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A proposed alternative wireless communication technique is developed and compared to the current radio frequency command link in a Flight Termination System. The command link in a Flight Termination System requires a reliable signal in a radio frequency environment that is becoming overcrowded and is susceptible to various sources of interference. The proposed wireless command link implements direct-sequence spread spectrum modulation (DS/SS) to provide additional interference rejection. The DS/SS modulation is paired with minimum shift keying (MSK) which is a spectrally efficient constant envelope digital modulation technique. MSK also benefits from bit error rates that are competitive with other common modulation schemes such as binary phase shift keying in an additive white Gaussian noise wireless channel. The proposed MSK-SS modulation scheme is simulated alongside the current digital modulation scheme, continuous phase frequency shift keying (CPFSK), against narrowband, co-channel and multipath sources of interference to measure its effectiveness of rejecting interference. The MSK-SS system is able to provide bit error rates less than ã10ã^(-6) at 11 dB E_b/N_0, while the CPFSK system requires at least 14 dB E_b/N_0. When subjected to narrowband interference, the MSK-SS scheme benefits from 18 dB of interference rejection to CPFSK. Co-channel interference rejection of MSK-SS is observed to be 12 dB greater than CPFSK. The MSK-SS system is also able to suppress the effects of multipath interference while CPFSK error rates are extremely affected both destructively and constructively. The proposed MSK-SS modulation scheme is able to greatly improve error rates while offering interference rejection with a 99% power bandwidth less than 200 KHz and a minimal impact on the overall acquisition time. This proposed MSK-SS solution could enhance the reliability of the safety critical wireless communication link for a future generation of Flight Termination Systems.
interference, msk, spread spectrum
Date of Defense
November 1, 2012.
A Thesis submitted to the Department of Electrical & Computer Engineering in partial fulfillment of the requirements for the degree of Master of Science.
Includes bibliographical references.
Geoffrey Brooks, Professor Directing Thesis; Bruce Harvey, Committee Member; Bing Kwan, Committee Member.
Florida State University
McCabe, G. (2012). Improving the Wireless Link Reliability of a Flight Termination System. Retrieved from http://purl.flvc.org/fsu/fd/FSU_migr_etd-5398