Pulse or digital communications – Receivers – Automatic baseline or threshold adjustment
Utility Patent
1998-01-08
2001-01-02
Chin, Stephen (Department: 2734)
Pulse or digital communications
Receivers
Automatic baseline or threshold adjustment
C375S287000, C375S349000, C342S013000
Utility Patent
active
06169770
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a tactical collision avoidance system (TCAS) or an air traffic control radar beacon system (ATCRBS). More particularly, the present invention relates to a mode select (mode S) squitter message receiver.
BACKGROUND OF THE INVENTION
Tactical collision avoidance systems (TCASs) are utilized to maintain separation between flying aircraft and, thereby, to prevent air traffic accidents. These systems allow an aircraft to calculate the distance between it and another aircraft within a predetermined range. According to TCAS protocol, a transceiver or transponder disposed in a first aircraft continuously emits a squitter message. A transmitter disposed in a second aircraft transmits an interrogate message in response to the squitter message. The transponder provides a reply message, which is received and utilized by the second aircraft to calculate distance between the first aircraft and the second aircraft.
The squitter message and the reply message are radio frequency (RF) signals that are generated by radio-based radar in the transponder. The interrogation message can be created by a transmitter associated with TCAS. The squitter message is broadcast in the 1090 megahertz (MHz) frequency range and includes an address of the aircraft which sent the squitter message. The squitter message typically includes a preamble followed by data. The preamble can be a pattern of four spaced-apart pulses at known widths and at known positions with respect to each other. After the preamble, the data is provided, which generally includes the address of the aircraft. The data can be a several microsecond message.
The interrogation message is sent in the 1030 MHz frequency range and includes the address of the aircraft which sent the squitter message. In this way, only the aircraft that is addressed by the interrogation message provides the reply message. The reply message is a time-synchronized RF signal that is transmitted in the 1090 MHz frequency range. The distance between the first aircraft and the second aircraft can be calculated by determining the amount of time between sending the interrogation message and receiving the time-synchronized reply message.
Conventional squitter messages are transmitted by an aircraft to inform other aircraft of its presence. Typically, squitter messages have been broadcast (e.g. have been receivable) over a relatively short range, thereby limiting the number of aircrafts which receive the squitter message to only those which are in relatively close proximity. The short range is also implemented by limiting the sensitivity of the receiver. However, future systems may extend the range for squitter messages by increasing the sensitivity of the squitter message receiver.
It may be desirous to have squitter messages include position information derived from global navigational satellite systems (GNSS). The position information can be provided in the data associated with the squitter message. When flying routes, an aircraft can maintain separation when it is aware of the position of another aircraft in the vicinity. Maintaining separation advantageously reduces fuel consumption costs and air traffic delays. Receiving squitter messages and position information from an aircraft at greater distances even further augments the efficiency advantages.
As the transmission or reception range of squitter messages is increased, the receiving aircraft must be able to distinguish between squitter messages from an aircraft which is either relatively far away or relatively close. Squitter messages from a relatively close aircraft should be processed (e.g., at a higher priority) first to appropriately effect collision avoidance operations. For example, if a squitter message from a far away aircraft is being processed, instead of a squitter message from a close aircraft, the purpose of the collision avoidance system may not be achieved.
Thus, there is a need for a transponder which can differentiate from squitter messages transmitted by aircraft which are relatively close and by aircraft which are relatively far away. Further, there is a need for a squitter message receiver system which receives squitter messages from a close aircraft instead of squitter messages from a far away aircraft. Further still, there is a need for a mode S squitter message system which can differentiate from squitter messages transmitted by aircraft that are relatively close and relatively far away.
SUMMARY OF THE INVENTION
The present invention relates to a preemptive processor for use in a mode-S receiver system including a message processing circuit. The preemptive processor includes a signal input, a high-level threshold circuit coupled to the signal input, a low-level threshold circuit coupled to the signal input, a first preamble circuit, a second preamble circuit and a signal path control circuit. The high-level threshold circuit provides a high threshold signal at a high output, and the low-level threshold circuit provides a low threshold signal at a low output. The first preamble circuit is coupled to the high output and provides a first control signal in response to the high threshold signal including a message preamble at the high output. The second preamble circuit is coupled to the low output and provides a second control signal in response to the low threshold signal including the message preamble at the low output. The signal path control circuit has a message initialization output coupled to the message processing circuit and an end of message input coupled to the message processing circuit. The signal path control circuit provides a message initialization signal in response to the first control signal, and the switch path control circuit provides the message initialization signal in response to the second control signal if an end of message signal has been received after a previous message initialization signal.
The present invention further relates to a squitter message receiver system which includes a preemptive processing means for generating a high threshold signal and a low threshold signal and a message processing means for receiving a message signal. The preemptive processing means allows the message signal to be processed in response to the high threshold signal including a message preamble or in response to the low threshold signal including the message preamble. The message receiver system preempts the processing of the message signal associated with low threshold signal including the message preamble in favor the message signal associated with the high threshold signal including the message preamble.
The present invention still further relates to a method of processing data in a mode-S signal. The method includes steps of receiving an RF signal, low-level threshold processing the RF signal to generate a low threshold signal, high-level threshold processing the RF signal to generate a high threshold signal, and providing a message initialization signal if the high threshold signal includes a preamble or providing the message initialization signal if the low threshold signal includes the preamble.
The present invention even further relates to a squitter message receiver system including a signal input, a preemptive processor coupled to the signal input, and a message processor. The preemptive processor generates a high threshold signal and a low threshold signal. The preemptive processor provides a message initialization signal on a preemption basis in response to the high threshold signal including a message preamble or in response to the low threshold signal including the message preamble. The message processor is coupled to the input and the preemptive processor and processes a signal received at the input in response to the message of initialization signal.
According to one exemplary aspect of the present invention, a preemptive processor for a squitter message receiver includes a high threshold path and a low threshold path. If a signal including a preamble is present on the high threshold path, the high threshol
Chin Stephen
Eppele Kyle
Jensen Nathan O.
Liu Shuwang
O'Shaughnessy J. P.
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