Single radio time slices GSM and Wi-Fi air interfaces

Already mobile handsets include at least two radios – the cellular radio and Bluetooth. With the surging popularity of Wi-Fi, it’s only a matter of time before that radio is added to the mix. In fact, a few phones already ship with integrated Wi-Fi, although today the cellular and Wi-Fi radios are generally implemented separately and used for separate tasks. The cellular radio handles voice communications while the Wi-Fi connection may support faster email synchronization or web surfing. But down the road, the voice call will sometimes be handled via Wi-Fi and VoIP as well. The mobile carriers were once adamant about not offering Wi-Fi, but all now have wireless LAN strategies. And there will be instances where it cost the carrier less to handle a call via a Wi-Fi hot spot rather than via the cellular network. From the subscriber perspective, a user may get a much better connection, or cheaper rates, when linked via a wireless LAN in the home or in the enterprise.

Quorum Systems has based its existence on the vision of what it calls a converged handset. VP of product management Steve Brown claims that devices that integrate cellular and Wi-Fi radios today really don’t mix the two functionally. He claims that a typical device will place an incoming cellular call directly into voice mail if the device is actively using Wi-Fi to synch email or contacts. Quorum not only believes that the two radios must function simultaneously, but also must hand-off voice connections between the two radios.

Early this year, Quorum announced its QS2000 CMOS transceiver that features a single radio that supports GSM, including Edge, and Wi-Fi. The radio uses a time-sliced approach to keep cellular and Wi-Fi links active simultaneously. I saw a demo this week in which a Wi-Fi link streamed video to a handset reference platform while the handset maintained a GSM call. The call was then swapped to the Wi-Fi link and VoIP while the video stream continued to play.

It’s tough to term the QS2000 a software defined radio, because its really driven by algorithms for each air interface that are implemented in dedicated state machines for each wireless link that the chip supports. The device can support a maximum of twowireless connections at any given times. Company CEO Bernard Xavier does think that the architecture could support other wireless standards in addition to GSM and Wi-Fi. The company is already planning a full slate of 3G support. And Xavier thinks that support of a video standard such as DVB-H is also possible.