Patent Application
20100036459
Embodiments of the disclosure relate to signaling in a medical implant based system.
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 transceiver forms a significant portion of the overall power consumption in the medical implant. Hence, it is desired to maximize efficiency of the medical implant transceiver to increase lifetime of the medical implant.
The power of the medical implant transceiver is utilized for performing various functions. In one example, power consumption in the medical implant transceiver is dominated by a listen mode of the medical implant transceiver. In the listen mode (when the implant transceiver listens for the signal), the medical implant transceiver wakes up periodically and searches for presence of a signal in a band of channels. It is desired to minimize time spent by the medical implant transceiver, in the listen mode, for detecting the signal to save power.
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 transceiver. Hence, the medical implant transceiver has to scan all channels to detect the signal. Currently, a power measurement technique is used to scan the channels. However, the power measurement technique may not be effective for the signals having low signal strength than the 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.
The signal once detected is decoded to determine whether the signal is intended for the medical implant transceiver. It is possible that the medical implant transceiver detects a signal which is not intended for the medical implant transceiver. For example, a signal for associating with a medical controller transceiver is not intended for the medical implant transceiver which is already associated. However, such determination is made at medium access control (MAC) layer at the medical implant transceiver leading to wastage of power. The situation worsens if several controllers are present in an area as the probability of detecting unwanted signals from different medical controllers increases.
An example of a method includes transmitting bits modulated with a predefined sequence in a band of channels by a first medical transceiver. The method includes detecting the predefined sequence by a second medical transceiver. The method also includes determining presence of a signal if the predefined sequence is detected.
Another example of a method includes transmitting bits modulated with a first predefined sequence of a plurality of predefined sequences by a first medical transceiver. The method includes detecting the first predefined sequence by a second medical transceiver when the second medical transceiver enters into an active state. The method also includes performing a predetermined action if the first predefined sequence is detected.
An example of a system includes a medical implant transceiver. The medical implant transceiver includes a radio frequency receiver that receives a signal. Further, the medical implant transceiver includes a demodulator that demodulates bits of the signal modulated with a predefined sequence. The medical implant transceiver also includes a correlator that correlates the signal with the predefined sequence to detect the predefined sequence and to determine presence of the signal in the channel.
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.
The implant transceiver 105a includes or is connected to an antenna 115a, and the implant transceiver 105b includes or is connected to an antenna 115b to transmit and receive signals. The implant transceiver 105a can also include or be connected to sensors, for example a sensor 120a and the implant transceiver 105b can also include or be connected to sensors, for example a sensor 120b. 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 110a also includes or is connected to an antenna 115c, and the controller transceiver 110a also includes or is connected to an antenna 115d to transmit and receive signals.
An implant transceiver, for example the implant transceiver 105a, and a controller transceiver, for example the controller transceiver 110a, 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 transceiver 105a and the controller transceiver 110a 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.
Each implant transceiver can have two states, an associated state and an unassociated state (listen mode). The associated state can be defined as a state in which an implant transceiver is associated with a controller transceiver. The unassociated state can be defined as a state in which an implant transceiver is not associated with a controller transceiver. The implant transceivers (105a and 105b) transition between an active state and an inactive state (a sleep state) irrespective of being in the associated state or the unassociated state. The implant transceivers (105a and 105b) spend bulk of the time in the inactive state. In the active state, the implant transceivers (105a and 105b) receive, transmit and process signals which lead to power consumption.
A communication session is initiated by the controller transceiver 110a. The controller transceiver 110a selects a channel for transmission based on certain parameters. In one example, the controller transceiver 110a 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 110a then transmits a signal in the channel. The signal can be of various types, for example a signal for association, a poll signal and a signal for data transfer.
When in the unassociated state, the implant transceiver 105a searches for the signal for association from the controller transceiver 110a. The channel in which the signal for association is present is unknown to the implant transceiver 105a and hence, the implant transceiver 105a needs to scan various channels to determine presence of the signal for association. The implant transceiver 105a needs to detect the signal for association in a time efficient manner. The controller transceiver 110a may transmit different types of signals for different implant transceivers. For example, in a hospital ward the controller transceiver 110a may be associated with different implant transceivers of various living organisms, and may be transmitting various poll signals and signals for data transfer. Hence, the implant transceiver 105a also needs to discard the poll signals and the signals for data transfer.
When in the associated state, the implant transceiver 105a searches for the poll signal or the signal for data transfer from the controller transceiver 110a. The implant transceiver 105a needs to detect the poll signal or the signal for data transfer in a time efficient manner. The controller transceiver 110a may transmit different types of signals for different implant transceivers. Hence, the implant transceiver 105a also needs to discard unwanted signals, for example the signal for association.
The controller transceivers (110a and 110b) transmit signals for respective implant transceivers (105a and 105b), and it is desired that the implant transceiver 105a detects the signal transmitted by the controller transceiver 110a and not from the controller transceiver 110b. For example, a living organism having the implant transceiver 105a and residing in an apartment having the controller transceiver 110a does not want the implant transceiver 105a to detect signals from the controller transceiver 110b present in a neighboring apartment. In another example, in an ICU, a living organism having the implant transceiver 105a concerned with brain details does not want the implant transceiver 105a to detect signals from the controller transceiver 110b used for monitoring heart. Detection of the signal from the controller transceiver 110b by the implant transceiver 105a may lead to malfunctioning of the implant transceiver 105a and can cause damage to the living organism. Further, such detection also leads to unnecessary power consumption.
A method for determining the signal in the band of channels in a power efficient manner is explained in detail in conjunction with
At step 205, bits of the signal modulated with a predefined sequence are transmitted. The bits can be transmitted by a first medical transceiver. The first medical transceiver can be a medical controller transceiver, hereinafter referred to as the controller transceiver or a medical implant transceiver, hereinafter referred to as the implant transceiver.
The predefined sequence is selected based on desired autocorrelation properties. Autocorrelation can be defined as a measure of correlation of a signal with itself. Examples of the predefined sequence include, but are not limited to, a pseudorandom sequence, a gold code sequence, a barker sequence, and a walsh code sequence. The length of the predefined sequence may be selected based on requirement, for example to achieve a desired processing gain.
In one embodiment, the bits are spread using the predefined sequence. For example, if the predefined sequence is of length 7 then a bit is spread using the predefined sequence and for every bit 7 chips are transmitted. A binary sequence that does not carry information but is used only for spreading is referred to as a chip. The processing gain that can be achieved in the implant transceiver is equal to 10*log10(Length)=10*log10(7) dB. After the bits are spread using the predefined sequence, the bits are modulated and transmitted. Various techniques can be used for modulation. Examples of the modulation techniques include, but are not limited to, binary phase shift keying, quadrature phase shift keying, and differential phase shift keying.
At step 210, presence of the predefined sequence is detected by a second medical transceiver, functioning as a receiver. Detecting presence of the predefined sequence includes detecting the predefined sequence. The second medical transceiver can be the implant transceiver or the controller transceiver. For example, if the first medical transceiver is the controller transceiver then the second medical transceiver can be the implant transceiver.
The implant transceiver alternates between an active state and an inactive state. When the implant transceiver is in the active state, the implant transceiver scans a band of channels. A signal present in a channel is received and correlated with the predefined sequence. An output of correlation is then processed to detect the predefined sequence. In some embodiments, the output of the correlation is averaged across multiple lengths of the predefined sequence. For example, if the predefined sequence of length 7 is used, then the output of the correlation may be averaged across 7 chips to improve strength of the signal and suppress noise. The averaging can be performed coherently or non-coherently. Different metrics can be used to detect the predefined sequence at the output of the correlation. For example, a ratio of a peak value of a sample, having a maximum peak, to an average value of peaks of off-peak samples can be used as a metric. The samples correspond to the signal. In one example, when there is no noise and the length of the predefined sequence is 7, the ratio is 7. The metric can then be compared against a threshold to detect the predefined sequence. The threshold can be selected to minimize probability of false alarm and to minimize probability of missing detection for a length of time allowed for detection of the predefined sequence. If the ratio exceeds the threshold then the predefined sequence is detected. Other metrics, for example comparing the peak value against another threshold can also be used. The processing gain achieved by the predefined sequence helps in detection of the signals with low strength, thereby enabling the implant transceiver to have high sensitivity.
The predefined sequence is embedded in the implant transceiver. If the predefined sequence is detected then step 215 is performed.
At step 215, presence of the signal is determined.
In some embodiment, the bits are demodulated and de-spreaded over the predefined sequence to obtain data. The signal can then be processed further.
At step 305, bits modulated on a first predefined sequence of a plurality of predefined sequences are transmitted by a first medical transceiver. The first medical transceiver can be a controller transceiver or an implant transceiver.
The predefined sequences can be selected based on autocorrelation and cross-correlation properties of the predefined sequences. The predefined sequences that have autocorrelation separated by a value exceeding an autocorrelation threshold and cross-correlation by a value less than a cross-correlation threshold can be selected. Cross-correlation can be defined as a measure of similarity of two signals. Autocorrelation can be defined as a measure of correlation of a signal with itself. In one example, four pseudorandom sequences of length 7 satisfying the autocorrelation and cross-correlation properties can be determined. The predefined sequences can then be assigned to and used by the controller transceiver for different functions.
In one scenario, for example an ICU, the ICU can be divided into cells, for example hexagonal cells. The four pseudorandom sequences (P1, P2, P3 and P4) can be assigned to the cells based on requirement. For example, P1 can be assigned to the cells for transmitting signal for association. P2, P3 and P4 can be assigned for transmitting signals indicating a predefined function. Examples of the predefined function include, but are not limited to, polling and data transfer. P2, P3 and P4 can be assigned in a way that controller transceivers in neighboring cells do not have same predefined sequence for transmission of signals for same function. Assigning of the sequences based on requirement minimizes interference among signals from different controller transceivers in adjacent cells. Predefined sequences with higher length, yielding more predefined sequences satisfying the autocorrelation and cross-correlation properties can also be used.
In another scenario, the ICU can have different controller transceivers for different organs of a living organism. For example, a controller transceiver for brain and another controller transceiver for heart. Different predefined sequences can then be assigned and used for different organs.
In some embodiments, the predefined sequences are hardcoded into the controller transceiver. The controller transceiver can select the predefined sequence for a specific use in response to an input from a user. The selected predefined sequence can be referred to as the first predefined sequence.
The bits are then spreaded and modulated with the predefined sequence, and transmitted. The spreading and modulating can be performed at a physical layer of the controller transceiver.
At step 310, presence of the predefined sequence is detected by a second medical transceiver. Detecting presence of the predefined sequence includes detecting the predefined sequence. The second medical transceiver can be the implant transceiver or the controller transceiver. For example, if the first medical transceiver is the controller transceiver then the second medical transceiver can be the implant transceiver.
The predefined sequence is detected at a physical layer of the implant transceiver and step 315 is then performed.
At step 315, a predetermined action is performed. The predetermined action includes at least one of determining presence of a signal for association, determining presence of a poll signal and determining presence of a signal for data transfer.
In some embodiments, if the signal for association is determined then the implant transceiver can get associated with the controller transceiver after performing further processing of the signal. The implant transceiver can send an acknowledgement to indicate association. The controller transceiver can then also send information indicating the predefined sequence that will be used by the controller transceiver for transmitting data in subsequent signals.
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.
The controller transceiver 110a includes a predefined sequence spreader 505 that spreads bits with a predefined sequence. The controller transceiver 110a also includes a modulator 510 that modulates the bits with the predefined sequence. The controller transceiver 110a includes a radio frequency transmitter 515 that transmits signals. The radio frequency transmitter 515 transmits the signals through an antenna 115c.
The controller transceiver 110a also includes a radio frequency receiver that receives signals. In one embodiment, a radio frequency transceiver can be present for performing functions of the radio frequency transmitter 515 and the radio frequency receiver.
The modulator 510 and the predefined sequence spreader 505 are present at a physical layer of the controller transceiver 110a.
The implant transceiver 105a includes a radio frequency receiver 605 that scans a band of channels and receives signals in the band of channels. The implant transceiver 105a includes a demodulator 610 that demodulates the bits modulated with the predefined sequence. The implant transceiver 105a also includes a correlator 615 that correlates the received signal with the predefined sequence. The correlator 615 also de-spreads the bits modulated with the predefined sequence. The implant transceiver 105a also includes an accumulator 620 that adds signals with a delay. In one example if the PN sequence length=7, then the accumulator 620 adds a delay equal to 7.
In some embodiments, the implant transceiver 105a further includes a peak-to-off-peak signal to noise ratio detector 625 that detects the predefined sequence.
The demodulator 610, the correlator 615, the accumulator 620, and the peak-to-off-peak signal to noise ratio detector 625 are present at a physical layer of the implant transceiver 105a.
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.
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”, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61086663 | Aug 2008 | US |
