Telecommunications – Transmitter – Diversity
Reexamination Certificate
2000-12-15
2004-05-25
Vuong, Quochien B. (Department: 2685)
Telecommunications
Transmitter
Diversity
C455S103000, C455S138000, C455S273000
Reexamination Certificate
active
06741838
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The present invention claims priority from Japanese Patent Application No. 11-356020 filed Dec. 15, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radio communications, and particularly to radio communications in which the conditions of radio wave propagation vary over time. More particularly, the present invention relates to a diversity technique for use in interoffice radio communications, interbuilding communications, or satellite communications, in which temporal variations in radio wave propagation characteristics due to fading are not substantial.
2. Description of Related Art
In line-of-sight point-to-point communications using micro waves or millimeter waves, space diversity communication systems are widely used as effective means for avoiding temporal variations in radio wave propagation characteristics due to fading. Also in mobile communications such as portable telephones, diversity communication systems are widely used in order to avoid temporal variations in radio wave propagation characteristics due to multipath fading. In these conventional diversity communication systems, the transmission side device defines two radio wave propagation paths for carrying one transmission signal, and the reception side device uses two independent receivers for receiving the transmitted signals via the two radio wave propagation paths, respectively, thereby obtaining two reception outputs. Then, the two reception outputs are diversity-combined with each other. Diversity maximum ratio combining is a known technique used for combining the reception outputs together.
FIG. 6
is a block diagram illustrating a conventional device for use in such systems. Single transmission data is provided to a modulator
301
of the transmission side device. The modulated output signal diverges into two signals of the same information, which are then input to two independent transmitters
302
and
303
, respectively. Local oscillators
304
and
305
provide carrier frequencies to the two transmitters
302
and
303
, respectively, for frequency conversion of the two signals. The signals are then transmitted to two propagation paths
306
and
307
.
The signals from the two propagation paths
306
and
307
are received by receivers
308
and
309
, respectively, in the reception side device. Local oscillators
310
and
311
provide carrier frequencies to the receivers
308
and
309
, respectively, for frequency de-conversion of the received signals. The signals are then subjected to a gain adjustment process by two automatic gain controllers (AGCs)
312
and
313
, respectively. The outputs from the automatic gain controllers are subjected to a multiplication operation by complex multipliers
316
and
317
with a weighting coefficient which is calculated by correlation control circuits
314
and
315
, respectively. The two output signals are added together by an addition circuit
318
into a single signal. Each of the two correlation control circuits
314
and
315
generates the weighting coefficient based on the output from the addition circuit
318
so that the output signal from the addition circuit
318
will have an amplitude that is in proportion to the square of each of the signals received via the two propagation paths and be in phase with the received signals. Thus, a diversity maximum ratio combining operation is performed, and reception data corresponding to the transmission data is obtained by a demodulator
319
.
For example, JP S59-105727A describes a reception side structure for diversity communications based on maximum ratio combining.
However, with the conventional diversity communication systems as described above, while two independent radio wave propagation paths are occupied, the total signal transmission capacity is equivalent to that achieved by a system which uses only one radio wave propagation path. Thus, the radio wave resources are not efficiently used except when the characteristics of one of the radio wave propagation paths has degraded to a point where the path is substantially unusable.
The hardware resources of the transmitter/receiver are also not used efficiently. Specifically, while each of the transmission side device and the reception side device is provided with two independent sets of hardware equipment, only a single signal can be transmitted between the transmission side and the reception side.
SUMMARY OF THE INVENTION
The present invention has been made in view of such circumstances in the prior art, and it is an object of the present invention to provide a diversity communication system with which the signal transmission capacity can be increased if the quality of the propagation paths is kept at a certain level. It is another object of the present invention to provide a diversity communication device with which two different signals can be transmitted while providing diversity maximum ratio combining for each of the signals, as long as each of the two independent propagation paths maintains a certain level of quality. It is a further object of the present invention to improve the efficiency of use of radio wave resources and hardware resources.
In order to achieve these objects, according to the present invention, the transmission side device combines together two transmission signals independent of each other so as to produce two combined signals which are vector-wise in a mirror image relationship with respect to each other, and transmits the two combined signals over two propagation paths, respectively. The reception side device receives the combined signals (or “reception signals”) and restores the two independent transmission signals therefrom, based on the mirror image relationship between the reception signals, by eliminating one of the transmission signals from one of the reception signals and eliminating the other one of the transmission signals from the other one of the reception signals.
In other words, the present invention is based on a principle that if two transmission signals (i.e., a first transmission signal and a second transmission signal) are combined together to produce two reception signals to be transmitted over two propagation paths, respectively, so that the produced reception signals are in a mirror image relationship (i.e., so that the second transmission signal, for example, in one reception signal has a vector which is oppositely oriented with respect to that of the second transmission signal in the other reception signal with the vector of the first transmission signal of one reception signal being aligned with that of the first transmission signal of the other reception signal), then, the second transmission signal can be eliminated on the reception side by using the two reception signals. Based on such a principle, the transmission side device combines two transmission signals together so that the obtained reception signals are vector-wise in a mirror image relationship with respect to each other, and transmits the obtained reception signals. The reception side device restores each transmission signal by eliminating the other transmission signal which has been superimposed on the transmission signal to be restored. In this way, the present invention realizes a transmission capacity that is up to twice as much as that achieved by conventional diversity communication systems.
Specifically, according to the present invention, the transmission side device combines two independent transmission signals (S
1
, S
2
) together to produce two combined signals, i.e., a sum signal (S
1
+S
2
) and a difference signal (S
1
−S
2
), and transmits the produced signals over two propagation paths, respectively. After the sum signal and the difference signal are received by the reception side device, the sum signal and the difference signal, as received, are subjected to an AGC control operation and a complex-level multiplication operation with a weighting coefficient based on cor
Vuong Quochien B.
Whitham Curtis & Christofferson, PC
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