Abstract:
An active antenna system and a method for relaying radio signal in the mobile communications network is disclosed. The active antenna system comprises a plurality of antenna elements for relaying radio signals at a first frequency band. The antenna elements are connected to a plurality of signal paths. A plurality of signal inputs for inputting radio signals at a second frequency band is connected to the signal paths. A plurality of first mixers in the signal paths converts the frequency of the radio signals between the first frequency band and the second frequency band. A single first local oscillator is connected to the first mixers through a first oscillator signal path and supplies first oscillator signals to the first mixers and at least one dispersion element is connected to at least one of the signal paths.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 12/650,021 entitled “An Active Antenna Array with a Single Common Clock and a Method for Relaying a Plurality of Radio Signals” filed on Dec. 30, 2009. The entire contents of the forgoing application is incorporated herewith. 
     FIELD OF THE INVENTION 
     The field of the invention relates to an active antenna system for a mobile communications network as well as a method for relaying a plurality of radio signals through the active antenna system. 
     BACKGROUND OF THE INVENTION 
     In a typical base station of the prior art, local oscillator signals are provided for each one of the transceivers in the base station. Likewise, in a remote radio head application, individual local oscillator signals are also provided individually for each one of the transceivers located in the remote radio head application. It is necessary to provide a multiple number of individual local oscillator signals, since each one of the transceivers may be operating on different channels. The multiple numbers of local oscillators may also be included to improve reliability through the removal of the single point of failure which a single local oscillator would provide. 
     One issue associated with the approach of utilizing a multiple number of individual local oscillators is the expense and real estate on a chip associated with providing a plurality of local oscillators and the possible need to calibrate the different ones of the oscillators. This can be an issue during a start-up phase. For example, if the individual local oscillators are not correctly calibrated at the start-up, this may lead to difficulties in ensuring that the required beam forming operations for the radio signals are undertaken correctly. In particular, this may mean that the correct beam shapes for the radio signal in the required directions are not correctly calculated. 
       FIG. 1  shows an example of an active array system  1  as known in the prior art and comprising a plurality of transmission paths. Only a first signal path  16   a  at the top, a second signal path  16   b  in the middle and a last or n&#39;th signal path  16   n  at the bottom are illustrated in  FIG. 1  (as well as in the subsequent FIGUREs). The third to the (n−1)th transmission path are not illustrated for the sake of clarity. 
     A radio signal  10  in the digital domain to be transmitted reaches the active antenna array  1  from the left and is fed to the digital signal processor  15 . The digital signal processor  15  distributes the radio signals to be transmitted to the plurality of output paths  16   a ,  16   b , . . . ,  16   n . In the prior art example illustrated the radio signals  10  to be transmitted by the plurality of output paths  16   a ,  16   b , . . . ,  16   n  are digital IF transmission signals which have undergone upconversion in the digital signal processor  15 . Other processes may also take place in digital signal processor  15  and these include, but are not limited to, crest factor reduction, digital predistortion and digital beamforming The inclusion or omission of these processes has no impact on the teachings of the disclosure as described herein. For simplicity the letters relating to all of the paths will be left out in future reference numerals. 
     Only the passage of the transmission signal through the top one of the output paths  16   a  will be described in detail. It will be appreciated that all of the other output paths  16   b , . . . ,  16   n  are identical. The output path  16  is connected to a digital-analogue converter  20  which converts the digital IF transmission signals from the digital signal processor  15  to analogue signals prior to passing the analogue signals through a first filter  25  to obtain those filtered transmission signals in the desired frequency band. The filtered transmission signals in the desired frequency band are forwarded to a first mixer  30 . The first mixer  30  upconverts the filtered transmission signals by means of a first local oscillator  35  to an analogue intermediate frequency band. 
     The output of the first mixer  30  is filtered in a second filter  40  and passed to an intermediate frequency amplifier  45  for amplification. The output of the intermediate frequency amplifier  45  is passed to a second mixer  50  at which it is upconverted with an oscillator signal from the second local oscillator  55 . 
     The transmission signals from the first mixer  50  are now at a transmission frequency band (i. e. the radio frequency) and are passed through a third filter  60  into a radio frequency amplifier  65  before entering a transmission filter  70  and being passed to the radio frequency output  80 . The radio frequency output  80  is connected to one of the plurality of antenna elements from the antenna array (not shown). A tap  75  provides a feedback loop  76  to the digital signal processor  15  through paths  85  which allow calibration and updating of the predistortion processing of the radio signals to be taken into account. 
     SUMMARY OF THE INVENTION 
     An active antenna array for mobile communications network is disclosed herein. The active antenna system comprises a plurality of antenna elements for relaying radio signals. The plurality of antenna elements is connected to a plurality of signal paths. The active antenna signal system has a plurality of signal inputs which are connected to the plurality of signal paths. At least one first mixer is present in two or more of the plurality of the signal paths which convert the frequencies of the radio signals between a first frequency band and a second frequency band. A single first local oscillator is connected to different ones of the at least one first mixer through a first oscillator signal path and supplies first oscillator signals to the at least one first mixer. At least one first dispersion element is connected to at least one of the plurality of signal paths. A setting of the at least one first dispersion element is dependent on a length of the first oscillator signal path or on a delay of the radio signals traversing the active antenna array. 
     The term “relaying” or “relay” in this description is intended to encompass both the transmission of radio signals and the reception of radio signals. 
     The use of a single reference clock enables the plurality of first local oscillators to be accurately calibrated with each other, since there is only a single reference clock. This allows additionally real estate to be saved on the chip. 
     In one aspect of the invention, the first dispersion elements are included either in the first oscillator signal paths or between the single first oscillator and the at least one mixer. The first dispersion elements allow a delay and/or phase of the first oscillator signal to be changed to take into account different lengths of the signal paths through the active antenna array and/or the first oscillator signal path. The degree of change is indicated by the setting of the first dispersion element. It will be noted that the setting may be further adjusted to take account of other delays or errors in various signal processing elements and paths within the active antenna array which delay the radio signals traversing the signal paths in the active antenna array (so-called phase or delay error metrics). 
     The active antenna array may also comprise a plurality of second mixers which are connected to the output of the plurality of first mixers and which convert the frequency of the radio signals between the second frequency band, for example an intermediate frequency, and a third frequency band, for example the radio frequency. The plurality of second mixers is connected to a plurality of second oscillators which are clocked by the single reference clock through a plurality of second oscillator signal paths. The plurality of second mixers enable a two-stage conversion of the frequency of the radio signals. 
     A method for a transmission of a plurality of radio signals is also disclosed. This method comprises inputting a plurality of radio signals at a first frequency band, for example a base band, generating a plurality of first oscillator signals from a single first oscillator and converting the plurality of the radio signals from the first frequency band to a second frequency band using first mixers supplied by the plurality of first oscillator signals. The dispersion of at least one of the plurality of first oscillator signals or the plurality of radio signals is adjusted based primarily on a length of a first oscillator signal path between one of the first mixers and the remainder of the plurality of first mixers, but may also be adjusted to take account of other delays or errors in various signal processing elements and paths within the active antenna array (as discussed above). 
     The method may also comprise generating a plurality of second clock signals from the signal reference clock signal and converting the plurality of radio signals from the second frequency band to a third frequency band using the plurality of second clock signals. In one aspect of the invention the one or more of the plurality of single clock signals can be delayed using dispersion elements. 
     A chip set for use in the antenna system is also disclosed. The chip set comprises a plurality of signal inputs for inputting the radio signals and being connected to the plurality of signal paths. At least one first mixer is present in two or more of the plurality of the signal paths which convert the frequencies of the radio signals between a first frequency band and a second frequency band. A single first local oscillator is connected to different ones of the at least one first mixer through a first oscillator signal path and supplies first oscillator signals to the at least one first mixer. At least one first dispersion element is connected to at least one of the plurality of signal paths. A setting of the at least one first dispersion element is dependent on a length of the first oscillator signal path. 
     A computer program provides comprising a computer-useable medium having control logic stored in the computer-useable medium is also disclosed. The control logic is able to code a computer and associated manufacturing apparatus to manufacture an active antenna array for the mobile communications network. The active antenna array comprises a plurality of antenna elements for relaying radio signals, wherein the plurality of antenna elements are connected to a plurality of signal paths. At least one first mixer is present in two or more of the plurality of the signal paths which convert the frequencies of the radio signals between a first frequency band and a second frequency band. A single first local oscillator is connected to different ones of the at least one first mixer through a first oscillator signal path and supplies first oscillator signals to the at least one first mixer. At least one first dispersion element is connected to at least one of the plurality of signal paths. A setting of the at least one first dispersion element is dependent on a length of the first oscillator signal path or on other phase or delay error metrics. 
     A computer program product comprising a computer-useable medium having control logic for causing an active antenna array to execute a method for relaying a plurality of radio signals is also disclosed. The computer program product has first computer readable code means for inputting a plurality of radio signals at a first frequency band and second computer readable code means for generating a plurality of first oscillator signals from a single first oscillator. The computer program product further comprises third computer readable code means for converting the plurality of radio signals from the first frequency band to a second frequency band using the plurality of the first oscillator signals and fourth computer readable code means for adjusting the dispersion of at least one of the plurality of first oscillator signals or the plurality of radio signals based on a length of a first signal oscillator signal path between one of the first mixers and the remainder of the first mixers or other phase or delay error metrics within the active antenna array (as discussed above). 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a prior art antenna array for mobile communications network. 
         FIG. 2  shows an active antenna array employing common clocks for all of the local oscillators. 
         FIG. 3  shows an active antenna array employing common clocks with phase compensation. 
         FIG. 4  shows an active antenna array with a single upconversion system. 
         FIG. 5  shows another aspect of the active antenna array with a single upconversion system. 
         FIG. 6  shows an active antenna array with digital dispersion. 
         FIG. 7  shows an active antenna array with a feedback compensation. 
         FIG. 8  shows an exemplary method for the operation of the active antenna array. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described on the basis of the drawings. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect can be combined with a feature of a different aspect or aspects. 
       FIG. 2  shows a first aspect of the invention. It will be appreciated that many of the elements in  FIG. 2  are identical with the elements in  FIG. 1  and have been allocated the same reference numerals. This disclosure outlines in detail aspects of the disclosure relating to the transmission of radio signals. Modifications of the circuit depicted in  FIG. 2  and the other Figures required for the reception of radio signals will be disclosed later. 
     The aspect of the invention shown in  FIG. 2  differs from the prior art method in  FIG. 1  in that a single first oscillator  35  and a single second local oscillator  55  is connected to the plurality of first mixers  30   a ,  30   b , . . . ,  30   n  and to the plurality of second mixers  50   a ,  50   b , . . . ,  50   n  through first dispersion elements  37   a ,  37   b , . . . ,  37  or second dispersion elements  57   a ,  57   b , . . . ,  57   n . One of the first dispersion elements  37   n  and one of the second dispersion elements  37   n  is shown in  FIG. 2  as a dotted line. This dotted line indicates that the one of the first dispersion elements  37   n  connected to the signal paths  16   n  is not in fact required. It is only necessary that the first oscillator signals from the single first oscillator reach the first mixers  30   a ,  30   b , . . . ,  30   n  at a time which enables the upconversion of the radio signals to occur in tandem with each other. 
     The first dispersion elements  37   a ,  37   b , . . . ,  37   n  are either phase shifters (as shown in  FIG. 2 ), or delay elements (see  FIG. 3  reference numeral  38   a ,  38   b , . . . ,  38   n ). The first dispersion elements  37   a ,  37   b , . . . ,  37   n  need to delay the time of arrival of the first oscillator signals with respect to one of the first mixers—in this case the first mixer  37   n . The single first oscillator  35  is used in the active antenna array  1 , rather than a plurality of first local oscillators  35   a ,  35   b , . . . ,  35   n  for each one of the signal paths  16  used in the prior art antenna array as shown in  FIG. 1 . Similarly the single second oscillator  55  is used instead of the plurality of second local oscillators  55   a ,  55   b , . . . ,  55   n  of the prior art antenna array of  FIG. 1 . 
     Similarly one of the second dispersion elements (e.g.  57   n ) can also be eliminated as a second oscillator signal from the single second oscillator needs to be delayed for all but one of the second mixers  50   a ,  50   b , . . . ,  50   n.    
       FIG. 3  shows a second aspect of the invention in which the first dispersion elements  38   a ,  38   b , . . . ,  38   n  and the second dispersion elements  58   a ,  58   b , . . . ,  58   n  are shown here as delay elements (as noted above). 
     The function of the first dispersion elements  37  and  38  in  FIGS. 2 and 3  is to take into account that the length of the paths, or the delay experienced by a signal traversing one of the paths, of the radio signals through the complete radio signal paths may vary slightly between different ones of the radio signal paths. The dispersion elements  37 ,  38 ,  57 ,  58  can therefore slightly change the time of arrival of the local oscillator signals supplied to the first mixers  30  and the second mixers  50  in order to take this change of path length into account. 
       FIG. 4  shows an aspect of the invention in which there is a single upconversion system. In this aspect of the invention the radio signals  10  are converted to analogue signals by the first digital to analogue convertor  20  and than upconverted to the transmissions signal by the plurality of first mixers  30 . There are no second mixers present in this aspect of the invention. Similarly there is only a single local oscillator  35  which is connected to the plurality of first mixers  30  through the dispersion elements  37  (here shown as a phase shifter, but also potentially a delay element). 
       FIG. 5  shows a further aspect of the active antenna array in which the radio signals are output from the digital signal processor  15  as an I-component and a Q-component. A plurality of third digital to analogue convertors  21  is connected between the digital signal processor  15  and a plurality of third mixers  31  to digitally to analogue convert the I-component of the digital signals to an analogue signal. The analogue signal is then upconverted in the plurality of third mixers  31 . 
     Similarly the Q-components are converted in a fourth digital to analogue convertor  22  and upconverted in the plurality of fourth mixers  32 . A local oscillator signal is supplied through the first oscillator signal path and a plurality of first dispersion elements  37   a ,  37   b , . . . ,  37   n  from the first local oscillator  35  to a plurality of phase change elements  29 . The plurality of phase change elements  29  are connected to the plurality of third mixers  31  and the plurality of fourth mixers  32  to supply a local oscillator signal to each one the third mixers  31  and with a phase difference of 90° to the fourth mixers  32 . The outputs of the third mixers  31  and the outputs of the fourth mixers  32  are passed to a plurality of combiners  33  and sent to a plurality of amplifiers  65 . 
     In  FIG. 6  a further aspect of the invention is shown in which digital dispersion elements  39  are in the digital domain and located between the digital signal processor  15  and the plurality of first digital to analogue convertors  20 . It will be appreciated that the settings for the plurality of digital dispersion elements  39  can be supplied through the feedback loop  70  as it is illustrated in more detail in  FIG. 7  which further includes a switch  200  for switching between the individual ones of the taps  75 . The signals from the plurality of taps  75  are passed through an attenuator  210  and then downconverted in element  220  before being converted into an analogue signal by means of the analogue to digital convertor  230 . The output of the analogue to digital convertor  230  is passed to a processing element  240  which changes settings of the digital dispersion elements  39 . The feedback loop  76  allows a dynamic change in the settings of the digital dispersion elements  39  to take into account, for example temperature fluctuations. 
       FIG. 8  shows a method for relaying the plurality of radio signals according to the disclosure. In  FIG. 8  in step  400  the digital transmission signals are input into the digital signal processor  15  where beam forming operations are carried out on the transmission signals. The manipulated digital transmission signals are output over the signal paths  16  to the digital to analogue convertor  20  in step  405  at which point the manipulated digital transmission signals are converted to analogue signals and in step  410  the analogue signals are filtered to remove out-of-band frequencies. In step  415  the analogue radio signals from the first filter  25  are upconverted with the first local oscillator signal supplied by the single first local oscillator  35  through the first dispersion elements  37  or  38 . This generates analogue signals at an intermediate frequency. The individual radio signals at the intermediate frequency band are filtered in the second filter  40  to remove out-of-band signals and than amplified in an intermediate frequency amplifier  45  before being passed to a second mixer  50 , where they are modulated with the second oscillator signal in step  430 . The second mixer  55  receives the second oscillator signal from the second oscillator  55  through the second dispersion elements  57  or  58 . 
     In step  435  out-of-band frequencies from the individual radio signals from the second mixer  55  are filtered in the third filter  60  before the individual radio signals at the radio frequency are amplified once again in the second amplifier  65  in step  440 . In step  445  out-of-band frequencies are filtered out of the individual radio signals in the fourth filter  70 . A feedback signal is generated in step  450  which is supplied to calibration and pre-distortion feedback elements (for example the processing element  240 ). The feedback signal can be used to change settings in one or more of the first dispersion elements  37  or  38  and the second dispersion elements  57  or  58 . Finally in step  455  the individual radio signals are transmitted through individual ones of the antenna array elements  80 . 
     The active antenna array  1  of the current disclosure has been described with respect to the transmission of radio signals from the base station. It will, however, be appreciated that the provision of the single first oscillator  35  and/or the single second oscillator  55  in the active antenna array  1  can also be used for the reception of individual radio signals at the radio frequency through the plurality of antenna array elements  80  and downconversion to the base band frequency. 
     In this receive case, the first local oscillator  35 , the second local oscillator  55 , the first mixers  30  and the second mixers  50  are used to downconvert the plurality of receive signals incident upon the antenna elements  80   a  and the plurality of receive signal paths will ultimately supply a plurality of digital IF signals to the digital signal processor  15  (or to a separate receive digital signal processor, not shown). The transmit and receive ones of the first local oscillator  35  and the second local oscillators  55  may, however, operate on different frequencies from one another, for example where a frequency split occurs between the transmit and receive bands in a duplex system. The first dispersion elements  37  or  38  and the second dispersion elements  57  or  58  may also be used in the plurality of receive paths or the plurality of local oscillator signal paths (or both) in the same manner and for the same purpose as was described above for the transmit aspects of the invention. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that various changes in form and detail can be made therein without departing from the scope of the invention. In addition to using hardware (e.g., within or coupled to a central processing unit (“CPU”), micro processor, micro controller, digital signal processor, processor core, system on chip (“SOC”) or any other device), implementations may also be embodied in software (e.g. computer readable code, program code, and/or instructions disposed in any form, such as source, object or machine language) disposed for example in a computer useable (e.g. readable) medium configured to store the software. Such software can enable, for example, the function, fabrication, modelling, simulation, description and/or testing of the apparatus and methods describe herein. For example, this can be accomplished through the use of general program languages (e.g., C, C++), hardware description languages (HDL) including Verilog HDL, VHDL, and so on, or other available programs. Such software can be disposed in any known computer useable medium such as semiconductor, magnetic disc, or optical disc (e.g., CD-ROM, DVD-ROM, etc.). The software can also be disposed as a computer data signal embodied in a computer useable (e.g. readable) transmission medium (e.g., carrier wave or any other medium including digital, optical, analogue-based medium). Embodiments of the present invention may include methods of providing the apparatus described herein by providing software describing the apparatus and subsequently transmitting the software as a computer data signal over a communication network including the internet and intranets. 
     It is understood that the apparatus and method describe herein may be included in a semiconductor intellectual property core, such as a micro processor core (e.g., embodied in HDL) and transformed to hardware in the production of integrated circuits. Additionally, the apparatus and methods described herein may be embodied as a combination of hardware and software. Thus, the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.