Integrated sensing and communication (ISAC), near-field communication, and extremely large-scale antenna arrays are transformative and indispensable technologies that revolutionize 6G communications. This work proposes a monostatic ISAC architecture for near-field systems employing extremely large-scale uniform planar arrays (XL-UPAs). A theoretical analysis of multi-user interference and sensing-over-communication interference is provided for the considered near-field ISAC system, where the sensing and communication channels are modeled using a non-uniform spherical wave (NUSW) model. In addition to communication, the monostatic ISAC system must ensure simultaneous target detection with a constant probability of false alarm, independent of noise statistics. A grid-based two-dimensional constant false alarm rate (2D-CFAR) detection scheme is proposed to address the issue. Furthermore, an analytical expression is derived to quantify the achievable range resolution in near-field ISAC systems.

In this paper, we propose the construction of Golay complementary array pairs (GCAP) with zero correlation zone ($\text{Z C Z}$) properties, having array lengths of$\left(2^{n_{1}+2}, 10 \cdot 2^{n_{2}-4}\right)$and$\left(2^{n_{1}+2}, 26 \cdot 2^{n_{2}-5}\right)$, and corresponding$\text{Z C Z}$widths of the forms$\left(2^{n_{1}}, 10 \cdot 2^{n_{2}-4}-1\right)$and$\left(2^{n_{1}}, 26 \cdot 2^{n_{2}-5}-1\right)$, respectively. These flexible Golay-ZCZ arrays have potential applications in multiple-input multiple-output (MIMO) omnidirectional transmission as precoding matrices, sound source arrays, phased array antennas, and orthogonal time frequency space (OTFS) communication systems as a two-dimensional (2-D) pilot to improve channel estimation. For the first time, we propose the construction of Golay-ZCZ arrays based on generalized Boolean functions (GBFs), constructing the arrays with non-power-oftwo lengths through truncation techniques. Further, we show that, under specific constraints, we construct one-dimensional (1-D) and 2-D Golay-ZCZ sequences and array pairs for lengths, powers of two as well.

Golay complementary set (GCS) and its extension, the mutually orthogonal Golay complementary set (MOGCS), have important applications in modern wireless communication. Historically, GCS was used in multi-carrier systems such as orthogonal frequency division multiplexing (OFDM) to reduce the peak-to-mean envelope power ratio (PMEPR) of the unencoded signal via encoding. In contrast, the MOGCS has been used in multi-access systems to support a large pool of users in a cell in spread-spectrum communication. The recent decade has seen significant advancement in this area regarding the flexibility of the sequence parameters, such as set size, flock size, alphabet size, etc. Apart from that, many substitutes of GCSs and MOGCSs have also been introduced to serve extensive application requirements. Quite a few times, the constructions of these sequence sets are based on an existing MOGCS. Hence, MOGCS has theoretical importance in the sequence design area, apart from its applied significance. However, it is still an open problem to construct a complete MOGCS with respect to the theoretical set size bound, having flexible parameters. In this paper, we search for MOGCS with as much flexibility as possible in the parameter choices.

This letter introduces an efficient method for constructing two-dimensional (2D) complete complementary codes (CCCs) with novel non-power-of-two lengths, addressing a major limitation of existing direct constructions. Specifically, we construct 2D-CCCs of array sizes$2^{n} \times 10 \cdot 2^{m-4}$($m \geq 4, n \in \mathbb {Z}^+$) and$2^{n} \times 26 \cdot 2^{m-5}$($m \geq 5, n \in \mathbb {Z}^+$) using generalized Boolean functions (GBFs). Binary 2D-CCCs are especially beneficial in spread spectrum communication due to their simple modulo-2 arithmetic, modulation, and correlation characteristics. Additionally, our construction unifies and generalizes existing results, as 2D-CCCs with power-of-two lengths and one-dimensional (1D) CCCs naturally emerge as special cases. Thus, our work not only advances the field but also contributes to the literature related to the direct construction of binary 2D-CCCs.

Golay sequences with the zero correlation zone (ZCZ), known as Golay-ZCZ sequences, play a pivotal role in reducing intersymbol interference (ISI) during the process of channel estimation in one dimension. Two-dimensional (2-D) Golay complementary array set (GCAS) within their ZCZ has the potential application in multiple input multiple output (MIMO) omnidirectional transmission. In this letter, 2-D Golay-ZCZ array set is constructed by using generalized Boolean function (GBF) without utilizing any kernels. The proposed construction provides 2-D Golay-ZCZ array set with various array sizes and large ZCZ sizes. Also, we get the one dimensional (1-D) Golay- ZCZ sequence set as a special case of the proposed construction.

In this paper, a reconfigurable intelligent surface (RIS)-assisted full duplex communication for quadrature channel modulation (QCM) is proposed. The proposed scheme exploits transmit antennas and radio frequency mirror selection to transmit the real and imaginary parts of a QCM symbol independently to improve spectral efficiency. A dual polarized RIS is also employed to extend the indexing of receive antennas at a dual polarized half duplex receiver to separate the real and imaginary parts of the QCM symbol transmitted during downlink communication. This setup facilitates quadrature spatial modulation at the half duplex receiver and further enhances spectral efficiency. After transmit antenna selection, the remaining silent antennas at the base station are further harnessed to receive the QCM modulated uplink symbol from the half duplex transmitter unit. A decision-making method is adopted at the base station to find these silent antennas that receive uplink signals. Each antenna functions as either a transmit or a receive antenna with the help of a duplexer switch which assists in full duplex communication with minimal self-interference. Finally, an enhanced greedy detector is proposed to detect the signal with lower computational complexity. The system performance is evaluated using measures like average bit error rate, throughput, ergodic capacity, and energy efficiency, and compared with that of the existing state-of-the-art techniques.

We propose new constructions for a two-dimensional (2D) perfect array, complete complementary code (CCC), and multiple CCCs as an optimal symmetrical$Z$-complementary code set (ZCCS). We propose a method to generate a two-dimensional perfect array and CCC. By utilising mutually orthogonal sequences, we developed a method to extend the length of a CCC without affecting the set or code size. Additionally, this concept is extended to include the development of multiple CCCs, and the correlation characteristics of these multiple CCCs are identical with the characteristics of optimal symmetrical ZCCS.

In orthogonal frequency division multiplexing (OFDM), peak-to-mean envelope power ratio (PMEPR) plays a vital role in the system's performance. In binary Golay comple-mentary pair (GCP), PMEPR is less than or equal to 2. However, the binary GCPs are limited in length. This paper proposes a novel construction of a new family of binary complementary pairs, named an odd shift complementary pair (OSCP), having all possible lengths. The PMEPR depends on the function we choose. However, we have calculated the PMEPR of OSCP having a length of$2^{m}-1$, where the function is a second-order Boolean function and asymptotically bounded by 4. OSCP is the pair of two complex-valued sequences having their sum of aperiodic auto-correlation function (AACF) zero at every odd time shift.

One of the important applications of Golay complementary sets (GCSs) is the reduction of peak-to-mean en-velope power ratio (PMEPR) in orthogonal frequency division multiplexing (OFDM) systems. OFDM has played a major role in modern wireless systems such as long-term-evolution (LTE), 5th generation (5G) wireless standards, etc. This paper searches for systematic constructions of GCSs of arbitrary lengths and alphabet sizes. The proposed constructions are based on extended Boolean functions (EBFs). For the first time, we can generate codes of independent parameter choices.

The multi-input multi-output (MIMO) millimeter wave (mmWave) is a promising technology for beyond 5G communication systems, which provides high data rates, ultra-low latency, massive connectivity, and high spectral efficiency. However, a typical mmWave communication link is severely impaired by path loss, nonlinear device impairments, and non-Gaussian noise. Furthermore, MIMO mmWave channel exhibits sparseness due to blockage and scattering. The conventional orthogonal matching pursuit (OMP), zero-attracting least mean square (ZA-LMS), and their variants deliver suboptimal performance for nonlinear mmWave systems. To improve the estimation accuracy, we propose a random Fourier features (RFF) based sparsity-aware kernel maximum correntropy (SA-KMC) algorithm, which is robust for MIMO mmWave sparse channel estimation in the presence of nonlinear hardware impairments and non-Gaussian distortions. Simulations indicate that the proposed RFF-SA-MCC algorithm outperforms the existing state-of-art approaches.

Orthogonal-time-frequency-space (OTFS) modulation is getting special attention for fifth-generation and beyond wireless communication due to its remarkable capability to establish stable communication links in high-speed environments. However, replacing present orthogonal-frequency-division-multiplexing (OFDM) communication systems with OTFS systems is a sophisticated and time-consuming task. Hence, an OTFS model is developed by employing discrete-fractional-Fourier-transform (DFrFT)-OFDM to improve bit-error-rate (BER) performance over the traditional OTFS systems. But DFrFT-based is limited by matrix multiplication which introduces additional computational complexity in the system. In this work, we propose a weighted fractional fast Fourier transform (WFrFFT)-based OTFS system. The complexity analysis shows that the proposed WFrFFT-based OTFS provides lower computation complexity than DFrFT-based OTFS system. Furthermore, the performance of the proposed system is also compared with that of the DFrFT-based OTFS and FFT-based OTFS systems.

Numerous anti-jamming techniques are available for wireless communication systems in the literature. However, no work offers a spectrum-efficient anti-jamming technique for orthogonal time frequency space (OTFS) systems under delay Doppler domain jamming attacks, despite it being the most promising waveform for future wireless communication. In this work, we propose two novel and robust anti-jammers based on the maximum correntropy criterion (MCC) and maximum Versoria criterion (MVC). The proposed anti-jamming receivers can withstand most practical jammers, such as shot jammers, chirp jammers, and others. This is because the MCC and MVC-based cost functions are robust under impulsive interference (jamming signals are also high-power impulses that interfere with the intended signals). The theoretical mean deviation of error is computed for proposed anti-jammers to demonstrate their ability to withstand the impacts of jamming. The bit-error rates of the proposed anti-jamming detectors are simulated and compared with the existing detectors for OTFS systems.

Multiple-input-multiple-output (MIMO) ambient backscatter communication (ABC) is emerging as one of the promising techniques to combat the deeper fading effects offered by the backscatter link. Based on earlier studies, multiple-antenna backscatter setup has been exploited to ensure lower bit error rate (BER) performance and higher spectral efficiency (SE) with the utilization of spatial modulation (SM) in ABC systems, but its investigations in the literature have assumed that the perfect channel state information (CSI) is available at the Reader, which is practically unreasonable. In an attempt to retain the key feature of SM and eliminate the need for a channel estimation block, this paper takes the first step in establishing a preliminary study of the Differential Spatial Modulation (DSM) scheme in MIMO ABC systems, which interestingly enough exploits a newly set of linearized MIMO ABC channel for its implementation. Simulation results verify that the computational complexity of the proposed DSM backscatter scheme achieves 53% lower in comparison to the SM backscatter scheme over the linearized channel model for a 2 x$R$MIMO ABC system, where$R$indicates the number of receive antennas at the Reader.

This letter presents a blind carrier frequency offset (CFO) estimator for multi-user multiple input multiple output-orthogonal frequency division multiple access (MIMO-OFDMA) uplink system by Capon method using covariance matrix decomposition in the presence of Rayleigh fading channel. In this method, a covariance matrix is derived from the received signal, followed by QR factorization of the covariance matrix to get the upper triangular matrix. Then, a cost function is formulated by calculating the inverse of the upper triangular matrix. The proposed estimator does not require channel state information or any pilot symbols, which makes the system spectrum efficient. The exact Cramer Rao lower bound is also derived, establishing a lower limit for the mean squared error of the proposed estimator. Simulation results indicate that our proposed method outperforms existing methods. The proposed method also provides a lower computational complexity.

Quasi-complementary sequence sets (QCSSs) have attracted sustained research interests for simultaneously supporting more active users in multi-carrier code-division multiple-access (MC-CDMA) systems compared to complete complementary codes (CCCs). In this paper, we investigate a novel class of QCSSs composed of multiple CCCs. We derive a new aperiodic correlation lower bound for this type of QCSSs, which is tighter than the existing bounds for QCSSs. We then present a systematic construction of such QCSSs with a flexible alphabet size and a low maximum correlation magnitude, and also show that the constructed aperiodic QCSSs can meet the newly derived bound asymptotically.

Intelligent vehicles detection (IVD) provides information to manage traffic efficiently, drive autonomous vehicles and feed data to intelligent traffic management systems (ITMS). IVD is a challenging task for the close proximity vehicles in lane-less traffic and heterogeneous systems. Most vehicle detection models are complex and limited to multi-scale feature extraction due to the involvement of existing feature extraction backbones. Also, they do not include heterogeneous traffic vehicles, usually present in developing countries. Therefore, this paper proposes a multi-class vehicle detection (MCVD) model to detect vehicles in heterogeneous traffic using a realistic traffic dataset from a developing country. MCVD is a deep learning (DL) model that consists of a convolutional neural network backbone called VDnet, a light fusion bi-directional feature pyramid network (LFBFPN) and a modified vehicle detection head (MVDH). VDnet extracts multi-scale features from the traffic input images using feature reuse methods. LFBFPN combines these features bi-directionally and provides robust feature maps. Finally, MVDH is applied to detect multi-class vehicles and classify them into respective categories. The proposed model achieves 91.45 mean average precision (mAP) on the heterogeneous traffic labeled dataset (HTLD). The proposed MCVD is tested over Nvidia Jetson TX2 edge computing boards to verify the real-time performance. It achieves 17 frames per second (FPS) on TX2. The performance evaluation results indicate that the proposed MCVD model is fast, accurate and better than the existing works. © 2000-2011 IEEE.

This paper presents a direct construction of an optimal symmetrical Z-complementary code set (SZCCS) of prime power lengths using a multi-variable function (MVF). SZCCS is a natural extension of the Z-complementary code set (ZCCS), which has only front-end zero correlation zone (ZCZ) width. SZCCS has both front-end and tail-end ZCZ width. SZCCSs are used in developing optimal training sequences for broadband generalized spatial modulation systems over frequency-selective channels because they have ZCZ width on both the front and tail ends. The construction of optimal SZCCS with large set sizes and prime power lengths is presented for the first time in this paper. Furthermore, it is worth noting that several existing works on ZCCS and SZCCS can be viewed as special cases of the proposed construction.

Multiple sets of multiple zero correlation zone (MZCZ) sequence sets are suitable for a quasi-synchronous code division multiple access (QS-CDMA) system in multi-user, multi-cluster and multi-cell environments to eliminate the interferences. In this paper, we present a two-folded direct construction of asymptotically optimal multiple sets of MZCZ sequence sets with inter-set zero-cross correlation zone (ZCCZ) from multivariable functions (MVFs). Each MZCZ sequence set forms a ZCZ sequence set after taking the union of elements in the MZCZ sequence set. Therefore, multiple sets of MZCZ sequence sets will form a new MZCZ sequence set, which is referred to as fold one. Further, this newly formed MZCZ sequence set again generates a ZCZ sequence set in the same manner, which is referred to as fold two. Also, for the first time in the literature, we are presenting multiple sets of MZCZ sequence sets. In this paper, many new lengths of MZCZ sequence sets are covered. Finally, the construction is compared with the existing state-of-the-art.

Golay complementary set (GCS) plays a vital role in reducing peak-to-mean envelope power ratio (PMEPR) in orthogonal frequency division multiplexing (OFDM). A more general version of GCS is a multiple shift complementary set (MSCS), where by relaxing the condition of zero auto-correlation sum throughout all the non-zero time shifts to the integer multiples of some fixed time shift, more sequence sets can be made available. In this paper, we propose direct constructions of MSCSs with flexible and arbitrary lengths and flexible set sizes, by using multivariable functions, which have not been reported before.

This paper proposes index modulation (IM) based on pilot location for an Orthogonal time frequency space (OTFS)based dual function radar communication (DFRC) system to circumvent the complexity involved in conventional IM schemes. A joint channel and indexing of the pilot estimation algorithm is proposed at the communication receiver. A joint target range and precise channel prediction algorithm is proposed at the joint transmitter and radar (JTR). The precise channel information predicted by the JTR is utilized to perform zero-forcing beamforming for providing physical layer security to the proposed autonomous vehicle network (AVN) over limited feedback and high mobility scenario. A closed-form expression of ergodic secrecy capacity over an outdated and generalized Norton channel is derived to provide the analytical guarantees of the proposed algorithms. Simulations of different performance metrics for the proposed schemes are provided and corroborated with existing works.

Golay complementary pairs (GCPs) and complete complementary codes (CCCs) have found a wide range of practical applications in coding, signal processing and wireless communication due to their ideal correlation properties. The binary CCCs have special advantages in spread spectrum communication for their simple modulo-2 arithmetic operation, modulation, and correlation simplicity; however, they are limited in length. In this paper, we present a direct construction of GCPs, mutually orthogonal Golay complementary sets (MOGCSs) and$q$-ary, including binary CCCs of non-power of two lengths to widen their application in the recent communication field. First, a generalised Boolean function (GBF) based truncation technique is used to construct GCPs of non-power of two lengths which has never been reported before. Then Golay complementary sets (GCSs) and MOGCSs of lengths of the form$2^{m-1}+2^{m-3}$($m \geq 5$) and$2^{m-1}+2^{m-2}+2^{m-4}$($m \geq 6$) are generated by higher order GBFs. The later length of MOGCSs with direct construction is not available in the literature. Finally,$q$-ary sequences including binary CCCs with non-power of two lengths are constructed using the union of MOGCSs. There is no such direct construction of binary CCC of non-power of two lengths available in the literature. The column sequence peak to mean envelope power ratio (PMEPR) have been investigated for GCSs and CCCs respectively, and compared with existing works. The column sequence PMEPR of resultant CCCs is effectively upper bounded by 2, which is much lower than that of paraunitary based CCC construction. The proposed construction is also compared with existing works.

During network planning phase, optimal network planning implemented through efficient resource allocation and static traffic demand provisioning in IP-over-elastic optical network (IP-over-EON) is significantly challenging compared with the fixed-grid wavelength division multiplexing (WDM) network due to increased flexibility in IP-over-EON. Mathematical programming based optimization models used for this purpose may not provide solution for large networks due to large computational complexity. In this regard, a greedy heuristic may be used that intuitively selects traffic elements in sequence from static traffic demand matrix and provisions the traffic elements after necessary resource allocation. However, in general, such greedy heuristics offer suboptimal solutions, since appropriate traffic sequence offering the optimal performance is rarely selected. In this regard, we propose a reinforcement learning technique (in particular a Q-learning method), combined with an auxiliary graph (AG)-based energy efficient greedy method to be used for large network planning. The Q-learning method is used to decide the suitable sequence of traffic allocation such that the overall power consumption in the network reduces. In the proposed heuristic, each traffic from the given static traffic demand matrix is successively selected using the Q-learning method and provisioned using the AG-based greedy method.

The Z-complementary code set (ZCCS) is well-known for being used in multicarrier code-division multiple access (MC-CDMA) systems to provide interference-free communication in a quasi-synchronous environment. Based on the existing literature, the direct constructions of optimal ZCCSs are limited to their lengths. This letter proposes a direct construction of optimal ZCCSs for all possible even lengths using generalized Boolean functions. The maximum column sequence peak-to-mean envelope power ratio (PMEPR) of the proposed ZCCSs is upper-bounded by two which can benefit in managing PMEPR over a ZCCS-based MC-CDMA system.

Sparsity-induced kernel adaptive filters have emerged as a promising candidate for a nonlinear sparse system identification (SSI) problem. The existing zero-attracting kernel least mean square (ZA-KLMS) algorithm relies on minimum mean square error criterion, which considers only second order statistics of error, thereby resulting in suboptimal performance in the presence of non-Gaussian/impulsive distortions. In this letter, we propose a novel random Fourier features (RFF) based ZA kernel maximum Versoria criterion (ZA-KMVC) algorithm, and their variants, which are robust for nonlinear SSI in the presence of non-Gaussian distortions over both stationary and time-varying environments. Furthermore, the mean-square convergence analysis of the proposed RFF-ZA-KMVC algorithm is performed. It has been observed from the simulation results that the proposed algorithm delivers better convergence performance as compared to the existing state-of-art approaches.

Underlay device-to-device (D2D) communication network is becoming a promising solution for the fifth generation (5G) and beyond wireless technology. It exploits the proximity of the D2D pairs and improves the overall network’s latency, capacity, and spectral efficiency by sharing/reusing the existing cellular resources. However, due to the frequency-sharing/reusing, the security of the device users (DUs) and the cellular users (CUs) becomes vulnerable. This paper presents a novel physical-layer security (PLS) scheme for the underlay multiple-input multiple-output (MIMO) D2D communications in the presence of multiple eavesdroppers. The proposed new PLS scheme can significantly reduce the information leakage for both CUs and DUs by adopting a null steering scheme at the transmitter. A signal alignment technique is also employed to eradicate the stringent requirement of a larger number of transmitter antennas than that of the receiver antennas. A generalized nonlinear optimization problem has been formulated to improve the PLS performance for MIMO-D2D communications. A closed-form and generalized analytical expression of the secrecy outage probability for CUs and DUs is derived over the imperfect Nakagami-$m$and Norton fading channels. Theoretical and simulation results of our proposed new PLS scheme have shown significant improvement in the secrecy capacity and secrecy outage probability for both CUs and DUs in comparison with the existing methods.

Single carrier frequency division multiple access (SC-FDMA), a modified form of orthogonal frequency division multiple access (OFDMA), is a promising technique for high data rate and low peak-to-average power ratio for uplink communications in cellular networks. However, similar to OFDMA, SC-FDMA also suffers from carrier frequency offset (CFO). Particularly, in the presence of multiple users, the uplink SC-FDMA introduces multiple CFOs. The CFOs must be estimated and compensated before demodulating the signal to minimize the inter-carrier interference (ICI) and ensure the efficiency of the SC-FDMA uplink system. In this paper, we propose a method for multi-user CFOs estimation that exploits the property of minimum variance of signal amplitudes at the receiver across different subcarriers. It utilizes the mean and variance of the output magnitude based on its probability density function. The variance approaches minimum value when CFO is fully compensated. The CFO estimation performance is evaluated on the basis of simulation and comparison with other methods over frequency selective fading channel environments.

This paper aims to construct optimal Z-complementary code set (ZCCS) with non-power-of-two (NPT) lengths to enable interference-free multicarrier code-division multiple access (MC-CDMA) systems. The existing ZCCSs with NPT lengths, which are constructed from generalized Boolean functions (GBFs), are sub-optimal only with respect to the set size upper bound. For the first time in the literature, we advocate the use of pseudo-Boolean functions (PBFs) (each of which transforms a number of binary variables to a real number as a natural generalization of GBF) for direct constructions of optimal ZCCSs with NPT lengths.

The zero correlation zone (ZCZ) ratio, i.e., the ratio of the width of the ZCZ and the length of the sequence plays a major role in reducing interference in an asynchronous environment of communication systems. However, to the best of the authors knowledge, for q = 2, the highest ZCZ ratio for even-length Zcomplementary pairs which are directly constructed using generalized Boolean functions (GBFs), is 2/3. In this letter, we present a direct construction of q-ary even-length Z-complementary pairs through GBFs, which can achieve aZCZ ratio of 3/4.In general, the constructed q-ary even-length Z-complementary pairs are of length 2m-1+ 2 (m ∈ Z+), having a ZCZ width of 2m-2+ 2π(m-3)+ 1 where π is a permutation over m - 2 variables.

A major drawback of orthogonal frequency division multiplexing (OFDM) systems is their high peak-to-mean envelope power ratio (PMEPR). The PMEPR problem can be solved by adopting large codebooks consisting of complementary sequences with low PMEPR. In this paper, we present a new construction of polyphase complementary sets (CSs) using generalized Boolean functions (GBFs), which generalizes Schmidt's construction in 2007, Paterson's construction in 2000 and Golay complementary pairs (GCPs) given by Davis and Jedwab in 1999. Compared with Schmidt's approach, our proposed CSs lead to lower PMEPR with higher code-rate for sequences constructed from higher-order (≥ 3) GBFs. We obtain polyphase complementary sequences with maximum PMEPR of 2k+1and 2k+2- 2M where k,M are non-negative integers that can be easily derived from the GBF associated with the CS.

A pair of sequences is called a Z-complementary pair (ZCP) if it has zero aperiodic autocorrelation sums (AACSs) for time-shifts within a certain region, called zero correlation zone (ZCZ). Optimal odd-length binary ZCPs (OB-ZCPs) display closest correlation properties to Golay complementary pairs (GCPs) in that each OB-ZCP achieves maximum ZCZ of width (N + 1)/2 (where N is the sequence length) and every out-of-zone AACSs reaches the minimum magnitude value, i.e. 2. Till date, systematic constructions of optimal OB-ZCPs exist only for lengths 2α± 1, where α is a positive integer. In this paper, we construct optimal OB-ZCPs of generic lengths 2α10β26γ+ 1 (where α, β, γ are non-negative integers and α ≥ 1) from inserted versions of binary GCPs. The key leading to the proposed constructions is several newly identified structure properties of binary GCPs obtained from Turyn's method. This key also allows us to construct OB-ZCPs with possible ZCZ widths of 4 × 10β-1+ 1, 12 × 26γ-1+ 1 and 12 × 10β26γ-1+ 1 through proper insertions of GCPs of lengths 10β, 26γ, and 10β26γ, respectively. Our proposed OB-ZCPs have applications in communications and radar (as an alternative to GCPs).

A salient disadvantage of orthogonal frequency division multiplexing (OFDM) systems is the high peak-to-mean envelope power ratio (PMEPR). The PMEPR problem can be solved by using complementary sequences with low PMEPR. In this paper, we present a new construction of complementary set (CS) by using generalized Boolean functions (GBFs), which generalizes the constructions given by Davis et al., Paterson and Schmidt. The proposed CS provides lower PMEPR upper bound as compared to Schmidt's method for the sequences corresponding to higher order (≥ 3) GBFs. We obtain complementary sequences with maximum PMEPR of 2k+1and 2k+2- 2M where k, M are non-negative integers that can be easily derived from the GBF associated with the CS.

Zero correlation zone (ZCZ) sequence sets play an important role in interference-free quasi-synchronous code-division multiple access communications. In this paper, for the first time, we investigate the periodic correlation properties of polyphase sequences obtained from paraunitary (PU) matrices, which shows the inherent relationship between PU matrix and ZCZ sequence sets. Our investigation suggests that any arbitrary PU matrix can produce ZCZ sequence sets by controlling its expanded form. The key idea is to impose certain restrictions on the expanded forms of the PU matrices to enable precise computation of the periodic correlation functions of the constructed sequences. We show that our proposed construction leads to near-optimal ZCZ sequence sets with regard to the ZCZ set size upper bound.

This paper proposes a blind modulation classification (MC) algorithm for linearly modulated signals of orthogonal frequency division multiplexing (OFDM) system. The proposed MC algorithm works with unknown frequency, timing, and phase offsets and without the prior requirement of channel statistics. In this research, a larger pool of modulation formats, i.e., binary phase-shift keying (BPSK), quadrature PSK (QPSK), offset QPSK (OQPSK), minimum shift keying (MSK), and 16-quadrature amplitude modulation (16-QAM) for OFDM signal has been classified. Classification takes place in two stages. First, we compute the discrete Fourier transform (DFT) of the received OFDM signal and then a normalized fourth-order cumulant is used in frequency domain to classify OQPSK, MSK, and 16-QAM modulation formats. At the second stage, the normalized fourth-order cumulant is used on the DFT of the square of the received OFDM signal to classify BPSK and QPSK modulation formats. The success rate and computation of the proposed MC algorithm are evaluated and compared with the previous methods.

Z-complementary code set (ZCCS), an extension of perfect CCs, refers to a set of 2-D matrices having zero correlation zone properties. ZCCS can be used in various multi-channel systems to support, for example, quasi-synchronous interference-free multicarrier code-division multiple access communication and optimal channel estimation in multiple-input multiple-output systems. Traditional constructions of ZCCS heavily rely on a series of sequence operations which may not be feasible for rapid hardware generation particularly for long ZCCSs. In this paper, we propose a direct construction of ZCCS using the second-order Reed-Muller codes with efficient graphical representation. Our proposed construction, valid for any number of isolated vertices present in the graph, is capable of generating optimal ZCCS meeting the set size upper bound.

In this paper, a blind carrier frequency offset (CFO) estimation algorithm for multi-input multi-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems employing constant modulus signaling has been proposed. The CFO incorporated frequency domain received signal has been utilized for the purpose of CFO estimation in block fading channel. Thereafter, frequency domain sum and difference signals have been formulated using the received signal and the expression for corresponding signal powers have been derived. Here, a cost function has been deduced which minimizes the signal power difference between all the subcarriers in two neighbouring space-time-coded blocks. The complexity of proposed estimation algorithm has significantly been reduced by using the sinusoidal nature of the cost function. The proposed method is verffied for $2\times2$ MIMO using Alamouti codes. Simulation results have been presented to demonstrate the proposed CFO estimation algorithm. The proposed method exhibits improved performance when compared with the existing techniques over Rayleigh frequency-selective fading channels.

This paper presents the optimal physical-layer security scheme of both primary user (PU) and secondary user (SU) in the underlay multiple-input multiple-output cognitive-radio network (MIMO-CRN) by using bi-directional zero-forcing beamforming technique. The proposed method enables the PU to communicate along with the SU without sacrificing their individual secrecy capacity, i.e., without causing interference to each other in the presence of eavesdropper(s). In this method, a bi-directional beamforming has been applied to eradicate the necessity of involving artificial noise for preventing the active eavesdropper(s). Both theoretical and numerical analyses of the secrecy outage probability are provided to demonstrate the effectiveness of our proposed method. The secrecy outage probability is also derived to evaluate the performance variations of our proposed scheme when the channel-estimation error occurs.

This work proposes the blind modulation classification (MC) of different variants of quadrature phase-shift-keying (QPSK), i.e.,$\pi/4$-QPSK, offset QPSK (OQPSK), and minimum-shift-keying (MSK), and 8-PSK. The problem of MC for multiple antenna systems is investigated over frequency-selective fading channels with transmission impairments, i.e., phase, timing, and frequency offsets, without having prior information about channel coefficients. The MC algorithm proposed in this paper employs the cyclostationarity and higher-order statistical properties of the received baseband signal for classification. The MC is performed in three stages: at the first stage, the second-order cyclic cumulant uses the position of the cycle frequency to classify MSK and OQPSK. At the second and third stages, the fourth-order correlation function of the signals received from different antennas exhibits peaks, which are employed as discriminating features for QPSK,$\pi/4$·QPSK, and 8-PSK. Monte Carlo simulations are used to evaluate the performance of the proposed algorithm.

This letter is focused on increasing the zero correlation zone (ZCZ) of even-length binary Z-complementary pairs (EB-ZCPs). Till date, the maximum ZCZ ratio (i.e., ZCZ width over the sequence length) for systematically constructed EB-ZCPs is 2/3. In this letter, we give a construction of EB-ZCPs with lengths 2α+210β26γ+ 2 (where α, β, and γ are nonnegative integers) and ZCZ widths 3 × 2α10β26γ+ 1, thus achieving asymptotic ZCZ ratio of 3/4. The proposed EB-ZCPs are constructed via proper insertion of concatenated odd-length binary ZCPs. The ZCZ width is proved by exploiting several newly identified intrinsic structure properties of binary Golay complementary pairs, obtained from Turyn's method. The proposed EB-ZCPs have aperiodic autocorrelation sums (AACS) magnitude of 4 outside the ZCZ region (except for the last time-shift taking AACS value of zero).

Owing to their ideal correlation properties, complete complementary codes (CCCs) have attracted great research attentions, particularly in wireless communications. In this letter, we propose a construction of CCCs having size M and length P N (M, P ≥ 2, P |M; N ∈ N) based on Kronecker product of paraunitary (PU) matrices, which generalizes our previous PU generator for CCCs. We show that our proposed construction leads to new antipodal PU (APU) matrices, which can be used as precoding matrices for orthogonal frequency division multiplexing (OFDM), multiple-input multiple-output OFDM, and spread-signature code division multiple access systems in order to obtain better error probability performances. The proposed construction has an advantage over our previous PU method and some previous constructions for APU matrices with regard to the availability of wide range of sequence lengths.

This paper presents the optimal physical-layer security scheme of both primary user (PU) and secondary user (SU) in the underlay multiple-input multiple-output cognitive-radio network (MIMO-CRN) by use of a bi-directional zero-forcing beamformer. The proposed new method enables the PU to communicate along with the SUs through a relay node without sacrificing their individual secrecy capacity, i.e., without causing interference to each other even in the presence of eavesdropper(s). In the first phase, a transmitting beamformer at the PU/SU transmitters and a receiving beamformer at the relay have been adopted to separate PU and SU data. In the second phase, a bi-directional beamformer has been applied to eradicate the necessity of involving artificial noise for preventing the active eavesdropper(s). To maximize the total secrecy capacity, a generalized non-linear optimization problem has been formulated and converted to a simplified constrained optimization problem by utilizing the beamformer and the associated subspace restriction. Then, this problem is solved by the Lagrangian method. Both theoretical and numerical analyses of the total and individual ergodic secrecy rates are provided to demonstrate the effectiveness of our proposed method. The secrecy outage probability is also derived to evaluate the performance variations of our proposed scheme when the channel-estimation error occurs.

Spatial multiplexing is an important factor usable for improving the throughput of future millimeter-wave (mm-wave) backhaul links. One conventional strategy in mm-wave multiple-input multiple-output (MIMO) systems uses densely packed antennas and exploits the spatial signature of multiple paths. Meanwhile, spatial multiplexing over a single line-of-sight (LoS) path, known as LoS MIMO communication, offers an alternative option with widely spaced antennas exploiting the phases of spherical waves. In this paper, we first show that those two conventional approaches exploit two different degrees in the channel matrices, which we denote as inter- and intra-path multiplexing, respectively. Then, we show that the two kinds of spatial multiplexing can be jointly exploited and identify their different requirements on system design. Fulfilling all requirements simultaneously, we propose a system with multiple widely spaced subarrays. With the help of analog beamforming, the intra-path multiplexing of conventional LoS MIMO systems can be introduced to other non-LoS paths owing to its robustness. Merging the two kinds of spatial multiplexing in a combined channel model and connecting it with a hybrid beamforming architecture, the proposed system achieves spatial multiplexing of a higher order than conventional ones. Simulation results for a backhaul scenario illustrate that the channel of the proposed method has higher ranks than that of conventional approaches.

Owing to their ideal correlation properties, complete complementary codes (CCC) have found numerous applications in wireless engineering, in particular they have been employed to support interference-free multi-carrier code-division multiple access systems with improved spectral efficiency. In this paper, we propose a simple construction of CCCs of length Nn(n e N) based on paraunitary matrices of size N × N. This algorithm can generate CCCs from N-shift cross-orthogonal sequence sets for n > 1. Then, we introduce an easy implementation of the proposed algorithm by multiplexers and read-only memories (ROMs), i.e., a multiplier-free implementation. As multipliers are avoided, substantial reduction of construction complexity for CCCs is obtained as compared to the existing works.

This paper presents blind modulation classification algorithm of circular linearly modulated signals using cyclic cumulant. The classification uses positions of non-zero cyclic frequencies (symbol rate frequency or carrier frequency) of the received signals. The method works over flat and frequency selective fading channels without having any knowledge of the signal parameters and channel statistics. The proposed method is used for classifying circular constellation modulation format which has not been addressed before. It requires lower complexity than the maximum likelihood approach. The performance of this novel algorithm is compared with the existing methods. In this paper, we have considered a four-class problem including quadrature phase-shift keying (QPSK), offset-QPSK, π/4-QPSK, minimum shift keying.

A pair of sequences is called a periodic complementary pair (PCP) if the periodic autocorrelations of the constituent sequences sum up to zero for all nonzero time shifts. Owing to the scarcity of PCPs, we investigate optimal binary periodic almost-complementary pairs (BP-ACPs), each displaying correlation property closest to that of PCP. We show that an optimal BP-ACP of even length N has zero out-of-phase periodic autocorrelation sums (PACSs) except at the time shift of N/2, where the corresponding PACS has minimum magnitude of 4. We also show that for any arbitrary odd N, all the out-of-phase PACSs of an optimal BP-ACP should have identical magnitude of 2. A number of optimal BP-ACPs from analytical constructions as well as computer search are presented. In addition, our proposed optimal BP-ACPs for the even-length case lead to two new families of base-two almost difference families.

Blind symbol or baud rate estimation is one of the most important parts of the blind signal detection process. Most of the blind symbol rate estimation algorithms provided in the literature either estimate symbol rate from the baseband signal or require prior knowledge of transmitted signal parameters. Moreover, these algorithms had been mostly limited to theoretical studies. In this paper, a cyclic correlation based blind symbol rate estimation is considered for linearly modulated signals. The estimation is performed directly from an intermediate frequency (IF) signal and without having prior knowledge of transmitted signal parameters. The algorithm is implemented on a National Instruments (NI) hardware to measure its performance in a realistic environment. Theoretical and experimental results are provided and compared with existing methods.

This paper analyzes the outage probability of cooperative communications over asymmetric fading environments. This work investigates the scenario where cooperative nodes are located at different geographical locations. Some cooperative nodes experience line of sight (LOS) signals and some nodes may experience non-LOS (NLOS) signals. As a result, signals in different links are affected by different fading distributions, one link may undergo Rician fading distribution and others links may undergo Rayleigh fading distribution. Such scenario is referred to as asymmetric fading channel. Assuming decode-and-forward, we provide an analytical model of outage probability for repetition-based relaying over different asymmetric fading channels. We show that the outage performance is better when the relays are in LOS situation with respect to the source rather than to the destination for the large number of relay nodes regime. The conclusions are verified through analytical and Monte-Carlo simulation studies.

The paper analyzes power spectral density (PSD) of orthogonal pulse-based signals for time hopping ultra wideband (TH-UWB) systems. Our extensive studies show that the PSD of these signals not only depends on the time dithering code and the modulation schemes, but also on the energy spectral density (ESD) of orthogonal pulses. The different order orthogonal pulses provide different ESD which changes the shape of continuous spectral component with symbols. We show that orthogonal pulse-based signals reduce the dynamic range of amplitude of discrete spectral components. Further, we reduce the dynamic range by adopting longer TH code over orthogonal pulse-based signals. As a result, UWB system performance improves with average transmitted power. The theoretical analysis of PSD of orthogonal pulse-based TH-UWB signal is provided in details and verified through simulation results.

The paper describes information theoretic capacity of orthogonal pulse based modulation schemes for time hopping ultra wideband (TH-UWB) systems over a multiple access and multipath fading channel. Orthogonal pulse based modulation schemes such as pulse shape modulation (PSM), biorthogonal PSM (BPSM) and a combination of orthogonal pulse position modulation (OPPM) and BPSM have been proposed for reducing inter symbol interference (ISI) and multiple access interference (MAI) as well as for improving system performance. System capacity of TH-UWB systems can be increased by employing these modulations for higher level modulation schemes. The capacity of OPPM-BPSM outperforms PSM and BPSM schemes over a multipath fading channel. The complete mathematical analysis and theoretical simulation results are provided in detail.

Inspired by the overwhelming popularity of nowadays wireless local area networks (wireless LAN, or Wi-Fi), researchers and developers have uncovered their wide application perspectives in a vehicular environment. Currently, several prototypes of dedicated short range communications (DSRC) for vehicular networks have been developed by some companies for both intelligent transportation systems (ITS) and vehicular infrastructure integration (VII). However, most of the designers simply apply the existing indoor wireless technologies, such as Wi-Fi, into a vehicular environment without redesigning them for a vehicular environment. The vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) channels feature with doubly selective fading due to the high mobility of vehicles. Both theoretical analysis and experiments have verified that the indoor wireless technologies are unable to achieve optimized and robust performance when applied to a vehicular environment. Industry is calling for new physical and MAC layer protocols for ITS and VII. The IEEE 802.11p workgroup is currently working on standardizing the wireless access for vehicular environment (WAVE), which is anticipated to be ratified in 2009. In this paper, we brief the design of a WAVE prototype based on the IEEE 802.11p protocol, which allows us to implement and evaluate the performance of the IEEE 802.11p standard in a practical approach.

This letter proposes a novel random Fourier features (RFF) based sparsity-aware Kernel recursive adaptive filtering algorithm which employs generalized maximum Versoria criterion (GMVC) as an adaptation cost and generalized Versoria zero attraction (GVZA) as a sparsifying-norm. The proposed RFF-based GVZA kernel recursive GMVC (RFF-GVZA-KRGMVC) algorithm is robust for nonlinear sparse channel estimation under non-Gaussian noise over both stationary and non-stationary environments. Simulations indicate that the proposed RFF-GVZA-KRGMVC approach delivers better convergence and bit error rate performance over the existing stochastic gradient based RFF-ZA-kernel-MVC (RFF-ZA-KMVC) algorithm at the cost of increased computational complexity. Furthermore, detailed convergence analysis is also performed for the proposed algorithm and corroborated by Monte-Carlo simulations.

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems based on biphase shift keying (BPSK), orthogonal pulse position modulation (OPPM) and pulse shape modulation (BPSM). A set of M = 2ksymbols are constructed by using L = 22lorthogonal pulse positions and N = 22k-l-1biorthogonal pulses, where k and l are nonnegative integers such that 0 ≤ l ≤ k - 1. The selection of number of pulse positions and pulses depend on the system performance and the availability of orthogonal pulses with estimable auto-correlation properties. The proposed scheme achieves higher data rate by introducing more number of orthogonal pulses in the same pulse repetition interval. It also reduces the system complexity by half by introducing antipodal version of orthogonal pulses. The proposed transmission scheme is analyzed through computer simulations in the presence of multipath channel.

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems using on-off keying (OOK) and pulse shape modulation (PSM). For this scheme, a set of orthogonal pulses is used to represent bits in a symbol. These orthogonal pulses are transmitted simultaneously in the same time slot resulting in a composite pulse. By assigning different subset of orthogonal pulses for each user, multi-user interference can be reduced considerably. The proposed transmission scheme can achieve higher data rate by using fewer pulses and can use fewer number of receiver correlators than those used in PSM. Due to the presence of OOK, the proposed scheme requires minimum energy and is applicable for energy constrained UWB systems. The bit-error-rate (BER) performance of the proposed transmission scheme is analyzed both mathematically and through computer simulations in additive white Gaussian noise (AWGN) channel and modified IEEE 802.15.3a S-V UWB multipath channel model. The present paper also compares the proposed scheme with existing PSM and its combined modulation schemes.

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems based on orthogonal pulse position modulation (OPPM) and bi-orthogonal pulse shape modulation (BPSM). A set of M=2ksymbols are constructed by using L = 2lorthogonal pulse positions and N = 2k-l-1biorthogonal pulses, where k > 1 and l are nonnegative integers such that 0 les l les k-1. The selection of the number of pulse positions and pulses depends on the system performance and the availability of orthogonal pulses with estimable auto-correlation properties. This scheme allows an increase in the number of bits per symbol and consequently, reduces the duration of the pulse repetition interval which is obtain by increasing the number of orthogonal pulses. The proposed scheme achieves higher data rate by using a large number of orthogonal pulses in the same pulse repetition interval. It also reduces the system complexity by half by introducing antipodal version of orthogonal pulses. The proposed transmission scheme is analyzed through computer simulations in a multipath channel using two sets of orthogonal pulses.