595 research outputs found
Timing Jitter Analysis and Mitigation in Hybrid OFDM-DFMA PONs
Hybrid orthogonal frequency division multiplexing-digital filter multiple access passive optical networks (OFDM-DFMA PONs) offer a cost-effective solution to the challenging requirements of next-generation optical access networks and 5G and beyond radio access networks. It is crucial to consider the impact of timing jitter in any ADC/DAC-based system, therefore this paper presents an in-depth investigation into the impacts of DAC/ADC timing jitter on the hybrid OFDM-DFMA PON's performance. We introduce improved accuracy white and coloured, DAC and ADC timing jitter models, applicable to any DSP-based transmission system. We prove that DAC and ADC timing jitter effects are virtually identical and investigate the effects of white/coloured timing jitter on upstream performance in hybrid OFDM-DFMA PONs and determine the associated jitter-induced optical power penalties. To mitigate against the timing jitter-induced performance degradations, a simple, but highly effective DSP-based technique is implemented which increases robustness against the timing jitter effects and significantly reduces timing jitter-induced optical power penalties. This consequently relaxes DAC/ADC sampling clock jitter requirements and so reduces implementation costs. White (coloured) timing jitter effects are shown to be independent of (dependent on) ONU operating frequency band and a trade-off between DAC and ADC jitter levels can be exploited to reduce ONU costs
EavesDroid: Eavesdropping User Behaviors via OS Side-Channels on Smartphones
As the Internet of Things (IoT) continues to evolve, smartphones have become
essential components of IoT systems. However, with the increasing amount of
personal information stored on smartphones, user privacy is at risk of being
compromised by malicious attackers. Although malware detection engines are
commonly installed on smartphones against these attacks, attacks that can evade
these defenses may still emerge. In this paper, we analyze the return values of
system calls on Android smartphones and find two never-disclosed vulnerable
return values that can leak fine-grained user behaviors. Based on this
observation, we present EavesDroid, an application-embedded side-channel attack
on Android smartphones that allows unprivileged attackers to accurately
identify fine-grained user behaviors (e.g., viewing messages and playing
videos) via on-screen operations. Our attack relies on the correlation between
user behaviors and the return values associated with hardware and system
resources. While this attack is challenging since these return values are
susceptible to fluctuation and misalignment caused by many factors, we show
that attackers can eavesdrop on fine-grained user behaviors using a CNN-GRU
classification model that adopts min-max normalization and multiple return
value fusion. Our experiments on different models and versions of Android
smartphones demonstrate that EavesDroid can achieve 98% and 86% inference
accuracy for 17 classes of user behaviors in the test set and real-world
settings, highlighting the risk of our attack on user privacy. Finally, we
recommend effective malware detection, carefully designed obfuscation methods,
or restrictions on reading vulnerable return values to mitigate this attack.Comment: 15 pages, 25 figure
Real-Time Demonstration of Concurrent Upstream and Inter-ONU Communications in Hybrid OFDM DFMA PONs
This paper presents the first real-time experimental demonstration of concurrent upstream and inter-ONU communications in a hybrid OFDM DFMA PON, enabled by a simple low-cost alteration to the remote node. Real-time FPGA-based DSP, incorporating a 128-pt FFT and a joint sideband processing technique, is used to demultiplex different sub-wavelength channels at the ONU and OLT receivers. The simple modification in the remote node removes the need for direct user-to-user data to pass via the OLT and core network thus providing ultra-low latency inter-ONU connectivity to support a variety of newly emerging latency sensitive 5G services. The presented PON is validated with two subwavelength bands, each capable of carrying one of two possible orthogonal channels ( I or Q ). The dynamic channel and subcarrier allocation allows flexible allocation of PON capacity between upstream and inter-ONU links for dynamic on-demand capacity allocation and also performance optimisation according to the different length dependent link characteristics. Moreover, the backscattering effect associated with upstream signals is shown to have negligible effect on the BER performance of the inter-ONU communications
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