Radio receiver and diversity receiver

Details Radio receiver and diversity receiver Radio receiver and diversity receiver

2000-07-11

2003-05-27

Nguyen, Lee (Department: 2683)

Telecommunications

Receiver or analog modulated signal frequency converter

With wave collector

C455S132000, C375S347000

Reexamination Certificate

active

06571090

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio receiver that receives, in parallel, reception waves respectively reaching branches and a diversity receiver that is incorporated in such a radio receiver.
2. Description of the Related Art
In general, in mobile communication systems, the landforms and planimetries around the radio base station and the mobile station vary every moment as the mobile station (including the vehicle) moves and hence a multipath is formed in a complicated manner and the transmission characteristic of the radio transmission channel vary to a large extent.
Therefore, to maintain desired transmission quality by reducing the degree of fading that is caused by the above-mentioned variation in transmission characteristic, a diversity receiving method is frequently used in mobile stations that access such a mobile communication system.
FIG. 10
shows the configuration of a first conventional diversity receiver.
As shown in
FIG. 10
, the feeding point of an antenna
91
-
1
is connected to one contact of a switch
93
and the feeding point of an antenna
91
-
2
is connected to the other contact of the switch
93
. The common contact of the switch
93
is connected to the input of a receiving part
94
, and the RSSI output of the receiving part
94
is connected to the control input of the switch
93
via a level comparing part
92
. The output of the receiving part
94
is connected to the input of a decision decoding part
97
via an A/D converter
95
and a demodulating part
96
that are cascaded. Transmission information as symbol sequence (described later) appears at the output of the decision decoding part
97
.
In the diversity receiver having the above configuration, the switch
94
selects one of reception waves reaching the respective antennas
91
-
1
and
91
-
2
.
The receiving part
94
generates an intermediate frequency signal by frequency-converting and amplifying the selected reception wave. Further, the receiving part
94
measures the level of the selected reception wave and supplies a measurement result to the level comparing part
92
.
Comparing the reception wave level thus supplied with a prescribed lower limit value, the level comparing part
92
requests the switch
93
to select the other reception wave when the reception wave level becomes lower than the lower limit value.
The A/D converter
95
generates, in the intermediate frequency domain or the baseband domain, a digital signal corresponding to the one reception wave by sampling the intermediate frequency signal sequentially at a prescribed frequency and coding resulting individual sampling values.
The demodulating part
96
extracts components (e.g., the amplitude and phase of a subcarrier component) suitable for a modulation scheme that was used for generating the reception wave from the components of the reception wave that are represented by the digital signal.
The decision decoding part
97
sequentially recognizes sequences of those components as symbol positions having maximum likelihood based on the signal space diagram of the above-mentioned modulation scheme and restores transmission information in the form of a symbol sequence that indicates individual symbol positions in time-series order.
It is assumed that the above processing performed by the demodulating part
96
and the decision decoding part
97
is realized as a digital signal processing that is executed by a single DSP (digital signal processor)
98
as indicated by a chain line in FIG.
10
.
FIG. 11
shows the configuration of a second conventional diversity receiver. The components in
FIG. 11
having the same function and configuration as the corresponding components in
FIG. 10
are given the same reference symbols as the latter and will not described.
The diversity receiver shown in
FIG. 11
is different from the diversity receiver shown in
FIG. 10
in that the level comparing part
92
and the switch
93
are not provided, that the feeding points of the antennas
91
-
1
and
91
-
2
are connected to the inputs of A/D converters
102
-
1
and
102
-
2
via receiving parts
101
-
1
and
101
-
2
, respectively, that a demodulating part
103
and a selecting part
104
that are cascaded are provided interstage between the A/D converters
102
-
1
and
102
-
2
and the decision decoding part
97
, that the two outputs of the demodulating part
103
are connected to the corresponding inputs of a transmission quality monitoring part
105
, and that the output of the transmission quality monitoring part
105
is connected to the selection input of the selecting part
104
.
In the diversity receiver having the above configuration, the receiving parts
101
-
1
and
101
-
2
convert reception waves reaching the antennas
91
-
1
and
91
-
2
into intermediate frequency signals, respectively.
The A/D converters
102
-
1
and
102
-
2
convert the intermediate frequency signals into digital signals, respectively. The demodulating part
103
extracts, in parallel, sets of components (e.g., the amplitude and phase of a subcarrier component) suitable for a prescribed modulation scheme from the sets of components of the reception waves represented by the respective digital signals. For the sake of simplicity, it is assumed here that the modulation scheme is the &pgr;/4 differential QPSK.
The transmission quality monitoring part
105
determines an error in the signal space (an error with respect to a standard value according to the above-mentioned modulation scheme), symbol by symbol, of each of the sets of components that have been extracted parallel by the demodulating part
103
and correspond to the respective reception waves that reached the antennas
91
-
1
and
91
-
2
in parallel, and sequentially computes average values of those errors.
The transmission quality monitoring part
105
outputs binary information indicating a smaller one of the average values.
The selecting part
104
selects one set of components indicated by the binary information from the sets of components that were extracted parallel by the demodulating part
103
as described above and correspond to the respective reception waves that reached the antennas
91
-
1
and
91
-
2
in parallel, and supplies the selected components to the decision decoding part
97
.
That is, in the diversity receiver shown in
FIG. 11
, switching diversity is realized by a digital signal processing in the intermediate frequency domain through cooperation between the transmission quality monitoring part
105
and the selecting part
104
.
It is assumed that the demodulating part
103
, the selecting part
104
, the decision decoding part
97
, and the transmission quality monitoring part
105
are implemented by a single DSP (digital signal processor)
106
as indicated by a chain line in FIG.
11
.
Incidentally, the diversity receiver shown in
FIG. 10
is small in hardware scale and power consumption and provides high reliability at a low cost because it has only one receiving part
94
to be mounted.
However, since only one of reception waves reaching the antennas
91
-
1
and
91
-
2
in parallel is level-monitored by the level comparing part
92
, it is not necessarily the case that the other reception wave has a higher level than the one reception wave.
Therefore, for example, where reception waves are given as a prescribed time slot sequence and switching is made between the contacts of the switch
93
in synchronism with those time slots, the diversity gain is not necessarily kept high when the level of a reception wave received as a certain sets of time slots rapidly decreases. In general, the diversity gain obtained by the diversity receiver shown in
FIG. 10
is lower than that obtained in accordance with the post-detection diversity scheme by about 3 dB.
The diversity receiver shown in
FIG. 11
provides a higher diversity gain than the diversity receiver shown in
FIG. 10
as long as the two receiving parts
101
-
1
and
101
-
2
corresponding to the respective antennas
91
-
1
and
91
-
2
pe

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