Analysis of the Decoupled Access for Downlink and Uplink in Wireless Heterogeneous Networks

Wireless cellular networks evolve towards a heterogeneous infrastructure, featuring multiple types of Base Stations (BSs), such as Femto BSs (FBSs) and Macro BSs (MBSs). A wireless device observes multiple points (BSs) through which it can access the infrastructure and it may choose to receive the downlink (DL) traffic from one BS and send uplink (UL) traffic through another BS. Such a situation is referred to as decoupled DL/UL access. Using the framework of stochastic geometry, we derive the association probability for DL/UL. In order to maximize the average received power, as the relative density of FBSs initially increases, a large fraction of devices chooses decoupled access, i.e. receive from a MBS in DL and transmit through a FBS in UL. We analyze the impact that this type of association has on the average throughput in the system.Comment: 4 pages, 3 figures, submitted to IEEE Wireless Communications Letter

Geometric Interpretation of Theoretical Bounds for RSS-based Source Localization with Uncertain Anchor Positions

The Received Signal Strength based source localization can encounter severe problems originating from uncertain information about the anchor positions in practice. The anchor positions, although commonly assumed to be precisely known prior to the source localization, are usually obtained using previous estimation algorithm such as GPS. This previous estimation procedure produces anchor positions with limited accuracy that result in degradations of the source localization algorithm and topology uncertainty. We have recently addressed the problem with a joint estimation framework that jointly estimates the unknown source and uncertain anchors positions and derived the theoretical limits of the framework. This paper extends the authors previous work on the theoretical performance bounds of the joint localization framework with appropriate geometric interpretation of the overall problem exploiting the properties of semi-definiteness and symmetry of the Fisher Information Matrix and the Cram{\`e}r-Rao Lower Bound and using Information and Error Ellipses, respectively. The numerical results aim to illustrate and discuss the usefulness of the geometric interpretation. They provide in-depth insight into the geometrical properties of the joint localization problem underlining the various possibilities for practical design of efficient localization algorithms.Comment: 30 pages, 15 figure

Generic Multiuser Coordinated Beamforming for Underlay Spectrum Sharing

The beamforming techniques have been recently studied as possible enablers for underlay spectrum sharing. The existing beamforming techniques have several common limitations: they are usually system model specific, cannot operate with arbitrary number of transmit/receive antennas, and cannot serve arbitrary number of users. Moreover, the beamforming techniques for underlay spectrum sharing do not consider the interference originating from the incumbent primary system. This work extends the common underlay sharing model by incorporating the interference originating from the incumbent system into generic combined beamforming design that can be applied on interference, broadcast or multiple access channels. The paper proposes two novel multiuser beamforming algorithms for user fairness and sum rate maximization, utilizing newly derived convex optimization problems for transmit and receive beamformers calculation in a recursive optimization. Both beamforming algorithms provide efficient operation for the interference, broadcast and multiple access channels, as well as for arbitrary number of antennas and secondary users in the system. Furthermore, the paper proposes a successive transmit/receive optimization approach that reduces the computational complexity of the proposed recursive algorithms. The results show that the proposed complexity reduction significantly improves the convergence rates and can facilitate their operation in scenarios which require agile beamformers computation.Comment: 30 pages, 5 figure

Optimal time sharing in underlay cognitive radio systems with RF energy harvesting

Due to the fundamental tradeoffs, achieving spectrum efficiency and energy efficiency are two contending design challenges for the future wireless networks. However, applying radio-frequency (RF) energy harvesting (EH) in a cognitive radio system could potentially circumvent this tradeoff, resulting in a secondary system with limitless power supply and meaningful achievable information rates. This paper proposes an online solution for the optimal time allocation (time sharing) between the EH phase and the information transmission (IT) phase in an underlay cognitive radio system, which harvests the RF energy originating from the primary system. The proposed online solution maximizes the average achievable rate of the cognitive radio system, subject to the $\varepsilon$-percentile protection criteria for the primary system. The optimal time sharing achieves significant gains compared to equal time allocation between the EH and IT phases.Comment: Proceedings of the 2015 IEEE International Conference on Communications (IEEE ICC 2015), 8-12 June 2015, London, U

Fast Packet Switches with Shared Buffer Memory

Modern networks (such as BISDN, gigabit networks, parallel computer networks, LANs, etc.) introduce fast packet switches as a new concept of a switching node. Fast packet switches which employ shared storage are able to utilize the buffer efficiently. Several analytical techniques to evaluate the performance of shared buffer switches have been proposed. They range from the simple convolution technique which is fast but inaccurate, to the approach proposed by Eckberg and Hou, which is accurate, but computationally slow. This paper proposes a new approach to performance analysis of shared buffer switches, called the reduced variance approximation (RVA). The new method appears to offer accurate results and efficient computation in comparison to other approaches. Implementation of this method provides reduction in the required shared buffer size

Analysis of Reconfigurability, Control and Resource Management in Heterogeneous Wireless Networks

Modern communications networks integrate different access technologies that require interoperability for seamless and user-transparent transfer of multimedia-reach content. Latest standardization activities in this area pinpoint the IEEE 802.21 standard as an enabler of media independent handovers in various scenarios. Additionally, the implementation of the heterogeneous network paradigm yields optimized and efficient resource management techniques emphasizing the need for reconfiguration and interoperability capabilities within future wireless networks. This paper analyzes a combination of reconfigurability, interoperability and resource management aspects in heterogeneous wireless networks based on the IEEE 802.21 standard. It introduces a novel platform for wireless heterogeneous communication systems and a prototype of a reconfigurable mobile terminal that rely on the IEEE 802.21 standard. The introduced platforms are extensively validated through simulations and laboratory experiments showcasing that the IEEE 802.21-backed interoperability is able to support uninterrupted content delivery across multiple communication technologies with high performance