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Foreword

It is required by the Wireless Telegraphy Acts, 1949 and 1998 that no radio apparatus shall be installed or used in the United Kingdom, except under the authority of a licence granted by the Secretary of State. It is a condition of such a licence that the performance of the radio equipment meets certain minimum standards laid down in the UK Radio Interface Requirement 2000 (UK RIR 2000). Compliance will have been notified in accordance with the R&TTE (Radio Equipment and Telecommunications Terminal Equipment) Directive.

This document details the frequency assignment criteria and principles that will be employed by Radiocommunications Agency (RA) in the selection of frequencies for use by compliant fixed terrestrial (point-to-point) digital radio equipment operating in the band or frequency range specified.

These assignment criteria are subject to updating and amendment, and intending operators/manufacturers should consult the latest version of this document complete with any amendments. Single copies of this document are available free from the RA library at the address below:

Radiocommunications Agency
Library Services
Wyndham House
189 Marsh Wall
London E14 9SX.

Switchboard and 24 hour enquiry service:
Telephone: 020 7211 0211

Library and Publicity:
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1. General

1.1 Introduction

This document outlines the frequency assignment criteria and principles that will be employed by RA in the selection of frequencies for use by fixed terrestrial (point-to-point) digital radio services operating in the frequency range 12.75 to 13.25 GHz.

The channel plan shall be in accordance with that given in section 5.

This document has been generated to take into account the equipment standard EN 301 128 V1.2.1, EN 300 639 V1.3.1 and EN 300 234 V1.3.2. RA will currently license the following classes of equipment:

1.2 Licensee's Responsibility

The Foreword of this document states that the establishment, use or installation of transmitting or receiving apparatus is subject to the issue of a licence by the Secretary of State. The licensee must ensure that equipment conforms with and is maintained to the standards referenced in UK RIR 2000.

1.3 Link Length Policy

RA operates a link length policy to promote the use of the highest possible frequency band for the distance over which the link is to operate. For the 12.75 to 13.25 GHz band the minimum path length is 9.5 km for systems with traffic rates equal to or above 2 Mbit/s, below 140 Mbit/s and including Analogue FM-video. Systems at 140 Mbit/s and above will be permitted over path lengths ≥5.5 km. Below these distances there will be some expectation that a higher frequency band or alternative means of traffic transfer could be used.

2. Transmitting and Receiving Installations

2.1 General

The transmitting and receiving installations shall conform to sections 2.2 and 2.3 below. The installations shall be implemented in accordance with good engineering practice.

2.2 Antenna Directivity

The antenna installation at the licensed premises shall be such that the antenna pattern will not exceed the co-polar and cross-polar Radiation Pattern Envelopes (RPE) given in UK RIR 2000 with the zero degree datum being the boresight path between the two stations.

2.3 Antenna Polarisation

The plane of polarisation of emissions for a particular radio link will be specified by RA and will normally be vertical or horizontal linear polarisation. The antenna alignment surface shall be aligned as precisely as possible to the true vertical or true horizontal and the misalignment shall be no greater than 3°.

2.4 Equivalent Isotropically Radiated Power (EIRP)

The assigned value of EIRP will be stated in the licence and must not be exceeded, although a tolerance of ±3 dB on this assigned value will be allowed in practice. Under no circumstance is the EIRP to exceed 45 dBW.

3. Principles of Assignment and EIRP Derivation

3.1 Normal Assignment

A normal frequency assignment for a single or multi-section bi-directional link shall comprise a pair of radio frequencies of corresponding channel number; one from each of the low and high frequency groups.

3.1.1 Normal Assignment Flow Diagram

Annex C shows a flow diagram for the normal assignment process.

3.2 Multi-Section Links and Repeater Stations

3.2.1 Multi-Section Links

In the case of a multi-section link the direction of transmission of the two frequencies shall alternate for successive repeater sections so that the transmitter frequency assigned to any station shall be taken from only one of the frequency groups in the lower or upper half of the band.

3.2.2 Passive Repeaters

Passive repeater operation using either back-to-back antennas or planar reflectors will be allowed only under certain specific conditions. Use of these systems will be judged on a case-by-case basis and they are expected to be used only for availabilities of 99.99% or less under the following conditions:

1. at remote sites where power provision is extremely difficult;
2. there is a clear spectrum saving by the use of one repeater station to overcome the obstructed path rather than going around the obstruction with two or more conventional links;
3. use of the higher power needed for this operation does not unnecessarily sterilise the surrounding area and block further normal assignments;
4. higher performance antennas (if available) should be used at the end stations along with as large as reasonably possible repeater station antennas to maximise the repeater gain. Detail of the assignment process modifications to deal with passive repeater operation is given in Annex D.

3.3 Go – Return Separation

The frequency difference between a pair of corresponding go and return frequencies in the 12.75 to 13.25 GHz band shall be 266 MHz.

3.4 Parallel Links Operating Over the Same Path

Due to the fading characteristics in this frequency band the interference assessment for parallel links operating over the same path will be calculated by assuming that fading of wanted and interfering signals is uncorrelated. However, it is expected that cross-polar operation in adjacent channels will be possible for the majority of links assigned to an availability of 99.99%. Co-polar operation may need to be separated by at least two channels.

Table 1 lists the minimum frequency separations for like systems operating under these conditions. For mixed capacity systems, the appropriate minimum separations are derived by the sum of half of the individual minimum separations given. The assignment software identifies available channels that meet the minimum frequency separation criteria, in accordance with the channel plan defined in section 5.

3.5 Antenna Discrimination

In assigning frequencies for links which are in the same geographical area, due consideration shall be taken of antenna discrimination. When available, data derived from a manufacturer's guaranteed RPE will be used. Otherwise, the appropriate RPE specified in ETSI standard EN 300 833 will be assumed.

3.6 Path Clearance

RA will usually assume that each hop has a clearance from obstructions of not less than 0.577F between the transmitting and receiving antennas at the two stations under conditions corresponding to values of the ratio K greater than 0.7.

F : First Fresnel zone clearance

K : Ratio of effective earth radius to real earth radius

3.6.1 Obstructed Paths

Obstructed paths will be allowed where their need is clearly demonstrated, with an EIRP increased up to a maximum of 6 dB above the normal assignment level providing that the maximum limit of 45 dBW is not exceeded. Above this level operators will be expected to accept the possible lower link availability. The following conditions will apply:

1. the higher power needed for this operation does not unnecessarily sterilise surrounding area and block further normal assignments;
2. the increase in EIRP will only be allowed if the obstruction cannot be overcome by increasing the antenna height;
3. higher performance antennas (if available) should be used to minimise the sterilisation of surrounding areas, considering the higher than normal EIRP associated with this type of operation;
4. the increased EIRP will only be allowed on link availabilities ≥ 99.9% and ≤ 99.99%.

Detail of the assignment process modifications to deal with operation over an obstructed path is given in Annex E.

3.7 Path Loss

3.7.1 Median Path Loss

The median path loss between two stations is equal to the free-space-path-loss (FSPL) plus the atmospheric gaseous absorption:

3.7.2 Gaseous Absorption

The link budget shall include contributions from gaseous absorption in addition to the basic FSPL. The predicted gaseous absorption is based on oxygen and water vapour data obtained from ITU-R Rec. P.676-2. At 13.25 GHz a worst case gaseous specific attenuation of 0.027 dB/km shall be assumed, based on ground level air temperature of 15^oC and a water vapour density of 10 g/m³ (see ITU-R Rec. P.836-1, Figure 4).

3.8 Availability

An availability greater than 99.99% is to be agreed with RA on a case-by-case basis.

NOTE: Throughout this specification, availability will be taken to mean propagation availability.

3.9 Receiver Input Levels

RA will in general examine applications for the use of radio links on the assumption that the median signal level of the receiver input is as detailed in Table 2 and a transmitter power shall be assigned accordingly.

The levels in Table 2 are derived from a link budget as given in Annex A.

3.10 Fade Margin

3.10.1 General

Fade margins are calculated according to Recommendation ITU-R P.530-7 §2.3 and §2.4 for clear-air and hydrometeor (rain) fading respectively. Note that the Recommendation refers to clear-air fading as due to "multipath and related factors"; the more general term "clear-air" is used here.

Fade margin is calculated by apportioning the overall permissible unavailability between clear-air and rain fading. The assignment software utilises the equations for clear-air and rain fading given in P.530-7 §2.3 and §2.4 respectively to iterate for the value of fade for which the sum of the individual (clear-air and rain) unavailabilities equals the required overall unavailability. It is assumed that rain and total atmospheric fades are unlikely to occur simultaneously. For cases where the ratio of outage times for rain and clear-air exceeds 40 only the dominant method is calculated.

3.10.2 Clear-Air Fade Margin

The fade margin required for clear-air effects depends on frequency, path length, radio-climatic factors, and the service availability required. The fade exceeded for a given percentage of an average year is calculated according to Recommendation ITU-R P.530-7 §2.3.

3.10.3 Rain Fade Margin

The rain fade margin for a given availability depends on the path length, frequency, polarisation and geographic location. UK rain rates exceeded for 0.01% of an average year are shown in Annex F at the centre of each 100 km grid square. This rain-rate data is obtained from UK meteorological records. The rain fade is derived as follows:

• The higher of the rain rates exceeded for 0.01% of the time at the two terminals of each link, mm/hr, is used to calculate the fade.
• The specific attenuation,, for the rain intensity, , of interest is calculated for the required frequency and polarisation using equation 1 of ITU-R Rec. P.838-1:

  

Values of regression coefficients,and , are given in Table 3 below for both horizontal (H) and vertical (V) polarisation. These have been derived by interpolation between the values in Table 1 of ITU-R Rec. P.838-1, for the highest frequency in the band:

Frequency
7.9 GHz	0.025	0.023	1.189	1.168

The path reduction term, r, is given in ITU-R Rec. P.530-7 as:

The effective path length, L_e, is found by multiplying the actual physical path length, L, by the reduction term, r, found above.

The path attenuation exceeded for 0.01% of time is given by equation 37 of ITU-R Rec. P.530-7:

The attenuation, A_p, exceeded for other time percentages, P, (over the range 0.001% to 1%) can be deduced from equation 38 of ITU-R Rec. P.530-7:

Links whose calculated fade is less than 15 dB will be allocated a fade margin of 15 dB.

3.11 Equivalent Isotropically Radiated Power Calculation

The licence schedule will detail the assigned EIRP for each transmitting station. This is based on the following calculation:

EIRP = Rx median signal level + Rx station feeder losses - Rx antenna gain + Path loss

Where the Rx (receiver) median signal level is as defined in Table 2. The maximum co-polar gain figure for the receiving antenna is used.

4. Interference Assessment

4.1 General

The link to be assigned is co-ordinated with all other links in the same frequency band within a co-ordination zone radius of 200 km around each site. The size of the co-ordination zone may be reviewed from time to time as operational experience is gathered. Interference to and from the proposed link is assessed taking into account the path profile between the two stations. Use is made of antenna radiation patterns to obtain the gain of antennas in the direction of unwanted signals.

The two conditions considered in the evaluation of interference from each single-entry interference source are:

1. the median unwanted signal must be at least the wanted to unwanted (W/U) ratio below the faded wanted signal;
2. the enhanced wanted signal must be at least the W/U below the median wanted signal.

If either of the above two conditions are not met, and an alternative frequency cannot be ascertained, the link will not be assigned. The procedures followed are in line with ITU-R Rec. P.452-7 and outlined in the flow diagram shown in Annex E.

4.2 Interference Limits

The interference limits are derived as follows:
Interference limit = receiver sensitivity level (RSL) for a bit error rate (BER) of 10^-6 – W/U ratio.

4.3 Co and Adjacent Channel Limits

The maximum co-channel and adjacent channel interference limits, at the receiver input, from a single unwanted source are shown in Table 4 and Table 5. W/U ratios for single-entry interferers relating to mixed capacity digital systems are shown in the matrices in Annex B.

4.4 Multiple Interferers

In Table 4 and Table 5 as well as Annex B, the single-entry digital W/U ratios include allowances for multiple interferers. The allowances are 4 dB for co-channel interferers and 6 dB for adjacent channel interferers independent of bit-rate.

5. Channel Plan

5.1 Derivation of Radio Frequency Channels for the Band 12.75GHz to 13.25GHz

For the band 12.75 GHz to 13.25 GHz, the radio frequency channel arrangements based on CEPT/ERC Recommendation 12-02 E for carrier spacings of 28 MHz, 14 MHz, 7 MHz and 3.5 MHz as illustrated in Figure 1 shall be derived as follows:

Annex A: Receiver Input Levels and Interference Levels

Table A.1 and Table A.2 give examples of receiver input levels and maximum permitted interference levels for digital systems operating in the frequency band 12.75 to 13.25 GHz.

Annex B: Wanted to Unwanted Ratios

Tables B1 to B12 give the Wanted to Unwanted (W/U) ratios for all frequency offsets up to three times and, in some cases, beyond three times the mean value of the wanted and unwanted channel spacing.

The figures in the Annex B tables have been derived on the following basis:

Co-channel and adjacent channel W/U ratios for like with like systems have been linked to Tables 4 and 5 and therefore to the appropriate equipment standard. W/U ratios for all other combinations have been derived using RA's Net Filter Discrimination (NFD) spreadsheet. However, where the established W/U ratios, defined in earlier assignment criteria, are lower than those obtained using the filter discrimination methodology, those values have been retained.

Important Note:

• When the wanted and unwanted channels of digital systems are not equal, Step 1 in the W/U tables is equal to 1/2 the narrowest bandwidth. Thereafter the step sizes are equivalent to the narrowest bandwidth. When the wanted and unwanted channels are the same size, all step sizes are equal to the channel width of these systems. Shaded steps indicate a W/U ratio of -40 dB.

Click [here] to view tables B1 to B12

Annex C: Normal Assignment Process – Flow Diagram

Click [here] to view the Flow Diagram

Annex D: Assigning Passive Repeater Stations

Consider a link from A to D comprising two hops A to B and C to D where B and C are a co-located passive repeater station.

Back to Back Antenna Type

It is necessary to calculate the EIRP from the central repeater station and determine the required input level to the repeater station. This involves both standard and non standard assignments in the following manner:

1) enter the data for all sites and make the feeder loss at both B and C equal to the loss between the two antennas;

2) perform a standard assignment for the link A to B. From the EIRP and antenna gain at B calculate the required receive level at C. Ignore the direction A to B;

3) carry out a non-standard assignment from C to D using the calculated receive level from 2) at station C;

4) from the EIRP and antenna gain at C calculate the required receive level at B;

5) repeat the assignment from A to B using the receive level calculated in 4) at station B.

Step 3) provides the final EIRP at station D and step 5) provides the final EIRP at station A.

It may be useful in some frequency bands to change polarisation at the repeater station.

Plane Reflector

The procedure for these types of passive repeater is the same as points 2) to 5) above except that B is the same point as C and the gain of the reflector needs to be calculated from the following expression:

The antenna gain for point B should be half the value Grep for each hop A to B(C) and C B) to D. Interference at the reflector only needs to be considered if it arrives from the same direction as the wanted signal.

Annex E: High-Level Flow Diagram for Recommendation ITU-R P.452

Click [here] to view the Flow Diagram