Papers by Youssef El Hajj Shehadeh
2012 8th International Wireless Communications and Mobile Computing Conference (IWCMC), 2012
Recently, key extraction from multipath wireless channels has been largely investigated. This pap... more Recently, key extraction from multipath wireless channels has been largely investigated. This paper tackles practical issues affecting the reliability of key agreement. We first analyze the effect of delay between the channel estimates on the probability of disagreement, and we propose a robust key extraction mechanism against delay. Later, we study the effect of mobility and improve our key generation mechanism taking into account the decorrelation of the channel. Finally, we investigate the impact of mobility on the overall secret bit generation rate.
With the growing number of infotainment services,
the demand on high speed internet in vehicles ... more With the growing number of infotainment services,
the demand on high speed internet in vehicles is increasing.
Yet, ensuring a high speed internet access at high mobility
is challenging. Indeed, high mobility leads to Doppler shifts
that result in Inter Carrier Interference (ICI) in OFDM-based
wireless systems. Many ICI equalization techniques have been
proposed, yet these incur an additional computational complexity
and hence higher energy consumption. In this work, we propose
a very low complexity interference reduction method. Based on
a linear modeling of the channel variation, we derive relations
between the interference terms at the different subcarriers and
show that interference can be significantly reduced through
simple linear operations.
In Orthogonal Frequency Division Multiplexing (OFDM) based systems, symbol timing errors and freq... more In Orthogonal Frequency Division Multiplexing (OFDM) based systems, symbol timing errors and frequency offsets may lead to a significant performance degradation. For this reason, it is very important to achieve a high precision time and frequency synchronization. With the absence of pilot symbols, blind synchronization algorithms are necessary by either using different metric functions or statistics of the received signal. In this paper a new blind symbol timing and frequency offset estimation algorithm is proposed, based on the Maximum Likelihood (ML) principle. It only utilizes the redundant infor- mation contained in the guard interval and is suitable within the acquisition as well as the tracking phase of an OFDM receiver. To provide a fair comparison between the proposed and the most recent blind synchronization algorithms, all simulations are applied to the practical OFDM based Digital Audio Broadcasting (DAB/DAB+) system under different realistic multipath fading channel conditions to extract the best method for Software Defined Radio (SDR) based receivers.
One of the fundamental tasks of the MAC layer in wireless networks is coordinating channel access... more One of the fundamental tasks of the MAC layer in wireless networks is coordinating channel access securely and efficiently. However, the contention-based medium access scheme used in IEEE 802.11 networks has been found to be suboptimal, especially for a large number of users. Moreover, it is vulnerable to misbehavior resulting in an unfair share of the wireless channel. To tackle these two problems, we propose a distributed scheduling-based medium access scheme. In addition to its high efficiency, this scheme also provides security by design and ensures a fair distribution of wireless resources.
Coordinating channel access is a fundamental task of the MAC layer in wireless networks. Whereas ... more Coordinating channel access is a fundamental task of the MAC layer in wireless networks. Whereas most proposed medium access techniques involve a pure contention-based mechanism or a centralized polling scheme, we explore distributed scheduling-based medium access. Intuitively, a scheduling-based scheme would achieve a higher bandwidth efficiency and a lower collision rate than contention-based mechanisms. We develop the Self-Organized Distributed Channel Access (SODCA) scheme, that combines the advantages of both contention and scheduling mechanisms. Distinctively from other proposed solutions, SODCA does not incur any additional overhead and is a distributed, highly efficient, compatible, and a dynamic schedule establishment scheme. Through simulation results based on the OMNeT++ network simulator, we demonstrate the high efficiency of SODCA compared to the IEEE 802.11 DCF contention mechanism in both static and dynamic scenarios. SODCA is proven to achieve a collision-free and fair medium access leading to a 20% higher network throughput than DCF in a static scenario, and a significantly lower collision rate in a dynamic scenario.
Traditional security mechanisms are mainly based on the distribution of shared secret keys. Yet, ... more Traditional security mechanisms are mainly based on the distribution of shared secret keys. Yet, this task is non trivial in large wireless networks, due to mobility and scalability issues.
Recently, it has been found that some properties of the physical layer of wireless communications can be leveraged for the purpose of secret key generation. In particular, the wireless channel has been investigated as a common source of secrecy
to generate a shared secret key. We explore the most recent approaches in this area. RSSI-based key generation is firstly
investigated. After that, we present some of the most recent approaches of key generation based on the channel impulse
response. Moreover, we discuss some other physical layer methods. Thus, this paper provides a survey on the latest key
generation mechanisms on the physical layer of wireless communications.
Abstract. We investigate applying an error correcting code of small block size to enhance the per... more Abstract. We investigate applying an error correcting code of small block size to enhance the performance of key generation from wireless channels. A trade-off between performance and secrecy is then studied. Preliminary results show that using a simple lower ...
Recently, key extraction from multipath wireless channels has been largely investigated. This pap... more Recently, key extraction from multipath wireless channels has been largely investigated. This paper tackles practical issues affecting the reliability of key agreement. We first analyze the effect of delay between the channel estimates on the probability of disagreement, and we propose a robust key extraction mechanism against delay. Later, we study the effect of mobility and improve our key generation mechanism taking into account the decorrelation of the channel. Finally, we investigate the impact of mobility on the overall secret bit generation rate.
This paper tackles the problem of generating shared secret keys based on the physical characteris... more This paper tackles the problem of generating shared secret keys based on the physical characteristics of the wireless channel. We propose intelligent quantization mechanisms for key generation, achieving high secret bits generation rate. Moreover, some practical issues affecting the performance of the key generation mechanism are deeply investigated. Mainly, we investigate the effects of delay and mobility on the performance and we enhance the key generation mechanism accordingly. As a result, this paper presents a framework towards robust key generation from multipath wireless channels.
This paper tackles the problem of fast varying channel estimation in LTE systems. Particular atte... more This paper tackles the problem of fast varying channel estimation in LTE systems. Particular attention is given to downlink transmission where OFDMA is used as the multiple access technique for the air interface. In OFDMA, fast variation of the channel results in significant inter-carrier interference (ICI) which cannot be mitigated with conventional estimation and equalization techniques. In this paper, we
Next generation wireless systems are foreseen to adopt OFDM based transmission schemes. Unfortuna... more Next generation wireless systems are foreseen to adopt OFDM based transmission schemes. Unfortunately, conventional OFDM schemes suffer from the high mobility associated with next generation wireless systems, thus they need to be supported with enhanced techniques that alleviate the effects of the mobility. Among these, techniques for channel identification bear a particular importance. In this paper, we present two problems regarding channel identification and the corresponding solutions in mobile communications. In the first part, we investigate a linear modeling to estimate rapidly varying channels using an equispaced pilot distribution. We present a method to improve the estimation performance based on two successive OFDM symbol observations. It is shown by simulations that the proposed method provides a considerable performance enhancement by means of a simple linear filtering. The second one considers Bayesian approach to track time varying subcarrier gains. It is shown that the Bayesian tracking/detecting scheme is a fast and a rather reliable solution for lower mobile speeds. The presented scheme does not exploit any frequency correlation, hence, it is simple to implement and it can be utilized in any subchannel permutation scheme.
The wireless communication channel has been found recently to have some interesting properties. I... more The wireless communication channel has been found recently to have some interesting properties. In particular, it has been found that the multipath wireless channel can be leveraged for the purpose of key generation. In this paper, we investigate this property and propose an intelligent key generation method based on phase shifting and correction. Further, we discuss improvements of this approach and finally, we test our algorithm on a typical outdoor wireless channel. Our simulation results show that more than 90 bits can be generated from a single channel observation.
Recently, multipath in wireless channels has shown an interesting aspect. It has been found that ... more Recently, multipath in wireless channels has shown an interesting aspect. It has been found that wireless channels may provide a common reciprocal source of randomness for any two communicating nodes. This seems particularly interesting for secret key generation in wireless networks. In this paper, we consider the randomness property of wireless channels and present an intelligent algorithm for key generation. We analyze the multipath channel and derive optimal parameters enabling efficient key extraction leveraging the richness of a wireless environment. Finally, we test our algorithm in a typical outdoor wireless channel. Our simulation results show that more than 70 secret bits can be extracted from a single channel observation.
This paper deals with pilot-based channel estimation for fast varying channels in Orthogonal Freq... more This paper deals with pilot-based channel estimation for fast varying channels in Orthogonal Frequency Division Multiplexing (OFDM) systems. Due to the variation of the channel during one OFDM symbol, one-tap channel estimation and the corresponding equalization is no longer the optimum solution and such a variation results in inter-carrier interference (ICI). One of the possible approaches to predict this interfering effect is to use basis expansion model (BEM) with which the variation of the channel can be approximated successfully. However, as the pure BEM does not solve completely the problem, we investigate the estimation problem using decision feedback to enhance the performance. In particular, we propose a simple algorithm based on using two successive OFDM symbols to filter channel coefficients and improve not only the convergence of pure decision feedback based estimation but also the system performance. Simulation results based on Jake's channel model with a high Doppler spread and a practical high data rate system sustain our claims.
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Papers by Youssef El Hajj Shehadeh
the demand on high speed internet in vehicles is increasing.
Yet, ensuring a high speed internet access at high mobility
is challenging. Indeed, high mobility leads to Doppler shifts
that result in Inter Carrier Interference (ICI) in OFDM-based
wireless systems. Many ICI equalization techniques have been
proposed, yet these incur an additional computational complexity
and hence higher energy consumption. In this work, we propose
a very low complexity interference reduction method. Based on
a linear modeling of the channel variation, we derive relations
between the interference terms at the different subcarriers and
show that interference can be significantly reduced through
simple linear operations.
Recently, it has been found that some properties of the physical layer of wireless communications can be leveraged for the purpose of secret key generation. In particular, the wireless channel has been investigated as a common source of secrecy
to generate a shared secret key. We explore the most recent approaches in this area. RSSI-based key generation is firstly
investigated. After that, we present some of the most recent approaches of key generation based on the channel impulse
response. Moreover, we discuss some other physical layer methods. Thus, this paper provides a survey on the latest key
generation mechanisms on the physical layer of wireless communications.
the demand on high speed internet in vehicles is increasing.
Yet, ensuring a high speed internet access at high mobility
is challenging. Indeed, high mobility leads to Doppler shifts
that result in Inter Carrier Interference (ICI) in OFDM-based
wireless systems. Many ICI equalization techniques have been
proposed, yet these incur an additional computational complexity
and hence higher energy consumption. In this work, we propose
a very low complexity interference reduction method. Based on
a linear modeling of the channel variation, we derive relations
between the interference terms at the different subcarriers and
show that interference can be significantly reduced through
simple linear operations.
Recently, it has been found that some properties of the physical layer of wireless communications can be leveraged for the purpose of secret key generation. In particular, the wireless channel has been investigated as a common source of secrecy
to generate a shared secret key. We explore the most recent approaches in this area. RSSI-based key generation is firstly
investigated. After that, we present some of the most recent approaches of key generation based on the channel impulse
response. Moreover, we discuss some other physical layer methods. Thus, this paper provides a survey on the latest key
generation mechanisms on the physical layer of wireless communications.