WiMAX has incredible potential in the wireless world, ranging in usage models from fixed to portable to mobile.  It is clear, however, that "plugged in" wireless does not take advantage of wireless' key attribute -- the ability to move about. Once the end user is un-tethered from a plug in the wall and allowed to move around in either a portable or eventually mobile manner, the requirements demanded from the products becomes intense.  These demands largely fall on the ASICs or SoCs inside the products, and include power consumption, size and signal gain to name a few.


Most of the focus for developers of WiMAX equipment has been on the fixed aspect, while portable and mobile functionalities have generally been relegated to the next technology, WiMAX Mobile.  However, there is no need to push portability until Mobile arrives, and by delivering portability in laptops and USB devices sooner, WiMAX Mobile can truly focus on handsets as opposed to laptops.  This article will discuss what is required to move WiMAX from fixed to portable to mobile, and for WiMAX to meet the mobile broadband needs as defined by industry giants such as Intel, Alcatel and the WiMAX Forum.

WiMAX Versions

There is a great deal of confusion today, much of it instigated by vendors, about competing technology in terms of what are the various versions of WiMAX, what they can do, and when they will be available.

To begin, the relationship between IEEE 802.16 and WiMAX needs to be understood. Essentially, the WiMAX Forum follows the model of 802.11 and the WiFi Alliance. The IEEE standards body specifies PHY and MAC protocol, but does not go far enough to ensure interoperability. This is where the WiMAX Forum and the WiFi Alliance add value. These organizations define, set up and operate the next level of specifications and testing to guarantee that devices from different vendors will work together. Thus, the "sticker" on the box gives confidence to the consumer.

The 802.16 standard has been released in several versions over the past four years. The first addressed high frequency operation, 11GHz and above. This was to address the LMDS market, whose story has been written. The next major upgrade addressed the lower frequency operations, and this is where the WiMAX Forum is focused. This version, 802.16-2004, only addresses fixed, nomadic and portable operation, not mobile.

In December of 2005, 802.16e was ratified, adding mobility to the standard via MAC layer changes, BTS hand-offs and a new physical layer SOFDMA. It is important to note that 802.16e SOFDMA, the mode that the WiMAX Forum will introduce to the market, is not compatible with the existing 802.16-2004 OFDM version which is being deployed today.

The WiMAX Forum, responsible for developing testing protocols and managing the lab set up and test for interoperability, is currently working on both versions of the standard -- what are referred to as 802.16-2004 and the newer 802.16e. For the former, after years of work, the lab opened last summer and the first certified interoperable products conforming to the 802.16-2004 standard have reached the market in January of 2006.

The work to certify 802.16e products has been on-going, and it is expected that the lab will be ready to test and certify this equipment beginning in January of 2007. However, this is somewhat misleading as the first wave of products based on 802.16e will not be certified for mobility. This will happen approximately 6 months later. The first wave of certified products will only address nomadic and portable functionality, something that is available from the existing 802.16-2004 standard. Products based on 802.16-2004 and supporting portable WiMAX will hit the consumer shelves in late Q3 of 2006, a full 6 to 9 months ahead of the most aggressive WiMAX Forum Mobile schedule.

Portable WiMAX Today

The concept of portable broadband wireless is often overlooked beyond the WLAN ability, and this is largely limited to in-building coverage. Most people tend to think of WiMAX in terms of either a box on the wall of a house, or a fully mobile smart phone/PDA operating in a car moving at 100km/hour. The truth is portable service, a la WiFi but covering an entire city, has a great deal of value and will deliver to the market the next step towards broadband ubiquity.

If one assumes that the primary user device for WiMAX Fixed and Portable systems will be the laptop or PDA, the ability to receive email, web access, and even VoIP via some of the more popular service providers without searching for a coffee shop has clear value for the consumer. Being able to walk around or move at slow speeds (<40kmh) and have coverage over an entire city is a service that WiMAX can provide with a lower cost and better service as compared to the citywide Wi-Fi movement.

For the operator, WiMAX portable has several advantages.

For the same infrastructure that is delivering a solid business case for last mile access, the number of subscribers can be double or tripled with portable Broadband access. The consumer will buy the PC Card or small USB device, and the operator will sell service to them with no additional capital outlay.

Last mile access for the fixed market tends to be limited to those areas where cable or DSL are not offered. With portability, the operator can offer a service that cable or DSL can never deliver, securing them against competition in the future.

With portability, an operator is not limited to deploying in tier two or three countries or cities where broadband does not exist. Rather, the operator can go into downtown Chicago or San Jose because the service they are offering is unique, has value to the end user and can be done cost effectively by the operator.

It is important to keep in mind that this scenario is not something that needs to wait until 802.16 products are certified and infrastructure has been built out. As base stations (BTS) are deployed based on WiMAX Fixed and Portable technology, these services will be offered. 

Figure 1: Range of coverage possible via a single WiMAX BTS, 
covering the campus of Stanford University (approximate radius of 1 mile) 

Portable WiMAX -- What it takes

The question must be asked, if this service can be offered today, why don't I hear more about it? The reasons for this are simple. The primary features and requirements placed on a product to offer portable service are largely derived from the chips contained in the device. When a portable application is supported, several technical issues must be addressed:

Power Consumption -- When moving about, obviously the devices -- PC card, USB device, etc. -- are battery powered. This means low power chips are required, typically with a power consumption under 700mw.

Performance -- Another side effect of being used in a portable device has to do with performance, or range. Implemented in laptops et al., there is typically no room for a high gain antenna to help connect to the BTS. The antennas will be small and low gain, meaning the chip must have advanced signal processing to supply additional link budget. This can be accomplished via MIMO and other advanced techniques.

Size -- Again, in a PC card or small USB device, the size of the chip and associated parts is critical must be kept to a minimum.

When these attributes are examined, it becomes clear that virtually none of the 802.16-2004 based ASICs offered today can meet the requirements above. There is only one chip on the market today that delivers this functionality, the TCW 1620 from TeleCIS Wireless.

Mobile WiMAX

While it has been stated and shown that portable WiMAX is a service that can be offered now, it is also clear that, down the road, full mobility is in the future for WiMAX. Indeed it is the lure of the 1 billion cellular handset market; the portable gaming device and portable DVD and TV players are all end user devices that would benefit from true broadband connectivity. Fully mobile broadband wireless is significantly more difficult then just delivering voice and a few hundred kbps. Delivering multi-megabit service while zooming down the road will not appear from WiMAX until late 2007 early 2008. It is expected that the superior efficiency, advanced MAC and all IP design will help propel WiMAX Mobile to the forefront of the race to 4G.

For service providers to deliver on this promise, the demands of the consumer devices listed above become even more challenging. The power requirement shrinks, performance needs increase, and size remains a challenge. It is widely expected that MIMO and other multi-antenna techniques will be a necessary component to all consumer devices delivering true broadband in a truly mobile environment.

Summary

While the debate rages on about whether or not "Fixed" WiMAX has a real opportunity and if so, where it is (underdeveloped areas) and how big it is, a huge potential upside from a portable service offering is overlooked. Indeed, for any wireless technology to be truly viable, it must take advantage of the one unassailable attribute wireless has over all other access technologies -- the ability to move about.

While we all look forward to WiMAX Mobile and 4G, we can move a large step along the path to this vision of broadband ubiquity via portable services. WiMAX Portable has tremendous market potential. Operators and consumers do not need to wait two more years to receive many of the benefits of WiMAX Mobile; these can be delivered via a portable offering, something that can be done today. From an operator perspective, taking advantage of wireless means higher revenue and a more defensible service offering.

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