CA2056914A1 - Motion sensor based on rayleigh faded signal - Google Patents
Motion sensor based on rayleigh faded signalInfo
- Publication number
- CA2056914A1 CA2056914A1 CA 2056914 CA2056914A CA2056914A1 CA 2056914 A1 CA2056914 A1 CA 2056914A1 CA 2056914 CA2056914 CA 2056914 CA 2056914 A CA2056914 A CA 2056914A CA 2056914 A1 CA2056914 A1 CA 2056914A1
- Authority
- CA
- Canada
- Prior art keywords
- signal
- rayleigh
- velocity
- radio
- rate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Abstract
Abstract of the Disclosure In a radio receiver, a motion sensor includes means for determining the velocity of the receiver with respect to a source of an RF signal having Rayleigh fade characteristics, including a receiver for receiving the RF signal, a received signal strength indicator for producing an indicator related to the strength of the RF
signal, and a means for determining the rate of Rayleigh fading of the indicator, from which can be determined the velocity of the radio with respect to the source of the RF signal based on the Rayleigh fade rate.
signal, and a means for determining the rate of Rayleigh fading of the indicator, from which can be determined the velocity of the radio with respect to the source of the RF signal based on the Rayleigh fade rate.
Description
~691~
MOTION SENSOR BASED ON RAYLEIGH FADED SIGNAL
Field of the Invention This invention relates to motion sensors or detectors, and more particularly to motion sensors which sense motion by relying on the characteristics of a radio signal.
Background of the Invention There are many applications in analog or digital radio communications where it is desirable to know whether the radio terminal is ~tationary or moving, and, if it is moving, the approximate speed. Some conventional techniques of detecting motion and speed use external devices, such as sensors on a vehicle speedometer, wheels, or transmission, which are only useful in permanently mounted mobile units and are difficult to install.
Other techniques use motion detectors based on accelerometers mounted inside the radio. These devices are often too sensitive to be useful since they may cause false triggering from vibrations caused by vehicles moving past, or when the operator types on a keyboard of a mobile data terminal.
205~91~
Summary of the Invention This invention relates to a motion sensor which operates by sensing the fade rate of a Rayleigh fading radio signal. The fade rate is proportional to the vehicle speed, so the fade rate provides an indication of the velocity of the radio receiving the signal. This approach has several significant advantages over conventional 0 methods~ in that no external devices or cabling are required, and the method can be used with a portable as well as with a vehicle mounted terminal.
Brief Description of the Drawings FIG. 1 is a graph which shows the amplitude of a typical Rayleigh faded signal as a function of time.
FIG. 2 is a graph showing the level crossing rate of a signal vs. a reference signal level.
FIG. 3 is a block diagram of a radio adapted to includ~ a motion detector according to the invention.
FIG. 4 is a flow chart descri~ing an algorithm capable of determining motion according to the invention.
Detailed Description of a Preferred Embodiment In a cellular telephone or mobile data radio system a radio signal does not generally follow a direct path between the mobile or portable unit and the base station. In most cases there are multiple reflections of the signal which result in 2~691~
Rician or Rayleigh fading. Rician fading refers to the situation in which there is a strong direct path component of the received signal, and Rayleigh fading refers to the situation in which there is no direct path component. This invention is particularly useful in those cases where the radio channel propagation characteristics are closer to Rayleigh than Rician.
In Rayleigh fading the received radio signal 0 is diminished by periodic fades, the periodicity being related to the speed that the mobile or portable unit is moving. FIG. 1 shows the amplitude of a typical Rayleigh faded signal as a function of time.
It has been shown (D.O. Reudink, "Properties of Mobile Radio Propagation above 400 MHz", IEEE
Transac~ions on Vehicular Technology, vol. VT-23, pp. 143-159, Nov. 1974.) that the level crossing rate, Nrr which is the expected rate at which a carrier envelope crosses a specified signal level R in the positive direction, is given by:
Nr= t2~)1/2 fm ~ exp(_g2) where Nr= level crossing rate fm= the maximum Doppler shift ~ = specified signal level R
divided by RMS average signal level since fm= ~ = ~ = vf 2~ ~ c Nr= (2~)1/2 v f ~ exp(~2) where v= velocity c f= RF frequency c= speed of light 20~691~
FIG. 2 shows the level crossing rate as a function of the specified received signal level R.
The received signal level R is measured relative to the RMS average signal level. The maximum level crossing rate is obtained for a received signal level R which is 3 dB lower than the RMS
average signal level.
By measuring the level crossing rate, the velocity of the mobile or portable unit relative 0 to the base station or the source of the received signal can be calculated:
v= ~_~r ex~ L
(2O 1/2 If the signal level R is set equal to the RMS
average signal level, then ~=1.0, and v= 2.718 c NL
(2O 1/2f Since the fre~uency f is known, the level crossing rate Nr is the only variable on the right side of the equation. Calculation of the velocity is simply a matter of multiplying the level crossing rate Nr by the other values, which are constant. An error of less than plus or minus 5 dB in measuring the RMS average signal level will likely produce an error of less than 50% in measuring vehicle speed, an error level which is tolerable in a system where it is desired only to know whether a vehicle or a radio is in motion, and the actual velocity thereof is not critical.
FIG. 3 shows one embodiment of the motion 3~ sensor. A radio 10 provides a Received Signal Strength Indicator (RSSI) analog output 12, which 20~69~
is proportional to the received signal strength compared to a reference signal level. Since this i9 proportional to the signal strength, the RMS
average signal level can be calculated by averaging or low pass filtering this signal, rather than squaring and averaging as would be the case if it wexe on a linear scale. An upper low pass filter 14 has a corner frequency of 2 Hz, and serves to average the RSSI output to provide an RMS average signal level. The ~ilter corner frequency is selected to be longer than one Rayleigh fade cycle at the slowest speed that the circuit is designed to operate at, which in this case is a comfortable walking speed of 3 mph for an 850 MHz radio.
The lower low pass filter 16 reduces the bandwidth o~ the Rayleigh faded RSSI signal such that it can be sampled by a microprocessor without aliasing. This requires that the low pass filter 16 have a corner frequency less than one-half the planned sampling rate. The corner frequency o~
this filter must also be higher than the highest Rayleigh fade rate expected, which is about 68 Hz for a vehicle travelling at 60 mph and an 850 MHz radio. A corner frequency of 200 Hz is selected as being arbitrarily high, which would allow a corresponding microprocessor sampling rate of ~00 Hz or one sample every 2.5 milliseconds.
The outputs of the two filters are brought into a comparator 18. The output of the comparator 18 makes a 0 to 1 transition when the RSSI signal drops below the RMS average, and a 1 to 0 transition when it rises above the RMS
average. This one bit signal is input to a microprocessor 20, which counts either 0 to 1 2~569:~
transitions or 1 to 0 transitions, but not both.
The count of transitions in one second is the level crossing ra~e, from which the velocity can be calculated.
The RMS average level is also input from the low pass filter 14 to the microprocessor unit 20 through the A/D converter 22. This RMS average signal level can be used to assess the li~ely accuracy of the velocity calculation. This information would be useful if ~he system were used to calculate cell handoff information in, for example~ a cellular telephone system during cell handoff. The main contributor to error in the velocity calculation is error in measuring the RMS
average signal level, and the error is more likely during periods when the RSSI level is fluctuating wildly. This could occur, for example, when there is shadowing caused b~ large buildings or other concrete structures. Short term fluctuations caused by Rayleigh fading are filtered out by the low pass filter 14, so if the RMS average signal level sampled by the microprocessor 20 varies by no more than 5 dB over a period of several seconds the accuracy of the velocity calculation is questionable.
The process described above as implemented within a microprocessor or digital signa~l processor is shown in FIG.4 which is a flow chart describing an algorithm which could be used in such an implementation. The RSSI is sampled at 30, at a rate of, for example, 400 samples per second. The samples are filtered at 32 as previously described, and the filtered samples are compared to unfiltered samples at 34 where the z~ro to one transitions are detected. These 7 2~91~
transitions are counted at 36, and the velocity of the radio is calculated at 38.
MOTION SENSOR BASED ON RAYLEIGH FADED SIGNAL
Field of the Invention This invention relates to motion sensors or detectors, and more particularly to motion sensors which sense motion by relying on the characteristics of a radio signal.
Background of the Invention There are many applications in analog or digital radio communications where it is desirable to know whether the radio terminal is ~tationary or moving, and, if it is moving, the approximate speed. Some conventional techniques of detecting motion and speed use external devices, such as sensors on a vehicle speedometer, wheels, or transmission, which are only useful in permanently mounted mobile units and are difficult to install.
Other techniques use motion detectors based on accelerometers mounted inside the radio. These devices are often too sensitive to be useful since they may cause false triggering from vibrations caused by vehicles moving past, or when the operator types on a keyboard of a mobile data terminal.
205~91~
Summary of the Invention This invention relates to a motion sensor which operates by sensing the fade rate of a Rayleigh fading radio signal. The fade rate is proportional to the vehicle speed, so the fade rate provides an indication of the velocity of the radio receiving the signal. This approach has several significant advantages over conventional 0 methods~ in that no external devices or cabling are required, and the method can be used with a portable as well as with a vehicle mounted terminal.
Brief Description of the Drawings FIG. 1 is a graph which shows the amplitude of a typical Rayleigh faded signal as a function of time.
FIG. 2 is a graph showing the level crossing rate of a signal vs. a reference signal level.
FIG. 3 is a block diagram of a radio adapted to includ~ a motion detector according to the invention.
FIG. 4 is a flow chart descri~ing an algorithm capable of determining motion according to the invention.
Detailed Description of a Preferred Embodiment In a cellular telephone or mobile data radio system a radio signal does not generally follow a direct path between the mobile or portable unit and the base station. In most cases there are multiple reflections of the signal which result in 2~691~
Rician or Rayleigh fading. Rician fading refers to the situation in which there is a strong direct path component of the received signal, and Rayleigh fading refers to the situation in which there is no direct path component. This invention is particularly useful in those cases where the radio channel propagation characteristics are closer to Rayleigh than Rician.
In Rayleigh fading the received radio signal 0 is diminished by periodic fades, the periodicity being related to the speed that the mobile or portable unit is moving. FIG. 1 shows the amplitude of a typical Rayleigh faded signal as a function of time.
It has been shown (D.O. Reudink, "Properties of Mobile Radio Propagation above 400 MHz", IEEE
Transac~ions on Vehicular Technology, vol. VT-23, pp. 143-159, Nov. 1974.) that the level crossing rate, Nrr which is the expected rate at which a carrier envelope crosses a specified signal level R in the positive direction, is given by:
Nr= t2~)1/2 fm ~ exp(_g2) where Nr= level crossing rate fm= the maximum Doppler shift ~ = specified signal level R
divided by RMS average signal level since fm= ~ = ~ = vf 2~ ~ c Nr= (2~)1/2 v f ~ exp(~2) where v= velocity c f= RF frequency c= speed of light 20~691~
FIG. 2 shows the level crossing rate as a function of the specified received signal level R.
The received signal level R is measured relative to the RMS average signal level. The maximum level crossing rate is obtained for a received signal level R which is 3 dB lower than the RMS
average signal level.
By measuring the level crossing rate, the velocity of the mobile or portable unit relative 0 to the base station or the source of the received signal can be calculated:
v= ~_~r ex~ L
(2O 1/2 If the signal level R is set equal to the RMS
average signal level, then ~=1.0, and v= 2.718 c NL
(2O 1/2f Since the fre~uency f is known, the level crossing rate Nr is the only variable on the right side of the equation. Calculation of the velocity is simply a matter of multiplying the level crossing rate Nr by the other values, which are constant. An error of less than plus or minus 5 dB in measuring the RMS average signal level will likely produce an error of less than 50% in measuring vehicle speed, an error level which is tolerable in a system where it is desired only to know whether a vehicle or a radio is in motion, and the actual velocity thereof is not critical.
FIG. 3 shows one embodiment of the motion 3~ sensor. A radio 10 provides a Received Signal Strength Indicator (RSSI) analog output 12, which 20~69~
is proportional to the received signal strength compared to a reference signal level. Since this i9 proportional to the signal strength, the RMS
average signal level can be calculated by averaging or low pass filtering this signal, rather than squaring and averaging as would be the case if it wexe on a linear scale. An upper low pass filter 14 has a corner frequency of 2 Hz, and serves to average the RSSI output to provide an RMS average signal level. The ~ilter corner frequency is selected to be longer than one Rayleigh fade cycle at the slowest speed that the circuit is designed to operate at, which in this case is a comfortable walking speed of 3 mph for an 850 MHz radio.
The lower low pass filter 16 reduces the bandwidth o~ the Rayleigh faded RSSI signal such that it can be sampled by a microprocessor without aliasing. This requires that the low pass filter 16 have a corner frequency less than one-half the planned sampling rate. The corner frequency o~
this filter must also be higher than the highest Rayleigh fade rate expected, which is about 68 Hz for a vehicle travelling at 60 mph and an 850 MHz radio. A corner frequency of 200 Hz is selected as being arbitrarily high, which would allow a corresponding microprocessor sampling rate of ~00 Hz or one sample every 2.5 milliseconds.
The outputs of the two filters are brought into a comparator 18. The output of the comparator 18 makes a 0 to 1 transition when the RSSI signal drops below the RMS average, and a 1 to 0 transition when it rises above the RMS
average. This one bit signal is input to a microprocessor 20, which counts either 0 to 1 2~569:~
transitions or 1 to 0 transitions, but not both.
The count of transitions in one second is the level crossing ra~e, from which the velocity can be calculated.
The RMS average level is also input from the low pass filter 14 to the microprocessor unit 20 through the A/D converter 22. This RMS average signal level can be used to assess the li~ely accuracy of the velocity calculation. This information would be useful if ~he system were used to calculate cell handoff information in, for example~ a cellular telephone system during cell handoff. The main contributor to error in the velocity calculation is error in measuring the RMS
average signal level, and the error is more likely during periods when the RSSI level is fluctuating wildly. This could occur, for example, when there is shadowing caused b~ large buildings or other concrete structures. Short term fluctuations caused by Rayleigh fading are filtered out by the low pass filter 14, so if the RMS average signal level sampled by the microprocessor 20 varies by no more than 5 dB over a period of several seconds the accuracy of the velocity calculation is questionable.
The process described above as implemented within a microprocessor or digital signa~l processor is shown in FIG.4 which is a flow chart describing an algorithm which could be used in such an implementation. The RSSI is sampled at 30, at a rate of, for example, 400 samples per second. The samples are filtered at 32 as previously described, and the filtered samples are compared to unfiltered samples at 34 where the z~ro to one transitions are detected. These 7 2~91~
transitions are counted at 36, and the velocity of the radio is calculated at 38.
Claims (7)
1. A motion sensor including means for receiving an RF signal having Rayleigh fade characteristics comprising:
means for producing an indicator related to the strength of a received signal, and means responsive to the indicator for calculating the Rayleigh fade rate of the RF
signal.
means for producing an indicator related to the strength of a received signal, and means responsive to the indicator for calculating the Rayleigh fade rate of the RF
signal.
2. An RF communications device including means for receiving an RF signal having Rayleigh fade characteristics comprising:
means for producing an indicator related to the strength of a received signal, and means responsive to the indicator for calculating the Rayleigh fade rate of the RF
signal.
means for producing an indicator related to the strength of a received signal, and means responsive to the indicator for calculating the Rayleigh fade rate of the RF
signal.
3. A device in accordance with claim 2, further comprising means responsive to the Rayleigh fade rate for calculating the velocity of the RF communications device.
4. A device in accordance with claim 2, further comprising means responsive to the Rayleigh fade rate for calculating the velocity of the RF communications device with respect to the source of the received signal.
5. A radio receiver including means for determining the velocity of the receiver with respect to a source of an RF signal having Rayleigh fade characteristics comprising:
means for receiving the RF signal, means coupled to the means for receiving for producing an indicator related to the strength of the RF signal, means responsive to the indicator for producing a Rayleigh fade rate signal, and means responsive to the fade rate signal for indicating the velocity of the radio with respect to the source of the RF signal.
means for receiving the RF signal, means coupled to the means for receiving for producing an indicator related to the strength of the RF signal, means responsive to the indicator for producing a Rayleigh fade rate signal, and means responsive to the fade rate signal for indicating the velocity of the radio with respect to the source of the RF signal.
6. A radio receiver including means for determining the velocity of the receiver with respect to a source of an RF signal having Rayleigh fade characteristics comprising:
means for receiving the RF signal, means coupled to the means for receiving for producing an indicator related to the strength of the RF signal, means for determining the rate of Rayleigh fading of the indicator, and means for indicating the velocity of the radio with respect to the source of the RF signal based on the Rayleigh fade rate..
means for receiving the RF signal, means coupled to the means for receiving for producing an indicator related to the strength of the RF signal, means for determining the rate of Rayleigh fading of the indicator, and means for indicating the velocity of the radio with respect to the source of the RF signal based on the Rayleigh fade rate..
7. In a radio receiver, a method for determining the velocity of the receiver with respect to a source of an RF signal having Rayleigh fade characteristics, comprising the steps of:
receiving the RF signal, producing an indicator related to the strength of the RF signal, determining the rate of Rayleigh fading of the indicator, and indicating the velocity of the radio with respect to the source of the RF signal based on the Rayleigh fade rate.
receiving the RF signal, producing an indicator related to the strength of the RF signal, determining the rate of Rayleigh fading of the indicator, and indicating the velocity of the radio with respect to the source of the RF signal based on the Rayleigh fade rate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US62383690A | 1990-12-05 | 1990-12-05 | |
| US623,836 | 1990-12-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2056914A1 true CA2056914A1 (en) | 1992-06-06 |
Family
ID=24499582
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2056914 Abandoned CA2056914A1 (en) | 1990-12-05 | 1991-12-04 | Motion sensor based on rayleigh faded signal |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2056914A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6310573B1 (en) | 1997-06-18 | 2001-10-30 | Telefonaktiebolaget Lm Ericsson (Publ) | Velocity calculation |
| WO2007016181A1 (en) | 2005-07-27 | 2007-02-08 | Symbol Technologies, Inc. | System and method for monitoring a mobile computing product/arrangement |
| US7647049B2 (en) | 2006-07-12 | 2010-01-12 | Telefonaktiebolaget L M Ericsson (Publ) | Detection of high velocity movement in a telecommunication system |
| GB2464289A (en) * | 2008-10-08 | 2010-04-14 | Samsung Electronics Co Ltd | Estimating link qualities in a multi-carrier wireless communication system |
-
1991
- 1991-12-04 CA CA 2056914 patent/CA2056914A1/en not_active Abandoned
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6310573B1 (en) | 1997-06-18 | 2001-10-30 | Telefonaktiebolaget Lm Ericsson (Publ) | Velocity calculation |
| WO2007016181A1 (en) | 2005-07-27 | 2007-02-08 | Symbol Technologies, Inc. | System and method for monitoring a mobile computing product/arrangement |
| EP1915628B1 (en) * | 2005-07-27 | 2013-12-11 | Symbol Technologies, Inc. | System and method for monitoring a mobile computing product/arrangement |
| US7647049B2 (en) | 2006-07-12 | 2010-01-12 | Telefonaktiebolaget L M Ericsson (Publ) | Detection of high velocity movement in a telecommunication system |
| GB2464289A (en) * | 2008-10-08 | 2010-04-14 | Samsung Electronics Co Ltd | Estimating link qualities in a multi-carrier wireless communication system |
| GB2464289B (en) * | 2008-10-08 | 2012-12-05 | Samsung Electronics Co Ltd | Estimating link qualities in multi-carrier systems |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1287378C (en) | Apparatus for judging quality of mobile data communication | |
| US5625364A (en) | Apparatus and method for finding a signal emission source | |
| US5748108A (en) | Method and apparatus for analyzing traffic and a sensor therefor | |
| CA2390000A1 (en) | System and method for signal validation and leakage detection | |
| JPS61240725A (en) | Method and apparatus for measuring quality of wireless transmission channel | |
| JPS62279736A (en) | Apparatus and method for determining indication of received radio frequency signal intensity with high speed | |
| MX9800614A (en) | Method and apparatus for indicating an operable or non-operable connection between a portable radio and a vehicle kit. | |
| WO1998016079A3 (en) | Method for determining speed of terminal, and receiver | |
| CA2056914A1 (en) | Motion sensor based on rayleigh faded signal | |
| US5432442A (en) | Speed sensor including output signal proportional to air gap size | |
| CA1277014C (en) | Roadside beacon system | |
| JP3042755B2 (en) | Mobile station zone transfer control method | |
| JPH02222233A (en) | Same channel interference quantity measuring instrument | |
| JP3388540B2 (en) | Bit error rate measuring method and its measuring device | |
| EP1944618B1 (en) | Mobile terminal device, mobile speed determining method and program therefor | |
| JP3101635B2 (en) | Moving object detection device for data transmission equipment | |
| US6289058B1 (en) | Method and circuit arrangement for detecting short pulses of a digital input signal | |
| JP2797595B2 (en) | Receive level measuring instrument | |
| JPH01305393A (en) | System for measuring amount of rainfall | |
| JPH03291027A (en) | Reception level detection method in mobile communication | |
| Soares et al. | Signal sampling method for power measurements in mobile UHF environments | |
| JP2931771B2 (en) | Moving speed detector | |
| JPH10262005A (en) | Reception level measurement device and measurement method | |
| JPH1169418A (en) | Movement detection method for base station | |
| JPS62255886A (en) | Moving position measuring instrument |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |