This paper investigates the implementation of artificial noise (AN) in a combinatorial design based multiple-input single-output non-orthogonal multiple access (MISO-NOMA) communication system to enhance physical layer security. To address the risk of eavesdropping and enhance the physical layer security, we propose an artificial noise-aided transmission scheme designed to protect the confidential information of legitimate NOMA users by intentionally degrading the channel quality of potential eavesdroppers. Our proposed system leverages a combinatorial design-based approach to configure the MISO-NOMA framework, ensuring effective user pairing and beamforming strategies. The artificial noise is carefully injected into the null space of the legitimate users’ channels to minimize interference to them while significantly deteriorating the eavesdropper’s reception capability. Maximum likelihood detection is applied to detect the transmitted message of each user. We provide a comprehensive performance evaluation through numerical simulations, demonstrating the effectiveness of the proposed method in enhancing the secrecy rate and overall security of the MISO-NOMA system under various network conditions and channel scenarios.

It is known that when the constellation points of the combined signal are close to each other in conventional SIC, the received signals will be corrupted severely by mutual interference. To tackle this problem, an improved Successive Interference Cancellation (SIC) in the uplink Non-orthogonal multiple access (NOMA) system has been proposed in this paper. Specifically, artificial time offsets have been inserted into each transmission to achieve higher degrees of freedom for the power levels of users and cancel the mutual interference. Besides, inserted time offsets can introduce additional resources to increase the accuracy of recognizing the superimposed signals at the receiver side. Our goal is to minimize the error probability of the users' transmission by searching for optimal power allocation. Computer simulation under the 3-user case displays that the improved SIC's bit error rate (BER) performance outperforms the P-NOMA with other SIC-based schemes.

It is known that the Non-Orthogonal Multiple Access (NOMA) system is capable of obtaining higher spectral efficiency and massive connectivity owing to the fact that multiple users are superimposed over each resource. However, as the number of users is more than that of resources, the resultant surjective-only mapping and expanded constellation increase the multiuser detection (MUD) complexity at the receiver inherently. In this paper, a downlink code-domain NOMA design based on combinatorial structures with balanced incomplete block design (BIBD) is studied. The unique discretizing distribution of BIBD provides an inherent mapping pattern for the linear combination of multiuser data. To accommodate with our system, a heuristic constellation forming paradigm is proposed. Message Passing Algorithm (MPA) is used at the receiver in this design. Simulation results on additive white Gaussian (AWGN) and Rayleigh fading channel demonstrate that our system obtain an equivalent even better performance compared with other similar code-domain NOMA techniques with much lower design complexity.

In this study, novel designs of embedded space–time multiplexing codes are presented. The space–time codes are constructed initially based on the decomposition of normal matrices that produce diagonal structures. The eigenvalue decomposition of circulant matrices, a type of normal matrices, can generate these codes. A key constraint in the design is that only the diagonal matrices are function of data. Since the components of the diagonal matrix are linear combinations of the data, the codes are called embedded. These codes provide an embedded diversity, full rate and enable multi‐user applications with reduced interference. Later constructions in Galois fields are used to reduce the constellations expansion introduced by the dependency of the eigenvalues of the diagonal matrix to the data. The pairwise error probability for the codes is derived. Performance of the codes based on simulation and theoretical analysis, are compared with the conventional spatial‐multiplexing codes and other complex orthogonal designs. Simulation results demonstrate the advantage of the proposed codes. Simulation has been done for Rayleigh‐fading channels with known channel‐state information.

Orthogonal Frequency Division Multiplexing (OFDM) has attracted significant interests in wireless communications due to its robustness against multi-path fading and high-data-rate transmission. However, conventional OFDM systems are sensitive to the Carrier Frequency Offset (CFO), which causes the Inter-Carrier Interference (ICI) and greatly degrades the system performance. In this paper, we proposed a novel OFDM system using a permutated On-Off-Keying Quadrature-Phase-Shift-Keying (OOK-QPSK) modulation to reduce the ICI. The performance analysis and the simulation results show the proposed OFDM system performs better than conventional OFDM systems using QPSK modulation under the impact of the CFO.

New modulation formats are presented that increase the transmission rate over that of conventional systems, without degrading the bit error rate (BER) and with minimal bandwidth variation. A time-varying function called an "extra phase variation function" (EPVF) is added to the discrete phase of conventional modulation formats such as M-PSK and QAM to transmit additional data bits. A receiver configuration is presented that allows the decoding of information represented by the discrete and extra phases. It is shown that in an additive white Gaussian noise (AWGN) channel, the BER performance of the bits carried by the discrete phase and the extra phase in the modified format improves over the BER of conventional modulation formats.

An effective method to match a desired group delay function using an all-pass digital filter is presented. This iterative eigen-delay technique uses the Rayleigh principle to solve the least squares delay error problem. Performance improvement over other design techniques is evident for low and medium order filters when a mean-squared error metric is computed.

We obtain optimum continuous time wavelet waveforms for chip pulse shaping waveforms of DS-CDMA signals. We first derive a performance measure for a DS-CDMA system, which is the normalized interference in terms of the chip waveform. Then, we design the optimum wavelet waveform to minimize the interference under a bandwidth constraint by utilizing the relationship between the wavelets and FIR filter banks. We evaluate the probability of error of the optimum wavelets, and they are compared with conventional chip waveforms such as the raised cosine and sinc.

A new domain, termed the frequency-delay is used to design stable, all-pass digital filters resembling a given delay response in the least-squares sense. This spectral technique identifies the delay response of a stable, second-order, all-pass digital filter as a double sideband suppressed carrier amplitude modulated signal in the frequency-delay domain. Iterative maximum likelihood techniques are used to render the filter coefficients. The algorithm is a significant improvement over related methods because it results in a physically realizable stable all-pass filter that closely approximates a desired delay response.

We present a new multirate/multimedia system, which we call scale-code division multiple access (SCDMA) that depends on the code, and time and scale orthogonality introduced by pseudo-noise (PN) sequences, and wavelets. Wavelets are used for signaling. In this system, the channel is divided into different scales, and each scale into time slots. In addition, the PN sequences are used in each scale to identify multiple users. In other words, each user encodes its successive information symbols with time-shifted replicas of the same basic wavelet in a specific scale and spreads its scaled and translated wavelets by its PN sequence. However, the finer the scale, the more the symbols are transmitted. We analyze this system over an asynchronous additive white Gaussian noise (AWGN) channel by using conventional detectors and show that it is attractive for multirate/multimedia applications due to its reasonable performance.

Orthogonal wavelets have been applied to communications since the early 90s. We prove that the Hilbert transform of a wavelet is orthogonal to its time shifts and it is also orthogonal to the corresponding wavelet and its time shifts. On the other hand, since the Hilbert transform only shifts the phase of the wavelet function by 90-degree, the magnitude spectrums of the wavelet and its transform are the same. Therefore they are located on the same frequency band. In order to utilize the above properties, we propose to use the wavelet and its Hilbert transform for waveform encoding of data bits. With this, we are able to double the bit rate without increasing the bandwidth or affecting the bit error rate (BER). Daubechies (1992) wavelets are used in the analyses of the proposed system.

Efficient use of bandwidth and the design of efficient modulators remains a primary concern in the design of many emerging communication systems including systems for personal communication services (PCS). The bandwidth required by a communication system depends on a number of factors including the type of source encoders, channel encoders, modulation format, and the access technique. In conventional modulation formats such as PAM, FSK, and PSK, the error rate performance is traded for either bandwidth expansion or larger signal power. The amount of increase of power or bandwidth for the tradeoffs vary from one modulation format to another. Here we develop a modulation technique that improves the performance by creating signal constellations that allow transmission of more information than in a conventional system. We analyze the performance of this new modulation format in fading multipath channels. This method can be used with signal constellations that allow coded modulation formats, such as TCM, as well as uncoded modulation.

Modern wireless communication systems require an efficient use of the spectrum. Here we introduce the use of permutation codes (PC) as a combined source coding and channel modulation system using M-ary phase shift keying as the modulation formats. We combine the features of a permutation code vector quantizer and a permutation code as channel modulator. For source coding the permutation code is a class of constant weight vector quantizer, and its rate-distortion performance is near optimal considering practical vector lengths. We obtained the rate-total distortion performance for the combined system when an M-ary PSK modulation formats is used as channel symbols. The performance is obtained using numerical methods for AWGN channel and for frequency nonselective slowly fading channel. We found that the combined system has the advantage over non combined systems of lower encoding delay, and hence simpler transmitter and receiver. Also, we would be able to optimize the overall distortion as a function of the design parameters.

An optical communication system using coded multipulse position modulation is described. The position of the pulses in each signalling interval are derived from general binary constant weight codes. The combined coding and modulation of multiple pulses provides a minimum distance between any two signaling frames. Photon counting is used at the receiving end for noiseless optical channel in which only quantum noise exists. For noisy optical channel with avalanche photodetector, threshold demodulation is used in which an optical pulse is considered present in a slot where the photoelectron count exceeds a given threshold. It is shown that this multipulse system gives better performance than the conventional single pulse system. The performance analysis can be applied to and binary constant weight code since only the general parameters of length, minimum distance, and weight of the code are needed.>

The performance of a hybrid modulation technique derived from binary frequency shift keying is presented. In the hybrid scheme, each frequency is allowed to be phase modulated with any of p discrete, equally spaced phase shifts. The spectral separation between frequencies is chosen to make the carriers orthogonal, thus generating a multidimensional modulation scheme. The performance of complete and expurgated phase codes is examined for the Gaussian and Rayleigh fading channels, and their spectral characteristics are determined.>

Steiner systems constitute an example of codes that achieve asymptotic error-free transmission for the Gaussian channel. In contrast to simplex and orthogonal codes which also have this property, these codes make more efficient use of the bandwidth by reducing the required dimensionality to generate the M signals. Tight upper bounds for the symbol error probability are derived for coherent and noncoherent detection that include previously reported results as special cases. The relative bandwidth efficiency with respect to orthogonal codes is presented, and a combined performance plot is given that allows a meaningful comparison between the different coding schemes considered.>

An orthogonalized input-output characterization of nonlinear bandpass quadrature amplitude modulation systems with memory is developed. The orthogonal expansion is used with a nonlinear canceller structure to counteract the effect of nonlinear distortion introduced by high-power amplifiers at the transmitter. It is shown through simulations that when the transmitted symbols are known at the canceller, relatively simple structures can eliminate the effect of the nonlinearity. Even when the transmitted symbols are not known at the canceller, the improvement in performance with the nonlinear canceller, with respect to a linear receiver, is significant.>

The performance of a bandwidth-efficient multiple-tone modulation scheme for M-ary frequency-shift keying (MFSK) is presented. The use of balanced incomplete block (BIB) designs is proposed to form the signaling frames. On each symbol interval the modulator selects a group of elements from a BIB design and divides its energy into the orthogonal waveforms corresponding to these elements. The multiple-tone FSK scheme based on these block designs is shown to increase greatly the bandwidth efficiency of a conventional M-ary FSK system. An implicit diversity is incorporated in the modulation scheme. Thus, a performance improvement comparable to that obtained by using time or frequency diversity is shown on a Rayleigh fading channel and also on an interference channel with partial-band Gaussian noise. The multiple-tone scheme based on this design is compared to a multiple-tone scheme based on Hadamard matrices suggested by J.F. Pieper et al. (1978). It is shown that similar performance is achieved on a fading channel, while an advantage close to 4 dB is obtained for the proposed scheme on an AWGN (additive white Gaussian noise) channel.>

A novel type of diversity signaling for an M-ary frequency-shift keyed modulation format involving the transmission of multiple tones on each diversity branch is considered. The properties of such a system are investigated, and its performance in the presence of tone jamming is analyzed. It is shown that significant gains can be realized with such a technique. The performance in the presence of worst-case partial band noise is briefly considered and shown to be worse than, though comparable to, that of the single-tone case.>