Telecommunications – Receiver or analog modulated signal frequency converter – Plural receivers
Patent
1991-01-11
1993-04-13
Eisenzopf, Reinhard J.
Telecommunications
Receiver or analog modulated signal frequency converter
Plural receivers
375100, 455134, 455137, 455273, 4552771, H04B 708
Patent
active
052030237
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a diversity receiver in radio transmission, and more specifically, to a diversity receiver which can improve transmission characteristics of a circuit which transmits digital signals by phase modulated signals.
BACKGROUND TECHNOLOGY
As radio waves are used as the transmission medium in radio communications, level deviation or phase deviation of received signals takes place due to fading or interference to deteriorate transmission characteristics. Diversity reception has been known as an effective method to prevent such deterioration in transmission characteristics. The most typical diversity reception is postdetection diversity receiver which instantaneously selects a fading signal having the highest received signal level out of plural fading signals each of which changes independently. The reception system is based on the assumption that the higher the level of received signals, the higher is the S/N ratio (signal
oise ratio) and the smaller is phase deviation, and thus the transmission quality is expected to improve.
FIG. 1 shows a prior art typical 2-branch postdetection diversity receiver wherein two antennas 101, 102 are installed with a suitable interval distance between them in order to obtain fading waves independently, and are respectively connected to receivers 103, 104. As the detector of the received signal levels, IF log-amplifiers 105, 106 are used for intermediate frequency. The IF log-amplifiers 105, 106 are equipped with a means to output DC voltage proportionate to decibel of the received signal level. By comparing the output voltages from the two log amplifiers 105, 106 by a level comparator 107, the received signal levels can be compared. With the comparator output, output from one of the detectors 108 or 109 with the higher received signal level is selected by a diversity select switch 110. This allows an output terminal 111 to constantly receive detector outputs with a higher S/N ratio and smaller phase deviation.
However, the system requires plural receivers, and the size of the whole system inevitably becomes large. There has been proposed an antenna select diversity reception system as a simpler structure wherein plural antennas are switched to receive signals by only one receiver.
FIG. 2 shows a prior art typical 2-branch antenna select diversity reception circuit wherein two antennas 121 and 122 are placed at a suitable interval distance therebetween so as to obtain fading waves independently (not correlated) from each other. Either one of the antennas 121, 122 is connected to a receiver 124 with an antenna selector 123. The switching is conducted with the comparator data from a level comparator 126. More particularly, the received signal level of the receiver 124 is detected by a received signal level detector 125, which in turn is compared with the reference level by the comparator 126, and when, for example, IF signal envelope of the received signal becomes lower than a predetermined threshold value, the antennas 121 and 122 are switched.
To distinguish from said antenna select diversity reception, the receiver shown in FIG. 1 which switches detection outputs will be referred to as "post-detection diversity" hereinafter.
The following problems will occur if the received signal level is used as the data for branch selection in the postdetection diversity system.
The first problem is that the log-amplifiers 105, 106 are required to have a level detection performance over a wide range of signal levels. In practice, however, log-amplifiers could not quite meet such requirements as their level detection characteristics are often saturated in the extremely high or low levels or deviated from linearity in the intermediate range. In the ranges where the characteristics are saturated or deviated, the difference in output voltages decreases although the received signal levels differ between branches, to thereby hamper accurate comparison of received signal levels. As it is difficult to make level detection characteristics of log-amplifiers
REFERENCES:
patent: 4864641 (1989-09-01), Nakamura
patent: 4868890 (1989-09-01), Lennartsson
D. O. Reudink, et al., "Diversity Techniques", Microwave Mobile Communications, Chapter 6, Apr. 1974.
J. Chuang, et al., "A High Performance Diversity Selection Technique for TDMA Portable Radio Communications", IEEE Communications Society, Nov. 1989.
Saito Shigeki
Yamao Yasushi
Eisenzopf Reinhard J.
Nippon Telegraph and Telephone Corporation
Pham Chi H.
LandOfFree
Phase likelihood comparison diversity receiver does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Phase likelihood comparison diversity receiver, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Phase likelihood comparison diversity receiver will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1161794