Spread spectrum diversity transmitter/receiver

Details Spread spectrum diversity transmitter/receiver Spread spectrum diversity transmitter/receiver

1999-09-21

2003-04-29

Chin, Stephen (Department: 2734)

Pulse or digital communications

Spread spectrum

Direct sequence

C714S789000

Reexamination Certificate

active

06556617

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a spread spectrum diversity transmitter/receiver that performs code division multiple access communication by a spread spectrum technology at a digital radio transmission that has a severe multi path fading problem in particular.
DESCRIPTION OF THE RELATED ART
At a radio transmission by a fading channel, generally a diversity reception is needed. As fading, there are a flat fading and a selective fading. At the flat fading, a multi path propagation is not generated, but an amplitude/phase of a receiving wave itself is directly varied during the propagation. At the selective fading, the multi path propagation is generated, and an amplitude/phase of arrival waves by each multi path is independently varied. In this case, since the received signal becomes a combined wave of plural multi path waves, depending on a state of the phase shift, the received signal may become an inverse phase combination at a frequency. That is, a frequency selective fade (notch) occurs in a received spectrum. At the flat fading, a variation of a received level is a problem and the received waveform itself is not distorted. However, at the selective fading by the multi path, in addition to the variation of the received level, a distortion of the waveform occurs.
For the fading channel mentioned above, a diversity reception and an adaptive equalizing technology have been conventionally applied. There are several conventional technologies, however in this, as a conventional technology, a spread spectrum communication which is said to be effective against the multi path distortion, is mentioned. The object of the spread spectrum technology is originally developed for military communication being robust against jamming wave. The multi path wave whose delay time is long has a low correlation with a desired main wave signal. In the case that the spread spectrum technology is applied, the correlation between the multi path wave and a spread code can not be established and the multi path wave is suppressed at a de-spread operation. That is, at the spread spectrum technology, the multi path wave is regarded as interference, therefore the spread spectrum technology is a kind of adaptive equalizer.
However, the multi path wave whose delay time is short has a high correlation with a main wave signal, therefore the suppression by the de-spread operation can not be expected. In this case, since the delay time between the multi path wave and the main wave is short, at the time when the relation between the multi path wave and the main wave becomes an inverse phase, a decline of level, that is, a fade out can be generated. In order to cope with this kind of fade out, a diversity reception utilized non-correlation among plural propagation paths becomes indispensable.
FIG. 1
is a diagram showing the structure of a diversity reception. Referring to
FIG. 1
, the diversity reception is explained. In
FIG. 1
, the transmission is performed from a transmitter
401
to a receiver
402
, radio waves transmitted from the transmitter
401
arrive the receiver
402
via three different paths
403
,
404
and
405
.
In this, it is assumed that the transmitter
401
transmits the radio waves by using one non-directional antenna. The radio waves emitted from the non-directional antenna are propagated through the path
404
being a direct propagation path, and the paths
403
and
405
through which reflected waves are propagated. By the radio waves emitted from the non-directional antenna are propagated through the different paths, therefore multi path propagation occurs.
FIGS. 2A
,
2
B and
2
C are diagrams showing the variation of a received electric field level at each path. In this case, the paths are different in space, the fading generated at each path is independent, and the variations of the received electric field level in the passage of time are shown in
FIGS. 2A
,
2
B and
2
C.
In
FIG. 2A
, the variation of a received electric field level at the path
403
is shown, in
FIG. 2B
, the variation of a received electric field level at the path
404
is shown and in
FIG. 2C
, the variation of a received electric field level at the path
405
is shown.
For this kind of propagation, the diversity reception selects or combines the parts not faded out in each diversity branch and makes the probability of fading out decrease. This kind of diversity reception is named as a space diversity or a path diversity because of utilizing the non-correlation among the propagation paths. As a means to realize this diversity, generally an adaptive array using plural antennas is applied. That is, by extracting plural multi path arriving waves using a directional control of the adaptive array, and combining the maximum ratio, a diversity combination can be performed.
However, at the space diversity, plural antennas are needed, therefore a disadvantage at cost occurs. In particular, at microwave communication, the cost of antenna is high and the apparatus becomes large, therefore the number of antennas can not be increased without careful consideration.
In order to improve the problem of this space diversity, Japanese Patent Application Laid-Open No. HEI 8-191289 discloses a spread spectrum diversity transmitter/receiver that utilizes a code division multiplex and a time diversity by a spread spectrum. This conventional spread spectrum diversity transmitter/receiver is shown in
FIGS. 3 and 4
.
FIG. 3
is a block diagram showing the structure of a transmitting section of this conventional spread spectrum diversity transmitter/receiver, and
FIG. 4
is a block diagram showing the structure of a receiving section of this conventional spread spectrum diversity transmitter/receiver.
As shown in
FIG. 3
, the transmitting section of this conventional spread spectrum diversity transmitter/receiver provides an error correction encoder
101
, M−1 pieces of delay element whose delay time is &tgr;M
103
1
to
103
M−1
, M pieces of interleave circuit
102
1
to
102
M
, M pieces of modulator
105
1
to
105
M
, M pieces of spread spectrum circuit
106
1
to
106
M
, a combining circuit
107
, a transmitter
108
and a transmitting antenna
109
.
The error correction encoder
101
performs an error correction encoding for one series of transmitting data.
The delay elements
103
1
to
103
M−1
, by giving delay time of &tgr;M to an output of the error correction encoder
101
respectively, makes the output of the error correction encoder
101
branch to M−1 pieces.
The interleave circuits
102
1
to
102
M
perform interleave respectively for the output from the error correction encoder
101
and the outputs from the delay elements
103
1
to
103
M−1
.
The modulators
105
1
to
105
M
modulate the outputs from the interleave circuits
102
1
to
102
M
.
The spread spectrum circuits
106
1
to
106
M
perform a spread spectrum operation to the outputs from the modulators
105
1
to
105
M
by different spread codes.
The combining circuit
107
combines the outputs from the spread spectrum circuits
106
1
to
106
M
and performs code division multiplex for them and outputs the result.
The transmitter
108
transmits the code division multiplex signal outputted from the combining circuit
107
, through the transmitting antenna
109
.
As shown in
FIG. 4
, the receiving section of this conventional spread spectrum diversity transmitter/receiver provides a receiving antenna
110
, a receiver
111
, a branching circuit
112
, M pieces of de-spread spectrum circuit
113
1
to
113
M
, M pieces of demodulator
114
1
to
114
M
, M pieces of deinterleave circuit
118
1
to
118
M
, M pieces of delay element whose delay time is &eegr;N
116
1
to
116
M
, a majority judging circuit
117
and an error correction decoder
119
.
The receiver
111
receives the code division multiplex signal transmitted from the transmitting section shown in
FIG. 3
, through the receiving antenna
110
.
The branching circuit
112
makes the signal received at the receiver
111
branch to M

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