Wireless local loop

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Wireless local loop (WLL), also called Broadband Wireless Access (BWA) radio in the loop (RITL) or fixed-radio access (FRA) or fixed-wireless access (FWA) or Fixed Wireless Terminal (FWT), is the use of a wireless communications link as the "last mile / first mile" connection for delivering plain old telephone service (POTS) and broadband Internet to telecommunications customers. Various types of WLL systems and technologies exist.

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[edit] Definition of Fixed Wireless Service

Fixed Wireless Terminals or FWT units differ from conventional mobile terminal units operating within cellular networks -such as GSM- in that a fixed wireless terminal or deskphone will be limited to an almost permanent location with almost no roaming or find-me anywhere facilities.

WLL and FWTs are generic terms for radio based telecommunications technologies and the respective devices which can be implemented using a number of different wireless and radio technologies.

Wireless Local Loop service is segmented into three broad market and deployment.

[edit] Licensed Point to Point Microwave service

Licensed Microwave service has been used since the 1960s to transmit very large amounts of data. The AT&T coast to coast backbone was largely carried over a chain of microwave towers. These systems have been largely using 1500-2500 MHz and 5000-6200 MHz. The 5 GHz band was even known as the "common carrier" band. This service typically was prohibitively expensive to be used for Local Loop, and was used for backbone networks. In the 80s and 90s it flourished under the growth of cell towers. This growth spurred research in this area by companies such as DMC, and gradually the equipment cost has come down, and this technology is now being used as an alternative to T-1, T-3 and fiber connectivity.

[edit] Licensed Point to Multi Point Microwave service

Multipoint microwave licenses are hundreds of times more expensive than point to point licenses. A single point to point system could be installed and licensed for 50,000 to 200,000 USD. A multipoint license would start in the millions of dollars. MMDS and LMDS were the first true multi point services for wireless local loop. While Europe and the rest of the world developed the 3500 MHz band for affordable broadband fixed wireless, the U.S. provided LMDS and MMDS, and most implementations in the United States were conducted at 2500 MHz. The largest was Sprint Broadbands deployment of Hybrid Networks equipment. Sprint was plagued with difficulties operating the network profitably, and service was often spotty, due to inadequate radio link quality.

[edit] License-Free Multi Point Wireless Service

Most of the growth in long range radio communications since 2002 has been in the license free bands. Terago Networks in Canada and NextWeb Networks of Fremont were two of the early leaders in deploying reliable license free service. The equipment that they used employed proprietary protocols.

[edit] 1995 - 2004: License-Free Equipment

Most of the early vendors of license free fixed wireless equipment such as Adaptive Broadband (Axxcelera), Trango Broadband, Proxim Networks, RedLine and BreezeCom (Alvarion) used propietary protocols and hardware, creating pressure on the industry to adopt a standard for unlicensed fixed wireless. These Mac Layers typically used a 15-20 MHz channel using Direct Sequence Spread Spectrum and BPSK, CCK and QPSK for modulation.

These devices all describe the customer premises wireless system as the Subecriber Unit "SU", and the operator transmitter delivering the last mile local loop services as the "Access Point" (AP). 802.11 uses the terms AP and STA (Station).

[edit] 2002 - 2005: The growth of Wi-Fi technology for use in wireless local loop service

Originally designed for short range mobile internet and local area network access , 802.11 has emerged as the defacto standard for Wireless Local Loop. There is more 802.11 equipment deployed for long range data service than any other technology. These systems have provided varying results, as the operators were often small and poorly trained in radio communications, additionally 802.11 was not intended to be used at long ranges and suffered from a number of problems, such as the hidden node problem. Many companies such as KarlNet began modifying the 802.11 MAC to attempt to deliver higher performance at long ranges.

[edit] 2005 - Present: Maturation of the Wireless ISP market

In nearly every metropolitan area worldwide, operators and hobbyists deployed more and more unlicensed broadband fixed wireless multipoint systems. Providers that had rave reviews when they started, faced the prospect of seeing their networks degrade in performance, as more and more devices were deployed using the license free UNII and ISM bands.

[edit] The growing interference problem

Interference caused the majority of unlicensed wireless loop services to have much higher error rates and interruptions than equivalenty wired networks, such as the copper telephone network, and the coaxial cable network. This caused growth to slow, customers to cancel, and many operators to rethink their business model.

There were several responses to these problems.

[edit] 2003: Voluntary frequency coordination

NextWeb, Etheric Networks, GateSpeed and a handful of other companies founded the first voluntary spectrum coordination body - working entirely independently of government regulators. This organization was founded in March of 2003 as BANC, "Bay Area Network Coordination". By maintaining frequencies used in an interoperator database, disruptions between coordinating parties were minimized, as well as the cost of identifying new or changing transmission sources, by using the frequency database to determine what bands were in use. Because the parties in BANC, comprised the majority of operators in the Bay Area, they used peer pressure to imply that operators who did not play nice would be collectively punished by the group, through interfering with the non cooperative, while striving not to interfere with the cooperative. Banc was then deployed in Los Angeles. Companies such as Deutsche Telekom joined. It looked like the idea had promise.

[edit] 2005: Operators flee unlicensed for licensed

However the better capitalized operators began reducing their focus on unlicensed and instead focused on licensed systems, as the constant fluctuations in signal quality caused them to have very high maintenance costs. NextWeb, acquired by Covad for a very small premium over the capital invested in it, is one operator who focused on licensed service, as did WiLine. This led to fewer of the more responsible and significant operators actually using the BANC system. Without its founders active involvement, the system languished.

[edit] 2002 to present: Operators get into "Noise, power and gain Arms Race"

Certain companies began to adopt "Wild West" tactics, violating Spectrum regulations by increasing the power and gain of the wireless systems. This was particularly true in parts of the world that were either already lawless, such as Nigeria, and in the U.S. in areas where the operators were usually "mom and pops", often with no real knowledge of radio technology, predominantly the midwest. Operators in the coastal metro areas often had capital and technically experienced staff. These tactics have included shooting and sabotaging equipment on wireless towers, as well as installing wireless devices whose sole purpose was to disrupt competitor operations by focusing the antenna directly at the competitors base stations.

[edit] 2005 to present: Operators develop adaptive network technology.

Third, the operators began to apply the principles of self healing networks. Etheric Networks followed this path. Etheric Networks focused on improving performance by developing dynamic interference and fault detection and reconfiguration. As well as optimizing quality based routing software, such as MANET and using multiple paths to deliver service to customers. Success can be evidenced as Etheric Networks is the fastest wireless local loop operator in the World, per DSL Reports. This approach is generally called "Mesh Networking" which relies on Ad-Hoc Networking Protocols, however Mesh and ad-hoc networking protocols have yet to deliver high speed low latency business class end to end reliable local loop service, as the paths can sometimes traverse exponentially more radio links than a traditional star (AP->SU) topology.

Adaptive network management actively monitors the local loops quality and behaviour, using automation to reconfigure the network and its traffic flows, to avoid interference and other failures.

[edit] 2006 - 2008: The Next Technology - WiMAX (or IEEE 802.16)

Currently more operators are running on the 802.11 MAC at 2 and 5 GHz. 802.16 is unlikely to outperform 802.11 until at least late 2007. It may become the dominant medium for wireless local loop. Intel is promoting this standard, while Atheros and Broadcom are still focused largely on 802.11. Atheros, using its highly succesful 802.11 OFDM chipsets, will likely be able to deliver comparable service levels to Intel's 802.16 TDM OFDM chipsets for the forseeable future.

[edit] Mobile Technologies

These are available in Code Division Multiple Access(CDMA), Digital Enhanced Cordless Telecommunications - DECT (TDMA/DCA) ( See ETSI 6 EN 300 765-1 V1.3.1 (2001-04) -"Digital Enhanced Cordless Telecommunications (DECT); Radio in the Local Loop (RLL) Access Profile (RAP); Part 1: Basic telephony services"), Global System for Mobile Communications(GSM), IS136 Time Division Multiple Access(TDMA) as well as analog access technologies such as Advanced Mobile Phone System(AMPS), for which there will be independent standards defining every aspect of modulation, protocols, error handling, etc.

[edit] Deployment

The Wireless Local Loop market is currently an extremely high growth market, offering Internet Service Providers immediate access to customer markets without having to either lay cable through a metropolitan area MTA, or work through the ILEC's, reselling the telephone, cable or satellite networks, owned by companies that prefer to largely sell direct.

This trend revived the prospects for local and regional ISPs, as those willing to deploy fixed wireless networks were not at the mercy of the large telecommunication monopolies. They were at the mercy of unregulated re-use of unlicensed frequencies upon which they communicate.

Due to the enormous quantity of 802.11 "Wi-Fi" equipment and software, coupled with the fact that spectrum licensed are not requires in the ISM and UNII bands, the Industry has moved well ahead of the regulators and the standards bodies.

Sprint and ClearWire are preparing to roll out massive WiMAX networks in the United States.

[edit] Wireless Local Loop (WLL) Standards

  • Mobile:
  • Fixed or local area network:
    • DECT, for local loop
    • corDECT (variant of DECT originates from India)
    • LMDS
    • 802.11, originally designed for short range mobile internet and network access service, it has emerged as the facto standard for Wireless Local Loop.
    • WiMAX or IEEE 802.16 may become the dominant medium for wireless local loop. Currently more operators are running on the 802.11 MAC at 2 and 5 GHz. 802.16 is unlikely to outperform 802.11 until at least late 2007. Intel is promoting this standard, while Atheros and Broadcom are still focused largely on 802.11.

[edit] Manufacturers

[edit] See also

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