ZTE fine-tuning CDMA for VoIP

ZTE said today it has successfully performed a VoIP call over the a CDMA 1X EV-DO Revision B network, demonstrating the viability of dedicating an entire CDMA network to 3G while still supporting both voice and data. ZTE said its Rev. B solution will be available for commercial deployment in the third quarter.

Rev. B is a 3GPP2 standard that stacks EV-DO Rev. A channels on top of one another, creating a wide high-capacity channel for bandwidth-hungry applications. Rev. B doesn’t improve upon the overall capacity of the individual channels, so technically the total capacity of the overall network does not increase. But by combining multiple 1.25 MHz carriers into a single large carrier, the average transaction time for every user decreases—files are downloaded faster, a Web page loads more quickly—allowing the network to move onto the next user and next transaction more quickly. The phenomenon, explained by queuing theory, allows the network to perform more transactions at a faster pace over a single broad channel than it could over several narrower ones, leading to a higher capacities available to each individual user, if not in the network overall. ZTE said its trials achieved over 9.3 megabits per second on the downlink and 5.3 Mb/s on the uplink over 3 bundled carriers.

Despite its advantages, Rev. B has received a rather lukewarm reception from CDMA operators, though it technically requires only a software upgrade at the base station to implement. One of the main reasons is that all EV-DO channels are by definition data channels and cannot carry circuit-switched voice. For every 1.25 MHz channel used to create a stacked Rev. B channel, a 1X voice channel must be taken out of commission.

ZTE proposes, however, that circuit-switched voice capacity can be replaced with VoIP as Rev. B will have both the capacity and low latency to support high-volumes of VoIP traffic. Eventually the majority of CDMA 1X network could be replaced with Rev. B. While ZTE is focusing on bundling three 1.25 MHz in its initial Rev. B platform, as many as 15 carriers could be stacked in the future supporting downlink rates as high as 73.5 Mb/s.

In order to fully take advantage of Rev. B’s gains, though, operators would have to introduce Rev. B handsets and mobile devices into their networks, which may ultimately explain their reluctance to deploy Rev. B. Many of the major CDMA operators worldwide have already committed to deploying Long Term Evolution (LTE) networks, and, in the case of Verizon Wireless, those networks will start popping up this year. LTE will not only give CDMA operators the same wide channels as Rev. B—allowing them to take advantage of the queuing theory principles—but it is also a more efficient technology that crams more bits into a hertz of spectrum. With those sorts of capital investments -- and the associated introduction of new 4G devices -- on the horizon, CDMA operators are likely to bypass Rev. B entirely, and focus their broadband efforts on LTE.