Tropospheric Scatter Communications In High-speed Merge

Troposcatter communication with far simple-hop communication distance, high reliability,good confidentiality and strong anti-nuclear explosion is widely used in military andcivilian communication fields. This paper studies diversity combining of high rate scattercommunication on basis of narrowband system and presents some improved algorithmswhich improve system performance and satisfy requirements of different traffic businesses.In narrowband troposcatter communication system, maximal ratio combining is researched.A conclusion is educed that each diversity path's weighted coefficient of maximal ratiocombining is conjugation of complex channel gain, which is consistent with principle ofmatching filter, so it can obtain the largest SNR in all combining algorithms. Comparedwith traditional approach, this method has lower complexity. Meanwhile, in order to meetthe requirements of different troposcatter communication business and reduce systemcomputation, an improved maximal ratio combining algorithm based on SNR threshold ispresented. This method both considers probability density function of SNR of the receivedsignal and different users' requirements, adjusts the threshold accordingly, and combinesthe signals whose SNR are higher than the threshold. This algorithm can efficientlydecrease computation while keeping system performance.In ordcr to cancel the effect of ISI and channel deep fading that medium transmission ratetroposcattcr communication system encounters, a time-domain diversity combining andequalization algorithm based on minimum mean square error criterion is presented, whichjointly equalizes the combined signal following passing through channel matching filters.This algorithm cancels system's ISI together with maximizing output signal's SNR andmake narrowband system upgrade to megabits communication system with stable andreliablc performance.Wideband troposcattcr communication has more serious ISI and channel deep fading. Thispaper introduces SC-FDE technology into wideband troposcattcr communication and afrequency-domain equalization and diversity combining algorithm is proposed, whichjointly equalizes thc maximal ratio combined signal in frequency domain, and the outputsignal without ISI has the largest SNR. This algorithm deals with signal combining andchannel equalization in frequency domain, so it has lower computation for wideband signaland increases transmission rate up to 10 MHz/s above.