Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
2000-01-31
2004-05-18
Bocure, Tesfaldet (Department: 2631)
Pulse or digital communications
Receivers
Interference or noise reduction
C455S343100, C455S343200
Reexamination Certificate
active
06738439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diversity reception method and diversity receiver used to receive a packet made up of a preamble field and data field.
2. Description of the Prior Art
According to a conventional method as disclosed in Japanese Unexamined Patent Publication No. 63-158922, an antenna branch having a maximum reception signal power upon reception of a preamble field is selected, and a data field is demodulated based on a reception signal from the selected antenna branch.
Japanese Unexamined Patent Publication No. 10-28107 discloses a diversity receiver shown in the block diagram of
FIG. 1
as a diversity receiver for receiving a packet made up of a preamble field and data field having undergone direct spread modulation.
FIG. 1
shows a receiver using two antenna branches.
In
FIG. 1
, reference numerals
1000
-
1
and
1000
-
2
denote antenna branches;
1001
, a switch (SW);
1002
, a gate;
1003
, a demodulation circuit;
1004
, an antenna switching control circuit; and
1005
, an output terminal.
This diversity receiver cannot predict packet arrival. For this reason, the antenna branches
1000
-
1
and
1000
-
2
are selected by the switch
1001
at a predetermined period, and a reception signal from the selected antenna branch is supplied to the antenna switching control circuit
1004
and gate
1002
.
The antenna switching control circuit
1004
calculates the correlation between an input signal and spreading code. When the peak value of the correlation is equal to or higher than a predetermined threshold, a packet arrival detection pulse is output to the switch
1001
and gate
1002
. Upon reception of this pulse, the switch
1001
stops periodic switching operation and holds the current state.
Upon reception of the pulse reception detection pulse, the gate
1002
opens its gate to supply an input signal to the demodulation circuit
1003
. The demodulation circuit
1003
demodulates the input signal and outputs the demodulation result to the output terminal
1005
on the basis of the signal via the gate
1002
. These methods can be classified into a pre-detection antenna switching diversity method, which can be implemented by a simple receiver.
According to another method, a diversity receiver which provides more excellent characteristics uses a signal obtained after detecting a reception signal from each antenna branch, though the structure of the receiver is complicated.
For example, Japanese Unexamined Patent Publication No. 03-214819 discloses a post-detection selection diversity method of selecting an antenna branch using a signal after detection.
This method is shown in FIG.
2
.
FIG. 2
shows a receiver using two antenna branches
1000
-
1
and
1000
-
2
. Reception signals from the antenna branches
1000
-
1
and
1000
-
2
are detected by detection circuits
1100
-
1
and
1100
-
2
, and channel impulse responses of reception signals are estimated by channel impulse response estimation circuits
1101
-
1
and
1101
-
2
.
Based on the channel impulse responses estimated by the channel impulse response estimation circuits, an antenna branch receiving a reception signal, which has the smallest distortion, and supplying the channel impulse response estimated from the reception signal is selected by a selection control circuit
1102
and switches
1103
and
1104
. The data field is equalized and demodulated by an equalizer
1105
.
In
FIG. 2
, the receiver comprises the antenna branches
1000
-
1
and
1000
-
2
, detection circuits
1100
-
1
and
1100
-
2
, channel impulse response estimation circuits
1101
-
1
and
1101
-
2
, selection control circuit
1102
, switches
1103
and
1104
, and equalizer
1105
. Reference numeral
1106
denotes an output terminal.
Further, Japanese Unexamined Patent Publication No. 08-163103 discloses a post-detection combining diversity method of detecting a reception signal from each antenna branch and combining the post-detection signals.
This method is shown in FIG.
3
.
FIG. 3
shows a receiver using two antenna branches
1000
-
1
and
1000
-
2
. Reception signals from the antenna branches
1000
-
1
and
1000
-
2
are respectively detected by detection circuits
1100
-
1
and
1100
-
2
, and the channel impulse responses of the reception signals are estimated by channel impulse response estimation circuits
1101
-
1
and
1101
-
2
.
Branch metrics for the reception signals from the respective antenna branches are calculated by branch metric calculation circuits
1201
-
1
and
1201
-
2
on the basis of the reception signals from the respective antenna branches and their estimated channel impulse responses. The calculated branch metrics are combined by a combining circuit
1202
, and the data field is demodulated by a Viterbi equalizer
1203
based on the synthesized value.
In
FIG. 3
, the receiver comprises the antenna branches
1000
-
1
and
1000
-
2
, detection circuits
1100
-
1
and
1100
-
2
, channel impulse response estimation circuits
1101
-
1
and
1101
-
2
, branch metric calculation circuits
1201
-
1
and
1201
-
2
, synthesis circuit
1202
, and Viterbi equalizer
1203
. Reference numeral
1204
denotes an output terminal.
In the conventional pre-detection antenna switching diversity method shown in
FIG. 1
, even if packet arrival is detected based on a signal from a given antenna branch, a signal received by another antenna branch may have a larger reception power.
However, shortening the preamble field to increase the transmission efficiency limits the time required to confirm the reception state of other antenna branches. Thus, if the number of antenna branches is increased to improve reception characteristics, the antenna branch is not always switched to an optimum one.
By applying to packet transfer the post-detection selection diversity method and post-detection combining diversity method shown in
FIGS. 2 and 3
, the number of antenna branches can be increased while the length of the preamble field remains the same. However, these methods cannot predict packet arrival, so demodulators equal in number to antenna branches must always operate. This leads to large power consumption of the receiver.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide a diversity reception method and diversity receiver capable of suppressing the power consumption of the receiver and increasing the number of antenna branches to improve reception characteristics even in communicating a packet having a short preamble field.
To achieve the above object, according to the first aspect of the present invention, there is provided a diversity reception method for a diversity receiver having n (integer not smaller than 2) antenna branches for receiving a packet made up of a preamble field and data field, comprising the steps of switching the n antenna branches to detect packet arrival when no packet arrival is detected, stopping switching the n antenna branches when packet arrival is detected, and performing reception operation by demodulating the packet based on all signals received by the n antenna branches after the packet detection.
According to the second aspect of the present invention, there is provided a diversity receiver having n (integer not smaller than 2) antenna branches for receiving a packet made up of a preamble field and data field, comprising n first switches for receiving signals respectively received by the n antenna branches and a “packet receive pulse” representing that the packet is being received, and changing an output destination based on the “packet receive pulse”, a second switch for receiving an antenna switching signal and outputs from the n first switches, and when no “packet receive pulse” is output, selecting and outputting the outputs from the n first switches based on the antenna switching signal, a packet detection circuit for receiving an output from the second switch, and when the packet is being received, outputting the “packet receive pulse”
Okanoue Kazuhiro
Osawa Tomoki
Yamamoto Takeshi
Bocure Tesfaldet
Dickstein Shapiro Morin & Oshinsky LLP.
Ghulamali Qutbuddin
NEC Corporation
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