This paper considers robust CDMA receiver design and jamming evaluation under disguised jamming, where the jammer generates a fake signal using the same spreading code, constellation and pulse shaping filter as that of the authorized signal. First, we analyze the performance of conventional CDMA systems under disguised jamming, and show that due to the symmetricity between the authorized signal and the jamming interference, the receiver cannot really distinguish the authorized signal from jamming, leading to complete communication failure. Second, by exploiting the small time difference between the authorized signal and the jamming interference, the conventional CDMA receiver can be redesigned to achieve robust performance under disguised jamming. More specifically, we propose to estimate the authorized signal, the phase and power level or range of the jamming interference by minimizing the MSE between the received signal and the jammed signal, which is the sum of the authorized signal and the disguised jamming. The effectiveness of the proposed approach is demonstrated through simulation examples. It is shown that with the proposed receiver design, the BER performance of CDMA can be improved significantly under disguised jamming, and an analytical evaluation about jamming can also be obtained.

This paper considers optimal multiband transmission under hostile jamming, where both the authorized user and the jammer are power-limited and operate against each other. The strategic decision making of the authorized user and the jammer is modeled as a two-party zero-sum game, where the payoff function is the capacity that can be achieved by the authorized user in the presence of the jammer. First, we investigate the game under AWGN channels. It is found that: either for the authorized user to maximize its capacity, or for the jammer to minimize the capacity of the authorized user, the best strategy for both of them is to distribute the transmission power or jamming power uniformly over all the available spectrum. The minimax capacity can be calculated based on the channel bandwidth and the signal-to-jamming and noise ratio, and it matches with the Shannon channel capacity formula. Second, we consider frequency selective fading channels. We characterize the dynamic relationship between the optimal signal power allocation and the optimal jamming power allocation in the minimax game, and then propose an iterative water pouring algorithm to find the optimal power allocation schemes for both the authorized user and the jammer.

This paper considers robust code division multiple access (CDMA) system design and capacity analysis under disguised jamming, where the jammer generates a fake signal using the same spreading code, constellation, and pulse shaping filter as that of the authorized signal. Unlike Gaussian jamming, which is destructive only when jamming is dominant, disguised jamming can be devastating even if the jamming power is comparable to the signal power. In this paper, first, we analyze the performance of the conventional CDMA under disguised jamming, and show that due to the symmetricity between the authorized signal and the jamming interference, the receiver cannot really distinguish the authorized signal from jamming, leading to complete communication failure. Second, we propose to combat disguised jamming using secure scrambling. Instead of using conventional scrambling codes, we apply advanced encryption standard to generate the security-enhanced scrambling codes. Theoretical analysis based on the arbitrarily varying channel model shows that the capacity of conventional CDMA without secure scrambling under disguised jamming is actually zero; however, secure scrambling can break the symmetricity between the authorized signal and the jamming interference, and hence ensures positive channel capacity under disguised jamming. Numerical examples are provided to demonstrate the effectiveness of secure scrambling in combating disguised jamming.

Hostile jamming can cause significant performance degradation in wireless communications, but it also provides an unexplored source of additional signal power. In this letter, we propose an energy-harvesting receiver for two-way orthogonal frequency division multiplexing (OFDM) systems under hostile jamming. More specifically, in the downlink, the receiver is designed to simultaneously process information and harvest energy from the received desired signal as well as the jamming interference through a power splitter. The harvested energy can then be used as an additional source of power to enhance the uplink transmission. We investigate the optimal power allocation and power splitting ratio to maximize the sum-rate of the uplink and downlink transmissions. To reduce the complexity, a suboptimal energy harvesting scheme with closed-form solution is proposed. We also obtain a lower bound on the sum-rate of the proposed scheme under strong full-band jamming.

This paper considers malicious user detection and energy harvesting in orthogonal frequency division multiplexing-based cognitive radio networks under primary user emulation attack (PUEA). The digital TV (DTV) model adopted is the second generation terrestrial digital television standard (DVB-T2). In this paper, first, we propose an efficient advanced encryption standard (AES)-based DTV scheme, where the existing reference sequence used to generate the P2 pilot symbols in the DVB-T2 frames is encrypted using the AES algorithm to facilitate accurate primary user and malicious user detection. With the proposed scheme, we can detect PUEA accurately over all subcarriers or subbands where the P2 symbols present. Second, we come up with an effective communication scheme for the secondary users (SUs) under PUEA by exploiting the energy harvesting techniques. Optimal power splitting is considered for sum-rate maximization. As the optimal solution relies on multidimensional exhaustive search, we propose an effective suboptimal solution with much lower computational complexity. It is observed that the sum-rate of the SU network can be improved significantly with the energy harvesting technique. Third, we evaluate the worst case PUEA interference in terms of minimizing the sum-rate for the SUs. We show that for practical systems, as channel state information among the SUs is not available to the malicious user, the worst jamming for the SUs is when the malicious user performs equal power allocation over all the white space subcarriers. Simulation results are provided to illustrate the proposed approaches.

This paper considers jamming-resistant OFDM system design under full-band disguised jamming, where the jamming symbols are taken from the same constellation as the information symbols over each subcarrier. First, we analyze the impact of disguised jamming on OFDM systems. It is shown that due to the symmetricity between the authorized signal and jamming, the BER of OFDM systems without symbol-level precoding or only with repeated symbol-level coding is lower bounded by a modulation specific constant, which cannot be improved by increasing SNR. Second, we develop an optimal precoding scheme which minimizes the BER of OFDM systems under full-band disguised jamming. It is shown that the most efficient way to combat full-band disguised jamming in OFDM systems is to concentrate the total available power and distribute it uniformly over a particular number of subcarriers instead of the entire spectrum. The underlying argument is that for a particular subcarrier, when the signal-to-jamming ratio is large enough, then the receiver can distinguish the authorized signal from disguised jamming under the presence of noise. Both theoretical analysis and numerical results demonstrate that the BER performance of OFDM systems under full-band disguised jamming can be improved significantly with the proposed precoding scheme.

This paper develops two spectrally efficient orthogonal frequency division multiplexing (OFDM)-based multicarrier transmission schemes: a scheme with message-driven idle subcarriers (MC-MDIS) and another with message-driven strengthened subcarriers (MC-MDSS). The basic idea in MC-MDIS is to carry part of the information, which is named carrier bits, through an idle subcarrier selection while regularly transmitting the ordinary bits on all the other subcarriers. When the number of subcarriers is much larger than the adopted constellation size, higher spectral and power efficiency can be achieved compared with OFDM. The reason is that each idle subcarrier carries more bits than a regular symbol, with no power consumption. Moreover, the existence of idle subcarriers can also decrease possible intercarrier interference between their neighboring subcarriers. In MC-MDSS, the idle subcarriers are replaced by strengthened subcarriers, which, unlike idle subcarriers, can carry both carrier bits and ordinary bits. Therefore, MC-MDSS achieves even higher spectral efficiency than MC-MDIS. Both theoretical analysis and numerical results are provided to demonstrate the performance of the proposed schemes.

This paper develops a highly efficient multi-carrier transmission scheme by using message-driven idle subcarrier identification. The basic idea is to carry part of the information, named carrier bits, through idle subcarrier selection while transmitting ordinary bits regularly on all the other subcarriers. When the number of subcarriers is much larger than the adopted constellation size (e.g., in most OFDM systems), a high spectral efficiency as well as power efficiency can be achieved. This is because that the number of carrier bits transmitted through each idle subcarrier is larger than the number of ordinary bits carried by a regular symbol, and all the carrier bits are transmitted with no power consumption through idle subcarrier selection. When applied to the OFDM framework, the proposed scheme can achieve an even higher spectral efficiency than OFDM, while keeping a higher power efficiency.We further enhance its security and error-tolerance using secure subcarrier assignment, secure symbol mapping and bit vector rearrangement. Both theoretical analysis and numerical results are provided to demonstrate the performance of the proposed scheme.