| In this research, we investigated, modeled, and evaluated the performance of efficient satellite transponders in a jamming environment. Both the conventional Bandpass Transponder (BPT) and the Dehop-Rehop Transponder (DRT) are considered for this purpose.; Major concerns are on the verification of the system performance under practical channel conditions including channel noise, TWTA non-linearity and realistic jamming scenarios. However, an emphasis is on the analysis of Antijamming (AJ) capability of frequency-hopped spread spectrum system using DRT, which is a partial processing satellite transponder known to be most practical. Against the jamming and thermal noise, available countermeasures, which mainly depend on a frequency hopping technique and forward error correction coding, are modeled and their AJ capacities are analyzed. A conventional transponder, BPT, is assumed to have a hard-limiter to combat against the jammer and its AJ performances are thoroughly compared with those of DRT case under various channel conditions.; Performance analyses were done with available analytical methods as well as computer simulations, and their results are expressed in Bit Error Rate (BER). Considering the difficulties of the analytical approach toward error performance of the overall satellite link, all possible analytical modeling and their results are used as references for the computer simulation.; Using a Partial Band Noise Jammer (PBNJ) and a MultiTone Jammer (MTJ) which are known to be the most effective against a frequency hopping system, multiple jamming scenarios are investigated and their effects are analyzed along with the effects of additive white Gaussian background noise.; In this regard, perfect jammer side information is assumed to be unavailable to reflect the practical jamming condition.; Results of extensive performance analysis using software simulation showed that both the hard-limited BPT and the DRT links are effective for the conceivable jamming threats. Especially, under the two types of worst case jamming, PBNJ and MTJ, the DRT system exhibits solid performance advantages over the hard-limited passive transponder; mainly due to its spreading gain.; However, the performances of both systems highly depend on the general constraints of power and bandwidth of the satellite system.; To overcome these fundamental limitations, error correction coding combined with frequency hopping that uses diversity combining, brings a certain level of performance improvement even under severe jamming conditions. |
