Simultaneous Communications Research Articles

Joint Detection of Primary Systems Using UWB Impulse Radios

Regulation in Europe and Japan requires the implementation of detect-and-avoid (DAA) techniques in some bands for the coexistence of licensed primary systems and secondary ultra wideband (UWB) systems. In a typical coexistence scenario, a primary system may have potentially interdependent uplink-downlink communication channels (e.g., simultaneous uplink-downlink communications in a frequency division duplex system) overlapping with the frequency band of a UWB system. If such interdependencies of primary systems' activities are known, the UWB system's ability to detect primary systems can be improved. In this study, we are interested in determining the possible gains in the detection performance when taking interdependencies into account for practically implementable detection methods. Contrary to selecting the detection thresholds individually for each band as in a conventional detection approach, the bands are jointly processed. To this end, maximum a posteriori (MAP) decision variables are generated at the receiver, and bias terms are introduced to achieve a desired trade-off between the probabilities of detection and false alarm. In addition to finding the optimal detection results based on the Neyman-Pearson (NP) test, a suboptimal but practically implementable approach is also considered, and the gain compared to conventional independent detection is quantified for various practical scenarios. The results obtained from this study can be used for improving the primary system detection performance of UWB systems, as well as for cognitive radios that perform spectrum sensing in multiple bands.

RAMC: A RSU-Assisted Multi-Channel Coordination MAC Protocol for VANET

Dedicated Short Range Communication (DSRC) employs one control channel for safety-oriented applications and six service channels for non-safety commercial applications. However, most existing multi-channel schemes require all neighboring vehicles periodically (e.g. every 100 milliseconds) tune to the control channel for a full update of safety-oriented data before they can switch to the service channels for non-safety services. The safety exchange interval increases with the increase of traffic density. Consequently, under high traffic densities, the service channels are often completely idle while the control channel is congested. We propose a RSU Assisted Multi-channel Coordination MAC (RAMC) protocol that fully utilizes all channels to provide simultaneous safety and non-safety communications. Within the radio range of a roadside unit (RSU), vehicles are free to tune to any service channel. The RSU monitors all the safety messages being transmitted in both the control and service channels. Periodically, the RSU broadcasts a consolidated traffic view report to all neighboring vehicles in all channels. Therefore, a vehicle can operate in a service channel as long as it needs to achieve high throughput for non-safety applications, while maintaining adequate and timely safety awareness. Our simulation results show that the proposed RAMC protocol consistently achieves very high percentage of non-safety usage, while maintaining high safety message delivery ratios in various traffic density conditions.

Discrete-time simulation of smart antenna systems in Network Simulator-2 Using MATLAB and Octave

This paper presents two platforms that exploit the scalability properties of Network Simulator-2 for the discrete-event simulation of a telecommunication network, and the modeling capabilities of two development tools for the discrete-time implementation of adaptive antenna arrays at the physical layer. The two tools are the proprietary MATLAB and the open source Octave, both of which are used to implement the physical antenna system, the beamforming algorithm, the channel coding scheme, and the multipath and fading statistics. The adopted approach enables detailed modeling of the antenna radiation pattern generated by each network node, thus improving the accuracy of the signal-to-interference ratio estimated at the receiver. This study describes the methods that can be adopted to interface MATLAB and Octave with Network Simulator-2, and discusses the advantages and disadvantages that characterize the integration of the two tools with Network Simulator-2. The proposed numerical platforms, which can be interfaced with any wireless network supported by Network Simulator-2, are used to investigate the possibility of exploiting smart antenna systems in a wireless mesh network to enable the coexistence of multiple simultaneous communications.

Scan Loss Pattern Synthesis for Adaptive Array Ground Stations

We present several techniques for maximizing the contact time between low Earth orbiting satellites (LEOs) and a ground station (GS). The GS comprises an adaptive array of electronically steered space-fed lenses (SFLs). Each SFL is manufactured as a low-cost printed circuit with the result that it exhibits scanning loss. By differently orienting the boresights of the SFLs in the adaptive array, the SFL's scanning losses can be made to optimally complement the path loss of the LEO, thereby reducing the cost of the GS while maximizing the download capacity of the satellite link. The optimization, implemented with a genetic algorithm (GA), can be viewed as a kind of pattern synthesis. Such arrays will benefit Earth exploration satellite service (EESS) and telemetry applications, promising a decreased cost and increased reliability as compared with GSs consisting of a large dish antenna. We show that a network of these GSs comprising a total of fourteen small antennas can achieve an average daily data rate that is comparable with that of a single large dish antenna for the Earth Observing One (EO-1) satellite, without increasing the output power of the satellite. We also analyze the case in which the satellite transmits with a variable bit rate (VBR). Furthermore, we show that by selectively populating the focal surface of the SFL with feeds, simultaneous communications with multiple satellites can be achieved with a single GS.

Performance Improvement of Routing Protocol in Ad-hoc Networks Using Smart Antenna with Balance Load

We have presented a balanced routing protocol for Mobile Ad-hoc Networks using the smart antenna in this paper. Multipath routing can be effectively used to maximize the utilization of network resources for real-time traffic. In mobile ad-hoc network, this approach can suffer from co-channel interference or route coupling due to simultaneous transmission of packets via multiple routes. We use zone-disjoint routes and define maximally zone disjointness as route selection criteria. An adaptive routing strategy is proposed that use the advantages of directional antennas in ad hoc networks through the selection of maximally zone disjoint routes. Zone-disjoint routes would reduce the route coupling effect in wireless media by selecting routes in such that it produce minimal interference among communication over multiple routes. The proposed routing protocol provide effective load balancing in wireless media and it is implemented for both single path and multipath routing on ad hoc networks with directional antennas. Simulation results show that zone-disjoint single path routing can produce better throughput compare to multipath and AODV (Ad-hoc on-demand distance vector) routing protocol for more number of simultaneous communications.

Performance comparison of advanced antenna systems for wireless mesh routers in an outdoor environment

PurposeThe purpose of this paper is to compare the low‐cost switched‐beam antennas and the more expensive adaptive antennas in a wireless mesh network (WMN) scenario.Design/methodology/approachA mathematical framework is adopted in order to determine, for the two antenna systems, the number of sustainable simultaneous communications and the achievable throughput of a backbone WMN in a realistic outdoor environment.FindingsThe paper includes a thorough examination of benefits and crucial implementation issues concerning the adoption multiple antennas on mesh routers.Originality/valueThe paper investigates the relationship between the antenna system and the adopted channel coding technique, to determine the set‐up that may offer the best compromise between performance and complexity.

UMTS femtocell performance in massive deployments: Capacity and GoS implications

The base station router (BSR) femto node—a Universal Mobile Telecommunications System (UMTS) Node B for domestic use that admits a limited number of simultaneous communications—is gaining interest among mobile operators worldwide. Its main advantages are that it connects with the mobile core network through the land digital subscriber line (DSL) at the user's home, relieving the macro network from the indoor traffic that uses a substantial part of the mobile network resources. This paper explains the network deployment and dimensioning rules used in the massive deployment of this type of node. The proposed models are verified through node performance network simulations in different types of residential configurations, taking into account challenging aspects such as the neighboring effect, macro-femto cell interaction, arbitrary node localization, and service (voice, data, and video) mix. The model is applied to 2 GHz and 850MHz bands.

Threshold jumping and wrap-around scan techniques toward efficient tag identification in high density RFID systems

With the emergence of wireless RFID technologies, the problem of Anti-Collision has been arousing attention and instigated researchers to propose different heuristic algorithms for advancing RFID systems operated in more efficient manner. However, there still have challenges on enhancing the system throughput and stability due to the underlying technologies had faced different limitation in system performance when network density is high. In this paper, we present a Threshold Jumping (TJ) and a Wrap-Around Scan (WAS) techniques, which are query tree based approaches, aiming to coordinate simultaneous communications in high density RFID environments, to speedup tag identification, to increase the overall read rate and to improve system throughput in large-scale RFID systems. The main idea of the Threshold Jumping is to limit the number of collisions. When the number of collisions exceeds a predefined threshold, it reveals that tag density in RF field is too high. To avoid unnecessary enquiry messages, the prefix matching will be moved to next level of the query tree, alleviating the collision problems. The method of setting frequency bound indeed improves the efficiency in high density and randomly deployed RFID systems. However, in irregular or imbalanced RFID networks, inefficient situation may happen. The problem is that the prefix matching is performed in single direction level-order scheme, which may cause an imbalance query tree on which the right sub-tree always not been examined if the identification process goes to next level before scan the right sub-tree due to threshold jumping. By scanning the query tree from right to left in alternative levels, i.e., wrap-around, this flaw cold be ameliorated. To evaluate the performance of proposed techniques, we have implemented the TJ and the WAS method along with the query tree protocol. The simulation results show that the proposed techniques provide superior performance in high density environments. It is shown that the TJ and WAS are effective in terms of increasing system throughput and minimizing identification delay.

Throughput and Delay Analysis of 802.11-Based Wireless Networks Using Smart and Directional Antennas

This paper proposes a mathematical framework for comparing the performance of wireless networks based on the IEEE 802.11 standard, employing switched-beam, directional and adaptive antennas. The analysis adopts detailed models for the antenna system behavior and the propagation environment, taking into account multipath and interference. The purpose of this study is to determine the number of simultaneous communications that may be sustained by adopting advanced antenna systems, and to investigate, by analysis and simulation, the resulting performance improvements, in terms of throughput and packet delay. Both saturated and non-saturated traffic conditions are treated. Suitable 802.11 Medium Access Control (MAC) layer parameter settings, able to exploit smart and directional antenna capabilities for maximizing the throughput, are also discussed.

A Priority Based Transaction mechanism towards high reliable RFID services

With the emergence of RFID technologies, the problem of scheduling reader-tag transmissions in dynamic systems has been arousing attention. This paper presents a priority based approach to coordinate simultaneous communications among multiple readers in order to increase the overall read rate in dynamic RFID systems. Through a contention-free scheduling, the reader-tag transmissions can be performed without collisions even the environment has hidden terminal. To evaluate the effectiveness of the proposed techniques, both network density and mobility of readers' join and leave are conducted in the tests. Experimental results show that the proposed techniques provide superior system throughput in both static and dynamic circumstances.

Modèle de communications concurrentes sur des grappes SMP

SMP clusters are cost-effective clusters largely used in parallel computing. Parallel applications using message passing as communication mechanism may introduce complex communication behaviors on such clusters. Precisely, MPI communications on a same node with a common interval time create concurrent accesses to node's resources. Concurrent access implies resource sharing, depending on the underneath network architecture and the MPI implementation used. This paper presents a case study of simultaneous MPI communications over SMP clusters. We express a model, which predict times of such communications giving insight of bandwidth division.

Sustainable simultaneous communications in ad-hoc networks using smart antenna systems

This article proposes an analytical model for evaluating the number of simultaneous communications that can be sustained by an ad-hoc network in which the nodes are equipped with fully adaptive smart antennas. The presented mathematical framework adopts realistic models for the antenna radiation pattern and the channel behavior, and is able to take into account the network topology and the characteristics of the medium access control (MAC) protocol in the spatial domain. The model is employed to investigate the impact of the spatial channel model and of the angular spread on network performance. Additionally, this article examines the influence of the transmission policy of the control and data packets of the MAC layer on the number of simultaneous communications.

Directional medium access control for ad hoc networks

Using directional antennas in ad hoc networks may introduce the well-known deafness problem, exacerbate the hidden terminal problem and the exposed terminal problem, add difficulty on mobile communication, and distort the operation of existing routing and TCP protocols. Although a lot of studies have been undertaken on the directional MAC protocols, most of them focus only on one or several aspects in their design and performance evaluations, and a comprehensive comparative study is missing. In this paper, we first explore the design space of directional MAC and present a taxonomy of existing schemes. Then, we discuss the major problems in using directional antennas under different category of MAC schemes. After that, we propose coordinated directional medium access control (CDMAC), a novel directional MAC protocol to improve throughput via facilitating the simultaneous contention-free communications for multiple local node-pairs. We evaluate our CDMAC, one representative existing scheme and IEEE 802.11 via extensive ns2 simulations. Our results show CDMAC provides a satisfactory solution to all the major problems and significantly improves the throughput performance.

Routing in Multi-Channel Wireless Ad-hoc Networks: OSPF-MCDS-MC

The availability of low-cost network interface cards (NICs) has made the IEEE 802.11 medium access control (MAC) protocol the de facto MAC standard for wireless mobile ad-hoc networks. Although the IEEE 802.11 MAC protocol is designed to have stations share a single channel in a network, many of the IEEE 802.11 physical (PHY) layer standards define multiple channels and allow the simultaneous, non-interfering use of some of these channels. Therefore, simultaneous communications can occur through different channels, offering the opportunity to increase effectivenetwork capacity. We present an innovative routing protocol that utilizes multiple channels to improve performance in a mobile ad hoc network. The key feature of the protocol is that nodes can effectively use multiple channels for simultaneous useful transmissions, thus improving networkcapacity. The proposed scheme requires minor changes to existing proactive or table-driven routing protocols and no modifications to current the IEEE 802.11 MAC protocol. To mitigate the overhead of periodic updates in proactive routing protocols, the proposed scheme divides the network layer into control and data planes. To demonstrate the multi-channel routing scheme, we extend the OSPFMCDS routing protocol to a multi-channel version, OSPFMCDS- MC or, more simply, OMM. Simulation and experimental results indicate OMM successfully exploits multiple channels to increase network capacity. The protocol allows the network goodput to increase in proportion to the number of available channels, even as the number of nodes and network load increase, in both single-hop and multiple-hop networks. We also present a prototype implementation for experimental validation of the proposed multi-channel routing protocol scheme. The implementation includes the multi-channel routing protocol and a virtual interface module, which acts as a buffer for outgoing packets and performs channel-related functions, such as channel selection and switching, while ensuring portability.

ACR: an adaptive communication‐aware routing through maximally zone‐disjoint shortest paths in ad hoc wireless networks with directional antenna

AbstractA fundamental problem that distinguishes wireless networks from wired networks is the mutual interference between routes within the proximity of each other. This phenomenon is known as route coupling and it restricts the possibility of occurrence of simultaneous communications along the coupled routes. In this context, the use of directional antenna, having smaller transmission beam‐width compared to omni‐directional antenna, helps to easily decouple interfering routes, and improves network performance through space division multiple access (SDMA). However, even if we have an efficient directional MAC protocol, it alone would not be able to guarantee good system performance, unless we have a proper routing strategy in place that exploits the advantages of directional antenna. So, in this paper, an adaptive routing strategy is proposed that exploits the advantages of directional antenna in ad hoc networks through the selection of maximally zone‐disjoint shortest routes. Zone‐disjoint routes would minimize the effect of route coupling and improve the overall network performance. The proposed strategy ensures effective load balancing and is applied to design and implement both single path and multipath routing protocols in ad hoc networks with directional antennas. Simulation results obtained on QualNet network simulator shows the effectiveness of the proposed routing protocols. Copyright © 2006 John Wiley & Sons, Ltd.

Compiler-directed channel allocation for saving power in on-chip networks

Increasing complexity in the communication patterns of embedded applications parallelized over multiple processing units makes it difficult to continue using the traditional bus-based on-chip communication techniques. The main contribution of this paper is to demonstrate the importance of compiler technology in reducing power consumption of applications designed for emerging multi processor, NoC (Network-on-Chip) based embedded systems. Specifically, we propose and evaluate a compiler-directed approach to NoC power management in the context of array-intensive applications, used frequently in embedded image/video processing. The unique characteristic of the compiler-based approach proposed in this paper is that it increases the idle periods of communication channels by reusing the same set of channels for as many communication messages as possible. The unused channels in this case take better advantage of the underlying power saving mechanism employed by the network architecture. However, this channel reuse optimization should be applied with care as it can hurt performance if two or more simultaneous communications are mapped onto the same set of channels. Therefore, the problem addressed in this paper is one of reducing the number of channels used to implement a set of communications without increasing the communication latency significantly. To test the effectiveness of our approach, we implemented it within an optimizing compiler and performed experiments using twelve application codes and a network simulation environment. Our experiments show that the proposed compiler-based approach is very successful in practice and works well under both hardware based and software based channel turn-off schemes.

Perfect state transfer, effective gates, and entanglement generation in engineered bosonic and fermionic networks

We show how to achieve perfect quantum state transfer and construct effective two-qubit gates between distant sites in engineered bosonic and fermionic networks. The Hamiltonian for the system can be determined by choosing an eigenvalue spectrum satisfying a certain condition, which is shown to be both sufficient and necessary in mirror-symmetrical networks. The natures of the effective two-qubit gates depend on the exchange symmetry for fermions and bosons. For fermionic networks, the gates are entangling (and thus universal for quantum computation). For bosonic networks, though the gates are not entangling, they allow two-way simultaneous communications. Protocols of entanglement generation in both bosonic and fermionic engineered networks are discussed.

Redundant wireless communication technologies for real-time surveillance

Catastrophic events including those sparked by terrorism have cast a pall over society in recent years. Events such as September 11th or the bombing of the Alfred P. Murrah Federal Building in Okalahoma City demonstrated a sudden surge in telephone call volume. These events indicated that communications systems, including cellular, can fail as a result from damage or capacity overload. Cellular systems have significant capacity given the limited radio spectrum allocated but much like airlines that oversell seats because inevitably some passengers do not show up, cellular providers typically have more customers than operational spectrum can handle in aggregate. Normally this is perfectly acceptable because a high percentage of the customer base would never be making calls simultaneously; except in an emergency. Such emergencies can be active or passive in nature. The release of dangerous airborne agents is one such scenario. The purpose of this study was to use a portable air particulate sensor as a data acquisition platform to evaluate the capability of real-time data throughput using existing wireless topologies, Java, eXtensible Markup Language (XML) and Internet protocols when cellular transmission frequencies are compromised. Results show that high levels of cellular voice traffic in a given area can hamper simultaneous data communications; however, Low Earth Orbiting Satellites (LEOS) can provide redundancy.

An adaptive media access control protocol and system performance of wireless ad hoc network using smart antenna

AbstractA smart antenna can increase the number of simultaneous transmissions by reducing interference and improving the throughput performance. In this paper, we propose an adaptive media access control (MAC) protocol that periodically updates neighboring node information in a distributed network, such as a wireless ad hoc network, and uses smart antennas to achieve simultaneous communications by directionality control to neighboring nodes other than those currently communicating. We also verify that the overhead for updating the neighboring node information can be reduced to 15% or less than in conventional schemes and the number of simultaneous communications can be 2 to 3.5 times higher than when using omnidirectional antennas. Furthermore, we considered the effects of the overhead accompanying neighboring node updates, node density, beam width, and moving speed on the communication efficiency when using the proposed MAC protocol. The communication efficiency was improved by controlling the transmission power to shorten the transmission range, lower the node density, and widen the beam width more than by extending the transmission range and increasing the node density. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(3): 50–58, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10140

A "Small World" Approach to Heterogeneous Networks

We consider a heterogeneous (also called hybrid) ad-hoc network with wired and wireless links. This type of network was previously considered by Kulkarni and Viswanath in (9) where achievable transport capacity growth rates were demonstrated for a structured wired infrastructure. The present paper improves on this work by demonstrating that efficiency can be increased significantly if the wired links are introduced at random. 1. Introduction. In this paper we consider the effect of adding a wired in- frastructure to an unstructured (ad-hoc) wireless network. The impact of such a modification on the original wireless network can be tremendous. Unlike the wireless channel, which suffers both from interference issues as well as from path loss over large distances, the wired infrastructure can provide low-cost transport of a signifi- cant amount of data over large distances without interference with other simultaneous communications. However, the existence of such an infrastructure often carries a sig- nificant cost in and of itself. Thus, in particular, one would like to use as little wired infrastructure as necessary. A systematic study of scaling laws in ad-hoc wireless networks has been initiated in the work of Gupta, Kumar and Xie (6),(21) and (5). In particular, Xie and Kumar showed that for a large range of path loss models the transport capacity (the distance - bandwidth product) of a purely wireless network scales no better than Θ( √ n )w hen the network size is fixed. Furthermore, Gupta and Kumar demonstrated how such scaling laws are achievable for all path loss models using an interference-avoiding communication sp rotocol. The recent work by Kulkarni and Viswanath (10) gives a simple deterministic protocol that achieves the scaling laws of Gupta and Kumar (6) eliminating much of the complexity of the original routing protocol. The protocol in (10) is based on the related problem of packet routing on a square grid of parallel processors (7),(11). The protocol is straightforward and deterministic and thus provides a natural starting point to include a wired infrastructure into the ad-hoc wireless network. The reference