Image compression and transmission for HF radio systems

This paper presents a novel image compression technique coupled with three HF transmission schemes. The image compression scheme is based on a phase dispersion technique originally developed for the design of pulse compression radar waveforms. The technique forms the basis for a lossless, invertible transform that converts sub-band coefficients to an intermediate domain. This image compression scheme generates significance map bits, which must be transferred across the HF link error free (hard bits) as well as magnitude vectors, which can sustain some degree of received errors (soft bits). The paper gives a brief overview of the image compression scheme followed by a discussion of three transmission schemes. The first transmission scheme investigated is the forward transmission HF modem. In this technique an HF modem is utilized set at an appropriate on-air data rate for the current HF channel conditions. This is a one way broadcast technique with no feedback from the destination. The second transmission scheme investigated is an automatic repeat request (ARQ) technique. This technique utilizes requests from the destination to resend data packets received in error and guarantees error free transmission of the image data. The third transmission scheme examined is a hybrid scheme, which couples an ARQ technique for the error free delivery of the hard bits with a forward transmission HF modem to provide good protection for the soft bits.