1,591 research outputs found
Joint Scheduling and ARQ for MU-MIMO Downlink in the Presence of Inter-Cell Interference
User scheduling and multiuser multi-antenna (MU-MIMO) transmission are at the
core of high rate data-oriented downlink schemes of the next-generation of
cellular systems (e.g., LTE-Advanced). Scheduling selects groups of users
according to their channels vector directions and SINR levels. However, when
scheduling is applied independently in each cell, the inter-cell interference
(ICI) power at each user receiver is not known in advance since it changes at
each new scheduling slot depending on the scheduling decisions of all
interfering base stations. In order to cope with this uncertainty, we consider
the joint operation of scheduling, MU-MIMO beamforming and Automatic Repeat
reQuest (ARQ). We develop a game-theoretic framework for this problem and build
on stochastic optimization techniques in order to find optimal scheduling and
ARQ schemes. Particularizing our framework to the case of "outage service
rates", we obtain a scheme based on adaptive variable-rate coding at the
physical layer, combined with ARQ at the Logical Link Control (ARQ-LLC). Then,
we present a novel scheme based on incremental redundancy Hybrid ARQ (HARQ)
that is able to achieve a throughput performance arbitrarily close to the
"genie-aided service rates", with no need for a genie that provides
non-causally the ICI power levels. The novel HARQ scheme is both easier to
implement and superior in performance with respect to the conventional
combination of adaptive variable-rate coding and ARQ-LLC.Comment: Submitted to IEEE Transactions on Communications, v2: small
correction
Wireless Network Control with Privacy Using Hybrid ARQ
We consider the problem of resource allocation in a wireless cellular
network, in which nodes have both open and private information to be
transmitted to the base station over block fading uplink channels. We develop a
cross-layer solution, based on hybrid ARQ transmission with incremental
redundancy. We provide a scheme that combines power control, flow control, and
scheduling in order to maximize a global utility function, subject to the
stability of the data queues, an average power constraint, and a constraint on
the privacy outage probability. Our scheme is based on the assumption that each
node has an estimate of its uplink channel gain at each block, while only the
distribution of the cross channel gains is available. We prove that our scheme
achieves a utility, arbitrarily close to the maximum achievable utility given
the available channel state information
Using Channel Output Feedback to Increase Throughput in Hybrid-ARQ
Hybrid-ARQ protocols have become common in many packet transmission systems
due to their incorporation in various standards. Hybrid-ARQ combines the normal
automatic repeat request (ARQ) method with error correction codes to increase
reliability and throughput. In this paper, we look at improving upon this
performance using feedback information from the receiver, in particular, using
a powerful forward error correction (FEC) code in conjunction with a proposed
linear feedback code for the Rayleigh block fading channels. The new hybrid-ARQ
scheme is initially developed for full received packet feedback in a
point-to-point link. It is then extended to various different multiple-antenna
scenarios (MISO/MIMO) with varying amounts of packet feedback information.
Simulations illustrate gains in throughput.Comment: 30 page
Green Communication via Power-optimized HARQ Protocols
Recently, efficient use of energy has become an essential research topic for
green communication. This paper studies the effect of optimal power controllers
on the performance of delay-sensitive communication setups utilizing hybrid
automatic repeat request (HARQ). The results are obtained for repetition time
diversity (RTD) and incremental redundancy (INR) HARQ protocols. In all cases,
the optimal power allocation, minimizing the outage-limited average
transmission power, is obtained under both continuous and bursting
communication models. Also, we investigate the system throughput in different
conditions. The results indicate that the power efficiency is increased
substantially, if adaptive power allocation is utilized. For instance, assume
Rayleigh-fading channel, a maximum of two (re)transmission rounds with rates
nats-per-channel-use and an outage probability constraint
. Then, compared to uniform power allocation, optimal power
allocation in RTD reduces the average power by 9 and 11 dB in the bursting and
continuous communication models, respectively. In INR, these values are
obtained to be 8 and 9 dB, respectively.Comment: Accepted for publication on IEEE Transactions on Vehicular Technolog
Ultra reliable communication via optimum power allocation for repetition and parallel coding in finite block-length
Abstract. In this thesis we evaluate the performance of several retransmission mechanisms with ultra-reliability constraints. First, we show that achieving a very low packet outage probability by using an open loop setup is a difficult task. Thus, we resort to retransmission schemes as a solution for achieving the required low outage probabilities for ultra reliable communication. We analyze three retransmission protocols, namely Type-1 Automatic Repeat Request (ARQ), Chase Combining Hybrid ARQ (CC-HARQ) and Incremental Redundancy (IR) HARQ. For these protocols, we develop optimal power allocation algorithms that would allow us to reach any outage probability target in the finite block-length regime. We formulate the power allocation problem as minimization of the average transmitted power under a given outage probability and maximum transmit power constraint. By utilizing the Karush-Kuhn-Tucker (KKT) conditions, we solve the optimal power allocation problem and provide closed form solutions. Next, we analyze the effect of implementing these protocols on the throughput of the system. We show that by using the proposed power allocation scheme we can minimize the loss of throughput that is caused from the retransmissions. Furthermore, we analyze the effect of the feedback delay length in our protocols.Optimaalista tehoallokointia toisto- ja rinnakkaiskoodaukseen käyttävä erittäin luotettava tiedonsiirto äärellisillä lohkonpituuksilla. Tiivistelmä. Tässä työssä arvioidaan usean uudelleenlähetysmenetelmän suorituskykyä erittäin luotettavan tietoliikenteen järjestelmäoletuksin. Aluksi osoitetaan, että hyvin alhaisen pakettilähetysten katkostodennäköisyyden saavuttaminen avoimen silmukan menetelmillä on haastava tehtävä. Niinpä työssä turvaudutaan uudelleenlähetyspohjaisiin ratkaisuihin, joilla on mahdollista päästä suuren luotettavuuden edellyttämiin hyvin alhaisiin katkostodennäköisyyksiin. Työssä analysoidaan kolmea uudelleenlähetysprotokollaa, nimittäin tyypin 1 automaattista uudelleen lähetystä (ARQ), Chase Combining -tyyppistä hybridi-ARQ -protokollaa (CC-HARQ) ja redundanssia lisäävää HARQ-protokollaa (IR-HARQ). Näille protokollille kehitetään optimaalisia tehon allokointialgoritmeja, joiden avulla päästään halutulle katkostodennäköisyystasolle äärellisillä lohkonpituuksilla. Tehon allokointiongelma muotoillaan keskimääräisen lähetystehon minimointiongelmaksi toteuttaen halutun katkostodennäköisyyden ja maksimilähetystehorajoituksen. Käyttämällä Karush-Kuhn-Tucker (KKT) -ehtoja ratkaistaan optimaalinen tehoallokointiongelma ja esitetään ratkaisut suljetussa muodossa. Seuraavaksi analysoidaan näiden protokollien järjestelmätason toteutusta läpäisykykytarkastelujen avulla. Niillä osoitetaan, että ehdotetulla tehon allokointimenetelmällä voidaan minimoida uudelleen lähetyksistä aiheutuvia suorituskykyhäviöitä. Lisäksi työssä tutkitaan takaisinkytkentäviiveen vaikutusta esitettyihin protokolliin
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