Lecture Series in Mobile Telecommunications and Networks (1583KB)

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From plain old Telephony to flawless mobile audio communication bit rates which are more transparent for non-voice signals. In the not too distant future, UMTS LTE might be available within the next two or three years. We have AMR wideband-plus and higher bit rates, and new stereo codecs. In the future, we will no longer need to distinguish between speech and audio. The wireless network technology is not a bottleneck The wireless network technology is not a bottleneck. Even if there is a severe coverage problem, we have the GSM network. We have a fallback solution, and we have the fallback modes of the AMR codec. Even with a GSM network, we can employ bandwidth extension eventually, with hidden side information which supports the introduction which is much cheaper but which gives a clear impression of wideband coding. Finally, if we have UMTS LTE, we have plenty of bit rate and there is no alternative to true wideband coding: if you can afford to do true wideband coding, the quality is better than that of artificial wideband extension, and better than the lower rates of the AMR codec. We can preserve the quality of adverse channel conditions if we apply processing power – a turbo process at the receiving end. Therefore, my conclusion is that a mobile phone does not have to sound like an old telephone but can sound significantly better and we can hopefully expect terrific improvements in the future – even in the near future. There is a vision that binaural stereo communication might become a new philosophy. That is an interesting discussion. Is it just a further step in improving the quality, or is it a new world? If you remember the introduction of the Walkman, until then no one had thought of running through the forest with stereo equipment, but how it has changed our way of listening to music. It might be that binaural telephony will do a similar job, and wideband is the first step to increased intelligibility and naturalness, such that it is more or less comparable with face-to-face communication. From plain old telephony to flawless mobile audio communication I would like to finish my talk with a recent statement by Peter Isberg from Sony Ericsson. He said: “Despite the challenges, wideband will be the most significant quality upgrade in telephone history. Mobile phones will surpass traditional fixed line phones in terms of speech quality.” Thank you very much. [Applause] The Royal Academy of Engineering 55
Questions & Answers Michael Walker: Thank you, Peter, for that splendid talk. Peter has agreed to take questions, so we have the opportunity to tease out more information. John Lowe (Institution of Mechanical Engineers): Thank you, Peter – it is a fascinating future that you have described. What worries me is the duplication of standards between the three territories of the Far East, Europe and North America. Could you fill us in on the prospect of some compatibility or singularity of direction? Peter Vary: Yes, that is a very good question. We have many standards – perhaps too many – but this is also evolution. We are in the happy situation that, in the meantime, we have worldwide agreement on two sides. One is the ITU (International Telecommunications Union), which is more or less responsible for fixed line, voice-over IP business. On the other side we have what is called the 3GPP (Third Generation Partnership Programme). They talk to each other and take over the standards we have for cellular radio meanwhile in the ITU world. Things are getting better. There will be many different standards but there will be a convergence, I am pretty sure but, for reasons of compatibility, you will need to have the old codecs. I have a collection of some old phones – my first one is the Motorola shown on the slide, and it still works. If I switch it on, it says that it is no longer compatible with the system, but it works. We have to keep the compatibility but, on the other side, it is not too expensive because it is just software – but, saying that it is ‘just software’ means that most of the signalling processing is carried out on a programmable signal processor in the mobile phone. You have a lot of memory there and selecting a different codec is just a matter of selecting a different part of the memory where you have the programme for the codec A, B, C, D, E. It is not that difficult, but it is more difficult than in the old world where you just had one or two different versions of A-law PCM and Mu-law PCM. It is becoming more difficult but it is not too expensive. Professor Ralph Benjamin (Visiting Professor, Bristol University): Right at the beginning, you mentioned the importance of understanding the physiological constraints on speech generation as a guide to the optimum use of a limited number of bits in the information, which will probably be even more important in speech extension, bandwidth expansion, or in turbo decoding. However, this is only one of probably three separate elements because you also have the constraints of language and dialect. In American southern states, people talk with a long drawl; other languages are totally different from English and, in one extreme, some African languages consist of a lot of staccato clicks. The features you have to encode depend rather critically on this. A third feature might be that different elements in your speech may be of different sensitivity in terms of recognition and understanding, or acceptability by the user. You may need rather a clever combination of those three features to make the best use of the information in encoding in the first place, or in knowing which preamble or supporting parameters are required to tell you how to do your bandwidth extension. Thank you. Peter Vary: The standardisation of the different speech codecs is always based on subjective listening tests. In the codec competition, different companies are proposing codec candidates and there is no objective measure that is so reliable that you can rely on the objective measure. Therefore, we need subjective listening tests, which are very expensive, in different languages, with native listeners and native speakers. That, first of all, is a necessary constraint which is fulfilled for the coding part. For bandwidth extension, I can tell you that it makes a big difference to apply bandwidth extension for German or French or Japanese. You hear the variation and it might work better for one language than for another. You could implement a language switch, or language recognition, or something like that. That is why the artificial bandwidth extension without any side information is only the second best solution: it gives you some wideband impression and sometimes it works well. If you could adapt it to the speaker, then it would be very nice. Therefore, the proposal to add side information – in that case, the concept will hide these bits in the bit-stream, but we first have to get the bits. This is done in such a way that, at the transmit side, we have the higher frequency band and then we apply there locally the artificial bandwidth extension and we compare it with the original. We then transmit the correction terms as hidden information to the receiver. If you have a strange language there, hopefully the 56 The Royal Academy of Engineering
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Lecture Series in Mobile Telecommun
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Foreword This compilation brings to
Page 5 and 6: From wireless networks to sensor ne
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Page 23 and 24: Welcome and introduction Professor
Page 25 and 26: ComReg Collection - Start 16/Apr/20
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Lecture Series in Mobile Telecommunications and Networks (1583KB)

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