JP2004363812A - Mobile communications system, base station, mobile terminal, and wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve communication quality without making the scale and throughput of a mobile communication device larger than that in normal W-CDMA by realizing polarization diversity and spatial diversity with simple constitution in a mobile communication system. <P>SOLUTION: The mobile communication system performs wireless communication through a plurality of polarized waves having different planes of polarization, and has: a branch antenna composed of a horizontally polarized wave antenna and a vertically polarized wave antenna; a frequency setting part 33 which sets a frequency for horizontally polarized wave specific to the horizontally polarized wave antenna and a frequency for vertically polarized wave specific to the vertically polarized wave antenna; and a branching filter circuit 11 which selects the horizontally polarized wave antenna and vertically polarized wave antenna according to the settings by the frequency setting part and inputs and outputs signal concerned with wireless communication. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mobile communication system, particularly a mobile communication system, a base station, a mobile terminal, and a radio communication method using a plurality of antennas having different polarization planes in CDMA and W-CDMA.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a mobile communication system represented by W-CDMA, in order to compensate for a decrease in received signal power at a base station caused by an inclination of the antenna of the mobile station, the base station antenna and a vertically polarized antenna are used. Two types of wave antennas are provided to perform diversity reception such as selective combining and maximum ratio combining.
[0003]
When the diversity reception is not performed, the antenna of the base station is installed vertically and used as a vertically polarized antenna, and is often fixed at the time of installation. However, the antenna on the mobile station side is transmitted at a predetermined angle from the vertical depending on the usage of the user, so that the vertical polarization component reaching the base station decreases as the tilt of the antenna of the mobile station increases. At the same time, the horizontal polarization component increases, and the received signal power at the base station decreases.
[0004]
The amount of reduction of the vertical polarization component depends on the inclination of the mobile station antenna and the surrounding urban structure. When the inclination of the mobile station antenna is 90 °, it becomes 6 to 8 dB in an urban area and 10 to 12 dB in a suburban area. There is a report. The value of this decrease indicates the amount of leakage from one polarization plane to another polarization plane, and is called “cross polarization discrimination degree”.
[0005]
This decrease in received signal power can be compensated for by receiving a horizontally polarized component that increases contrary to a decrease in the vertically polarized component. Conventionally, a base station antenna is provided with a horizontally polarized antenna. A method has been developed (for example, see Non-Patent Document 1).
[0006]
As a method of using the horizontal polarization component, the reception signal power in each of the vertical polarization antenna and the horizontal polarization antenna of the base station is constantly monitored, and a polarization antenna having a large reception signal power is connected to the receiver. Selective combining and maximum ratio combining in which signals from both polarization antennas are weighted and combined by their signal power to interference power ratio (SIR) are exemplified. The above technique is called polarization diversity.
[0007]
FIG. 6 shows an example of an antenna used for conventional polarization diversity. As shown in the figure, in the antenna used for polarization diversity, a horizontal polarization antenna and a vertical polarization antenna are used as basic units, and transmission power is supplied to the horizontal polarization antenna by a horizontal polarization feed system, and the vertical polarization antenna is used. Transmission power is supplied to the vertically polarized antenna by the feed system.
[0008]
On the other hand, there is a space diversity system in which a plurality of antennas having the same or different polarization planes are installed at intervals, and there is a method for improving the received signal quality. FIG. 7 shows an example (vertical polarization) of an antenna used for space diversity. In the example shown in the figure, a pair of vertically polarized antennas are separated in the horizontal direction by a predetermined distance (several tens of wavelengths), and radio waves received by each antenna are combined.
[0009]
In a mobile communication system, a transmitted radio wave is received via a multiplex wave propagation path of a terrestrial object, so that instantaneous fluctuations (fading) of received signal power become independent of each other at antennas spaced by several tens of wavelengths. . For this reason, the received signal quality can be improved by performing selective combining and maximum ratio combining as in the case of the polarization diversity. In the above description, the reception at the base station has been described. However, the same effect can be obtained even at the reception at the mobile station, and the effect of improving the communication quality even when applied to the transmission at the base station and the mobile station.
[0010]
Further, it is known that communication quality is further improved by combining polarization diversity and space diversity, and a configuration for transmission and reception in a base station has been proposed. For example, in a base station, two pairs of a vertically polarized antenna and a horizontally polarized antenna (diversity branch) are installed at a distance that makes the fading independent, and are respectively set as branch 1 and branch 2. Then, the reception signal powers of the vertical polarization antenna and the horizontal polarization antenna are constantly measured and compared. If the reception signal power of the vertical polarization antenna is larger than the reception power of the horizontal polarization antenna, the vertical polarization of both branches is measured. The switch is rapidly switched so as to connect the wave antenna to the receiver, and if the relationship between the received signal powers is reversed, the switch is rapidly switched so as to connect the horizontally polarized antenna to the receiver. The receiver is a diversity receiver, and performs selective combining or maximum ratio combining using received signals from branches 1 and 2. Further, the transmitter switches to connect to the antenna on the polarization plane of the branch 1 where the received signal power is large (conventional method 1).
[0011]
As another method, two diversity branches are installed in the base station in the same manner as above, and a total of four antennas (two polarization antennas × 2 branches) are always connected to the diversity receiver to selectively combine or combine the maximum ratio. There is one that performs synthesis and switches the transmitter to connect to the antenna on the polarization plane of the branch 1 where the received signal power is large (conventional method 2).
[0012]
The measurement, comparison, and switching control in these two methods are performed by the base station for each communication partner mobile station. (For example, see Non-Patent Document 2).
[0013]
[Non-patent document 1]
Sakagami, Akiyama, IEICE, J70-B, 3, pp. 385-395, “Polarization diversity characteristics of mobile communication base station and relationship with polarization tilt angle on mobile station side”, March 1987.
[Non-patent document 2]
Sato, Fujii, IEICE Technical Report, RCS 2001-39, pp55-61, "W-CDMA base station diversity reception characteristics when mobile station antennas are used at an angle", May 2001.
[Problems to be solved by the invention]
However, this conventional mobile communication method has the following problems.
[0016]
That is, in the base station, it is necessary to measure and compare the received signal power for each polarization antenna of the branch for the received signal from each mobile station, but in a mobile communication system, several tens or more per base station are required. Since it is required to accommodate mobile stations at the same time, the size of the base station apparatus increases as the number of polarization planes used increases.
[0017]
Further, in the above-mentioned conventional method 1, it is necessary to frequently and quickly switch the antenna connected to each communication partner mobile station based on the comparison result of the received signal power at the base station. The processing volume at the station increases. Further, in the above-mentioned conventional method 2, since all are connected to the receiver without determining whether or not the antenna is an effective antenna, the device scale is increased.
[0018]
Further, since the antennas that can be simultaneously connected by the transmitter are limited to antennas of one polarization plane in one branch, effective transmission diversity is required to improve communication quality of base station transmission signals in CDMA and W-CDMA. There is a problem that technology cannot be applied. That is, in the transmission diversity technology, it is necessary to transmit two sequences of data (transmission diversity signals) having the same average received signal power to the mobile station and affected by independent fading from the base station. It is necessary to connect the transmitter to two antennas having the same polarization plane so as not to generate an unequal median value (difference in average received signal power).
[0019]
Therefore, the present invention has been made in view of the above points, and realizes simultaneously polarization diversity and space diversity with a simple configuration in a mobile communication system, particularly CDMA or W-CDMA, and realizes the scale and processing of a mobile communication device. An object of the present invention is to provide a mobile communication system, a base station, a mobile terminal, and a radio communication method that can improve communication quality without greatly increasing the amount from normal W-CDMA.
[0020]
[Means for Solving the Problems]
In order to solve the above problem, the present invention provides a first polarization antenna for transmitting and receiving a first polarization when performing wireless communication through a plurality of polarizations having different polarization planes, and a transmission and reception for a second polarization. And a second polarization frequency specific to the first polarization antenna and a second polarization frequency specific to the second polarization antenna are set. The first polarization antenna and the second polarization antenna are selected in response to input / output of a signal related to wireless communication. In the above invention, the first polarization may be a vertical polarization and the second polarization may be a horizontal polarization.
[0021]
According to the present invention, since a plurality of polarization antennas having different polarization planes are used, even when the inclination of the antenna of the communication terminal changes, the polarization antennas having different polarization planes are installed. In addition, the amount of reduction in one polarization can be compensated for by the other polarization, and the received signal power at the time of arrival can be prevented from being reduced by the cross polarization discrimination degree.
[0022]
Further, the reception quality of the first polarization antenna and the reception quality of the second polarization antenna are detected, and the reception quality of the first polarization and the reception quality of the second polarization are compared according to the detection result. It is preferable to change the settings of the first polarization frequency and the second polarization frequency in accordance with the following.
[0023]
In this case, an appropriate polarization antenna can be selected based on the reception quality, and communication can be performed through a frequency unique to the corresponding polarization antenna, so that communication according to the attitude of the communication terminal and the propagation environment can be performed. It is possible to do. In addition, since the frequency setting change according to the reception quality can be easily performed by applying the existing handover process, the present invention can be implemented without making a significant change to the existing system. it can.
[0024]
In the above invention, it is preferable that the first polarization antenna and the second polarization antenna form a branch antenna of at least a pair of diversity antennas. In this case, since the polarization diversity system and the space diversity system can be used together, communication quality can be further improved.
[0025]
The mobile communication system and the mobile communication method according to the present invention can be applied to a base station, a mobile station, a base station control device, and the like.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram illustrating the mobile communication system according to the present embodiment. In the present embodiment, the present invention will be described using a mobile communication system using W-CDMA as an example. Although FIG. 2 illustrates a case where two mobile terminals 2a and 2b are located for convenience of explanation, in actuality, a large number of mobile stations are located in a service area, and code division multiple access is used. They share the same frequency.
[0027]
Further, in the W-CDMA system, the mobile terminals 2a and 2b search a frequency band allocated to the system, identify a scrambling code and a frequency having the highest received signal power of the pilot channel, and determine a communication partner candidate ( Cell search operation). In this embodiment, the frequencies fu1, fu2, fu3, fu1, fd2, and fd3 are allocated to the system, and the uplink (mobile station to base station) frequency fu1, as shown in FIG. A set of fu2 and downlink (base station to mobile station) frequencies fd1 and fd2 is assigned, and an uplink frequency fu3 and a downlink frequency fd3 are assigned to the horizontally polarized antenna.
[0028]
Here, the mobile terminals 2a and 2b exist in various postures (inclinations) in the service area, and the inclination of the antenna from the vertical is different for each mobile device. Therefore, in mobile terminal 2a whose antenna tilt is nearly vertical, the pilot signal of fd1 or fd2 transmitted from the vertically polarized antenna has a larger received signal power than the pilot channel of fd3 transmitted from the horizontally polarized antenna. Received at. On the other hand, in the mobile terminal 2b whose antenna tilt is nearly horizontal, the pilot channel of fd3 transmitted from the horizontally polarized antenna has a larger received signal power than the pilot channel of fd1 or fd2 transmitted from the horizontally polarized antenna. Received.
[0029]
FIG. 3 is a block diagram illustrating an internal configuration of the base station according to the present embodiment. This embodiment is a configuration example in which spatial diversity is not applied and transmission diversity and reception diversity are not considered.
[0030]
The base station 1 has a branch # 1 including a horizontal polarization antenna and a vertical polarization antenna. The horizontal polarization antenna is supplied with transmission power by a horizontal polarization feed system, and the vertical polarization antenna has a vertical power supply. Transmission power is supplied by the polarization feeding system. Further, the base station 1 includes a demultiplexing circuit 11, a transceiver 12, and a polarization control device 3.
[0031]
The demultiplexing circuit 11 is a circuit that selects the first polarization antenna and the second polarization antenna according to the frequency setting in the polarization control device 3 and performs input / output of a signal related to wireless communication. It comprises a wave filter H, a vertical splitter V, and a reception quality monitoring unit 11a for monitoring the reception quality of the horizontal polarization and the vertical polarization.
[0032]
The duplexer V is a filter device that passes fd1, fd2 and fu1 and fu2 and blocks other frequency signals, and the duplexer H is a filter that passes fd3 and fu3 and blocks other frequency signals. Device. The reception quality monitoring unit 11a is a module that detects the reception quality of the horizontal polarization antenna and the reception quality of the vertical polarization antenna, and outputs the detection result to the polarization control device 3.
[0033]
The transceiver 12 is an interface for inputting and outputting a signal related to communication, and includes a transmitter 12a for transmitting a signal, a receiver 12c for receiving a signal, and the transmitter 12a and the receiver 12c. A duplexer 12b for inputting and outputting signals to and from the demultiplexer 11 is provided.
[0034]
The transmitter 12a transmits the W-CDMA signal at the downlink frequencies fdl, fd2, fd3 shown in FIG. Further, the receiver 12c receives the W-CDMA signal at the same uplink frequency fu1, fu2, fu3.
[0035]
The duplexer 12b allows the transmission signal from the transmitter to be guided to the demultiplexing circuit without flowing to the receiver side, and at the same time prevents the reception signal from the demultiplexing circuit from flowing to the transmitter side. This is a device for guiding to a receiver.
[0036]
The polarization control device 3 includes a handover detection unit 31 that detects the occurrence of a handover when the reception quality of the reception quality monitoring unit 11a is equal to or less than a predetermined value, and a horizontal polarization frequency unique to the horizontal polarization antenna. A frequency setting unit 33 for setting a vertical polarization frequency unique to the vertical polarization antenna, and a reception quality of the horizontal polarization and a reception quality of the vertical polarization according to a detection result in the reception quality monitoring unit 11a. And a notifying unit 34 for notifying the mobile station when the frequency setting is changed.
[0037]
When the handover detection unit 31 detects a handover, the frequency setting unit 33 changes the setting of the horizontal polarization frequency and the vertical polarization frequency according to the comparison result by the polarization comparison unit 32.
[0038]
The operation of the mobile communication system according to the present embodiment will be described. FIG. 4 is a sequence diagram showing an operation of the mobile communication system according to the present embodiment.
[0039]
As shown in the figure, first, when transmitting or receiving a call, the mobile station identifies a scrambling code and a frequency with the largest received signal power of the pilot channel (S101), selects a communication partner candidate, and Communication is started with the selected code and frequency (S102 and S103).
[0040]
Then, when the attitude of the mobile station changes during a call (S104), a handover is detected by the handover detector 31 (S105). When this handover is detected, the polarization comparison unit 32 compares the vertical polarization and the horizontal polarization based on the reception quality detected by the reception quality monitoring unit 11a, and selects an appropriate polarization plane ( S106). In accordance with the selection of the polarization plane, the frequency setting unit 33 executes a handover process to change the frequency (S107).
[0041]
The changed frequency is notified from the notifying unit 34 to the mobile terminal 2a or 2b through the transmitter 12a, and the frequency of the mobile terminal is changed by this notification (S109), and communication using the antenna with the optimal polarization plane is performed. It is continued (S110).
[0042]
As described above, in the present embodiment, since the base station 1 is provided with the vertical polarization antenna and the horizontal polarization antenna, the mobile terminal 2 recognizes an antenna having an appropriate polarization plane as a communication partner candidate. No power reduction occurs. That is, in the mobile terminal 2, even when the inclination of the antenna is almost horizontal, the horizontal polarization antenna is installed in addition to the vertical polarization antenna, It is possible to compensate by vertical polarization, and it is possible to prevent the reception signal power of the downlink signal from the base station when reaching the mobile station from being reduced by the cross polarization discrimination degree. Since the downlink and the uplink have a reversible relationship, the same effect can be obtained with the uplink.
[0043]
Further, in particular, in the mobile communication system according to the present embodiment, switching between the vertically polarized antenna and the horizontally polarized antenna can be performed using the existing handover processing, and it is necessary to add new processing to the base station side. Absent.
[0044]
[Second embodiment]
Next, a second embodiment of the present invention will be described. FIG. 5 is a block diagram illustrating a configuration of the mobile communication system according to the present embodiment. This embodiment is a configuration example in which a transmission diversity technique and a reception diversity are applied using both spatial diversity and polarization diversity, and a base station with two branches will be described as an example.
[0045]
Diversity transmitter 12a 'transmits W-CDMA transmission diversity signals at downlink frequencies fd1, fd2, fd3. Also, the diversity receiver 12c 'receives a W-CDMA signal for each branch at the uplink frequency fu1, fu2, fu3.
[0046]
The demultiplexing circuit 11 'has the same function as that of the first embodiment described above. However, in the present embodiment, in particular, in the present embodiment, the transmission of the W-CDMA diversity signal requires N The transmission / reception duplexer 12b 'and the demultiplexing circuit 11' are also provided for N systems so that the antenna is separated from the system and the transceiver 12 'is connected.
[0047]
According to such a mobile communication system according to the present embodiment, the base station 1 can selectively combine or maximally combine received signals from the mobile terminal 2 using the branch # 1 and the branch #N. Since the station can receive the transmission diversity signal, the communication quality can be improved.
[0048]
In each of the above-described embodiments, the base station detects handover and changes the frequency. However, the present invention is not limited to this. For example, a mobile station or a base station control device may perform handover. The detection and the setting change of the frequency may be executed.
[0049]
【The invention's effect】
As described above, according to the present invention, polarization diversity and space diversity can be achieved using an existing handover function and a cell search function of a mobile station without adding new processing to a normal W-CDMA base station. Since both can be used and the transmitter can be connected to two or more antennas having the same polarization plane, transmission diversity technology can be applied, and communication quality can be improved with a simple configuration. it can.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a mobile communication system according to a first embodiment.
FIG. 2 is an explanatory diagram showing frequencies assigned to a system in the first embodiment.
FIG. 3 is a block diagram illustrating an internal configuration of a base station according to the first embodiment.
FIG. 4 is a sequence diagram showing an operation of the mobile communication system according to the first embodiment.
FIG. 5 is a block diagram showing a configuration of a mobile communication system according to a second embodiment.
FIG. 6 is an explanatory diagram showing an example of an antenna used for conventional polarization diversity.
FIG. 7 is an explanatory diagram showing an example (vertical polarization) of an antenna used for conventional space diversity.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Base station 2 (2a, 2b) ... Mobile terminal 3 ... Polarization control apparatus 11, 11 '... Demultiplexing circuit 11a, 11a' ... Reception quality monitoring part 12, 12 '... Transceiver 12a ... Transmitter 12a' ... Diversity transmitter 12b Transmitter / receiver 12c Receiver 12c 'Diversity receiver 31 Handover detector 32 Polarization comparator 33 Frequency setting unit 34 Notification unit

Claims (7)

A mobile communication system that performs wireless communication through a plurality of polarizations having different polarization planes,
A first polarization antenna for transmitting and receiving the first polarization;
A second polarization antenna for transmitting and receiving a second polarization;
A frequency setting unit that sets a first polarization frequency specific to the first polarization antenna and a second polarization frequency specific to the second polarization antenna;
A mobile communication system comprising: a demultiplexing circuit that selects the first polarization antenna and the second polarization antenna according to a setting by the frequency setting unit and that inputs and outputs a signal related to wireless communication. . The mobile communication system according to claim 1, wherein the first polarization is a vertical polarization, and the second polarization is a horizontal polarization. A reception quality monitoring unit that detects reception quality in the first polarization antenna and the second polarization antenna;
A polarization comparison unit that compares the reception quality of the first polarization and the reception quality of the second polarization according to a detection result in the reception quality monitoring unit;
The said frequency setting part changes the setting of the said 1st polarization frequency and the said 2nd polarization frequency according to the comparison result by the said polarization comparison part, The Claim 1 or 2 characterized by the above-mentioned. Mobile communication system. The mobile communication system according to any one of claims 1 to 3, wherein the first polarization antenna and the second polarization antenna form a branch antenna of at least a pair of diversity antennas physically separated from each other. . A base station that performs wireless communication through a plurality of polarizations having different polarization planes,
A first polarization antenna for transmitting and receiving the first polarization;
A second polarization antenna for transmitting and receiving a second polarization;
A frequency setting unit that sets a first polarization frequency specific to the first polarization antenna and a second polarization frequency specific to the second polarization antenna;
A demultiplexing circuit that selects the first polarization antenna and the second polarization antenna according to the setting by the frequency setting unit and performs input / output of a signal related to wireless communication, the first polarization antenna, and the second polarization antenna; A reception quality monitoring unit that detects reception quality in the polarization antenna,
A polarization comparison unit that compares the reception quality of the first polarization and the reception quality of the second polarization according to a detection result in the reception quality monitoring unit;
The base station, wherein the frequency setting unit changes settings of the first polarization frequency and the second polarization frequency according to a comparison result by the polarization comparison unit. A mobile terminal that performs wireless communication through a plurality of polarizations having different polarization planes,
A first polarization antenna for transmitting and receiving the first polarization;
A second polarization antenna for transmitting and receiving a second polarization;
A frequency setting unit that sets a first polarization frequency specific to the first polarization antenna and a second polarization frequency specific to the second polarization antenna;
A mobile terminal comprising: a demultiplexing circuit that selects the first polarization antenna and the second polarization antenna according to a setting by the frequency setting unit and performs input / output of a signal related to wireless communication. A wireless communication method for wireless communication through a plurality of polarizations having different polarization planes,
Setting a first polarization frequency specific to the first polarization and a second polarization frequency specific to the second polarization (1);
(2) detecting reception quality related to the first polarization and the second polarization;
The reception quality of the first polarization and the reception quality of the second polarization are compared according to the detection result in the step (2), and the first polarization frequency and the second reception frequency are compared according to the comparison result. A wireless communication method comprising changing a setting of a frequency for dual polarization.

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