Group Talks
2011
Efficient Data Transmission for an Energy Harvesting Node with Battery Capacity Constraint
by Maria Gregori
Thursday, December 1st at 10:00 in Room 001
Energy harvesting is increasingly gaining importance as a means to charge battery powered devices such as sensor nodes. Efficient transmission strategies must be developed taking into account both the availability of energy and data in the node. In this talk, we will present the best data transmission strategy by taking into account that the node has a finite battery capacity and that the data and energy arrivals occur at known time instants. Losing energy due to overflows of the battery is proved to be inefficient unless there is no more data to transmit. Finally, an algorithm that computes the data transmission curve minimizing the total transmission time while spending the minimum energy and that satisfies energy and data constraints has been developed.
At Low SNR Asymmetric Quantizers Are Better
by Dr. Tobias Koch, University of Cambridge
Friday, October 28th at 12:00 in Auditorium
In many of today's communication systems, the receiver uses digital signal processing techniques. This requires the conversion of the analog received signal to a digital signal by means of an analog-to-digital converter (ADC). For ADCs with a high resolution, the effects of quantization are negligible. However, using a high-resolution ADC may not be practical, especially when the ADC needs to operate at a high sampling rate. In this case, a low-resolution ADC needs to be employed. To better understand how the use of low-resolution ADCs affects the achievable data rates of a communication system, we study the channel capacity of the Gaussian channel when the channel output is quantized using a one-bit quantizer.
In my presentation, I will focus on the low signal-to-noise ratio regime, where communication at very low spectral efficiencies takes place, as in Spread-Spectrum and Ultra-Wideband communications. It is well known that, in this regime, a symmetric one-bit quantizer reduces the capacity by a factor of 2/pi, corresponding to a power loss of approximately two decibels. Hence the rule of thumb that "hard decisions cause a 2dB power loss." I will demonstrate that if we allow for asymmetric one-bit quantizers with corresponding asymmetric signal constellations, these two decibels can be recovered in full.
A Framework for Cross-Layer Technology Implementation based on the Cognitive and Docitive Radio Paradigms
by Prof. Andres Kwasinski, Rochester Institute of Technology
Tuesday, October 25th at 15:30 in Auditorium
The advantages of cognitive radios go beyond those associated with the capabilities provided by dynamic spectrum access and co-existence. Cognitive radio provides the framework for seamless integration of cross-layer techniques and, in the process, deliver performance improvements to resource allocation mechanisms. In this talk we will discuss the application of the cognitive radio framework to the adaptation of source and channel coding jointly with physical layer parameters. While we will see that the cross-layer approach notably improves performance in terms of average end-to-end distortion and network's congestion rate, it will also increase the complexity of the resource allocation solution. In this talk, we will also discuss how the extra complexity in the cross-layer approach can be addressed through the application of the docitive radio paradigm in a cross-layer setup. We will see that this approach notably reduces complexity with little or no sacrifice in performance.
Real-time Broadcasting over Block-Fading Channels
Thursday, October 20th at 15:00 in Room 001
In this talk, we study the broadcast transmission from a base station (BS) to a group of users. It is assumed that the BS receives data at a constant rate and tries to broadcast this data to a set of users within a certain deadline. The channels are assumed to be block fading and independent over blocks and users. Our performance measure is the total rate of received information at the users within the transmission deadline. Three different encoding schemes are proposed, and they are compared with an informed transmitter upper bound in terms of the average total reception rate for a set of users with varying channel qualities. It is shown that no single transmission strategy dominates for all channel settings, and the best broadcasting technique depends on the distribution of the average channel conditions over the users.
Distributed Field Reconstruction in Wireless Sensor Networks Based on Hybrid Shift-Invariant Spaces
by Gunter Reise (Vienna University of Technology)
Thursday, April 14th at 12:00am in Room 001
We use the theory and algorithms developed for so-called shift-invariant spaces to develop a novel distributed architecture for sampling and reconstructing time-varying non-bandlimited physical fields in wireless sensor networks. Generalizing shift-invariant spaces and introducing hybrid shift-invariant spaces allows to better adapt to local smoothness properties of the field in the reconstruction. The use of compactly supported generator functions allows us to split the global reconstruction into several smaller local problems that can be solved independently. Capitalizing on the resulting sparsity of the matrices involved in the reconstruction, we propose direct and iterative reconstruction algorithms whose complexity per time slots scales only linearly with the number of sensors. We furthermore analyze the impact of sensor localization errors on the mean square error of the reconstructed field.
Building the Internet of Things: From the basics to a practical example
by Nicola Bui and Nicola Bressan
Tuesday, March 8th at 11:00am in the Auditorium
Internet of Things aims at extending the Web paradigm to smart objects. This talk will start from a definition of the scenario and its challenges, will describe the communication solutions under standardization and will present a practical example of the advantages offered. In particular, the talk will focus on the description of the protocol stack for wireless sensor networks and its performance. A demo will conclude the talk showing the wireless sensor network testbed at the University of Padova controlled via a web application.
2010
Control of wireless networks with rechargeable batteries -- Part II: Paper results
by David Gregoratti
Wednesday, December 22nd at 10am in Room 001
This talk will present the results of the above paper by M. Gatzianas, L. Georgiadis and L. Tassiulas. More specifically, we will consider a base-station (BS) serving L different users and discuss how to allocate resources (power and flows) in a cross-layer framework. At the BS, a rechargeable battery guarantees infinite life-time to the system. Then, stability analysis is required that takes into account arrival (traffic), channel and recharge (battery) processes. The Lyapunov drift tools introduced last week properly serve this purpose.
Control of wreless networks with rechargeable batteries -- Part I: Background review
by David Gregoratti
Thursday, December 16th at 12pm in Room 001
Next week, the paper by M. Gatzianas et al. with the above title will conclude the series about energy harvesting. The main difference with previous works in the series is that the authors study the infinite time horizon stability of the network, as opposed to optimal resource allocation with finite delay constraints. In other words, they are interested in assuring that, in the long term, all traffic from upper layers can be served with no risk of overloading the system. With a view to facilitating this approach transition, this week's talk introduces some basic concepts of control theory for networks. In particular, based on the definitions of "stable queues" and "network-layer capacity (stability) region", we will show how to employ Lyapunov's theory for optimal resource allocation under stability constraints.
Energy harvesting technologies for autonomous sensors
by Apostolos Georgiadis
Thursday, December 9th at 12pm in Room 001
The presentation will review commonly employed energy harvesting technologies such as solar, electromagnetic, thermal and vibration, and provide performance limits and application scenarios.
Hybrid digital-analog transmission for the Gaussian one-helper problem
Thursday, December 2nd at 12pm in Room 001
In this talk, we consider the one-helper joint source-channel coding problem, in which a main source is to be reconstructed with minimum distortion with the help of a correlated helper source. Focusing on the case of Gaussian sources and a Gaussian multiple access channel (MAC), a generalized hybrid digital-analog scheme is proposed, in which each user allocates its available power among the analog and digital signals and transmits a superposition of the two. It is shown that this generalized hybrid scheme reduces to pure analog or pure digital transmission depending on the system parameters. Finally, the optimal hybrid transmission strategy is identified analytically in certain special scenarios modeling legacy systems.
A calculus approach to energy-efficient data transmission with quality of service constraints
by Deniz Gündüz
Thursday, November 25th at 12pm in Room 001
This talk will review the paper with the above title by M. Zafer and E. Modiano. They present a general methodology to solve a number of problems for energy-efficient data transmission including the one in Biyiklioglu et al. paper that we have discussed two weeks ago.
In particular, this paper studies energy efficient transmission with quality-of-service (QoS) constraints through optimal rate-control. Considering a static point-to-point wireless channel with strict QoS constraints on data transmission, the authors obtain the optimal rate control policy that minimizes the total transmission energy expenditure under the assumption of known data arrival curve. The solution uses the cumulative curves methodology and the formulation has a simple and appealing graphical visualization. Utilizing the optimal "offline" results, an online transmission policy is also obtained for an arbitrary stream of packet arrivals and deadline constraints; and it is shown, via simulations, that it is significantly more energy efficient than a simple head-of-line drain policy.
Optimal packet scheduling in an energy harvesting communication system
by Javier Matamoros
Friday, November 19th at 12pm in Room 001
In this talk we will review the paper titled "Optimal Packet Scheduling in an Energy Harvesting Communication System" by Jing Yang and Sennur Ulukus.
The idea behind this paper is the following: The authors address the optimal packet scheduling problem in a single-user energy harvesting wireless communication system. In this system, both the data packets and the harvested energy are modeled to arrive at the source node randomly. The goal of the paper is to adaptively change the transmission rate according to the traffic load and available energy, such that the time by which all packets are delivered is minimized. Under a deterministic system setting, the main assumptions are that the energy harvesting times and harvested energy amounts are known before the transmission starts. For the data traffic arrivals, the authors consider two different scenarios. In the first scenario, all bits have arrived and are ready at the transmitter before the transmission starts. In the second scenario, packets arrive during the transmissions, with known arrival times and sizes. The authors develop optimal off-line scheduling policies which minimize the time by which all packets are delivered to the destination, under causality constraints on both data and energy arrivals.
Energy-efficient packet transmission over a wireless link
Thursday, November 11th at 12pm in Room 002
In this talk, we will review the results presented in the 2002 paper "Energy-efficient packet transmission over a wireless link" from E. Uysal-Biyikoglu et al.
The basic idea behind this paper is the following observation: with many channel coding schemes, the transmission energy (i.e. the energy required to transmit a packet) can be lowered by reducing transmission power and transmitting a packet over a longer period of time. However, in practice, transmission times cannot be made arbitrarily long, as delay constraints have to be satisfied. In particular, this paper tackles the problem of minimizing the energy used by a node on a point-to-point link to transmit a given number of packets withing a given amount of time. First, the authors derive an optimal offline schedule, where it is assumed that the arrival times of the different packets are known. Based on this optimal solution, an online schedule is then proposed and is shown, through simulations, to perform closely to the optimal one.
Efficient computation of mutual information
by Stephan Pfletschinger
Thursday, November 4th at 12pm in Room 001
In this last talk of the short series on the application of non-binary coding to vector channels, an efficient method for computing mutual information will be presented. This method has been invented in the context of EXIT chart but it can also be applied to e.g. the calculation of the capacity of discrete-input channels. We will see some results for the MIMO channel obtained with this method and discuss other possible applications.
Application of non-binary codes to MIMO
by Stephan Pfletschinger
Wednesday, October 27th at 12pm in Room 001
Abstract: After some relevant properties of non-binary LDPC codes have been presented last week, this talk discusses their application to MIMO systems. We will present a very simple scheme which performs significantly better than e.g. the Alamouti scheme or spatial multiplexing with binary coding. The objective of this presentation is to present the obtained results and to discuss possible consequences for the design of MIMO systems.
Non-binary coding for vector channels. Part I: Non-binary LDPC codes
by Stephan Pfletschinger
Thursday, October 21st at 10am in Room 001
Abstract: This talk is the first one of two about the same topic. In this first part, we review some important properties of modern channel codes, focusing on non-binary LDPC codes and prepare the ground for the second part (next week) in which we will address the application of non-binary LDPC codes to multiple-antenna transmission and report significant improvements. This first talk will be quite basic and give a brief overview on modern channel codes and describe some of their characteristics which are relevant for modern wireless systems.
Distributed Multiple Access and Flow Control for Wireless Network Coding
Thursday, April 22nd at 4pm in Room 002
In this talk we will address network coding and distributed schemes to control the code based on game theory. More specifically, we address the problem of reducing redundancy in the completely distributed operation of network coding, so as to increase network throughput. In order to do so, we propose a distributed system where network nodes autonomously make decisions with respect to the packets to encode and forward, with the goal of maximizing the data detection probability and minimizing the overhead of transmitted packets. The underlying application scenario are networks with high mobility, such as vehicular networks, were no stable topology can be easily maintained. Other open problems related to network coding will also be discussed.
From WLAN to M2M
by Jesús Alonso-Zárate
Thursday, April 8th at 4pm in Room 001
In this SHORT talk I will briefly present an overview of what I have been working on so far (mainly within the scope of my PhD thesis). Then, I will present one of my new research topics: Machine-to-Machine (M2M) communications. M2M is an emerging topic, a facilitator of data flows between machines used, e.g., in mission-critical applications. I will present the main motivation towards the exploration of this new topic and will try to provide a very general and high-level view of the opportunities that M2M systems offer to researchers. I will also talk about EXALTED, a new FP7 project that will start in September 2010 and wherein the CTTC is involved.
Opportunistic adaptive transmission for network coding using non-binary LDPC codes
by Giuseppe Cocco
Tuesday, March 23rd at 3pm in Room 001
Network coding (NC) allows to exploit spatial diversity naturally present in mobile wireless networks and can be seen as an example of cooperative communication at levels higher than MAC. Such promising technique needs to rely on a suited physical layer in order to achieve its best performances. In this talk we present a new opportunistic packet scheduling method based on physical layer considerations. The method consists of adapting the information rate for each receiving node according to its channel status and independently of the other nodes. In this way a higher network throughput can be achieved at the expense of a slightly higher complexity at the transmitter. In the proposed technique we invert the order of network coding and channel coding while doing soft decoding at the receiver. This configuration is superior to other approaches since it allows to perform rate adaptation while fully preserving the benefits of channel and network coding. We carried out an information theoretical analysis of our approach and of that typically used in network coding. Numerical results based on non-binary LDPC codes confirm the effectiveness of our approach with respect to previously proposed opportunistic scheduling techniques.
Efficient Uplink Subcarrier and Power Allocation Algorithm in Cognitive Radio Networks
by Mosbah Shaat
Thursday, February 25th at 3pm in Room 001
Quick development of wireless communication makes the spectrum scarcity as one of the serious problems. Cognitive radio is considered to be one of the possible solutions to solve the spectrum efficiency problem. In this talk, an efficient uplink resource algorithm in multicarrier based cognitive radio systems will be presented. The algorithm allocates subcarriers among the different users considering their channel quality, the amount of interference that they may introduce to the primary system and the increment in the overall data rate. Afterwards, an efficient power allocation algorithm is used to distribute the per-user available power among the different subcarriers. The interference to the primary system is guaranteed to be under the prescribed interference temperature limit. Simulation results will illustrate that the proposed resource allocation algorithm with low computational complexity improves the total data rate of the cognitive radio system.
Decentralized Q-learning for Aggregated Interference Control for Cognitive Radio Networks
by Ana Maria Galindo
Thursday, February 11th at 2pm in Room 001
In this talk, we will give an introduction to the multi-agent reinforcement learning technique, specifically the decentralized Q-learning method, which is a learning algorithm where agents learn the utility of performing actions in states. We introduce the learning technique to deal with the problem of aggregated interference generated by multiple cognitive radios (CR) at the receivers of primary users. In particular, we consider a secondary CR system based on the IEEE 802.22 standard for wireless regional area networks (WRAN). We will present results for both situations of complete and partial information about the environment showing that the multi-agent system is able to learn, in the first case, an efficient policy to solve the problem and, in the second case, a reasonably good suboptimal policy.
On the majorization relationship between the SVD and QR decompositions
Thursday, January 28th at 3pm in Room 001
In this talk, we will first give a brief introduction to the majorization theory, a powerful mathematical tool for proving inequalities. We will provide some illustrating example. Then, we will focus on the majorization relationship (in the product sense) there is between the SVD and QR decomposition of a matrix (more precisely between the singular values and the diagonal elements of the upper triangular matrix R). In particular, we will try to apply/exploit this results in two different scenarios: (i) the use of Tomlinson-Harashima precoding in a MIMO broadcast channel. (ii) the multipath diversity extraction in a cyclic prefixed single carrier system with DFE.
2009
Joint source-channel coding in networks
by Deniz Gündüz
Thursday, November 26th at 3pm in Room 001
In this talk I will first talk about the basics of joint source-channel coding in a point-to-point system from an information theoretic point of view. I will introduce an alternative scheme to the classical separate source and channel coding scheme of Shannon and motivate this alternative with some applications to networks. In particular, I will focus on sensor networks and propose cooperative source-channel coding techniques to exploit the relay simultaneously for source and channel cooperation. The main goal of this talk is to review some of the existing results in the literature, propose some new problems and explore possible joint research directions if there is interest.
