JP2004297750A - Radio communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system that is capable of dealing with environmental fluctuation, for improving a communication quality while maintaining information transmission efficiency. <P>SOLUTION: In the radio communication system composed of a radio base station for forming beams with a plurality of different directions, and a plurality of terminal stations for communicating with the radio base station, each of the terminal stations is provided with a means for respectively estimating desired SIR(desired signal power/interference signal power)s of outgoing lines transmitted from the plurality of beams of the radio base station, a beam selecting means for selecting an optimal beam out of the desired SIRs, and a means for reporting the selected beam number by using an incoming line from the terminal station to the radio base station, and the radio base station is equipped with a transmission control means for transmitting an information signal to a terminal station by using a beam corresponding to the beam number when there is the beam number reported from the terminal station. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to wireless communication between a wireless base station and a terminal station used for mobile communication or the like, and in particular, to follow interference of propagation path characteristics, reduce interference, and achieve good information transmission efficiency. The present invention relates to a wireless communication system capable of performing the following.
[0002]
[Prior art]
2. Description of the Related Art In recent years, wireless communication systems centered on mobile phones have been recognized for their convenience, and have become widespread at a remarkable pace. On the other hand, as the number of users increases, problems such as tight use of frequencies and deterioration of communication quality have arisen. In particular, the occurrence of multipath fading due to reflection and scattering at surrounding structures is a problem specific to wireless communication, and is a major factor in deterioration of communication quality. Conventionally, as a countermeasure, in a radio base station, a method has been adopted in which a plurality of directional antennas having different directivities are arranged in a sector configuration to sequentially select an antenna having the best reception state. .
[0003]
Further, in a conventional FDD (Frequency Division Duplex) wireless communication system in which the frequency is different between the uplink and the downlink, information on the propagation path characteristics of the downlink is measured by a terminal station, and a transmission beam is controlled by a wireless base station. There is a feedback-type control method that extracts information necessary for the transmission and inserts the information into an uplink transmission signal to notify the radio base station.
[0004]
For example, in the conventional antenna selection control method, a pilot symbol of each beam (assuming N beams) is inserted into each slot of a downlink information symbol sequence and transmitted. Then, the terminal station detects the N pilot symbol strings transmitted from the respective beams, measures the respective received powers, and broadcasts the beam number having the largest received power on the uplink, thereby transmitting the next slot. , The radio base station transmits information symbols using the selected beam (for example, see Patent Document 1).
[0005]
[Patent Document 1]
JP-A-11-252614
[0006]
[Problems to be solved by the invention]
However, in the conventional antenna selection control method, as the number of beams increases, the ratio of pilot symbols to information symbols in the entire slot increases, and as a result, there is a problem in that the information transmission efficiency in the downlink deteriorates.
[0007]
An object of the present invention is to provide a wireless communication system which solves the above problems and realizes improvement of communication quality while maintaining information transmission efficiency while being robust, that is, capable of responding to environmental changes.
[0008]
[Means for Solving the Problems]
In view of the above object, the present invention provides a wireless base station that forms a beam having a plurality of different directional directions, and a wireless communication system including a plurality of terminal stations that communicate with the wireless base station, wherein each of the terminal stations is Means for estimating a ratio of desired signal power to interference signal power of a downlink transmitted from a plurality of beams of the radio base station, and beam selection for selecting an optimal beam from the desired signal power to interference signal power ratio Means, and means for reporting the selected beam number from the terminal station to the radio base station by using an uplink, wherein the radio base station receives the beam number reported from the terminal station. For example, there is provided a wireless communication system comprising: a transmission control unit that transmits an information signal to the terminal station using a beam corresponding to the beam number.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
First, this type of wireless communication system will be described a little more. As described above, in recent years, a wireless communication system centering on a mobile phone such as a PDC (Personal Digital Cellular) or a PHS (Personal Handy-phone System) has been considered to be convenient. Has been recognized and spread at a remarkable rate. On the other hand, as the number of users increases, problems such as tight use of frequencies and deterioration of communication quality have arisen. In particular, the occurrence of multipath fading due to reflection and scattering at surrounding structures is a problem specific to wireless communication, and is a major factor in deterioration of communication quality. As a countermeasure against this, a method has been adopted in a radio base station in which a plurality of directional antennas having different directivities are arranged in a sector configuration to sequentially select an antenna having the best reception state.
[0010]
Further, as a technique for further enhancing the functionality, a plurality of beams spatially orthogonal to each other are arranged in accordance with the positions of a plurality of terminal stations unevenly distributed in the service area and the arrival direction of a signal transmitted from the terminal station. And assigning them for reception of signals from each terminal station.
[0011]
Specifically, there is an adaptive array antenna that actively removes a signal from a terminal station (interfering station) that is in an arbitrary direction and is different from a terminal station that desires communication. An adaptive array antenna is a signal processing system that suppresses an interference signal at an output by adjusting and combining the amplitudes and phases of the received signals using a plurality of antenna elements. That is, in an environment in which an interference signal that affects communication quality exists, the beam is directed to the arrival direction of a desired signal, and the directional null is formed in the arrival direction of the interference signal. . Adjusting the amplitude and phase of the received signal is equivalent to complex weighting the output signal from each antenna element.
[0012]
In the case of the TDD (Time Division Duplex) method (a method in which the same frequency is used by time division in transmission and reception) for the downlink (base station transmission and terminal station reception), the transmission / reception channel characteristics are short sections. In the case of a sector configuration, the antenna selected in the uplink (base station reception, terminal station transmission) is used for the downlink as well, and when an adaptive array antenna is used, interference can be considered. By directing the null of directivity toward the station, sub-optimal control can be performed.
[0013]
On the other hand, in the case of the FDD (Frequency Division Duplex) scheme in which the frequency is different between the uplink and the downlink, the transmission / reception propagation path characteristics are different, and the above-described scheme for determining the downlink transmission method from the uplink reception signal has good characteristics. May not be obtained.
[0014]
Therefore, information on the propagation path characteristics of the downlink is measured by the terminal station, and information necessary when the radio base station controls the transmission beam is extracted. Then, there is a feedback-type control method of notifying the radio base station by inserting the information into an uplink transmission signal. In this case, it becomes possible to control the beam used for transmission on the radio base station side so that the reception state of the terminal station is always good irrespective of the difference between the transmission and reception frequencies, and the communication quality can be expected to be improved.
[0015]
For example, in the existing antenna selection control method, as described above, pilot symbols of each beam (assuming N beams in the figure) are inserted into each slot of a downlink information symbol sequence and transmitted. The terminal station detects the N pilot symbol strings transmitted from each beam, measures the respective received powers, and broadcasts the beam number having the largest received power on the uplink, so that the next slot , The radio base station transmits information symbols using the selected beam.
[0016]
Also, when an adaptive array antenna is applied, information to be broadcast in the uplink includes a propagation path transfer coefficient for each antenna element of the radio base station, and when estimating a transmission weight at a terminal station, It becomes a weight coefficient for the antenna element.
[0017]
In this way, by estimating parameters related to channel characteristics in the terminal station and notifying the radio base station using the uplink, even in a system where the uplink and downlink frequencies are different, fluctuations in the channel characteristics can be obtained. Followed beam control becomes possible.
[0018]
However, the beam selection type control method has a problem that as the number of beams increases, the ratio of pilot symbols to information symbols in the entire slot increases, and as a result, information transmission efficiency in the downlink deteriorates.
[0019]
On the other hand, when an adaptive array antenna is used, the channel transfer coefficient or weight coefficient broadcast from the terminal station is a complex number composed of amplitude and phase information, and it is necessary to feed back each coefficient corresponding to the number of antenna elements in the uplink. Therefore, the amount of information increases. For example, when the number of bits per weight coefficient is k and the number of beams is n, the amount of information to be fed back is also k * n bits. It is necessary to insert this control signal into an uplink information symbol for each slot, for example, and the ratio of control symbols to be inserted with respect to the uplink information symbol increases, so that the uplink information transmission efficiency may be significantly reduced. There is.
[0020]
The technique of forming null in the direction of the interfering station is an extremely effective method in ideal operation.However, considering the actual operation, the effects of processing delay in the terminal station and control delay due to feedback are considered. And the interference suppression effect may not be sufficiently obtained with respect to the processing complexity.
[0021]
Therefore, the present invention provides a wireless communication system that can improve communication quality while maintaining information transmission efficiency while being able to cope with environmental fluctuations.
[0022]
Embodiment 1 FIG.
A radio communication system, a radio base station, and a terminal station according to an embodiment of the present invention will be described with reference to the drawings. FIGS. 1 and 2 are block diagrams showing an example of the configuration of a radio base station and a terminal station, respectively, of a radio communication system according to an embodiment of the present invention. FIG. FIG. 3 is a diagram illustrating an example of a signal format.
[0023]
1 includes a plurality of antenna elements (# 1 to #N) 101 to 103 having directivity in different directions, duplexers 104 to 106, transmitters (Tx) 107 to 109, and a receiver ( Rx) 110 to 112, a reception beam control circuit 113, a demodulator 114, a beam number detector 115, a modulator 116, a pilot symbol generator 117, and a beam switching circuit 118.
[0024]
2 includes an antenna element 141, a duplexer 142, a receiver (Rx) 143, a transmitter (Tx) 144, each beam SIR estimator 145, a beam selection circuit 146, and a modulator 147. Is done.
[0025]
An operation of the wireless communication system according to the embodiment of the present invention will be described. In the terminal station shown in FIG. 2, a signal received by the antenna 141 is input to the receiver (Rx) 143 via the duplexer 142. The receiver 143 converts an RF (Radio Frequency) band received signal into a baseband digital signal. Each beam SIR estimating section 145 detects a pilot symbol (known signal) of each beam multiplexed and inserted at the head of each slot as shown in FIG. A signal power ratio (SIR: Signal-to-Interference Ratio) is estimated.
[0026]
As an example of a specific configuration of each beam SIR estimating section 145, a configuration as shown in FIG. 4 is given, and a pilot symbol generator 151, correlators (1 to N) 152 to 154, and a timing detector (1 to N) 155 to 157, and SIR calculators (1 to N) 158 to 160.
[0027]
The pilot symbol generator 151 generates the same pilot symbol for each beam as that inserted in the transmission slot in the radio base station. Correlators 152 to 154 perform a correlation operation between these pilot symbols and an output signal from receiver 143 to extract a desired signal component. After that, the timing detectors 155 to 157 detect the sample whose timing matches with the pilot symbol included in the received signal, that is, the timing of the sample whose SIR is most improved, and then use the sample of the detected timing. , SIR calculators 158 to 160 derive the SIR of each beam. The SIR value of each of these beams is input to the subsequent beam selection circuit 146.
[0028]
In addition, in the calculation in the SIR calculators 158 to 160, an accurate value can be estimated by performing an averaging process using a plurality of samples.
[0029]
The beam selection circuit 146 selects a beam having the highest SIR. This is reported to the radio base station in the uplink. The procedure is to insert the information of the selected beam number into the information symbol to be transmitted, perform modulation processing in the modulator 147, and then transmit the signal to the transmitter (Tx ) 144 is converted into an RF band signal, and radiated from the antenna 141 via the duplexer 142.
[0030]
As described above, since the information fed back from the terminal station may be only the beam number, it hardly affects the transmission efficiency of the uplink. For example, when eight beams are used, the control information only needs to be three bits. Further, since the beam number is broadcast, no matter what shape the beam is used in the radio base station, it is not necessary for the terminal station to consider it, and the system is excellent in expandability. The signal components including various information data such as voices transmitted from the radio base station are detected by a demodulator or the like. However, in the configuration example of FIG. This part is omitted for easier understanding.
[0031]
On the other hand, in the radio base station of FIG. 1, the modulated signals transmitted from the terminal station are received by N antenna elements 101 to 103 having directivities in different directions, respectively, and received via duplexers 104 to 106. (Rx) 110-112, and converts an RF band signal into a baseband digital signal.
[0032]
The antenna element groups 101 to 103 have different directivities, and are set according to the communication range of the wireless base station. For example, when 360 degrees around the entire circumference is covered by eight antenna elements, the beam width of each antenna element may be set to about 45 degrees and may be evenly arranged.
[0033]
The reception beam control circuit 113 adjusts the amplitude and phase of the reception signal of each antenna element and combines them to obtain an output signal. At this time, various existing algorithms are used in the control means of the reception beam control circuit 113. For example, various control algorithms of an adaptive array antenna for forming a null for an interference signal and a diversity combining technique such as selective combining and maximum ratio combining are used. No.
[0034]
The output signal after the array combination is demodulated by the demodulator 114, and the beam number detector 115 detects the information of the selected beam number included in the received data. In FIG. 1, a process of determining an information symbol from received data obtained from demodulator 114 is omitted to simplify the description and to make the features of the present invention easier to understand.
[0035]
The transmission operation will be described. Pilot symbol generator 117 generates pilot symbols of the designated length by the number of beams to be formed, and modulates the information symbols by modulator 116 and the beam numbers detected by beam number detector 115. The information is input to the beam switching circuit 118 together with the information.
[0036]
The beam switching circuit 118 creates a transmission slot having a format as shown in FIG. That is, an information symbol is added to the rear of the pilot symbol of the beam corresponding to the beam number detected by the beam number detector 115 (FIG. 3 shows an example when Beam2 is selected). For other beams, nothing is added or a null symbol such as an all-zero value is inserted. By performing multiplexing for simultaneously transmitting the transmission slots (here, N transmission slots) of these beams, it is possible to reduce the ratio of pilot symbols in the slots and prevent a reduction in transmission efficiency.
[0037]
In the embodiment of the present invention, since the pilot symbols of each beam are multiplexed and transmitted at the same time, the correlation characteristics of each pilot symbol should be as small as possible in consideration of the accuracy of the SIR estimation in the terminal station. Preferably, each pilot symbol is set to be orthogonal.
[0038]
For example, in a CDMA (Code Division Multiple Access) communication system, communication at the same time is made possible by identifying a user by using a spreading code. The present invention can be applied to the CDMA system by allocating orthogonal spreading codes to the pilot symbols and performing spreading processing, thereby realizing an efficient transmission system.
[0039]
Of course, if an orthogonal relationship is given between the pilot symbols, the spreading code can be the same between the beams, and in this case, the code can be used effectively.
[0040]
Then, the signals are converted into RF band signals by transmitters (Tx) 107 to 109 and radiated by antenna elements 101 to 103 via duplexers 104 to 106.
[0041]
In this way, a plurality of beams are formed in the radio base station, signals orthogonal to each other are multiplexed from each other and transmitted, and the terminal station selects and broadcasts the beam having the best reception state, so that the uplink and downlink can be obtained. Even in a wireless communication system using different frequencies used in a line, it is possible to maintain information transmission efficiency and follow a change in propagation path characteristics.
[0042]
Also, as shown in FIG. 5, in the radio base station, a plurality of array antennas 10a, 10b... Composed of antenna elements 101 to 103 are installed, and each of them is set so that the propagation path characteristics become uncorrelated with each other. By performing the above-described control in the array antenna described above, it is also possible to obtain a diversity effect. Each of the array antennas 10a, 10b,... That forms a beam having a plurality of different directional directions may select and transmit a beam used for transmission, or may transmit the beam as a whole (of all beams). One optimal beam (highest SIR) may be selected and transmitted. The control sections 104 to 118 in FIG. 1 may be provided individually for each array antenna, or one set may be provided in common and switched for connection.
[0043]
Embodiment 2 FIG.
Next, a radio base station according to another embodiment of the present invention will be described. FIG. 6 is a block diagram showing a configuration of a radio base station according to another embodiment of the present invention. The radio base station in FIG. 6 forms each beam by digital signal processing, and includes a plurality of omnidirectional antenna elements (# 1 to #N) 121 to 123, duplexers 124 to 126, and a transmitter ( Tx) 127 to 129, receivers (Rx) 130 to 132, receive beam control circuit 133, demodulator 134, beam number detector 135, modulator 136, pilot symbol generator 137, and beam switching A circuit 138 and a beam forming circuit 139 for forming a plurality of beams by digital signal processing.
[0044]
Explaining a specific operation, components other than the antenna elements (# 1 to #N) 121 to 123 and the beam forming circuit 139 are basically the same as corresponding portions shown in FIG.
[0045]
Arbitrary N antenna elements 121 to 123 each have a so-called non-directional antenna element having no directivity in a specific direction.
[0046]
Subsequent operations are the same as those of the radio base station shown in FIG. 1, except that a beam switching circuit 138 creates a transmission slot for each beam, and a beam forming circuit 139 performs digital signal processing on a plurality of directional directions. Are formed and transmitted by the antenna elements 121 to 123.
[0047]
FIG. 7 shows an example of a specific configuration of the beam forming circuit 139. In FIG. 7, the beam forming circuit includes distributors (1 to L) 171 to 173, a weight coefficient adder 174 for assigning weight coefficients, and combiners (1 to N) 175 to 177. FIG. 7 shows an example in which the number of beams to be formed is L, but the number L of beams need not be the same as the number N of antenna elements. The transmission slots of the respective beams generated by the beam switching circuit 138 in FIG. 6 are distributed to N by the distributors 171 to 173.
[0048]
Each distributed slot has a complex weighting factor w_i ^j(I = 1,..., N; j = 1,..., L), the amplitude and phase components are adjusted by 174, and then combined by the combiners (1 to N) 175 to 177 and multiplexed. You.
[0049]
That is, w₁ ^j~ W_N ^jCorresponds to the weighting factor of the array antenna for beam j, and by preparing L sets of such weighting factors, beamforming is performed in the digital stage.
[0050]
Further, these processes can be realized not only by hardware as shown in FIG. 7 but also by software. Therefore, it becomes easy to use orthogonal multi-beams by DFT (Discrete Fourier Transform) or FFT (Fast Fourier Transform).
[0051]
By forming each beam, that is, setting the beam shape by the digital signal processing as described above, the beam can be freely re-formed according to the installation environment of the wireless base station and according to the environmental fluctuation.
[0052]
Embodiment 3 FIG.
Next, a radio base station according to another embodiment of the present invention will be described. FIG. 8 is a configuration block diagram of a radio base station according to this embodiment, and FIG. 9 is a diagram showing an example of a signal format of a transmission slot in the radio base station according to this embodiment.
[0053]
In FIG. 8, the receiving unit is the same as in the first or second embodiment, and a description thereof is omitted. The third radio base station according to this embodiment transmits a known signal for identifying each beam as a common pilot of a common channel, and includes a plurality of antenna elements 301 to 303, duplexers 304 to 306, (Tx) 307 to 309, a beam forming circuit 310 for forming a plurality of beams, a pilot symbol generator 311, a beam switching circuit 312, and a modulator 313. FIG. 8 shows a configuration accommodating M terminal stations, and includes a beam switching circuit and a modulator corresponding to an individual channel with each terminal station.
[0054]
In the above embodiment, a known signal for identifying a beam, that is, a pilot symbol is added to the head of an information symbol to be transmitted to a terminal station, that is, a dedicated channel with each terminal station. In the embodiment, the efficiency is further improved by adopting a configuration in which these pilot symbols are commonly used by one base station using a common pilot of a common channel.
[0055]
Specifically, as shown in FIG. 8, in the individual channel of each terminal, a signal obtained by modulating information to be transmitted by modulator 313 is input to beam switching circuit 312 together with a selected beam number detected from an uplink received signal. , The beam used for transmitting the information symbol is sequentially switched. This process is performed on each channel corresponding to each terminal, and transmission signals for all terminals are multiplexed. Then, pilot symbols (known signals) generated by pilot symbol generator 311 are further multiplexed as common pilots of a common channel. You. Subsequent processing is the same as in the above embodiment.
[0056]
By using the common pilot of the common channel in this manner, the transmission slot configuration as shown in FIG. 9 is obtained, and it is possible to further reduce the influence on the individual channel throughput of the terminal station in the downlink. The common pilot in the common channel is also standardized as a CPICH (Common Pilot Channel) in 3GPP (3rd Generation Partnership Project). In particular, since the Secondary CPICH is a specification that can use a plurality of channels, a plurality of beams are used. Can be assigned a CPICH. Therefore, the present embodiment can be easily applied to the CDMA communication system.
[0057]
Although FIG. 9 shows a configuration in which the number of pilot symbols is smaller than the number of information symbols of the dedicated channel, it is of course possible to improve the beam selection accuracy by increasing the number of pilot symbols. In particular, in the CDMA communication system, a similar effect can be expected by increasing the spreading factor of the common pilot channel.
[0058]
Embodiment 4 FIG.
FIG. 10 shows an example of the configuration of each beam SIR estimator (145 in FIG. 2) of the terminal station according to the present invention in the CDMA communication system. Each beam SIR estimator 145a in FIG. 10 includes a spreading code generator 181, MFs (matched filters) (1-N) 182-184, and respective path timing detectors (1-N) 185-187. , RAKE (1-N) combiners 188-190 and SIR calculators (1-N) 191-193.
[0059]
The spreading code generator 181, Matched Filters (MF) 182 to 184, the respective path timing detectors 185 to 187, and the SIR calculators 191 to 193 include a pilot symbol generator 151 and a correlator shown in FIG. Operations similar to those of the 152 to 154, the timing detectors 155 to 157, and the SIR operation units 158 to 160 are performed.
[0060]
In the CDMA communication system, a spread code having a data rate higher than that of an information symbol is spread over a wideband signal and transmitted. On the receiver side, the original information symbols are reproduced by performing correlation detection using the same spreading code as that used on the transmitting side (referred to as despreading processing). At this time, the smaller the cross-correlation characteristic of the spreading code assigned to each user, the greater the interference suppression effect in the despreading process.
[0061]
In the wireless communication system according to the embodiment of the present invention, this characteristic is used for beam selection processing in the terminal station. This will be specifically described below.
[0062]
As described in the first embodiment, when a terminal station receives a transmission slot in which a pilot symbol is spread by using a spreading code orthogonal to each beam, a spreading code generator 181 shown in FIG. The same spreading code as that used in is generated and input to the MFs 182 to 184. After performing a correlation detection process (despreading process) between the received signal and the spread code in the MFs 182 to 184, the path timing detectors 185 to 187 detect the paths of the desired signal arriving through various propagation paths. Detect the delay timing. The RAKE combiners 188 to 190 perform RAKE combining for maximal ratio combining of the respective path components based on the respective path timings, and use the combined output to estimate the SIR value of each beam in the SIR calculators 191 to 193. I do.
[0063]
By assigning orthogonal spreading codes to each beam in this manner, a high interference suppression effect can be obtained at the time of correlation detection, and more accurate and most efficient by estimating the SIR of each beam using the signal after RAKE combining. It is possible to select a good beam.
[0064]
Embodiment 5 FIG.
FIG. 11 shows an example of the configuration of each beam SIR estimating unit of the terminal station in another embodiment of the present invention in the CDMA communication system. Each beam SIR estimating unit 145b in FIG. 11 includes a spreading code generator 201, MFs (matched filters) (1 to N) 202 to 204, and maximum path timing detectors (1 to N) 205 to 207. , SIR calculators (1 to N) 208 to 210.
[0065]
The spreading code generator 201, the MFs 202 to 204, and the SIR calculators 208 to 210 have the same operations as the spreading code generator 181, the MFs 182 to 184, and the SIR calculators 191 to 193 in the fourth embodiment. Is omitted.
[0066]
The maximum path timing detectors 205 to 207 detect the timing of the path having the highest reception level among the paths of the desired signal arriving through various propagation paths. Then, based on the detected sample timing of the maximum path, the SIR calculators 208 to 210 estimate the SIR value of each beam.
[0067]
By adopting a configuration in which only the path having the maximum reception level is detected, the timing detector can be simplified and the number of RAKE combiners can be reduced, so that the device configuration of the terminal station can be simplified.
[0068]
Embodiment 6 FIG.
FIG. 12 shows a configuration example of each beam SIR estimating unit of the terminal station in another embodiment of the present invention in the CDMA communication system. It comprises a spreading code generator 331, Matched Filters (MF) 332 to 334, path timing detectors 335 to 337, RAKE combiners 338 to 340, and SIR calculators 341 to 343. The operation other than the spreading code generator 331 is the same as that of the fourth embodiment, and the description is omitted. Of course, a configuration using only the path of the maximum reception level as shown in FIG. 11 described in the fifth embodiment is also possible.
[0069]
In Embodiments 4 and 5, an orthogonal spreading code is assigned to each beam, so that excellent separation characteristics can be obtained. However, the number of orthogonal codes is limited, and in order to accommodate more terminals, it is not efficient to allocate codes for each beam of each terminal. Therefore, in the present embodiment, as shown in FIG. 12, only one spreading code is generated by the spreading code generator 331, and this is commonly used between beams. Of course, in this case, as described in the first embodiment, it is necessary for the radio base station to spread pilot symbols (known signals) of each beam with the same spreading code.
[0070]
Therefore, RAKE combining and SIR estimation of each beam in the present embodiment are performed using only pilot symbols that are orthogonal to each other.
[0071]
Further, this configuration can realize a terminal station corresponding to the radio base station using the common pilot of the common channel shown in the third embodiment, and can provide one base station with one common pilot channel for beam identification. It is sufficient to prepare two spread codes, and the orthogonal code can be effectively used.
[0072]
Embodiment 7 FIG.
In the above embodiment, the terminal station selects the beam having the best SIR. However, depending on the propagation path characteristics, a beam having a high SIR may be generated due to multipath arriving from a distant angle. There may be more than one. The beam selection method in such a case will be described.
[0073]
In the terminal station, the target SIR is set in advance as a threshold. The SIR of each beam is estimated using pilot symbols in a transmission slot from the radio base station, and a plurality of beams having a value larger than the previous target SIR are selected. Each of these selected beam numbers is reported to the radio base station via the uplink, and the radio base station transmits information symbols using the plurality of beams.
[0074]
FIG. 13 shows a transmission slot configuration in a radio base station according to the present embodiment. Multiplexing is performed to simultaneously transmit the transmission slots of these N beams. FIG. 13 shows an example in which J beams among N beams are selected by the terminal station. By adding an information symbol to each transmission slot of the selected beam and multiplexing the information, FIG. Thus, it is possible to efficiently use a beam having a good propagation path characteristic.
[0075]
Also, in a wireless base station configuration using a common pilot channel as in Embodiment 3, transmission using a plurality of beams is of course possible.
[0076]
Embodiment 8 FIG.
A method of forming a transmission beam in the radio base station according to the present embodiment will be described. FIG. 14 shows an example in which beams are formed at equal intervals in a horizontal plane. The selected beam 221 is a beam selected by the terminal station, and is used by the radio base station to transmit an information symbol in the next slot. The adjacent beams 222, 223 are beams adjacent thereto.
[0077]
In a system that feeds back some control information from a terminal station to a radio base station, the amount of information affects the information transmission efficiency of the uplink. Therefore, it is desirable that the control information is as small as possible. This embodiment shows a method for realizing this.
[0078]
A specific operation will be described. It is assumed that in an initial state of communication, pilot symbols are transmitted using all beams, and beam number information selected by the terminal station is broadcast to the radio base station via the uplink. As described in the above embodiment, the radio base station detects the selected beam number and creates a transmission slot. At this time, a transmission slot is not created using all beams, but a slot is created using only the selected beam 221 and adjacent beams 222 and 223 adjacent thereto. Then, the beam to be sequentially selected is updated.
By doing so, it is possible to reduce the processing amount in the radio base station, and also to reduce the beam selection processing in the terminal station and the number of control information symbols inserted into the uplink.
[0079]
Although FIG. 14 shows an example in the horizontal plane, when a beam is formed also in the vertical plane, the beam configuration of each radio base station can be handled by using an adjacent beam around the selected beam 221.
[0080]
In addition, by regularly determining the selected beam using all the beams, it becomes possible to more accurately follow a change in propagation path characteristics.
[0081]
Embodiment 9 FIG.
Another transmission beam forming method in the radio base station according to the present embodiment will be described. FIG. 15 shows an example in which beams are formed at equal intervals in a horizontal plane. The selected beam group 225 is a set of beams selected by the terminal station in the initial state.
[0082]
In the initial state of communication, the radio base station transmits pilot symbols of all beams as described in the first embodiment. The terminal station estimates the SIR of each beam, and designates a selected beam group 255 from a favorable SIR angle range. At this time, the number of beams included in the selected beam group 255 is specified in advance.
[0083]
For setting the range of the beam group, a method of sliding one beam at a time or a method of continuously setting the beam group can be used.
[0084]
In the radio base station notified of the information of the selected beam group by the uplink, the pilot symbols are transmitted using the beams in the selected beam group 225, and the beam selection process is sequentially updated.
[0085]
In addition, by periodically resetting the beam group to be used as described above, it becomes possible to follow a change in propagation path characteristics.
[0086]
Embodiment 10 FIG.
Another transmission beam forming method in the radio base station according to the present embodiment will be described. FIG. 16 shows an example in which beams are formed at equal intervals in a horizontal plane. In FIG. 16, a indicates an initial state, and b indicates a beam group at the start of communication. The selected beam group 230 is a set of beams selected by the terminal station in the initial state. The method of setting the selected beam group 230 is the same as that described in the ninth embodiment.
[0087]
The radio base station densely reshapes the beam using the maximum allowable degree of freedom in the angular range of the selected beam group 230 broadcast from the terminal station. After the start of communication, the information symbols are transmitted using the re-formed beam group 231.
[0088]
By arranging the beams densely in the SIR good angle range in this way, it is possible to more accurately follow the fluctuation of the propagation path characteristics.
[0089]
In addition, by periodically resetting the beam group to be used as described above, it becomes possible to follow a change in propagation path characteristics.
[0090]
【The invention's effect】
As described above, according to the present invention, in a wireless communication system including a wireless base station that forms beams having a plurality of different directional directions and a plurality of terminal stations that communicate with the wireless base station, each of the terminal stations is Means for estimating a ratio of desired signal power to interference signal power of a downlink transmitted from a plurality of beams of the radio base station, and beam selection for selecting an optimal beam from the desired signal power to interference signal power ratio Means, and means for reporting the selected beam number from the terminal station to the radio base station by using an uplink, wherein the radio base station receives the beam number reported from the terminal station. For example, since the wireless communication system includes transmission control means for transmitting an information signal to the terminal station using a beam corresponding to the beam number, it is possible to cope with environmental changes. While retaining information transmission efficiency, provide improved communication quality can be provided a wireless communication system.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a wireless base station in a wireless communication system according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a terminal station of the wireless communication system according to one embodiment of the present invention.
FIG. 3 is a diagram showing an example of a signal format of a transmission slot in the radio base station according to one embodiment of the present invention.
FIG. 4 is a diagram illustrating an example of a specific configuration of each beam SIR estimator in FIG. 2;
FIG. 5 is a block diagram showing a configuration of a wireless base station of the wireless communication system according to the present invention provided with a plurality of array antennas.
FIG. 6 is a block diagram illustrating a configuration of a wireless base station of a wireless communication system according to another embodiment of the present invention.
FIG. 7 is a diagram illustrating an example of a specific configuration of the beam forming circuit of FIG. 6;
FIG. 8 is a configuration block diagram of a radio base station according to another embodiment of the present invention.
9 is a diagram illustrating an example of a signal format of a transmission slot in the wireless base station in FIG.
FIG. 10 is a diagram showing an example of a specific configuration of each beam SIR estimating unit of the terminal station in the CDMA communication system of the present invention.
FIG. 11 is a diagram showing another example of a specific configuration of each beam SIR estimating unit of the terminal station in the CDMA communication system of the present invention.
FIG. 12 is a diagram showing another example of a specific configuration of each beam SIR estimating unit of the terminal station in the CDMA communication system of the present invention.
FIG. 13 is a diagram illustrating an example of a signal format of a transmission slot in a radio base station according to another embodiment of the present invention.
FIG. 14 is a diagram for explaining a transmission beam forming method in a radio base station according to another embodiment of the present invention.
FIG. 15 is a diagram for explaining a transmission beam forming method in a radio base station according to still another embodiment of the present invention.
FIG. 16 is a diagram for explaining a transmission beam forming method in a radio base station according to still another embodiment of the present invention.
[Explanation of symbols]
10a, 10b array antennas, 101 to 103, 141 antenna elements, 104 to 106, 142 duplexers, 107 to 109, 144 transmitters (Tx), 110 to 112, 143 receivers (Rx), 113 reception beam control circuits, 114 Demodulator, 115 beam number detector, 116 modulator, 117 pilot symbol generator, 118 beam switching circuit, 145 each beam SIR estimator, 146 beam selection circuit, 147 modulator, 151 pilot symbol generator, 152-154 correlation Units (1 to N), 155 to 157 Timing detectors (1 to N), 158 to 160 SIR calculators (1 to N).

Claims (15)

In a wireless base station that forms a beam having a plurality of different directional directions, and a wireless communication system including a plurality of terminal stations that communicate with the wireless base station,
Each of the terminal stations,
Means for estimating the ratio of the desired signal power to the interference signal power of the downlink transmitted from the plurality of beams of the radio base station,
Beam selection means for selecting an optimal beam from the desired signal power to interference signal power ratio,
Means for reporting the selected beam number using an uplink from the terminal station to the radio base station,
With
The wireless base station,
If there is the beam number broadcast from the terminal station, transmission control means for transmitting an information signal to the terminal station using a beam corresponding to the beam number,
A wireless communication system comprising: The radio base station, an array antenna configured by a plurality of antenna elements for forming a plurality of beams, and a beam forming means for arbitrarily setting the beam shape according to the environment in which the radio base station is installed The wireless communication system according to claim 1, comprising: The transmission control means of the radio base station multiplexes and adds a known signal different for each of a plurality of beams formed by the radio base station to an information signal transmitted from the radio base station to the terminal station, The wireless communication system according to claim 1, wherein the desired signal power to interference signal power ratio estimating means of the station detects the known signal and estimates a desired signal power to interference signal power ratio. The wireless communication system according to claim 3, wherein the known signal is allocated as a common pilot of a common channel and multiplexed on a transmission signal of a dedicated channel with each terminal station. The wireless communication system according to claim 3, wherein mutually orthogonal data symbols are used as the known signal. A radio communication system performs communication of a CDMA communication system, and a transmission control means of the radio base station spreads the known signal with an orthogonal code, and multiplexes a spread signal of a known signal for each beam. To the information signal transmitted to the terminal station, the desired signal power to interference signal power ratio estimating means of the terminal station detects the spread known signal, the desired signal power to interference signal power ratio The wireless communication system according to claim 3, wherein the estimation is performed. The known signal is formed into a bit sequence or a symbol sequence orthogonal to each other, spread by a common spreading code, and then multiplexed as a common pilot of a common channel to a transmission signal of an individual channel with each terminal station. Item 7. A wireless communication system according to item 6. 4. The radio according to claim 3, wherein the desired signal power to interference signal power ratio estimating means of the terminal station detects the known signal after RAKE combining and estimates the desired signal power to interference signal power ratio. Communications system. The desired signal power to interference signal power ratio estimating means of the terminal station detects the known signal included in a path having the highest received power in the desired signal group received by the terminal station and detects the desired signal power to interference signal. The wireless communication system according to claim 3, wherein the signal power ratio is estimated. The beam selection means of the terminal station selects all beams whose desired signal power to interference signal power ratio is larger than a set threshold, and the transmission control means of the radio base station transmits an information signal using these beams. The wireless communication system according to claim 1, wherein: In the terminal station desired signal power to interference signal power ratio estimating means, beam selecting means, notifying means, and transmission control means of the radio base station, in the initial state of communication start, determine the beam number using all beams. After that, by using the beam corresponding to the beam number and the beam adjacent thereto, the ratio of the desired signal power to the interference signal power in the downlink is estimated, and the beam to be sequentially selected is updated. 2. The wireless communication system according to 1. In the desired signal power to interference signal power ratio estimating means of the terminal station, the beam selecting means, the notifying means, and the transmission control means of the radio base station, in the initial state of communication start, the terminal station downloads using all beams Estimate the desired signal power to interference signal power ratio of the line, broadcast the information of the good reception angle range using the uplink to the radio base station, and then in the radio base station selected range 2. The wireless communication system according to claim 1, wherein a ratio of the desired signal power to the interference signal power in the downlink is estimated using a plurality of beams formed in the step (b), and a beam to be sequentially selected is updated. 13. The wireless communication system according to claim 12, wherein the ratio of the desired signal power to the interference signal power in the downlink is periodically estimated using all beams, and information on an angle range in a good reception state is updated. 13. The wireless communication system according to claim 12, wherein, based on the angle range notified by the terminal station, a plurality of beams are re-formed within the range by making maximum use of an allowed degree of freedom. A plurality of array antennas for forming the plurality of beams having different directivity directions are arranged at a distance such that the correlation characteristics of the propagation path can be sufficiently ignored, and a beam used for transmission is selected and transmitted. The wireless communication system according to claim 1, wherein

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