This paper proposes a novel optimization approach for Primary Synchronization Signal (PSS) detection, introducing optimized correlator coefficients that incorporate assistive sequences to minimize sidelobes and cross-correlations without altering existing 5G New Radio (NR) PSS sequences. The convex optimization framework employs different optimization strategies based on a parameter that controls the penalty on sidelobes and cross-correlations, including closed-form solutions and a Projected Gradient Descent (PGD)-based iterative algorithm. Numerical evaluations demonstrate the proposed method's ability to reduce sidelobes and cross-correlations, highlighting the feasibility of detector optimization to enhance synchronization performance in current 5G deployments.

This paper proposes a novel approach to designing Primary Synchronization Signal (PSS) sequences for next-generation mobile communication systems. The proposed scheme formulates the PSS sequence design as an optimization problem, minimizing a cost function that captures the desired properties and requirements of PSS sequences. A gradient descent algorithm is employed to iteratively update the sequences, leading to optimized PSS sequences with superior synchronization performance compared to 5G New Radio (NR) PSS sequences. The proposed method offers a versatile and adaptable approach to designing synchronization sequences tailored to specific system requirements, making it a promising solution for 6G and future wireless networks.

Mobile devices perform cell search for initial access in cellular-based industrial Internet of Things (IoT) systems. Existing fifth-generation (5G) new radio (NR) cell-search scheme provides timing synchronization and cell identification. Usage scenarios emerging with the growth of the IoT market require unprecedented precision, reliability, and scalability in the future network, and a shift toward high-frequency bands can be one of the key enablers to achieve these stringent requirements. However, in high-frequency bands, hardware (HW) impairments, including carrier frequency offset and phase noise are exacerbated, and a sharp beam causes the problem of cell identity (ID) ambiguity that can reach further than a reduced cell coverage. In this article, a cell-search scheme is proposed for time-critical industrial IoT over mobile networks operating in high-frequency bands. To achieve high timing accuracy under the increased HW impairments, primary synchronization signals (SSs) are designed based on the distributed concatenations of a Zadoff–Chu sequence and its modification. Next, a secondary SS is designed based on the distributed concatenation of a Kasami sequence and its modification, which provides a larger set of cell IDs and is robust to the impairments. Compared to 5G NR under the increased HW impairments, our analysis and evaluation show that the proposed cell-search scheme has advantages, such as 25% lower timing detection complexity, 150% larger set of cell IDs, up to 15 and 6-dB signal-to-noise ratio gain in terms of timing and cell ID detection performance, respectively, and 60% shorter cell-search time, thereby realizing 80% lower battery consumption.

Biologically inspired pulse-coupled synchronization has received increasing attention as one of key techniques for developing decentralized wireless networks due to its inherent scalability and simplicity. While it has been actively studied in recent years, most of the previous works have focused on the synchronization only in fault/attack free networks. However, in reality, a network may have malfunctioning nodes and/or attackers, and thus robustness against these threats in the pulse- coupled synchronization must be an important practical issue on its path to realization. Motivated by this, we analyze the influence of attacker's behaviors in a network of pulse-coupled oscillators. The analysis shows that when the number of attackers is less than a certain number, i.e. a threshold, the network sustains its synchronization. Moreover, the threshold is proportional to both of coupling strengths among the pulse-coupled oscillators and the number of legitimate oscillators. Finally, numerical experiments are given to confirm the analytic results.

We propose a new contention resolution scheme designed for large scale autonomous wireless systems and fully distributed D2D (device-to-device) communications networks. The proposed contention resolution scheme is designed for scalability, efficiency, and fairness. Unlike traditional contention resolution schemes, the proposed contention resolution scheme uses idle time of channel as a measure of the channel condition. Idle time of channel is not only a much more reliable and versatile measure of channel condition than the traditional way of collision detection using ACK, it also makes it possible to use the proposed contention resolution scheme in situations where ACK is not expected such as with broadcast and multicast messages or in fully distributed synchronization procedures. The simulation study confirms that the proposed scheme exhibits high degree of scalability, efficiency, and fairness.

In this paper, a full-duplex (FD) amplify-and-forward (AF) relay is designed to compensate for the duplexing loss of the half-duplex (HD) AF relay. In particular, when there is no direct link between a source and a destination, joint analog domain self-interference suppression and digital domain residual self-interference cancellation is considered with an FD-AF relay having single receive antenna but multiple transmit antennas. Unlike previous approaches, a nonconvex quadratically constrained quadratic programming problem is formulated to find the optimal solution. The end-to-end spectral efficiency or, equivalently, the end-to-end signal-to-interference-plus-noise ratio from the source to the destination is chosen as the objective function to be maximized subject to the average transmit power constraint at the relay. In addition, an average power constraint is imposed on the output of the relay's receive antenna to avoid the nonlinear distortion in the low noise amplifier and the excessive quantization noise in the analog-to-digital converter. Through the systematic reduction and the partitioning of the constraint set, the optimal solution is derived in a closed algorithmic expression and shows how it allocates the transmission power not only in the direction of maximal performance improvement but also in the orthogonal direction in order to balance the system performance and the amount of self interference. It is shown that the optimal FD-AF relay significantly outperforms the optimal HD-AF relay even with the hardware limitations in the RF chain of the relay's receiver being well taken into account.

In this paper, a joint analog and digital domain self-interference cancellation is considered for the full-duplex (FD) amplify-and-forward (AF) relay with a single receive antenna but multiple transmit antennas. Under the assumption that there is no direct link between a source and a destination, the end-to-end spectral efficiency is maximized subject to the average transmit power constraint at the relay. Unlike previous approaches, an average power constraint is imposed also on the output of the relay's receive antenna to take into account the hardware limitations in the RF chain of the relay's receiver. A nonconvex quadratically constrained quadratic programming problem is formulated and the optimal beamforming vector is derived in a closed algorithmic expression through the systematic reduction and the partitioning of the constraint set. It is shown that the FD-AF relay significantly outperforms the half-duplex (HD) AF relay by properly compensating for the duplexing loss of the HD-AF relay.

This paper presents a coding scheme for the Gaussian wiretap channel based on low-density parity-check (LDPC) codes. The messages are transmitted over punctured bits to hide data from eavesdroppers. The proposed coding scheme is asymptotically effective in the sense that it yields a bit-error rate (BER) very close to 0.5 for an eavesdropper whose signal-to-noise ratio (SNR) is lower than the threshold SNRE, even if the eavesdropper has the ability to use a bitwise maximum a posteriori (MAP) decoder. Such codes also achieve high reliability for the friendly parties provided they have an SNR above a second threshold SNRB. It is shown how asymptotically optimized LDPC codes are designed with differential evolution where the goal is to achieve high reliability between friendly parties while keeping the security gap SNRB/SNREas small as possible to protect against passive eavesdroppers. The proposed coding scheme is encodable in linear time, applicable at finite block lengths, and can be combined with existing cryptographic schemes to deliver improved data security by taking advantage of the stochastic nature of many communication channels.

In this contribution, we derive the spread function and power spectrum of the so-called "relay channel'' along which electromagnetic waves propagate from a source station to a destination station via multiple amplify-and-forward (AF) relay stations. These results show analytically that the propagation over such a relay channel can be influenced by the propagation in individual "hops'' and the responses of the relay stations. Furthermore, we find that the uncorrelated-scattering assumption is inapplicable for the AF-relay channels in the case where the relay stations receive and retransmit signals using mulitple antennas. We propose to simulate the relay channels by three steps: i) selecting channel models for individual "hops''; ii) defining the correlations of model parameters among the hops; and iii) constructing realizations of relay channels by taking into account the responses of relay stations, which are specified by considering the response of antennas and the relay mode according to system configurations. We also show in this contribution that the spreads of a multi-relay channel in delay, Doppler frequency and directions are lower-bounded by the weighted summation of the spreads of individual source-relay-destination channels.

This paper presents a coding scheme for the Gaussian wiretap channel based on low-density parity-check (LDPC) codes. The messages are transmitted over punctured bits to hide data from eavesdroppers. It is shown that this method is asymptotically effective in the sense that it yields a BER very close to 0.5 for an eavesdropper whose SNR is lower than the threshold SNRE, even if the eavesdropper has the ability to use a bitwise MAP decoder. Such codes also achieve high reliability for the friendly parties provided they have an SNR above a second threshold SNRB. It is shown how asymptotically optimized LDPC codes can be designed with differential evolution where the goal is to achieve high reliability between friendly parties and security against a passive eavesdropper while keeping the security gap SNRB/SNREas small as possible. The proposed coding scheme is applicable at finite block lengths and can be combined with existing cryptographic schemes to deliver improved data security by taking advantage of the stochastic nature of many communication channels.

The paper considers a hybrid ARQ (HARQ) scheme for a linear pre-coding-based closed-loop multiple-input multiple- output (MIMO) system, in which a pre-coding matrix is dynamically selected for every retransmission by taking into account a symbol-level combining gain obtained from the previous receptions. A new retransmission structure with a sequence of multiple codebooks is proposed that are optimized for combining gain, rather than using a single identical codebook for every retransmission. Furthermore, a criterion for selecting a pre-coding matrix for each retransmission can be provided so as to minimize the retransmission error probability. Under the proposed multiple codebook structure for MIMO-HARQ systems, a sequence of optimum codebooks is constructed for the subsequent retransmissions. Simulation results are presented for showing that the proposed scheme achieves significant error performance advantages over conventional schemes with a single codebook and furthermore, a near-optimal performance is achieved as the codebook size chosen is large enough.

While the conventional codebook is defined only for the initial transmission in the closed-loop MIMO system, this paper proposes a new retransmission structure with a sequence of multiple codebooks, rather than using a single identical codebook for every retransmission. The pre-coding matrices, in each codebook, are sequentially linked so that each one can be used for a sequential hybrid ARQ transmission attempt, without invoking any index feedback from the receiver. It has been shown that the proposed codebook structure provides a performance gain of more than 3 dB over the conventional scheme in the long-term static channel.

Multilevel modulation schemes have variations in bit-reliabilities and each has different symbol reliabilities. Choosing the modulation scheme which has the greatest symbol reliability at target SNR on retransmissions offers more chances to get higher Hybrid ARQ performance by making the sum of total bit-reliabilities greater in the entire decoding block. This paper presents a novel Hybrid ARQ scheme which is focused on reducing the number of bits whose reliabilities are low and increasing the total sum of reliabilities of transmitted bits. Proposed Hybrid ARQ scheme achieves more performance gain when in combination with modulation level switching.

In this paper, we introduce a new modulation scheme called Spiral QAM, which is optimized for phase noise, and thus robust in the presence of phase noise. Symbol mapping rules for 16 and 64 Spiral QAM are also presented. SER and BER performance of 64 Spiral QAM was compared with the conventional 64 QAM to show the superior performance of Spiral QAM in the presence of phase noise.

A new accurate analysis model of the IEEE 802.11 DCF is presented. The analysis model is based on a close observation of the IEEE 802.11 DCF behavior. We observe that an infinite number of probabilities of collision need to be defined to accurately represent the behavior of the IEEE 802.11 DCF. Simulation results are included to verify the analytical results.

EIED backoff algorithm was proposed in Song et al., (2003) to enhance the performance of the IEEE 802.11 DCF. EIED provides significant performance improvement without additional complexity. In this paper, we applied EIED to the periodic ranging process of IEEE 802.16, where BEB was originally used. As a performance metric, the average number of tries per periodic ranging attempt was used. The performance was shown analytically, which was verified by computer simulation. The performance results of EIED in the periodic ranging process of IEEE 802.16 are compared to those of BEB. The performance results show that EIED provides a significant performance gain over BEB. Using EIED, we can achieve comparable performance as BEB with significantly smaller set of ranging CDMA codes.

In the event of PNC failure, the event of PNC leaving a piconet without a proper handover procedure, it is critical to have a scheme that allows one of the PNC capable DEVs to take over the role of PNC to minimize the interruption of services. A new proactive coordinator appropriation (PCA) scheme is proposed to prevent piconets from collapsing in the event of PNC failure. PCA is an efficient and reliable scheme that detects PNC failure in a timely manner, while minimizing the probability of false detection. An analytical comparison of PCA with the existing schemes of similar functionality is provided.

In this paper, the two differential detection architectures which are capable of estimating and compensating a large carrier frequency offset of up to above 80 ppm without performance degradation are proposed. The proposed frequency offset estimation and compensation techniques can achieve optimum performance, even if the amount of carrier frequency offset is much larger than the symbol rate. Since the proposed receiver structures are extremely simple, those are appropriate for IEEE 802.15.4 LR- WPAN system with the motto "Low-cost and low-complexity."

New analytical results are given for the performance of the exponential backoff (EB) algorithm. Most available studies on EB focus on the stability of the algorithm and little attention has been paid to the performance analysis of EB. In this paper, we analyze EB and obtain saturation throughput and medium access delay of a packet for a given number of nodes N. The analysis considers the general case of EB with backoff factor r; binary exponential backoff (BEB) algorithm is the special case with r=2. We also derive the analytical performance of EB with maximum retry limit M (EB-M), a practical version of EB. The accuracy of the analysis is checked against simulation results.

We investigate the inherent scalability problem of ad hoc networks that originated from the nature of multi-hop networks. First, the expected packet traffic at the center of a network is analyzed. The result shows that the expected packet traffic at the center of a network is linearly related with the network size, that is, the expected packet traffic at the center of a network is O(k), where k is the radius of a network. From the result, the upper bound of the diameter of a network D = 2k, that guarantees the network is scalable, is obtained. The upper hound is given by C/r - 1, where C is the channel capacity available to each node and r is the packet arrival rate at each node.

New analytic results are given for the stability and performance of the exponential backoff (EB) algorithm. Previous studies on the stability of the (binary) EB have produced contradictory results instead of a consensus: some proved instability, others showed stability under certain conditions. In these studies, simplified and/or modified models of the backoff algorithm were often used to make analysis more tractable. In this paper, care is taken to use a model for backoff that reflects the actual behavior of backoff algorithms. We show that EB is stable under a throughput definition of stability; the throughput of the network converges to a non-zero constant as the offered load N goes to infinity. We also obtain the analytical expressions for the saturation throughput and the medium access delay of a packet for a given number of nodes, N. The analysis considers the general case of EB with backoff factor r, where BEB is the special case with r = 2. The accuracy of the analysis is checked against simulation results.

For a wireless LAN or a cluster of nodes in an ad hoc wireless network, multicast transmissions from a controlling station must be acknowledged by the nodes that are addressed. To ensure reliable reception at all the nodes, the multicast packet may be repeated on different transmissions, or on the same transmission as a form of diversity, or both. In this paper, policies for repeat transmissions of multicast packets are analyzed in terms of the average number of repeat transmissions required and the corresponding efficiency of the signaling on the multicast channel. The analytical results are parametric in packet/ACK error probability, the number of nodes, and the number of required ACKs. It is shown that a policy of accumulating ACKs and addressing only unacknowledged nodes on repeated non-diversity transmissions is more efficient than simply using a higher order of diversity on the multicast transmissions. Methods are shown for avoiding unnecessary repetitions in the case of a missing node.

The convergence speed of the steepest descent (SD) adaptive algorithm is determined by the eigenvalue spread of the correlation matrix. When the correlation matrix is singular, the algorithm will take a long time to converge. The problem can be regularized by adding a small constant to the diagonal, but this comes at the price of introducing bias. This paper introduces a new adaptive algorithm that uses a family of steepest descent iterations which converge quickly while making the bias arbitrarily small. A numerical example discusses in some detail the operation of the new algorithm.

We present a finite-state memory model for parametric system identification of the lip seal friction process in a hydraulic actuator. The performance of the finite-state memory model is compared with two Hammerstein type models using experimental results.

We present two Hammerstein-type models for parametric system identification of the lip seal friction process in a hydraulic actuator. Adaptive algorithms with least squares criteria are derived, and the performances of the two models are evaluated using experimental results.