Abstract:
A communication system can utilize a STANAG 5066 profile and include a data rate link mechanism. The data rate link mechanism can reside in a linking layer, such as, a subnetwork management sublayer according to the STANAG 5066 application. The mechanism allows data rate change functions of HF messages to increase throughput upon link establishment. Link quality can be determined by LQA signals generated according to MIL-STD-188-141B profiles.

Description:
FIELD OF THE INVENTION 
   The present invention relates to high frequency data communication. More particularly, the present invention relates to linking mechanisms for high frequency communications. 
   BACKGROUND OF THE INVENTION 
   Communication systems generally include transmitters and receivers which must negotiate a data rate at which encoded data is transferred. The encoded data can be digital or analog data. Typically, the transmitter provides data at a first data rate and increases or decreases the data rate in response to errors associated with the communicated data. The receiver analyzes the received data according to a number of error detection schemes and requests that the data rate be increased or decreased depending upon the number of errors detected. 
   According to a conventional high frequency (HF) data communication system defined by Standard Agreement 5066 (STANAG 5066 V1.2), communication between the communication units begins at an initial or default data rate. The default data rate is defined in Paragraph C.6.4.1 of STANAG 5066. In addition, an initial or default interleaving level for STANAG 5066 systems is defined in Paragraph C.6.4.1. Paragraph C.6.4.1 of STANAG 5066 states:
         All connections on which the data rate or other modem parameters can be controlled shall be initiated at 300 bits per second using short interleaving.       

   Therefore, communication systems operating according to STANAG 5066 utilize a relatively low initial data rate and a low throughput interleaving level. For example, a first communication unit operating according to STANAG 5066 provides data at a relatively low data rate (300 bits per second (BPS)) using short interleaving to establish a first leg of communication. The use of relatively low data rate with short interleaving ensures that initial communications are not error prone. 
   Using this relatively low data rate with short interleaving severely limits the amount of data which can be transferred upon the initial establishment of the link. Thereafter, increased data rates and other interleaving schemes can be negotiated based upon the quality of the channel between the first and second communication units. For example, if the initial communication leg is communicated without any errors, the data rate and the interleaving parameters can be increased to achieve a higher overall transfer rate of data according to paragraph C.1.4 of STANAG 5066. However, this technique requires additional time before information is communicated at its optimal rate. 
   Thus, there is a need for an initial adaptive data rate algorithm which does not rely on low initial data rate. Further, there is a need for an initial adaptive data rate algorithm which does not rely on a relatively short interleaving parameter. Further still, there is a need for increased throughput between communication units during initial communication. 
   SUMMARY OF THE INVENTION 
   An exemplary embodiment relates to a STANAG 5066 communication system. The communication system includes a first unit and a second unit. The first unit provides an LQA command to the second unit during initial linking. The second unit records a first LQA value in response to the LQA command and transmits the first LQA value to the first unit. The first unit records a second LQA value in response to the LQA value and transmits the second LQA value to the first unit. The first unit and the second unit communicate at a data rate selected in response to the first LQA value and the second LQA value. 
   Another exemplary embodiment relates to a STANAG 5066 communication unit. The communication unit includes a receiver and a transmitter and an initialization circuit. The initialization circuit determines a data rate for at least one of the receiver and the transmitter. The initialization circuit selects the data rate in response to a first LQA value received by receiver during link initiation. 
   Still another exemplary embodiment relates to a STANAG 5066 communication unit. The communication unit includes a transmitter, a receiver and an initialization means for selecting a data rate in response to an exchange of link quality values. The link quality values being derived from an initial waveform. 
   Still yet another exemplary embodiment relates to a method of setting a data rate for a STANAG 5066 communication link. The method includes receiving a quality command signal, recording a quality command value in response to the quality command signal, transmitting a quality command value signal related to the quality command value and receiving an acknowledgement of the quality command signal. The method further includes setting the data rate in response to the acknowledgement and the quality command value. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The exemplary embodiments will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements, and: 
       FIG. 1  is a block diagram of a communication system in accordance with an exemplary embodiment; 
       FIG. 2  is a more detailed schematic view of a communication unit for use the communication system illustrated in  FIG. 1 ; 
       FIG. 3  is an even more detailed schematic view of the communication system illustrated in  FIG. 2 ; 
       FIG. 4  is a schematic diagram of a linking operation for the system illustrated in  FIG. 1 , in accordance with another exemplary embodiment; and 
       FIG. 5  is a flow diagram showing the linking operation illustrated in  FIG. 4 , in accordance with still another exemplary embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIG. 1 , a communication system  10  includes a first unit  12  and a second unit  14 . Communication unit  12  includes a transmitter  22  and a receiver  24 . Communication unit  14  includes a transmitter  32  and a receiver  34 . Although communication system  10  is shown with two communication units  12  and  14 , any number of communication units can be utilized. Principles of the present invention are applicable to any type of networking or other communication applications. 
   Communication system  10  can be a wireless wide area network (WAN) connected via HF links, a wireless local area network (LAN), or other sets of wireless communicating units. For example, system  10  can include any number of communication units and can even support three-way or more communication. In a preferred embodiment, system  10  is a wireless high frequency (HF) system. Data can be communicated according to the STANAG 5066 specification. 
   In operation, communication unit  12  is a master link unit and unit  14  is a slave link unit. Master link unit  12  initiates communication by providing a link quality command to unit  14  (e.g., a call phase). Unit  14  recognizes the link quality command and provides a link quality parameter to unit  12  (e.g., response phase). The link quality parameter indicates how well the unit  14  heard unit  12  (how well receiver  34  heard transmitter  22 ). 
   Unit  12  transmits an acknowledgement of value quality parameter (e.g., acknowledge phase). Units  12  and  14  communicate according to a data rate and interleaving parameter set in response to the link quality determinations made by units  12  and  14 . For example, unit  12  can compare the quality measurements in accordance with minimum, maximum and default quality values which have been provided as initial parameters. In this way, units  12  and  14  are not required to initially communicate at a fixed data rate or a preset interleaving characteristic. 
   With reference to  FIG. 2 , unit  12  or  14  generally includes a link layer  40  and a physical layer  42 . Physical layer  42  includes a modem unit  44  and link layer  40  includes an initialization circuit  46 . Modem unit  44  receives data from an external source and modulates onto waveforms transmitted by layer  42 . 
   Link layer  40  establishes a link or a connection between units  12  and  14  ( FIG. 1 ) and physical layer  42  providing various radio frequency (RF) processing functions including modulating and demodulating (modem) functions. 
   Initialization circuit  46  is an automatic link establishment circuit or Adaptive Data Rate Link mechanism which sets a data rate and interleaving parameter for units  12  and  14  of system  10  in response to the determination of the quality of a link between units  12  and  14 . The quality of link can be determined by using link quality analysis (LQA) data such as LQA data described in “Interoperability and Performance Standards for Medium and High Frequency Data Systems,” (MIL-STD-188-141B). The LQA data can be generated internally and does not require an external data source. 
   System  10  can be an autobaud or a non-autobaud system. In an autobaud system, receiver  34  and receiver  24  are capable of recognizing the baud rate or data rate associated with the transmitted waveform. Accordingly, in the autobaud system, transmitter  22  selects the data rate for the link between transmitter  22  and  34  and transmitter  32  selects the data rate for the link between transmitter  32  and  24 . In the autobaud system, units  12  and  14  independently select the initial data rate. 
   In the non-autobaud mode, receiver  34  must be given the appropriate data rate by transmitter  22 . Accordingly, with such a system, transmitter  22  selects the data rate and provides an indication of the data rate in the acknowledge phase of the link. With such a system, the initial data rate is the same for the link between transmitter  22  and transciever  34  and for the link between transmitter  32  and receiver  24 . 
   With reference to  FIG. 3 , link layer  40  includes a subnet manager sublayer  50  that includes an adaptive data rate link mechanism  52 . Adaptive data rate link mechanism  52  generates and processes the link quality parameters to set a data rate through data rate change function  54 , data transfer sublayer  56 , channel access sublayer  58  and subnetwork interface sublayer  60 . Generally, the functions of mechanism  52  can be achieved by a the hose processor programmed according to the operations described herein. The processor can utilize a look-up table to choose the data rate based upon the LQA values. For example, a minimum data rate, a maximum data rate, a default rate and data rates corresponding to ranges of LQA values can be stored in the look-up table. 
   With reference to  FIGS. 1 ,  3 , and  4 , the operation of system  10  is described below as follows. In  FIG. 4 , communication unit  12  ( FIG. 1 ) as a link master unit and provides a link request including a command link quality analysis (LQA) signal. The command LQA signal can be provided in accordance with MIL-STD-188-141B. In one embodiment the LQA signal is a frequency shift keyed (FSK) signal. Communication unit  14  receives the command LQA signal and determines a RxLQA value indicating how well unit  14  received the link request from unit  12 . As discussed in MIL-STD-188-141B, the LQA signal can include a 4 bit noise report, a 7 bit first character field, a 1 bit control field, a 3 bit MP field, a 5 bit SINAD bit field, and a 5 bit BER bit field. The specific format given is described in an exemplary fashion. The first character field can provide any number of CMD functions for system  10  including the command LQA function. The SINAD fields provide signal to noise and distortion measurement ((S+N+D)/(N+D)) averaged over the duration of each signal. The MP field provides a measurement of multipath. The BER field provides a measurement of bit error rate. 
   Unit  14  calculates and stores the RxLQA value and provides the RxLQA value to unit  12  as the TxLQA value. Unit  12  stores the TxLQA value and provides an acknowledgement of the receipt of the TxLQA value to the unit  14 . The acknowledgement indicates how well unit  12  received the TxLQA value. 
   With reference to  FIG. 5 , at a step  102 , unit  12  sends a command LQA signal to unit  14 . At a step  104 , unit  14  receives the command LQA signal. At a step  106 , unit  14  determines the LQA parameter or the quality of the channel between units  12  and  14  based upon the command LQA signal. At a step  108 , unit  14  sends receive LQA data to unit  12 . At a step  110 , unit  12  receives the receive LQA data. At a step  112 , unit  12  determines transmit LQA data. At a step  114 , unit  12  transmits the transmit LQA data. At a step  116 , unit  14  establishes a link based upon the receive LQA data and transmit LQA data and communicates at a step  118 . 
   It is understood that while the detailed drawings, specific examples, and particular values given provide a preferred exemplary embodiment of the present invention, it is for the purpose of illustration only. The method and apparatus of the invention is not limited to the precise details and conditions disclosed. Various changes may be made to the details disclosed without departing from the spirit of the invention which is defined by the following claims.