Mobile WiMAX – 4Ging the Future?

By Vijay Nagarajan, Guest Author

In my last piece, I gave a brief historical perspective of WiMAX as a fixed wireless broadband standard. This article provides an insight into mobile WiMAX and its future as a 4G standard.

Mobile WiMAX is a different ball-game. In order for a mobile version of this technology to work, there are several features that have to work seamlessly. Chief among them are-

• Power Control: Controls the amount of transmission power by the mobile and the base-stations. This in turn determines battery-life and the amount of interference each user sees. Interference reduces the data-rate thereby pulling down user-experience along with it.
• Synchronization: For OFDMA to work, it is required that all users are synchronized in time during transmission. If this synchronization fails, the users are no longer orthogonal, meaning that the underlying communication principles are destroyed.
• Hand-over: For a seamless user experience, it is important that the base-stations silently transfer connection between themselves as you move in your vehicle.
• Edge of Cell: The peak data-rates are practically impossible to achieve in any real network. It is more of a nightmare for a user caught in the edge of coverage. The base-station not only has difficulty giving the user good rates but also suffers from increased interference from neighboring base-station signals.
• Battery Life: Like all mobile devices, energy savings become important due to the dependence on a battery.

These engineering challenges dog most OFDMA standards. Mobile WiMAX is no exception. 802.16e is the mobile version of WiMAX and is heavily influenced by the Korean standard WiBRO. While mobile WiMAX has addressed these issues, it is not backward compatible with its fixed predecessor.

802.16e is not technically 4G and is often regarded as the direct competition to 3G HSDPA. In the summer of 2006, mobile WiMAX received a major boost when Intel and Motorola financed Clearwire to accelerate its deployment. The $600 million investment from Intel Capital was its single largest investment ever and as Arvind Sodhani, the President of Intel Capital put it, underscores their “commitment to supporting wireless broadband using WiMAX networks in the United States.” This was followed up with successful field trials this summer. Intel on its part said that the success of the trial meant that its mobile WiMax chip was on pace for a launch next year.

Sprint is the other US carrier with mobile WiMAX ambitions. It sought to use WiMAX to increase its footprint in the US. The company pledged close to $3 billion for 2007 and 2008 in order to deploy mobile WiMAX in its 2.5 GHz spectrum holdings. It was planning to provide service to around 100 million people in 100 of its top US markets by 2008. The plan was gloriously christened Xohm. Of late, however, these plans have been somewhat derailed due to investor pressure and the exit of its CEO Gary Forsee. For more analysis on Sprint’s WiMAX moves, I will refer you to my blog articles.

With Sprint even contemplating spinning a separate entity for its WiMAX plans, there is an uncertainty in the future of mobile WiMAX. While there is no chance of WiMAX supplanting the 3G standards today, the impact of its 4G successor remains to be seen. 802.16m, which is the next generation (4G) mobile WiMAX promises mobile speeds of 100 Mbps and is a direct competition to 3GPP-backed Long-Term Evolution (LTE) and Qualcomm’s Ultra-Mobile Broadband (UMB), both of which use OFDMA as well. With both Vodafone and Verizon announcing their allegiance to LTE, the standard has taken an initial lead among the 4G standards. Besides, the prevalence of GSM and WCDMA networks should help LTE dominate the future. While the announcements effectively spelt the death of UMB, WiMAX can still thrive, especially in emerging markets.