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Efficient millimetre broadband radio access for convergence and evolution


The Intelligent Multicast Push and Proxy (IMPPS) software is a transparent multicast caching system which supports on-line and off-line interactive multimedia service. IMPPS is optimized for a network architecture that uses a broadband forward channel (usually based on DVB/MPEG-2) and a separate, usually narrowband, return channel. It represents an intelligent, interactive content delivery system, covering Web content and audio/video streams. As an example, the forward link is usually provided by a geostationary satellite whereas the return channel uses a different network technology, e.g. dial-up connection, a direct Ku-band return link, a LEO satellite network, a DVB-RCS system or a broadband distribution system. Within the EMBRACE project an LMDS channel was used. The Intelligent Multicast Push and Proxy System (IMPPS) is a software solution for interactive multicast proxy/cache servers running both at the end-user’s site and at the base station. HTTP requests coming from the user’s web browser are transparently intercepted and checked against a local cache at the user’s terminal. Whenever this cache contains a “fresh” copy of the requested web-site content, it is directly sent back to the web browser. This eliminates the need for fetching the web content from the Internet. In order to improve the cache hit ratio of the local cache, two different update mechanisms are used: (1) the replies to requests from individual users are multicast by the base-station IMPPS proxies; i.e. all users update all user-terminal caches with their individual requests. (2) Web content that is expected to be interesting to the user community can be pushed into the user caches by ISPs. The software is highly portable and has been implemented so far on Microsoft Windows 98/2000/XP, Solaris and Linux operating systems. A potential market for the IMPPS software are backbone providers offering global content and Internet service providers that are looking for an efficient delivery system for local and regional content.
A significant amount of new propagation information has been obtained on the effects of vegetation and non-uniform rain. Telenor and CCLRC will exploit the results to improve the design guidance issued by ITU-R recommendations on millimetre radio access systems. Input documents will be written with clear advice on how the relevant recommendations should be improved, in particular on the effects of and how to alleviate vegetation caused distortion and rain attention. The new knowledge will also be incorporated in courses and education. The ITU-R recommendations in the field will become better, to the benefit for all radio communication. Also frequency regulatory bodies, either national or international, need the best possible propagation information.
Although European countries early identified the 40.5 –42.5 GHz as suitable for multimedia, included return or communication later and expanded it finally up to 43.5 GHz it has taken time to make use of the band. In 2000 EMBRACE did provide inputs for CEPT on the deployment of this band in the form of super frames or blocks. These were, in fact, accepted and became a recommendation. This is considered important in the motivation of taking this particular frequency range into use. Telenor has exploited the issued frequencies in the 40.5 GHz to 43.5 Hz band by allying for and obtaining a licences in Norway. Also the contribution to CEPT allowing for both TDD and FDD is important for the future efficient use of these bands. Telenor and TUCR will further pursue frequency standards within this band, in particular within Spectrum Engineering group SE19 of the CEPT/ERC. Faster deployment of access systems at 40 GHz is important, as here there is a sufficient large bandwidth for true broadband to many users simultaneously. Lower frequency bands may face difficulties in managing such a challenge; in some lower frequency bands it will be impossible to reach beyond a fairly limited number of users due to interference.
EMBRACE has studied traffic patterns taking available information from open resources in order to evaluate the potential business case. The operators have a prime interest in this area, but also a university study was performed in relation to Eastern European cities. The scenarios worked out have also been used for traffic modelling and technical and economical studies (Business, Soho, residential, mass market). Telenor and Telewest are planning to provide broadband services to their national residential customers. Telenor, additionally, has firm plans to continue being interested in the markets abroad. Radio based technology is a good candidate either in competing environments with other service providers or alternative cable based technologies and where no infrastructure or suitable access network exist. In particular Telenor has kept an interest for some Eastern European locations, such as in the Czech Republic. In Norway Telenor has a licence in the 40.5 to 43.5 GHz band, which it intends to use given there is appropriate equipment available. Telenor intends to make use of broadband fixed wireless access networks as backhaul for cellular mobile systems, such as UMTS. The millimetre cellular system offers large enough capacity to serve other base stations as well as individual users. In this fairly early period for broadband access delivery it has often been argued that radio access is for the business market to replace leased lines. This seems to be an argument pursued by vendor industry in accordance to their business plans. However, realising that low-cost solutions are possible it becomes evident that small and medium sized business, small offices, home office, organisations, public services, community authorities as well as individual residents will take advantage of the system. In fact, the vendor industry would get the invested money back also if the systems were targeted for the mass market. With the approach of low-cost systems, Europe will gain the lead both in penetration (or utilisation) and production of equipment.
Both individual users and community regulatory authorities are very interested in efficient spectrum utilisation. A number of investigations has resulted in convincing material in favour of time division duplex techniques, new multiplexing methods, efficient synchronisation, adaptive modulation and coding and efficient design of MAC protocol for multi-service system with many subscriber terminals. Telenor and TUCR will exploit the results for contributions to standardisation work for future broadband fixed wireless access systems. In a competitive market both vendors and operators have to pay considerable attention to cost-effective solutions. The results of particular interests are: potential in time division duplex, multiplexing methods, effective synchronisation, and adaptive modulation and coding. The manufacturers TUCR and Ericsson Lab Italy consider carefully making equipment based on these results in the future. From the community point of view better frequency utilisation means more services for the same allocated bandwidth, and more operators can be allowed usually beneficial for the end users. Hardware developers will find the results on TDD interesting as the technology do offer better spectrum utilisation and critical technical parts will be cheaper as a diplexer is not needed. With larger degree of integration the TDD system may even become cheaper than the alternative FDD system. A mixed traffic including broadcasting and communication will be seen beneficial to large parts of the populations. Given that a broadband system to the people is feasible, it becomes evident that a large number of smaller industries can take advantage of that. Creating business where people live has a great impact on the environment, traffic and transport. The results on synchronisation are directly beneficial to lower the cost of radio equipment e.g., by relaxing oscillator's stability. As there will always be some signal processing necessary, the added software complexity on connection with synchronisation schemes cost little extra, but may lower the equipment cost considerably.
Research work was concentrated to what extent the microwave hardware of FRA systems can be made less expensive by the application of advanced signal processing. It is recognised that one of the most expensive requirements of a microwave equipment operating at high microwave frequencies - at 40 GHz or so - is high frequency stability. If this can be lowered by the application of (even complex) signal processing, the expenses can be decreased. Namely, digital signal processing is rather cheap, in particular if some signal processing must anyway be applied and consequently the equipment contains FPGAs. The impact of such result can finally be a wider or earlier spreading of these systems in broadband communications. The possible application of not-extremely-stable oscillators requires efficient frequency estimation and phase recovery methods. Various frequency and phase estimation methods were described, investigated in detail and factors influencing their performance categorized. The thorough simulation studies give hints for the equipment designer to design equipment architecture (decision directed or non-decision-directed methods etc) and to design signal format (e.g. frame structure, preamble length, etc). The impact of these studies is thus: as giving methods for compensating the effects of oscillator instability, they make possible to apply cheaper oscillators.
The idea of providing diversity routes across a broadcast RFA network using MPLS techniques is a major development of packet network architectures. A user station may optionally be connected to two (or more) base stations. One of the routes is defined as the direct flow whereas the other route(s) are designated as shadow flow(s). Shadow flows will become active when a rain fade is detected on the direct flow. The shadow flow will carry a duplicate IP stream through a different MPLS labelled path and will recombine with the direct flow on leaving the diversity domain taking good packets from either flow. Shadow flows will be turned off once the rain fade is over. This diversity routing mechanism is purely asynchronous and will allow packet flows that differ greatly in their timings both at the exit router and at any intermediate routers. The project has also looked at synchronous techniques and to deploy space-time or route-time coding. This is very promising and a large additional code gain is achieved. The CCLRC will look to develop interest in these techniques by direct involvement with the IETF committee on MPLS and by promoting these ideas with the UK academic network, JANET (UKERNA), which is also sited on the same site as CCLRC. The diversity solution supports the idea for combined business market and mass market since the business market can be offered better service availability and capacity but still using a mass market system. The combination of diversity and nomadic mechanisms using extensions to MPLS would result in a significant change in how IP networks and packet routing is handled.
The propagation and optimisation models developed in the project are already implemented in software, using proper windows-based graphical user interfaces. It is believed that the optimisation techniques used is unique and well in advance of anything that is available in current commercial planning tools. While still at the development stage, these tools are a "proof of concept" that could rapidly be developed into a full commercial product. Both CCLRC and UWC (Cardiff University) have previous experience of commercialising propagation and network planning software by means of spin-out companies. Consideration will be given to the best means of moving these tools into the commercial sector. In the price-sensitive market of broadband delivery, tools for designing networks based on "profit" optimisation will be essential in competing with other services, and for achieving the best possible network design The optimisation/planning tools are also very useful in the initial concept phase of planning new networks as they can be used to investigate the sensitivity of profit to the business cost model parameters.
Research work leading to this result was concentrated to the following: to what extent can the microwave hardware of FRA systems such be made more economic i.e. less expensive, by the application of advanced signal processing. It is recognized that one of the most expensive requirements of microwave equipment operating at these microwave frequencies is high power. If this can be lowered by the application of (even complex) signal processing, the expenses can be decreased further. Improvement can lead to cheaper equipment by decreasing the RF power needed or lead to cheaper systems by decreasing the occupied bandwidth. The results are based on the recognition: a route diversity system is a particular multi-antenna (or: MIMO) system. If the signals transmitted by the two base stations are regarded as one entity and appropriate coding is applied, significant coding gain can be achieved (according to simulation results gain of 6-18 dB). Or, puncturing the codes, coding gain can be traded off to decrease occupied bandwidth (say occupied bandwidth can be decreased by 25% still realising coding gain of about 6 dB).