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Mobile WiMAX – 4Ging the Future?

Posted on Tuesday, Dec 11th 2007

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.

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Great Post,However many of the shortcomings frequently mentioned about WiMAX( and indeed OFDMA technology) are in fact well addressed in Mobile WiMAX. This is particularly true of wave 2, for which devices are being certified now.
Wave 2 devices include MIMO and beamforming technologies which are designed to provide very good coverage upto the cell edges by directing the power to the receiver or by providing a spatially separated stream. This coupled with partial usage of subcarriers (PUSC) can provide a high quality of service even at cell edges.

WiMAX has been depicted as a technology competing with HSDPA. This is true only to an extent. WiMAX provides multiple classes of services and each connection is linked to service flows. This ensures that services such as streaming video can still be delivered over mobile WiMAX while it may fail on other networks.
WiMAX also has other features which can not be ignored, especially when looking at future technologies. It is based on open standards. It interfaces naturally to IP networks, is not saddled with legacy architectures. It permits new applications, high data rates and applications which need to remain connected. It provides many elements which were lacking i.e. quality of services ( QoS) in a wireless environment, mobility and use of universally available applications. It is not a castle with walled gardens like the mobile networks.

The delay mentioned about XOHM is also not surprising, to say the least. We consider XOHM to be a big bang introduction of mobile WiMAX.
What will be the impact of WiMAX “big bang”?

We expect it to be multidimensional, just as happens in a big bang, creating galaxies in all directions.

Firstly, mobile broadcasting. And we are not talking of only mobile TV or multicasting here. Mobile broadcasting with WiMAX will have two facets. The first is the integration of web 2.0 applications, location based services and providing mobile Web with high speed and QoS. This first facet of mobile broadcasting relates to web content, the YouTube, video on demand , RSS feeds and multimedia rich web sites. The second facet is the typical broadcast services i.e. linear TV, streaming video content etc. TV however will not remain linear for long in this manifestation but will get more and more user controlled.

The second dimension of the big bang relates to new devices which will be information enabled by the WiMAX connectivity. These are the media players, gaming devices and handsets which are today powered mostly by WiFi. Amazon Kindle® or equally new innovative devices will get a place in the Sun, as they will no longer be tied to wifi or mobile networks.

The third dimension relates to the growth of the handset, devices and chipset industry which is inevitable, when users are lapping up the new devices and new found freedom.

The fourth dimension will be the way applications are designed. Multimedia content will get much better integrated into application without them being “heavy” or not being to run on mobile networks. An entirely new generation of connected applications will arise which take care of new connectivity available. To an extent it is happening under the M-Taiwan initiative, but what happens next will be much more profound, as it will be based on a much lower cost of components, devices and communications costs.

The fifth dimension will be the network architectures. The new networks need not depend on legacy TDM networks to run packet based services. These will be pure IP based wired and wireless extensions complementing each other for access and backhaul.

The new networks will give a Phillip to mobile TV and mobile multimedia.

Such big bangs in technology happen very rarely.2008 is slated to be the year for it. We can hardly wait!.

Amitabh Kumar Thursday, December 20, 2007 at 1:49 AM PT


Thanks for your valuable comments. Your technical insights provide a deeper perspective to this discussion. While I agree that 2008 will see WiMAX-related activity, I am not yet bullish about it exploding into the market next year. With the infrastructure costs and the inertia, and not to mention the other OFDMA-entrants promoted by the mobile operators and vendors alike, WiMAX will have to work hard to prove its mettle. As you have mentioned, its broader applicability (at least at the moment) and its design and development lead will be its drivers.


Vijay Friday, December 21, 2007 at 12:47 AM PT