Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-02-24
2001-12-04
Hunter, Daniel (Department: 2684)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S205000, C455S275000
Reexamination Certificate
active
06327481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile radio communication system, and more particularly to an apparatus for and a method of antenna-switched diversity reception.
2. Description of the Related Art
Antenna diversity reception schemes are roughly classified into a post-detection selection diversity system and an antenna-switched diversity system. In the post-detection selection diversity system, antenna branches are associated with respective demodulators, and a demodulated signal from the antenna branch which represents the best signal reception is selected. While the post-detection selection diversity system is capable of good signal reception in fading environments, the circuit used by the system is relatively large in scale, expensive, and consumes a large amount of electric power because each of the antenna branches needs to be associated with a demodulator. There have been proposed various attempts to eliminate the above problems. For example, reference should be made to Japanese patent application laid-open No. 6-268635.
The antenna-switched diversity reception system switches between a plurality of antennas located in spatially different positions to select one of the antennas which provides a good reception quality. Since only the antennas are switched, the antenna-switched diversity reception system can easily meet the requirements for rendering communication apparatus small, lightweight, and low-power-consumption. However, the quality of received signals remains to be improved, and various efforts have been made to receive high-quality signals.
For example, Japanese patent application laid-open No. 5-206905 discloses an antenna-selected diversity receiver which measures reception powers of two antennas, twice for each antenna, immediately before a burst signal is received, linearly predicts reception powers of the antennas for the burst signal from the measured values, and stores the predicted values in a memory. For receiving the burst signal, one of the antennas whose predicted value is higher is selected.
Furthermore, using the reception power of the antenna which is being selected, a subsequent reception power is predicted, and the data stored in the memory is updated by the predicted value.
An antenna-selected diversity reception apparatus disclosed in Japanese patent application laid-open No. 7-235901 has a holding means for holding the reception levels of two antennas. When a certain signal inserted in a received signal is reached, one of the antennas whose reception level is higher is selected.
According to each of the above proposals, an antenna whose reception level is higher is selected to ensure a desired level of reception quality by switching between antennas even while a burst signal is being received.
With the antenna-selected diversity receiver which employs the linear predict for the reception powers in advance, since the switching between the antennas is controlled by the predicted values, the antennas may not be properly switched, resulting in a relatively high probability that a reception error occurs.
Furthermore, the antenna-selected diversity receiver needs a control system for performing predictive calculations. Such predictive calculations causes a large burden on the processor of the control system, and require the control system to have an increased circuit scale and consume an increased power.
The antenna-selected diversity reception apparatus which triggers the switching between the antennas with a certain signal inserted in a received signal is unable to switch between the antennas until the certain signal is received even when the reception state is impaired. Consequently, the antenna-selected diversity reception apparatus tends to cause a reception error.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an antenna-switched diversity reception apparatus which is small and lightweight, has low power requirements, and can control antenna switching highly reliably without causing a reduction in reception quality.
Another object of the present invention is to provide a method of antenna-switched diversity reception to control antenna switching highly reliably without causing a reduction in reception quality.
According to the present invention, there is provided an apparatus for antenna-switched diversity reception, comprising demodulating means for demodulating data from a phase-modulated signal received by a selected one of antennas, phase error detecting means for detecting a phase error of each symbol of the received signal as a deviation from an ideal phase, accumulating means for accumulating phase errors, and control means for controlling switching between the antennas if an accumulated value of the phase errors is greater than a predetermined value. Preferably, the control means comprises means for switching the selected one of the antennas temporarily to another one of the antennas if the accumulated value of the phase errors is greater than the predetermined value, and controlling switching between the antennas by comparing a reception status of the selected one of the antennas with a reception status of the other one of the antennas.
Since the antenna switching is determined on the basis of the accumulated value of the phase errors, the antenna switching can be determined using a simple adder. Therefore, no special calculations are required, and the load on a control system and the power consumption thereby are reduced. Since when the accumulated value of the phase errors becomes greater than the predetermined value, the antenna is switched temporarily to the other antenna for comparison between the reception statuses. Consequently, the reception status of the other antenna can be known before normal antenna switching is effected, so that antenna switching can be effected highly reliably.
Furthermore, there is also provided in accordance with the present invention an apparatus for antenna-switched diversity reception of a phase-modulated signal composed of frames, comprising demodulating means for demodulating data from each of the frames of the phase-modulated signal received by a selected one of antennas, phase error detecting means for detecting a phase error of each symbol of the received signal as a deviation from an ideal phase, accumulating means for accumulating phase errors of the respective frames, and control means for controlling switching between the antennas in a next frame if an accumulated value of the phase errors is greater than a predetermined value at a predetermined position in one of the frames.
The demodulating means comprises phase holding means for holding phases of a plurality of demodulated clock signals, selecting means for selecting the phase of a desired one of the demodulated clock signals, and a demodulator for demodulating the data according to the selected phase of the demodulated clock signal. Preferably, the control means comprises means for, if the accumulated value of the phase errors in a past frame is smaller than the predetermined value at the predetermined position in the frame, holding the phase of the demodulated clock signal in the frame in the phase holding means, holding the phase of the demodulated clock signal of a first antenna selected in a present frame in the phase holding means, and when the accumulated value of the phase errors is greater than the predetermined value, switching the first antenna temporarily to a second antenna, holding the phase of the demodulated clock signal of the second antenna in the phase holding means, selecting either one of the antennas based on a reception status of the first antenna and a reception status of the second antenna, selecting one of the phases of the demodulated clock signals held by the phase holding means, and providing the selected one of the phases to the demodulator.
According to the present invention, furthermore, a method of antenna-switched diversity reception of a phase-modulated signal composed of frames holds the phases of demodulat
Hunter Daniel
NEC Corporation
Nguyen Thuan T.
Scully Scott Murphy & Presser
LandOfFree
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