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UK Link Length Policy (bands above ~15GHz)

UK Link Length Policy (bands above ~15GHz). Chris Cheeseman. Date: 11 th Oct 2001 Document Reference: prRSSP 0401 031 0 Meeting: RSSPWG Paper No: RSSP (04-01)/031. Outline. Factors relevant to link length policy Technical considerations Link availability and performance

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UK Link Length Policy (bands above ~15GHz)

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  1. UK Link Length Policy (bands above ~15GHz) Chris Cheeseman Date: 11th Oct 2001 Document Reference: prRSSP 0401 031 0 Meeting: RSSPWG Paper No: RSSP (04-01)/031

  2. Outline • Factors relevant to link length policy • Technical considerations • Link availability and performance • Rain fading statistics • Equipment parameters • Example calculations and current guidelines • The way forward

  3. Factors relevant to policy • Ensure efficient use of the radio spectrum resource BUT cannot ignore: • Environmental / site sharing impact of larger antennas than would otherwise be required • Increased costs of larger than necessary antennas • Practical availability of alternative bands (PTO; RA capability) • Safety/maintenance issues (equipment up mast >~15GHz)

  4. Technical aspects - Availability • Link availability target (e.g. 0.01, 0.001%) is critical to policy • Link planning based on Availability, but Performance targets also relevant • ITU-T G.821, G.826, G.828 Performance targets must be met: • Errored Seconds, Severely Errored Seconds etc. • Experimental measurements at 18GHz in Sweden (COST 235) indicated that when faded to 10-3 BER for say 0.001% time, some 95% of this period results in “Unavailability” and 5% of this period(after translation to worst month) manifests as degraded performance. (e.g. SESR=4.10-4 in a COST235 example). Note: A period of unavailable time begins at the onset of 10 SES events.

  5. Technical aspects - Availability • The relationship of performance and availability in rain faded bands is still under study, as is the definition of some of these parameters in ITU-R WP9A based on ITU-T G.821, G.826, G.827, G.828, G.829, e.g for IP networks. Other than BT (and RA) there is little UK effort in WP9A. • G.828 (high capacity SDH) requirements more stringent than G.826; G.826 more stringent than G.821 • For example ITU-R F.1491 indicates the example of a 20km 2Mbit/s access link where performance targets are: • ESR= 3 x 10-3; SESR=1.5 x 10-4; BBER=1.5 x 10-5 • More study is needed, but indications are that 0.01% unavailability is not good enough to achieve UK commitment to ITU performance standards.

  6. Example calculations • Using ETSI/actual equipment specifications • Typical UK rain, gas and water vapour data • Same size antennas at each end of the link, 60% aperture efficiency

  7. 18GHz link lengths • Historical situation means that some links are shorter than would be usual practice now, even taking into account 0.001% unavailability • 38GHz band product being phased in now to accommodate NEW shorter links [ <xkm] • Exact link length policy to be discussed with RA on a bilateral basis (initially), following general debate on link length policy for all bands in FLCC.

  8. Conclusion • BT actively working on this issue in the international for a (WP9A) and in the UK • Further studies are needed to properly understand all the issues (FLCC activity needed) • BT addressing 18GHz link length issue and working with RA to reach mutually acceptable solutions.

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