Showing papers presented at "Wireless Conference - Sustainable Wireless Technologies , European in 2011"

Investigation on Cell Selection Methods Associated with Inter-cell Interference Coordination in Heterogeneous Networks for LTE-Advanced Downlink

Abstract: In LTE-Advanced, a heterogeneous network where femtocells and picocells overlaid onto macrocells is extensively discussed in addition to traditional well-planned macrocell deployment to improve further the system throughput. In heterogeneous network deployment, cell selection as well as intercell interference coordination (ICIC) is very important to improve the system and cell-edge throughput. Therefore, this paper investigates three cell selection methods associated with ICIC in heterogeneous networks in the LTE-Advanced downlink: signal-to-interference plus noise power ratio (SINR)-based cell selection, reference signal received power (RSRP)-based cell selection, and reference signal received quality (RSRQ)-based cell selection. Simulation results (4 pico eNodeBs and 25 set of user equipment are uniformly located within 1 macro eNodeB) assuming full buffer model show that the downlink cell and cell-edge user throughput levels of RSRP-based cell selection are degraded by approximately 3% and 10% compared to those of SINR-based cell selection under the condition of the maximizing the cell-edge user throughput due to the impairment of the interference level. Furthermore, it is shown that the downlink cell-edge user throughput of RSRQ-based cell selection is improved approximately 5%, although the cell throughput is degraded approximately 5% compared to that for SINR-based cell selection under the condition of the maximizing the cell-edge user throughput.

Improving RSS-Based Indoor Positioning Algorithm via K-Means Clustering

Abstract: Advances in mobile technologies and devices has changed the way users interact with devices and other users. These new interaction methods and services are offered by the help of intelligent sensing capabilities, using context, location and motion sensors. However, indoor location sensing is mostly achieved by utilizing radio signal (Wi-Fi, Bluetooth, GSM etc.) and nearest neighbor identification. The most common algorithm adopted for Received Signal Strength (RSS)-based location sensing is K Nearest Neighbor (KNN), which calculates K nearest neighboring points to mobile users (MUs). Accordingly, in this paper, we aim to improve the KNN algorithm by enhancing the neighboring point selection by applying k-means clustering approach. In the proposed method, k-means clustering algorithm groups nearest neighbors according to their distance to mobile user. Then the closest group to the mobile user is used to calculate the MU's location. The evaluation results indicate that the performance of clustered KNN is closely tied to the number of clusters, number of neighbors to be clustered and the initiation of the center points in k-mean algorithm.

Energy Efficiency Analysis of Two-Tier Heterogeneous Networks

Abstract: With the exponential increase in data traffic driven by a new generation of wireless devices, data is expected to overwhelm cellular network capacity in the next few years. To address this issue, heterogeneous networks have recently being considered as a comprehensive approach to provide high cellular network capacity and coverage. However, the dense and random deployment of small cells and their uncoordinated operation raise important questions about the energy efficiency implications of multi-tier networks. In this paper, we analyze the energy efficiency of downlink two-tier heterogeneous networks, i.e. a network of macrocell base stations overlaid by randomly distributed picocell base stations, where each tier serves a disjoint set of users. Using tools from stochastic geometry, we first derive analytical expressions of success probabilities for each tier when a disjoint set of subchannels is employed. In addition, we evaluate the performance of two-tier networks in terms of energy efficiency and fairness of resource allocation. Numerical results confirm that there exists an optimal pico-macro density ratio that maximizes the overall energy efficiency of such a two-tier network. This work provides essential understanding for successful deployment of green heterogeneous networks.

Latency for Real-Time Machine-to-Machine Communication in LTE-Based System Architecture

Abstract: Machine-to-machine communication has attracted a lot of interest in the mobile communication industry and is under standardization process in 3GPP. Of particular interest is LTE-Advanced support for various M2M service requirements and efficient management and handling of a huge number of machines as mobile subscribers. In addition to the higher throughput, one of the main advantages of LTE/LTE-A in comparison with the previous cellular networks is the reduced transmission latency, which makes this type of networks very attractive for real-time mobile M2M communication scenarios. This paper presents a M2M system architecture based on LTE/LTE-A and highlights the delays associated with each part of the system. Three real-time M2M applications are analyzed and the main latency bottlenecks are identified. Proposals on how the latency can be further reduced are described.

On the performance of an IEEE 802.15.6 Wireless Body Area Network

Abstract: Wireless Body Area Networks (WBANs) are becoming increasingly important for a wide range of applications, from medical to entertainment services. Since 2007, IEEE 802.15 Task Group 6 has been working on a communication standard for low power devices and operation on, in, or around the human body. We consider an IEEE 802.15.6 WBAN where wearable sensor devices are distributed on the body and have to send the measured data to a coordinator. Upon reception of a query coming from the coordinator, nodes of the WBAN compete to access the channel, using the Carrier Sense Multiple Access with Collision Avoidance algorithm defined in the standard, for transmitting their data via a direct link. We evaluate network performance in terms of packet loss rate, delay, and throughput, through simulation. Two different channel models for on-body communication are considered. A comparison with a WBAN based on the IEEE 802.15.4 standard is also provided.

Implementation Aspects of Channel Estimation for 3GPP LTE Terminals

Abstract: In this paper, hardware implementation aspects of the channel estimator in 3GPP LTE terminals are investigated. A channel estimation ASIC, which handles the real-time channel estimation, is presented. Compared to traditional correlator-based channel estimators, the channel estimator presented boosts the throughput at feasible silicon cost by adopting a recently proposed estimation method named Approximate Linear Minimum Mean Square Error (ALMMSE). In this paper, both the architecture and VLSI implementation of the estimator are elaborated. Implemented using a 65nm CMOS process, the channel estimator supports the full 20MHz bandwidth of 3GPP LTE and consumes only 49 kgates.

Comparison of Hybrid Localization Schemes using RSSI, TOA, and TDOA

Abstract: This paper presents a simulation study of nonhybrid and hybrid localization techniques using RSSI, TOA, and TDOA location dependent parameters. Maximum likelihood and weighted least squares are considered and developed for both non-hybrid and hybrid cases. Monte-Carlo simulations using realistic radio parameters extracted from an ultra wide band measurement campaign are carried out in order to assess the performances of different techniques and to show the importance of hybrid data fusion for localization.

AoA, AoD and ToA Characteristics of Scattered Multipath Clusters for THz Indoor Channel Modeling

Abstract: At Terahertz frequencies, commonly used indoor building materials like plaster must be considered as rough, so that rough surface scattering exerts a significant impact on ultra broadband THz propagation channels. Allowing for the modeling of scattering, the characteristics of scattered multipath components like angle and time of arrival as well as phase distributions are investigated in a small office scenario. A double directional channel model is derived in the AoA, AoD and ToA domain. The dependence of the multipath characteristics on the surface roughness is demonstrated. Exemplary channel realizations are generated according to the proposed approach and are contrasted to ray tracing simulations for the evaluation of the applicability of the model.

Cognitive Radio Spectrum E volution Prediction using A rtificial Neural Networks based Multivariate T ime Series Modelling

Abstract: Cognitive Radio (CR) is an efficient answer to spectrum scarcity as it can sense the spectrum steadily based on previous information about the spectrum evolution in time, thus predicting the future occupancy status. Framed within this statement, this paper proposes a new methodology for spectrum prediction by modelling licensed signal Radio F requency (RF) features as a multivariate chaotic time series, which is then given as input to Artificial Neural Network (ANN), that predicts the evolution of RF time series to decide if the unlicensed user can exploit the spectrum band. We exploit the inherent cyclostationarity in primary signals for Non-linear Autoregressive Exogenous T ime Series Modelling of RF features, which is an extremely challenging task due to interdependence of different R F features. Experimental results show a similar trend between predicted and observed values. We target this work at cognition incorporation in our designed Software Defined Radio (SDR) waveform.

WSN Implementation of the Average Consensus Algorithm

Abstract: This paper is motivated by the lack of distributed algorithm implementations on wireless sensor networks (WSN) in hardware. We deal exemplary with the implementation of the well-known average consensus algorithm. By formulating the algorithm into nesC, a C derivative, it is possible to enrich the knowledge of the algorithm with practical information, specific to embedded devices such as nodes. We created a simple mechanism of a time scheduled access to share the wireless channel among the nodes and guarantee a collision free environment, in which our implementation is tested. Our achieved results are consistent with theory. Index Terms—WSN; average consensus; distributed algo- rithms; implementation

A Study on the Wide-Sense Stationarity of the Underwater Acoustic Channel for Non-coherent Communication Systems

Abstract: In this paper we study the wide sense stationarity of the energy of the underwater acoustic channel impulse response and we provide an estimate of the interval during which the wide sense stationarity property holds. We analyze the SPACE08 data set, which has been collected near Martha's Vineyard Island during October 2008. In this data set the environmental conditions such as the height of the waves and the wind direction vary significantly in time. We consider the time series recorded in four different fixed positions. This allows us to compare the results between different locations and environmental conditions.

Wireless M2M Communication Networks for Smart Grid Applications

Abstract: Future Smart Grid applications rely on highly reliable and secure connectivity between various infrastructure components from utilities, grid operators and households in order to cover requirements on communications for smart metering and decentralized energy management including electric mobility. Therefore several approaches for communication infrastructures are currently discussed based on different architectural concepts including wired and wireless access and inhouse communication technologies. In this paper we provide an overview on wireless-enabled networking architectures and discuss two exemplary network planning approaches. On one hand, network planning algorithms for the neighbourhood area network (NAN) are introduced. On the other hand, we present results for an integrated, wireless network coverage-aware planning of public and private charge point locations. In addition we address in the paper the design and implementation of embedded, wirelessWeb Services to enable the efficient and reliable data exchange within distributed energy systems. The paper concludes with the comparison of two approaches for the optimal coding of energy-management-related SOAP messages.

On the Capacity of the 2-user Gaussian MAC Interfering with a P2P Link

Abstract: A multiple access channel and a point-to-point channel sharing the same medium for communications are considered. We obtain an outer bound for the capacity region of this setup, and we show that this outer bound is achievable in some cases. These cases are mainly when interference is strong or very strong. In the low interference regime, a simple strategy using Gaussian codes and treating interference as noise is considered. An upper bound on the sum capacity is derived and shown to be tight (but not coinciding) with the sum-rate achievable using this scheme.

On Circularity of Receiver Front-end Signals Under RF Impairments

Abstract: The circularity of receiver front-end signals is analyzed under various link impairments, including transmitter in-phase/quadrature-phase (I/Q) imbalance and local oscillator (LO) leakage, power amplifier nonlinearity, time-varying channel, carrier frequency offset, receiver phase noise, and DC offsets. Expressions are derived for the complementary autocorrelation functions of signals affected by these impairments. The circularity of the received waveform is shown to hold in the presence of transmitter I/Q imbalance and other impairments under certain realistic and non-restrictive conditions, while receiver I/Q imbalance makes the signal non-circular. These findings are important for receiver I/Q imbalance compensation, since many of these algorithms rely on the circularity of the received waveform, either explicitly or implicitly. Receiver DC offsets can potentially make the signal noncircular, but the effect is shown to be insignificant under realistic RF-to-LO isolation values. The results build confidence that low-complexity blind receiver I/Q imbalance compensation is applicable even in the presence of transmitter I/Q imbalances and other system impairments.

Energy Efficiency Evaluation of State of the Art Packet Scheduling algorithms for LTE

Abstract: In this contribution, the performance of LTE system with various scheduling algorithm taken from the literature are considered. In order to assess the performance of state of the art schedulers a dynamic system level simulator is used that models in details all the features of the downlink of an LTE system in a multi-cell environment. The simulator will be used to analyze the impact of different scheduling policies from an energy efficiency point of view, considering different traffic models. In particular the first step involves analyzing the performances of SOTA algorithms, because up to now these schedulers have been compared from a more traditional point of view (e. g. SE, spectral efficiency) and not for the energy efficiency (EE) evaluation.

Resource Sharing in Relay-enhanced 4G Networks

Abstract: Type 1 inband relay nodes and time-division transmit and receive advanced relay stations are to be supported by 3GPP LTE-Advanced and IEEE 802.16m, respectively. Both classifications support a similar relaying mode where the relay link transmission is time- division multiplexed with the access link transmission, whereas macro users share the same resources with the relays. Hence, system performance depends strongly on the resource partitioning strategy among and within the links as well as how well the competition on resources is managed at the donor eNB. In this paper, we present performance evaluation of different schemes for resource sharing among relay nodes and prioritization techniques of relay users on the relay link coupled with the corresponding scheduling on the access link. In particular, we propose a combination of resource sharing based on the number of relay users and relay link prioritization and scheduling of relay users achieving max-min fairness. A comprehensive system-level simulation campaign is carried out in 3GPP urban and suburban models considering 4 and 10 relays per cell. Results show that the proposed scheme achieves high system fairness and significant throughput gains at the low and mid throughput regime at no or negligible loss in cell throughput.

Demonstration of an OLA-based Cooperative Routing Protocol in an Indoor Environment

Abstract: Concurrent cooperative transmission (CCT) is a cooperative transmission (CT) technique, also known as distributed transmit diversity, where a collection of single-antenna nodes induce a signal-to-noise-ratio advantage in a receiver by transmitting multiple copies of the same message, at the same time, in multiple diversity channels. CCT has been considered in many physical layer system studies including realistic demonstrations, which presented cooperative diversity gain in terms of error rate improvement or range extension. However, there have been very few attempts to evaluate CCT-based network routing schemes on a testbed with consideration of the overheads and challenges that CCT poses to the higher layers. In this paper, we compare the OLAROAD cooperative routing protocol with the conventional Ad hoc On Demand Distance Vector (AODV) protocol, on an ad hoc network of software defined radios. OLAROAD is based on a physical layer that forms opportunistic large arrays (OLAs). We evaluate the performance of the protocols on a linear network topology in a typical office building in terms of hop count, round trip time, packet delivery ratio and route discovery time, so that the advantages and disadvantages of CCT-based routing algorithm may be observed.

A MAC Protocol for Body Area Networks using Out-of-Band Radio

Abstract: Applications of wearable and implanted wireless sensor devices are hot research area. A specialized field called the Body Area Networks (BAN) has emerged to support this area. Energy consumption and delay are major concern for Medium Access Control (MAC) protocols in a BAN. Low cost wake up radio module attached with sensor devices can help to reduce energy consumption and prolong the network lifetime by reducing idle state energy consumption and increasing sleep time of a BAN node. In this paper, we propose a new MAC protocol for body area network using an out-of-band wake up radio. We have used an on-demand scheduling procedure for communication through a centralized and coordinated external wake up mechanism. We compared our method with some existing MAC protocols and is found to outperform them in terms of energy consumption and delay. Use of wake up radio improved the overall performance of the proposed on-demand MAC.

WSN Coverage & Connectivity Improvement Utilizing Sensors Mobility

Abstract: Mobility in Wireless Sensor Networks may significantly affect the network performance. This paper proposes distributed algorithm that improves the network coverage and connectivity, performing controlled reorganization of mobile sensor nodes (C2 algorithm). The algorithm initially organizes the network in a clustered topology, assuming hexagonal grid structure. The Cluster Heads are positioned in the centres of hexagonal cells designed according the nodes transmission range. The C2 reorganizes the sensor nodes between the adjacent hexagonal cells and equally distributes them within the cells, thus improving the network coverage and providing more uniform energy utilization. The algorithm chooses the optimal nodes to perform the movements, maintaining the connectivity between the sensor nodes and minimizing the energy that the nodes consume for their movement. The simulation results show the benefits of the proposed algorithm implementation for coverage and connectivity improvement in a homogeneous WSN.

Delay-Aware NUM System for Wireless Multi-Hop Networks

Abstract: In order to design an effective utility-aware optimization framework for wireless multi-hop networks, it is necessary to explicitly incorporate the delay factor into the Network Utility Maximization (NUM) model. It is especially important in the case of multi-service networks aimed at serving both the file transfer and streaming media traffic. In this paper, we present a novel delay-aware NUM framework for wireless multi-hop networks. The application-layer system that has been derived from this framework consists of a delay-aware indirect flow control mechanism based on a system transporting virtual utility units and a packet forwarding component aimed at providing an approximation of Max-Weight Scheduling (MWS). To the best of the authors' knowledge the proposed solution is the first delay-aware NUM system interoperable with widely used protocols of the most typical wireless networking stack, such as TCP, UDP, IP, and 802.11 MAC.

Distributed Interference Alignment in Cellular Systems: Analysis and Algorithms

Abstract: A fading environment is assumed and the degrees of freedom of a cellular system with an arbitrary number of base stations and users is determined. The base stations and users may have multiple antennas. Algorithms, which are based on alternating the optimization of the receive filters and transmit precoders, are proposed and shown to achieve the optimal degrees of freedom under certain conditions. Simulations sustain the analytic results and demonstrate the superior performance of the proposed algorithms.

LTE Rate Matching Performance with Code Block Balancing

Abstract: In this paper, we compare the performance of the LTE rate matcher for different code rates when segmentation occurs. We present that, for certain cases of segmentation where the different segments are of dissimilar size, the rate applied to each segment may be different and thus degraded overall performance may occur. We show how a simple method which balances the code rate on a per-segment basis can improve the overall block error ratio performance. The whole simulation environment together with the results of this paper are made available for download at our homepage.

Adaptive MMSE turbo equalization with high-order modulations and spatial diversity applied to underwater acoustic communications

Abstract: This paper presents some results on adaptive minimum mean-square error (MMSE) turbo equalization obtained from underwater experiments in the Atlantic ocean. The performance gain is evaluated as a function of the number of hydrophones at the receiver side. Single-carrier transmission with high-order modulations is considered, at a coded bit rate as high as 24 kb/s on the underwater acoustic channel. The all-digital receiver performs timing recovery, equalization, interleaving and channel decoding.

On interference management for uncoordinated LTE-Femto cell deployments

Abstract: In this paper we investigate interference management techniques for uncoordinated and dense residential LTE-Femto cell deployments implementing LTE Release-10 with closed subscriber group configuration. In particular we outline the possible interference management techniques defined in the standard. We present a distributed and centralized interference management strategy operating in the frequency domain. We evaluate the presented strategies for a dense deployment with closed subscriber groups and a scenario where multiple operators share the same band. Our results show that the distributed scheme performs similar to the centralized scheme and that both schemes outperform reuse one.

Challenges for Body Area Networks Concerning Radio Aspects

Abstract: Body Area Networks engage a network of sensors either wearable or implanted into the human body, with a wide range of promising applications in medicine (health care and patient monitoring), firemen/military forces outfits, advanced sports training, personal identification, navigation or multimedia entertainment, among others. This paper gives an insight into the challenges for applications of Body Area Networks, looking forward to energy efficiency and sustainability. A cross-layer perspective is proposed foreseeing effective and efficient systems, comprising cooperation and knowledge sharing between the various system layers (e. g., from antenna design and channel modelling to physical and media access control layers). Central topics are addressed and interrelated, like services and applications, security and privacy issues, interoperability, node and network architecture (e. g., cooperative/relay, distributed schemes), data rate and bandwidth, or energy management. The paper stresses the core position of the radio channel on the overall system, prompting the strong influence of the human body and discussing strategies to overcome connectivity problems (e. g., smart deployment of relays on the body).

Closed-form Approximation for the Trade-Off between Energy Efficiency and Spectral Efficiency in the Uplink of Cellular Network

Abstract: In this paper we propose a tight closed-form approximation of the Energy Efficiency vs. Spectral Efficiency (EE-SE) trade-off for the uplink of a cellular communication system. We model the uplink of the cellular system by considering the Wyner model with Raleigh fading. We first demonstrate the accuracy of our expression by comparing it with Monte-Carlo simulation and the EE-SE trade-off expression based on lowpower approximation. Results show the great tightness of our expression with Monte-Carlo simulation. We utilize our closed-form for assessing the EE performance of base station (BS) cooperation against non-cooperative system for both a theoretical power model and a realistic power model. The theoretical power model includes only the transmit power, whereas the realistic power model incorporates the backhaul and signal processing powers in addition of the transmit power. Results indicate that BS cooperation is more energy efficient than non cooperative system and the former always outperforms the latter in terms of EE-SE trade-off. This is however no more the case with the realistic power model: the EE performance is then highly dependent on the number of cooperating BSs.

Expanding LTE for Devices: Requirements, Deployment Phases and Target Scenarios

Abstract: The vast majority of wireless traffic is expected to be dominated by machines and/or devices before the end of this decade. However, wireless communication networks have been designed mainly with human users in mind. Whilst scale and type of M2M (machine-to-machine) applications are growing rapidly over today's cellular networks, they are still defined following mainly human-to-human communication requirements. To meet the requirements of M2M applications, a new kind of network is needed to serve efficiently a huge number of devices which may have rather modest communications needs. In this paper we address the requirements, challenges, and taxonomy criteria for M2M applications and use cases. Three typical target scenarios are proposed, namely traffic control with smart navigation, smart metering and monitoring, and e-healthcare, which are expected to be the basis for the technical specifications of the extension of LTE system concept for M2M communications. The requirements and challenges identified for these scenarios could serve as the common starting platform for further and detailed investigations of the technical assumptions.

Mobility Control for Machine-to-Machine LTE Systems

Abstract: In this paper, we propose an efficient mobility control algorithm in the downlink multi-cell orthogonal frequency division multiple access (OFDMA) system for co-channel interference reduction. Our scheme divides each cell into several areas. The mobile nodes in each area find their own optimal position according to their present location. Both the signal to interference plus noise ratio (SINR) and the capacity for each node are increased by the proposed mobility control algorithm. Simulation results say that, even when the frequency reuse factor (FRF) is equal to 1, the average capacity is improved after applying the mobility control algorithm, compared to existing partial frequency reuse (PFR) scheme.

Transmit Impairments Influence on the Performance of MIMO Receivers and Precoders

Abstract: This work focuses on the impact of residual transmit impairments on the performance of Multiple-Input Multiple-Output (MIMO) systems with linear and non-linear receivers and precoders. We show that transmit noise significantly affects the performance of systems using precoding. Also, we show that non-linear MIMO receivers and precoders are more sensitive to transmit noise than their respective linear counterpart. Nevertheless, performance degradation can be noticeably alleviated if transmit noise is considered into filter optimization.