Progress in human behavior modeling involves understanding both implicit, early-stage perceptual behavior, such as human attention, and explicit, later-stage behavior, such as subjective preferences or likes. Yet most prior research has focused on modeling implicit and explicit human behavior in isolation; and often limited to a specific type of visual content. We propose UniAR -- a unified model of human attention and preference behavior across diverse visual content. UniAR leverages a multimodal transformer to predict subjective feedback, such as satisfaction or aesthetic quality, along with the underlying human attention or interaction heatmaps and viewing order. We train UniAR on diverse public datasets spanning natural images, webpages, and graphic designs, and achieve SOTA performance on multiple benchmarks across various image domains and behavior modeling tasks. Potential applications include providing instant feedback on the effectiveness of UIs/visual content, and enabling designers and content-creation models to optimize their creation for human-centric improvements.

This paper introduces an efficient method for communication resource use in dense wireless areas where all nodes must communicate with a common destination node. The proposed method groups nodes based on their distance from the destination and creates a structured multi-hop configuration in which each group can relay its neighbor's data. The large number of active radio nodes and the common direction of communication toward a single destination are exploited to reuse the limited spectrum resources in spatially separated groups. Spectrum allocation constraints among groups are then embedded in a joint routing and resource allocation framework to optimize the route and amount of resources allocated to each node. The solution to this problem uses coordination among the lower-layers of the wireless-network protocol stack to outperform conventional approaches where these layers are decoupled. Furthermore, the structure of this problem is exploited to obtain a semi-distributed optimization algorithm based on the alternating direction method of multipliers (ADMM) where each node can optimize its resources independently based on local channel information.

This paper investigates the performance gain obtained by creating a hotspot-slave configuration of nodes in densely populated areas. In doing so, a semi-distributed algorithm, referred to as CaSRA (Clustering and Spectrum assignment and Resource Allocation), that allows the hotspots to tether over locally available white-spaces is proposed. CaSRA, performs in three-steps: 1) clusters the nodes based on the K-means clustering algorithm, 2) assigns white-space spectrum to each cluster based on a distributed graph-coloring approach to maximize spectrum reuse, and 3) allocates physical layer resources to individual users based on local channel information. Unlike small cells (femtocells, relays, and WiFi networks), this approach does not require any additions to the existing infrastructure, but allows the nodes, themselves, to act as hotspots. Simulation results show that given fixed amount of network resources, the proposed algorithm can significantly improve the overall performance of network users.

This paper introduces an efficient method for communication resource use in dense wireless areas, where all nodes must communicate with a single destination node. By employing a large number of active radio nodes as relays, and exploiting a common direction of communication toward the single destination, this method groups nodes based on their location and creates a structured multi-hop configuration in which each group can forward its neighbor's data. Such configuration allows spatially separated groups to reuse the limited spectrum resources. Optimum spectral allocation among groups is then embedded in a conventional joint routing and resource allocation framework to obtain a centralized convex optimization problem. This problem's solution achieves optimal coordination among wireless-network lower-layer protocol stack and thereby significantly improves network performance.

Global connectivity and broad coverage of cellular networks constitute a platform for ubiquitous machine-to-machine (M2M) service provisioning on a large scale. However, the access attempt to the radio access network from a massive number of devices demands new cellular access mechanism and signaling design to avoid congestion of control channels. We propose group-based access and signaling policies through a two-level device partitioning, namely, paging groups and access groups. Group paging enables the base station to coordinate access to the network and hence control the random access channel (RACH) overload. However, unlike the conventional scheme where each individual device attempts access to the network, our proposed group-based access mechanism delegates the random access procedure of the devices in an access group to a designated device, referred to as group delegate. In addition, we develop signaling schemes that enable resource allocation at the level of access groups for direct data report as well as a group-based connection via group delegate. Numerical results show that the group access procedure achieves significantly smaller access delay than the conventional access scheme. It is also shown that the group-based signaling policies require signaling overhead proportional to the number of group delegates instead of the number of devices. The proposed group-based schemes enable scaling the number of devices paged simultaneously while controlling the access signaling congestion, access delay, and overhead. Furthermore, the group-based connection enables more resource re- use and hence more efficient resource usage for data transmission.

In dense wireless areas where the cellular spectrum resources are insufficient, the conventional approach is to install more base-stations (BS) or offload some of the traffic onto unlicensed WiFi bands. Both approaches require adding new infrastructure that might be necessary for only a short time. Taking advantage of dual-hop communication, frequency reuse policies, and opportunistic use of white-spaces, this paper proposes an algorithm for operator-controlled tethering over TV white-space (TVWS). As such, in a dense wireless area, some nodes can act as hotspots and tether data to and from their corresponding slaves over TVWS. The proposed algorithm iteratively clusters the nodes into hotspots and slaves, and allocates resources with the objective of maximizing spectrum utilization. Evaluations show that the proposed algorithm can effectively exploit TVWS spectra, and given a fixed amount of network resources, it can significantly increase the number of supported users.

Maximizing the run-time of battery-limited mobile devices is contingent on efficient energy management at the mobile device wireless interface. IEEE 802.11 wireless local area network (WLAN) power save mode (PSM) minimizes the mobile device energy consumption by allowing the device to de-activate its wireless interface periodically while the access point (AP) stores its incoming packets. Further increase in energy conservation occurs through the proposed decision-making algorithm, Intelligent-PSM (IPSM), that determines dynamic, as opposed to fixed, activation times based on the state of the mobile user. IPSM can be implemented with minimal change to the standard PSM transmission scheme. Simulation results show that with a maximum allowable packet delay of 1 second and limited AP buffering capacity, energy conservation of up to about 37% compared to standard PSM can be achieved.

The satisfaction of a mobile user in a heterogeneous wireless environment relies heavily on the appropriate choice of network. With the presence of various wireless technologies and advances in smart mobile devices, the mobile terminal in next generation wireless communications will likely make intelligent handoff decisions to optimize the user Quality of Experience (QoE). This paper investigates network selection and handoff decision with the goal of maximizing user QoE. An algorithm based on Q-learning is obtained that chooses the best network based not only on the current network state but also the potential future network and device states. As opposed to other dynamic programming-based algorithms, this method does not require the knowledge of the statistics of the wireless environment, but learns an optimum policy by utilizing the mobile device's past experience. It is shown that the QoE results of the proposed Dynamic Handoff Decision (DHD) algorithm come very close to the performance of an optimum oracle algorithm, while on average fewer number of network handoffs are required.

An amplify-and-forward (AF) multihop relaying system employing constant-power rate-adaptive M-QAM transmission is investigated. Accurate expressions for performance evaluation in Nakagami-m fading of adaptive continuous rate (ACR) and adaptive discrete rate (ADR) M-QAM are obtained. The analysis is based on a new approximation for the instantaneous end-to-end received SNR in the form of a scaled version of the harmonic mean of the individual per-hop SNRs. The scaling factor is determined based on the average link SNRs. Performance results evaluated using the proposed approximation are more accurate than the performance bounds obtained using the conventional harmonic- mean-based upper bound on the instantaneous received SNR, even though they are obtained with the same computational complexity. Numerical results show that the approximate performance results are very close to the exact results especially in small SNR regimes and for larger values of the Nakagami parameter. It is shown that the ACR QAM achieves an average spectral efficiency within a certain distance of the Shannon limit. The ADR QAM achieves smaller bit error rates than the target bit error rate but at the expense of an additional penalty on the average spectral efficiency, especially for smaller numbers of region boundaries.

A new multihop relaying scheme based on repetition transmission is developed. The performance in Rayleigh fading of the proposed system with amplify-and-forward (AF) and decode-and-forward (DF) relaying is studied. In AF relaying systems, the source re-transmits the same signal in every three time slots, each relay simply amplifies and forwards the received signal, and the destination employs maximal ratio combining (MRC). In DF relaying systems, the source re-transmits the same signal in subsequent time slots, each relay detects the received signal based on square-law selection combining and then forwards the estimated signal, and the destination employs MRC or square-law combining. Using simple closed-form bounds on the average error probability, it is shown that the proposed repetition-based multihop transmission systems with AF relaying and DF relaying achieve diversity order equal to the number of repetitions. Numerical results are provided to assess the tightness of the proposed bounds. It is shown that repetition-based DF relaying systems achieve better symbol error rate performance than repetition-based AF relaying systems in medium to large SNRs. It is also shown that DF relaying systems with balanced links employing square-law combining at the destination achieve almost the same performance as those employing MRC. In addition, the throughputs of various multihop transmission systems are obtained. It is seen that multihop transmission systems employing a DF relaying scheme achieve higher throughput than multihop transmission systems employing an AF relaying scheme.

With the coexistence of various wireless technologies, next generation wireless communications will likely consist of an integrated system of networks, where the Access Points (APs) and Base Stations (BSs) work together to maximize the mobile-user Quality of Service (QoS). In such heterogeneous environment where handheld devices with different access technologies are not uncommon, it should be possible to select networks and seamlessly switch from one AP/BS to another in order to elevate user performance. In this paper, this type of network selection and handover mechanism with the goal of maximizing QoS is formulated as a Markov Decision Process (MDP). An algorithm based on Reinforcement Learning (RL) is then obtained that selects the best network based not only on the current network load but also the potential future network states. This algorithm aims at balancing the number of handovers and the achievable QoS. The results illustrate that while the QoS performance of the proposed algorithm is comparable to the performance of the optimum opportunistic selection algorithm, fewer number of network handovers (on average) are required. In addition, compared to the existing predefined network selection strategies with no handover, the MDP-based algorithm offers significantly better QoS.

A new repetition-based multi-hop transmission with non-coherent detection is proposed. The symbol error probability (SEP) of this system is derived for both amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes. It is shown that the repetition-based non-coherent AF relaying achieves diversity order equal to the number of repetitions, while the repetition-based non-coherent DF relaying does not achieve diversity order. In addition, throughput of the proposed systems is evaluated. Repetition does not enhance the throughput of the DF relaying systems, whereas it improves the throughput of the AF relaying systems for small and moderate values of signal-to-noise ratio.

The instantaneous end-to-end received signal-to-noise ratio (SNR) in K-hop amplify-and-forward (AF) relaying systems is commonly upper bounded by 1/k of the harmonic mean of the individual per-hop instantaneous SNRs. It is shown that performance results in Nakagami-m fading of AF multihop relaying systems obtained based on this upper bound are not tight for small values of SNR or for larger values of the Nakagami parameter and, depending on certain channel conditions, these bounds may become looser as the number of hops increases. A new approximation to the instantaneous end-to-end received SNR is introduced in the form of a scaled version of the harmonic mean of the individual per-hop SNRs. The scaling factor is determined based on the average link SNRs. Performance results evaluated using the proposed approximation are more accurate than all performance bounds previously reported in the literature, even though they are obtained with the same computational complexity. Numerical results show that the approximate performance results are very close to the exact results especially in small SNR regimes or for larger values of the Nakagami parameter.

A spectral efficient multihop relaying scheme is proposed based on scheduling the source transmission in alternate time slots. Each relay processes its received signal and forwards it in the subsequent time slot. An interference cancellation mechanism is developed to eliminate the interference term at each relay caused by the source alternate-based transmission. The frame error probability and the achievable rate of the proposed scheme are evaluated. It is shown that the individual bit-by-bit detection at the destination performs almost as well as the optimal joint detection, and achieves a data rate that approaches the Shannon channel capacity limit. In addition, the proposed scheme significantly outperforms the conventional orthogonal multihop transmission in terms of the achievable data rate, especially for larger numbers of hops, with slightly inferior frame error rate performance.

A decentralized power allocation scheme for amplify-and-forward (AF) multi-hop relaying systems is proposed. The scheme maximizes a harmonic mean-based approximate expression for the instantaneous received signal-to-noise ratio (SNR). The outage probability in Rayleigh fading of the proposed power-optimized system is evaluated. Numerical results show the superior performance of AF multi-hop relaying systems employing the proposed power allocation scheme over those with uniform power allocation. The asymptotic outage behavior for sufficiently large values of SNR is also studied and it is demonstrated that AF multi-hop relaying systems employing the proposed power allocation scheme achieve diversity order 2.

Distributed coherent receivers, that require no instantaneous channel amplitude information, are developed for amplify-and-forward (AF) cooperative diversity systems. According to the availability of phase information at the relays and the destination, repetition-based and spectral-efficient distributed equal gain combining (DEGC) schemes are obtained. In the former scheme, relays transmit over separate orthogonal subchannels, whereas in the latter scheme all relays transmit simultaneously. An expression for evaluation of the symbol error probability is derived and it is demonstrated that these schemes achieve full spatial diversity. It is also shown that the spectral-efficient DEGC scheme outperforms the repetition-based DEGC scheme especially by increasing the number of relays.

The capacity of amplify-and-forward multi-hop relaying systems under different adaptive transmission schemes over Nakagami-m fading channels is considered. Accurate theoretical approximations for the capacity of these systems are derived in terms of the characteristic function of the reciprocal of the instantaneous received signal-to-noise ratio. An accurate theoretical approximation for the probability of outage is also obtained. The accuracy of the expressions obtained is verified by Monte Carlo simulation. It is shown that a system with optimal power and rate adaptation outperforms the system with truncated channel inversion adaptive technique. Systems employing optimal rate adaptation with constant power achieve almost the same capacity as those with optimal rate and power adaptation at large values of signal-to-noise ratio. However, the capacity performance of a system with the truncated channel inversion adaptive technique is better than the corresponding system employing optimal rate adaptation with constant power for small values of signal-to-noise ratio.

The performance of multi-hop diversity transmission systems in Rayleigh fading is studied. Simple closed-form approximations for the outage and bit error probabilities of multi-hop diversity systems employing fixed amplify-and-forward relaying are derived. An exact closed-form expression for calculating the outage probability of a multi-hop diversity transmission scheme employing fixed decode-and-forward relaying is obtained. In addition, a selective relaying protocol for multi-hop diversity transmission systems, which adapts transmissions at the source and relays based on the instantaneous received signal-to-noise ratio at each relay, is developed and analyzed in terms of outage probability and bit error rate. The mathematical analyses show that multi-hop diversity transmission systems with fixed decode-and-forward relaying offer no diversity order gain, while those employing the other relaying schemes achieve diversity order equal to the number of hops. It is also shown that multi-hop diversity transmission systems employing fixed amplify-and-forward relaying attain the best outage probability and bit error rate performances, despite the noise amplification at the relays.

A maximum energy selection (MES) receiver scheme is proposed for noncoherent amplify-and-forward (AF) cooperative diversity systems. An expression for the symbol error probability of this system when deployed with M-ary frequency shift keying (FSK) modulation is derived. It is shown that a noncoherent AF system employing the proposed MES scheme achieves full spatial diversity, while requiring neither instantaneous nor statistical channel gain information at the destination, but only knowledge of the average source-relay link signal-to-noise ratio (SNR) at the corresponding relay. The average source-relay link SNR information can be locally obtained at each relay using conventional practical estimation techniques, which in turn allows fully distributed implementation of the proposed scheme.

Low complexity receivers for coherent amplify-and-forward (AF) cooperative diversity systems are developed. According to the availability of phase information at the relays and the destination, repetition-based and spectral-efficient distributed equal gain combining (DEGC) schemes are developed. In the former scheme, relays transmit over separate orthogonal subchannels, whereas in the latter scheme all relays transmit simultaneously. Analytical expressions for evaluation of the average output signal-to-noise ratio (SNR) and symbol error probability are derived and it is demonstrated that these schemes achieve full spatial diversity. In addition, upper and lower bounds on the ergodic capacity are obtained. The upper bound is tight in small-SNR regions whereas the lower bound is accurate for sufficiently large values of SNR. It is shown that the spectral-efficient DEGC scheme outperforms the repetition-based DEGC scheme especially by increasing the number of relays. The impact of combining loss on the performance of the proposed schemes is also studied. The average output SNR expression can be used as a simple theoretical tool for choosing the best number of relays that avoids the combining loss.

The ergodic capacity in Rayleigh fading of multi- hop wireless transmission systems employing either amplify- and-forward relaying or decode-and-forward relaying is studied, assuming channel state information is only known at the receiving terminals. Two upper bounds based on Jensen's inequality and the harmonic-geometric means inequality as well as an infinite series representation for the ergodic capacity of an amplify-and- forward multi-hop transmission system are derived. Numerical results are provided to examine the tightness of the upper bounds as well as to show the high accuracy of the infinite series approach. In addition, the ergodic capacity of a decode- and-forward multi-hop transmission system is obtained. It is shown that multi-hop transmission systems employing a decode- and-forward relaying scheme achieve higher ergodic capacities than multi-hop transmission systems with amplify-and-forward relaying schemes.

Optimal power allocation schemes that maximize the instantaneous received signal-to-noise ratio in an amplify-and- forward multi-hop transmission system under short-term (ST) and long-term (LT) power constraints are presented. The optimal power allocation strategy under a ST power constraint requires a centralized architecture for implementation. However, the power allocation solutions to the LT power constraints can be implemented in a decentralized manner. Theoretical expressions for evaluation of the outage probability of the proposed power-optimized multi-hop relaying systems over Rayleigh fading channels are obtained. Numerical results show the superior performance of amplify-and-forward multi-hop relaying systems with the power allocation scheme over those with uniform power allocation. It is shown that at sufficiently large values of signal-to-noise ratio (SNR), an amplify-and-forward K-hop relaying system employing the optimal power allocation scheme under ST power constraint achieves K times better outage performance than that of the corresponding system employing uniform power allocation. It is also shown that the optimal power allocation schemes under LT power constraints provide substantial performance gain at both small and large values of SNR and achieve diversity gain.

The ergodic capacity in Rayleigh fading of multi- hop wireless transmission systems employing either amplify-and-forward relaying or decode-and-forward relaying is studied, assuming channel state information is only known at the receiving terminals. Two upper bounds based on Jensen's inequality and the harmonic-geometric means inequality as well as an infinite series representation for the ergodic capacity of an amplify-and- forward multi-hop transmission system are derived. Numerical results indicate the upper bound obtained based on Jensen's inequality is tight. This upper bound is tighter than the upper bound based on harmonic and geometric means for larger numbers of hops and especially for systems in non-identical fading. Numerical results are provided to show the high accuracy of the infinite series approach. In addition, the ergodic capacity of a decode-and-forward multi-hop transmission system is obtained. It is shown that multi-hop transmission systems employing a decode-and-forward relaying scheme achieve higher ergodic capacities than multi-hop transmission systems with amplify-and- forward relaying schemes.

The ergodic capacities in Rayleigh fading of various wireless relaying systems with an arbitrary number of half- duplex relays are analyzed, assuming channel state information is only known at the receivers. Closed-form analytical expressions for calculation of the ergodic capacities of wireless relaying systems with regenerative relays and nonregenerative relays employing decode-and-forward relaying and amplify-and-forward relaying, respectively, are derived. It is shown that systems with regenerative relays employing decode-and-forward relaying offer higher ergodic capacities than systems with nonregenerative relays employing amplify-and-forward relaying.

Simple, closed-form expressions for the outage probability and bit error rate of multi-hop diversity transmission systems employing either fixed or selective amplify-and-forward relaying are derived. Numerical results show the accuracy of the obtained analytical results for sufficiently large values of signal- to-noise ratio. In addition, it is shown that a multi-hop diversity transmission system employing fixed amplify-and-forward relaying outperforms the corresponding systems employing fixed decode-and-forward, selective decode-and-forward or selective amplify-and-forward relaying, despite the noise amplification at all relays.

Multi-hop and multi-branch wireless transmission systems with nonregenerative fixed gain relays employing amplify-and-forward relaying are studied. Simple closed-form expressions for the outage and bit error probabilities of these systems are derived. The analysis is valid for an arbitrary number of hops, arbitrary number of branches and any fading channel model whose signal power probability density function has nonzero value at the origin. It is shown that while a multi-hop transmission system does not offer diversity gain, it can perform better than a single hop system if its average individual link SNRs satisfy a certain condition. In addition, the analysis clearly shows the diversity gains achieved by multi-branch systems for any fading channel model.

Multi-hop, multi-branch, and multi-branch multi- hop wireless transmission systems with nonregenerative fixed gain relays employing amplify-and-forward relaying are considered. Simple closed-form expressions for the outage and bit error probabilities of these systems are derived. It is shown that while a multi-hop transmission system does not offer diversity gain, it can perform better than a single hop system if its average individual link SNRs satisfy a certain condition. In addition, the analysis clearly shows the diversity gains achieved by multi- branch and multi-branch multi-hop systems. A design criterion is also presented which guarantees better outage and bit error performances for a multi-branch multi-hop system compared to a multi-branch system with the same number of branches.

The ergodic capacities in Rayleigh fading of various wireless relaying systems with an arbitrary number of half duplex relays are analyzed, assuming channel state information is only known at the receivers. Closed-form analytical expressions for calculation of the ergodic capacities of these systems are derived. It is shown that systems with nonregenerative fixed gain relays achieve higher ergodic capacities than the corresponding systems with nonregenerative variable gain relays. A modified fixed gain relay, which incorporates the power constraint at the relays, is proposed. It is shown that systems with modified fixed gain relays slightly outperform the corresponding systems with nonregenerative variable gain relays and fixed gain relays at small signal-to-noise ratios, but attain almost the same ergodic capacities as systems with nonregenerative variable gain relays as the signal-to-noise ratio increases. In addition, the ergodic capacity of a hybrid system with both regenerative and nonregenerative relays is studied. Systems with regenerative relays employing decode-and-forward relaying offer higher ergodic capacities than the corresponding systems with any classes of nonregenerative relays or hybrid relays.

A selective decode-and-forward relaying protocol for serial multi-hop diversity schemes, which adapts transmissions at the source and relays based on the instantaneous received signal-to-noise ratio at each relay, is developed and analyzed. Based on the proposed selective protocol, if the received signal- to-noise ratio at each relay exceeds a certain threshold, that relay combines, decodes, and re-encodes its received signals and then re-transmits. Otherwise, the source repeats its signal. It is shown that employing the proposed method significantly improves the system performance by achieving diversity order equal to the number of hops while maintaining the same maximum normalized spectral efficiency compared to a multi-hop transmission system employing a fixed decode-and-forward relaying scheme. An exact closed-form expression for calculating the outage probability of a serial multi-hop diversity scheme employing fixed decode-and-forward relaying strategy is also obtained. A rigorous mathematical analysis showing that the serial multi-hop diversity scheme offers no diversity gain is given.

An analytical approach to study the effects of node mobility in mobile ad hoc wireless networks is presented. The bit error rate is evaluated over fast Rician fading channels. It is shown that there is a threshold node velocity, and that a network with a certain number of mobile nodes (following the random waypoint mobility scheme) with slower velocities than the threshold velocity performs better than the corresponding network with static nodes. In particular, for a given signal- to-noise ratio and transmission range, the minimum threshold velocity is obtained. Restricting the velocities of the nodes to be at most this minimum threshold velocity results in an improvement in the bit error rate performance of ad hoc networks with an arbitrary number of nodes.

We present new closed-form analytical expressions for the probability of connectivity and average delay of a mobile ad hoc network with N nodes which move according to the random waypoint (RWP) mobility model. The minimum transmission range for which the network is connected is also derived. Our results show that by increasing the number of nodes, the probability of connectivity increases and the minimum transmission range decreases. It is also shown that the average delay is maximum for the minimum transmission range and this maximum increases by increasing the number of users. In transmission ranges for which the networks are disconnected, increasing the number of users increases the average delay; however, this is reversed when the networks are connected. Particularly, our results show that mobility contributes to the network connectivity, but at the expense of tolerating more average delay when the networks are disconnected. However, mobility decreases the average delay in the connected regions.

We study the exact bit error rate (BER) performance of convolutional codes with hard decision Viterbi decoding when used over fading additive white Gaussian noise (AWGN) channels with maximum ratio combining (MRC) diversity. Analytical expressions for the bit error rates in Rayleigh, Rician and Nakagami-m fading channels are derived. The accuracy of the analytical results is verified by computer simulation.

One- and two-dimensional ad hoc wireless networks with uniformly distributed (static) nodes and networks with nodes which move according to the random waypoint mobility model are considered. The inter-distance distributions between any two nodes within these networks are obtained. The network connectivity is considered and the minimum transmission range is derived. The bit error rate performance is then analytically evaluated in the connected regions of the networks taking into account the effect of path loss and Nakagami-mor Rician fading. It is shown that increasing the number of users increases the network connectivity, decreases the minimum transmission range, and improves the performance. It is also shown that node mobility enhances the network connectivity and performance.