Optimum Resource Allocation for Relay Networks with Differential Modulation

Abstract-In this paper, we investigate the resource allocation in a differentially modulated relay network. In addition to the energy optimization, we also consider location optimization to minimize the average symbol error rate (SER). The closedform solution is derived for the single-relay case, and formulas allowing numerical search are provided for multiple-relay cases. Analytical and simulated comparisons confirm that the optimized systems provide considerable improvement over the unoptimized systems, and that the minimum SER can be achieved via the joint energy-location optimization. Index Terms-Differential phase shift keying, resource management, relays, cooperative system

Analysis of channel uncertainty in ARQ relay networks

Several power allocation algorithms for cooperative relay networks are presented in the literature. These contributions assume perfect channel knowledge and capacity achieving codes. However in practice, obtaining the channel state information at a relay or at the destination is an estimation problem and can generally not be error free. The investigation of the power allocation mechanism in a wireless network due to channel imperfections is important because it can severely degrade its performance regarding throughput and bit error rate. In this paper, the impact of imperfect channel state information on the power allocation of an adaptive relay network is investigated. Moreover, a framework including Automatic Repeat reQuest (ARQ) mechanism is provided to make the power allocation mechanism robust against these channel imperfections. For this framework, the end-to end SNR is calculated considering imperfect channel knowledge using ARQ analytically. The goal is to emphasize the impact of imperfect channel knowledge on the power allocation mechanism. In this paper, the simulation results illustrate the impact of channel uncertainties on the average outage probability, throughput, and consumed sum power for different qualities of channel estimation. It is shown that the presented framework with ARQ is extremely robust against the channel imperfections

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

Cooperative Strategies for Simultaneous and Broadcast Relay Channels

Consider the \emph{simultaneous relay channel} (SRC) which consists of a set of relay channels where the source wishes to transmit common and private information to each of the destinations. This problem is recognized as being equivalent to that of sending common and private information to several destinations in presence of helper relays where each channel outcome becomes a branch of the \emph{broadcast relay channel} (BRC). Cooperative schemes and capacity region for a set with two memoryless relay channels are investigated. The proposed coding schemes, based on \emph{Decode-and-Forward} (DF) and \emph{Compress-and-Forward} (CF) must be capable of transmitting information simultaneously to all destinations in such set. Depending on the quality of source-to-relay and relay-to-destination channels, inner bounds on the capacity of the general BRC are derived. Three cases of particular interest are considered: cooperation is based on DF strategy for both users --referred to as DF-DF region--, cooperation is based on CF strategy for both users --referred to as CF-CF region--, and cooperation is based on DF strategy for one destination and CF for the other --referred to as DF-CF region--. These results can be seen as a generalization and hence unification of previous works. An outer-bound on the capacity of the general BRC is also derived. Capacity results are obtained for the specific cases of semi-degraded and degraded Gaussian simultaneous relay channels. Rates are evaluated for Gaussian models where the source must guarantee a minimum amount of information to both users while additional information is sent to each of them.Comment: 32 pages, 7 figures, To appear in IEEE Trans. on Information Theor

Cooperative Relay Broadcast Channels

The capacity regions are investigated for two relay broadcast channels (RBCs), where relay links are incorporated into standard two-user broadcast channels to support user cooperation. In the first channel, the Partially Cooperative Relay Broadcast Channel, only one user in the system can act as a relay and transmit to the other user through a relay link. An achievable rate region is derived based on the relay using the decode-and-forward scheme. An outer bound on the capacity region is derived and is shown to be tighter than the cut-set bound. For the special case where the Partially Cooperative RBC is degraded, the achievable rate region is shown to be tight and provides the capacity region. Gaussian Partially Cooperative RBCs and Partially Cooperative RBCs with feedback are further studied. In the second channel model being studied in the paper, the Fully Cooperative Relay Broadcast Channel, both users can act as relay nodes and transmit to each other through relay links. This is a more general model than the Partially Cooperative RBC. All the results for Partially Cooperative RBCs are correspondingly generalized to the Fully Cooperative RBCs. It is further shown that the AWGN Fully Cooperative RBC has a larger achievable rate region than the AWGN Partially Cooperative RBC. The results illustrate that relaying and user cooperation are powerful techniques in improving the capacity of broadcast channels.Comment: Submitted to the IEEE Transactions on Information Theory, July 200