Signal Receiving Apparatus and Method

The present application is related to a patent application Ser. No. 920,317, now U.S. Pat. No. 4,209,828 which was filed on June 28, 1978 by D. L. Rush et al and entitled "Speed Decoding And Speed Error Determinating Control Apparatus And Method".

It is known in the prior art to provide a signal receiving apparatus for responding to an applied signal from an input device such as an antenna to produce a decoded serial or parallel binary data output. The well known, modem apparatus in current use with telephone line communication systems, includes such a signal receiving apparatus. The use of multiple bandpass filter devices for decoding an input signal is shown in U.S. Pat. No. 3,810,161 of A. P. Sahasrabudhe, in U.S. Pat. No. 3,966,149 of T. C. Matty et al. and in U.S. Pat. No. 4,015,082 of T. C. Matty.

An article, entitled "Atlanta Airport People Mover" that was published in the Conference Record of the 28th IEEE Vehicular Technology Group for a Denver, Colorado meeting in March 1978, describes a prior art information transfer system operative with a vehicle stopped in a passenger station.

Another article, entitled "Recent Applications of Microprocessor Technology To People Mover Systems" that was published in the Conference Record of the 29th IEEE Vehicular Technology Group for a Chicago, Illinois meeting in March 1979, describes a prior art information transfer system operative with a vehicle stopped in a passenger station.

An additional article entitled Sao Paulo Metro E-W Line Innovations was published in the Conference Record of the IEEE Industry Applications Society for a Los Angeles California meeting in October 1977 and discloses the use of a train identification system including a high speed communication link to load a train identification information signal message.

An input signal receiving apparatus provides decoding to determine if one or more of desired signal frequency components are present in a given input signal. A predetermined noise rejection operation is provided from a selected number of samples of that input signal that are taken, with the actual frequency discrimination being determined by establishing the number of such samples that are taken for this purpose in relation to known desired signal frequency components to be identified. The input signal samples are compacted in accordance with the known desired frequency signal to accentuate the desired frequency components to be detected. Correlation coefficients are established for each of selected sine and cosine reference waves that are selected in accordance with the known signal frequency components, which sine and cosine coefficients are used as multipliers and the resulting products are summed to provide a magnitude in relation to each of the desired signal frequency components. A multiple comparison is made of these magnitudes with each other and with predetermined threshold values to provide the required detection of the desired frequency signal components.

FIG. 1 is a functional block diagram of a prior art input signal receiver apparatus;

FIG. 2 shows the input signal receiving apparatus of the present invention;

FIG. 3 graphically shows the input signal divided into a selected group of data samples and in relation to the f1 reference wave and the f2 reference wave;

FIG. 4A and B taken together show the compacting operation and the fourier transform operation applied to determine one of the first frequency f1 component or the second frequency f2 component in the input signal;

FIG. 5 shows the fourier transform operation performed in relation to a sine wave to determine the desired first frequency f1 component in the input signal;

FIG. 6 shows the fourier transform operation performed in relation to a cosine wave to determine the desired first frequency f1 component in the input signal;

FIG. 7 shows the fourier transform operation performed in relation to a sine wave to determine the desired second frequency f2 component in the input signal;

FIG. 8 shows a fourier transform operations performed in relation to a cosine wave to determine the presence of the desired second frequency f2 component in the input signal;

FIG. 9 shows a typical FSK coded information message signal;

FIG. 10 shows a typical information message signal transfer apparatus provided to transfer information signals from a passenger station to a vehicle stopped in that station;

FIG. 11 shows a microprocessor program flow chart to provide the frequency signal component determination of the present invention;

FIG. 12 shows the comparison between desired frequency signal identification by prior art Fourier transform analysis techniques and by the present invention;

FIG. 13 shows the improved signal to noise ratio desired frequency signal identification in accordance with the present invention; and

FIG. 14 shows the hardware block diagram of the signal receiver in accordance with the present invention.

In FIG. 1, there is shown a prior art input signal receiver apparatus including an antenna 10 for receiving input signals from a suitable source a first bandpass filter 12 having a center frequency corresponding to the f1 signal component of the applied input signal and a second bandpass filter 14 having a center frequency corresponding to the f2 component of the applied input signal. The f1 and f2 signal components pass through an amplifier 18 to a discriminator 20 which has a data output 22 for providing either one of the f1 or f2 signal components received by the antenna 10 and a clock output 24 for synchronizing the subsequent processing of the frequency component data on output 22, such as by the control apparatus 26.

In FIG. 2, there is shown the input signal receiver apparatus for providing the input signal, including for example two desired frequency components, to the signal determination operation of the present invention and including an antenna 50 for receiving input signals from a suitable source, and an isolation transformer 52 which limits the current into the apparatus and protects against high voltage surges and provides isolation between the antenna and the subsequent receiver module. The bandpass filters 54 are high pass in design but due to the secondary inductance of the transformer 52, they are operative as effectively bandpass filters. The bandpass filter 54 removes low frequency components such as 720 Hz and limits the spectrum to the desired range of interest. A pre-amplifier 56 is provided for additional gain. A summing amplifier 58 sums the signals from the two desired signal frequency components, which could be provided by dual channel inputs, and provides a signal which is fed to a sample and hold circuit 60, which samples the input signal and holds the value for subsequent processing. A clipper 62 limits the input signal at each of plus and minus predetermined voltage values. An analog-to-digital converter 64 digitizes the analog signal and transfers it to a signal processor CPU 66. A program is stored in read only memory ROM which provides instructions to signal processing microprocessor or CPU 66. After processing has occurred, the CPU 66 outputs data to a flip-flop memory 68 in serial format. The desired f1 and the f2 signal frequency components are now identified and supplied to a subsequent control apparatus 70, such as for a controlled transit vehicle or the like.

As shown in FIG. 3, the known desired f1 frequency component is such that with twenty-four input signal samples taken, there are included two full cycles or groups of the f1 signal component, with each f1 signal component cycle including 12 samples. Compacting can be done to assist the determination of the f1 frequency signal component by superimposing the second group of twelve samples on the first group of twelve samples to provide a first improved input signal waveform. As shown in FIG. 3, the f2 frequency is such that with twenty-four input signal samples taken, there are included three full cycles or groups of the f2 signal component, with each f2 signal component cycle including 8 samples. Compacting can be done to assist the determination of the f2 frequency signal component by superimposing each of the second group of eight samples and the third group of eight samples on the first group of eight samples to provide a second improved input signal waveform. For this example, the f1 frequency can be 8.769 KHz and the f2 frequency can be 5.845 KHz.

For the purpose of example only, assume that input signal that is received by the antenna 50 includes four groups of twenty-four signal samples. These four groups of input signal samples are then respectively superimposed as will be later described to provide the summed input signal waveform 74 shown in FIG. 3. The twenty-four signal samples are selected because the desired f1 signal component is known to have two full cycles during the time period of the twenty-four samples as shown by curve 76, and the desired f2 signal component is known to have three full cycles during the time period of the twenty-four samples as shown by the curve 78.

In FIG. 4, there is shown a process chart of the operations performed in the signal processor CPU 66 in accordance with the present invention to determine the desired f1 and f2 frequency components in the input signal. At block 100, the antenna senses the input signal. At block 102, a first group of 24 initial data samples is taken. At block 104, a second group of 24 initial data samples is taken of the input signal and the second group of data samples is superimposed on the first group of data samples, such that the first samples of each group are summed, the second samples of each group are summed and so forth. At block 106, a third group of 24 initial data samples is taken and superimposed on top of the first two groups of data samples, such that the first samples of each group are summed, the second samples of each group are summed and so forth. At block 108, a fourth group of 24 initial data samples is taken and superimposed on top of the previous first, second and third groups of data samples, such that the first samples of each group are summed, the second samples of each group are summed and so forth. For purpose of example, assume that the curve 74 shown in FIG. 3 is the resulting summed waveform provided at block 108 from the described superimposition of these first, second, third and fourth groups of 24 initial input signal data samples.

At block 110, and as shown in FIG. 5, an input signal waveform 80 is determined in relation to the desired f1 frequency component, and in accordance with the known frequency relationship between f.sub.1 and f.sub.2, by superimposing the second 12 data samples shown by curve 74(B) of the summed input signal waveform 74 with the first 12 data samples shown by curve 74(A) of the summed input signal waveform 74, as shown in FIG. 3. It is to be understood that superimposing here is understood to include summing each of the first samples, each of the second samples and so forth.

At block 112, and as shown in FIG. 5, the data samples for each of the four indicated (1) positions of the now provided f1 frequency signal component waveform 80 are algebraically added together and multiplied by the value of the f1 frequency reference sine wave 82 at the (1) position. Since all of the (1) positions of the sine wave 82 have the same magnitude coefficient, by algebraically adding together the (1) position values of the waveform 80 these can then be multiplied once by the (1) position coefficient of the sine wave 82. At block 114, and as shown in FIG. 5, the data samples for each of the four indicated (2) positions for the f1 frequency signal component waveform 80 are algebraically added together and multiplied by the f1 frequency reference sine wave 82 value for the (2) position. At block 116, and as shown in FIG. 5, the data samples for the two indicated (3) positions of the f1 frequency signal component waveform 80 are algebraically added and then multiplied by the sine wave 82 value for the (3) position. At block 118, the respective products resulting from the operations in blocks 112, 114 and 116 are added in relation to the f1 frequency signal component. At block 120, and as shown in FIG. 6, the f1 frequency signal component waveform 80 values corresponding to the two indicated (1) positions of the f1 frequency reference cosine wave 84 are algebraically added and then multiplied by the cosine wave 84 value for the (1) position. At block 122 and as shown in FIG. 6, the f1 frequency signal component waveform 80 values corresponding to the four indicated (2) positions of the f1 frequency reference cosine wave 84 are algebraically added and then multiplied by the cosine wave 84 value for the (2) position. In block 124 and as shown in FIG. 6, the f1 frequency signal component waveform 80 values corresponding to the four indicated (3) positions of the f1 frequency reference cosine wave 84 are algebraically added and then multiplied by the cosine wave value for that (3) position. At block 126, the total of the above products obtained at blocks 120, 122 and 124 are added together in relation to the f1 frequency signal component. At block 128, the square of the f1 sine component obtained at block 118 is added to the square of the f1 cosine component obtained at block 126 and set equal to f1.sup.2.

The resulting summed waveform 74 of the superimposed four groups of 24 samples obtained at block 108 is operated on at block 130 such that the second eight data samples shown by curve 74(D) and the third eight data samples shown by curve 74(E) of that summed waveform 74 obtained at block 108 are superimposed on the first eight data samples shown by curve 74(C). At block 132 and as shown in FIG. 7, the data samples for each of the four indicated (1) positions of the now provided f2 frequency signal component waveform 86 are algebraically added together and multiplied by the value of the f2 frequency reference sine wave 88 for the (1) position. At block 134 and as shown in FIG. 7, the data samples values for each of the two indicated (2) positions of the f2 frequency signal component waveform 86 are algebraically added together and multiplied by the value of the f2 frequency reference sine wave 88 for the (2) position. At block 136, the respective products obtained in the blocks 132 and 134 are added together. At block 138, and as shown in FIG. 8, the f2 frequency signal component waveform 86 values corresponding to the two indicated (1) positions of the f2 frequency cosine wave 90 are algebraically added together and then multiplied by the value of the cosine wave 90 for the (1) position. At block 140 and as shown in FIG. 8, the f2 frequency signal component waveform 86 values corresponding to the four indicated (2) positions of the f2 cosine wave 90 are algebraically added together and multiplied by the value of the cosine wave 90 for the (2) position. At block 142, the products obtained at the respective blocks 138 an 140 are added together in relation to the f2 frequency signal component. In block 144, the square of the f2 sine component obtained at block 136 is added to the square of the f2 cosine component obtained at block 142 and set equal to f2 squared.

At block 146, a comparison is made of the f1.sup.2 value obtained at block 128 with the f2.sup.2 value obtained at block 144, and the larger is selected. At 148, a comparison is made of the selected f1.sup.2 or f2.sup.2 value with a predetermined threshold magnitude to determine if the desired f1 or f2 frequency component is above a threshold value and therefore considered to be present in the input signal summed waveform 74.

The here described signal receiving apparatus and method are operative to decode serial input signals having at least one frequency component that contains coded information. The above described Fourier transform analysis, as performed in accordance with blocks 112, 114, 116, 118, 120, 122, 124, 126 and 128 for the f1 signal component and in accordance with blocks 132, 134, 136, 138, 140, 142 and 144 for the f2 signal component is per se well known in the prior art to decompose an unknown signal waveform into a sum of sinusoid relationships of different frequencies. The amplitude and frequency of each determined sinusoid can be established to identify respective signal frequency components comprising that unknown signal waveform. This general technique is described in a book entitled The East Fourier Transform by E. O. Brigham that was published in 1974 by Prentice-Hall, Inc. The above described compaction operation on the input signal samples, as performed in accordance with blocks 104, 106 and 108 for the input signal data samples and at block 110 for the f1 frequency component and at block 130 for the f2 frequency component, in relation to f1 and f2 known desired signal components will operate to filter out a considerable portion of the noise in the received input signal. The above described compaction operation in conjunction with the Fourier analysis operation enables a better determination of the desired input signal f1 and f2 frequency components than could be obtained with either one of those operations taken alone.

The threshold magnitude of block 148 is selected in relation to known signal levels that are normally expected in a given signal system. For example, persons skilled in this art know how to adjust the internal dynamic range of the signal receiving apparatus shown in FIG. 2, such that reasonable signal values result in relation to available signal data memory space. Thusly, the threshold magnitude is selected in accordance with the known normal magnitude of the desired input signal f1 and f2 frequency components. The expected minimum and maximum signal component levels are established and the threshold magnitude is provided just below the expected normal minimum signal level.

In FIG. 9, there is shown a typical frequency shift keyed information message including f1 and 2 signal that can be sent to the signal receiving apparatus shown in FIG. 2, and could relate to an information message transmission from a wayside station to a transit vehicle to indicate a new destination for the vehicle or a new performance level such as a different speed to expect in the next track signal block or a different acceleration or deceleration rate for the vehicle to follow. The information message signal shown in FIG. 9 has eight bits in accordance with 110010.

In FIG. 10, there is shown one practical application for the input signal message receiving apparatus provided in accordance with the present invention. For a vehicle 200 stopped in a passenger station 202, it may be desired that an information message be sent from the station to the vehicle and then a confirmation message be sent from the vehicle in a predetermined time period, such as 1/2 second, as set forth in the above referenced additional article. This information message can include identification ID signals or a vehicle performance modification such as 70% of the provided input speed command from the next occupied track signal block and the like. The involved signal environment is very noisy with vehicle propulsion currents flowing in the tracks in the order of 10,000 amperes in addition to the message signals of the order of 10 milliamps, with many auxiliary motors and other electrical devices located in relation to the vehicle and the passenger station. The station transmitter 204 supplies the information message signal bits through the station ID antenna 206. The vehicle ID antenna 208 senses and provides these message signal bits to the vehicle receiver 210, which then decodes the signal bits in accordance with the teachings of the present invention and stores the received message signal in memory. In addition, the received message signal is sent by the vehicle transmitter 212 through the vehicle ID antenna 208 back through the station antenna 206 to the station receiver 214 for confirmation that the correct message signal was received. The station transmitter 204, in response to the vehicle being sensed to have arrived at a stopped position in the station adjacent the passenger platform, outputs an FSK message through the ID antenna 206. The vehicle ID antenna 208 picks up the FSK message from the wayside station and supplies it to the vehicle receiver 210. The vehicle receiver 210 includes the apparatus shown in FIG. 2, and receives the input analog signal such as shown in FIG. 3 and includes an analog to digital converter 64 to supply digital samples of the received input message, such as the 24 digital samples shown in FIG. 3, to the vehicle microprocessor CPU 66 including a memory. The CPU 66 takes four groups of 24 digital signal samples, as shown in FIG. 3 for each such group, for a total of 96 signal samples. The signal processor 66 within the vehicle receiver 210 decodes these signal samples to determine the identity of either a ONE or a ZERO frequency component in those signal samples. The receiver 210 includes a Z80A microprocessor which operates with the application program in accordance with the listing included in Appendix A. The flow chart shown in FIG. 1 functionally describes this application program. This particular application program takes in the order of 2.2 milliseconds execution time operating with the Z80A microprocessor, which is merely one suitable example chosen for the purpose of illustrating the present invention. This program is free-running and operates independently.

The signal decoding program flow chart is shown in FIG. 11. At block 300 a collection is made of a group of 24 input signal samples, with four such superimposed groups being taken, as illustrated in FIG. 3, and stored in the memory of the Z80A microprocessor.

The Z80A microprocessor is made by Mostek, Inc. and is presently available in the open marketplace in the United States, with a general operational description of the Z80A microprocessor being provided in a Technical Manual currently available from Mostek, Inc., 1215 W. Crosby Drive, Carrollton, Tex. 75006.

At block 302, the stored samples are compacted, with the second group of 24 samples being superimposed on and summed with the first group of 24 samples, the third group of 24 samples being superimposed on and summed with the first and second groups of samples, and the fourth group of 24 samples being superimposed on and summed with the first, second and third groups of samples to form a combination grouping of 24 samples, such as generally illustrated by curve 74 shown in FIG. 3. For the f1 and f2 frequency relationship shown in FIG. 3, this combination grouping of 24 samples is further compacted to identify which of the signal frequency components f1 or f2 is present in the combination grouping of 24 samples shown by waveform 74 of FIG. 3.

The selection of the number of digital signal samples in each group collected, for example, the 24 samples shown in FIG. 3, is determined by the known frequency relationship between the desired f1 and f2 frequency signals. The f1 signal shown in FIG. 3 is known to have two full cycles for each three full cycles of f2. This integer relationship between f1 and f2, when 24 digital signal samples are taken per group, establishes 12 signal samples for each full wave of the f1 signal and 8 signal samples for each full wave of the f2 signal. In addition, it is desired that a reasonable and adequate number of signal samples be taken for each full wave of both the f1 and the f2 signals to the signal to noise ratio to improve the identification of the f1 and f2 signal components for each message signal bit.

At block 304, the fourier transform coefficients are calculated for each of the f1 and f2 signal components. This is done as previously explained for the f1 frequency component in relation to blocks 112, 114, 116 and 118 of FIG. 4 for the sine wave and in relation to blocks 120, 122, 124 and 126 of FIG. 4 for the cosine wave, with block 128 establishing the relative magnitude of the f1 frequency component. This is done as previously explained for the f2 frequency component in relation to blocks 132, 134 and 136 of FIG. 4 for the sine wave and in relation to blocks 138, 140 and 142 of FIG. 4 for the cosine wave, with block 144 establishing the relative magnitude of the f2 frequency component. It should be understood that for a greater than unity signal to noise ratio of the actual input signal received by the present signal receiving apparatus, the operation provided by block 304 might not be required to satisfactorily determine one of the desired f1 and f2 frequency components in that input signal.

At block 306 of FIG. 11 at least a predetermined threshold signal magnitude must be sensed before one of the two desired f1 or f2 frequency components is identified and output. In addition a signal confidence level is determined by running through the application program shown in FIG. 11 for a predetermined number of times for each bit of the 8 bit information message. Since the program execution time is 2.2 milliseconds, this permits five runs through the program for each bit of 11 milliseconds, and then the threshold check is made to see if one of the frequency f1 or f2 components has been determined for this predetermined number of times, such as two or three. This was previously explained in relation to block 148 of FIG. 4.

A small time delay between the respective four groups of 24 digital signal samples, as shown in FIG. 3, can be provided to widen the effective signal filter bandwidth of the present invention. For example, if the collection of each group of 24 digital signal samples requires about 14 microseconds, a time delay in the order of 1 microsecond can be provided before the collection of each succeeding group of 24 digital signal samples.

For one practical embodiment of the present invention that was actually built and tested, the program running time was 11 milliseconds per bit of an eight bit information message, for a message BAUD rate of about 90 hertz. The apparatus satisfactorily identified one of the f1 or f2 signal components with less than a unit signal to noise ratio, because of the provided correlation for two known f1 and f2 frequency desired signal components and the effective masking of random noise signals by the additive superimposition of the groups of sampled data signals. The prior art signal receivers for the similar noise environment were limited to about a 6 dB signal to noise ratio.

In FIG. 12, curve 400 illustrates the input signal frequency component analysis that would be expected using the conventional prior art Fourier transform analysis to identify component frequencies of the input signal, and shows the apparent frequency response for the purpose of frequency component identification between input and output signals. Curve 402 shows the improved operation frequency response provided by the present signal receiving apparatus to in effect provide a better signal frequency response in relation to predetermined desired f1 and f2 frequency signal components, with the centerline 404 being respectively determined as shown in FIG. 4 in relation to each of the desired frequency components f1 and f2. In addition, increasing the number of signal sample groups taken, for example take 8 groups of 24 data samples instead of the previously described 4 groups of 24 data samples as shown in FIG. 3, will operate to tighten the filter characteristic frequency response of the present signal receiving apparatus.

In FIG. 13 there is shown for practical operation of the present signal receiving apparatus, how the magnitude of the desired frequency signal 410 can relate to the unity or average noise signal level 412 and still provide a satisfactory identification of the desired frequency signal 410. An illustrative provided signal threshold 414 is generally shown, such as would be utilized in block 148 of FIG. 4 and block 306 of FIG. 11.

In FIG. 14 there is shown a block diagram of one practical embodiment of the signal receiving apparatus of the present invention. The antenna 50A, the isolation transformer 52A, the filter 54A and the preamplifier 56A operate with the desired f1 signal frequency component, and the antenna 50B, the isolation transformer 52B, the filter 54B and the preamplifier 56B operate with the desired f2 signal frequency component. The circuit elements shown in FIG. 14 correspond with similar circuit elements shown in FIG. 2. The signal processor CPU 66, which can include the Z80A microprocessor, operates in accordance with the functional diagram of FIG. 4 and the program flow chart of FIG. 11. The input port 66A is an 8 bit data register with a clock to input the data, which goes to the Z80A microprocessor 66B when the input port is enabled by the microprocessor. The program shown in FIG. 11 is stored in the EPROM 66C and controls the operation of the microprocessor 66B. The microprocessor 66B controls the analog to digital conversion by the A to D converter 64, and the resulting parallel data enters through the input port 66A. The program shown in FIG. 11 is executed every 2.2 milliseconds to analyze the input data samples, and the individual bits of the information message input signal that are identified are clocked through the output port 66D to a suitable utilization apparatus. If desired, a memory can be provided to store the output signal bits.

When the microprocessor 66B executes the program illustrated in FIG. 11, the input signal is processed one bit at a time. After a predetermined number of such program executions for the purpose of determining the confidence level of a particular identified signal bit, for example three such executions, the data bit is output through the output port 66D. With each input bit providing eleven milliseconds of data and the program execution taking 2.2 milliseconds of time, this permits five program executions per bit. Since the five program executions might overlap and fall between two f1 and f2 frequency portions, when a frequency change does occur and the new frequency component is determined for three consecutive times to be above the desired threshold magnitude, then the new frequency is output. For each 2.2 milliseconds execution of the program, the signal bit data is stored in the RAM 66E, and for each execution of the program the identified bit data is compared with the previously determined bit data. If the identified signal bits for all of a predetermined number of program executions are the same and above the threshold magnitude then the satisfactory confidence level of the identified signal bit is established.

The initial superimposed signal bit samples, in accordance with blocks 102, 104, 106, and 108 of FIG. 4 are also stored in RAM storage 66E. The EPROM storage 66C contains the application program in accordance with FIG. 11 and additional and well known multiplication look up tables to simplify the respective multiplications of blocks 128 and 144 of FIG. 8 to develop the squared values of f1 and f2, for the value range of interest of the frequencies f1 and f2. For example, the typical value range of interest here can be from 16 up to 255, with the look up tables including each of the values for (16).sup.2 and (17).sup.2 and so forth up to (255).sup.2.

For the signal receiving apparatus as shown in FIG. 14, the following components are presently available in the marketplace in the United States and were utilized to make one suitable embodiment of the present invention.

In the Appendix there is included an instruction program listing that has been prepared to control the operation of the here disclosed signal receiving apparatus and method. The instruction program listing is written in the assembly language of the Mostek Z80A microprocessor. Many of these microprocessors have already been supplied to customers, including technical instruction manuals and descriptive documentation to explain to persons skilled in this art the operation of the microprocessor apparatus. This instruction program listing is included to provide an illustration of one suitable embodiment of the present invention that has actually been made and operated. This instruction program listing at the present time is a more or less development program and has not been extensively debugged through the course of practical operation for the real time control of a signal receiving apparatus. It is well known by persons skilled in this art that most real time control application programs contain some bugs or minor errors, and it usually takes varying periods of actual operation time to identify and routinely correct the more critical of these bugs. ##SPC1## ##SPC2##