Written by leading authority Ramjee Prasad, this timely new work offers a complete understanding of OFDM technology and applications in wireless communications systems, placing emphasis on wireless LANs and PANs. OFDM is a key technology for beyond 3G communications, promising robust, high capacity, high speed wireless broadband multimedia networks. In this practical resource, established and new technologies are explained clearly and comprehensively, from OFDM basics to a detailed account of a new technique, hybrid OFDM CDMA slow frequency hopping. The book offers an in-depth treatment of the underlying technologies and applications of PANs and describes and evaluates a practical OFDM system concept. Invaluable for wireless engineers and researchers, this cutting edge new book is a must-have for anyone who needs to understand this critical technology and its implementation in WLANs and WPANs.

OFDM for Wireless Communications Systems

Previous research in wireless ad hoc networks typically assumes the use of omnidirectional antennas at all nodes. With omnidirectional antennas, while two nodes are communicating using a given channel, MAC protocols such as IEEE 802.11 require all other nodes in the vicinity to stay silent. With directional antennas, two pairs of nodes located in each other's vicinity may potentially communicate simultaneously, depending on the directions of transmission. This can increase spatial reuse of the wireless channel. In addition, the higher gain of directional antennas allows a node to communicate with other nodes located far away, implying that messages could be delivered to the destination in fewer hops. In this paper, we propose a MAC protocol that exploits the characteristics of directional antennas. Our design focuses on using multi-hop RTSs to establish links between distant nodes, and then transmit CTS, DATA and ACK over a single hop. Results show that our directional MAC protocol can perform better than IEEE 802.11, although we find that the performance is dependent on the topology configuration and the flow patterns in the system.

/pdf/using-directional-antennas-for-medium-access-control-in-ad-a8cupucoqf.pdf

Using directional antennas for medium access control in ad hoc networks

With the success of wireless technologies in consumer electronics, standard wireless technologies are envisioned for the deployment in industrial environments as well. Industrial applications involving mobile subsystems or just the desire to save cabling make wireless technologies attractive. Nevertheless, these applications often have stringent requirements on reliability and timing. In wired environments, timing and reliability are well catered for by fieldbus systems (which are a mature technology designed to enable communication between digital controllers and the sensors and actuators interfacing to a physical process). When wireless links are included, reliability and timing requirements are significantly more difficult to meet, due to the adverse properties of the radio channels. In this paper, we thus discuss some key issues coming up in wireless fieldbus and wireless industrial communication systems: 1) fundamental problems like achieving timely and reliable transmission despite channel errors; 2) the usage of existing wireless technologies for this specific field of applications; and 3) the creation of hybrid systems in which wireless stations are incorporated into existing wired systems.

/pdf/wireless-technology-in-industrial-networks-3inkv4crnj.pdf

Wireless Technology in Industrial Networks

The wireless medium being inherently broadcast in nature and hence prone to interferences requires highly optimized medium access control (MAC) protocols. This holds particularly true for wireless sensor networks (WSNs) consisting of a large amount of miniaturized battery-powered wireless networked sensors required to operate for years with no human intervention. There has hence been a growing interest on understanding and optimizing WSN MAC protocols in recent years, where the limited and constrained resources have driven research towards primarily reducing energy consumption of MAC functionalities. In this paper, we provide a comprehensive state-of-the-art study in which we thoroughly expose the prime focus of WSN MAC protocols, design guidelines that inspired these protocols, as well as drawbacks and shortcomings of the existing solutions and how existing and emerging technology will influence future solutions. In contrast to previous surveys that focused on classifying MAC protocols according to the technique being used, we provide a thematic taxonomy in which protocols are classified according to the problems dealt with. We also show that a key element in selecting a suitable solution for a particular situation is mainly driven by the statistical properties of the generated traffic.

/pdf/mac-essentials-for-wireless-sensor-networks-7v5zc579kv.pdf

MAC Essentials for Wireless Sensor Networks

Sensor networks can be considered distributed computing platforms with many severe constraints, including limited CPU speed, memory size, power, and bandwidth. Individual nodes in sensor networks are typically unreliable and the network topology dynamically changes, possibly frequently. Sensor networks also differ because of their tight interaction with the physical environment via sensors and actuators. Because of this interaction, we find that sensor networks are very data-centric. Due to all of these differences, many solutions developed for general distributed computing platforms and for ad-hoc networks cannot be applied to sensor networks. After discussing several motivating applications, this paper first discusses the state of the art with respect to general research challenges, then focuses on more specific research challenges that appear in the networking, operating system, and middleware layers. For some of the research challenges, initial solutions or approaches are identified.

https://www.cse.wustl.edu/~lu/papers/pieee03.pdf

Real-time communication and coordination in embedded sensor networks

Technological advances, coupled with the flexibility and mobility of wireless systems, are the driving force behind the Anyone, Anywhere, Anytime paradigm of networking. At the same time, we see a convergence of the telephone, cable and data networks into a unified network that supports multimedia and real-time applications like voice and video in addition to data. Medium access control protocols define rules for orderly access to the shared medium and play a crucial role in the efficient and fair sharing of scarce wireless bandwidth. The nature of the wireless channel brings new issues like location-dependent carrier sensing, time varying channel and burst errors. Low power requirements and half duplex operation of the wireless systems add to the challenge. Wireless MAC protocols have been heavily researched and a plethora of protocols have been proposed. Protocols have been devised for different types of architectures, different applications and different media. This survey discusses the challenges in the design of wireless MAC protocols, classifies them based on architecture and mode of operation, and describes their relative performance and application domains in which they are best deployed.

/pdf/wireless-medium-access-control-protocols-eu9s5ys5dz.pdf

Wireless medium access control protocols

A system and method for providing high speed wireless media access is disclosed. A local transceiver is provided, which is capable of transmitting data via a transmit path while receiving a feedback signal via a receive path. The local transmitter is connected to a feedback generator for generating and transmitting a feedback signal in response to receiving data from a wireless transceiver. A feedback detector is also connected to the local transceiver for detecting feedback signals received from other wireless transceivers. When a feedback signal is detected, data associated with the signal is decoded. The wireless transceivers then transmit a feedback signal within the series of wireless transceivers in order to stop the transmission of data until a destination of the data is determined. A destination address associated with a destination wireless transceiver is then identified and the transmission of feedback signals by all wireless transceivers within the system then ceases, except from the identified destination wireless transceiver.

System and method for providing high speed wireless media access

A multi-source data multiplexing system that accepts information packets from a plurality of signal sources, evaluates the relative efficiencies of data transmission, and transmits the information packets in provided grant regions for maximum efficiency. The multi-source data multiplexing system may accept any form of information packet from any form of signal source. The system receives a grant region, typically comprising a transmission time on a data channel, and inserts a information packet into the grant region. The actual information packet placed in the grant region may be one other than the packet for which the grant region was intended. Further, the multi-source data multiplexing system may fragment an information packet and transmit only a portion of the information packet in the grant region. Alternately, the multi-source data multiplexing system may concatenate multiple information packets, or information packet fragments, from any combination of signal sources and transmit the concatenated result in the grant region. As long as any signal source is active, the composite flow of information packets remains active, and the composite flow then serves as the primary mechanism for requesting and transmitting additional bandwidth on the network.

System and method for multiplexing data from multiple sources

The cable TV plant is a broad bandwidth channel into the home and community that has been used primarily for the distribution of television. As the plant is upgraded, there is an opportunity to use it for the transport of high-speed digital signals. While the downstream channel is relatively easy to exploit, the topology and physical characteristics of the upstream channel present new challenges at both the physical and the media access layers. We present a media access protocol that efficiently transfers data on this channel. A primary goal of the design is to keep that portion of the protocol resident in the station as simple as possible. Thus, we use centralized control located in the cable head-end. A station wishing to transmit sends a request to the head-end using a contention channel. The head-end acknowledges the request and then schedules the request, informing the station, by means of a grant message, exactly when to transmit. The protocol performs efficiently under a wide range of conditions, and is robust in the presence of channel errors.

A protocol for efficient transfer of data over hybrid fiber/coax systems

A revolution is occurring in the scope and range of information, communication and education services that will be made available to schools, libraries, town-halls, clinics and, most importantly, residences. These services will be provided initially, primarily over hybrid fiber-cable systems, either by telephone companies or cable companies. The old cable plant is being upgraded and used in totally new ways. The topology and physical characteristics of the upstream channel present new challenges for efficient channel access. We present a media access protocol that efficiently transfers data on this channel. A primary goal in the design was to keep the portion of the protocol resident in the station as simple as possible. Thus we use centralized control located in the cable head-end and minimize intelligence in the station. We refer to this protocol as centralized priority reservation or CPR. A station wishing to transmit sends a request to the head-end using a contention channel. The head-end acknowledges the request and then schedules the request, informing the station by means of a grant message when to transmit. The protocol performs well under heavy load. Performance is affected little by the number of stations, the speed of the system and the physical length of the system.

John O. Limb

Papers

Wireless medium access control protocols

System and method for providing high speed wireless media access

System and method for multiplexing data from multiple sources

A protocol for efficient transfer of data over hybrid fiber/coax systems

A protocol for efficient transfer of data over fiber/cable systems