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Even as WiMAX adopts mobility, questions remain about the transition,
handing off and achieving seamlessness.

Sprint is committed to WiMAX. It boasts a 2-year headstart over LTE’s implementation by AT&T, Verizon Wireless and other 3G operators. With its new partner Clearwire, Sprint is creating a national footprint with sufficient spectrum to deliver significantly increased capacity in wireless broadband.

Keith Mallinson
Keith Mallinson

There is a missing link, however. Customer expectations exceed what a simple overlay implementation of IEEE 802.16e – the mobile version of WiMAX – can deliver. It will be several years before any next-generation network (NGN) – including WiMAX, LTE or UMB – can match the coverage of existing networks.

In the meantime, dual- or multi-mode devices that interwork with and hand off to and from established 3G technologies are crucial. To achieve this, WiMAX urgently needs a capability such as the soon-to-be-completed IEEE 802.21 standard for Media Independent Handoff (MIH).

NEXT-GENERATION HANDOFF
I applaud the Sprint team for forging the WiMAX deal with Clearwire, Comcast, Google, Time Warner and Intel. This was an expedient move, although it’s a mixed blessing for Sprint which retains 51% ownership of the merged entity while ceding operational control. It taps the new investors for $3.2 billion.

The deal is a landmark development for WiMAX. It should be no surprise that even Qualcomm wants to pursue this opportunity. Bill Davidson,

Qualcomm’s senior vice president of global marketing and investor relations,was quoted in the Wall Street Journal as saying that Qualcomm increasingly views WiMAX as complementary technology to its own, not a rival. It would consider helping the new venture offer dual-function devices, especially since Sprint is a long-time user of Qualcomm technology. “We remain ready and willing to help a key customer,” he said.

Sprint claims it will launch mobile WIMAX later this year, but for an indefinite period its dual-mode devices will not be able to hand off with its CDMA network. Sprint agrees that dual-mode devices with WiMAX and CDMA will be required to provide full coverage for several years. Terminals initially will require selection of one technology for the duration of the connection. For handsets, PDAs and ultra-mobile PCs in particular this will be a significant deficiency.

MOBILITY
The key difference between what the world already has and what is needed in WiMAX is mobility. Fixed wireless access is already in service with 802.16d in most nations worldwide, whereas 802.16e will provide handoff. Initially, however, this capability will be restricted to transitions among WiMAX cells. This is a crucial shortfall, making the technology little more useful than the 802.16d technology it supersedes.

WiMAX mobility will be incidental rather than significant because WiMAX coverage will be a small fraction of that with CDMA or HSDPA for at least a few years.

Whereas WiMAX has a major need for handoff with CDMA and HSPA, most CDMA and HSPA players will not regard this significant development task as important. In fact, the incumbent technology proponents and operators that are not planning to offer WiMAX may benefit from neglecting or shunning interoperability with WiMAX. Doing so diminishes the competitive challenge.

LTE standardization is yet to be completed, but you can be sure that 3GPP will make LTE roaming and handoff with established and more closely related GSM, HSPA and CDMA technologies a much higher priority. As an alternative to waiting for 3GPP and 3GPP2 with IMS-based or other methods, IEEE’s 802.21 standard proposes to bring Wi-Fi and WiMAX into the high-mobility fold by providing a handoff solution incorporating these 3G networks. The technology and standard are being developed by InterDigital, Intel and others. Trials by SK Telecom in South Korea are bridging WiMAX (WiBro) mode operation with both CDMA and HSDPA.

Something more is urgently needed if WiMAX is to succeed as a mobile technology. Seamless mobility is a pipedream, but even something approximating it will require significant device integration and special functionality. Initial terminal deployments will become obsolete unless they can be remotely updated when MIH or an alternative is implemented.

Mallinson is founder of WiseHarbor, solving commercial problems in wireless and mobile communications. www.wiseharbor.com

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