Low-Complexity Noncoherent Demodulation Method for Underwater Electromagnetic Communication.

Ultrasonic intra-body communication (IBC) demands high data rates and high reliability to achieve revolutionary medical and healthcare applications. This paper proposes an ultrasonic multidimensional index modulation (U-MIM) technique for IBCs. The core idea is to utilize ultrasonic pulses to transmit modulation bits whilst jointly utilizing indices in time and code domains to transmit index bits without adding extra pulses, significantly improving the data rate. Then, a maximum likelihood (ML) receiver is investigated to reveal the optimal bit-error rate (BER) performance. To address the high computational complexity of the ML receiver, a low-complexity ML (L-ML) receiver is proposed by employing maximum-minimum selection and joint estimation of index bits and modulation bits to reduce the number of template signals. Furthermore, this paper analyzes the theoretical BER, spectral efficiency (SE), and computational complexity of the proposed L-ML receiver considering the proposed U-MIM and the existing ultrasonic index modulation (UsIM) and UsIM with spread spectrum (UsIM-SS) systems. Theoretical and simulation results demonstrate that U-MIM achieves higher SE than UsIM-SS and lower BER than UsIM. Moreover, U-MIM with the L-ML receiver can attain the same BER as UsIM-SS but with significantly reduced complexity. Compared with traditional ML receivers, the L-ML receiver can reduce the complexity by up to twelve orders of magnitude for both U-MIM and UsIM-SS, while maintaining equivalent BER performance. The joint use of U-MIM and L-ML can provide a promising solution for versatile IBC applications requiring high data rate, high reliability, and low complexity.

In VLF/LF communication systems, atmospheric noise is the dominant interference, which is usually highly impulsive and can be effectively modeled as symmetric α-stable (SαS) distribution. It has been known that communication techniques designed under Gaussian noise assumption always have poor performance under impulsive noise. In this work, we focus on the detection problem of minimum shift keying (MSK) signals under SαS noise, because this modulation is widely used in VLF/LF communication systems. As SαS distribution usually has no closed form probability density function (PDF), the optimal maximum likelihood (ML) based detection of MSK signals is hard to implement. To address this problem, we proposed a closed form approximation of the branch metric used in the Viterbi algorithm (VA) for MSK coherent detection, and provided a closed form approximation of the local optimal MSK non-coherent detection. Compared with ML based algorithms, the proposed algorithms have closed form and are simple to implement. Simulation results show that the bit error ratio (BER) performance of the proposed MSK coherent detector can closely approach that of the ML based coherent detector. Meanwhile, the proposed MSK non-coherent detector can attain the similar BER performance as that of the ML based non-coherent detector in low signal-to-noise ratio region.

The performance of the downlink physical channels of 3GPP LTE/LTE-A system is typically limited by co-channel interference from neighboring cells. Therefore, the development of efficient algorithms for interference mitigation at the mobile receiver has recently attracted a lot of attention in academia and industry. There have been a number of studies on advanced interference cancellation and suppression techniques for the physical downlink shared channel (PDSCH) of LTE/LTE A carrying data packets to the users. One of the most promising schemes identified for demodulation of PDSCH is the maximum likelihood (ML) receiver. It was shown by link-level analysis that the joint ML detection of serving and interfering signals can provide performance improvement. Due to its performance benefits, the ML receiver should be also considered for demodulation of other downlink channels including the physical downlink control channel (PDCCH) which carries downlink and uplink scheduling assignments. However, a number of issues specific only to PDCCH could make problematic the use of the conventional ML receiver designed for PDSCH. More specifically, transparent power control on PDCCH (i.e., without network signaling to the user) at both serving and interfering cells as well as random interference hit from PDCCH transmissions of interfering cells may result to non-negligible performance degradation of PDCCH when the conventional ML receiver is used. Therefore, in this paper we propose an enhanced ML receiver for the PDCCH with the ability of blind power boosting estimation and interference hit detection. Using link-level simulations it is shown that in interference limited scenarios the proposed ML receiver provides remarkable error rate improvements for PDCCH over the conventional ML and linear receivers such as Maximum Ratio Combining (MRC) and Enhanced Minimum Mean-Squared Error with Interference Rejection Combining (E-MMSE-IRC).

The design of finite alphabets is an application-oriented work for communication systems. In this paper, we investigate this for photon-counting based broadcast underwater visible light communication (UVLC) systems. For the demand of energy-efficiency and unique identification, our designs are conducted under the constraints of Hellinger distance criterion and uniquely decomposable constellation group (UDCG) theory and generate two kinds of multilayer modulation (MLM) constellation for different overall bit rate cases: Integer and non-integer. Correspondingly, for these two kinds of designs, we provide fast square root (FSR) receivers whose complexity are lower than that of the currently available maximum likelihood (ML) receiver. Finally, we investigate the achievable rates of downlink Poisson non-orthogonal multiple access (NOMA) and our proposed MLMs. The benefits of these designs revealed by demonstrations or simulations include that: 1) For the considered system, the proposed MLMs have a considerable performance advantage over TDMA and admit fast square root receiver at the cost of a moderate performance penalty compared with the ML receiver; 2) Compared with the Poisson NOMA, the proposed MLMs do not require successive interference cancellation (SIC) and their achievable rates exceed the achievable rate region of Poisson NOMA in high power regimes.

Based on the likelihood ratio, we derive the maximum-likelihood (ML) receiver for a synchronous fast frequency-hopped multiple-access system employing M-ary frequency-shift-keying (MFSK) modulation over frequency-selective Rayleigh-fading channels. The derived ML receiver is proposed and analyzed to obtain bit-error rate (BER) expressions. Analytical results are then validated by computer simulations. All system users are assumed to experience independent frequency-selective Rayleigh fading. Performance comparison among several commonly-used receivers shows that the proposed ML receiver gives the best BER performance for different combinations of parameters of the analyzed system under various fading conditions.

In this thesis, we consider interference suppression for fast frequency-hopped (FFH) communication systems over fading channels. Three types of interference, namely, partial-band noise jamming (PBNJ), multitone jamming (MTJ) and multiple-access interference (MAI), are of interest. To suppress the effect of PBNJ, we propose a maximum-likelihood (ML) receiver for frequency-selective Rayleigh-fading channels and derive the corresponding analytical bit-error rate (BER) expressions. We then focus on a more general frequency-selective Rician-fading channel, in which an optimum ML receiver structure is proposed. In addition, two suboptimum ML receivers and their corresponding analytical BER expressions are presented. Furthermore, the linear-combining and product-combining receivers are also investigated under the same channel conditions.

We derive two suboptimum maximum-likelihood (ML) receivers for fast frequency-hopped M-ary frequency-shift-keying (FSK) spread-spectrum (SS) communication systems. These two receiver structures attempt to countermeasure the effects of the worst case multitone jamming (MTJ) and additive white Gaussian noise over Rayleigh- and Rician-fading channels, respectively. In addition, analytical bit-error-rate (BER) expressions for the two proposed suboptimum structures are derived and validated by simulation results. Performance comparisons among various receivers show that the proposed suboptimum receivers significantly outperform the other existing receivers over fading channels. The optimum diversity level of the suboptimum ML receiver for the Rayleigh-fading case is found to be higher than that of the Rician-fading case. In addition, the proposed suboptimum ML receivers with optimum diversity levels can effectively remove the effect of MTJ, even under very low signal-to-jamming ratio conditions.

In this work, we apply the idea of random phase rotation of the modulated symbols to a system with interfering transmitters and a Maximum-likelihood (ML) receiver. Expressions for Bit Error Rate (BER) for a given channel realization and the average Block Error Rate (BLER) for an error correcting code are derived for the Hard-Decision based ML receiver (HDML). The derived expressions are verified through simulation results and it is observed that at high signal to noise ratio (SNR), when the channel is quasi-static (block fading), random phase rotation provides a gain in BLER when compared to the case without random phase rotation. Also it is observed that the BLER for a system with random phase rotation approaches the BLER for the case of no co-channel interference. The gain due to random phase rotation is also verified for an LTE framework with Soft-Decision based ML receiver (SD-ML).

In this research work, we have developed a communication system (transmitter / receiver) to control peak to average power (PAPR) with small bit error rate (BER) for a 4G system called multicode code division multiple access (MCCDMA). Proposed communication system works on modified Reed Muller encoded data (MRMED) string. In MRMED data is first encoded with Reed Muller (RM) code. Thereafter, encoded RM message is XORed with optimal binary string, which results lower Peak to Average Power ratio (PAPR). A well-known fact is that, bit error rate (BER) is the best performance measurement tool for a communication system. To check the integrity of our communication system, we have run the simulation for monitoring BER using MRMED sequence. Simulation work conducted, with multipath Rayleigh fading, Minimum Shift Keying (MSK) modulation and several orders of RM codes. Our results show that implementing MRMED sequences of the suggested MCCDMA communication structure, returns noticeable lower BER. For instance, in case of RM(1,4), that has error improvement proficiency of 3 (three) errors , returns BER = 8.2x10−5 adopting MSK, at SNR = 12dB. Similarly, for RM(2,3), which has error improvement efficiency of 0 error and shows distinct BER of 4.9x10−4 at 12dB (SNR).In addition to using simulation for checking BER performance of our communication system, we have also shown in our results that, as the error improvement capability of different RM codes surges, correspondingly we get a lower BER.

A fast frequency-hopped (FFH) system has an efficient anti-interference capability and is robust against fading. The performance of FFH systems is mainly affected by the intentional or unintentional interference, additive white Gaussian noise, timing and frequency offsets, as well as fading channels. The interference can be mitigated or avoided by hopping the carrier frequency of the transmitted signal over a wide bandwidth in a pseudorandom pattern. Fading channels can cause a significant degradation in the performance of a communication system. The concept of diversity methods for fading channels was therefore introduced in the literature. Diversity methods have been shown to help overcome the performance degradation caused by fading channels. In practice, the two commonly encountered interference models against the FFH systems are partial-band noise interference (PBNI) and multitone interference (MTI). Hence, it is essential to investigate the composite effect of PBNI and MTI on FFH systems over fading channels. The analytical bit-error rate expressions are derived for FFH M-ary frequency-shift-keying (MFSK) maximum-likelihood (ML) receivers under the composite effect of MTI and PBNI over either frequency-nonselective Rician fading or frequency-selective Rayleigh fading channels. The ML structures are also proposed and analyzed. The numerical results show that the proposed systems can effectively suppress the composite interference effect over fading channels. In practical systems, it is well known that there always exists time and frequency mismatch between the transmitter and the receiver. Based on the log-likelihood ratio criterion, a ML receiver for FFH/MFSK systems is proposed to combat the composite effect of PBNI and MTI with the presence of timing and frequency offsets over frequency-nonselective Rayleigh fading channels. Analytical bit-error rate (BER) expression for the proposed receiver is derived and validated by simulations. Comparing with other existing diversity-combining receivers such as the linear-combining and product-combining receivers, the proposed receiver achieves the best performance at the expense of system complexity. In addition, the sensitivity of system performance to imperfect side information is also examined. The effect of multiple-access interference (MAI) on the performance of FFH multiple-access (MA) systems is investigated. The analysis of FFH-MA systems over frequency-selective Rayleigh fading channels is first performed, followed by the frequency-selective Rician fading. For the case of frequency-selective Rayleigh fading, the exact closed-form expression of the characteristic function of the ML decision variable will be derived. For the case of frequency-selective Rician fading, we derive the probability density function (pdf) of the ML decision variable. Following that, the discrete convolution approach will be applied to obtain the pdf of the final decision statistics. Our analysis shows that the proposed ML receivers can suppress the MAI more effectively than the conventional receivers, i.e., up to two orders of magnitude in the BER performance improvement.

A maximum-likelihood (ML) receiver structure is proposed for fast frequency-hopped M-ary frequency-shift keying communication systems over Rayleigh-fading channels with the composite effects of multitone jamming (MTJ) and partial-band noise jamming (PBNJ). The corresponding semi-analytical bit-error rate (BER) expressions of the proposed ML receiver are also presented and validated by simulation results. Numerical results show that the BER performance with both MTJ and PBNJ is bounded by the two extreme cases, where only MTJ or PBNJ is present. It is also found that the proposed ML receiver can better counteract MTJ than PBNJ.

The symmetric α-stable (SaS) distribution has been widely used to model the impulsive noise, which typically exists in many communication scenarios, such as atmospheric noises in very low frequency and low frequency (VLF/LF) communication systems and network interferences in wireless communication networks, etc. Since Gaussian noise model based signal processing algorithms always perform poorly under impulsive noise, designing robust signal processing methods for impulsive noise is therefore well-motivated. In this work, we focus on the non-coherent detection problem of minimum shift keying (MSK) signals under the impulsive noise modeled as S α S distribution, because this modulation scheme is widely used in VLF/LF communication systems. The local optimal symbol-by-symbol non-coherent detection algorithm of MSK signals is first given by the principle of maximum likelihood (ML) detection. As the ML based algorithm has no closed form and is hard to implement, a robust symbol-by-symbol non-coherent detection algorithm of MSK signals is further proposed based on a closed form approximation to the ML based algorithm. Simulation results illustrate the robustness of the proposed algorithm for SaS noise. Moreover, an analytical symbol error rate (SER) upper bound of our proposed algorithm is derived, and simulation results verify the effectiveness of the analytical SER upper bound.

Cooperative engagement capability of unmanned aerial vehicle (UAV) will be the key to the future warfare. The prerequisite is a stable and reliable UAV communication data link. Minimum shift keying (MSK) modulation has good bandwidth and power efficiency. Meanwhile, it has good anti-phase noise deterioration capability. Therefore, MSK modulation is quite suitable for UAV communication data link. However, the traditional MSK receiver either has a large difference between receiving performance and the theoretical value, or has high complexity, which means it is not applicable. Based on the maximum likelihood criterion, this paper introduces an MSK receiver structure for UAV data link. We made use of the phase continuity among MSK modulation symbols and bring in a low-complexity non-coherent block detection module which is called NBD module. We simplified the receiver structure while ensuring the receiving performance. The simulations show that, with the condition of AWGN channel and bit error rate (BER) of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> , the demodulation threshold of NBD algorithm with 5-channel differentials is 2.6 dB lower than that of one-bit differential algorithm and 3.3dB lower than that of the non-coherent envelope detection.

We analyze the performance of the maximum likelihood (ML) receiver for the stronger channel user of non-orthogonal multiple access (NOMA), when no successive interference cancelation (SIC) is performed. This paper compares the non-SIC ML receiver to the standard receiver with the SIC. It is shown that the performance of the non-SIC ML receiver is almost the same as that of the standard receiver with the SIC for the operating range of the power allocation factor less than 20 %. In result, the non-SIC ML receiver could be a promising scheme for the NOMA stronger channel user, reducing the SIC complexity.

This paper proposes a new multiple input multiple output receiver based on the Kalman filtering algorithm. The Kalman filtering algorithm is based on the Gaussian assumption of the input signal. However, the assumption is not appropriate for the digital communication system which has non-Gaussian input signal. The proposed receiver overcomes the problem by using multiple Kalman filters and its output is obtained using the weighted sum of the outputs of the Kalman filters by the Gaussian sum approximation method to make the data signal approximately Gaussian. Simulation results show that the bit error rate (BER) performance of the proposed receiver is better than the previous Kalman-based receivers and its BER performance is close to the maximum likelihood (ML) receiver with lower computational complexity than the ML receiver.