Electronic Design

Power-Pinching WiMAX SoC Still Extends Range

With the lowest power consumption of its type, this chip makes embedded fixed and portable broadband wireless applications practical.

WiMAX is coming—oh, you know, the broadband wireless technology that promises highspeed Internet service and other broadband offerings such as TV to homes and businesses, which will be in direct competition with entrenched DSL and cable TV. While few WiMAX ISPs have yet to be established in the U.S., several already exist in Europe and Asia.

Like any new wireless technology, how successful WiMAX will be is really anyone's guess. Some people say it will compete with the latest 2.5G and 3G cell-phone systems like GSM/ EDGE/HSDPA, cdma2000 EV-DO, or 3GPP WCDMA. You already can get a PC card for your laptop that will give you 500 kbits/s to 2 Mbits/s via the cell-phone networks.

Another potential competitor is Wi-Fi. With the growing number of hot spots and the spreading municipal Wi-Fi mesh systems, can WiMAX be justified?

The standard is certainly robust enough to compete with either of the systems. Nevertheless, wireless broadband based on WiMAX is expected to roll out later this year and beyond in the U.S. To help make this happen, semiconductor companies are creating chips for both basestations and customer premise equipment (CPE).

Entering the fray is TeleCIS Wireless' TCW1620 systemona-chip (SoC). The device not only complies with the standard, it also offers some significant benefits over other similar chips already on the market.

THE BASICS
The TCW1620 comprises the baseband part of a WiMAX radio (Fig. 1). It uses almost any of the RF front ends available from vendors like SiGe Semiconductor, Sierra Monolithics, and Texas Instruments. It performs all of the data conversion, modulation and demodulation, plus other processing. An ARM9 processor resides on-chip.

The device fully complies with the WiMAX standard IEEE 802.16-2004. Designed primarily for CPE products, it offers the lowest power consumption in its class with an average of less than 750 mW—and that's with two channels of operation. As a result, according to TeleCIS VP of marketing David Sumi, it's well-suited for inclusion in portable equipment like laptops or PDAs, or in PC cards and USB dongles.

The TCW1620 supports all standard WiMAX features: binary phase-shift keying (BPSK), quadrature phase-shift keying-(QPSK), 16QAM (quadrature amplitude modulation) and 64QAM, aggregate speeds to 75 Mbits/s, bandwidths from 1.25 to 20 MHz, and Reed-Solomon/Convolutional-Viterbi error correction. Security is via Data Encryption Standard (DES), 3DES, or optionally Advanced Encryption Standard (AES). Furthermore, it offers special features over and above those required by 802.16-2004.

For example, TeleCIS's Rx Technologies support a twoantenna (receiver and transceiver) multiple-input/ multipleoutput (MIMO) architecture. With such an arrangement, the receiver performs diversity combining and space-time coding on-chip to produce a gain increase of 15 dB over standard solutions. This extends CPE range and improves reliability in the difficult non-line-of-sight operation (NLOS) conditions expected in most WiMAX installations.

Two sets of analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) are provided in addition to the on-chip two-antenna support. As such, the bill of materials shrinks substantially for the MIMO feature, making it highly attractive for smaller portable devices.

The 802.16-2004 standard defines the fixed version of WiMAX to be delivered by one or more basestations to fixed customer premises. Previous microwave broadband systems suffered from low signal strength and multipath problems prevalent in microwave services. Line-of-sight (LOS) operation, in which the customer's antenna could "see" the basestation antenna, was mandatory for satisfactory operation.

The problem was solved, thanks to the new standard's use of orthogonal frequency-division multiplexing (OFDM). This form of modulation/access is much more immune to multipath problems, making NLOS operation possible—essential for low-cost, indoor, selfinstalled CPE.

PORTABLE WIMAX
The OFDM and other unique TeleCIS features are the ingredients needed for portable WiMAX, also known as nomadic WiMAX. Consumer devices equipped with WiMAX may be portable, but the standard does not yet support its use while they're in motion. Laptops are the most common example, but PDAs and other devices also could be WiMAX-enabled.

"Service providers, knowing now that appropriate WiMAX portable consumer products are coming soon, will have a very attractive business case, particularly in urban areas, for the deployment of WiMAX services," says Sam Endy, chief executive officer of TeleCIS.

Most laptops already embed Wi-Fi, but future models may feature embedded WiMAX, too. In the meantime, WiMAX PC cards will help new broadband wireless service providers compete successfully with 3G cell-phone carriers who offer similar portable broadband services.

The TCW1620 integrates standard PCI and Card Bus interfaces, a 10/100 Ethernet port, a standard UART, and some general-purpose input/output (GPIO) lines. It operates from 1.2 V internally, with 3.3 V for the interfaces. The package is a 17- by 17-mm, 400-pin thin and fine-pitch ball-grid array. Base price is $35. Discounts are available for high volume. TeleCIS also offers a full development kit (Fig. 2).

The company continues on with its development, which will see the TCW1620 evolve into the next-generation TCW2720. It will comply with the new 802.16e standard. The standard defines a fully mobile version of WiMAX that enables products in motion to use the broadband services. The TCW2720 also will incorporate MIMO and smart-antenna functionality, extending WiMAX capability to handheld devices.

Thus, WiMAX becomes an even more compelling wireless solution. On top of that, the new chip will incorporate a full Wi-Fi 802.11a/g capability, making it even more attractive for embedded portable and mobile applications. The TCW2720 will not be available until next year.

TeleCIS Wireless Inc.
www.telecis.com

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