Method and transmitter for analog beam steering - Patents.com

Abstract

A transmitter configured for analog beam steering is disclosed, the transmitter comprising a plurality of antenna branches, each having an antenna (326). The transmitter comprises, in each of the antenna branches, a signal splitter (308) for splitting an analog radio signal into several beam signals, the number of beam signals being equal to the number of desired beams to be transmitted. The transmitter further comprises, for each of the several beam signals, a phase shifter (310, 312) for phase-shifting the beam signal according to a phase-shift setting for that beam and for that antenna branch, the phase-shift settings being taken from a single look-up table, and a signal combiner (314) for combining the phase-shifted beam signals into a single combined signal. The transmitter is further configured to transmit the combined signal from the antenna (326) of that antenna branch toward a receiver.

Description

[Technical field]

[0001] The present disclosure generally relates to a transmitter-implemented method and transmitter for analog beam steering in a wireless communication network, the transmitter comprising a plurality of antenna branches, each antenna branch comprising an antenna. The present disclosure further relates to a computer program and carrier corresponding to the method and transmitter. [Background technology]

[0002] In order to understand the special conditions when describing analog beamforming in a transmitter for wireless transmission of a signal, it is useful to first consider digital beamforming. Digital beamforming is a technique in which several independent beams in baseband frequencies can be formed, which simultaneously transfer independent signals across several beams. Here, it is assumed that each antenna branch in the array antenna of the transmitter is equipped with its own radio unit with its own digital-to-analog converter (DAC). With digital beamforming, there is no need for analog phase shifters to steer one or more beams in any direction. In this way, several parallel beams can be defined in the digital baseband, and independent signals can be transmitted in these different beam directions.

[0003] However, when only one DAC is available in one common digital radio, this means that the signal to be transmitted is converted from digital to analog form before it is split to each antenna branch. Thus, the same signal will be split to each antenna branch and each antenna will transmit the same signal. In order to steer such a composite signal to a certain beam direction when transmitted over the air, so-called analog beam steering, the signal transmitted from each antenna needs to have its own phase shift. For this reason, each antenna branch is equipped with its own analog phase shifter.

[0004] The resulting beam direction can be changed by uploading the phase shift information for each phase shifter at a required pace. However, if the beam direction is to be shifted in a rapid manner by changing direction multiple times over a period of time, the digital control signals with the phase shift information for the phase shifters can be quite voluminous in terms of data transmission.

[0005] Therefore, a method has been developed by the applicant in which a local look-up table (LUT) is developed for an existing transmitter, with phase shift information for each participating phase shifter to achieve a certain beam direction for the transmitted composite signal. The table is shared between all of the phase shifters at the RF level in the radio front end. In that case, a digital control signal with phase shift information may only need one entry to define the required beam direction, and a local pointer can use this one entry information to choose the correct phase to be set for each phase shifter. As a result, to control the phase shifters to obtain, for example, 32 beam directions, it is only necessary to transport a number represented by 5 bits. This 5-bit signal is sent to the central processing unit (CPU) of the transmitter, which looks up the look-up table (LUT) and then locally outputs the phase shifter setting to the appropriate phase shifter. This kind of procedure is very simple to steer an array antenna to a predefined beam angle.

[0006] In some scenarios it may be of interest to define a second beam as illustrated in Figure 1, or even more beams, to be presented to two or several receivers in an analog beamforming setup. The same signal will be transported by the transmitter in almost all of the beams, but it may still be a scenario one wishes to support. For this scenario, there is no simple solution in the same way as for just one beam and a LUT to switch the phase shifter to a predefined position.

[0007] For this scenario, in addition to the phase shifter position, an amplitude taper mechanism that keeps the antenna pattern in a good and controlled manner would also be needed. The combination of different directions and amplitude tapers makes a simple LUT strategy for single beam steering extremely complicated. Therefore, existing solutions, if they exist at all, would define a multi-dimensional LUT. However, this would require a high degree of memory to be allocated. Also, a lot of processing power would be required. As shown, there is a need for an analog beam steering method and transmitter that can achieve two or more beams transmitted over the air from the transmitter. Furthermore, such a method and transmitter should be easy to use, require little control data to be sent to the phase shifters, and require little memory in the analog front end. Summary of the Invention

[0008] The object of the present invention is to address at least some of the problems and issues outlined above. These and other objects can be achieved by using a method and a transmitter as defined in the accompanying independent claims.

[0009] According to one aspect, a method for analog beam steering implemented by a transmitter of a wireless communication network is provided. The transmitter comprises a plurality of antenna branches, each antenna branch comprising an antenna. The method includes: for each antenna branch, receiving an analog radio signal, the analog radio signal being the same in each of the antenna branches; splitting the analog radio signal into several beam signals, the number of beam signals being equal to the number of desired beams to be transmitted, the number of beams being at least two; and for each of the several beam signals, phase shifting the beam signal according to a phase shift setting for that beam and for that antenna branch, the phase shift setting being taken from a single look-up table that is common for the number of beams; combining the phase-shifted beam signals into one composite signal; and transmitting the composite signal from the antenna of the antenna branch towards a receiver.

[0010] According to another aspect, a transmitter configured for analog beam steering is provided. The transmitter comprises a plurality of antenna branches. Each antenna branch comprises an antenna. The transmitter comprises a signal splitter for receiving an analog radio signal at each of the antenna branches, the analog radio signal being the same at each of the antenna branches, the signal splitter further configured for splitting the analog radio signal into several beam signals, the number of beam signals being equal to the number of desired beams to be transmitted, the number of beams being at least two. The transmitter further comprises, for each of the several beam signals, a phase shifter for phase shifting the beam signal according to a phase shift setting for that beam and for that antenna branch, the phase shift settings being taken from a single look-up table, and a signal combiner for combining the phase-shifted beam signals into one combined signal. The transmitter is further configured for transmitting the combined signal from an antenna of the antenna branch towards a receiver.

[0011] According to another aspect, a transmitter operable in a wireless communication system and configured for analog beam steering is disclosed. The transmitter comprises a processing circuit and a memory. The memory includes instructions executable by the processing circuit, whereby the transmitter is operable to receive an analog radio signal, where the analog radio signal is the same in each of the antenna branches, and to split the analog radio signal into several beam signals, where the number of beam signals is equal to the number of desired beams to be transmitted, where the number of beams is at least two. Furthermore, the transmitter is operable to phase shift, for each of the several beam signals, the beam signal according to a phase shift setting for that beam and for that antenna branch, where the phase shift setting is taken from a single look-up table that is common for the number of beams, to combine the phase-shifted beam signals into one composite signal, and to transmit the composite signal from the antenna of that antenna branch towards a receiver.

[0012] According to other aspects, there is also provided a computer program and a carrier, the details of which are set out in the claims and in the detailed description.

[0013] Further possible features and benefits of this solution will become apparent from the detailed description that follows.

[0014] The solution will now be explained in more detail by means of exemplary embodiments and with reference to the accompanying drawings. [Brief description of the drawings]

[0015] [Figure 1] 1 is a diagram of an exemplary dual beam antenna array pattern that can be produced by the present invention. [Diagram 2]1 is a block diagram illustrating a wireless communication network in which the present invention may be used; [Diagram 3] FIG. 2 is another block diagram of a wireless communication network or scenario in which the present invention may be used. [Figure 4] 4 is a flow chart illustrating a method implemented by a transmitter, according to a possible embodiment. [Diagram 5] 4 is another flowchart of a method according to an embodiment. [Figure 6] FIG. 2 is a block diagram of a device according to an embodiment configured in an antenna branch. [Figure 7] FIG. 11 is another block diagram of a device according to a further possible embodiment, in the case of four beams, in which the device is configured in the antenna branch. [Figure 8] FIG. 2 is a block diagram of an equivalent electrical device. [Figure 9] FIG. 2 is a block diagram of a transmitter having four antennas according to a possible embodiment. [Figure 10] FIG. 2 is an xy diagram showing the resulting transmission from an embodiment having 32 antennas, with two beams neatly formed in the desired direction. [Figure 11] FIG. 11 is an xy diagram showing amplitude taper from the 32 antenna embodiment of FIG. [Figure 12] FIG. 2 is a block diagram of a transmitter according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The inventors have found that it is possible to use the same look-up table as used for the case where only one beam is to be transmitted by splitting the analog radio signal at each antenna branch into a number of beam signals equal to the number of beams to be transmitted, then performing a phase shift separately for each of the beam signals, and then combining the beam signals of one antenna branch again. In other words, the analog signal coming to each antenna branch is split into a number of beam signals equal to the number of beams to be transmitted. Then each of those beam signals per antenna branch is phase shifted by its own phase shifter. The phase shifters then get their phase settings from the same look-up table used for the single beam case. As an example, if two beams are to be sent, one in a direction 30° and one in 100°, then for each antenna beam, the first phase shifter takes their phase settings from the 30° position in the single look-up table, and for each antenna beam, the second phase shifter takes their phase settings from the 100° position in the same single look-up table. The phase-shifted signals of the same antenna branch are then combined in a combiner and sent to the antenna of the antenna branch for wireless transmission towards the receiver, thus achieving analog beam steering that is easy to use, requires little control data to be sent to the phase shifter, and requires little memory in the analog front end, while still forming a qualified beam with the transmitted wireless signal.

[0017] Fig. 2 shows a wireless communication network 100 in which the present invention can be used. The wireless communication network comprises a transmitter 110 in communication with a receiver 120 or adapted for wireless communication with the receiver 120. The transmitter 110 has multiple antennas 111, 112, 113 but only one digital-to-analog converter (DAC) 118, meaning that there can be only one composite signal transmitted over the air from the multiple antennas 111, 112, 113. The transmitter 110 has an incoming line 119 on which the DAC 118 is located. After the DAC, the incoming line is split into multiple antenna branches 114, 115, 116, each terminating at one of the antennas 111, 112, 113. There is one antenna branch 114, 115, 116 for each antenna 111, 112, 113, and is therefore called an antenna branch. When in use, an incoming signal is received, for example originating from a signal generator in the transmitter. An incoming signal is received through an incoming line 119. The incoming signal is converted from digital to analog form in a DAC 118. The converted analog signal is split to multiple antenna branches 114, 115, 116, and an analog signal is transmitted from each of the antennas 111, 112, 113. In other words, the same analog signal is sent through each of the antennas 111, 112, 113. In such a transmitter, the composite signal transmitted over the air may be steered using analog beam steering, which involves phase shifting the analog signal differently in the different antenna branches.

[0018] 3 shows an example of another wireless communication network 125 in which the present invention may be used. The network 125 comprises a radio access network node 130 in wireless communication with, or adapted for wireless communication with, a wireless communication device 140. The transmitter 110 of FIG. 2 may be the radio access network node 130 and the receiver 120 of FIG. 2 may be the wireless communication device 140. Alternatively, the transmitter 110 of FIG. 2 may be the wireless communication device 140 and the receiver 120 may be the radio access network node 130.

[0019] The wireless communication networks 100, 125 can be any type of wireless communication network capable of providing wireless access to wireless communication devices. Examples of such wireless communication networks are the Global System for Mobile Communications (GSM), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Code Division Multiple Access 2000 (CDMA2000), Long Term Evolution (LTE), LTE Advanced, Wireless Local Area Networks (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), WiMAX Advanced, as well as fifth generation wireless communication networks based on technologies such as New Radio (NR).

[0020] The radio access network node 130 may be any type of network node that alone or in combination with another network node provides wireless access to the wireless communication device 140. Examples of the radio access network node 130 are a base station (BS), a radio BS, a base transceiver station, a BS controller, a network controller, a Node B (NB), an evolved Node B (eNB), a NR BS, a multi-cell / multicast coordination entity, a relay node, an access point (AP), a radio AP, a remote radio unit (RRU), a remote radio head (RRH), and a multi-standard BS (MSR BS).

[0021] The wireless communication device 140 may be any type of device capable of wirelessly communicating with the radio access network node 130 using radio signals. For example, the wireless communication device 140 may be a user equipment (UE), a machine-type UE or a UE capable of machine-to-machine (M2M) communication, a sensor, a tablet, a mobile terminal, a smartphone, a laptop embedded equipment (LEE), a laptop mounted equipment (LME), a USB dongle, a customer premises equipment (CPE), etc.

[0022] Figure 4, in conjunction with Figure 2, describes a method for analog beam steering implemented by the transmitter 110 of the wireless communication network 100. The transmitter comprises a number of antenna branches 114, 115, 116, each antenna branch comprising an antenna 111, 112, 113. The method includes, for each antenna branch 114, 115, 116, receiving 206 an analog radio signal, where the analog radio signal is the same in each of the antenna branches, and splitting 208 the analog radio signal into several beam signals, where the number of beam signals is equal to the number of desired beams to be transmitted, where the number of beams is at least two. The method further includes, for each of several beam signals, phase shifting 210 the beam signal according to a phase shift setting for that beam and for that antenna branch 114, 115, 116, where the phase shift settings are taken from a single look-up table that is common for the number of beams, combining 212 the phase-shifted beam signals into one composite signal, and transmitting 214 the composite signal from the antennas 111, 112, 113 of that antenna branch 114, 115, 116 towards the receiver 120.

[0023] The transmitter 110 may be located, for example, in a radio access node 130 or in a wireless communication device 140. The antennas 111, 112, 113 may be arranged, for example, in a one-dimensional array or in a two-dimensional array. A "single lookup table" denotes that the same lookup table is used for all phase shifts of the beam signals. The single lookup table comprises preset phase shift settings for a certain beam angle and for each antenna branch for that certain transmitter with that antenna setting. In case of phase shifts of different beam signals in the same antenna branch, the transmitter will look up values ​​at different beam angles but at the same antenna branch. In case of phase shifts of the same beam signal but for different antenna branches, the transmitter will look up values ​​at the same beam angle but at different antenna branches. For an example of a lookup table, see Table 1 further below. See in particular the columns marked "phase shifter" representing "different phase shifter beam settings per antenna branch" and the rows marked for different beam angles. In other words, in one example with two beams and 16 antenna settings for Table 1, if the first beam angle should be 50° and the second beam angle should be 100°, then the two beam signals of the first antenna should be phase shifted by 115.8° and 31.1°, respectively. In other words, the phase shift value in the table for a beam is independent of how much, if any, other beams should be transmitted. For a given beam, only a single phase shift value per antenna branch is needed from the table.

[0024] By splitting each antenna branch into a number of beam branches or beam signals, where the beam signal per antenna branch is equal to the number of beams to be transmitted, and then performing a phase shift separately on each of those beam signals, the inventors have found that it is possible to use the same lookup table as is used for the case where only one beam is to be transmitted. In other words, by inserting additional splitting and combining steps and phase shifts per beam and per antenna branch, a single lookup table used for one beam can be reused for two or more beams. As a result, very limited control data needs to be sent from the beam management system to the transmitter, since the control data only needs to specify which positions to look at in a single lookup table.

[0025] A step 204 of splitting the analog radio signal into a number of analog radio signals at least equal to the number of antenna branches may be inserted before receiving 206 to provide that there is a first one signal split to each antenna branch before the split analog radio signal is received 206 at each antenna branch.

[0026] According to one embodiment, the method further includes, for each antenna branch, performing 213 amplitude taper of the composite signal using an isolation impedance configured at the antenna branch. By placing an isolation impedance at each antenna branch, the transmitter of the present invention will automatically provide the desired amplitude taper to the antenna array without the need for pre-calculation for the amplitude taper. An isolation impedance may be placed at the output of the signal combiner, which achieves combining 212 the phase-shifted beam signals into one composite signal. By "antenna branch", it is meant a branch that is "one branch per antenna", i.e. a branch that leads to an antenna, regardless of whether the branch passes through any other unit before it meets the antenna.

[0027] According to another embodiment, shown in FIG. 5, the method further includes receiving 201 a digital baseband signal, converting 202 the signal to an analog form, converting 203 the signal from a baseband frequency to a radio frequency, and splitting 204 the signal into a number of signals equal to the number of antenna branches, before receiving 206 an analog radio signal at each of the antenna branches. Converting 202, converting 203 and splitting 204 may be performed in any possible order, as long as D / A conversion 202 is performed before splitting 204. For example, converting 202 from a digital form to an analog form may be performed at a radio frequency as well as at a baseband frequency, i.e., before or after converting 203. As another example, splitting 204 may be performed before converting 203.

[0028] To appreciate the present invention, the reader is first introduced to existing methods that address analog beam steering to only one transmitted beam and require only one single look-up table (LUT). The reader is then shown that the same simple LUT can in fact be reused to achieve one or more more beams in entirely other directions.

[0029] First, consider a LUT supported array antenna where the phase setting can be obtained from a single entry row across all columns representing the phase setting for a certain angular beam position. In that case, beam steering can be calculated as follows: TIFF0007633271000001.tif9170 or TIFF0007633271000002.tif10170, where θ is the transmission angle, θ0 is the required beam angle, d is the distance between the antenna elements, aka antennas, and n is the number of antenna elements. Note that d is given in terms of wavelength. Thus, the radiation pattern, aka transmission pattern, is seemingly normalized and frequency independent. However, this formulation should not impose any restrictions on the general formulation. Another way to describe the radiation pattern is to extract the complex amplitude, as in the following formula: TIFF0007633271000003.tif10170, where TIFF0007633271000004.tif9170This defines a beam pointing in the direction θ0. Note that in the case of such a single beam, for example with no tapering to obtain lower side lobes, there is no need for the complex amplitudes to have tapering, i.e., the magnitude of these amplitudes is unity. The phase shift φ that must be applied to each of the elements in the array n teeth, φ n =360 n d cos(θ0) 5) It can be derived by: Usually, the element distance d is defined as d=λ / 2, so that in that case it is φ n =180 n cos(θ0) 6) Simplify to: This can be equated to a Grid of Beams (GoB) as a single entry LUT as defined in the following exemplary Table 1, which describes one example of a 1D array in which the present invention can be used. The beam granularity in this example is in steps of 10 degrees each, and the number of elements, n, in this exemplary 1D array is 16. TIFF0007633271000005.tif81170 Table 1. An example of a beam LUT with an entry marking the beam direction, here 50°, and the output is the phase shifter settings for all 16 antenna elements in a 16 element linear array with 0.5λ antenna element distance. For other beam directions or array settings, the table values ​​will be different than those shown in this example. The table has a pointer to the row that corresponds to the beam pointing at an angle of 50° in this example. The phase angle shown in the table cell is the phase setting that will be sent to the phase shifter. Therefore, there is no need to calculate anything except to be able to point to the correct row.

[0030] To form a second beam in a different direction than the one defined above, one can simply add another beam equation to equation 1) above. This is done formally as defined below: where θ1 is the desired beam angle for the second beam and θ0 is the desired beam angle for the first beam. This is equivalent to the following equation for the radiation pattern: TIFF0007633271000007.tif15170The astute reader will realize that this complex value will have different amplitudes depending on the two directions θ0 and θ1, and that the resulting phase will also depend on the particular values ​​of θ0 and θ1. It is therefore clear that combining two beams implies, at least in this case, a fairly complex 2D table. However, A nLooking again at the complex phasors described by vectors, it leads to different solutions that exploit hardware implementations. In particular, if two phase shifters act on the split signals and then combine the split signals again after the phase shift, the appropriate combined phase will be derived automatically and the required amplitude taper will be taken into account by the power losses to the isolated ports. Assuming an angular direction θ0=θ1 as the first case, the total amplitude will be 2 from equation 9). If instead the beam directions are in fact different, the total amplitude will be something between 0 and 2, again depending on the indexing "n" in equation 9). Thus, the complex addition after the signal split + individual phase addition will again give the appropriate amplitude to the signal going through the dual beam (multi-beam) phase adjuster. Since the combined amplitude is different in each antenna branch, the lost power has to be somehow addressed, which is done in the case of a hybrid combiner, at the termination / isolated load on the output, or in the isolated impedance when having a Wilkinson combiner / splitter. Such an insulating impedance of the Wilkinson combiner / divider would be configured between the branches where the split signals are fed into the combiner.

[0031] According to an embodiment shown in Fig. 6, a new electrical device 301 has been developed: The electrical device 301, which is part of the transmitter 110, comprises a signal splitter 308, two phase shifters 310, 312 and a signal combiner 314. Such an electrical device is configured in each antenna branch (see Fig. 1). The electrical device 301 of Fig. 6 works as follows: In each antenna branch, an analog radio signal S nis received. The analog radio signal is split into a first beam signal and a second beam signal in a signal splitter 308 for each antenna branch. The first beam signal is directed to a first phase shifter 310. The first phase shifter 310 shifts the first beam signal with a first phase φ0 according to a value found in a single LUT for a requested first beam angle θ0. The first phase is different for each antenna branch. See exemplary Table 1. The second beam signal is directed to a second phase shifter 312. The second phase shifter 312 shifts the second beam signal with a second phase φ1 according to a value found in a single LUT for a requested second beam angle θ1. The first phase shifted beam signal and the second phase shifted beam signal are then sent to a signal combiner 314, where the phase shifted beam signals are combined to form a combined signal x n The resulting signal is x n may be considered as the output of the electrical device 301. The electrical device 301 is further connected to an antenna 326 via a power amplifier 322 and a filter 324. Thus, the combined output signal x n are sent through a power amplifier 322 and a filter 324 to an antenna 326 of the respective antenna branch for wireless transmission to a receiver. The combined power loss is collected at an isolation resistor 318 configured on the output of the combiner 314. The combined power loss collected at the isolation resistor 318 will be equal to the required taper loss, thereby giving the required beam and taper of the side lobes. See further description below. A second isolation resistor 320 may be configured on the input of the signal splitter 308 to handle the reflected power not absorbed by the isolation resistor 318.

[0032] The illustrated device of FIG. 6 makes it possible to achieve two different beams. It should be observed that by repeating new devices, three or more beams can be achieved. An exemplary implementation for achieving four beams is shown in FIG. 7. Here, at each antenna branch, the incoming analog signal S nis fed through a first signal splitter 416, and then the two split signals are each fed to a signal splitter 408, 418, where each of the two signals is split again, making a total of four signals per antenna branch. The four split signals are then fed with phase shift data φ, which is taken from a common LUT, such as that shown in Table 1, according to the four required beam angles. 11 , φ 12 , φ 13 , φ 14 The phase-shifted signals are then phase-shifted by their own phase shifters 410, 412, 420, 422 in the combiners 414, 424, 426 as the combiners shown in FIG. n 7 also shows possible isolation resistors 428, 430, 432 configured at the outputs of the combiners 414, 424, 426 as well as possible isolation resistors 434, 436, 438 configured at the inputs of the signal splitters 408, 416, 418.

[0033] Furthermore, according to the above embodiment, the combined loss into the isolation resistors 318, 428, 430, 432 on the output of the combiner or combiners 314, 414, 424, 426 will be equal to that required by a single combination of phase shifter and attenuator. It is therefore not necessary to calculate or tabulate this attenuation as it is inherently provided by the described device and transmitter. The circuits of Figures 6 and 7 will be equivalent to the circuit function of Figure 8. Figure 8 therefore shows a complex phase shifter equivalent φ for a multi-beam phase shifter such as the circuits shown in Figures 6 and 7. n and attenuator equivalent A n However, A n and φ n It is not necessary to calculate separately and instead one can use a first identical LUT but with different entries for the phase settings.

[0034] FIG. 9 shows an example of a transmitter according to an embodiment, the transmitter has four antennas 501, 502, 503, 504, and two beams should be transmitted. In addition, the transmitter has an acquisition unit 511 that acquires a baseband signal with information to be wirelessly transmitted from the antennas 501, 502, 503, 504 to the receiver. The acquisition unit 511 can be a baseband signal generator, or the acquisition unit 511 can receive a baseband signal from another unit. The transmitter further includes a DAC 512 that converts the baseband signal from a digital format to an analog format, and a frequency converter 513 that converts the baseband signal from a baseband frequency to a radio frequency. In the example of FIG. 9, the frequency converter 513 is a mixer that mixes the baseband signal with a radio frequency signal originating from a local oscillator (LO) to achieve a radio signal s to be transmitted. Furthermore, since the transmitter has four antennas, there are four antenna branches 521, 522, 523, 524 into which the radio signal s is split. Each split signal is then fed to one inventive electrical device 531, 532, 533, 534, respectively. The electrical devices 531, 532, 533, 534 are exemplified here with the electrical device 301 of FIG. 6. The incoming signal s is split and phase shifted in each antenna branch 521, 522, 523, 524. The phase settings for each of the respective phase shifters of each antenna branch 521, 522, 523, 524 are taken from a LUT 540 adapted for this four-antenna setup. As an example, the first phase shifters of each antenna branch are assigned their phase setting φ from the LUT 540 in the first beam angle row, e.g., 50°. 11 , φ 21 , φ 31 , φ 41 and the second phase shifters of each antenna branch obtain their phase setting φ from the LUT 540 in the second beam angle row, e.g., 100°. 12 , φ 22 , φ 32 , φ 42After phase shifting, the two phase shifted signals of each antenna branch 521, 522, 523, 524 are combined in a combiner of each electrical device 531, 532, 533, 534. The resulting combined signal of each antenna branch 521, 522, 523, 524 is sent to the antenna of the antenna branch via a power amplifier 541, 542, 543, 544 and a filter 551, 552, 553, 554.

[0035] As a practical case of dual beam excitation, one can take an example of 32 elements given complex amplitude synthesis to create dual beams at off broadside directions -10° and +20°. The resulting transmit pattern is shown in Figure 10, where the beam steering angle is on the x-axis and the signal strength in dB is on the y-axis. The transmit pattern exhibits a side lobe roll-off that matches the common Sin(x) / x pattern obtained for a large continuous antenna aperture.

[0036] The transmit pattern is obtained by the transmitter as described in FIG. 10 above by using a single entry table similar to that in Table 1. However, in the -10°, +20° example, 0° is similar to 90° in Table 1, in other words, -10° is similar to 80° and +20° is similar to 110° in Table 1. The corresponding amplitude taper that will be performed on the antenna elements from the combined phase shifter structure is shown in FIG. 11 for this particular beam angle setup, with the antenna element number on the x-axis and the attenuation in dB on the y-axis. Note that the amplitude taper is achieved by the relative power loss to any isolated port in the phase shifter network. The correct complex amplitude and phase settings will be applied to the array by simply choosing two entries from only one lookup table, in this case given by the steering angles -10° and +20°. The summation over the array tapers in FIG. 11 corresponds to a -3dB total tapering loss.

[0037] According to one embodiment, the phase shifter shown above can be changed to a True Time Delay unit. Furthermore, according to another embodiment, the characteristics for the proposed implementation are a common taper loss of 10 log 10 (N), where N is the number of beams to be supported, i.e., 3 dB, 6 dB, and 9 dB losses for 2, 4, and 8 beams, respectively. The directivity per beam will also be reduced as much as the tapering losses. Finally, the equivalent isotropic radiated power (EIRP) will lose 6 dB, 12 dB, and 16 dB for 2, 4, and 8 beams, respectively. This is irrelevant for the implementation. However, recall that the taper losses are experienced before amplification at low powers, so the actual impact will be rather on the splitting of directivity between different beams.

[0038] Further, a transmitter 110 configured for analog beam steering is described with respect to Figures 1 and 6, the latter of which describes the details of the antenna branches. The transmitter comprises a number of antenna branches 114, 115, 116, each of which comprises an antenna 111, 112, 113. The transmitter 110 comprises a signal splitter 308 for receiving an analog radio signal at each of the antenna branches 114, 115, 116, the analog radio signal being the same at each of the antenna branches, the signal splitter 308 being further configured for splitting the analog radio signal into several beam signals, the number of beam signals being equal to the number of desired beams to be transmitted, the number of beams being at least two. The transmitter 110 further comprises, for each of several beam signals, a phase shifter 310, 312 for phase shifting the beam signal according to a phase shift setting for that beam and for that antenna branch, where the phase shift setting is taken from a single look-up table, and a signal combiner 314 for combining the phase-shifted beam signals into one composite signal. Furthermore, the transmitter 110 is configured for transmitting the composite signal from antennas 111, 112, 113 of its antenna branches 114, 115, 116 towards the receiver 120. The transmitter 110 may be located, for example, in a radio access network node or in a wireless communication device. The antennas 111, 112, 113 may be configured, for example, in a one-dimensional array or a two-dimensional array.

[0039] According to an embodiment, the transmitter 110 further comprises an isolation impedance 318 for each antenna branch 114, 115, 116 and in the signal combiner 314 for amplitude tapering of the signal. By having an isolation impedance 318 placed in each antenna branch in the signal combiner 314, the transmitter of the present invention will automatically provide the desired amplitude taper to the antenna array without the need for pre-calculation for the amplitude taper. The isolation impedance 318 may have a value designed according to the type of signal combiner used, such as 50Ω or 100Ω. With such isolation impedance, the aim is to achieve an impedance match on the branches so that no power is reflected back to the generator of the signal, which would otherwise jeopardize the generator if it is not ready to take on such reflected power.

[0040] According to one embodiment, the signal splitter 308 is a hybrid power splitter and the signal combiner 314 is a hybrid combiner. Furthermore, an isolation impedance 318 is configured at the output of the signal combiner 314 between each antenna branch 114, 115, 116 and ground.

[0041] According to another embodiment, the signal splitter 308 is a Wilkinson splitter and the signal combiner 314 is a Wilkinson combiner. Furthermore, each antenna branch 114, 115, 116 is split into several beam branches, the number of beam branches being equal to the number of beam signals, and an isolation impedance 318 is configured between at least two of the number of beam branches at the input of the signal combiner 314.

[0042] According to another embodiment, the transmitter 110 further comprises a second isolation impedance 320 configured at the input of the signal splitter 308 for each antenna branch 114, 115, 116. By configuring such a second, additional isolation impedance 320 at the input of the signal splitter, the power reflected towards the generator due to a mismatch of the isolation impedance 318 in the signal combiner 314 can be taken up by the second isolation impedance.

[0043] According to another embodiment, the phase shifters 310, 312 are implemented as true time delay units.

[0044] 12 illustrates another embodiment of a transmitter 110 operable in a wireless communication system 100 and configured for analog beam steering. The transmitter 110 comprises a processing circuit 603 and a memory 604. The memory includes instructions executable by the processing circuit 603 such that the transmitter 110 is operable to receive an analog radio signal, where the analog radio signal is the same in each of the antenna branches, and to split the analog radio signal into several beam signals, where the number of beam signals is equal to the number of desired beams to be transmitted, where the number of beams is at least two. Further, the transmitter 110 is operable to, for each of several beam signals, phase shift the beam signal according to a phase shift setting for that beam and for that antenna branch 114, 115, 116, where the phase shift settings are taken from a single look-up table that is common for the number of beams, combine the phase-shifted beam signals into one composite signal, and transmit the composite signal from the antennas 111, 112, 113 of that antenna branch towards the receiver 120.

[0045] According to one embodiment, the transmitter 110 is further operable, for each antenna branch 114, 115, 116, to perform amplitude tapering of the combined signal using an isolation impedance configured in the antenna branch.

[0046] According to one embodiment, the transmitter 110 is further operable to receive a digital baseband signal, convert the signal to analog form, translate the signal from baseband frequency to radio frequency, and split the signal into a number of signals equal to the number of antenna branches before an analog radio signal is received at each of the antenna branches 114, 115, 116.

[0047] According to other embodiments, the transmitter 110 may further comprise a communication unit 602, which may be considered to comprise conventional means for wireless communication with the receiver 120. The instructions executable by said processing circuitry 603 may for example be configured as a computer program 605 stored in said memory 604. The processing circuitry 603 and the memory 604 may be configured in a sub-arrangement 601. The sub-arrangement 601 may be a microprocessor and sufficient software and storage, thus a programmable logic device (PLD), or other electronic component(s) / processing circuit(s), configured to perform the above-mentioned method. The processing circuitry 603 may comprise one or more programmable processors, application specific integrated circuits, field programmable gate arrays, or combinations thereof adapted to execute instructions.

[0048] The computer program 605 may be configured such that, when its instructions are run on the processing circuit, they cause the transmitter 110 to perform the steps described in any of the described embodiments of the transmitter 110 and its methods. The computer program 605 may be carried by a computer program product connectable to the processing circuit 603. The computer program product may be the memory 604 or at least be configured in the memory. The memory 604 may be realized, for example, as a RAM (random access memory), a ROM (read only memory) or an EEPROM (electrically erasable programmable ROM). Furthermore, the computer program 605 may be carried by a separate computer readable medium, such as a CD, a DVD or a flash memory, from which the program may be downloaded to the memory 604. Alternatively, the computer program may be stored on a server or any other entity to which the transmitter 110 has access via the communication unit 602. The computer program 605 may then be downloaded from the server to the memory 604.

[0049] Although the above description includes multiple specificities, these specificities should not be construed as limiting the scope of the concepts described herein, but merely providing illustrations of some example embodiments of the concepts described herein. It will be appreciated that the scope of the concepts described herein fully encompasses other embodiments that may become apparent to one of ordinary skill in the art, and thus the scope of the concepts described herein is not limited. Reference to an element in the singular is not intended to mean "only one" unless expressly so stated, but rather "one or more." All structural and functional equivalents to the elements of the above-described embodiments known to one of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by this specification. Moreover, it is not necessary for an apparatus or method to address every problem to be solved by the concepts described herein in order to be encompassed by this specification. In the exemplary figures, dashed lines generally represent that the features within the dashed lines are optional.

Claims

1. A method for analog beam steering implemented by a transmitter (110) of a wireless communication network (100), the transmitter comprising a plurality of antenna branches (114, 115, 116), each antenna branch comprising an antenna (111, 112, 113), the method comprising, for each antenna branch (114, 115, 116): Receiving (206) an analog radio signal, the analog radio signal being the same at each of the antenna branches; Splitting (208) the analog radio signal into several beam signals, the number of beam signals being equal to the number of desired beams to be transmitted, the number of beams being at least two; for each of the number of beam signals, phase shifting (210) the beam signal according to a phase shift setting for that beam and for that antenna branch (114, 115, 116), the phase shift settings being taken from a single lookup table that is common for the number of beams, the single lookup table defining the phase shift settings for each angle of the beam steering according to a certain beam granularity; Combining (212) the phase shifted beam signals into a combined signal; transmitting (214) said composite signal from said antennas (111, 112, 113) of said antenna branches towards a receiver (120); A method comprising:

2. For each antenna branch (114, 115, 116), performing an amplitude taper (213) of the composite signal using an isolation impedance configured in said antenna branch. The method of claim 1 further comprising:

3. Before the analog radio signal is received (206), in each of the antenna branches (114, 115, 116): Receiving a digital baseband signal (201); Converting (202) the digital baseband signal to an analog form; converting (203) the converted signal from a baseband frequency to a radio frequency; splitting (204) the converted signal into a number of signals equal to the number of antenna branches; The method of claim 1 or 2, further comprising:

4. A transmitter (110) configured for analog beam steering, the transmitter comprising a plurality of antenna branches (114, 115, 116), each antenna branch comprising an antenna (111, 112, 113), the transmitter comprising, in each of the antenna branches: a signal splitter (308) for receiving an analog radio signal, said analog radio signal being the same in each of said antenna branches, said signal splitter (308) being further configured for splitting said analog radio signal into several beam signals, the number of beam signals being equal to the number of desired beams to be transmitted, said number of beams being at least two; a phase shifter (310, 312) for phase shifting, for each of the number of beam signals, the beam signal according to a phase shift setting for that beam and for that antenna branch, the phase shift settings being taken from a single look-up table that is common for the number of beams, the single look-up table defining the phase shift settings for each angle of the beam steering according to a certain beam granularity; a signal combiner (314) for combining the phase shifted beam signals into one combined signal; Equipped with The transmitter (110), configured for transmitting the composite signal from the antennas (111, 112, 113) of its antenna branches (114, 115, 116) towards a receiver (120).

5. The transmitter (110) of claim 4, further comprising an isolation impedance (318) for each antenna branch (114, 115, 116) and in the signal combiner (314) for amplitude tapering of the combined signal.

6. 6. The transmitter (110) of claim 5, wherein the signal splitter (308) is a hybrid power splitter, the signal combiner (314) is a hybrid combiner, and the isolation impedance (318) is configured at an output of the signal combiner (314) between the respective antenna branches (114, 115, 116) and ground.

7. 6. The transmitter of claim 5, wherein the signal splitter is a Wilkinson splitter, the signal combiner is a Wilkinson combiner, each antenna branch is split into several beam branches, the number of beam branches is equal to the number of beam signals, and the isolation impedance is configured between at least two of the number of beam branches at the input of the signal combiner.

8. The transmitter (110) of any one of claims 5 to 7, further comprising, for each antenna branch (114, 115, 116), a second isolation impedance (320) configured at an input of the signal splitter (308).

9. The transmitter (110) of any one of claims 4 to 8, wherein the phase shifters (310, 312) are implemented as true time delay units.

10. A transmitter (110) operable in a wireless communication system (100) configured for analog beam steering, the transmitter (110) comprising a processing circuit (603) and a memory (604), the memory containing instructions executable by the processing circuit, such that the transmitter (110) receiving an analog radio signal, the analog radio signal being the same at each of the antenna branches; splitting the analog radio signal into several beam signals, the number of beam signals being equal to the number of desired beams to be transmitted, the number of beams being at least two; for each of said several beam signals, phase shifting said beam signal according to a phase shift setting for that beam and for that antenna branch (114, 115, 116), said phase shift settings being taken from a single look-up table that is common for said number of beams, said single look-up table defining said phase shift settings for each angle of said beam steering according to a certain beam granularity; combining the phase shifted beam signals into a combined signal; transmitting said composite signal from the antennas (111, 112, 113) of said antenna branch towards a receiver (120); a transmitter (110) operable to:

11. For each antenna branch (114, 115, 116), performing amplitude tapering of the composite signal using an insulating impedance configured in the antenna branch. The transmitter (110) of claim 10, further operable to:

12. Before the analog radio signal is received at each of the antenna branches (114, 115, 116), Receiving a digital baseband signal; converting the digital baseband signal to an analog form; converting the converted signal from a baseband frequency to a radio frequency; splitting said converted signal into a number of signals equal to the number of antenna branches; The transmitter (110) of claim 10 or 11, further operable to:

13. When executed by at least one processing circuit of a transmitter (110) of a wireless communication network configured for analog beam steering, the transmitter (110) is receiving an analog radio signal, the analog radio signal being the same at each of the antenna branches; splitting the analog radio signal into several beam signals, the number of beam signals being equal to the number of desired beams to be transmitted, the number of beams being at least two; for each of said several beam signals, phase shifting said beam signal according to a phase shift setting for that beam and for that antenna branch (114, 115, 116), said phase shift settings being taken from a single look-up table that is common for said number of beams, said single look-up table defining said phase shift settings for each angle of said beam steering according to a certain beam granularity; combining the phase shifted beam signals into a combined signal; transmitting said composite signal from the antennas (111, 112, 113) of said antenna branch towards a receiver (120); A computer program (605) comprising instructions for causing the computer to carry out the steps of:

14. A computer readable storage medium containing a computer program (605) according to claim 13.

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