re: 3G Evolution
Above average article here from CMP about the various third generation wireless flavors.
>> Growing Toward 3G
01/07/02
Richard "Zippy" Grigonis
Communications Convergence
cconvergence.com
Zippy unsnarls the tangled family tree of wireless technologies reaching for 144 Kbps and 384 Kbps convergent mobility.
The evolution of wireless networks, from simple first-generation analog through 2G, 2.5G, and 3G, involve enormous complexity and rapid change. They also involve convergence, for 3G is the long-sought juncture at which the GSM and CDMA evolutionary paths come together into a single, official, globally roamable system.
As defined by a standards body called the Third Generation Partnership Program (3GPP), a global wireless standard called the Universal Mobile Telephone Standard (UMTS) should be firmly in operation by 2005. UMTS will have circuit-switched voice and packet-switched data. 3G networks must be able to transmit wireless data at 144+ Kbps at mobile user speeds, 384 Kbps at pedestrian user speeds, and an impressive 2+ Mbps in fixed locations (home and office).
This flexibility derives from UMTS' two complementary radio access modes: Frequency-Division Duplex (FDD), which offers full mobility and symmetrical traffic, and Time-Division Duplex (TDD), which offers limited (indoor) mobility and handles asymmetric traffic, such as web browsing.
Ultimately, UMTS itself will evolve into an "all IP" or "end-to-end IP" network, or at least a network in which IP is used as much as possible.
UMTS is Europe's answer to an earlier (and ongoing) project, the ITU-T's International Mobile Telecommunications 2000 (IMT-2000), which stakes out frequencies for future use. Amusingly, the independent-minded allies of the U.S. and Japan refer to 3G as IMT-2000 (not UMTS), despite the fact that the Europeans, to keep the Americans in the loop, established a separate Third Generation Partnership Project Number 2 (3GPP-2) body.
Furthermore, the exact line separating 3G from its predecessors has blurred lately, especially since the highest-end 2.5G technology is called "3G" by both manufacturers and the IMT-2000. The great dream is that all of the high-end technology will interoperate with UMTS under the general term "3G."
A 3G phone is supposed to handle more than simple voice mobility. Cramming streaming color video, multimedia messaging, and broadband Internet surfing into a single device may make some of the first true 3G phones a bit bulky, a throwback to the 1980s.
Indeed, the cell phone should run as many timesaving intelligent agents as possible. When you must use the phone, you should be able to efficiently use voice, data, and touch-sensitive screen simultaneously. In fact, Cisco, Comverse, Intel, Microsoft, Philips, and SpeechWorks recently formed the Speech Application Language Tags (SALT) Forum to develop a device- and network-independent de facto standard to do just that.
Aside from the mobile phone, the wireless broadband-enabled laptop and PDA will also play a role in the wireless future. Some people may prefer making VoIP calls from a laptop in a higher-bandwidth, fixed-wireless scenario (an animal different from a pure mobility play), while others may prefer a more portable, integrated cell phone/PDA.
The Family Tree
In the 1980s, some of us were using thick-as-a-brick analog phones. In the early 1990s, things began to change. At the moment, we're in a digital 2G wireless world. The Global System for Mobile Communications (GSM) is the world's most popular 2G mobile standard, having conquered Europe, Asia, Australia, and New Zealand, and is spreading through the U.S. thanks to an aggressive marketing campaign by Voice-Stream. GSM operates on the 900 mHz and 1.8 gHz bands worldwide except for the Americas, where it occupies the 1.9 gHz band.
Other 2G systems include the Integrated Digital Enhanced Network (iDEN), which Motorola launched in 1994. iDEN runs in the 800 mHz, 900 mHz, and 1.5 gHz bands. GSM and iDEN use Time Division Multiple Access (TDMA), which involves timesharing a channel somewhat like a T1 does.
Another 2G system, cdmaOne (also called IS-95A, which debuted in 1996), doesn't use timesharing. It uses a unique spread-spectrum technology, Code Division Multiple Access (CDMA), which relies on a special encoding technique to let lots of users share the same pair of 1.25 mHz bands.
Qualcomm owns most of the CDMA-related patents. Major cdmaOne carriers include Verizon and Sprint in the U.S.; Bell Mobility and Telus in Canada.
Unfortunately, typical data transmission rates for 2G networks range between 9.6 and 14.4 Kbps. This isn't great for web browsing and multimedia applications, but okay for SMS - short (160 Latin character) text messages.
Between Two G's
The major improvement 2.5G brings over 2G is the introduction of packet-switched data services that conserve bandwidth even though they're "always on." This means that when you use a data service over 2.5G you only occupy bandwidth when you actually send and receive packets (shades of the Internet!). Voice calls on 2.5G, however, are definitely still circuit-switched, and use a constant bandwidth.
On the GSM path, an effort was made to send packets over GSM circuit-switched voice channels, called High Speed Circuit Switched Data (HSCSD). More powerful, however, is General Packet Radio Service (GPRS), a GSM-based packet data protocol that can be configured to gobble up all eight timeslots that exist in a GSM channel. With some software and hardware upgrades, GPRS can commandeer existing spectrum, servers, and billing engines.
GPRS can support a 115 Kbps data rate, though 50 to 60 Kbps is more likely in practice, especially since the packets must contend for the same bandwidth as GSM circuit-switched voice, and providers will tweak the bandwidth based on the number of subscribers as they try to find a profitable mix of number-of-users versus bandwidth-per-user.
To enjoy both GPRS data and GSM voice, one must have a new Subscriber Terminal or "TE" (mobile phone, PDA, PC or laptop card) that supports packets as well as voice. One also needs to upgrade software at the GSM Base Transceiver Site (BTS) and the Base Station Controller (BSC). The BSC also must have a new piece of hardware called Packet Control Unit (PCU), which helps direct data traffic to the GPRS network. Also, databases such as the Home Location Register (HLR) and the Visitor Location Register (VLR) should be upgraded to register GPRS user profiles.
Existing GSM Mobile Switching Centers (MSCs) don't handle packets, so two new network elements, collectively referred to as GPRS Support Nodes, must be introduced. The Serving GPRS Support Node (SGSN) delivers packets to mobile devices around the service area. SGSNs query HLRs for GPRS subscriber profile data, they detect new GPRS mobile devices entering a service area, and record their location.
The second new element is the Gateway GPRS Support Node (GGSN), which is an interface to external Packet Data Networks (PDNs) that work with Protocol Data Units (PDUs). One or more GGSNs may support multiple SGSNs
Motorola has championed GPRS with its Aspira GPRS network infrastructure, an offering that gives GSM network operators immediate wireless data services without having to rebuild the central infrastructure. Motorola's Aspira GPRS network subsystem - including the GPRS support node (GSN), MSC and location register - is functionally separate from the base station subsystem. Operators can increase node capacity by just adding modular interface cards and downloading software and firmware processors. Motorola's Packet Controller Unit (PCU), the interface between the voice GSM network and the packet network, performs radio functions and Aspira GPRS network functions, and is built on a standard 16-slot CompactPCI card cage.
In the field of GPRS software, Hughes Software Systems, employs 1,700 programmers in India who work on ready-to-go GPRS solutions for carriers. Ajay Kumar Gupta, vice president and general manager for U.S. software operations, says, "Instead of deploying GPRS to everybody (100,000+ subscriber base), some providers are zeroing in on business campuses and more lucrative areas of likely adopters (10,000 subscriber base)."
For even more bandwidth, GPRS can be upgraded to use a modulation technique called EDGE, which stands for Enhanced Data-rates for GSM (or Global) Evolution. EDGE lets GSM operators use existing GSM radio bands to increase the data rates within GPRS' 200 kHz carrier bandwidth to a theoretical maximum of 384 Kbps, with a bit-rate of 48 Kbps per timeslot and up to 69.2 Kbps per timeslot in good radio conditions. Existing cell plans can remain intact, and there is little investment or risk involved in the upgrade.
AT&T has announced it will move its entire network to GSM/GPRS and thence to EDGE. VoiceStream is also converting to GPRS, and Cingular Wireless says it will take the GPRS/ EDGE route, too. Cingular announced it was going to launch GPRS in Seattle, where AT&T recently trialed its GPRS service on Nokia phones.
Network operators wary of the seemingly lengthy GSM-GPRS-EDGE-UMTS path should take a look at Alcatel's highly flexible Alcatel 1000 Mobile Switching Center (MSC) for GSM and GPRS/ EDGE, which evolved from the Alcatel 1000 switch. Its UMTS features make it ready for 3G, as the switch is part of Alcatel's planned end-to-end UMTS solution leading toward all-IP multimedia services. The MSC comes in both a small stand-alone version for small networks and a high-capacity version based on ATM switching matrix and UNIX servers. There are even specific functions for GSM satellite gateways
The CDMA Route To 3G
The GPRS equivalent in the CDMA world is CDMA2000 1XRTT, which can assign more of the 1.2 mHz radio channel per user. It can also employ a more sophisticated modulation scheme to boost bandwidth for individual users, up to 144 Kbps (bursting at 153.6 Kbps, and up to 307 Kbps in the future). It also involves a new phone and demands a change to some of the base station equipment, doubling voice network capacity and allowing data to be packetized and sent without the need to establish a traditional circuit.
CDMA2000 1XRTT lets service providers evolve gradually from 2G to 3G, since it's backwardly compatible with cdmaOne. By the same token, any combination of 2G and 3G capabilities can be deployed in a network simply by inserting new or upgraded "1X" cells at strategic network locations among the 2G cells.
While Europeans want GSM and its descendants to be the foundation of 3G, Americans are particularly fond of promoting CDMA derivatives. Indeed, Sprint already refers to CDMA2000 1XRTT as a "3G" service and will offer it throughout the entire Sprint PCS all-digital network by mid-2002. Even now, Sprint will sell you a backward-compatible silver SCP-5000 Sanyo phone with a full color display for $399. Like Japanese carriers, Sprint will charge for screen savers and ring tones.
Another operator, Nextel, currently offers Motorola iDEN phones, but many in the industry feel that Nextel will also install a CDMA2000 1XRTT overlay on its nationwide integrated digital enhanced network.
Just to muddy the waters further, CDMA2000 1XRTT has two new descendants, CDMA2000 1XEV-DO and CDMA2000 1XEV-DV. CMDA2000 1XEV-DO (Evolution-Data Optimized) is about to be deployed in bandwidth-crazed South Korea, where 60% of the population have broadband access. Faster than CDMA2000 1XRTT, 1XEV-DO is essentially 3G in its prodigious handling of bandwidth, supporting fixed and mobile applications at 1.2 to 800 Kbps on average and 2.5 Mbps peak.
In the U.S., Verizon may do 1XEV-DO deployments at the end of 2002, as will an operator in Japan. Airvana specializes in building 1XEV-DO end-to-end IP infrastructures. President and CEO Randy Battat says, "In North America certain regional operators are looking to use 1XEV-DO to come up with not a mobile but a fixed wireless technology that delivers Internet access at about 200 to 250 Kbps without line-of-sight transmission and without a truck roll. Semi-urban areas with little DSL deployment are candidates."
Airvana is working with Nortel Networks to jointly develop all-IP 1XEV-DO products. Nortel Networks expects its CDMA2000 1XEV-DO solution to be available in the second half of 2002.
Many network operators converting to CDMA2000 1XRTT or 1XEV-DO are using Lucent Technologies' Flexent products designed to support 2G to 3G evolution. (Lucent knows a few things about CDMA, having installed 50,000 CDMA base stations among 60 customers over the years, giving them a 40% market share.)
Moving to Lucent's "1X" architectures is made as painless as possible: For most Lucent Series II and Flexent base stations, adding circuit cards and upgrading network software is all that's needed to move from cdmaOne to CDMA2000 1X.
Lucent's platforms can be deployed in whatever frequency bands are allowed from 450 to 2100 mHz. They double voice capacity and support mobile Internet-based applications (144 Kbps with CDMA2000-1X and up to 2.4Mbps with 1XEV-DO), yet they can use existing 2G overhead/ control channels for system acquisition, call establishment, and control.
Lucent's CDMA comprehensive solutions include Flexent 3G-ready base stations; Operations, Administration and Management Solutions (OA&M); billing solutions, optical backhaul; and high-capacity MSCs.
Whose 3G Is It, Anyway?
Americans pushed for descendants of cdmaOne to be the "official" 3G.
The CDMA camp, however, suffered from a schism. The European Telecommunications Standards Institute (ETSI) and the Japanese operator NTT DoCoMo wanted Ericsson's Wideband (W-CDMA) to serve as the basis for 3G, which demands a large swath of new spectrum. Qualcomm and the Korean carriers wanted backward compatibility and found they could achieve the same objective as Ericsson's W-CDMA by simply aggregating existing codes and channels. Qualcomm therefore promoted the series of incremental upgrades leading to the various flavors of cdma2000, which they hoped would be adopted as an official 3G system.
As things turned out, 3G UMTS is a combination of GSM technology and the W-CDMA radio interface.
For forward-looking operators, another amazingly flexible platform that's available now is the UltraSite from Nokia. It's a triple-mode site solution that supports HSCSD, GPRS, EDGE and W-CDMA. UltraSite includes a compact, high-capacity base station housing GSM/EDGE transceivers or W-CDMA carriers, or a mix of them, expandable through cabinet chaining. UltraSite can be installed at new or existing GSM sites, to increase the cell capacity, or to enhance the data features of the site simply by adding new EDGE-capable transceivers or upgrading the site to W-CDMA.
When Nokia and AT&T Wireless Services completed the first live EDGE data call using GSM/EDGE technology and a live GSM network environment recently, the call was made using a 1900 mHz Nokia UltraSite base station, and a prototype Nokia EDGE handset connecting a laptop to the Internet. <<
- Eric - |
