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This excerpt is from Chapter 9 of Fixed Mobile Convergence and Beyond, Unbounded Mobile Communications, by Richard Watson. Watson observes that solutions targeted to meet evolving communication requirements are often labeled "fixed/mobile convergence" (FMC). He argues in earlier chapters that delivery of communications solutions with such sophistication of technology will result in unbounded mobile communications (UMC) by virtually eliminating the communication dependencies of geography or wireless access types. In Watson's terminology, "UMC" encompasses the amalgamation of multiple technologies that work together, resulting in a seamless communications solution. This Chapter covers mobile handset issues in respect to UMC.
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Dual-Mode Handset Landscape
The technology lynchpin of any UMC solution is the commercial availability of a dualmode
(WiFi and cellular) enabled handset or terminal. These devices have been on the market since 2004 with such offerings as the HP iPAQ 6315 and others, but these early dual-mode devices were not positioned as UMC or FMC devices but rather as devices that were network agile on an application-by-application basis. The value of the WiFi services was viewed primarily as a higher-speed Internet access option rather
than for any VoIP application. Such a perspective so permeated the design philosophy
that audio directed through the WiFi connection was hard-routed to a back speakerphone and not to the front speaker expected for telephony use. Initial FMC developers quickly found that, with these devices, a cellular phone call audio would be played through the front speaker, as expected, but any wireless VoIP audio would play out of the back speaker. This behavior, of course, is not acceptable to a phone user.
Early dual-mode products were also weak in the support of WiFi connectivity. Often the embedded antenna design was not RF-sensitive enough, the effective connection range was significantly shortened, and RSSI values were inaccurate. Also, AP-to-AP roam logic was not optimized for voice. As pointed out in an earlier chapter, a voice application needs such roams to occur in fewer than 500 milliseconds or voice quality may suffer. WiFi driver architecture was often modeled after a standard Ethernet driver, and roam decisions were handled by desperation; that is, when the existing AP signal deteriorated to the point of a lost connection, the driver would then launch a "scan" to seek a nearby AP to roam to. This operation could take up to 30 seconds when 0scanning all 14 channels and waiting for potential AP responses on each
channel. In many cases, VoIP implementations on such devices would drop the call when roaming between APs. It was quickly very clear that the functionality of the WiFi layer 2 driver required significantly more sophistication than was being delivered.
A third critical consideration for UMC-supported dual-mode devices was battery life. Power design and management have been optimized for cellular services. All users expect four to six hours of talk time and days of standby time on cellular phones. Using WiFi as a voice transport, however, was a different matter. Transmit power requirements for WiFi are significantly higher than for cellular radios; for this reason talk times were found to be sub-one hour and standby times measured in hours, not days. Such characteristics were a major hurdle for UMC adoption. What was missing was aggressive power management implementation in the drivers and chip-level enhancements of power design for the radio circuits. Fortunately, the second and third
generations of dual-mode devices now sport such enhancements. Battery life is still a
characteristic that can be improved, but the current commercial offerings are acceptable for most UMC users.
Major UMC Handset Manufacturers
Because UMC is a nascent market, initially there were few handset manufacturers that would boldly step into this market. Since wireless carriers were concerned about WiFi cannibalizing their minutes or subscribers, they were more than mildly reluctant to back dual-mode offerings. Indeed, in some markets, certain models of phones were introduced with dual-mode configurations while the same design was introduced into other markets with the WiFi radios absent. In some cases, when the WiFi radios were present, the network services were hobbled to only support halfduplex traffic and not the voice-required full-duplex. In this manner, the WiFi
connection could be used to surf the Web but could not sustain a real-time voice connection.
Traditionally, the carriers have been the sole source for purchasing cellular phones; thus they were able to hold tight rein over the market. This market reality is, however, changing. End users may now procure unlocked (noncarrier-specific) dualmode phones from noncarrier distribution sources. The European market was the first to become more "customer friendly" and to broadly support unlocked phones. Within the past 12 months there has been a shift in market availability for such devices in the North American market. Such shifts result in a more competitive
environment, resulting in the end customer having lower-cost UMC device choices available.
There are still relatively few manufacturers that produce dualmode handsets. The most aggressive in this market have been Nokia, Samsung, Motorla, Sony-Ericsson, and the Taiwanese High Tech Computer (HTC). Nokia has committed that going forward, all its cellular phones will be dual-mode and will have a full line of Eseries smart phones based on the Symbian OS that are fully 3GPP compliant.
Historically, HTC has been an OEM source of manufactured phones that were marketed under various brands, including UTStarcom, Hewlett-Packard, and Cingular. These were Microsoft Windows Mobile PDA-class devices and filled a niche in the market not taken by the Nokia offerings. HTC is now self-branding its phones and is expanding its dual-mode portfolio with consumer-centric smartphones such as the T-Mobile Shadow and T-Mobile Wing.
Other manufacturers of dual-mode devices are Motorola/Symbol, Intermec, Research in
Motion (RIM), Sony-Ericsson, and others (see Figure 9.1). Each of these vendors has targeted some subsection of the UMC mobile communication market and sold through its channels.
Because these devices were designed as phones, they all have built-in dialers and standard cellular phone interfaces. Some even come preconfigured with a SIP-based softphone for use with VoIP applications. Few of them, however, come from the factory UMC ready. If a device does come configured to support UMC, it will most likely be a 3G-UMA/GAN device. Research in Motion has announced its first dual-mode device, the Blackberry 8820, being sold through a UMA/FMC-supporting wireless carrier.
One major challenge for vendors entering the UMC market is determining how to add the UMC functional components to the commercial phone. If the UMC vendor has not successfully partnered with the handset manufacturer to replace the native dialer, the challenge is to install an adjunct UMC dialer in such a way that it can coexist with the native dialer. Because the native dialer is tightly coupled with the OS, it is virtually impossible to replace, and UMC "add-ons" have to contend with working around certain functional limitations resulting from this situation. More details follow in the next section.
UMC Platform Challenges
Regardless of whether the dual-mode device is based on Symbian, Microsoft Windows Mobile, or Linux, they all seem to have generic functional challenges: WiFi robustness and reliability, network flexibility, audio routing between front and back speakers, and battery life.
WiFi Robustness
How reliable and dependable the WiFi connection is related to a number of characteristics of both the hardware circuitry and the sophistication of the layer 2 MAC driver:
Antenna sensitivity The higher the antenna sensitivity of a device, the greater the effective coverage range that can be experienced. Most handheld mobile devices will never achieve the antenna sensitivity experienced with a laptop computer, but the effective sensitivity has a great deal to do with the maximized utilization of the WLAN. Erratic RSSIlevel
reporting has plagued early WiFi-VoIP implementations in managing voice quality. Handhelds that have an optimized antenna design will include a feature called diversity. This is a two-antenna design whereby transmit/receive interference is minimized by alternating use of the two antennas.
Roam agility. Fast, secure roams between any two APs within a WLAN are important to ensure voice quality for the wireless call. The fast-roaming IEEE (802.11r) standard has been ratified but no commercially is available support as of the publishing of this book Support for such features is embedded in the layer 2 driver logic.
Association robustness. The ability to remain associated with a specific AP is critical, especially in an environment of high interference. This behavior is a characteristic of the MAC-level driver and varies from vendor to vendor. Lack of a solid, sustainable association results in too many roam attempts, which directly impacts voice quality.
Proper level of security support. This characteristic has to do with conformance with both standards and proprietary-based wireless security solutions. For example, Cisco Systems has developed its Cisco Compatible Extensions (CCX) that supports a number of beneficial features that are Cisco unique and not specified by any standard. If a company has selected Cisco as the vendor of choice for wireless, CCX fast roaming and QoS services will be important as supported features on the mobile handset.
Each device will exhibit its own unique WiFi characteristics, and it is important that a company evaluate that specific device in the operating environment before a final buy decision is made. One of these factors may become a key decision metric in the final purchase.
Printed with permission from Newnes, a division of Elsevier. Copyright 2009. "Fixed/Mobile Convergence and Beyond, Unbounded Mobile Communications" by Richard Watson. For more information about this title and other similar books, please visit www.elsevierdirect.com.
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