Showing papers in "Wireless Personal Communications in 2008"

A Survey on Wireless Position Estimation

Abstract: In this paper, an overview of various algorithms for wireless position estimation is presented. Although the position of a node in a wireless network can be estimated directly from the signals traveling between that node and a number of reference nodes, it is more practical to estimate a set of signal parameters first, and then to obtain the final position estimation using those estimated parameters. In the first step of such a two-step positioning algorithm, various signal parameters such as time of arrival, angle of arrival or signal strength are estimated. In the second step, mapping, geometric or statistical approaches are commonly employed. In addition to various positioning algorithms, theoretical limits on their estimation accuracy are also presented in terms of Cramer---Rao lower bounds.

Cooperative Communication Protocols in Wireless Networks: Performance Analysis and Optimum Power Allocation

Abstract: In this paper, symbol-error-rate (SER) performance analysis and optimum power allocation are provided for uncoded cooperative communications in wireless networks with either decode-and-forward (DF) or amplify-and-forward (AF) cooperation protocol, in which source and relay send information to destination through orthogonal channels. In case of the DF cooperation systems, closed-form SER formulation is provided for uncoded cooperation systems with PSK and QAM signals. Moreover, an SER upper bound as well as an approximation are established to show the asymptotic performance of the DF cooperation systems, where the SER approximation is asymptotically tight at high signal-to-noise ratio (SNR). Based on the asymptotically tight SER approximation, an optimum power allocation is determined for the DF cooperation systems. In case of the AF cooperation systems, we obtain at first a simple closed-form moment generating function (MGF) expression for the harmonic mean to avoid the hypergeometric functions as commonly used in the literature. By taking advantage of the simple MGF expression, we obtain a closed-form SER performance analysis for the AF cooperation systems with PSK and QAM signals. Moreover, an SER approximation is also established which is asymptotically tight at high SNR. Based on the asymptotically tight SER approximation, an optimum power allocation is determined for the AF cooperation systems. In both the DF and AF cooperation systems, it turns out that an equal power strategy is good, but in general not optimum in cooperative communications. The optimum power allocation depends on the channel link quality. An interesting result is that in case that all channel links are available, the optimum power allocation does not depend on the direct link between source and destination, it depends only on the channel links related to the relay. Finally, we compare the performance of the cooperation systems with either DF or AF protocol. It is shown that the performance of a systems with the DF cooperation protocol is better than that with the AF protocol. However, the performance gain varies with different modulation types and channel conditions, and the gain is limited. For example, in case of BPSK modulation, the performance gain cannot be larger than 2.4 dB; and for QPSK modulation, it cannot be larger than 1.2 dB. Extensive simulation results are provided to validate the theoretical analysis.

Disruptive Technologies, Services, or Business Models?

Abstract: Convergence in the realm of media, consumer electronics, computer technologies, and telecommunications has contributed to societal changes in terms of individual expectations and behavior leading to the re-appraisal of traditional market segments. Key innovations like the internet create a global platform that provides for new means in product and services configuration. This expands opportunities and threats in the business environment contributing to increased competition in a dynamic environment where traditional boundaries are shifting. In a world of converging technologies, increasing marketplace dynamics and rapid technological advances, new upcoming "disruptive technologies" such as Voice-over-IP (VoIP) pose threats to traditional telecommunications companies. Business leaders in order to succeed need to be "thinking outside the box". We introduce the concept of a business model as a tool in crafting strategy for the purpose of achieving sustainable innovation in the face of the reshaping of the industry and the market. We apply this model to the VoIP market and in particular the Skype technology and service. The significance of this contribution is that it highlights the importance of developing an innovative business model to take advantage of disruptive technologies. Our analysis of the dimensions of innovations shows that the more dimensions the greater the impact. ICT convergence is leading to a paradigm shift with innovation effects that are both effective and disruptive. Thus, leading to equally disruptive business models reshaping innovation strategy.

Network Virtualization: A Viable Path Towards the Future Internet

Abstract: New technologies as well as new ways of using network services are rapidly changing the Internet's landscape. These developments will have far-reaching implications for the architecture of the networks of the future. However, the current Internet design is plagued with a number of fundamental limitations, which makes its use as the sole basis for the networking applications of the future questionable. We believe that the Future Internet must allow the co-existence of diverse network designs and paradigms, both new and old, to remain open to innovation and meet the challenges of the future. In this paper, we propose to use network virtualization, embedded in an architectural framework, to achieve this goal and to lay the foundation for the deployment of novel concepts such as content-centric networking.

Cognitive Radio Dynamic Access Techniques

Abstract: The ever growing demand for wireless services has placed enormous burden on valuable resources such as spectral bandwidth. This has resulted in a major rethinking in resource allocation policies culminating in an explosion of research activity in the field of Cognitive Radio (CR) towards optimum resource usage. In this tutorial paper the physical layer design and transmission techniques for CR in the context of efficient spectrum utilization are discussed. Spectrum sensing as the key element of CR awareness is described. Orthogonal frequency division multiplexing (OFDM) as a spectrally efficient modulation scheme is discussed and the rationale for its use in the CR system is explained. Spectrum pooling for efficient use of spectrum is studied and the role of adaptive OFDM techniques in this method is highlighted. Wavelet basis function as a replacement of Fourier transform in OFDM is evaluated. MIMO system as an added value to the CR performance is described. Adaptive Waveform and beamforming as alternative techniques in CR are reviewed.

Symbiotic Networks: Towards a New Level of Cooperation Between Wireless Networks

Abstract: In the future, many wireless networks, serving diverse applications, will co-exist in the same environment. Today, wireless networks are mostly optimized in a rather opportunistic and/or selfish way: optimizations methods only use a local view of the network and environment, as they try to achieve the best performance within its own network. The optimizations are very often limited to a single layer and cooperation between networks is only happening through the use of gateways. In this paper, we suggest an alternative paradigm for supporting cooperation between otherwise independent networks, called `symbiotic networking'. This new paradigm can take many forms, such as sharing of network resources, sharing of nodes for communal routing purposes and sharing of (networking) services. Instead of optimizing network parameters within the individual networks, symbiotic networking solutions operate across network boundaries. Parameters are optimized between the networks and communal protocols are developed, leading to a more global optimization of the scarce network resources. In this paper, we describe several scenarios which can profit from symbiotic networking and illustrate a strategy for supporting networking protocols which can operate across network boundaries. Ultimately, through the disappearance of network boundaries and the introduction of cross-layer/cross-node/cross-network cooperation, symbiotic networks takes the notion of cooperation to a new level, paving the way for a true network symbiosis.

A Novel Wireless Positioning System for Seamless Internet Connectivity based on the WLAN Infrastructure

Abstract: Nowadays, several positioning systems are available for outdoor localization, such as the global positioning system (GPS), assisted GPS (A-GPS), and other systems working on cellular networks, for example, time difference of arrival (TDOA), angle of arrival (AOA) and enhanced observed time difference of arrival (E-OTD). However, with the increasing use of mobile computing devices and an expansion of wireless local area networks (WLANs), there is a growing interest in indoor wireless positioning systems based on the WLAN infrastructure. Wireless positioning systems (WPS) based on this infrastructure can be used for indoor localization to determine the position of mobile users. In this paper, we present a novel wireless positioning system, based on the IEEE 802.11b standard, using a novel access point (AP) with two transceivers to improve the performance of WPS in terms of accuracy of the location estimation and to avoid service connectivity interruption. In our proposed system, the novel AP uses the second transceiver to find information from neighboring mobile stations (STAs) in the transmission range and then sends information in advance to associated APs, which estimate the location of the STA based on an internal database. We also use a TDOA technique to estimate the location of the STA when there is not enough information in the database (in this case, the STA moves into a new area where the system has not run the calibration phase). Using TDOA, the database can be generated and updated automatically. The initial results from our simulations show that the proposed system provides higher accuracy of location estimation than other related work and does not interrupt the Internet connection for end users in contrast with other proposed schemes.

Stimulating Node Cooperation in Mobile Ad hoc Networks

Abstract: Mobile Ad hoc Networks (MANETs) rely on the cooperation of nodes for packet routing and forwarding. Much of the existing work in MANETs assume that mobile nodes (possibly owned by selfish users) will follow prescribed protocols without deviation. However, a user may misbehave due to several advantages resulting from noncooperation, the most obvious being power saving. As such, the network availability is severely endangered. Hence, enforcing the cooperation among nodes becomes a very important issue. Several different approaches have been developed to detect non-cooperative nodes or deal with the non-cooperative behavior of mobile nodes in MANETs. These protocols are first surveyed in details in this paper. It is found that the proposed approaches have several concerns that prevent them from really enforcing the node cooperation in MANETs. Thus, a new scheme that can stimulate and also enforce nodes to cooperate in a selfish ad hoc environment is presented. We also present a mechanism to detect and exclude potential threats of selfish mobile nodes. The simulation results indicate that by using the proposed scheme, MANETs can be robust against nodes' misbehaving and the performance of the network is enhanced many folds when compared to other existing schemes.

Virtual Identity Framework for Telecom Infrastructures

Abstract: Identity Management has so far been a field mainly applications and Web focused. This paper describes a novel approach to cross layer identity management that extends digital identities to the network, the virtual identity (VID) framework. The VID framework provides strong privacy to the user, while easily supporting personalization cross-service providers. While other identity management solutions are tailored to one specific application and/or protocol domain, the proposed framework extends the use of one's digital identity to all aspects of the network and services architecture. It is also the first to consider legal constrains, such as ownership of data and legal intercept issues, in such a broad scope. One major aspect reported here is the relevance for operators.

A Context Driven Architecture for Cognitive Radio Nodes

Abstract: A cognitive radio (CR), in its generic form, needs to be highly flexible and adaptive while desirably hiding its complexities from users and system programmers. For the autonomic management the CR needs to be aware of the `self' and the `world' around it. Embedded intelligence with cognitive and collaborative adaptations require innovative techniques for managing the functionality of the device. Complexity of the cognitive processes involved demand for formal methods for run time evaluations and verification. In this paper we propose a generic architecture for a cognitive node with a context driven approach which incorporates some formalisms including context spaces, ontology, process algebra to represent and manipulate various cognitive processes managing the cognitive node functionality.

A Unified Architecture and Key Techniques for Interworking between WiMAX and Beyond 3G/4G Systems

Abstract: The trend of inter-connection among a multitude of different wireless access networks presents the great and bright potential business opportunities for communication operators However, such a trend also creates a huge challenge for the network designers to manage the different radio access technologies in a cooperative mode Therefore, this paper proposes two advanced functional architectures to support the functionalities of interworking between WiMAX and beyond 3G/4G systems, ie, Radio Control Server (RCS) and Access Point (AP) based centralized architectures Both control and user planes are defined in these two architectures This paper further describes the corresponding key techniques for the interworking These techniques can be partitioned into four categories: the key mechanisms in Generic Link Layer (GLL), the key mechanisms in Multi-Radio Resource Management (MRRM), the end-to-end Quality of Service (QoS) provision, and the heterogeneous paging For the mechanisms in GLL, Multi-radio transmission diversity (MRTD) and Multi-Radio Multi-Hop networking (MRMH) schemes are researched Meanwhile, Radio Access Technology (RAT) selection and load balancing schemes in aspect of MRRM are presented to improve the performance of interworking In particular, the heterogeneous paging procedures for the convergence of WiMAX and beyond 3G/4G are proposed and evaluated, which can decrease the transmission load and save the power consumption

Dynamic Channel Selection for Cognitive Radios with Heterogenous Primary Bands

Abstract: Technological advances coupled with regulatory initiative for more efficient utilization of radio spectrum resulted in the introduction of dynamic spectrum access enabled radio called Cognitive Radio (CR). A CR network is allowed to access a frequency band owned by primary user, which can provide higher throughput and better serviceability in wireless networks. The availability of multiple primary bands requires a CR network to select the best operating band which can maximize the total system performance. The selection should be made according to heterogenous properties of primary bands which offer different maximum data rate for secondary use and generate diverse traffic pattern. In this paper, assuming such heterogenous primary bands for secondary use, simple and distributed dynamic channel selection strategies are proposed and evaluated. In addition, we introduce a measurement metric for interference experienced by primary users due to secondary network's access in primary band. We investigate the impact of different channel selection strategies and parameters on the primary and secondary performance.

Optimization of Handover Parameters for Traffic Sharing in GERAN

Abstract: Cellular network traffic is unevenly distributed both in time and space, which greatly complicates network dimensioning. As a result, some cells in the network are permanently congested, while others are underutilized. In a previous paper, the authors showed that this problem can be effectively solved in GSM/EDGE Radio Access Networks (GERAN) by modifying handover boundaries. However, several drawbacks prevent operators from fully exploiting the potential of this technique. This paper investigates the limitations of current traffic-sharing approaches with tight frequency reuses in GERAN. To deal with such limitations, an algorithm is proposed to jointly optimize handover margins and signal-level constraints based on network statistics for traffic sharing in GERAN. A complementary algorithm is proposed to adjust cell (re)selection offsets to minimize the number of handovers. Simulation results show that the proposed method achieves a significant reduction in call blocking without excessive call quality impairment or increase of network signaling load when compared to the current approaches. More traffic can thus be handled without the need for any hardware upgrades, providing a cost-effective means to increase network capacity.

Evaluation of Performance Improvement Capabilities of PAPR-reducing Methods

Abstract: One of the major drawbacks of multicarrier modulation is the large envelope fluctuations which either require an inefficient use of high power amplifiers or decrease the system performance. Peak-to-average power ratio (PAPR) is a very well known measure of the envelope fluctuations and has become the cost function used to evaluate and design multicarrier systems. Several PAPR-reducing techniques have been proposed with the aim to alleviate back-off specifications or increase the system performance. Besides the fact that these techniques have varying PAPR-reduction capabilities, power, bandwidth and complexity requirements, it is interesting to notice that the performance of a system employing these techniques has not been fully analyzed. In this paper we, first, develop a theoretical framework for both PAPR and the distortion introduced by a nonlinearity, and then simulate an OFDM system employing several well known PAPR-reducing techniques from the literature. By means of the theoretical analysis and the simulation results we will show the relation between PAPR and the performance of OFDM systems when a clipping device is present and we will evaluate the real performance improvement capabilities of the PAPR-reducing methods. The agreement between the theoretical and the simulation results demonstrate the validity of the analysis.

Spectrum Challenges and Solutions by Cognitive Radio: An Overview

Abstract: This paper provides an overview of major problems that are confronting wireless communication with regard to spectrum use in general i.e. by all sectors, government, private, other telecom service providers and military communication. It is commonly believed that there is a crisis of spectrum availability due to tremendous growth in the wireless based systems and the evolution of the radio communication technologies. In fact, there is no shortage of radio spectrum, only a dearth of affordable communications infrastructure. There is potential to make considerably better usage of the radio-spectrum. There are many areas of the radio spectrum which are not fully utilized. Cognitive radios (CR) have been proposed as a way to reuse this underutilized spectrum in an opportunistic manner. A CR is an autonomous unit in a communications environment that senses its environment, tracks changes, and reacts upon its findings and frequently exchanges information with the networks. We show the how the radio frequency is being managed in India and what India is doing to face the challenges to improve the spectrum management. The radio Communication Assembly of ITU is also studying the plan for implementation of CR systems including technical and regulatory issues.

Vision for 2020

Abstract: Mobile and wireless communications provide today high global penetration especially for voice and lower rate data services. In future such systems will be applied in many different usage scenarios from mobile and stationary applications in different radio environments for different communication relations between humans and machines. Today different types of systems are being applied for different application areas. In future, systems and applications will be mainly designed from a user-centric perspective. The vision of future systems is based on an integration and cooperation of different cooperating access systems in a heterogeneous environment at a packet-based core network. ITU-R provided this vision and basic requirements already in 2003, which are the basis for the preparation of World Radiocommunication Conference (WRC 2007) for the potential identification of additional frequency spectrum. In addition, international bodies and communities developed general vision statements on the future development and identified the necessary research areas. Availability of sufficient frequency spectrum is an issue for systems especially with high user throughput versus Quality of Service requirements for full area coverage. Limitations in the availability of sufficient frequency spectrum for wideband communication may change the role models for operators and may potentially result in infrastructure sharing. In the last years huge research activities have been launched in Asia, Europe and North America, which were originally triggered by the ITU-R vision and are following a similar technical approach. There are also parallel activities ongoing in the global wireless IT sector for different application scenarios. These developments have also to consider economic trends and a parallel deployment of wideband fixed line systems. This will result in different scenarios such as Fixed-Mobile-Convergence (FMC) versus competition between operators for mobile and/or fixed line services. In addition, an increasing use of IP for voice and data communication has to be considered in future system design. With respect to the huge deployed infrastructure future developments are expected to evolve from existing and emerging systems. However, all players have also to be prepared for disruptive developments driven by new players. This paper will provide an overview on these different trends and developments towards future systems.

Performance of the Proposed Galileo CBOC Modulation in Heavy Multipath Environment

Abstract: In the framework of the modernization plans of Global Navigation Satellite Systems (GNSS) a new Multiplexed Binary Offset Carrier (MBOC) modulation has been proposed as a possible Signal-In-Space (SIS) with improved performance with respect to the robustness against external sources of degradation. Discussion around such signal format are still on-going at the time of writing, anyway it is the most probable candidate signal that will be adopted by both GPS L1C and the Galileo E1 Open Service (OS) signals [( http://ec.europa.eu/dgs/energy_transport/galileo/documents/doc/2004_06_21_summit_2004_en.pdf , 2004)] as modernization of the present BOC(1,1). In the context of the integration between wireless communication and satellite navigation, one of the major problems is that usually the GNSS receiver has to work in a critical environment characterized by a heavy presence of multipath or interference sources. Some examples are urban canyons or light indoor spaces. These are also typical situations for the usage of personal communications systems. The new MBOC modulation have been studied with the specific goal to create a signal more robust with respect to multipath, bringing the high performance of Galileo in situations in which the present BOC(1,1) shows limitations. In this sense, future Location Based Services (LBS) provided on the basis of the GNSS OS will benefits from this intrinsic robustness of the signal. Throughout the paper a review of the MBOC structure will be presented, specifying that in the Galileo framework such a structure has been proposed in a version named Composite BOC (CBOC). In particular, the paper presents the simulation of the CBOC behavior in presence of multipath showing the extreme improvement with respect to other BOC solutions.

Very Low Energy Consumption Wireless Sensor Localization for Danger Environments with Single Mobile Anchor Node

Abstract: In wireless sensor networks (WSN), it is very important for sensor nodes to locate with low energy consumption and high accuracy, especially in a dangerous environment. This paper describes a range-free layered localization scheme using one mobile anchor node which can transmit gradient signals, and whose moving track is a straight-line along the x-axis. And this paper proposes a sleep/wake mechanism called sensor sleep-time forecasting to save energy consumption during localization. The relationship, between the key factors in localization algorithm and the average location error, is analyzed in detail. Simulation results show that the scheme performs better than other range-free mechanisms--the average location error is less than 0.7 m, and it is independent on sensor nodes density or sensor nodes radio range, the accuracy of the algorithm can be adjusted in different occasions, and the algorithm beacon overhand is small and average localization time is short.

Cognitive Mesh Network Under Interference from Primary User

Abstract: In a commonly accepted usage scenario, a cognitive radio appears as a secondary user of certain spectrum which is licensed to another, primary system. A prominent example of cognitive system is a mesh network operating under the interference from primary system. For such a scenario, we propose techniques for efficient secondary usage of spectrum, which rely on the adaptive array antenna in order to reduce the interference between the primary and the cognitive system. In order to keep the hardware complexity as small as possible, the number of antennas at each cognitive node should be small. However, with the simplest 2-element linear adaptive array, the created antenna pattern can result in non-optimized pattern between cognitive nodes in the mesh network. In order to solve such a problem, this paper introduces a simple antenna pattern switching where each cognitive node is equipped with three antennas, and tries to select the antenna configuration constituting 2-element linear array with the best antenna pattern for each link. The proposed configuration requires three antennas but only two transceiver chains, which can reduce the hardware complexity. We also introduce 3-element linear array and design a simple procedure to heuristically select the pattern. Our numerical results show that the proposed techniques can significantly increase the available bandwidth and networking connectivity with small complexity when a cognitive mesh network is located inside the communication area of the primary system.

Performance of Video Telephony Services in UMTS using Live Measurements and Network Emulation

Abstract: While speech services in mobile communication systems are investigated quite well, video telephony services are relatively novel in this sector. Because of the market penetration of camera equipped mobile phones the video telephony service is expected to become a widely used service. In this article an introduction of the protocols used for video telephony in UMTS is given. Concepts for the performance evaluation in terms of video (PEVQ) and audio quality (PESQ) are presented and utilized. Evaluations are performed by both live measurements and network emulation. The results show that there is quite potential for improvements related to video telephony in UMTS in terms of video quality and channel setup time. Finally, an improved radio bearer configuration is provided which aims at a better integration of video telephony services into the UMTS architecture.

Multi-user Detection of Nonlinearly Distorted MC-CDMA Symbols by Microstatistic Filtering

Abstract: Multi-carrier code division multiple access is a powerful modulation technique that is being considered in many emerging broadband communication systems. In a downlink scenario orthogonal spreading sequences are used since they reduce multiple access interference compared to non-orthogonal. However, the nonlinear amplification of the transmitted signal destroys the orthogonality and, thus, reduces the system performance. In order to avoid performance degradation without requiring large back-offs in the transmitter amplifier, it becomes necessary to use multi-user detection techniques at the receiver side. Conventional multi-user detectors (MUD) are designed for linear environments and, as a result, might not exhibit enough performance improvement. In this paper a new MUD based on microstatistic filtering is proposed. The presented MUD uses piece-wise linear filtering in conjunction with threshold decomposition of the input signal, which introduces a nonlinear effect, to improve performance when a nonlinearity is present. Maximum performance improvement compared to conventional MUD is achieved for low spreading factors and user loads no greater than 50%.

A Low Complexity Algorithm for Generating Turbo Code s-Random Interleavers

Abstract: In this paper we present a low complexity algorithm based on the bubble search sorting method that can be used to generate Turbo code interleavers that fulfill several criteria like spreading (s-randomness), code matched criteria and even the odd---even property for Turbo Trellis Coded Modulation. Simulation results show that for $$s < \sqrt{N/2}$$ the algorithm is extremely efficient for short to medium interleaver lengths.

Bounds on Inter-carrier Interference Power of OFDM in a Gaussian Scattering Channel

Abstract: This letter derives the upper and lower bounds on inter-carrier interference power P ICI of Orthogonal Frequency Division Multiplexing (OFDM) in a Gaussian scattering channel. The bounds are computed as functions of f d T s product of the maximum Doppler spread f d and symbol duration T s , ? frequency tracking and ? mobile travelling direction. Insightful discussions on the characteristics of P ICI are given. Future work is also outlined.

Robust Transmission Over Fast Fading Channels on the Basis of OFDM-MFSK

Abstract: We present an OFDM-based transmission scheme which is suitable for robust transmission in fast fading environments, where a reliable channel estimate is impossible or very difficult to obtain. Our scheme is based on the combination of noncoherently detected M-ary frequency shift keying (MFSK) and orthogonal frequency division multiplexing (OFDM). Noncoherent detection of OFDM-MFSK allows an arbitrary phase choice for all subcarriers in the transmitter. One possibility to exploit this degree of freedom is to choose the subcarrier phases such, that the peak-to-average power ratio (PARR) is reduced. A second possibility is to use the subcarrier phases to transmit additional data. This can be done by differentially modulating the subcarriers that are occupied by the OFDM-MFSK scheme. Both possibilities do not affect the robustness of the underlying noncoherently detected OFDM-MFSK modulation.

Modeling Channel Access Delay and Jitter of IEEE 802.11 DCF

Abstract: With the ever-increasing requirement of WLAN to support real-time services, it is becoming important to study the delay properties of WLAN protocols This paper constructs a new model to analyze the channel access delay and delay jitter of IEEE 80211 DCF in saturation traffic condition Based on this analytical model, average channel access delay and delay jitter are derived for both basic access and RTS/CTS-based access scheme The accuracy of the analytical model is validated by simulations and furthermore we discuss the impact of initial contention window, maximal backoff stage, and packet size on channel access delay and delay jitter of 80211 DCF using the proposed model

A Novel GPS-free Method for Mobile Unit Global Positioning in Outdoor Wireless Environments

Abstract: This paper investigates a Global Positioning system (GPS)-free positioning method for mobile units (MUs) in outdoor wireless environments by using the Bayesian filtering formulation. The procedure utilizes simulated inertial measurements, cell-ID of the serving base station, and pre-determined locations grouped according to cell antennas radio coverage in the experimentation area. The developed algorithm makes no assumptions on the initial position of the MU. However, the algorithm takes some time to converge. Experiments show the range of inertial measurement errors that would maintain reliable location information with accuracy comparable to GPS positioning.

An Overview of Scaling Laws in Ad Hoc and Cognitive Radio Networks

Abstract: Currently, wireless communications are changing along the lines of three main thrusts. The first is the introduction of secondary spectrum licensing (SSL). Regulations on the usage of licensed spectra are being loosened, encouraging unused primary spectrum to be licensed, often in an opportunistic manner, to secondary devices. The second is the introduction of cognitive radios. These wireless devices are able to sense and adapt in a "smart" manner to their wireless environment, making them prime candidates to becoming secondary users in SSL initiatives. Finally, as we approach the communication limits of point-to-point channels, and as wireless devices become cheap and ubiquitous, the focus is shifting from single to multiple communication links, or networks. In this paper, we provide an overview of the recently established theoretical limits, in the form of sum-rates, or throughput, of two main types of networks: ad hoc networks, in which the devices are homogeneous, and cognitive networks, in which a mixture of primary and secondary (or cognitive) devices are present. We summarize and provide intuition on how the throughput of a network scales with its number of nodes n, as n ? ?, under different network and node capability assumptions.

Channel Adaptive Power Control in the Uplink of CDMA Systems

Abstract: In this paper, we propose an adaptive power control algorithm using optimal control theory for CDMA cellular systems. With linear quadratic control, each mobile transmits to achieve a desired SIR under the fast varying environment of practical CDMA cellular systems. We apply Kalman filter theory to estimate a channel variation which is vulnerable to nonconstant link gain, mutual interference and uncertain noise. Through simulation comparison with DCPC algorithm, the suggested power control algorithm shows an increased uplink channel capacity.

On the Performance of Broadband Mobile Internet Access System

Abstract: In this paper, we evaluate the performance of OFDMA/TDD-based broadband mobile internet access system with the features of adaptive modulation & coding (AMC) and hybrid ARQ. We present a framework of system-level simulation and furthermore, intend to derive the insightful results towards understanding the performance of broadband mobile internet access system. The average system throughput as well as delay performance is evaluated for the different channel characteristics and system parameters, which allows for predicting the system capacity in the varying cellular network environment.

Convergence Transforms Digital Home: Techno-Economic Impact

Abstract: This paper discusses the past, the present, and the future of digital home and in particular, how convergence transforms home networking. It describes technology adoption-, consumer-, and behavioural-trends and discusses the business impact from consumer demand for "living in real-time" and from the convergence of applications, services, networks, and terminals. With the explosion of mobile and broadband usage with high Wi-Fi penetration at home and emerging trends such as online social networks, mashups, blogs, etc. will create unparalleled value to customers that will disrupt existing business models of fixed and mobile operators. Consumers expect access to applications and services instantaneously, irrespective of the location, place and all at real-time. Telco's and business are beginning to understand how those behavioural trends, and convergence could have major impact on their service offering, marketing, products, price, go-to-market and how they can leverage these trends to attract and seek global talents. Proliferation of IP enabled device and applications will lead to the development of IP-based home networking in the areas of personal communications, network entertainment, communications and monitoring & management. Finally, a new law was established that will drive the future development of digital home, E = mc3, where E equates to Entertainment experience, m for media (content) and c3 for convergence of communications, computing technologies and consumer electronics. Success of home networking will heavily depend on industries ability to hide networks and systems complexities from end-users where simplicity of the user interface is the key.