Optimizing Quantize-Map-and-Forward Relaying for Gaussian Diamond Networks

We evaluate the information-theoretic achievable rates of Quantize-Map-and-Forward (QMF) relaying schemes over Gaussian $N$-relay diamond networks. Focusing on vector Gaussian quantization at the relays, our goal is to understand how close to the cutset upper bound these schemes can achieve in the context of diamond networks, and how much benefit is obtained by optimizing the quantizer distortions at the relays. First, with noise-level quantization, we point out that the worst-case gap from the cutset upper bound is $(N+\log_2 N)$ bits/s/Hz. A better universal quantization level found without using channel state information (CSI) leads to a sharpened gap of $\log_2 N + \log_2(1+N) + N\log_2(1 + 1/N)$ bits/s/Hz. On the other hand, it turns out that finding the optimal distortion levels depending on the channel gains is a non-trivial problem in the general $N$-relay setup. We manage to solve the two-relay problem and the symmetric $N$-relay problem analytically, and show the improvement via numerical evaluations both in static as well as slow-fading channels

Physical Layer Cooperation:Theory and Practice

Information theory has long pointed to the promise of physical layer cooperation in boosting the spectral efficiency of wireless networks. Yet, the optimum relaying strategy to achieve the network capacity has till date remained elusive. Recently however, a relaying strategy termed Quantize-Map-and-Forward (QMF) was proved to achieve the capacity of arbitrary wireless networks within a bounded additive gap. This thesis contributes to the design, analysis and implementation of QMF relaying by optimizing its performance for small relay networks, proposing low-complexity iteratively decodable codes, and carrying out over-the-air experiments using software-radio testbeds to assess real-world potential and competitiveness. The original QMF scheme has each relay performing the same operation, agnostic to the network topology and the channel state information (CSI); this facilitates the analysis for arbitrary networks, yet comes at a performance penalty for small networks and medium SNR regimes. In this thesis, we demonstrate the benefits one can gain for QMF if we optimize its performance by leveraging topological and channel state information. We show that for the N-relay diamond network, by taking into account topological information, we can exponentially reduce the QMF additive approximation gap from $\Theta(N)$ bits/s/Hz to $\Theta(\log N)$ bits/s/Hz, while for the one-relay and two-relay networks, use of topological information and CSI can help to gain as much as $6$ dB. Moreover, we explore what benefits we can realize if we jointly optimize QMF and half-duplex scheduling, as well as if we employ hybrid schemes that combine QMF and Decode-and-Forward (DF) relay operations. To take QMF from being a purely information-theoretic idea to an implementable strategy, we derive a structure employing Low-Density-Parity-Check (LDPC) ensembles for the relay node operations and message-passing algorithms for decoding. We demonstrate through extensive simulation results over the full-duplex diamond network, that our designs offer a robust performance over fading channels and achieves the full diversity order of our network at moderate SNRs. Next, we explore the potential real-world impact of QMF and present the design and experimental evaluation of a wireless system that exploits relaying in the context of WiFi. We deploy three main competing strategies that have been proposed for relaying, Amplify-and-Forward (AF), DF and QMF, on the WarpLab software radio platform. We present experimental results--to the best of our knowledge, the first ones--that compare QMF, AF and DF in a realistic indoor setting. We find that QMF is a competitive scheme to the other two, offering in some cases up to 12% throughput benefits and up to 60% improvement in frame error-rates over the next best scheme. We then present a more advanced architecture for physical layer cooperation (termed QUILT), that seamlessly adapts to the underlying network configuration to achieve competitive or better performance than the best current approaches. It combines on-demand, opportunistic use of DF or QMF followed by interleaving at the relay, with hybrid decoding at the destination that extracts information from even potentially undecodable received frames. We theoretically quantify how our design choices affect the system performance. We also deploy QUILT on WarpLab and show through over-the-air experiments up to $5$ times FER improvement over the next best cooperative protocol

Energy Harvesting in Cooperative Communications

Ühiskommunikatsioon on võimalik meetod lahendamaks informatsiooni levimist juhtmeta võrgus mitmikteekonna korral. See võimaldab laiendada võrgu katvust ning pakkuda võimendust kasutades olemasolevat taristut. Praktikas tehakse seda kasutades sõlmpunkte vahereleedena. Nii mitmese ligipääsuga releede süsteem kui paralleelsete releede süsteem on võimalikud kandidaadid tulevastes juhtmeta ühisvõrkudes nende ülekandekiiruse efektiivsuse ning parema energiatarbe tõttu.\n\r\n\rVõimenda-ja-edasta (AF) ning dekodeeri-ja-edasta (DF) on peamised ühisreleede protokollid, mida kasutatakse üle releekanalite. Me uurime käesolevas magistritöös paralleelseid releesid AF ühiskommunikatsiooni võrkudes kasutades QPSK signaliseerimist üle Rayleigh’ kiirelt hajuva kanali koos valge aditiivse Gaussi müraga. Sihtkohas vastuvõetud signaali detekteerimiseks kasutades võrgus olevaid tegevuseta kasutatakse maksimaalse suhte ühendamise (MRC) meetodit. Mõõtes sihtkohast vastu võetud ühendsignaali sümbolite veasuhet (SER) arvutusliku simulatsiooni abil, uurime me suhet releede arvu ning kommunikatsiooni kvaliteedi vahel.\n\r\n\rSüsteemi energeetiline efektiivsus määrab selle operatsioonilise jätkusuutlikkuse. Energiakogumise (EH) meetod on hädavajalik tehnoloogia juhtmeta süsteemides, kus on piiratud ligipääs usaldusväärsele elektritoitele ja laadimisvõimalustele. Käesolevas magistritöös uurime me mitmese ligipääsuga releede süsteeme kasutades EHtehnoloogiat. Me eeldame, et lähte- ja releesõlmedel pole ühendatud energiaallikat, kuid on taaslaetav energiatalletus. Seega, iga sõlme käivitatakse ligipääsupunkti (AP) edastatud raadiosignaalidelt kogutud energiast ning iga sõlm toimib salvesta-siis- koostööta (STC) režiimis. Me simuleerime arvutuslikult ühendusetaseme jõudlust kasutades füüsilise ühenduse võrgukodeerimist EHja DF protokolli olemasolul. Käesolev magistritöö esitab erinevaid energiakogumise meetodeid (EH ja STC) ning nende katkemistõenäosusi. Esitatud skeemid saavutavad SER jõudluse, mis läheneb püsiva toiteallikaga jõudlusele ning laiendab oluliselt süsteemi energiapüsivust, samas säilitades pidevat läbilaskejõudlust.Cooperative communications is a promising technique used to combat the multipath propagation in wireless networks. It can also extend the network coverage and provide the diversity gain by using the existing infrastructure. In practice, this is often achieved by using idle nodes in the network as relays. The multiple access relay system and parallel relay system are appealing candidates for emerging wireless cooperative networks due to bandwidth efficiency and improved power consumption.\n\r\n\rThe amplify and forward (AF) and decode and forwards (DF) protocols are basic cooperative relay protocols used over the relay channels. In this thesis, we study parallel relays in AF cooperative communication networks using QPSK signalling over the Rayleigh fast fading with additive Gaussian noise channels. The maximum ratio combining (MRC) method is employed to detect the received signals at the destination. By simulating the symbol error rate (SER) of the combined received signal at the destination, we study a trade-off between the number of relays and the quality of the communications. \n\r\n\rThe energy efficiency of a system determines its operational sustainability. Energy harvesting (EH) is a crucial technology for a variety of wireless systems that have limited access to a reliable electricity supply or recharging sources. In this thesis, the design of a multiple access relay system (MARS) using EH is considered. We assume that the sources and the relay have no embedded power supply but rechargeable energy storage devices. Thus, each node is powered by harvesting the energy from the RF signals broadcasted by an access point (AP), and it operates in store-then-cooperate (STC) mode. We simulate the link level performance by using the physical layer network coding in the presence of EH with DF protocol. The thesis presents energy harvesting schemes (EH and STC) and outage probability analysis. The schemes presented in this thesis achieve SER performance approaching that of a fixed power supply and contribute significantly to sustaining the energy in the system while maintaining a constant throughput

Distributed Detection and Estimation in Wireless Sensor Networks

In this article we consider the problems of distributed detection and estimation in wireless sensor networks. In the first part, we provide a general framework aimed to show how an efficient design of a sensor network requires a joint organization of in-network processing and communication. Then, we recall the basic features of consensus algorithm, which is a basic tool to reach globally optimal decisions through a distributed approach. The main part of the paper starts addressing the distributed estimation problem. We show first an entirely decentralized approach, where observations and estimations are performed without the intervention of a fusion center. Then, we consider the case where the estimation is performed at a fusion center, showing how to allocate quantization bits and transmit powers in the links between the nodes and the fusion center, in order to accommodate the requirement on the maximum estimation variance, under a constraint on the global transmit power. We extend the approach to the detection problem. Also in this case, we consider the distributed approach, where every node can achieve a globally optimal decision, and the case where the decision is taken at a central node. In the latter case, we show how to allocate coding bits and transmit power in order to maximize the detection probability, under constraints on the false alarm rate and the global transmit power. Then, we generalize consensus algorithms illustrating a distributed procedure that converges to the projection of the observation vector onto a signal subspace. We then address the issue of energy consumption in sensor networks, thus showing how to optimize the network topology in order to minimize the energy necessary to achieve a global consensus. Finally, we address the problem of matching the topology of the network to the graph describing the statistical dependencies among the observed variables.Comment: 92 pages, 24 figures. To appear in E-Reference Signal Processing, R. Chellapa and S. Theodoridis, Eds., Elsevier, 201

Forwarding strategies and optimal power allocation for coherent and noncoherent relay networks

In fading wireless channels, relays are used with the aim of achieving diversity and thus overall performance gain. In cooperative relay networks, various forwarding techniques like amplify and forward (AF) and decode and forward (DF) are used at the relay for better throughput and improved BER performance than traditional multihop systems. In a power constrained environment, the performance can be further improved by using an optimal power allocation strategy. The relative position of the relay with respect to the source and destination also has an immense effect on the efficacy of the relay.;We position the relay at various positions in a planar grid, with the position of source and destination being fixed, and we investigate the effect that the positioning of the relay has on a relaying system. We use our three terminal model to optimize the power allocation under total transmit power constraint, to maximize the instantaneous signal-to-noise ratio (SNR) at destination, and thus achieve improved throughput and BER performance, while using AF and DF protocols. We evaluate the performance of our system for both coherent and noncoherent modulation in a Rayleigh block fading channel. Quadrature phase shift keying (QPSK) is used in the coherent case and 4-Frequency shift keying (4-FSK) is used in the noncoherent case.;Previous works involving power allocation schemes have mainly concentrated on optimizing information theoretic quantities like capacity and outage probability. We derive expressions for instantaneous SNR using our model and optimize the power allocation based on that, with the final aim of achieving improved uncoded BER. Analytical expressions of the instantaneous SNR at the destination are derived for both AF and DF. These expressions are numerically optimized to obtain an optimum power allocation strategy for each position of the relay in both the AF and DF schemes using coherent or noncoherent detection.;We compare the performance of the AF and DF protocols based on their positional BER and throughput at different received SNR and notice that our power optimized schemes outperform existing power control schemes at certain areas. Finally we also identify the shape and area of the regions where relaying would provide performance gains for both the protocols at different received SNRs

Integer-Forcing Linear Receivers

Linear receivers are often used to reduce the implementation complexity of multiple-antenna systems. In a traditional linear receiver architecture, the receive antennas are used to separate out the codewords sent by each transmit antenna, which can then be decoded individually. Although easy to implement, this approach can be highly suboptimal when the channel matrix is near singular. This paper develops a new linear receiver architecture that uses the receive antennas to create an effective channel matrix with integer-valued entries. Rather than attempting to recover transmitted codewords directly, the decoder recovers integer combinations of the codewords according to the entries of the effective channel matrix. The codewords are all generated using the same linear code which guarantees that these integer combinations are themselves codewords. Provided that the effective channel is full rank, these integer combinations can then be digitally solved for the original codewords. This paper focuses on the special case where there is no coding across transmit antennas and no channel state information at the transmitter(s), which corresponds either to a multi-user uplink scenario or to single-user V-BLAST encoding. In this setting, the proposed integer-forcing linear receiver significantly outperforms conventional linear architectures such as the zero-forcing and linear MMSE receiver. In the high SNR regime, the proposed receiver attains the optimal diversity-multiplexing tradeoff for the standard MIMO channel with no coding across transmit antennas. It is further shown that in an extended MIMO model with interference, the integer-forcing linear receiver achieves the optimal generalized degrees-of-freedom.Comment: 40 pages, 16 figures, to appear in the IEEE Transactions on Information Theor

Distributed Turbo Product Coding Techniques Over Cooperative Communication Systems

In this dissertation, we propose a coded cooperative communications framework based on Distributed Turbo Product Code (DTPC). The system uses linear block Extended Bose-Chaudhuri-Hochquenghem (EBCH) codes as component codes. The source broadcasts the EBCH coded frames to the destination and nearby relays. Each relay constructs a product code by arranging the corrected bit sequences in rows and re-encoding them vertically using EBCH as component codes to obtain an Incremental Redundancy (IR) for source\u27s data. Under this frame, we have investigated a number of interesting and important issues. First, to obtain, independent vertical parities from each relay in the same code space, we propose circular interleaving of the decoded EBCH rows before reencoding vertically. We propose and derive a novel soft information relay for the DTPC over cooperative network based on EBCH component codes. The relay generates Log-Likelihood Ratio (LLR) values for the decoded rows are used to construct a product code by re-encoding the matrix along the columns using a novel soft block encoding technique to obtain soft parity bits with different reliabilities that can be used as soft IR for source\u27s data which is forwarded to the destination. To minimize the overall decoding errors, we propose a power allocation method for the distributed encoded system when the channel attenuations for the direct and relay channels are known. We compare the performance of our proposed power allocation method with the fixed power assignments for DTPC system. We also develop a power optimization algorithm to check the validity of our proposed power allocation algorithm. Results for the power allocation and the power optimization prove on the potency of our proposed power allocation criterion and show the maximum possible attainable performance from the DTPC cooperative system. Finally, we propose new joint distributed Space-Time Block Code (STBC)-DTPC by generating the vertical parity on the relay and transmitting it to the destination using STBC on the source and relay. We tested our proposed system in a fast fading environment on the three channels connecting the three nodes in the cooperative network