Data receiver capable of invalidating erroneous pulses

Details Data receiver capable of invalidating erroneous pulses Data receiver capable of invalidating erroneous pulses

2001-12-05

2003-10-14

Pham, Chi (Department: 2631)

Pulse or digital communications

Synchronizers

Self-synchronizing signal

C375S340000, C340S445000

Reexamination Certificate

active

06633620

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
The present application relates to and incorporates herein by reference Japanese Patent Applications No. 2000-402417 filed on Dec. 28, 2000 and No. 2001-321948 filed on Oct. 19, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data receiver for receiving data encoded employing predetermined encoding.
2. Related Art
Some of vehicles which employ pneumatic tires include a tire condition monitoring system for improving running safety. The tire condition monitoring system monitors the internal state of the tires. Specifically, in the tire condition monitoring system, tire condition warning devices incorporated inside the tires detect the air pressure in the tires or an abnormal condition therein, and then the detected information is transmitted to a data receiver installed in the vehicle body via radio waves.
The tire condition warning devices encode information on the tire pressure into binary data, and then carrier waves is modulated using the encoded information and transmitted to the data receiver. Various signal formats for representing binary data is known, and particularly a non-return-to-zero (NRZ) format or a differential bi-phase (DBP) format is known as a typical signal format for representing binary data. According to the NRZ format, each bit (‘0’ or ‘1’) of binary data is represented by polarity. According to the DBP format, each bit of binary data is represented by presence or absence of a pulse edge synchronized with a reference clock signal, that is, it is represented by the pulse width between two pulse edges synchronized with regular reference clock signals.
The tire condition warning system usually employs DBP format, because each bit of the binary data can be obtained only by detecting pulse edges and pulse widths between two consecutive pulse edges from a pulse string. That is, the binary data can be restored from the pulse string without using clock signals in this case, while it is restored using clock signals in the case of synchronous communication or the like.
The tire condition monitoring system employs the data receiver for receiving the carrier waves modulated using a signal that represents the binary data in the DBP format from the tire condition warning devices. The data receiver detects and demodulates the received signal so that a pulse string which represents the binary data is extracted. Further the pulse edges and the pulse widths between two consecutive pulse edges are sequentially detected from the extracted pulse string, so that each bit of the binary data is restored. Thus the original binary data is restored from the received signal.
However, the data receiver sometimes obtains incorrect binary data as a result of restoration due to external noise or the like incorporated in the signals. The obtained binary data may be considerably incorrect when the condition (level of electromagnetic field) of the space through which the signals are transmitted to the data receiver is relatively poor. This problem is not limited to the transmission of the signals in the DBP format. That is, this problem usually arises when data is transmitted by cables or via radio waves.
Therefore, the data receiver usually eliminates the external noise using a hardware filter during detection and modulation of the received signal, so that components within a required frequency band (e.g., the frequency band of carrier waves which a transmitter modulates using the encoded binary data) are extracted.
Further, if the data receiver detects a pulse edge from the pulse string during the restoration of the binary data, it validates the detected pulse edge using a software twice-match filter. That is, the detected pulse edge is not validated immediately after it is detected. Specifically, the data receiver samples the pulse string according to predetermined reference clock signals. When the pulse edge is detected at a sampling time, the detected pulse edge is validated only if the same level is detected at the next sampling time. Thus, if an erroneous pulse whose width is shorter than the sampling interval is incorporated in the pulse string due to noise or the like, it is invalidated by the twice-match filter. As a result, the precision of the decoding is improved.
However, external noise within the required frequency band is not eliminated by the hardware filter. If the intensity of the external noise is relatively high, the noise is incorporated in the pulse string as an erroneous pulse.
If the erroneous pulse has a pulse width shorter than the sampling interval, it is eliminated by the twice-match filter even when it passes through the hardware filter. However, the sampling interval usually corresponds to the cycle of the reference clock incorporated in a microcomputer for operating its CPU. The cycle of the reference clock is very short (several microseconds), and therefore the erroneous pulse which has a very short width is only eliminated by the twice-match filter.
That is, an erroneous pulse which is within the required frequency band and has a width longer than the sampling interval is not eliminated, and therefore the edges of such an erroneous pulse is detected and validated. As a result, the original binary data is not accurately restored from the pulse string, and consequently a reception error occurs.
In the data receiver of the above tire condition monitoring system, the pulse string would include many erroneous pulses which cannot be eliminated by the software twice-match filter. The reason is as follows. The tire condition warning devices of the tire condition monitoring system are mounted inside the tires (on external surface of the wheels) as described above. Therefore, when the vehicle travels, the tire condition warning devices rotate as the tires rotate. On the other hand, the data receiver is fixed to the vehicle body, and therefore the level of the signals received by the data receiver constantly varies.
Particularly, the data receiver cannot receive the signals from the transmitter of the tire condition warning devices during a period (non-receipt period) whenever the tires make one rotation, because the level of the signals are low during the period due to an adverse effect of the directivity of antennas of the transmitter and the receiver. The null angle, which is a mechanical angle of the tires corresponding to the non-receipt period, varies depending on physical relationship between the antennas of the transmitter and the receiver, the power of the transmitted signals and the like. In the case of the tire condition monitoring system, it is known as a result of trail measurement that the null angle is several degrees.
When a vehicle, which has tires whose periphery is 2 meters long, travels at a speed of 100 km/h (low speed), the level of signals received by the data receiver varies as shown in
FIG. 6A
as the tires rotate. In this case, the tires make one rotation in 72 ms. Assuming the null angle is 2 degrees, the data receiver can receive signals during 71.6 ms (T
1
: receipt period) out of 72 ms, while it cannot receive signals during 400 &mgr;s (Tf
1
: non-receipt period) out of 72 ms. That is, the data receiver cannot receive signals during the non-receipt period Tf
1
corresponding to the null angle whenever the tires make one rotation.
When the same vehicle travels at a speed of 300 km/h (high speed), the level of signals received by the data receiver varies as shown in
FIG. 6B
as the tires rotate. In this case, similarly to the case of the low-speed travel, the data receiver cannot receive signals during a period whenever the tires make one rotation. However, a receipt period T
2
is 23.867 ms, and the non-receipt period Tf
2
is 133 &mgr;s That is, both of the receipt period T
2
and the non-receipt period Tf
2
are shorter than the case of the low-speed travel, because the tires rotate at a high speed in this case.
Assuming that time required for receiving one frame of the binary data is 64 ms, the receipt of one frame can be completed within the recei

Affiliated with

Also associated with

Rating

Data receiver capable of invalidating erroneous pulses does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Data receiver capable of invalidating erroneous pulses, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Data receiver capable of invalidating erroneous pulses will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3157814