Patent Publication Number: US-11044033-B2

Title: Method, apparatus and system to amplify and transport analog and digital signals

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. patent application Ser. No. 16/317,607, filed on Jan. 14, 2019, which is a 371 National Phase of International Application No. PCT/USB2017/041844, filed on Jul. 13, 2017, which claims the benefit of U.S. Provisional Application No. 62/362,977, filed on Jul. 15, 2016, which are incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The field of invention is communication systems and more specifically to amplify and transport communication signals in a wireless communication system. 
     BACKGROUND 
     Radio Frequency (RF) active components such as amplifiers and passive components generate harmonics, intermodulation, spurious signals and noise. Passing multiple frequencies simultaneously through active components adds additional noise which reduces the signal-to-noise ratio (SNR) performance. Passing multiple frequencies simultaneously through active components also generates distortion and unwanted spurious signals due to the non-linearity of the device. This reduces the signal to noise and distortion (SINAD) performance. These unwanted signals can interfere, distort and otherwise detrimentally impact the clear transmission and amplification of communication signals used in communication systems. 
     In the case of wireless communication systems, the unwanted signals are radiated into the free-space causing interference and a noise build-up for other wireless systems operating near the noisy transmitter and or near the same frequency bands. The amount of noise and spurious signal permitted to be emitted is tightly regulated by the Federal Communications Commission (FCC) in the United States and comparable agencies in other countries. The FCC has recently further reduced the spurious signal level permitted to be transmitted by a radiating system making it even more difficult to amplify and transport a compliant signal meeting the FCC&#39;s standards. 
     In addition, multicarrier amplifiers are inefficient in their conversion of power from DC to RF. To reduce the intermodulation requires higher powered amplifiers that further add to the inefficient power consumption. 
     Furthermore, the invention has a positive impact on system reliability. The fact that a single amplifier is used to amplify multiple signals, when a single multicarrier amplifier fails, all the signals in the system are lost and unusable creating a risk to first responder users. A single multicarrier amplifier creates a single point of failure highly undesirable for the first responder users who are relying on the system for their communication during an emergency incident. 
     SUMMARY 
     Embodiments of the present invention improve the power efficiency by utilizing high efficiency amplifiers that amply one RF carrier at a time. In these configurations, each amplifier is dedicated to amplifying a single carrier and improves the DC to RF power conversion efficiency. Embodiments of the present invention also improve SINAD performance by providing parallel communication pathways throughout the entire transport and distribution chain. By creating parallel processing paths, both optically and electrically, the interaction of multiple signals are limited, thereby never generating the unwanted intermodulation and noise. In some embodiments, a digital signal processor can be used to filter and separate the multitude of frequencies and, after digital filtering and processing, convert them back to the analog (radio frequency) domain with individual analog-to-digital converters and amplifying the individual frequencies with individual amplifiers dedicated and optimized to amplify one frequency. In the embodiments, the intermodulation commonly associated with multi-carrier amplifiers can be avoided and the signals are amplified without generating significant intermodulation or noise. This may permit the use of efficient single frequency amplification and reduce the power consumption and/or battery use in the case of battery powered applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         FIG. 1A  is a block diagram of a prior art transport and amplification system. 
         FIG. 1B  is a spectral graph of an example multi-frequency input signal. 
         FIG. 1C  is a spectral graph of an example output of the prior art transport and application system. 
         FIG. 2A  is a high level diagram of the parallel paths of an embodiment of the transport and amplification system. 
         FIG. 2B  is a block diagram of an embodiment of the transport and amplification system. 
         FIG. 2C  is a spectral graph of an example multi-frequency input signal. 
         FIG. 2D  is a spectral graph of an example output of the embodiment of transport and application system. 
         FIG. 3  is an example of an embodiment that receives a multi-frequency input signal using an antenna. 
         FIG. 4  is an example of another embodiment that uses a multiplexer and de-multiplexer. 
         FIG. 5  is an example of another embodiment that uses multiple transmit antennae. 
         FIG. 6  is an example of another embodiment that uses a digital connection. 
         FIG. 7  is an example of another embodiment that uses a digital connection. 
         FIG. 8  is an example of another embodiment that uses a digital connection. 
         FIG. 9  is an example of a bi-directional embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
       FIG. 1A  depicts a prior art transport and amplification system  100 . In the prior art transport and amplification system  100 , a Fiber Optic Transmitter  110  receives a multi-frequency Radio Frequency (RF) input signal  105 . A spectral graph of the multi-frequency RF input signal  105  is shown in  FIG. 1B . The multi-frequency RF input signal  105  includes a plurality of signals modulated at discrete frequencies ( 105 A,  105 B and  105 C). Although three frequencies are depicted, a person of ordinary skill in the art would appreciate that any number of frequencies may be used. The Fiber Optic Transmitter  110  then transmits an optical signal  115  over a Fiber Optic Cable  120  to a Fiber Optic Receiver  130 . The Fiber Optic Receiver  130  receives the optical signal  115  and transmits an RF signal  125  to a multi-frequency amplifier  140 . The multi-frequency amplifier  140  amplifies the RF signal  125  to generate amplified RF signal  135 . 
     A spectral graph of the amplified RF signal  135  is shown in  FIG. 1C . The amplified RF signal  135  includes a combination of the multi-frequency RF input signal  105 , intermodulation distortions  135   i , harmonic distortions  135   h , and additional noise  135   n . The intermodulation distortions  135   i  are the result of the amplitude modulation of the multi-frequency RF input signal  105  containing the plurality of different frequencies ( 105   a ,  105   b  and  105   c ) caused by nonlinearities in transport and amplification system  100 . The intermodulation between each frequency component (e.g.  105   a ,  105   b  and  105   c ) will form additional signals at frequencies that are not just at harmonic frequencies (integer multiples) of either, like harmonic distortion ( 135   h ), but also at the sum and difference frequencies of the original frequencies and at multiples of those sum and difference frequencies. The additional noise  135   n  is the result of noise generated by the power amplifier and further stimulated within the power amplifier by the injection of the multicarrier signals. These unwanted signals may interfere, distort and otherwise detrimentally impact the clear transmission and amplification of multi-frequency RF input signal  105 . 
       FIG. 2A  depicts an example transport and amplification system  200  that minimizes the intermodulation by creating parallel transport pathways  200   a ,  200   b  and  200   c  for separate frequencies of an input signal  205 . Specifically, the parallel transport pathways  200   a ,  200   b  and  200   c  may minimize intermodulation distortions because two or more frequencies are not present in both active (i.e. electrically powered stages) and passive (i.e. non-powered stages—to a lesser extent but also seen within passive combiners, splitters etc.) stages. Therefore, the parallel transport pathways  200   a ,  200   b  and  200   c  permit the use of a multi-frequency RF input signal  205  with a high strength that improves signal-to-noise ratio without significantly increasing the total distortion. 
     As shown in  FIG. 2A , the transport and amplification system  200  includes a plurality of stages. In Stage  1 , separate signals  205   a ,  205   b  and  205   c  are obtained for Multi-frequency Radio Frequency (RF) input signal  205 . The input signal  205  may be obtained from a radio base-station signal source so that the signals may already be delivered on separate clean signal paths. In other embodiments, such as a distributed antenna system (DAS), additional circuitry may be required to separate the separate signals  205   a ,  205   b  and  205   c  that are obtained for Multi-frequency RF signal  205 . Although three frequencies are depicted, a person of ordinary skill in the art would appreciate that any number of frequencies may be used and any number of parallel transport pathways utilized. 
     In stage  2 , the separate signals  205   a ,  205   b  and  205   c  are injected into the Fiber optic link  220 . The separate signals  205   a ,  205   b  and  205   c  are maintained along separate channel pathways in order to improve the signal to noise performance at the output of the link. Then, in stage  3 , the separate signals  205   a ,  205   b  and  205   c  are amplified individually. Amplifiers operating in or near saturation mode may be used to deliver very high DC power to analog output signal power inefficiencies. As a result of utilizing the separate parallel transport pathways  200   a ,  200   b  and  200   c  for each separate signal  205   a ,  205   b  and  205   c , the drive levels can be increased at each stage so as to maximize signal to noise. 
       FIG. 2B  depicts a more detailed diagram of the embodiment of a transport and amplification system  200  that can amplify a multi-frequency RF input signal  205  while minimizing the detrimental impacts on an amplified RF signal  235 . The multi-frequency RF input signal  205  includes a plurality of signals ( 205 A,  205 B and  205 C) modulated at discrete frequencies. A spectral graph of the multi-frequency RF input signal  205  is shown in  FIG. 2B . Although three frequencies are depicted, a person of ordinary skill in the art would appreciate that any number of frequencies may be used. 
     The transport and amplification system  200  includes parallel transport pathways  200   a ,  200   b  and  200   c  for each of the plurality of signals  205 A,  205 B and  205 C. Each of the parallel transport pathways  200   a ,  200   b  and  200   c  have a similar configuration, albeit tuned to a different signal. The parallel transport pathways can  200   a ,  200   b  and  200   c  be tuned to a specific frequency or can be broadband to allow for any single frequency over a broad range of frequencies. 
     The parallel transport pathways  200   a ,  200   b  and  200   c  each include Fiber optic transmitters  210  ( 210 A,  210 B and  210 C). The Fiber optic transmitter  210  may receive a signal using the specific frequency of the respective parallel transport pathways and ignore any signals received at different frequencies. The Fiber optic transmitter  210  then modulates the received signal over a respective Fiber optic link  220  to a Fiber optic receiver  230  ( 230   a ,  230   b  and  230   c ). For example, in parallel transport pathway  200   b , Fiber optic transmitter  210   b  receives a signal at the frequency of separate signal  205   b , modulates the signal over Fiber optic link  220   b , and the modulated signal is received by Fiber optic receiver  230   b . The Fiber optic link  220  may be analog or digital fiber optic cable, Ethernet, twisted pair, coaxial or any other cable known in the art. In some embodiments, highly linear fiber optic links may be used to minimize the harmonic and intermodulation distortion. In some embodiments, the Fiber optic transmitters  210  and the Fiber optic receivers  230  may be compliant to the DWDM or CWDM ITU Grid Specification such as ITU-T G.671 or other similar standards which define CWDM and DWDM conventions. 
     In some embodiments, Fiber optic transmitter  210  converts analog signal  205  into a fiber optic signal in a linear fashion by (for example) intensity modulating a laser diode. The input impedance must be compatible with the output impedance of the previous stage which typically is either 50 ohms or 75 ohms. It is important at this stage that the proper filtering has been performed so that only a single dominant frequency or carrier is present at the input to the fiber optic transmitter. Dominant means that the signal should be at least 30 to 40 dB above any other spurious (although the invention will still operate with lower signal to spurious). The larger the dominance, the better the invention will perform. 
     The Fiber optic receivers  230  then output the modulated signal from the Fiber optic transmitters  210  along the respective parallel transport pathway  200   a ,  200   b  and  200   c . The Fiber optic receivers  230  then output analog signals for each frequency in input signal  205  to pre-amp filter  250  ( 250   a ,  250   b  and  250   c ). For example, in parallel transport pathway  200   a , Fiber optic receiver  230   a  outputs an analog signal at the frequency of separate signal  205   a  to pre-amp filter  250   a.    
     The pre-amp filter  250  may be a band pass filter that removes all frequencies, other than the specific frequency of the input signal  205  that generated the modulated signal, to generate filtered analog signal  225  ( 225   a ,  225   b  and  225   c ). For example, pre-amp filter  250   c  may remove all frequencies other than  205   c  to generate filtered analog signal  225   c . Without the proper filtering, spurious signals will cause significant intermodulation and will negate the efficiency of the amplifiers  240 . It is important for the amplifier to be compatible with the frequency of operation and the desired signal levels. It is critical to select the proper amplifier for the frequency band and to provide impedance matching as required. As a result, pre-amp filter  250  may filter out the harmonic distortion and prepare it for amplification. In some embodiments, saw or crystal filters, ADC&#39;s/digital signal processors/DAC&#39;s, or other filtering techniques may be used. 
     The filtered analog signal is then received by a corresponding amplifier  240  ( 240   a ,  240   b  and  240   c ) along the respective parallel transport pathway  200   a ,  200   b  and  200   c . The amplifier  240  may then amplify the filtered analog signal  225  at the specific frequency of the respective parallel transport pathway  200   a ,  200   b  and  200   c  to a level required by the application. For example, in parallel transport pathway  200   a , amplifier  240   a  may amplify filtered analog signal  225   a  at the frequency of separate signal  205   a . The amplifiers  240  may be high efficiency single frequency amplifiers operating near or beyond the 1 dB compression point. The amplifiers  240  may also be a chain of amplifiers with filters in between stages so as to amplify the signal to the appropriate levels and properly and effectively remove the harmonic spurious signals. 
     The signal amplified by the amplifiers  240  may then pass through final filters  260  ( 260   a ,  260   b  and  260   c ) along the respective parallel transport pathway  200   a ,  200   b  and  200   c . The final filters  260  may be a band pass, low pass, or high pass filter. The final filters may be matched to specific frequency of the filter signal. For example, final filter  260   a  may permit the frequency of separate signal  205   a  to pass. In addition, that eliminates the harmonic spurious signals generated by the amplifiers  240 . The final filters  260  may match the amplifier output to the proper system, such as 50 or 75 ohm. 
     A combiner  270  may then receive the outputs of the final filters  260  to generate amplified RF signal  235 . The combiner  270  may be a passive low distortion combiner. The combiner  270  may permit the use of a single antenna where free-space transmission is required with a single multi-frequency antenna. However, in alternate embodiments (such as shown in  FIG. 5 ), the combiner  270  may be omitted, and multiple antennae may be used. 
     In some embodiments, the combiner  270  may be a multistage combiner. For example, a first stage of the combiner may combine frequencies within a relatively narrow band. A second stage of the combiner  270  then may utilize “cross-band” combiners that allow widely spaced frequency groups to be combined with very low loss. For example, a group of VHF signals can be cross-band combined with a group of UHF signals with 1 dB or less attenuation per band. Alternatively, in place of the combiner and a single antenna, the combiner can be eliminated, and individual antenna can be used on each amplifier and low pass filter output. 
       FIG. 2D  depicts a spectral graph of the amplified RF signal  235 . The amplified RF signal  235  includes combination of the multi-frequency RF input signal  205  harmonic distortions  135   h  and additional noise  135   n . As shown in the  FIG. 2D , the intermodulation distortions  135   i  of  FIG. 1C  have been eliminated, and amplitude of the harmonic distortion  235   h  have been dramatically reduced. As a result, transport and amplification system  200  reduces the unwanted signals that interfere, distort and otherwise detrimentally impact the clear transmission produced by transport and amplification system  100 . 
       FIG. 3  depicts an embodiment of transport and amplification system  200  where the Multi-frequency RF signal  205  is obtained using antennae  310 . Although one antenna  310  is depicted, a person of ordinary skill would appreciate that an array of antennae may also be used. In stage  1 , the antenna  310  transmits the Multi-frequency RF signal  205  to a splitter  350 . The splitter  350  provides the Multi-frequency RF signal  205  in parallel to narrow band pass filters  330  ( 330   a ,  330   b ,  330   c ). The narrow band pass filters  330  separate the RF signal  205  into the separate signal  205   a ,  205   b  and  205   c  by allowing only a single frequency to pass. The number of narrow band pass filters  330  utilized corresponds to the number of independent signals carried by the Multi-frequency RF signal  205 . Although three narrow band pass filters  330  are depicted, a person of ordinary skill in the art would appreciate that any number of narrow band pass filters can be used. The narrow band pass filters  330  allow each separate signal  205   a ,  205   b  and  205   c  to pass to the corresponding Fiber optic transmitter  210 . For example, in parallel transport pathway  200   a , the narrow band pass filter  330   a  allows signal  205   a  to pass to Fiber optic transmitter  210   a . Once the Fiber optic transmitter  210  receives each separate signal  205   a ,  205   b  and  205   c , stages  2 - 4  of transport and amplification system  200  operate as described above. 
     Another embodiment of transport and amplification system  200  is depicted in  FIG. 4 . In stage  2  of this embodiment, a Multiplexer  410  receives the modulated signal from the Fiber optic transmitters  210 . The Fiber optic transmitters  210  may use Wavelength Division Multiplexing (WDM) or other known multiplexing techniques known in the art. The modulated signal from the Fiber optic transmitters  210  may have tuned wavelength outputs corresponding to the filter passbands of the Multiplexer  410 . The Multiplexer  410  outputs a multiplexed signal over a single fiber strand  420 . A de-multiplexer  430  received the multiplexed signal from the single fiber strand  420 . The de-multiplexer  430  may have matched tuned optical filters to extract the individual optical channels corresponding to separate signal  205   a ,  205   b  and  205   c . The output of the de-multiplexer is transmitted to Fiber optic receivers  230  ( 230   a ,  230   b  and  230   c ). Once the Fiber optic receivers  230  receive the signal corresponding to separate signal  205   a ,  205   b  and  205   c  for each of the parallel transport pathways  200   a ,  200   b  and  200   c , stages  3  and  4  of transport and amplification system  200  operate as described above. 
       FIG. 5  depicts an embodiment where in stage  4  of transport and amplification system  200 , the Combiner  270 , is replaced by antennas  510  ( 510   a ,  510  and  510   c ). In this embodiment, each parallel transport pathway  200   a ,  200   b  and  200   c  has an associated antenna  510 . Each respective antenna  510  receives the output from the corresponding final pass filter  260  along the parallel transport pathways  200   a ,  200   b  and  200   c . The antennas  510  then propagate the amplified RF signal  235  as an electromagnetic wave. 
       FIG. 6  depicts an embodiment of transport and amplification system  200  that utilizes digital transmission. In stage  1  of this embodiment, an Analog to Digital Converter (ADC)  640  converts the Multi-frequency RF input signal  205  to a digital signal. In stage  2 , the digital signal is received by an optical transmitter  610 , and the optical transmitter  610  then transmits an optical signal over a fiber optical cable strand  620 . A fiber optic receiver  630  then receives the optical signal from the fiber optical cable strand  620  and converts the signal from optical back to an electrical signal. In some embodiments, the levels at the input of the optical transmitter  610  would be similar to the levels at the output of the fiber optic receiver  630 . In the case of an analog or RF fiber optic link, the levels at the output of the receiver are lower, and additional gain stages can be added to boost the signal at the output of the fiber optic receiver  630 . The signal from the fiber optic receiver  630  is output to a Digital Signal Processor (DSP)  650 . The DSP  650  extracts digital equivalents of separate signals  205   a ,  205   b  and  205   c  from the received signal. The DSP then transmits the digital equivalents of separate signals  205   a ,  205   b  and  205   c  to Digital to Analog Converters (DAC)  660  ( 660   a ,  660   b  and  660   c ). The DAC  660  then outputs an analog signal to respective pre-amplifiers  250  for each of the parallel transport pathways  200   a ,  200   b  and  200   c . Stages  3  and  4  of transport and amplification system  200  then proceed as described above. 
       FIG. 7  depicts an embodiment of transport and amplification system  200  where stage  1  and stage  2  utilize digital signals. In stage  1  of this embodiment, a splitter  750  receives the multi-frequency RF input signal  205 . The splitter  750  then transmits the multi-frequency RF input signal  205  in parallel to an array of ADC  770  ( 770   a ,  770   b ,  770   c ). The number of ADC  770  may correspond to the number of parallel transport pathways  200   a ,  200   b  and  200   c  in the transport and amplification system  200 . Each ADC  770  then extracts respective separate signals  205   a ,  205   b  and  205   c  and outputs the digital equivalence of the extracted separate signal to a respective optic transmitter  710  ( 710   a ,  710   b  and  710   c ). Each of the optic transmitters  710  transmit digital equivalence of the extracted separate signal over a fiber optical channel  720  ( 720   a ,  720   b  and  720   c ). In some embodiments, each parallel communication pathway may have a dedicated fiber optic channel  720 . In other embodiments, an optical multiplexer  410  may be used. 
     The fiber optic receivers  730  ( 730   a ,  730   b  and  730   c ) receive the digital equivalent of the respective separate signals  205   a ,  205   b  and  205   c  fiber optical cable strand. The digital equivalence of the respective separate signals  205   a ,  205   b  and  205   c  is then sent in parallel to an array of DAC  760 . The DAC  760  then outputs an analog signal to respective pre-amplifiers  250  for each of the parallel transport pathways  200   a ,  200   b  and  200   c . Stages  3  and  4  of transport and amplification system  200  then proceed as described above. In some embodiments, the DAC  760  may include a Digital Signal Processor (DSP) or a Field Programmable Gate Array (FPGA) that applies additional narrowband digital filters which eliminate the unwanted spurious signals and isolate one desired frequency as the dominant signal for each parallel transport pathways  200   a ,  200   b  and  200   c.    
       FIG. 8  shows another embodiment that utilizes a signal digital communication channel. In stage  1  of this embodiment, a splitter  850  receives the multi-frequency RF input signal  205 . The splitter  850  then transmits the multi-frequency RF input signal  205  in parallel to an array of ADC  870  ( 870   a ,  870   b ,  870   c ). The number of ADC  870  may correspond to the number of parallel transport pathways  200   a ,  200   b  and  200   c  in the transport and amplification system  200 . Each ADC  870  then extracts respective separate signals  205   a ,  205   b  and  205   c  and outputs the digital equivalence of the extracted separate signals to a Parallel to Serial Converter  880 . The Parallel to Serial Converter  880  multiplexes digital equivalence of the extracted separate signals. The multiplexed single digital stream output by the Parallel to Serial Converter may be composed of interlaced bits of the extracted separate signals. The multiplexed single digital stream is converted into a serial optic data stream by Digital Fiber Optic Transmitter  810 . The Digital Fiber Optic Transmitter  810  transmits the serial optic data stream over fiber optic cable  820  to a Digital Fiber Optic Receiver  830 . The Digital Fiber Optic Receiver  830  then receives the incoming serial stream of data and converts it to a serial electrical digital signal. The Digital Fiber Optic Receiver  830  then transmits the serial electrical digital signal to a Serial to Parallel converter  890 . Even though the signals are combined into a single stream, since they are transmitted as a digital signal, they do not detrimentally interact creating intermodulation distortion or excess noise in the way the active analog combining would. 
     The Serial to Parallel converter  890  multiplexes the serial signal back into the parallel data streams. The number of data streams corresponds to the number of parallel transport pathways  200   a ,  200   b  and  200   c . The parallel data streams are then sent in parallel to an array of DAC  860  ( 860   a ,  860   b  and  860   c ). The DAC  860  then outputs an analog signal to respective pre-amplifiers  250  for each of the parallel transport pathways  200   a ,  200   b  and  200   c . Stages  3  and  4  of transport and amplification system  200  then proceed as described above. 
     A bi-directional embodiment is depicted in  FIG. 9 . In this embodiment, an additional fifth stage is added to the transport and amplification system  200 . In stage  5  of this embodiment, the amplified RF signal  235  is output to a duplexer  980 . The duplexer  980  transmits the amplified output signal via duplexed signal  985 . The duplexer  980  also receives an inbound data signal from the duplexed signal  985 . The duplexer  980  then transmits the inbound data signal to a receiver  990 . The receiver then transports the uplink signal back to the Stage  1  for processing. 
     The design presented herein and the specific aspects illustrated are meant not to be limiting, but may include alternate components while still incorporating the teachings and benefits of the invention. While the invention has thus been described in connection with specific embodiments thereof, it will be understood that the invention is capable of further modifications. For example, components from one embodiment may be combined and substituted for components in other embodiments. This application is intended to cover any variations, uses or adaptations of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within known and customary practice within the art to which the invention pertains.