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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:
Telephone: 020 7211 0502/0505
Fax: 020 7211 0507

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 6.425 GHz to 7.125 GHz.

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

This document has been generated taking into account the following equipment capacities:

2 x STM-1 in 40 MHz - - - - - - - - - - - - - - - (EN 301 669) - - - - - - - - - - - - - - - Based on 512-QAM

2 x STM-1 in 40 MHz - - - - - - - - - - - - - - - (EN 301 461) - - - - - - - - - - - - - - - Assumes use of XPIC

The equipment performance parameters relating to these capacities can be found in UK RIR 2000.

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 6.425 to 7.125 GHz band the minimum path length is 16 km for systems operating at 140 Mbit/s and above. Below this distance there will be some expectation that a higher frequency band, or alternative means of traffic transfer could be used.

1.4 Other Services

1.4.1 Satellite Services

The Upper 6 GHz band up to 7075 MHz is shared with FSS terrestrial uplinks. Co-ordination between FSS earth stations and FS systems will be undertaken by RA during the assignment period.

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°. Links using ATPC and engineered to meet very high levels of performance may require alignment accuracy in the order of 1°.

2.4 Adaptive Transmitter Power Control (ATPC)

In order to help maximise use of the frequency band, ATPC must be employed on all bi-directional radio links (including passive repeater end stations) operating with a normal assigned fade margin of 20 dB or more. ATPC must be activated by detection of a drop in received signal level at the distant end of the radio link caused by fading along the path. A minimum ATPC range of 10 dB must be used and will be assumed by the assignment tool. In the reduced power configuration the EIRP must be at least 10 dB below the maximum assigned value detailed in section 2.5 below and will be known as the normal EIRP (See also section 3.11).

ATPC operation will not be assumed for radio links operating with assigned fade margins of 15 dB or for uni-directional links. ATPC operation will be optional for radio links operating with an assigned fade margin between 15 dB and 20 dB but will need to be declared by the operator/applicant.

2.5 Equivalent Isotropically Radiated Power (EIRP)

Where appropriate, two values of assigned EIRP will be stated for each transmitting station in the licence. The maximum assigned value of EIRP must not be exceeded under any condition. The normal assigned EIRP is the level for operation under normal steady propagation conditions during which ATPC has not been activated. This will also be the level used by the assignment system for interference assessment purposes. A tolerance of ±3 dB on these assigned values will be allowed in practice. The upper limit for the maximum EIRP normally assigned will be 50 dBW.

For uni-directional links and bi-directional links not employing ATPC the normal assigned EIRP and the maximum assigned EIRP value will be the same. (i.e. the ATPC range will be 0 dB).

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 are expected to only be used for availabilities of 99.99% or less under the following conditions:

a) at remote sites power provision is extremely difficult;

b) 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;

c) use of the higher power needed for this operation does not unnecessarily sterilise the surrounding area and block further normal assignments;

d) 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 6.425 to 7.125 GHz band shall be 340 MHz.

3.4 STM-1 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. Links operating on channels 1 or 8 may require additional Tx and Rx filtering – see EN 301 461 and EN 301 669 for further details.

3.5 Antenna Discrimination

In assigning frequencies for links which are in the same geographical area, due consideration shall be taken of the 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 50 dBW is not exceeded. Above this level operators will be expected to accept the possible lower link availability. The following conditions will apply:

a) the higher power needed for this operation does not unnecessarily sterilise surrounding area and block further normal assignments;

b) the increase in EIRP will only be allowed if the obstruction cannot be overcome by increasing the antenna height;

c) 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;

d) 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 H.

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). Atmospheric gaseous absorption is considered negligible in this frequency band.

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 1 and a transmitter power shall be assigned accordingly.

The figures in Table 1a 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 2 below for both horizontal (H) and vertical (V) polarisations. 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
7.125 GHz	0.003	0.002	1.331	1.312

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

where:

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

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

where:

The attenuation, , exceeded for other time percentages, , (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 maximum assigned EIRP for each transmitting station and the normal EIRP where ATPC is in operation based on the following calculations:

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

Normal EIRP = Maximum EIRP - ATPC Range

Where the Rx (receiver) median signal level is as defined in Table 1. 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 250 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:

a) the median unwanted signal must be at least the Wanted to Unwanted (W/U) ratio below the faded wanted signal;

b) 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 Tables 3 and 4. 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 3 and Table 4 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 Band 6.425 MHz to 7.125 GHz

For the band 6.425 GHz to 7.125 GHz, the radio frequency channel arrangements based on CEPT Recommendation 14-02 E, for carrier spacing of 40 MHz and 20 MHz as illustrated in Figure 1 shall be derived as follows:

Annex A: Receiver Input Levels and Interference Levels

Table A.1 gives examples of receiver input levels and maximum permitted interference levels for digital systems operating in the frequency band 6.425 GHz to 7.125 GHz.

Annex B: Wanted to Unwanted Ratios

Tables B1 to B6 give the Wanted to Unwanted (W/U) ratios within the Upper 6 GHz frequency band
for all frequency offsets up to three times the mean value of the sum of the wanted and unwanted channel spacing.

Tables B7 to B18 give the W/U ratios for systems operating at the common boundary between the Lower 6 GHz and Upper 6 GHz frequency bands.

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

Co-channel and Adjacent channel W/U ratios for like with like RA allocated systems have been linked to Tables 2 and 3 and therefore to the appropriate European equipment standard. W/U ratios for all other combinations have been derived from the methodology detailed in document RSWG (97) 13 Rev.1. This RSWG paper is available from RA. W/U ratios for systems originally managed by British Telecom on an exclusive basis are based on frequency offset rejection levels calculated by British Telecom.

Table B1a – RA Wanted System 2 x STM-1 in 40 MHz (EN 301 669)

Table B1b – RA Wanted System 2 x STM-1 in 40 MHz (EN 301 669)

Table B2a – RA Wanted System 2 x STM-1 in 40 MHz (EN 301 461)

Table B2b – RA Wanted System 2 x STM-1 in 40 MHz (EN 301 461)

Table B3 – BT Wanted System 140 / STM-1 in 40 MHz

Table B4 – BT Wanted System 34 Mbit/s in 20 MHz

Table B5 – BT Wanted System 960 Channel FM FDM in 20 MHz

Table B6 – BT Wanted System FMTV in 20 MHz

Table B7 – Lower 6 GHz Wanted System – RA STM-1 in 29.65 MHz (EN 300 234)

Table B8 – Lower 6 GHz Wanted System – RA 2 x STM-1 in 29.65 MHz
(EN 301 127 Co-channel Cross-Polar)