The SCTE Spring Lecture Meeting, 2003.

Alternative Broadband Access Technologies And System Reliability This was the SCTE's fifteenth full day Lecture presentation and was hosted on Tuesday 4 March 2003 in the Council Chambers at the IEE building in Savoy Place, London WC2 in a similar format to previous Lecture Meetings. The Programme was organised by the SCTE Papers Committee led by Dr Mark Burns. Dr Burns also chaired the Lecture day. Following is a summary of the presentations.

	Microwave Local Loops in Cable Systems Mike Thornton, Technical Director, Newtel Solutions Broadband Internet Access is emerging as a significant success story for the UK Cable Industry, but with some 50% of UK households unable to access broadband services, alternative access technologies are receiving much attention. In the first paper of the day Mike Thornton of Newtel Solutions presented a paper on microwave delivery, which has enabled the Channel Islands' cable operator to establish itself as a quality service provider, overcoming difficult construction conditions. Jersey Cable has been using a 10.7GHz trunk for some time to provide to link opposite sides of St Helier. This however had bandwidth limitations being one way. They also operated an IDA voice network and established ISP POPs in both Jersey and Guernsey. These latter services were both operated on virtual networks provided by BT, JT or GT as appropriate. In 1999 the Education Department of Jersey tendered for interconnection of around 50 schools. Many of these were in St Helier and could be served by the existing network but the remainder were spread across the island. The only possible way of supplying bandwidth economically and in the timeframe required was to use microwave links. Both 38GHz trunk and 2.4Ghz local loop links were required to provide a resilient and network. A great deal of attention was needed to the security aspects of the system especially at the local level with both frequency hopping and encrypted direct sequence options being investigated. The addition of a CMTS at the co-location of CATV headend and IP router node allowed a fully integrated network to be implemented. As more capacity is required the fibre network can be extended and the radio links re-used.

Performance Evaluation and Optimisation of the European Cable Modem Television Protocol: DVB/DAVIC Dr Victor Rangel, UNAM (Univeridad Nacional Autonoma de Mexico) Dr Rangel, previously with the University of Sheffield, presented an in-depth analysis of the DVB-DAVIC protocol, with the emphasis on performance evaluation and optimisation. Although based on the 'Euromodem' the results are expected to be similar with corresponding modes in Docsis and EuroDocsis. Typical traffic profiles had been used (internet/voip/mixed) to computer model the effect of changing parameters such as retry delay and contention slot allocation (both size and mode). It was interesting and assuring to know that the results mirrored intuitive expectations with highly predictable traffic such as voice being optimised by modes approximating to switched circuits. This presentation was based on the paper that appeared in the September 2002 (Volume 24 No 3) edition of CTE.

	Active Harmonic Filtering based on the Current Injection Principal Mostafa Bandar, Telecom Accounts Manager, MGE UPS Systems Ltd Harmonic distortion in the incoming mains has long been a problem in power installations, for example at switch sites and CATV headends. Many of the typical loads, such as Computers, Motors etc. exhibit current waveforms which are far from sinusoidal. The harmonic content is high and often the higher order harmonics are present at high level. The power factor is similar affected and can be significantly less than unity. Since the current requirement will be much higher than that expected from simple RMS assumptions, problems may be encountered both with circuit supply and protection (e.g. fuse ratings) as well as undersizing of conductors (e.g. excessive neutral current in 3-phase supplies). Various solutions have been proposed including supply filtering; this involves substantial inductive components and only effectively removes one harmonic at a given load. An alternative approach is to consider active filtering. This involves monitoring the current waveform with a Hall-effect based current sensor (clamp-on versions for existing installations) and injecting current to reduce the distortion. Examples were shown where significant reduction of all harmonics was possible and power factors close to unity attained. Since the correction current is only a fraction of the total load current, the size of the active filter unit is normally small compared with the normal supply switchgear.

Broadband Wireless Access - Complementary or Competing Technology? David Whitehead, Director of Engineering, Motorola BCS There are a multiplicity of competing technologies currently in use for broadband wireless data transmission. Whilst Bluetooth, IEEE802.11b, WiFi and other flavours competed for local access there seems no doubt that wireless technology per se is hear to stay and is very much complimentary to cable in the local loop. It also has, potentially, a significant role in rural broadband access where economics prevent either cable or twisted pair xDSL solutions. Broadband wireless access is also becoming a much more common service offered in airports, railway stations and some larger hotels. David Whitehead commented on the significant growth of wireless LANs in office environments, replacing structure wiring where the latter did not exist or was too expensive to install retrospectively. Echoing the comments of the earlier speaker, Mike Thornton, David was amazed at the lack of security on many of these wireless LANs. At best there was the potential for third party broadband access to the internet (and the resultant chalk marks found outside such 'free' access points), at worst the security of the internal network was compromised and commercial data freely available.

	The Weakest Link - Single Points of Failure Jerry Lyle, Director of Engineering, BTL One of the problems in today's multi-channel head-ends is the overall reliability of the transmission chain, from programme acquisition to delivery on the network. With significant numbers of equipments involved the likelihood of a single failure is high. Traditional 1 + 1 redundancy schemes would be very expensive and therefore careful design of the overall system architecture and choice of equipments is vital to ensure that a single point of failure does cause loss of signal and revenue. Jerry Lyle, whilst drawing on examples of equipments produced by BTL, expounded the general principles and requirements that are necessary to build reliable systems. Many examples were given dealing with satellite and terrestrial reception, signal processing and re-modulation for transmission. The combination of N+1 techniques together with alternative A-B routing provided solutions to these scenarios. One of the most important conclusions was to ensure that equipments had dual (A-B) inputs and at least two outputs to allow routing without reliance on additional external switch-routing elements.

Once again our speakers were some of the world's foremost experts and the audience of over 50 top engineers from the Cable Telecommunications Industry enjoyed the day and went away to contemplate the new concepts and ideas which were raised. The journey home was eased by the usual SCTE Cocktail Party held, as usual, on the TS Queen Mary moored on the Embankment just outside the IEE building. An opportunity to unwind, discuss the day's events and to network with colleagues from other companies. Follow the links below for reports on previous lecture meetings. The 2002 Autumn Lecture Meeting & AGM. The 2002 European Lecture Meeting. The 2002 Spring Lecture Meeting.


© Society of Cable Telecommunication Engineers.