WiFi and cellular convergence faces technology challengesThe availability of WiFi-equipped mobile phones and the growing popularity of VoIP are breaking down the boundaries between cellular telecoms and the Internet. But, reports Siân Harris, there are still obstacles to overcome.Until recently the cellular-telecoms and the information-technology (IT) industries were separate worlds. Mobile phones were for purely voice communications and computers exchanged digital information over the Internet. Today, a growing number of data services are available on mobile phones while many PC-based devices are equipped with WiFi wireless connectivity and allow users to make telephone calls.Skype VoIP services WiFi technology is also beginning to appear in mobile phones and a wide range of telecoms providers – cellular or otherwise – are hoping to capitalize on this convergence. The UK's fixed-line operator BT, for example, has big plans for WiFi. "Many things happening in the broadband world are transferable to wireless – it's just a case of giving the users the right services at the right prices," said Steven Evans, chief executive of wireless broadband and future products at BT. The fact that operators do not have to pay to use unlicensed spectrum means that WiFi is cheaper than 3G and can be deployed by companies such as BT that do not have GSM or UMTS licences. It also achieves much higher data rates than current cellular technologies.Corporate plansBT plans to pilot a new service with corporate customers in early 2007. Called Enterprise FMC, the service will use WiFi/GSM phones and enable voice calls over a company's WiFi wireless local-area network (WLAN) using voice-over-Internet protocol (VoIP). Evans explained that all the calls within the offices will go through the WLAN, but if the user leaves the office the call will be handed over to the GSM network.BT's plans do not stop at corporate customers. "Our strategy is to wireless-enable as many environments as we can, including homes, BA lounges and Hilton hotels. We have also announced plans for 12 WiFi cities across the UK where the central areas will have street-based networks," said Evans. Although the initial development of WiFi hotspots was driven by business users, the big incentive for BT's new plans is the consumer electronics market, for gaming, image transfer, music and television.This vision has significant overlaps with the "killer applications" for cellular telecoms that were such hot topics when the UMTS spectra were allocated about five years ago. "We believe that the current generation of mobile technologies are not going to deliver enough bandwidth for the services that people will want," said Evans. "WAP and GPRS have a very short lifetime. They are just stepping stones to something more seductive." However, he believes that UMTS and especially HSDPA have more longevity. Indeed they are part of BT's wireless strategy, although only as a way to provide coverage outside the high-speed access of the WiFi hotspots.Evans and his colleagues are keeping a close eye on developments in mobile-phone technology. "The key thing with any new service is always handset availability, but we are confident that there will be a range, albeit a fairly small one, of WiFi/GSM devices by the end of this year," he predicted, adding that BT is testing handsets from several major handset makers. "We are encouraging the handset makers and developing services that will take advantage of these new devices."Nokia is one manufacturer that needs no encouragement. The world's leading handset maker started shipping mobile devices that include both cellular (GSM and UMTS) and WiFi technology in high volumes earlier this year. It now has around 10 different models available and plans for WiFi to become standard in many of its devices by the end of 2006. "We don't see them as mobile phones but as converged devices," explained Kari Tuutti, the company's communications director. "We want to offer the best possible wireless connectivity in our devices."From a user perspective this sounds attractive, but there are the inevitable technical challenges. As Olli-Pekka Lintula, director of Nokia's strategic marketing explained, these fall into three main categories. The first hurdle is deciding how to design the device's hardware to incorporate WiFi radio capabilities. This has implications for power management, processor load, RF design and the design and location of the antenna.Computer protocolsA particular challenge is that WiFi protocols were originally developed for personal computers and so were not subject to the strict power constraints imposed on mobile-phone components. According to Lintula, power requirements can be minimized by addressing low-layer software issues at the protocol level. The way that the device searches for WiFi networks must also be designed carefully to minimize energy consumption.The second challenge is related to the integration of the WiFi transceiver with other radio communications. As Lintula explained, "WiFi frequencies could interfere with other radio technologies either in the same band or harmonics". He said that co-existence with Bluetooth – which also uses the 2.4 GHz spectrum – has been solved using agreed scheduling standards. However, co-existence challenges with other radio technologies remain, and must be dealt with on a case-by-case basis. "Interference issues are not significant when they are properly taken into account from the project start," he said.Beyond interference concerns, a WiFi-enabled mobile phone must be able to hand over to a cellular network and vice versa. Lintula explained that the device must listen to both GSM and WiFi signals and determine if handover is desired – which can be a challenge to achieve while optimizing energy management. Nokia's Tuutti added that current Nokia users must select the WiFi option manually if they find themselves in a WiFi hotspot. "We have some work to do to make it a smooth handover between the technologies," he said.Standardizing handoverHandover has been the main focus of WiFi/cellular standardization efforts. Crucially, the Unlicensed Mobile Access (UMA) specification has recently been adopted by the Third Generation Partnership Project (3GPP), which defines UMTS cellular standards. UMA dictates the protocols for call handling, routing and identity management between unlicensed and licensed spectrum resources. For example, it describes how a call is routed from a mobile phone, through a GSM network and via the Internet to a WiFi hotspot.Meanwhile, release 7 of the 3GPP's UMTS standard includes voice-call continuity (VCC), which specifies handover between 3G networks and WLANs. Of course, the existence of more than one standard in itself poses challenges for the device design. "The device needs to support the right one," explained Lintula. "This is more of a business challenge as handover might involve two operational entities."The third area of concern is related to the creation of applications, user interfaces and development environments that take full advantage of WiFi connectivity. Cellular voice services are still delivered via circuit-switched networks, whereas WiFi networks use packet-based communications for both voice and data. As a result, both circuit-switched and packet-switched protocols must be integrated within one user interface. Similarly, any development environment must support the co-existence of both circuit-switched and packet-switched modes. However, as 3G becomes fully packet-based this challenge will vanish.The progress of these dual-mode handsets is being monitored closely by companies that are developing applications and services for WiFi networks. This includes Skype, which offers free VoIP calls between its users in addition to a range of low-cost Internet voice services. The 100 million or so people that use Skype currently do so with their PCs, but the company has set its sights on the mobile world and WiFi is among the technologies helping to achieve this.According to Eric Lagier, head of business development for Skype Mobile, the company is working with all the major device manufacturers to ensure that its users will have a range of products to choose from. "Skype is working very hard with device manufacturers to overcome the challenges of CPU power, battery consumption and form factor," he said.Voice-over-WiFiWhile these issues are being ironed out, the company is already launching some voice-over-WiFi services. Skype has partnered with WiFi network provider The Cloud to offer low-cost WiFi access and Internet voice calls at 6000 hotspots in the UK and Sweden. This is part of Skype's global roll-out of its Skype Zones, which enable low-rate voice calls via WiFi at thousands of hotspots across the world. The company has a similar partnership with Broadreach Networks in the UK. These early systems use Pocket PCs with Skype functionality and WiFi cards. However, the company is launching a dedicated WiFi phone with Netgear, and more devices are planned for later this year.Fortunately for cellular operators, Skype is not constrained to WiFi. "We want to be agnostic to the access network. There are many different technologies, including WiFi, and we want to make sure we can use all of them," said Lagier. Skype already has partnerships with E-Plus in Germany and Hutchison 3 Group in several European countries. These enable users with a Skype data card in their PCs to connect over the cellular network and be mobile. "It gives users a choice and will be another way to generate revenue," said Lagier.And even WiFi itself can be an opportunity for mobile operators. As Lagier pointed out: "Operators are in a unique position because they already have the customer relationship and the services and they know how to do the billing."About the authorSiân Harris is a UK-based technology journalist.