re: Current Status of 1xRTT, GPRS, WCDMA
>> Lessons Learned From Current Next-Gen Nets
By Peggy Albright
December 17, 2001
Wireless Week
When Verizon Wireless' William Stone presented the findings from his company's CDMA2000 1X trials at the CDMA Development Group's Americas Congress in November, he was able to provide important data on how 1X works in a real-world environment.
His findings show what most carriers already know - the peak performances that next-generation networks reach in the lab don't pan out in a real environment. As they move toward third-generation services, operators need to look at successful deployments and borrow those tactics where applicable. They also should watch for the potential pitfalls and develop strategies to avoid them.
Verizon's 1X Experience
Although information has been available from 1X deployments in Korea - where several operators now offer 1X services with largely favorable reviews - Stone's presentation was particularly interesting because Verizon is a U.S. operator and the industry here is eagerly anticipating 3G's domestic debut. Customers, investors and wireless product and application developers likely will relate better to 3G when they can see it for themselves. Stone's presentation provided some welcome findings about speeds and capacity.
Stone, executive director for strategy at Verizon, described his company's trials in positive terms. He said engineering the system proved to be virtually identical to the carrier's experience with the current CDMA technology, IS-95. Verizon found that voice quality is almost identical to the second-generation system. The carrier also realized a small improvement in the forward link budget that it believes should help improve battery life for 1X devices.
1X provides operators a fair amount of flexibility when it comes to configuring data rates, and Stone's summary of what is practical confirms observations from Korea. At least initially, carriers may find it more cost-effective to offer commercial data speeds at somewhat conservative rates. While 1X can provide peak data rates of 144 kilobits per second and higher, Verizon plans to offer data speeds of 40 kbps to 60 kbps initially.
Canada's Bell Mobility, another company testing 1X, also is following the conservative approach. Brian O'Shaughnessy, vice president for technology development at Bell Mobility, who also spoke at the CDG Congress, says his company found the typical data rate averaged 100 kbps in tests with one mobile unit running on the system. Bell Mobility plans to promise rates of about 80 kbps.
Despite the hype surrounding data rates, CDMA operators also are motivated to introduce 1X because it provides additional voice capacity.
Stone says Verizon found that capacity gain is 1.6 to 1.7 times what carriers have on their IS-95 networks. Although contrary to previous promises that 1X would double voice capacity, these findings confirm similar results from South Korea.
Achieving that voice capacity gain doesn't happen automatically, however. Stone emphasizes it depends on having a high percentage of subscribers using 1X handsets. "Capacity scales linearly with penetration," he says. In other words, operators will not achieve the full capacity gain unless all users adopt 1X handsets, a factor that should motivate carriers to migrate their customers to 1X devices.
The GSM/GPRS Path
The GSM industry, which has a multi-step evolutionary path to 3G that begins with the 2.5G standard GPRS, has not enjoyed a smooth next-generation debut. GPRS has been criticized for exaggerated claims of data speeds and a lack of handsets; the latter was a problem that delayed GSM's initial rollouts and in turn delayed commercialization of CDMA2000 1X in Korea.
"The whole industry, not just Motorola, has taken longer to get GPRS performing and stable than we all thought it was going to," says Andy Watts, director of 2G/GPRS in Motorola's global telecom solutions sector.
Watts says one of the early GPRS problems was in tweaking the system so that it would consistently provide worthwhile data rates, such as 23 kilobits per second in a two time slot configuration. Another problem was latency, the amount of time it takes to deliver packets end-to-end. The industry didn't realize, he says, how noticeable latency is to the end-user, or how much latency was involved in GPRS networks.
GPRS uses eight time slots, each one capable of about 13 kbps, and data rates are contingent on the number of channels allocated for data. In theory, increasing the number of time slots used by both the device and the network and deploying higher rate coding schemes to the equipment would improve both performance and latency issues, Watts says. In practice, however, the mobile device adapts to the configuration of the network, so if the phone has four time slots and the network has just two, the phone will adjust accordingly. The result is the service slows down, but the user doesn't know why. The allocation of network time slots presents a conundrum for operators because they must try to forecast data traffic to appropriately allocate the channels.
GPRS is finally up and running on several networks in the United States, although only VoiceStream Wireless has deployed the data service systemwide. Those carriers that waited to deploy GPRS were able to avoid some potential problems.
Dave Williams, vice president of strategic planning at Cingular, which uses Nortel and Ericsson for its GPRS networks, says his company's GPRS deployments have been far less painful than expected. "This wasn't as hard as launching SMS," he says. He adds: "The great thing is we weren't the first to launch globally and a lot of [performance] issues have been resolved."
Williams won't say how his company configured GPRS on its network, but he did say the operator has dedicated capacity to GPRS to prevent those services from being affected by voice traffic. At press time, the operator was offering customers data speeds of 10 kbps on the uplink and 20 kbps on the downlink via the Motorola Timeport.
Motorola, the first to market with GPRS handsets, now is launching more options, and other handset vendors, including Ericsson, Nokia and Samsung, are following suit.
W-CDMA: Still Unknown
According to its original deployment targets, wideband-CDMA, the 3G technology GSM operators eventually will use, should have been online by now. But to date, NTT DoCoMo is the only operator worldwide running a commercial network. Two other networks have been built–one on the Isle of Man and another in Monaco.
DoCoMo's system was delayed repeatedly and dogged by numerous problems, including an inability for devices to complete call handoffs at high data speeds, as well as numerous handset recalls. The carrier finally launched commercial services Oct. 1, and it apparently is working well. Bernd Eylert, chairman of the UMTS Forum, recently visited Tokyo where he used the W-CDMA system for about an hour while touring the city. It worked consistently, he says, except when he drove through tunnels - an expected drawback.
DoCoMo says its service, called Freedom of Multimedia Access, supports circuit-switched voice and data at 64 kbps and packet data services at up to 384 kbps. About 70 percent of the carrier's popular i-mode services are capable of running on FOMA, but most still are running at 9.6 kbps. Customers can upgrade their i-mode services to three new terminals, including one that has a digital camera and one with a PC card. Videophones are offered commercially as well.
Eylert says DoCoMo's subscriber numbers are promising. The carrier lassoed in 10,000 3G subscribers in the first four weeks of service. It expects 150,000 by the end of March and hopes to serve 6 million by the end of 2004.
Because DoCoMo adopted an early version of W-CDMA that has since been enhanced, the carrier has taken some heat for building a 3G network that isn't compatible with others. That situation may soon be resolved, however. DoCoMo says that beginning next spring, its terminals will comply with the 3GPP enhancements standard the rest of the W-CDMA world will use. That will enable its customers and those from other W-CDMA networks to roam on each other's systems. Eylert and some vendors, such as Lucent, say they expect to see W-CDMA systems running in Europe in 2002.
Other Approaches
While the 2.5G and true 3G standards get all the attention, other wireless operators and technology providers believe they, too, are covering new ground with approaches that may not be classified as 3G but go beyond 2G.
Nextel Communications Inc.'s always-on, packet-based iDEN system is an example, says Barry West, Nextel's chief technology officer.
"In terms of its services, it looks pretty much like GPRS," he says. In fact, he considers it a more efficient technology because the Nextel service uses packet-based services for both voice and data, whereas GPRS operators still use circuit-switched networks for voice. About 2 million of Nextel's 8.5 million subscribers are using its packet data services, West says.
Nextel currently delivers data speeds of about 20 kbps, West says, and the carrier is working with Motorola to add data compression technologies networkwide.
"We're seeing three to five times current speeds in data rate, so we're looking at 50 to 100 kbps" with those enhancements, he says. "We will be able to deliver that in the first half of next year."
West says Nextel plans to add CDMA2000 1X to its network but will delay that until it becomes more cost-effective and until some anticipated enhancements to the technology, such as a new vocoder now in development, are available.
Other post-2G approaches include systems that work in different types of spectrum, such as ArrayComm Inc.'s IntelliCell smart antenna technology and its iBurst wireless modems. ArrayComm says its network technology, which already is used in 80,000 base stations installed primarily in China and Japan, can serve nine times more people than systems already using advanced technology. It guarantees data rates of 1 megabit per second per user in a fully loaded network that uses just 5 megahertz of unpaired spectrum.
But carriers will all need to get past the early deployment phase of their next-generation networks before any of us can see which applications are desirable and even practical. Perhaps that's what the next phase of these technology developments will provide. <<
- Eric - |
