Patent Application
20090003498
The present invention generally relates to a system and method for receiving signals, and more particularly, to a system and method for receiving signals on multiple antennas and combining the multiple signals.
Generally, when a receiver is mobile, such as being located onboard a vehicle, the probability of the antenna of the receiver being blocked and unable to receive the signal generally is more likely than if the receiver was non-mobile. When the antenna is blocked, the receiver typically does not adequately receive the signal and cannot produce a proper output. One way of increasing the probability that the receiver will receive the signal while the receiver is mobile is to transmit multiple signals and include multiple antennas on the receiver for receiving the multiple signals.
There are several techniques that have been developed for receiving the multiple signals when using multiple antennas. One such technique is the scanning/selection or switching diversity technique, which generally operates on the premise that if one antenna disposed on the vehicle is receiving a poor signal, another antenna spaced from the first antenna may be receiving a better signal. Thus, only one antenna is typically used for receiving the signal at any particular point in time. Generally, the system either compares the signals that are being received by the system's antennas to ascertain which antenna is receiving the better quality signal, or the system evaluates the signal received by a single antenna to determine a quality of the signal and simply switches to another antenna if the current signal is designated as unacceptable. However, the switching transients caused by switching between antennas can be audible under some circumstances, and since only one antenna is typically used at any point in time, the system may provide only marginal improvement during fringe reception when compared to single antenna systems.
Another technique is the equal-gain combining technique, which generally combines signals received by the antennas and an antenna array by correcting the phase differences between antennas, and then adding the signals coherently. Typically, no adjustments are made to the signals for any difference in the gains of the input signals, because only the phases of the input signals are adjusted for alignment in an equal-gain system. However, it is possible that the signal-to-noise ratio may be less than optimal. For example, if two inputs are combined, and one of those inputs contains mostly noise, the combined signal is likely to be of lower quality than the single non-corrected signal. In such a situation, it generally would have been ideal to use only the signal from the antenna that was not mostly noise.
According to one aspect of the present invention, a receiver system includes a plurality of antennas that receive signals, a plurality of tuners, a signal combiner, and a symbol timing combiner. The plurality of antennas are approximate to one another. The plurality of tuners are in communication with the plurality of antennas, and the received signals are communicated to the plurality of tuners from the plurality of antennas. The signal combiner is in communication with the plurality of tuners, and combines an output of each of the plurality of tuners. The symbol timing combiner is in communication with the signal combiner and the plurality of tuners, and a combined output of the combiner is received by the symbol timing combiner. The symbol timing combiner emits a combined symbol timing output that is received by each of the plurality of tuners, such that the plurality of tuners process the signals communicated from the plurality of antennas based upon the combined symbol timing output.
According to another aspect of the present invention, a method of receiving signals includes the steps of receiving a signal by at least one of a plurality of antennas, communicating the signal from the plurality of antennas to a plurality of tuners, and combining an output of each of the plurality of tuners. The method further includes the steps of communicating a combined symbol timing output to the plurality of tuners, where the combined symbol timing output is based upon the combined output, and processing the signal by each of the plurality of tuners based upon the combined symbol timing output.
According to another aspect of the present invention, a method of receiving signals includes the steps of providing first and second antennas having at least partially overlapping first and second antenna patterns, respectively, communicating signals from the first and second antennas to first and second tuners, respectively, and combining an output of each of the first and second tuners. The method further includes the steps of determining a combined symbol timing output by a symbol timing combiner, wherein the symbol timing combiner receives the combined output and outputs from each of the first and second tuners, communicating the combined symbol timing output to the plurality of tuners, and processing the signal and maintaining symbol timing lock by each of the plurality of tuners based upon the combined symbol timing output.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
In reference to
The receiver system 10 also includes a plurality of tuners that are in communication with the plurality of antennas. Typically, a first tuner 16 of the plurality of tuners is in communication with the first antenna 12, and a second tuner 18 of the plurality of tuners is in communication with the second antenna 14. The receiver system 10 also includes a signal combiner generally indicated at 20 that is in communication with each of the plurality of tuners, such that the signal combiner 20 combines an output of the first and second tuners 16,18. It should be appreciated by those skilled in the art that any number of antennas 12,14, and tuners 16,18 can be used, so long as at least a portion of the antennas 12,14 are proximate to one another.
Generally, the maximal-ratio combining (MRC) technique of combining the signals includes adjusting the input signals according to the detected phase thereof, the magnitudes of the input signals are adjusted according to the detected phase thereof, and the magnitudes of the input signals are adjusted to yield the maximum signal-to-noise ratio. Typically, there are two methods available for implementing the MRC technique. According to one embodiment, the first method combines the antenna outputs using analog or digital circuitry. However, this method can be very expensive and complex to design due to the proper phase alignment and high-speed requirements. According to another embodiment, the second method of the MRC technique performs the combining at base band, such that each antenna path is down-converted from the radio frequency (RF). Further, the phase of the RF carrier is determined and processed through a matched filter, and the symbol timing is determined independently for each antenna path.
However, when one of the signals is blocked, and one of the antennas of a receiver system using the MRC technique does not receive the blocked signal, the receiver associated with the blocked antenna typically loses phase and symbol timing lock. When the antenna becomes un-blocked, and the receiver begins to receive the signal, the receiver must re-establish phase and symbol timing lock of the signal for the un-blocked antenna. Typically, re-establishing phase and symbol timing lock for the signal can cause the receiver to emit an undesirable output.
According to one embodiment, the receiver system 10 further includes a symbol timing combiner device 22 that is in communication with the signal combiner 20 and the first and second tuners 16,18. A combined output of the signal combiner 20 and outputs from each of the first and second tuners 16,18 are received by the symbol timing combiner device 22. The symbol timing combiner device 22 determines a combined symbol timing output that is received by each of the first and second tuners 16,18. Thus, the first and second tuners 16,18 process the signals received from the first and second antennas 12,14, respectively, based upon the combined symbol timing output. It should be appreciated by those skilled in the art that the first and second tuners 16,18 and the receiver system 10 can include additional suitable components or devices for processing the signals.
According to one embodiment, the signal combiner 20 includes a weight computation device 24 and an MRC coherent combiner device 26. The weight computation device 24 receives an input from each of the first and second tuners 16,18, and determines a required number of samples for each of the inputs from the first and second tuners 16,18 in order for the weight computation device 24 to emit an output at a suitable signal-to-noise ratio (Eb/No). Thus, the output of the weight computation device 24 is typically a value communicated to the MRC coherent combiner device 26, such that the MRC coherent combiner device 26 can emit an output that is biased towards a stronger signal communicated to the signal combiner 20 from the tuners 16,18. The output of the weight computation device 24 is received by the MRC coherent combiner device 26 and the symbol timing combiner device 22. The MRC coherent combiner device 26 combines the outputs of the first and second tuners 16,18 based upon the output of the weight computation device 24. The MRC coherent combiner device 26 then emits an audio and/or video output 28.
In reference to both
By way of explanation and not limitation, when a signal is received by only the first antenna 12, such that the signal is being received through the non-overlapping portion of the first antenna pattern 32, the symbol timing combiner device 22 determines a combined symbol timing rate based upon only the signal received by the first antenna 12. The symbol timing combiner device 22 communicates the combined symbol timing output, which is only based upon the symbol timing of the signal received by the first antenna 12 at this time, to the first and second tuners 16,18. Thus, the second tuner 18 does not lose symbol timing lock, because the combined symbol timing output can be used to maintain symbol timing lock by the second tuner 18, while the second antenna 14 is not receiving a signal due to the proximate location of the second antenna 14 to the first antenna 12. Thus, the symbol timing of the signal received by the first antenna 12 sufficiently corresponds to the symbol timing of the blocked signal not being received by the second antenna 14, such that the symbol timing of the two signals can be substituted for one another, and the first and second tuners 16,18 have a symbol timing value to maintain symbol timing lock even when the associated antenna 12,14 is not receiving a signal.
According to one embodiment shown in
In reference to
The method 100 then proceeds to step 110, where the output of the signal combiner 20 is communicated to symbol timing combiner device 22. The output of the signal combiner 20 includes outputs from the weight computation device 24 and the MRC coherent combiner device 26. The symbol timing combiner device 22 combines the outputs of the signal combiner 20 at step 112. The symbol timing combiner device 22 emits a symbol timing combined output at step 114.
The method 100 includes the symbol timing combined output being communicated back to the plurality of tuners, so that the plurality of tuners can process the signals based upon the symbol timing combined output at step 108. Thus, at step 116, the plurality of tuners maintain symbol timing lock. An output is emitted at step 118, and the method ends at step 120.
Advantageously, the receiver system 10 and method 100 determine a combined symbol timing output that is used by the plurality of tuners, when processing the signals received by the plurality of antennas in order for each of the plurality of tuners to maintain symbol timing lock. Thus, when an antenna of the plurality of antennas is blocked and does not receive a signal, the tuner associated with the blocked antenna does not lose symbol timing lock, which typically takes a considerable amount of time to re-establish once the blocked antenna becomes un-blocked and begins receiving the signal again. Thus, the combined symbol timing output is an adequate value in order for the plurality of tuners to maintain symbol timing lock even though it is not the exact symbol timing rate that would be received by the signal. The combined symbol timing output can be used to maintain symbol timing lock for the plurality of receivers due to the proximate location of the plurality of antennas to one another.
The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.
