Use of high rate projection coding with trellis coding for tactical VHF radios

Current tactical VHF radios, such as SINCGARS, employ frequency hopped, narrowband FM to transmit data or digitized voice. The VHF channel bandwidth of 25 kHz limits the number of hopping frequencies to about 2000. As a result of the large number of nets operating simultaneously in a tactical environment, numerous `hits´ occur, causing the data rate to decrease to maintain a low error rate. The authors describe the use of a high rate projection code (patents granted) with a trellis coded FM system. Using this system, with an information bit rate of 16 kb/s and a rate -5/6 projection code, data with a 19.2 kb/s bit rate can be transmitted in a bandwidth of 8.5 kHz, thereby more than doubling the number of hopping frequencies. As a result, `hits´ occur less frequently. In addition, the high rate projection code with the trellis code provides a coding gain of 5 dB. The proposed system is also more LPI and LPE. Indeed, without the appropriate receiver the FM `eye´ appears to be closed. Simulation results are presented