Telecommunications – Transmitter – Measuring – testing – or monitoring of transmitter
Patent
1994-08-23
1996-04-09
Pham, Chi H.
Telecommunications
Transmitter
Measuring, testing, or monitoring of transmitter
455126, 455129, H04B 104
Patent
active
055070140
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a radio transmitter having a power amplifier incorporating linearization which uses a training sequence.
BACKGROUND TO THE INVENTION
Continuing pressure on the limited radio spectrum available for radio communication systems is focusing attention on the development of spectrally efficient linear modulation schemes. Recent studies of digital mobile radio systems propose the use of linear modulation methods such as QPSK and .pi./4 QPSK which are considered to improve spectrum efficiency. The schemes, however, require a highly linear power amplifier or distortion will lead to intermodulation products, i.e. adjacent channel interference or "splatter". In the field of private mobile radio, stringent restrictions are placed on out-of-band emissions.
There is a demand for a strict linearity performance in power amplifiers.
SUMMARY OF THE PRIOR ART
A known linearization method in power amplifiers particularly suitable in the private mobile radio environment is that of Cartesian feedback, the linearizing of the power amplifier requires the accurate setting of the phase and amplitude of a feedback signal. In such known systems, a training sequence is transmitted, during which time the operation of the Cartesian feedback loop, is measured and the gain and phase are adjusted. The pahse is adjusted to ensure stability and the gain is monitored and adjusted to optimise efficiency and avoid saturation. The training sequence is ignored at the receiver.
The problem with such known systems is that a finite amount of time is allocated to the training sequence to be transmitted. In time division multiple access systems, the allocating of a finite amount of air time for training is a particularly costly overhead which reduces overall system throughput.
It is also a problem that, during the training sequence, a search is made for the optimum amplitude setting of the amplifier for maximum efficiency of operation. During this search, the amplifier is pushed into a saturation or "clip" mode at which linearity is lost and out of band spectral emissions are generated.
SUMMARY OF THE INVENTION
According to the present invention, a radio transmitter circuit is provided comprising: a power amplifier coupled to an antenna for transmission of radio signals; linearizer means for compensating for non-linearity in the power amplifier; means for inputting a training sequence to the linearizer means and outputting a training signal from the power amplifier resulting from the training sequence; and a feedback circuit for feeding the training signal output from the power amplifier back to the linearizer means to adjust the linearizer means and/or feedback circuit; characterized by means for inhibiting transmission of radio signals through the antenna while the training signal is being output from the power amplifier.
The means for inhibiting preferably comprise switching means and a load, for switching the signal from the power amplifier to the load when the training sequence is being output and for switching the signal to the antenna at the end of the training sequence.
A circulator may be provided coupled between the output of the power amplifier and the switching means and coupled to the load, for directing the output of the power amplifier to the switching means and for directing signals reflected from the switching means to the load. In another embodiment, the switching means is a multi-way switch coupled to the output of the power amplifier and to the antenna and the load, for selectively switching the signal from the output of the power amplifier to the antenna and the load.
Receive circuitry may be provided coupled to the switching means and a multi-way switch coupled to the output of the power amplifier and to the receive circuitry, for selectively switching the output from the power amplifier to the antenna and a received signal from the antenna to the receive circuitry.
Switching means control means are preferably provided for causing the switching means to switch the signal
REFERENCES:
patent: 4491973 (1985-01-01), Idol
patent: 5175879 (1992-12-01), Ellingson et al.
Valentine Stephen T.
Wray Anthony J.
Motorola Inc.
Pham Chi H.
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