Satellite communication can be operated with various levels of on-board processing in order to transmit the signal effectively. In this paper, the BER performances of the bent pipe transponder (BPT), dehop only transponder (DOT) and dehop and rehop transponder (DRT) systems with FH-MFSK modulation are investigated in the presence of broad band interference, narrow band interference and tone-type interference. In this case, the BER performances are compared for the variants of the data rates, spreading bandwidth and interference power. The numerical results show that DRT outperforms BPT and DOT. DOT is less sensitive to uplink interference power under broad band interference environment than DRT. In the case of narrow band interference, the DRT system is more sensitive to ρ value, i.e., the ratio of the interference bandwidth to the spreading bandwidth, than DOT. Among various interference types, the performance in n = 1 band multi-tone interference is shown to be the worst.

The bit error rate (BER) performance of a fast frequency-hopped frequency division multiple access (FH-FDMA) system is evaluated with diversity combining receivers. The clipper receiver and the normalized envelope detection (NED) receiver which show better performance than other diversity combining receivers under n = 1 band multitone interference (MTI) are chosen as combining alternatives. From simulation results, n = 1 band MTI is the most destructive multitone interference strategy for the FH-FDMA system. As the number of groups increases, eventually becoming a FHMA system, the worst case performance of FH-FDMA with the clipper receiver improves monotonically, while that of the NED receiver hardly improves when the effect of the interference is relatively large. From the viewpoint of BER performance, the FHMA system with the clipper receiver is the most effective solution among the FH-FDMA systems in the presence of the worst case band MTI.

In this paper, we investigate the bit error rate (BER) of OMC-CDMA (Orthogonal Multi-Carrier-Code Division Multiple Access) with Maximal Ratio Combining (MRC) scheme on two-ray Rayleigh multipath fading channels, and compare the MRC scheme with the Equal Gain Combing (EGC) scheme according to not only the number of users (M) and subcarriers (N) but also the power of delayed signal. We found that the MRC scheme outperforms the EGC scheme, and the BER of OMC-CDMA depends greatly on the power of delayed signal. If the delayed path power is increased from 10% to 50%, as compared with the direct path power, CDMA capacity is decreased approximately by 30% at BER=10-3, N=256 and SNR=15 dB. When the system is heavily loaded by users in large decaying parameter, the performance of OMC-CDMA with the MRC scheme can not increase the BER significantly compared to that with the EGC scheme.

In fast frequency hopped (FFH) non-coherent MFSK systems, the diversity combining scheme can be used effectively in order to combat the interference, especially jamming noise. In this paper, we simulate and discuss the BER performance of FH/MFSK system for different diversity combining schemes, such as linear combining, clipped-linear combining, normalized envelop detection (NED), order statistics (OS) NED and product combining receiver (PCR), in the presence of both the worst case partial band jamming (PBJ) and the fading channel. The performances of those combining schemes except for linear combining are similar each other in the worst case PBJ without the fading. In the existence of both the worst case PBJ and the fading channel, the clipped-linear combining scheme suffers a larger drop in performance than other combining schemes. It is noteworthy that the performances of OSNED and PCR are the best in Rayleigh fading channel among those combining schemes.

In order to investigate the sensitivity of fast frequency hopping-multiple access (FFH-MA) systems due to the frequency offset under Rician fading, we evaluate the bit error rate (BER) performance of the FFH-MA system using noncoherent M-ary frequency shift keying (FSK) with the hard decision decoding and the majority logic decision. Numerical results show that for satisfying the BER performance of 10-5 at a given normalized frequency offset of 0.2, the additional signal to noise ratio (SNR) of about 4 dB is required with the 8-ary FSK signaling compared to the case of the perfect frequency synchronization. While the frequency offset increases at a given SNR, the BER is more severely degraded, and subsequently, the BER performance is saturated at the normalized frequency offset of 0.5 regardless of fading environments. For the SNRs of more than 15 dB, the threshold level of the receiver suffering from normalized frequency offsets of less than 0.4 should be larger than that of the perfectly frequency synchronized receiver.

Orthogonal Multi-Carrier-Code Division Multiple Access (OMC-CDMA) is a scheme that combines multi-carrier modulation with Direct Sequence Spread Spectrum (DS-SS) and allows the efficient utilization of the bandwidth, the resistance against frequency selective fading in broadband mobile radio channels and the efficient implementation by the FFT algorithm. In this paper, we analyze the bit error probability (BER) of OMC-CDMA on two-ray Rayleigh multipath fading channels with the delay time and compare the BER performances of OMC-CDMA according to the number of users (M) and subcarriers (N), and the power of delayed path. We found that the performance of OMC-CDMA depends greatly on the power of delayed signal. If the power of delayed signal is increased from 10% to 50% as compared with the direct path power, the capacity of OMC-CDMA is decreased approximately by 40% at BER=10-3, N=256 and SNR=12 dB. And, though more subcarriers are used in the circumstance that the power of delayed signal is relatively great, the performance is not significantly improved.