Lecture Series in Mobile Telecommunications and Networks (1583KB)

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From plain old Telephony to flawless mobile audio communication have been converted, to introduce wideband services everywhere, where you have the GSM phone. However, that is not a standard but just an idea from research. Mobile audio – communication Now we have nice coding schemes, you might introduce wideband, super-wideband, or artificial extension or whatever, but we have adverse conditions on the radio channel and we need error protection. There are very sophisticated techniques. You have heard about turbo-coding, turbo error protection, turbo error correction and error concealment. 4 Turbo error protection The turbo concept can be extended, which was originally defined for two channel codes which help each other in an iterative way at the receiver. It can be extended to a channel decoder and to a source decoder. At the receiving end, we have a channel decoder which produces soft information – and soft information means that the channel decoder does not produce 0 and 1, but it produces reliability information. It says, eventually it is 0 or 1, with the probability. Then we have a soft decision source decoder, where the decoder exploits some residual redundancy which is still in the parameters. If we model the speech tract, the vocal tract, then the parameters evolve more or less smoothly, because we do the analysis every 20 milliseconds, 50 times per second, and the vocal track doesn’t make any jumps. There is still correlation in the parameters – and redundancy in terms of the distribution. The parameters are not white noise. This can be used such that we do a preliminary parameter decoding and we exploit the redundancy on the level of the parameters, and we feed that information back – it is called extrinsic information – through the channel decoder and the channel decoder tries once more. There is a second decoding using the knowledge from the channel end, the additional auxiliary information from the source decoder. In this slide, the source decode has better information and can improve once more and so, by several iterations, you have iterative source channel decoding and we can improve tremendously. Example 5: iterative source-channel decoding Let’s listen to one example of how we can improve by spending at the receiving end on just additional signal processing complexity. If the channel is clear, we do not need it but, if the channel is getting worse, we can improve it by additional processing. [Example of speech recording played] In this case, we used just plain PCM to demonstrate the concept. [Music played] We can maintain the quality if we are allowed to use this complexity. Mobile audio – communication Now I would like to share a vision of what more we can do than just introducing wideband and artificial wideband extensions. Iterative source-channel decoding (ISCD) This is a comparison with state-of-the-art decoding, where we have hard-decision decoding that is table look-up decoding in the source decoder, or soft decoding in the source decoder without iteration. We then do some iterations – here, in this case, it is 10 iterations – and we see a significant improvement. This is the parameter signal-to-noise ratio, the quality of the filter coefficients of the speech model, for example. This is the channel quality here, and we have a good channel here, and a bad channel. If we have a demand for a certain quality, we can maintain it, even in very adverse channel conditions. The Royal Academy of Engineering 53
4 Vision: ambience audio communication The vision is very simple: let’s call it ambience audio communication – or, you could say, stereo of binaural telephony. What is it good for? We would like to have a situation where the quality is as in a face-to-face communication. In binaural telephony you transmit, so to speak, a picture of the audio environment, which is interesting if there is more than a single person at one end, because you have spatial information. What we need is the wireless transmission of two channels in both directions. Ambience audio conferencing There is a special situation where you might agree that this could be useful: attending a meeting, for example. Everyone who has attended telephone conferences which take two hours, with 10 participants from seven countries, knows that it would be desirable to have such a device. You might send your dummy head to the meeting, or there could be some dummy head, with two microphones and a loudspeaker. In this case, we have binaural transmission only in one direction. Sitting here, in the environment B, you get the directivity, the spatial information. You have to have wideband or super-wideband. If you use that, you will save a lot of travelling costs and time: you will like it, I can tell you – we have some experience of it. By the way, environment A is the meeting room at the airport and environment B is a nice spot at the beach where you can attend the meeting. The experimental binaural headset We have done some experiments with the dummy head. Here are the ear canals and the microphones are placed there so that we can make measurements. The transparency you get is amazing. You cannot buy it yet, but you can get an idea about it. Wireless (narrowband) speech communication There are some nice devices, including the earset from Bang & Olufsen: it is still mono and it is still narrowband. It has a microphone here and only one earpiece, but such implementation is not far off. You get some impression about how attractive and relaxing audio communication could be. Ambience audio communication We need stereo coding, and there is stereo coding even for the AMR wideband plus. There is an mpeg codec and there are recent developments with new versions and additions of codecs that will be available by the end of this year, so we can do it. 5. Conclusion: flawless mobile audio communication My conclusion is that flawless mobile audio communication is feasible because the coding technology is available, or will soon be available. We have wideband coding and super-wideband coding in mono and stereo and, if we have to use the GSM network, there is a bit rate for the wideband codec which can be transmitted over GSM. There are higher 54 The Royal Academy of Engineering
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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 and 48: From plain old Telephony to flawles
Page 49 and 50: You can see that there is much room
Page 51 and 52: 1024, we transmit 10 bits, so to sp
Page 53: Bandwidth extension with hidden sid
Page 57 and 58: Questions & Answers Michael Walker:
Page 59 and 60: I said five years ago and what I he
Page 61 and 62: them and perhaps leave out some of
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Lecture Series in Mobile Telecommunications and Networks (1583KB)

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