This paper presents a new construction method for binary cross Z-complementary pairs (CZCPs) with mutually orthogonal mates. Our approach, which utilizes Boolean functions, achieves a cross Z-complementary ratio (CZCratio) of 6/7. These CZCP mates can be used in generalized spatial modulation (SM) systems to enhance the channel estimation performance, thanks to their zero auto- and cross-correlation zone properties at the front-/tail-ends. We show that our method demonstrates the ability to generate new binary CZCP mates with improved CZCratioand flexible sequence lengths. Through numerical studies, we illustrate that the constructed mutually orthogonal CZCP mates can enhance the channel estimation performance in generalized SM systems.

For any alphabet, consider sequences that both contain no consecutive repeated symbols and have the same number of occurrences of symbols from a specified subset of the alphabet. These properties are particularly valuable in applications such as DNA data storage, where avoiding repeated patterns improves stability and robustness. A Homopolymer-Free Constant Weighted Sum (HFCWS) code, defined over an alphabet, is a set of sequences that satisfies two specific properties: (1) Constant Weighted Sum (CWS) Property: For a designated subset of the alphabet, the number of total occurrences of symbols from a given subset of the alphabet remains the same across all sequences in the code. (2) Homopolymer-Free (HF) Property: Each sequence in the code is Homopolymer-Free, with no consecutive identical symbols. In this paper, for a given code defined over an alphabet, we enumerate the total number of sequences that satisfy the Constant Weighted Sum property with a specific weight$\mathbf{w}$and the Homopolymer-Free property. The asymptotic code rate of HFCWS codes is derived for both large and small constant weighted sums. Also, a lower bound on asymptotic code rate is established for the case when the constant weighted sum is approximately half of the sequence length. We establish an equivalence between HFCWS codes over the quaternary alphabet and Homopolymer-Free GC-Balanced DNA codes, demonstrating that our derived code rate formula not only aligns with existing results but also provides new theoretical insights for Homopolymer-Free GC-Balanced DNA codes.

Inspired by G. Tenengolts' 1984 construction of nonbinary single error-correcting codes for deletion and insertion errors, we develop families of DNA codes that simultaneously address multiple biological and combinatorial constraints. These codes satisfy Hamming, Reverse, Reverse-Complement, and GCcontent constraints while maintaining single error-correction capabilities for insertion, deletion, and substitution errors. Additionally, our constructed codes are free from homopolymers exceeding run length four and from secondary structures with stem lengths greater than two, both in individual codewords and their concatenations. This work presents the first known construction of DNA codes capable of single-error correction (insertion, deletion, and substitution) while satisfying multiple constraints: the GC-content constraint, Hamming constraint, Reverse constraint, and Reverse-Complement constraint. Additionally, these codes are constructed to be free from homopolymers exceeding run length four and secondary structures with stem lengths greater than two.

Molecular Communication via Diffusion (MCvD) systems face significant performance degradation due to Intersymbol Interference (ISI), which remains one of their primary challenges. In contrast to the conventional zero-padding constraints for ISI mitigation, this paper proposes a family of channel codes ($\mathcal{C}_{\alpha, \beta}^{(n)}$) characterized by two key constraints: the weight constraint ($\alpha$) and the maximum length of consecutive ones ($\beta$). We present a theoretical framework, first deriving the size of the codes satisfying both constraints, followed by deducing an expression for average ISI as a function of code weight density. We further establish an upper bound on the asymptotic code rate and average ISI of the code$\mathcal{C}_{\alpha, 2}^{(n)}$and compare the code performance for different values of$\alpha$. The results demonstrate that the code$\mathcal{C}_{\alpha, 2}^{(n)}$achieves a superior code rate while exhibiting enhanced ISI performance compared to the best-known codes.

This paper proposes Dense KO (DKO) codes to enhance the recently introduced KO coding framework for faster convergence and reduced model complexity. The key idea is to replace the stacked fully-connected layers in the KO encoder and decoder with a DenseNet-inspired architecture to improve parameter efficiency. Additional modifications like Mish activations further aid representation. A cyclical learning rate policy accelerates training convergence within fewer epochs. DKO codes match the error resilience of KO codes for short blocklengths, while requiring less parameters. The reduction in training time and model size facilitates the adoptability of learned coding schemes for latency-sensitive short blocklength applications.

This work analyzes the performance of a cache-enabled vehicular communication network with platooned vehicular users aided by base stations (BSs) for cellular connectivity. We consider a caching scheme that prioritizes searching for files within the same platoon to minimize latency and resorts to the BS connection if the file is unavailable in the platoon. The file access probability representing the probability of the typical vehicular user acquiring a file from another vehicle in the same platoon or from a BS is presented. We also study the design of optimal caching placement that maximizes the total file access probability subject to memory constraints. Further, design insights are provided with the help of derived expressions and numerical results. Results indicate that based on the system parameters and relative link quality of vehicular and cellular links, it may be optimal to cache more popular files or may not be optimal to cache any file at all.

For any given alphabet of size q, a Homopolymer Free code (HF code) refers to an (n, M, d)qcode of length n, size M and minimum Hamming distance d, where all the codewords are homopolymer free sequences. For any given alphabet, this work provides upper and lower bounds on the maximum size of any HF code using Sphere Packing bound and Gilbert-Varshamov bound. Further, upper and lower bounds on the maximum size of HF codes for various HF code families are calculated. Also, as a specific case, upper and lower bounds are obtained on the maximum size of homopolymer free DNA codes.

In this paper, we first propose a new design strategy of 2D Z-complementary array quads (2D-ZCAQs) with feasible array sizes. A 2D-ZCAQ consists of four distinct unimodular arrays satisfying zero 2D auto-correlation sums for non-trivial 2D time-shifts within certain zone. Then, we obtain the upper bounds on the column sequence peak-to-mean envelope power ratio (PMEPR) of the constructed 2D-ZCAQs by using specific auto-correlation properties of some seed sequences. The constructed 2D-ZCAQs with bounded column sequence PMEPR can be used as a potential alternative to 2D Golay complementary array sets for practical applications.

Molecular-communication-via-diffusion (MCvD) is one of the popular communication methods between bio-nano machines (BNMs) in nano-scale regions. However, the MCvD channel experiences significant inter-symbol interference (ISI) due to the probabilistic migration of the molecules. In this paper, we first introduce a family of novel ISI-reducing channel codes. We have shown that the proposed code can achieve a much higher code rate with a substantially lower ISI than the existing channel codes proposed in the literature to deal with ISI. Furthermore, we also derive an upper bound on the code rate and ISI. The numerical results show that ISI-reducing codes improve BER performance in a high-memory channel by reducing the effect of ISI on the channel.

In this paper, we have considered a cooperative Molecular Communication via Diffusion (MCvD) network in the presence of adversaries. We have mathematically modelled the adversarial receiver distribution and analyzed its effect on the system performance. The fusion center (FC) gathers all the local information from the receivers and applies the OR or AND rule to the local decisions to arrive at a global decision. We have computed the bit error rate (BER) performance and proposed "η-min filtering" and "η-max filtering" algorithms to improve the system reliability by reducing the BER. It is also shown that the FC chooses the proper filtering algorithm depending on the adversarial receiver distribution and the logical operation to get the best performance.

Molecular communication has emerged as a promising candidate to provide communication capability to nano-networks. In this paper, we model and analyze a molecular ad hoc network (MolAN) consisting of multiple molecular communication links in a 3D medium. The transmitter end of each link has individual data to communicate to the receiver. We first develop an analytical framework to model the MoIAN. In particular, we model the receivers as marked Poisson point process with transmit message as their marks. We then compute the mean signal strength, inter-symbol-interference and co-channel interference for degradable and non-degradable molecules. We derive the performance of the network in terms of the probability of successful bit detection. We also study the network throughput as a function of link active probability to show the existence of an optimal network density. Finally, we present some numerical results to derive interesting design insights.

Motivated from Reed-Muller codes, families of reversible, reversible-complement, and GC-balanced DNA codes are constructed from the ring ℤ6. In addition, DNA codewords are free from any secondary structures having stems of length more than two and homopolymers with run-length more than three. Also, DNA strings obtained from concatenations of those DNA codewords avoid secondary structures and homopolymers. We have also given a lower bound on the size of DNA codes with all these properties together.

In this paper, we present a new family of cross Z-complementary pairs (CZCPs) based on generalized Boolean functions and two roots of unity. Our key idea is to consider an arbitrary partition of the set {1,2,⋯,n} with two subsets corresponding to two given roots of unity for which two truncated sequences of new alphabet size determined by the two roots of unity are obtained. We show that these two truncated sequences form a new q-ary CZCP with flexible sequence length and large zero-correlation zone width. Furthermore, we derive an enumeration formula by considering the Stirling number of the second kind for the partitions and show that the number of constructed CZCPs increases significantly compared to the existing works.

In this paper, we present a novel design strategy of DNA codes with length 3n over the non-chain ring ℤ4+uℤ4+u2ℤ4with 64 elements and u3=1, where n denotes the length of a code over R. We first study and analyze a distance conserving map defined over the ring R into the length-3 DNA sequences. Then, we derive some conditions on the generator matrix of a linear code over R, which leads to a DNA code with reversible, reversible-complement, homopolymer 2-run-length, and3wn-GC-content constraints for integer w (0 ≤ w ≤ 3n). Finally, we propose a new construction of DNA codes using Reed-Muller type generator matrices. This allows us to obtain DNA codes with reversible, reversible-complement, homopolymer 2-run-length, and -GC-content constraints.

Recently, different architectures based on coding theory have been proposed to reduce the storage and communication costs associated with a blockchain system. However, many of these methods have high bandwidth requirements for repairing the share of a failed node or decoding a particular requested block. The bandwidth required for decoding a requested block becomes an important factor in some blockchain applications like healthcare, where historical data needs to be frequently accessed. In this work, we introduce two new architectures for blockchain-based systems, which reduce the storage and communication costs associated with blockchain’s historical data and simultaneously provides confidentiality of the stored data. The two protocols are designed using a combination of fountain codes and a proposed communication and repair efficient secret sharing scheme. We also present a construction of the secret sharing scheme which meets our requirements.

Projection based algorithms are popular in the literature for online convex optimization with convex constraints and the projection step results in a bottleneck for the practical implementation of the algorithms. To avoid this bottleneck, we propose a projection-free scheme based on Frank-Wolfe: where instead of online gradient steps, we use steps that are collinear with the gradient but guaranteed to be feasible. We establish performance in terms of dynamic regret, which quantifies cost accumulation as compared with the optimal at each individual time slot. Specifically, for convex losses, we establish $\mathcal{O}\left( {{T^{1/2}}} \right)$ dynamic regret up to metrics of non-stationarity. We relax the algorithm’s required information to only noisy gradient estimates, i.e., partial feedback and derived the dynamic regret bounds. Experiments on matrix completion problem and background separation in video demonstrate favorable performance of the proposed scheme.

We develop general techniques to bound the size of the balls of a given radius r for q-ary discrete metrics, using the generating function for the metric and Sanov's theorem, that reduces to the known bound in the case of the Hamming metric and gives us a new bound in the case of the Lee metric. We use the techniques developed to find Hamming, Elias-Bassalygo and Gilbert-Varshamov bounds for the Lee metric.

We consider a wireless network where multiple energy harvesting transmitters communicate with the common receiver in a time-sharing manner. In each slot, a transmitter can either harvest energy or send its data to the receiver. Given a time deadline, the goal is to maximize the sum rate of transmitters under random energy arrivals with both perfect and imperfect channel state information at the receiver. The original sum-rate maximization (SRM) problem is a non-convex mixed integer non-linear program (MINLP). To obtain the optimal scheduling policy, we first reduce the original optimization problem to a convex MINLP and solve it using the generalized Benders decomposition algorithm. We observe that the SRM problem results in an unfair rate allocation among transmitters, i.e., the transmitter closer to the receiver achieves a higher rate than that by the transmitter farther from the receiver. Hence, to induce fairness among transmitters, we consider the minimum-rate maximization (MRM) problem. For the bounded channel estimation error, we obtain a robust scheduling policy by solving the worst-case SRM and MRM problems. Finally, we compare the proposed policies with myopic policies studied in the literature and show that the former outperform the latter in terms of achievable rates.

We focus on a scenario where two wireless source nodes wish to exchange confidential information via an RF energy harvesting untrusted two-way relay. Despite its cooperation in forwarding the information, the relay is considered untrusted out of the concern that it might attempt to decode the confidential information that is being relayed. To discourage the eavesdropping intention of the relay, we use a friendly jammer. Under the total power constraint, to maximize the sum-secrecy rate, we allocate the power among the sources and the jammer optimally and calculate the optimal power splitting ratio to balance between the energy harvesting and the information processing at the relay. We further examine the effect of imperfect channel state information at both sources on the sum- secrecy rate. Numerical results highlight the role of the jammer in achieving the secure communication under channel estimation errors. We have shown that, as the channel estimation error on any of the channels increases, the power allocated to the jammer decreases to abate the interference caused to the confidential information reception due to the imperfect cancellation of jammer's signal.

This paper considers an energy harvesting underlay cognitive radio network operating in a slotted fashion. The secondary transmitter scavenges energy from environmental sources in half duplex fashion and stores it in finite capacity rechargeable battery. It splits each slot into two phases: harvesting phase and transmission phase. We model the energy availability at the secondary user as first order stationary Markov process. We propose a robust online transmission policy by jointly optimizing the time sharing between the two phases and transmit power of secondary user, which maximizes its average throughput by a given time deadline.We show the comparison of our proposed policy with the offline and myopic policies.

We integrate a wireless powered communication network with a cooperative cognitive radio network, where multiple secondary users (SUs) powered wirelessly by a hybrid access point (HAP) help a primary user relay the data. As a reward for the cooperation, the secondary network gains the spectrum access where SUs transmit to HAP using time division multiple access. To maximize the sum throughput of SUs, we present a secondary sum-throughput optimal resource allocation (STORA) scheme. Under the constraint of meeting target primary rate, the STORA scheme chooses the optimal set of relaying SUs and jointly performs the time and energy allocation for SUs. In particular, by exploiting the structure of the optimal solution, we find the order in which SUs are prioritized to relay primary data. Since the STORA scheme focuses on the sum throughput, it becomes inconsiderate toward individual SU throughput, resulting in low fairness. To enhance fairness, we investigate three resource allocation schemes, which are: 1) equal time allocation; 2) minimum throughput maximization; and 3) proportional time allocation. Simulation results reveal the tradeoff between sum throughput and fairness. The minimum throughput maximization scheme is the fairest one as each SU gets the same throughput, but yields the least SU sum throughput.

In this paper, we study cooperative cognitive radio networks consisting of a primary user (PU) and multiple secondary users (SUs). SUs transmit only when PU is sensed as silent and may interfere with primary transmission due to imperfect sensing. When primary activity is sensed correctly, SUs cooperate with PU by assisting retransmission of failed packets of PU. We analyze packet throughput of PU and SU for three variations of the proposed cooperation method. A signal flow graph-based approach is employed to obtain the closed-form expressions of packet throughput. The analysis is done for two cases: individual sensing and cooperative sensing. Furthermore, we characterize the optimal transmission probability of SUs that maximizes individual secondary packet throughput keeping all queues in the system stable. Results present a comparison of throughput performance of the proposed cooperation methods under different scenarios and show their benefits for both PU and SU throughput.

We consider a spectrum sharing scenario, where a secondary network coexists with a primary network of multiple transceivers. The secondary network consists of an energy-constrained decode-and- forward secondary relay which assists the communication between a secondary transmitter and a destination in the presence of the interference from multiple primary transmitters. The secondary relay harvests energy from the received radio- frequency signals, which include the information signal from the secondary transmitter and the primary interference. The harvested energy is then used to decode the secondary information and forward it to the secondary destination. At the relay, we adopt a time switching policy due to its simplicity that switches between the energy harvesting and information decoding over time. Specifically, we derive a closed-form expression for the secondary outage probability under the primary outage constraint and the peak power constraint at both secondary transmitter and relay. In addition, we investigate the effect of the number of primary transceivers on the optimal energy harvesting duration that minimizes the secondary outage probability. By utilizing the primary interference as a useful energy source in the energy harvesting phase, the secondary network achieves a better outage performance.

Energy harvesting (EH) cognitive relays are an exciting solution to the problem of inefficient use of spectrum while achieving green communications and spatial diversity. In a spectrum sharing scenario, we investigate the performance of a cognitive relay network, where a secondary source communicates with its destination over Nakagami-m channels via decode-and-forward EH relays while maintaining the outage probability of the primary user below a predefined threshold. Specifically, we derive a closed-form expression for the secondary outage probability and show that it is a function of the probability of an EH relay having sufficient energy for relaying, which in turn, depends on the energy harvesting and consumption rates of the EH relay and the primary outage probability threshold. We also show that relaxing the primary outage constraint may not always benefit the cognitive EH relay network due to the limitations imposed on the relay's transmit power by the energy constraint.

This paper considers the cooperation between primary and secondary users at information and energy levels when both users are energy harvesting nodes. In particular, a secondary transmitter helps relaying the primary message, and in turn, gains the spectrum access as a reward. Also, the primary transmitter supplies energy to the secondary transmitter if the latter is energy-constrained, which facilitates an uninterrupted cooperation. We address this two-level cooperation over a finite horizon with the finite battery constraint at the secondary transmitter. While promising the rate-guaranteed service to both primary and secondary users, we aim to maximize the primary rate. We develop an iterative algorithm that obtains the optimal offline power policies for primary and secondary users. To acquire insights about the structure of the optimal solution, we examine specific scenarios. Furthermore, we investigate the effects of the secondary rate constraint and finite battery on the primary rate and the probability of cooperation. We show that the joint information and energy cooperation increases the chances of cooperation and achieves significant rate gains over only information cooperation.

In this paper, we consider a cognitive radio system with a primary user and a secondary user, both powered by batteries that can recharge over time by harvesting energy from renewable sources. Both users store packets in queues for transmission. We consider a cooperation scenario where secondary user receives unsuccessful packets transmitted by primary user and relays them to primary receiver. For the system to be stable, all queues in the system should be stable. We find the stable throughput region for given system model. In battery powered transmitters, amount of energy available at a transmitter affects the activity of users, therefore affecting the stable throughput region of system. Based on the analysis of stability region, we present numerical results and study the effect of energy arrival rate as well as battery capacity on stability region and on delay of primary user packets. Finally, we compare the cooperation scheme with non-cooperation case for different energy arrival rates.

Block outlier detection methods, based on Tietjen- Moore (TM) and Shapiro-Wilk (SW) tests, are proposed to detect and suppress spectrum sensing data falsification (SSDF) attacks by malicious users in cooperative spectrum sensing. First, we consider basic and statistical SSDF attacks, where the malicious users attack independently. Then we propose a new SSDF attack, which involves cooperation among malicious users by masking. In practice, the number of malicious users is unknown. Thus, it is necessary to estimate the number of malicious users, which is found using clustering and largest gap method. However, we show using Monte Carlo simulations that, these methods fail to estimate the exact number of malicious users when they cooperate. To overcome this, we propose a modified largest gap method.

We consider a cognitive radio system in which primary user stores packets in a queue for transmission. For proper functioning of primary system, the cognitive user must ensure that primary queue remains stable. We show that such a queue stability constraint can be converted to an equivalent interference constraint on cognitive user's transmission. Under this constraint, we propose a power allocation technique to maximize sum of individual outage capacities achieved on each sub-channel of an OFDM based cognitive user. We present simulation results depicting effect of channel gains of direct links and interference links on primary user's stable throughput and cognitive user's sum-outage capacity. The results show that proposed method performs better than only interweave mode of transmission used in literature.

Energy detection (ED) is a popular spectrum sensing technique in cognitive radio to detect the primary user. But the detection performance of ED deteriorates in the presence of noise uncertainty and exhibits associated SNR wall phenomenon. In this paper, the generalized energy detector (GED) is investigated, where the squaring operation of amplitude of received samples in conventional energy detector (CED) is replaced by an arbitrary positive operation p. Our aim is to study the effect of noise uncertainty on the detection performance of GED. We consider different distributions of noise uncertainty. Initially, uniform distribution of noise uncertainty is considered and an expression of the SNR wall for the same is derived. It is shown that the SNR wall for uniformly distributed noise uncertainty is independent of p. The study of the detection performance of GED is further extended for log-normally distributed noise uncertainty, where the SNR wall is calculated numerically.

In this paper, a new nonlinear companding technique, called the modified exponential companding technique, is proposed to reduce the peak to average power ratio (PAPR) of the orthogonal frequency division multiplexed (OFDM) signals. Instead of transforming the Rayleigh distributed OFDM signal into uniformly distributed signal as in the case of exponential companding proposed by Jiang, et al. (2005), we consider different probability distributions of the transformed signal, by introducing a control parameter a, which reduces the PAPR further. Simulation study demonstrates that the proposed method results in better PAPR reduction and improved BER performance compared to the exponential companding.

For a given blocklength we determine the number of interleavers which have spread equal to two. Using this, we find out the probability that a randomly chosen interleaver has spread two. We show that as blocklength increases, this probability increases but very quickly converges to the value 1 - e-2ap 0.8647. Subsequently, we determine a lower bound on the probability of an interleaver having spread at least s. We show that this lower bound converges to the value e-2(s-2)2, as the blocklength increases

In this paper, we introduce the concept of nonsystematic turbo codes and compare them with classical systematic turbo codes. Nonsystematic turbo codes can achieve lower error floors than systematic turbo codes because of their superior effective free distance properties. Moreover, they can achieve comparable performance in the waterfall region if the nonsystematic constituent encoder has a low-weight feedforward inverse. A uniform interleaver analysis is used to show that rate R=1/3 turbo codes using nonsystematic constituent encoders have larger effective free distances than when systematic constituent encoders are used. Also, mutual information-based transfer characteristics and extrinsic information transfer charts are used to show that rate R=1/3 turbo codes with nonsystematic constituent encoders having low-weight feedforward inverses achieve convergence thresholds comparable to those achieved with systematic constituent encoders. Catastrophic encoders, which do not possess a feedforward inverse, are shown to be capable of achieving low convergence thresholds by doping the code with a small fraction of systematic bits. Finally, we give tables of good nonsystematic turbo codes and present simulation results comparing the performance of systematic and nonsystematic turbo codes.

In this paper, we address the design of high rate turbo codes using high rate nonsystematic constituent encoders and compare their distance and iterative decoding convergence properties with systematic turbo coding schemes.

In this paper, bandwidth efficient Type-I and Type-II hybrid-ARQ (HARQ) schemes using turbo trellis coded modulation (TTCM) are proposed. These schemes combine the power efficiency of turbo codes with the bandwidth efficiency of trellis coded modulation (TCM) to create an effective hybrid FEC/ARQ system. Several packet combining schemes are presented for use in conjunction with iterative turbo decoding over wireless time-varying Rayleigh fading channels. The packet combining schemes provide improved throughput and reliability compared to a standard Type I hybrid ARQ system without combining with only a small increase in transmitter and receiver complexity. Simulation results show that, for high throughput values, HARQ schemes based on TTCM give substantial improvement over conventional TCM schemes with the same throughput over wireless channels.