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dimensional problem, but the principle is the same.) Take every other symbol in each group and repeat the procedure for each tree limb. He next described a method of assigning the encoded bit stream onto the symbols in a very systematic procedure. Once this procedure was fully described, his next step was to program the algorithms into a computer and let the computer search for the best codes. The results were astonishing. Even the most simple code (4 state) produced error rates nearly one one-thousandth of an equivalent uncoded system. For two years
Ungerboeck kept these results private and only conveyed them to close colleagues. Finally, in 1982, Ungerboeck published a paper describing the principles of trellis modulation.
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34.3 kilobits/s (limited by maximum power regulations to 33.8 kilobits/s). Today, the most common trellis-modulated V.34 modems use a 4-dimensional set partition—achieved by treating two two-dimensional symbols as a single lattice. This set uses 8, 16, or 32 state convolutional codes to squeeze the equivalent of 6 to 10 bits into each symbol the modem sends (for example, 2,400 baud × 8 bits/symbol = 19,200 bit/s).
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Though hard to visualize in multiple dimensions, a simple one-dimension example illustrates the basic procedure. Suppose the symbols are located at . Place all odd symbols in one group, and all even symbols in the second group. (This is not quite accurate, because
Ungerboeck was looking at the two
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modulation at 2,400 baud (symbols/second). This bit rate ceiling existed despite the best efforts of many researchers, and some engineers predicted that without a major upgrade of the public phone infrastructure, the maximum achievable rate for a POTS modem might be 14 kbit/s for two-way
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had published a standard, V.32, for the first trellis-modulated modem at 9.6 kilobit/s (2,400 baud and 4 bits per symbol). Over the next several years further advances in encoding, plus a corresponding symbol rate increase from 2,400 to 3,429 baud, allowed modems to achieve rates up to
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for POTS lines (approximately 35 kbit/s). Ungerboeck's theories demonstrated that there was considerable untapped potential in the system, and by applying the concept to new modem standards, speed rapidly increased to 14.4, 28.8 and ultimately 33.6 kbit/s.
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invented trellis modulation while working for IBM in the 1970s, and first described it in a conference paper in 1976. It went largely unnoticed, however, until he published a new, detailed exposition in 1982 that achieved sudden and widespread recognition.
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Forney, G. David; et al. (September 1984). "Efficient modulation for band-limited channels".
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scheme that transmits information with high efficiency over band-limited channels such as
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derives from the fact that a state diagram of the technique closely resembles a
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536:, for the history of various encoding modulations from 0.3 to 56 kbit/s
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14 kbit/s is only 40% of the theoretical maximum bit rate predicted by
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G. Ungerboeck, "Channel coding with multilevel/phase signals,"
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communication (3,429 baud Ă— 4 bits/symbol, using QAM).
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A flurry of research activity ensued, and by 1984 the
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may be too technical for most readers to understand
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443:Learn how and when to remove this message
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27:Modulation scheme in telecommunication
500:International Telecommunication Union
425:make it understandable to non-experts
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379:by employing four bits per symbol
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619:Oral-History:Gottfried Ungerboeck
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598:"ITU-T Recommendation database"
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375:) typically achieved 9.6
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471:. The scheme is basically a
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369:plain old telephone service
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237:Capacity-approaching codes
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489:mapping by set partitions
635:Telecommunication theory
341:Trellis coded modulation
542:, in the article about
514:IEEE Trans. Inf. Theory
396:A new modulation method
174:Hierarchical modulation
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357:Gottfried Ungerboeck
544:convolutional codes
363:In the late 1980s,
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96:Digital modulation
18:Trellis modulation
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389:Shannon's theorem
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53:Analog modulation
16:(Redirected from
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302:Multiplexing
242:Demodulation
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247:Line coding
629:Categories
550:References
475:of rates (
349:modulation
37:modulation
463:The name
584:13818684
528:See also
229:See also
34:Passband
465:trellis
419:Please
347:) is a
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534:Modems
485:symbol
377:kbit/s
365:modems
155:SC-FDE
580:S2CID
252:Modem
373:POTS
292:OFDM
221:THSS
216:FHSS
211:DSSS
125:MFSK
110:APSK
572:doi
423:to
381:QAM
345:TCM
297:FDM
287:ΔΣM
282:PWM
277:PDM
272:PCM
267:PAM
262:PoM
257:AnM
206:CSS
188:WDM
183:QAM
165:WDM
160:TCM
150:QAM
145:PSK
140:PPM
135:OOK
130:MSK
120:FSK
115:CPM
105:ASK
87:SSB
77:QAM
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