Patent Publication Number: US-2023135015-A1

Title: Receiver apparatus and transmitter apparatus

Description:
TECHNOLOGICAL FIELD 
     Examples of the disclosure relate to receiver apparatus and transmitter apparatus. Some relate to receiver apparatus and transmitter apparatus that can be used for Ultra Reliable Low-Latency Communications (URLLC) or other types of wireless communications. 
     The project leading to this application has received funding from the European Union&#39;s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 861222. 
     BACKGROUND 
     Digital beamforming provides for reliable and robust communication compared to analog and low rank hybrid beamforming. However, digital beamforming requires a large number of expensive components such as analog to digital converters (ADCs) and digital to analog converters (DACs). The ADCs and DACs have a high-power consumption and produce a lot of raw data that needs to be processed. 
     BRIEF SUMMARY 
     According to various, but not necessarily all, examples of the disclosure there is provided a receiver apparatus comprising:
         a plurality of downconverting means for downconverting separate antenna signals;   one or more analog to digital converters; and   one or more multiplexing means configurable in at least a first configuration and a second configuration, wherein;   when the multiplexing means is configured in the first configuration the plurality of downconverting means and the one or more analog to digital converters are configured to enable separate antenna signals to be combined to provide hybrid beamforming or analog beamforming and when the multiplexing means is configured in the second configuration the plurality of downconverting means and the one or more analog to digital converters are configured to enable separate antenna signals to be used to enable digital beamforming.       

     The hybrid beamforming or analog beamforming may be enabled across a bandwidth of the receiver apparatus and the digital beamforming may be enabled across a sub-section of the bandwidth. 
     The receiver apparatus may comprise one or more downconverting means for downconverting combined antenna signals. 
     The receiver apparatus may be configured so that when the multiplexing means is configured in the first configuration only downconverted combined antenna signals are provided to the one or more analog to digital converters and when the multiplexing means is configured in a second configuration at least a sub-set of the downconverted separate antenna signals are sampled and provided to the one or more analog to digital converters. 
     The receiver apparatus may comprise a plurality of analog to digital converters configured to convert the downconverted separate antenna signals such that when the multiplexing means is in the first configuration outputs of the plurality of analog to digital converters are combined to provide hybrid beamforming or analog beamforming and when the multiplexing means is in the second configuration the downconverted separate antenna signals are used to provide digital beamforming. 
     The multiplexing means may be configured to use time interleaving. 
     The multiplexing means may be configured to use frequency interleaving. 
     The one or more multiplexing means and the one or more analog to digital converters may be configured to enable the analog beamforming to be provided in parallel with the digital beamforming. 
     The one or more multiplexing means may be configured to enable a rank of the digital beamforming to be varied. 
     The multiplexing means may comprise one or more switches. 
     The multiplexing means may be configured to control a rank of digital beamforming by controlling the number of separate antenna signals that are sampled. 
     The downconverting means may comprise one or more mixers. 
     The receiver apparatus may comprise one or more multiplexers configured to multiplex separate antenna signals before they are provided to the plurality of downconverting means for downconverting separate antenna signals. 
     According to various, but not necessarily all, examples of the disclosure there may be provided a transmitter apparatus comprising:
         a plurality of upconverting means for upconverting separate signals for different antennas;   one or more digital to analog converters; and   one or more demultiplexing means configurable in at least a first configuration and a second configuration, wherein;   when the demultiplexing means is configured in the first configuration the plurality of upconverting means and the one or more digital to analog converters are configured to enable antenna signals to be combined to provide hybrid beamforming or analog beamforming and when the demultiplexing means is configured in the second configuration the plurality of upconverting means and the one or more digital to analog converters are configured to enable separate antenna signals to be used to enable digital beamforming.       

     The hybrid beamforming or analog beamforming may be provided across a bandwidth of the transmitter apparatus and the digital beamforming is provided across a sub-section of the bandwidth. 
     The transmitter apparatus may comprise one or more upconverting means for upconverting signals for a plurality of antennas. 
     The demultiplexing means may be configured in the first configuration only the signals from the one or more digital to analog converters are provided to the plurality of upconverting means for upconverting signals for a plurality of antennas and when the demultiplexing means is configured in a second configuration at least a sub-sample of the signals from the one or more digital to analog converters are provided to the plurality of upconverting means for upconverting separate signals for different antennas. 
     The one or more demultiplexing means and the one or more analog to digital converters may be configured to enable the hybrid beamforming or analog beamforming to be provided in parallel with the digital beamforming. 
     The one or more demultiplexing means may be configured to enable a rank of the digital beamforming to be varied. 
     The demultiplexing means may comprise one or more switches The demultiplexing means may be configured to control a rank of digital beamforming by controlling the sampling rate of the signals provided to the demultiplexing means. 
     The upconverting means may comprise one or more mixers. 
     According to various, but not necessarily all, examples of the disclosure there may be provided an electronic device comprising at least one transmitter apparatus and/or at least one receiver apparatus as claimed in any preceding claim. 
     According to various, but not necessarily all, examples of the disclosure there may be provided a receiver apparatus comprising:
         one or more downconverting means for downconverting added antenna signals;   a plurality of downconverting means for downconverting separate antenna signals;   one or more analog to digital converters; and   one or more multiplexing means configurable in at least a first configuration and a second configuration, wherein;   when the multiplexing means is configured in the first configuration only downconverted added antenna signals are provided to the one or more analog to digital converters and when the multiplexing means is configured in a second configuration at least a sub-set of the downconverted separate antenna signals are sampled and provided to the one or more analog to digital converters.       

     According to various, but not necessarily all, examples of the disclosure there may be provided a transmitter apparatus comprising:
         one or more upconverting means for upconverting signals for a plurality of antennas;   a plurality of upconverting means for upconverting separate signals for different antennas;   one or more digital to analog converters; and   one or more demultiplexing means configurable in at least a first configuration and a second configuration, wherein;   when the demultiplexing means is configured in the first configuration only the signals from the one or more digital to analog converters are provided to the upconverting means for upconverting signals for a plurality of antennas and when the demultiplexing means is configured in a second configuration at least a sub-sample of the signals from the one or more digital to analog converters are provided to the one or more upconverting means for upconverting separate signals for different antennas.       

     According to various, but not necessarily all, examples of the disclosure there may be provided a receiver apparatus comprising:
         a plurality of downconverters for downconverting separate antenna signals;   one or more analog to digital converters; and   one or more multiplexers configurable in at least a first configuration and a second configuration, wherein;   when the multiplexers are configured in the first configuration the plurality of downconverters and the one or more analog to digital converters are configured to enable separate antenna signals to be combined to provide hybrid beamforming or analog beamforming and when the multiplexers are configured in the second configuration the plurality of downconverters and the one or more analog to digital converters are configured to enable separate antenna signals to be used to enable digital beamforming.       

     According to various, but not necessarily all, examples of the disclosure there may be provided a transmitter apparatus comprising:
         a plurality of upconverters for upconverting separate signals for different antennas;   one or more digital to analog converters; and   one or more demultiplexers configurable in at least a first configuration and a second configuration, wherein;   when the demultiplexers are configured in the first configuration the plurality of upconverters and the one or more digital to analog converters are configured to enable antenna signals to be combined to provide hybrid beamforming or analog beamforming and when the demultiplexers are configured in the second configuration the plurality of upconverters and the one or more digital to analog converters are configured to enable separate antenna signals to be used to enable digital beamforming.       

     According to various, but not necessarily all, examples of the disclosure there is provided a receiver apparatus comprising:
         a plurality of downconverting means for downconverting separate antenna signals;   one or more analog to digital converters; and   one or more multiplexing means configurable in at least a first configuration and a second configuration, wherein;   in the first configuration the plurality of downconverting means and the one or more analog to digital converters are configured to enable separate antenna signals to be combined to provide hybrid beamforming or analog beamforming and,   in the second configuration the plurality of downconverting means and the one or more analog to digital converters are configured to enable separate antenna signals to be used to enable digital beamforming.       

     According to various, but not necessarily all, examples of the disclosure there may be provided a transmitter apparatus comprising:
         a plurality of upconverting means for upconverting separate signals for different antennas;   one or more digital to analog converters; and   one or more demultiplexing means configurable in at least a first configuration and a second configuration, wherein;   in the first configuration the plurality of upconverting means and the one or more digital to analog converters are configured to enable antenna signals to be combined to provide hybrid beamforming or analog beamforming and,   in the second configuration the plurality of upconverting means and the one or more digital to analog converters are configured to enable separate antenna signals to be used to enable digital beamforming.       

    
    
     
       BRIEF DESCRIPTION 
       Some examples will now be described with reference to the accompanying drawings in which: 
         FIG.  1    shows an example receiver apparatus; 
         FIG.  2    shows an example receiver apparatus; 
         FIG.  3    shows an example receiver apparatus; 
         FIG.  4    shows an example receiver apparatus; 
         FIG.  5    shows an example transmitter apparatus; 
         FIG.  6    shows an example transmitter apparatus; and 
         FIG.  7    shows an example phase shifter. 
     
    
    
     DETAILED DESCRIPTION 
     Examples of the disclosure relate to receiver apparatus and corresponding transmitter apparatus that can be configured in different operational states at different times. In a first operational state hybrid beamforming or analog beamforming can be provided across the bandwidth of the apparatus. In a second operational state the apparatus can be configured to provide digital beamforming across a sub-section of the bandwidth. The receiver apparatus and corresponding transmitter apparatus are dynamic so that they can be switched between the different operational states as appropriate. 
       FIG.  1    schematically shows a receiver apparatus  100  according to examples of the disclosure. Other arrangements of the components within the receiver apparatus  100  could be used in other examples of the disclosure. 
     In the example of  FIG.  1    the receiver apparatus  100  comprises first downconverters  107 , second downconverters  115 , one or more ADCs  111  and at least one multiplexing means  119 . The receiver apparatus  100  can comprise additional components that are not shown in  FIG.  1   . 
     In the example shown in  FIG.  1    the receiver apparatus  100  also comprises a plurality of adders  103 . the plurality of adders  103  are configured to add a plurality of antenna signals  101 . The plurality of antenna signals  101  can comprise a plurality of signals received from a plurality of different antennas. Some processing can be performed on the antenna signals  101  before they are provided to the adder  103 . For example, the antenna signals  101  could be phase shifted before they are provided to the adders  103 . 
     The antenna signals  101  can be received from any suitable type of antenna. In some examples the antennas could comprise phased arrays. The phased arrays could comprise a plurality of antenna elements with phase shifters and power combiners/adders and/or any other suitable components. 
     The adders  103  can comprise any suitable components. The adders  103  can comprise any suitable circuitry or other means that enables the plurality of antenna signals  101  to be added together. The adders  103  receive a plurality of antenna signals  101  as an input and provide an added antenna signal  105  as an output. 
     In some examples the receiver  100  can comprise components that also enable the antennas signals to be phase shifted and/or amplified. This can enable a combined antenna signals to be provided. The combined antenna signal can comprise an antenna signal that has been added and/or phase shifted and/or amplified and/or had any other suitable process performed on it. 
     The first downconverters  107  can comprise any means that can be configured to convert a high frequency signal to a low frequency signal. The first downconverters  107  can be configured to convert a high radio frequency signal to a low radio frequency signal. The first downconverters  107  can comprise circuitry or any other suitable means. In some examples the first downconverters  107  can comprise a mixer and local oscillator or any other suitable means. 
     The first downconverters  107  are configured to receive the added antenna signals  105  as an input and to provide a low frequency signal  109  as an output. 
     The low frequency signals  109  are provided as inputs to the ADCs  111 . The ADCs  111  can comprise any means or circuitry that can be configured to convert the analog low frequency signal  109  to a digital output. 
     In the example of  FIG.  1    the receiver apparatus  100  comprises a plurality of adders  103  and first downconverters  107 . This can enable different outputs of the first downconverters  107  to be provided to different ADCs  111 . In the schematic example of  FIG.  1 A  a multiplexer  119  is provided between at least one of the first downconverters  107  and an ADC  111 . 
     The receiver apparatus  100  also comprises a plurality of second downconverters  115 . The second downconverters  115  can comprise any means that can be configured to convert a high frequency signal to a low frequency signal. The second downconverters  115  can be configured to convert a high radio frequency signal to a low radio frequency signal. The second downconverters  115  can comprise circuitry or any other suitable means. In some examples the second downconverters  115  can comprise a mixer and local oscillator or any other suitable means. 
     The second downconverters  115  are configured to receive separate antenna signals  113  as an input. The separate antenna signals  113  comprise antenna signals that have not been added together. Different second downconverters  115  can be configured to receive different separate antenna signals  113  as an input. 
     In the example of  FIG.  1    the receiver apparatus  100  comprises a plurality of second downconverters  115 . Each of the different second downconverters  115  is associated with a different antenna so that each of the second downconverters  115  receives a different separate antenna signal  113 . In some examples, the receiver apparatus  100  can comprise a second downconverter  115  for each of the available antennas so that all of the signals from the antennas can be separately downconverted. 
     The second downconverters  115  are configured to receive the separate antenna signals  113  as an input and to provide a low frequency signal  117  as an output. 
     The low frequency signal  117  can be provided as an input to a multiplexer  119 . The multiplexer  119  can comprise any suitable multiplexing means. The multiplexer  119  can be configured to enable different signals to be selected. In some examples the multiplexer  119  could comprise a switch. 
     The multiplexer  119  can be configured in a first configuration in which only downconverted added antenna signals  109  are provided to the ADC  111 . In this configuration only the signals from the first downconverters  107  would be provided to the ADC  111  and the signals from the second down converters  115  would not be provided to the ADC  111 . When the multiplexer  119  is in this configuration the receiver apparatus  100  provides hybrid beamforming or analog beamforming across the whole bandwidth. The beamforming can be analog beamforming if only one Radio Frequency (RF) chain is used on the full bandwidth. The beamforming can be hybrid beamforming if a plurality of RF chains are used on the full bandwidth. When the multiplexer  119  is in this configuration the second downconverters  115  can be turned off to reduce power consumption. 
     The multiplexer  119  can also be configured in a second configuration in which one or more of the downconverted separate antenna signals  117  are provided to the ADC  111 . In some examples the multiplexer  119  can be configured to enable a plurality of the downconverted separate antenna signals  117  to be sampled and provided to the ADC  111 . When the multiplexer  119  is in this configuration the receiver apparatus  100  provides digital beamforming across a sub-section of the bandwidth. 
     The multiplexer  119  can therefore enable the receiver apparatus  100  to be switched between hybrid beamforming or analog beamforming and digital beamforming. The hybrid beamforming or analog beamforming is provided across a bandwidth of the receiver apparatus and the digital beamforming is provided across a sub-section of the bandwidth. The rank of the digital beamforming can be up to the number of separate antenna signal  113 . The digital beamforming can be high rank digital beamforming. 
       FIG.  2    schematically shows an example receiver apparatus  100  in more detail. 
     The example receiver apparatus  100  comprises a plurality of antennas  201  and a plurality of low noise amplifiers  203 . In this example, the receiver apparatus  100  comprises N antennas  201  and N low noise amplifiers  203 . N can be any whole number that is equal to or greater than two. In the example of  FIG.  1    the number of low noise amplifiers  203  is the same as the number of antennas  201  so that each of the antenna signals from the respective antennas  201  can be amplified separately. 
     The example apparatus also comprises a plurality of phase shifters  205 . The phase shifters can comprise any means or circuitry that can be configured to add a delay into the signals from the antennas  201 . In this example the receiver apparatus  100  comprises N phase shifters  205 . In the example of  FIG.  1    the number of phase shifters  205  is the same as the number of antennas  201  so that each of the antenna signals from the respective antennas  201  can be phase shifted separately. The phase shifters  205  can perform a plurality of phase shifting operations so that the phase shifter provides a plurality of outputs where different outputs have different phases. An example of a phase shifter  205  is shown schematically in  FIG.  7   . 
     The receiver apparatus  100  also comprises a plurality of adders  103  and a plurality of first downconverters  107 . 
     In this example the receiver apparatus  100  comprises M adders  103  and M first downconverters  107 . The M adders  103  are configured to add the phase shifted antenna signals. The added antenna signals are provided as an input to the first downconverters  107 . 
     The first downconverters  107  can comprise mixers and local oscillators. In the example of  FIG.  2    only the mixers are shown for clarity. 
     The receiver apparatus  100  also comprises M ADCs  111 . The ADCs  111  are configured to convert the signals from the first downconverters  107 . 
     A multiplexer  119  is provided between at least one of the first downconverters  107  and an ADC  111 . 
     The receiver apparatus  100  also comprises a plurality of second downconverters  115 . In this example the receiver apparatus  100  comprises N−1 second downconverters  115 . In other examples the receiver apparatus  100  could comprise any number between 1 and N−1 second downconverters  115 . In other examples, other numbers of second downconverters  115  could be used. 
     The second downconverters  115  can comprise mixers and local oscillators. In the example of  FIG.  2    only the mixers are shown for clarity. The local oscillators that are used to provide input signals for the mixers in the second downconverters  115  can be different to the local oscillators that are used to provide the input signals for the mixers in the first downconverters  107 . The local oscillators that are used to provide input signals for the mixers in the second downconverters  115  can provide an input signal at a different frequency to the local oscillators that are used to provide the input signals for the mixers in the first downconverters  107 . 
     The second downconverters  115  are configured to receive separate antenna signals as an input. That is, the second downconverters  115  do not receive added antenna signals. 
     The receiver apparatus  100  also comprises a plurality of low pass filters  207 . In this example the receiver apparatus  100  comprises N−1 low pass filters  207 . The receiver apparatus  100  comprises the same number of low pass filters  207  as second downconverters  115 . 
     The multiplexer  119  is provided between the second downconverters  115  and the ADC  111   M . In this example the multiplexer  119  comprises a switch that acts in the time domain. Other types of multiplexers  119 , such as but not limited to frequency domain multiplexers, could be used in other examples of the disclosure. 
     In the example of  FIG.  2    only one multiplexer  119  is shown however more than one multiplexer  119  could be provided in other examples of the disclosure. 
     The multiplexer  119  can be configured into a first configuration so as to cause the receiver apparatus  100  to provide hybrid beamforming across the whole bandwidth. 
     This is shown as configuration  0  in  FIG.  2   . In this configuration the receiver apparatus  100  provides a hybrid beamforming system with N antennas and rank M. 
     The multiplexer  119  can also be configured into a second configuration so as to cause the receiver apparatus  100  to provide high rank digital beamforming across a sub-section of the bandwidth. In the second position the multiplexer  119  can be configured to enable one of the K antennas in the subset of all of the N antennas to be sampled for every sample of the ADC M . 
     In the example of  FIG.  2    each of the K antennas  201  in the sub-set of antennas  201  are sampled every K samples of the ADC M    111 . This enables the ADC M    111  to support 1/K of the bandwidth of the receiver apparatus  100 . The section of the bandwidth that is digitalized by this ADC M    111 , will also be digitalized by the M−1 ADCs  111  such as ADC 1    111  in  FIG.  2    that performs hybrid beamforming. This therefore enables the receiver apparatus  100  to provide rank K+M−1 digital beamforming when the multiplexer  119  is in the second configuration. 
     In the example of  FIG.  2    only one ADC 1    111  is shown as being used for hybrid beamforming. The number of ADC 1 s  111  can be M−1. If M is greater than two more than one ADC 1    111  that is used for hybrid beamforming could be provided. This provides a rank M−1 system that be provided on the full bandwidth of the receiver apparatus. The M−1 system can be provided in parallel with the high rank low bandwidth beamforming. 
     As an example, a receiver apparatus  100  with 300 Mhz bandwidth, N=64 and M=4 would be a rank  4  system without examples of the disclosure. However, the additional second downconverters  115  and the multiplexer  119  can enable the receiver apparatus  100  to be switched to a rank  3  system with a 300 Mhz bandwidth and a rank  16  system with a 23 Mhz bandwidth by setting K=13. 
     The example of  FIG.  2    shows a single radio Frequency (RF) chain for the receiver apparatus  100 . Examples of the disclosure could be provided on any number of RF chains within a receiver apparatus  100 . 
     In some examples different local oscillator signals with different frequencies can be used for the second downconverters  115  compared to the first downconverters  107 . This can enable the receiver apparatus  100  to be configured to provide a rank K+M−1 beamforming on any part of the hybrid system bandwidth, or a rank K beamforming outside that bandwidth. 
     The multiplexing of the ADC M    111  can be done in the time domain or in the frequency domain. To enable the multiplexing to be done in the frequency domain each of the mixers in the second downconverters  115  can use a different frequency for the local oscillator. In such examples a band pass filter could be use instead of a low pass filter. Once the signals have been converted by the ADC M    111  the signals from each antenna  201  can be filtered and further downconverted in the digital domain. The further downconversion can bring all of the antenna signals to the same baseband frequency. In such examples the different local oscillators for the different down converters can be generated by phase locked loops from the same base lock. This can provide a predictable phase shift between the different local oscillators. The receiver apparatus  100  can be configured so that different phase shifts can be compensated for in the digital domain. 
       FIG.  3    schematically shows another example receiver apparatus  100 . The example receiver apparatus  100  of  FIG.  3    comprises a plurality of antennas  201 , a plurality of low noise amplifiers  203 , a plurality of phase shifters  205  a plurality of adders  103 , a plurality of first downconverters  107 , a plurality of second downconverters  115 , low pass filters  207  and a plurality of ADCs  111 . These components can be arranged similar to the receiver apparatus  100  of  FIG.  2   . Corresponding reference numerals are used for corresponding features. The receiver apparatus  100  can comprise additional components that are not shown in  FIG.  3   . 
     The example receiver apparatus  100  of  FIG.  3    also comprises at least one multiplexing means  119 . In this example the multiplexing means  119  comprises an interleaver  301  and a plurality of switches  303 . 
     In this example a switch  303  is provided for an output of each of the second downconverters  115  and low pass filters  207 . In this example N−1 switches  303  are provided. Other numbers of switches  303  could be provided in other examples. 
     The switches  303  are provided between the second downconverters  115  and the ADCs  111 . In the example of  FIG.  3    the switches  303  are provided between low pass filters  207  and the ADCs  111 . 
     The interleaver  301  is configured to receive an input from one of the plurality of the first downconverters  107 . The interleaver  301  can be configured to enable interleaving in the frequency domain or in the time domain. The interleaver can be configured to enable interleaving of the downconverted separate antenna signals. 
     The interleaver  301  can comprise any means that takes an input signal with a wide frequency content and splits it into a plurality of narrower signals. The narrower signals can be digitized by a suitable ADC  111 . The wideband signal can then be reconstructed in the digital domain. 
     When the switches  303  are in a first configuration, as shown in  FIG.  3   , the output of the interleaver  301  is provided to the plurality of ADCs  111   M-1 - 111   M . This allows the plurality of ADCs  111   M-1 - 111   M  to be combined. This causes the receiver apparatus  100  to provide hybrid beamforming across the whole bandwidth of the receiver apparatus  100 . In this configuration the receiver apparatus  100  provides a hybrid beamforming system with N antennas and rank M. 
     When the switches  303  are in a second configuration the outputs from the second downconverters  115  and low pass filters  207  are provided to the plurality of ADCs  111   M-1 - 111   M . This causes the receiver apparatus  100  to provide high rank digital beamforming across a sub-section of the bandwidth. 
     The interleaver  301  and plurality of switches  303  can therefore enable the receiver apparatus  100  to be switched between hybrid beamforming or analog beamforming and digital beamforming. 
       FIG.  4    schematically shows another example receiver apparatus  100 . The example receiver apparatus  100  of  FIG.  4    is similar to the receiver apparatus  100  of  FIG.  2   . Corresponding reference numerals are used for corresponding features. However, in the example of  FIG.  4    the receiver apparatus  100  comprises a plurality of additional multiplexers  401 . 
     The additional multiplexers  401  are provided between the low noise amplifiers  203  and the second downconverters  115 . The additional multiplexers  401  can comprise switches or any suitable type of multiplexing means. 
     The additional multiplexers  401  can be configured to enable the separate antenna signals to multiplex the signals from a plurality of different antennas  201 . This enables the input for the ADC  111  to be switched between antenna signals. 
     The additional multiplexers  401  can reduce the number of second downconverters  115  that are needed. This can reduce the number of second downconverters  115  within the receiver apparatus  100 . This reduces the power needed by local oscillators used within second downconverters  115 . 
     In the example of  FIG.  4    the additional multiplexers  401  can comprise fast radio frequency switches and the mixers within the second downconverters  115  can be configured to settle in a time that is shorter than several samples of the ADC  111 . 
       FIG.  5    schematically shows an example transmitter apparatus  501 . The transmitter apparatus  501  is a corresponding apparatus to the receiver apparatus  100  of  FIGS.  1  to  4   . 
     In the example of  FIG.  5    the transmitter apparatus  501  comprises first upconverters  509 , second upconverters  519 , one or more DACs  503  and at least one demultiplexing means  505 . The transmitter apparatus  501  can comprise additional components that are not shown in  FIG.  5   . For example, the transmitter apparatus  501  could comprise phase shifters or other suitable components. The phase shifters could be provided before the adders  513  in the example of  FIG.  5   . 
     The DACs  503  can comprise any means of circuitry that can be configured to convert a digital input signal to an analog output signal  507 . The transmitter apparatus  501  can comprise any suitable number of DACs  503 . 
     The transmitter apparatus  501  is configured so that output signals of the DACs  503  can be provided to the first upconverters  509 . The first upconverters  509  can comprise any means that can be configured to convert a low frequency signal to a high frequency signal. The first upconverters  509  can be configured to convert a low radio frequency signal to a high radio frequency signal. The first upconverters  509  can comprise circuitry or any other suitable means. In some examples the first upconverters  509  can comprise a mixer and local oscillator or any other suitable means. 
     The first upconverters  509  are configured to receive the analog output signal  507  from the DACs  503  and provide the upconverted signal  511  as an output. 
     In the example shown in  FIG.  5    the transmitter apparatus  501  also comprises a plurality of adders  513 . The plurality of adders  513  are configured to add a plurality of signals from the first upconverters  509  and the second upconverter  519 . The added signals can then be provided to a plurality of antennas for transmission. The adders  513  can comprise any suitable circuitry or other means that enables the plurality of antenna signals  511  to be added together. 
     The transmitter apparatus  501  also comprises a plurality of second upconverters  519 . The second upconverters  519  can comprise any means that can be configured to convert a low frequency signal to a high frequency signal. The second upconverters  519  can be configured to convert a low radio frequency signal to a high radio frequency signal. The second upconverters  519  can comprise circuitry or any other suitable means. In some examples the second upconverters  519  can comprise a mixer and local oscillator or any other suitable means. 
     The second upconverters  519  are coupled to the demultiplexer  505  so that the outputs from a DAC  503  can be sampled and provided to the second upconverters  519 . The outputs from the second upconverters can also be provided to the adders  513 . Each of the outputs from the second upconverters  519  are provided to a single adder  513  so that signals  521  from the second upconverters  519  are only provided to a single antenna within the transmitter apparatus  501 . 
     The transmitter apparatus  501  is configured so that the outputs  515  from the adders  513  are provided to a plurality of antennas for transmission. The transmitter apparatus  501  comprises a plurality of adders  513  and antennas so that the output from each of the adders  513  is provided to a single antenna. 
     The transmitter apparatus  501  can therefore be configured in two different configurations. When the demultiplexer  505  is configured in the first configuration the transmitter apparatus  501  is configured so that the second upconverters  519  are not used. In this configuration the second upconverters can be turned off to reduce power consumption. In this configuration the signals from the DACs  503  are combined to provide hybrid beamforming or analog beamforming. The beamforming can be analog beamforming if only one RF chain is used on the full bandwidth. The beamforming can be hybrid beamforming if a plurality of RF chains are used on the full bandwidth. 
     When the demultiplexer  505  is configured in the second configuration the transmitter apparatus  501  is configured so that the second upconverters  519  are used. In this configuration the signals from the DACs  503  are provided as separate signals to the antennas to enable digital beamforming. The hybrid beamforming or analog beamforming is provided across a bandwidth of the transmitter apparatus  501  and the digital beamforming is provided across a sub-section of the bandwidth. 
       FIG.  6    shows an example transmitter apparatus  501  in more detail. 
     The transmitter apparatus  501  comprises M DACs  503 . The DACs  503  are configured to provide analog output signals for the upconverters  509 ,  519 . 
     A demultiplexer  505  is provided between at least one of the DACs  513  and the upconverters  509 ,  519 . The demultiplexer  505  can comprise one or more switches or any other suitable means. 
     When the demultiplexer  505  is configured in a first configuration the outputs from the DAC  503  are provided to the first upconverters  509  to enable the transmitter apparatus  501  to provide hybrid beamforming or analog beamforming. In this example the transmitter apparatus  501  comprises M first upconverters  509 . The transmitter apparatus  501  comprises the same number of first upconverters  509  as DACs  503 . 
     The transmitter apparatus  501  also comprises a plurality of antennas  607  and a plurality of power amplifiers  605  and a plurality of phase shifters  603 . In this example the transmitter apparatus  501  comprises N antennas  607 , N power amplifiers  605  and N phase shifters  603 . The output signals from the first upconverters  509  are provided to the plurality of phase shifters  603  and the phase shifted signals are then provided to the power amplifiers  605  before being transmitted by the antennas  607 . The phase shifters  603  can be configured to add a phase shift to the plurality of input signals and then combine the phase shifted signals into a single output. The phase shifters  603  could be corresponding phase shifters to the example shown in  FIG.  7   . 
     When the demultiplexer  505  is configured in a second configuration the outputs from the DAC  503  are provided to the second upconverters  519  to enable the transmitter apparatus  501  to provide high rank digital beamforming. In this example the transmitter apparatus  501  comprises N−1 second upconverters  519 . 
     In the example of  FIG.  6    the transmitter apparatus  501  a comprises a plurality of low pass filters  601 . In this example the transmitter apparatus  501  comprises N−1 low pass filters  601 . The low pass filters  601  are configured to filter the analog signals before they are provided to the second upconverters  519 . 
     The outputs from the second upconverters  519  are each provided to a single antenna  607 . The outputs are combined with signals from the first upconverters  509  using the plurality of adders  513 . In this example N−1 adders  513  are provided. Other numbers of adders  513  could be used in other examples of the disclosure. 
       FIG.  7    schematically shows an example phase shifter  205  that could be used in some receiver apparatus  101  in examples of the disclosure. 
     The phase shifter  205  comprises a power splitter  703  and a plurality of phase shift modules  705 . 
     The phase shifter  205  receives a single input signal  701 . The input signal  701  is provided to the power splitter  703 . The power splitter  703  is configured to split the input signal  701  into a plurality of signals. In this example the power splitter  703  is configured to split the input signal  701  into M signals. 
     The phase shifter  205  comprises M phase shift modules  705 . Each of the phase shift modules receives an input signal from the power splitter  703 . The phase shift modules  705  are configured to add a phase shift the signals from the power splitter  703 . 
     Each of the phase shift modules  705  provide an output signal  707  so that the phase shifter  205  provides M output signals. Different output signals have different phase shifts. 
     The example phase shifter  205  shown in  FIG.  7    is configured for use in a receiver apparatus  100 . It is to be appreciated that corresponding phase shifters could also be used in transmitter apparatus  501 . In such cases the phase shifter would comprise a power combiner instead of a power splitter. The phase shifters in the transmitter apparatus  501  would be configured to receive a plurality of input signals having different phases and then add a different phase different to each of the input signals before combining the signals to provide a single output. 
     Other configurations for the phase shifters  205 ,  603  could be used in other examples. 
     Variations to the receiver apparatus  100  and transmitter apparatus  501  could be used in other examples of the disclosure. For instance, in some example receiver apparatus  100  the multiplexing means  119  could be combined with one or more ADCs  111 . This can enable the multiplexing means  119  and an ADC  111  to be provided in a single logical block. For instance, an interleaved ADC could be used 
     Examples of the disclosure therefore provide the advantage that the receiver apparatus  100  or transmitter apparatus  501  can be switched between an operational state in which hybrid beamforming or analog beamforming can be provided across the bandwidth of the apparatus and an operational state in which the apparatus can be configured to provide digital beamforming across a sub-section of the bandwidth. The digital beamforming can be high rank digital beamforming. This can enable the high rank digital beamforming to be used when required but also reduces the number of expensive components and/or components that use a lot of power. 
     In this description the term coupled means operationally coupled. Any number or combination of intervening elements can exist between coupled components including no intervening elements. 
     The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one . . . ” or by using “consisting”. 
     In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. 
     Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims. 
     Features described in the preceding description may be used in combinations other than the combinations explicitly described above. 
     Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. 
     Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. 
     The term ‘a’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. 
     The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. 
     In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. 
     Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not emphasis has been placed thereon.