Pulse or digital communications – Repeaters – Testing
Patent
1991-04-22
1994-05-10
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
370 19, H04L 2728
Patent
active
053115503
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a transmitter as well as a transmission method which are particularly high-performance. The invention also relates principally to a receiver.
2. Discussion of Background
It is known to transmit ion by using modulated waves, such as, for example, electromagnetic waves. It is known to try to increase the transmitted information throughputs. However, the increase in the throughput more often than not comes through an increase in the band of frequencies used. Now, in the case of guided transmissions there is a limitation due to the passband of the channel, for example a coaxial cable or an optical fibre, whilst in transmissions over the air there are no longer sufficient frequencies to satisfy all the needs.
Moreover, the Patent Application FR 86 09622 published under the No. 2,601,210 describes a method of transmission using symbols A (f, t) . Each symbol corresponding to a frequency and a given transmission time. The transmission time not being fixed, the device does not use any means of fine synchronization, which thus limits the spectral response to approximately 0.7 bit/(Hz.s). Moreover, the French certificate of addition 86 13271 published under the No. 2,604,316 describes the use of devices for calculation of the discrete Fourier transform for the demodulation of the signal. This certificate of addition suggest moreover the use of a guard period between the symbols. However, the nonorthogonality of the channels used limits the spectral response, in the best of cases, to 1 bit/(Hz.s).
With the device according to the present invention, it is possible to exceed 5 bits/(Hz.s) under analogous conditions.
The present invention relates to an improvement in the means and of transmission methods described in the Patent 86 13937; 86 13938; 86 13939; 86 13940; 86 13941; 86 18351; 86 18352.
In the devices of known type it has often been tried to increase the information throughput by decreasing the transmission times allocated to each information unit, (or by increasing the number of possible symbols). Thus, a broadened spectrum was generated, whose secondary lobes have to be filtered on transmission, thus creating a distortion in the signal. For a square signal with a period .tau. a spectrum possessing numerous secondary lobes is obtained; the principle has a width of 2/.tau.. In the remainder of this specification this distortion in the signal is called auto-distortion.
SUMMARY OF THE INVENTION
The device according to the present invention offers the original feature of reducing or eliminating the auto-distortion of the signal by using long transmission intervals for the information elements (often called symbols) to be transmitted. To obtain a high throughput a plurality of information elements are simultaneously transmitted by using orthogonal channels. An information element is, for example, a digital word of 6 bits. Advantageously, one information element per transmission channel is transmitted. The orthogonality at the receiving end of the transmission channels enables the separation of the information belonging to various channels. The orthogonalization at the receiving end of the various channels is the result of a choice of several transmission frequencies regularly spaced by k/T, k is a natural number and T the period of the useful transmission interval. This type of transmission assumes a synchronous sampling at the receiving end in order to obtain the separation of the channels.
The subject of the invention is principally a method for transmission of modulated waves simultaneously using a plurality of frequencies, characterized in that it comprises successive steps of transmission of digital words for a period T+.DELTA.T, two transmission frequencies being separated by 1/T, T being the useful transmission interval and .DELTA.T being the transition interval.
The subject of the invention is also a method characterized in that .DELTA.T>0.
The subject of the invention is also a method characterized in that synchronizatio
REFERENCES:
patent: 3456202 (1969-07-01), Miyagi
patent: 4881241 (1989-11-01), Pommier et al.
EBU Review Technical, Nr 224, Aug. 1987 (Bruxelles, BE), M. Alard et al.: "Principles of modulation and channel coding for digital broadcasting for mobile receivers", pp. 168-190.
IEEE Transactions on Communications, vol. COM-34, Nr 6, Jun. 1986 IEEE, (New York, US), B. Hirosaki et al: "Advanced groupband data modem using orthogonally multi-lexed QAM technique" pp. 587-592.
IEEE Transactions on Communications, vol. COM-20, Nr 3, Jun. 1972, (New York, US), U. Timor: "Equivalence of time-multiplexed and frequency-multiplexed signals in digital communications" pp. 435-438.
Couasnon Tristan de
Elleaume Philippe
Fouche Yvon
Hergault Stephane
Monnier Raoul
"Thomson-CSF"
Chin Stephen
Ghebretinsae T.
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