Showing papers in "IEEE Communications Magazine in 2005"

A survey on wireless mesh networks

Abstract: Wireless mesh networks (WMNs) have emerged as a key technology for next-generation wireless networking. Because of their advantages over other wireless networks, WMNs are undergoing rapid progress and inspiring numerous applications. However, many technical issues still exist in this field. In order to provide a better understanding of the research challenges of WMNs, this article presents a detailed investigation of current state-of-the-art protocols and algorithms for WMNs. Open research issues in all protocol layers are also discussed, with an objective to spark new research interests in this field.

Cross-layer design: a survey and the road ahead

Abstract: Of late, there has been an avalanche of cross-layer design proposals for wireless networks. A number of researchers have looked at specific aspects of network performance and, approaching cross-layer design via their interpretation of what it implies, have presented several cross-layer design proposals. These proposals involve different layers of the protocol stack, and address both cellular and ad hoc networks. There has also been work relating to the implementation of cross-layer interactions. It is high time that these various individual efforts be put into perspective and a more holistic view be taken. In this article, we take a step in that direction by presenting a survey of the literature in the area of cross-layer design, and by taking stock of the ongoing work. We suggest a definition for cross-layer design, discuss the basic types of cross-layer design with examples drawn from the literature, and categorize the initial proposals on how cross-layer interactions may be implemented. We then highlight some open challenges and new opportunities for cross-layer design. Designers presenting cross-layer design proposals can start addressing these as they move ahead.

A centralized energy-efficient routing protocol for wireless sensor networks

Abstract: Wireless sensor networks consist of small battery powered devices with limited energy resources. Once deployed, the small sensor nodes are usually inaccessible to the user, and thus replacement of the energy source is not feasible. Hence, energy efficiency is a key design issue that needs to be enhanced in order to improve the life span of the network. Several network layer protocols have been proposed to improve the effective lifetime of a network with a limited energy supply. In this article we propose a centralized routing protocol called base-station controlled dynamic clustering protocol (BCDCP), which distributes the energy dissipation evenly among all sensor nodes to improve network lifetime and average energy savings. The performance of BCDCP is then compared to clustering-based schemes such as low-energy adaptive clustering hierarchy (LEACH), LEACH-centralized (LEACH-C), and power-efficient gathering in sensor information systems (PEGASIS). Simulation results show that BCDCP reduces overall energy consumption and improves network lifetime over its comparatives.

Mesh networks: commodity multihop ad hoc networks

Abstract: In spite of the massive efforts in researching and developing mobile ad hoc networks in the last decade, this type of network has not yet witnessed mass market deployment. The low commercial penetration of products based on ad hoc networking technology could be explained by noting that the ongoing research is mainly focused on implementing military or specialized civilian applications. On the other hand, users are interested in general-purpose applications where high bandwidth and open access to the Internet are consolidated and cheap commodities. To turn mobile ad hoc networks into a commodity, we should move to more pragmatic "opportunistic ad hoc networking" in which multihop ad hoc networks are not isolated self-configured networks, but rather emerge as a flexible and low-cost extension of wired infrastructure networks coexisting with them. Indeed, a new class of networks is emerging from this view: mesh networks. This article provides an overview of mesh networking technology. In particular, starting from commercial case studies we describe the core building blocks and distinct features on which wireless mesh networks should be based. We provide a survey of the current state of the art in off-the-shelf and proprietary solutions to build wireless mesh networks. Finally, we address the challenges of designing a high-performance, scalable, and cost-effective wireless mesh network.

Broadband wireless access with WiMax/802.16: current performance benchmarks and future potential

Abstract: The IEEE 802.16 family of standards and its associated industry consortium, WiMax, promise to deliver high data rates over large areas to a large number of users in the near future. This exciting addition to current broadband options such as DSL, cable, and WiFi promises to rapidly provide broadband access to locations in the world's rural and developing areas where broadband is currently unavailable, as well as competing for urban market share. WiMax's competitiveness in the marketplace largely depends on the actual data rates and ranges that are achieved, but this has been difficult to judge due to the large number of possible options and competing marketing claims. This article first provides a tutorial overview of 802.16. Then, based on extensive recent studies, this article presents the realistic attainable throughput and performance of expected WiMax compatible systems based on the 802.16d standard approved in June 2004 (now named 802.16-2004). We also suggest future enhancements to the standard that could at least quadruple the achievable data rate, while also increasing the robustness and coverage, with only moderate complexity increases

Approaches to spectrum sharing

Abstract: Many complain about severe spectrum shortage. The shortage comes from outdated spectrum policies that allows for little sharing. Regulators have granted licenses that offer exclusive access to the spectrum. When these licensees are not transmitting, the spectrum sits idle. A new technology regarding spectrum shortage enables more spectrum sharing that unleashes innovative products and services, provided that we adopt the appropriate spectrum policies. Two camps are pushing for extreme reform, one for "property rights" and the other for "spectrum commons". This article presents concepts underlying the "property" and "commons" debate, clarifies options for spectrum reform, and describes the trade-offs of spectrum sharing

Self-organization in communication networks: principles and design paradigms

Abstract: The trend toward ubiquitous wireless communication demands for a higher level of self-organization in networks. This article gives an introduction and overview on this topic and investigates the fundamental question: What are design paradigms for developing a self-organized network function? We propose four paradigms and show how they are reflected in current protocols: design local interactions that achieve global properties, exploit implicit coordination, minimize the maintained state, and design protocols that adapt to changes. Finally, we suggest a general design process for self-organized network functions.

Self-policing mobile ad hoc networks by reputation systems

Abstract: Node misbehavior due to selfish or malicious reasons or faulty nodes can significantly degrade the performance of mobile ad hoc networks. To cope with misbehavior in such self-organized networks, nodes need to be able to automatically adapt their strategy to changing levels of cooperation. Existing approaches such as economic incentives or secure routing by cryptography alleviate some of the problems, but not all. We describe the use of a self-policing mechanism based on reputation to enable mobile ad hoc networks to keep functioning despite the presence of misbehaving nodes. The reputation system in all nodes makes them detect misbehavior locally by observation and use of second-hand information. Once a misbehaving node is detected it is automatically isolated from the network. We classify the features of such reputation systems and describe possible implementations of each of them. We explain in particular how it is possible to use second-hand information while mitigating contamination by spurious ratings.

A road to future broadband wireless access: MIMO-OFDM-Based air interface

Abstract: Orthogonal frequency-division multiplexing is a popular method for high-data-rate wireless transmission. OFDM may be combined with multiple antennas at both the access point and mobile terminal to increase diversity gain and/or enhance system capacity on a time-varying multipath fading channel, resulting in a multiple-input multiple-output OFDM system. In this article we give a brief technical overview of MIMO-OFDM system design. We focus on various research topics for the MIMO-OFDM-based air interface, including spatial channel modeling, MIMO-OFDM transceiver design, MIMO-OFDM channel estimation, space-time techniques for MIMO-OFDM, and error correction code. The corresponding link-level simulation results are encouraging, and show that MIMO-OFDM is a promising road to future broadband wireless access.

TCP in wireless environments: problems and solutions

Abstract: The Internet provides a platform for rapid and timely information exchange among a disparate array of clients and servers. TCP and IP are separately designed and closely tied protocols that define the rules of communication between end hosts, and are the most commonly used protocol suite for data transfer in the Internet. The combination of TCP/IP dominates today's communication in various networks from the wired backbone to the heterogeneous network due to its remarkable simplicity and reliability, TCP has become the de facto standard used in most applications ranging from interactive sessions such as Telnet and HTTP, to bulk data transfer like FTP. TCP was originally designed primarily for wired networks. In a wired network, random bit error rate, a characteristic usually more pronounced in the wireless network, is negligible, and congestion is the main cause of packet loss. The emerging wireless applications, especially high-speed multimedia services and the advent of wireless IP communications carried by the Internet, call for calibration and sophisticated enhancement or modifications of this protocol suite for improved performance. Based on the assumption that packet losses are signals of network congestion, the additive increase multiplicative decrease congestion control of the standard TCP protocol reaches the steady state, which reflects the protocol's efficiency in terms of throughput and link utilization. However, this assumption does not hold when the end-to-end path also includes wireless links. Factors such as high BER, unstable channel characteristics, and user mobility may all contribute to packet losses. Many studies have shown that the unmodified standard TCP performs poorly in a wireless environment due to its inability to distinguish packet losses caused by network congestion from those attributed to transmission errors. In this article, following a brief introduction to TCP, we analyze the problems TCP exhibits in the wireless IP communication environment, and illustrate viable solutions by detailed examples.

Utility-based resource allocation and scheduling in OFDM-based wireless broadband networks

Abstract: This article discusses downlink resource allocation and scheduling for OFDM-based broadband wireless networks. We present a cross-layer resource management framework leveraged by utility optimization. It includes utility-based resource management and QoS architecture, resource allocation algorithms, rate-based and delay-based multichannel scheduling that exploits wireless channel and queue information, and theoretical exploration of the fundamental mechanisms in wireless resource management, such as capacity, fairness, and stability. We also provide a solution that can efficiently allocate resources for heterogeneous traffic with diverse QoS requirements.

Ultra-wideband for multiple access communications

Abstract: Ultra-wideband wireless communications techniques have many merits, including an extremely simple radio that inherently leads to low-cost design, large processing gain for robust operations in the presence of narrowband interference, covert operations, and fine time resolution for accurate position sensing. However, there are a number of challenges in UWB receiver design, such as capturing multipath energy, intersymbol interference especially in a non-line-of-sight environment, and the need for high-sampling-rate analog-to-digital converters. In this article, we provide a comprehensive review of UWB multiple access and modulation schemes, and their comparison with narrowband radios. We also outline the issues with UWB signal reception and detection, and explore various suboptimal low-complexity receiving schemes

NGN architecture: generic principles, functional architecture, and implementation

Abstract: This article summarizes the architectural aspects of a next-generation network in terms of general principles, functional representation, and typical implementation. According to the general reference model, which assumes decoupling of services and transport, NGN can be represented by multiple functional groups. One of the key implementations for session-based services, utilizing an IP multimedia subsystem, is introduced with enhanced features to meet both fixed and mobile network requirements.

Routing in ad hoc networks: a case for long hops

Abstract: For multihop wireless networks, a fundamental question is whether it is advantageous to route over many short hops (short-hop routing) or over a smaller number of longer hops (long-hop routing). Short-hop routing has gained a lot of support, and its proponents mainly produce two arguments: reduced energy consumption and higher signal-to-interference ratios. Both arguments stem from a simplified analysis based on crude channel models that neglects delay, end-to-end reliability, bias power consumption, the impact of channel coding, mobility, and routing overhead. In this article we shed more light on these issues by listing 18 reasons why short-hop routing is not as beneficial as it seems to be. We also provide experimental evidence to support this claim. The conclusion is that for many networks, long-hop routing is in every aspect a very competitive strategy.

Ad hoc peer-to-peer network architecture for vehicle safety communications

Abstract: This article addresses the design of an architecture for ad hoc peer-to-peer networking of neighboring vehicles to help achieve near-instantaneous communication for safety applications such as collision avoidance warnings. We propose a local peer group (LPG) architecture to organize neighboring vehicles that have frequently changing neighbors and have no inherent relationships with one another. We study two architectural alternatives for LPG in this article, and consider areas of improvement for ad hoc vehicle networking protocols to support safety communications including multihop throughput, connection setup time, and configuration.

Network Recovery, Protection and Restoration of Optical, SONET-SDH, IP, and MPLS [Book Review]

Abstract: Who should control the Internet? A dozen years after the Internet became a mass medium, this issue has continued to grow in urgency, becoming white hot in fall 2005. At the September 2005 preparatory meeting for the UN World Summit on the Information Society (WSIS), a coalition of countries criticized the United States' unilateral control of the Internet's domain name system (DNS) and proposed the establishment of a multinational Council to supervise it. This proposal emerged from the Final Report of the UN Working Group on Internet Governance. Researchers from the Internet Governance Project, a university-based consortium for policy analysis, have concluded that the United States should internationalize governance of the Internet, but in a way that avoids intrusive, centralized control.

Bandwidth allocation for multiservice access on EPONs

Abstract: Ethernet passive optical networks are a low-cost high-speed solution to the bottleneck problem of the broadband access network. A major characteristic of EPONs is the shared upstream channel among end users, mandating efficient medium access control to facilitate statistical multiplexing and provision multiple services for different types of traffic. This article addresses and provides an overview of the upstream bandwidth allocation issue for multiservice access provisioning over EPONs, and proposes an algorithm for dynamic bandwidth allocation with service differentiation. Based on the multipoint control protocol (MPCP) and bursty traffic prediction, our algorithm enhances QoS metrics such as average frame delay, average queue length, and frame loss probability over other existing protocols

Broadband access in Japan: rapidly growing FTTH market

Abstract: This article describes the latest FTTH technologies and market developments in Japan today. It focuses in particular on FTTH services, the deployment of FTTH systems, and lessons learned from actual deployments. The article also discusses the key R&D issues that must be completed if we are to enter the full-scale FTTH era.

Design guidelines for routing protocols in ad hoc and sensor networks with a realistic physical layer

Abstract: We present guidelines on how to design network layer protocols when the unit disk graph (UDG) model is replaced by a more realistic physical layer model. Instead of merely using the transmission radius in the UDG model, physical, MAC, and network layers share the information about a bit and/or packet reception probability as a function of distance between nodes. We assume that all nodes use the same transmission power for sending messages, and that a packet is received when all its bits are correctly received. The MAC layer reacts to this probabilistic reception information by adjusting the number of acknowledgments and/or retransmissions. We observe that an optimal route discovery protocol cannot be based on a single retransmission by each node, because such a search may fail to reach the destination or find the optimal path. Next, we discuss that gaining neighbor knowledge information with "hello" packets is not a trivial protocol. We describe localized position-based routing protocols that aim to minimize the expected hop count (in case of hop-by-hop acknowledgments and fixed bit rate) or maximize the probability of delivery (when acknowledgments are not sent). We propose a guideline for the design of greedy position-based routing protocols with known destination locations. The node currently holding the message forwards it to a neighbor (closer to the destination than itself) that minimizes the ratio of cost over progress, where the cost measure depends on the assumptions and metrics used, while the progress measures the difference in distances to the destination. We consider two basic medium access layer approaches, with fixed and variable packet lengths. This article serves as a preliminary contribution toward the development of network layer protocols that match the assumptions and criteria already used in simulators and ultimately in real equipment.

Design and implementation of a simulator based on a cross-layer protocol between MAC and PHY layers in a WiBro Compatible.IEEE 802.16e OFDMA system

Abstract: In this article we propose cross-layer design frameworks for 802.16e OFDMA systems that are compatible with WiBro based on various kinds of cross-layer protocols for performance improvement: a cross-layer adaptation framework and a design example of primitives for cross-layer operation between its MAC and PHY layers. In addition, we provide a simulation framework for cross-layer analysis between the MAC and PHY layers in 802.16e systems. Through this cross-layer simulator, we show that average cell throughput can be improved by 25-60 percent by applying careful cross-layer adaptation schemes.

Using Game Theory to Analyze Wireless Ad Hoc Networks

Abstract: The application of mathematical analysis to the study of wireless ad hoc networks has met with limited success due to the complexity of mobility and traffic models, the dynamic topology, and the unpredictability of link quality that characterize such networks. The ability to model individual, independent decision makers whose actions potentially affect all other decision makers renders game theory particularly attractive to analyze the performance of ad hoc networks. In this article we describe how various interactions in wireless ad hoc networks can be modeled as a game. This allows the analysis of existing protocols and resource management schemes, as well as the design of equilibrium-inducing mechanisms that provide incentives for individual users to behave in socially-constructive ways. We survey the recent literature on game theoretic analysis of ad hoc networks, highlighting its applicability to power control and waveform adaptation, medium access control, routing, and node participation, among others.

A ubiquitous mobile communication architecture for next-generation heterogeneous wireless systems

Abstract: Rapid progress in research and development of wireless networking and communication technologies have created different types of wireless systems (e.g., Bluetooth, IEEE 802.11, UMTS, and satellite networks). These systems are envisioned to coordinate with each other to provide ubiquitous high-data-rate services to mobile users. In this article, the architecture for ubiquitous mobile communications (AMC) is introduced that integrates these heterogeneous wireless systems. AMC eliminates the need for direct service level agreements among service providers by using a third party, a network interoperating agent. Instead of deploying a totally new infrastructure, AMC extends the existing infrastructure to integrate heterogeneous wireless systems. It uses IP as the interconnection protocol. By using IP as the gluing protocol, transparency to the heterogeneities of the individual systems is achieved in AMC. Third-party-based authentication and billing algorithms are designed for AMC. New mobility management protocols are also developed to support seamless roaming between different wireless systems.

TDCS, OFDM, and MC-CDMA: a brief tutorial

Abstract: This article gives a brief tutorial on transform-domain communication system (TDCS), OFDM, and MC-CDMA. The primary goal of this article is to give a detailed description of the TDCS transmitter and receiver systems and to highlight the fundamental differences relative to OFDM and MC-CDMA. The fundamental idea in TDCS is to synthesize a smart adaptive waveform to avoid interference at the transmitter instead of the more traditional mitigating of interference at the receiver. Unlike OFDM and MC-CDMA, TDCS has very little exposure in the current literature.

A tutorial on multiple access technologies for beyond 3G mobile networks

Abstract: In this article, some fundamental technical concepts of the main multiple access schemes for wireless mobile systems are reviewed, and a path for the development of appropriate multiple access technologies for next-generation mobile networks, or so-called beyond 3G (B3G), is established. We first review the multiple access technologies in second- and third-generation wireless cellular systems from historical and technical points of view. This review is followed by a novel formulization of the multiple access schemes through mathematical expressions that could simplify the process of development of new multiple access schemes for B3G wireless cellular systems. We then list the most important features of multiple access schemes in 3G mobile systems. Finally, we conclude the article by reviewing the most promising multiple access technologies for B3G mobile cellular systems

Communication paradigms for sensor networks

Abstract: When compared with now classical MANETs, sensor networks have different characteristics, and present different design and engineering challenges. One of the main aspects of sensor networks is that the solutions tend to be very application-specific. For this reason, a layered view like the one used in OSI imposes a large penalty, and implementations more geared toward the particular are desirable. This survey presents the three main paradigms for communication in ad hoc networks and discusses their applicability for routing, querying, and discovery. We conclude that the node-centric approach, although the oldest and best understood, is not the most appropriate for large-size low-energy application-specific sensor networks.

Complement block coding for reduction in peak-to-average power ratio of OFDM signals

Abstract: In this article a new coding scheme, complement block coding (CBC), is proposed to reduce the PAPR of OFDM signals. This method utilizes the complement bits that are added to the original information bits, which can effectively reduce the PAPR of OFDM signals with random frame size N and the coding rate R /spl les/ (N - k)/N, where k is a positive integer and k /spl les/ N/2. The performance results obtained with CBC are given and compared with that of some well known schemes, such as simple block coding, modified simple block coding, simple odd parity code, and cyclic coding, for the same purpose. The results show that at the same coding rate 3/4, CBC can achieve almost the same performance as SBC and MSBC, but with lower complexity, and the same performance can be obtained with a higher coding rate using CBC. The PAPR reductions of CBC with coding rate (N - 1)/N are almost the same as with a coding rate less than (N - 1)/N, but almost the twice as these of SOPC when N /spl ges/ 16. Moreover, we can find that PAPR is the lowest for all block codes using CBC with coding rate 3/4. So modified CBC (MCBC) is also proposed and analyzed, combined with the subblock processing technique to make CBC effective for OFDM systems with large frame sizes. The flexibility in coding rate choice and low complexity make the proposed CBC more suitable for random frame size with high coding rate and can also provide error detection.

Interleave-division multiple access and chip-by-chip iterative multi-user detection

Abstract: This article outlines a multiple access scheme in which interleaving is the only means of user separation. As a special form of CDMA, the new scheme inherits many advantages of CDMA, such as dynamic channel sharing, mitigation of cross-cell interference, asynchronous transmission, ease of cell planning, and robustness against fading. Furthermore, it allows a low-cost interference cancellation technique applicable to systems with large numbers of users in multipath channels. Performance close to theoretical limits has been observed based on an unequal power control strategy.

Policy-based management of networked computing systems

Abstract: This article provides an overview of the Policy Management for Autonomic Computing (PMAC) platform, and shows how it can be used for the management of networked systems. We present the policy information model adopted by PMAC and the system model for interaction between the policy manager and the managed resource. We also present the main components of PMAC for policy creation, storage, evaluation, and enforcement, and present practical applications of PMAC in networks management.

Ultrascience net: network testbed for large-scale science applications

Abstract: UltraScienceNet is an experimental wide area network testbed to enable the development of networking technologies required for next-generation large-scale scientific applications. It provides on-demand dedicated high-bandwidth channels for large data transfers, and also high-resolution high-precision channels for fine control operations. In the initial deployment its data plane consists of several thousand miles of dual 10 Gb/s lambdas. The channels are provisioned on demand using layer 1 and 2 switches in the backbone and multiple service provisioning platforms at the edges in a flexible configuration using a secure control plane. A centralized scheduler is employed to compute future channel allocations, and a signaling daemon is used to generate the configuration signals to switches at appropriate times. The control plane is implemented using an out-of-band virtual private network, which encrypts the switching signals, and also provides authenticated user and application access. Transport experiments are conducted on a smaller test connection that provides us useful information about the basic properties and issues of utilizing dedicated channels in applications.

Unlicensed cognitive sharing of TV spectrum: the controversy at the Federal Communications Commission

Abstract: As societies become increasingly mobile and more dependent on information technologies, their radio spectrum also needs change. The basic spectrum management structure in all countries was developed over a long period, and much of the basic framework has remained stable for decades. The FCC is interested in making more spectrum available to unlicensed devices because of the explosive growth of IEEE 802.11/Wi-Fi unlicensed wireless LAN technology, and because the FCC recognizes that there is a great deal of "white space" that could be exploited by unlicensed devices. The FCC proposal selected the TV bands as an initial home for cognitive radio based on several factors. First, the frequencies used for TV can give greater range in rural areas than the microwave frequencies used for Wi-Fi, and can also give better building penetration than Wi-Fi in all areas. Second, TV broadcast systems usually use high antennas, and the intended receivers need greater than 10 dB signal-to-noise ratio (SNR) to function. A variety of controversial issues have emerged from public comments. One concern is that the confusion resulting from the proposal might discourage purchase of new digital televisions and hence delay the transition from analog to digital televisions. This would also delay the transfer of some current TV spectrum to new mobile uses, including public safety.