Wireless Waffle - A whole spectrum of radio related rubbish
Mobile Spectrum Demand: The Last Word?signal strength
Sunday 31 August, 2014, 12:28 - Spectrum Management
Posted by Administrator
Yet another challenge to the seemingly overinflated forecast demand for IMT spectrum has been raised. This time, a paper entitled, 'Overestimating Wireless Demand: Policy and Investment Implications of Upward Bias in Mobile Data Forecasts' which has been written by Aalok Mehta of the University of Southern California and J. Armand Musey of Goldin Associates.

http   www allbum it  zager evans in the year 2525 2Rather than do the maths on what their paper says, Wireless Waffle thought that it might be better to take a different approach and try and estimate how much spectrum may be needed in the far future, say in the year 2525. How much data could each person possibly consume? If it is assumed that each person lives in a totally immersive environment where there visual, audio and maybe even sensory experience is completely connected (a bit like a man-made version of The Matrix!) the question is how much data would this take?

There are three things to consider:
  • Firstly how much data is needed for such an immersive experience;
  • Secondly, how much progress will have been made on the various audio and video codecs which squish the raw data into a more manageable form; and
  • How spectrally efficient will the mobile technology be?

Video is currently the main bandwidth hog and whilst touch, feel and smell may turn out to be equally hungry for connectivity, let's focus on the video requirements first. If it is assumed that 3D video using ultra-high definition is required, today this would require a connection of 40 Mbps or faster. With improvements in coding technology, this could easily drop to 10 Mbps. If audio and other sensory data (including any personal machine-to-machine communications detecting, for example, heartbeat, ambient temperature and so on) doubles this, then a working assumption that a constant 20 Mbps of connectivity would allow a fully immersive experience would seem about right.

Finally we need to think about spectrum efficiency - how much spectrum would be needed to deliver this 20 Mbps. Current technologies such as LTE can deliver many bits per second per Hz of spectrum but performance becomes worse the futher away from the centre of a cell a user is. The ITU's model uses values of up to 5 bits per second per Hz in a 2020 timeframe, though other forecasts show values ranging from 2 to 15. By 2525, it ought to be possible to at least achieve the 5 bits per second per Hz value that the ITU forecasts is feasible by 2020, even as an average across a cell, and even those at the edge of coverage. This means that (whilst awake and living in the immersive environment) our mobile subscriber of 2525 would require around 4 MHz of spectrum dedicated to their sole usage.

How much spectrum is needed is therefore simply dictated by how many simultaneous users there are in each cell. Looking at this from a different direction, with around 1 GHz of mobile spectrum (not that different from the amount available today), 250 users could be supported in each cell. This seems perfectly realistic. Of course this amount of data would not be required by anyone who is asleep, and those at home or in an office could surely connect to the WiFi of the future and offload their data to an alternative service so 250 users per cell does not seem unreasonable.

So... even in a futuristic world in which everyone is immersed in a fully interactive environment for every waking hour, given developments in technology, 1000 MHz of spectrum dedicated to mobile networks seems sufficient. This result ties in with an interesting result posited by the Australian spectrum regulator ACMA in its report 'Towards 2020 - Future spectrum requirements for mobile broadband' (Figure 4.3) which indicates that spectrum demand may decrease in the future as the spectrum efficiency of newer technologies and improved coding techniques outpace the exponential growth in demand for data.

It therefore seems possible that we are going through a period in which spectrum demand for mobile broadband is at its peak as we phase out older mobile technologies and bring in the new and that in the long-term future, the amount of spectrum already available today will be enough to meet requirements. With this (albeit rather simplistic) analysis, we can now close the door on all the debate over spectrum for mobile services and instead focus on something more interesting...
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ITU forecasts 'from another planet'signal strength
Wednesday 9 July, 2014, 08:57 - Spectrum Management
Posted by Administrator
According to an article in DigitalSpy (and several other sources) UK mobile operator EE have announced that during the recent Glastonbury Festival, 0.74 TeraBytes (TB) of data was uploaded and 2.49 TB of data was downloaded (a total of 3.23 TB). EE built a special network at the site as part of its role as the sponsor. However it would be reasonable to assume that the other 3 mobile operators in the UK also carried traffic and despite them not having bespoke networks, designed to cover the event, let's give them the benefit of the doubt and assume that they carried as much traffic as EE. Thus, the total traffic from the event would be 12.9 TB.

It is interesting to compare this level of traffic with that which is predicted by the ITU spectrum demand forecast model that Wireless Waffle has discussed several times in the past. First some facts and figures about the festival:
  • The 2014 Glastonbury festival ran from 25 - 29 June inclusive - 5 days in total.
  • The area of the site is approximately 900 acres, which is 3.6 square km.
  • Around 135,000 people attended the festival.
glastonbury 2014We can therefore calculate some traffic figures and compare these to the ITU's forecasts. First of all, the easy one: 135,000 people in an area of 3.6 square kilometres equates to 37,500 people per square kilometre. The ITU's model shows up to 222,333 people per square kilometre in the densest (albeit urban) areas, but it would be hard to imagine an area more densely populated than that surrounding the festival, even in Central London.

There was 12.9 TeraBytes of data traffic over the 5 day event, the equivalent of 78 TeraBytes per month if the same level of traffic was to continue over a whole month. This equates to 21.7 TB per month per square kilometre. For a densely populated (urban) area, the ITU's forecasts show 30 to 100 PetaBytes per month per square kilometre, 1,400 to 4,700 times more than was consumed by revellers at Glastonbury.

Finally, if 78 TB of data was generated by 135 000 people, this equates to 578 MegaBytes per person per month. Compare this with the 212 GigaBytes per person per month preducted by the ITU, and we find a that the ITU's values are 366 times larger.

itu live on another planetSo the ITU's traffic forecasts for 2020 show traffic density over 1,500 times greater than that which was generated at Glastonbury, with individual (per person) traffic that is 366 times larger. Even given the likely growth in data between 2014 and 2020 (which the ITU's highest forecasts indicate a growth of a factor of 14 times), the ITU's figures remain far in excess of any reality - at least any reality that exists on planet Earth. Just what the value of a set of forecasts that might be valid on Kepler 22b is, is anyone's guess. Perhaps that's where the ITU spends its summer vacation?
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Who's zoomin' (in on) who?signal strength
Tuesday 17 June, 2014, 15:21 - Satellites
Posted by Administrator
google space logoThere is growing evidence to suggest that Google is planning to enter space by launching satellites of its own. Two seperate pieces of news point in this direction. Firstly, Google has announced plans to purchase Skybox. Skybox operates low-earth orbit satellites whose purpose is to take high resolution images, of exactly the kind that are used by Google maps. Following the recent lifting of US government restrictions on the use of images with better than 50 cm resolution, the move by Google to own its own earth imaging satellites makes complete sense.

Secondly, there is talk of Google becoming involved in the delivery of broadband via satellite through a network called WorldVu. WorldVu, if it goes ahead as described, suffers from many of the same problems that O3B will, but has a lot more to deal with due to its use of Ku-Band as opposed to O3B's use of Ka-Band.

Why is the use of Ku-Band more complex? Ku-Band is already very heavily used for satellite broadcasting, as well as for a number of satellite broadband networks (e.g. networks such as Dish in the USA). As it is proposed that the WorldVu network will be non-geostationary (e.g. the satellites will move around in the sky as seen from the Earth), the downlinks will have to be switched off when the satellites are in a position that could cause interference to existing geostationary satellite services (which will generally be when the WorldVu satellites are over the equator, and whilst a few degrees either side of it). This is made worse because any uplink that could cause interference also needs to be switched-off as well if it is pointing at the geostationary arc. The same is true of O3B, but the more dense packing of Ku-Band satellites will make the situation far more complex.

For example, there are over 60 Ku-band satellites visible in the sky in the UK. As the arc as viewed from the UK is 70 degrees from end-to-end, this means there is approximately one satellite every degree.

geostationary arc from uk
Source: satellites.co.uk

All of this switching on and off every time a satellite is over the equator (and, of course, when a satellite disappears beyond the horizon), and the requisite requirement to connect to a different satellite at those times to maintain a connection is both complex and also creates the environment for tremendous problems with 'dropped calls', if handover between satellites fails for any reason. Similarly, this switching will cause severe jitter (changes in timing) which in itself can cause problems for some internet applications (e.g. streaming).

Finally, and probably the weirdest issue with WorldVu, is the antennas that are planned to be deployed for user ground stations. It is suggested that Google plan to use antennas based on meta-materials. O3B have also, apparently, signed a deal to work on the development of meta-material based antennas. But at present such antennas have been proven only at Ka-Band (and then only in a developmental and not commercial form), and not at the Ku-Band proposed by Google. Even if they could be made to work at Ku-Band, there would be a loss in efficiency making transmission from Earth to space next to impossible and the fact that the antennas can only be steered around +/- 45 degrees will mean that some satellites, even when in view, will not be able to be connected to.

There is a suggestion that Google's purchase of Skybox will provide a potential platform for an early launch of the WorldVu space segment. One the one hand it makes some sense. If you are launching one satellite, why not make it multi-purpose. Though it would increase the size and weight of the satellite, and the launch cost too, having the cameras directly connected to the Internet might make sense. Then again, eyes in the sky connected to the Internet is eerily similar to the world-changing paradigm that is posited in Arthur C. Clarke's book, The Light Of Other Days. Big Brother will definitely be able to watch you, as will your neighbour, your partner, the government, and anyone else with voyeuristic tendencies who wants to. Who's zoomin (in on) you?

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Trains halted by 'Wrong Kind Of Programme'signal strength
Wednesday 11 June, 2014, 09:00 - Spectrum Management
Posted by Administrator
You would have thought that those designing systems that use the radio spectrum would check that the frequencies they planned to use would not cause interference to other systems and equally importantly that they would not suffer interference from other users. Such basic compatibility checks are critical to ensure that different communication systems can inter-operate successfully. So it is a bit of a surprise to find that the designers of the Eurobalise, a technology that forms part of the European Rail Traffic Management System and whose purpose is to assist in the control of train movements (to control their movement and help them know where they are) has chosen a frequency which fails these simple safeguards.

ertms eurobalise

Where they have gone wrong is to use a frequency for transferring information between the Eurobalise and the train that is in a European broadcast band!

yellow eurobaliseThe Eurobalise uplink operates on a centre frequency of 4234 kHz, with a frequency deviation of +/- 282 kHz. This means that a logic '1' is sent on a frequency of 4516 kHz and a logic '0' is sent on a frequency of 3952 kHz (source: Mermec Eurobalise specification). Interfering signals on, or near, frequencies of 3952 or 4516 kHz would cause the most trouble, but as the Balise's receiver is listening across the whole range 3952 to 4516 kHz, any transmission in this range would cause a problem. The (European) 75 metre broadcast band runs from 3950 to 4000 kHz. Any broadcasts in the 75 meter band could therefore cause a problem to nearby trains, but those on frequencies from approximately 3950 to 3955 kHz will have the greatest potential to interfere with the Balise's operation.

Do any such transmissions exist? According to short-wave.info, the BBC and Korean broadcaster KBC use a frequency of 3955 kHz on a daily basis, from the BBC's transmitter at Woofferton, Shropshire. If you click on the link (which will take you to Google maps) you will notice that running alongside the village of Woofferton is a grey line - a railway!

But surely fears of interference are unfounded and just another example of scare tactics by spectrum managers bent on safeguarding their highly paid jobs. Sadly not... It appears that the transmissions from Woofferton have been disrupting trains between Leominster and Ludlow! According to the article in the Hereford Times, Network Rail, the organisation responsible for operating the rail infrastructure in the UK, claim:
while the interference does not pose a risk to the safe operation of the railway, it has been stopping trains en-route.


soldiers stop trainThe only other high power transmitter in this band in Europe is at Issoudun in central France. A quick check of Google maps shows that there are no train tracks in the immediate vicinity. There is a transmitter in Kall-Krekel in north west Germany which also uses frequencies in the 75 metre broadcasting band that could also cause interference to Eurobalises, but that transmitter uses much lower power than those at Woofferton or Issoudun.

Maybe, given that there is only one potential location where the choice of frequency, and proximity to a broadcast transmitter, could be a problem, the designers did do their homework after all and decided that it was alright for occasional problems to arise. Maybe. Then again, the other frequencies used by the Eurobalise include a military band and the middle of the 27 MHz Citizens Band!
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