Catering to emerging satellite-based free-space optical (FSO) communication networks and exploiting polarization encoding via Stokes operators, we propose a novel simultaneous quantum-classical communications (SQCC) protocol. The protocol enables the coexistence of secure quantum communications and high-throughput classical communications with minimal alterations in both the infrastructure and the energy input. Compared to the conventional SQCC protocol, our new approach provides superior practicality in the real world, eliminates the need for a separate local oscillator, and allows for the simple readout of both quantum and classical information using direct detection. The protocol also minimizes the undesirable interplay between the quantum and the classical parts of communication. We provide a detailed mathematical formulation of the protocol, along with theoretical and numerical analysis of its performance, illustrating a promising path to practical and effective realization of combined classical-quantum communications.

Despite being an integral part of the vision of quantum Internet, Earth-to-satellite (uplink) quantum communications have been considered more challenging than their satellite-to-Earth (downlink) counterparts due to the severe channel-loss fluctuations (fading) induced by atmospheric turbulence. The question of how to address the negative impact of fading on Earth-to-satellite quantum communications remains largely an open issue. In this work, we explore the feasibility of exploiting spatial diversity as a means of fading mitigation in Earth-to-satellite Continuous-Variable (CV) quantum-classical optical communications. We demonstrate, via both our theoretical analyses of quantum-state evolution and our detailed numerical simulations of uplink optical channels, that the use of spatial diversity can improve the effectiveness of entanglement distribution through the use of multiple transmitting ground stations and a single satellite with multiple receiving apertures. We further show that the transfer of both large (classically-encoded) and small (quantum-modulated) coherent states can benefit from the use of diversity over fading channels. Our work represents the first quantitative investigation into the use of spatial diversity for satellite-based quantum communications in the uplink direction, showing under what circumstances this fading-mitigation paradigm, which has been widely adopted in classical communications, can be helpful within the context of Earth-to-satellite CV quantum communications.

Catering for the emerging satellite-based free-space optical (FSO) communication networks, exploiting polarization encoding via Stokes operators, we propose a novel simultaneous quantum-classical communications (SQCC) protocol that enables the coexistence of secured quantum communications and high-throughput classical communications under minimal alterations in both infrastructure and energy input. Relative to the conventional SQCC protocol, our new protocol provides superior real-world practicability by eliminating the need for a separate local oscillator, allowing for the simple readout of both quantum and classical information using direct detection, and minimizing the undesirable interplay between the quantum and classical parts of communication. We provide a detailed description, along with theoretical and numerical analyses on the feasibility and performance of our protocol, illustrating a promising pathway towards the practical and effective realization of combined classical-quantum communications.

Precision navigation and timing, very-long-baseline interferometry, next-generation communication, sensing, and tests of fundamental physics all require a highly synchronized network of clocks. With the advance of highly-accurate optical atomic clocks, the precision requirements for synchronization are reaching the limits of classical physics (i.e. the standard quantum limit, SQL). Efficiently overcoming the SQL to reach the fundamental Heisenberg limit can be achieved via the use of squeezed or entangled light. Although approaches to the Heisenberg limit are well understood in theory, a practical implementation, such as in space-based platforms, requires that the advantage outweighs the added costs and complexity. Here, we focus on the question: can entanglement yield a quantum advantage in clock synchronization over lossy satellite-to-satellite channels? We answer in the affirmative, showing that the redundancy afforded by the two-mode nature of entanglement allows recoverability even over asymmetrically lossy channels. We further show this recoverability is an improvement over single-mode squeezing sensing, thereby illustrating a new complexity-performance trade-off for space-based sensing applications.

With sub-threshold quantum error correction on quantum hardware still out of reach, quantum error mitigation methods are currently deemed an attractive option for implementing certain applications on near-term noisy quantum devices. One such application is quantum routing - the ability to map an incoming quantum signal into a superposition of paths. In this work, we use a 7-qubit IBM quantum device to experimentally deploy two promising quantum error mitigation methods, Zero-Noise Extrapolation (ZNE) and Probabilistic Error Cancellation (PEC), in the context of quantum routing. Importantly, beyond investigating the improved performance of quantum routing via ZNE and PEC separately, we also investigate the routing performance provided by the concatenation of these two error-mitigation methods. Our experimental results demonstrate that such concatenation leads a very significant performance improvement relative to implementation with no error mitigation. Indeed, an almost perfect performance in terms of fidelity of the output entangled paths is found. These new results reveal that with concatenated quantum error-mitigation embedded, useful quantum routing becomes feasible on current devices without the need for quantum error correction - opening up a potential implementation pathway to other applications that utilize a superposition of communication links.

Quantum State Tomography (QST) is a fundamental tool for quantum signal processing. However, in real noisy quantum devices construction of the state’s density matrix via QST can utilize a large amount of resources. Here, we discuss some signal processing techniques that are currently applied to this resource issue, and implement on current quantum chips a modification that can assist in reducing resources. An application of QST to quantum entanglement distillation is provided for further insight.

Quantum states of light being transmitted via realistic free-space channels often suffer erasure errors due to several factors such as coupling inefficiencies between transmitter and receiver. In this work, an error correction code capable of protecting a single-mode quantum state against erasures is presented. Our three-mode code protects a single-mode Continuous Variable (CV) state via a bipartite CV entangled state. In realistic deployments, it can almost completely reverse a single erasure on the encoded state, and for two erasures can it improve the fidelities of received states relative to direct transmission. The bipartite entangled state used in the encoding can be Gaussian or non-Gaussian, with the latter further enhancing the performance of the code. Our new code is the simplest code known that protects a single mode against erasures and should prove useful in the construction of practical CV quantum networks that rely on free-space optics.

Geographic routing is an important function for many Internet of Things (IoT) applications, but such routing is vulnerable to spoofed-location attacks, rendering any deployment potentially insecure. Attempts at combating such insecurity via an embedded location-verification solution have previously proved successful in that the additional overhead incurred by the verification does not violate the scalability of the routing protocol. However, these previous solutions assume a priori knowledge of all the path loss exponents that describe the channels between a device and its anchor reference stations - an assumption violated in actual deployment scenarios. Critical to real-world deployment of location-verified geographic routing, therefore, is the ability to remain scalable despite all relevant path loss exponents being unknown. Here, we show that the impact of unknown path loss exponents can in fact be accommodated within a location-secured geographic routing protocol without any significant impact on the routing scalability. Our work demonstrates, for the first time, a deployment pathway for IoT geographic routing that is secured against the most detrimental effects of location-spoofing attacks.

Designing a practical Continuous Variable (CV) Quantum Key Distribution (QKD) system requires an estimation of the quantum channel characteristics and the extraction of secure keys based on a large number of distributed quantum signals. On standard processors, it can take hours to reconcile the required number of quantum signals. This problem is exacerbated for Low Earth Orbit (LEO) satellite CV-QKD, where the satellite flyover time is less than a few minutes. A potential solution is massive parallelisation of the classical reconciliation where a large-code block is subdivided into many shorter blocks for individual decoding. However, the penalty of this procedure on the important final secured key rate is non-trivial to determine and hitherto has not been formally analysed. In this work, we fill this important knowledge gap via detailed analyses and experimental verification of a CV-QKD sliced reconciliation protocol that uses large block-length low-density parity-check decoders. Our new solution results in a significant increase in the final key rate relative to non-optimised reconciliation. In addition, it allows for the acquisition of quantum secured messages between terrestrial stations and LEO satellites within a flyover timescale even using off-the-shelf processors. Our work allows for optimised global quantum networks secured via fundamental physics.

Continuous Variable (CV) non-Gaussian resources are fundamental in the realization of quantum error correction for CV-based quantum communications and CV-based computing. In this work, we investigate the use of CV non-Gaussian states as quantum teleportation resource states in the context of the transmission of coherent and squeezed states through noisy channels. We consider an array of different non-Gaussian resource states, and compute the fidelity of state teleportation achieved for each resource. Our results show that the use of non-Gaussian states presents a significant advantage compared to the traditional resource adopted for CV teleportation; the Gaussian two-mode squeezed vacuum state. In fiber-based quantum communications, the range of quantum teleportation is increased by approximately 40% via the use of certain non-Gaussian states. In satellite-to-ground quantum communications, for aperture configurations consistent with the Micius satellite, the viable range of quantum teleportation is increased from 700 km to over 1200 km. These results represent a significant increase in the performance of pragmatic and realizable quantum communications in both terrestrial and space-based networks.

Artificial intelligence (AI) solutions for wireless location estimation are likely to prevail in many real-world scenarios. In this work, we demonstrate for the first time how the Cramer-Rao bound on localization accuracy can facilitate efficient neural-network solutions for wireless location estimation. In particular, we demonstrate how the number of neurons for the network can be intelligently chosen, leading to AI location solutions that are not time-consuming to run and less likely to be plagued by over-fitting. Experimental verification of our approach is provided. Our new algorithms are directly applicable to location estimates in many scenarios including the Internet of Things, and vehicular networks where vehicular GPS coordinates are unreliable or need verifying. Our work represents the first successful AI solution for a communication problem whose neural-network design is based on fundamental information-theoretic constructs. We anticipate our approach will be useful for a wide range of communication problems beyond location estimation.

Continuous variable quantum key distribution (CV-QKD) offers information-theoretic secure key sharing between two parties. The sharing of a phase reference frame is an essential requirement for coherent detection in CV-QKD. Due to the potential attacks related to transmitting the local oscillator (LO) alongside quantum signals, there has been a focus on using local LOs (LLOs) to establish a shared phase reference. In this work, we develop a new noise model of a current state-of-the-art LLO scheme in the context of the satellite-to-Earth channel. In doing this, we encapsulate detailed phase-screen calculations that determine the coherent efficiency - a critical parameter in free-space CV-QKD that characterizes the wavefront aberrations caused by atmospheric turbulence. Using our new noise model we then determine the CV-QKD key rates for the satellite-to-Earth channel, secure under general attacks in the finite-size regime of the LLO scheme. Our results are of practical importance for next-generation quantum-enabled satellites that utilize multi-photon technology as opposed to single-photon technology.

Satellite-based quantum cryptography has already been demonstrated using discrete variable technology. Nonetheless, there is great interest in using weak coherent pulses to perform quantum key distribution (QKD) in the continuous variable (CV) paradigm. In this work, we study the feasibility of performing coherent-state CV-QKD via the satellite-to-ground channel. We use numerical methods to simulate atmospheric turbulence and compare the results with ground-based experimental data so as to confirm the validity of our approach. We find the results obtained from the numerical simulations agree well with the experimental data and represent an improvement over the state-of-the-art analytical models. Using the simulation results we then derive QKD key rates and find that useful non-zero key rates can be found over a limited range of zenith angles. Determination of QKD key rates using experimentally validated simulations of low-zenith-angle atmospheric channels represents an important step towards proving the feasibility of real-world satellite-to-Earth CV-QKD.

Vehicles moving at high speed in Vehicular Ad Hoc Networks (VANETs) may change the network topology arbitrarily. The mobility patterns followed by the vehicles in VANETs play an important role in the scalability performance of routing protocols and can be classified into mobility models, each of which is defined by their own unique features. In this work, we investigate the impact of three important mobility models on the scalability performance of the well-known Hybrid Location-Aided Routing (HLAR) protocol that has been enhanced by the inclusion of a location verification step. The location verification utilises any available sensor data to verify GPS positions reported by the vehicles and is embedded in a stand-alone Location Verification System (LVS). Our results show that despite the enhanced security features embedded, the routing protocol investigated will remain scalable under realistic mobility patterns. Our work is important for many applications within VANETs, including the efficient dissemination of network-wide location sensor data needed for future vehicle applications.

In this work we investigate, for the first time, the bandwidth cost of a Location Verification System (LVS) on the control overhead of a well-known geographical routing protocol for vehicular networks. In our new system, at the onset of a new connection, all vehicles in the selected route report their locations using the Global Positioning System (GPS) to an LVS which is installed at a base station. The LVS verifies the reported locations and broadcasts the decisions to all vehicles in the transmission range. Via local updating of all routing tables, all vehicles are notified of the decisions. This results in a geographical routing protocol that is significantly more secure compared to one with no LVS in place. Specifically, the likelihood of a malicious vehicle causing significant degradation to the network routing via location spoofing is significantly reduced. We demonstrate that the additional control overhead needed for this more secure routing protocol is manageable, and the protocol remains scalable provided the likelihood of a vehicle being malicious is below a determined value. Our work is of significance in that proves for the first time that advanced location verification techniques can be seamlessly integrated into the hybrid routing protocols embedded in vehicular networks.

Non-Gaussian operations have been studied intensively in recent years due to their ability to enhance the entanglement of quantum states. However, most previous studies on such operations are carried out in a single-mode setting, even though in reality any quantum state contains multi-mode components in frequency space. Whilst there have been general frameworks developed for multi-mode photon subtraction (PS) and photon addition (PA), an important gap exists in that no framework has thus far been developed for multi-mode photon catalysis (PC). In this work we close that gap. We then apply our newly developed PC framework to the problem of continuous variable (CV) entanglement distribution via quantum-enabled satellites. Due to the high pulse rate envisioned for such systems, multi-mode effects will be to the fore in space-based CV deployments. After determining the entanglement distribution possible via multi-mode PC, we then compare our results with the entanglement distribution possible using multi-mode PS and PA. Our results show that multi-mode PC carried out at the transmitter is the superior non-Gaussian operation for certain regions of the parameter space. The size of this region is highly dependent on the squeezing of the initial state. When carried out at the receiver, multi-mode PC is again found to be the superior non-Gaussian operation for certain regions of the parameter space. In this latter region, the region size is more dependent on the channel loss. Our new results should prove valuable for next-generation deployments of CV quantum-enabled satellites.

Hybrid entanglement swapping supports the teleportation of any arbitrary states, regardless of whether the quantum information in the state is encoded in Discrete Variables (DV) or Continuous Variables (CV). In this work, we study the CV teleportation channel created between two ground receivers via direct lossy-distribution from a low-Earth-orbit (LEO) satellite. Such a flexible teleportation protocol has the potential to interconnect a global array of quantum-enabled devices regardless of the different intrinsic technology upon which the devices are built. However, past studies of hybrid entanglement swapping have not accounted for channel transmission loss. Here we derive the general framework for teleporting an arbitrary input mode over a lossy CV teleportation channel. We investigate the specific case where the input modes are part of DV states entangled in the photon number basis, then identify the optimal teleportation strategy. Our results show that, relative to DV photon-number entanglement sourced directly from the satellite, there are circumstances where our teleported DV states retain higher entanglement quality. We discuss the implications of our new results in the context of generating a global network of ultra-secure communications between different quantum-enabled devices which possess line-of-sight connections to LEO satellites. Specifically, we illustrate the impact the teleportation process has on the key rates from a Quantum Key Distribution protocol.

Location information claimed by devices will play an ever-increasing role in future wireless networks such as wireless vehicular networks, 5G, and the Internet of Things (IoT). Against this background, the verification of such claimed location information will be an issue of growing importance. A formal information-theoretic Location Verification System (LVS) can address this issue to some extent, but such a system usually operates within the limits of idealistic assumptions on a-priori information on the proportions of genuine and malicious users in the field. In this work, we address this critical limitation by using a Neural Network (NN) showing how such a NN based LVS is capable of efficiently functioning even when the proportions of genuine and malicious users are completely unknown a-priori. We demonstrate the improved performance of this new form of LVS based on Time of Arrival measurements from multiple verifying base stations within the context of vehicular networks, quantifying how our NN-LVS outperforms the stand-alone information-theoretic LVS in a range of anticipated real-world conditions. We also show the efficient performance for the NN-LVS when the users' signals have added Non-Line-of-Sight (NLoS) bias in them. This new LVS can be applied to a range of location-centric applications within the domain of the IoT.

Satellite-based quantum communications enable a bright future for global-scale information security. However, the spin angular momentum of light, currently used in many mainstream quantum communication systems, only allows for quantum encoding in a two-dimensional Hilbert space. The orbital angular momentum (OAM) of light, on the other hand, enables quantum encoding in higher-dimensional Hilbert spaces, opening up new opportunities for high-capacity quantum communications. Due to its turbulence-induced decoherence effects, however, the atmospheric channel may limit the practical usage of OAM. In order to determine whether OAM is useful for satellite-based quantum communications, we numerically investigate the detection likelihoods for OAM states that traverse satellite-to-ground channels. We show that the use of OAM through such channels is in fact feasible. We use our new results to then investigate design specifications that could improve OAM detection - particularly the use of advanced adaptive optics techniques. Finally, we discuss how our work provides new insights into future implementations of space-based OAM systems within the context of quantum communications.

Quantum signal processing invokes the injection of abstract quantum mechanical frameworks into classical signal processing problems. In this work we apply this idea to the notion of optimal likelihood ratio tests within the context of the location verification problem. We first draw parallels with quantum mechanical measurements and the notion of generalized likelihood ratio measurements. As we show, these quite different measurement frameworks are mathematically similar since both can be described in the language of projections into subspaces - the projections removing the nuisance parameters of the underlying system in the latter case. We then show how the imposition of an `artificial' mathematical constraint, borrowed from a similar constraint imposed on quantum mechanics by the uncertainty principle, is likely to assist in machine-learning solutions of the location verification problem - such solutions being more useful in real-world deployments.

Quantum Key Distribution (QKD) via satellite offers up the possibility of unconditionally secure communications on a global scale. Increasing the secret key rate in such systems, via photonic engineering at the source, is a topic of much ongoing research. In this work we investigate the use of photon-added states and photon-subtracted states, derived from two mode squeezed vacuum states, as examples of such photonic engineering. Specifically, we determine which engineered-photonic state provides for better QKD performance when implemented over channels connecting terrestrial receivers with Low-Earth-Orbit satellites. We quantify the impact the number of photons that are added or subtracted has, and highlight the role played by the adopted model for atmospheric turbulence and loss on the predicted key rates. Our results are presented in terms of the complexity of deployment used, with the simplest deployments ignoring any estimate of the channel, and the more sophisticated deployments involving a feedback loop that is used to optimize the key rate for each channel estimation. The optimal quantum state is identified for each deployment scenario investigated.

Terahertz (THz) communication is a topic of much research in the context of high-capacity next-generation wireless networks. Quantum communication is also a topic of intensive research, most recently in the context of space-based deployments. In this work we explore the use of THz frequencies as a means to achieve quantum communication within a constellation of micro-satellites in Low-Earth-Orbit (LEO). Quantum communication between the micro-satellite constellation and high-altitude terrestrial stations is also investigated. Our work demonstrates that THz quantum entanglement distribution and THz quantum key distribution are viable deployment options in the micro-satellite context. We discuss how such deployment opens up the possibility for simpler integration of global quantum and wireless networks. The possibility of using THz frequencies for quantumradar applications in the context of LEO deployments is briefly discussed.

The work reported here utilizes the best aspects of information theory and deep-learning concepts so as to provide, for the first time, a solution for a real-world location verification system (LVS) in the context of vehicular networks. it is well established that global positioning system coordinates supplied by vehicles will be a vital component of such emerging networks. This supplied location information, if erroneous and not verified, can seriously degrade the overall system performance and lead to significant safety issues. A number of location verification protocols and systems have been developed to address this important problem but all have operational constraints and performance limitations due to their requirement for ideal static channel conditions and assumed threat models. In this article, we remove such limitations by designing a neural-network-based LVS (NN-LVS) that can accommodate a priori unknown channel conditions and unknown threat models. Under most channel conditions, the NN-LVS shows a performance improvement of 50%, or more, relative to other LVSs. We also derive a new information-theoretic bound on the total error for an LVS and show how this new bound allows for a useful tradeoff in learning-time versus verification-performance for the NN-LVS. We demonstrate an improved performance for the NN-LVS within the context of vehicular networks using time of arrival measurements of the vehicles' transmitted signals measured at multiple verifying base stations. The work reported here, we believe, paves the way to the actual deployment in real-world conditions of LVSs for emerging vehicular networks.

Quantum Key Distribution (QKD) has been regarded as a novel approach to establish a secure communication between two legitimate partners. With the recent success of space based experimental QKD systems, researchers are now focussing on implementing more practical and efficient QKD systems that meet the challenges faced in space-based implementations. One pressing problem is the need for efficient and easy to implement reconciliation schemes for practical QKD systems. Rate-adaptive schemes based on LDPC codes constitute an appealing implementation of the key reconciliation process since they cover the entire range of the channel parameter space with a limited set of pre-defined Mother codes. In this paper, we investigate in detail some rate- adaptive reconciliation schemes based on LDPC codes, illustrating how their performance compares to other set-ups in which fixed-rate non- adaptive LDPC codes optimised for different channel conditions are adopted. In particular, the impact rate-adaptive codes have on decoding complexity, and subsequently the overall secure key throughput, is quantified through full blown simulations of an entanglement-based version of the QKD protocol within the context of an entanglement source onboard a satellite. Our work highlights that even though rate adaptive schemes schemes for QKD reconciliation appear ideal for future space-based implementations of single- photon QKD, identification of ideal Mother codes for such schemes remains to be resolved.

In this work we explore the security of secret keys generated via the electromagnetic reciprocity of the wireless fading channel. Identifying a new sophisticated colluding attack, we explore the information-theoretic-security for such keys in the presence of an all-powerful adversary constrained only by the laws of quantum mechanics. Specifically, we calculate the reduction in the conditional mutual information between transmitter and receiver that can occur when an adversary with unlimited computational and communication resources places directional antenna interceptors at chosen locations. Such locations, in principal, can be arbitrarily far from the intended receiver yet still influence the secret key rate. We show how, in principal, the key rate can be driven to zero. We then investigate how assumed limitations on an adversary's knowledge of transceiver positions can potentially restore some level of information-theoretic security. Finally, we compare our new results with the secret key rates anticipated from quantum-technology implementations that are deployed in next generation wireless networks under the assumption of an all-powerful adversary.

In this work we analyze the distribution of quantum entanglement over communication channels in the millimeter-wave regime. The motivation for such a study is the possibility for next- generation wireless networks (beyond 5G) to accommodate such a distribution directly - without the need to integrate additional optical communication hardware into the transceivers. Future wireless communication systems are bound to require some level of quantum communications capability. We find that direct quantum- entanglement distribution in the millimeter-wave regime is indeed possible, but that its implementation will be very demanding from both a system-design perspective and a channel requirement perspective.

In this work we analyse the structure of highly- entangled multimode squeezed states, such as those generated by broadband pulses undergoing type-II parametric down-conversion (PDC). Such down-conversion has previously been touted as a natural and efficient means of cluster-state generation, and therefore a viable future pathway to quantum computation. We first detail how broadband PDC processes lead directly to a series of orthogonal supermodes that are linear combinations of the original frequency modes. We then calculate the total squeezing of the multimode entangled states when they are assumed to be measured by an ideal homodyne detection in which all supermodes of the states are detected by an optimally shaped local oscillator (LO) pulse. For comparison, squeezing of the same entangled states are calculated when measured by a lower- complexity homodyne detection scheme that exploits an unshaped LO pulse. Such calculations illustrate the cost, in the context of squeezing, of moving from higher complexity (harder to implement) homodyne detection to lower-complexity (easier- to-implement) homodyne detection. Finally, by studying the degradation in squeezing of the supermodes under photonic loss, multimode entangled state evolution through an attenuation channel is determined. The results reported here push us towards a fuller understanding of the real-world transfer of cluster-states when they take the form of highly-entangled multimode states in frequency space.

In this work we investigate the effectiveness of continuous-variable (CV) entangled states, transferred through high-loss atmospheric channels, as a means of viable quantum key distribution (QKD) between terrestrial stations and low-Earth orbit (LEO) satellites. In particular, we investigate the role played by the Gaussian CV states as compared to non-Gaussian states. We find that beam-wandering induced atmospheric losses results in QKD performance levels that are in general quite different from those found in fixed-attenuation channels. For example, circumstances can be found where no QKD is viable at some fixed loss in fiber but is viable at the same mean loss in fading channels. We also find that, in some circumstances, the QKD relative performance of Gaussian and non-Gaussian states can in atmospheric channels be the reverse of that found in fixed-attenuation channels. These findings show that the nature of the atmospheric channel can have a large impact on the QKD performance. Our results should prove useful for emerging global quantum communications that use LEO satellites as communication relays.

In this work we introduce the concept of quantum geo-encryption - a protocol that invokes direct quantum encryption of messages coupled to quantum location monitoring of the intended receiver. By obfuscating the quantum information required by both the decrypting process and the location verification process, a communication channel is created in which the encrypted data can only be decrypted at a specific geographic locale. Classical wireless communications can be invoked to unlock the quantum encryption process thereby allowing for any deployment scenario regardless of the channel conditions. Quantum geo-encryption can also be used to realize quantum computing instructions that can only be implemented at a specific location, and allow for a specified geographical data-route through a distributed network. The allowed decryption region can be limited to a region determined by the location error bounds and classical information theory. Here we consider the operational aspects of quantum geo-encryption in generic Rician channels, demonstrating that the likelihood of a successful spoofing attack can be driven to zero as the allowed decrypting region expands. The work introduced here resolves a long-standing quest to directly deliver information which can only be decrypted at a given location free of assumptions on the physical security of a receiver.

We propose a new location-based beamforming (LBB) scheme for wiretap channels, where a multi-antenna source communicates with a single-antenna legitimate receiver in the presence of a multi-antenna eavesdropper. We assume that all channels are in a Rician fading environment, the channel state information from the legitimate receiver is perfectly known at the source, and that the only information on the eavesdropper available at the source is her location. We first describe how the optimal beamforming vector that minimizes the secrecy outage probability of the system is obtained, illustrating its dependence on the eavesdropper’s location. We then derive an easy-to-compute expression for the secrecy outage probability when our proposed LBB scheme is adopted. We also consider the positive impact a friendly jammer can have on our beamforming solution, showing how the path to optimality remains the same. Finally, we investigate the impact of location uncertainty on the secrecy outage probability, showing how our solution can still allow for secrecy even when the source only has a noisy estimate of the eavesdropper’s location. This paper demonstrates how a multi-antenna array, operating in the most general channel conditions and most likely system setup, can be configured rapidly in the field so as to deliver an optimal physical layer security solution.

We design a new relay-aided secure transmission scheme, in which a source communicates with a destination through a trusted decode-and-forward relay in the presence of spatially random-distributed non-colluding eavesdroppers. We consider a general antenna configuration, in which the source, relay, destination, and eavesdroppers are equipped with multiple antennas. We assume that both the source and the relay transmit artificial noise signals in addition to information signals. We also assume that the source and the relay adopt different codebooks, and that the transmitted signals from the source and relay are not jointly processed at each eavesdropper. We first derive a closed-form expression for the transmission outage probability and a new expression for the secrecy outage probability. Notably, these expressions are valid for an arbitrary number of antennas at the source, relay, and destination. We then derive simple yet valuable expressions for the asymptotic transmission outage probability and the asymptotic secrecy outage probability, which reveal the secrecy performance when the number of antennas at the source grows sufficiently large. Using our expressions, we quantify a practical performance metric, namely, the secrecy throughput, under a secrecy outage probability constraint. We further determine the system and channel parameters that maximize the secrecy throughput, leading to analytical security solutions suitable for real-world deployment.

We propose a new optimal location-based beamforming (LBB) scheme for the wiretap channel, where both the main channel and the eavesdropper's channel are subject to Rician fading. In our LBB scheme, the two key inputs are the location of the legitimate receiver and the location of the potential eavesdropper. Notably, our scheme does not require any channel state information of the main channel or the eavesdropper's channel being available at the transmitter. This makes our scheme easy to deploy in a host of application settings in which the location inputs are known. Our beamforming solution assumes a multiple-antenna transmitter and a multiple-antenna eavesdropper, and its aim is to maximize the physical layer security of the channel. To obtain our solution, we first derive the secrecy outage probability of the LBB scheme in an easy-to-evaluate expression that is valid for arbitrary real values of the Rician K-factors of the main channel and the eavesdropper's channel. Using this expression, we then determine the location-based beamformer solution that minimizes the secrecy outage probability. To assess the usefulness of our new scheme, and to quantify the value of the location information to physical layer security, we compare our scheme to other schemes, some of which do not utilize any location information. Our new beamformer solution provides optimal physical layer security for a wide range of location-based applications.

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.

In this work we analyze a quantum communication scheme for entanglement-based continuous variable quantum key distribution between two ground stations. Communication occurs via a satellite over two independent atmospheric fading channels dominated by turbulence-induced beam wander. In this scheme the engineering complexity remains largely on the ground transceivers, with the satellite acting simply as a reflector. We show how the use of a highly selective post-selection strategy may lead to a useful quantum key generation rate for this system. This work represents the first quantitative assessment of continuous variable quantum key rates in the pragmatic scenario of reflection off low-earth-orbit satellites.

In this work we examine the performance of a Location Spoofing Detection System (LSDS) for vehicular networks in the realistic setting of Rician fading channels. In the LSDS, an authorized Base Station (BS) equipped with multiple antennas utilizes channel observations to identify a malicious vehicle, also equipped with multiple antennas, that is spoofing its location. After deriving the optimal transmit power and the optimal directional beamformer of a potentially malicious vehicle, robust theoretical analysis and detailed simulations are conducted in order to determine the impact of key system parameters on the LSDS performance. Our analysis shows how LSDS performance increases as the Rician K-factor of the channel between the BS and legitimate vehicles increases, or as the number of antennas at the BS or legitimate vehicle increases. We also obtain the counter-intuitive result that the malicious vehicle's optimal number of antennas conditioned on its optimal directional beamformer is equal to the legitimate vehicle's number of antennas. The results we provide here are important for the verification of location information reported in IEEE 1609.2 safety messages.

Location information has been shown to be useful for a wide variety of applications in wireless networks, while its role in physical layer security has so far drawn little attention. In this work, we propose a new location-based secure transmission scheme for wiretap channels, where the accurate locations of the sources, destinations and any other authorized transceivers are known, but only an estimate of the eavesdropper's location is available. We outline how such an estimate of the eavesdropper's location can still allow for quantitative assessment of key security metrics. To provide focus, we describe how optimization of the effective secrecy throughput of a relay wiretap channel is obtained in our scheme, and investigate in detail the impact of the location uncertainty on the system performance. The work reported here provides insights into the design of new location-based physical layer security schemes in which the only information available on an eavesdropper is a noisy estimate of her location.

We analyze and optimize the secrecy performance of artificial noise (AN) in multi-input single-output wiretap channels with multiple antennas at the transmitter and a single antenna at the receiver and the eavesdropper. We consider two transmission schemes: 1) an on-off transmission scheme with a constant secrecy rate for all transmission periods, and 2) an adaptive transmission scheme with a varying secrecy rate during each transmission period. For the on-off transmission scheme, an easy-to-compute expression is derived for the hybrid outage probability, which allows us to evaluate the transmission outage probability and the secrecy outage probability. For the adaptive transmission scheme where transmission outage does not occur, we derive a closed-form expression for the secrecy outage probability. Using these expressions, we determine the optimal power allocation between the information signal and the AN signal and also determine the optimal secrecy rate such that the effective secrecy throughput is maximized for both transmission schemes. We show that the maximum effective secrecy throughput requires more power to be allocated to the AN signal when the quality of the transmitter-receiver channel or the transmitter-eavesdropper channel improves. We also show that both transmission schemes achieve a higher maximum effective secrecy throughput while incurring a lower secrecy outage probability than existing schemes.

We propose a new framework for determining the wiretap code rates of single-input-single-output multiantenna eavesdropper wiretap channels when the capacity of the eavesdropper's channel is not available at the transmitter. In our framework, we introduce the effective secrecy throughput (EST) as a new performance metric that explicitly captures the two key features of wiretap channels, namely, reliability and secrecy. Notably, the EST measures the average rate of the confidential information transmitted from the transmitter to the intended receiver without being eavesdropped on. We provide easy-to-implement methods to determine the wiretap code rates for two transmission schemes: 1) adaptive transmission scheme in which the capacity of the main channel is available at the transmitter and 2) fixed-rate transmission scheme in which the capacity of the main channel is not available at the transmitter. Such determinations are further extended into an absolute-passive eavesdropping scenario where even the average signal-to-noise ratio of the eavesdropper's channel is not available at the transmitter. Notably, our solutions for the wiretap code rates do not require us to set reliability or secrecy constraints for the transmission within wiretap channels.

In relay assisted wireless communications, the multi-source, single relay and single destination system (an M-1-1 system) has garnered significant interest, due to the increased demand for higher network throughput and connectivity. Previously, power allocation at the relay in M-1-1 systems have assumed availability of instantaneous channel state information (CSI), which is rather idealistic. In this paper we consider an M-1-1 Decode-and-Forward (DF), Full-Duplex, orthogonal frequency division multiple access (OFDMA) based relay system with statistical-CSI and analyze the achievable rate R of such a system. We show how R can only be maximized by numerical power allocation schemes which have high-complexity of order O(M3). By introducing a rational approximation in the achievable rate analysis, we develop a low-complexity power allocation scheme at the relay that can obtain a system achievable rate very close to the maximum R. Most importantly, we show that the complexity of our power allocation scheme is of the order O(M log M). Our power allocation scheme is suitable for a multiuser relay system, where the priority is to maximize the system throughput. The work we present in this paper will be of value to the design and implementation of real-time multi-user relay systems operating under realistic channel conditions.

We propose two beamforming schemes supporting multi-stream transmission in multi-input multi-output multi-antenna eavesdropper wiretap channels with imperfect channel state information of the eavesdropper. We first propose a generalized eigenvalue decomposition (GEVD)-based beamforming scheme by designing the beamforming matrix and determining the power allocation matrix. In particular, we determine a general power allocation matrix for arbitrary signal-to-noise ratio (SNR) and a simplified power allocation matrix for high SNR. We demonstrate that our GEVD-based beamforming scheme delivers a higher achievable secrecy rate than the existing beamforming schemes in the medium and high SNR regime. We also demonstrate that the simplified power allocation matrix delivers the same achievable secrecy rate as the general power allocation matrix at high SNRs. We then propose an easy-to-construct EVD-based beamforming scheme which reduces signal processing cost and eliminates power allocation. We demonstrate that our EVD-based beamforming scheme delivers a higher secrecy rate than the GEVD-based beamforming scheme and the existing beamforming schemes in the low SNR regime.

We propose a new framework for optimizing the target secrecy rate for SISOME wiretap channels when the instantaneous capacity of the eavesdropper's channel is not available at the transmitter. In our framework we introduce the effective secrecy throughput, a new optimization metric that implicitly captures the two key features of wiretap channels, namely, reliability and secrecy. We derive target secrecy rates which maximize the effective secrecy throughput for two different schemes, an on-off transmission scheme and an adaptive transmission scheme. Our analysis demonstrates that the adaptive transmission scheme outperforms the on-off transmission scheme and that the difference in the effective secrecy throughput between the two schemes increases with the SNR of the main channel. The work reported here solves the important problem of how to optimally set the target secrecy rate of wiretap codes for an important class of channels. Notably, our solution for the target secrecy rate does not require us to set a priori any reliability or secrecy constraint for the channel.

Given the growing role of location information in emerging wireless networks, the authentication of such information is becoming increasingly important. Perhaps the most obvious example of this is in network-based Intelligent Transport Systems (ITS), where authentication of location information is of critical importance to the safety and security of the system users. In this work, we investigate for the first time the performance limits of a Location Verification System (LVS) in the realistic setting of correlated log-normal fading channels. Utilizing the wireless signal strengths measured by authorized base stations as the input location information metrics, robust theoretical analysis and detailed simulations are used in order to determine the impact of key parameter settings on the LVS performance. Specifically, we show how the performance of an LVS depends on the correlation of the shadowing, and illustrate how such correlation can in fact lead to significant location-authentication performance improvement in some circumstances. The impact on performance of utilizing differential signal strengths, rather than raw received signal strengths, at the LVS is also analyzed. In a wider context, the work reported on here provides new insights into the performance of location authentication in channel settings that are anticipated for a wide range of emerging wireless networks.

We analyze and optimize the use of artificial noise (AN) for a predefined secrecy rate in wiretap channels with a multi-antenna transmitter, a single-antenna receiver, and a single-antenna eavesdropper. We derive a new closed-form expression for the secrecy outage probability that is independent of the channel realization. Based on this expression, we first optimize the power allocation between the information signal and the AN signal such that the secrecy outage probability is minimized. We then optimize jointly the power allocation and secrecy rate such that the secrecy throughput is maximized. As demonstrated by our analysis, the minimum secrecy outage probability requires more power to be allocated to the AN signal when the quality of the main channel quality or the eavesdropper's channel improves.

We propose linear precoding with power control to achieve confidential broadcasting in multi-input-multi-output multiuser networks such that the base station (BS) with Ntantennas securely broadcasts messages to K users with Nrantennas each. We focus on the practical non-homogeneous scenario where the distances between the BS and the users are not equal. We first design a linear precoder based on regularized channel inversion, and derive new channel-independent expressions for the achievable secrecy sum-rate in the large system regime. With the aid of these expressions, we examine the impact of user dispersion, Nt, and K on the secrecy sum-rate. We then propose a power reduction strategy and power allocation algorithms to increase the secrecy sum-rate. We demonstrate that our power reduction strategy increases the secrecy sum-rate at high signal-to-noise ratios. We also show the secrecy sum-rate advantage of optimal power allocation over equal power allocation. Furthermore, we consider channel correlation and derive an easy-to-compute expression for the secrecy sum-rate to examine its impact on the secrecy performance.

In this work, we propose a new transmit antenna selection (TAS) scheme which examines the trade-off between feedback overhead and secrecy performance in multiple-input multiple-output wiretap channels. Our new scheme is carried out in two steps. First, the transmitter selects the first two strongest antennas to maximize the instantaneous signal-to-noise ratio (SNR) of the transmitter-receiver channel. Second, Alamouti coding is employed at the selected antennas in order to perform secure data transmission. When equal power is applied to the selected antennas, we refer to our new scheme as TAS-Alamouti. To provide valuable insights into TAS-Alamouti, we derive new closed-form expressions for the secrecy performance metrics. In terms of these metrics, we show how in a Rayleigh fading channel that our TAS-Alamouti scheme outperforms the traditional single TAS scheme conditioned on the SNR of the transmitter-receiver channel being larger than a specific value. We show how in some antenna configurations no additional feedback, relative to single TAS, is required in order to realize such performance enhancements. Furthermore, we show how optimal power allocation (OPA) across the selected antennas at the transmitter leads to a new scheme, which we refer to as TAS-Alamouti-OPA, that outperforms single TAS unconditionally. Relative to TAS-Alamouti, TAS-Alamouti-OPA requires only one additional feedback bit.

In this paper, we propose a new beamforming scheme for multi-input multi-output (MIMO) Gaussian wiretap channels where the channel state information (CSI) from the eavesdropper is imperfectly known to the transmitter. A stochastic model is constructed to characterize the imperfect CSI of the eavesdropper, in which a factor 0 ≤ τ ≤ 1 is introduced to describe the degree of the available eavesdropper's channel knowledge at the transmitter. When τ varies from 0 to 1, the eavesdropper's channel knowledge available at the transmitter ranges from statistically known to perfectly known. We design the proposed beamforming scheme by maximizing a lower bound on the achievable secrecy rate. We first demonstrate that our scheme achieves higher secrecy rate than the existing eigenvalue decomposition-based beamforming scheme which is optimal for τ = 0. We then demonstrate that the proposed scheme achieves higher secrecy rate than the existing generalized eigenvalue decomposition-based beamforming scheme which is optimal for τ = 1. Furthermore, we derive tight approximations for the proposed beamforming scheme in the high signal-to-noise ratio (SNR) regime and the low SNR regime. The accuracy of these approximations is validated via numerical results. Finally, we demonstrate that our proposed scheme achieves almost the same secrecy performance as the optimal beamforming solution that is obtained through numerical search.

This paper proposes a new transmit antenna selection (TAS) scheme which provides enhanced physical layer security in multiple-input multiple-output (MIMO) wiretap channels. The practical passive eavesdropping scenario we consider is where channel state information (CSI) from the eavesdropper is not available at the transmitter. Our new scheme is carried out in two steps. First, the transmitter selects the two strongest antennas based on the feedback from the receiver, which maximizes the instantaneous signal-to-noise ratio (SNR) of the transmitter-receiver channel. Second, the Alamouti scheme is employed at the selected antennas in order to perform data transmission. At the receiver and the eavesdropper, maximal-ratio combining is applied in order to exploit the multiple antennas. We derive a new closed-form expression for the secrecy outage probability in non-identical Rayleigh fading, and using this result, we then present the probability of non-zero secrecy capacity in closed form and the ε-outage secrecy capacity in numerical form. We demonstrate that our proposed TAS-Alamouti scheme offers lower secrecy outage probability than a single TAS scheme when the SNR of the transmitter-receiver channel is above a specific value.

In this work we have developed a new method to construct general quantum stabilizer codes of variable block size by adopting the notion of a difference set. The proposed method comprises an efficient way to obtain the difference set, and from that set the construction of a quantum stabilizer code, which we refer to as a DSS (Difference Set Stabilizer) code. Our efficient method to generate the difference set requires no computer search, instead only a single parameter is required to generate the set.

We investigate the use of rate-compatible lowdensity parity-check (RC-LDPC) codes as part of a soft decodeand- forward (SDF) protocol over the half-duplex relay channel. We propose a new methodology to design the degree distribution of the RC-LDPC codes with a lower triangular parity-check matrix, enabling the additional parity bits to be linearly and systematically encoded at the relay. Our proposed methodology introduces the concept of a K-layer doping matrix to represent the structure of a lower triangular parity-check matrix. As a result of our methodology, the asymptotic performance of RC-LDPC codes can be analyzed and predicted using the multi-edge-type density evolution. Then, we derive the soft-re-encoding of the additional parity symbols at the relay using our designed RCLDPC codes. Moreover, we propose a novel method, which we refer to as soft fading, to compute the log-likelihood ratio (LLR) of the received signal at the destination for the SDF protocol. We demonstrate that our proposed soft fading method outperforms the best known method in the literature by up to 0.7 dB in terms of BER performance. Finally, we derive a new bound for the power multiplication factor at the relay, which limits the amount of soft-errors forwarded by the relay to the destination. The BER performance of our new RC-LDPC codes improves significantly once the power multiplication factor at the relay satisfies this bound.

As location-based applications become ubiquitous in emerging wireless networks, a reliable Location Verification System (LVS) will be of growing importance. In this paper we propose, for the first time, a rigorous information-theoretic framework for an LVS. The theoretical framework we develop illustrates how the threshold used in the detection of a spoofed location can be optimized in terms of the mutual information between the input and output data of the LVS. In order to verify the legitimacy of our analytical framework we have carried out detailed numerical simulations. Our simulations mimic the practical scenario where a system deployed using our framework must make a binary Yes/No “malicious decision” to each snapshot of the signal strength values obtained by base stations. The comparison between simulation and analysis shows excellent agreement. Our optimized LVS framework provides a defence against location spoofing attacks in emerging wireless networks such as those envisioned for Intelligent Transport Systems, where verification of location information is of paramount importance.

In relay networks, we may not possess the ability to tune all system parameters in order to achieve the maximum achievable rate promised by theoretical analysis. This paper investigates the pragmatic issue of sub-optimal relay networks, where we can only optimize either on the time allocation, or on the power allocation. Our study concludes that optimizing on the power allocation, or on the time allocation, can achieve more than 95% of the relaying gain relative to the optimization of both time and power simultaneously. To produce the result, we derive the closed-form expression of the optimum power allocation for the source and relay that obtains the achievable rate of the half-duplex relay channel with fixed (equal) time allocation. We also derive the closed-form expression of the optimum time allocation between the source and relay transmission that obtains the achievable rate of the half-duplex relay channel with fixed power allocation. We demonstrate that for small SNR, where relaying is most advantageous, almost all relaying gain can be achieved by only optimizing the power allocation. Conversely, optimizing the time allocation alone is sufficient to achieve most of the relaying gain when the system's SNR is large. This result is important for pragmatic designs of emerging relay communication systems.

This paper studies the problem of determining the optimum degree distribution for distributed LDPC codes in two-way relay channels. Based on the framework of multi-edge type (MET) LDPC codes, we propose a methodology to asymptotically optimize the code's ensemble when different segments within the distributed codeword have been transmitted through different channels and experience different SNRs. An average noise threshold is formulated to compute the convergence threshold of the distributed LDPC codes under density evolution and acts as the performance gap between the optimized distributed codes and the theoretical limit. We demonstrate that the optimized distributed LDPC code using our proposed method performs asymptotically within a fraction of a dB away from the theoretical limit.

We study the design of network codes for M-source, N-relay wireless networks over slow fading channels. Specifically, vector-wise binary field network coding (BFNC) schemes are proposed. In the construction of our BFNC schemes, we utilize a diversity achieving criterion which can be expressed in terms of the linear independence of quasi-cyclic matrices. Our codes can be implemented with low-complexity encoders at the relays as only binary operations are used. Meanwhile at the destination, for small code lengths, ML decoder can be applied. For large code lengths, we propose a modified BP decoder with low decoding complexity. From analysis and simulations, we show that our proposed BFNC schemes can achieve full diversity for the ML decoder, as well as full diversity for the modified BP decoder we propose for large block lengths. Our simulations also show that our proposed BFNC schemes achieve a higher coding gain relative to previous network coding schemes.

This paper proposes a new soft decode-and-forward (SDF) protocol using LDPC codes in the half-duplex relay channels. In order for the encoding of the additional parity-check symbols at the relay to be linear and systematic, we introduce a structured rate-compatible (RC) LDPC code. We then develop the soft-decoding and soft-re-encoding algorithms for the proposed RC-LDPC code, which allows the relay to forward soft messages to the destination when the relay fails to decode the source's message. Furthermore, we propose a new method, which we refer to as soft fading, to compute the log-likelihood ratio (LLR) of the received signal at the destination for the SDF protocol. We show that our proposed method performs better when compared to a previous reported method in literature.

Vehicular ad hoc networks (VANETs) are highly mobile wireless networks that are designed to support vehicular safety, traffic monitoring, and other applications. Within VANETs, vehicle mobility will cause the communication links between vehicles to be broken frequently. Such link failures require a direct response from the routing protocols, leading to an excessive increase in the routing control overhead and a degradation in network scalability. In this work we investigate how such high link failure rates impact the scalability and performance of a recently proposed hybrid location-based routing protocol, HLAR. A novel feature of HLAR is its ability to possess effective routing strategies which are a spatial function of the location information quality. We show that even in the presence of high link failure rates, HLAR shows high scalability performance, making it an ideal candidate for future routing within emerging intelligent transportation systems. The optimality of HLAR and the impact of location error on its scalability is also discussed.

In this work we develop a new tracking-based wireless intrusion detection algorithm that allows for the identification of malicious vehicle network users who are not at their appropriate locations. Based on a particle filter implementation and detection thresholds set by Cramer-Rao lower bounds we show how our tracking-verification algorithm is capable of verifying any reported positions within a reasonable time frame of order 30 seconds. We explicitly determine how the performance of the algorithm, as measured by detection and false positive rates, is influenced by the amount of tracking information collected. The results presented here are important for implementation of safe vehicular networks where only users at the expected locations can access and participate in the network communications.

We investigate LDPC code design for a multi-source single-relay system, with uniform phase-fading Gaussian channels. We specifically consider the asymmetric channels for multiple sources, where the channel condition for each source in the system is different. We focus on LDPC code design when network coding (NC) at the relay is utilized. For the asymmetric sources, we firstly introduce a binary field rate splitting theorem which is used to discover an appropriate NC scheme at the relay. This NC scheme is then used to determine the achievable rates of each source and the whole system. These steps assist us in the development of the main contribution of our work, namely, network coded multi-edge type LDPC (NCMET-LDPC) code design. Extrinsic mutual information transfer (EXIT) chart analysis is utilized to optimize the code profiles. Our results demonstrate two key points. (1) From the whole system point of view, our NCMET-LDPC codes achieve better error performance than that of LDPC codes designed for the system without NC. (2) As a consequence of the binary field rate-splitting theorem, our NCMET-LDPC codes also guarantee better error performance of each asymmetric source. The improvement in error performance is typically about 0.3 dB relative to a system without NC.

A key design issue in routing for wireless ad hoc networks is scalability. By scalability we mean the ability of the network to support increases in node numbers without significantly degrading network performance. In this work we introduce a new hybrid wireless routing protocol specifically designed to address this issue. Our new protocol combines features of reactive routing with location-based geographic routing, in such a manner so as to efficiently use all the location information available. The protocol is designed to gracefully exit to reactive routing as the location information degrades. Another aspect of our protocol is that it can be spatially dependent - meaning different physical areas of the network can be using quite different routing procedures at the same epoch. That our protocol can dramatically increase scalability can be measured via the routing control overhead which we show, through analysis and simulation, to be significantly reduced relative to current protocols. This is particularly so when a large fraction of nodes possess up-to-date accurate location information. Our new protocol operates even though nodes can be mobile, and it provides an enhanced, yet pragmatic, location-enabled solution that can be deployed in all emerging wireless ad hoc networks.

Recently it has been shown how the use of quantum entanglement can lead to the creation of real-time communication channels whose viability can be made location dependent. Such functionality leads to new security paradigms that are not possible in classical communication networks. Key to these new security paradigms are quantum protocols that can unconditionally determine that a receiver is in fact at an a priori assigned location. A limiting factor of such quantum protocols will be the decoherence of states held in quantum memory. Here we investigate the performance of quantum location verification protocols under decoherence effects. More specifically, we address the issue of how decoherence impacts the verification using N = 2 qubits entangled as Bell states, as compared to N >; 2 qubits entangled as GHZ states. We study the original quantum location verification protocol, as well as a variant protocol, introduced here, which utilizes teleportation. We find that the performance of quantum location verification is in fact similar for Bell states and some N >; 2 GHZ states, even though quantum decoherence degrades larger-qubit entanglements faster. Our results are important for the design and implementation of location-dependent communications in emerging quantum networks.

In this work we introduce a new routing protocol for Wireless Ad hoc Networks specifically designed for VoIP. Based on modifications to standard geographic routing protocols, our new protocol is designed to deliver two key attributes that hitherto are not simultaneously present in any other single ad hoc routing protocol. Specifically, our protocol maximizes VoIP capacity whilst remaining scalable. Prior to this work, state-of-the-art routing protocols which best address the issue of maximizing VoIP capacity in ad hoc networks can be considered to be those based on the Expected Transmission Count (ETX) metric. As such, the performance benefits of our protocol relative to protocols using ETX are detailed. In the context of VoIP, the most important performance improvement for our protocol relative to ETX protocols, is an up-to factor of two improvement in VoIP capacity for anticipated ad hoc network scenarios. Although designed primarily for wireless VoIP, our protocol can be readily adapted to any real-time application deployed over wireless architectures which contain an ad hoc component.

Mobile location estimation via the use of a spatially-dependent signal database is of growing importance. However, this location estimation method usually requires an a priori experimental measurement campaign. To overcome this drawback we propose here a new method of location estimation via the real-time creation of a virtual signal database. The virtual database is created on-demand by an optimized ray-tracing algorithm embedded on the user device. We explore how the creation of the virtual database can be optimized so as to determine the required location at the lowest time-to-fix. Our results demonstrate that in current 3G cellular mobile systems, and using current mobile phone hardware, sub-50 m accuracy can be achieved in less than a few seconds. Our work shows that accurate real-time location estimation via user embedded ray tracing is now viable and can lead to more accurate solutions in a range of circumstances.

In this work, we introduce a new Markov model for the distributed coordination function (DCF) protocol which accurately predicts the network throughput of 802.11 networks under realistic traffic load. Specifically, we provide an improved treatment of the post backoff, the probability of immediate transmission after DIFS, and the probability of having a new packet for transmission after the post backoff. A key feature of our model is the ability to predict the optimal network throughput and the network capacity (in terms of number of stations with acceptable QoS). Knowledge of the network capacity aids to network planning and QoS for multimedia applications. Another feature is that the model converges to a saturated model when the number of stations becomes large. Based on this feature, we introduce a new method to estimate the lower bound of network capacity.

Location tracking in wireless networks has many applications, including enhanced network performance. In this report we investigate a new SIP-based architecture for wireless networks that allows for the fusion of different positioning technologies (GPS and Particle Filters). The architecture is specifically designed for outdoor users possessing intermittent GPS availability, a characteristic commonly found in real outdoor wireless networks. The architecture also includes the novel use of a user profile database in the particle filter algorithm, which we show can lead to factor two gains in position accuracy. Implementation of our architecture is described, and simulations of its performance in the multi-user setting are provided. We show how the architecture's effect on network operations is minimal. The architecture we propose here, builds on our already deployed particle filter tracking algorithms in wireless networks.

In this work we report on a wireless intrusion detection system based on the use of position tracking for location verification. Using optimal error bounds developed for extended Kalman filters as the comparison basis, we show how wireless signal strength measurements can be used to reliably detect intruders whose true position tracks are far removed from their claimed tracks. We show how the system is immune to malicious attacks that adjust transmitted signal strengths in attempts to circumvent the intrusion detection algorithms. We compare our results with earlier work that utilized static position information as a means for intrusion detection, showing how verification errors determined via tracking can be an order of magnitude smaller. Contrary to the static case, we also show how position verification via tracking is viable in the case where only one access point is within range of the mobile device. Our work outlines the theoretical underpinning of position verification via nonlinear tracking, in addition to providing detailed Monte Carlo simulations of the verification performance.

Location tracking in wireless networks has many applications, including enhanced network performance. In this work we investigate the experimental use of "particle filter" techniques as applied to the mobile device tracking problem in WiFi networks. Particle filters are well suited to the non-Gaussian and biased error conditions characteristic of signals found in most WiFi networks, as well as allowing for seamless data fusion with intermittent GPS availability and prior map information. Our experimental results show that particle filter tracking can indeed deliver significant performance gains. In some physical regions of our test area, factors of three improvement in location accuracy - relative to optimal unfiltered WiFi positioning - is found. We show how these gains are achieved at a relatively small particle number of 300, meaning real-time implementation of the particle filter can be easily achieved.

The ability to accurately locate devices in wireless communication networks is of growing interest. Many of the position algorithms deployed in such networks are completely, or partially, based on received signal strength (RSS) measurements. However, the role played by nuisance parameters in RSS-based positioning algorithms has been largely overlooked. In this work we focus on a key nuisance parameter of such algorithms, the propagation path loss exponent of the log-normal fading model. We show how this nuisance parameter can have a significant impact on the location accuracy of RSS-based algorithms which assume log-normal fading, and how geometrical distributions of the reference nodes can be found where the error in the location estimate becomes unbounded. The analysis and results reported here help identify algorithms and geometric configurations of the reference nodes where an a priori measurement campaign related to the propagation model would be important

The secure and efficient deployment of enhanced emergency services (E911) is a critical component of emerging wireless VoIP applications. In this work we detail a new scheme for a secure and energy efficient E911 service that can be deployed over wireless networks. The scheme involves the intermittent use of embedded GPS on a VoIP phone in an optimally energy efficient manner. GPS acquisition is only requested when the network's positioning system dictates its necessity. The mathematical techniques deployed in this system naturally lend themselves to an authentication procedure based on location verification. Here we focus on WiFi networks, and show how our scheme can lead to substantial energy savings, and robust location verification, even in the presence of significant biases on the WiFi positioning metrics.

In this work we quantify the usefulness of particle filters applied to the problem of mobile device tracking in WiFi networks, under the assumption of log-normal fading. Our principal aim was to determine if a real-time deployment of a particle filter was possible while still providing factor two gains in the prediction performance relative to a stand-alone optimal Wi-Fi positioning algorithm. We conclude that the required gains are achieved in our adopted filter algorithm when the particle number is set to the relatively small number of 300, meaning that a real-time deployment is possible. In addition, we quantify the performance gain of the particle filter when intermittent GPS information is available to the mobile device. We propose the fusion of the GPS information be implemented as a renormalization of the particle cloud. Finally, we probe the limits of the filter performance under biased-error distributions. Our simulations show that tracking of people, vehicles and robotic devices in an outdoor Wi-Fi network, where non-linear and nonGaussian conditions exist, can be significantly enhanced by the pragmatic real-time particle filter algorithm presented here.

Differential VoIP services for Wi-Fi will greatly enhance the experience of mobile wireless users who have requested premium service for their VoIP applications. In this work we present detailed simulations of modified 802.11b protocols that purport to provide differential service to wireless VoIP users. The modified protocol we identify as providing the best differential service whilst maintaining the least starvation to best effort users - involves a modified minimum contention window, combined with a modified back-off time. A detailed differential VoIP capacity analysis of this modified protocol is presented. Also, we introduce the notion of a "priority service QoS map" for wireless VoIP. Such a map is a two dimensional representation of the VoIP QoS metrics available to a mobile priority VoIP user, as a function of location. We outline how our VoIP capacity analysis is used to construct a priority service QoS map, and discuss the practical benefits of relaying such maps to mobile users of wireless VoIP

In this work we investigate position-based enhancements to indoor Wi-Fi network security. Specifically, we investigate whether received signal strength (RSS) measurements can identify attempts at network access by malicious nodes exterior to an authorized network perimeter. We assume the malicious nodes will spoof their received or transmitted power-levels in attempts to circumvent standard position-based security techniques. We outline why residual analysis of the RSS measurements cannot robustly identify illegal network access requests. However, we show that by referencing the residual RSS analysis to a "claimed position," interior to the authorized perimeter, a robust position-based verification system for secure network access can be developed.

We describe a method for merging the concepts of GPS positioning and intrinsic wireless network positioning into a high-level wireless security system. Specifically, we outline how the wireless network can assign a quantitative security level associated with the probability that a wireless network node is in a false location. We demonstrate the operational limits of the system using unbiased Cramer-Rao bounds in an ad hoc network. We also outline several additions that can be added to the security system, when position locations are influenced by other factors. This new location-based method allows for a tamper-proof security technique designed to complement existing encryption technologies.