CN1120544C - Method and apparatus for directional radio communication - Google Patents

Abstract

The present invention relates to a method for directional wireless communication between a first website and a second website, and a mobile communication network. The method comprises the following steps: continuous communication data pulse trains transmitted from the second website is identified by the first website; a corresponding beam direction for the first website receives orderly communication data pulse trains is determined according to a plurality of adjacent beam directions; one or multiple beam directions transmitting signals to the second website from the first website are selected so that when the first website receives the orderly communication data pulse trains from different beam directions, two different beam directions are simultaneously selected and transmit the signals to the second website from the first website.

Description

Method and device for directional wireless communication

technical field

The present invention relates to a method and device for directional wireless communication, wherein signals between a first base station and a second base station can only be sent in a certain direction. In particular, but not exclusively, the invention is applicable to cellular communication networks using space division multiple access.

Background technique

In the currently implemented cellular communication network, in order for a base transceiver station (BTS) to send a signal to a designated mobile station (MS), the base transceiver station (BTS) generally transmits within the entire cell or cell sector served by the base transceiver station. Signal. Now, however, a Space Division Multiple Access (SDMA) system has been proposed. In a space division multiple access system, the base transceiver station does not send signals to a given mobile station throughout the cell or cell sector, but only sends signals in the direction of the beam from which the mobile station receives the signal. SDMA systems can also allow base transceiver stations to determine the direction from which signals are received from mobile stations.

SDMA systems can achieve some advantages over existing systems. Specifically, since the beam transmitted by the BTS can only be transmitted in one specific direction, and the direction is relatively narrow, the power of the transceiver can be concentrated on the narrow beam. It can be determined that this method can obtain a better signal-to-noise ratio for both the signal sent by the base transceiver station and the signal received by the base transceiver station. In addition, as a result of the directional nature of the base transceiver station, the signal-to-noise ratio of signals received by the base transceiver station can be improved. Also, in the transmit direction, the directional nature of the BTS allows the energy to be concentrated into a narrow beam so that the signal transmitted by the BTS can reach mobile stations farther away at a lower power level than conventional BTS requirements. This allows the mobile station to function at a great distance from the base transceiver station, thus meaning that the area of the cell or cell sector of the cellular network can be increased. As a result of increasing the cell area, the number of base stations required can be reduced, thereby reducing network costs. SDMA systems typically require several antenna elements in order to obtain the desired number of different beam directions for transmitting and receiving signals. Providing multiple antenna elements increases the sensitivity of the BTS to receive signals. This means that a larger cell size does not adversely affect the reception of signals by the BTS from the mobile station.

The SDMA system can also increase the capacity of the system, that is, the number of mobile stations that the system can support at the same time is increased. The reason for this is the directional nature of the communication, which means that the BTS will pick up less interference from mobile stations in other cells using the same frequency. When communicating with a given MS in the associated cell, the BTS causes less interference to mobile stations in other cells using the same frequency.

Finally, SDMA systems allow simultaneous use of the same frequency to transmit signals to two or more different mobile stations located at different locations in the same cell. This greatly increases the amount of transmission that a cellular network can undertake.

SDMA can be implemented over analog and digital cellular networks, and can incorporate a variety of existing standards such as GSM, DCS1800, TACS, AMPS and NMT. The SDMA system can also be used in conjunction with other existing multiple access techniques such as Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), and Frequency Division Multiple Access (FDMA) techniques.

One problem with SDMA systems is the need to determine the direction in which a signal should be sent to a mobile station. In some cases, a relatively narrow beam is used to transmit a signal from a base transceiver station to a mobile station. Therefore, the direction of the mobile station needs to be estimated fairly accurately. If a mobile station is moving relative to the base transceiver station, it may move from a cell area covered by a first beam to a cell area covered by an adjacent beam. The base transceiver station needs to decide when the adjacent beam should be used to send a signal to the mobile station instead of the first beam. This determination is complicated by the fact that the first beam and the adjacent beam will partially overlap.

Another problem is determining the direction in which the BTS sends signals to the mobile station based on the uplink signals the BTS receives from the mobile station. But the frequency at which downlink signals are sent from the mobile station to the BTS is different from the frequency at which the BTS sends signals to the mobile station. The difference in the frequencies used in the uplink and downlink signals means that the behavior of the channel in the uplink direction is different from the behavior of the channel in the downlink direction. Thus, the optimal direction determined for uplink signals is not always the optimal direction for downlink signals.

Contents of the invention

The aim of the present invention is to overcome these difficulties.

According to a first aspect of the present invention, there is provided a method for directional wireless communication between a base station and a mobile station in a mobile communication network, the method comprising the steps of:

identifying, at the base station, consecutive bursts of communication data transmitted from the mobile station;

determining respective beam directions of communication data bursts sequentially received by said base station based on a plurality of adjacent beam directions;

selecting the beam directions for transmitting signals from the base station to the mobile station such that when it is determined that the base station sequentially receives communication data bursts from two different beam directions, the two beam directions are simultaneously selected different beam directions for transmitting said signal from said base station to said mobile station, and when the two different beam directions are not adjacent, in both beam directions and an intervening beam direction , transmitting the signal from the base station to the mobile station.

In this way, ambiguities caused by a second station moving from an area covered by one beam to an area covered by another beam can be compensated for by embodiments of the present invention. Specifically, the probability that a signal from a first station reaches the second station is increased.

If the different beam directions are not adjacent, one of them may correspond to an anomalous path taken by a burst of communication data from the first station. A signal sent from a first station to a second station does not necessarily take this anomalous path. By transmitting in all inserted beam directions, the impact of detecting signals that have traveled anomalous paths can be reduced.

Preferably the first and second beam directions can be used to predetermine a plurality of consecutive signals to be transmitted from the first station. Optionally, the first and second beam directions may only be used for a single signal sent from the first station. Where possible, it is preferable to transmit the signal from the first station only in a single beam direction.

The certain direction in which each sequential data burst is received may be defined as the beam direction in which the strongest signal is received. This direction corresponds to the path that provides the least attenuation for a given burst. Alternatively, the determined direction for receiving respective sequential data bursts may be defined as the direction of the beam receiving the signal via the shortest path.

The method preferably includes a monitoring of a distance parameter representing the distance between the first and second stations, wherein if the distance between the first and second stations is less than a predetermined value, regardless of the direction in which the first and second signals are received How to send a signal to the above-mentioned second station with a relatively wide spreading angle. In practice, this means that if the distance between the first and the second station is less than a critical distance, the signal is transmitted in a relatively large number of beam directions. If the distance between the first and second stations is smaller than the predetermined value, the signal can be sent to the second station with relatively low power, and if the distance is greater than the predetermined value, the signal can be sent with higher power.

According to a second aspect of the present invention, there is provided a base station for performing directional wireless communication with a mobile station in a mobile communication network, the base station comprising:

identifying means for identifying, at said base station, consecutive bursts of communication data transmitted from said mobile station;

means for determining, based on a plurality of adjacent beam directions, determining respective beam directions of communication data bursts sequentially received by said base station;

transmitter means for transmitting a signal to said mobile station;

control means for selecting said beam direction for transmitting a signal from said base station to said mobile station, whereby when it is determined that said base station sequentially receives communication data bursts from two different beam directions, simultaneously select the two different beam directions for transmitting the signal from the base station to the mobile station, and when the two different beam directions are not adjacent, in the two beam directions and inserting In the direction of the beam, the signal is transmitted from the base station to the mobile station.

The invention is particularly applicable to cellular communication networks in which the first station is a base transceiver station. However, it should be understood that the embodiments of the present invention may be applicable to non-cellular directional wireless communication networks. It should be understood that the term "burst" herein means only a portion of the signal received from the second station and is not intended to limit the scope of application of the present invention to a standard system such as GSM, where the term "burst" has a specific meaning. Alternatively, the term "burst" may refer to a specified portion of data sent from the second station.

Description of drawings

In order to better understand the present invention and realize the present invention, it is described by way of example with reference to accompanying drawing now, wherein:

FIG. 1 shows a structural diagram of a base transceiver station (BTS) and its associated cell sectors;

Figure 2 shows a simplified diagram of an antenna array and base transceiver station;

Figure 3 illustrates the fixed beam pattern provided by the antenna array of Figure 2;

Fig. 4 shows the structural diagram of the digital signal processor of Fig. 2;

Figure 5 illustrates the channel impulse responses for four of the eight channels.

Figures 6a-h show the beam directions where eight consecutive data bursts sent by the MS to the base transceiver station are expected to be received;

Figures 7a-h illustrate selected beams in 8 consecutive data bursts transmitted by an SDMA base transceiver station to an MS according to one embodiment of the present invention.

Detailed ways

Referring first to Figure 1, there is shown three cell sectors 2 defining a cell 3 of a cellular mobile telephone network. Three cell sectors 2 are served by respective base transceiver stations (BTS) 4 . Each BTS 4 has a transceiver for transmitting and receiving signals for a corresponding one of the three cell sectors 2. In this way, a dedicated base transceiver station is provided for each cell sector 2 respectively. Each BTS 4 is thus able to communicate with a mobile station (MS), such as a mobile phone located in the corresponding cell sector 2.

The present embodiment is described in the context of a GSM (Global System for Mobile Communications) network. In the GSM system, the frequency/time division multiple access F/TDMA system is used. Send data between BTS 4 and MS in bursts. The data burst contains a training sequence which is a known data sequence. The purpose of the training sequence will be described below. Each data burst is transmitted in a given frequency band through a predetermined time slot within that frequency band. Using a directional antenna array allows for space division multiple access. Thus, in the embodiment of the present invention, each data burst will be sent through a designated frequency band, a designated time slot and a designated direction. An associated channel can be defined for a given burst of data sent over a given frequency band, a given time slot, and a given direction. As described below, in some embodiments of the invention, the same data burst is transmitted over the same frequency band, the same time slot, but in two different directions.

Fig. 2 shows a block diagram of an antenna array 6 of a BTS 4 used as a transceiver. It should be understood that the array 6 shown in FIG. 2 serves only one of the three cell sectors 2 shown in FIG. 1 . The other two antenna arrays 6 serve the other two cell sectors 2 . The antenna array 6 has 8 antenna elements a _{1 .} . . a ₈ . The intervals between the respective antenna elements a ₁ ... a ₈ are half a wavelength, and are arranged in a row along a vertical line. The individual antenna elements a ₁ ...a ₈ are used to transmit and receive signals and may have any suitable structure. Each antenna element a ₁ ... a ₈ may be a dipole antenna, a patch antenna or any other suitable antenna. The eight antenna elements a ₁ . . . a ₈ jointly define a phased array antenna 6 .

As is known, the individual antenna elements _a1 ... _a8 of the phased array antenna 6 are provided with the same signal to be transmitted to a mobile station MS. However, the phases of the signals supplied to the respective antenna elements a ₁ ... a ₈ are shifted from each other. The phase difference between the signals supplied to the respective antenna elements _a1 ... _a8 produces a directional transmission pattern. In this way, signals from the BTS 4 can only be sent in certain directions in the cell sectors 2 associated with the array 6 . The directional transmission patterns achieved by the array 6 are the result of constructive and destructive interference occurring between the signals which are phase shifted from each other and which are transmitted by the individual antenna elements a ₁ . . . a ₈ . In this regard, reference is made to FIG. 3 , which illustrates the directional transmission pattern achieved by the antenna array 6 . The antenna array 6 can be controlled to provide a beam b ₁ . . . b ₈ in any one of the eight directions illustrated in FIG. 3 . For example, the antenna array 6 can be controlled to transmit signals to one MS only in the direction of beam _b5 or _b6 . As described below, it is also possible to control the antenna array 6 to transmit signals in more than one beam direction simultaneously. For example, signals may be sent in two directions defined by beams _b5 and _b6 . FIG. 3 is only a structural representation of the eight possible beam directions that can be realized by the antenna array 6 . In practice, however, there will be an overlap between adjacent beams to ensure that the antenna array 6 serves all cell sectors 2 .

The relative phases of the signals provided on the individual antenna elements _a1 ... _a8 are controlled by a Butler matrix circuit 8 so that the signals can be transmitted along the desired beam directions. Thus the Butler matrix circuit 8 provides a phase shift function. The Butler matrix circuit 8 has 8 inputs 10a-h from the BTS 4 and 8 outputs, each of which is output to a respective antenna element a ₁ ...a ₈ . The signal received by each input 10a-h comprises the data burst to be transmitted. Each of the eight inputs 10a-h indicates the beam direction in which a given data burst can be sent. For example, when the Butler matrix circuit 8 receives a signal on the first input 10a, the Butler matrix circuit 8 supplies the signal on the input 10a to the respective antenna elements _a1 ... _a8 with the required phase difference to generate the beam _b1 , A data burst is thus transmitted in the direction of beam _b1 . Similarly, a signal provided on input 10b causes a beam to be generated in the direction of beam _b2 , and so on.

As mentioned above, the antenna elements _a1 ... _a8 of the antenna array 6 receive signals from one MS and transmit signals to one MS. A signal sent by an MS is usually received by 8 antenna elements a ₁ . . . a ₈ . However, there will be a phase difference between the individual signals received by the individual antenna elements a ₁ . . . a ₈ . The Butler matrix circuit 8 is thus able to determine the beam directions of the received signals from the relative phases of the signals received by the individual antenna elements a ₁ . . . a ₈ . The Butler matrix circuit 8 thus has 8 inputs, one input from the antenna elements a ₁ . . . a ₈ for the signal received by each antenna element. The Butler matrix circuit 8 also has 8 outputs 14a-h. Each output 14a-14h corresponds to a particular beam direction that can receive a given burst of data. For example, if antenna array 6 receives a signal from an MS in the direction of beam _b1 , Butler matrix circuit 8 will output the received signal on output 14a. A signal received in the direction of beam _b2 results in a received signal output from the Butler matrix circuit 8 on output 14b, and so on. In summary, the Butler matrix circuit 8 will receive 8 mutually offset versions of the same signal at the antenna elements a ₁ . . . a ₈ . From the relative phase offset, the Butler matrix circuit 8 determines the direction in which said received signal has been received and outputs a signal on a designated output 14a-h according to the direction in which the received signal has been received.

It should be understood that under certain circumstances a single signal or data burst from one MS may appear to come from more than one beam direction due to signal reflections passing between the MS and BTS4 at the same time, assuming the reflections have a relatively wide spread angle. Butler matrix circuit 8 provides a signal on each output 14a-h, each output corresponding to each beam direction in which a given signal or data burst occurs. In this way, the same data burst can be provided on more than one output 14a-h of the Butler matrix circuit 8 . However, the signals on the individual outputs 14a-h may be time-delayed from each other.

Each output 14a-h of the Butler matrix circuit 8 is connected to the input of a corresponding amplifier 16 which amplifies the received signal. An amplifier 16 is provided for each output 14a-h of the Butler matrix circuit 8 . The amplified signal is then processed by a corresponding processor 18 which processes the amplified signal to reduce the frequency of the received signal to baseband frequency so that the BTS 4 can process the signal. To this end, the processor 18 removes the carrier frequency component from the input signal. Also, one processor 18 is provided for each output 14a-h of the Butler matrix circuit 8 . The received signal in analog form is then converted into a digital signal by an analog-to-digital (A/D) converter 20 . Eight A/D converters 20 are provided, one for each output 14a-h of the Butler matrix circuit 8 . The digital signals are then fed via corresponding inputs 19a-h to a digital signal processor 21 for subsequent processing.

The digital signal processor 21 also has eight outputs 22a-h, each outputting a digital signal representing the signal to be sent to a given MS. The selected output 22a-h indicates the beam direction in which the signal is to be transmitted. The digital signal is converted into an analog signal by a digital-to-analog (D/A) converter 23 . A digital-to-analog converter 23 is provided for each output 22a-h of the digital signal processor 21 . The analog signal is then processed by a processor 24, which is a modulator that modulates the analog signal to be transmitted onto a carrier frequency. Before the processor 24 processes the signal, the signal is at baseband frequency. An amplifier 26 then amplifies the resulting signal and passes it to the corresponding input 10a-h of the Butler matrix circuit 8 . A processor 24 and an amplifier 26 are provided for each output 22a-h of the digital signal processor 21 .

Reference is now made to FIG. 4 which illustrates a digital signal processor 21 . It should be understood that the blocks illustrated in Figure 4 do not necessarily correspond to the elements of an actual digital signal processor 21 embodying the present invention. Specifically, the respective blocks illustrated in FIG. 4 correspond to various functions performed by the digital signal processor 21 . In one embodiment of the invention, the digital signal processor 21 is at least partially implemented by an integrated circuit, and the same unit may perform several functions.

Each signal received by the digital signal processor 21 on a respective input 19a-h is input to a respective channel impulse response (CIR) estimator module 30 . The CIR estimator module 30 includes memory capacity for storing the received signal and memory capacity for storing the estimated channel impulse response. The channel impulse response estimator module 30 is used to estimate the channel impulse response of the channel corresponding to the input 19a-h. As described above, an associated channel may be defined for a given data burst to be transmitted over a selected frequency band, assigned time slot and beam direction of the received signal. The Butler matrix circuit 8 determines the beam direction of the received signal so that the signal received at the input 19a of the digital signal processor is primarily representative of the signal which has been received from the direction of beam _b1 , and so on. It should be understood that a signal received on a given input may also contain side lobes of a signal received on an adjacent input.

Each data burst sent from the mobile station MS to the BTS 4 contains a training sequence TS. But the training sequence TS _RX received by the BTS 4 is distorted by noise and multipath effects which create interference between adjacent bits of the training sequence. The latter interference is called inter-symbol interference. The TS _RX is also affected by interference from other mobile stations, such as mobile stations located in other cells or cell sectors, using the same frequency which would cause joint channel interference. It will be appreciated that a given signal from the MS will follow more than one path to the BTS, and that the antenna array 6 will detect more than one version of the given signal from a given direction. The CIR estimator module 30 cross-correlates the training sequence TS _RX received from the input 19 a with the reference training sequence TS _REF stored in a data memory 32 . The reference training sequence TS _REF is the same as the training sequence originally sent by the mobile station. In practice the received training sequence TS _RX is a signal modulated to the carrier frequency, while the reference training sequence TS _REF is stored in the data memory 32 as a bit sequence. Correspondingly, the stored reference training sequence is similarly modulated before performing the cross-correlation. In other words, correlate the distorted training sequence received by BTS 4 with the undistorted version of the training sequence. In an optional embodiment of the invention, the received training sequence is demodulated before being correlated with the reference training sequence. In this case, the reference training sequence will again have the same form as the training sequence being received. In other words, the reference training sequence is not modulated.

Both the reference training sequence TS _REF and the reception training sequence TS _RX have a length L corresponding to L data bits, and may be 26 bits. The exact position of the received training sequence TS _RX in the allocated time slot may be indeterminate. This is due to the fact that the distance between the mobile station MS and the BTS 4 affects the position of the data bursts transmitted by the MS in the allocated time slots. For example, if a mobile station MS is relatively far from the BTS 4, the training sequence will appear later in the allocated time slot than if the mobile station MS is closer to the BTS 4.

Considering the uncertainty of the position of the received training sequence TS _RX in the allocated time slot, the reference training sequence TS _REF is used to perform n times of correlation processing on the received training sequence TS _RX . Typically, n can be 7 or 9. n is preferably an odd number. n-fold correlations are usually made on both sides of the maximum acquisition correlation. The relative position of the received training sequence TS _RX with respect to the reference training sequence TS _REF is shifted by one position between successive correlations. Each position is equivalent to a bit in the training sequence and represents a delay segment. Each individual correlation of the received training sequence TS _RX with the reference training sequence TS _REF produces a tap representing the channel impulse response of the correlation. n individual correlations produce a sequence of taps with n values.

Referring now to FIG. 5, this figure shows channel impulse responses for 4 of 8 possible channels corresponding to 8 spatial directions. In other words, Figure 5 shows the channel impulse responses for 4 channels corresponding to a given data burst received from the mobile station in 4 of the 8 beam directions, the data burst being in the given frequency band and time slot . The x-axis of each legend is a measure of time delay and the y-axis is a measure of relative power. Each line (or tap) marked in the figure represents the received multipath signal corresponding to the specified relative delay. Each legend has n lines or taps, where one tap corresponds to each correlation.

From the estimated channel impulse response, the position of the training sequence in the allocated time slot can be determined. The maximum tap value is obtained when the optimal correlation between the received training sequence TS _RX and the reference training sequence TS _REF is obtained.

For each channel, the CIR estimator module 30 also determines 5 (or any other suitable number) consecutive taps that give the maximum energy. Calculate the maximum energy for a given channel as follows: $\mathrm{E.}=\underset{j=1}{\overset{5}{\mathrm{\Σ}}}{\left(h_j\right)}^2$

Where h represents the tap amplitude obtained by cross-correlating the received training sequence TS _RX and the reference training sequence TS _REF . The CIR estimator module 30 estimates the maximum energy of a given channel by using a sliding window technique. In other words, the CIR estimator module 30 considers 5 adjacent values at a time and calculates the energy from these 5 values. The 5 adjacent values given the maximum energy are chosen to represent the impulse response of the channel.

Energy can be viewed as a measure of the relative strength of a desired signal from a given MS received by the BTS 4 in a given direction. This process is performed for all 8 channels representing 8 different directions in which the same data burst can be received. A signal received with maximum energy takes the path that least attenuates that signal.

An analysis module 34 is provided which stores the maximum energy calculated by the CIR estimator module 30 for the corresponding channel from the 5 adjacent values selected by the CIR estimator module 30 to represent the channel impulse response. The analysis module 34 may also analyze the channel impulse response determined by the CIR estimator module 30 to determine the minimum delay. This delay is a measure of where the training sequence TS _RX is received in the allocated time slot, and thus a relative measure of the distance the signal travels between the mobile station and the BTS 4 . The channel with the least delay has the signal that traverses the shortest distance. In some cases this shortest distance may represent the line of the direct path between the mobile station MS and the BTS 4 .

The analysis module 34 is used to determine the start position of a window that determines the five values that provide the greatest energy. A time delay is then determined based on the time between a reference point and the start of the window. The reference point may be a common time at which all received training sequences in the respective branches start to be correlated, corresponding to the earliest window edge of all branches or a similar common point. In order to accurately compare the various delays of the different channels, a common timing scale is used which depends on the synchronization signal provided by the BTS 4 to control the TDMA mode of operation. In other words, the position of the received training sequence TS _RX in the allocated time slot is a measure of the time delay. It will be appreciated that in known GSM systems the delay of a given channel is calculated in order to provide timing advance information. The timing advance information is used to ensure that the signal sent by the mobile station to the BTS falls within its assigned time slot. The timing advance information can be determined from the calculated relative delay and the current timing advance information. If the mobile station is far away from the base station, the BTS will instruct the MS to send its data burst at a time earlier than if the mobile station MS were closer to the BTS.

The analysis results from the various analysis modules 34 are input to a beam selection control module 36 which determines the direction from which a given burst of data is expected to be received. This desired direction may be the direction of the beam in which the signal with the greatest strength is received, or alternatively may be the direction in which the data burst is received first. The beam selection module 36 then stores this beam direction and performs the same steps for the next burst received from the mobile station. If two determined beam directions are the same in two consecutive data bursts, the signal from the BTS to the MS is sent in that determined beam direction. In a preferred embodiment, the base transceiver station is controlled to transmit signals to the MS only in a single beam direction under normal circumstances. But if the beam directions for receiving the first and second consecutive bursts are different, the BTS will send the next signal to the MS in the direction in which the second signal was received and in the direction in which the first signal was received.

If the beam direction in which the BTS receives the first signal is not adjacent to the beam direction in which the second data burst is received, the signal transmitted by the BTS is also transmitted in the insertion beam direction. For example, if it is determined that the first burst is from the direction of beam _b1 and the second burst is from the direction of beam _b3 , the base station will transmit to the mobile station in the directions of beams _b1 , _b2 , and _b3 Signal.

Referring now to Figures 6a-h and 7a-h, there are illustrated the principles used by embodiments of the present invention. Figures 6a-h illustrate the beam directions for receiving 8 consecutive data bursts sent by a mobile station to the base station.

Alternatively, the beam directions illustrated in Figure 6 can be considered as the beam directions that should be selected for successive data bursts sent by the BTS to the MS, in the case where only a single beam direction should be selected for each data burst . The first and second data bursts from mobile station MS are expected to come from the direction of beam _b3 . The third and fourth data bursts are expected to come from the direction of beam _b4 . The fifth and sixth data bursts are expected to come from the direction of beam _b3 and the seventh data burst is expected to come from the direction of beam _b5 .

The beam directions for the BTS to send 8 consecutive data bursts to the MS are shown in Figures 7a-h. Since the first and second signals from the mobile station are expected to be received in the direction of beam _b3 , the BTS 4 each transmits a first and a second data burst to the mobile station in the direction of beam _b3 . But since it expects to receive the second and third bursts from the mobile station in the direction of beam _b3 and beam _b4 respectively, the BTS sends the second burst to the mobile station in the direction of beam _b3 and beam _b4 Three bursts. The third and fourth bursts from the mobile station are expected to be received from the same beam direction, ie the direction of beam _b4 . Correspondingly, BTS 4 transmits the fourth burst only in the direction of beam b ₄ . The fourth burst received by the BTS is received in the direction of beam _b4 , and the BTS 4 receives the fifth burst in the direction of beam _b3 . Thus, the BTS transmits the fifth burst in the direction of beam _b3 and beam _b4 . The sixth burst received by the BTS is expected to be received from the direction of beam b ₃ and the seventh burst received by the BTS is expected to be received from the direction of beam b ₅ . Accordingly, a seventh burst is sent to the MS in the direction of beams _b3 and _b5 and in the direction of the insertion beam, ie beam _b4 . Finally, since BTS 4 expects to receive the seventh and eighth bursts from the directions of beams _b5 and _b3, respectively, the BTS sends the eighth bursts in the direction of beams _b3 , _b4 and _b5 . hair.

In a modification of the above embodiment, two consecutive data bursts are respectively received from two different directions, and the BTS will send N consecutive bursts to the MS in these two different directions and any insertion direction. N can be any suitable number of bursts, such as 3 or 4.

It can be found that the above method is very suitable for the case where the distance between the BTS and the MS is greater than a specified distance. This distance largely depends on the local environment, but can be greater than about 0.5km. If the distance between the mobile station and the BTS is less than 0.5 km, the signal to the MS is sent through a wider spread angle. This involves selecting several possible beam directions, eg 4 or more directions. Typically, the power level for each beam will be lower when more beams are selected.

One way of determining the distance between the MS and the BTS is based on timing advance information that provides a measure of the distance between the BTS 4 and the MS. This first method is optimal in some embodiments of the invention as it gives reasonably accurate results. Alternatively, the spread angle of the BTS received signal can be used as a measure of the distance between the MS and the BTS. When the distance between the BTS and the MS is greater than a critical distance, most of the energy received from the MS is distributed over one, two or three beams. But when the distance between the BTS and the MS is less than the critical distance, the received desired energy is distributed over a larger number of beams. To determine the spread angle, beam selection control module 36 compares the channel impulse responses obtained for each possible beam direction for a given signal. If the majority of received energy is distributed in three or fewer beam directions, it is assumed that the distance between the BTS and the MS is greater than the critical distance. Optionally, the distance between the BTS and the MS is assumed to be less than the critical distance if most of the received energy comes from four or more beam directions.

Correspondingly, in the embodiment of the present invention, the method of using two preamble signals received from the MS to determine the direction or directions for sending signals to the MS can only be used when the distance between the MS and the BTS 4 is greater than the critical distance Down. When the distance between MS and BTS 4 is less than the critical distance, BTS 4 will send signals to MS through relatively more beam directions. The power level used when transmitting over a relatively wide spread angle will generally be less than the power level used on the beam or beams when the distance between the MS and the BTS 4 is greater than a critical distance. The desired power level is selected by beam selection module 36 .

The generation module 38 is responsible for generating the signals to be output from the digital signal processor 21 . The generation module 38 has an input 40 representing speech and/or information to be sent to the mobile station MS. The generation module 38 is responsible for encoding speech or information sent to the mobile station MS and includes in the signal a training sequence and a synchronization sequence. Module 38 is also responsible for generating the modulation signal. Depending on the generated signal and the determined beam direction, the generation module 38 provides a signal at a corresponding output 22 a - h of the digital signal processor 21 . Generation module 38 also provides an output 50 which is used to control the amplification provided by amplifier 24 to ensure that the signals in the direction of the main and auxiliary beams have the required power levels.

The output of the channel impulse response module 30 is also used to equalize and match the signal received from the mobile station MS. Specifically, a matched filter (MF) and equalizer module 42 may eliminate or mitigate the effects of inter-symbol interference in the received signal resulting from multipath propagation. It should be understood that the matched filter (MF) and equalizer block has an input (not shown) that receives the received signal from the MS. The outputs of the various modules 42 are received by a recovery module 44 responsible for recovering voice and/or information sent by the MS. The steps performed by the recovery module include demodulating and decoding the signal. The recovered speech or information is output on output 48 .

It should be understood that although the above-described embodiments have been implemented in a GSM cellular communication network, the present invention can also be used in other digital cellular communication networks and analog cellular networks. The above embodiment uses a phased array with 8 elements. Arrays can of course have any number of cells. Alternatively, the phased array can be replaced by discrete directional antennas, each emitting a beam in a given direction. Where desired, the Butler matrix circuit may be replaced by any other suitable phase shifting circuit. The Butler matrix circuit is an analog beamformer. Of course a digital beamformer DBF or any other suitable type of analog beamformer could be used. Depending on the signals provided to the individual elements, the array can be controlled to produce more than 8 beams even with only 8 elements.

Multiple phased arrays may also be provided. Phased arrays can provide different numbers of beams. Arrays with a smaller number of elements are used when a wider spread angle is required, and arrays with a larger number of elements are used when a relatively narrow beam is required.

It will be appreciated that the above embodiment has been described as providing 8 outputs from the Butler matrix circuit. It should be understood that in practice several different channels are simultaneously output on each output of the Butler matrix. Those channels can have different frequency bands. Channels of different time slots are also provided on the corresponding outputs. Although the foregoing has described separate amplifiers, processors, analog-to-digital converters and digital-to-analog converters, in practice all of the above components could be provided by a single unit with multiple inputs and outputs.

It should be understood that embodiments of the present invention have application not limited to cellular communication networks. For example, embodiments of the present invention may be used in any environment where directional wireless communication is required. For example, this technique can be used in a PMR (Private Radio Network) or similar network.

For two consecutive signals there is no need to determine the direction in which to receive the two consecutive signals. For example, the direction in which a data burst is expected to be received may be determined every N bursts, where N is a specified integer. For example, the BTS may determine the direction to receive a first burst from the MS and the direction to receive a third burst. If the two directions are different, the BTS sends the signal in both directions.

Similarly, the direction in which the first station is signaling will not immediately respond to the receipt of a leading communication data burst from the MS. In some embodiments, the BTS may select different beam directions for transmission based on sequential communication data bursts formed from one or more data bursts previously received from the MS.

Embodiments of the present invention may have application not limited to cellular communication networks. For example, embodiments of the present invention may be used in any environment where directional wireless communication is required. For example, this technique can be used in a PRN (Private Radio Network) or similar network.

Claims (10)

1. A method for directional wireless communication between a base station and a mobile station in a mobile communication network, the method comprising the steps of: identifying, at the base station, consecutive bursts of communication data transmitted from the mobile station; determining respective beam directions of communication data bursts sequentially received by said base station based on a plurality of adjacent beam directions; selecting the beam directions for transmitting signals from the base station to the mobile station such that when it is determined that the base station sequentially receives communication data bursts from two different beam directions, the two beam directions are simultaneously selected different beam directions for transmitting said signal from said base station to said mobile station, and when the two different beam directions are not adjacent, in both beam directions and an intervening beam direction , transmitting the signal from the base station to the mobile station. 2. The method of claim 1, wherein said two beam directions are for a predetermined plurality of consecutive signals transmitted from said base station. 3. A method according to claim 1 or 2, wherein the determined direction in which each data burst is sequentially received is defined as the beam direction in which the strongest signal is received. 4. A method according to claim 1 or 2, wherein the determined direction for sequentially receiving each data burst is defined as the beam direction for receiving the signal via the shortest path. 5. The method according to claim 1, further comprising the step of monitoring a distance parameter representing the distance between said base station and said mobile station, and if the distance between the base station and said mobile station is less than a predetermined value, using a relatively wide spread The angle transmits a signal to the mobile station regardless of the direction in which the two signals were received. 6. The method according to claim 5, wherein if the distance between the base station and the mobile station is less than said predetermined value, using a relatively low power level to transmit a signal to said mobile station, and if said distance is greater than Said predetermined value transmits said signal with a higher power level. 7. The method of claim 1, wherein said network is a cellular communication network. 8. A base station for performing directional wireless communication with a mobile station in a mobile communication network, the base station comprising: identifying means for identifying, at said base station, consecutive bursts of communication data transmitted from said mobile station; means for determining, based on a plurality of adjacent beam directions, determining respective beam directions of communication data bursts sequentially received by said base station; transmitter means for transmitting a signal to said mobile station; control means for selecting said beam direction for transmitting a signal from said base station to said mobile station, whereby when it is determined that said base station sequentially receives communication data bursts from two different beam directions, simultaneously select the two different beam directions for transmitting the signal from the base station to the mobile station, and when the two different beam directions are not adjacent, in the two beam directions and inserting In the direction of the beam, the signal is transmitted from the base station to the mobile station. 9. The base station according to claim 8, wherein said control means is arranged to monitor the step of a distance parameter representing the distance between said base station and said mobile station, if the distance between the base station and said mobile station is less than a predetermined value, using A relatively wide spread angle transmits signals to the mobile station regardless of the direction in which the two signals are received. 10. A base station according to claim 8, wherein said control means is arranged to control said transmitter means to transmit a predetermined plurality of consecutive signals in said two beam directions.

Images