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Orthogonal Frequency Division Multiplexing (OFDM) systems are very sensitive to symbol timing and frequency offsets. Therefore, it is very important to achieve a high precision time and frequency synchronization. With the absence of pilot symbols, blind synchronization algorithms using different metric functions or statistics of the received signal can be used. In this paper, a new blind symbol timing...
In this paper, a new blind symbol timing and frequency offset estimation algorithm is proposed for Orthogonal Frequency Division Multiplexing (OFDM) systems in multipath fading channels. The method utilizes the redundant information contained in the cyclic prefix and is suitable within the acquisition as well as tracking phase of an OFDM receiver. The method is based on a new timing function which...
In OFDM systems, fast channel variation leads to the loss of orthogonality between the subcarriers. This results in intercarrier interference which cannot be mitigated with conventional single-tap equalization, and hence more complex equalization techniques are required. We seek in this paper low complexity interference equalization (linear in FFT size). Whereas successive interference cancellation...
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...
Modern routers should be able to support many new functions to meet the needs of customers. To achieve such flexibility, programmable packet processors have replaced traditional fixed-function custom logic in the data path of routers. This programmability introduces new vulnerabilities in these systems that can lead to new types of network attacks. We propose a monitoring subsystem which functions...
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...
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,...
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...
Providing a fair and secure medium access scheme is a fundamental requirement in centralized wireless networks. However, IEEE 802.11 systems do not provide any fairness control mechanism and assume a cooperative behavior of participating nodes. We tackle the problem of misbehavior on the MAC layer, mainly the backoff manipulation attack, and we propose the Random Backoff Control (RBC) mechanism. This...
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...
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...
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...
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...
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...
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,...
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...
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