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This article proposes a new, nondestructive method for detecting recycled integrated circuits (ICs) using the backscattering side-channel analysis (BSCA). In particular, this article explains the impact that aging has on the backscattering side-channel signal and validates the findings through simulations. Then, a new detection algorithm based on singular value decomposition for distinguishing unaged and aged ICs from their backscattered measurements is presented. The proposed method is then validated in a series of experiments. The results show that the proposed method is effective in detecting recycled ICs after being aged for a small fraction of the IC’s lifetime (roughly 66 days). The experiments also demonstrate the impact that circuit size and complexity have on detection accuracy. [ABSTRACT FROM AUTHOR]

Recent proliferation of CPS and IoT devices has led to an increasing demand for analyzing performance and timing of event-driven computational activity, especially interrupts and exceptions. However, these devices typically lack hardware resources, power, and system-software infrastructure for profiling/monitoring such events. Even when feasible, the profiling/monitoring activity itself can perturb the performance and timing of the timing-sensitive activity to be analyzed, therefore producing misleading results. Thus, we present Primer, a novel approach for profiling interrupts. Primer leverages existing unintentional (side-channel) electromagnetic emanations of the profiled/monitored device to identify its asynchronous execution (e.g., interrupt handlers). Primer leaves the monitored system (and its behavior) completely unchanged, requires no system resources or support, and introduces neither overheads nor perturbation in the monitored system. We validate Primer by analyzing signals that correspond to five different types of interrupts on an IoT device (ARM Cortex-M), achieving 99.5% accuracy (with no false positives), and on an MSP430 microcontroller-based device with even better accuracy. We also demonstrate the effectiveness of Primer in analyzing page faults and network interrupts when executing real-world applications on a more sophisticated embedded device (ARM Cortex-A8), and show that the results provided by Primer can provide useful insights about an application's interaction with the system's virtual memory and network-oriented services. [ABSTRACT FROM AUTHOR]

The emergence of cyber-physical systems (CPS) and internet of things (IoT) devices impose significant security and privacy concerns that necessitate robust monitoring and malware detection systems. This paper proposes PITEM, a framework for instruction-level monitoring and malware detection using electromagnetic (EM) side-channels. PITEM identifies instruction types with similar EM emanations using hierarchical clustering. To track all combinations of these instruction types, we generate EM signatures for all permutations of them. In testing, we predict the permutation class of testing traces by a matched-filter-like predictor. We test the performance on two devices (FPGA-based and ARM-based) with 50 MHz and 1 GHz clock frequencies. We achieve 95.67 and 87.35 percent accuracies for these devices for single execution of permutations. We note that the accuracy increases to 100 percent when permutation blocks are repeated. Furthermore, we test the limits of the system by tracking permutations of instructions of the same type. With sufficient bandwidth and number of repetitions, individual instructions can be resolved with 87.5 and 95.78 percent accuracies for these devices. The performance is evaluated for different relative signal-to-noise ratio (SNR) levels and performance is stable for relative SNR values $>15$ > 15 dB. Finally, we demonstrate PITEM's ability to detect fine-grained malware with 99.89 percent accuracy. [ABSTRACT FROM AUTHOR]

This article presents the sensing and detection of backscattered terahertz (THz) side channels unintentionally created by field-programmable gate array (FPGA) activity using a bistatic arrangement. At first, a single frequency is modulated onto a THz carrier due to the switching activity inside the FPGA and this modulated frequency is received at a distance. The effects of polarization and the receiver distance on the backscattered signal are studied and it is found that deliberately introducing a polarization mismatch between the transmitter and the receiver can improve the signal-to-noise ratio (SNR) by more than 10 dB. This allows the signal to be received at distances greater than 45 cm with SNR above 54 dB, making detection feasible at several meters away. Through the use of a near-field focuser, the properties of the side-channel signal are measured over the surface of the FPGA board with a resolution of 0.5 mm. Next, a backscatter signal at four distinct frequencies is created and detected through splitting the FPGA into four distinct modules. The relative strength of the frequencies is compared, and conclusions about the physical location and the strength of these signals originating from distinct modules are analyzed. It is found that focusing the backscatter system on certain locations on the FPGA can preferentially receive the signal from one module while filtering out the other modules. This helps isolating the signals created by various modules in an FPGA and significantly improving the effectiveness of side-channel detection techniques. [ABSTRACT FROM AUTHOR]

Objective: This paper presents a Proof-of-Concept (POC) design and implementation of a biosensing and communication system that can be used for biotelemetry in neural and Gastrointestinal (GI) applications. Methods: Our proposed system is based on backscattering from a semi-passive Radio-Frequency-Identification-Device (RFID) implemented using an Application Specific Integrated Circuit (ASIC) in which electronic switching between transistor gates in high and low states create an impedance difference, thereby effectively changing the ASIC's Radar Cross Section (RCS) and thus modulating its backscattered field. The ASIC is used in conjunction with a biosensor to measure and transmit vital signs from within the body. With this system, we conducted backscatter propagation experiments through different biological and phantom tissues (in ex-vivo and in-vitro) in the GI and neural environments. Results: Our results show that the backscattered waveforms can penetrate tissues of various compositions and thicknesses with power received at distances of up to 55 cm away from the RFID ASIC. Furthermore, results from single- and multi-bit biotelemetry measurements showed a high signal fidelity with low Bit-Error-Rate (BER) while being able to resolve varying tissue temperatures measured by the biosensor in our system. Conclusion: We realized a POC system in which on-chip transistor switching in an ASIC can be used to achieve backscatter communication and biosensing. This system is deployable in neural and GI applications. Significance: Our findings in this work will provide an important practical basis for the design and development of RFID ASIC for biosensing and biotelemetry in medical applications. [ABSTRACT FROM AUTHOR]

Presented is a new, low-cost system for locating the strongest sources of high-frequency EM side-channel emanations on PCBs. These sources indicate the best locations to monitor or mitigate the leakage. The challenges inherent in both side-channel and high-frequency measurements are addressed through careful design of the measurement and localization system. The system is time efficient, requiring only measurements taken around the edge of the device. Instead of testing specific cryptographic programs, this system focuses on identifying and then measuring the side-channel sources of the basic instructions that are commonly used by a multitude of programs on the device. The accuracy of the measurement setup was verified by comparing measurements with simulated results. The setup was then used to locate the instruction-dependent sources at 1 GHz on an field-programable gate array (FPGA) development board and an Internet-of-Things device. The 1 GHz sources are compared to previously identified sources on the same devices taken at significantly lower frequencies. The results demonstrate that the sources of the EM side channel can vary not only with the executed instruction, but also with the frequency of the side-channel signal. [ABSTRACT FROM AUTHOR]

The ubiquitous interconnectivity of electronic devices offered by Internet-of-Things (IoT) networks has been increasingly embraced in a wide range of applications. In IoT networks, threats to hardware security are often not perceived as serious, with the assumption that an attack could only be carried out at close proximity. However, in this article, we show that through electromagnetic (EM) side-channel signal leakage, operational information and program activities of IoT devices and field-programmable gate array (FPGA) modules can be garnered from approximately 200 m away in an outdoor line-of-sight (LOS) environment. We describe an extensive measurement campaign conducted to investigate the aforementioned leakage and provide propagation models that can be used to predict the power (and corresponding variation i.e., shadowing gain) of the EM side-channel signal emanation at various distances, scenarios, and environments. With a circularly polarized receiver antenna, our results show that the received power of the emanated EM side-channel (carrier) signal varies from about −61 dBm at 1 m to about −112 dBm at 200 m in the outdoor LOS environment. Furthermore, a received signal power of about −73 dBm was observed at 1 m and −88 dBm was recorded at 10 m in an indoor LOS environment. Power variation (shadowing gain) of about 3.6 and 2.0 dB was observed in the outdoor and indoor environments, respectively. This work is relevant for EM side-channel leakage countermeasure development and provides pertinent information to embedded systems and wireless network security engineers. [ABSTRACT FROM AUTHOR]

This article proposes leveraging EM side-channels to recognize/authenticate electronic components integrated onto a motherboard. By focusing on components on a motherboard, our method provides an opportunity to authenticate devices assembled by third parties. This method identifies components based on the modulated signals emanated while they are excited in a controlled manner. When testing an unknown component, the spectrum is compared to previously recorded training signatures. To improve efficiency, the size of the spectrum is reduced by projecting it into a vector space generated from training signatures. The identity of the tested component is then determined using a k-nearest neighbors algorithm. This method successfully classified memory, processor, and Ethernet transceiver components integrated on seven types of Internet-of-Things devices. Since manufacturers commonly use the same components in multiple designs, cross-type testing of motherboards is conducted. Collecting the training signatures on one motherboard and testing components from different motherboards speeds up the process and decreases the cost. Using measurements taken while exciting the components for 1 s, our method achieves a classification accuracy greater than 96 % across all components tested. These results demonstrate that this method can recognize components based on their emanations, even if the components are integrated onto completely different motherboards. [ABSTRACT FROM AUTHOR]

It has been shown that digital and/or analog characteristics of electronic devices during executing programs can create a side-channel which an attacker can exploit to extract sensitive information such as cryptographic keys. When the attacker modifies the software application to exfiltrate sensitive information through a channel, this channel is called a covert channel. In this paper, we model this covert channel as a communication channel and derive upper and lower capacity bounds. Because the covert channels are not designed to transmit information, they are exposed not only to the errors created by the transmission, but also by varying the execution time of computer activities, and/or by insertions from other activities such as interrupts, stalls, etc. Combining all of these effects, we propose to model the covert channel as an insertion channel where the transmitted sequence is a pulse amplitude modulated signal with random pulse positions. Utilizing this model, we derive capacity bounds of the covert channel with random insertion and substitution due to the noise and jitter errors, and propose a receiver design that can correctly detect the computer-activity-created signals. To illustrate the severity of leakages, we perform experiments with high clock speed devices at some distance. Further, the theoretical derivations are compared to empirical results, and show good agreement. [ABSTRACT FROM AUTHOR]

The side-channel leakage is a consequence of program execution in a computer processor, and understanding relationship between code execution and information leakage is a necessary step in estimating information leakage and its capacity limits. This paper proposes a methodology to relate program execution to electromagnetic side-channel emanations and estimates side-channel information capacity created by execution of series of instructions (e.g., a function, a procedure, or a program) in a processor. To model dependence among program instructions in a code, we propose to use Markov source model, which includes the dependencies among sequence of instructions as well as dependencies among instructions as they pass through a pipeline of the processor. The emitted electromagnetic (EM) signals during instruction executions are natural choice for the inputs into the model. To obtain the channel inputs for the proposed model, we derive a mathematical relationship between the emanated instruction signal power (ESP) and total emanated signal power while running a program. Then, we derive the leakage capacity of EM side channels created by execution of series of instructions in a processor. Finally, we provide experimental results to demonstrate that leakages could be severe and that a dedicated attacker could obtain important information. [ABSTRACT FROM AUTHOR]

This paper proposes a two dimensional (2-D) statistical channel model for Terahertz (THz) chip-to-chip wireless communication in desktop size metal enclosures. This model differs from traditional statistical channel models as it models both traveling and resonant waves that exist inside metal enclosures. Based on the cavity environment and the statistical properties of the channel inside the metal cavity, the geometrical model which describes propagation in resonant cavity as a superposition of LoS, single bounced (SB), double bounced (DB), and multi-bounced (MB) rays is proposed. Based on the geometrical model, a parametric reference model is proposed. Furthermore, the path loss model that captures signal strength variation in a resonant cavity is proposed. Frequency correlation functions (FCF) and power delay profiles (PDP) for different possible chip-to-chip communication scenarios are derived and compared with the measured ones. The results show a good agreement between the simulated and measured statistics. [ABSTRACT FROM AUTHOR]

Cyber-physical systems (CPS) are controlling many critical and sensitive aspects of our physical world while being continuously exposed to potential cyber-attacks. These systems typically have limited performance, memory, and energy reserves, which limits their ability to run existing advanced malware protection, and that, in turn, makes securing them very challenging. To tackle these problems, this paper proposes, Remote, a new robust framework to detect malware by externally observing Electromagnetic (EM) signals emitted by an electronic computing device (e.g., a microprocessor) while running a known application, in real-time and with a low detection latency, and without any a priori knowledge of the malware. Remote does not require any resources or infrastructure on, or any modifications to, the monitored system itself, which makes Remote especially suitable for malware detection on resource-constrained devices such as embedded devices, CPSs, and Internet of Things (IoT) devices where hardware and energy resources may be limited. To demonstrate the usability of Remote in real-world scenarios, we port two real-world programs (an embedded medical device and an industrial PID controller), each with a meaningful attack (a code-reuse and a code-injection attack), to four different hardware platforms. We also port shellcode-based DDoS and Ransomware attacks to five different standard applications on an embedded system. To further demonstrate the applicability of Remote to commercial CPS, we use Remote to monitor a Robotic Arm. Our results on all these different hardware platforms show that, for all attacks on each of the platforms, Remote successfully detects each instance of an attack and has $<$ < 0.1 percent false positives. We also systematically evaluate the robustness of Remote to interrupts and other system activity, to signal variation among different physical instances of the same device design, to changes over time, and to plastic enclosures and nearby electronic devices. This evaluation includes hundreds of measurements and shows that Remote achieves excellent accuracy ($<$ < 0.1 percent false positive and $>$ > 99.9 percent true positive rates) under all these conditions. We also compare Remote to prior work EDDIE and SYNDROME , and demonstrate that these prior work are unable to achieve high accuracy under these variations. [ABSTRACT FROM AUTHOR]

This article presents details about an extensive channel measurement campaign and subsequent statistical channel models for the characterization of 300 GHz channels for wireless rack-to-rack (R2R) and blade-to-blade (B2B) communications in a data center-like environment. Measurements were conducted in various scenarios such as R2R line-of-sight (LoS), R2R obstructed-LoS (OLoS), R2R reflected-non-LoS (RNLoS), R2R obstructed-RNLoS (ORNLoS), B2B RNLoS, B2B ORNLoS, and B2B LoS scenarios. In the aforementioned scenarios, we explored the impact of transmitter (Tx)/receiver (Rx) misalignment and obstructions such as cables, metal cabinets, and mesh structures on terahertz (THz) propagation, as well as feasibility of using existing metal objects as reflectors for NLoS links. For the R2R LoS scenario, an optical lens was used to extend the Tx-Rx separation distance. This led to a waveguide effect in the channels measured thereby resulting into a path loss exponent (PLE) of 1.48 with a shadowing gain of 0.7 dB. When obstructions of cables are present, ORNLoS link outperforms OLoS link with 2.5 dB lower shadowing gain and weaker multipath. Reflector in the RNLoS link has reflection coefficients very close to 1 for all incident angles. For the B2B scenario, a dual-reflector THz transceiver rack system is proposed to enable wireless links across vertically stacked servers and allow easy maintenance and repair of servers. The measured path loss closely follows the Friis values in the LoS link and in the RNLoS link with hollow vertical ground plane. When obstructions of cables are present, the ORNLoS link experiences 5–10 dB higher path loss and on average 0.25 GHz lower coherence bandwidth than the RNLoS link. The measured statistical channel properties show that the shadowing gain caused by cable clusters follows the log-normal distribution. [ABSTRACT FROM AUTHOR]

This article presents characterization of terahertz (THz) wireless channel inside a desktop size metal enclosure with the consideration of several different scenarios. Measurements indicate that both traveling wave and resonating modes exist inside the metal enclosure. Measurements for line-of-sight (LoS) propagation inside the empty metal enclosure show that the path loss significantly changes as a function of the transceiver’s height. It is found that this variation is due the resonant modes, contribution to the received power. Reflected-non-LoS (RNLoS) measurements show that for the same distance, the difference between the mean path loss measured inside the metal box and in a free space is limited to 1 dB, with traveling wave dominating the channel. This indicates that reflectors can be used as wave-guiding objects in metal enclosures. Finally, obstructed-LoS (OLoS) path loss measurements with the parallel dual in-line memory modules (DIMMs) as obstructions show the constructive/destructive effect on the waves due to multipath introduced by the parallel-plate structures. Compared to the free space scenarios, multipath is introduced by the traveling wave bouncing back and forth between the transceiver sides of the cavity, which introduces stronger fluctuations in observed pathloss and reduces the coherence bandwidth of the channel. [ABSTRACT FROM AUTHOR]

This paper presents the use of terahertz near-field focusing for backscatter side-channel detection. Near-field focusing is done by using a Cassegrain reflector configuration. The focuser is designed to produce the focused beam 28 cm away from the antenna aperture. The focusing is done in the near-field region by axially moving the subreflector from the focal point. It is observed that the subreflector position has to shift approximately 11 wavelengths along the axis to create the focus at the required location. The focused antenna gain is 46 dBi, while the 3 dB focus width and depth of the designed antenna is ~4 mm and 10 cm, respectively. It is found that the focal plane position is sensitive to the subreflector shifts and it is observed that 1 mm change in the subreflector position can shift the focal plane by ~2 cm. The simulations are compared with the measurement results of a fabricated prototype and good agreement is observed. The antenna is fabricated by using 3-D printing technology, which allows rapid prototyping. Finally, we have demonstrated the detection of backscatter side channel from the board placed at 28 cm away from the designed antenna. The received power level of the backscatter signal increases by 6 dB as compared to horn antenna. [ABSTRACT FROM AUTHOR]

This paper describes a new physical side channel, i.e., the backscattering side channel, created by transmitting a signal toward the integrated circuits (ICs), where the internal impedance changes caused by on-chip switching activity modulate the signal that is backscattered (reflected) from the IC. To demonstrate how this new side channel can be used to detect small changes in circuit impedances, we propose a new method for nondestructively detecting hardware Trojans (HTs) from outside the chip. We experimentally confirm, using measurements on one physical instance for training and nine other physical instances for testing, that the new side channel, when combined with an HT detection method, allows detection of a dormant HT in 100% of the HT-afflicted measurements for a number of different HTs while producing no false positives in HT-free measurements. Furthermore, additional experiments are conducted to compare the backscattering-based detection to one that uses the traditional EM-emanation-based side channel. These results show that backscattering-based detection outperforms the EM side channel, confirm that dormant HTs are much more difficult for detection than HTs that have been activated, and show how detection is affected by changing the HT’s size and physical location on the IC. [ABSTRACT FROM AUTHOR]

This paper proposes a novel high-gain planar antenna design that consists of conducting metallic disks suspended on air and operates at 1 GHz. The antenna is designed for receiving the unintentional electromagnetic emanations generated by one or multiple embedded, “smart” electronic systems. The antenna consists of two layers of slotted conducting metal disks suspended on air and placed above the ground plane using teflon screws. The circular disks are designed to operate in higher order ${TM}_{12}$ mode. The screws’ location is the electric field nulls along the disk radius. The upper layer is $2 \times 2$ array of slotted circular disks electromagnetically coupled by the lower identical disk which is fed directly by a single coaxial feed. The complete fabrication of the antenna is done using aluminum metal sheets and involves no use of the dielectric substrate. The antenna has a peak gain of 19 dBi with impedance bandwidth ($S_{11}\le -6$ dB) of 6.7%. The simple and cost-effective design can be easily scaled to higher frequencies. [ABSTRACT FROM AUTHOR]

This paper proposes a method for efficient identification of instruction-dependent sources on a printed circuit board (PCB) by localizing magnetic field sources from a limited number of measurements around the PCB. We first excite the processor by generating an artificial leakage signal at a specific frequency that is directly related to processor instructions. Then, we collect all three components of the magnetic field, but only at locations around the edge of the board. Furthermore, we model these magnetic field sources and then solve a forward–backward optimization problem using the model and measured data to identify the locations of the magnetic field sources, the magnitudes of the moments, and their orientations. The localization results are first verified using simulations, then tested when noise is added to the simulation results, and finally verified against measurements on field-programmable gate array (FPGA) and internet of things (IoT) development boards. The results show that the number of strong magnetic field sources on a board depends on the instructions used to excite the board. Furthermore, the results show that the proposed localization algorithm can accurately identify those sources, regardless of the frequency at which the measurements are conducted and the instruction pairs that are executed. Finally, the proposed method can significantly reduce the number of measurement points and the time needed to identify magnetic field sources on a PCB. [ABSTRACT FROM PUBLISHER]

This paper proposes a new geometry-based shallow underwater acoustic (UWA) channel model allowing for nonisovelocity ocean conditions. The fact that the isovelocity assumption does not hold in many real-world scenarios motivates the need for developing channel models for nonisovelocity UWA propagation environments. Starting from a geometrical model, we develop a stochastic channel model for a single-input single-output (SISO) vehicle-to-vehicle UWA channel assuming that the ocean surface and bottom are rough and that the speed of sound varies with depth. The effect of the nonisovelocity condition has been assessed regarding its influence on the temporal autocorrelation function, the frequency correlation function (FCF), and the power delay profile of the UWA channel model. The UWA channel model has also been validated by matching its FCF as well as the therefrom derived main characteristic quantities, such as the average delay, delay spread, and coherence bandwidth against measurement data. The proposed UWA channel model is very useful for the design and performance analysis of UWA communication systems under realistic propagation conditions. [ABSTRACT FROM PUBLISHER]

The goal of this paper is to answer how much information is “transmitted” by the execution of particular sequence of instructions in a processor. Introducing such a measure would provide quantitative guidance for designing programs and computer hardware that minimizes inadvertent (side channel) information leakage, and would also help detect parts of a program or hardware design that have unusually high leakage (i.e., were designed to function as covert channel “transmitters”). To answer this question, we propose a new method to estimate the maximum information leakage through EM signals generated by the execution of instructions in a processor. We start by deriving a mathematical relationship between electromagnetic side-channel energy of individual instructions and the measured pairwise side-channel signal power. Then, we use this measure to calculate the transition probabilities needed for estimating capacity. Finally, we propose a new method to estimate side/covert channel capacity created by the execution of instructions in a processor and illustrate our results in several computer systems. [ABSTRACT FROM PUBLISHER]

This paper presents an algorithm for finding carriers of frequency-modulated (FM) and amplitude-modulated (AM) electromagnetic (EM) emanations from computer systems. Computer systems create EM emanations across the RF spectrum making it difficult, error-prone, and time consuming to find the relatively few emanations that expose sensitive information. One of the most common and simplest mechanisms for information leakage occurs when an amplitude or a frequency of an existing strong signal (e.g., a processor or memory clock) is amplitude or frequency modulated by a system activity. If the system activity can be linked to sensitive information, this results in information leakage. We present an algorithm for automatically finding these AM and FM signals, demonstrate the algorithm's performance on several different types of processors and systems (desktop, laptop, and smartphone), and compare the results to an exhaustive manual search. We also verify that all signals identified by the algorithm can be traced to plausible unintentional modulation mechanisms to illustrate that these signals can potentially cause information leakage. This algorithm can be an important tool for system designers to quickly identify circuits that are leaking sensitive information. [ABSTRACT FROM PUBLISHER]

This paper presents characterization of 300-GHz wireless channel on a computer motherboard, where several different measurement scenarios have been considered. Results indicate that the presence of the ground plane and/or vertical parallel-plate structures in the channel introduces multipath that, if constructively superimposed, may create a path loss lower than free-space propagation path loss. In addition, it has been found that a few centimeters of vertical misalignment between the transmitter and the receiver result in a path loss greater than 5 dB. Furthermore, the results indicate that vertical components such as dual in-line memory modules with reflection coefficient close to one for all incident angles can be used to create directed non-line-of-sight (LoS) links with wide coherence bandwidth. Finally, for LoS propagation obstructed by large objects, such as a heatsink, the path-loss exponent of 1.77 is found, while the rotating fan causes periodic fading in the received power, indicating that channel equalization techniques will be needed to overcome deep fades. All these results indicate that optimal communications can be achieved by carefully positioning the antennas with respect to the motherboard layout. [ABSTRACT FROM PUBLISHER]

A 2-D geometrical propagation model for short-range device-to-device desktop communication channels at sub-terahertz (sub-THz) frequencies is proposed. Based on the geometrical model, a parametric reference model for short-range sub-THz multipath fading channels is developed. From the reference model, the corresponding frequency correlation function and the power delay profile (PDP) are derived and compared with the measured data. The results show good agreement between the measured and theoretical PDPs. Finally, a new sum-of-sinusoids-based simulation model for wideband sub-THz channels is proposed. The statistics of the reference model are verified by simulation. The results show that the simulation model is a good approximation of the reference model. [ABSTRACT FROM PUBLISHER]

This paper presents measurements and statistical characterization of 300- to 320-GHz desktop channels. The measurements are performed in line-of-sight (LoS) and non-LoS (NLoS) environments. From the large set of LoS measured data, the parameters for the single-slope path-loss model with shadowing are devised. The results show that the path-loss exponent is around 1.9 and that the variations due to shadowing are similar across different frequencies and different bandwidths. Furthermore, the impact of different materials on the path loss is studied in the NLoS environment. The results show that metal objects in the propagation path cause multiple strong reflections, leading to a higher path loss. Furthermore, the statistical analysis of multipath propagation is performed. The root-mean-square (RMS) delay spread, the mean excess delay, the maximum excess delay, and the coherence bandwidth for LoS and NLoS environments are calculated. The results show that the mean excess delay and RMS delay spread increase with distance and that the RMS delay spread in the desktop terahertz channel is much smaller than that in typical indoor ultrawideband channels. In addition, the power delay profiles for LoS and NLoS environments are analyzed. The results show that strong reflections from the transmitter and receiver electronics are present in both LoS and NLoS environments. Finally, the statistical analysis of the measured signal amplitude in LoS and NLoS environments is performed. For both LoS and NLoS propagation environments, it is found that the lognormal distribution provides the best fit. [ABSTRACT FROM PUBLISHER]

This paper presents measurements and characterization of D-band indoor channels. The measurements are performed in line-of-sight (LoS), obstructed-LoS (OLoS), and reflected non-LoS (RNLoS) environments. For OLoS sceanrio, cylindrical objects of different materials are used as an obstruction. For RNLoS, different surfaces are used as reflectors. From the large set of LoS and OLoS measured data, the parameters for single-slope path loss model with shadowing are devised. Furthermore, the analysis of multipath propagation is performed. The results show that strong multiple reflections from the transmitter and receiver electronics are present both in LoS and OLoS environments. Additionally, the results show that glass and ceramic objects in the propagation path produce surface-diffracted rays which clock-wise and counter clock-wise superposition leads to frequency-dependent path loss. Finally, the results show that the RNLoS measured path loss with aluminum plate as a reflector is very similar to free-space path loss when the angle of incidence and the angle of reflection are equal. [ABSTRACT FROM PUBLISHER]