GB2396501A

GB2396501A - Directing radio beam

Info

Publication number: GB2396501A
Application number: GB0405061A
Authority: GB
Inventors: Hajime Hamada; Michiharu Nakamura; Yasuyuki Oishi
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 2000-02-23
Filing date: 2000-12-20
Publication date: 2004-06-23
Anticipated expiration: 2020-12-20
Also published as: GB2396501B; GB0405061D0

Abstract

A radio beam carrying data is directed from an array LAA of n equally spaced antenna elements A0 ... A4 towards a receiver of a mobile unit MS by applying a first reference signal S1 to elements 1 to n-1, ie. A0 ... A3; applying a second reference signal S2 to elements 2 to n, ie. A1 ... A4, which causes the phase centre PAT1, PAT2 of the transmission to move along the array by a distance d equal to the spacing of the antenna elements; receiving both signals at the mobile unit MS and determining their relative phase phil in phase detector PDT; and using the relative phase as the phase difference between weighted copies of a data signal applied respectively to adjacent elements of the antenna array. The two reference signals may be different spread spectrum signals, or the same signal transmitted at different times. The system may be used in a cellular telephone base station BS, the mobile unit MS being in a handset. A modification to the receiver (figure 20) uses only the first copy of each signal received, enabling multipath to be circumvented.

Description

GB 2396501 A continuation (74) Agent and/or Address for Service: Haseltine

Lake & Co Imperial House, 15-19 Kingsway, LONDON, WC2B BUD, United Kingdom

239650 1

RADIO TRANSMITTER AND METHOD OF CONTROLLING DIRECTION OF

RADIO-WAVE EMISSION

This invention relates to a method of controlling the 5 direction of emission of radio waves from a radio transmitter which transmits radio waves (a beam) from a base-station antenna in the direction of a mobile station while providing the radio waves with directivity and to a radio transmitter for implementing this method.

10 In mobile radio communication systems, a base station cannot use a fixed directional pattern for communication with a mobile station; the base station performs communication using a non-directional antenna.

however, since transmission by a non-directional antenna emi s radio waves in directions in which the target mobile station aces not exist, not only is power 20 efficiency poor but the fact that mobile stations other than 'he target mobile station are subjected to radio interference degrades communication quality. As a consequence of such interference, a frequency that has 25 been used - commun-caticn with a certain mobile station - - / - 35. /

- 2 - can be re-utillzed only at a location far enough away for the radio waves to be attenuated sufficiently This results in inefficient utilization of frequencies. A method of improving frequency ui_lization efficiency by 5 establishing sectors (sector zones) and using a sector antenna is known in the art (see Okumura, Shinji, "Foundations of Mobile Communications", Electronic Information Commmication Institute, 1986. Fig. 21 of the acacmrranymg drawings is a Emu Via a As 10 shown in (a) of Fig. 21, the 360 perimeter of a base station is equally divided to split a cell into a plurality of sectors SC. A sector antenna is an antenna that is allocated to each sector SC. There is no directivity within a sector. The technique for 15 establishing sectors merely reduces the 360. range of non-directivity to a narrower range of non-d-.rectivi.y such as 120. The narrower sector is still susceptible to interference from other users or subjects other users to interference. Such interference is the main cause of 20 a decline in channel capacity and transmission quality.

For this reason, it is necessary to measure the position of the mobile station successively in order to transmit radio waves with a narrow directivity in the direction of the mobile station, as illustrated in (b) 25 of Fig. 21. The position of a mobile station can be determ ned if the mobile station is set up for a position measurement system such as the GPS (Global Positioning System). However, not 212 mobile stations

- - are necessarily capable of utilizing a position measurement system and therefore the method of relying upon a position measurement system is not appropriate.

A proposed method that does not employ a position 5 measurement system is to find the direction of arrival of uplink radio waves by subjecting a received signal to signal processing and then transmit radio waves in this direction For example, see L.C. Godara, "Application of antenna arrays to mobile communications, PT. II; 10 Beamforming and direction-of- arrival considerations," Proc. ISLE, vol. 85, no. 8, pp. 1195 - 1245, Aug. 1977.

However, the proposed method of measuring the direction of arrival of uplink radio waves by the signa, processing of a received signal involves a heavy 15 processing load, such as a requirement to calculate eigenvalues, and necessitates a complicated apparatus Accordingly, lt is desirable _ _ to find -

the direction of a mobile station (the direction in which a radio base station should point its Radio waves) through a simple arrangement, and emit the radio waves 25 in this direction upon providing the radio waves with directivity. Furthermore, i. is desirable to emit -do waves in the measured direction of a mobile

- 4 - station using an array antenna.

(a) Measurement of receiver direction In order to measure the direction of a receiver . (Gil s^ 5 signals that have been spread by mutually orthogonal spreading codes are transmitted from antennas of a base station that are disposed at different positions, or the same signal is time-shared and transmitted as first and second signals from antennas of a base station that are 10 disposed at different positions; (2) the first and second signals that have been transmitted from the respective antennas are received by- a receiver and the phase difference between:hese signals is found; and (3) the direction of the receiver as seen from the 15 transmitter of the base station is calculated based upon the phase difference, In this case, in a multipat;a environment, the path among multipaths along which a signal will arrive earliest is found and the phase difference between the first and second signals that 20 arrive via this path is calculated. If we let represent the interval between the two antennas, A the wavelength of the radio waves, the direction of the mobile station and the phase difference between the first and second received signals, these will be related 25 as follows: = 2(/A) D sine. Accordingly, if is measured, then can be found from the above equation.

Thus, in accordance with the method of measuring the rxtlm a =i=

- 5 - -the receiver direction can be measured in a spearer. r, -- since the direction of a mobile station is measured using a signal that arrives earliest via 5 multipaths, there is no influence from radio waves that arrive owing to reflection or scattering. This makes it possible to measure direction accurately.

(b) Controlling direction of radio-wave emission In order to emit radio waves with directi-ity in 10 the nxtrof and, -a - - (1) the direction of a receiver is measured by the above-described method of measuring receiver direction; (2) the direction is fed back from the receiver to the base station; and (3) radio waves are 15 emitted from the transmitter of the base station in the direction Cal the receiver on the basis of the receiver direction using a directional antenna, whereby data is transmitted. According to another method --

20 - (1) the interval between two antennas that emit first and second signals is made equal to the interval between antenna elements of an equally spaced linear array antenna for data transmission) (2) a receiver receives the first and second signals 25 transmitted from the antennas and finds a phase difference between the received signals; (3) the phase difference is fed back from the receiver to a base station; (4) a transmitter of the base station emits

- À 6 - radio waves in the direction of the receiver upon providing the radio waves with directivity by applying the phase difference successively in steps of to a data signal that is input to each of the antenna 5 elements of the equally spaced linear array antenna. If this arrangement is adopted, the phase difference need only be detected and fed back, making it unnecessary to calculate the receiver direction 8.

According to an embodiment of the present _ 10 invention, (1) first and second reference signals that have been spread by mutually orthogonal spreading codes are generated; (2) a prescribed phase difference is successively applied to the first reference signals the resultant signals are input to each of the antenna 15 elements of an equally spaced linear array antenna, the phase difference is successively applied to the second reference signal and the resultant signals are input to each of the antenna elements of the equally spaced linear array antenna in such a manner that a phase 20 reference point of the first and second reference signals shifts by an amount equivalent to the interva_ between antenna elements of the equally spaced linear array antenna; (3) a receiver receives the first and second reference signals sent from a transmitter of a 25 base station and finds a phase difference l between the received first and second reference signals; (4) the phase difference l is fed back from the receiver to the base station; and (5) the transmitter of the base

- 7 - station emits radio waves in the direction of the receiver upon providing the radio waves with directivity by applying the phase difference l successively to a data signal that s input to each of the antenna 5 elements of the equally spaced linear array antenna.

In order to so arrange it that the phase reference point of the first and second reference signals shifts by an amount eulvalent to the interval between antenna elements of the equally spaced linear array antenna, (1) 10 a prescribed phase difference is successively Applied to the first reference signal and the resultant signals are input to the equally spaced linear array antenna from a first antenna element thereof to an (n- 1)th antenna element thereof in success-on; and (2) the prescribed 15 phase difference is successively applied to the second reference signal and the resultant signals are input to the equally spaced linear array antenna from a second antenna element thereof to an nth antenna element thereof in succession.: 20 If the above-described arrangement is adopted, reference signals for direction measurement can be emitted from an equally spaced linear array antenna for data transmission. This makes it unnecessary to separately provide an antenna for direction measurement.

25 Further, the same signal can be generated in time-shared fashion and input to an equally spaced linea- array antenna as the First and second reference signals, thereby making it possible to simplify the construction

- 8 - of the apparatus.

Reference will now be made, by way of example, to the accompanvinq drawings, in which: Figs. 1A to 1C are diagrams useful in describing 10 the principle of an embodiment of 'the present invention Fig. 2 is a diagram useful in describing the directivity of an equally spaced linear array antenna; Figs. 3A, 3B are diagrams useful in describing the principle of m3- n= b= wall It 15 for transmitting a direction-measu. rement signal is eliminated; Fig. 4 is a diagram useful in describing an overview of a first example not embodying the present invention; Fig. 5 is a diagram illustrating an example of 20 implementation in which reference signals are transmitted by a directional antenna; Fig 6 is a diagram useful in describing the relationship between direction and phase difference of a directional antenna; 25 Fig. 7 is a diagram showing the construction of the first example;

Fig. 8 is a vector representation of first and second reference signals So', Sz', which have been

- 9 - rotated in terms of phase, in an i-jQ complex plane; Fig. 9 is a diagram illustrating a modification of the first example, in which the same signal is time shared and transmitted; 5 Fig. 10 is a diagram illustrating the construction of a COCA transmitter of 2 base station; Fig 11 is a diagram useful in describing phase rotation in beam forming; Fig. 12 is a diagram illustrating the construction 10 of a receiver at a base station; Fig 13 is a diagram illustrating the construction of a mobile station; Fig. 14 is a diagram useful in describing signal point position vectors of data (symbols) for phase 15 measurement at a mobile station; Fig. 15 is a diagram useful in describing an overview of a second example not embodying the present invention; Fig. 16 is a diagram illustrating the construction 20 of the second example; Fig. 17 is a diagram illustrating a modification of the second example, in which the same signal is time-

shared and transmitted; Fig. 18 is a diagram illustrating the construction 25 of a first embodiment of the present invention; Fig. 19 is a diagram useful in describing the construction of a base-stat-on transmitter according to the first embodiment;

! À JO Fig. 20 is a diagram useful in describing a second embodiment; and Fig. 21 (desm-ibed above) is a diagrammeful in describing a preriomlyproposed sector antenna.

5 Like nx Era luLe-P e shy= Lo US tic Fly. (A) Principle and overview of the present invention (a) Principle Figs. 1A to 1C are diagrams useful in describing 10 the principle of an embodiment of e óEun,-dsh ala. MA is a diagram showing the relationship between the direction of a mobile station and the phases of received signals at the mobile station, Fig. 1B is a diagram useful in describing the path difference of each 15 radio wave when radio waves are emitted in the direction from two antennas disposed with a distance D between them, and Fis. 1C is a d--gram showing the relationship between a phase difference between two signals received by the mobile station and the direction of 20 the mobile station as seen from the base station.

A radio base station transmits two signals So, S2 from antennas ATE, AT2, respectively, placed at two points Pi, Pz, respectively, spaced apart by the distance D, as shown in Fig. 1A. If the receiver (mobile 25 station) is present at Any point PA in the A direction, the radio waves emitted from the respective antennas arrive at the receive' at point PA simultaneously. As a consequence, there is no phase difference between the

- 11 received signals from the antennas (ó - 0).

If the mobile station is present at any point PB in the B direction, on the other hand, the distance from the first point PI to the point PB will be greater than 5 the distance from the second point P2 to the point PB As a consequence, the radio waves from the antenna ATE placed at the first point arrive at the receiver of the mobile station later than the radio waves from the antenna AT2 placed at the second point P2, as a result of 10 which a phase difference (> 0) is produced.

Similarly, if the mobile station is present at any point Pc in the C direction, on the other hand, the distance from the first point PI to the point Pc will be less than the distance from the second point P2 to the point Pc.

15 As a consequence, the radio waves From the antenna All placed at the First point arrive at the receiver of the mobile station earlier than the radio waves from the antenna AT2 placed at the second point P2, as a result of which a phase difference (< 0) is produced. The 20 magnitude of the phase difference has 1:1 correspondence to the difference (path difference) between the distance from the first point PI to the receiver of the mobile station and the distance from the second point P2 to the receiver of the mobile station.

25 More specifically, if two waves transmitted from different points Pi, P2 are received, as shown in Fig. 1B, a path aif erence D sine is produced between the two waves owing to the direction of the point of reception

(the receiver of the mobile station). Here D represents the difference between the two points of transmission and represents the direction of the reception point as an angle which the vertical direction serving as a 5 reference forms with the direction or a straight line connecting the two transmission points. Owing to this path difference, a phase difference indicated by = kDsin (1) is produced between the two received waves, where k = 10 2x'\ and represents the wavelength of the radio waves.

For example, if D is selected such that D = i/2 holds, we have -- sine and the phase difference between the two received signals becomes as shown in Fig. 1C The phase difference and the direction have a 1:1 15 relationship and = sin) holds. Accordingly, the receiver of the mobile station is capable of calculating the direction of the reception point by measuring the phase difference between the two signals. If the direction of the reception point is fed back to the 20 side of the transmitter, the transmitter of the base station can transmit data in this direction. This makes it possible to reduce transmission power and, moreover, to reduce interference applied to other mobile stations.

(b) Signal separating method 25 The two signals S', S2 sent from the base station are received by the receiver of the mobile station in superimposed form. As result, it is necessary that the signals So, Sz be separated frog each other. In

- 13 other words, it is necessary to transmit the signals S', S2 in such a manner that the receiver can separate them from the superimposed signals. There are two methods of achieving this.

5 According to a first method, the base station transmits, as the first and second signals So, S2, signals obtained by spreading directionmeasurement data using mutually orthogonal spreading codes C(t), C2(t), and the receiver of the mobile station separates the 10 first and second signals So, S2 by applying despread processing to received data using codes C(t), C2(t) identical with the spreading codes According to a second method, the same signal is transmitted alternately from two antennas by time 15 division, thereby obtaining the first and second signals. Even if one signal is transmitted as the first and second signals from antennas at different points upon being divided in terms or timer as in the second method, the signals are related just as described in 20 Figs 1A to 1C and it is possible to determine the direction (angle) or the reception point from the phase difference l.

(c) Reporting phase or phase difference The calculation - sin 4(/) for obtaining the 25 direction of the reception point (receiver of the mobile station) need not necessarily be performed on the side of the receiver. This calculation can be carried out on the sloe of the transmitter by feeding back the measured

phase or phase difference By obtaining the direction of the reception point on the transmitter side and transmitting data destined for the receiver from a directional antenna in the direction that has been 5 obtained, interference imposed upon other mobile stations can be reduced and the circuit arrangement on the receiver side can be simplified.

(d) Use of equally spaced linear array antenna The base station uses an equally spaced linear 10 array antenna as the directional antenna. The equally spaced linear array antenna is an array antenna in which antenna elements Ao to Am (m = 4) are arrayed linearly at a uniform spacing d, as depicted in Fig. 2. If shifters PA to PA (m = 4) apply a phase difference = kdsinG 15 (where k = 2/) successively to an input signal S and current is fed to the antenna elements Ao to Am, directivity is produced in the direction 0.

Accordingly, if the base station uses an equally spaced linear array antenna as the antenna for data 20 transmission, the base station finds the phase difference in accordance with the following equation = -kdsinG (a) using the measured direction 6, applies the phase difference to the input signal S successively in steps 25 of (0, l, 2l, 3ó,), feeds current to the antenna elements Ao to Am and transmits data in the direction of the receiver upon providing the data with directivity 6.

(e) Simplification of direction computation

In a case where the base station uses an equally spaced linear array antenna as the antenna for data transmission, the spacing of the antennas which radiate the first and second signals S. and S: is made equal to 5 the antenna element spacing d of the equally spaced linear array antenna. I f this arrangement is adopted, the phase difference p detected by the receiver will be as follows from Equation (1):--

= kDsinO 10 = kdsinO If this is compared with Equation (2) above, it will be understood that this phase difference differs only in terms oF sign from the phase difference found on the side o the base station. Accordingly, the receiver 15 need only send the phase difference between the first and second signals to the base station. If the base statics then applies the phase difference to the data signal S successively in steps of -l and feeds current to the antenna elements Ao to Am of the equally spaced 20 linear array antenna, the directivity will be imposed upon the data and the data can be transmitted in the direction of the receiver. As a result, the calculation of the direction can be abbreviated, the computation load reduced and the construction of the apparatus 25 simplified.

(f) Eliminating antenna which radiates first and second signals So, S2 When the base station uses _n equally spaced linear

fit - 16 array antenna LAA as an antenna for data transmission, it is so arranged that first and second signals So, Sz are emitted from this equally spaced linear array antenna, thereby making it possible to eliminate an 5 antenna for direction measurement.

More specifically, as shown in Fig. 3A, shifters PSAo to PSAm_, (m = 4) delay the phase of signal S' successively by 0, +, 2+, 3i,--, (m-1)l, respectively, and input the delayed signals to antenna elements ATo to 10 Ate_, respectively, of the equally spaced linear array antenna via combiners ADDo to AADm- (m = 4), respectively. Further, shifters PSBo to PSBm' (m -- 4) delay the phase of the other signal S2 successively by 0 r +, 2ó, 3ó, À, (m-1)l, respect very, so as to shirt the 15 signal So and phase reference point by the antenna element spacing of the equally spaced linear array antenna, and input the decayed signals to antenna elements ATE to AIR via combiners ADDS to AADm (m = 4).

If current is fed to the antenna elements o- the 20 equally spaced linear array antenna in the manner set forth above, it will be just as if first and second reference signals So' = S[1 + exp(j ) + exp(2jó) + exp(3jl)] S2' = S2[1 + exp(jl) + exp(2jl) + exp(3jl)] 25 had been emitted from two antennas having a spacing d between them. However, the phase difference between the first and second reference signals received from the base station by the mobile station in the direction 6' is

ó7. That is, ó is the phase difference between the signals received by the mobile station in the direction D from two antennas spaced apart by the distance d Accordingly, if the receiver of the mobile station 5 feeds the phase difference ( back to the base station and the base station supplies current to the antenna elements ATo to ATOP of the equally spaced linear array antenna upon delaying the phase of the data signal S successively by 0, ó,, 2, 3,, (m-1, the base 10 station can transmit a signal to the receiver upon applying the directivity Hi. By virtue of the foregoing, calculation of the direction can be eliminated, computation load can be alleviated and an antenna for measurement of direction can be eliminated.

15 (g) Multipath environment In a multipath environment, a receiver finds the path among multipaths along which a signal arrives earliest and calculates the phase difference between first and second signals that arrive via this path. If 20 this arrangement is adopted, direction can be measurement accurately without the influence of radio waves that arrive because of reflection or scattering.

(B) First example (a) Overview 25 Fig. 4 is a diagram useful in describing an overview of the first example not embodying the present invention Here BS represents a base station and MS a mobile station The base station BS has two direction

- 18 measuring antennas ATE, AT2 disposed at different positions having a spacing D between them and emits first and second reference signals S', S2 obtained by spreading prescribed data using orthogonal spreading 5 codes C7 (t), C2(t). The base station BS further includes a transmit beamformer BFM and a directional antenna AND, e.g., the equally spaced linear array antenna illustrated in Fig. 2. The transmit beamformer EFM executes beamforming processing to feed current to the lo directional antenna AND, whereby the directional antenna AND emits radio waves (a beam) in the direction of the mobile station MS.

The mobile station MS includes an antenna ATR; a phase detector PDT for receiving first and second 15 reference signals So, S2 transmitted from respective ones of the antennas ATE, AT2 and detecting the phase difference between these signals; and a direction estimator DES which, on the basis of the phase difference i, estimates the direct-ion of the mobile 20 station MS as seen from the base station BS. Let D represent the spacing between the antennas AT, AT2, and let 9 represent the direction of the mobile station as seen from the base station As described earlier with reference to Fig. 1 regarding the principle of the 25 invention, a phase difference exists between first and second reference signals So', S2' received and demodulated by the receiver of the mobile station MS.

The phase detector PDT detects this phase c fference

- 1 9 -

(= kDsin6) and the direction estimator DES performs the calculation = sin 3(/kD) to estimate the direction of the mobile station MS as seen from the base station AS. The transmitter (not shown) of the mobile station 5 MS subsequently transmits the signal representing the direction to the base station AS, and the transmit beamformer BUM in the transmitter of the base station IS applies beamforming in such a matter that radio waves will be emitted in the direction and feeds current to 10 the directional antenna ATD. As a result, the directional antenna ANN emits radio waves (the beam) in the direction of the mobile station MS.

Fig. 5 is a diagram illustrating an example of imp ementation in which a reference signal is 5 transmitted by a directional antenna Here a range of 1SQ is divided up into three zones SC1 to SC3 of 60 each, the zones are provided with two antennas ATOP and ATE, ATE and AT22, AT3' and AT32, respectively, and the two antennas of respective zones transmit reference 20 signals SO and S2, S3 and S4, S5 and S6, respectively, the beam width of which is 60. In this case, the distance D between the antennas that transmit the two reference signals is selected in such a manner that the phase difference will be -a to +x when signals are received 25 over a directivity range = -30 to +30 . The value of can be uniquely decided by making the selection in this m owner. In the example of Fig. 5, if the phase -ee-ence points (antenna positions) from which the two

- 20 reference signals are transmitted are spaced apart by the wavelength (D = A) of the radio waves, the phase difference between two reference signals received by the mobile station in a range in which the distance Q 5 satisfies the relation -30 < < +30 will be -x < < + and can be found uniquely within these limits.

More specifically, if D = and = 30 hold, as shown in Fig. 6, the path difference between two signals S3, S4 emitted from antennas ATE, AT2z, respectively, 10 will be \/. If this path difference is converted to a phase difference, we have (/2) x (2/A) = a.

Similarly, if D = A and = -30 hold, the path difference between two signals S3, SO emitted from antennas ATE, AT22, respectively, will be -/2. If this 15 path difference is converted to a phase difference, we have (/2) x (2/) = -a. This means that a direction of -30. to +30 corresponds to a phase difference of -a to +x between two reference signals received by the mobile station.

20 The base station BS transmits the first and second reference signals So and S2, S3 and S4, S5 and S6 from the directional antennas ATE and AT'2, ATE and AT22, ATOM and AT3z, respectively, shown in Fig. 5. The receiver of the mobile station selects signals having a strong reception 25 power to thereby decide the zone (SC1 to SC3) in which these signals are being transmitted. This makes it possible to determine the reception position and the direction thereof. Furthermore, by measuring the phase

difference in this zone, the direction can be measured accurately The foregoing describes a case where the mobile station calculates and feeds it back to the base 5 station. However, it is also possible to adopt an arrangement in which the phases A, ó2 of first and second received signals So', S2' or the phase difference (=-42) between the signals-S', S2' are (is) fed back to the base station and the base station calculates D. 10 Further, the foregoing relates to a case where first and second signals So, S2 obtained by spreading prescribed data using mutually orthogonal spreading codes C'(t), C2(t) are emitled from antennas AT,, AT2.

However, the same signal can be applied to the antennas 15 ATE, AT2 intime-shared fashion and transmitted as the first and second signals S, S2.

(b) Construction of first example Fig. 7 is a diagram illustrating the construction of the first example, in which components identical 20 with those of Fig. 4 are designated by like reference characters. The base station BS has a reference signal generating unit RSG for generating two reference signals S. = C'(t)ejt, S2 = C2(t)e3t. By way of example, the reference signal generating unit RSG converts a 25 direction-measurement data sequence to two sequences I(t), Q(t), namely an in-phase component (also referred to as an "I component") and a quadrature component (also referred to as a ''Q component"), multiplies (spreads)

- 22 each of these by a spreading code C(t), then applies QPSK quadrature modulation to generate a signal C'(t)ei=t0' (=0, ix/2, a), similarly multiplies the two sequences of in-phase and quadrature components by a 5 spreading code C2(t) and then applies QPSK quadrature modulation to generate a signal C2(t)ej<-t+, (=0, /2, a). If = 0 holds, the first and second reference signals S. = C'(t)eit, S2 = C:(t)eit are obtained. It should be noted that C,(t), C:(t) employ spreading codes 10 for which the cross-ccrrelation value is 0, i.e., spreading codes which are orthogonally related as follows: Jo (t)C2(t)dt = 0.

These reference signal So, S2 are frequency up-

converted (IF i RF) and frequency amplified by a 15 transmitting unit (not shown), the resultant signals are input to the antennas "aT', AT2, respectively, and the signals then radiate out into space.

The reference signals S., S2 are received by the antenna ATR or the mobile station--MS as signals that 20 have been rotated in phase by l1,-2 owing to propagation delay, after which the signals are subjected to an RF IF frequency conversion and QPSK quadrature detection by a receiving unit (not shown). The resultant signals are input to despreaders RSC,, RSC2 for direction 25 measurement. The despreaders RSC, RSC2 multiply (respread) their input signals by the spreading codes C,(t), C2(t), respectively, and apply phase-rotated first and second sign21s So' = eJ fit i]', S2' = edge 62) to a phase

À 23 difference measurement unit PDT. The first and second ignals S ' = e: (rat -] S2 = ej (rDt+2) are as illustrated in Fig. 8 when expressed as vectors in an I-jQ complex plane.

5 The phase-difference measurement unit PDT has a complex-conjugate calculation unit CONJ for outputting the complex conjugate S2'* = e j(t+ 62) of the signal S2' = em i', and a multiplier MEL for calculating S''ÀS:*.

As a result, x = eit+2) is obtained from a low-pass 10 filter LPF. A phase-difference calculation unit PDC calculates the phase difference in accordance with the equation = tan [Im(x)/Re(x)] (3) and inputs the phase difference to the direction 15 estimator DES Here Im(x) represents the imaginary part of x and Re(x) the real part of x.

The phase difference can be written = Adding food Equation (1) and since k = 2/, D - X/2 hold, the 20 following equation holds: = using (4) Accordingly, the direction estimator DES calculates and outputs the direction on the basis of the following equation: 25 = sin i(óJ=) (5) The transmitter (not shown) of the mobile station MS thenceforth transm ts the signal representing the direction to the base station AS.

(A - 24 When the base station BS receives the direction from the mobile station, the base station inputs the direction to the transmit beamformer BUM. The latter has a calculation unit CUP which, on the basis of the 5 following equation: = kdsinG = -2dsinD/\ (6) calculates the phase difference of the signal input to each antenna element of the equally spaced linear array 10 antenna ATD. Phase shifters PSO to PSn apply the phase differences 0, (= -kdsin8), 2, 3,) to the input signal (transmit signal) S successively and input the resultant signals to the antenna elements AD to An. As a result, the equally spaced linear array antenna AND 15 emits radio waves in the direction of and thus transmit data.

(c) Modification Fig. 9 illustrates a modification of the first example, in which the same signalis transmitted, in 20 time-shared fashion, as first and second signals.

Components in Fig. S identical with those shown in Fig. 7 are designated by like reference characters. Here the base station BS differs from that of Fig. 7 in the following respects: 25 (1) the reference signal generating unit RSG generates one reference signal C(t)eiti (2) G time share switch TSW1 is provided and inputs the Reference signal to the first transmit antenna ATE in

- 25 odd-numbered time slots t = 1, 3, 5, -À and to the second transmit antenna ATz in even-numbered time slots t = 2, 4, 6,, whereby the reference signal is transmitted as the first and second reference signals So, 5 S2; and (3) the transmit beamformer BUM and equally spaced linear array antenna AND are not illustrated.

The mobile station MS differs From that of Fig. 7 in the following respects: 10 (1) One Respreader RSC is provided and outputs the first and second reference signals So', S2' the phases whereof have been rotated by Respreading; and (2) a time share switch TSW2 is provided and outputs, as the first reference signal So', the signal 15 delivered from the Respreader RSC in odd-numbered time slots t = 1, 3, 5, À and outputs, as the second reference signal S2', the signal delivered from the Respreader RSC in even-numbered time slots t = 2 r 4 r 6, 20 The reference signal generating unit RSG converts the direction-measurement data sequence to two sequences, namely the in-phase and quadrature components, multiplies each of these by a spreading code C(t) to spread them, then applies QPSX quadrature 25 modulation to the spread data to generate a baseband reference signal S = C(t)e3t. The time share switch TSW1 outputs the reference signal S as the first reference signal So n odd-numbered time slots t = 1,3,

- 26 5, and outputs the reference signal as the second reference signal S2 in even-numbered time slots t = 2, 4, 6,. These reference signal So, S2 are thenceforth frequency up-converted (IF -9 RF) and frequency 5 amplified by a transmitting unit (not shown), the resultant signals are input to the antennas AT, AT2, respectively, and the signals then radiate out into space. The reference signals S., Sz are received by the 10 antenna ATR of the mobile station MS as signals that have been rotated in phase by A, 12 owing to propagation delay, after which the signals are subjected to an RF -9 IF frequency conversion and QPSK quadrature detection by a receiving unit (not shown). The resultant signals are 15 input to the Respreader RSC. The latter multiplies (respreads) the input signals by the spreading code C(t). The time share switch TSW2 applies the despread signal to the phase-difference measurement unit PDT as the first reference signal So' = e+ in odd-numbered 20 time slots t = 1, 3, 5, and applies the Respread signal to the phase-difference measurement unit PDT as the second reference signal S2'= ei(mt2) in even-numbered time slots t = 2, 4, 6,. The phase-difference measurement unit PDT and direction estimator DES operate 25 as in Fig. 7 so that the direction is transmitted to the base station AS The base station BS also operates as in Fig. 7 so that the input signal is transmitted in the direction B upon being provided with direc.-vity.

- 27 -

(d) Construction of base station (d-1) Construction of transmitter Fig. 10 is a diagram illustrating the construction of a CDMA transmitter in a base station for code 5 multiplexing and transmitting n channels of transmit data. The transmitter includes spread-spectrum modulators 11 to 11 n Of 1 st to nth channels; an equally spaced linear array antenna 12 serving as an antenna for data transmission, the array antenna having antenna 10 elements Al to Am uniformly spaced apart by a distance d; and transmitting units 13' to 1 3m for applying transmit signals to the antenna elements A' to Am or the equally spaced linear array antenna 12. Though not shown, each transmitting unit has a DA converter, a QPSK modulator, 15 a frequency converter (IF -9 RF) and a high-frequency amplifier. Combiners 14i', 14 respectively combine, Q signals VI' ', Vet' output from the spread-spectrum modulators 11 to 11n of the respective channels and input to the first antenna element Al, and combiners 2G 14im, 14q respectively combine I, Q signals V=', V=' output from the spreadspectrum modulators 11-, to 11 n of the respective channels and input to the mth antenna element An. The apparatus further includes a signal transmitting unit 15 for direction measurement.

25 Each of the spread-spectrum modulators 11' to 11 n has a frame generator 21, a serial/parallel (SIP) converter 22 for converting frame data to parallel data/ a spreading circuit 23 and a transmit beamormer 24.

- 28 The frame generator 21 has a transmit data generator 21a for generating serial transmit data D1, a pilot generator 21b for generating a pilot P. and a framing unit 21c for dividing the serial data D1 into blocks a 5 prescribed number of bits at a time and inserting a pilot and other control data before and after every block to thereby form frames. The SIP converter 22 alternately distributes the frame data (the pilot signals and transmit data) one bit at a time to convert 10 the frame data to _-component (in-phase component) data DI and Q-component (quadraturecomponent) data DQ.

The spreading circuit 23 includes a pn sequence generator 23a for generating a pn sequence (long code) specific to the base station, an orthogonal Gold code 15 generator 23b for generating an orthogonal Gold code (short code) for user identification, an EX-OR gate 23c for outputting a spreading code C by taking the exclusive-OR between the pn sequence and the Gold code, and EX-OR gates 23d, he for performing spreadspectrum 20 modulation by eking the exclusive-ORs between the data DI and DQ of the two sequences, respectively, and the code C. It should be noted that since "1" is level -1 and "0" is level +1, the exclusive-OR between signals is the same as the product between them.

25 The transmit beamformer 24 performs beamrorming based upon the mobilestation direction 0 reported from the user (mobile station). In order to emit the beam upon providing c rectivlty in the direction 6 in a case

- 29 where the equally spaced linear array antenna 12 is used as the antenna for data transmission, it is necessary to find the phase difference in accordance with the following equation: 5 = -kdsinD = 2xdsinD/X (6)' and to feed current upon applying the phase difference successively to the input signal of each antenna element, as will be evident from the description of

10 principles set forth earlier. Feeding current while applying the phase difference successively to the input signal of each antenna element is equivalent to rotating, by A, the signal point position vector V of the spread-spectrum modulated signals Vl r VQ output from 15 the spreading circuit 23, as shown in Fig. 11 Accordingly, using the following vector rotation equations: VI] = VI COST - VQ sing VQ] ' = VI sing) T VQ COS4) 20 the transmit beamformer 24 calculates the signal input to the first antenna element Al and outputs the calculated signal. Specifically, I, Q components VI] ' VQ] ' of a position vector V' obtained by rotating the signal point position vector V by are output as the 25 input signal of the first antenna element.

Similarly, using the following vector rotation equations: V,-j' = V' cost - it s-n

- 3C -

VQ] = VI À sings + VQ costs the transmit beamformer 24 calculates the signal input to the j th antenna element Aj and outputs the calculated signal. 5 By applying the above-mentioned signals to the 1 st to m antenna elements An to Am, the data of the first channel can be emitted with directivity in the direction of the mobile station of the first channel user the direction of which is 0. The spread-spectrum modulators 10 11 to 11 n of the respective channels operate in a similar manner so that the signal of each channel can be emitted with directivity in the direction of the mobile station that corresponds to the channel.

The combiner 14i combines the I-signal components 1 5 VT] input from each of the channels to the first antenna element Al, and the combiner 14q combines the Q-signal components VQ] ' input from each of the channeled to the first antenna element Al. Each of these combined signals is input to the first antenna transmitting urn' 13.

20 Similarly, the combiner 14ij (j = 1 to m) combines the I-

signai components VIj ' input from each of the channels to the j th antenna element Aj, and the combiner 14qj combines the Q-signal components Van' input from each of the channels to the j th antenna element As. Each of these 25 combined signals is input to the j th antenna transmitting unit 13j.

The transmitting units 1 31 to 1 3m apply QPSK quadrature modulation to the input signals, convert the

- 31 obtained baseband signals to high-frequency signals, apply highfrequency amplification and input the resultant signals to the antenna elements A, to Am Of the equally spaced linear array antenna 12. The signal 5 transmitting unit 15 for direction measurement transmits the two reference signals So = C(t)eit, S2 = C2(t)eit to from the antenna ATE, AT2. More specifically, an SIP converter 16a of the control signal generator 16 alternately distributes a drection-measurement data 10 sequence one bit at a time to convert the data to in phase component and quadrature-component data sequences DIP, DQ', and a first despreader 16b multiplies the sequences DIl, DQ' by the spreading code Cart) to spread the same and input the resultant signals to a first 15 directionmeasurment transmitting unit 17. Further, a second spreader 16c multiplies the sequencer DIP, DQ' by the spreading code C2(t) to spread the same and input the resultant signals to a second direction- measurement transmitting unit 18. The first and second d rection 20 measurement transmitting units 17, 18 apply QPSK quadrature modulation to their input signals to generate the baseband first and second reference signals SO = C,(t)eit, Sz = C2(t)eit, up-convert the baseband signals to high-frequency signals, apply high-frequency 25 modulation and input the amplified signals to the antennas ATE, AT2 for direction measurement. Mobile stations MS' to MSn receive the direction-measurement signals emitted from the antennas AT, AT2, calculate the

- 32 directions 0, to On Of the mobile stations as seen From the base station and feed these directions back to the base station.

(d-2) Construction of receiver 5 Fig. 12 illustrates an example of the construction of one channel of a base-station COMA receiver. This receiver has a diversity structure in which the output from each branch is subjected to maximum-ratio combining and data is judged based upon the results of such 10 combining, A radio unit 31 of a branch B1 (or B2) freuency-converts a high-freuenc: signal received by an antenna 3Q to an intermediate-frequency signal (i.e., executes an RF-to-IF conversion). A quadrature detector 32 subjects the OF signal to quadrature detection and 15 outputs in-phase component (I-component) data and quadrature component (Q-component) data. The quadrature detector 32 has a receive carrier generator 32a, a phase shifter 32b rc' shifting the phase of a receive carrier by /2, and multipliers 32c, 32d for multiplying the 20 baseband signal by the receive carrier and outputting I-

and Q-component signals, respectively. Low-pass filters (LPF) 33a, 33b limit the band of the output signals and AD converters 35a, 35b convert the I- and Q-component signals, respectively, to digital signals and input 25 these digital signals to a searcher 36, fingers 37a to 37a4 and a receive-power measurement unit 38.

When a direct-sequence signal (DS) signal that has been influenced by multlpath enters the searcher 36, the

- 33 latter detects multipath by performing an autocorrelation operation using a matched filter and inputs despreading-start timing data and delaytime adjustment data of each path to the fingers 37a' to 37a4.

A despread/delay-time adjustment unit 41 of each finger performs dump integration by subjecting a direct wave or a delayed wave that arrives aria a prescribed path to despread processing using a code identical with the spreading code, and for subsequently applying delay 10 processing that conforms to the path and outputting a pilot signal (reference signal) and an information signal. A phase compensator (channel estimation unit) 2 averages voltages of the I and Q components of the pilot signal over a prescribed number of slots and 15 outputs channel estimation signals It, Ct. A synchronous detector 43 restores the phases of Respread information signals I', Q' to the original phases based upon a phase difference between a pilot signal contained in a receive signal and an already exist ng 20 pilot signal. More specifically, the channel estimation signals It, Qt are cosine and sine components of the phase difference 0, and therefore the synchronous detector 43 demodulates the receive information sign-l (I,Q) (performs coherent detection) by applying phase 25 rotation processing to the receive information signal (I',Q') in accordance with the following equation using the channel estimation signal (It,Qt):

- 34 (Q) (-Qt It)() A rake combiner 37b combines signals output from the fingers 37a - 37a<, and a multiplier 37d multiplies the output of the RAKE combiner by a weight conforming to 5 reception power and outputs the product A maximum-

ratio combiner 39 combines the outputs of the branches at a ratio that conforms to the magnitude of reception power, and a decision unit 40 judges the data based upon the output of the macimum-ratio combiner 39 A 10 direction identification unit 44 identifies the direction H sent from the mobile station and inputs the identified direction to the corresponding spread-

spectrum modulator 11i of the transmitter (Fig 10).

(e) Construction of mobile station 15 Fig. 13 is a diagram showing the construction of a CDMA transceiver in a mobile station. The transceiver includes a CDMA transmitting unit 51, a CDMA receiving unit 52, a duplexer 53 and a transceiving antenna 54.

The transmitting unit 51 includes an error 20 correction encoder 51a for subjecting transmit data to error correction encoding processing and applying the resultant signal to a mapping unit 51b Further, a control data generator 51c generates control data such as a pilot and inputs the control data to the mapping 25 unit 51b. The mapping 'nit 51b outputs the encoded data sequence from the error correction encoder 51a as a quadrature-modulated in-phase component at a

- 35 predetermined symbol rate and outputs the control data sequence, which includes the pilot, as a quadrature component at a fixed symbol rate. Spreaders 51d, 51d2 subject the in-phase component (I component) and 5 quadrature component (Q component) to spread-spectrum modulation using predetermined spreading codes and input the spread data to DA converters 51ú, 51f2 via filters 51e, 51e2 for shaping the waveforms. A quadrature modulator 51g applies QPSK quadrature modulation to I 10 and Q- channel signals output from the DA converters, and a radio unit 51h converts the baseband signal output from the quadrature modulator 51g to a high-frequency signal (i.e., executes a IF-to-RF conversion), applies high-frequency amplification and transmits the amplified 15 signal from the antenna 54.

The CDMA receiver 52 has a radio unit 52a for amplifying a high-frequency signal received by the antenna 30 and frequency-converting the Amplified signal o an intermediate-frequency signal (i.e., for executing 20 an RFto-IF conversion). A quadrature detector 5b demodulates _- and Q-channel signals by quadrature detection and inputs the demodulated signals to AD converters 52c', 52c. Despreaders 52d, 52d2 multiply the outputs of the DA converters by codes identical with 25 the spreading codes of the base station to thereby Respread the converter outputs, and a coherent detector discriminates the received data by coherent detection.

An error correction decoder 52f subjects The received

- 36 data to error correction decoding processing and outputs the result. The foregoing is an arrangement for receiving ordinary communication data. However, the receiving unit includes also an arrangement for 5 receiving direction-measurement data sent from the base station. A first Respreader 52g for direction measurement performs Respreading by multiplying the outputs of the AD converters 52c, 52c2 by the spreading code Cut) and 10 outputs a signal point position vector R. (R:-r, R1Q) (see Fig. 14). A second Respreader 52h for direction measurement performs Respreading by multiplying the outputs of the AD converters 52c1 r- 2c2 by the spreading code Apt) and outputs a signal point Position vector Rz 1 5 (R2I' R2Q). The spreading codes C1 (t), C2 (t) are codes identical with the mutually orthogonal spreading codes by which the base station mu_.tiplies the direcLion-

measurement data in order to spread this data.

Using the signal point position -vectors R', R2, a 20 phase-difference calculation unit 52 calculates the phase difference of each vector, and a direction calculation unit 52j calculates the direction of the mobile station, as seen From the base station, in accordance with the following equation: 25 = sin 4(/) and inputs the direction to the control data generator 51c or the transmitting unit 51c. Ate COMA transmitter 51 transmits the direction to the base station as

- 37 control data.

(C) Second example Fig. 15 is a diagram useful in describing an overview of a second example not embodying the present 5 invention. Components identical with those of the first example shown in Fig. 4 are designated by like reference characters. This example differs in the following respects: (1) the equally spaced linear array antenna LAA is 10 used as the directional antenna for data communication; (2) -he distance D between the antennas AT, AT2 for direction measurement is made equal to the spacing d of the antenna elements of the equally spaced linear array antenna LAA (D = d); 15 (3) the direction estimator DES is removed from the mobile station MS and the phase difference is fed back: from the mobile station to the base station; and (4) the transmit beamformer BUM applies the phase difference successively in steps of to the data signal 20 directed to the mobile station and feeds current to the antenna elements AD to Am of the equally spaced linear array antenna LAA.

In a case where the base station uses the equally spaced linear array antenna LAA as the antenna for data 25 transmission, the spacing D between the antennas AT,, ATz that emit the First and second reference signal S., S2 is made emus' to the spacing d between the antenna elements of the equally spaced linear array ant enr.a LAA. If this

- 38 arrangement is adopted, the mobile station need only feed back the phase difference between the first and second reference signals to the base station BS.

Further, if the transmit beamformer BFM of the base 5 station BS applies phase differences 0, i, 2ó, 3ó, 4l, to the data signal S successively and feeds current to the antenna elements AD to Am of the equally spaced linear array antenna, the directivlty will be imposed upon the data and the data can be transmitted in the 10 direction of the receiver.

Fig. 16 is a diagram illustrating the construction of the second example, in which components identical with those shown in Fig. 7 are designated by like reference characters. This arrangement differs from 15 that of Fig. 7 in the respects (1) to (4) mentioned above. Fig. 17 illustrates a modification of the second example, in which the same signal is transmitted as the irst and second reference signals in time-shared 20 fashion. Components identical with those shown in Fig. 9 are designated by like reference characters. This arrangement differs in that the direction estimator DES is removed from the mobile station MS and the phase difference is fed back from the mobile station to the 25 base station.

(D) First embodiment Fig. 18 '- a diagram useful in describ no an overview of a first embodiment according to the present

- 39 invention. Components identical with those of the second example shown in Fig. 15 are designated by like reference characters. This embodiment differs in that the antenna for transmitting the direction 5 measurement signal is eliminated and the direction-

measurement signal is transmitted from the equally spaced linear array antenna LAA.

As described in conjunction with Fig. 3, the phase of the signal S7 is delayed successively by 0, l, 2ó, 3 , 10, (m-1)+ and the delayed signals are input to the antenna elements ATo to Atm_4, respectively, of the equally spaced linear array antenna LAA. Further, in order that the phase reference point of signal S2 will be shifted from the phase reference point of signal S. by 15 the spacing d of tee antenna elements of the equally spaced linear array antenna LAA, the phase of the signal S2 is delayed successively by 0, ó, 2+, 3ó,, (m-1) and the delayed signals are input to respective ones of the antenna elements AT' to ATE. If current is thus 20 applied to the antenna elements of the equally spaced linear array antenna LAA, it will be just as if first and second reference signals S.' = S'[1 + exp(ji) + exp(2jó) + exp(3jó)] Sz' = S2[1 + exp(jl) + exp(2j') + exp(3jl)] 25 had been emitted from two imaginary antennas PAT1, PAT2 having a spacing d between them. As a consequence, the phase difference between the first and second reference signals which the mobile station MS -n the direction al

- 40 receives from the base station BS becomes ó7. However, | is the phase difference between the first and second reference signals which the mobile station MS in the direction 8 receives from two imaginary antennas PAT1, 5 PAT2 having the spacing d between them.

Accordingly, the phase-difference measurement unit PDT of the mobile station MS detects the phase difference l and feeds the phase difference back to the base station BS, and the transmit beamformer BUM of the 10 base station supplies current to the antenna elements ATo to ATm_, of the equally spaced linear array ant Anna upon delaying the phase of the data signal S successively by 0, $,, 2, 34',, (m-l)', as shown in Fig. BE. As a result, the base station can transmit a signal to the 15 receiver upon applying the directivity O (b) Base-station transmitter of first embodiment Fig. 19 is a diagram showing the construction of a basestation transmitter according to the first embodiment, in which components identical with those of 20 the transmitter of the first example shown in Fig. 10 are designated by like reference characters. This embodiment differs in the following respects: (1) the construction of the signal transmitting unit 15 for direction measurement; and 25 (2) the construction of the signal transmitting unit 15 for direction measurement applies the d-.rection measurement signal to the antenna elements An to Am of the Flatly spaced linear array antenna LAY -i

- 41 combiners 17i7, 17q to 17i, 17q and transmitting units 13 to 13m.

The SIP converter 16a alternately distributes a direction-measurement data sequence one bit at a time to 5 convert the data to in-phase component and quadrature-

component data sequences DI ', DQ ', and the first despreader 16b multiplies the sequences DT' DQ' by the spreading code C'(t) to spread the same and input the resultant signals to a first phase rotator 19a. The 10 second spreader 16c multiplies the sequences DIP, Q' by the spreading code C2(t) to spread the same and input the resultant signals to a second phase rotator 19b. The first phase rotator 19a rotates the signal point position vector V, of the spread-spectrum modulated 15 signals Via, I] which enter from the first spreader 16b, successively by 0, ó,, 2, 3',, (m-1) and outputs the result. That is, the first phase rotator 19a performs the calculations indicated by the following phase rotation equations: 2 0 VIJ= VI COST - VQ: sing VQJ = VI] sing + VQ, COST (where As = j ó:, j - O to m-1) and outputs the result The second phase rotator 19b rotates the signal point position vector Vz of the spread-spectrum modulated 25 signals VIZ, VQZ, which enter from the second spreader 16c, successively by 0, ó,, 2, 3',, (m-l) and outputs the result. That is, the second phase rotator 13b performs the calculations indicated by the f22owng

( - 42

phase rotation equations: VIJ = V12 COST - VQ2 sing VQJ = VI2 sines + VQ2 COST (where is = jell, j = 0 to m-1) and outputs the result.

5 Combiners 20i, 20q to 20im, 20qm combine corresponding signals output from the first and second phase rotators 19a, 19b and feed current to the antenna elements A' to Am of the equally spaced linear array antenna LEA via the combiners Dig, 17q, to 17im, 17q and 10 transmitting units 13 to 13.

The above is equivalent to emitting the first and second reference signals from two imaginary antennas having the spacing d; the phase difference between the first and second reference signals received from the 15 base station BS by the mobile station in the direction e' is t' The phase-difference measurement unit PDT of the mobile station MS detects the phase dl=-erence l and feeds the phase difference back to the base station BS.

In the base station, the beamformer 24 of the channel 20 corresponding to the mobile station supplies current to the antenna elements ATo to ATE of the equally spaced linear array antenna upon delaying the phase of the input data successively by Q. i', 2', 3,, (m-1).

As a result, the transmitter of the base station can 25 transmit a signal to the mobile station upon applying the directivity 8.

The foregoing relates to a case where different signals S-, S2 are input to an equally spaced 'inear

array antenna simultaneously. However, it is possible to adopt an arrangement in which the same signal is input to the equally spaced linear array antenna alternately in time-shared fashion as the signals S., Sz 5 (E) Second embodiment Radio-wave propagation in mobile communication involves a multiplexed propagation environment (multipath environment) in which, in addition to direct waves (diffracted waves), eaves that have been reflected 10 and scattered by buildings and mountains, etc., arrive simultaneously. In such a multipath environmen-_, direction:rom a transmitter cannot be determined accurately even it the phase difference between received signals is measured. Among waves that arrive v-= 15 multiple paths, a wave that arrives earliest in time is considered to be a wave that arrives directly from a transmit antenna or wave that is directly diffracted.

Accordingly, if a wave that arrives earliest in time- is selected and then phase difference is measured, the 20 direction of the mobile station can be measured accurately Fig. 20 is a diagram illustrating the construction of a mobile-station receiver according to the second embodiment. Components in Fig. 20 identical with those 25 of the mobile- station receiver of the first example shown in Fig. 7 are designated by like reference characters. This embodiment differs in that a path searcher ITS is provided for detecting arrival time t Of

- 44 a direct wave, and in that the despreaders RSC1, RSC2 perform Respreading at the timing of the detected time t. This method of measuring phase difference upon selecting a wave that arrives earliest can be applied to 5 the embodiment described above.

Thus, In accordance Ash odm=t de 3i=tn, d required transmission directivity can be obtained by simple computation, transmission power can be reduced and so can the power of interference. This makes it 10 possible to increase the subscriber capacity of a mobile wireless communication system, Further, in accordance why nU tti=ri, the phase difference between first and second signals transmitted from two antennas for direction measurement 15 is measured and the direction of a mobile station is found based upon the phase difference +. As a result, the direction of the receiver can be measured in a simple manner.

slather, In accordance with evident dn Non, 2C direction is measured us ng the earliest arriving signal among signals that arrive on multiple paths. This makes it possible to measure direction accurately without the influence of radio waves that arrive owing to reflection or scattering.

25 D.=ther, accordance wade cI te Non, the spacing between two antennas that transmit first and second signals for direction measurement is made equal to the spacing be ween Antenna elements of an equally

- 45 spaced linear array antenna for data transmission, the phase difference between the first and second signals at the mobile station is measured, the phase of the transmit signal is delayed by 0, l, 2ó, 3l, and the 5 resultant signals are applied to the antenna elements or the equally spaced l near array antenna, whereby the transmit signal s emitted in the direction of the mobile station. As a result, the direction of the mobile station need not be calculated, thereby making it -10 possible to simplify the construction of the apparatus.

Further, in--=n=W1 amp n t 3, reference signals for direction measurement can be emitted from an equally spaced linear array antenna for data transmission and it is unnecessary, therefore, to 15 separately provide an antenna for direction measurement.

=her, in x= high *. often t I, the same signal can be generated in timeshared fashion and input as first and second reference signals to an antenna for direction measurement. This makes it 20 possible to simplify the construction of the apparatus.

As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific 25 embodiments thereof.

Claims

l. A method of controlling direction of radio-wave emission of a basestation transmitter which emits radio 5 waves from an equally spaced linear array antenna, which has lS' to nth antenna elements, upon providing the radio waves with directivity in the direction of a receiver, comprising the steps of: generating first and second reference signals; 10 inputting signals, which have been obtained by applying a predetermined phase difference successively to the first reference signal, to l' to (n-l)th antenna elements of the equally spaced linear array antenna in succession, and inputting signals, which have been obtained by applying 15 said phase difference successively to the second reference signal, to 2nd to nth antenna elemelts of the equally spaced linear array antenna in succession in such a manner that a phase reference point of the first and second reference signals will be shifted by an amount equivalent 20 to an interval of the antenna elements of the equally spaced linear array antenna; receiving by a receiver the first and second reference signals transmitted from a base-station transmitter and obtaining a phase difference l, between the first and 25 second reference signals received; feeding the phase difference Aback from the receiver to the base station; and emitting radio waves upon providing the radio waves with directivity in the direction of the receiver by 30 successively applying the phase difference in steps of l, to a data signal input to each of the antenna elements of the equally spaced linear array antenna at the base-station transmitter. 35 2. The method according to claim l, wherein the first and second reference signals are obtained by spreading direction-measurement data using mutually orthogonal

1/- spreading codes and are transmitted from the equally spaced linear array antenna at the same time.

3. The method according to claim 1, wherein the first 5 reference signal is the same as the second reference signal and the first and second reference signals are transmitted by time-shared transmission from the equally spaced linear array antenna at the same time.

10 4. The method according to claim 2 or 3, wherein the receiver obtains a path among multipaths along which a signal arrives earliest and calculates the phase difference |1 between the first and second reference signals that err ve via this path.

5. A method of controlling direction of radio-wave emission of a basestation transmitter substantially as hereinbefore described with reference to Figures 18 to 20 of the accompanying drawings.

6. A base-station transmitter for emitting radio waves from an antenna upon providing the radio waves with directivity in the direction of a receiver, comprising: means for generating first and second reference 25 signals; an equally spaced linear array antenna, which has apt to nth antenna elements, for emitting the first and second reference signals and a data signal; means for inputting signals, which have been obtained 30 by applying a predetermined phase difference successively to the first reference signal, to 1t to (n-l)th antenna elements of the equally spaced linear array antenna in succession, and inputting signals, which have been obtained by applying said phase difference successively to the 35 second reference signal, to 2 to ntn antenna elements of the equally spaced linear array antenna in succession in such a manner that a phase reference point of the first and second reference signals will be shifted by an amount

- equivalent to an interval of the antenna elements of the equally spaced linear array antenna; a demodulator for receiving from the receiver and demodulating a phase difference: between the first and 5 second signals, which have been transmitted from respective ones of said antennas, at the receiver; and means for successively applying the phase difference in steps of +1 to the data signal and inputting the resultant signals to each of the antenna elements of said equally 10 spaced linear array antenna; whereby data is transmitted toward the receiver by emitting radio waves upon providing the radio waves with directivity in the direction of the receiver.

15 7. The base-station transmitter according to claim 6, wherein said reference signal generating means generates the first and second reference signals that have been spread by mutually orthogonal spreading codes and said equally spaced linear array antenna transmits said first 20 and second reference signals at the same time.

8. The base-station transmitter according to claim 6, wherein said reference signal generating means generates one signal as the first and second signals and said equally 25 spaced linear array antenna transmits said first and second reference signals by time-sharing.

9. A base-station transmitter substantially as hereinbefore described with reference to Figures 18 to 20 30 of the accompanying drawings.