Marc Lichtman

PHY-Layer Resiliency in OFDM Communications: A Tutorial

This tutorial paper addresses the physical layer security concerns and resiliency of Orthogonal Frequency Division Multiplexing (OFDM) communications; the de facto air-interface of most modern wireless broadband standards including 3GPP Long Term Evolution (LTE) and WiMAX. The paper starts with a brief introduction to the OFDM waveform and then reviews the robustness of the existing OFDM waveform in the presence of noise, multipath fading, and interference. The paper then moves on to build comprehensive adversarial models against OFDM waveforms. Robustness of OFDM is first investigated under AWGN noise and noise-like jamming attack scenarios, then under uncorrelated yet colored interferences from modulated sources (both intentional and unintentional). Finally, the paper explores some of the more recent developments in the field of energy efficient correlated jamming attacks that can disrupt communication severely by exploiting the knowledge of the target waveform structure. Potential countermeasures against such jamming attacks are presented, in an attempt to make a robust and resilient OFDM waveform.

Vulnerability of LTE to hostile interference

LTE is well on its way to becoming the primary cellular standard, due to its performance and low cost. Over the next decade we will become dependent on LTE, which is why we must ensure it is secure and available when we need it. Unfortunately, like any wireless technology, disruption through radio jamming is possible. This paper investigates the extent to which LTE is vulnerable to intentional jamming, by analyzing the components of the LTE downlink and uplink signals. The LTE physical layer consists of several physical channels and signals, most of which are vital to the operation of the link. By taking into account the density of these physical channels and signals with respect to the entire frame, as well as the modulation and coding schemes involved, we come up with a series of vulnerability metrics in the form of jammer to signal ratios. The “weakest links” of the LTE signals are then identified, and used to establish the overall vulnerability of LTE to hostile interference.

Practical Issues for Spectrum Management With Cognitive Radios

The policy of permanently assigning a frequency band to a single application has led to extremely low utilization of the available spectrum. Cognitive radio, with its ability to be both intelligent and frequency agile, is thought to be one of the prime contenders to provide the necessary capabilities needed for dynamic spectrum access systems. With this in mind, this paper discusses the practical issues inherent to the deployment of spectrum management systems utilizing cognitive radios.

LTE/LTE-a jamming, spoofing, and sniffing: threat assessment and mitigation

LTE is currently being proposed for use in a nationwide wireless broadband public safety network in the United States as well as for other critical applications where reliable communication is essential for safety. Unfortunately, like any wireless technology, disruption of these networks is possible through radio jamming. This article investigates the extent to which LTE is vulnerable to RF jamming, spoofing, and sniffing, and assesses different physical layer threats that could affect next-generation critical communication networks. In addition, we examine how sniffing the LTE broadcast messages can aid an adversary in an attack. The weakest links of LTE are identified and used to establish an overall threat assessment. Lastly, we provide a survey of LTE jamming and spoofing mitigation techniques that have been proposed in the open literature.

Security Challenges with LTE-Advanced Systems and Military Spectrum

LTE is universally recognized as the world-wide standard for next-generation mobile broadband services. Operating LTE in military spectrum has recently been proposed for a variety of use cases. First, due to the lack of available commercial spectrum, commercial operators are seeking to leverage underutilized military bands to offer improved commercial service. Second, given the ability for LTE to operate at high data rates in multipath environments, the technology could provide the military with more resilient communications in tactical environments. However, these proposed use cases for LTE are non-standard and certain military requirements cannot be immediately supported within the scope of the 3GPP standards. Emerging features within LTE-Advanced provide the initial building blocks for supporting LTE operations in heterogeneous environments that may include hostile interferers. LTE operation in military bands may be possible through the use of distributed spectrum sensing, spectrum allocation databases, carrier aggregation with non-military bands, and real-time radio resource management to cope with interference.

Analysis and Mitigation of Interference to the LTE Physical Control Format Indicator Channel

In LTE, the Physical Control Format Indicator Channel (PCFICH) is a downlink control channel that indicates the number of OFDM symbols used by the primary downlink control channel in each sub frame. Even though the PCFICH only carries two bits of control information, it is essential to the operation of LTE. Since the PCFICH is a vital physical channel that only occupies a small fraction of the downlink signal, it acts as a weak link in terms of vulnerability to targeted interference. Due to recent interest in using LTE for military and public safety applications, it would be beneficial to better understand this vulnerability. This paper investigates the performance of the PCFICH under various harsh wireless conditions and proposes strategies to prevent interference against the PCFICH from causing link degradation.

If At First You Don't Succeed, Ganbare, Ganbare, Ganbare

RésuméAu Japon il est courant de penser que tout le monde peut réussir; il suffit de faire preuve de la plus tenace persévérance et rien n’est impossible. Cette étude a fait une enquête sur les reflexions, d’enfants japonais, de parents et d’éducateurs au sujet du phénomène culturel du “ganbare” (continuité) que imprègne la société japonaise à tous les niveaux. Des enfants qui fréquentent une école maternelle axée sur l’organisation en groupes, leurs éducateurs et des specialistes universitaires de l’éducation préscolaire ont été interviewes. Les mères des enfants ont répondu par écrit à des questions sur leur conception de la persistance “ganbare”. Les résultats de cette étude a indiqué que cette continuité était interpretée par les enfants comme un encouragement heureux et positif. Les adultes utilisent spontanément ce mot comme l’expression d’un encouragement pour enseigner aux enfants l’importance de la persévérance dans leur vie, bien que certains adultes ont émis l’hypothèse qu’une trop forte accentuation de la persévérance auprès des enfants pourrait créer chez eux une trop forte pression. L’étude a révélé que l’introduction de la continuité chez les enfants est de première importance dans las culture japonaise.ResumenEn Japón, es una creencia común que cualquiera puede tener éxito, que sólo le falta a uno persistir con extrema aplicación, y así cualquier cosa puede ser realizada. Este estudio investiga ideas de niños, padres y educadores japoneses respecto al fenómeno cultural de “ganbare” (persistencia) lo cual penetra la sociedad japonesa en todos los niveles. Niños que atienden un grupo orientado en kindergarten, sus padres, sus maestros y instructores de colegio en temprana educación preescolar fueron entrevistos. Las madres de los niños respondieron a preguntas escritas respecto a su concepto de “ganbare”. Los resultados de este estudio indicaron que “ganbare” fue interpretada por los niños como alentamiento feliz y positivo. Los adultos espontáneamente usan esta palabra como una expresión de alentamiento para enseñsar a los niños la importancia de persistencia en sus vidas, aunque algunos adultos especulan que un sobre énfasis de persistencia dirigido hacia los niños podria crear alguna presión sobre ellos. Este estudio sugiere que poner persistencia en niños es de primera importancia en la cultura japonesa.

Anomaly-based intrusion detection of protocol-aware jamming

In this paper, we apply the existing framework of anomaly-based intrusion detection (ABID) to the problem of detecting protocol-aware jammers. These types of jammers target MAC or NET layer control messages in an attempt to increase jamming effectiveness and remain harder to detect. ABID systems detect activities that deviate significantly from the normal profile. Signature recognition is based on storing signatures of known intrusion scenarios, and detecting the presence of these signatures in real-time. By choosing a suitable set of features, a high probability of correct detection can be achieved. Our proposed detection strategy involves tracking the statistics of signal-to-noise ratio (SNR) and packet type (critical or non-critical). An alternative strategy that only requires information about packet loss is also provided. Through simulation, we show that these types of jammers can be detected in a large portion of scenarios.

Automatic Modulation Classification under IQ Imbalance Using Supervised Learning

The process of classifying digital modulation schemes given IQ imbalance at the transmitter or receiver is studied using fourth and sixth order cumulants as features. Various methods of supervised learning are proposed in order to mitigate the effect of IQ imbalance at the receiver, including K-Nearest Neighbors (k-NN), Support Vector Machine (SVM), and decision tree learning. The impact of IQ imbalance at the transmitter is also observed, as well as the effect of IQ imbalance on the theoretical cumulant values for each modulation scheme. Through simulation, it is shown that supervised learning approaches are effective at compensating for the IQ imbalances that can occur at the receiver.

FSK-Based Reactive Jammer Piggybacking

The complexity and sophistication of communications jamming will continue to increase over time. The traditional approach to jammer mitigation is to harden radios, often sacrificing communications performance for more advanced jamming protection. To provide an escape from this trend, we propose a jammer exploitation strategy in which the communications system causes an enemy reactive jammer to act as an unwitting relay. This can lead to an improvement in communications as a result of the jamming attack itself. The strategy proposed in this letter revolves around using a frequency-shift keying waveform that is tuned in such a way to exploit the jammer’s behavior. We derive the channel capacity when using the waveform along with practical coding, and provide numerical results to gain insight.