METHOD AND APPARATUS FOR WIRELESS COMMUNICATION USING COMPRESSIVE

SENSING The present invention relates to method and an apparatus for receiving information in a wireless communication system.

In wireless communication, it is often useful to measure the received signal strength of communication. Measurement of received signal strength often benefits applications for sensing where a wireless sensor transmits a signal whose frequency is modulated by a stimulus that the sensor intends to measure. Examples of such systems are wireless pressure sensors or strain sensors where the tuned frequency is modulated by external pressure or strain being measured. A receiver would seek to read the tuned frequency as a function of time and obtain data about the variations of

pressure/strain . In order to estimate the tuned frequency, it is required that the receiver should listen at various frequencies and

identify the particular frequency where the signal strength is the highest. This would mean that the overall system would need some form of frequency sweeping. The sweeping renders the process slow. Further, for a time varying stimulus, the sensor would require to transmit signals continuously, hence consuming more power .

The object of the invention is to reduce power consumption in a wireless communication system.

The object of the invention is achieved by a method and an apparatus for receiving information from a transmitter system in a wireless communication system, wherein the transmitter system transmits a signal with a timely modulated frequency, wherein the modulation of the frequency corresponds to the information, wherein the method comprises receiving the signal having the timely modulated frequency, tuning to a plurality of discrete frequencies at a plurality of different time instances and estimating a strength of the signal corresponding to the plurality of discrete frequencies, and reconstructing a tuning frequency of the transmitter system responsive to the plurality of discrete frequencies and the respective strength of the signal as a function of time.

The frequency of the signal transmitted is modulated

corresponding to the information to be transmitted. Thus, the frequency of the signal varies with time. The receiver system tunes to a plurality of discrete frequencies at different time instance and estimates the strength of the received signal corresponding to the discrete frequencies at the respective time instances. Thus, the strength of the

frequency components of the signal corresponding to the plurality of discrete frequencies is estimated as a function of time. From the plurality of discrete frequneices and the respective signal strength estimated, the tuning frequency of the transmitter is reconstructed. This enables in receiving the data with less number of samples. Additionally, as the receiver system tunes to the plurality of discrete

frequencies, the requirement of frequency sweeping is

eliminated . According to an embodiment, the method further comprises analyzing the reconstructed tuning frequency to extract the information. The information is extracted by analyzing the reconstructed tuning frequency of transmission. According to another embodiment, the tuning to the plurality of discrete frequencies includes storing at a memory the respective said discrete frequency and a value of the

respective strength of the signal. Thus, for each frequnecy of the plurality of discrete frequnecies, the respective value of the signal stregth is stored at the memory as a fucntion of time. This allows reconstructing the tuning frequency as a function of time as the stored values can be accessed for reconstruction. According to yet another embodiment, the tuning to the plurality of discrete frequencies includes selecting the frequencies randomly.

According to another embodiment, the tuning to the plurality of discrete frequencies is at a rate lower than a Nyquist sampling rate. According to another embodiment, the transmitter system is a sensor adapted to measure a physical parameter and the information is the physical parameter measured. The sensor is capable of transmitting a siganl corresponding to the

measured physical parameter wirelessly.

Another embodiment includes an apparatus for receiving information from a transmitter system in a wireless

communication system wherein the transmitter system transmits a signal with a timely modulated frequency, wherein the modulation of the frequency corresponds to the information, wherein the the apparatus comprises a receiver configured to receive the signal having the timely modulated frequnecy and configured to tune to a plurality of of discrete frequencies at a plurality of different time instances, a signal strength estimator operably coupled to the receiver for estimating the strength of the signal corresponding to the plurality of frequencies and output an output signal corresponding to the estimated strength of the signal, and a receiver processor operably coupled to the signal strength estimator and

configured to receive the output signal and reconstruct a tuning frequency of the transmitter system responsive to the plurality of discrete frequencies and the respective strength of the signal as a function of time. Another embodiment includes a wireless communication system, wherein the wireless communication system comprises a

transmitter system for transmitting a signal with a timely modulated frequency, wherein the modulation of the frequency corresponds to an information to be transmitted, and a receiver system comprising a receiver configured to receive the signal having the timely modulated frequnecy and

configured to tune to a plurality of discrete frequencies at a plurality of different time instances, a signal strength estimator operably coupled to the receiver for estimating the strength of the signal corresponding to the plurality of discrete frequencies and output an output signal

corresponding to the estimated strength of the signal, and a receiver processor operably coupled to the signal strength estimator and configured to receive the output signal and reconstruct a tuning frequency of the transmitter system responsive to the plurality of discrete frequencies and the respective strength of the signal as a function of time.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the

accompanying drawings, in which: FIG 1 illustrates an exemplary block diagram of a

wireless communication system comprising a transmitter system and a receiver system according to an embodiment herein,

FIG 2 is a graphical representation of a stimulus

measured by a sensor responsive to which a tuning frequency of the sensor is modulated,

FIG 3 with reference to FIG 2 is a graphical

representation of strengths of the signal received and the tuned frequency for different instances of time,

FIG 4 4 is an exemplary graphical representation

representing a transmission frequency of a sensor,

FIG 5 is a graphical representation representing strength of the frequency component 62 of the received signal 45 at different time instances over a time interval, and

FIG 6 with reference to FIG 1 through FIG 6 is a flow

diagram illustrating a method of receiving information in a wireless communication system according to an embodiment herein.

The concept of the invention is based on the principle of compressive sensing. Compressive sensing is a concept wherein less information than that suggested by Nyquist sampling theorem can be used to recover the signal transmitted. In the invention herein, this principle is applied to recover signal transmitted by a sensor wirelessly in order to reduce the power consumption of the sensor.

FIG 1 illustrates an exemplary block diagram of a wireless communication system 10 comprising a transmitter system 15 and a receiver system 20 according to an embodiment herein. The transmitter system 15 illustrated herein is configured to transmit wirelessly an information and the receiver system 20 is adapted to receive the information.

The information is transmitted by modulating the tuning frequency of the transmitter system 15 corresponding to the information. In the shown example of FIG 1, the transmitter system 15 is a sensor configured to measure a physical parameter and transmit a signal indicative of the measured physical parameter wirelessly. The indication of the physical parameter measured is the information herein. For example, the sensor can be a power sensor, a breathing rate sensor, a pressure sensor and the like and the physical parameter can be breathing rate, pressure accordingly. However, in other aspects, the transmitter system 15 can be any transmission system capable of transmitting a signal wirelessly.

Accordingly, in the shown example of FIG 1, the transmitter system 15 is shown as comprising a detector 25, a modulator 30, a transmitter 35 and a transmitter antenna 40. The detector 25 is adapted for detecting the physical parameter. For example, the detector 25 can be a probe or an arrangement of parallel plates for detecting the physical parameter.

Generally, the detector 25 is configured for detecting a stimulus caused by the change in the environment which the detector 25 intends to detect. The transmitter 35 is adapted to send a signal 45 using the transmitter antenna 40. The signal 45 is sent with a tuning frequency of the transmitter 35. Thus, the tuning frequency of the transmitter 35 is the transmission frequency of the transmitter system 15. However, the modulator 30 is operably coupled to the detector 25 and to the transmitter 35 and is configured to modulate the tuning frequency of the transmitter 35 and therewith the frequency of the signal 45 responsive to a stimulus caused by the physical parameter being detected. The modulated signal 45 is transmitted wirelessly by the transmitter 35. The information to be transmitted is coded in the modulation of the tuning frequency of the signal 45.

The receiver system 20 is configured to receive the signal 45 via the receiver antenna 50. The receiver antenna 50 is operably coupled to a receiver 55 and the received signal 45 is provided to the receiver 55. The receiver 55 comprises a tuning circuit and is configured to tune to a particular frequency for receiving the signal 45. According to an aspect herein, the receiver 55 is configured to tune to a plurality of discrete frequencies as a function of time. To achieve this, the receiver 55 is operably coupled to a receiver processor 60. The receiver processor 60 is configured to control the receiver 55 so that the receiver 55 is tuned to a desired frequency out of the plurality of discrete

frequencies . In the illustrated example of FIG 1, the discrete frequencies are selected randomly. Thus, in the shown example of FIG 1, the receiver processor 60 is configured to randomly select discrete frequencies and the receiver 55 is controllable to tune to the selected frequency.

A "processor" as used herein is a device for executing machine-readable instructions stored on a computer readable medium for performing tasks and may comprise any one or combination of hardware and firmware. For example, the processor may be implemented using a microcontroller,

microprocessor, digital signal processor, electronic devices, or other electronic units to perform the functions described herein or a combination thereof. The machine-readable

instructions may be stored within the processor or external to the processor. Referring still to FIG 1, according to an aspect herein, the frequnecy component 62 of the signal 45 corresponding to the frequency to which the receiver 55 is tuned is provided from the receiver 55 to a signal strength estimator 65. The signal strength estimator 65 is configured to estimate the strength of the frequency component 62 of the signal 45 received corresponding to the respective frequency the receiver 55 is tuned to and to output an output signal 67 corresponding to the estimated strength of the frequency component 62 of the signal 45. In the shown example of FIG 1, the signal strength estimator 65 is operably coupled to the receiver processor 60 and the receiver processor 60 is configured to receive the output signal 67. The receiver processor 60 is configured to store the value of the strength of the frequency component 62 of the signal 45 and the corresponding frequency. Since the receiver processor 60 is configured to randomly seelct the frequnecy the receiver 55 is to be tuned to, the frequnecy the receievr 55 is tuned to at a time instance is known to the receievr processor 60. The receiver processor 60 can store the value of the strength of frequency component 62 the signal 45 and the corresponding frequency at a memory

internal to the receiver processor 60 or at a memory external to the receiver processor 60. In the shown example of FIG 1, the receiver processor 60 is operably coupled to a memory device 70 and is configured to store the strength of the frequency component 62 of the signal 45 and the corresponding frequency in the memory device 70. Thus, the strength of the frequency component 62 of the signal 45 corresponding to each frequency in the set of discrete frequencies can be estimated over a period of time and stored in the memory device 70. In another aspect, the signal strength estimator 65 can be operably coupled to the memory device 70 and configured to store the strength of the frequency component 62 of the signal 45 onto the memory device 70.

For example, the signal strength estimator 65 can be

implemented using a logic circuit adapted to estimate the strength of the signal. However, in another implementation, the receiver processor 60 can be configured to estimate the strength of the signal. In such cases, the receiver processor 60 can be configured to perform the functions of the signal strength estimator 65. Referring still to FIG 1, according to an aspect herein, the receiver processor 60 is configured to re-construct the tuning frequency of the transmitter system 15 using the signal strengths of the corresponding discrete frequnecies of the signal 45 as a function of time. The tunning frequnecy of the transmitter system 15 is re-contructed using certain number of pairs of discrete frequneices and the respective signal strength over a period of time. The receiver processor 60 is configured to re-construct the tuning frequency of the transmitter system 15 using the pairs of discrete frequnecies and the respective signal strength as a function of time. The reconstruction can be performed using any suitable

reconstruction algorithm known in the art. For example, reconstruction algorithms, such as, but not limited to, total variation minimization, L-l minimization and the like, which operate on minimizing the L-l norm can be used.

Referring still to FIG 1, the receiver processor 60 is further configured to extract the information transmitted by analyzing the reconstructed tuning frequency. As the tuning frequency of the transmitter system 15 is modulated

responsive to the information to be transmitted, analyzing the tuning frequency as a function of time enables in

extracting the transmitted information. Thus, the process of tuning the receiver 55 to the pluralities of discrete

frequneices may be repeated over a period of time for

receieving the information transmitted by the transmitter system 15. The transmitter system 15 being a sensor in the present example, in an aspect, the receiver processor 60 can be operably coupled to a visual indication device. For example, the visual indication device can be a display for displaying the physical parameter measured. In certain aspects, an audio indication device can also be connected to the receiver processor 60. For example, in case the sensor 15 is a breathing rate sensor, the receiver processor 60 can be configured to output a signal in case the breathing rate is above a threshold value and the audio device can be

configured to provide an indication responsive to the same.

The use of compressive sensing achieves is determining the tuning frequency of the transmitter system 15 using

relatively less information. Thus, the sampling rate of the receiver system 20 can be lower than the Nyquist sampling rate. As the tuning frequency of the transmitter system 15 is re-constructed using the strength of the signal corresponding to the set of discrete frequencies, the transmitter system 15 is not required to transmit the signal 45 in a continuous manner. Thus, the transmitter system 15 can transmit the signal 45 in a discrete manner. This achieves in reducing the power consumption of the transmitter system 15. Additionally, as the receiver system 20 is not required to perform

frequency sweeping, the power consumption of the receiver system 20 is also reduced.

FIG 2 is a graphical representation of an exemplary stimulus 75 detected by a detector 25 responsive to which stimulus 75, a tuning frequency of the transmitter system 15 is modulated. In the shown exmaple of FIG 2, the horizontal axis corresponds to time and the vertical axis corresponds to amplitude. The stimulus 75 represents the detectable change in the environment which the sensor 15 intends to measure. This detectable change may relate to a change in a physical parameter which the sensor 15 intends to measure. It can be seen that the frequency of the stimulus 75 varies with time and is different at different time instances tl, t2, t3, and t4. The varying frequnecy of the stimulus represent the change in the physical paramter which the sensor 15 intends to measure.

FIG 3 with reference to FIG 2 is a graphical representation of strengths of the signal received by the receiver system 20 and the tuned frequency for different instances of time. In the shown example of FIG 3, x-axis corresponds to the

frequency and the y-axis corresponds to the strength of the signal received and output by the receiver 55. The

representation 80 corresponds to the time instance tl of the stimulus 75 of FIG 2 wherein the strength of the signal corresponding to the tuning frequency is the highest.

Similarly, the representations, 85, 90, 95 correspond to the time instances t2, t3, t4 of the stimulus 75 respectively. From the representations 80, 85, 90, 95, it can be observed that the tuning frequency of the transmitter system 15 varies with time and with respect to the stimulus 75.

FIG 4 is an exemplary graphical representation representing a tuning frequency of a transmitter system 15 of FIG 1

comprising a detector 25 and other components as described above in connection with FIG 1. In the shown example of the representation 100, the horizontal axis corresponds to time and the verical axis corresponds to frequency. As can be derived from the curve, the detector 25 detects a sinusoidal physical parameter. The tuning frequency of the sensor 15 is modulated responsive to the stimulus 75 of FIG 2. FIG 5 is a graphical representation representing strength of the frequency component 62 of the received signal 45 at different time instances over a time interval. In the shown example of FIG 5, the horizontal axis corresponds to time t and the vertical y-axis corresponds to the signal strength S. In the shown example of FIG 5, the strength of the signal is illustrated for different discrete frequencies fl, f2, f3, f3, f5 over a time interval at different instances of time. The representation 101 corresponds to the signal strrength of the frequency component f1. Simialrly, the respecrentations 102, 103, 104, 105 corresponds to the signal stregnth of the respective frequnecy components f2, f3, f4 , f5. The

frequencies fl, f2, f3, f3, f5 are constituents of the set of discrete frequencies and the receiver 55 of FIG 1 is tuned to the frequencies fl, f2, f3, f3, f5 over the time interval. The receiver processor 60 of FIG 1 is configured to reconstruct the tuning frequency of the transmitter system 15 using the signal strengths 101, 102, 103, 104, 105 of the respective frequnecy components fl, f2, f3, f4 , f5 of the signal 45 as a function of time. For a signal 45 received, the strength of the frequnecy component 62 of the signal 45 is highest if the frequency of the frequnecy component 62 is the tuning frequency of the transmitter system 15 of FIG 1. FIG 6 with reference to FIG 1 through FIG 5 is a flow diagram illustrating a method of receiving information from a

transmitter system 15 in a wireless communication system 10 according to an embodiment. The transmitter system 15

transmits a signal 45 with a timely modulated frequency. The modulation of the frequency of the signal 45 corresponds to the information to the trnsmitted by the transmitter system 15. At block 110, a signal 45 having the timely modulated frequnecy is received. Next, at block 115, the receiver system 20 is tuned to a plurality of discrete frequencies at a plurality of different time instances and the strength of the signal 45 corresponding to the plurality of discrete frequencies is estimated. At block 120, a tuning frequency of a transmitter system 15 is reconstructed responsive to the plurality of discrete frequencies and the respective strength of the signal 45 as a function of time.

The embodiments described herein achieve in reducing the power consumption in a wireless communication system 10. The power consumption can be reduced at the transmitter system 15 and at the receiver system 20. Additionally, as the receiver system 20 tunes to a set of discrete frequencies, the

requirement of frequency sweeping at the receiver system is eliminated. Frequency sweeping makes the process slow as the receiver system 20 would have to tune to various frequencies and identify the particular frequency having the highest signal strength. Additionally, in case of a sensor 15, the disadvantage where the tuning frequency is modulated

responsive to detected stimulus at rate faster than the scanning process of the receiver system 20 is eliminated. Also, since the amount of processing is reduced at the transmitter system 15 and the receiver system 20, reduction in overall size and associated cost is achieved. Moreover, as the transmitter system 15 is not required to transmit the signal 45 in a continuous manner, reduction is radiation is achieved. Also, since the tuning frequency is reconstructed using signal strengths of discrete frequencies, increase in the transmission range can be achieved. Additionally, increased tolerance to noise and interference is achieved.

While this invention has been described in detail with reference to certain preferred embodiments, it should be appreciated that the present invention is not limited to those precise embodiments. Rather, in view of the present disclosure which describes the current best mode for

practicing the invention, many modifications and variations would present themselves, to those of skilled in the art without departing from the scope and spirit of this

invention. The scope of the invention is, therefore,

indicated by the following claims rather than by the

foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.