SIGNAL PROCESSING PROJECTS
SIGNAL PROCESSING PROJECTS
1. Optimum Co-Design for Spectrum Sharing Between Matrix Completion Based MIMO Radars and a MIMO Communication System
ABSTRACT
Spectrum sharing enables radar and communication systems to share the spectrum efficiently by minimizing mutual interference. Recently proposed multiple input multiple output radars based on sparse sensing and matrix completion (MIMOMC), in addition to reducing communication bandwidth and power as compared to MIMO radars, offer a significant advantage for spectrum sharing. The advantage stems from the way the sampling scheme at the radar receivers modulates the interference channel from the communication system transmitters, rendering it symbol dependent and reducing its row space. This makes it easier for the communication system to design its waveforms in an adaptive fashion so that it minimizes the interference to the radar subject to meeting rate and power constraints. Two methods are proposed. First, based on the knowledge of the radar sampling scheme, the communication system transmit covariance matrix is designed to minimize the effective interference power (EIP) to the radar receiver, while maintaining certain average capacity and transmit power for the communication system. Second, a joint design of the communication transmit covariance matrix and the MIMO-MC radar sampling scheme is proposed, which achieves even further EIP reduction.
2. Performance of Low-Complexity Uniform Power Loading OFDM Systems With Reduced Feedback Over Rayleigh Fading Channels
ABSTRACT
In this paper, we consider a low-complexity uniform power loading scheme for orthogonal frequency division multiplexing (OFDM) systems with two reduced feedback mechanisms and analyze its performance over Rayleigh fading channels. In the first feedback mechanism, the receiver feeds back to the transmitter the channel gains and the indices of the best M subchannels; while for the second feedback mechanism, the receiver feeds back only the indices of the best M subchannels. The available power budget is equally distributed over the best M subchannels for both feedback mechanisms. We derive closed-form expressions for the achievable capacity and an upper bound on the outage capacity of the first and second mechanisms, respectively. A simple elimination algorithm is provided to find the optimal number of best subchannels M that maximizes the achievable capacity. Numerical results show the dependence of the optimal number of the best subchannels M on the system parameters. Additionally, the presented results interestingly show that the low-complexity uniform power loading scheme can achieve up to 98.72% of the channel capacity, obtained using the well-known waterfilling solution, when the optimal value of M is used. Moreover, the uniform power loading scheme can achieve up to 88.86% of the energy efficiency at reduced complexity.
3. Impact of Inter-Relay Cooperation on the Performance of FSO Systems with any Number of Relays
ABSTRACT
In this paper, we study the impact of inter-relay cooperation on the performance of Decode-and-Forward (DF) cooperative Free Space Optical (FSO) communication systems with any number of relays. The idea of inter-relay cooperation (IRC) was introduced very recently where the relay-relay links are activated for further boosting the system performance. We evaluate the outage probability under forward and forwardbackward IRC that constitute the two variants of this transmission strategy. We also derive the diversity orders that can be achieved over a composite channel model that takes both turbulence-induced fading and misalignment-induced fading into consideration. We present a comprehensive asymptotic analysis that is effective for tackling the usefulness of IRC with an arbitrary number of relays and for deriving the network conditions under which implementing IRC in any of its variants can be beneficial for enhancing the diversity order of the FSO system. The introduced framework answers the question on what is the optimal solution for a particular FSO network (among the parallel-relaying solution with no IRC, forward IRC or forwardbackward IRC).
4. The Ergodic Rate Density of Slotted and Unslotted CSMA Ad-Hoc Networks
ABSTRACT
The performance of random Wireless Ad-hoc Networks (WANETs) is primarily limited by their self-interference. The utilization of a decentralized Carrier Sensing Multiple Access (CSMA) protocol protects the participating receivers from the presence of strong interferers and enhances the performance compared to the simpler ALOHA protocol. In this work we analyze the Ergodic Rate Density (ERD) of slotted and unslotted CSMA WANETs in the small back-off probability regime. Our main result is the derivation of simple expressions which describe the ERD of CSMA WANETs as a function of the back-off probability, the path-loss exponent and the ERD of the same WANET when applying the ALOHA protocol. The ERD expressions for both the slotted and the unslotted variants are shown to grow with the back-off probability. For the slotted variant the gain of CSMA over ALOHA is equal to the back-off probability. On the other hand, for the unslotted variant this gain is smaller by a constant factor, which is within the range of 0.57 to 0.67 for all cases of practical interest. Simulation results validate the precision of the derived expressions and demonstrate their capability to predict the optimal system parameters with very goodaccuracy
5. Self-Sustainable Communications with RF Energy Harvesting: Ginibre Point Process Modeling and Analysis
ABSTRACT
RF-enabled wireless power transfer and energy harvesting has recently emerged as a promising technique to provision perpetual energy replenishment for low-power wireless networks. The network devices are replenished by the RF energy harvested from the transmission of ambient RF transmitters, which offers a practical and promising solution to enable self-sustainable communications. This paper adopts a stochastic geometry framework based on the Ginibre model to analyze the performance of self-sustainable communications over cellular networks with general fading channels. Specifically, we consider the point-to-point downlink transmission between an access point and a battery-free device in the cellular networks, where the ambient RF transmitters are randomly distributed following a repulsive point process, called Ginibre α-determinantal point process (DPP). Two practical RF energy harvesting receiver architectures, namely time-switching and power-splitting, are investigated. We perform an analytical study on the RF-powered device and derive the expectation of the RF energy harvesting rate, the energy outage probability and the transmission outage probability over Nakagami-m fading channels. These are expressed in terms of so-called Fredholm determinants, which we compute efficiently with modern techniques from numerical analysis. Our analytical results are corroborated by the numerical simulations, and the efficiency of our approximations is demonstrated. In practice, the accurate simulation of any of the Fredholm determinant appearing in the manuscript is a matter of seconds. An interesting finding is that a smaller value of α (corresponding to larger repulsion) yields a better transmission outage performance when the density of the ambient RF transmitters is small. However, it yields a lower transmission outage probability when the density of the ambient RF transmitters is large. We also show analytically that the power-splitting architecture outperfor- s the time-switching architecture in terms of transmission outage performances. Lastly, our analysis provides guidelines for setting the time-switching and power-splitting coefficients at their optimal values.
6. Queue-Aware Energy-Efficient Joint Remote Radio Head Activation and Beamforming in Cloud Radio Access Networks
ABSTRACT
In this paper, we study the stochastic optimization of cloud radio access networks (C-RANs) by joint remote radio head (RRH) activation and beamforming in the downlink. Unlike most previous works that only consider a static optimization framework with full traffic buffers, we formulate a dynamic optimization problem by explicitly considering the effects of random traffic arrivals and time-varying channel fading. The stochastic formulation can quantify the tradeoff between power consumption and queuing delay. Leveraging on the Lyapunov optimization technique, the stochastic optimization problem can be transformed into a per-slot penalized weighted sum rate maximization problem, which is shown to be nondeterministic polynomial-time hard. Based on the equivalence between the penalized weighted sum rate maximization problem and the penalized weighted minimum mean square error (WMMSE) problem, the group sparse beamforming optimization-based WMMSE algorithm and the relaxed integer programming-based WMMSE algorithm are proposed to efficiently obtain the joint RRH activation and beamforming policy. Both algorithms can converge to a stationary solution with low-complexity and can be implemented in a parallel manner, thus they are highly scalable to large-scale C-RANs. In addition, these two proposed algorithms provide a flexible and efficient means to adjust the power-delay tradeoff on demand.
7. Analysis of Downlink Connectivity Models in a Heterogeneous Cellular Network via Stochastic Geometry
ABSTRACT
In this paper, a comprehensive study of the downlink performance in a heterogeneous cellular network (or HetNet) is conducted via stochastic geometry. A general HetNet model is considered consisting of an arbitrary number of open-access and closed-access tiers of base stations (BSs) arranged according to independent homogeneous Poisson point processes. The BSs within each tier have a constant transmission power, random fading factors with an arbitrary distribution and arbitrary path-loss exponent of the power-law path-loss model. For such a system, analytical characterizations for the coverage probability are derived for the max-SINR connectivity and nearest-BS connectivity models. Using stochastic ordering, interesting properties and simplifications for the HetNet downlink performance are derived by relating these two connectivity models to the maximum instantaneous received power (MIRP) connectivity model and the maximum biased received power (MBRP) connectivity models, providing good insights about HetNets and their downlink performance in these complex networks. Furthermore, the results also demonstrate the effectiveness and analytical tractability of the stochastic geometric approach to study the HetNet performance
8. A New Cyclic-Prefix Based Algorithm for Blind CFO Estimation in OFDM Systems
ABSTRACT
Real-world wireless communication channels are typically highly underspread: their coherence time is much greater than their delay spread. In such situations, it is common to assume that, with sufficiently high bandwidth, the capacity without channel state information (CSI) at the receiver (termed the noncoherent channel capacity) is approximately equal to the capacity with perfect CSI at the receiver (termed the coherent channel capacity). In this paper, we propose a lower bound on the noncoherent capacity of highly underspread fading channels, which assumes only that the delay spread and coherence time are known. Furthermore, our lower bound can be calculated recursively, with each increment corresponding to a step increase in bandwidth. These properties, we contend, make our lower bound an excellent candidate as a simple method to verify that the noncoherent capacity is indeed approximately equal to the coherent capacity for typical wireless communication applications. We precede the derivation of the aforementioned lower bound on the information capacity with a rigorous justification of the mathematical representation of the channel. Furthermore, we also provide a numerical example for an actual wireless communication channel and demonstrate that our lower bound does indeed approximately equal the coherent channel capacity
9. Performance Characterization of Relay-Assisted Wireless Optical CDMA Networks in Turbulent Underwater Channel - Optical Communications
ABSTRACT
In this paper, we characterize the performance of relay-assisted underwater wireless optical code division multiple access (OCDMA) networks over turbulent channels. In addition to scattering and absorption effects of underwater channels, we also consider optical turbulence as a log-normal fading coefficient in our analysis. To simultaneously and asynchronously share medium among many users, we assign a unique optical orthogonal code (OOC) to each user in order to actualize OCDMA-based underwater network. The most significant challenge in underwater optical communication is in the ability to extend the short range of its coverage. In order to expand the viable communication range, we consider multi-hop transmission to the destination. Moreover, we evaluate the performance of a relay-assisted point-to-point UWOC system as a special case of the proposed relay-assisted OCDMA network. Our numerical results indicate significant performance improvement by employing intermediate relays, e.g., one can achieve 32 dB improvement in the bit error rate (BER) of 10-6 using only a dual-hop transmission in a 90 m point-to-point clear ocean link.
10. Efficient Tracking Area Management Framework for 5G Networks
ABSTRACT
One important objective of 5G mobile networks is to accommodate a diverse and ever-increasing number of user equipment (UEs). Coping with the massive signaling overhead expected from UEs is an important hurdle to tackle so as to achieve this objective. In this paper, we devise an efficient tracking area list management (ETAM) framework that aims for finding optimal distributions of tracking areas (TAs) in the form of TA lists (TALs) and assigning them to UEs, with the objective of minimizing two conflicting metrics, namely paging overhead and tracking area update (TAU) overhead. ETAM incorporates two parts (online and offline) to achieve its design goal. In the online part, two strategies are proposed to assign in real time, TALs to different UEs, while in the offline part, three solutions are proposed to optimally organize TAs into TALs. The performance of ETAM is evaluated via analysis and simulations, and the obtained results demonstrate its feasibility and ability in achieving its design goals, improving the network performance by minimizing the cost associated with paging and TAU.
11. Location Verification Systems Under Spatially Correlated Shadowing
ABSTRACT
The verification of the location information utilized in wireless communication networks is a subject of growing importance. In this work, we formally analyze, for the first time, the performance of a wireless location verification system (LVS) under the realistic setting of spatially correlated shadowing. Our analysis illustrates that anticipated levels of correlated shadowing can lead to a dramatic performance improvement of a received signal strength (RSS)-based LVS. We also analyze the performance of an LVS that utilizes differential received signal strength (DRSS), formally proving the rather counter-intuitive result that a DRSS-based LVS has identical performance to that of an RSS-based LVS, for all levels of correlated shadowing. Even more surprisingly, the identical performance of RSS and DRSS-based LVSs is found to hold even when the adversary does not optimize his true location. Only in the case where the adversary does not optimize all variables under his control, do we find the performance of an RSS-based LVS to be better than a DRSS-based LVS. The results reported here are important for a wide range of emerging wireless communication applications whose proper functioning depends on the authenticity of the location information reported by a transceiver.
12. An Efficient Bayesian PAPR Reduction Method for OFDM-Based Massive MIMO Systems
ABSTRACT
We consider the problem of peak-to-average power ratio (PAPR) reduction in orthogonal frequency-division multiplexing (OFDM) based massive multiple-input multiple-output (MIMO) downlink systems. Specifically, given a set of symbol vectors to be transmitted to K users, the problem is to find an OFDM-modulated signal that has a low PAPR and meanwhile enables multiuser interference (MUI) cancelation. Unlike previous works that tackled the problem using convex optimization, we take a Bayesian approach and develop an efficient PAPR reduction method by exploiting the redundant degrees-of- freedom of the transmit array. The sought-after signal is treated as a random vector with a hierarchical truncated Gaussian mixture prior, which has the potential to encourage a low PAPR signal with most of its samples concentrated on the boundaries. A variational expectation-maximization (EM) strategy is developed to obtain estimates of the hyperparameters associated with the prior model, along with the signal. In addition, the generalized approximate message passing (GAMP) is embedded into the variational EM framework, which results in a significant reduction in computational complexity of the proposed algorithm. Simulation results show our proposed algorithm achieves a substantial performance improvement over existing methods in terms of both the PAPR reduction and computational complexity
13. Coupled Detection and Estimation Based Censored Spectrum Sharing in Cognitive Radio Networks
ABSTRACT
A novel spectrum sharing strategy based on coupled detection and estimation is proposed for cognitive radio networks. The proposed approach is able to tradeoff throughput for reduced interference at the primary user (PU) via censored transmissions. We derive the optimum censoring strategy that maximizes the throughput of the cognitive radio system under an average interference power constraint at the PU. We then extend the proposed framework to jointly optimize the censoring and the power allocation strategies of the secondary user (SU) that maximize the throughput of the secondary network under average transmit power and average interference power constraints. Finally, we provide extensive simulation results to demonstrate the enhanced performance of the proposed censoring based spectrum sharing approach.
14. Joint Resource Allocation and Relay Selection in LTE-Advanced Network Using Hybrid Co-Operative Relaying and Network Coding
ABSTRACT
The problem of joint resource allocation and relay selection is studied for bidirectional LTE-advanced relay networks. The bidirectional communication between user equipment (UE) and eNodeB (eNB) is performed via direct transmission, co-operative relaying (CoR), or a combination of network coding (NC) and CoR (NC/CoR). In this paper, an enhanced three-time-slot per cycle time-division duplexing (TDD) scheme is proposed for LTE-Advanced frame architecture to accommodate a hybrid transmission scheme. More specifically, we formulate the problem of joint resource assignment, relay selection, and bidirectional transmission scheme selection as a combinatorial optimization problem with the objective to maximize the total product of backlog and rate (back-pressure principle). Two approaches are considered to solve our combinatorial optimization problem. First, a graph-based framework is proposed in which the problem is transformed into a maximum weighted Clique problem (MWCP). In addition, our problem is also transformed into a three-dimensional assignment problem (3DAP) which is solved using a hybrid ant colony optimization (ACO) algorithm. Using simulations, it is concluded that the hybrid transmission scheme outperforms all conventional nonhybrid schemes. Moreover, the simulation results confirm that while the two proposed solutions provide similar results, the ACO algorithm is faster due to its lower complexity.
15. A General MIMO Framework for NOMA Downlink and Uplink Transmission Based on Signal Alignment
ABSTRACT
The application of multiple-input multiple-output (MIMO) techniques to nonorthogonal multiple access (NOMA) systems is important to enhance the performance gains of NOMA. In this paper, a novel MIMO-NOMA framework for downlink and uplink transmission is proposed by applying the concept of signal alignment. By using stochastic geometry, closed-form analytical results are developed to facilitate the performance evaluation of the proposed framework for randomly deployed users and interferers. The impact of different power allocation strategies, namely fixed power allocation and cognitive radio inspired power allocation, on the performance of MIMO-NOMA is also investigated. Computer simulation results are provided to demonstrate the performance of the proposed framework and the accuracy of the developed analytical results
16. Achievable Rates of Secure Transmission in Gaussian MISO Channel With Imperfect Main Channel Estimation
ABSTRACT
A Gaussian multiple-input single-output (MISO) fading channel is considered. We assume that the transmitter, in addition to the statistics of all channel gains, is aware instantaneously of a noisy version of the channel to the legitimate receiver. On the other hand, the legitimate receiver is aware instantaneously of its channel to the transmitter, whereas the eavesdropper instantaneously knows all channel gains. We evaluate an achievable rate using a Gaussian input without indexing an auxiliary random variable. A sufficient condition for beamforming to be optimal is provided. When the numberof transmit antennas is large, beamforming also turns out to be optimal. In this case, the maximum achievable rate can be expressed in a simple closed form and scales with the logarithm of the number of transmit antennas. Furthermore, in the case when a noisy estimate of the eavesdropper’s channel is also available at the transmitter, we introduce the SNR difference and the SNR ratio criterions and derive the related optimal transmission strategies and the corresponding achievable rates.
17. A Comparison of MIMO Techniques in Downlink Millimeter Wave Cellular Networks With Hybrid Beamforming
ABSTRACT
Large antenna arrays will be needed in future millimeter wave (mmWave) cellular networks, enabling a large number of different possible antenna architectures and multiple-input multiple-output (MIMO) techniques. It is still unclear which MIMO technique is most desirable as a function of different network parameters. This paper, therefore, compares the coverage and rate performance of hybrid beamforming enabled multiuser (MU) MIMO and single-user spatial multiplexing (SM) with single-user analog beamforming (SU-BF). A stochastic geometry model for coverage and rate analysis is proposed for MU-MIMO mmWave cellular networks, taking into account important mmWave-specific hardware constraints for hybrid analog/digital precoders and combiners, and a blockage-dependent channel model which is sparse in angular domain. The analytical results highlight the coverage, rate, and power consumption tradeoffs in multiuser mmWave networks. With perfect channel state information at the transmitter and round robin scheduling, MU-MIMO is usually a better choice than SM or SU-BF in mmWave cellular networks. This observation, however, neglects any overhead due to channel acquisition or computational complexity. Incorporating the impact of such overheads, our results can be re-interpreted so as to quantify the minimum allowable efficiency of MU-MIMO to provide higher rates than SM or SU-BF.
18. Network Selection and Channel Allocation for Spectrum Sharing in 5G Heterogeneous Networks
ABSTRACT
The demand for spectrum resources has increased dramatically with the advent of modern wireless applications. Spectrum sharing, considered as a critical mechanism for 5G networks, is envisioned to address spectrum scarcity issue and achieve high data rate access, and guaranteed the quality of service (QoS). From the licensed network’s perspective, the interference caused by all secondary users (SUs) should be minimized. From secondary networks point of view, there is a need to assign networks to SUs in such a way that overall interference is reduced, enabling the accommodation of a growing number of SUs. This paper presents a network selection and channel allocation mechanism in order to increase revenue by accommodating more SUs and catering to their preferences, while at the same time, respecting the primary network operator’s policies. An optimization problem is formulated in order to minimize accumulated interference incurred to licensed users and the amount that SUs have to pay for using the primary network. The aim is to provide SUs with a specific QoS at a lower price, subject to the interference constraints of each available network with idle channels. Particle swarm optimization and a modified version of the genetic algorithm are used to solve the optimization problem. Finally, this paper is supported by extensive simulation results that illustrate the effectiveness of the proposed methods in finding a near-optimal solution.
19. A Scheduling Algorithm for MIMO DoF Allocation in Multi-Hop Networks
ABSTRACT
Recently, a new MIMO degree-of-freedom (DoF) model was proposed to allocate DoF resources for spatial multiplexing (SM) and interference cancellation (IC) in a multi-hop network. Although this DoF model promises many benefits, it hinges upon a global node ordering to keep track of IC responsibilities among all the nodes. An open question about this model is whether its global ordering property can be achieved among the nodes in the network through distributed operations. In this paper, we explore this question by studying DoF scheduling in a multi-hop MIMO network, with the objective of maximizing the minimum throughput among a set of sessions. We propose an efficient DoF scheduling algorithm to solve it and show that our algorithm only requires local operations. We prove that the resulting DoF scheduling solution is globally feasible and show that there exists a corresponding feasible global node ordering for IC, albeit such global ordering is implicit. Simulation results show that the solution values obtained by our algorithm are relatively close to the upper bound values computed by CPLEX solver, thereby indicating that our algorithm is highly competitive.
20. On the Capacity of the Intensity-Modulation Direct-Detection Optical Broadcast Channel - Optical Communications
ABSTRACT
The capacity of the intensity-modulation direct-detection optical broadcast channel (OBC) is investigated, under both average and peak intensity constraints. An outer bound on the capacity region is derived by adapting Bergmans’ approach to the OBC. Inner bounds are derived by using superposition coding with either truncated-Gaussian (TG) distributions or discrete distributions. While the discrete distribution achieves higher rates, the TG distribution leads to a simpler representation of the achievable rate region. At high signal-to-noise ratio (SNR), it is shown that the TG distribution is nearly optimal. It achieves the symmetric-capacity within a constant gap (independent of SNR), which approaches half a bit as the number of users grows. It also achieves the capacity region within a constant gap. At low SNR, it is shown that on-off keying (OOK) with time-division multiple-access (TDMA) is optimal. This is interesting in practice since both OOK and TDMA have low complexity. At moderate SNR (typically [0,8] dB), a discrete distribution with a small alphabet size achieves fairly good performance.
21. Secure Broadcasting with Imperfect Channel State Information at the Transmitter
ABSTRACT
We investigate the problem of secure broadcasting over fast fading channels with imperfect main channel state information (CSI) at the transmitter. In particular, we analyze the effect of the noisy estimation of the main CSI on the throughput of a broadcast channel where the transmission is intended for multiple legitimate receivers in the presence of an eavesdropper. Besides, we consider the realistic case where the transmitter is only aware of the statistics of the eavesdropper’s CSI and not of its channel’s realizations. First, we discuss the common message transmission case where the source broadcasts the same information to all the receivers, and we provide an upper and a lower bound on the ergodic secrecy capacity. For this case, we show that the secrecy rate is limited by the legitimate receiver having, on average, the worst main channel link and we prove that a nonzero secrecy rate can still be achieved even when the CSI at the transmitter is noisy. Then, we look at the independent messages case where the transmitter broadcasts multiple messages to the receivers, and each intended user is interested in an independent message. For this case, we present an expression for the achievable secrecy sum-rate and an upper bound on the secrecy sum-capacity and we show that, in the limit of large number of legitimate receivers K, our achievable secrecy sum-rate follows the scaling law log ((1-α)log(K)), where α is the estimation error variance of the main CSI. The special cases of high SNR, perfect and no-main CSI are also analyzed. Analytical derivations and numerical results are presented to illustrate the obtained expressions for the case of independent and identically distributed Rayleigh fading channels.
22. General Stochastic Channel Model and Performance Evaluation for Underwater Wireless Optical Links - Optical Communications
ABSTRACT
In underwater wireless optical communications (UWOC), absorption and scattering characterize the link properties since photons may suffer these two processes with energy loss and direction change, respectively, when interacting with water molecules or suspended particles. In this work, we consider the effects of absorption and scattering on the probability distribution, i.e., normalized intensity distribution, of photons in space and time domains. Our prior work proposed a stochastic channel model to represent the spatial-temporal probability distribution of propagated photons only for nonscattering and single scattering components of UWOC links. However, multiple scattering will dominate the scattering behavior of the underwater environment with long communication distance and/or more turbid water type. In this work, we take into account all three types of components including nonscattering, single and multiple scattering, and present a more general stochastic channel model which fits well with Monte Carlo simulations in turbid water environment such as coastal and harbor water. Based on the proposed channel model, we also evaluate the performance of path loss, scattering richness, and attenuation of UWOC links. Numerical results suggest that multiple scattering can compensate the path loss overestimated by traditional approaches. Furthermore, scattering richness and attenuation tend to increase but have opposite effects to raise and reduce the received probabilities of higher order scattered photons, respectively, as link range increases.
23. Achieving High Energy Efficiency and Physical-Layer Security in AF Relaying
ABSTRACT
For transmitting data in a secret and energy-efficient manner in collaborative amplify-and-forward relay networks, the secure energy efficiency (EE) defined as the secret bits transferred with unit energy is maximized to satisfy each node power constraint and target secrecy rate requirement, based on physical security framework. The secure EE is maximized by joint source and relay power allocation, which is a nonconvex optimization problem. To cope with this difficulty, a solution scheme and corresponding algorithms are developed by jointly applying fractional programming, exact penalty, alternate search, and difference of convex functions programming. The key idea of the scheme is to convert the primal problem into simple subproblems step by step, such that related methods are adopted. It is verified that, compared with secrecy rate maximization, the proposed scheme improves the secure EE significantly yet with a certain loss of the secrecy rate due to the tradeoff between secure EE and secrecy rate. Furthermore, the proposed scheme achieves higher secure EE and secrecy rate than total transmission power minimization does, while with a certain increase of power consumption. These results indicate that a reasonable balance among secure EE, secrecy rate, and power consumption can be reached by the proposed scheme.
24. A Batch-based MAC Design with Simultaneous Assignment Decisions for Improved Throughput in Guard-band-constrained Cognitive Networks
ABSTRACT
The adjacent channel interference (ACI) resulting from imperfect filtering can severely degrade the performance of any wireless communication system. Despite this fact, most of previously proposed medium access control (MAC) protocols for cognitive radio networks (CRNs) were designed while ignoring the effects of ACI (assuming ideal filtering). The effect of ACI can be reduced by introducing guard bands (GBs). However, this solution comes at the expense of degrading spectrum efficiency. In this paper, we develop an efficient GB-aware MAC protocol that attempts at maximizing network throughput while improving fairness in CRNs. Unlike most of previously proposed GB-aware MAC protocols that perform channel assignment sequentially, our MAC performs the channel assignment for multiple CR links simultaneously (the so-called batch method). Batching enables concurrent channel assignment for multiple CR links, which consequently allows for concurrent data transmissions. Batching can be realized by introducing an admission control phase for CR users to share their control information. The batch method can effectively provide distributed decisions that achieve better throughput while reducing the number of GBs. Our MAC also allows the CR users to utilize the reserved GBs of primary networks under predefined FCC power constraints. Simulation results indicate that our protocol achieves significant performance improvement compared to previous GB-aware protocols.
25. Impact of Antenna Correlation on the BER Performance of a Cognitive Radio Network with Alamouti STBC
ABSTRACT
This letter presents an average bit error-rate (BER) performance analysis for spectrum sharing in a cognitive radio network in which primary and secondary users employ Alamouti space-time block coding (STBC) under correlated antennas over Rayleigh fading channels. Closed-form expressions are derived for the cumulative density function (CDF) of the secondary user’s signal-to-noise-ratio (SNR) under correlated antennas. Then, closed-form expressions are derived for the average BER of the system with coherent modulation schemes as well as with noncoherent modulation techniques. Using numerical evaluation results from the derived expressions, verified by Monte Carlo simulations, the impacts of antenna correlation on the average BER of the system in different cases are evaluated.
26. Heterogeneous Cellular Network with Energy Harvesting Based D2D Communication
ABSTRACT
The concept of mobile user equipment (UE) relay (UER) has been introduced to support device-to-device (D2D) communications for enhancing communication reliability. However, as the UER needs to use its own power for other UE’s data transmission, relaying information in D2D communication may be undesirable for the UER. To overcome this issue, motivated by the recent advances in energy harvesting (EH) techniques, we propose a D2D communication provided EH heterogeneous cellular network (D2D-EHHN), where UERs harvest energy from an access point (AP) and use the harvested energy for D2D communication. We develop a framework for the design and analysis of D2D-EHHN by introducing the EH region (EHR) and modeling the status of harvested energy using Markov chain. The UER distribution is derived, and a transmission mode selection scheme including the efficient UER selection method is proposed. The network outage probability is derived in close form to measure the performance of D2D-EHHN. Based on our analysis results, we explore the effects of network parameters on the outage probability and the optimal offloading bias in terms of the outage probability. Particularly, we show that having a high EH efficiency enhances the performance of D2D-EHHN, but can also degrade, especially for dense network.
27. Artificial Noise Aided Secrecy Information and Power Transfer in OFDMA Systems
ABSTRACT
In this paper, we study simultaneous wireless information and power transfer (SWIPT) in orthogonal frequency division multiple access (OFDMA) systems with the coexistence of information receivers (IRs) and energy receivers (ERs). The IRs are served with best-effort secrecy data and the ERs harvest energy with minimum required harvested power. To enhance the physical layer security for IRs and yet satisfy energy harvesting requirements for ERs, we propose a new frequency-domain artificial noise (AN) aided transmission strategy. With the new strategy, we study the optimal resource allocation for the weighted sum secrecy rate maximization for IRs by power and subcarrier allocation at the transmitter. The studied problem is shown to be a mixed integer programming problem and thus nonconvex, while we propose an efficient algorithm for solving it based on the Lagrange duality method. To further reduce the computational complexity, we also propose a suboptimal algorithm of lower complexity. The simulation results illustrate the effectiveness of proposed algorithms as compared against other heuristic schemes.
28. Dynamic Clustering and ON/OFF Strategies for Wireless Small Cell Networks
ABSTRACT
In this paper, a novel cluster-based approach for maximizing the energy efficiency of wireless small cell networks is proposed. A dynamic mechanism is proposed to locally group coupled small cell base stations (SBSs) into clusters based on location and traffic load. Within each formed cluster, SBSs coordinate their transmission parameters to minimize a cost function, which captures the tradeoffs between energy efficiency and flow level performance, while satisfying their users’ quality-of-service requirements. Due to the lack of intercluster communications, clusters compete with one another to improve the overall network’s energy efficiency. This intercluster competition is formulated as a noncooperative game between clusters that seek to minimize their respective cost functions. To solve this game, a distributed learning algorithm is proposed using which clusters autonomously choose their optimal transmission strategies based on local information. It is shown that the proposed algorithm converges to a stationary mixed-strategy distribution, which constitutes an epsilon-coarse correlated equilibrium for the studied game. Simulation results show that the proposed approach yields significant performance gains reaching up to 36% of reduced energy expenditures and upto 41% of reduced fractional transfer time compared to conventional approaches
29. Cooperative Multicasting in Renewable Energy Enhanced Relay Networks – Expending More Power to Save Energy
ABSTRACT
Power and on-off control problems are examined for renewable energy enabled base-stations (BSs) and relay nodes (RNs) in cooperative multicast networks. Renewable energy is utilized at BSs and RNs to reduce the overall grid energy cost. By considering a practical energy consumption model and the statistics of the renewable energy arrival, the optimal transmit powers are first determined by minimizing the expected grid energy consumption subject to an average outage probability constraint at MUs. The optimal solution is found via line search in the general case and is obtained in closed-form at high SNR. In addition, an on-off control policy is also proposed to further reduce the basic operational energy costs. The joint on-off and power control problems are solved approximately using two sequential deflation techniques, namely, the subset-search and the convex-relaxation-based approaches. The power control problem is also extended to the multicarrier scenario with unequal transmit powers and is solved using successive convex approximation. Simulations using the photovoltaic energy arrival model are provided to demonstrate the effectiveness of the proposed schemes. The results show that expending more power at RNs allows for more efficient use of renewable energy and, thus, increases energy-savings.
30. Iterative Distributed Minimum Total MSE Approach for Secure Communications in MIMO Interference Channels
ABSTRACT
In this paper, we consider the problem of jointly designing transmit precoding (TPC) matrix and receive filter matrix subject to both secrecy and per-transmitter power constraints in the multiple-input multiple-output (MIMO) interference channel, where K legitimate transmitter-receiver pairs communicate in the presence of an external eavesdropper. Explicitly, we jointly design the TPC and receive filter matrices based on the minimum total mean-squared error (MSE) criterion under a given and feasible information-theoretic degrees of freedom. More specifically, we formulate this problem by minimizing the total MSEs of the signals communicated between the legitimate transmitter-receiver pairs, while ensuring that the MSE of the signals decoded by the eavesdropper remains higher than a certain threshold. We demonstrate that the joint design of the TPC and receive filter matrices subject to both secrecy and transmit power constraints can be accomplished by an efficient iterative distributed algorithm. The convergence of the proposed iterative algorithm is characterized as well. Furthermore, the performance of the proposed algorithm, including both its secrecy rate and MSE, is characterized with the aid of numerical results. We demonstrate that the proposed algorithm outperforms the traditional interference alignment algorithm in terms of both the achievable secrecy rate and the MSE. As a benefit, secure communications can be guaranteed by the proposed algorithm for the MIMO interference channel even in the presence of a sophisticated/strong eavesdropper, whose number of antennas is much higher than that of each legitimate transmitter and receiver.
31. A Novel Coding Scheme for Secure Communications in Distributed RFID Systems
ABSTRACT
Privacy protection is the primary concern when RFID applications are deployed in our daily lives. Due to the computational power constraints of passive tags, non-encryption-based singulation protocols have been recently developed, in which wireless jamming is used. However, the existing private tag access protocols without shared secrets rely on impractical physical layer assumptions, and thus they are difficult to deploy. To tackle this issue, we first redesign the architecture of RFID system by dividing an RF reader into two different devices, an RF activator and a trusted shield device (TSD). Then, we propose a novel coding scheme, namely Random Flipping Random Jamming (RFRJ), to protect tags’ content. Unlike the past work, the proposed singulation protocol utilizes only the physical layer techniques that are already implemented. Analyses and simulation results validate our distributed architecture with the RFRJ coding scheme, which defends tags’ privacy against various adversaries including the random guessing attack, correlation attack, ghost-and-leech attack, and eavesdropping
32. A Configurable Energy-Efficient Compressed Sensing Architecture with Its Application on Body Sensor Networks
ABSTRACT
The past decades have witnessed a rapid surge in new sensing and monitoring devices for well-being and healthcare. One key representative in this field is body sensor networks (BSNs). However, with advances in sensing technologies and embedded systems, wireless communication has gradually become one of the dominant energy-consuming sectors in BSN applications. Recently, compressed sensing (CS) has attracted increasing attention in solving this problem due to its enabled sub-Nyquest sampling rate. In this paper, we investigate the quantization effect in CS architecture and argue that the quantization configuration is a critical factor of the energy efficiency for the entire CS architecture. To this end, we present a novel configurable quantized compressed sensing (QCS) architecture, in which the sampling rate and quantization are jointly explored for better energy efficiency. Furthermore, to combat the computational complexity of the configuration procedure, we propose a rapid configuration algorithm, called RapQCS. According to the experiments involving several categories of real biosignals, the proposed configurable QCS architecture can gain more than 66% performance-energy tradeoff than the fixed QCS architecture. Moreover, our proposed RapQCS algorithm can achieve over 150× speedup on average, while decreasing the reconstructed signal fidelity by only 2.32%.
33. Limited Rate Feedback Scheme for Resource Allocation in Secure Relay-Assisted OFDMA Networks
ABSTRACT
In this paper, we consider the problem of resource allocation for secure communications in decode-and-forward (DF) relay-assisted orthogonal frequency-division multiple access (OFDMA) networks. In our setting, users want to securely communicate to the base station (BS) with the help of a set of relay stations (RSs) in the presence of multiple eavesdroppers. We assume that all channel state information (CSI) of the legitimate links and only the channel distribution information (CDI) of the eavesdropper links are available. We formulate our problem as an optimization problem whose objective is to maximize the sum secrecy rate of the system subject to individual transmit power constraint for each user and RS. As a first work which considers limited feedback schemes for secure communications in cooperative OFDMA networks, we consider the limited-rate feedback case, where in addition to transmit power and subcarrier assignments, channel quantization should be performed and boundary regions of channels should be computed. We further consider the noisy feedback channel. We solve our problem using the dual Lagrange approach and propose an iterative algorithm whose convergence is analyzed. Using simulations, we evaluate the performance of the proposed scheme in numerous situations.
34. Delay and Power Consumption in LTE/LTE-A DRX Mechanism with Mixed Short and Long Cycles
ABSTRACT
Energy consumption is a major concern in today’s wireless communications due to the consensus for a greener world. LTE-Advanced (LTE-A) has been standardized for the fourth-generation mobile communications to meet the growing demands for high-speed wireless communications. However, high-speed signal processing on LTE/LTE-A user equipment (UE) causes excessive power consumption. The discontinuous reception (DRX) mechanism is a critical technique for tackling this issue. Delay constraint and power savings are two contradictory performance metrics associated with the DRX mechanism. Using recursive deduction and Markov model, this paper provides an in-depth analysis on the average delay and average power consumption of the DRX mechanism. Two performance metrics, namely, power-saving factor and relative power saving, are devised to assess the power-saving performance of the DRX mechanism. The accuracy of theoretical analysis is validated by computer simulations using the parameters in compliance with LTE specifications. The performance of the DRX mechanism is governed by a set of parameters that interact with one another in an intricate manner. Therefore, the values of key parameters are tested to assess their impacts on the performance of the DRX mechanism. The results shown in this paper give an insight into the operation and further improvement of the DRX mechanism.
35. A Simple Recursively Computable Lower Bound on the NoncoherentCapacity of Highly Underspread Fading Channels
ABSTRACT
Real-world wireless communication channels are typically highly underspread: their coherence time is much greater than their delay spread. In such situations, it is common to assume that, with sufficiently high bandwidth, the capacity without channel state information (CSI) at the receiver (termed the noncoherent channel capacity) is approximately equal to the capacity with perfect CSI at the receiver (termed the coherent channel capacity). In this paper, we propose a lower bound on the noncoherent capacity of highly underspread fading channels, which assumes only that the delay spread and coherence time are known. Furthermore, our lower bound can be calculated recursively, with each increment corresponding to a step increase in bandwidth. These properties, we contend, make our lower bound an excellent candidate as a simple method to verify that the noncoherent capacity is indeed approximately equal to the coherent capacity for typical wireless communication applications. We precede the derivation of the aforementioned lower bound on the information capacity with a rigorous justification of the mathematical representation of the channel. Furthermore, we also provide a numerical example for an actual wireless communication channel and demonstrate that our lower bound does indeed approximately equal the coherent channel capacity.
36. On the Capacity of the Intensity-Modulation Direct-Detection Optical Broadcast Channel
ABSTRACT
The capacity of the intensity-modulation direct-detection optical broadcast channel (OBC) is investigated, under both average and peak intensity constraints. An outer bound on the capacity region is derived by adapting Bergmans’ approach to the OBC. Inner bounds are derived by using superposition coding with either truncated-Gaussian (TG) distributions or discrete distributions. While the discrete distribution achieves higher rates, the TG distribution leads to a simpler representation of the achievable rate region. At high signal-to-noise ratio (SNR), it is shown that the TG distribution is nearly optimal. It achieves the symmetric-capacity within a constant gap (independent of SNR), which approaches half a bit as the number of users grows. It also achieves the capacity region within a constant gap. At low SNR, it is shown that on–off keying (OOK) with time-division multiple-access (TDMA) is optimal. This is interesting in practice since both OOK and TDMA have low complexity. At moderate SNR (typically [0,8] dB), a discrete distribution with a small alphabet size achieves fairly good performance.
37. Optimum Co-Design for Spectrum Sharing Between Matrix Completion Based MIMO Radars and a MIMO Communication System
ABSTRACT
Spectrum sharing enables radar and communication systems to share the spectrum efficiently by minimizing mutual interference. Recently proposed multiple input multiple output radars based on sparse sensing and matrix completion (MIMOMC), in addition to reducing communication bandwidth and power as compared to MIMO radars, offer a significant advantage for spectrum sharing. The advantage stems from the way the sampling scheme at the radar receivers modulates the interference channel from the communication system transmitters, rendering it symbol dependent and reducing its row space. This makes it easier for the communication system to design its waveforms in an adaptive fashion so that it minimizes the interference to the radar subject to meeting rate and power constraints. Two methods are proposed. First, based on the knowledge of the radar sampling scheme, the communication system transmit covariance matrix is designed to minimize the effective interference power (EIP) to the radar receiver, while maintaining certain average capacity and transmit power for the communication system. Second, a joint design of the communication transmit covariance matrix and the MIMO-MC radar sampling scheme is proposed, which achieves even further EIP reduction.
38. SLRMA: Sparse Low-Rank Matrix Approximation for Data Compression
ABSTRACT
Low-rank matrix approximation (LRMA) is a powerful technique for signal processing and pattern analysis. However, its potential for data compression has not yet been fully investigated in the literature. In this paper, we propose sparse lowrank matrix approximation (SLRMA), an effective computational tool for data compression. SLRMA extends the conventional LRMA by exploring both the intra- and inter-coherence of data samples simultaneously. With the aid of prescribed orthogonal transforms (e.g., discrete cosine/wavelet transform and graph transform), SLRMA decomposes a matrix into a product of two smaller matrices, where one matrix is made of extremely sparse and orthogonal column vectors, and the other consists of the transform coefficients. Technically, we formulate SLRMA as a constrained optimization problem, i.e., minimizing the approximation error in the least-squares sense regularized by 0- norm and orthogonality, and solve it using the inexact augmented Lagrangian multiplier method. Through extensive tests on realworld data, such as 2D image sets and 3D dynamic meshes, we observe that (i) SLRMA empirically converges well; (ii) SLRMA can produce approximation error comparable to LRMA but in a much sparse form; (iii) SLRMA-based compression schemes significantly outperform the state-of-the-art in terms of ratedistortion performance.
39. Gammatone Filter Based on Stochastic Computation
ABSTRACT
This paper introduces a design of a gammatone filter based on stochastic computation for area-efficient hardware. The gammatone filter well expresses the performance of human auditory peripheral mechanism and has a potential of improving advanced speech communications systems, especially hearing assisting devices and noise robust speech recognition systems. Using stochastic computation, a power-and-area hungry multiplier used in a digital filter is replaced by a simple logic gate, leading to area-efficient hardware. However, a straightforward implementation of the stochastic gammatone filter suffers from significantly low accuracy in computation, which results in a low dynamic range (a ratio of the maximum to minimum magnitude) due to a small value of a filter gain. To improve the computational accuracy, gain-balancing techniques are presented that represent the original gain as the product of multiple larger gains introduced at the second-order sections. As a result, the proposed techniques maintain the original gain of the filter while improving the computational accuracy. The proposed stochastic gammatone filters are designed and evaluated using MATLAB that achieves a high dynamic range of 71.71 dB compared with a low dynamic range of 5.47 dB in the straightforward implementation.
40. A Scertain Privacy Conservation And Data Security Protection Onboard Small Uas
ABSTRACT
The potential application areas for small Unmanned Aerial Systems (sUAS) are massive. This paper takes into account the unstoppable trend toward the widespread use of sUAS for a large number of applications and reports on the needed privacy preserving measures and techniques. Specifically, this work researches the prospect of implementing object detection and blurring techniques on the actual sUAS hardware, such that the privacy of sensitive objects captured by the sUAS camera is preserved. The solution approach is to embed FPGA development boards with connected image sensors onboard the sUAS and implement MATLAB image processing algorithms into VHDL/Verilog code. Given the fact that the sUAS may run out of battery or crash during flight, and thus be captured by unauthorized persons, data encryption on the FPGA development boards needs also be studied for security purposes.
41. Effective Range Doppler Algorithm Simulator Using Vectorization Technique
ABSTRACT
This paper deals with a new adaption technique for general simulator of using vectorization. This approach is more time effective in comparing with the standard method. In the article, the simulation process of the RDA is analyzed and describes which is widely used for Synthetic Aperture Radar (SAR) imaging techniques. The simulation algorithm uses vectorization which satisfies algorithm performance. There are also depicted all parts of RDA and its results. The echoed signal which was assumed in simulation is described and also its parameters.
42. Auto Target Detection of Humanoid and Auto Shooting Using Sniper: A Design Approach
ABSTRACT
In this paper a new defense mechanism using image processing has been implemented which can acquire targets at long distances with high precision in various weather conditions. The main objective is to make an effective tool for the armed forces which can guard the border areas. The mechanism consists of two modules: targeting unit and firing unit. The targeting unit has a microcontroller along with sensors to detect the presence of humans in the targeted area and processes various atmospheric parameters electronically. LASER pointer is used to determine if the desired target is hit or missed by tracking the path of the bullet and determining the point of intersection with the LASER. The targeting unit has special mechanism which can position the gun automatically once the parameters are obtained.
43. A System Concept for a 3D Real-Time OFDM MIMO Radar for Flying Platforms
ABSTRACT
In this paper a new system concept for a low cost, miniaturized and real-time imaging radar system for flying platforms is presented. The proposed solution is based on the MIMO radar architecture, orthogonal signals for simultaneous transmit capabilities and highly integrated SiGe chipsets. Using beamforming techniques at the receiver together with radar processing techniques, a 3D sensing of the range, azimuth, elevation and Doppler information for an arbitrary number of objects can be estimated through a simultaneous transmission and with real-time hardware implementable FFT processing techniques. A top-level system concept and a complete parametrization is proposed for a radar system which is intended for obstacle warning for helicopters and to enhance flight safety in approach, landing and take-off phases of flight even in degraded visual conditions. The full OFDM MIMO Radar system has been implemented and tested in a MATLAB environment and simulation results are here presented. This paper is the first step towards the implementation of a compact and real-time radar system demonstrator
44. Onboard Radar Processor Development for Rapid Response to Natural Hazards
ABSTRACT
The unique capabilities of imaging radar to penetrate cloud cover and collect data in darkness over large areas at high resolution makes it a key information provider for the management and mitigation of natural and human-induced hazards. Researchers have demonstrated the use of UAVSAR data to determine flood extent, forest fire extent, lava flow, and landslide. Data latency of at most 2–3 h is required for the radar data to be of use to the disaster responders. We have developed a UAVSAR on-board processor for real time and autonomous operations that has high fidelity and accuracy to enable timely generation of polarimetric and interferometric data products for rapid response applications. This on-board processor design provides a space-qualification path for technology infusion into future space missions in a high-radiation environment with modest power and weight allocations. The processor employs a hybrid architecture where computations are divided between field-programmable gate arrays, which are better suited to rapid, repetitious computations, and a microprocessor with a floating-point coprocessor that is better suited to the less frequent and irregular computations. Prior to implementing phase preserving processor algorithms in FPGA code, we developed a bit-true processor model in MATLAB that is modularized and parameterized for ease of testing and the ability to tradeoff processor design with performance. The on-board processor has been demonstrated on UAVSAR flights.
45. Experimental 210GHz tera hertz nondestructive testing foraerospace composite materials
ABSTRACT
In this paper we proposed a terahertz nondestructive testing method to achieve the image of the aerospace composite materials. We commence in the following manner, using the continuous back wave oscillator (BWO) as the source of terahertz radiation, which the frequency is 210 GHz. By the reflection type imaging testing system, the terahertz probe focus moves from the surface to inside of the concealed composite materials. And the materials are bonded on the two-dimensional scanning translation units towards the focal of the terahertz mirror, which can move in real-time to get the data by the phase-locked amplifier. All the system is controlled by the computer. The interior structure can be tested by the images range from 0.5mm to 1mm resolution. The images are calculated by principal component analysis (PCA) and the least square method(LSM). With the proper math to calculate in Matlab, the structure, the size, position and shape defects such as cracks, inclusions, empty and bubbles in the aerospace insulation composite materials can be tested by the terahertz image system. It is a more convenient and intuitive method of imaging inner aerospace composite material.