Title of Invention

METHOD AND SYSTEM FOR PULSED SIGNAL STRENGTH MEASUREMENT IN RADIO FREQUENCY SIGNALS

Abstract

A system for accurately measuring the pulsed signal strength in radio frequency signals with long off-time and short on-time, said system comprising a receiver to receive input radio frequency signals with long-off time and short-on time, a high-speed sampler cum holder to sample the non-uniform input signals and generate sampled periodic pulses, a memory unit to store the sampled periodic pulses, a high-speed analog to digital converter to convert the sampled periodic pulses into binary patterns, a database unit with a range of pre-determined limiting values and past records, a processor to compare the binary patterns with a range of limiting values stored in the database unit, said processor to store the middle value of the binary patterns, said processor to compare the middle value of binary patterns with past records to generate the final value of signal strength, a digital to analog converter to reconvert said binary patterns into analog signals, and an output device to display the final value of the signal strength of the radio frequency signals. The present invention also provides a method for measuring pulsed strength.

Full Text

METHOD AND SYSTEM FOR PULSED SIGNAL STRENGTH MEASUREMENT IN RADIO FREQUENCY SIGNALS Technical field The present invention relates to a method and a system for pulsed signal strength measurement in RF (radio frequency) signals on a pulse to pulse basis. The present invention particularly relates to a method and a system for pulsed strength measurement in RF signals with long OFF-time and short ON-time. Background and prior art Signal strength measurement circuits are used in applications like multi-radar and other hostile applications. The systems already available for signal measurement are basically of two types These systems are used for measuring the amplitude or signal strength of the detected signal pulses. These can be broadly classified as: (i) Integration of pulse along with a suitable RC time constant circuit (ii) Amplitude to Width modulator. In the first method, the radio frequency (RF) pulse is integrated using a RC (Resistance-Capacitance) circuit to produce a DC voltage proportional to the amplitude. The voltage developed is a function of RC, which is known as time constant. This gives the measure of signal strength. In this method, the time constant RC plays a major role. A small time constant can follow the input amplitude faithfully, but has the disadvantage of large droop rate. On the contrary a large time constant has sluggish response and will not produce a DC volt when pulse strength is very small. In the second method, the amplitude of the RF pulse is directly converted to width information. The width modulated signal is rectified to generate a volt proportional to the amplitude. In amplitude to width converter the pulse amplitude is converted to proportional width. That is, as the amplitude of the pulse of the signal increases the generated pulse width increases, whereas the amplitude of the pulse remains constant. DC voltage generated to measure the signal strength is proportional to the width of the pulse. Hence, for larger amplitude, the DC volt generated is also high. In this method, the amplitude of the pulse is directly converted to width information. This is less accurate, even though it is simple. The accuracy is poor and cannot follow the fluctuations in the signal strength. The response of these circuits is poor. In this method there are two conversions involved to get the final DC voltage. Hence, probability of error introduction is more. Also, depending on the circuit configuration, impulses can generate large output variations. "Apparatus and methods for signal strength measurement in a wireless communication system" described in US patent no. 6,044,270 relates to a system which schedules stolen slots while omitting reception or transmission when signal strength measurement can not be made at idle time slots for a continuous signal. This method carrots be an actual indicator of signal strength as it measures signal strength at random intervals. Another US patent no. 6,556,552 - "Signal strength measurement method and device" describes a method which prevents loss of information in CDMA mobile communication systems, when communications are interrupted with local base station, while the mobile station is searching for chaimels other than the communication chaimels. Here mobile station transmits the required information after suspension period to the base station at a rate higher than the transmission rate before the suspension period so as to transmit possible information which was not transmitted during suspension period. "Apparatus and methods for signal strength measurement in a wireless communication system" is illustrated in another US patent no. 6,018,661, which describes a system in which signal strength measurement is made at predetermined times. Signal strength measurement is scheduled so as to minimise interference with transmission and reception of signal. When scheduled signal strength measurements are delayed while mobile is transmitting and receiving on a channel then more frequent signal strength measurement can be made when there is no communication. Another US patent no. 5,822,686 - "Carmel scaring scheme for signal strength measurement systems and methods" describes signal strength measurement of radio-signals in radio-communication systems which is applicable to multiple mobile stations. List of chaimels to be measured is sorted into frequency order and by taking into account a last tuned channel as well as radio specific tuning characteristics, the overall time spent tuning to each channel in the list is reduced. US patent no. 5,410,733 - "Received signal strength information measurement useful in a mobile telephone system having mobile assisted handoff capability" describes a system which causes the power of a narrow bandwidth signal to be spread to a wider bandwidth. The power of the spectral components that are located close to carrier frequency is modulated which reduces DC component of a base band signal and correspondingly reduces the charging of an AC coupling capacitors in the base band circuitry. This results in increase in receiver recovery time and a more accurate signal strength measurement is made by a mobile telephone. Another US patent no. 5,953,660 - "Method and apparatus for signal strength measurement of supervisory audio tones (SATS) in a radio communication system" describes how an estimate of signal strength measurement can be made by considering sliding average of signal samples which includes both current and previous blocks of samples rather than processing a complete measurement interval of received SAT samples. This enables reporting SAT signal strength more frequently but without the number of computations that would be required to process all the SAT signal samples received during a measurement interval. US patent no. 2,003,028,891 on "System and method for diagnosing RF signal strength at a set-top terminal" describes how a network characterization diagnostic tool measures the RF signal strength for the entire bandwidth of the spectrum and produces a visual display to assist diagnosis of RF signal strength. Similar systems are described in US patent no. 4,868,885 on "Apparatus and method for high speed determination of received RF signal strength indicator" wherein it describes a system in which rapid measurement of the received signal strength indicator (RSSI) of a radio frequency signal is performed by sampling received signal amplitudes and averaging only selected ones of the sampled amplitudes. The average value is very close to true average signal amplitude and is substantially unaffected by Raleigh fading phenomenon, but still it is sensitive to rapid changes in received signal amplitude. The above mentioned systems illustrate signal strength measurement in different ways, but none of these inventions provide signal strength measurement for pulsed RF signals, in canes where the ON time is much smaller than the OFF time. In most of the cases referred above signal strength measurement gives an average indication but in pulsed RF signal the requirement is instantaneous peak amplitude at all the received pulses. Averaging technique is a conventionally known method, and this meets most of the requirements although the update rate is small (and time is large). But present day communication systems demand accurate and fast signal strength measurement techniques due to different applications. In addition to this the measurement should be highly accurate as it is used for decision making process. The present system provides an accurate and simultaneously faster method of signal strength measurement. And as the signal strength measurement of the present system is on a pulse to pulse basis, it finds application in multi-radar and hostile environment. Objects of the invention The primary object of the present invention is to provide a method and a system for Pulsed Signal Strength Measurement in radio frequency (RF) signals. An object of the present invention is to provide a method and a system for Pulsed Signal Measurement on pulse to pulse basis. Yet another object of the present invention is to provide a method and a system for Pulsed Signal Measurement with high accuracy and speed. Still another object of the present invention is to provide a method and a system for Pulsed Signal Measurement that performs in highly hostile environments. Further object of the present invention is to provide a method and a system for Pulsed Signal Measurement which operates with both synchronous as well as asynchronous input modes. It is also an object of the present invention to provide a method and a system for Pulsed Signal Measurement by using high speed Analogue to Digital converters and signal processing devices which are suitable for such high speed pulse applications. Summary of the invention A system for accurately measuring the pulsed signal strength in radio frequency signals with long off-time and short on-time, said system comprising a receiver to receive analog input radio frequency signals with long-off time and short-on time, a high-speed sampler cum holder to non-uniformly sample the input radio frequency signals and generate sampled periodic pulses, high-speed analog to digital converter coupled to the sample holder to convert the sampled periodic pulses into corresponding binary patterns, a database including a range of pre-determined limiting values and past records, a processor to compare the binary patterns with a range of limiting values stored in the database unit, said processor to store and compare the middle value of the binary patterns with past records to generate final value of signal strength, a digital to analog converter to reconvert said binary patterns into analog signals, and an output device to display the final value of the signal strength of the analog signals. The present invention also provides a method for accurately measuring the pulsed signal strength in radio frequency signals with long off-time and short on-time Brief description of the diagrams Fig 1 depicts the block diagram of the system of the present invention. Fig 2 is a flow diagram depicting the method of working of the present system. Fig 3 depicts the graphical representation of the signal in form of sampled periodic pulses. Detailed description of the invention The present invention provides a method and a system for pulsed signal strength measurement in Radio Frequency (RF) signals. Fig 1 is a block diagram representation of the system of the present invention. The system of the present invention comprises a receiver (1), a high-speed sampler cum holder (2), memory unit (7), a high-speed analog to digital converter (3), a database (8), digital processing unit (6) a processor (4), a digital to analog converter (5) and an output device (9). The input signal is an analog signal in the radio frequency range and the analog signal have a long OFF-time and a short ON-time. The input analog radio frequency signals are received at the input by a receiver (1). The receiver (1) used in the present invention is any receiver that is used for receiving radio frequency signals. The high-speed sampler cum holder (2) is placed adjacent to the receiver (1). The sampler cum holder (2) accepts the analog signals from the receiver (1) and non-uniformly samples the input radio frequency signals to generate a plurality of sampled periodic pulses. The sampled periodic pulses generated by the sampler cum holder (2) are stored in a memory unit (7). The high-speed analog to digital converter (3) is coupled to the sampler cum holder (2) to convert the plurality of sampled periodic pulses into corresponding plurality of binary patterns. The Analog to Digital Converter (ADC) (3) is an 8-bit converter. The 8-bit ADC enables convenient storage of one binary pattern in a single memory location. The system of the present invention has a database (8) which includes a range of pre¬determined limiting values and past records. The range of limiting values stored in the database (8) of the present system is in the range of 5 - 10 %. The limiting value is taken as 5% for normal signals and 10% is considered for signals where there is lot of noise or discontinuities. This limit of 10% is taken considering the overshoot and undershoots at discontinuities. The past records are usually ten past values of signal strength which are stored in memory (7) as a stack. The stack retains the most recent ten values of signal strength as the stack grows. From the stored values the signal strength profile and extrapolate to predict the next value are computed on a time scale basis. The actual value of the next pulse and time from the most recent record is measured using the past values. If the difference is within ±5%, the data is accepted. The plurality of binary patterns generated by the analog to digital converter (3) and stored in the memory (7) unit is retrieved by a processor (4). The processor (4) is selected from any micro processor used for signal processing that is well known in the art. The processor (4) also retrieves the range of pre-determined limiting values from the database (8). The processor (4) then compares the plurality of binary patterns retrieved from the memory (7) with the pre-determined limiting values from the database (8). After comparison in case the binary patterns lie within the range of limiting values, the processor (4) stores the middle value of the plurality of binary patterns in the memory unit (7). The processor (4) also performs further comparison of middle value with the past records stored in the database. After this comparison the processor (4) generates the final value of the signal strength. This final value of the signal strength is stored in the memory unit (7). This final value of signal strength is stored as the most recent past record data in the memory stack and is used for fiiture comparisons with the middle values of new binary patterns. After obtaining the signal strength, the binary patterns of the signal are reconverted back to their corresponding analog form using a digital to analog converter (DAC) (5). The final result which is the final value of the signal strength is displayed at the output (9). The method of the present invention for measuring signal strength in radio frequency signals is explained by referring to Figs 2 and 3. Fig 2 depicts the flow diagram explaining the method of the present invention and Fig 3 depicts the graphical representation of the periodic sampled signals on a time basis. The desired signal whose strength or amplitude is to be measured is provided as the input signal to the system of the present invention. The system of the present invention is capable of perfoiming in both synchronous and asynchronous sampling mode. Synchronous mode means that the source of the input signal is known whereas in asynchronous mode the source of the input signal is not known. In synchronous sampling mode, the signal strength is measured and stored in synchronous with the input signal frequency. In asynchronous sampling mode, irrespective of the input signal, the system on its own asynchronously looks for signals and measures its strength. In synchronous mode of operation, in the event of missing pulsed signals, this synchronous input can be used to initiate actions to improve the input signal strength: making use of the circuit"s ability to store and compute. In multi-input configuration, in synchronous mode, the input signal can be uniquely identified and characterized, by having coded signal. Either synchronous or asynchronous mode of input can be provided in the present system. The Radio Frequency input signal provided for the present system has a very long signal OFF time and short ON time (1:1700). The input signal (either from synchronous or asynchronous mode) is an analog signal and said signal is fed into the receiver of the system of the present invention. At the receiver of the system of the present invention, a high-speed sampler cum holder is provided. The sampler cum holder is a high-speed sample and hold circuit. The sampler cum holder accepts the analog signal as its input and non-uniformly samples the analog signal to generate a plurality of sampled periodic pulses at a time. These sampled periodic pulses lie within a certain period. A plurality of sampled periodic pulses is selected from a certain period. These selected sampled periodic pulses are stored in a memory unit of the system of the present invention. A high-speed Analog to Digital Converter is coupled to the sampler cum holder to convert the plurality of sampled periodic pulses into corresponding plurality of binary patterns. Here, within a single selected pulse period a plurality of periodic sampled pulses are considered and converted to binary. In the present invention the number of periodic sample pulses selected from a single pulse period is limited to three. However it also within the scope of the present invention to consider more than three periodic sampled pulses. Once these three periodic sampled pulses are converted to binary patterns, the binary patterns are stored in a memory unit. Each of the three binary patterns of the corresponding periodic sampled pulses are stored individually in separate memory locations in the memory unit to ensure an easy retrieval. A processor is provided which retrieves the stored binary patterns from their corresponding memory locations in the memory unit. On retrieving the binary patterns the processor compares all the three binary patterns with the range of limiting values stored in the database. If the binary patterns are within the limiting values, then the middle value of the binary patterns is accepted. The middle binary pattern out of the three binary patterns is taken as the middle value and processed ftirther. This middle value is considered as the signal strength for ftirther processing. If during the comparison stage in the processor, the binary patterns are found to be out of the range of limiting values then they are rejected and a new set of periodic sampled pulses is accepted and the above steps are repeated again for the new set of periodic sampled pulses. The memory unit also contains previously measured values, which are based on signal strength variation profile generated from past records. The previously measured values, which are stored in the memory unit, are retrieved from the memory unit and are provided as the first input to a comparator of the processor. The second input to the comparator is the middle value, which is considered as the signal strength or amplitude of the signal. Both these values are compared in the comparator. The three binary values are taken to ensure that the signal is valid, because received signal is always corrupted with noise, which may override the video signal after detection. At discontinuities, due to overshoot and undershoot, the value will always be higher than the steady state value. Hence to measure the steady state value, the three samples are shifted properly in time. If the three pulse values are within 5%, the middle value is accepted. After the comparison, the comparator either accepts the middle value or rejects the middle value. In case the comparator accepts the middle value, then the middle value is taken as the amplitude or the strength of the signal. In case the comparator rejects the middle value, then the previous value is taken as the signal. This value is the value stored in the memory just before the current three pulses that are used for identifying the present value. Once the signal strength is determined for the three sample pulses under consideration, then the system stores the value of the signal strength in the memory and then goes back to the input to retrieve the next set of pulses. This value of signal strength stored in the memory as the most recent past record data in the memory stack is used for future comparisons with the middle values of new binary patterns. The above steps are repeated again for the next three signal pulses present at the input. The value of the signal strength or amplitude is measured and stored in the memory this storage enables the direct measurement of signal strength. The instantaneous peak amplitude or signal strength of the signal is measured on a pulse to pulse basis and this enables application in multi-radar applications and other hostile environment. After the signal pulses for the entire signal are analyzed the sampled periodic pulses are fed into a Digital to Analog converter (DAC) to finally convert the sampled pulses back into an analog equivalent. The applications of the present invention are in Dynamic switching antenna, when the system uses more antennae, to get the required coverage, we use a combiner, to combine the outputs of individual antennae. This process can cause deep nulls and loss of signals. In such cases, this invention is used to identify the best antennae (only one) giving good signal and coverage always. Another application of the present invention is in Gain programmability, here dynamic programming of receiver is performed; where in, the gain (sensitivity) of the receiver can be adjusted, once the receiver detects a low level signal reception. This capability is advantages in battery operated systems where dc power is at a premium. Subsystems can be switched ON and OFF according to the need, in power save mode. Yet another application of the present invention is in Ack-Nack communication for better data transmission, here the present invention finds application in error fi-ee data transmission systems. Once the receiver detects low signal to noise ratio, it will communicate to the source negative acknowledgement. Transmission restores when sufficient S/N prevails. This prevent lose of vital data. Advantages 1. The measurement accuracy of the system of the present invention is highly precise and is usefiil in decision-making applications. 2. The system of the present invention is useful in high pulse speed applications 3. The storage of result in the memory enables direct measurement of signal strength. 4. The application of the present invention is to provide signal strength measurement on a pulse to pulse basis with a cooperative target. Co-operative Target is one, which can identify the source of transmission and reply back. We claim: 1. A system for accurately measuring the pulsed signal strength in radio frequency signals with long off-time and short on-time, said system comprising: a receiver to receive analog input radio frequency signals with long-off time and short-on time, a high-speed sampler cum holder to sample the non-uniform input radio frequency signals and generate sampled periodic pulses, a memory unit to store the sampled periodic pulses a high-speed analog to digital converter coupled to the sampler cum holder to convert the sampled periodic pulses into corresponding binary patterns, a database including a range of pre-determined limiting values and past records, a processor to compare the binary patterns with a range of limiting values stored in the database unit, said processor to store the middle value of the binary patterns in the memory unit when the binary patterns fall within the range of limiting values, said processor to compare the middle value of binary patterns with past records stored in the database unit to generate the final value of signal strength, a digital to analog converter to reconvert said binary patterns into analog signals, and an output device to display the final value of the signal strength of the radio frequency signals. 2. The system as claimed in claim 1, wherein the analog input radio frequency signal received at the receiver is either synchronous or asynchronous. 3. The system as claimed in claim 1, wherein the range of limiting values of signals are in the range of 5-10 % for normal and discontinuities respectively. 4. The system as claimed in claim 1, wherein said past records consist of pre-stored pulsed signal strengths to compute the signal strength of the input radio frequency signal. 5. A method for accurately measuring the pulsed signal strength in radio frequency signals with long off-time and short on-time, said method comprising the steps of: receiving analog input radio frequency signals with long off-time and short on-time at the receiver, sampling the analog signals by means of a high-speed sampler cum holder and storing the same in the form of sampled periodic pulses, selecting a desired pulse period, selecting a plurality of sampled pulses from within said selected pulse period, converting the selected plurality of sampled pulses into binary pattern using a analog to digital converter to generate a corresponding plurality of binary patterns, storing said plurality of binary patterns in the memory unit, comparing the plurality of binary patterns with pre-determined limiting values as stored in the database, selecting conditionally new set of plurality of sampled pulses where the value of binary patterns exceed the limiting value, storing the middle value from the plurality of binary patterns where the binary patterns fall within the limiting value, comparing said stored middle value with past records stored in the database, storing the value of past records as a signal strength in the memory where middle value of binary pattern is not accepted by the processor after comparison, storing the middle value of binary pattern value as a signal strength in the memory unit in case the middle binary pattern is accepted by the processor after comparison, verifying if all the sampled pulses of the signal are considered, selecting a new set of sampled pulses in case all samples have not been considered, repeating the steps of converting to binary patterns using analog to digital converter, storing binary patterns in memory unit, comparing with limiting value by a processor means, comparing with past records from database unit and storing the result in memory unit, said steps repeated for all the sampled pulses, reconverting binary patterns back to analog signal by means of a digital to analog converter, storing the final value of signal strength of the signal in the memory unit and displaying final value of signal strength at the output device. 6. The method as claimed in claim 5, wherein the input signal may be of either synchronous or asynchronous input modes. 7. The method as claimed in claim 5, wherein the plurality of samples for a given pulse period is preferably 3. 8. The method as claimed in claim 5, wherein the range of limiting values of signals are in the range of 5-10 % for normal and discontinuities respectively. 9. The method as claimed in claim 5, wherein said past records consist of pre-stored pulsed signals to compute the signal strength.

Documents:

0844-che-2004 abstract-duplicate.pdf

0844-che-2004 abstract.pdf

0844-che-2004 claims-duplicate.pdf

0844-che-2004 claims.pdf

0844-che-2004 correspondence-others.pdf

0844-che-2004 correspondence-po.pdf

0844-che-2004 description (complete)-duplicate.pdf

0844-che-2004 description (complete).pdf

0844-che-2004 drawings-duplicate.pdf

0844-che-2004 drawings.pdf

0844-che-2004 form-1.pdf

0844-che-2004 form-19.pdf

0844-che-2004 form-26.pdf

0844-che-2004 form-3.pdf

0844-che-2004 form-5.pdf