Shortwave software modem, 14400 bps in 3 kHz

The German contribution to NATO standardization of high data rate waveforms for STANAG 4539 and STANAG 5066 is a suite of non-hopping traffic waveforms, capable to transmit up to 14400 bps (user data rate) within a 3 kHz bandwidth. All waveforms are designed for broadcast as well as for short message traffic. Late-traffic-entry and autobaud-detection are supported, being unrenouncable for adaptive ARQ systems. A powerful coding scheme is implemented based on multilevel codes, corresponding to partitioned symbol constellations. The basic coding scheme on each level is Reed Solomon decoded with erasure detection. For improved performance especially on AWGN-like channels, the default Reed Solomon code can be substituted on the first level by a concatenation providing soft decision capability. One complete interleaver block is formed exactly by one multilevel code word. This gives best performance on channels with heavy burst-error characteristics like the shortwave channel. As a demonstrator, the proposed waveform suite is running on a standard PC with Pentium processor and a real-time operating system QNX, yet without any further plug-in DSP cards. Digital input/output is realized by the PC's ordinary COM ports, analogue input/output by a commercial-off-the-shelf (COTS) sound board. In this paper, we describe the waveform suite and its implementation on a PC. Therefore this is one step towards a shortwave software radio. In addition, we present performance figures.