Telecommunications – Receiver or analog modulated signal frequency converter – With wave collector
Reexamination Certificate
1998-06-23
2001-05-22
Maung, Nay (Department: 2681)
Telecommunications
Receiver or analog modulated signal frequency converter
With wave collector
C455S137000, C375S347000
Reexamination Certificate
active
06236844
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to space diversity radio receivers with spaced antennas, and more specifically, to a diversity radio receiver system with proportional mixing of output signals from different tuners attached to different spaced antennas.
Space diversity radio receiver systems are a well known attempt to reduce the effects of multipath distortion in mobile receivers. Multipath distortion is a localized effect resulting from interaction between signals from a transmitter which traverse different paths to reach a receiving antenna. By switching between spaced antennas in a diversity radio receiver, specific multipath events can be avoided since the spacing of the antennas helps insure that not both of the antennas will experience the same multipath event at the same time.
In short time delay multipath, reflected radio signals from nearby objects combine in anti-phase with the direct radio signal at certain locations resulting in the partial or total cancellation of the signal. An undesirable burst of noise known as a “spit” or “pop” is heard as the signal to noise ratio of the received signal decreases. When a vehicle antenna passes through these multipath points, the signal strength voltage detected in the radio tuner decreases momentarily due to the decreased signal strength at the antenna. Proportional diversity systems are known, such as described in patent application GB-2257605, wherein audio signals from separate tuners connected to separate diversity antennas are combined in a manner proportional to the signal strength measured at each tuner. Since the signal strength voltage drops for a particular tuner during a multipath event, its relative contribution to the combined signal is likewise decreased. This provides an improvement in the audio signal during short time delay multipath events by attenuating the spits which may be present at one antenna, but not at the other.
Long time delay multipath is a type of multipath distortion which cannot be accurately detected by monitoring the signal strength voltage and which therefore has gone uncorrected by prior art systems. In longtime delay multipath, reflected radio signals from more distant objects (e.g., 500 meters or more from the receiving antenna) combine with the direct radio signal. Due to the longer time delay between the signals, the signals are not correlated and therefore do not cause a cancellation of the received signal but rather the superposition or overlap of the signals' frequency spectra. This spectral overlap causes audio distortion which is not accompanied by a drop in the signal strength (in fact, the signal strength may increase), and, as a result, prior proportional diversity systems do not provide an improvement under these conditions.
SUMMARY OF THE INVENTION
The present invention provides the advantage that long time delay multipath events can be detected and corrected, so that all types of multipath distortion are minimized.
In one aspect, the invention provides a proportional diversity radio system for a mobile vehicle having first and second space diversity antennas. The first tuner is connected to one of the antennas and produces a first tuner output signal in response to a broadcast signal at a selected broadcast frequency. The first tuner also produces a first signal strength signal. The second tuner is connected to the other one of the antennas and produces a second tuner output signal in response to the broadcast signal at the selected broadcast frequency. The second tuner also produces a second signal strength signal. A proportional mixer combines the first and second tuner output signals to produce a mixed tuner output signal. The first and second tuner output signals proportionally contribute to the mixed tuner output signal in response to at least one mix control signal. The mixer control detects multipath distortion in each of the first and second tuner output signals caused by long time delay multipath conditions. The mixer control generates the mix control signal in response to the first and second signal strength signals and in response to the detected long time delay multipath distortion.
REFERENCES:
patent: 3934204 (1976-01-01), Hill
patent: 4210871 (1980-07-01), Hill et al.
patent: 4397036 (1983-08-01), Hirade et al.
patent: 4403343 (1983-09-01), Hamada
patent: 4525869 (1985-07-01), Hamada et al.
patent: 4654884 (1987-03-01), Sakai et al.
patent: 4742563 (1988-05-01), Fukumura
patent: 4926498 (1990-05-01), Suzuki et al.
patent: 4939791 (1990-07-01), Bochmann et al.
patent: 5345602 (1994-09-01), Wiedemann et al.
patent: 5379449 (1995-01-01), Porambo
patent: 5603107 (1997-02-01), Gottfried et al.
patent: 6029056 (2000-02-01), Kiyanagi et al.
patent: 6097773 (2000-08-01), Carter et al.
patent: 0 221 475 (1987-05-01), None
patent: 1 373 644 (1974-11-01), None
patent: 1 433 590 (1976-04-01), None
patent: 2 257 605 (1993-01-01), None
Cvetkovic Milan
McCall David John
Page Martin Gerard
Gelin Jean A
Maung Nay
Mollon Mark L.
Visteon Global Technologies Inc.
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