Showing papers in "Eurasip Journal on Wireless Communications and Networking in 2011"
TL;DR: It is shown that MU-MIMO only offers marginal performance gains with respect to single-user MIMO and calls for improved schemes for the upcoming releases.
Abstract: A relatively recent idea of extending the benefits of MIMO systems to multiuser scenarios seems promising in the context of achieving high data rates envisioned for future cellular standards after 3G (3rd Generation). Although substantial research has been done on the theoretical front, recent focus is on making Multiuser Multiple-Input Multiple-Output (MUMIMO) practically realizable. This paper presents an overview of the different MU-MIMO schemes included/being studied in 3GPP standardization from LTE (long-term evolution) to LTE Advanced. MU-MIMO system concepts and implementation aspects have been studied here. Various low-complexity receiver architectures are investigated, and their performance assessed through link-level simulations. Appealing performance offered by low-complexity interference aware (IA) receivers is notably emphasized. Furthermore, system level simulations for LTE Release 8 are provided. Interestingly, it is shown that MU-MIMO only offers marginal performance gains with respect to single-user MIMO. This arises from the limited MU-MIMO features included in Release 8 and calls for improved schemes for the upcoming releases.
123 citations
TL;DR: A 5.9 GHz NLOS path-loss and fading model based on real-world measurements at a representative selection of intersections in the city of Munich is developed and it is shown that the measurement data can very well be fitted to an analytical model and could be used in large-scale packet-level simulations.
Abstract: Inter-vehicle communication promises to prevent accidents by enabling applications such as cross-traffic assistance. This application requires information from vehicles in non-line-of-sight (NLOS) areas due to building at intersection corners. The periodic cooperative awareness messages are foreseen to be sent via 5.9 GHz IEEE 802.11p. While it is known that existing micro-cell models might not apply well, validated propagation models for vehicular 5.9 GHz NLOS conditions are still missing. In this article, we develop a 5.9 GHz NLOS path-loss and fading model based on real-world measurements at a representative selection of intersections in the city of Munich. We show that (a) the measurement data can very well be fitted to an analytical model, (b) the model incorporates specific geometric aspects in closed-form as well as normally distributed fading in NLOS conditions, and (c) the model is of low complexity, thus, could be used in large-scale packet-level simulations. A comparison to existing micro-cell models shows that our model significantly differs.
98 citations
TL;DR: This article proposes power allocation techniques for the downlink of distributed, precoded, multicell cellular-based systems and shows that the proposed suboptimal schemes achieve a performance very close to the optimal but with lower computational complexity.
Abstract: Multicell cooperation is a promising solution for cellular wireless systems to mitigate intercell interference, improve system fairness, and increase capacity. In this article, we propose power allocation techniques for the downlink of distributed, precoded, multicell cellular-based systems. The precoder is designed in two phases: first the intercell interference is removed by applying a set of distributed precoding vectors; then the system is further optimized through power allocation. Three centralized power allocation algorithms with per-BS power constraint and different complexity trade-offs are proposed: one optimal in terms of minimization of the instantaneous average bit error rate (BER), and two suboptimal. In this latter approach, the powers are computed in two phases. First, the powers are derived under total power constraint (TPC) and two criterions are considered, namely, minimization of the instantaneous average BER and minimization of the sum of inverse of signal-to-noise ratio. Then, the final powers are computed to satisfy the individual per-BS power constraint. The performance of the proposed schemes is evaluated, considering typical pedestrian scenarios based on LTE specifications. The numerical results show that the proposed suboptimal schemes achieve a performance very close to the optimal but with lower computational complexity. Moreover, the performance of the proposed per-BS precoding schemes is close to the one obtained considering TPC over a supercell.
93 citations
TL;DR: Techniques for sense through wall human detection for different types of walls based on breathing movements and a new approach based on short time Fourier transform is discussed.
Abstract: In this article, we discuss techniques for sense through wall human detection for different types of walls. We have focused on detection of stationary human target behind wall based on breathing movements. In detecting the breathing motion, a Doppler based method is used. Also a new approach based on short time Fourier transform is discussed and an already proposed clutter reduction technique based on singular value decomposition is applied to different measurements.
91 citations
TL;DR: This article presents a new algorithm dedicated to the blind recognition of convolutional encoders in the general k/n rate case, and develops a new iterative method dedicated toThe blind estimation of Convolutional Encoding in a noisy context.
Abstract: In order to enhance the reliability of digital transmissions, error correcting codes are used in every digital communication system. To meet the new constraints of data rate or reliability, new coding schemes are currently being developed. Therefore, digital communication systems are in perpetual evolution and it is becoming very difficult to remain compatible with all standards used. A cognitive radio system seems to provide an interesting solution to this problem: the conception of an intelligent receiver able to adapt itself to a specific transmission context. This article presents a new algorithm dedicated to the blind recognition of convolutional encoders in the general k/n rate case. After a brief recall of convolutional code and dual code properties, a new iterative method dedicated to the blind estimation of convolutional encoders in a noisy context is developed. Finally, case studies are presented to illustrate the performances of our blind identification method.
82 citations
TL;DR: The most recent regulatory rules for TV White Space opportunistic usage are considered, and technologies to operate in these bands are proposed, focusing on the two incumbent systems of the TV bands, namely TV stations and wireless microphones.
Abstract: Cognitive radio has been an active research area in wireless communications over the past 10 years. TV Digital Switch Over resulted in new regulatory regimes, which offer the first large-scale opportunity for cognitive radio and networks. This article considers the most recent regulatory rules for TV White Space opportunistic usage, and proposes technologies to operate in these bands. It addresses techniques to assess channel vacancy by the cognitive radio, focusing on the two incumbent systems of the TV bands, namely TV stations and wireless microphones. Spectrum-sensing performance is discussed under TV White Space regulation parameters. Then, modulation schemes for the opportunistic radio are discussed, showing the limitations of classical multi-carrier techniques and the advantages of filter bank modulations. In particular, the low adjacent band leakage of filter bank is addressed, and its benefit for spectrum pooling is stressed as a means to offer broadband access through channel aggregation.
75 citations
TL;DR: Experiments and analyses show that EDDK has a very low overhead in terms of computation, communication, and storage and does not depend on such infrastructure as base stations and robots and thus has a high level of flexibility.
Abstract: Energy efficiency is an essential requirement for wireless sensor networks while security must also be ensured for mission-critical applications. In this paper, we present an energy-efficient distributed deterministic key management scheme (EDDK) for resource-constrained wireless sensor networks. EDDK mainly focuses on the establishment and maintenance of the pairwise keys as well as the local cluster keys and can fix some flaws in some existing key management schemes. Not only can the neighbor table constructed during key establishment provide the security for key maintenance and data transfer, but it can also be used to effectively manage the storage and update of the keys. By using the elliptic curve digital signature algorithm in EDDK, both new and mobile sensor nodes can join or rejoin a sensor network securely. Unlike some centralized and location-based key management schemes, EDDK does not depend on such infrastructure as base stations and robots and thus has a high level of flexibility. Experiments and analyses show that EDDK has a very low overhead in terms of computation, communication, and storage.
73 citations
TL;DR: The performance of IEEE 802.15.4 standard operating in different modes respectively over wireless sensor and actuator networks is analyzed to examine how network QoS will be impacted by some critical parameters.
Abstract: With rapid advancements in sensing, networking, and computing technologies, recent years have witnessed the emergence of cyber-physical systems (CPS) in a broad range of application domains. CPS is a new class of engineered systems that features the integration of computation, communications, and control. In contrast to general-purpose computing systems, many cyber-physical applications are safety critical. These applications impose considerable requirements on quality of service (QoS) of the employed networking infrastruture. Since IEEE 802.15.4 has been widely considered as a suitable protocol for CPS over wireless sensor and actuator networks, it is of vital importance to evaluate its performance extensively. Serving for this purpose, this paper will analyze the performance of IEEE 802.15.4 standard operating in different modes respectively. Extensive simulations have been conducted to examine how network QoS will be impacted by some critical parameters. The results are presented and analyzed, which provide some useful insights for network parameter configuration and optimization for CPS design.
69 citations
TL;DR: Titan is introduced, a service-oriented framework supporting design, development, deployment, and execution of activity-aware Pervasive Apps, geared to streaming data processing and machine learning, which is key for activity recognition.
Abstract: Upcoming ambient intelligence environments will boast ever larger number of sensor nodes readily available on body, in objects, and in the user's surroundings. We envision "Pervasive Apps", user-centric activity-aware pervasive computing applications. They use available sensors for activity recognition. They are downloadable from application repositories, much like current Apps for mobile phones. A key challenge is to provide Pervasive Apps in open-ended environments where resource availability cannot be predicted. We therefore introduce Titan, a service-oriented framework supporting design, development, deployment, and execution of activity-aware Pervasive Apps. With Titan, mobile devices inquire surrounding nodes about available services. Internet-based application repositories compose applications based on available services as a service graph. The mobile device maps the service graph to Titan Nodes. The execution of the service graph is distributed and can be remapped at run time upon changing resource availability. The framework is geared to streaming data processing and machine learning, which is key for activity recognition. We demonstrate Titan in a pervasive gaming application involving smart dice and a sensorized wristband. We comparatively present the implementation cost and performance and discuss how novel machine learning methodologies may enhance the flexibility of the mapping of service graphs to opportunistically available nodes.
61 citations
TL;DR: This article derives optimal bandwidth and transmit power for each dedicated mode at first, and an ergodic capacity-based mode switching strategy is proposed to further improve the BPJ-EE, which provides insights into the preferred mode under given scenarios.
Abstract: Adaptively adjusting system parameters including bandwidth, transmit power and mode to maximize the "Bits per-Joule" energy efficiency (BPJ-EE) in the downlink MIMO systems with imperfect channel state information at the transmitter (CSIT) is considered in this article. By mode, we refer to choice of transmission schemes i.e., singular value decomposition (SVD) or block diagonalization (BD), active transmit/receive antenna number and active user number. We derive optimal bandwidth and transmit power for each dedicated mode at first, in which accurate capacity estimation strategies are proposed to cope with the imperfect CSIT caused capacity prediction problem. Then, an ergodic capacity-based mode switching strategy is proposed to further improve the BPJ-EE, which provides insights into the preferred mode under given scenarios. Mode switching compromises different power parts, exploits the trade-off between the multiplexing gain and the imperfect CSIT caused inter-user interference and improves the BPJ-EE significantly.
60 citations
TL;DR: This paper introduces sociable routing, a novel routing strategy that selects a subset of optimal forwarders among all the nodes and relies on them for an efficient delivery.
Abstract: The problem of choosing the best forwarders in Delay-Tolerant Networks (DTNs) is crucial for minimizing the delay in packet delivery and for keeping the amount of generated traffic under control. In this paper, we introduce sociable routing, a novel routing strategy that selects a subset of optimal forwarders among all the nodes and relies on them for an efficient delivery. The key idea is that of assigning to each network node a time-varying scalar parameter which captures its social behavior in terms of frequency and types of encounters. This sociability concept is widely discussed and mathematically formalized. Simulation results of a DTN of vehicles in urban environment, driven by real mobility traces, and employing sociable routing, is presented. Encouraging results show that sociable routing, compared to other known protocols, achieves a good compromise in terms of delay performance and amount of generated traffic.
TL;DR: This paper introduces security modules which can be retrofitted to provide end-to-end integrity and authentication measures by utilizing the black channel concept and improves the WirelessHART standard with periodic and deterministic downlink transmissions.
Abstract: Wireless communication has gained more interest in industrial automation due to flexibility, mobility, and cost reduction. Wireless systems, in general, require additional and different engineering and maintenance tasks, for example cryptographic key management. This is an important aspect that needs to be addressed before wireless systems can be deployed and maintained efficiently in the industry. In this paper, we take an holistic approach that addresses safety and security regardless of the underlying media. In our proposed framework we introduce security modules which can be retrofitted to provide end-to-end integrity and authentication measures by utilizing the black channel concept. With the proposed approach, we can extend and provide end-to-end security as well as functional safety using existing automation equipment and standards, such as Profisafe, Profinet IO, and WirelessHART. Furthermore, we improve the WirelessHART standard with periodic and deterministic downlink transmissions to enable efficient usage of wireless actuators, as well as improving the performance of functional safety protocols.
TL;DR: A set of probabilistic protocols that detect the absence of a tag from a system composed of a set of tags and a reader and are able to detect which tag and for how long it has been taken away from the system are provided.
Abstract: We leverage RFID tag cooperation to enforce tampering detection. That is, we provide a set of probabilistic protocols that detect the absence of a tag from a system composed of a set of tags and a reader. Our proposals are able to detect which tag and for how long it has been taken away from the system. The grain of the detection can be tuned with respect to the resources available on the tags. Another merit of our solutions is to provide a proof-of-concept that a small level of cooperation among tags can further extend the range of applications RFID can support, possibly opening new veins of research. The proposed protocols fit the resource constraints of the several classes of RFID available on the market. In particular, the memory requirement ranges fromfew memory slots to a number of memory slots that is proportional to the number of rounds the presence of a tag is going to be checked. Computation is just one hash per round. This fully fledged set of protocols is thought to trade off the detection grain with the resources on the tag: the finer the item removal detection grain, the more resources a protocol requires. A thorough analysis for the removal detection probability is provided. Finally, extensive simulations support the analytical results, showing the viability of the proposed solutions.
TL;DR: By forming a spanning tree used once for distances and a second time for bearings, the localization problem can be made solvable in linear time with significantly less number of sensing links and smaller sensing radii of nodes compared with the cooperative networks with distance-only or bearing-only measurements.
Abstract: This article provides the graphical properties which can ensure unique localizability in cooperative networks with hybrid distance and bearing (angle of arrival) measurements. Furthermore, within the networks satisfying these graphical properties, this article identifies further sets of conditions so that the associated computational complexity becomes linear in the number of sensor nodes. We show how, by forming a spanning tree used once for distances and a second time for bearings where the underlying graph is connected, the localization problem can be made solvable in linear time with significantly less number of sensing links and smaller sensing radii of nodes compared with the cooperative networks with distance-only or bearing-only measurements. These easily localizable networks can be localized in polynomial time when measurements are noisy.
TL;DR: Simulation results demonstrate that the modified EKE algorithm in list decoding of a GRS code provides low complexity, particularly at high signal-to-noise ratios.
Abstract: This work presents a modified extended key equation algorithm in list decoding of generalized Reed-Solomon (GRS) codes. A list decoding algorithmof generalized Reed-Solomon codes has two steps, interpolation and factorization. The extended key equation algorithm (EKE) is an interpolation-based approach with a lower complexity than Sudan's algorithm. To increase the decoding speed, this work proposes a modified EKE algorithm to perform codeword checking prior to such an interpolation process. Since the evaluation mapping is engaged in encoding, a codeword is not generated systematically. Thus, the transmission information is not directly obtained from a received codeword. Therefore, the proposed algorithm undertakes a matrix operation to obtain the transmission information once a received vector has been checked to be error-free. Simulation results demonstrate that the modified EKE algorithm in list decoding of a GRS code provides low complexity, particularly at high signal-to-noise ratios.
TL;DR: TheIDRA architecture is introduced, which is designed specifically to enable connectivity between heterogeneous resource-constrained objects and evaluates the performance of the IDRA architecture and discusses the feasibility of introducing IDRA in existing networks.
Abstract: In a future internet of things, an increasing number of everyday objects are connected with each other. These objects can be very diverse in terms of the used network protocols and communication technologies, which leads to a wild growth of co-located networking technologies. Unfortunately, current consumer items are not designed to communicate with co-located devices that use different communication technologies. In addition, commercially available internet of things devices, such as sensor nodes, often use vendor-specific propriety network solutions. As a result, communication between these devices is only possible through the use of gateway nodes, resulting in inefficient use of the wireless medium. To remedy this situation, this paper discusses which features are required to integrate such a diverse number of heterogeneous objects into a single internet of things. In addition, the paper introduces the IDRA architecture, which is designed specifically to enable connectivity between heterogeneous resource-constrained objects. The IDRA architecture has the following advantages. (1) IDRA can connect co-located objects directly, without the need for complex translation gateways. (2) The architecture is clean slate, but supports backward compatibility with existing deployments. (3) Due to its low memory footprint, the architecture can be used in resource-constrained objects. Finally, the paper evaluates the performance of the IDRA architecture and discusses the feasibility of introducing IDRA in existing networks.
TL;DR: The results proved that the Village Telco infrastructure is deployable in severe and under-resourced environments as a means to make cheap phone calls and render Internet and IP-based services.
Abstract: VoIP (Voice over IP) over mesh networks could be a potential solution to the high cost of making phone calls in most parts of Africa. The Village Telco (VT) is an easy to use and scalable VoIP over meshed WLAN (Wireless Local Area Network) telephone infrastructure. It uses a mesh network of mesh potatoes to form a peer-to-peer network to relay telephone calls without landlines or cell phone towers. This paper discusses the Village Telco infrastructure, how it addresses the numerous difficulties associated with wireless mesh networks, and its efficient deployment for VoIP services in some communities around the globe. The paper also presents the architecture and functions of a mesh potato and a novel combined analog telephone adapter (ATA) and WiFi access point that routes calls. Lastly, the paper presents the results of preliminary tests that have been conducted on a mesh potato. The preliminary results indicate very good performance and user acceptance of the mesh potatoes. The results proved that the infrastructure is deployable in severe and under-resourced environments as a means to make cheap phone calls and render Internet and IP-based services. As a result, the VT project contributes to bridging the digital divide in developing areas.
TL;DR: An automated method is presented to optimize and calibrate the experimental data before offering them to a positioning engine and introduces a new method to provide bounds for the range, thereby further improving the accuracy of the simple and fast 2D localization algorithm based on corrected distance circles.
Abstract: Received signal strength indication (RSSI)-based localization is emerging in wireless sensor networks (WSNs). Localization algorithms need to include the physical and hardware limitations of RSSI measurements in order to give more accurate results in dynamic real-life indoor environments. In this study, we use the Interdisciplinary Institute for Broadband Technology real-life test bed and present an automated method to optimize and calibrate the experimental data before offering them to a positioning engine. In a preprocessing localization step, we introduce a new method to provide bounds for the range, thereby further improving the accuracy of our simple and fast 2D localization algorithm based on corrected distance circles. A maximum likelihood algorithm with a mean square error cost function has a higher position error median than our algorithm. Our experiments further show that the complete proposed algorithm eliminates outliers and avoids any manual calibration procedure.
TL;DR: This semi-tutorial paper considers the well-known projection onto convex sets (POCS) technique and shows how the POCS estimate can be upper bounded by solving a non-convex optimization problem.
Abstract: In this semi-tutorial paper, the positioning problem is formulated as a convex feasibility problem (CFP). To solve the CFP for non-cooperative networks, we consider the well-known projection onto convex sets (POCS) technique and study its properties for positioning. We also study outer-approximation (OA) methods to solve CFP problems. We then show how the POCS estimate can be upper bounded by solving a non-convex optimization problem. Moreover, we introduce two techniques based on OA and POCS to solve the CFP for cooperative networks and obtain two new distributed algorithms. Simulation results show that the proposed algorithms are robust against non-line-of-sight conditions.
TL;DR: In this article, the authors provide an overview of the research progress in applying TCP algorithms to the problem of multi-hop conditions and characteristics, including cross-layer, network layer protocols and medium access control (MAC) layer protocols.
Abstract: Transmission control protocol (TCP) performance over multi-hop wireless networks is currently attracting considerable interest from the research community. The characteristics of multi-hop wireless networks, such as mobility, link layer contention, high bit error rate, asymmetric path, network partition, hidden exposed nodes and dynamic routing, do not fit the requirements of TCP for a good reliable data delivery. Here we want to provide an overview of the research progress in applying TCP algorithms to the problem of multi-hop conditions and characteristics. The scope of this review will encompass core methods and protocols of TCP over multi-hop networks, including cross-layer, network layer protocols and medium access control (MAC) layer protocols. The research contributions in each field are systematically summarized and compared, allowing us to clearly define existing research challenges, and to highlight promising new research directions. The findings of this review should provide useful insight into current multi-hop networks literature and be a good source for anyone who is interested in "TCP in wireless" approaches or related fields.
TL;DR: A routing scheme named mobile multimedia geographic routing (MGR) is specially designed to minimize energy consumption and satisfy constraints on the average end-to-end delay of specific applications in MMSNs, andSimulations verify the MGR's performance to satisfy QoS requirement while saving energy for MMSN's.
Abstract: Recent advances in the fields of wireless technology and multimedia systems have exhibited a strong potential and tendency on improving human life by enabling smart services in ubiquitous computing environments. This paper investigates a mobile multimedia system through combining various technologies, such as wireless sensor networks, embedded multimedia system and node mobility. In particular, we will employ some powerful sensor node with both mobility and multimedia functionalities, which can be controlled by contextual information collected by other systems to enable interactive multimedia services. The new architecture is called mobile multimedia sensor network (MMSN) in this paper. A routing scheme named mobile multimedia geographic routing (MGR) is specially designed to minimize energy consumption and satisfy constraints on the average end-to-end delay of specific applications in MMSNs. Simulations verify the MGR's performance to satisfy QoS requirement while saving energy for MMSNs.
TL;DR: This work presents an embedded camera prototype that uses Trusted Computing to provide security guarantees for streamed videos and incorporates image timestamping, detection of platform reboots, and reporting of the system status.
Abstract: Camera systems are used in many applications including video surveillance for crime prevention and investigation, traffic monitoring on highways or building monitoring and automation. With the shift from analog towards digital systems, the capabilities of cameras are constantly increasing. Today's smart camera systems come with considerable computing power, large memory, and wired or wireless communication interfaces. With onboard image processing and analysis capabilities, cameras not only open new possibilities but also raise new challenges. Often overlooked are potential security issues of the camera system. The increasing amount of software running on the cameras turns them into attractive targets for attackers. Therefore, the protection of camera devices and delivered data is of critical importance. In this work we present an embedded camera prototype that uses Trusted Computing to provide security guarantees for streamed videos. With a hardware-based security solution, we ensure integrity, authenticity, and confidentiality of videos. Furthermore, we incorporate image timestamping, detection of platform reboots, and reporting of the system status. This work is not limited to theoretical considerations but also describes the implementation of a prototype system. Extensive evaluation results illustrate the practical feasibility of the approach.
TL;DR: An overview of current platforms and analyzes the related architectural choices, the current issues in SDR, as well as potential future trends are presented.
Abstract: Software Defined Radio (SDR) is an innovative approach which is becoming a more and more promising technology for future mobile handsets. Several proposals in the field of embedded systems have been introduced by different universities and industries to support SDR applications. This article presents an overview of current platforms and analyzes the related architectural choices, the current issues in SDR, as well as potential future trends.
TL;DR: A large-scale MIMO system operating in the 60 GHz band employing beamforming for high-speed data transmission is considered, and an iterative antenna selection algorithm based on discrete stochastic approximation that can quickly lock onto a near-optimal antenna subset is proposed.
Abstract: We consider a large-scale MIMO system operating in the 60 GHz band employing beamforming for high-speed data transmission. We assume that the number of RF chains is smaller than the number of antennas, which motivates the use of antenna selection to exploit the beamforming gain afforded by the large-scale antenna array. However, the system constraint that at the receiver, only a linear combination of the receive antenna outputs is available, which together with the large dimension of the MIMO system makes it challenging to devise an efficient antenna selection algorithm. By exploiting the strong line-of-sight property of the 60 GHz channels, we propose an iterative antenna selection algorithm based on discrete stochastic approximation that can quickly lock onto a near-optimal antenna subset. Moreover, given a selected antenna subset, we propose an adaptive transmit and receive beamforming algorithm based on the stochastic gradient method that makes use of a low-rate feedback channel to inform the transmitter about the selected beams. Simulation results show that both the proposed antenna selection and the adaptive beamforming techniques exhibit fast convergence and near-optimal performance.
TL;DR: This paper proposes a secure clustering scheme along with a deterministic pairwise key management scheme based on public key cryptography that guarantees node-to-node authentication, high resiliency against node capture, and minimum memory space requirement in WSNs.
Abstract: Information security in infrastructureless wireless sensor networks (WSNs) is one of the most important research challenges. In these networks, sensor nodes are typically sprinkled liberally in the field in order to monitor, gather, disseminate, and provide the sensed data to the command node. Various studies have focused on key establishment schemes in homogeneous WSNs. However, recent research has shown that achieving survivability in WSNs requires a hierarchy and heterogeneous infrastructure. In this paper, to address security issues in the heterogeneous WSNs, we propose a secure clustering scheme along with a deterministic pairwise key management scheme based on public key cryptography. The proposed security mechanism guarantees that any two sensor nodes located in the same cluster and routing path can directly establish a pairwise key without disclosing any information to other nodes. Through security performance evaluation, it is shown that the proposed scheme guarantees node-to-node authentication, high resiliency against node capture, and minimum memory space requirement.
TL;DR: An analysis of the joint impact of path-loss, shadowing and fast fading on cellular networks and two analytical methods are developed to express the outage probability, based on the Fenton-Wilkinson approach and the central limit theorem for causal functions.
Abstract: In this paper, we propose an analysis of the joint impact of path-loss, shadowing and fast fading on cellular networks. Two analytical methods are developed to express the outage probability. The first one based on the Fenton-Wilkinson approach, approximates a sum of log-normal random variables by a log-normal random variable and approximates fast fading coefficients in interference terms by their average value. We denote it FWBM for Fenton-Wilkinson based method. The second one is based on the central limit theorem for causal functions. It allows to approximate a sum of positive random variables by a Gamma distribution. We denote it CLCFM for central limit theorem for causal functions method. Each method allows to establish a simple and easily computable outage probability formula, which jointly takes into account path-loss, shadowing and fast fading. We compute the outage probability, for mobile stations located at any distance from their serving BS, by using a fluid model network that considers the cellular network as a continuum of BS. We validate our approach by comparing all results to extensive Monte Carlo simulations performed in a traditional hexagonal network and we provide the limits of the two methods in terms of system parameters. The proposed framework is a powerful tool to study performances of cellular networks, e.g., OFDMA systems (WiMAX, LTE).
TL;DR: A cross-layer attack to TCP connections in cognitive radio networks is presented, its impact on TCP throughput is analyzed via analytical model and simulation, and potential countermeasures to mitigate it are proposed.
Abstract: Cognitive radio is a promising technology aiming to improve the utilization of the radio electromagnetic spectrum. A cognitive radio is a smart device which runs radio applications software to perform signal processing. The use of this software enables the device to sense and understand its environment and actively change its mode of operation based on its observations. Unfortunately, this solution entails new security challenges. In this paper, we present a cross-layer attack to TCP connections in cognitive radio networks, analyze its impact on TCP throughput via analytical model and simulation, and propose potential countermeasures to mitigate it.
TL;DR: This article uses convex optimization technique to find optimal power distribution to the preamble by casting the MSE minimization problem into a semidefinite programming problem and iteratively select the placement and optimally distribute power to the selected pilot symbols.
Abstract: In this article, design of preamble for channel estimation and pilot symbols for pilot-assisted channel estimation in orthogonal frequency division multiplexing system with null subcarriers is studied. Both the preambles and pilot symbols are designed to minimize the l2 or the l∞ norm of the channel estimate mean-squared errors (MSE) in frequency-selective environments. We use convex optimization technique to find optimal power distribution to the preamble by casting the MSE minimization problem into a semidefinite programming problem. Then, using the designed optimal preamble as an initial value, we iteratively select the placement and optimally distribute power to the selected pilot symbols. Design examples consistent with IEEE 802.11a as well as IEEE 802.16e are provided to illustrate the superior performance of our proposed method over the equi-spaced equi-powered pilot symbols and the partially equi-spaced pilot symbols.
TL;DR: In this article, the authors proposed dynamic parameter adjustment techniques to accommodate a varying (and potentially high) number of contenders in CSMA/E2CA, in which a deterministic backoff is used two consecutive times after a successful transmission.
Abstract: Carrier sense multiple access with enhanced collision avoidance (CSMA/ECA) is a distributed MAC protocol that allows collision-free access to the medium in WLANs. The only difference between CSMA/ECA and the well-known CSMA/CA is that the former uses a deterministic backoff after successful transmissions. Collision-free operation is reached after a transient state during which some collisions may occur. This paper shows that the duration of the transient state can be shortened by appropriately setting the contention parameters. Standard absorbing Markov chain theory is used to describe the behaviour of the system in the transient state and to predict the expected number of slots to reach the collision-free operation. The paper also introduces CSMA/E2CA, in which a deterministic backoff is used two consecutive times after a successful transmission. CSMA/E2CA converges quicker to collision-free operation and delivers higher performance than CSMA/ECA, specially in harsh wireless scenarios with high frame-error rates. The last part of the paper addresses scenarios with a large number of contenders. We suggest dynamic parameter adjustment techniques to accommodate a varying (and potentially high) number of contenders. The effectiveness of these adjustments in preventing collisions is validated by means of simulation.
TL;DR: It is shown that multi-user MIMO can deliver its promised gains in modern wireless systems in spite of the limited channel state information at the transmitter (CSIT) only if users resort to intelligent interference-aware detection rather than the conventional single-user detection.
Abstract: In this paper, we propose a novel low-complexity interference-aware receiver structure for multi-user MIMO that is based on the exploitation of the structure of residual interference. We show that multi-user MIMO can deliver its promised gains in modern wireless systems in spite of the limited channel state information at the transmitter (CSIT) only if users resort to intelligent interference-aware detection rather than the conventional single-user detection. As an example, we focus on the long term evolution (LTE) system and look at the two important characteristics of the LTE precoders, i.e., their low resolution and their applying equal gain transmission (EGT). We show that EGT is characterized by full diversity in the single-user MIMO transmission but it loses diversity in the case of multi-user MIMO transmission. Reflecting on these results, we propose a LTE codebook design based on two additional feedback bits of CSIT and show that this new codebook significantly outperforms the currently standardized LTE codebooks for multi-user MIMO transmission.