Study on the simulation and analysis of an FH/FDMA OBP satellite based mobile communication system under critical channel impairment.

摘要

Fully regenerative satellite On-Board Processing (OBP) systems are endorsed in literature as being the most effective architecture for maintaining signal quality under jamming circumstances. Dehop-Rehop Transponder (DRT) systems have been proposed as economical alternatives, bridging the gap between passive repeaters and full OBP architectures; however, no openly published literature quantifies the performances of either DRT or OBP payloads through simulation or closed form analysis. The objectives of this study are to provide modeling and simulation of a frequency hopped, frequency division multiple access (FH-FDMA) DRT and OBP satellite based tactical mobile communications system under critical channel impairment. Analyses of the resulting end-to-end BER performances are provided for both architecture types. Two variants of phase shift keying (PSK ) modulation are considered for the system waveforms: convolutional coded non-coherent Gaussian Minimum Shift Keying (GMSK) (1-bit differentially detected) and convolutional coded Symmetric Differential PSK (SDPSK). SDPSK and GMSK modulation schemes have been commonly cited in tactical satellite applications wherein bandwidth efficiency and immunity towards adjacent channel interference (ACI) and inter-symbol interference (ISI) are desirable. While some literature has been published quantifying the performance of SDPSK modems under critical impairment, no such study considering GMSK in this context has been published. Consequently, this study also seeks to determine the feasibility of using 1-bit differentially detected GMSK modems in satellite-based tactical mobile communications systems.;Channel impairment is modeled as partial band noise jamming (PBNJ), and band multi-tone jamming (BMTJ) with AWGN. Degrading factors pertaining to the system hardware including quantization and nonlinear travelling wave tube amplifier (TWTA) are also considered.;Simulations were conducted to illustrate the end-to-end BER for the described system and waveforms of interest. Results show that SFH/SDPSK exhibits excellent immunity towards PBNJ and BMTJ with AWGN channel impairments which can be further enhanced by low rate convolutional codes. OBP processing gains range from 2 - 6.5 dB at a BER of 10-3 over corresponding DRT systems, depending on jamming intensity and coding rate used. Results further show that using OBP architectures with SFH/GMSK (BT = 0.5) waveforms with code rate 1/3 under uplink PBNJ can realize power efficiency gains between 11.5 dB - 15.5 dB at a BER of 10-3 when compared to DRT systems. Increasing the BT product to 1 can provide gains of 3.5 dB - 7.5 dB for DRT system architectures (over BT = 0.5). While the increased BT product also results in improved performances for OBP architectures, it is not as pronounced.;SFH/GMSK with convolutional coding cannot realize sufficient performance to be considered for practical application under PBNJ and BMTJ with AWGN impairments, irrespective of the BT product values; in order to use SFH/GMSK modems in tactical communications systems (both DRT and OBP based architectures), powerful concatenated coding or iterative decoding schemes are required.;Consequently, a theoretical analysis of the performance of 1-bit differential detected GMSK under AWGN is developed herein, so that turbo coding can be applied. Modem level simulations of turbo-coded GMSK under AWGN exhibit an approximate 2 dB gain over convolutional coded GMSK for a BER of 10 -3 with further gains realized for additional decoding iterations. Substantial improvements in power efficiencies were also realized when subjecting turbo coded GMSK to the effects of PBNJ interference, particularly for code rate 2/3. Both empirical investigations into differential GMSK BER performance under AWGN and PBNJ interferences effectively demonstrate that greater bandwidth efficiencies can be realized by using high code rates turbo codes with modest BER performance degradation. These results strongly support use of turbo coding with differential GMSK under AWGN and PBNJ interferences, and in turn application in satellite-based tactical mobile communications systems. The results also warrant further investigation into the feasibility of using differential GMSK under tone jamming conditions.