Patent Application
20120245845
In data communication systems, certain environments can cause multi-path signals to be received at the same receiver. In other words, copies of the signal radiated from a transmit antenna travel different paths to the receiver antenna. The different paths result in phase differences which causes interference and noise at the receiver antenna.
In one embodiment, a system is provided. The system comprises an outer shell having an inner spherical cavity and an inner sphere located in the spherical cavity of the outer shell. The inner sphere comprises a sensor configured to obtain data; at least three transmit antennas each configured to radiate signals at a respective transmit frequency; and at least three transmitters each coupled to the sensor and to a respective one of the at least three transmit antennas, each of the at least three transmitters configured to control transmission of the sensor data via the respective at least one transmit antennas. The system also comprises at least three receive antennas each located in the spherical cavity of the outer shell, wherein each of the at least three receive antennas is frequency matched to the transmit frequency of a respective one of the at least one transmit antennas. The system also comprises at least three receivers each coupled to a respective one of the at least three receive antennas, each of the at least three receivers configured to process a signal received at the respective receive antenna; and a data selection logic circuit coupled to the at least three receivers and configured to select at least one signal from the signals received from each of the at least three receivers based on the respective signal quality of the received signals.
Understanding that the drawings depict only exemplary embodiments and are not therefore to be considered limiting in scope, the exemplary embodiments will be described with additional specificity and detail through the use of the accompanying drawings, in which:
In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the exemplary embodiments.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. However, it is to be understood that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. Furthermore, the method presented in the drawing figures and the specification is not to be construed as limiting the order in which the individual steps may be performed. The following detailed description is, therefore, not to be taken in a limiting sense.
In the exemplary embodiment of
The sensor 110 provides data to the transmitters 108-1 . . . 108-N for transmission through the spherical cavity 106. In particular, the sensor 110 provides the same data to each of the plurality of transmitters 108-1 . . . 108-N. Each of the transmitters 108-1 . . . 108-N control modulation of a signal radiated from a respective one of a plurality of transmit antennas 112-1 . . . 112-N. Each of the transmit antennas 112-1 . . . 112-N is configured to radiate signals at a predetermined transmit frequency. The predetermined frequency for each transmit antenna 112 is different than the predetermined transmit frequency of the other transmit antennas 112. For example, in one embodiment, transmit antenna 112-1 is configured to transmit at 900 MHz, transmit antenna 112-2 is configured to transmit at 2.4 GHz, and the transmit antenna 112-N is configured to transmit at 5.6 GHz. It is to be understood that these transmit frequency values are provided by way of example and not by way of limitation. In particular, each of the transmit antennas 112 can be configured to transmit in any appropriate radio frequency band such as the Ultra High Frequency (UHF) band, S-band, or L-band. Each transmitter 112-1 . . . 112-N is fed by the same oscillator clock source 109 for data coherency. The inner sphere 102 includes a respective slit or opening for each of the transmit antennas 112 to transmit data. Thus, in this example, the transmit antennas 112 are isolated inside the inner sphere 102 to reduce noise.
Located inside the spherical cavity 106 are a plurality of receive antennas 116-1 . . . 116-N. For example, in some embodiments, each receive antenna 116 is located in a position that is approximately ½ wavelength from the other transmit antennas. The wavelength is the wavelength corresponding to the respective signal frequency received at receive antennas 116. However, it is to be understood that the location of the receive antennas 116-1 . . . 116-N may be different in other embodiments based on various factors, such as, sizes of sphere 102 and shell 104, and configuration of components in the spherical cavity 106.
Each receive antenna 116 is frequency matched to the transmit frequency of one of the transmit antennas 112. For example, receive antenna 116-1, 116-2, and 116-N can be frequency matched to the transmit frequency of transmit antenna 112-1, 112-2, and 112-N, respectively. Due to the spherical cavity 106 and movement of the inner sphere 102 in the spherical cavity 106, each of receive antennas 116-1 . . . 116-N receives multiple versions of the same signal, each version travelling a different path. The multi-path signals received at each antenna 116 can cause increased noise or interference in the signal received. In addition, as the inner sphere 102 moves within the spherical cavity 106, one of the receive antennas 116 can be blocked by other components in the spherical cavity 106 which further reduces the signal to noise ratio. However, since the signals transmitted by the transmit antennas 112-1 . . . 112-N are redundant, when one of the receive antennas 116-1 . . . 116-N is blocked, the other antennas 112 are located to be off-centered from the blocking component.
Furthermore, the system 100 is configured to mitigate the interference effects of the multi-path signals. In particular, each transmit antenna 112-1 . . . 112-N is coupled to a respective receiver 120-1 . . . 120-N. Each receiver 120 is configured to demodulate the signal received from its respective receive antenna 116 and bit synchronize the demodulated signal data. In some embodiments, each transmitted signal includes error coding such as Forward Error Coding (FEC). In such embodiments, each receiver 120 uses the FEC to correct errors if applicable. Each receiver 120 is coupled to the same oscillator clock 121 for data coherency. The bit rate time coherent (synchronized) data from each of the receivers 120 is provided to a data selection logic circuit 122.
The data selection logic circuit 122 is configured to determine the quality of the respective data signals received from the receivers 120-1 . . . 120-N. Based on the respective signal quality, the data selection logic circuit 122 selects at least one data signal to be passed on to a processing unit 124. In this example, the data selection logic circuit 122 uses a cyclic redundancy check (CRC) to determine the quality of each respective data signal. In some embodiments, the data selection logic circuit 122 selects a subset of the total number of data signals received. In particular, the data selection logic circuit 122 selects the subset of signals having the higher quality based on the CRC. For example, in embodiments using three redundant data signals, the data selection logic circuit 122 can be configured to select the two signals with the better quality. In other embodiments, the data selection logic circuit 122 is configured to select the single data signal with the best quality of the plurality of data signals received.
A signal having better quality can be determined by comparing the CRC values. For example, each block of data in a given signal is sent with a calculated check value or CRC. The data selection logic circuit 122 calculates the CRC for each block of data and compares the calculated result to the CRC sent with the block of data. If they match, no error is detected in that block of data. Signals having better quality will have fewer blocks of data with detected errors. In other words, by comparing the number of detected errors for each signal, the data selection logic circuit 122 is able to determine which signals have better quality.
In other embodiments, the data selection logic circuit 122 is configured to select a user defined default signal provided that the default signal passes a quality check. For example, if a user configures the data selection logic circuit 122 to select the signal from receiver 120-1 as the default signal, then data selection logic circuit 122 checks the CRC of the blocks in the signal from the receiver 120-1. If the signal passes the CRC check, then the data selection logic circuit 122 selects the signal from receiver 120-1. For example, if the number of detected errors is less than a predetermined threshold, the signal passes the CRC check. If the signal does not pass the CRC check, then the data selection logic circuit 122 checks the CRC of one of the other signals and selects the next signal which passes the CRC check.
The data selection logic circuit 122 outputs the selected signal to a processing unit 124. The processing unit 124 uses the selected signal from the data selection logic circuit 122 for additional processing depending on the implementation of the sensor 110. For example, in some embodiments, the sensor 110 is an IMU that outputs inertial navigation data which is used by the processing unit 124 in calculating navigation parameters. The navigation parameters can be output to a display unit 128 for display to a user. In addition, the navigation parameters can be commands output to one or more actuators to control movement of a vehicle in which the sensor system 100 is located. The implementation of the actuators is dependent on the vehicle. For example, in an aircraft, the processing unit can output commands to control engine thrust, wing flaps, etc. It is to be understood that implementations of the sensor system 100 are not to be limited to navigation sensors and data and that other sensor systems can communicate other data from the sensor 110 to the receiver 120 via the spherical cavity 106.
At block 204, each of the transmitted signals is received via multiple paths at a respective one of at least three receive antennas located in the spherical cavity. Each of the at least three receive antennas is frequency matched to one of the at least three transmit antennas. At block 206, each of the received signals is processed in a respective receiver located outside the spherical cavity. Processing the signals includes demodulating and bit synchronizing the received signals. In particular, each receiver is coupled to the same local oscillator for data coherency between the different receivers. In addition, in some embodiments, processing the signals includes performing error correction using coding such as forward error coding.
At block 208, the processed signals from each of the receivers is provided to a data selection logic circuit where at least one of the signals is selected based on the respective signal quality of the signals. For example, the signal quality can be determined using a CRC calculation for the data blocks in each signal. At block 210, the at least one selected signal is output. For example, the at least one selected signal can be output to a processing unit for navigation or other processing as described above.
If the total number of detected errors is greater than the threshold, then the default signal does not pass the quality check and the signal quality of a second signal is determined at block 406. The second signal to be checked can also be predetermined by a user. At block 408, the signal quality of the second signal is checked. If the second signal passes the quality check, then the second signal is selected at block 410. If the second signal does not pass the quality check, then the signal quality of another signal is determined at block 406. The acts of blocks 406 and 408 are then repeated until either a signal is found that passes the quality check or no more signals remain to be checked.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.
This application is related to U.S. patent application Ser. No. ______ (attorney docket number H0028909-5478) entitled “RF DATA TRANSFER IN A SPHERICAL CAVITY” filed on even date herewith and which is referred to herein as the '909 application. The '909 application is hereby incorporated herein by reference.
