Amplifiers – With pilot frequency control means
Patent
1995-06-14
1996-11-19
Mottola, Steven
Amplifiers
With pilot frequency control means
330151, 330149, H03F 366, H03F 126
Patent
active
055766595
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for substituting another type of signal for a pilot signal where the pilot signal would provide a reference for level and/or frequency and/or phase, for example. The invention also, of course, relates to applications where a reference signal is required but no pilot signal has previously been used or contemplated.
BACKGROUND OF THE INVENTION
The disadvantages of pilot signals include additional loading for any circuit which uses the pilot signal, the provision of a slot in the frequency spectrum for a pilot signal where it does not interfere with other signals, and where the pilot signal is used to characterize changes in a transmission path, the characterization is strictly speaking only applicable to the frequency region occupied by the pilot signal.
The present invention is particularly useful in the removal of distortion in broadband linear amplifiers such as are described in U.S. Pat. Nos. 5,334,946 and 5,157,345. Another method of reducing distortion in such amplifiers is described in U.S. Pat. No. 4,580,105 assigned to A.T & T (inventor Myer). The correction method of this U.S. Pat. No. 4,580,105 suffers from the above mentioned disadvantages and a further disadvantage in that the pilot signal restricts channel usage within the amplifier where a multi-channel input is applied to the amplifier. Previously mentioned U.S. Pat. No. 5,334,946 and 5,157,345 overcame these problems by avoiding the use of a pilot signal but a further problem exists in the particular situation where it is required to combine a large number of input channels for application to the broadband linear amplifier. Such an amplifier is usually used as the final power amplifier of a radio transmitter and for this reason it must be near a transmission antenna. The antenna is usually situated on the top of a building where rentals are high. A large number of input cables, one for each input channel, for example 30 to 100, have to be run to the top floor of this building. In addition some circuits have to be duplicated for each channel near the amplifier and high rental space is required for this purpose.
Another important application of the invention is in radio repeaters, especially for cellular radio, where a repeater for a "hole" in coverage, for example in a tunnel, receives signals at a low level and transmits at a high level on the same frequency. Instability is likely in such repeaters but can usually be avoided by using directional antennas and positioning transmit and receive antennas as far apart as possible. However in many situations one omnidirectional antenna is required and suitable spacing is inconvenient. A similar application which uses a derivative of the technique is in frequency translating repeaters. An advantage then gained is the elimination of the complex filtering otherwise required in these systems.
In code-division multiple access (CDMA) systems each channel employs a spread spectrum signal and the channel signals are added before transmission. U.S. Pat. No. 4,962,507 describes a system in which a pilot signal for transmitting a timing reference is also transmitted in spread spectrum form.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a method of processing signals comprising the steps of and adjusting the phase and/or amplitude of the intermediate signal in response to control signals, signal of the processing to improve processing, and
Methods according to the first aspect of the invention, and corresponding apparatus, may be used where the signals to be processed are spread spectrum signals.
According to a second aspect of the present invention there is provided a method of processing signals comprising the steps of combining a reference signal, having a predetermined characteristic, with the input signals which are not spread spectrum modulated, signals, and processed signals to control, at least partially, the processing and/or further processing of the processed signals
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patent: 4394624 (1983-07-01), Bauman
patent: 4580105 (1986-04-01), Myer
patent: 4962507 (1990-10-01), Renshaw
patent: 5130663 (1992-07-01), Tattersall, Jr.
patent: 5157345 (1992-10-01), Kenington et al.
patent: 5166634 (1992-11-01), Narahashi et al.
patent: 5327096 (1994-07-01), Sakamoto et al.
patent: 5334946 (1994-08-01), Kenington
patent: 5386198 (1995-01-01), Ripstrand et al.
patent: 5455537 (1995-10-01), Larkin et al.
Vehicular Technology society 42nd VTS Conference Frontiers of Technology, vol. 1 of 2, pp. 1-576 S. A. Allpress et al, pp. 506-510.
Introduction to Spread-Spectrum Antimultipath Techniques and Their Application to Urban Digital Radio G. L. Turin, Proceedings of the IEEE, vol. 68, No. 3, Mar. 1980, pp. 328-353.
Principles of Communication System 1980 Taub et al, pp. 720-749.
Beach Mark A.
Kenington Peter B.
McGeehan Joseph P.
British Technology Group Limited
Mottola Steven
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