Now that certified WiMAX equipment is available will it live up to its full potential?

Nicolas Salamina and Ramesh Kumar, Texas Instruments

At the beginning of this year, the first WiMAX equipment was certified by the WiMAX forum, the body set up in 2001 to promote and certify WiMAX broadband wireless technology. As WiMAX becomes more widely used it will be possible to determine its true potential and establish the effect it will have on existing broadband and cellular technologies such as DSL and 3G.

WiMAX can be divided into two main types, ‘fixed' and ‘mobile'. Fixed or 802.16d WiMAX is based on IEEE 802.16-2004 and is the technology used in the recently certified WiMAX equipment. It is designed to support data rates of up to 40 Mbps per channel. Base stations will cover a radius of up to 10 km. Mobile or 802.16e WiMAX will support data rates of up to 15 Mbps. Although mobile WiMAX will require a higher density of base stations (area coverage is only 3 km), it is anticipated that when the first mobile WiMAX equipment becomes available in 2007, it will prove more popular than fixed WiMAX as it can serve both fixed and mobile applications.

Why WiMAX?

WiMAX provides wider frequency bandwidths (10MHZ plus) than current broadband wireless technologies. This is made possible by using Orthogonal Frequency Division Multiple Access (OFDMA) technology. Much narrower bandwidths are supported by 3G, ranging from 1.25MHz with cdma2K and 5MHz with UMTS or WCDMA. A major advantage of WiMAX is that OFDMA allows it to operate without a clear line of sight between the customer-premise equipment (CPE) and the base station. Therefore, this will, enable WiMAX to capture a wide base of potential customers. Consumers will be able to buy WiMAX modems at retail stores and install them up at home. In addition to the wider frequency bandwidths, WiMAX will support higher data rates, made possible by using multiple in/ multiple output (MIMO) and smart antennas. Another important aspect to the success of WiMAX, is multi-vendor interoperability. A key role of the WiMAX Forum certification process has been to ensure that there will be interoperability between different vendor base stations and CPEs.

There are a wide variety of potential applications for WiMAX, some of which have already been deployed commercially using pre-certified equipment. These are shown in Figure 1.

Figure 1: WiMAX Infrastructure Applications

Spectral flexibility

The spectral flexibility offered by WiMAX (frequency bands between 2 GHz and 11 GHz; although up to 66GHz might be possible in the future) will provide a competitive edge over existing technologies in two ways. First, the ability to operate multiple frequency bands allows WiMAX to tap into the global market, where there is no single band available in every country. This will allow WiMAX to compete with DSL and 3G. However, supporting multiple frequency bands using RF components will increase the cost of WiMAX products to consumers. Second, in rural or remote areas, WiMAX can operate in unlicensed frequency bands reducing the needed for expensive spectrum licenses. This reduces overhead costs and ensures competitiveness with rival wired and wireless services. However, in order to maintain quality-of-service (QoS) in unlicensed bands, sophisticated filtering will be required to prevent interference, adding to equipment costs.

DSP solutions

Creating WiMAX designs based on programmable DSP solutions will be essential if vendors are to develop cost-effective equipment that can be tuned to each country-specific frequency band (Figure 2). This will become particularly important for WiMAX frequency-agile mobile applications (laptops and handsets) that customers will use to roam from country to country. Programmable DSPs provide vendors with the flexibility to accommodate country-specific frequency, power and emission requirements, without major product redesigns for each country. This flexibility helps establish a global cost structure, one of the strengths of WiMAX.

Figure 2: WiMAX Primary Deployment Bands

Infrastructure system designers are now in the difficult position of having to develop equipment for multiple applications including cdma2000 EV-DO, 3GPP UMTS, TD-SCDMA, WiMAX and even 802.20. For each of these applications, a range of equipment is required including traditional macro base stations as well as smaller form factor base stations providing in-building coverage (Figure 3).

Figure 3: WiMAX Deployment Options

Consequently, to ensure support for all these applications, vendors are increasingly trying to find ways to re-use baseband or channel card hardware and software for multiple applications. A significant advantage would be to have a single silicon platform available that is capable of supporting all these applications (Figure 4).

Figure 4: Silicon Options for Multiple Standards

This would reduce R&D time and costs. With this in mind, Texas Instruments (TI) has specially designed the TMS320TCI6482 DSP to address this requirement. The DSP offers a single software programme that enables a high density, low-power solution for 3G applications like cdma2000 EV-DO, 3GPP UMTS, TD-SCDMA. The DSP is ideal for OFDMA applications like WiMAX and future applications like 802.20 and 3GPP LTE (Figure 5).

Figure 5: DSP Solutions for Multiple Standards

Conclusions

Although pre-standard WiMAX equipment has been in limited commercial use for 12 months or so, the arrival of the final, certified equipment means that vendors and service providers will now begin to establish a clear picture of the real-world performance and cost structure of the WiMAX technology. This will determine whether WiMAX can live up to its promise of both competing and complementing current broadband and cellular technologies, ranging from DSL to 3G. Only time will tell whether WiMAX will reach its potential and capture a significant share of these markets.