Abstract:
A radio transceiver includes an alternate channel searching algorithm that reduces alternate channel search times. The alternate channel search algorithm determines the actual availability of alternate channels by receiving squitter messages. The alternate channels are ranked according to signal-to-noise ratios and displayed for selection by an operator. The squitter messages are received while the radio is not communicating on the main channel.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is related in its disclosure to the subject matter disclosed in the following application by David A. Miller, with Ser. No. 09/266,075 filed on an even date herewith, entitled “A Display for a High Frequency (HF) Radio”. 
    
    
     A portion of the disclosure including microfiche Appendix A of this patent document contains material which is subject to copyright protection. The copyright or owner has no objection to the facsimile reproduction by any-one of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all (copyright or mask work) rights whatsoever. 
     CROSS REFERENCE TO APPENDICES 
     The present application includes a computer listing on microfiche Appendix A attached hereto. Microfiche Appendix A includes frames 1-178 disposed on 2 sheets. 
     FIELD OF THE INVENTION 
     The present invention relates generally to radio frequency (RF) communication systems. More particularly, the present invention relates to channel searching techniques for radio transceivers. 
     BACKGROUND OF THE INVENTION 
     Radio systems are utilized in diverse applications to provide a variety of communication operations. Radio systems, such as, the commercial high-frequency (HF) data link radio, can be used to support air traffic control (ATC) and airline operational control (AOC). The HF data link radio can be used to transmit and receive voice, tactical, data, and navigational messages between aircraft and ground stations. 
     Radios or transceivers generally communicate messages on a channel of a communication link in accordance with a protocol associated with the communication link. For example, commercial HF data link radios or transceivers transmit and receive messages on one of about 400 channels in the frequency range between 2-30 Megahertz (MHZ). Each channel has a bandwidth of approximately 1800 bytes per second. 
     Commercial HF data link radios communicate ATC and AOC messages in accordance with a time division multiplexing scheme, such as, the time division multiplex access (TDMA) protocol defined in Aeronautical Radio, Inc. (Air Inc.) specification 635. The TDMA protocol allows several radios to use a single channel without interference from each other. 
     Conventional radio systems establish contact or connections on a channel in accordance with the protocol associated with the data link. The radio system is tuned to the appropriate channel and transmits and receives messages in accordance with the protocol. According to the commercial HF data link radio example, the airborne radio system establishes contact or connects to a base station on a particular HF frequency (e.g., channel). The radio system connects or logs on by receiving a squitter message on a particular channel and transmits information in accordance with the squitter message on the particular channel. 
     The particular channel (e.g., the main channel) is selected by the HF Data Link frequency search algorithm in accordance with the signal-to-noise ratios that have been experienced on the received frequencies. The HF data link frequency search algorithm attempts to choose a robust channel that will be available for the entire communication session with a ground station. Nonetheless, radio systems can have contact broken or lose the connection due to a variety of internal and external conditions. For example, an aircraft utilizing HF data link may lose contact at any time due to operational conditions of the radio system, geographic conditions (e.g., mountains and valleys), distance, weather, solar conditions, and other external situations. In radio systems, particularly HF data link radio systems utilized in aircraft applications, the amount of time during which the radio system is incapable of communicating (e.g., lost contact time) should be minimized. 
     In conventional voice HF operations, when the radio system loses connectivity, the radio operator must search for another channel. The search can be augmented by various products and techniques which can help the radio operator predict the availability of alternative channels (channels other than the main channel, which is no longer operational). Additionally, the skill and experience of the radio operator are extremely important when determining the availability of alternate channels. Even with a highly skilled radio operator, the time spent searching for alternate channels adversely affects the operation of the radio system. In fact, search times for alternative channels can be as long as several minutes. Once a suitable alternative channel is found, connectivity is reestablished on the alternate channel, which then becomes the main channel. 
     Thus, there is a need for a radio system that reduces search time associated with selecting alternate channels. Further still, there is a need for an automatic channel search algorithm that can automatically select a channel for HF data link operations, and make a list of best available alternate channels for human-operator use. Further still, there is a need for a channel selection algorithm that does not affect communication on the main channel. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a transceiver apparatus for use with a high frequency (HF) radio communication system. The communication system includes channels. The communication system operates in time slots; one time slot of the time slots includes a protocol message. The transceiver apparatus includes an antenna and a control circuit coupled to the antenna. The control circuit communicates information on a selected channel in a particular time slot via the antenna in accordance with the protocol message. The control circuit receives the protocol message from at least one different channel of the channels when the information on the selected channel is not germane to the protocol operation on the selected channel. The control circuit determines the availability of the different channel in response to the protocol message from the different channel. 
     The present invention further still relates to a radio capable of receiving radio signals on an HF data link. The radio signals are communicated on at least a first channel, a second channel, and a third channel. The radio signals are communicated in accordance with a time division multiplex protocol including a plurality of time slots. A first squitter message is provided on the first channel in a first time slot; a second squitter message is provided on the second channel in a second time slot, and third squitter message is provided on the third channel in a third time slot. The radio includes a receiver means for receiving the radio signals and a control means for tuning the receiver means to at least the first channel, the second channel, and the third channel. The control means causes the receiver means to receive the second squitter message while the radio is waiting to communicate information on the first channel in accordance with the time division multiplex protocol. The control means monitors the availability of the second channel in response to the second squitter message. Synchronization to alternate channels is achieved more quickly in the radio. 
     The present invention still further relates to a method of determining availability of alternative channels on a high frequency (HF) link. The method includes receiving a main squitter message on a main channel, communicating in at least one assigned time slot on the main channel, receiving at least one alternative squitter message on at least one of the alternative channels in a non-assigned time slot, and determining the availability of the at least one alternative channel in response to the alternative squitter message. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will hereafter be described with reference to the accompany drawings, wherein like numerals denote like elements and: 
     FIG. 1 is a general block diagram of a communication system including a radio apparatus in accordance with an exemplary embodiment of the present invention; 
     FIG. 2 is a timing diagram demonstrating a time division multiplexed protocol for the communication system illustrated in FIG. 1; 
     FIG. 3 is a block diagram of the radio apparatus illustrated in FIG. 1, in accordance with another exemplary embodiment of the present invention; 
     FIG. 4 is a more detailed block diagram of the radio apparatus illustrated in FIG. 3, in accordance with still another exemplary embodiment of the present invention; and 
     FIG. 5 is a block diagram of a display for the radio apparatus illustrated in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1, communication system  10  includes a radio unit or transceiver  12  and a radio unit or transceiver  14 . Transceiver  12  communicates with transceiver  14  across a link  16 . Preferably, communication system  10  operates according to a high frequency (HF) communication system, such as, the Aeronautical Radio, Inc. (ARINC) protocol (e.g., ARINC specification 635), although the principles of the present invention can be utilized with other protocols and other types of data links. Information, such as, data, voice, video, navigational, or other information, can be provided between transceiver  12  and transceiver  14 . 
     Transceiver  14  is preferably a ground station, and transceiver  12  is preferably an airborne station provided in an airplane  24 . Additionally, transceiver  12  can communicate with a ground-based radio unit or transceiver  26 ,  28 , or  30 . Further, transceivers  14 ,  26 ,  28 , and  30  are also capable of communicating with other airborne stations similar to transceiver  12 . Transceivers  14 ,  26 ,  28 , and  30  are generally at fixed locations, and each communicates on a unique, preselected channel or frequency. 
     Transceiver  12  is advantageously equipped to determine availability of alternate channels to minimize synchronization to alternate channels (or alternate channel acquisition times for transceiver  12 ). For example, transceiver  12  determines the actual availability of alternate channels (channels other than the main channel upon which transceiver  12  is communicating). With the actual availability of alternative channels known, transceiver  12  automatically, can switch channels if the main channel becomes unoperational. Time is saved because an alternate channel search is not necessary. The main channel can become unoperational because of geographic objects, such as, a mountain range  22 , weather conditions, solar conditions, other air traffic, or other interference. 
     With reference to FIG. 2, communication system  10  can operate in accordance with a time division multiple access (TDMA) protocol. The TDMA protocol can be an ARINC protocol  38 , such as, the ARINC specification 635. ARINC protocol  38  includes a number of channels  40 A-I. Channels  40 A-I are preferably provided in a frequency range of 2 to 30 (MHz) and each has a bandwidth of 1800 bytes/second. 
     Each of transceivers  14 ,  26 ,  28 , and  30  communicates on a unique channel of channels  40 A-I. Alternatively, the protocol can have any number of channels frequency ranges and bandwidth. Channel  40 A has the highest frequency, and channel  40 I has the lowest frequency. 
     In FIG. 2, protocol  38  includes thirteen time slots  44  in a time frame  48 . On each of channels  40 A-I, a squitter message is provided in a squitter message time slot  42 A-I respectively. Preferably, squitter message time slots  42 A-I are spaced apart (in time) from other neighboring squitter message time slots  42 A-I. Time slots  44  are preferably 2462 (32 seconds per frame/13 slots per frame/1000 milliseconds per second) milliseconds. Alternatively, time slots  44  can be any time period, and any number of time slots  44  in frame  48  can be utilized. 
     Generally, transceiver  14  (FIG. 1) provides a squitter message in the associated squitter time slot  42 A-I for the preselected channel of channels  40 A-I. As an example, transceiver  14  can provide the squitter message in slot  42 A on channel  40 A. The squitter message can include identification information, availability information, position information, and connection information. 
     Transceiver  12  receives the squitter information from transceiver  14  and communicates with transceiver  12  in time slots  44 . Communication in the particular slots  44  is negotiated through the squitter message and is performed in accordance with protocol  38 . For example, transceiver  12  may receive information on channel  40 A in time slot  48  and transmit information in time slot  46  of channel  40 A. The assignment of slots  44  for transmission of squitter messages, transmission of non-squitter messages and reception of non-squitter message can be governed by a variety of control schemes. Further, any method of negotiating time slots  44  and conveying protocol information can be utilized in accordance with the present invention. 
     When transceiver  12  is not able to communicate on a main channel (channel  40 A associated with transceiver  14 ), transceiver  12  tunes to an alternate channel, such as, any of remaining channels  40 B-I, to communicate with an alternative transceiver, such as, transceivers  26 ,  28 , and  30 . Once tuned to the alternate channel, transceiver  12  receives the appropriate squitter message in one of slots  42 B-I and communicates on the alternative channel of channels  40 B-I with the alternative transceiver in accordance with the appropriate protocol. The selected alternative channel  40 B-I then becomes the main channel. Alternatively, when the radio tunes to the alternate channel, the squitter currently in affect on the alternate channel has already been received by the radio, and the radio can immediately begin data link operations on the alternate channel. 
     Alternatively, transceiver  12  can immediately become operational on the alternative channel. Transceiver  12  utilizes the previously received squitter message to begin data link operations (e.g., the squitter message received while transceiver  12  was logged onto the main channel). The data link operations can begin as soon as transceiver  12  tunes to the alternate frequency. 
     Transceiver  12  is capable of determining the actual availability of other channels  40 B-I. The time for synchronization to the alternate channel is reduced because the actual availability of channels is known. Other channels  40 B-I may not be available because of geographic situations, weather conditions, operation of transceivers  14 ,  26 ,  28 , and  30  sun spot activity, or other considerations. 
     With reference to FIG. 3, transceiver  12  includes a control circuit  54  and an antenna  50 . Radio frequency (RF) signals are provided via antenna  50 . Control circuit  54  receives and transmits radio signals through antenna  50 . Control circuit  54  includes an alternate channel search module  56 . 
     Module  56  can be implemented in software, such as, the software described in Appendix A. Software provided in Appendix A is shown in exemplary fashion and does not limit the scope of the claim. Alternatively, hardware can be configured to perform the operations set forth in Appendix A. 
     Module  56  receives squitter messages  42 A-I while transceiver  12  is communicating on (e.g., logged into) a main channel of channels  40 A-I. Module  56  determines the actual availability of alternate channels by analyzing the signal strength associated with the received alternate squitter messages. Preferably, module  56  analyzes the signal-to-noise ratio associated with the squitter messages to determine which channel of channels  40 A-I are available as alternate channels. 
     Module  56  ranks the alternate channels in accordance with the signal-to-noise ratio. The ranking is continually updated as alternate squitter messages are received. The signal-to-noise ratio is an indication of the closeness as well as the suitability of the alternate transceiver. Module  56  can track as many as 120 channels. 
     Alternate channel search module  56  can be updated with information indicative that channels  40 A-I have been turned off or are unreachable due to geographic circumstances. In such circumstances, alternate channel search module  56  does not attempt to receive alternate squitter messages associated with those channels which are not available, thereby focusing more time receiving squitter messages from channels  40 A-I, which may actually be available. 
     According to one particular control scheme set forth in Appendix A, module  56  includes a channel status table describing all ground-based transceivers, such as, transceivers  14 ,  26 ,  28 , and  30 , and the squitter offset for each of the stations. The information in the table can be broadcast periodically (e.g., every few hours or every day). In addition, transceiver  12  can request the information to be sent. The channel status table is used to determine whether an attempt to receive an alternative squitter message should be made. 
     According to another exemplary embodiment of the control scheme for module  56 , a counter associated with each frequency or channel  40 A-I tracks an alternate channel merit value. Every time a squitter message on channels  40 A-I is received, the counter value is incremented by a value describing the squitter merit of the received squitter, that is the numeric value associated with the positive characteristics of the received squitter. Whenever the squitter message is listened for but not received, the counter value is divided by three. Only alternate squitter messages which have high counter values are attempted to be received by transceiver  12 . After every frame, such as, frame  48 , all squitter merit values are incremented. In this way, squitter merit values occasionally rise even if there has not been a recent attempt to receive it. Accordingly, transceiver  12  continually attempts to receive a diverse group of alternate squitter messages. Additionally, transceiver  12  focuses on those channels with the most preferred characteristics. 
     With reference to FIG. 4, transceiver  12  includes control circuit  54 , which includes a digital signal processor circuit  62 , an antenna coupler  64 , and a system processor  66 . Digital signal processor circuit  62  includes a receive circuit  70  and an excite circuit  72 . Receive circuit  70  and excite circuit  72  can be digital processing circuits, analog circuits, or combinations thereof. Coupler  64  can be a digital coupler or an analog coupler. System processor  66  includes alternate channel search module  56 . Coupler  64  is coupled to antenna  50 . 
     System processor  66  is coupled to antenna coupler  64  by a frequency line  74  and a key line  76 . Coupler  64  is set to a particular frequency indicated by a code on frequency line  74 . Coupler  64  is configured in accordance with the code on frequency line  74  when a key line enable signal is provided on line  76 . Transmitter radio signals are provided from excite circuit  72  to coupler  64  across signal path  82 . System processor  66  provides signals for modulation and transmission to excite circuit  72 . Excite circuit  72  and coupler  64  are tuned to the chosen channel of channels  40 A-I through a frequency control line  84  and frequency line  74 . 
     System processor  66  controls the frequency associated with receive circuit  70  through frequency control line  84 . Received signals are received from antenna  50  through coupler  64  across signal path  82  and into receive circuit  70 . Receiver circuit  70  provides demodulated signals to processor  66 . Received circuit  70 , as well as coupler  64 , is tuned by system processor  66 . 
     When transceiver  12  is communicating on a main channel (logged on to one channels  40 A-I), system processor  66  communicates in accordance with protocol  38 . When system processor  66  is not actually receiving or transmitting data on the main channel, system processor  66  listens for any number of squitter messages in squitter time slots  42 A-I. Once system processor  66  receives the last bit associated with the squitter message on an alternate channel, system processor  66  tunes receive circuit  70  to another alternate frequency or to the main frequency. System processor  66  tunes to the main frequency if communication (either transmission or reception) is required in the next time slot  44  on the main channel. Thus, when, in accordance with the TDMA protocol, transceiver  12  is connected on a main channel but not actually receiving or transmitting, transceiver  12  scans for squitter messages on alternative channels. The channels for the alternative squitter messages can be chosen as described above with reference to FIG.  3 . 
     Squitter messages are received through coupler  64  by receive circuit  70 . Coupler  64  is maintained at the main channel frequency. However, system processor  66 , through alternate channel search module  56 , tunes receive circuit  70  to alternate frequencies associated with alternate channels  40 A-I to receive squitter messages from squitter time slots  42 A-I. With such a scheme, the time period associated with tuning coupler  64  is eliminated. 
     Module  56  ranks the alternate channels in accordance with signal-to-noise ratio associated with the squitter messages. Preferably, transceiver  12  can be equipped to receive a squitter message from squitter time slots  42 A-I before or after a scheduled time of slots  44  is used for receiving or transmitting signals on the main channel. Module  56  preferably tallies a weighted average value representative of the signal-to-noise ratio. The average value is stored in a table. 
     With reference to FIG. 5, a display  92  can be coupled to system processor  66  for displaying the actual availability of channels. Channels  40 A-I can be provided in a list format  94  by channel number, frequency number, or other indicia. Display  92  can be an LCD display, a CRT display, or other apparatus. Display  92  can even be an audio display that provides audio indications of alternative channels. 
     Display data  90  shows the location (in longitude and latitude) of the transceiver associated with the channel. Display data  90  can also provide an indication of the strength of each channel by percentage, signal-to-noise ratio, or other indicia. The radio operator can select an actual available channel via a control knob, a key pad or buttons  93 . The benefit is that if the radio operator needs to talk to San Francisco, for example, and display data  90  is indicating that 11.348 data frequency is working well, then the radio operator may select voice frequency 11.400 frequency to talk to San Francisco and expect that that frequency will provide good connectivity. 
     It is understood that, while the preferred embodiments and examples are given, they are for the purpose of illustration only. The scope of the claim is not limited by the precise details disclosed. For example, although actual availability of channels is monitored by signal-to-noise ratio associated with squitter messages, other signal strength techniques can be utilized. Thus, changes may be made to the details disclosed in the application without departing from the scope of the invention, which is defined by the following claims.