This complete guide to physical-layer security presents the theoretical foundations, practical implementation, challenges and benefits of a groundbreaking new model for secure communication. Using a bottom-up approach from the link level all the way to end-to-end architectures, it provides essential practical tools that enable graduate students, industry professionals and researchers to build more secure systems by exploiting the noise inherent to communications channels. The book begins with a self-contained explanation of the information-theoretic limits of secure communications at the physical layer. It then goes on to develop practical coding schemes, building on the theoretical insights and enabling readers to understand the challenges and opportunities related to the design of physical layer security schemes. Finally, applications to multi-user communications and network coding are also included.

Physical-Layer Security: From Information Theory to Security Engineering

This paper describes MIXIT, a system that improves the throughput of wireless mesh networks. MIXIT exploits a basic property of mesh networks: even when no node receives a packet correctly, any given bit is likely to be received by some node correctly. Instead of insisting on forwarding only correct packets, MIXIT routers use physical layer hints to make their best guess about which bits in a corrupted packet are likely to be correct and forward them to the destination. Even though this approach inevitably lets erroneous bits through, we find that it can achieve high throughput without compromising end-to-end reliability.The core component of MIXIT is a novel network code that operates on small groups of bits, called symbols. It allows the nodes to opportunistically route groups of bits to their destination with low overhead. MIXIT's network code also incorporates an end-to-end error correction component that the destination uses to correct any errors that might seep through. We have implemented MIXIT on a software radio platform running the Zigbee radio protocol. Our experiments on a 25-node indoor testbed show that MIXIT has a throughput gain of 2.8x over MORE, a state-of-the-art opportunistic routing scheme, and about 3.9x over traditional routing using the ETX metric.

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Symbol-level network coding for wireless mesh networks

Opportunistic routing significantly increases unicast throughput in wireless mesh networks by effectively utilizing the wireless broadcast medium. With network coding, opportunistic routing can be implemented in a simple and practical way without resorting to a complicated scheduling protocol. Due to constraints of computational complexity, a protocol utilizing network coding needs to perform segmented network coding, which partitions the data into multiple segments and encode only packets in the same segment. However, existing designs transmit only one segment at any given time while waiting for its acknowledgment, which degrades performance as the size of the network scales up. In this paper, we propose CodeOR, a new protocol that uses network coding in opportunistic routing to improve throughput. By transmitting a window of multiple segments concurrently, it improves the performance of existing work by a factor of two on average (and a factor of four in some cases). CodeOR is especially appropriate for real-time multimedia applications through the use of a small segment size to decrease decoding delay, and is able to further increase network throughput with a smaller packet size and a larger window size.

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CodeOR: Opportunistic routing in wireless mesh networks with segmented network coding

On-demand video streaming is becoming a killer application for wireless networks. Recent information-theoretic results have shown that a combination of caching on the users’ devices and device-to-device (D2D) communications yields throughput scalability for very dense networks, which represent critical bottlenecks for conventional cellular and wireless local area network (WLAN) technologies. In this paper, we consider the implementation of such caching D2D systems where each device pre-caches a subset of video files from a library, and users requesting a file that is not already in their library obtain it from neighboring devices through D2D communication. We develop centralized and distributed algorithms for the delivery phase, encompassing a link scheduling and a streaming component. The centralized scheduling is based on the max-weighted independent set (MWIS) principle and uses message-passing to determine max-weight independent sets. The distributed scheduling is based on a variant of the FlashLinQ link scheduling algorithm, enhanced by introducing video-streaming specific weights. In both cases, the streaming component is based on a quality-aware stochastic optimization approach, reminiscent of current Dynamic Adaptive Streaming over HTTP (DASH) technology, for which users sequentially request video “chunks” by choosing adaptively their quality level. The streaming and the scheduling components are coupled by the length of the users’ request queues. Through extensive system simulation, the proposed approaches are shown to provide sizeable gains with respect to baseline schemes formed by the concatenation of off-the-shelf FlashLinQ with proportional fair link scheduling and DASH at the application layer.

Quality-Aware Streaming and Scheduling for Device-to-Device Video Delivery

For routers and switches to handle ever-increasing bandwidth requirements, the packet “fast-path” must be handled with specialized hardware. There have been two approaches to building such packet forwarding hardware. The first is to embed particular algorithms in hardware; this is what most commodity forwarding chips do (e.g., those from Broadcom, Marvell, and Fulcrum). These chips have led to amazing increases in performance and reductions in cost; for instance, one can now get 24 ports of gigabit ethernet for under $1000. Unfortunately, this approach offers only very rigid functionality; one can’t change protocols or add new features that require hardware acceleration without redoing the chip. This forces network forwarding enhancements to evolve on hardware design timescales, which are glacially slow compared to the rate at which network applications and requirements are changing. To counter this inflexibility, several vendors have taken a different approach by introducing more flexible “network processors”. These have not been as successful as anticipated, for at least two reasons. First, designers were never able to find a sweet-spot in the tradeoff between hardware simplicity and flexible functionality, so the performance/price ratios have lagged well behind commodity networking chips. For another, the interface provided to software has proven hard to use, requiring protocol implementors to painstakingly contort their code to the idiosyncrasies of the particular underlying hardware to achieve reasonable performance. These two problems (among others) have prevented general-purpose network processors from dislodging the more narrowly targeted commodity packet forwarding hardware that dominates the market today. In this paper, we step back from these two well-known approaches and ask more fundamentally: what would we want from packet forwarding hardware, how might we achieve it, and what burden does that place on networking software? Ideally, hardware implementations of the forwarding paths should have the following properties:

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Rethinking Packet Forwarding Hardware.

Emerging practical schemes indicate that algebraic mixing of different packets by means of random linear network coding can increase the throughput and robustness of streaming services over wireless networks. However, concerns with the security of wireless video, in particular when only some of the users are entitled to the highest quality, have uncovered the need for a network coding scheme capable of ensuring different levels of confidentiality under stringent complexity requirements. We show that the triple goal of hierarchical fidelity levels, robustness against wireless packet loss and efficient security can be achieved by exploiting the algebraic structure of network coding. The key idea is to limit the encryption operations to a critical set of network coding coefficients in combination with multi-resolution video coding. Our contributions include an information-theoretic security analysis of the proposed scheme, a basic system architecture for hierarchical wireless video with network coding and simulation results.

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Secure network coding for multi-resolution wireless video streaming

Designing high throughput wireless mesh networks involves solving interrelated scheduling, routing, and interference problems. In this paper, we exploit the broadcast properties and the path diversity of wireless meshes to implement an efficient multipath routing protocol, Multipath Code Casting (MC2).In contrast to prior work in opportunistic routing, which required strong coordination across nodes to prevent information repetition, our design is based on network coding and does not require node coordination. Moreover, it provides a unified framework to deal with data transmissions across multiple and, often, unreliable transmission paths. Our design also includes a novel rate-scheduling algorithm that guarantees (proportionally) fair allocation of resources across multiple (multipath) flows, ensures that data use the paths with the best performance, and prevents information overflow by controlling the data rate across each path. Using simulations and a prototype implementation, we show that our algorithms provide over 30% performance improvement compared to traditional singlepath approaches when applied to realistic and other exemplar topologies; in some scenarios, our approach can even double the throughput. Our approach also performs better than 20% compared to other multipath routing schemes.

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Multipath code casting for wireless mesh networks

In wireless multihop networks, techniques such as multipath, local retransmissions and network coding have been successfully used to increase throughput and reduce losses. However, while these techniques improve forwarding performance for UDP, they often introduce side effects such as packet reordering and delay that heavily affect TCP traf&#64257;c. In this paper we introduce CoMP, a network coding multipath forwarding scheme that improves the reliability and the performance of TCP sessions in wireless mesh networks. CoMP exploits the wireless mesh path diversity using network coding, performs congestion control and uses a credit-based method to control the rate at which linear combinations are transmitted. CoMP uses a simple algorithm to estimate losses and to send redundant linear combinations in order to maintain the decoding delay at a minimum and to prevent TCP timeouts and retransmissions. We evaluate CoMP through extensive simulations and compare it to state-of-the-art protocols. We show that CoMP not only achieves a higher throughput, but also is more ef&#64257;cient than existing protocols, making TCP sessions feasible for wireless mesh networks even under heavy losses.

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Multipath TCP with Network Coding for Wireless Mesh Networks

Scalable video can be used to provide video streaming reliably to an heterogeneous set of receivers with different subscription levels. However, the performance of such schemes can be highly affected by scheduling constraints and unreliable feedback. Network coding, on the other hand, has been shown to reduce scheduling and prioritization problems and to perform well in wireless scenarios with perfect feedback. Motivated by this observation, we implement and analyze a system architecture for network coding-based multiresolution video streaming in a wireless environment. In contrast to existing work, we take into account realistic feedback, where the control packets are sent over the same unreliable channel as data packets, and compare it to the case of perfect feedback, where the server has perfect knowledge of the state of the buffer at every receiver. We provide an evaluation of the system via simulation and show that even in highly volatile environments, a network coding-based scheme with limited and unreliable feedback can achieve a good performance.

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On the Performance of Network Coding in Multi-Resolution Wireless Video Streaming

Described herein is a method and system for hierarchical wireless video with network coding which limits encryption operations to a critical set of network coding coefficients in combination with multi-resolution video coding. Such a method and system achieves hierarchical fidelity levels, robustness against wireless packet loss and efficient security by exploiting the algebraic structure of network coding.

Steluta Gheorghiu

Papers

Secure network coding for multi-resolution wireless video streaming

Multipath code casting for wireless mesh networks

Multipath TCP with Network Coding for Wireless Mesh Networks

On the Performance of Network Coding in Multi-Resolution Wireless Video Streaming

Secure Network Coding for Multi-Resolution Wireless Transmission