Shaping of signal constellations
Başlık:
Shaping of signal constellations
Yazar:
Deliot, Eric, author.
ISBN:
9780438084964
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (161 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Özet:
This thesis is concerned with the shaping of signal constellations. Shaping is a relatively new approach to making telephone modems more energy efficient, and although the gains obtained are modest, they can be achieved without great complexity. Furthermore shaping can be combined with coding to give systems with very good energy efficiency and lower complexity than if coding was used alone. In this thesis though, we look at the performance of shaping without coding. We first introduce elements of the theory of shaping. We explain that shaping multi-dimensional constellations is equivalent to using non-equiprobable signalling with two-dimensional (2-D) constellations. We evaluate the influence of the shape of the 2-D probability distribution on the shaping gain and show that the main concern of practical shaping schemes is the mismatch between achievable entropy and required information rate. We then review the existing main shaping techniques. We briefly describe a few methods using variable length codes, Voronoi regions and generalised cross-constellations but concentrate on three practical schemes: shaping on regions, trellis shaping and shell mapping. Shaping of signal constellations is certainly advantageous on analogue channels but the influence of Pulse Code Modulation (PCM) codecs, which are present in increasingly large numbers within the telephone network, needs investigation. We model a modem-to-modem link containing several PCM codecs and use this to assess the effect of PCM on shaping. Surprisingly, we show that shaping performs better on PCM channels than on the Gaussian channel. The origin of the extra-gain is analysed. Since shaping is potentially useful in many circumstances, we continue our work by developing shaping techniques. One method combines Shell Mapping with Trellis shaping (SMT) and gives good symbol and bit error performances but is quite complex. Another proposed technique uses block codes and is presented in two slightly different variants: ring-Block Shaping (ring-BS) and point-BS. We develop a method of constructing optimum ring-BS codes. Finding optimum codes for point-BS is an intractable problem but we show that ring-BS codes can be used successfully for the point-BS variant. We show that point-BS is very competitive with existing shaping schemes.
Notlar:
School code: 1543
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(686914.1) | 686914-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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