US20100036460A1

US20100036460A1 - Parallel search circuit for a medical implant receiver

Info

Publication number: US20100036460A1
Application number: US12/536,562
Authority: US
Inventors: Sthanunathan RAMAKRISHNAN; Jawaharlal Tangudu; Visvesvaraya Pentakota
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 2008-08-06
Filing date: 2009-08-06
Publication date: 2010-02-11
Also published as: US20100036461A1; US20120106602A1; US20100036459A1; US8401660B2

Abstract

Parallel search circuit for a medical implant receiver. The circuit includes a radio frequency receiver that receives a first set of contents of a band of channels. The circuit also includes a processing circuit coupled to the radio frequency receiver to process in parallel a second set of contents of a plurality of channels of the band of channels and to detect a signal in the band of channels.

Description

REFERENCE TO PRIORITY APPLICATION

This application claims priority from U.S. Provisional Application Ser. No. 61/086,663 filed Aug. 6, 2008, entitled “Wake-up signaling in MICS implants” and U.S. Non-provisional application Ser. No. 12/536,520 filed Aug. 6, 2009, entitled “Signaling in a medical implant based system”, which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

Embodiments of the disclosure relate to a parallel search circuit for a receiver.

BACKGROUND

A medical implant based system includes a medical controller and a medical implant. The medical implant is present inside body of a living organism and the medical controller is external. Power consumption of the medical implant is one of the major determinants of lifetime of the medical implant. The power consumption in a medical implant receiver forms a significant portion of the overall power consumption in the medical implant. Hence, it is desired to maximize efficiency of the medical implant receiver to increase lifetime of the medical implant.
The energy of the medical implant receiver is utilized for performing various functions. In one example, the power consumption in the medical implant receiver is dominated by a listen mode of the medical implant receiver. In the listen mode, the medical implant receiver wakes up periodically and search for presence of a signal in a band of channels. A medical controller transceiver selects a channel based on certain parameters and transmits the signal in that channel. The channel, in which the signal is transmitted, is unknown to the medical implant receiver. Hence, the medical implant receiver has to scan all channels to detect the signal.
Currently, a power measurement technique is used to detect a channel that carries the signal. Power is estimated in the band of channels before and after filtering noise from the band of channels. If the power measured in both the cases differ by a magnitude greater than a threshold then it is determined that the band of channels does not include the signal, else presence of the signal is detected. However, the power measurement technique may not be effective for the signals having strength lesser than a threshold. Further, the power measurement technique is sensitive to filter attenuation and noise. Also, the power measurement technique is prone to false alarms with interference and spurs.
Another technique includes processing channels one by one to detect presence of the signal in the channel. However, processing channels one by one is time inefficient. Further, power consumption is also high as a radio frequency receiver, an analog filter and an analog-to-digital converter is active during the processing.

SUMMARY

An example of a method for signaling in a medical implant based system includes receiving a first set of contents of a band of channels by a receiver. The method further includes processing in parallel a second set of contents of a plurality of channels from the band of channels. The method also includes detecting a signal in the band of channels based on the processing.
An example of a method for signaling in a medical implant based system includes receiving a first set of contents of a band of channels by a receiver. The method further includes converting the first set of contents into digital samples. The method also includes storing the digital samples of the first set of contents. Moreover, the method includes selecting a subset of the digital samples, the subset including contents of a plurality of channels from the band of channels. The method also includes correcting one or more frequency offsets in the subset in parallel to obtain a filtered content for each channel. Further, the method includes correlating the filtered content with a predefined sequence. Furthermore, the method includes detecting a signal in the band of channels based on an output of the correlating.
An example of a receiver circuit includes a radio frequency receiver that receives a first set of contents of a band of channels. The receiver circuit also includes a processing circuit coupled to the radio frequency receiver to process in parallel a second set of contents of a plurality of channels of the band of channels, and to detect a signal in the band of channels.

BRIEF DESCRIPTION OF THE VIEWS OF DRAWINGS

In the accompanying figures, similar reference numerals may refer to identical or functionally similar elements. These reference numerals are used in the detailed description to illustrate various embodiments and to explain various aspects and advantages of the disclosure.

FIG. 1 illustrates an environment, in accordance with one embodiment;

FIG. 2 illustrates a block diagram of a receiver, in accordance with one embodiment;

FIG. 3 illustrates a block diagram of a processing circuit of a receiver, in accordance with one embodiment;

FIG. 4 illustrates an exemplary correlation graph, in accordance with one embodiment; and

FIG. 5 is a flow diagram illustrating a method for signaling in a medical implant based system, in accordance with one embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates an environment 100 including, for example a medical implant based system. Examples of the environment 100 include, but are not limited to, intensive care units (ICUs), hospital wards, and home environment. The environment 100 includes a receiver, for example a medical implant receiver 105, herein referred to as the implant receiver 105, and a medical controller transceiver 110, herein referred to as the controller transceiver 110. The implant receiver 105 is present inside living organisms.
The implant receiver 105 includes or is connected to an antenna 115a to receive signals. The implant receiver 105 can also include or be connected to sensors, for example a sensor 120. Each sensor monitors and senses various health details. Examples of the sensors include, but are not limited to, pacemakers and brain sensors. Similarly, the controller transceiver 110 also includes or is connected to an antenna 115 b to transmit and receive signals.
The implant receiver 105 and the controller transceiver 110 can communicate with each other in a medical implant communication service (MICS) frequency band. The MICS frequency band ranges from 402 megahertz (MHz) to 405 MHz. The implant receiver 105 and the controller transceiver 110 can also communicate with each other in a medical data services (MEDS) frequency band. The MEDS frequency band ranges from 401 MHz to 402 MHz, and from 405 MHz to 406 MHz. The frequency band can be referred to as a band of channels.
A communication session is initiated by the controller transceiver 110. The controller transceiver 110 selects a channel for transmission based on certain parameters. In one example, the controller transceiver 110 selects either a least interfered channel or a channel which has interference power below a threshold. The selection process can be referred to as “Listen Before Talk” (LBT). The controller transceiver 110 then transmits a signal in the channel.
The implant receiver 105 scans the band of channels, and detects the signal and identifies the channel that carries the signal. A portion of the implant receiver 105 is explained in detail in conjunction with FIG. 2.
Referring to FIG. 2, the implant receiver 105 includes a radio frequency receiver 205 that receives a first set of contents of a band of channels through an antenna 115 a. The content in the band of channels can be referred to as the first set of contents. The first set of contents can be referred to as the contents received at the radio frequency receiver 205. The implant receiver 105 includes a processing circuit 210 that is coupled to the radio frequency receiver 205. The radio frequency receiver 205 can be centered in middle of MICS+MEDS band to receive the band of channels. The radio frequency receiver 205 includes a low noise amplifier 215 for amplifying the first set of contents of the band of channels. The radio frequency receiver 205 also includes a mixer 220 for down-converting the first set of contents. The radio frequency receiver 205 can also include an analog filter 225 that is capable to filter the first set of contents.
In one embodiment, the first set of contents is converted to digital samples using an analog to digital converter. The digital samples can then be referred to as a second set of contents which is processed in parallel by the processing circuit 210.
In another embodiment, the digital samples can be stored and subset of the digital samples can be processed in parallel by the processing circuit 210.
In yet another embodiment, the first set of contents can be processed in parallel using analog circuit.
The processing circuit 210 includes various components for processing the second set of contents. The processing circuit 210 is explained in detail in conjunction with FIG. 3.
Referring to FIG. 3, the processing circuit 210 includes an analog-to-digital converter (ADC) 301 that converts the first set of contents into digital samples. Examples of the ADC 301 include, but are not limited to, a flash type ADC, a successive-approximation type ADC, and a sigma-delta type ADC. The bandwidth and operating rate of ADC 301 are capable to process the band of channels simultaneously. The digital samples are then processed in parallel.
In some embodiments, the processing circuit 210 includes a storage device, coupled to the ADC 301, to store the digital samples. The stored digital samples are then processed one by one or in parallel. The storage device helps in reducing number of parallel paths and hence reduction in area. Further, the ADC 301 and radio frequency components of an implant receiver can be inactivated, after the digital samples are stored, to save power.
The processing circuit 210 includes at least one mixer, for example, a mixer 310 a and a mixer 310 n, that divides the digital samples into multiple paths, for example a first path and a second path. Each path corresponds to a channel. In one embodiment, the processing circuit 210 can include a single path. For example, if the processing circuit 210 includes the storage device, then the digital samples can be processed one by one in a single path. The path can be programmed differently every time to search for the signal in the different channels. For example, there can be 10 channels each of bandwidth 300 KHz in the MICS band. Each channel of 300 KHz can be processed one by one. If we do not want to use a memory then we need to have processing circuit that can process all 10 channels in parallel, thereby increasing the area. Once we have the memory, then each channel may even be processed one at a time using only area for one channel. The channel is then programmed differently every time to search for signal in the different channels.
In another embodiment, the processing circuit 210 can have two paths. For example, a first path corresponds to channels Fch0 to Fch4 and a second path corresponds to channels Fch5 to Fch9. The two paths can then further be divided to yield a path for each channel.
In yet another embodiment, the processing circuit 210 can have a plurality of paths. For example, the processing circuit 210 can have a first path for channel Fch0, a second path for channel Fch1, a third path for channel Fch2 and so on. For example, there can be 10 channels each of bandwidth 300 KHz in the MICS band. The 10 channels can be processed in parallel. In some embodiments, various numbers of channels for example 2 or 3 or 4 channels can be processed in parallel.
The mixer 310 a can be referred to as a first one of the plurality of mixers. The mixer 310 a in conjunction with the RRC filter 315 a selects content from the first set of contents to form a first path. The first path and the content correspond to a channel.
A frequency band corresponding to a path can be selected using the mixer 310 a and a frequency Fch0. The frequency band corresponding to another path can be selected using the mixer 310 n and a frequency Fch9. The processing circuit 210 further includes at least one filter, for example a root-raised-cosine (RRC) filter 315 a and a RRC filter 315 n coupled to the mixer 310 a and the mixer 310 n respectively. The filter can also be a low-pass filter. The RRC filter 315 a, in one embodiment, is matched to a transmit pulse shaping filter, which is used for pulse shaping the transmitted signal in the transmitter. The RRC filter 315 a also removes out of band signals and noise from the input.
The processing circuit 210 can further include a circuit for correcting a frequency offset. Each path includes at least one mixer. For example, the first path includes a mixer 310 a 1, a mixer 310 a 2, and a mixer 310 a 3. A second path includes a mixer 310 n 1, a mixer 310 n 2, and a mixer 310 n 3. Each mixer hypothesizes on the frequency offset. Any mismatch between the transmit carrier frequency and the receiver's channel frequency produces a frequency offset in the digital samples. The frequency offset can be removed by hypothesizing on the offset and correcting the hypothesized frequency from the signal. In one example, three hypotheses are used per path. By using three hypotheses, any radio frequency error in the digital samples is reduced to one third of total error. For example, for the frequency offset in the range of ±25 parts per million (ppm) which is approximately equal to ±18 degrees per digital symbol for a symbol rate of 200 KHz, the phase change can be calculated as follows:
Phase change=360*delta*10̂(−6)*fc*Ts.
where delta is the ppm mismatch between the transmission and receiving frequencies, fc is the channel frequency and Ts is the time between one digital symbol and the next. For example, consider delta=25, fc˜=400 MHz and Ts= 1/200 KHz=5 usecs. Therefore, phase change=360×25×400×5e−6=18 degrees
By using three hypotheses, the uncertainty is reduced to ±6 degrees per digital symbol. The reduction of phase change helps in detection of certain types of signals. For example, if a pseudo-random sequence is used to modulate the bits at the controller transceiver, then the implant receiver depends on the correlation pattern of the pseudo-random sequence to detect the signal in presence of noise. The correlation pattern deviates from a desired correlation pattern, if the frequency offset between transmission and reception is large. In one example, the frequency offset can be calculated as follows:
Frequency offset=±25e−6×400e6=±10 KHz
In one example, corresponding to each mixer in the first path, three frequencies F0, F1, and F2 can be selected for hypothesizing. The three frequencies can be F0=+6.6 KHz, F1=0 KHz, and F2=−6.6 KHz respectively. The frequency offset of the signal to be detected can be 7 KHz. Then the output of mixer 310 a 1 corresponds to +13.6 KHz, the output of mixer 310 a 2 corresponds to 7 KHz, and the output of mixer 310 a 3 corresponds to 0.4 KHz. The lowest frequency offset is also referred to as residual frequency offset. For example, the residual frequency offset is 0.4 KHz in the illustrated example. Further, correlation of the digital samples can result in a peak amplitude for the frequency corresponding to mixer 310 a 3 as the residual frequency offset is lowest in the output of mixer 310 a 3, thereby determining the signal in the channel.
Each path includes at least one correlator. For example, the first path includes a correlator 320 a 1, a correlator 320 a 2, and a correlator 320 a 3. The second path includes a correlator 320 n 1, a correlator 320 n 2, and a correlator 320 n 3. Each correlator correlates the digital sample with a predefined sequence, for example a pseudorandom sequence, a gold coded sequence, a barker sequence, and walsh code sequence, present in the implant receiver. Correlation is a measure of the similarity of the two signals. Each correlator determines a peak value of a sample of the signal and checks the peak value against a threshold.
Each path further includes at least one accumulator. For example, the first path includes an accumulator 325 a 1, an accumulator 325 a 2, and an accumulator 325 a 3. The second path includes an accumulator 325 n 1, an accumulator 325 n 2, and an accumulator 325 n 3. Each accumulator, for example the accumulator 325 a 1, adds an output of corresponding correlator, for example the correlator 320 a 1, non-coherently across multiple periods to yield a correlation peak. The multiple periods can be equal to storage length of the pseudorandom sequence. For example, for the pseudorandom sequence with length 7, the accumulator 325 a 1 adds successive correlated signals every 7 samples. If y(n) is the output of the accumulator 325 a 1 and x(n) is the input of the accumulator 325 a 1, then y(n)=y(n−7)+x(n). In other embodiments, block addition can also be performed, where y(n)=Σx(n−7i), where i=0,1, . . . ,N−1, where N is the number of blocks of length 7 that are added. If the correlation peak exceeds a correlation threshold then the signal is detected.
In some embodiments, each path also includes at least one peak to off-peak estimator. For example, the first path includes a peak to off-peak estimator 330 a 1, a peak to off-peak estimator 330 a 2, and a peak to off-peak estimator 330 a 3. The second path includes a peak to off-peak estimator 330 n 1, a peak to off-peak estimator 330 n 2, and a peak to off-peak estimator 330 n 3. Each peak to off-peak estimator determines a ratio of a peak value of a sample in an output of the accumulator or the correlator to an average value of off-peak samples in the output and compares the ratio against a threshold.
The processing circuit 210 further includes a state machine circuit 335 that identifies a channel carrying the signal based on at least one of the correlation peak and peak to off-peak ratio of each channel. Each path is connected to the state machine circuit 335. In one example, the state machine circuit 335 selects the channel that has the highest peak-to-off-peak ratio or correlation peak. The state machine circuit 335 indicates presence of the signal in the path and identifies the channel corresponding to the path as the signal carrying channel. In other embodiments, the state machine 335 may indicate the most likely channels which may then be searched for longer time to detect the actual channel in which signal is present.
It is noted that any existing circuit for the state machine circuit 335 can be used.
In some embodiments, the processing circuit 210 also includes an automatic gain controller (AGC) 340 coupled to the ADC 301 to adjust the gain based on input power and output power of the filter 305. The processing circuit 210 also includes a received signal strength indicator (RSSI) circuit coupled to the AGC. The RSSI is a power estimation circuit that estimates power in the digital samples. The RSSI can also detect presence of the signal having high strength. The RSSI can be used for when the implant receiver is in low sensitivity mode.
The processing circuit 210 can be included in a physical layer circuit of the implant receiver. The implant receiver can have several layers, for example a radio frequency layer, a physical layer, a medium access control layer and other layers.
FIG. 4 illustrates an exemplary correlation graph. X-axis represents time corresponding to various signals and Y-axis represents amplitudes of various signals. A peak value of a sample 405 having a maximum peak indicates that the predefined sequence is detected. In some embodiments, ratio of the peak value and an average value of off-peak samples 410 can also be calculated and checked against a threshold. If the ratio exceeds the threshold then the predefined sequence is detected. The ratio can be referred to as peak-to-off-peak signal to noise ratio.
In one example, the off-peak samples can include samples other than the sample having the maximum peak. In another example, the off-peak samples can include samples other than the sample having the maximum peak and other than adjacent samples of the sample having the maximum peak.
FIG. 5 is a method for signaling in a medical implant based system.
At step 505, a first set of contents of a band of channels is received by a receiver, hereafter referred to as implant receiver. In one embodiment, the first set of contents can be converted into digital samples and processed.
At step 510, a second set of contents of a plurality of channels from the band of channels is processed in parallel.
In one embodiment, the first set of contents is converted to digital samples using an analog to digital converter. The digital samples can then be referred to as a second set of contents which is processed in parallel.
In another embodiment, the digital samples can be stored and subset of the digital samples can be processed in parallel.
In yet another embodiment, the first set of contents can be processed in parallel.
The processing includes forming a first path for contents of a first channel, a second path for contents of a second channel and so on. One path is formed for one channel. Several such paths can be formed based on area requirement of the implant receiver. In each path a frequency offset can be corrected. The correcting includes hypothesizing on the frequency offset to yield a filtered content which has less residual frequency offset. The removal of frequency improves correlation. Further, the filtered content obtained from the hypothesis is correlated with a predefined sequence. The correlation results in a correlation peak. The correlation peak is checked against a correlation threshold. If the correlation peak exceeds the correlation threshold then step 515 is performed, else the path and hence the channel is discarded.
It is noted that various methods of correcting frequency offset can be used.
In some embodiments, a ratio of a peak value of a sample in an output of the correlation to an average value of off-peak samples in the output can be determined and checked against a threshold. The output of the correlation can be referred to as the output of the processing. If the threshold is exceeded then step 515 is performed, else the path and hence the channel is discarded.
At step 515, a signal is detected in the band of channels. Further, a channel that carries the signal is identified, for example by using a state machine circuit.
In the foregoing discussion, the term “coupled or connected” refers to either a direct electrical connection between the devices connected or an indirect connection through intermediary devices. The term “signal” means at least one current, voltage, charge, data, or other signal.
The foregoing description sets forth numerous specific details to convey a thorough understanding of embodiments of the disclosure. However, it will be apparent to one skilled in the art that embodiments of the disclosure may be practiced without these specific details. Some well-known features are not described in detail in order to avoid obscuring the disclosure. Other variations and embodiments are possible in light of above teachings, and it is thus intended that the scope of disclosure not be limited by this Detailed Description, but only by the Claims.

Claims

1. A method for signaling in a medical implant based system, the method comprising:

receiving a first set of contents of a band of channels by a receiver;

processing in parallel a second set of contents of a plurality of channels from the band of channels; and

detecting a signal in the band of channels based on the processing.

2. The method as claimed in claim 1, wherein the receiver is a medical implant receiver.

3. The method as claimed in claim 1, wherein the processing comprises:

converting the first set of contents into digital samples.

4. The method as claimed in claim 3, wherein the second set of contents comprises:

the digital samples of the first set of contents.

5. The method as claimed in claim 3, wherein the processing further comprises:

storing the digital samples of the first set of contents in a storage device; and

selecting the second set of contents from the digital samples.

6. The method as claimed in claim 1, wherein processing content of each channel comprises:

correcting a frequency offset to obtain a filtered content; and

correlating the filtered content with a predefined sequence.

7. The method as claimed in claim 1, wherein processing content of each channel comprises:

hypothesizing on one or more frequency offsets; and

correlating filtered content obtained from each hypothesis with a predefined sequence.

8. The method as claimed in claim 7, wherein the predefined sequence is one of:

a pseudorandom sequence;

a gold coded sequence;

a barker sequence; and

a walsh code sequence.

9. The method as claimed in claim 1, wherein processing content of each channel comprises:

determining a peak value of a sample in an output of the processing; and

checking the peak value against a threshold.

10. The method as claimed in claim 1, wherein processing content of each channel comprises:

determining a ratio of a peak value of a sample in an output of the processing to an average value of off-peak samples in the output of the processing; and

checking the ratio against a threshold.

11. The method as claimed in claim 1 and further comprising:

identifying a channel that carries the signal.

12. A method for signaling in a medical implant based system, the method comprising:

receiving a first set of contents of a band of channels by a receiver;

converting the first set of contents into digital samples;

storing the digital samples of the first set of contents;

selecting a subset of the digital samples, the subset comprising contents of a plurality of channels from the band of channels;

correcting one or more frequency offsets in the subset in parallel to obtain a filtered content for each channel;

correlating the filtered content with a predefined sequence; and

detecting a signal in the band of channels based on an output of the correlating.

13. A receiver circuit comprising:

a radio frequency receiver that receives a first set of contents of a band of channels;

a processing circuit coupled to the radio frequency receiver to

process in parallel a second set of contents of a plurality of channels of the band of channels, and

detect a signal in the band of channels.

14. The receiver circuit as claimed in claim 13 and further comprising:

an analog-to-digital converter, coupled to the radio frequency receiver, that converts the first set of contents into digital samples.

15. The receiver circuit as claimed in claim 14 and further comprising:

a storage device, coupled to the analog-to-digital converter, that stores the digital samples.

16. The receiver circuit as claimed in claim 13, wherein the processing circuit comprises:

a plurality of mixers; and

a plurality of filters, a first one of the plurality of filters coupled to a first one of the plurality of mixers, the first one of the plurality of filters selecting content from the first set of contents in conjunction with the first one of the plurality of mixers to form a first path, the first path and the content being corresponding to a first channel.

17. The receiver circuit as claimed in claim 16, wherein the first path of the processing circuit comprises:

at least one mixer that hypothesizes on a frequency offset of the content;

at least one correlator responsive to hypothesizing to correlate filtered content obtained from the hypothesizing with a predefined sequence; and

at least one accumulator that adds correlated content.

18. The receiver circuit as claimed in claim 17, wherein the first path of the processing circuit further comprises:

at least one peak to off-peak estimator that determines a ratio of a peak value of a sample in an output of processing to an average value of off-peak samples in the output of the processing and compares the ratio against a threshold.

19. The receiver circuit as claimed in claim 13 and further comprising:

a state machine circuit, coupled to the processing circuit, that identifies a channel that carries the signal.

20. The receiver circuit as claimed in claim 13, wherein the receiver circuit is a medical implant receiver.