Diversity receiver

Details Diversity receiver Diversity receiver

1999-04-06

2002-10-15

Chin, Stephen (Department: 2634)

Pulse or digital communications

Receivers

Interference or noise reduction

C445S060000

Reexamination Certificate

active

06466632

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diversity receiver used in a digital radio communication appliance for digital mobile communications, digital satellite communications, digital mobile satellite communications, or the like.
2. Description of the Related Art
In digital mobile communication systems, a fading phenomenon may occur, since electromagnetic waves are reflected, diffracted, and scattered by regions and articles located around a mobile station. In the fading phenomenon, amplitudes of received signals and phases of these received signals are severely varied. Under such a fading environment, since the amplitudes of the received signals and the phases thereof are severely varied, a coherent detection using recovered carrier can be hardly realized.
As a result, a differential detection may be usually employed. In the differential detection, a differential coding operation is carried out on a transmission side, whereas a received signal before 1 symbol is used as a reference signal.
As one of the conventional techniques capable of improving the performance under such a fading environment, the diversity reception technique is known in the field, by which signals are received in plural branches, and then these received signals are combined with each other, or selected. Also, as the diversity reception techniques using the differential detection, there are the antenna selecting diversity reception, the postdetection selecting diversity reception, and the postdetection combining diversity reception. In the antenna selecting diversity reception, the demodulated result of such a branch that the received signal power is larger than other received signal power is selected every burst. In the postdetection selecting diversity reception, the demodulated result of such a branch that the received signal power is larger than other received signal power is selected every symbol. In the postdetection combining diversity reception, the differential detection results of the respective branches are combined with each other.
As one prior art, a description will now be made of an arrangement of a differential detection diversity receiver and operation of the diversity receiver in which a quadrature phase shift keying (QPSK) signal which has been differentially coded is detected, and thereafter the detected QPSK signals are combined with each other for the diversity reception.
FIG. 17
is a block diagram for showing a conventional differential detection diversity receiver. The differential detection diversity receiver is described in, for example, the publication “BER Performance of QDPSK with Postdetection Diversity Reception in Mobile Radio Channels” written by F. Adachi and K. Ohono, IEEE Transactions on Vehicular Technology, Volume 40, No. 1, in 1991, pages 237 to 249. In the drawing reference numerals
11
and
12
show delay circuits, reference numerals
13
and
14
indicate multipliers, reference numeral
15
represents an adder, and reference numeral
16
shows a detector. Also, reference numerals
101
and
102
show received baseband signals, reference numerals
103
and
104
represent received baseband signals before 1 symbol, reference numerals
105
and
106
denote differential detection results, reference numeral
107
indicates soft decision data, and reference numeral
108
shows hard decision data.
Next, the operation of the differential detection diversity receiver will now be explained.
When the received baseband signal
101
of the branch
1
is inputted, the delay circuit
11
delays the received baseband signal
101
by time corresponding to 1 symbol to output the delayed received baseband signal as the received baseband signal
103
before 1 symbol.
The multiplier
13
performs the complex multiplication between the received baseband signal
101
and the received baseband signal
103
before 1 symbol to output the differential detection result
105
.
When the received baseband signal
102
of the branch
2
is inputted, the delay circuit
12
delays the received baseband signal
102
by time corresponding to 1 symbol to output the delayed received baseband signal as the received baseband signal
104
before 1 symbol.
The multiplier
14
performs the complex multiplication between the received baseband signal
102
and the received baseband signal
104
before 1 symbol to output the differential detection result
106
.
The adder
15
performs the complex adding operation between the differential detection result
105
of the branch
1
and the differential detection result
106
of the branch
2
to output the soft decision data
107
.
The detector
16
performs the hard decision with respect to the soft decision data
107
to output the hard decision data
108
.
As previously explained, the differential detection diversity receiver for executing the postdetection combining diversity reception can improve the performance by combining the differential detection results of the respective branches, as compared with the other receiver which does not execute the diversity reception. Also, the postdetection combining diversity may represent better performances than that of the antenna selection diversity, or that of the postdetection selection diversity for selecting the demodulated result of such a branch that the received signal power is larger than other received signal power every burst, or every symbol.
On the other hand, in digital mobile communication systems, one trial has been made in order to effectively utilize a frequency by reducing a zone radius of a cell and by repeatedly using the same frequency. At this time, there is such a problem that the co-channel interference will occur, which is caused by the electromagnetic waves leaked from the adjoining cells with using the same frequency, and therefore the performance is deteriorated.
As one of the techniques capable of mitigating the deterioration in the performance caused by the co-channel interference, the least-squares combining diversity technique is known. In the least-squares combining diversity, the received signals of the respective branches are combined with each other in order that the square mean value of the error signals can be reduced as small as possible.
As second prior art, an arrangement and operations of a least-squares combining diversity receiver capable of performing least-squares combining with respect to a QPSK signal will now be described.
FIG. 18
is a block diagram for indicating an arrangement of a conventional least-squares combining diversity receiver. The conventional least-squares combining diversity receiver is described in, for example, the publication “Interference Cancelling Characteristics of Diversity Reception with Least-Squares Combining—MMSE Characteristics and BER Performance” written by H. SUZUKI, IEICE Transactions on Communications, volume J 74-B-II, No. 12 in 1991, pages 637 to 645.
In the drawing, reference numerals
21
and
22
indicate multipliers, reference numeral
23
shows an adder, reference numeral
24
indicates a detector, reference numeral
25
represents a subtracter, and reference numeral
26
shows a tap coefficient control circuit. Also, reference numerals
201
and
202
show received baseband signals, reference numerals
203
and
204
represent tap coefficients, reference numerals
205
and
206
are multiplication results, reference numeral
207
shows soft decision data, reference numeral
208
indicates hard decision data, and reference numeral
209
denotes an error signal.
Next, the operation of the least-squares combining diversity receiver will now be described.
The multiplier
21
performs the complex multiplication between the tap coefficient
203
determined by the tap coefficient control circuit
26
and the received baseband signal
201
of the branch
1
to output the multiplication result
205
.
The multiplier
22
performs the complex multiplication between the tap coefficient
204
determined by the tap coefficient control circuit
26
and the received baseband signal
202
of th

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