How WiMAX is causing massive disruption of broadcasting signals

In places where regulators have allowed BWA services to use the C, Ku and Ka Bands, massive interruptions of satellite services, radar and microwave links, which also operate in this frequency band, have continues to occur. Reports Spacewatchafrica editors


Conceived almost 14 years ago in the Institute of Electrical Engineers (IEEE), few technologies have evoked more controversy and disappointment than WiMAX, says Peter Thornycroft of U.S based Aruba Network. Some of its optimistic claims and projections have contrasted with slow progress on the ground. Also, not many internet technologies have taken longer than expected time to reach a mass market than WiMAX. Though proponents of WiMAX claim that already more than 500 operators worldwide hold spectrum licenses suitable for the technology, and over 150 are in trials, but there are few, if any large-scale commercial networks. Despite these revelations, analysts argue that WiMAX as a technology is ready for takeoff, but various non-technical obstacles have conspired to keep it grounded thus far. The recent launch of 4G/LTE mobile technology will further reduce the scale of WiMAX deployment.

Most of the current WiMAX trials are of this 802.16-2004, fixed-client version of WiMAX, delivering broadband Internet in rural areas where there is little cable in the ground. But the proponents of this technology had a much bigger target in mind: a better mobile cellular network. WiMAX is excellent technology, but – trials aside – it has not yet enjoyed success in worldwide markets. Accordingly, many of the reasons are not technical, any new service provider technology faces hurdles, with industry early struggles to promote CDMA a good example. As WiMAX is a technology for licensed spectrum, suitable spectrum must be available and licensees must use that spectrum for WiMAX rather than competing technologies.

Incidentally, a major issue brought up at the recent Asian confer­ence on satellite communications was a desire among the terrestrial wireless industry to share and use the spectrum set aside for the satellite indus­try. In order to handle the demand for more capacity and higher speed due to the introduction of mobile phones with high speed data service like, WiMAX, LTE or 4G, the terrestrial wire­less industry would like to use more of the spectrum, includ­ing not only C-band which was debated previously but also Ku and Ka band. There is a movement among the terrestrial wireless industry to approach various governments about sharing this broad spectrum with the satellite industry. This issue is likely to become a major point of debate at the 2015 World Radio-communications Conference (WRC 2015) and members of the satellite industry are aware they must begin making plans to protect the spectrum they are currently using.


C- Band controversy

At the moment, stakeholders in the broadcast industry are calling on governments to take rapid action to halt the disruption of TV services suffered by millions of viewers world wide. In Bangladesh, recently launched WiMAX operators using the 3.5 GHz frequency are causing interference with broadcast and cable transmissions across the country and the rest of the region. “The largely unanticipated implications of the introduction of WiMAX services at 3.5 GHz is causing widespread transmission failures throughout Bangladesh and have been especially serious for news broadcasters which use the lower end of the Standard C-band spectrum,” said Gregg Daffner, Chairman of CASBAA’s Wireless Action Group.

Satellite communications technology in the C band is used for broadcasting television signals, internet delivery, data communications, voice telephony and aviation systems. The satellite systems that operate in the 3.4 – 4.2 GHz band (C-band) are suffering substantial interference, to the point of system failure, in places where national administrations are allowing broadband wireless access (BWA) system to share the same spectrum bands already being used to provide satellite services. The same will happen if 3G and the planned

4G mobile system are allowed to use the frequencies used in the C band for satellite downlink services as is being contemplated b y some authorities.

To eliminate the harmful interference, operators of satellite earth stations and users of satellite communications services have united to communicate their position and technical requirements to national and international telecommunications regulators. Regulators and radio frequency managers need to allocate spectrum in the ways that recognise the reality of harmful interference and validate the right of incumbent operators to operate, and their customers enjoy their services, without disruption by the new ones. C band satellite and the BWA are all important services and there are ways to find suitable spectrum for all of them to operate.

The problem

Several national administrations have designed portions of the frequency band 3.4 – 4.2 GHz for terrestrial wireless applications such as BWA and future mobile applications. This band is already in use by satellite services, radar systems and domestic microwave links. This band is commonly referred to as the C band. In places where administrations have allowed BWA services to use the C Band, there have been massive interruptions of satellite services. Interference with radar and microwave links, which also operate in this frequency band, is likely.

Importance of C band

Use of C band for satellite communications is widespread throughout the world. It is particularly vital for many developing countries because of its resilience in the pre4sencde of heavy rains. C band earth stations are also used extensively in many developed countries. C  band frequencies have been aligned for satellite downlinks since the industry was inaugurated more than 40 years ago. C band services cover large areas. They facilitate intercontinental and global communications, and provide a wide range of services in developing countries. Services in this band now provide critical applications such as distance learning, telemedicine, universal access, disaster recovery and television transmission in many tropical countries. Antennas which receive satellite downlink signals in the C band are by necessity extremely sensitive devices. They are designed to receive a low-power signal emanated by small transmitters located in orbit 36,000 kilometres above the equator. In the C band, satellite services have co-existed with domestic microwave links and radars for many years, because the later systems operate via tightly focused beams from fixed points, and de-confliction ca take place when necessary.

By contrast, terrestrial wireless applications are by definition ubiquitous and increasingly mobile/nomadic. Mobile and base stations for terrestrial applications emit signals from many locations, in all directions, simultaneously that is powerful enough to saturate the sensitive C band satellite receiving systems, causing a potential for total loss of service in the C band. The sensitivity of C band satellite receiving systems also means that trhey may be disrupted by mobile terrestrial use of frequencies in immediately adjacent bands.

Competition from incumbents

Broadband communications service providers are usually few in number in a particular geography. It has been argued that the business is a natural monopoly, as increased size drives economies of scale and beneficial network effects in terms of population covered. Whether or not this may be true, the services offered by WiMAX, broadband fixed and mobile IP services are already offered by large, well-capitalized incumbents, and this represents a barrier to the technology.

The first question to be answered is why, since WiMAX offers a superior customer experience at a lower infrastructure cost, these incumbents would not adopt it for their next generation networks. In the case of DSL and cable, the answer is likely that their already-depreciated plant can be extended at lower cost than building a wireless network for which they have no expertise. Similarly, incumbent cellular operators are more likely to look first at extending the life of their existing architecture rather than face the disruption from building a new overlay WiMAX network. To date, incumbents have seen WiMAX more as a competitive threat to their business than an easy choice of next-generation technology: in fact, in US, Sprint’s sudden endorsement of WiMAX was seen by many as an act of desperation, as it was losing ground in the marketplace and sought to disrupt its larger, more successful competitors.

If incumbents see significant costs and risks in switching to WiMAX, there should be room in the market for new entrants that are not encumbered by legacy networks. However, building a national WiMAX network will require not only spectrum, but capital investment of maybe $10 billion, and WiMAX clients and handsets are not yet on the market at price points that challenge existing cellular and DSL products. Hence there are significant barriers to entry in this market – not that it cannot be done, but the required set of circumstances has not yet converged.

The most common figures quoted for WiMAX are a bandwidth of 70 Mbps over a range of 30 miles (50 km). Both these figures are misleading. 70 Mbps is a reasonable maximum data rate for a single client very close to the base station. And while it is certainly possible to achieve communications over 50 km, large (high-gain) antennas will be required, and the bandwidth will be very low, perhaps sub-1 Mbps. In reality, bandwidth is shared among all active clients in the cell, and bandwidth decreases as distance increases.

Mobile WiMAX is even more constrained, as antennas are smaller, devices are battery-powered and signals fluctuate as the client moves. Recent mobile WiMAX trials in Malaysia prompted estimates from Motorola of 3-4 Mbps per client with a cell radius of 1-2 km, while the operator involved in the trial indicated current performance is closer to 1 Mbps. It was not clear how many simultaneous clients the network could support.

Licensing the 5.8 GHz band

As the fixed WiMAX standard was in development, one of the interested constituencies was the wireless Internet service providers (WISPs). This is a group of mostly small, mostly rural U.S. ISPs that deliver wireless broadband Internet service to fixed clients in just the model adopted for fixed WiMAX. Since they own no spectrum, and so cannot use the 2.5 or 3.5 GHz bands, many of them currently use point-to-multipoint and mesh wireless products with outdoor radios, operating in the 5.75-5.85 GHz band which is an unlicensed band also used by Wi-Fi.

There are other applications today for private, point-to-point wireless connections, and a wide variety of solutions exist. In the U.S. most use unlicensed bands at 900-928, 2400-2480 or 5150-5850 MHz. Many WiMAX equipment vendors have a history of serving this market, and may be able to deliver a targeted product line combining appropriate ruggedization, power and packaging options. However, one would not expect such WiMAX equipment to perform any better than Wi-Fi in range or data rate terms, as it would be subject to the same regulatory constraints. In order to provide a solution for these WISPs, the WiMAX Forum have defined a profile in the 5.75 – 5.85 GHz band for fixed WiMAX, and a number of radio vendors have developed products for this market.

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