Sunday 5 February 2012

Contents of module

Spectrum Management and EMC

OFTA, or rather its predecessor unit within the Post Office, did not start serious spectrum management and planning until the early 1980s. Until then frequencies were issued on a first-come-first-served basis within the spectrum band allocations. For example, there was considerable demand for frequency assignments for the paging industry.

Public Mobile Radio Services

The turning point was the advent of public mobile radio services. The first three analogue cellular mobile services began in 1985, and interference between pagers and mobile phones was a serious problem. A senior OFTA official describes the situation in those days as follows:

Before OFTA instituted a proper frequency planning system, there was only a simple frequency registration process. Radio assignment was done in a very simple way. If there was a vacant channel, you simply put the operator in it. You didn’t look at the technical aspects of a particular transmitter. You didn’t look for problems of mutual interference caused by a combination of transmitters. You didn’t look at the location of paging transmitters in relation to mobile transmitters.

The situation in Hong Kong was particularly bad because you had so many tranmsmitters in a densely packed populated area. Operators preferred the same locations, high-rise buildings. They liked to put all their transmitters all together on the rooftops of taller buildings.

In the 1990s a new interference problem arose from the introduction of GSM and PCN cellphone networks. Transmitters even 2-4 km apart can still interfere if “they see each other.”

To widen the level of industry representation and advice which OFTA can draw upon, and to encourage cross-industry cooperation and discussion of the problems, OFTA has established two advisory committees in this area: the Radio Spectrum Advisory Committee (RSAC) and the Technical Standards Advisory Committee (TSAC). All the major issues of spectrum management and allocation and procedures for assignment are aired at the meetings of these advisory committees and in the papers presented at the meetings.

Computer-based EMC

Before assigning a frequency, OFTA now looks carefully at potential interference on

  1. intermodulation problems of transmitter location,
  2. co-channel systems problems of spurious emissions, and
  3. interference problems between adjacent channels.

Many technical parameters need to be taken into account, including the radio propagation characteristics of the frequency, the type and nature of the equipment such as the transmitter’s radiation signal characteristics and the sensitivity of the receiver, power levels, directional and positioning issues, to calculate the level of mutual interference.

Originally OFTA made these calculations manually, but in the early 1980s switched to a computer. After upgrades of specially written software, the computer now stands at the centre of OFTA’s spectrum management operations. Its effectiveness depends entirely upon the quality of the database from which all calculations follow.

In making a new frequency assignment OFTA will use the computer to make electromagnetic compatibility (EMC) calculations, based upon the considerations listed above.

As explained in the fifth meeting of the RSAC, 11 July 1995, in making a new frequency assignment, the culling distance and the culling frequency could vary in accordance with the frequency band in the EMC calculation.

The culling distance and culling frequency would be at least 2 - 3 MHz and 1/2 - 1 km respectively. But the EMC calculations exclude mobile-to-base and base-to-mobile because

  1. the interference is transient in nature,
  2. the calculation time would be unduly long, and
  3. the number of assignable frequencies would be significantly reduced.

In anticipation that the problems of mobile-to-base would worsen as more networks were licensed, OFTA has encouraged operators to informally cooperate by making known the locations of their base stations and channel frequencies at the band boundaries so that adjacent channel interference can be avoided. The possibility of using guard bands has been ruled out due to the short supply of frequencies available given the strength of demand for cellphones in Hong Kong.

Fixed Links Assignments

A user who wishes to operate a fixed link has to submit an application for frequency assignment to OFTA. OFTA then has to conduct electromagnetic compatibility calculations before approving the application, but the tendency now is to move fixed radio services off spectrum and onto cables and fibre and into leased circuits to make way for the growing demand for mobile wireless services.

This is especially true for spectrum below 13 GHz. Notable recent exceptions have been the use of 23 and 38 GHz point-to-point fixed links used by mobile operators and the issuing of five multi-directional broadband fixed wireless licences, using 24 GHz and above.

Where other microwave applications are made, OFTA follows the FCC approach in the US where microwave users themselves have to carry out the necessary frequency coordination and submit their coordination report with their applications for frequency assignments. This dramatically speeds up the frequency assignment process.

Private Radio Mobile Services

Following a recommendation in a report commissioned by OFTA from Deloitte Touche Tohmatsu (DTT) Consultancy Study on the Introduction of Economic Mechanisms to Spectrum Management in Hong Kong, March 1995,7 Hong Kong adopted a standard 12.5 kHz channel spacing for the use of private radio mobile systems. OFTA advised the RSAC on 15 September 1995, that

The Electrical and Mechanical Services Department had suggested that the equipment life was 7 years and 60% of the UHF portable radios were licensed within the past 4 years. It was therefore reasonable to start changing the equipment in 3 years’ time. The assignment of existing users should remain unchanged and they had to change their equipment into 12.5 kHz channeling in 7 years. Following adoption of a migration plan, OFTA would monitor the situation and would review the type approval specification for the 12.5 kHz channeling equipment of UHF band. The main target was to narrow channel bandwidth in the UHF band.

Re-assignment of Spectrum

Re-assignment of spectrum is a task that becomes necessary as new technologies give rise to new types of devices and new radio services while making old ones redundant. Conforming to ITU guidelines is another factor.

For example, OFTA needed to reallocate the 1.9 – 2 GHz spectrum for PCN use by 1997 when it was being used extensively by fixed links. In accordance with WRC 2000, OFTA must obtain the return of spectrum in the 11 – 12 GHz frequencies being used for MMDS and television broadcasting for future use by third generation (3G) mobile networks.

The process of returning spectrum can be an awkward one unless it was written into the licence awarding the original frequency assignment. In some cases the regulator has to wait for licences to expire, in other cases to trade one set of frequencies for another, or, in the case of many fixed radio services, encourage their migration to wirelines or cables or fibre.

New Licences and Services

When new technologies give rise to new radio services, for example third generation (3G) mobile radiocommunications, OFTA follows standard procedures.

These begin with a working group set up to examine the technology and the spectrum requirements. Here reference is made to Radio Regulation spectrum allocations and the Hong Kong Table of Frequency Allocations.

A consultant may be hired to provide further study, and visits to overseas administrations may be involved. The process can take a year or more. The results of the working group are put before the Advisory Committees for their consideration.

The second step is drawing up a licence and its conditions, a process involving legal drafters and taking about three months to complete. Licence conditions address coverage and the rollout plan of the operator.

The final considerations are frequency assignments, approval of transmitter sites, control of interference, and so forth.

One additional consideration is that the costs of this process are more than covered by the licence and spectrum fees charged, as OFTA has been set up as a Trading Fund under the Trading Funds Ordinance. (See http://www.justice.gov.hk/Home.htm for all Hong Kong legislation) Another consideration is the methods of issuing licences are beginning to change, notably with the possible use of auctions. These two issues are examined in Part 6.

Health and Safety

No-one doubts that radiation at high levels and in high doses causes health and safety risks, the problem is knowing for sure what transmitting devices emit dangerous levels, when and under what circumstances they may do so, over what periods of time exposure reaches critical levels, and so forth. No conclusive evidence really exists as yet for many applications, for example whether cellular mobile phone and base station emissions can cause harm.

OFTA follows the guidelines of the ICNIRP and regularly monitors sites in Hong Kong for radiation levels.

OFTA has issued a "Code of Practice for Protection of Workers and Members of the Public Against Non-Ionizing Radiation Harzards from Radio Transmitting Equipment" for all radio operators to follow. They should ensure that the electromagnetic radiation emitted from their antennae does not cause exposure of occupational personnel and members of the general public in excess of the limits set by the ICNIRP. To ensure that the radio operators comply with the requirements as set out in the Code of Practice, OFTA conducts inspections on randomly selected radio site locations.

One problem is that OFTA does not have sufficient technical details about every base station site that is negotiated between, say, the owner of a building rooftop and a radio service operator, and there are many hundreds of them. The assignment of frequencies is undertaken to avoid interference, and it is therefore primarily the responsibility of the radio site operators to ensure safe installation and operation of their radio systems/sites.

To tackle this potential problem OFTA has produced a Code of Practice to be followed by the industry in line with the recommendations of CIRPA, NRPD and IEEE, to govern the placement, height and usage of radio antennae to protect the public’s health and safety from any potential hazard of non-ionizing radiation.

These measures do not necessarily lessen public concern, and therefore OFTA responds to requests and concerns of the public by carrying out inspections and measurements to allay these concerns.