Lecture Series in Mobile Telecommunications and Networks (1583KB)

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From old telephony to audio communication A phone sounds like a phone because it is a phone and the main reason for that is because we have a limited frequency bandwidth, which comes from the old days of the old analogue telephone. The upper frequency limit is 3.4 kHz, which was specified in the old days when we had analogue telephones and we had frequency division multiplex on the long range connections. This was kept when we switched to digital, and it was kept when we switched to GSM. This is the reason why the intelligibility of syllables is only 91 per cent, which is not too much. Therefore, on some occasions, we need to use a spelling alphabet to communicate a name or term that you have never heard before. The original speech might have frequencies up to 10 kHz or even more. The idea is to improve the quality by increasing the audio bandwidth, perhaps from 3.4 to 7 or even more. This raises new questions, and that is what I would like to discuss in this talk. Mobile audio-communication 1.Technology evolution We have to discuss the technology in terms of the network, and in terms of the micro-electronics. We will then see what can be done as state of the art and in the near future to increase the audio bandwidth, such that we no longer need to make a distinction between speech and audio, and we increase the quality. If we have a better compression scheme, then the next question is, what is on the radio channel? We have a lot of interference and noise, but how can we protect and guarantee that, at the receiving end, we have the same excellent quality? Finally, I would like to share a vision with you – and that might be another topic for discussion. In the technology evolution in the network, there is the worldwide initiative NGMN on next generation mobile networks. This initiate was started by the leading network operators and the main goal is to increase - they are saying bandwidth, but it means bit rate - because this might be the driving force. The goals are very ambitious in terms of cost and performance, NGMN should be as close as possible to the digital subscriber line, the fixed network internet access. That is very ambitious but we, as engineers, like to have these ambitious goals. Evolution of data rates Let us look at DSL, which is a moving target because there are different versions. There is VDSL, for example with increasing data rates. We are presently somewhere here [on slide] and we can achieve reasonable data rates in the UMTS network – on the basic UMTS network, it is 384 kbits/s, but is depends how many users there are. If you study that more carefully, you can see that you can achieve 384 kbits/s, but perhaps five users at the same time because the data rate and the downlink is limited to 1.5 Mbits/s. However, there are efforts to increase it by HSPA (high speed packet access) in downlink and uplink and then you might really experience – and this is what my own experience is – that you will have 800 kbits/s or 1.2 Mbits/s and sometimes in the night perhaps even more in certain places. It was a decision of the NGMN initiative that their first solution would be the next generation of UMTS, which is called UMTS LTE. LTE stands for Long Term Evolution. The bit rate will be huge, and I do not know where the limit of this bar is but there is ongoing discussion about that. In any case, however, there will be plenty of bit rate. UMTS and GSM coverage in Germany – T-Mobile, Vodafone, 11/2007 What is the actual status? Let us look at Germany. This map is public information with the status at November 2007, but it has not changed much since then. I have tried to give it neutral colours so that you cannot distinguish whether it is T-Mobile or Vodafone but, in any case, you can see that they are very similar. The green indicates UMTS and the grey is GSM, or the GPRS with packet radio, or the EDGE system, and the white dots indicate those happy places where you cannot use the phone at all. The Royal Academy of Engineering 47
You can see that there is much room for improvement but, if you discuss it with the operators, they will tell you that that is already very expensive. For these green dots, the operators need 12,000 to 13,000 base stations already, and the coverage is 80 per cent of the population or even more. Perfect – but it is only 20% to 25% of the area and, if we compare that to GSM, for the grey area you need about 18,000 to 19,000 base stations, so UMTS is much more expensive. This has to do with the UMTS frequency band but it also has to do with the transmission scheme, with the CDMA concept (Code Division Multiple Access). The sales are smaller and there is a big question mark about whether UMTS will ever be available everywhere. What we can conclude here is that we will see increasing data rates but there is limited coverage and, therefore, with GSM, there will be the fall-back solution for a very long time. If we try to improve the audio quality, then we should take care to see that we transport the quality in the GSM network. What about the implementation and complexity? Every time we invent a new codec or a new radio interface, complexity increases because we are making progress towards the theoretical limits. We are trying to improve the quality, so what about complexity? Global system for mobile communications Technology evolution: Moore’s law All the time it is the same. I would like to go back about 20 years, when the GSM system was more or less stable and it was standardised. Experienced engineers in the company – I was with Philips – said that it would take 10 years or even longer until we would be able to implement it in mobile, because the GSM standard was so complex in comparison to the analogue FM radios that we had at that time, that the idea of the mobile should look like that. So much of the equipment is in the car and, to be honest, when we implemented the first test mobile station, it looked a little bit like that. This was in 1989. Just a few years later, in 1991/2, we had the first mobile, the Motorola International 3200. This was incredible progress in a couple of years. There are two reasons behind that. First, there is Moore’s law, which helps engineers to invent more complex things, and it says that the number of transistors on an integrated circuit has increased exponentially. The scale here is logarithmic, which means doubling approximately every two years. What does doubling mean? Implications of Moore’s law: 6 years later To get an idea, let’s take a chip of today and wait for six years. Six years is three times two, it is 2 to the power of 3, and that is a factor of eight. So we were able to reduce the chip size after six years, and we started the standardisation and then we entered the market and we were happy that the chips were becoming smaller and cheaper. On the other hand, if we have more space, we can also add additional functionality and new architectures. My conclusion for the voice service is that we should not worry too much about complexity, although that is a topic we could discuss. Mobile audio-communication Now let’s study the audio and speech compression schemes. In mobile radio, we use model-based speech coding, 48 The Royal Academy of Engineering
Page 1 and 2: Lecture Series in Mobile Telecommun
Page 3 and 4: Foreword This compilation brings to
Page 5 and 6: From wireless networks to sensor ne
Page 7 and 8: From wireless networks to sensor ne
Page 9 and 10: As far as the routing of packets is
Page 11 and 12: easons. In the internet, one never
Page 13 and 14: Implementation with laser pointers,
Page 15 and 16: here of laptops, and all these lapt
Page 17 and 18: adds a great deal of discrete compl
Page 19 and 20: Questions & Answers Mike Walker: Th
Page 21 and 22: Human beings will also evolve and w
Page 23 and 24: Welcome and introduction Professor
Page 25 and 26: ComReg Collection - Start 16/Apr/20
Page 27 and 28: evidence that people give in favour
Page 29 and 30: chunks of spectrum where you are in
Page 31 and 32: As an aside, I was reading a few of
Page 33 and 34: Of course, it is not just one mask,
Page 35 and 36: I apologise for hopping between top
Page 37 and 38: Questions & Answers Michael Walker:
Page 39 and 40: Nobody - believe you me, it came ou
Page 41 and 42: The second aspect of my comment is
Page 43 and 44: want to call it - that sits there a
Page 45 and 46: From plain old Telephony to flawles
Page 47: From plain old Telephony to flawles
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Lecture Series in Mobile Telecommunications and Networks (1583KB)

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