Abstract: IEEE 802.11n is an ongoing next-generation wireless LAN standard that supports a very highspeed connection with more than 100 Mb/s data throughput measured at the medium access control layer. This article investigates the key MAC enhancements that help 802.11n achieve high throughput and high efficiency. A detailed description is given for various frame aggregation mechanisms proposed in the latest 802.11n draft standard. Our simulation results confirm that A-MSDU, A-MPDU, and a combination of these methods improve extensively the channel efficiency and data throughput. We analyze the performance of each frame aggregation scheme in distinct scenarios, and we conclude that overall, the two-level aggregation is the most efficacious.

Abstract: The Time Synchronized Mesh Protocol (TSMP) enables reliable, low power, secure communication in a managed wireless mesh network. TSMP is a medium access and networking protocol designed for the recently ratified Wireless HART standard in industrial automation. TSMP benefits from synchronization of nodes in a multi-hop network to within a few hundred microseconds, allowing scheduling of collision-free pair-wise and broadcast communication to meet the traffic needs of all nodes while cycling through all available channels. Latency and reliability guarantees can be traded off for energy use, though our focus has been on providing high reliability (>99.9%) networks at the lowest power possible. TSMP has been demonstrated in multi-hop networks exceeding 250 nodes per access point, thousands of nodes with multiple access points, radio duty cycles of 0.01%, and with devices at radically different temperatures and traffic levels. With the 802.15.4 physical layer and 10 ms time slots, TSMP can theoretically achieve a secure payload throughput of 76 kbps at a single egress point.

Abstract: 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.

Abstract: Authentication is the process where claims of identity are verified. Most mechanisms of authentication (e.g., digital signatures and certificates) exist above the physical layer, though some (e.g., spread-spectrum communications) exist at the physical layer often with an additional cost in bandwidth. This paper introduces a general analysis and design framework for authentication at the physical layer where the authentication information is transmitted concurrently with the data. By superimposing a carefully designed secret modulation on the waveforms, authentication is added to the signal without requiring additional bandwidth, as do spread-spectrum methods. The authentication is designed to be stealthy to the uninformed user, robust to interference, and secure for identity verification. The tradeoffs between these three goals are identified and analyzed in block fading channels. The use of the authentication for channel estimation is also considered, and an improved bit-error rate is demonstrated for time-varying channels. Finally, simulation results are given that demonstrate the potential application of this authentication technique.

Abstract: If you've been searching for a way to get up to speed quickly on IEEE 802.11n without having to wade through the entire standard, then look no further. This comprehensive overview describes the underlying principles, implementation details, and key enhancing features of 802.11n. A detailed discussion of the key throughput, robustness, and reliability enhancing features (such as MIMO, 40 MHz channels, and packet aggregation) is given, in addition to a clear summary of the issues surrounding legacy interoperability and coexistence. Advanced topics such as beamforming and fast link adaption are also covered. With numerous MAC and physical layer examples and simulation results included to highlight the benefits of the new features, this is an ideal reference for designers of WLAN equipment, and network managers whose systems adopt the new standard. It is also a useful distillation of 802.11n technology for graduate students and researchers in the field of wireless communication.

Abstract: While the practical coding scheme has been shown to be able to improve throughput of wireless networks, there still lacks fundamental understanding on how the coding scheme works under realistic settings, namely, when it operates on a realistic physical layer and the medium access is controlled by some random access methods. In this paper, we provide a formal analysis on the performance of the practical coding scheme under such realistic settings. The key performance measure is the encoding number, i.e., the number of packets that can be encoded by a coding node in each transmission. We provide an upper bound on the encoding number for the general coding topology, and derive the average encoding number and system throughput for a general class of random access mechanisms. Based on the practical coding scheme, we also derive a tighter upper bound on the throughput gain for a general wireless network. Our results can be particularly useful for coding-related MAC/Routing protocol design and analysis.

Abstract: This article provides insight into the IEEE 802.1 In standard amendment development process, beginning with a general overview of the IEEE 802.11 process. Development of requirements and usage models in the study group and task group is discussed. The lengthy proposal down selection process used by 802.11n is described and critiqued. We also discuss the expected time to develop a standard from a market perspective. An overview of the physical layer technology used to achieve the 600 Mb/s data rate is presented. We outline the medium access layer features employed to enhance usable throughput to over 400 Mb/s. The added robustness afforded by techniques in the standard and issues with backward compatibility with legacy IEEE 802.1 la/g devices are addressed.

Abstract: We consider power control in cognitive radio networks where secondary users identify and exploit instantaneous and local spectrum opportunities without causing unacceptable interference to primary users. We qualitatively characterize the impact of the transmission power of secondary users on the occurrence of spectrum opportunities and the reliability of opportunity detection. Based on a Poisson model of the primary network, we quantify these impacts by showing that (i) the probability of spectrum opportunity decreases exponentially with respect to the transmission power of secondary users, where the exponential decay constant is given by the traffic load of primary users; (ii) reliable opportunity detection is achieved in the two extreme regimes in terms of the ratio between the transmission power of secondary users and that of primary users. Such analytical characterizations allow us to study power control for optimal transport throughput under constraints on the interference to primary users. Furthermore, we reveal the difference between detecting primary signals and detecting spectrum opportunities, and demonstrate the complex relationship between physical layer spectrum sensing and MAC layer throughput. The dependency of this PHY-MAC interaction on the application type and the use of handshake signaling such as RTS/CTS is illustrated.

Abstract: Embodiments of a method and system for automatically installing and managing consumer devices in a home network environment are described. A system implements automated configuration and maintenance of devices and their peripherals that connect to the home network, in particular the establishment of a distributed system that serves as a service platform which facilitates automated discovery and initial and ongoing deployment of a home networks and the devices that may interact with or connect to their network automatically or through manual means. An embodiment is directed to a distributed system and method for facilitated automatic configuration, maintenance, and diagnostics of a local area network that in parallel provides for the interoperability of connected intelligent independent computing devices using physical layer, network layer and application layer programmatic interfaces. This distributed system provides a generalized aggregated interface that is a programmatic resource for representing a continuous and historic reference of a local network and connected devices.

Abstract: We propose cross-layer optimization frameworks for multihop wireless networks using cooperative diversity. These frameworks provide solutions to fundamental relaying problems of determining who should be relays for whom and how to perform resource allocation for these relaying schemes jointly with routing and congestion control such that the system performance is optimized. We present a fully distributed algorithm where the joint routing, relay selection, and power allocation problem to minimize network power consumption is solved by using convex optimization. Via dual decomposition, the master optimization problem is decomposed into a routing subproblem in the network layer and a joint relay selection and power allocation subproblem in the physical layer, which can be solved efficiently in a distributed manner. We then extend the framework to incorporate congestion control and develop a framework for optimizing the sum rate utility and power tradeoff for wireless networks using cooperative diversity. The numerical results show the convergence of the proposed algorithms and significant improvement in terms of power consumption and source rates due to cooperative diversity.

Abstract: Cognitive radio technology has emerged as the novel and effective approach to improve the utilization of precious radio spectrum. Employing the cognitive radio technology, secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that constrains the level of interference to the primary (licensed) users. However, there are many new challenges associated with cognitive radio based wireless networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability is different for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient cognitive radio-enabled multi-channel MAC (CREAM-MAC) protocol, which integrates the spectrum sensing at physical layer and packet scheduling at MAC layer, over the wireless networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. In addition, we develop the analytical models to quantitatively analyze our proposed CREAM-MAC protocol in the saturated network case. We also conduct simulation experiments to validate our developed analytical models.

Abstract: The flexible interface between the medium access layer and the custom physical layer of the Rice University Wireless Open-Access Research Platform (WARP) provides a high performance research tool for clean-slate cross layer designs. As we target a community platform, we have implemented various basic PHY and MAC technologies over WARP. Moreover, we are implementing cross-layer schemes such as rate adaptation and crosslayer MIMO MAC protocols. In this demo, we demonstrate the flexibility of the interaction between the the WARP PHY and MAC layers by showing the capability to instantaneously change the modulation scheme, disabling/enabling MAC features such as carrier sensing or RTS/CTS 4-way handshake, and different multi-rate schemes.

Abstract: We propose a cross-layer design which combines truncated ARQ at the link layer and cooperative diversity at the physical layer. In this scheme, both the source node and the relay nodes utilize an orthogonal space-time block code for packet retransmission. In contrast to previous cooperative diversity protocols, here cooperative diversity is invoked only if the destination node receives an erroneous packet from the source node. In addition, the relay nodes are not fixed and are selected according to the channel conditions using CRC. It will be shown that this combination of adaptive cooperative diversity and truncated ARQ can greatly improve the system throughput compared to the conventional truncated ARQ scheme and fixed cooperative diversity protocols. We further maximize the throughput by optimizing the packet length and modulation level and will show that substantial gains can be achieved by this joint optimization. Since both the packet length and modulation level are usually discrete in practice, a computationally efficient algorithm is further proposed to obtain the discrete optimal packet length and modulation level.

Abstract: Wireless sensor networks pose numerous fundamental coordination problems. For example, in a number of application domains including homeland security, environmental monitoring, and surveillance for military operations, a network's ability to efficiently manage power consumption is extremely critical because direct user intervention after initial deployment is severely limited. In these settings, limited battery life gives rise to the basic coordination problem of maintaining coverage while maximizing the network's lifetime. In this paper, we propose a distributed scheme for efficient power management in sensor networks that is guaranteed to identify suboptimal topologies in an online fashion. Our scheme is based on a general (game-theoretic) mathematical structure that induces a natural mapping between the informational layer and the physical layer. We provide sufficient conditions for the convergence of the algorithm to a pure Nash equilibrium and characterize the performance of the algorithm in terms of coverage. We also present encouraging performance results on a MicaZ testbed as well as on large-scale topologies (obtained via simulation).

Abstract: In a network supporting cooperative communication, the sender of a transmission is no longer a single node, which causes the concept of a traditional link to be reinvestigated. Thus, the routing scheme basing on the link concept should also be reconsidered to ";truly"; exploit the potential performance gain introduced by cooperative communication. In this paper, we investigate the joint problem of routing selection in network layer and contention avoidance among multiple links in MAC layer for multi-hop wireless networks in a cooperative communication aware network. To the best of our knowledge, it is the first work to investigate the problem of cooperative communication aware routing in multi-source multi-destination multi-hop wireless networks. Several important concepts, including virtual node, virtual link and virtual link based contention graph are introduced. Basing on those concepts, an optimal cooperative routing is achieved and a distributed routing scheme is proposed after some practical approximations. The simulation results show that our scheme reduces the total transmission power comparing with non-cooperative routing and greatly increases the network throughput comparing with single flow cooperative routings.

Abstract: In this paper, we propose a cross-layer optimization scheme for delivery of scalable video over multirate wireless networks, in particular the popular 802.11 based wireless local area network (WLAN). The 802.11 based networks use a link adaptation mechanism in the physical layer (PHY) to maintain the reliability of transmission under varying channel conditions. When channel condition worsens, the reliability is maintained by employing more robust modulation and coding schemes, at the cost of reduced PHY bit rate. The reduced bit rate will result in lower available throughput for applications. For scalable video streaming applications, the conventional solution to this problem is to reduce the video bit rate by dropping the higher enhancement layers of the scalable video. We show in this article that the video quality can be improved, if the link adaptation scheme uses more intelligent reliability criteria and adjusts the PHY parameters used for delivering each video layer, according to the relative importance of that layer. Our scheme achieves better video quality without increasing the traffic load of the WLAN. For this purpose we present temporal fairness constraints and formulate an optimization problem for assigning different PHY modes to different layers of scalable video; the solution to this problem provides a set of PHY configuration parameters that achieve the highest possible video quality while meeting the admission control constraints in the network. Performance evaluations demonstrate that our method outperforms the existing mechanisms.

Abstract: The emergence of WiMAX has attracted significant interests from all the fields of wireless communications including students, researchers, systems engineers and operators. WiMAX has been tipped to bring a revolution in the way we use broadband services today. The WiMAX can also be considered to be the main technology in the implementation of other networks like wireless sensor networks. Developing an understanding of the WiMAX system can be best achieved by looking at a model of the WiMAX system. This paper discusses the model building of the WiMAX Physical layer using Simulink in Matlab. This model is a useful tool for performance evaluation of the WiMAX under different data rates, coding schemes and channel conditions besides serving as a helpful resource for the students and the researchers who want to base their studies and research on the fields related to the WiMAX. Standards from IEEE and ETSI have been used to develop this model. The model presented in this paper built with generic MAC PDU processed by the Physical Layer using Convolutional Encoding Rate of 5/6 with QPSK modulation and transmitted with 256 carrier OFDM symbols.

Abstract: In this paper, we address the following two questions concerning the capacity and configuration of fixed wireless networks: (i) given a set of wireless nodes with arbitrary but fixed locations, and a set of data flows, what is the max-min achievable throughput? and (ii) how should the network be configured to achieve the optimum? We consider these questions from a networking standpoint assuming point-to-point links, and employ a rigorous physical layer model to model conflict relationships between them. Since we seek capacity results, we assume that the network is operated using an appropriate schedule of conflict-free link activations. We develop and investigate a novel optimization framework to determine the optimal throughput and configuration, i.e., flow routes, link activation schedules and physical layer parameters. Determining the optimal throughput is a computationally hard problem, in general. However, using a smart enumerative technique we obtain numerical results for several different scenarios of interest. We obtain several important insights into the structure of the optimal routes, schedules and physical layer parameters. Besides determining the achievable throughput, we believe that our optimization-based framework can also be used as a tool, for configuring scheduled wireless networks, such as those based on IEEE 802.16.

Abstract: In this paper, we focus on the resources allocation for the OFDMA based two-hop relay network which consists of a single base station, dedicated fixed relay stations and subscriber stations. Subscriber stations are allocated the subcarriers and relay stations that are required to satisfy their minimum rate requirements in either non-cooperative mode (i.e., direct communication with the base station) or in cooperative mode with one of the available relay stations. The cooperation is limited to one relay station to reduce the complexity incurred by the need for synchronization with multiple relays and with the base station at the PHY layer. The subcarriers and relay stations allocation problem is formulated as a Binary Integer Programming (BIP) problem with QoS constraints (minimum rate) and a practical synchronization constraint (cooperation with a single relay). Since the formulated problem is NP-complete, a simple sub-optimal algorithm is proposed to manage the multi-service network resources. Simulations and complexity analysis show that the presented algorithm achieves a network near optimal resources allocation with low computational complexity.

Abstract: Rapid channel failure detection and recovery in wireless communication networks is needed in order to meet, among other things, carrier class Ethernet channel standards. Thus, resilient wireless packet communications is provided using a physical layer link aggregation protocol with a hardware-assisted rapid channel failure detection algorithm and load balancing, preferably in combination. This functionality may be implemented in a Gigabit Ethernet data access card with an engine configured accordingly. In networks with various topologies, these features may be provided in combination with their existing protocols.

Abstract: The 802.11p protocol, also known as wireless access for the vehicular environment (WAVE), has recently gained momentum in the area of research and development. The WAVE protocol provides enhancements to the physical (PHY) and medium access control (MAC) layers of the existing 802.11 wireless standards. These enhancements are required to support the intelligent transportation systems (ITS) initiatives of the US Department of Transportation regarding vehicle-to-vehicle, vehicle-to-infrastructure, and infrastructure-to-vehicle communication. Many research groups have contributed to the development of the protocol. Many of the same individuals have worked to extend the ns-2 network simulator to correctly simulate wireless mobile networking, specifically vehicle adhoc networks (VANETs). The objective of this research project is to measure the performance of the WAVE protocol at the MAC layer, using the ns-2 simulator. Specifically, the simulations measure aggregate throughput, average delay, and packet loss metrics.

Abstract: The exploitation of adaptive coding and modulation techniques for broadband multi-beam satellite communication networks operating at Ka-band and above has been shown to theoretically provide large system capacity gains. In this paper, the problem of how to accurately estimate the time-variant channel and how to adapt the physical layer taking into account the effects of estimator errors and (large) satellite propagation delays is analyzed, and practical solutions for both the forward and the reverse link are proposed. A novel pragmatic solution to the reverse link physical layer channel estimation in the presence of time-variant bursty interference has been devised. Physical layer adaptation algorithms jointly with design rules for hysteresis thresholds have been analytically derived. The imperfect physical layer channel estimation impact on the overall system capacity has been finally derived by means of an original semi-analytical approach. Through comprehensive system simulations for a realistic system study case, it is showed that the devised adaptation algorithms are able to successfully track critical Ka-band fading time series with a limited impact on the system capacity while satisfying the link outage probability requirement. Copyright © 2008 John Wiley & Sons, Ltd.

Abstract: A system that incorporates teachings of the present disclosure may include, for example, a server comprising a controller to monitor a physical layer, a data link layer and a network layer of an Internet Protocol Television (IPTV) network, obtain a plurality of alarm signals from one or more of the physical layer, the data link layer and the network layer that are associated with an undesired condition of the IPTV network, synthesize the plurality of alarm signals to determine a correlation, obtain topology information associated with network devices in the IPTV network, and isolate the undesired condition to a network component in the IPTV network using the correlation and the topology information. Other embodiments are disclosed.

Abstract: In WDM all-optical networks where electrical regeneration is not available, physical impairments due to propagation in the fibers, amplifier noise, and leaks between channels and in the switches cannot be removed at the physical layer These effects cause calls, especially between physically distant nodes, to be rejected because they cannot meet minimum Quality of Transmission (QoT) requirements, as measured by signal bit-error rates It is possible to mitigate physical layer effects at the network layer using appropriate Routing and Wavelength Assignment (RWA) algorithms We present new RWA algorithms which account for physical impairments in their design and increase QoT and fairness among users without sacrificing low blocking probabilities in metropolitan-sized networks We also present RWA algorithms that can sharply decrease blocking probabilities in regional-sized networks using optional channel coding All algorithms are evaluated through simulation in realistic scenarios and shown to successfully mitigate crosstalk effects and to perform better in terms of QoT and network access fairness than traditional algorithms

Abstract: A cross-layer multi-packet reception media access control and resource allocation technique is provided for wireless networks having receivers with multiple antennas. User devices on the wireless network access the network for data transmission by making a request to send (RTS) request after a random backoff time. In response to a request to send, an access point (or other receiver) determines transmission parameters that optimize the use of the physical layer based at least in part on channel state information. Those transmission parameters are transmitted along with a clear to send (CTS) message from the receiver to an indicated transmitter. Once the CTS message is received, data is transmitted in accordance with transmission parameters.

Abstract: A network data monitoring device provides for the flexible, programmable port-to-multi-port steering of data packet traffic between network port pairs, with tap data streams being directed to any of a plurality of monitor ports. The network data monitoring device is constructed utilizing one or more switching integrated circuits programmed to disable layer-2 routing and impose port-to-multiport data packet steering. Physical layer protocol encoding/decoding circuits enable connectivity to physical network media connectors though a system of fail-safe relays. A system controller, preferably implemented by a microprocessor, is connected to all switching integrated circuits and relays for configuration, status and control. Hardware-based logic selectively in complement to the switching integrated circuits provides for the programmable filtering, modification and programmable steering of data packets through the device.

Abstract: The benefits of using cognitive information at the physical layer, as in cognitive radios, are many. In this article, we propose CogNet -- a cognitive complete knowledge network system -- which makes use of a large amount of information that can be gained from the experience of each node to improve the overall network and user performance. CogNet gathers, processes, analyzes, and stores information available through a variety of devices and protocols to build an omnipresent, distributed repository that holds the spatiotemporal, network-experience information. The inexpensiveness and plentifulness of storage resources and increasing processing power in handheld devices help accelerate the development of CogNet-like systems. Our contribution in this article is the proposal of the architecture and of the communication elements, as well as a transport layer application of CogNet as a proof of concept for possible application scenarios of such a system. We also present performance evaluation of CogTCP, the CogNetenabled TCP, which exploits the transport layer experience of other nodes for improved performance. From our experiments, we found that the use of cognitive information is very useful for networking.

Abstract: As a part of the EU-FP7 R&D programme, the OMEGA project (hOME Gigabit Access) aims at bridging the gap between mobile broadband terminals and the wired backbone network in homes. To provide Gb/s connectivity a combination of various technologies is considered. Beside radio frequencies, the wireless links will use infrared and visible light. Combined with power-line communications this enables a home area network (HAN) that meets the vision of broadband home networking dasiawithout new wirespsila. A technology-independent MAC layer is foreseen to control such network and to provide services as well as connectivity to any device the user wishes to connect. Moreover, this MAC layer should allow the service to follow the user from device to device in any room of a building /apartment. The contribution presents ideas and approaches for broadband optical wireless (OW) communications using infrared Gb/s hotspots and 100 Mb/s information broadcasting by means of interior lighting based on white-light LEDs. Important issues concerning the physical layer are discussed.

Abstract: The idea of cognitive radio has created a great interest in academic and industrial research recently. As a result, there are a large number of proposals for physical and network layer functionalities. In this paper, we demonstrate an experimental platform with the USRP board developed by Ettus Research that can facilitate the development of PHY and MAC layers functionality. Some key results from this experience so far are presented, including an over-the-air interoperability analysis of two different SDR (software defined radio) architectures in the same frequency band, the effect of dynamic spectrum access on legacy system and analysis of actual co-existence experiences involving primary users and secondary opportunistic spectrum users. In particular, we focus our attention on spectrum sensing and spectrum coexistence as an example that incorporates both digital signal processing and networking techniques to show how this platform could be used to conduct comprehensive research in cognitive radio.