Channel Measurements of Device-to-Device Communications at 2.45 GHz

In the future, device-to-device communications will become a fundamental part of cellular communications. Interoperability between handsets will be facilitated using frequencies located in a number of bands including those found in the Industrial, Scientific and Medical (ISM) band at 2.45 GHz. In this paper, we present the results of channel measurements made between two hypothetical cellular handsets operating at 2.45 GHz in an outdoor environment. We consider a range of typical usage scenarios such as both user equipment being held at the head while imitating a voice call, placed in user's pocket for both stationary and dynamic links. A range of parameter estimates obtained using the shadowed κ-μ fading model are also presented.

Simultaneous Measurements of the Channel Response for Multiple Eavesdroppers Operating in the Vicinity of a Body Area Network at 2.45 GHz

Channel randomness can be exploited to generate secret keys. However, to ensure secrecy, it is necessary that the channel response of any eavesdropping party remain sufficiently de-correlated with that of the legitimate users'. In this paper, we investigate whether such de-correlation occurs for a body area network (BAN) operating in an indoor environment at 2.45 GHz. The hypothetical BAN configuration consisted of two legitimate transceivers, one situated on the user's left wrist and the other on the user's waist. The eavesdroppers were positioned in either a co-located or distributed manner in the area surrounding the BAN user. Using the simultaneous channel response measured at the legitimate BAN nodes and the eavesdropper positions for stationary and mobile scenarios, we analyze the localized correlation coefficient. This allows us to determine if it is possible to generate secret keys in the presence of multiple eavesdroppers in an indoor environment. Our experimental results show that although channel reciprocity was observed for both the stationary and the mobile scenarios, a higher de-correlation between the legitimate users' channels was observed for the stationary case. This indicates that mobile scenarios are better suited for secret key generation.

Real-Time Channel Model Selection Using Windowed Received Signal Strength Measurements

This paper investigates the potential for using the windowed variance of the received signal strength to select from a set of predetermined channel models for a wireless ranging or localization system. An 868 MHz based measurement system was used to characterize the received signal strength (RSS) of the off-body link formed between two wireless nodes attached to either side of a human thorax and six base stations situated in the local surroundings.

A novel inhibitor of channel activating proteases: Putting the CAP on ENaC

Background: Excessive activation of epithelial sodium channels (ENaC) contributes to CF lung pathophysiology due to the resultant dehydration of the airway surface liquid (ASL) and impaired mucociliary clearance. Regulated proteolysis of the endogenous α and γ subunits of ENaC by apical membrane-bound Channel Activating Proteases (CAPs) is a fundamental regulatory mechanism for channel activity. In the CF lung a stark imbalance between the levels of CAPs and their natural inhibitors drives the activation of normally inactive ENaC. On this basis inhibition of CAPs-ENaC signalling represents a potential therapeutic intervention. To this end we have developed a novel cell impermeable active-site directed compound (QUB-TL1) designed to inactivate key trypsin-like CAPs highly relevant in this regard. Objectives & Methods: Utilize differentiated non-CF and CF human airway epithelial cells to assess the impact of QUB-TL1 on a range of parameters including surface CAP activities, ENaC subunit processing/channel activity, ASL height and mucociliary clearance. Results: Treatment of airway epithelial cells with QUB-TL1 results in the significant downregulation of key endogenous CAP activities found to be excessively active at the surface of CF cultures. QUB-TL1-mediated CAP inhibition subsequently causes the internalisation of a pool of processed (active) ENaCγ prominent at the apical surface of CF cultures which correlates with a decline in channel activity. This downregulation of ENaC activity results in an increase in ASL height and improved mucociliary clearance in CF cells. We further find QUB-TL1 uniquely inhibits the ENaC activating enzyme furin, which is in contrast to the alternate trypsin-like CAP inhibitors camostat mesylate and aprotinin. QUB-TL1-mediated furin inhibition correlates with a reduction in neutrophil elastase-induced ENaC activation. Moreover we find QUB-TL1 treatment protects CF cultures from Pseudomonas aeruginosa exotoxin A-induced cytotoxicity. Pseudomonas aeruginosa exotoxin A is a major toxic product activated by furin and positively associated with mortality. Conclusion: The novel inhibitor (QUB-TL1) dampens CAPs-ENaC signalling which improves hydration status mucociliary clearance in CF airway epithelial cell cultures. Moreover this compound provides additional benefit by preventing Pseudomonas aeruginosa exotoxin A-induced cytotoxicity.

TRP channel expression in human gingival fibroblasts

Background: The transient receptor potential (TRP) super family of ion channels is believed to play a critical role in sensory physiology, acting as transducers for thermal, mechanical and chemical stimuli. Our understanding of the role of TRP channel expression in gingival fibroblasts is currently limited. The role of non-neuronal TRP channel expression is an area of much research interest particularly since TRP channel activation has recently been hypothesised to be associated with inflammation. Objectives: The present study was designed to determine the expression of TRPV1, TRPV2, TRPV3 and TRPV4 on human gingival fibroblasts. Methods: Human gingival fibroblasts were derived by explant culture from surgical tissue following ethical approval. Cells were maintained in Dulbecco's modified Eagle's medium (DMEM), containing 10% fetal calf serum (FCS) in 5% CO2. Cell lysates of gingival fibroblasts were electrophoresed and blotted on to nitrocellulose before probing with specific anti-TRP antibodies. Immunoreactive bands were detected using anti-species antibodies and chemiluminescent detection. Results: Gingival fibroblasts were shown to express proteins corresponding to the TRPV1, TRPV2, TRPV3 and TRPV4 channels as determined by western blotting. Conclusion: This study reports for the first time the expression of TRPV1, TRPV2, TRPV3 and TRPV4 by gingival fibroblasts. Knowledge of the expression of TRP channels by human gingival fibroblasts will guide future research on the roles of TRP channels in sensing the external environment in the oral cavity.

'Heat-sensing' TRP channel expression in human odontoblasts

Background: Thermal changes in the oral cavity are a common trigger of dental pain. Several members of the transient receptor potential (TRP) super family of ion channels are believed to play a critical role in sensory physiology, where they act as transducers for thermal, mechanical and chemical stimuli. Objectives: The present study was designed to determine the expression and functionality of the TRPV1 channel in human odontoblasts. Methods: Cultured human odontoblasts were derived from dental pulp cells induced with 2 mM beta-glycerophosphate. Molecular and protein expression of TRPV1 was confirmed by PCR, western blotting and immunohistochemistry. Functional expression of the ‘heat-sensing' TRPV1 channel was investigated using a Ca2+ microfluorimetry assay in the presence of agonists/antagonists or with appropriate adjustment of the recording chamber temperature. Results: The odontoblastic phenotype of the cells was confirmed by the expression of the odontoblast markers dentin sialophosphoprotein (DSPP) and nestin. Expression of TRPV1 in human odontoblastic cells was confirmed by PCR, western blotting and immunohistochemistry. Odontoblasts were shown to respond to pharmacological agonists and to increasing temperature by an increase in intracellular Ca2+. Both the pharmacological and temperature responses could be blocked by specific antagonists. These results indicate that odontoblasts may sense heat via TRPV1. Conclusion: This study reports that TRPV1 is expressed by human odontoblasts and is activated by specific pharmacological agonists and by heat.
This work was supported by Research Grants from the Royal College of Surgeons of Edinburgh and the British Endodontic Society

Transient receptor potential (TRP) channel expression in pulpal fibroblasts

Introduction: Transient receptor potential (TRP) channels are widely, but not uniformly, distributed in tissues. To date the dominant focus of attention has been on TRP expression and functionality in neurons. However, their expression and activation in selected non-neuronal cells suggest TRPs have a potential role in coordinating cross-talk during the inflammatory process. Fibroblasts comprise the major cell type in the dental pulp and play an important role in pulpal inflammation. Objectives: The aim of this study was to investigate the expression and functionality of the TRP channels TRPA1, TRPM8, TRPV4 and TRPV1 in human dental pulp fibroblasts. Methods: Dental pulp fibroblasts were derived by explant culture of pulps removed from extracted healthy teeth. Fibroblasts were cultured in DMEM supplemented with 10% FCS, 100U/ml penicillin and 100µg/ml streptomycin. Protein expression of TRP channels was investigated by SDS- polyacrylamide gel electrophoresis and Western blotting of cell lysates from fibroblast cells in culture. TRPA1, TRPM8, TRPV4 and TRPV1 expression was determined by specific antibodies, detected using appropriate anti-species antibodies and chemiluminescence. Functionality of TRP channels was determined by Ca2+ microfluorimetry. Cells were grown on cover slips and incubated with Fura 2AM prior to stimulation with icilin (TRPA1 agonist), menthol (TRPM8 agonist), 4 alpha-phorbol 12,13-didecanoate (4alphaPDD) (TRPV4 agonist) or capsaicin (TRPV1 agonist). Emitted fluorescence (F340/F380) was used to determine intracellular [Ca2+] levels. Results: Fibroblast expression of TRPA1, TRPM8, TRPV4 and TRPV1 was confirmed at the protein level by Western blotting. Increased intracellular [Ca2+] levels in response to icillin, methanol, 4alphaPDD and capsacin, indicated functional expression of TRPA1, TRPM8, TRPV4 and TRPV respectively. Conclusions: The presence and functionality of TRP channels on dental pulp fibroblasts suggests a potential role for these cells in the pulpal neurogenic inflammatory response. (Supported by a research grant from the Royal College of Surgeons of Edinburgh).

Secure key generation from OFDM subcarriers' channel responses

The ability to exchange keys between users is vital in any wireless based security system. A key generation technique which exploits the randomness of the wireless channel is a promising alternative to existing key distribution techniques, e.g., public key cryptography. In this paper, a secure key generation scheme based on the subcarriers' channel responses in orthogonal frequency-division multiplexing (OFDM) systems is proposed. We first implement a time-variant multipath channel with its channel impulse response modelled as a wide sense stationary (WSS) uncorrelated scattering random process and demonstrate that each subcarrier's channel response is also a WSS random process. We then define the X% coherence time as the time required to produce an X% correlation coefficient in the autocorrelation function (ACF) of each channel tap, and find that when all the channel taps have the same Doppler power spectrum, all subcarriers' channel responses has the same ACF as the channel taps. The subcarrier's channel response is then sampled every X% coherence time and quantized into key bits. All the key sequences' randomness is tested using National Institute of Standards and Technology (NIST) statistical test suite and the results indicate that the commonly used sampling interval as 50% coherence time cannot guarantee the randomness of the key sequence.

Efficient Key Generation by Exploiting Randomness from Channel Responses of Individual OFDM Subcarriers

Key generation from the randomness of wireless channels is a promising technique to establish a secret cryptographic key securely between legitimate users. This paper proposes a new approach to extract keys efficiently from channel responses of individual orthogonal frequency-division multiplexing (OFDM) subcarriers. The efficiency is achieved by (i) fully exploiting randomness from time and frequency domains and (ii) improving the cross-correlation of the channel measurements. Through the theoretical modelling of the time and frequency autocorrelation relationship of the OFDM subcarrier's channel responses, we can obtain the optimal probing rate and use multiple uncorrelated subcarriers as random sources. We also study the effects of non-simultaneous measurements and noise on the cross-correlation of the channel measurements. We find the cross-correlation is mainly impacted by noise effects in a slow fading channel and use a low pass filter (LPF) to reduce the key disagreement rate and extend the system's working signal-to-noise ratio range. The system is evaluated in terms of randomness, key generation rate, and key disagreement rate, verifying that it is feasible to extract randomness from both time and frequency domains of the OFDM subcarrier's channel responses.

A rising e-channel tide lifts all boats? the impact of manufacturer multi-channel encroachment on traditional selling and leasing

Organizing and managing channels of distribution is an important marketing task. Due to the emergence of electronic commerce on the Internet, e-channel distribution systems have been adopted by many manufacturers. However, academic and anecdotal evidence both point to the pressures arising from this new e-channel manufacturing environment. Questions marks therefore remain on how the addition of this e-channel affects the traditional marketing strategies of leasing and selling. We set up several two-period dual-channel models in which a manufacturer sells a durable product through both a manufacturer-owned e-channel and an independent reseller (leaser) who adopts selling (leasing) to consumers. Our main results indicate that, direct selling cost aside, product durability plays an important role in shaping the strategies of all members. With either marketing strategy, the additional expansion of an e-channel territory may secure Pareto gains, in which all members benefit.

Verification of Key Generation from Individual OFDM Subcarrier's Channel Response

This paper presents a key generation system derived from the channel response of individual subcarrier in orthogonal frequency-division multiplexing (OFDM) systems. Practical aspects of the security were investigated by implementing our key generation scheme on a wireless open-access research platform (WARP), which enables us to obtain channel estimation of individual OFDM subcarriers, a feature not currently available in most commercial wireless interface cards. Channel response of individual OFDM subcarrier is usually a wide sense stationary random process, which allows us to find the optimal probing period and maximize the key generation rate. The implementation requires cross layer design as it involves interaction between physical and MAC layer. We have experimentally verified the feasibility and principles of key generation, and also evaluated the performance of our system in terms of randomness, key generation rate and key disagreement rate, which proves that OFDM subcarrier's channel responses are valid for key generation.

IQ Imbalance in Multiuser Systems: Channel Estimation and Compensation

In this paper, we consider the uplink of a single-cell multi-user single-input multiple-output (MU-SIMO) system with in-phase and quadrature-phase imbalance (IQI). Particularly, we investigate the effect of receive (RX) IQI on the performance of MU-SIMO systems with large antenna arrays employing maximum-ratio combining (MRC) receivers. In order to study how IQI affects channel estimation, we derive a new channel estimator for the IQI-impaired model and show that the higher the value of signal-to-noise ratio (SNR) the higher the impact of IQI on the spectral efficiency (SE). Moreover, a novel pilot-based joint estimator of the augmented MIMO channel matrix and IQI coefficients is described and then, a low-complexity IQI compensation scheme is proposed which is based on the
IQI coefficients’ estimation and it is independent of the channel gain. The performance of the proposed compensation scheme is analytically evaluated by deriving a tractable approximation of the ergodic SE assuming transmission over Rayleigh fading channels with large-scale fading. Furthermore, we investigate how many MSs should be scheduled in massive multiple-input multiple-output (MIMO) systems with IQI and show that the highest SE loss occurs at the optimal operating point. Finally,
by deriving asymptotic power scaling laws, and proving that the SE loss due to IQI is asymptotically independent of the number of BS antennas, we show that massive MIMO is resilient to the effect of RX IQI.

Experimental Study on Channel Reciprocity in Wireless Key Generation

Key generation from wireless channels is a promising alternative to public key cryptography for the establishment of cryptographic keys. It is the first paper to experimentally study the channel reciprocity principle of key generation, through investigating and quantifying channel measurements' cross-correlation relationship affected by noise and non-simultaneous measurements. Channel measurements, both received signal strength and channel state information, are collected from a real experimental platform using the wireless open access research platform (WARP) in a multipath office room. We found that in a slow fading channel (e.g., with a coherence time of about 50~ms), the channel cross-correlation is impacted greatly by noise but little by non-simultaneous measurements with a small sampling time difference (e.g., 0.06 ms). The resolution of the sampling time difference can be satisfied by wireless systems such as IEEE 802.11 to maintain an acceptable cross-correlation coefficient without affecting the bandwidth and communication efficiency.