rob - looks like Q is participating too, eh?
WMAN has it's place...no big deal to Q IMO.
thought you might like the below article I found
late
3G TDD faces WLAN threat
Daniel Beaumont, daniel.beaumont@informa.com Planet Wireless
Issue 11, 01 April 2002
T-Mobile's plans to integrate WLANs into 2.5G and then 3G services (see page 13) is a blow to the Time Division Duplex mode of UMTS, which has some 5MHz of dedicated spectrum in most European 3G licenses. "If TDD devices were widely available we'd consider introducing TDD, but they're not," says Stephan Keuneke, senior manager of IP access at T-Mobile. "WLAN devices and infrastructure are here and the market is growing fast, so we're deploying WLAN."
But InterDigital, which provides technology for both the TDD and wide-area Frequency Division Duplex modes of UMTS, says WLAN is not the enemy.
"WLANs have, in fact, done us a favor by forcing operators to look more closely at higher data rate services over technologies such as TDD," says Alain Briancon, CTO at InterDigital.
Briancon argues that TDD and WLAN could be complementary, with operators using TDD to bridge the gap between 5-6Mbps WLAN and 300Kbps 3G networks (see below). Vendors also point to a recent major success for TDD in China, where a new operator is introducing a variant of the technology. Datang Mobile was recently launched to produce and license 3G infrastructure and handsets using the country's indigenous Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology. TD-SCDMA is a hybrid 3G standard that was created primarily to promote Chinese industries, and it will operate alongside other standards such as GSM and cdma2000.
UMTS TDD is a short-range wireless technology that delivers throughput of up to 2Mbps over several hundred meters. 3G operators can use TDD access points for indoor hotspot services or to boost the capacity of wide-area FDD base stations. Most European 3G licenses include spectrum for both FDD and TDD modes of UMTS operation. FDD uses paired spectrum and TDD unpaired, enabling synchronous and asynchronous communications, respectively.
3G ops focus on wide-area FDD
European 3G operators are naturally focusing on introducing wide-area FDD services, to generate revenue as quickly as possible from their massive investment in licenses and infrastructure. Most operators had planned to deliver broad FDD coverage before moving on to boost capacity in selected areas with TDD. Now, however, the rollout of TD-SCDMA in China, the growth of WLAN technology and the demand for high-speed mobile services have pushed TDD higher up the agenda.
Operators have to choose whether to deploy TDD alongside FDD to improve the user experience in densely populated indoor and outdoor hotspots.
Another option would be to wait two years or more for High-Speed Downlink Packet Access (HSDPA), which combines elements of FDD and TDD and promises speeds of 5-10Mbps. In the meantime, WLAN - which operates in the license-exempt 2.4GHz and 5GHz bands - could be seen as an alternative or complement to both FDD and TDD (see table, page 4), which operate in licensed UMTS spectrum.
WLAN base stations are inexpensive - with consumer versions under US$200 and some high-end models below US$1,000 - but operators also need to evaluate provisioning and management costs. "Nobody has really looked at the comparative costs of WLAN and TDD infrastructure," says Tommy Ljunggren, co-founder of consulting firm Northstream. "The cost of base stations is just one small part of the story. It's the back-end and operational costs that are the key."
Keuneke notes that TDD handset availability and costs are uncertain.
"It will probably be two to three years before we have handsets with TDD, and vendors still need to tell us how much it's going to cost to add it," he says. "Wi-Fi devices are here today and are being integrated into more and more laptops." That means many corporate users will get integrated Wi-Fi the next time they upgrade laptops, so cost will be marginal. On the other hand, laptops are a niche product compared to mass-market handsets, and Wi-Fi does not support voice and is too power-hungry to install in handsets. TDD supports voice and data and aims to be power-efficient enough for handsets.
TDD could bridge 3G-WLAN divide
In summer 2000, when the majority of Europe's 3G licenses were awarded, the use of TDD spectrum was viewed almost as a footnote. Operators believed the UMTS FDD mode, which is theoretically faster than GSM by a factor of 50 or even 100, would be more than adequate for five years. Since then, however, hundreds of thousands of early adopters have experienced very high access speeds via Wi-Fi WLANs in airports, hotels, offices and homes.
At the same time, 3G operators lowered projected speeds for UMTS FDD from 1Mbps to 500Kbps, then to 384Kbps, and now to under 300Kbps. In fact, Northstream's Ljunggren believes the first FDD handsets will deliver speeds closer to 60-140Kbps, although Philippe Laine, Network Strategy manager at vendor Alcatel, claims "3G tests in Paris using our products work well at 300Kbps."
Thus there is a growing chasm between the 5-6Mbps throughput of Wi-Fi hotspots and the 60-140Kbps of advanced cellular networks. Operators now have to decide whether there is a strong business case for bridging this gap with a technology that can provide moderate data rates for both voice and data. TDD is well suited for this.
"Last year it seemed as though we were shouting in the desert about the merits of wideband TDD, where nobody could hear us," says Briancon at InterDigital. But he notes interest is now increasing, partly because of InterDigital's demonstration of a combined wideband FDD/TDD solution at the 3GSM Congress in Cannes in February. "By utilizing the paired band with FDD technology and the unpaired band with TDD technology, operators will make more efficient use of spectrum and be better able to provide a broader range of data services," he believes.
InterDigital is a director member of the TD-SCDMA Forum in China, and Briancon is leading a TDD task force within the UMTS Forum. He argues that the rollout of TD-SCDMA in China could reduce the cost of TDD infrastructure.
That in turn might tempt European 3G operators to make an earlier migration to TDD, to safeguard existing license and infrastructure investments.
3G operator technnology choices (2002-2005)
Technology combination Likely maximum macro/micro speeds Possible launch
FDD mode only 300Kbps 2002
FDD+TDD modes combined 300Kbps/2Mbps 2004
FDD+802.11b 300Kbps/11Mbps 2002
FDD+TDD+802.11b 300Kbps/2Mbps/11Mbps 2004
HSPDA alone 5Mbps 2004
HSPDA+802.11a 5Mbps/54Mbps 2004
Source: Planet Wireless
TD-SCDMA Director Forum members
Alcatel InterDigital
China Mobile Nortel Networks
CNC Motorola
CATT Jitong
CRTC Qualcom
China Telecom Siemens
China Unicom UtStarcom
Huawei Zhongxing
Source: TD-SCDMA Forum
Two TDD deployment options
3G operators can deploy TDD to provide indoor hotspot coverage at speeds of up to 2Mbps, or to boost overall UMTS network capacity in densely populated and heavily congested areas to prevent network meltdown. "TDD is most effective when placed on top of FDD hot spots, where a high density of users is expected," says Eelco Jan Boonstra, UMTS key account manager at Siemens, one of the 3G vendors for T-Mobile.
Operators need to achieve a consistently good service - a minimum level of speed and QoS in all areas covered - if they are to achieve market share. One of the prime motivations behind 3G in Japan, for instance, has been the need for more voice capacity.
Higher-speed services via TDD could become service differentiators. In the UK this fall, Vodafone and Hutchison 3G will begin to roll out 3G services, and by next year they will be joined by three other operators: mmO2, Orange and T-Mobile. In such a crowded market, three key weapons will be speed, novel applications and branding.
Some 3G strategists believe having a two-speed service would confuse the market. One source close to a UK 3G license holder contends "it is better to concentrate on a minimum speed for all environments." Pekka Soini, vice president systems and business development at Nokia Networks, says: "I can remember the days when there were proposals for dual-mode DECT/GSM handsets for indoor and outdoor use. They never took off."
But others in the industry argue that customers are now much more attuned to differences in speed, signal coverage and QoS and could cope with different cellular speeds. Early adopter/early majority segments will already have experienced different fixed-line speeds over dialup, ISDN, and ADSL, for instance. And in the U.S., Korea and Japan, many professionals are accustomed to getting different speeds from a range of standards such as PHS, 802.11b/a and proprietary radio technologies such as the now defunct Ricochet.
New kinds of hotspots
In theory, a careful deployment of TDD at key locations would allow operators to promise customers "an even higher standard of service" at certain towns, cities or particular hotspot categories such as airports. Flashing icons on dual-mode FDD/TDD 3G handsets might even inform users when they are entering a high-speed area. These could be branded with names like "Turbo Spots" or "Hyper Zones." A 3G customer might be persuaded to download video clips or music from a Hyper Zone while killing time at a station, managing with only messaging and voice applications in a far-off suburb.
TDD can also be integrated into PC cards. If this happens then cellular customers could access applications over laptops and PDAs as well as smaller 3G handsets.
Much of the public-access WLAN debate has centered on traditional hotspots such as airports and hotels. Many of these sites have already been snapped up by wholesalers and WISPs (PW, March, pages 7-8), and operators might balk at site-acquisition costs.
Alhough TDD is best suited to indoor environments, where interference is better controlled, it can also work in outdoor settings and over a wider area than WLANs. Briancon says TDD base stations have a range of hundreds of meters, creating some overlap between pico and micro environments.
This could create many more new hotspot opportunities than are available with current WLANs. TDD base stations, which Briancon says can be as small as phone handsets, could be erected on lampposts, telegraph poles and other urban fixtures. One could compare a cluster of TDD base stations to the pole-top radios that formed the ill-fated Ricochet network. But unlike Ricochet, a TDD cluster would be backed by a fully integrated wide area network based on FDD. This means that a user could move seamlessly from macro, micro and pico environments.
In addition, an FDD/TDD network can be tightly controlled by a single operator. Boonstra says TDD "is very good at power control and resource management." WLANs, by contrast, are more likely to be tacked on to cellular networks in an ad hoc manner. This creates many more operational challenges in the form of additional layers of authentication, authorization and billing as well as security, roaming and other back-end integration costs (PW, February, pages 3-9). TDD also has the potential to be deployed in certain office and home environments for voice and data applications.
TD-SCDMA not a booster technology?
In China, the situation with TD-SCDMA is very different, in that TDD technology is much less likely to be used as a short-range booster. Soini believes the speed of TD-SCDMA will be in the tens of kilobits rather than hundreds in the first year. TD-SCDMA will then aim to provide a consistent speed over macro, micro and pico cells. Some analysts see it primarily as an expansion of the voice-centric services that already exist over CDMA and GSM. But Siemens, in partnership with the China Academy of Telecommunications, recently carried out TD-SCDMA field trials, and video calls were made successfully from moving vehicles.
TDD has advantages over WLANs
For operators, TDD has many practical and cost advantages over WLAN.
It can offer tightly integrated voice and data services at moderate speeds for both handheld and laptop devices. The pool of potential users is also far larger than it is for WLAN. In 2002, about 5% of airport visitors in western Europe will carry a laptop, but over 70% of them will have a mobile device. WLANs, on the other hand, have a head start in the data market. Many business users have had first-hand experience with high-speed data services at hotspots, and operators cannot turn back the clock.
WLAN users are also showing a preference for monthly flat-rate or per-session tariffs, which 3G operators will be reluctant to offer. Operators are now offering 2.5G GPRS services at per-megabyte rates, and they may offer some 3G services on the same basis to ensure revenues cover investment costs as quickly as possible. What's more, in the first two years of network rollout, operators will not have the capacity to offer flat rate-pricing, and they desperately need to increase ARPU. New forms of messaging, video calls and information services are likely to be priced on a per-unit basis like SMS.
Indebted 3G ops will not spend more
TDD infrastructure is already available, and Nokia, Siemens, NEC, Alacatel and InterDigital are among those who say they can offer integrated FDD/TDD products. Operators, however, have invested heavily in FDD mode for the first 3G rollouts and are highly unlikely to deploy TDD in 2002 or 2003.
UMTS handsets using FDD are still largely in development, so dual-mode FDD/TDD devices are unlikely to appear for two to three years, according to one 3G operator.
Soini at Nokia says FDD should give operators enough capacity until 2005 and that they will need to see which applications take off before making decisions about extra capacity. In addition, Laine points out that the capex of FDD has been so high that operators are unlikely to move on TDD until 2004 at the earliest. Ljunggren thinks the cost of making dual-mode handsets is yet another consideration. The first handsets will be dual-mode GSM/FDD, and GSM/GPRS will operate in parallel with 3G for a number of years. For example, Jan Boonstra notes that Siemens has demonstrated the first call over GSM and 3G networks in Monaco.
A Vodafone spokesman says that by the terms of its UK license, Vodafone needs to achieve 80% coverage by 2007.This should, in theory, give operators breathing room before they begin to figure out the next stage of 3G or 4G. But some TDD vendors are banking on 3G networks hitting capacity limits far sooner than anticipated. Briancon argues that dual-mode TDD/FDD phones or HSPDA handsets with both modes overlaid could be on the market within two years.
Operators point out that consumers have often fully used cellular capacity almost as soon as it is rolled out, and optimists say high take-up of MMS and videophone applications could lead to demand for UMTS TDD booster stations within a few years. Some analysts say video applications in particular will require 200Kbps and upward to work well on a small screen, while the first 3G services this fall may in fact only achieve speeds of 60Kbps.
In some countries, 3G license holders will also face stiff competition from nonlicense holders. GSM/GPRS operators and MVNOs can increase speed and capacity by buying surplus spectrum or deploying EDGE, TDD or WLANs.
In fact, some non-3G operators may be in a better position to offer complementary WLAN services since they have avoided the stiff license fees and 3G capex.
The worst possible scenario for 3G operators in 2003 would be if customers use relatively low-priced WLAN hotspots for heavy data transfer and see little reason to upgrade from "souped up" wide-area GPRS to 3G. TDD, advocates say, could improve 3G bandwidth and service to help 3G stay ahead of the game.
Contacts
InterDigital
T: (1) 610 878 7800
susan.sutton@interdigital.com
www.interdigital.com
Alain Briancon: CTO
Prabhakar Chitrapu: manager, wireless Internet architecture
Jack Indekeu: director of strategic marketing
Nokia Networks
T: (358) 7180 08000
pekka.soini@nokia.com
www.nokia.com
Pekka Soini: vice president of systems and business development manager
Siemens
T: (31) 70 333 3333
eelco.jan.boonstra@siemens.co.nl
www.siemens.com
Eelco Jan Boonstra: UMTS key account manager
Northstream
tommy.ljunggren@northstream.se
www.northstream.se
Tommy Ljunggren: consultant
Alcatel
philippe.laine@alcatel.com
www.alcatel.com
Philippe Laine: network strategy manager
TD-SCDMA Forum
www.tdscdma-forum.org
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