Performance analysis of alternative link-16/JTDS compatible waveforms with complex 64-bi-orthogonal-keyed modulationi

Abstract

The Joint Tactical Information Distribution System (JTIDS)/Link-16 is a hybrid frequency-hopped, direct sequence spread spectrum system which is used for the exchange of real-time tactical data. The five-bit data symbols are encoded with a (31,15) Reed-Solomon (RS) code and transmitted over the channel with cyclical code-shift keying modulation. Although JTIDS/Link-16 has proven to be operationally useful, one of its primary drawbacks is its limited data rate. This thesis focuses on performance analyses of alternative waveforms that achieve better data rates and better performance in terms of required signal power. Two alternative waveforms were considered in this thesis. The first alternative JTIDS/Link-16 waveform uses (31,15) RS encoding just as the original JTIDS/Link-16 waveform, but the five-bit symbol stream generated at the output of the RS encoder undergoes serial-to-parallel conversion to two five-bit symbol streams. Each five-bit symbol stream is then mapped into a six-bit symbol stream before being independently transmitted on the in-phase (I) and quadrature (Q) components of the carrier using complex 64-ary bi-orthogonal keying modulation (64-BOK). The second alternative JTIDS/Link-16 waveform uses (63,47) RS encoding, where the six-bit symbol stream generated at the output of the RS encoder undergoes serial-to-parallel conversion to six-bit symbol streams which are then each independently transmitted on the I and Q components of the carrier using complex 64-BOK modulation. The performance results obtained for the two alternative JTIDS/Link-16 waveforms are compared to those obtained for the existing JTIDS/Link-16 waveform for additive white Gaussian noise (AWGN) as well as when both AWGN and pulse-noise interference (PNI) are present. Errors-and-erasures decoding (EED) as well as errors-only decoding are also considered for the two alternative waveforms. From the analyses, we see that the two proposed alternative JTIDS/Link-16 waveforms perform better in the presence of AWGN as well as both AWGN and PNI. There is no significant advantage when EED is used for either of the two alternative waveforms considered. When perfect-side information demodulation is used, the results show significant improvements in performance for the two alternative waveforms when both AWGN and PNI are present.