Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1998-09-28
2002-09-24
Chin, Stephen (Department: 2734)
Pulse or digital communications
Receivers
Interference or noise reduction
C375S259000, C375S295000, C375S316000, C370S902000, C246S18700R
Reexamination Certificate
active
06456674
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of communication and control systems. It is particularly applicable to methods and apparatus for transmitting data and control information over transmission channels with multiple users.
BACKGROUND OF THE INVENTION
Microprocessors are commonly used in control systems to regulate a wide variety of systems from the simple hand held calculator to large mechanical systems such as valves and vehicles. In a specific example, microprocessors are used to control vehicles such as locomotives in order to perform functions including braking, traction control and acceleration. Radio frequency transmitter-receiver pairs are of particular interest for remotely controlling such vehicles.
In a typical locomotive control system, the operator communicates with a microprocessor-based controller onboard the locomotive using a remote control device, herein designated as transmitter. In a specific example, the transmitter is a portable device capable of emitting control signals. The operator enters requests into the transmitter via any suitable input such as a keyboard, touch screen or any other suitable system. Typical requests may include brake, accelerate and any function that a locomotive may be capable of performing. The transmitter encodes the request into a form suitable for transmission over a pre-determined frequency link. Usually, a tag is added on to the request to indicate the locomotive for which the request is destined as well as an identifier defining the remote control device from which the request originates. The complete request is then modulated at the pre-determined radio frequency and transmitted as a RF signal. Frequencies other than RF can also be used for this purpose.
Optionally, once the transmitter sends the RF signal, a repeater unit may receive the RF signal. Typical repeater units are ground-based units whose function is to extend the radio frequency (RF) range of the transmitter of the remote control device by amplifying the signal and filtering noise components. Repeater units are well-known in the art to which this invention pertains and typically comprise an RF antenna, an RF receiver, a decoder/encoder, an RF re-transmitter and any other equipment such as filters, duplexors and others required to receive a signal, process it and retransmit it. Commonly, the repeater unit re-transmits the signal at a frequency different from the frequency used by the transmitter as well as sufficiently spaced in frequency from the frequency used by the transmitter such that the two signals can be resolved if they are received simultaneously by a receiver unit.
A receiver aboard the locomotive has a decoder module that receives and demodulates the RF signal originating from the transmitter or from the repeater unit. The signal is then decoded and the validity of the request is verified. Typically, verifying the validity of a request involves performing a sequence of operations to verify if tho transmitter from which the request originates is permitted to issue requests to the particular locomotive as well as verifying if the signal received is intact. Generally, a computer readable medium in the receiver stores an identifier indicative of the transmitter assigned to the locomotive. The identifier is compared to the tag contained in the received demodulated request. Another operation in the verification of the signal involves verifying if the signal is intact by using a check sum or other suitable error detection or correction algorithm. Verifying that a message is intact is well known in the art of signal processing. If the signal is valid it is then processed further so the command contained in the request can be implemented.
Locomotive control systems of the type described above operate in railroad environments concurrently with many other similar locomotive control devices including transmitters and receivers. Commonly, many transmitters operate on the same radio frequency channel or on overlapping radio frequency channels often resulting in interference between the various signals. Signals transmitted in overlapping frequency channels cannot be resolved into their respective signals by the receiver module solely on the basis of frequency filtering. The interference of the signals typically causes commands to be lost.
A common solution to this problem is to transmit a command continuously at a given rate and where each transmitter is being assigned a unique repetition rate. The unique repetition rate reduces the likelihood of messages interfering with one another. A variant on this method is described in detail in U.S. Pat. No. 4,245,347 by Hutton et al. whose content is hereby incorporated by reference. In order to work adequately, the repetition rate of each transmitter must lie between a certain upper threshold, in order to prevent a single transmitter from monopolising the airways, and above a certain lower threshold in order to avoid a system receiving insufficient information. Furthermore, the repetition rates assigned to each transmitter must leave a time window that is sufficiently long to allow a complete message to be transmitted from a transmitter with no interference from other transmitter units operating at the same frequency. Finally, for systems requiring a high level of confidence such as systems that may create a potential safety hazard when a remotely transmitted command is not received properly or not received at all, the receiver stations are designed to expect a control message periodically from the transmitter. If the control message is not received within a pre-determined time period, the system assumes there is a problem and proceeds in executing an emergency default action. In order to assign a repetition rate to a set of transmitters, the above constraints must be taken into account. Consequently, the assignment and management of repetition rates by an administrator is a time consuming task resulting in significant labour costs. Also, the reliance on an administrator to assign transmission rate makes the system highly susceptible to human errors. For example, an administrator may erroneously give two transmission units the same repetition rate resulting in conflicting signals.
An additional problem with systems of the type described above is that the response time of a transmitter/receiver pair is substantially affected by the assigned repetition rate. Consider a system where two transmitter units are operating simultaneously and where the first unit has a repetition rate of 0.5/second and repeats its messages every 2 seconds and where the second unit has a repetition rate of 0.33/second and repeats its messages every 3 seconds. In the worst case scenario, every second message of the second transmitter will interfere with every third message of the first transmitter, the average response time for the receiver associated to the second transmitter will be 6 seconds and the average response time for the receiver associated to the first transmitter will be 3 seconds. Therefore, for identical transmitter/receiver pairs operating at different repetition rates, the response time of a transmitter/receiver may be substantially longer than that of another unit. This often leads to frustration for tho operator of the system who does not see a uniform delay in the response from one unit in the system to the next. Additionally, the battery life of system transmitting every 2 seconds will be distinctly shorter than that of the system transmitting every 3 seconds since the battery will have to supply power more frequently to the transmission device.
Thus, there exists a need in the industry to refine the process of signal transmission in the context of a transmitter/receiver pair.
OBJECTS AND STATEMENT OF THE INVENTION
An object of the invention is to provide an improved method and apparatus for signal transmission.
As embodied and broadly described herein, the invention provides an apparatus for transmitting a signal to a remote receiver, said apparatus comprising:
a signal transmitting unit including:
a) a f
Brousseau Andre
Ethier Luc
Horst Folkert
Szklar Oleh
Canac Inc.
Chin Stephen
Liu Shuwang
LandOfFree
Method and apparatus for automatic repetition rate... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for automatic repetition rate..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for automatic repetition rate... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2910796