My photo

Bill St. Arnaud is a consultant and research engineer who works with clients around the world on a variety of subjects such as next generation Internet networks and developing practical solutions to reduce CO2 emissions such as free broadband and dynamic charging of eVehicles. He is an author of many papers and articles on these topics and is a frequent guest speaker. For more details on my research interests see

Wednesday, March 7, 2007

Broadband 2.0 - UK regulator says fiber needed in the last mile

[It is nice to that a couple of regulator's in Europe who "get it". Thanks to Dirk van der Woude for this pointer ---BSA]

Executive Summary
The investigation considers whether there is a way forward to offering economic, ubiquitous broadband wireless access, given that previous solutions have had marginal business cases. The report time scale covers the next 10-20 years. The focus is fixed access, i.e. the local loop; mobile access is specifically excluded from the scope.

The first specific question to answer is: What is the future last mile wireless broadband requirement?

This really is a key question over the long time scale under consideration. We believe that the last mile requirement will increasingly be one in which there is a convergence of the services and platforms providing communications and entertainment to the home. We note that High Definition
(HD) displays and services are set to play an increasing role in this future. Whilst we cannot predict the exact, future HD services, we can take HDTV as a proxy - future requirements can then be estimated over the next 10-20 years. It was found that whilst video codecs have typically improved two-fold each five years, this fails to take into account two things: Firstly, users' quality demands will increase, secondly the amount of coding gain for a given codec depends on the quality and resolution of the source; at the highest quality and resolution, less coding gain is available. In conclusion, 10-15Mb/s of bandwidth is likely to be required, per channel, for HD services in 10-20 years time.

At first sight it may appear that the present-day ADSL service is close to what is required by HD services. This could not be further from the truth. In fact, examining a typical ADSL service advertised at 'up to' 8Mb/s results in two immediate problems
• the bandwidth of 8Mb/s may only be available at up to 2 miles from the exchange. Only 20% of customers live this close. At five miles from the exchange, the rate will have fallen, perhaps to only 2Mb/s or even 512 kb/s
• the present day ADSL service is a contended service. BT wholesale provide two contention levels; 20:1 and 50:1. Even a home user close to the exchange, who may access 8Mb/s peak rate, may access only 160kb/s when the system is fully loaded Hence present day contended ADSL is unsuited to deliver HDTV or even standard definition TV1.

In fact the requirements for HD services of at least 10Mb/s streaming is so vastly different to what contended ADSL presently provides, that we have termed the future bandwidth requirement 'Broadband 2.0', relative to today's 'Broadband 1.0'. This issue is summarised in Figure 1.

One obvious question then arises - can wireless address the needs of Broadband 2.0? It would have to do so at a competitive cost, which means preferring self install indoor systems and minimizing base station numbers, perhaps by working at the lower frequencies of the UHF band. But before evaluating specific wireless technology approaches, benchmarking against access technologies in other countries was performed, with the following results
1. It was quickly apparent that countries leading on bandwidth to the home are all using some form of fibre system. Whilst Japan/Korea are doing this with government sponsorship, Verizon and AT&T in the US have recently begun fibre roll-outs on a purely commercial basis. This is a watershed development for fibre in the local loop. 2. Interest in fibre is high in the EU too, but some operators have halted their roll-out plans due to the absence of an FCC-style forbearance on fibre unbundling within the EU. 3. Benchmarking against upcoming wireless standards showed these were biased towards small screen mobile content delivery, i.e. they are not attempting to address the challenge of the Broadband 2.0 requirements for delivery of HD services to the home.
Based on the requirements identified, the cost drivers and benchmarking, three fresh approaches to the physical technology are proposed. These are • Mesh and multihopping systems • UHF/TV band working • hybrid schemes with fibre or Gb/s 'wireless-fibre'
It was also appropriate to consider fresh approaches for
• licensing, including the licence mix
• creating a nationally tetherless last mile
• ubiquitous access, based on peering approaches
The subsequent evaluation of the technology approaches began by looking generally at the capacity-coverage trade-off involved in all point to multipoint wireless systems. We also looked in detail at WiMAX and 802.22 capacity planning. This provides a profound, if not entirely unanticipated result - the practical, economic capability of wireless, while adequate to provide today's Broadband 1.0, is very clearly inadequate for the very much more demanding Broadband 2.0. The capacity shortfall is about two orders of magnitude. For example, to provide even only an SDTV-capable uncontended streaming capacity to all subscribers would need 50x more base station resource than is needed to provide Broadband 1.0. This would either require 50x more spectrum allocation or 50x more base stations would need to be deployed. To provide HD services, this factor becomes 500x.
Applying this finding first to UHF and then to mesh working, in both cases we conclude that wireless cannot be expected to provide Broadband 2.0 in a cost-effective manner. It was noted further that our sister project2 also supports this view for frequencies over 30GHz.

Having thus concluded that neither today's contended ADSL nor wireless can provide Broadband 2.0, then attention must focus on what could - and whether wireless has any contributing part to play within that solution. The Broadband 2.0 solution must be based on fibre, which must in future reach further into the access network, and potentially all the way to the customer premises. Fibre can solve the contention issues by increasing back haul capacity, and can solve the last mile issue by acting as a point to point solution alone, or as a feeder to DSL distribution technologies - thus effectively reducing the length of DSL lines required. These findings are summarised by the broadband decision tree in Figure 2.

In addition we note that the desire to provide ubiquitous broadband access to the UK will probably be best met by a peering3 arrangement between legacy and future, fixed and mobile devices, rather than attempting to design a single last mile access scheme.
To find the Economic Value of wireless last mile access to the UK, we built on an earlier analysis4 based on increasing the range of base stations. We propose a counterfactual of the status quo and a factual consisting of
• fibre based access for urban customers at Broadband 2.0 level • wireless based access for rural customers at Broadband 1.0 level The resulting net benefit for wireless thus comes from rural customers alone and is estimated as an upper bound figure of £54M, which is relatively small. Further, from a social perspective we point out that there exists a clear danger of creating a new digital divide - those who can access applications which run only over Broadband 2.0 versus those who cannot. In conclusion, this report has found that • the future needs of fixed broadband will be driven by a convergence of the services and platforms providing communications and entertainment to the home, and in particular the use of HD displays and services. This demands access to streaming content at 10Mb/s and above. This is so far in excess of what today's contended ADSL systems can support, that we have termed it Broadband 2.0
• an increase in back haul capability will be needed to support Broadband 2.0, irrespective of the access method used • wireless cannot realistically compete with fibre for the provision of Broadband 2.0 over the whole of the last mile • coverage of fibre may be below 100%, leaving some scope for wireless based Broadband 1.0 systems, probably in rural areas Nonetheless, within Broadband 2.0, wireless does have application -
1. as a last mile feeder element, using Gb/s wireless as a fibre replacement 2. within the home, e.g. 802.11n

Finally, the key recommendations of this report are -
1. Fibre should be the foundation of a Broadband 2.0 capability for the UK. 2. In order to avoid a new digital divide, deployment of fibre would ideally extend to rural areas, although this may not be attractive as a wholly private venture. 3. In order to facilitate Broadband 1.0 in rural areas, spectrum should be made available at suitable frequencies, for example (i) within the UHF TV bands by re-allocation or sharing; or
(ii) by sharing of underused cellular or military spectrum at UHF.
4. With respect to DSO spectrum, market forces are unlikely to promote rural broadband access, so an alternative approach may need to be considered. 5. In licence exempt spectrum, where technology neutrality is desired, both codes of practice and polite protocols should be pursued in preference to application specific bands. 6. Given that home wireless usage is likely to increase and the traffic is likely to move over to mainly streaming or real-time, it would seem appropriate to reconsider the likely amount of licence exempt spectrum required, given that some estimations performed recently have considered only bursty data traffic. 7. Both service and platform convergences are key trends in the broadband future. In other words, the distinction between fixed, portable and mobile devices and services is becoming increasingly blurred. Whilst this report has concentrated on fixed wireless broadband, we recommend that future studies enable an integrated evaluation of technology, licensing and
spectrum considerations for broadband wireless.