design

Chip Enables Wireless-Internet Phone Design

This Highly Integrated Voice-Over-IP Device Pushes Popular Internet-Based Phones Into The Realm Of Wireless LANs

Since the early 1990s, telephone calls over the Internet have grown increasingly popular. Often, such calls are referred to as voice over Internet protocol (VoIP) or IP telephony. As old public-branch-exchange (PBX) systems are phased out, the rise of these IP calls is accelerating. Major telecommunications-equipment vendors like Nortel (www.nortel.com) and Avaya (www.avaya.com) are replacing existing PBX-only systems with IP-enabled PBXs. This newer alternative provides voice communications over wide-area, Internet, and traditional public-switched telephone networks (PSTNs).

Compared to PSTNs, VoIP phones on wireless LANs (WLANs) promise both cost savings and ease of replacement. The VoIP phones take advantage of the enormous proliferation of today's IEEE 802.11-based wireless networks. To welcome the growth of such IP phones, Atmel recently announced a highly integrated VoIP chip for Wi-Fi-based phones. The AT76C901 chip is specifically designed for wireless-VoIP applications (see figure). In addition to running VoIP software, the device enables 802.11 firmware and voice-compression/decompression functionality.

First-generation VoIP phones required several discrete components. Among them were RISC processors, DSPs, an Ethernet hub, voice codecs, and other peripheral devices like memory. The newer generation of VoIP phones is more integrated. These phones provide higher performance, a smaller footprint, and lower overall costs.

The AT76C901 effectively partitions the wireless-VoIP phone functionality into a central RISC processor and two subsystems for 802.11b control and voice communications. To complete a wireless-Internet phone, only the following peripheral components are required: SDRAM and Flash memory, liquid-crystal display (LCD), keypad, battery, 802.11b baseband, and RF front-end circuitry.

Thanks to this high level of on-chip integration, an AT76C901-based phone consumes little power. At the same time, it enables the talk and standby times that are required by VoIP devices.

Utilizing the low power and high performance of an ARM7 RISC processor, the AT76C901 chip supports common VoIP protocol stacks. It contains two subsystems. The first subsystem integrates an ARM7 processor with an 802.11b media access controller (MAC). Together, these subsystems implement WLAN operations. The second subsystem combines the DSP Group's (www.dspg.com) OakDSP core with a voice codec, which is optimized for DSP architectures. This core performs voice compression and decompression at varying bit rates in compliance with ITU standards G.711, G.723.1, and G.729ab.

When used with Atmel's AT76C511 WLAN Access Point (AP), telephone calls placed on an AT76C901-based wireless phone can be routed to a wired network. They can then be routed to a gateway. This capability should allow companies with existing WLAN infrastructures to lower their long-distance phone charges. Such VoIP phones also could be used throughout the growing number of public Wi-Fi hot spots.

To assuage the quality-of-service (QoS) issues concerning today's IP-based phones, the AT76C901 supports the enhanced Distributed Coordinated Function (e-DCF) for QoS. This protocol is one of the proposed QoS standards within IEEE 802.11e, which has yet to be ratified. The AT76C901 chip's 802.11 MAC is firmware upgradable. As a result, any changes to the evolving standard can be incorporated as needed.

To run the AT76C901, Atmel chose Wind River's (www.windriver.com) VxWorks real-time operating system (RTOS). This commonly used RTOS offers product developers a familiar and well-supported platform for application development.

To facilitate quick time to market and reduce engineering costs, a complete reference design kit (AT76C901-DK) is available to designers. Among other things, it incorporates RF Micro Devices' (www.rfmd.com) baseband (RF3000), single-chip RF transceiver (RF2958), and power amplifier (RF5117).

The AT76C901 comes packaged in a 217-pin µBGA chip. It has been released to production. In units of 50,000, pricing for the AT76C901 starts at around $22.

Atmel Corp.
2325 Orchard Parkway, San Jose, CA 95131; (408) 441-0311, www. atmel.com.

TAGS: Components
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