1,721,117 research outputs found
Asymptotic performance of M-estimator-based multiuser detectors in Rayleigh fading non-Gaussian channels
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Performance comparison of energy-efficient power control for CDMA and multiuser UWB networks
No full textSource coding under secrecy constraints
No full textDistributed compression involves compressing multiple data sources by exploiting the underlying correlation structure of the sources at separate non-cooperating encoders, while decoding is done jointly at a single decoder. Recent years have witnessed an increasing amount of research on the theoretical and practical aspects of distributed source codes, which find applications in distributed video compression, peer-to-peer data distribution systems, and sensor networks [1-3]. In many practical scenarios, limited network resources such as power and bandwidth, or physical limitations of the devices as in the case of sensor networks, pose challenges in terms of network performance and security. Oftentimes, the data aggregated in distributed compression systems may have commercial value as in the case of warehouse inventory monitoring systems, may contain sensitive information as in the case of distributed video surveillance systems, or might infringe personal privacy concerns as in the case of human body sensors measuring various health indicators. In all these scenarios, it is essential to develop distributed compression and communication protocols which exploit the limited power and bandwidth resources efficiently as well as satisfying the security requirements. Our goal in this chapter is to review fundamental limitations and tradeoffs for the overall performance optimization taking into account the quality and the security considerations jointly. There are two fundamental approaches to guarantee security in wireless networks. In the approach based on computational complexity [4], on which most practical cryptographic applications are based, the security of the system depends on the intractability assumption for a problem such as prime factorization. On the other hand, in the approach based on information theoretic secrecy introduced by Shannon in [5], the emphasis is on unconditional secrecy, which requires that, an eavesdropper with unbounded time and computational resources, and the knowledge of the encryption algorithm, does not gain any additional information about the underlying secret message upon intercepting the encrypted cryptogram. For a general review of recent progress in information theoretic security, see [6]. Although the complexity based approach has been successful in satisfying the security concerns of many practical networking applications such as the Internet, wireless networks pose additional limitations and threats that cannot be solved solely through encryption. The broadcast nature of the wireless medium makes it particularly vulnerable to eavesdropping and authentication attacks, and the energy and bandwidth limitations of wireless devices restrict their computational power, hence rendering high complexity encryption techniques undesirable. Furthermore, especially in the sensor network scenario, where the sensor nodes are generally deployed in remote locations highly vulnerable to tampering, secure key management becomes impractical. Issues such as mobility and lack of infrastructure (e.g., in mobile ad hoc networks) also pose significant challenges to traditional approaches based on maintaining secret keys. In such applications information theoretic security can support and enhance the computational complexity based approach. In this chapter, we survey information theoretic security in distributed source compression, and in particular how compression and communication can be achieved in an information theoretically secure way. Consider, for example, a sensor network in which correlated sensor observations are to be reconstructed at an access point either in a lossless fashion or within a prescribed distortion requirement. While some sensors might have secure (possibly wired) connections to the access point, others might be transmitting over the wireless medium, which can be accessed by an adversary trying to obtain information about the underlying phenomenon. Furthermore, this adversary might have her own observation of the main source. Our goal is to explore the fundamental information theoretic limitations for secure distributed compression and communication in this kind of situation. In practical applications, encryption is considered to be a separate block in the protocol stack applied in concatenation with source compression and channel transmission. The information theoretic unconditional secrecy obtained through secure source and/or channel coding or joint source-channel coding hence can be used in parallel with the existing computational encryption schemes enhancing the overall level of security. In order to fully exploit this concept of information theoretic security practical secure source and channel codes need to be developed. While there are many recent developments in this direction for channel coding [7-9] little is known for secure compression. However, design of such secure source codes is beyond the scope of this chapter, and constitutes a potential research direction. The chapter is organized as follows. After reviewing Shannon's model and the preliminaries of information theoretic secrecy in Sect. 8.2, in Sect. 8.3 we analyze distributed lossless compression under security constraints and present related fundamental results. In Sect. 8.4, we focus on lossy reconstruction at the legitimate receiver, and analyze the achievable distortion for given secrecy and communication rate constraints. Section 8.5 focuses on secure joint source-channel coding followed by the Conclusions and the Appendix. © 2010 Springer Science+Business Media, LLC
BICM Decoding of Jammed OFDM Transmissions Using the EM Algorithm
No full textWireless communications over unlicensed frequency bands are expected to suffer from significant co-channel interference, which inevitably limits the error-rate performance. In this letter, an orthogonal frequency-division multiplexing system employing bit-interleaved coded-modulation is considered and the problem of reliable decoding in the presence of unknown narrowband interference (NBI) is addressed. The proposed solution operates in an iterative fashion according to the expectation-maximization algorithm and is derived by modeling the interference power on each subcarrier as a random variable with an inverse gamma distribution. Computer simulations indicate that the resulting scheme is effective against NBI and, compared to existing alternatives, it achieves a better trade-off in terms of error rate performance, computational complexity and system overhead
High SNR secrecy rates with OFDM signaling over fading channels
Full text linkOrthogonal frequency division multiplexing (OFDM) systems have enjoyed widespread adoption in high data rate wired and wireless networks, due to their ability to efficiently cope with slowly varying dispersive channels. This paper considers the information theoretic secrecy rates that are achievable by an OFDM transmitter/receiver pair in the presence of an eavesdropper that might either use an OFDM structure or choose a more complex receiver architecture. The analysis is performed through modeling of the OFDM system with an eavesdropper as a special case of a high dimensional multiple-input multiple-output (MIMO) wiretap channel, which allows the secrecy loss due to the OFDM structure constraints, and the information gain for an eavesdropper that uses a more complex receiver to be quantified. The results are expressed in terms of both ergodic rates and outage probabilities for multipath Rayleigh fading channels, and in terms of dependence on the signal to noise ratio (SNR) ratio between the main and eavesdropper channels
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