Abstract:
A receiver is disclosed. The receiver includes a channel decoder select circuit, a plurality of communication channels, at least one maximum ratio combiner circuit, and a forward error correction circuit. The plurality of communication channels receives wireless information from channel demodulators and are in communication with respective channel decoder circuits, which are in communication with the channel decoder select circuit. The at least one maximum ratio combiner circuit receives the wireless information from the plurality of communication channels. The output of the maximum ratio combiner is communicated to the forward error correction circuit, the output of which is communicated to the channel decoder select circuit. A pseudo bit error measurement feedback signal communicated to the maximum ratio combiner from one of the plurality of channel decoder circuits. A method for finding wireless satellite signals that minimizes errors in a receiver system is also disclosed. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
TECHNICAL FIELD  
       [0001]     The present invention generally relates to receivers and, more particularly, to a satellite-based digital audio radio receiver that finds wireless satellite signals and minimizes errors in the receiver system.  
       BACKGROUND OF THE INVENTION  
       [0002]     Automotive vehicles are commonly equipped with audio radios for receiving broadcast radio frequency (RF) signals, processing the RF signals, and broadcasting audio information to passengers in the vehicle. More recently, satellite digital audio radio (SDAR) services have become available. SDAR services offer digital radio service covering a large geographic area, such as North America. Satellite-based digital audio radio services are available in North America, which generally employ either geo-stationary orbit satellites or highly elliptical orbit satellites that receive up-linked programming which, in turn, is rebroadcast directly to digital radios in vehicles on the ground that subscribe to the service. These systems also use terrestrial repeater networks in urban areas to supplement the availability of service. Each vehicle subscribing to the digital service generally includes a digital radio having a receiver and one or more antennas for receiving the digital broadcast.  
         [0003]     The radio receivers are programmed to receive and unscramble the digital data signals, which typically include many channels of digital audio. In addition to broadcasting the encoded digital quality audio signals, the satellite-based digital audio radio service may also transmit data within a data bandwidth that may be used for various applications. The broadcast signal may also include other information for reasons such as advertising, informing the driver of warranty issues, providing information about the broadcast audio information, and providing news, sports, and entertainment broadcasting. Accordingly, the digital broadcast may be employed for any of a number of satellite audio radio, satellite television, satellite Internet, and various other consumer services.  
         [0004]     In some systems with more than one signal source (i.e. multi-stream systems) and different data sources (i.e. same data with different signal sources), there is a need to find signal(s), such as, for example, wireless satellite signals, that maximizes performance of a receiver by minimizing errors in the receiver system, which results in an improved user experience. As illustrated in  FIG. 1 , traditional satellite-based digital audio radio services receivers  1   a  typically include multiple forward error correction (FEC) circuits that receive terrestrial and satellite signals provided over a terrestrial and satellite channel, respectively, to detect which communication path does not have an error, such as a burst-type error (i.e. where the signal to noise ratio is temporarily degraded). A form of FEC, which is known in the art as ‘concatenated coding,’ combines a convolutional code and a block code, which results in a code that has an inner code and an outer code.  
         [0005]     As illustrated in  FIG. 2 , other known satellite-based digital audio radio services using more than one signal (or antenna), comprises a receiver  1   b  including a maximum ratio combiner (MRC) that combines the satellite and terrestrial channel signals. Typically, an MRC receives and aligns two signals in time or phase, weights (magnitude adjusted) signals according to a quality criteria, which results in an improved signal magnitude upon being combined together. For example, the MRC can be thought of as adding a desired signal coherently (i.e. in phase) and adding noise non-coherently (i.e. random noise where phase is unknown) such that the signal will double in voltage (i.e. a 6 dB increase). Because noise is typically non-coherent for each source, the noise will, over some time, add at a square root of two (i.e. a 3 dB increase). Since the desired signal is increased by  6  dB and the noise is increased by 3 dB, the result is a net 3 dB increase in the signal to noise ratio. Accordingly, an MRC provides an improved system performance.  
         [0006]     The advantage of the system seen in  FIG. 1 , which uses multiple FEC circuits for each frequency or antenna source, is a direct selection of the frequency or antenna source that does not have any errors. By using multiple FEC algorithms, the best signal path having the least amount of bit errors carrying the RF signal from the antenna to the FEC hardware may be chosen for the source decoder. On the other hand, as seen in  FIG. 2 , the use of an MRC circuit prior to an FEC circuit optimally combines phase- and time-aligned signals to improve coded signal performance in a digital communication system. Essentially, the advantage of implementing an MRC circuit prior to the FEC circuit allows the receiver to obtain better performance in low signal to thermal noise (SNR) environments, such as additive white Gaussian noise (AWGN) environments.  
         [0007]     Although adequate for most situations, there are situations where the undistorted channels are combined with distorted channels, which produces a distorted input to the FEC algorithm. The combination of a distorted signal (that has a good quality measurement) and an undistorted signal may degrade the system performance. Thus, the FEC algorithm may be undesirably corrupted by the bad signal, which produces an output error, such as an audio mute in an SDAR system. In this situation, the receiver may actually use corrupted signals that appear to be in a usable condition. For example, a terrestrial signal, which may be typically corrupted more so than satellite signals, is then passed through the MRC into the FEC, which outputs an error, where, conversely, if only the satellite signal was used, no error would have occurred. Accordingly, it is therefore desirable to provide a satellite-based digital audio radio receiver that finds wireless satellite signals and minimizes errors in the receiver system to improve the overall system performance such that undesirable errors, such as audio mutes, do not occur.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention relates to a receiver. Accordingly, one embodiment of the invention is directed to a receiver that includes a channel decoder select circuit, a plurality of communication channels, at least one maximum ratio combiner circuit, and a forward error correction circuit. The plurality of communication channels receives wireless information from channel demodulators and are in communication with respective channel decoder circuits, which are in communication with the channel decoder select circuit. The at least one maximum ratio combiner circuit receives the wireless information from the plurality of communication channels. The output of the maximum ratio combiner is communicated to the forward error correction circuit, the output of which is communicated to the channel decoder select circuit. A pseudo bit error measurement feedback signal communicated to the maximum ratio combiner from one of the plurality of channel decoder circuits.  
         [0009]     Another embodiment of the invention is directed to a receiver that includes first and second wireless signals provided from respective first and second satellite channel demodulators, and a third wireless signal provided from a terrestrial channel demodulator. First, second, and third pseudo bit error measurement signals corresponding to the first, second, and third wireless signals are communicated to a maximum ratio combiner, and a Reed-Solomon decoder processes the output of the maximum ratio combiner.  
         [0010]     A method for finding wireless satellite signals that minimizes errors in a receiver system is also disclosed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0012]      FIG. 1  illustrates a known satellite-based digital audio radio services receiver;  
         [0013]      FIG. 2  illustrates another known satellite-based digital audio radio services receiver;  
         [0014]      FIG. 3  illustrates a satellite-based digital audio radio services receiver according to one embodiment of the invention;  
         [0015]      FIG. 4  illustrates a satellite-based digital audio radio services receiver according to another embodiment of the invention;  
         [0016]      FIG. 5  illustrates a satellite-based digital audio radio services receiver according to another embodiment of the invention; and  
         [0017]      FIG. 6  illustrates a satellite-based digital audio radio services receiver according to another embodiment of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     The above described disadvantages are overcome and a number of advantages are realized by the inventive receivers that are illustrated in  FIGS. 3-6 . As illustrated in  FIG. 3 , a receiver  10  includes a plurality of communication channels, which are labeled Channel  1  through Channel N. Channels  1  through N receive information from channel demodulators and are each input into an MRC  12 , whose output is communicated to FEC  14   a  over line  2 . Channels  1  through N are also each input to respective FEC circuits  14   b ,  14   n . Feedback from the FEC circuit  14   n  is communicated over line  5   a  to the MRC  12 , which is explained in greater detail below. The output of the FECs  14   a ,  14   b ,  14   n  (i.e. channel decoder circuits) is communicated to an FEC Select circuit  16  (i.e. channel decoder select circuit) over lines  3 ,  4 ,  5   b , respectively. The FEC select circuit  16  outputs the FEC path that contains the minimum number of decoded errors. The minimum error output of the FEC Select circuit  16  is communicated over line  6  to a source decoder that converts the data to audio.  
         [0019]     Communication Channels  1  through N may carry any desirable signal. According to one embodiment of the invention, if the receiver  10  is a satellite digital audio radio services (SDARS) receiver, two, three or four channels may be implemented in a design that includes multiple FEC circuits to receive satellite and terrestrial signals. For example, Channel  1 - 3  may carry satellite signals and Channel  4  may carry terrestrial signals. If desired, an additional MRC circuit may be implemented in the design of the receiver  10  such that one MRC processes (i.e. adds) terrestrial and satellite signals communicated over multiple channels and the second MRC processes (i.e. adds) only satellite signals communicated over other multiple channels. Essentially, the receiver  10  takes advantage of both the MRC and FEC signal switching methods such that multiple FECs are being processed and the FEC circuit having the best output is selected by the FEC Select  16 . The FEC path, which is seen over communication lines  2 ,  3  that includes the MRC circuit  12 , may be selected when the receiver  10  encounters a weak SNR environment and provides the channel decoder extra small signal performance (i.e. small signal to noise performance) to ensure that a strong corrupted signal (i.e. a signal having a signal to interference ratio) does not contaminate the channel decoder output, which results in a cross-mute.  
         [0020]     In operation, the FEC circuits  14   a - 1   4   n  may be ‘time sliced.’ Essentially, the FEC circuits  14   a - 14   n  can share the same hardware (circuits) and process each path during a specific time interval. All of the channels may appear to carry a usable signal, however, corrupted signals may be detected quicker by phasing-out the MRC circuit  12 , thus providing the best signal for the source decoder. Without the additional FEC processing, undetected corrupted signals cause system degradation. The additional FEC circuits  14   a - 14   n  essentially act as independent error correction devices in the receiver  10  such that when a corrupted signal is used in the MRC, the receiver  10  is able to detect an error and switch to a FEC circuit that is processing satellite signals.  
         [0021]     The FEC circuit  14   n  also provides pseudo-bit error measurement feedback to the MRC  12 . According to one possible implementation of the receiver system, Channel N, which communicates with the FEC circuit  14   n  and the MRC  12 , may carry the terrestrial signal. When received in cities, the terrestrial signal typically encounters multipath conditions, which can lead to inter-symbol-interference. This phenomenon can also cause the received terrestrial signal to appear strong. Strong signals may become corrupted via the inter-symbol-interference when a far away repeater is seen by the antenna and a near repeater is blocked. The far away repeater may be on a different multi-carrier-modulation (MCM) symbol, Orthogonal Frequency Division Multiplexing (OFDM) symbol, or coded OFDM (COFDM) symbol than the near repeater, which results in the corrupted signal or error. The actual signal level may be sufficient signal to noise, but the environment has corrupted the signal information before it reaches the antenna. If the terrestrial signal is corrupted, the receiver detects the corrupted signal and provides feedback over line  5   a  so that the combined terrestrial and satellite signal is not used by the source decoder. Thus, the use of the FEC circuits  14   b  through  14   n  allows the receiver  10  to quickly detect when one signal is corrupted, and if neither signal is corrupted, the MRC  12  does not get phased out.  
         [0022]     Referring now to  FIG. 4 , another embodiment of the receiver is seen generally at  100 . The receiver  100  also includes a plurality of communication channels, which are labeled Channel  1  through Channel N. In this embodiment, Channel N is directly input to an FEC  104   n  while Channel  1  is input to an FEC  104   a  via a switch  108 . Channels  1  though N are also input into an MRC circuit  102  whose output also communicates over line  2  with the FEC  104   a  via the switch  108 . Similar to the operation of the receiver  10  described above, feedback from the FEC circuit  104   n  is communicated over line  8   a  to the MRC  102 . The FEC  104   a  also receives a feedback signal over line  9 , which is labeled “Error Detection Signal From System Controller.” More specifically, the feedback signal may be an uncorrectable error detection signal from the Reed Solomon Decoder. The bit error may arise from a corrupted terrestrial signal, a corrupted satellite signal, or even a combination of usable signals that when added together, results in an error. The output of the FECs  104   a ,  104   n  (i.e. channel decoder circuits) is communicated to an FEC Select circuit  106  (i.e. channel decoder select circuit) over lines  7 ,  8   b  respectively. The output of the FEC Select circuit  106  is communicated over line  6  to the source decoder that converts the data to audio.  
         [0023]     Functionally, the MRC circuit  102  of the receiver  100  is disabled when the signal levels from Channels  1  through N are strong, and conversely, the MRC circuit  102  may be activated when the signal levels from Channels  1  through N are weak. Accordingly, some protection is provided against a strong corrupted signal dominating the input of the MRC circuit  102  and FECs  104   a ,  104   n . The receiver  100  may be able to estimate the strength of the received corrupted signal relative to the noise floor since narrow band power detection may be available to the system microcontroller.  
         [0024]     In this embodiment, the switch  108  may be adjusted based on the terrestrial and satellite power level seen by the receiver. For example, Channel  1  may carry the satellite signal and Channel N may carry the terrestrial signal. In this scenario, the receiver  100  may just look at the terrestrial and satellite signals independently by positioning the switch  108  at position B to monitor each signal on the respective FEC circuits  104   a ,  104   n . Conversely, the terrestrial and satellite signals maybe combined and monitored by positioning the switch  108  to position A such that the receiver sees the output from the MRC  102  at line  2 . Thus, signal processing time may be saved because one less FEC block is implemented (in view of  FIG. 3 ), however, additional hardware is needed to enable the receiver  100  to choose whether or not the MRC circuit  102  is to be used. Even further, the receiver  100  is less complex than the receiver  10  (because there aren&#39;t as many FECs) while also providing channel decoding enhancements. Essentially, the switch  108  acts as a blind switch because the receiver  100  does not look for all error possibilities simultaneously, whereas the receiver  10  does.  
         [0025]     Essentially, if all of the received signals from the Channels are sufficiently strong in the signal noise estimation, then the receiver  100  operates by just using the FECs  104   a ,  104   n  without the MRC  102 , because, if the signals are good to begin with, there is no need to use the MRC  102 . Accordingly, the receiver  100  keeps track of the occurrence of a bad signal (e.g. a corrupted terrestrial signal) input to an FEC. Conversely, if a weak signal is present, then the receiver  100  takes advantage of the MRC circuit  102  because the corrupted signal may not be some type of interference, but rather, noise.  
         [0026]     Referring now to  FIG. 5 , another embodiment of the receiver is seen generally at  200 . The receiver  200  also includes a plurality of communication channels, which are labeled A, B, and C. Communication channels A and B receive information from Satellite Channel Demodulators  1  and  2 , respectively, whereas, communication channel C receives information from a Terrestrial Channel Demodulator. As illustrated, communication channels A, B, C are directly fed into an MRC weighting block, which is seen generally at  202 , the output of which is communicated to an MRC  204  over lines  11 ,  13 ,  15 . The output of the MRC  204  is communicated over line  17  to an FEC circuit  206 , the output of which is communicated over line  19  to an FEC Select circuit  208 .  
         [0027]     In this embodiment, communication channel C, which carries the terrestrial signal, is split three ways. The first split enters the MRC weighting block  202 , the second split enters a hard detection circuit  212 , and the third split enters an FEC circuit  214 . The output of the FEC circuit  214  is communicated to an encoder  216  and to the FEC Select circuit  208  over line  21 . The output of the encoder  216  is communicated to a pseudo bit error rate (BER) circuit  218  over line  23 , which also receives the output of the hard detection circuit  212  over line  25 . The output of the pseudo BER circuit  218  is communicated over  27  to a weighting algorithm  220 , the output of which is communicated over line  29  to the MRC weighting block  202 .  
         [0028]     The receiver  200  permits weighting of a multi-carrier OFDM or COFDM signal, such as the terrestrial signal, into the MRC circuit  204  by using a pseudo bit error rate of the FEC circuit  214 . The FEC circuit  214  receives information over communication channel C in the form of soft bits (i.e. 0.50 or 0.25 are considered soft bits, whereas 1 or 0 are considered hard bits). In an SDARS implementation associated with the illustrated receiver  200 , the FEC circuit  214 , which may comprise a Viterbi or Turbo decoder, decodes soft bits and outputs hard bits, which are subsequently re-encoded by the encoder  216  into hard bits. Assuming that the output of the FEC circuit  214  is truth data (i.e. a corrected, decoded signal), the encoder  216  outputs hard bits that correspond to a corrected signal. The received transmitted signal from communication channel C is simultaneously processed by the hard detection circuit  212 , which produces a hard bit of the original terrestrial signal. The hard decision output and FEC corrected data output seen at lines  23 ,  25  is compared by the pseudo BER circuit  218 . As illustrated, the weighting algorithm  220  receives the output of the pseudo BER circuit  218 . The weighting algorithm may comprise a look-up table or other non-linear control, and is based upon the number of estimated errors for uncorrected bit error rates.  
         [0029]     The MRC weighting block  202  receives the output from the weighting algorithm  220  at a weighting amplifier  222   c . Two additional weighting amplifiers  222   a ,  222   b  process an SNR estimation and the information received from Satellite Channels  1  and  2  over communication lines A and B, respectively. The SNR estimation may be based on the power level into the receiver  200 , which may be signal power or noise power. The SNR estimation may also include a straight power detection where noise is assumed at some level, a correlation measurement where some known data signal is auto-correlated and compared to noise, or an examination at the carrier tracking loop (i.e. a noisy loop indicates a lower signal to noise ratio). The output of each weighting amplifier  222   a - 222   c  is communicated to the MRC circuit  204 . Functionally, the output of the MRC  204 , FEC  206 , and FEC  214  that is communicated into the FEC Select  208  behaves in a similar fashion as described above with respect to the receivers  10 ,  100 .  
         [0030]     Referring now to  FIG. 6 , another embodiment of the receiver is seen generally at  300 . The receiver  300  also includes a plurality of communication channels, which are labeled A, B, and C. Communication channels A and B receive information from Satellite Channel Demodulators  1  and  2 , respectively, whereas, communication channel C receives information from the Terrestrial Channel Demodulator. Similar to the receiver  200 , the receiver  300  provides a pseudo-bit error measurement prior to processing at the MRC circuit  308 . As illustrated, communication channels A, B, C are directly fed into convolutional decoders  302   a - 302   c  and Pseudo BER circuits  306   a - 306   c  over communication lines  33   a - 33   c , respectively. The output of the convolutional decoders  302   a - 302   c  are communicated to convolutional encoders  304   a - 304   c  over lines  35   a - 35   c , and an MRC circuit  308  over communication lines  37   a - 37   c , respectively. The output of the convolutional encoders  304   a - 304   c  are communicated to the Pseudo BER circuits  306   a - 306   c . The output of the Pseudo BER circuits  306   a - 306   c  is also communicated to the MRC circuit  308  over lines  39   a - 39   c . The output of the MRC circuit is communicated over line  41  to a Reed-Solomon decoder  310 , the output of which is communicated over line  43 .  
         [0031]     In this embodiment, the elements comprising an FEC circuit is split between the MRC circuit  308 . The FEC circuit typically includes a convolutional decoder, seen at elements  302   a - 302   c , and a Reed-Solomon decoder, seen at element  310 . In the illustrated SDARS-related implementation, the convolutional decoder  302   a - 302   c  may be Viterbi or Turbo decoders, which produces the inner code of a concatenated code. The Reed-Solomon decoder, on the other hand, produces the outer code of a concatenated code. As illustrated, the convolutional decoder  302   a - 302   c , convolutional encoder  304   a - 304   c , and pseudo BER  306   a - 306   c  each provide the MRC circuit  308  with an approximated bit error rate on the inner code and the Reed Solomon detector  310  provides improved signal to noise estimates based on the bit error rates.  
         [0032]     Accordingly, by ‘splitting the FEC circuit,’ the number of Reed-Solomon circuits is reduced to one unit that serves a plurality of convolutional decoders, which also reduces the number of computations carried out in the associated software. The output of the Reed-Solomon circuit  310  is time-division multiplexed such that the source decoder may acquire the desired data aligned in a specific time-slot. Although not illustrated, the MRC circuit  308  includes the weighting algorithm which can be carried out by a multiplier in an application specific integrated circuit (ASIC), based on the SNR to ensure that a good signal is not degraded by the noise of a bad signal.  
         [0033]     The present invention has been described with reference to certain exemplary embodiments thereof. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the exemplary embodiments described above. This may be done without departing from the spirit of the invention. The exemplary embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is defined by the appended claims and their equivalents, rather than by the preceding description.