This paper investigates the dynamics of spatio-temporal interference correlations in wireless networks, focusing on the interplay between node spatial distribution and interference patterns. The study employs analytical frameworks such as the Matérn hard-core point process (MHCP) and clustering models, revealing that spatial clustering typically enhances positive interference correlation, while spatial rejection mechanisms inherent to MHCP induce negative correlation. Notably, the analysis extends to various temporal traffic models, highlighting distinct interference correlation behaviors between temporally correlated and independent traffic scenarios. The novel contribution of this work lies in deriving advanced mathematical formulations to quantify the interference correlation coefficient, which uncover the non-monotonic relationship between correlation and network parameters like node density and burst traffic duration. These insights provide a deeper understanding of interference dynamics, offering valuable guidelines for optimizing network performance and reliability, particularly in the design of next-generation wireless systems.

Mobile computing devices are supporting higher information transmission and processing rates. However, the massive amount of information transmitted and processed also means that a vast amount of heat is produced. Due to the constraints of safety and portability, the problem of overheating is becoming a main challenge for mobile computing devices to achieve their ideal performance. Compared to studies on improving the quality of wireless communications and mobile computing, little attention has been paid to the temperature and its direct impact on the computing performance of the device. In this paper, we propose the heat transfer model of the processor of a mobile computing device based on thermodynamics. Considering Landauer’s principle, the maximum computing rate of the processor is derived. Moreover, the performance of devices adopting multi-processor is evaluated, where each processor works periodically to complete the computing task. The conditions for stable computing and the thermodynamic advantage of multi-processor are given. Based on the evaluation, an optimization method is proposed to lower the average temperature of the processor, and simulation results show that the maximum computing rate can be improved up to 20.9%.

The spatio-temporal correlation of interference is an important factor in affecting the performance of wireless networks. In this paper, we study how the spatio-temporal correlation of traffic affects the correlation of interference, in which the spatial correlation of traffic is captured by using Poisson cluster process (PCP) to characterize the spatial attraction, while the temporal correlation is described by correlated arrival and process of packets. The closed-form expressions to quantitatively describe the interference correlation caused by spatio-temporal correlated traffic are derived. Our results reveal that the spatial aggregation of traffic leads to an increase in interference correlation compared with spatially independent traffic. If the traffic is temporally independent, the interference correlation decreases with the increase of the distance between two receivers or the cluster size. For temporally intra-correlated traffic, when increasing the transmission probability, the interference correlation first increases and then decreases when increasing the cluster size. Considering the queuing process of the traffic, the interference correlation increases with the increase of packet arrival rate when all queues are stable.

In recent years, the conventional degrees of freedom in frequency and time have been fully used. It is difficult to further improve the performance of communication systems with such degrees of freedom. Orbital angular momentum (OAM), which provides a new degree of freedom for millimeter-wave (mmWave) wireless communication systems, has been recognized as a key enabling technique for future mobile communication networks. By combining OAM beams that have theoretically infinite and mutually orthogonal states with the generalized spatial modulation (GSM) strategy, a new OAM-GSM mmWave wireless communication system is designed in this paper. A bit error rate (BER) model of the OAM-GSM system is established based on channel flip precoding. The channel capacity, energy efficiency, and BER of the proposed OAM-GSM mmWave wireless communication system are simulated. Numerical results show that, compared with traditional GSM systems, the OAM-GSM system has more complex transmission and reception mechanisms but the channel capacity and maximum achievable energy efficiency are increased by 80% and 54%, respectively, and the BER drops by 91.5%.

The traffic in the wireless networks has become diverse and fluctuating both spatially and temporally due to the emergence of new wireless applications. The purpose of this paper is to explore the impact of the wireless traffic with violent fluctuation both spatially and temporally on the performance of the wireless networks. We analyze the spatial statistics, the stability of queues and the delay of users by considering two different spatial distributions of traffic, i.e., the uniformly and non-uniformly distributed cases. The simulation results indicate that although the fluctuations of traffic when the users are clustered, reflected by the variance of total arrival rate, is much fiercer than that when the users are uniformly distributed, the stability performance is much better. Our work provides a useful reference for the design of the wireless networks when the complex spatio-temporal fluctuation of the traffic is considered.

Exchange of crucial and confidential information in wireless networks leads to the unprecedented attention on the security problem. Though a number of works have studied the physical layer security, the joint optimization of the end-to-end delay management and the physical layer security, which requires a meticulous cross-layer design, has seldom been evaluated in the literature. In this work, by combining the tools from queueing theory and stochastic geometry, we analyze the tradeoff between delay and physical layer security in large wireless networks. Our numerical results reveal that the security performance is better for larger path loss exponent when the density of legitimate nodes is large, and it is reverse when the density is small. Meanwhile, it is observed that under the condition that a certain confidential rate is guaranteed, the delay performance is better in high signal-to-interference ratio regime than that in low SIR regime. In summary, this work provides an understanding and a rule-of-thumb for the practical design of wireless networks where both the delay and the security are key concerns.

In this paper, a hybrid modulation scheme combining quad-LED complex modulation (QCM) and spatial modulation (SM) has been proposed in indoor visible light communication (VLC) system. The SM scheme is firstly used to select one quad-LED (QLED). Then, QCM scheme is further employed by the selected QLED to map the complex modulation symbols. Hence, the hybrid quad-LED complex spatial modulation (QCSM) scheme obtains the advantages of both QCM and SM, and can improve the system performance and the transmission rate simultaneously. Symbol error rate (SER) and bit error rate (BER) of the proposed scheme are studied based on the maximal likelihood (ML) detection. Simulation results and theoretical analysis show the better performance of the proposed QCSM scheme, compared with the SM VLC system. The system performance with different distances of the QLEDs has also been analyzed.

Exchange of crucial and confidential information leads to the unprecedented attention on the security problem in wireless networks. Even though the security has been studied in a number of works, the joint optimization of the physical layer security and the end-to-end delay management, which requires a meticulous cross-layer design, has seldom been evaluated. In this paper, by combining the tools from stochastic geometry and queueing theory, we analyze the tradeoff between the delay and the security performance in large wireless networks. We further propose a simple transmission mechanism which splits a message into two packets and evaluate its effect on the mean delay and the secrecy outage probability. Our numerical results reveal that the security performance is better for larger path loss exponent when the density of legitimate nodes is large, and it is reverse when the density is small. Moreover, it is observed that by introducing the simple mechanism of message split, the security performance is greatly improved in the backlogged scenario and slightly improved in the dynamic scenario when the density of legitimate transmitters is large. In summary, this paper provides an understanding and a rule-of-thumb for the practical design of wireless networks where both the delay and the security are key concerns.

To meet massive wireless traffic demand in the future fifth generation (5G) cellular networks, small-cell networks are emerging as an attractive solution for 5G network deployments. The cellular coverage characteristic is a key issue for the deployment of the small-cell networks. Considering the anisotropic path loss in wireless channels of real cellular scenarios, in this paper the fractal coverage characteristic is first used to evaluate the performance of the small-cell networks. Moreover, the coverage probability, average achievable rate, and the area spectral efficiency are derived for fractal small-cell networks. Compared with the average achievable rate and area spectral efficiency with isotropic path loss models, the average achievable rate and area spectral efficiency with anisotropic path loss models have been underestimated in the fractal small-cell networks. Considering the impact of the anisotropic path loss on wireless channels, most of performances of wireless cellular networks need to be re-evaluated. This paper provides a tractable method to investigate the performance of the small-cell networks with fractal coverage characteristics.

In this paper, the high efficient ultra wideband (UWB) spatial modulation (SM) system has been proposed and the maximum ratio combining (MRC) based performance analysis has been presented. Compared with the traditional UWB system, the bit rate of the UWB SM system is improved through the extra information bit transmission based on the selection of the active transmit antenna from multiple antennas. Meanwhile, the high energy efficiency can be obtained in the proposed UWB SM system. The UWB SM system has lower implementation complexity than the multi-antenna UWB system. MRC detection is adopted to separately recover the modulated symbol and the active transmit antenna index in two stages, which leads to lower detection complexity compared with maximum likelihood (ML) detection. Theoretical symbol error rate (SER) of the UWB SM system is derived, and the simulation results and analysis show the efficiency and performance of the proposed UWB SM system.

Based on the distinguishing features of multi-tier millimeter wave (mmWave) networks such as different transmit powers, different directivity gains from directional beamforming alignment and path loss laws for line-of-sight (LOS) and non-line-of-sight (NLOS) links, we introduce a normalization model to simplify the analysis of multi-tier mmWave cellular networks. The highlight of the model is that we convert a multi-tier mmWave cellular network into a single-tier mmWave network, where all the base stations (BSs) have the same normalized transmit power 1 and the densities of BSs scaled by LOS or NLOS scaling factors respectively follow piecewise constant function which has multiple demarcation points. On this basis, expressions for computing the coverage probability are obtained in general case with beamforming alignment errors and the special case with perfect beamforming alignment in the communication. According to corresponding numerical exploration, we conclude that the normalization model for multi-tier mmWave cellular networks fully meets requirements of network performance analysis, and it is simpler and clearer than the untransformed model. Besides, an unexpected but sensible finding is that there is an optimal beam width that maximizes coverage probability in the case with beamforming alignment errors.

This paper investigates the energy saving of base station (BS) deployed in a 1-D multi-hop vehicular network with sleep scheduling strategy. We consider cooperative BS scheduling strategy where BSs can switch between sleep and active modes to reduce the average energy consumption utilizing the information of vehicular speeds and locations. Assuming a Poisson distribution of vehicles, we derive an appropriate probability distribution function of distance between two adjacent cluster heads, where a cluster is a maximal set of vehicles in which every two adjacent vehicles can communicate directly when their Euclidean distance is less than or equal to a threshold, known as the communication range of vehicles. Furthermore, the expected value of the sojourn time in the sleep mode and energy saving are obtained. The numerical results show that the sleep scheduling strategy significantly reduces the energy consumption of the base stations.

In this article, a network model incorporating both line-of-sight (LOS) and non-line-of-sight (NLOS) transmissions is proposed to investigate impacts of blockages in urban areas on heterogeneous network coverage performance. Results show that co-existence of NLOS and LOS transmissions has a significant impact on network performance. We find in urban areas, that deploying more BSs in different tiers is better than merely deploying all BSs in the same tier in terms of coverage probability.

Dense heterogeneous cellular networks (HCNs) with energy harvesting nodes are promising solutions to meet both the capacity and energy efficiency needs in the next generation cellular networks. This paper studies the system performance of both energy harvesting and information receiving in a K-tier cellular networks with time-switching simultaneous wireless information and power transfer (SWIPT). Based on stochastic geometry theory, we derive the closed-form formulas for the average harvested energy, the average transmission rate and the total power and information gains. Moreover, we propose a scheme that can optimally adjust the bias factors of tier selection while leveraging the system between energy harvesting and information receiving.

With the massive multi-input multi-output (MIMO) antennas technology adopted for the fifth generation (5G) wireless communication systems, a large number of radio frequency (RF) chains have to be employed for RF circuits. However, a large number of RF chains not only increase the cost of RF circuits but also consume additional energy in 5G wireless communication systems. In this paper, we investigate energy and cost efficiency optimization solutions for 5G wireless communication systems with a large number of antennas and RF chains. An energy efficiency optimization problem is formulated for 5G wireless communication systems using massive MIMO antennas and millimeter wave technology. Considering the nonconcave feature of the objective function, a suboptimal iterative algorithm, i.e., the energy efficient hybrid precoding (EEHP) algorithm is developed for maximizing the energy efficiency of 5G wireless communication systems. To reduce the cost of RF circuits, the energy efficient hybrid precoding with the minimum number of RF chains (EEHP-MRFC) algorithm is also proposed. Moreover, the critical number of antennas searching (CNAS) and user equipment number optimization (UENO) algorithms are further developed to optimize the energy efficiency of 5G wireless communication systems by the number of transmit antennas and UEs. Compared with the maximum energy efficiency of conventional zero-forcing (ZF) precoding algorithm, numerical results indicate that the maximum energy efficiency of the proposed EEHP and EEHP-MRFC algorithms are improved by 220% and 171%, respectively.

We consider a cooperative two-path relay channel (TPRC) where a data source transmits new packets to a corresponding destination, with the assistance of two intermediate relays alternatively. When the transmitted source packet is successfully decoded by a relay, the relay proceeds to forward this packet in the subsequent time slot, otherwise it simply stays silent. Due to the inter-relay channels, the decoding result at a relay in the current time slot depends on the decoding result at the other relay in the previous time slot and not on that preceded it. In view of this property, we employ a Markov framework to analyze the decoding performance at the relays. The decoding of successive packets received at the destination can be similarly analyzed by using a Markov chain. Closed-form expressions of the outage probability are derived for TPRC by exploiting the properties of a Markov chain. Numerical results demonstrate that with the proposed scheme, a reasonably good performance is achieved with only a single-slot delay and relatively low complexity.

Cell association scheme determines which base station (BS) and mobile user (MU) should be associated with and also plays a significant role in determining the average data rate a MU can achieve in heterogeneous networks. However, the explosion of digital devices and the scarcity of spectra collectively force us to carefully re-design cell association scheme which was kind of taken for granted before. To address this, we develop a new cell association scheme in heterogeneous networks based on joint consideration of the signal-to-interference-plus-noise ratio (SINR) which a MU experiences and the traffic load of candidate BSs1. MUs and BSs in each tier are modeled as several independent Poisson point processes (PPPs) and all channels experience independently and identically distributed (i.i.d.) Rayleigh fading. Data rate ratio and traffic load ratio distributions are derived to obtain the tier association probability and the average ergodic MU data rate. Through numerical results, We find that our proposed cell association scheme outperforms cell range expansion (CRE) association scheme. Moreover, results indicate that allocating small sized and high-density BSs will improve spectral efficiency if using our proposed cell association scheme in heterogeneous networks.

It is a great challenge to evaluate the network performance of cellular mobile communication systems. In this paper, we propose new spatial spectrum and energy efficiency models for Poisson-Voronoi tessellation (PVT) random cellular networks. To evaluate the user access to the network, a Markov chain based wireless channel access model is first proposed for PVT random cellular networks. On that basis, the outage probability and blocking probability of PVT random cellular networks are derived, which can be computed numerically. Furthermore, taking into account the call arrival rate, the path loss exponent and the base station (BS) density in random cellular networks, spatial spectrum and energy efficiency models are proposed and analyzed for PVT random cellular networks. Numerical simulations are conducted to evaluate the network spectrum and energy efficiency in PVT random cellular networks.

This paper investigates the information dissemination process in wireless communication networks formed by vehicles. As vehicles are moving constantly, a vehicular ad-hoc network exhibits a highly-dynamic network topology and a fast-changing radio environment. These distinguishing characteristics result in random and unreliable wireless connections between vehicles. Consequently, vehicles need to work cooperatively to disseminate a piece of information to the destination. This paper analyses cooperative information forwarding schemes where each vehicle determines whether or not to forward a received packet in a decentralized manner, without the costly or even impractical demand for the knowledge of network topology. Considering a generic wireless connection model incorporating wireless channel randomness, analytical results are derived for the probability of successful delivery and the expected number of packet forwardings. Moreover, analysis is conducted on the optimal information forwarding scheme that meets a pre-designated probability of successful delivery objective using the minimum number of packet forwardings.

It is of great importance for service providers to evaluate the impact of inter-cell co-channel interference on the achievable data rate in cellular networks. In this paper, the cumulative distribution function (CDF) of the inter-cell interference factor is derived. On this basis, closed-form expression of the maximum achievable rate subject to the interference from finite planar cells is analyzed over Nakagami-m fading uplink channels. Numerical results show that besides Nakagami-m fading severity parameters and path loss coefficient, the maximum achievable rate is also affected by the number of interference cells. According to the numerical results, with an increase in the number of interference cells, the maximum achievable rate is degraded.

This paper investigates the energy efficiency of base station sleep scheduling strategies in 1-D infrastructure-based wireless communication networks formed by vehicles traveling on a highway. In certain scenarios, vehicular speeds and locations can be measured with a high degree of accuracy, and this information can be exploited to reduce the energy consumption of base stations. This paper considers cooperative base station scheduling strategies where base stations can switch between sleep and active modes to reduce the average energy consumption, while guaranteeing the connectivity of every vehicle. Analytical results on the expected amount of energy saving for a base stations are derived, which reveals for the first time the existence of a threshold parameter, determined by both the vehicular density and mobility, below which base stations can switch off and save energy, but above which no energy saving can be achieved.

Recently, issues of power consumption at base stations (BSs) in wireless cellular networks have attracted great interest in both research communities and the industry. In this paper, we investigate the BS power consumption in multiple-input single-output (MISO) Poisson-Voronoi tessellation (PVT) random cellular networks. Taking into account the inter-cell interference, the impact of the traffic demands of users and the spatial traffic intensity on the BS power consumption are jointly considered for MISO PVT random cellular networks. Furthermore, the power consumption required at the BS in a typical PVT cell is modeled through characteristic functions. Simulation results are employed to evaluate the BS power consumption and the performance of the random cellular networks.

It is of great importance and interests for network operators to evaluate the impact of inter-cell co-channel interference on the achievable data rate in cellular networks. In this paper, a closed-form maximum achievable rate over Nakagami-m fading uplink channels based on multicell linear Wyner model is derived. Moreover, the maximum achievable rates in some special cases are investigated. Numerical results show that the maximum achievable rate decreases with the increase of the inter-cell signal interference factor and is also affected by Nakagami-m fading severity parameters and number of users in a cell.