Wireless secrecy is essential for communication confidentiality, health privacy, public safety, information superiority, and economic advantage in the modern information society. Contemporary security systems are based on cryptographic primitives and can be complemented by techniques that exploit the intrinsic properties of a wireless environment. This paper develops a foundation for design and analysis of wireless networks with secrecy provided by intrinsic properties such as node spatial distribution, wireless propagation medium, and aggregate network interference. We further propose strategies that mitigate eavesdropping capabilities, and we quantify their benefits in terms of network secrecy metrics. This research provides insights into the essence of wireless network intrinsic secrecy and offers a new perspective on the role of network interference in communication confidentiality.

At present, operators address the explosive growth of mobile data demand by densification of the cellular network so as to reduce the transmitter-receiver distance and to achieve higher spectral efficiency. Due to such network densification and the intense proliferation of wireless devices, modern wireless networks are interference-limited, which motivates the use of interference mitigation and coordination techniques. In this work, we develop a statistical framework to evaluate the performance of multi-tier heterogeneous networks with successive interference cancellation (SIC) capabilities, accounting for the computational complexity of the cancellation scheme and relevant network related parameters such as random location of the access points (APs) and mobile users, and the characteristics of the wireless propagation channel. We explicitly model the consecutive events of canceling interferers and we derive the success probability to cancel the n-th strongest signal and to decode the signal of interest after n cancellations. When users are connected to the AP which provides the maximum average received signal power, the analysis indicates that the performance gains of SIC diminish quickly with n and the benefits are modest for realistic values of the signal-to-interference ration (SIR). We extend the statistical model to include several association policies where distinct gains of SIC are expected: (i) maximum instantaneous SIR association, (ii) minimum load association, and (iii) range expansion. Numerical results show the effectiveness of SIC for the considered association policies. This work deepens the understanding of SIC by defining the achievable gains for different association policies in multi-tier heterogeneous networks.

In this paper the capability of a cognitive radio network to discover available frequency channels in the spectrum licensed to a primary user (e.g., digital TV) is analyzed. We rely on cooperative sensing where fusion of individual sensing outcomes is based on the r-out-of-k decision rule. The study is carried out assuming the point of view of a tagged network of cognitive devices that is surrounded by other uncoordinated transmitters competing for accessing the same portion of the spectrum. The contributions of this work are the following. First, the introduction of a three-state model of the wireless channel. Second, modeling the sensing process by means of the general framework provided by urn occupancy problems accessed in non-uniform fashion. Third, the evaluation of the number of available channels in the presence of interference limiting spectrum availability. Finally, the proposal of a cognitive protocol to mitigate the interference. Results are given for a specific case of interest where all networks are supposed ECMA-392 standard compliant.

Secrecy is a key enabler for various wireless applications in which distributed confidential information is communicated in a multilevel network from sources to destinations. Network secrecy can be accomplished by exploiting the intrinsic properties of multilevel wireless networks (MWNs). This paper introduces the concept of distributed network secrecy (DNS) and develops a framework for design and analysis of confidential MWNs. Our framework accounts for node distribution, network configuration, propagation medium, and communication protocol. This research offers the foundation of DNS and quantifies the impact of network configuration on DNS for self-organizing MWNs.

The demand of communication confidentiality in wireless network is rapidly increasing. The level of confidentiality can be enhanced by physical layer techniques exploiting intrinsic properties of a wireless network. We develop a framework for design and analysis of wireless network with secrecy that accounts for node distribution, propagation medium, and intentional interference. The framework enables the quantification of how intentional interference generated via legitimate network resources engineering mitigates the capability of the eavesdropping network. This research provides insight on the opportunistic use of legitimate network resources for enhancing network secrecy.

Heterogeneous networks consisting of a macrocell tier and a small cell tier are considered an attractive solution to cope with the fierce increase of mobile traffic demand. Nevertheless, a massive deployment of small cell access points (SAPs) leads also to a considerable increase in energy consumption. Motivated by growing environmental awareness and the high price of energy, the design of energy efficient wireless systems for both macrocells and small cells becomes crucial. In this work, we analyze the trade-off between traffic offloading from the macrocell and the energy consumption of the small cell. Using tools from stochastic geometry, we define the user detection performance of the SAP and derive the small cell capacity accounting for the uncertainties associated with the random position of the user, the propagation channel, activity of the users, and the aggregate network interference. The proposed framework yields design guidelines for energy efficient small cells.

Heterogeneous networks consisting of a macrocell tier and a small cell tier are foreseen as one of the solutions to meet the ever increasing mobile data demand. Since a massive deployment of small cell access points (SAPs) leads also to a considerable increase in energy consumption, the energy efficient design of those SAPs is crucial. Sleep mode techniques are a promising strategy to reduce the energy consumption, yet they require cognitive capabilities to detect the presence of a macrocell user. In this work, we define a fundamental limit on the interference density that allows robust user detection. Beyond this limit, which we call the interference wall, an energy efficient SAP design is impossible. In addition, we elucidate the relation between energy efficiency and sensing time using large deviations theory.

Secrecy is essential for a variety of emerging wireless applications where distributed confidential information is communicated in a multilevel network from sources to destinations. Network secrecy can be accomplished by exploiting the intrinsic properties of multilevel wireless networks (MWN). This paper introduces the concept of distributed network secrecy (DNS) and develops a framework for the design and analysis of secure, reliable, and efficient MWNs. Our framework accounts for node spatial distribution, multilevel cluster formation, propagation medium, communication protocol, and energy consumption. This research provides a foundation for DNS and offers a new perspective on the relationship between DNS and network lifetime.

Heterogeneous networks using a mix of macrocells and small cells are foreseen as one of the solutions to meet the ever increasing mobile traffic demand. Nevertheless, a massive deployment of small cell access points (SAPs) leads also to a considerable increase in energy consumption. Spurred by growing environmental awareness and the high price of energy, it is crucial to design energy efficient wireless systems for both macrocells and small cells. In this work, we evaluate a distributed sleep-mode strategy for cognitive SAPs and we analyze the trade-off between traffic offloading from the macrocell and the energy consumption of the small cells. Using tools from stochastic geometry, we define the user discovery performance of the SAP and derive the uplink capacity of the small cells located in the Voronoi cell of a macrocell base station, accounting for the uncertainties associated with random position, density, user activity, propagation channel, network interference generated by uncoordinated activity, and the sensing scheme. In addition, we define a fundamental limit on the interference density that allows robust detection and we elucidate the relation between energy efficiency and sensing time using large deviations theory. Through the formulation of several optimization problems, we propose a framework that yields design guidelines for energy efficient small cell networks.

Upper layer wireless security relies on the computational intractability assumption for solving certain number-theoretic problems. These methods can be complemented by techniques that exploit, at the physical layer, the intrinsic properties of the wireless channel and interference. This paper considers communications with intrinsic secrecy in the presence of spatially distributed nodes, namely legitimate users, eavesdroppers, and interferers. We characterize the role of aggregate interference on intrinsic network secrecy, providing insights into regimes in which interference is beneficial for network secrecy.

In this paper we compare impulse-radio ultra wideband (IR-UWB) physical layer related medium access control (MAC) protocols, Slotted Aloha and optional preamble mode six of IEEE 802.15.4-2011, and preamble sense multiple access when the events of false alarm and miss-detection are introduced. Furthermore, a generalized multi-slot channel access scheme is proposed that can, with a proper selection of slots, represent any of the above MAC protocols. As a result of the generalization, an efficiency factor is then proposed, which allows for the protocols to be compared efficiently. At present, the challenge of designing a random access protocol suitable for IR-UWB is however, not completely solved. The generalized multi-slot model and efficiency factor help in determining the optimal number of slots, given certain preamble lengths and channel conditions. While there does not exist a globally optimal solution for all combinations of preamble length and signal-to-noise ratio, this paper shows that dividing the maximum MAC protocol data unit from 4 to 8 equally-sized slots, each with their own preamble, provides the best solution in all but the extreme cases.

Wireless secrecy is becoming crucial in many commercial and governmental sectors. In this paper, the secrecy capacity of a wireless channel is analyzed in the presence of intentional network interference for denial of eavesdropping capability (DEC). We propose two different DEC strategies employing the closest interferer and the multiple interferers. We show the impact of the network interference on average and outage of secrecy capacity for the two DEC strategies with and without eavesdropper's countermeasures to create a region of interference neutralization. This work provides essentials for understanding how to increase wireless secrecy using intentional network interference.

Opportunistic spectrum access creates the opening of under-utilized portions of the licensed spectrum for reuse, provided that the transmissions of secondary radios do not cause harmful interference to primary users. Therefore, it is important to characterize the effect of cognitive network interference due to such secondary spectrum reuse. In this paper, we show how a new statistical model for aggregate interference of a cognitive network, which accounts for the sensing procedure, secondary spatial reuse protocol, and environment-dependent conditions such as path loss, shadowing, and channel fading can be used to assess the aggregate interference in specific environments. Specifically, we consider scenarios like power controlled primary network, secondary network with interference avoidance mechanism, and non-circular coverage region.

Opportunistic spectrum access creates the opening of under-utilized portions of the licensed spectrum for reuse, provided that the transmissions of secondary radios do not cause harmful interference to primary users. Such a system would require secondary users to be cognitive-they must accurately detect and rapidly react to varying spectrum usage. Therefore, it is important to characterize the effect of cognitive network interference due to such secondary spectrum reuse. In this paper, we propose a new statistical model for aggregate interference of a cognitive network, which accounts for the sensing procedure, secondary spatial reuse protocol, and environment-dependent conditions such as path loss, shadowing, and channel fading. We first derive the characteristic function and cumulants of the cognitive network interference at a primary user. Using the theory of truncated-stable distributions, we then develop the statistical model for the cognitive network interference. We further extend this model to include the effect of power control and demonstrate the use of our model in evaluating the system performance of cognitive networks. Numerical results show the effectiveness of our model for capturing the statistical behavior of the cognitive network interference. This work provides essential understanding of interference for successful deployment of future cognitive networks.

In this paper, we propose a new statistical interference model for cognitive network based on the amplitude aggregate interference, which accounts for the parameters related to the sensing procedure, spatial reuse protocol employed by secondary users, and environment dependent conditions like channel fading and shadowing. We derive the characteristic function and the nth cumulant of the cognitive network interference on the primary user. By using the theory of truncated-stable distribution, we show how we can approximate the cognitive network interference analytically. We further show how to apply our model to derive system performance measure such as bit error probability in the presence of cognitive network interference. Moreover, this work can serve to bring additional understanding of cognitive network interference for successful deployment of cognitive networks in the future.

There has been an emerging interest in non-coherent ultra-wide bandwidth (UWB) communications, particularly for low-data rate applications because of its low-complexity and low-power consumption. However, the presence of narrowband (NB) interference severely degrades the communication performance since the energy of the interfering signals is also collected by the receiver. In this paper, we compare the performance of two non-coherent UWB receiver structures - the autocorrelation receiver (AcR) and the energy detection receiver (EDR) - in terms of the bit error probability (BEP). The AcR is based on the transmitted reference signaling with binary pulse amplitude modulation, while the EDR is based on the binary pulse position modulation. We analyze the BEPs for these two non-coherent systems in a multipath fading channel, both in the absence and presence of NB interference. We consider two cases: a) single NB interferer, where the interfering node is located at a fixed distance from the receiver, and b) multiple NB interferers, where the interfering nodes with the same carrier frequency are scattered according to a spatial Poisson process. Our framework is simple enough to enable a tractable analysis and provide insights that are of value in the design of practical UWB systems subject to interference.

This paper analyzes and compares the performance of non-coherent and differential receivers under realistic channels for both synchronization and communication. The well-known error probabilities are reminded and the receiver operating characteristics (ROC) are calculated. It also provides some recommendations to system designers, proposes and discusses critical concepts for a low complexity implementation of the proposed schemes, in compliance with the ranging functionality

Energy detection receiver is one of the most interesting solution for non-coherent low data rate and low complexity UWB systems. In order to keep the complexity of the receiver structure low the same approach should be used also for ToA (time of arrival) estimation purposes. In this paper, after showing that a generalized maximum likelihood estimator for ToA is a sliding window energy based estimator, an improved version of it that uses partial channel state information is proposed in order to improve the accuracy of the estimation overcoming the hardware limitation related to the minimum integration time of the integration circuit and to the available number of integrators

The paper presents the architecture of a low power, low complexity ultra wideband (UWB) transceiver circuit. The circuit is designed for low data rate, low cost applications with built in location and tracking capabilities. The system is based on a non-coherent architecture which enables the receiver to be extremely simple and largely insensitive to the transmitted pulse shape. The circuit presented contains the oscillator, the transmitter, the receiver and the baseband digital signal processing (DSP) block. The oscillator contains the quartz oscillator, a delay locked-loop (DLL) and edge combiner for clock multiplication to generate a 528 MHz timing signal for pulse generation. The transmitter contains a second DLL to fix the delay of the UWB pulse, the UWB pulse generator and antenna. The transmitted UWB pulse is presented. The receiver contains low noise amplifier, variable gain amplifier, squaring circuits, integrators for energy collection, 4 bit analogue-to-digital converters (ADC), digital control logic, integrator and gain selection logic block and detection/bit decision block. The circuits are designed in a 0.35 /spl mu/m Si-Ge BiCMOS process from Austria Microsystems.

Spreading factor (SF) in code-division multiple-access (CDMA) systems depends on the data rate of the user, and is, therefore, unknown a priori for a communication receiver. In this letter, the blind SF-detection problem in an additive white Gaussian noise channel is studied, and a novel one-step autocorrelation-based SF detector is proposed. Three decision rules are derived to find simple and robust SF detectors for practical communication receivers. Performance of the detectors is studied and compared with the optimal detector via Monte Carlo computer simulations. The autocorrelation-based SF detector appears to give performance close to the optimal detector, assuming perfect knowledge of signal-to-noise ratio (SNR). It is also found to be significantly more robust to SNR estimation errors than the optimal detector.