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ABSTRACT: In some communication networks, such as passive RFID systems, the energy used
to transfer information between a sender and a recipient can be reused for
successive communication tasks. In fact, from known results in physics, any
system that exchanges information via the transfer of given physical resources,
such as radio waves, particles and qubits, can conceivably reuse, at least
part, of the received resources. This paper aims at illustrating some of the
new challenges that arise in the design of communication networks in which the
signals exchanged by the nodes carry both information and energy. To this end,
a baseline two-way communication system is considered in which two nodes
communicate in an interactive fashion. In the system, a node can either send an
"on" symbol (or "1"), which costs one unit of energy, or an "off" signal (or
"0"), which does not require any energy expenditure. Upon reception of a "1"
signal, the recipient node "harvests", with some probability, the energy
contained in the signal and stores it for future communication tasks. Inner and
outer bounds on the achievable rates are derived. Numerical results demonstrate
the effectiveness of the proposed strategies and illustrate some key design
insights.
09/2012;
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ABSTRACT: The design of Medium Access Control (MAC) protocols for wireless sensor networks (WSNs) has been conventionally tackled by assuming battery-powered devices and by adopting the network lifetime as the main performance criterion. While WSNs operated by energy-harvesting (EH) devices are not limited by network lifetime, they pose new design challenges due to the uncertain amount of harvestable energy. Novel design criteria are thus required to capture the trade-offs between the potentially infinite network lifetime and the uncertain energy availability. This paper addresses the analysis and design of WSNs with EH devices by focusing on conventional MAC protocols, namely TDMA, Framed-ALOHA (FA) and Dynamic-FA (DFA), and by accounting for the performance trade-offs and design issues arising due to EH. A novel metric, referred to as delivery probability, is introduced to measure the capability of a MAC protocol to deliver the measure of any sensor in the network to the intended destination (or fusion center, FC). The interplay between delivery efficiency and time efficiency (i.e., the data collection rate at the FC), is investigated analytically using Markov models. Numerical results validate the analysis and emphasize the critical importance of accounting for both delivery probability and time efficiency in the design of EH-WSNs.
01/2012;
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ABSTRACT: A source communicates with a remote destination via a number of distributed relays. Communication from source to relays takes place over a (discrete or Gaussian) broadcast channel, while the relays are connected to the receiver via orthogonal finite-capacity links. Unknowns to the source and relays, link failures may occur between any subset of relays and the destination in a nonergodic fashion. Upper and lower bounds are derived on average achievable rates with respect to the prior distribution of the link failures, assuming the relays to be oblivious to the source codebook. The lower bounds are obtained by proposing strategies that combine the broadcast coding approach, previously investigated for quasi-static fading channels, and different robust distributed compression techniques. Numerical results show that lower and upper bounds are quite close over most operating regimes, and provide insight into optimal transmission design choices for the scenario at hand. Extension to the case of nonoblivious relays is also discussed.
IEEE Transactions on Information Theory 08/2011; · 3.01 Impact Factor
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ABSTRACT: Cognitive radio technology enables the coexistence of Primary (PUs) and Secondary Users (SUs) in the same spectrum. In this work, it is assumed that the PU implements a retransmission-based error control technique (ARQ). This creates an inherent redundancy in the interference created by primary transmissions to the SU. We investigate secondary transmission policies that take advantage of this redundancy. The basic idea is that, if a Secondary Receiver (SR) learns the Primary Message (PM) in a given primary retransmission, then it can use this knowledge to cancel the primary interference in the subsequent slots in case of primary retransmissions, thus achieving a larger secondary throughput. This gives rise to interesting trade-offs in the design of the secondary policy. In fact, on the one hand, a secondary transmission potentially increases the secondary throughput but, on the other, causes interference to the reception of the PM at the Primary Receiver (PR) and SR. Such interference may induce retransmissions of the same PM, which plays to the advantage of the secondary user, while at the same time making decoding of the PM more difficult also at the SR and reducing the available margin on the given interference constraint at the PR. It is proved that the optimal secondary strategy prioritizes transmissions in the states where the PM is known to the SR, due to the ability of the latter to perform interference mitigation and obtain a larger secondary throughput. Moreover, when the primary constraint is sufficiently loose, the Secondary Transmitter should also transmit when the PM is unknown to the SR. The structure of the optimal policy is found, and the throughput benefit of the proposed technique is shown by numerical results.
Information Theory and Applications Workshop (ITA), 2011; 03/2011
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ABSTRACT: The Dynamic Framed-ALOHA (DFA) protocol is studied for wireless sensor networks with energy limitations and energy-harvesting capability. The performance of DFA in this scenario is evaluated in terms of the time efficiency (or throughput), which is routinely used to evaluate medium access protocols, and by introducing a new metric, referred to as detection efficiency, which is tailored to scenarios with energy constraints. Specifically, detection efficiency measures the ability of a multiple access protocol to collect data from nodes without depleting their energy reserves. Analysis is first performed by assuming that DFA is operated with a perfect backlog (i.e., number of sensors left to be interrogated) knowledge. Then, a low-complexity backlog estimation algorithm is presented, which is shown by numerical results to perform close to the ideal case of perfect backlog knowledge.
Global Telecommunications Conference (GLOBECOM 2010), 2010 IEEE; 01/2011
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ABSTRACT: The operation of communication protocols is conventionally independent of the information being transmitted. This paper puts forth the notion of protocol coding to refer to transmission strategies in which data can be encoded by modulating the protocol actions according to the information message. We focus on communication in the presence of half-duplex constraints, where the task of the protocol is to schedule the transmission/reception times of different nodes. Such a schedule is conventionally decided a priori in the form of time-sharing. While previous work has focused on protocol coding for standard relay channels, this paper tackles two-way communications aided by a relay. Since the techniques developed for standard relay channels cannot be applied to the scenario at hand, a novel simple strategy is proposed that is tailored to two-way communications. The proposed scheme is shown to significantly outperform conventional time-sharing for a deterministic two-way relay channel.
Global Telecommunications Conference (GLOBECOM 2010), 2010 IEEE; 01/2011
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ABSTRACT: In this paper, a primary (licensed) user leases part of its resources to independent secondary (unlicensed) terminals in exchange for a tariff in dollars per bit, under the constraint that secondary transmissions do not cause excessive interference at the primary receiver (PRX). The PRX selects a power allocation (PA) for the secondary user that maximizes the secondary rate (and thus its revenue) and enforces it by the following mechanism: Upon violation of a predefined interference level, PRX keeps silencing randomly selected secondary users, until the aggregate secondary interference is below the required threshold. This mechanism ensures that secondary users may not be willing to deviate from the allocated PA. Specifically, the scenario gives rise to a Stackelberg game, in which the primary determines the PA and a Nash equilibrium (NE) constraint is imposed on the PA to ensure that secondary users do not have incentives to deviate, given their knowledge of the silencing mechanism run at the PRX. In principle, the primary should find the set of all PAs that are NE and among them choose the one that maximizes the aggregate secondary utility, and thereby the revenue of the primary. For the most general setting of channel gains, we investigate the conditions for NE for a subset of PAs. When the scenario is symmetric in the sense that all secondary users have the same channel gains in the direct/interfering links, we prove that only two optimal power allocations exist. Finally, for the case of general channel gains with strong interference, we show that there is a unique NE of the game.
IEEE Transactions on Wireless Communications 01/2011; · 2.59 Impact Factor
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ABSTRACT: The problem of simultaneous multicasting of multiple messages with the help of a relay terminal is considered. In particular, a model is studied in which a relay station simultaneously assists two transmitters in multicasting their independent messages to two receivers. The relay may also have an independent message of its own to multicast. As a first step to address this general model, referred to as the compound multiple access channel with a relay (cMACr), the capacity region of the multiple access channel with a “cognitive” relay is characterized, including the cases of partial and rate-limited cognition. Then, achievable rate regions for the cMACr model are presented based on decode-and-forward (DF) and compress-and-forward (CF) relaying strategies. Moreover, an outer bound is derived for the special case, called the cMACr without cross-reception, in which each transmitter has a direct link to one of the receivers while the connection to the other receiver is enabled only through the relay terminal. The capacity region is characterized for a binary modulo additive cMACr without cross-reception, showing the optimality of binary linear block codes, and thus highlighting the benefits of physical layer network coding and structured codes. Results are extended to the Gaussian channel model as well, providing achievable rate regions for DF and CF, as well as for a structured code design based on lattice codes. It is shown that the performance with lattice codes approaches the upper bound for increasing power, surpassing the rates achieved by the considered random coding-based techniques.
IEEE Transactions on Information Theory 01/2011; · 3.01 Impact Factor
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ABSTRACT: In this paper, the performance of cellular networks with joint multicell processing and dedicated relay terminals is investigated. It is assumed that each relay terminal is capable of full-duplex operation and receives the transmission of relay terminals in adjacent cells. Focusing on intra-cell time division multiple access and non-fading channels, a simplified relay-aided uplink cellular model is considered. Addressing the achievable per-cell sum-rate, two non-regenerative relaying schemes are considered. Interpreting the received signal at the base stations as the outcome of a two-dimensional linear time invariant system, the multicell processing rate of an amplify-and-forward scheme is derived and shown to decrease with the inter-relay interference level. A novel form of distributed compress-and-forward scheme with decoder side information is then proposed. The corresponding multicell processing rate, which is given as a solution of a simple fixed-point equation, reveals that the compress-and-forward scheme is able to completely eliminate the inter-relay interference, and it approaches a "cut-set-like" upper bound for strong relay terminal transmission power. The benefits of base-station cooperation via multicell processing over the conventional single site processing approach is also demonstrated for both protocols.
IEEE Transactions on Wireless Communications 09/2010; · 2.59 Impact Factor
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ABSTRACT: A novel distributed scheme that combines cooperative ARQ with the spectrum leasing paradigm is proposed and analyzed. The strategy harnesses the opportunistic gains of cooperative communications, while inherently providing a spectrum-rewarding incentive for the otherwise non-cooperative relays to assist the source's transmission. As in cooperative ARQ, the source might decide to hand over the possible retransmission slots to nearby stations that were able to decode the original transmission. In the proposed scheme, however, in exchange for the cooperation, the relaying station is also awarded an opportunity to exploit the retransmission slot for its own traffic. Arbitration of relays' retransmissions is performed via an auction mechanism, with the source, the competing relays and the transmission slot acting as the auctioneer, the bidders and the bidding article, respectively. Auction theory (more generally, the theory of Bayesian games) is applied to analyze the scheme performance. It is noted that the setting here can be alternatively seen as a practical framework for implementation of property-rights cognitive radio networks. Numerical results and analysis show that the proposed scheme enables an efficient dynamic resource allocation that provides relevant gains (e.g., transmission reliability) for both the original source (primary) and the cooperating nodes (secondary users).
IEEE Transactions on Communications 07/2010; · 1.68 Impact Factor
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ABSTRACT: Spectrum leasing from a primary user to a set of secondary users may be implemented by requiring the secondary nodes to pay back the primary for the leased spectrum via cooperation (relaying). In this paper, this principle is studied from an information-theoretic standpoint by focusing on a scenario with one primary node and multiple secondary nodes, which may act as relays for the primary, communicating to a common receiver. The scenario is modelled as a multirelay channel where each relay (secondary user) has a private message for the destination. Achievable rate regions are derived for discrete memoryless and Gaussian models by considering Decode-and-Forward (DF), with both standard and parity-forwarding techniques, and Compress-and-Forward (CF), along with superposition coding at the secondary nodes. Numerical results for the Gaussian channel confirm that spectrum leasing via secondary cooperation is a promising framework to enable secondary spectrum access.
Communications (ICC), 2010 IEEE International Conference on; 06/2010
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ABSTRACT: A critical performance criterion in backscatter modulation-based RFID sensor networks is the distance at which a RFID reader can reliably communicate with passive RFID sensors (or tags). This paper proposes to introduce a power amplifier (PA) and an energy storage device (such as a capacitor or a battery), in the hardware architecture of conventional passive RFID tags, with the aim of allowing amplification of the backscatter signal to increase the read range. This new tag architecture, referred to as Amplified Backscattering via Energy Harvesting (ABEH), can still be considered as passive, since the energy storage device is charged exclusively by harvesting energy from the RF-signal transmitted by the reader and received by the tag during idle periods. The harvested and stored energy is then used by the tags to opportunistically amplify the backscatter signal. It is noted that this architecture is significantly different from active RFID tags where the battery, charged at the time of installation, is used to supply a complete onboard transceiver so that no backscatter modulation is employed. Energy scheduling strategies, based on the trade-off between energy harvesting rate and successful transmission probability, are proposed. Performance analysis of tags with the proposed ABEH architecture is carried out over quasi-static fading channels by framing the design problem as a Markov Decision Process. Numerical results show remarkable improvement of the ABEH approach with respect to conventional passive RFID tags and provide insight into the effect of system parameters on the energy scheduling.
Communications (ICC), 2010 IEEE International Conference on; 06/2010
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ABSTRACT: Consider an additive Gaussian noise channel affected by an additive interference sequence, taken from a given codebook, which is known non-causally at the transmitter (e.g., via prior decoding). It is known that in this case optimal performance is attained by Dirty Paper Coding, which treats the interference signal as unstructured. In other words, for this example, the knowledge of the specific interferer's codebook at the decoder is not useful in terms of capacity. In this paper, two variations of this basic scenario are presented in which treating interference as unstructured is instead generally suboptimal. In the first case, a second encoder of the source message is present in the system that is not aware of the interferer's sequence, and source and interference messages are uncorrelated; In the second case, the sources encoded by the informed transmitter and interferer are correlated (and an uninformed encoder may or may not be present). Results are given in terms of conditions for achievability for both discrete and Gaussian models of the scenarios discussed above, and corroborated by numerical results. Optimal strategies are also identified in special cases. The conclusions herein point to the importance of exploiting the interfererence structure in multiterminal and source-channel coding scenarios.
Information Sciences and Systems (CISS), 2010 44th Annual Conference on; 04/2010
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ABSTRACT: In this paper, the ergodic sum rate and the outage probability of a downlink single-antenna channel with K users are analyzed in the presence of Rayleigh flat fading, where limited channel state information (CSI) feedback is assumed. Specifically, only 1-bit feedback per fading block per user is available at the base station. We first study the ergodic sum rate of the 1-bit feedback scheme and consider the impact of feedback delay on the system. A closed-form expression for the achievable ergodic sum rate is presented as a function of the fading temporal correlation coefficient. It is proved that the sum rate scales as log log K, which is the same scaling law achieved by the optimal nondelayed full CSI feedback scheme. The sum-rate degradation due to outdated CSI is also evaluated in the asymptotic regimes of either large K or low SNR. The outage performance of the 1-bit feedback scheme for both instantaneous and outdated feedback is then investigated. Expressions for the outage probabilities are derived, along with the corresponding diversity-multiplexing tradeoffs (DMTs). It is shown that, with instantaneous feedback, a power allocation based on the feedback bits enables doubling of the DMT compared with the case with short-term power constraint in which a dynamic power allocation is not allowed. However, with outdated feedback, the advantage of power allocation is lost, and the DMT reverts to that achievable with no CSI feedback. Nevertheless, for finite SNR, improvement in terms of outage probability can still be obtained.
IEEE Transactions on Vehicular Technology 04/2010; · 1.92 Impact Factor
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ABSTRACT: We propose and analyze a novel decentralized mechanism that motivates otherwise non-cooperative stations to participate as relays in cooperative ARQ protocol. Cooperation incentive is provided by the possibility for the source to lease a portion of retransmission slot for the traffic of relaying terminals. To further leverage the opportunistic nature of cooperative ARQ and obtain a fully decentralized solution, the (motivated) relaying nodes compete for access to the retransmission slot by trying to make the best retransmission offer. Effective arbitration of cooperative retransmissions is performed using auction theory (bidding), with the source in the role of the auctioneer, the relaying nodes acting as the bidders and the (use of the) retransmission slot as the bidding article. It is noted that the proposed solution can be seen as a practical framework for the implementation of cognitive radio networks running according to the property-rights model (spectrum leasing). Numerical results and analysis confirm the efficient dynamic resource allocation property of the proposed scheme, revealing the relevant gains in terms of expected number of (re)transmissions required for successful data delivery for both the source (primary) and the cooperating (secondary) nodes.
Global Telecommunications Conference, 2009. GLOBECOM 2009. IEEE; 01/2010
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ABSTRACT: A single source communicates with a single destination via a remote wireless multiple-antenna (multiple-input multiple-output (MIMO)) transceiver. The source has access to each of the transmit antennas through a finite-capacity link, and likewise the destination is connected to the receiving antennas via capacity-constrained channels (e.g., as for wired or time-division multiple access (TDMA) channels). Targeting a nomadic communication scenario, in which the remote MIMO transceiver is designed to serve different standards or services, it is assumed that transmitters and receivers are oblivious to the encoding function shared by source and destination. Assuming a Gaussian symmetric interference network as the channel model (as for regularly placed transmitters and receivers), achievable rates are investigated and compared with an upper bound (that holds also for codebook-dependent operation). Closed-form expressions are derived for large numbers of antennas (and in some cases large signal-to-noise ratios (SNRs)), and asymptotics of the achievable rates are studied with respect to either link capacities or SNR. Overall, the analysis points to effective transmission/reception strategies for the distributed MIMO channel at hand, which are optimal under specified conditions. In particular, it is concluded that in certain asymptotic and nonasymptotic regimes there is no loss of optimality in designing the system for nomadic applications (i.e., assuming oblivious transmitters and receivers). Numerical results validate the analysis.
IEEE Transactions on Information Theory 01/2010; · 3.01 Impact Factor
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ABSTRACT: A single macrocell serving a number of outdoor users, overlaid with a femtocell which includes several home users, is studied. The home users in the femtocell are served by a home base station (HBS) that is connected to the macrocell base station (BS) via an unreliable connection (e.g., DSL). The unreliable link may take several possible capacity values. Robust communications strategies for the home users are investigated accounting for the facts that: (a) the home users (served by the HBS) may not be aware of the current state of the HBS-BS link; and that (b) the performance of the outdoor users (served directly by the BS) should not be disrupted by possible outages on the HBS-BS link. The problem is formulated in information-theoretic terms and inner and outer bounds are given to achievable sum-rates for outdoor and home users. Expected sum-rates with respect to the distribution over the HBS-BS link states are studied as well, and conditions are identified under which the proposed schemes are optimal.
Information Theory Workshop, 2009. ITW 2009. IEEE; 11/2009
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ABSTRACT: The throughput of a linear cellular uplink with a random number of users, different power control schemes, and cooperative base stations is considered in the large system limit where the number of cells is large for non fading Gaussian channels. The analysis is facilitated by establishing an analogy between the cellular channel per-cell throughput with joint multi-cell processing (MCP), and the rate of a deterministic intersymbol interference (ISI) channel with flat fading. It is shown that, under certain conditions, the dynamics of cellular systems (i.e., a random number of users coupled with a given power control scheme) can be interpreted, as far as the uplink throughput is concerned, as the flat fading process of the equivalent ISI channel. The results are used to demonstrate the benefits of MCP over the conventional single cell processing approach as a function of various system parameters in the presence of random user activity.
Information Theory Workshop, 2009. ITW 2009. IEEE; 11/2009
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ABSTRACT: A two-state compound relay channel is considered where the relay and the destination are informed about the channel state while the source is not. Achievable rates and upper bounds are derived for discrete memoryless and Gaussian models, and specialized to a scenario with orthogonal components. It is shown that, apart from some special cases, optimality conditions valid for decode-and-forward (DF)-based solutions on a standard relay channel do not carry over to a compound setting, and more flexible transmission strategies are generally advantageous. For instance, partial decode-and-forward (PDF) that superimposes transmission of three layers and uses joint decoding at the destination performs better than the standard two-layer PDF with successive decoding, even when the latter is optimal for the regular relay channel. Moreover, the capacity is derived in the special case in which the relay is not active in one state. Extension to the broadcast coding approach, as an alternative to the compound model, is also discussed.
Communication, Control, and Computing, 2009. Allerton 2009. 47th Annual Allerton Conference on; 11/2009
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ABSTRACT: Simultaneous multicasting of messages with the help of a relay is studied. A two-source two-destination network is considered, in which each destination can receive directly only the signal from one of the sources, so that the reception of the message from the other source (and multicasting) is enabled by the presence of the relay. An outer bound is derived, which is shown to be achievable in the case of finite-field modulo-additive channels by using linear codes, highlighting the benefits of structured codes in exploiting the underlying physical-layer structure of the network. Results are extended to the Gaussian channel model as well, providing achievable rate regions based on nested lattice codes. It is shown that for a wide range of power constraints, the performance with lattice codes approaches the upper bound and surpasses the rates achieved by the standard random coding schemes.
Information Theory, 2009. ISIT 2009. IEEE International Symposium on; 08/2009
