Optimisation of the STANAG 5066 ARQ protocol to support high data rate hf communications

The STANAG 5066 "Profile for HF Radio Data Communications" [1] is an open standard defining the requirements for building interoperable HF data communications systems. The ARQ (Automatic Repeat reQuest) protocol within this standard describes a number of implementation dependent parameters which can be configured to optimise the performance of the system according to the intended use. This paper describes the results of testing carried out to provide recommendations on a number of these parameters with the aim of producing a system which performs robustly under a wide range of typical HF channel conditions. STANAG 5066 was completed prior to the standardisation of a high data rate waveform capable of operation at data rates of 9600 bps and higher (although allowance was made within the standard for such a waveform to be accommodated as and when it became available). The standardisation of such a waveform suitable for use with the STANAG 5066 ARQ protocol under STANAG 4539 [2] has introduced a number of new configuration issues. This paper provides recommendations on the changes required to obtain maximum benefit from the integration of this waveform into existing HF systems currently providing adaptive operation over data rates of 75 to 2400 bps and discusses the optimisation of data rate adaption algorithms for effective use of the complete range of data rates currently available to HF users.