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Maximizing Link Length Efficiency: Technical Factors & Guidelines for Bands Above 15GHz

This document outlines factors relevant to radio link length policy, including technical considerations, rain fading statistics, equipment parameters, and example calculations. It emphasizes the need to ensure efficient use of the radio spectrum while considering environmental impact, costs, and safety issues. Link availability and performance targets, as well as ITU performance standards, are crucial aspects discussed with examples and calculations provided. The UK's commitment to achieving performance standards is highlighted, along with ongoing studies and collaborations to address link length issues in the 18GHz band.

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Maximizing Link Length Efficiency: Technical Factors & Guidelines for Bands Above 15GHz

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  1. UK Link Length Policy (bands above ~15GHz) Chris Cheeseman Date: 10th Sept 2001 Document Reference: prFLCC 0201 014 0 Meeting: FLCC Working Paper No: FLCC (02-01) / 014

  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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