WO2003073684A1 - Assessment of signal quality of a wirelessly received signal by estimation of a jitter - Google Patents

Assessment of signal quality of a wirelessly received signal by estimation of a jitter Download PDF

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Publication number
WO2003073684A1
WO2003073684A1 PCT/IB2003/000430 IB0300430W WO03073684A1 WO 2003073684 A1 WO2003073684 A1 WO 2003073684A1 IB 0300430 W IB0300430 W IB 0300430W WO 03073684 A1 WO03073684 A1 WO 03073684A1
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WO
WIPO (PCT)
Prior art keywords
signal
preamble
sum
indicative
values
Prior art date
Application number
PCT/IB2003/000430
Other languages
French (fr)
Inventor
Hendricus C. De Ruijter
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Koninklijke Philips Electronics N.V.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Priority to AU2003202754A priority Critical patent/AU2003202754A1/en
Publication of WO2003073684A1 publication Critical patent/WO2003073684A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/20—Arrangements for detecting or preventing errors in the information received using signal quality detector
    • H04L1/205—Arrangements for detecting or preventing errors in the information received using signal quality detector jitter monitoring
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0802—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection
    • H04B7/0805—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection with single receiver and antenna switching
    • H04B7/0808—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection with single receiver and antenna switching comparing all antennas before reception
    • H04B7/0811—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection with single receiver and antenna switching comparing all antennas before reception during preamble or gap period
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00—Arrangements for synchronising receiver with transmitter
    • H04L7/04—Speed or phase control by synchronisation signals
    • H04L7/041—Speed or phase control by synchronisation signals using special codes as synchronising signal
    • H04L7/046—Speed or phase control by synchronisation signals using special codes as synchronising signal using a dotting sequence

Definitions

  • the invention relates to wireless receiver systems for receiving a digital data signal for use in processors and other digital circuits, in particular in digital communication systems such as DECT cordless telephone handsets and base stations, GSM mobile phones, Bluetooth short-range RF communication, etc.
  • Eg in digital communication systems such as DECT data are transmitted in bursts, where each burst has a standardised preamble followed by the actual data.
  • One purpose of the preamble is to "alert" the receiver that data are underway and to provide bit synchronisation for synchronising the receiver.
  • the preamble usually consists of a series of alternating one's and zero's for a predetermined period of time.
  • the preamble is 16 bits with a frequency of 576 kHz, and the subsequent data rate is 1152 kbits/s.
  • the preamble is only 4 bits.
  • the preamble signal quality can be used to determine the start of the preamble, to facilitate long range applications, and to control an antenna switch selecting the receiving antenna among two or more receiving antennas having the best received signal quality.
  • Radio Signal Strength Indicator RSSI
  • This method only gives a good indication of quality under the assumption that a strong signal is a good signal, and this method only gives a very coarse indication of the true signal quality.
  • this quality assessment is inferior to other methods. Multi-path reception occurs when two or more versions of the same signal arrive at the receiver with different delays caused by reflecting and scattering objects.
  • Another known method detects out-of-band noise and requires quite some hardware.
  • the known cross correlation method requires recovering the clock signal from the received preamble signal, which takes at least a few bits of the preamble. In systems with a short preamble such as Bluetooth, valuable time will thereby be lost. In general, the reliability of this method is proportional to the number of bits used for recovering the clock signal.
  • the auto correlation method requires a one-bit time shifted version of the input signal. This method requires a large memory and a large computing capacity in order to execute the operations in real time.
  • US 5 960 046 discloses an antenna diversity radio system, in which a single receiver makes a performance measurement on each of two antennas in sequence during the beginning of a received data burst, ie the preamble.
  • a method of assessing the signal quality of the preamble signal of a received digital signal whereby time intervals between transitions between the high and low levels of the preamble signal are determined and compared to a predetermined reference time interval. For each determined time interval, a value indicative of the difference between the determined time interval and the predetermined reference time interval is calculated, and for the determined time intervals, a sum of the indicative values is formed and used as a quality indicator of frequency accuracy of the preamble signal.
  • a method of assessing the signal quality of the preamble signal of a received digital signal whereby time intervals between transitions between the high and low levels of the preamble signal are determined and compared to a predetermined reference time interval. For each determined time interval, a value indicative of the difference between the determined time interval and the predetermined reference time interval is calculated, and for the determined time intervals, a sum of the absolute values of the indicative values is formed and used as a quality indicator of phase accuracy of the preamble signal.
  • a weighted sum of the sum of the indicative values multiplied by a weighting factor and the sum of the absolute values of the indicative values multiplied by a weighting factor, and the weighted sum is used as a total quality indicator of the signal quality of the received signal.
  • the preamble signal is oversampled, and time intervals between transitions between the high and low levels of the preamble signal are determined by counting the number of sampling signal periods in such time intervals. For each determined time interval, a value indicative of the difference between the counted sampling signal periods and a predetermined number is calculated.
  • the thus obtained quality indicators can be used for assessing the received signal quality of each received signal and for selecting the antenna with best-received signal quality.
  • the quality of the preamble can be detected without spending time for clock recovery, since a fixed clock can be used.
  • the invention can be implemented using a relatively simple state machine, which has a very low requirement on hardware resources.
  • Figure 1 shows schematically a transmission system with a receiver having two receiving antennas
  • Figure 2 shows an example of the structure of received signal bursts with a preamble portion and a data portion
  • Figure 3 shows the principle of oversampling the preamble signal on a larger time scale than in Figure 2.
  • FIG. 1 shows a transmission system with a transmitter having a transmitting antenna TA.
  • a receiver has two receiving antennas RA1 and RA2.
  • the transmitter sends data in bursts, where each burst has a preamble, which is a sequence alternating between a high level and a low level at a fixed preamble frequency and for a predetermined period of time followed by the actual data.
  • the preamble signal is oversampled at a sampling frequency that is higher than the preamble frequency. In the shown example the sampling frequency is about 12 times higher than the preamble frequency.
  • a transition of the preamble signal from “low” level to “high” level or from “high” level to “low” level starts a counter (not shown) that counts the number of clock signal pulses in the time interval, until the next transition in the opposite direction occurs.
  • the receiver “knows” which preamble frequency can be expected, and thus how many clock signal pulses can be expected between two transitions between the low and high levels of the preamble signal. If the expected number is counted, an interim "error” value Ej of 0 (zero) is generated. For each additional counted clock signal pulse an error value Ej of +1 is generated, ie if two more clock signal pulses are counted than expected, an error value E, of +2 is generated.
  • an error value E is generated according to the formula:
  • the thus calculated frequency quality indicator I f is an indicator of the preamble frequency deviation from the expected preamble frequency.
  • a low I f value indicates a small deviation in preamble frequency from the expected frequency and thus a high preamble quality, which means that the received bit stream matches the bit rate of the preamble.
  • the thus calculated phase jitter quality indicator I p is an indicator of the phase jitter of the preamble signal.
  • a low I p value indicates a small amount of phase jitter in the preamble signal thus a high preamble quality.
  • the phase jitter quality indicator I p can only be used, if the frequency quality indicator I f is sufficiently low. If the preamble signal is sampled at an oversampling rate of 12, and if 16 transitions of the preamble signal are measured, then for a good preamble reception I p ⁇ 10, and for a poor preamble reception one might have I p > 60.
  • a total preamble quality indicator PQ can be calculated as a weighted sum of the frequency quality indicator I and the phase jitter quality indicator I p in accordance with the following formula:
  • the total preamble quality indicator PQ c f -I f + c p I p (4) where Cf and c p are appropriately chosen weighting factors.
  • the total preamble quality indicator PQ can also be calculated as a weighted sum of selected ones of the known signal quality indicators such as the Radio Signal Strength Indicator (RSSI), whereby the reliability can be further improved.
  • RSSI Radio Signal Strength Indicator
  • any one of the frequency quality indicator I f , the phase jitter quality indicator I p and the total preamble quality indicator PQ can be used as an indicator of the preamble quality, and in an antenna diversity system, ie a receiver system having two or more receiving antennas, the chosen quality indicator can be used to select the antenna with the best preamble quality, ie the lowest quality indicator value.

Abstract

In assessing the signal quality of the preamble signal of a received digital signal, time intervals between transitions between the high and low levels of the preamble signal are determined and compared to a predetermined reference time interval. For each determined time interval, a value indicative of the difference between the determined time interval and the predetermined reference time interval is calculated, and for the determined time intervals, a sum of the indicative values is formed and used as a quality indicator of frequency accuracy of the preamble signal. Alternatively, the sum of the absolute values of the indicative values is formed and used as a quality indicator of phase accuracy of the preamble signal, or a weighted sum of the two is used as a total quality indicator of the signal quality of the received signal.

Description

ASSESSMENT OF SIGNAL QUALITY OF A IRELESSLY RECEIVED SIGNAL BY ESTIMATION OF THE JITTER
FIELD OF THE INVENTION
The invention relates to wireless receiver systems for receiving a digital data signal for use in processors and other digital circuits, in particular in digital communication systems such as DECT cordless telephone handsets and base stations, GSM mobile phones, Bluetooth short-range RF communication, etc.
BACKGROUND OF THE INVENTION
Eg in digital communication systems such as DECT, data are transmitted in bursts, where each burst has a standardised preamble followed by the actual data. One purpose of the preamble is to "alert" the receiver that data are underway and to provide bit synchronisation for synchronising the receiver. The preamble usually consists of a series of alternating one's and zero's for a predetermined period of time. Eg in DECT cordless telephone systems the preamble is 16 bits with a frequency of 576 kHz, and the subsequent data rate is 1152 kbits/s. In Bluetooth the preamble is only 4 bits. In such systems the preamble signal quality can be used to determine the start of the preamble, to facilitate long range applications, and to control an antenna switch selecting the receiving antenna among two or more receiving antennas having the best received signal quality.
One known method of assessing the signal quality is to measure the strength of the received radio frequency signal (Radio Signal Strength Indicator = RSSI). This method only gives a good indication of quality under the assumption that a strong signal is a good signal, and this method only gives a very coarse indication of the true signal quality. However, under severe multi-path conditions, eg with delay spread of more than 180 ns, this quality assessment is inferior to other methods. Multi-path reception occurs when two or more versions of the same signal arrive at the receiver with different delays caused by reflecting and scattering objects.
Another known method detects out-of-band noise and requires quite some hardware.
The known cross correlation method requires recovering the clock signal from the received preamble signal, which takes at least a few bits of the preamble. In systems with a short preamble such as Bluetooth, valuable time will thereby be lost. In general, the reliability of this method is proportional to the number of bits used for recovering the clock signal.
The auto correlation method requires a one-bit time shifted version of the input signal. This method requires a large memory and a large computing capacity in order to execute the operations in real time.
US 5 960 046 discloses an antenna diversity radio system, in which a single receiver makes a performance measurement on each of two antennas in sequence during the beginning of a received data burst, ie the preamble.
SUMMARY OF THE INVENTION
In a first embodiment of the invention there is provided a method of assessing the signal quality of the preamble signal of a received digital signal, whereby time intervals between transitions between the high and low levels of the preamble signal are determined and compared to a predetermined reference time interval. For each determined time interval, a value indicative of the difference between the determined time interval and the predetermined reference time interval is calculated, and for the determined time intervals, a sum of the indicative values is formed and used as a quality indicator of frequency accuracy of the preamble signal. In a second embodiment of the invention there is provided a method of assessing the signal quality of the preamble signal of a received digital signal, whereby time intervals between transitions between the high and low levels of the preamble signal are determined and compared to a predetermined reference time interval. For each determined time interval, a value indicative of the difference between the determined time interval and the predetermined reference time interval is calculated, and for the determined time intervals, a sum of the absolute values of the indicative values is formed and used as a quality indicator of phase accuracy of the preamble signal.
In a third embodiment of the invention a weighted sum of the sum of the indicative values multiplied by a weighting factor and the sum of the absolute values of the indicative values multiplied by a weighting factor, and the weighted sum is used as a total quality indicator of the signal quality of the received signal.
In any of the embodiments the preamble signal is oversampled, and time intervals between transitions between the high and low levels of the preamble signal are determined by counting the number of sampling signal periods in such time intervals. For each determined time interval, a value indicative of the difference between the counted sampling signal periods and a predetermined number is calculated.
In a receiver system with two or more receiving antennas the thus obtained quality indicators can be used for assessing the received signal quality of each received signal and for selecting the antenna with best-received signal quality.
With the method of the invention the quality of the preamble can be detected without spending time for clock recovery, since a fixed clock can be used. The invention can be implemented using a relatively simple state machine, which has a very low requirement on hardware resources.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows schematically a transmission system with a receiver having two receiving antennas,
Figure 2 shows an example of the structure of received signal bursts with a preamble portion and a data portion, and
Figure 3 shows the principle of oversampling the preamble signal on a larger time scale than in Figure 2.
DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a transmission system with a transmitter having a transmitting antenna TA. A receiver has two receiving antennas RA1 and RA2. As illustrated in Figure 2, the transmitter sends data in bursts, where each burst has a preamble, which is a sequence alternating between a high level and a low level at a fixed preamble frequency and for a predetermined period of time followed by the actual data. As shown in Figure 3 the preamble signal is oversampled at a sampling frequency that is higher than the preamble frequency. In the shown example the sampling frequency is about 12 times higher than the preamble frequency. A transition of the preamble signal from "low" level to "high" level or from "high" level to "low" level starts a counter (not shown) that counts the number of clock signal pulses in the time interval, until the next transition in the opposite direction occurs. The receiver "knows" which preamble frequency can be expected, and thus how many clock signal pulses can be expected between two transitions between the low and high levels of the preamble signal. If the expected number is counted, an interim "error" value Ej of 0 (zero) is generated. For each additional counted clock signal pulse an error value Ej of +1 is generated, ie if two more clock signal pulses are counted than expected, an error value E, of +2 is generated. Correspondingly, if a number of clock signal pulses smaller than the expected number is counted, a negative error value E, is generated, ie if the number of clock signal pulses one less than the expected number, an error value E, of -1 is generated. In other words, in each time interval between transitions between the high and low levels of the preamble signal an error value E, is generated according to the formula:
E, = [actual count of clock pulses] - [expected count of clock pulses] (1)
In each time interval between transitions between the high and low levels of the preamble signal the frequency quality indicator If is calculated according to the formula: = ΣE. (2) ι=0 where N is the number of time intervals between transitions between the high and low levels of the preamble signal. The thus calculated frequency quality indicator If is an indicator of the preamble frequency deviation from the expected preamble frequency. A low If value indicates a small deviation in preamble frequency from the expected frequency and thus a high preamble quality, which means that the received bit stream matches the bit rate of the preamble.
If If has a low value, also a phase jitter quality indicator will be calculated. In each time interval between transitions between the high and low levels of the preamble signal the phase jitter quality indicator Ip is calculated according to the formula: ', = ∑ ι=0 l*,| (3)
The thus calculated phase jitter quality indicator Ip is an indicator of the phase jitter of the preamble signal. A low Ip value indicates a small amount of phase jitter in the preamble signal thus a high preamble quality. The phase jitter quality indicator Ip can only be used, if the frequency quality indicator If is sufficiently low. If the preamble signal is sampled at an oversampling rate of 12, and if 16 transitions of the preamble signal are measured, then for a good preamble reception Ip < 10, and for a poor preamble reception one might have Ip > 60.
A total preamble quality indicator PQ can be calculated as a weighted sum of the frequency quality indicator I and the phase jitter quality indicator Ip in accordance with the following formula:
PQ = cf -If + cp Ip (4) where Cf and cp are appropriately chosen weighting factors. The total preamble quality indicator PQ can also be calculated as a weighted sum of selected ones of the known signal quality indicators such as the Radio Signal Strength Indicator (RSSI), whereby the reliability can be further improved.
Any one of the frequency quality indicator If, the phase jitter quality indicator Ip and the total preamble quality indicator PQ can be used as an indicator of the preamble quality, and in an antenna diversity system, ie a receiver system having two or more receiving antennas, the chosen quality indicator can be used to select the antenna with the best preamble quality, ie the lowest quality indicator value.

Claims

CLAIMS:
1. A method of assessing the signal quality of a received digital signal having a preamble portion with a preamble signal alternating, at a predetermined preamble frequency, between a high signal level and a low signal level, and a data portion with a data signal, and deriving signal quality parameters from the preamble signal and used as an indicator of the signal quality of the received signal, characterized in that it comprises the steps of determining time intervals between transitions between the high and low levels of the preamble signal, comparing determined time intervals to a predetermined reference time interval, - calculating, for each determined time interval, a value (E,) indicative of the difference between the determined time interval and the predetermined reference time interval,
forming, for the determined time intervals, a sum /, = Y^ of the indicative ι=0 values (E,), where N is the number of time intervals between transitions between the high and low levels of the preamble signal, and using the thus formed sum of the indicative values (E,) as a quality indicator of frequency accuracy of the preamble signal.
2. A method according to claim 1, characterized in that it comprises the steps of
N-l - forming, for the determined time intervals, a sum I p = ∑|E,| of the absolute
/=0 values of the indicative values (E,), and using the thus formed sum of the absolute values of the indicative values (E,) as a quality indicator of phase stability of the preamble signal.
3. A method according to claim 2, characterized in that a weighted sum
PQ = cf If + cp - Ip of the sum (If) of the indicative values multiplied by a weighting factor
(Cf) and the sum (Ip) of the absolute values of the indicative values multiplied by a weighting factor (cp), and using the weighted sum (PQ) as a quality indicator of the signal quality of the received signal.
4. A method according to claim 1, characterized in that the preamble signal is sampled at a sampling frequency higher than the preamble frequency, and that time intervals between transitions between the high and low levels of the preamble signal are determined by counting the number of sampling signal periods in such time intervals, and calculating, for each determined time interval, a value (E,) indicative of the difference between the counted sampling signal periods and a predetermined number.
5. A method according to any one of claims 1-4, characterized in that the signal quality of two or more received digital signals is assessed, the two or more digital signals being received on respective receiving antennas (RA1, RA2), and that the receiving antenna receiving the signal with the best signal quality indicator is selected.
6. A method of assessing the signal quality of a received digital signal having a preamble portion with a preamble signal alternating, at a predetermined preamble frequency, between a high signal level and a low signal level, and a data portion with a data signal, and deriving signal quality parameters from the preamble signal and used as an indicator of the signal quality of the received signal, characterized in that it comprises the steps of determining time intervals between transitions between the high and low levels of the preamble signal, comparing determined time intervals to a predetermined reference time interval, - calculating, for each determined time interval, a value (E,) indicative of the difference between the determined time interval and the predetermined reference time interval,
forming, for the determined time intervals, a sum / = ∑|E,| of the absolute
/=0 values of the indicative values (E,), where N is the number of time intervals between transitions between the high and low levels of the preamble signal, and using the thus formed sum of the absolute values of the indicative values (E,) as a quality indicator of phase stability of the preamble signal.
7. A method according to claim 6, characterized in that it comprises the steps of
forming, for the determined time intervals, a sum I f = E, of the indicative ι=0 values (Ε,), and using the thus formed sum of the indicative values (Ε,) as a quality indicator of frequency accuracy of the preamble signal.
8. A method according to claim 7, characterized in that a weighted sum
PQ = cf -If +cp - I of the sum (If) of the indicative values multiplied by a weighting factor
(cf) and the sum (Ip) of the absolute values of the indicative values multiplied by a weighting factor (cp), and using the weighted sum (PQ) as a quality indicator of the signal quality of the received signal.
9. A method according to claim 1, characterized in that the preamble signal is sampled at a sampling frequency higher than the preamble frequency, and that time intervals between transitions between the high and low levels of the preamble signal are determined by counting the number of sampling signal periods in such time intervals, and calculating, for each determined time interval, a value (Ε,) indicative of the difference between the counted sampling signal periods and a predetermined number.
10. A method according to any one of claims 6-9, characterized in that the signal quality of two or more received digital signals is assessed, the two or more digital signals being received on respective receiving antennas (RA1, RA2), and that the receiving antenna receiving the signal with the best signal quality indicator is selected.
PCT/IB2003/000430 2002-02-27 2003-02-03 Assessment of signal quality of a wirelessly received signal by estimation of a jitter WO2003073684A1 (en)

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EP02075767 2002-02-27
EP02075767.0 2002-02-27

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2338314A4 (en) * 2008-09-24 2016-09-21 Honeywell Int Inc Apparatus and method for improved wireless communication reliability and performance in process control system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4975634A (en) * 1989-04-07 1990-12-04 General Signal Corporation Jitter measurement device
WO1999057842A1 (en) * 1998-05-01 1999-11-11 Wavetek Wandel Goltermann Plymouth Limited Jitter measurement
US20020006159A1 (en) * 1999-10-12 2002-01-17 Wagner Keely Anne Diversity reception employing periodic testing

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4975634A (en) * 1989-04-07 1990-12-04 General Signal Corporation Jitter measurement device
WO1999057842A1 (en) * 1998-05-01 1999-11-11 Wavetek Wandel Goltermann Plymouth Limited Jitter measurement
US20020006159A1 (en) * 1999-10-12 2002-01-17 Wagner Keely Anne Diversity reception employing periodic testing

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2338314A4 (en) * 2008-09-24 2016-09-21 Honeywell Int Inc Apparatus and method for improved wireless communication reliability and performance in process control system

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