Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1998-10-29
2001-01-30
Le, Amanda T. (Department: 2734)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S347000, C455S135000, C455S278100
Reexamination Certificate
active
06181749
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diversity reception apparatus which, in digital radio communications and the like, takes out demodulated data in two or more channels from one or a plurality of modulated signals and selects and combines the data to reduce transmission errors.
2. Description of the Background Art
In radio communications, especially in mobile communication, the diversity reception is widely used to reduce transmission errors caused by fading and interference.
In a typical method of the diversity reception, a signal at the highest reception signal strength is selected from among a plurality of channels of signals received at a plurality of antennas. However, in the presence of interference or multipath, error may occur even if the reception signal strength is high. Then a channel of signal of good quality cannot be correctly selected only with the reception signal strength. Conventionally, in order to solve this problem, Japanese Patent Laid-Open No. 1-265739 and Japanese Patent Laid-Open No. 4-8031 propose diversity reception apparatus which can detect errors in received data to select a channel containing the smallest number of errors. Such conventional diversity reception apparatus will now be described referring to the drawing.
FIG. 17
is a block diagram showing the structure of a conventional diversity reception apparatus. As shown in
FIG. 17
, this diversity reception apparatus has antennas
101
a
and
101
b,
receivers
102
a
and
102
b,
error detectors
103
a
and
103
b,
an error comparator
104
, and a data selector
105
. The receivers
102
a
and
102
b
demodulate signals received at the antennas
101
a
and
101
b
to output demodulated data d
100
a
and d
100
b,
respectively. The error detectors
103
a
and
103
b
respectively detect errors in the demodulated data d
100
a
and d
100
b
and count the numbers of errors. The error comparator
104
receives and compares the numbers of errors outputted from the error detectors
103
a
and
103
b
and outputs a selection signal s
100
for selecting one of the demodulated data d
100
a
and d
100
b
containing less errors. The data selector
105
selects the one with less errors from the demodulated data d
100
a
and d
100
b
on the basis of the selection signal s
100
from the error comparator
104
and outputs it as a selected signal d
101
. With this operation, the diversity reception apparatus shown in
FIG. 17
can select demodulated data with less errors from the signals received at the two channels of antennas.
However, the diversity reception apparatus with the above-described structure requires use of a highly redundant error detecting code or a long error detecting code to correctly detect errors. The use of a long error detecting code reduces the selecting rate and then it is impossible to follow a rapid change on the transmission path caused by fast fading, for example. However, the use of a highly redundant error detecting code reduces the data transmission efficiency. Further, if error correcting coding is used to improve the reliability, the redundancy further increases. Moreover, if the demodulated data in all channels include errors to the same extent, it is impossible to determine which channel of demodulated data has the best quality.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a diversity reception apparatus which performs error estimation by using-an error correcting code so as to maintain the reliability of the error estimation even when a less redundant and short code is used, and to accurately compare qualities of demodulated data even when demodulated data in all channels contain errors to a similar extent, so that a channel of good quality can accurately be selected. Another object of the present invention is to improve the reliability by error correction without increasing the redundancy, together with diversity selection.
To achieve the objects above, the present invention has the features shown below.
A first aspect of the present invention is directed to a diversity reception apparatus receiving one or a plurality of modulated signals modulated with error-correctably coded data. According to the first aspect, the diversity reception apparatus comprises:
a demodulator for demodulating the modulated signal(s) to obtain demodulated data in a plurality of channels corresponding to the coded data;
an error estimating portion for estimating the number of erroneous symbols and error locations thereof in the demodulated data in each channel;
a data comparator for comparing the data in the error locations estimated in the demodulated data in each channel with the data in the corresponding locations in the demodulated data in other channels to determine whether the error locations are correct or not; and
a data selector for selecting one of the plurality of channels on the basis of the numbers of erroneous symbols and results of the determination made by the data comparator.
In accordance with the above-described first aspect, the demodulated data are compared among channels to determine whether the error locations are correct. Accordingly, the reliability of the error estimation can be maintained even when a less redundant and short code is used, and a channel of good quality can be selected even when the demodulated data in all channels contain the same extent of errors.
According to a second aspect of the present invention, in the diversity reception apparatus of the first aspect,
when all data in the error locations estimated in the demodulated data in one channel of the plurality of channels respectively differ from the data in the corresponding locations in the demodulated data in all other channels, the data comparator determines that the error locations in the one channel are correct.
In accordance with the above-described second aspect, it is possible to determine whether the estimated error locations in each channel are correct on the basis of data comparison with simple structure.
According to a third aspect of the present invention, in the diversity reception apparatus of the first aspect,
when all data in the error locations estimated in the demodulated data in one channel of the plurality of channels respectively differ from the data in the corresponding locations in the demodulated data in at least one of other channels, the data comparator determines that the error locations in the one channel are correct.
In accordance with the above-described third aspect, it is possible to determine whether the estimated error locations in each channel are correct by data comparison with simple structure.
According to a fourth aspect of the present invention, in the diversity reception apparatus of the first aspect,
when data whose number is equal to or larger than a predetermined threshold in the data in the error locations estimated in the demodulated data in one channel of the plurality of channels differ from the data in the corresponding locations in the demodulated data in at least one of other channels, the data comparator determines that the error locations in the one channel are correct.
In accordance with the above-described fourth aspect, the determination by data comparison about the correctness of the error estimation can be made more flexibly by setting the threshold value.
According to a fifth aspect of the present invention, in the diversity reception apparatus of the first aspect,
the error estimating portion estimates the error locations in the demodulated data in each channel bit by bit, and
when all bits in the error locations estimated in the demodulated data in one channel of the plurality of channels respectively differ from the bits in the corresponding locations in the demodulated data in at least one of other channels, the data comparator determines that the error locations in the one channel are correct.
According to a sixth aspect of the present invention, in the diversity reception apparatus of the first aspect,
the error estimating portion estimates
Mori Ken-ichi
Takai Hitoshi
Urabe Yoshio
Yamasaki Hidetoshi
Le Amanda T.
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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