A multibeam transmitting/receiving apparatus is provided that is capable of increasing the accuracy of a direction in which a transmission beam is to be transmitted, with a simple arrangement. Signal power measuring units (8-1 through 8-L) of signal processing means (40-1 through 40-L) measure reception signal power levels averaged over a given time, using outputs from reception beam formers (5-1 through 5-L), and indicate the measured reception signal power levels to transmission antenna weight generator (30). Transmission antenna weight generator (30) generates transmission antenna weights, which has been weighted by a reception signal level, from a transmission antenna weight corresponding to reception signal power level P1 and a beam number B1 of a finger having a maximum reception signal power level, and a transmission antenna weight corresponding to reception signal power level P2 and a beam number B2 of a finger having the same path timing as the finger having the maximum reception signal power level. The generated transmission antenna weights are used in transmission beam former (16).

TECHNICAL FIELD

The present invention relates to a multibeam transmitting/receiving apparatus and method, and more particularly to a multibeam transmitting/receiving apparatus and transmitting/receiving method for receiving uplink signals with a plurality of antennas and controlling the directivities of downlink transmission signals transmitted from the antennas based on the received signals.

BACKGROUND ART

CDMA (Code Division Multiple Access) has attracted much attention as a wireless transmission process capable of greatly increasing the subscriber capacity and is expected as a wireless access process for the next-generation mobile communication cellular system. However, CDMA has a problem in that a base station receiver tends to suffer interference from another user's signal which is making simultaneous access with the same carrier, and a mobile station receiver is liable to cause interference due to a signal set to another user. One approach to remove such interference is the use of an array antenna. An array antenna has a plurality of antennas for receiving signals and combining complex-weighted values thereof to control the amplitudes and phases of the received signals for thereby forming a directivity beam to receive a desired user's signal and suppress other user's interference signals. A multi-beam process as one of control processes for such an array antenna is known from Document 1 shown below.

FIG. 1is a diagram showing by way of example a conventional multi-beam transmitting/receiving apparatus disclosed in Document 1. It is assumed that the number of antennas is N, N being an integer of 2 or greater, the number of multipaths is L, L being an integer of 1 or greater, and the multi-beam transmitting/receiving apparatus is assigned to a kth user, k being an integer of 1 or greater).

As shown inFIG. 1, the conventional multi-beam transmitting/receiving apparatus, which is assigned to the kth user, comprises N antennas1-1through1-N, duplexers2-1through2-N, L signal processing means40-1through40-L corresponding to L multipaths, adder10, decision unit11, searcher12, reception multibeam controller13, maximum signal power selector14, transmission multibeam controller15, and transmission beam former16.

L signal processing means40-1through40-L corresponding to L multipaths are identical in construction to each other. L signal processing means40-1through40-L comprise delay units3-1through3-L, despreading circuits4-1-1through4-L-N, reception beam formers5-1through5-L, channel estimating circuits6-1through6-L, complex conjugate circuits7-1through7-L, signal power measuring units8-1through8-L, and multipliers9-1through9-L.

Searcher12generates delay profiles for respective preset beams, using reception signals received through N antennas1-1through1-N and duplexers2-1through2-N. Searcher12detects delay times (path timing) of L multipaths from the generated delay profiles for respective preset beams, indicates the timing of the detected delay times of L multipaths to delay units3-1through3-L, and indicates the beam numbers of beams, with respect to which the delay times of multipaths are detected, to reception multibeam controller13.

A beam refers to a directivity pattern formed by assigning a preset antenna weight to each of antennas1-1through1-N, and a beam number refers to a number for specifying one of the preset beams.

Delay units3-1through3-N delay reception signals received by N antennas1-1through1-N by certain times based on multipath delay times set by searcher12, thereby delaying the reception signals depending on the L multipaths to differentiate the L multipaths as a first path to an Lth path. The reception signals output from delay units3-1through3-N are despread by despreading circuits4-1-1through4-L-N, and thereafter sent to reception beam formers5-1through5-L.

Reception multibeam controller13selects the reception antenna weights of beams corresponding to the beam numbers indicated by searcher12, sends the selected reception antenna weights to reception beam formers5-1through5-L, and indicates the beam numbers to maximum signal power selector14.

Reception beam formers5-1through5-L weights and combines the signals which have been delayed by delay units3-1through3-N and despread by despreading circuits4-1-1through4-L-N, using the reception antenna weights indicated by reception multibeam controller13.

The above operation of searcher12to indicate the timing of the delay times of the multipaths to delay units3-1through3-L of signal processing means40-1through40-L and also to indicate the beam numbers to reception multibeam controller13to enable them to start signal processing, is referred to as the assignment of fingers. A path detecting method disclosed in Document 2 entitled “Path detecting method, path detecting apparatus, and array antenna reception apparatus” may be used as a path detecting process performed by searcher12.

FIG. 2is a block diagram of each of reception beam formers5-1through5-L. Reception beam formers5-1through5-L are identical in construction to each other, and each comprise multipliers20-1through20-N, adder21, and complex conjugate circuits22-1through22-N. For the sake of brevity, signal processing means40-1will be described by way of example below.

Complex conjugate circuits22-1through22-N of reception beam former5-1generate complex conjugates of reception antenna weights selected by reception multibeam controller13and sends the generated complex conjugates to multipliers20-1through20-N. Reception signals that have been despread by despreading circuits4-1-1through4-1-N are multiplied by the complex conjugates of reception antenna weights which have been generated by complex conjugate circuits22-1through22-N, by multipliers20-1through20-N. The multiplied reception signals are then added together by adder21. Therefore, the reception signals are weighted and combined. The output from adder21is sent to channel estimating circuit6-1, signal power measuring unit8-1, and multiplier9-1. Thus, reception beam former5-1controls the amplitudes and phases of reception signals from antennas1-1through1-N to receive a reception signal with the directivity of a beam that has been formed in a certain direction.

Channel estimating circuit6-1estimates a channel distortion using the output from reception beam former5-1, and sends the estimated channel distortion to complex conjugate circuit7-1. Complex conjugate circuit7-1generates a complex conjugate of the channel distortion estimated by channel estimating circuit6-1. Multiplier9-1multiplies the complex conjugate of the channel distortion which has been generated by complex conjugate circuit7-1, by the output from reception beam former5-1, thereby compensating for the channel distortion. The output from multiplier9-1, which has been compensated for the channel distortion, is added by adder10for rake combination, and input to decision unit11. Decision unit11outputs its output as the reception data of the kth user.

Signal power measuring units8-1through8-L measure signal power levels averaged over a desired time, using the signals weighted and combined by reception beam formers5-1through5-L, and sends the measured signal power levels to maximum signal power selector14. Maximum signal power selector14selects the beam of a finger with respect to which the maximum signal power level has been obtained, using the signal power levels measured by signal power measuring units8-1through8-L and the beam numbers indicated by reception multibeam controller13, and indicates the selected beam to transmission multibeam controller15. Transmission multibeam controller15selects the transmission antenna weight of a corresponding beam from the beam number of the finger having the maximum signal power level indicated from maximum signal power selector14, and sends the selected transmission antenna weight to transmission beam former16.

Transmission beam former16weights and combines transmission signals, using transmission antenna weights generated by transmission multibeam controller15.

FIG. 3is a block diagram of transmission beam former16. Transmission beam former16comprises multipliers23-1through23-N and complex conjugate circuits24-1through24-N. Complex conjugate circuits24-1through24-N of transmission beam former16generate complex conjugates of transmission antenna weights selected by transmission multibeam controller15and sends the generated complex conjugates to multipliers23-1through23-N. The transmission data of the kth user is multiplied by the complex conjugates of transmission antenna weights which have been generated by complex conjugate circuits24-1through24-N, by multipliers23-1through23-N. The multiplied transmission data is then transmitted through duplexers2-1through2-N from antennas1-1through1-N.

Generally, the beams of a multibeam pattern are disposed so as to cover a given spatial area (e.g., a sector) as uniformly as possible. There are two ways of disposing the beams. According to one way, as shown inFIG. 4, the beams are disposed using an orthogonal multibeam pattern such that the peak direction of a beam is aligned with the null direction of another beam. According to the other scheme, as shown inFIG. 5, the beams are disposed using an equally spaced multibeam pattern such that a plurality of beams are arranged at equally spaced intervals. InFIGS. 4 and 5, the number of antennas is 6 and the number of beams is 6, with the horizontal axis representing angles in the given spatial area and the vertical axis beam gains. In the vicinity of a point of intersection between two adjacent beams, their beam gains are several dB lower than the peaks of the beams. Therefore, a desired signal coming from the direction of the point of intersection may be received with the two beams adjacent to the point of intersection, and the beam outputs may be combined with each other to compensate for a reception power level.

However, the conventional multi-beam transmitting/receiving apparatus suffers the following problems: Even if the beam of a finger having the maximum signal power level is selected using the signal power levels measured by signal power measuring units8-1through8-L and the beam numbers indicated by reception multibeam controller13, and a downlink transmission is performed using the selected beam, the transmission is not optimized. The reasons for the problem are as follows: If the user who is to transmit data is positioned near a point of intersection between two adjacent beams, then when one of the beams is selected and the data is transmitted with the selected beam, since the user is present in a position displaced off the peak direction of the beam, the direction of the beam for transmitting the data is not optimum, and the transmission tends to given interference to another user who is present in the peak direction of the beam. One solution to the above problem is to increase the number of beams of the multibeam pattern for increasing the resolution in the transmission direction. However, the solution is not practical as the amount of calculations required for searcher12to generate delay profiles is increased.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a multibeam transmitting/receiving apparatus and transmitting/receiving method which are capable of increasing the accuracy of the direction in which to transmit a transmission beam with a simple arrangement, even if a user who is to transmit data is positioned near a point of intersection between two adjacent beams.

To achieve the above object, there is provided in accordance with the present invention a multibeam transmitting/receiving apparatus for receiving uplink reception signals with a plurality of antennas and controlling the directivities of downlink transmission signals transmitted from the antennas based on the reception signals, wherein delay profiles for respective preset beams are generated, and if the same path timing as the path timing with respect to which a maximum reception power level has been detected is detected from different delay profiles, then it is judged that a mobile station to which data is to be transmitted is present in a position displaced off the peak direction of any beams, and the directivities of a downlink transmission signal are controlled based on reception antenna weights with respect to two beams from which the path timing has been detected and reception power levels obtained using two path timings.

According to the present invention, there is provided another multibeam transmitting/receiving apparatus for receiving uplink reception signals with a plurality of antennas and controlling the directivity of downlink transmission signals transmitted from the antennas based on the reception signals, the apparatus comprising:

a searcher for generating delay profiles for respective preset beams using the reception signals, detecting the path timing of a plurality of multipaths from the generated delay profiles for the respective beams, and outputting the detected path timing and a beam number with respect to which the path timing is detected;

a plurality of signal processing means each comprising a reception multibeam controller for outputting reception antenna weights corresponding to the beam number indicated from the searcher, a delay unit for delaying the reception signals by a given time based on the path timing set by the searcher, a reception beam former for weighting and combining the reception signals delayed by the delay unit using the reception antenna weight indicated from the reception multibeam controller, and a signal power measuring unit for measuring reception signal power level of the signal weighted and combined by the reception beam former;

a transmission antenna weight generator for detecting a maximum reception signal power level from the reception signal power levels indicated from the respective signal power measuring units of the signal processing means, determining whether the same path timing as the path timing set in first signal processing means in which the maximum reception signal power level is obtained is present in the path timing set in another signal processing means or not, and, if the same path timing as the path timing set in the first signal processing means is set in the other signal processing means, generating a transmission antenna weight based on the reception power level of the first signal processing means, the reception power level of second signal processing means in which the same path timing as the path timing set in the first signal processing means is set, and reception antenna weights set in the first and second signal processing means; and

a transmission beam former for weighting and combining the transmission signals using the transmission antenna weights generated by the transmission antenna weight generator.

According to the present invention, the searcher generates delay profiles for respective preset beams, and the signal processing means are associated with respective path timings to assign fingers. If the same path timing as the path timing with respect to which a maximum reception power level has been detected is detected from different delay profiles, then it is judged that a mobile station to which data is to be transmitted is present in a position displaced off the peak direction of any beams, and the directivities of a downlink transmission signals are controlled based on reception antenna weights with respect to two beams from which the path timing has been detected and reception power levels obtained using two path timings.

According to the present invention, therefore, a transmission beam is not formed in the same directivity pattern as a reception beam prepared in advance, but a transmission beam which is higher in accuracy than a reception beam is formed, so that a transmission antenna weight for transmitting data in the direction of a mobile station of a party to communicate with as a desired user can be generated with utmost ease. Therefore, data can be optimally transmitted to the desired user irrespective of the position where the user is present, and interference with other users which occurs if the peak direction of the beam is not optimum is reduced.

According to the present invention, there is provided still another a multibeam transmitting/receiving apparatus for receiving uplink reception signals with a plurality of antennas and controlling the directivities of downlink transmission signals transmitted from the antennas based on the reception signals, the apparatus comprising:

a searcher for generating delay profiles for respective preset beams using the reception signals, detecting the path timings of a plurality of multipaths from the generated delay profiles for the respective beams, and outputting the detected path timings, beam numbers with respect to which the path timing is detected, and reception power levels of respective fingers which are obtained when respective path timings are detected;

a plurality of signal processing means each comprising a reception multibeam controller for outputting reception antenna weights corresponding to the beam numbers indicated from the searcher, a delay unit for delaying the reception signals by a given time based on the path timing set by the searcher, and a reception beam former for weighting and combining the reception signals delayed by the delay unit using the reception antenna weights indicated from the reception multibeam controller;

a transmission antenna weight generator for detecting a maximum reception signal power level from the reception signal power levels for respective fingers indicated from the searcher, selecting a first finger in which the maximum reception signal power level is obtained, determining whether the same path timing as the path timing set in the first finger is present in the path timing set in another finger or not, and if the same path timing as the path timing set in the first finger is set in the other finger, generating a transmission antenna weight based on the reception power level of the first finger, the reception power level of a second finger in which the same path timing as the path timing set in the first finger is set, and reception antenna weights set in the first and second fingers; and

a transmission beam former for weighting and combining the transmission signals using the transmission antenna weights generated by the transmission antenna weight generator.

According to the present invention, since reception power levels of respective fingers which are obtained when path timings are detected are indicated from the searcher to the transmission antenna weight generator, it is possible to dispense with signal power measuring units for measuring reception power levels of signals that have been weighted and combined by the signal processing means.

The transmission antenna weight generator may generate transmission antenna weights using the angle of direction of a preset beam corresponding to the beam number.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention will first be described in detail below with reference to the drawings.FIG. 6is a diagram showing an arrangement of a multi-beam transmitting/receiving apparatus according to the first embodiment of the present invention. Those parts of the multi-beam transmitting/receiving apparatus which are identical to those shown inFIG. 1are denoted by identical reference characters. It is assumed inFIG. 6that the number of antennas is N, N being an integer of 2 or greater, the number of multipaths is L, L being an integer of 1 or greater, and the multi-beam transmitting/receiving apparatus is assigned to a kth user, k being an integer of 1 or greater.

As shown inFIG. 6, the multi-beam transmitting/receiving apparatus according to the present embodiment, which is assigned to the kth user, comprises N antennas1-1through1-N, duplexers2-1through2-N, L signal processing means40-1through40-L corresponding to multipaths with the number of paths being L, adder10, decision unit11, searcher12, reception multibeam controller13, transmission antenna weight generator30, and transmission beam former16.

The multi-beam transmitting/receiving apparatus according to the present embodiment differs from the conventional multi-beam transmitting/receiving apparatus shown inFIG. 1in that it has transmission antenna weight generator30replacing maximum signal power selector14and transmission multibeam controller15.

L signal processing means40-1through40-L corresponding to the respective multipaths are identical in construction to each other. L signal processing means40-1through40-L comprise delay units3-1through3-L, despreading circuits4-1-1through4-L-N, reception beam formers5-1through5-L, channel estimating circuits6-1through6-L, complex conjugate circuits7-1through7-L, signal power measuring units8-1through8-L, and multipliers9-1through9-L. Searcher12generates delay profiles for respective preset beams, using reception signals received through N antennas1-1through1-N and duplexers2-1through2-N. Searcher12detects delay times (path timing) of L multipaths from the generated delay profiles for respective preset beams, indicates the detected timing to delay units3-1through3-L and transmission antenna weight generator30, and indicates the beam numbers of beams, with respect to which the path timing is detected, to reception multibeam controller13.

The timing of the delay times of the respective multipaths is set in delay units3-1through3-L so that it will be used in common by all antennas1-1through1-N. This is because as N antennas1-1through1-N are closely disposed so that the reception signals are correlated to each other, all the delay profiles of respective N antennas1-1through1-N are can be regarded as being equal to each other.

Delay units3-1through3-N delay reception signals received by N antennas1-1through1-N by certain times based on multipath delay times set by searcher12, thereby delaying the reception signals depending on the L multipaths to differentiate the L multipaths as a first path to an Lth path. The reception signals output from delay units3-1through3-N are despread by despreading circuits4-1-1through4-L-N, and thereafter sent to reception beam formers5-1through5-L.

Reception multibeam controller13selects the reception antenna weights of corresponding beams from the beam numbers indicated by searcher12, sends the selected reception antenna weights to reception beam formers5-1through5-L, and indicates the beam numbers to transmission antenna weight generator30. Specifically, reception multibeam controller13may select the reception antenna weights of corresponding beams from the beam numbers easily by referring to a table, prepared in advance, storing the associative relationship between beams and reception antenna weights.

The above operation of searcher12to indicate the timing of the delay times of the multipaths to delay units3-1through3-L of signal processing means40-1through40-L and transmission antenna weight generator30and also to indicate the beam numbers to reception multibeam controller13to enable them to start signal processing, is referred to as the assignment of fingers.

Reception beam formers5-1through5-L are identical in construction to each other. As shown inFIG. 2, reception beam formers5-1through5-L each comprise multipliers20-1through20-N, adder21, and complex conjugate circuits22-1through22-N. For the sake of brevity, signal processing means40-1will be described by way of example below.

Complex conjugate circuits22-1through22-N of reception beam former5-1generate complex conjugates of reception antenna weights selected by reception multibeam controller13and sends the generated complex conjugates to multipliers20-1through20-N. Reception signals that have been despread by despreading circuits4-1-1through4-1-N are multiplied by the complex conjugates of reception antenna weights which have been generated by complex conjugate circuits22-1through22-N, by multipliers20-1through20-N. The multiplied reception signals are then added together by adder21. Therefore, the reception signals are weighted and combined. The output from adder21is sent to channel estimating circuit6-1, signal power measuring unit8-1, and multiplier9-1. Thus, reception beam former5-1controls the amplitudes and phases of reception signals from antennas1-1through1-N to receive a reception signal with the directivity of a beam that has been formed in a certain direction.

Channel estimating circuit6-1estimates a channel distortion using the output from reception beam former5-1, and sends the estimated channel distortion to complex conjugate circuit7-1. Complex conjugate circuit7-1generates a complex conjugate of the channel distortion estimated by channel estimating circuit6-1. Multiplier9-1multiplies the complex conjugate of the channel distortion which has been generated by complex conjugate circuit7-1, by the output from reception beam former5-1, thereby compensating for the channel distortion. The output from multiplier9-1, which has been compensated for the channel distortion, is added by adder10for rake combination, and input to decision unit11. Decision unit11outputs its output as the reception data of the kth user.

Signal power measuring units8-1through8-L measure signal power levels averaged over a desired time, using the signals weighted and combined by reception beam formers5-1through5-L, and sends the measured signal power levels to transmission antenna weight generator30.

Transmission antenna weight generator30generates a transmission antenna weight that forms a transmission beam having an accuracy higher than the resolution of a beam prepared in advance as selected by reception multibeam controller13, based on the reception signal power level measured by signal power measuring units8-1through8-L, the beam number indicated from reception multibeam controller13, and the path timing reception information indicated from searcher12, and sends the generated transmission antenna weight to transmission beam former16.

Specifically, transmission antenna weight generator30detects the maximum reception signal power level of reception signal power levels indicated by signal power measuring units8-1through8-L of signal processing means40-1through40-L, and determines whether the path timing which is the same as the path timing set in a first signal processing means where the maximum reception signal power level is obtained, is present in the path timing set in another signal processing means or not. If the path timing which is the same as the path timing set in the first signal processing means is set in another signal processing means, then transmission antenna weight generator30generates a transmission antenna weight based on the reception signal power level of the first signal processing means, the reception signal power level of a second signal processing means in which the path timing that is the same as the path timing set in the first signal processing means is set, and reception antenna weights set in the first and second signal processing means.

Transmission beam former16in the present embodiment weights and combines transmission signals, using transmission antenna weights generated by transmission antenna weight generator30.

As shown inFIG. 3, transmission beam former16comprises multipliers23-1through23-N and complex conjugate circuits24-1through24-N. Complex conjugate circuits24-1through24-N of transmission beam former16generate complex conjugates of transmission antenna weights generated by transmission antenna weight generator30and sends the generated complex conjugates to multipliers23-1through23-N. The transmission data of the kth user is multiplied by the complex conjugates of transmission antenna weights which have been generated by complex conjugate circuits24-1through24-N, by multipliers23-1through23-N. The multiplied transmission data is then transmitted through duplexers2-1through2-N from antennas1-1through1-N.

Operation of the multibeam transmitting/receiving apparatus according to the present embodiment will be described in detail below with reference to the drawings. Particularly, transmission antenna weight generator30shown inFIG. 6will be described in detail below. In a macrocell environment of land mobile communications, it is general that a radio wave transmitted from a mobile station is reflected, diffracted, and scattered by landscapes and features such as buildings and houses around the mobile station, and arrives at a base station as paths having substantially the same arrival angles. Therefore, when a transmission beam is formed based on an uplink reception signal, no problem often arises even if a transmission antenna weight is used for forming a transmission beam in the direction of a path having a maximum reception signal power level.

FIG. 7is a flowchart of an operation sequence of transmission antenna weight generator30according to the present embodiment. As shown in FIG.7, transmission antenna weight generator30selects a finger (signal processing means) with respect to which a maximum reception power level has been obtained (step A1). Then, transmission antenna weight generator30determines whether the path timing which is the same as the finger selected in step A1, with respect to which the maximum reception power level has been obtained, is present in the path timing set in another finger or not (step A2). If the path timing which is the same as the finger having the maximum reception power level selected in step A1is not present in the path timing set in another finger, then transmission antenna weight generator30judges that the path with respect to which the maximum reception power level has been obtained is coming from near the peak direction of the beam, and selects the transmission antenna weight of the transmission beam corresponding to the beam number of the finger selected in step A1with respect to which the maximum reception power level has been obtained (step A3). As with reception multibeam controller13, transmission antenna weight generator30may select the transmission antenna weights of corresponding beams from the beam numbers by referring to a table, prepared in advance, storing the associative relationship between beams and transmission antenna weights. If the path timing which is the same as the finger having the maximum reception power level selected in step A1is present in the path timing set in another finger, then transmission antenna weight generator30judges that the path with respect to which the maximum reception power level has been obtained is coming from near the direction of a point of intersection between beams and the finger of the same path is assigned to adjacent beams. Then, transmission antenna weight generator30generates a transmission antenna weight of a transmission beam from reception signal power level P1and beam number B1of the finger selected in step A1with respect to which the maximum reception power level has been obtained and reception signal power level P2and beam number B2of a finger having the same path timing as the finger selected in step A1(step A4). The transmission antenna weight selected in step A3or generated in step A4is sent from transmission antenna weight generator30to transmission beam former16(step A5).

The process of generating a transmission antenna weight in step A4shown inFIG. 7will be described in detail below. If it is assumed that the reception signal power level of the finger selected in step A1which has the maximum reception power level is represented by P1, the transmission antenna weight of the beam corresponding to beam number B1by W1(n)(n=1 through N), the reception signal power level of the finger in the same path timing as the finger selected in step A1by P2, and the transmission antenna weight of the beam corresponding to beam number B2by W2(n), then transmission antenna weight W(n) in step A4is calculated by the following equation:

If calculated transmission antenna weight W(n) is used as it is, then the value thereof is too large. Therefore, transmission antenna weight generator30normalizes transmission antenna weight W(n) weighted by the reception signal level as indicated by the above equation (1), as indicated by the equation shown below, to calculate transmission antenna weight WTX(n), and sends calculated transmission antenna weight WTX(n) to transmission beam former16.

FIG. 8shows by way of example transmission beam patterns formed by transmission beam former16when orthogonal multibeams are employed in a linear array of antennas in the present embodiment and the conventional multibeam transmitting/receiving apparatus. The horizontal axis represents angles in the given spatial area and the vertical axis beam gains.

InFIG. 8, the reception signal power level of the finger selected in step A1which has the maximum reception signal power level is indicated by P1, and the reception signal power level of the finger in the same path timing as the finger selected in step A1by P2. The solid-line curve represents the transmission beam pattern formed by the multibeam transmitting/receiving apparatus according to the present embodiment, and a broken-line curve the transmission beam pattern formed by the conventional multibeam transmitting/receiving apparatus. As a reference, the beam pattern of the finger in the same path timing as the finger selected in step A1is also indicated by a broken-line curve.

As shown inFIG. 8, it can be seen that the conventional transmission beam pattern forms a transmission beam displaced off the direction of arrival of the path having the maximum reception signal power level, whereas the transmission beam pattern formed by the multibeam transmitting/receiving apparatus according to the present embodiment forms a highly accurate transmission beam.

The process of generating a transmission antenna weight in step A4shown inFIG. 7may be differently performed as follows: If it is assumed that the reception signal power level of the finger selected in step A1which has the maximum reception signal power level is indicated by P1, the angle of direction of the beam corresponding to beam number B1by θ1, the reception signal power level of the finger in the same path timing as the finger selected in step A1by P2, and the angle of direction of the beam corresponding to beam number B2by θ2, then angle θTXof direction of the transmission beam is calculated by the following equation:

FIG. 9shows, by way of example, how signals are transmitted from a linear array of antennas1-1through1-N. The signals that are transmitted from a linear array of antennas1-1through1-N are caused to lead in phase at a mobile station, depending on the direction of arrival of the signals. Specifically, the signal that is transmitted from first antenna1-1and received by the mobile station leads the signal transmitted from nth antenna1-n in phase by (n−1)(2πd/λ)sin θTXwhere d represents the distance between adjacent ones of antennas1-1through1-N, and λ the wavelength of the carrier frequency. In order for the mobile station to receive the signals in phase, in view of the fact that complex conjugate circuits24-1through24-N of transmission beam former16generate complex conjugates of transmission antenna weights, it is necessary to calculate transmission antenna weight WTX(n) normalized by the following equation:

The angle of the beam direction of a corresponding beam may be selected from a beam number by referring to a table, prepared in advance, storing the associative relationship between beams and beam direction angles.

With the multibeam transmitting/receiving apparatus according to the present embodiment, searcher12generates delay profiles for respective preset beams, and if the same path timing as the path timing with respect to which the maximum reception power level has been detected is detected from different delay profiles, then transmission antenna weight generator30judges that the mobile station to which data is to be transmitted is present in a position displaced off the peak direction of any beams. When transmission antenna weight generator30makes such a judgement, transmission antenna weight generator30calculates a transmission antenna weight based on reception antenna weights with respect to two beams from which the path timing has been detected and reception power levels obtained using two path timings.

With the multibeam transmitting/receiving apparatus according to the present embodiment, therefore, it is possible to form a highly accurate transmission beam from the resolution of reception antenna weights of beams, prepared in advance, selected by reception multibeam controller13, and to generate a transmission antenna weight for transmission in the direction of a desired user, with utmost ease. Consequently, even if the desired user is present in any positions, data can optimally be transmitted to the desired user, and interference with other users, which has heretofore been problematic as it occurs if the peak direction of a beam is not optimum, is reduced.

A second embodiment of the present invention will be described in detail below with reference to the drawings.FIG. 10is a diagram showing an arrangement of a multi-beam transmitting/receiving apparatus according to the second embodiment of the present invention. Those parts of the multi-beam transmitting/receiving apparatus which are identical to those shown inFIG. 6are denoted by identical reference characters. The second embodiment is similar to the first embodiment. According to the first embodiment, for forming a transmission antenna weight, signal power measuring units8-1through8-L of signal processing means40-1through40-L utilizes a reception signal power level averaged over a desired time, using the outputs from reception beam formers5-1through5-L. According to the second embodiment, a reception signal power level at the time the delay times of respective multipaths are detected from the delay profiles of respective beams which are generated by searcher52is utilized.

The multi-beam transmitting/receiving apparatus according to the present embodiment differs from the multi-beam transmitting/receiving apparatus according to the first embodiment in that searcher12is replaced with searcher52, and signal processing means40-1through40-L with signal processing means50-1through50-L.

As shown inFIG. 10, signal processing means50-1through50-L of the multi-beam transmitting/receiving apparatus according to the present embodiment comprise delay units3-1through3-L, despreading circuits4-1-1through4-L-N, reception beam formers5-1through5-L, channel estimating circuits6-1through6-L, complex conjugate circuits7-1through7-L, and multipliers9-1through9-L. Operation of the multi-beam transmitting/receiving apparatus according to the present embodiment is the same as that of the first embodiment except that it is devoid of signal power measuring units8-1through8-L shown inFIG. 6, and will not be described below.

Searcher52according to the present embodiment indicates not only the timing of the delay times of respective multipaths, but also the reception signal power levels of respective fingers which are obtained when respective path timings are detected, to transmission antenna weight generator30. Other operation of antennas1-1through1-N, duplexers2-1through2-N, adder10, decision unit11, reception multibeam controller13, transmission antenna weight generator30, and transmission beam former16is the same as those of the first embodiment, and will not be described below.

According to the present embodiment, signal processing means50-1through50-L do not require a function to measure a reception signal power level. Therefore, the present embodiment offers a new advantage in that the amount of calculations performed by signal processing means50-1through50-L is reduced.

According to the present invention, it is possible to form a highly accurate transmission beam from the resolution of reception antenna weights of beams, prepared in advance, selected by reception multibeam controller13, and to generate a transmission antenna weight for transmission in the direction of a desired user, with utmost ease. Consequently, even if the desired user is present in any positions, data can optimally be transmitted to the desired user, and interference with other users, which has heretofore been problematic as it occurs if the peak direction of a beam is not optimum, is reduced.

In the first embodiment and second embodiment described above, the beam numbers used by transmission antenna weight generator30are indicated by searcher12through reception multibeam controller13. However, beam numbers at the time the delay times of respective multipaths are detected from the delay profiles of respective beams which are generated by searcher12may be directly indicated to transmission antenna weight generator30.

In the first embodiment and second embodiment described above, furthermore, the beam layout of either one of an orthogonal multibeam pattern and an equally spaced multibeam pattern may be employed as the beam layout of a multibeam pattern.

In the first embodiment and second embodiment described above, moreover, CDMA has basically been described. However, since TDMA (Time Division Multiple Access) or FDMA (Frequency Division Multiple Access) is capable of separating a plurality of arriving waves, the present invention is applicable to multibeam transmitting/receiving apparatus of the types other than CDMA.