Study: TDMA Networks Should Consider 1X

WHEATON, MD.— If they want to stay competitive with their CDMA rivals, U.S. TDMA-network operators should actively consider the installation of third-generation (3G) CDMA2000 1X technology in their existing spectrum, a Shosteck Group report said.

The alternative — deploying high-speed GPRS and EDGE packet-data technologies — faces daunting technical challenges in developing handsets and infrastructure and in delivering on the technologies' intended data rates, the report claimed. On top of that, the GPRS/EDGE strategy, as currently envisioned by TDMA carriers, would also postpone TDMA networks' launch of a 3G technology called W-CDMA until the FCC allocates new wireless-phone spectrum, and it's not certain when the FCC will act, the report said. In the meantime, CDMA operators will be rolling out 1X service in their existing spectrum.

The report was commissioned by the CDMA Development Group, which called it an independent analysis that might contain conclusions that its members don't support.

To illustrate the advantages of 1X over GPRS and EDGE, the report noted that a 1X network will deliver a maximum theoretical data rate (but not throughput) up to 307kbps, and it will almost double voice capacity over that of a 2G CDMA network. A 1X network can also evolve to the 1X EV-DO standard, offering theoretical maximum data rates up to 2.4Mbps, and then to the still-undefined 1X EV-DV standard, which could offer speeds up to 5Mbps and perhaps as much as twice the voice capacity of 1X.

In contrast, GPRS defines a maximum theoretical data rate of 115kbps with no voice-capacity expansion, and EDGE will deliver data at speeds up to 384kbps, the report said.

Whether GPRS and EDGE will ever achieve their promised speeds, however, is far from certain, the report said. GPRS data rates in overseas networks have fallen far short of expectations, and complaints have been raised about battery life, the report said. In addition, the GPRS handset rollout has been slow, and no prototype EDGE handsets have been demonstrated, although 1X handsets are commercially available overseas for use in existing 1X networks.

GPRS and EDGE also impose higher battery drains than CDMA technologies, even 3G W-CDMA.

The report assumes TDMA operators plan to deploy GSM 2G technology in their currently assigned 800MHz or 1.9GHz spectrum to parallel their existing TDMA network, which is based on a technology whose future is limited because of the dominance of GSM and CDMA networks worldwide. Next, TDMA carriers will add high-speed GPRS to the GSM network and later possibly upgrade the GPRS network to EDGE. Their next step would be to launch 3G W-CDMA, reusing much of their existing GSM infrastructure but deploying the technology in new spectrum yet to be allocated.

W-CDMA will increase voice capacity, deliver mobile data rates up to 384kbps, and data rates up to 2Mbps in fixed applications. An enhanced W-CDMA standard is also under development to deliver even higher data speeds.

Although still challenging, it will be relatively easier to add 1X to a TDMA network than it will be to add GSM to a TDMA network, the report said, because 1X is more spectrum-efficient, requiring carriers to take fewer TDMA channels off-line to make room for 1X.

To add CDMA 1X to their networks, TDMA carriers would have to clear 1.8MHz of their existing spectrum for the first CDMA 1X channel, and thus operators run the risk of degrading their TDMA service if they do so, the report admitted. But "depending on the bandwidth an operator has available," the initial spectrum needed to deploy 1X "may or may not be important," the report said.

Operators of 2G CDMA networks don't have to worry as much about spectrum availability when adding 1X to their networks, the report noted, because of 1X's compatibility with 2G CDMA and because most CDMA carriers in the U.S. have enough unused capacity to add 1X voice channels. The Shosteck Group pointed out that 2G CDMA phones can operate on 1X channels, and 1X handsets can operate on 2G CDMA channels.

In adding 1X to their networks, TDMA operators could forego the burden of subsidizing high cost dual-mode TDMA/CDMA handsets by deploying " a parallel CDMA2000 1X network as quickly as possible" — if it were designed initially "to provide wide coverage, not high capacity," the report said. "Once it provided sufficient area coverage, they would begin to migrate their subscribers to it." A fast build out could be accomplished because it would require few new base stations, and back-haul transmission is in place.

In their current evolution strategies, TDMA operators would require complex and expensive trimode GSM/GPRS/ EDGE handsets. They also are eager to get dual-mode GSM/TDMA handsets for the hybrid GSM/TDMA networks, but few manufacturers are interested in developing GSM/TDMA handsets because they're considered short-lived interim products with limited sales potential.

Another challenge for TDMA operators is that the availability of 800MHz GSM base stations is uncertain.

The report said implementing CDMA in TDMA networks would also pose challenges, but "their magnitude should not be as great as those that will arise in overlaying GSM onto TDMA."