The Wireless Edge: Integrated Voice/Data in 3G

One of the promises of 3G cellular has been integrated voice and data.In this column I examine what this means, why and where it's important,to what extent the different cellular technologies support it, and howthis capability will evolve over time. I'm bringing it up now because Cingularis currently rolling out an enhanced version of Universal MobileTelecommunications System (UMTS) that includes High Speed Downlink Packet Access(HSDPA), which supports integrated voice and data. Meanwhile, Sprint and Verizonhave recently made announcements about an upgrade to CDMA 2000 Evolved DataOptimized (EV-DO), called Revision A, that provides a key building block forintegrated voice and data, a capability currently not available for EV-DO.

Integrated voice and data means that while you're on a voice call you cansimultaneously engage in a data session using the same device. This allows youto do things like send pictures while on a call or do simultaneous voice andvideo. Not only are there personal scenarios where this might be entertaining,but this ability should prove invaluable for many job situations. Examplesinclude insurance adjusters at the scene of damaged property communicating withheadquarters, real-estate agents giving real-time interactive video tours ofhouses to their clients and medical technicians showing pictures/videos ofpeople they are treating while communicating with doctors. These examples assumea handset device. In a laptop scenario, it depends on your connection. If you'reusing a PC Card modem or a laptop with integrated 3G capability, then you'relikely in a data-only mode, where the integrated voice/data capability is notrelevant. But if you're using a phone as a modem, perhaps with a Bluetoothconnection, then you can make a voice call in the midst of a data session. Andfor those of you wanting to use a VoIP system like Skype over 3G, today'snetworks are simply not up to the task yet.

So which technology can do what? The most capable 3G technology in this area isUMTS/HSDPA, where handset devices support simultaneous voice and data. This ispossible because the UMTS voice channels and HSDPA data channels co-exist in thesame radio channel. However, in the case of EV-DO, the radio channel isdedicated to high-speed data functions while voice travels over 1XRTT (onecarrier radio transmission technology) channels. The 1XRTT channels also supportlower speed data services but require devices to be in either a data mode orvoice mode.

The lack of integrated voice/data puts EV-DO at a competitive disadvantagerelative to UMTS/HSDPA. EV-DO operators have another problem, too. WithUMTS/HSDPA, the entire radio channel is available for any combination ofvoice/data loading. With EV-DO, operators have much less flexibility todynamically allocate radio resources between voice vs. high-speed data. So farthis has not been an issue, as EV-DO networks have relatively few users, but asdata services become more popular, operators may have to add EV-DO channels;this assumes, however, available spectrum, and it also takes away from voicecapacity. The answer to this dilemma is EV-DO Rev A, which operators will beginto deploy next year. EV-DO incorporates improvements that will enable VoIPfunctionality, including QoS support, reduced latency and improved uplinkcapacity. VoIP will enable integrated voice and data for EV-DO, and it willallow more flexible radio resource management, because EV-DO channels now willbe able to support both voice and data functions.

However, implementing VoIP over 3G will still be a hugely complicated task.Current approaches of using dedicated CDMA channels for voice are extremelymature. Replicating the same level of voice quality and consistency in thepacket domain will involve a lot of radio engineering as well as additionalnetwork enhancements such as sophisticated IP packet header compression and anIP core for voice. An important potential element of this core will be the IPMultimedia Subsystem (IMS), a set of infrastructure elements that integratesvoice, data and multimedia. IMS is based on the Session Initiation Protocol(SIP) and allows for common core services (voice, voicemail, video, presence,push-to-talk and so on) to be implemented in applications that operateindependently of the access network. IMS is under consideration for GSM/UMTS,CDMA2000 and WiMAX networks as well as for wireline networks where it canfacilitate wireless/fixed convergence.

I expect the path to VoIP to be a two-stage process for EV-DO carriers. Thefirst step will be deploying the EV-DO Rev A upgrade in 2007, initially as adata-only enhancement, mostly for improved uplink speed and reduced latency. Thesecond part will be installing the ancillary VoIP functions, which probably willnot be ready for primetime until 2009. The end game is attractive, especially asit may result in additional voice capacity. VoIP is on the road map forUMTS/HSDPA as well, but the feeling of urgency in this community is much lowerbecause it already has the benefit of a combined voice and data offering.

If you want to get the latest on IMS, I'm chairing a PCCA meeting on IMS on May 17 in Boston where, among other topics, we'll be examining IMS adoption in CDMA 2000networks.