282 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
Goodbye, ALOHA!
©2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The vision of the Internet of Things (IoT) to interconnect and Internet-connect everyday people, objects, and machines poses new challenges in the design of wireless communication networks. The design of medium access control (MAC) protocols has been traditionally an intense area of research due to their high impact on the overall performance of wireless communications. The majority of research activities in this field deal with different variations of protocols somehow based on ALOHA, either with or without listen before talk, i.e., carrier sensing multiple access. These protocols operate well under low traffic loads and low number of simultaneous devices. However, they suffer from congestion as the traffic load and the number of devices increase. For this reason, unless revisited, the MAC layer can become a bottleneck for the success of the IoT. In this paper, we provide an overview of the existing MAC solutions for the IoT, describing current limitations and envisioned challenges for the near future. Motivated by those, we identify a family of simple algorithms based on distributed queueing (DQ), which can operate for an infinite number of devices generating any traffic load and pattern. A description of the DQ mechanism is provided and most relevant existing studies of DQ applied in different scenarios are described in this paper. In addition, we provide a novel performance evaluation of DQ when applied for the IoT. Finally, a description of the very first demo of DQ for its use in the IoT is also included in this paper.Peer ReviewedPostprint (author's final draft
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
A Free Space Optic/Optical Wireless Communication: A Survey
The exponential demand for the next generation of services over free space optic and wireless optic communication is a necessity to approve new guidelines in this range. In this review article, we bring together an earlier study associated with these schemes to help us implement a multiple input/multiple output flexible platform for the next generation in an efficient manner. OWC/FSO is a complement clarification to radiofrequency technologies. Notably, they are providing various gains such as unrestricted authorizing, varied volume, essential safekeeping, and immunity to interference.
Resource Allocation for Interference Management in Wireless Networks
Interference in wireless networks is a major problem that impacts system performance quite substantially. Combined with the fact that the spectrum is limited and scarce, the performance and reliability of wireless systems significantly deteriorates and, hence, communication sessions are put at the risk of failure. In an attempt to make transmissions resilient to interference and, accordingly, design robust wireless systems, a diverse set of interference mitigation techniques are investigated in this dissertation.
Depending on the rationale motivating the interfering node, interference can be divided into two categories, communication and jamming. For communication interference such as the interference created by legacy users(e.g., primary user transmitters in a cognitive radio network) at non-legacy or unlicensed users(e.g.,secondary user receivers), two mitigation techniques are presented in this dissertation. One exploits permutation trellis codes combined with M-ary frequency shift keying in order to make SU transmissions resilient to PUs’ interference, while the other utilizes frequency allocation as a mitigation technique against SU interference using Matching theory. For jamming interference, two mitigation techniques are also investigated here. One technique exploits time and structures a jammer mitigation framework through an automatic repeat request protocol. The other one utilizes power and, following a game-theoretic framework, employs a defense strategy against jamming based on a strategic power allocation. Superior performance of all of the proposed mitigation techniques is shown via numerical results
Cooperative diversity techniques for future wireless communications systems.
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.Multiple-input multiple-output (MIMO) systems have been extensively studied in the past
decade. The attractiveness of MIMO systems is due to the fact that they drastically reduce
the deleterious e ects of multipath fading leading to high system capacity and low error rates.
In situations where wireless devices are restrained by their size and hardware complexity, such
as mobile phones, transmit diversity is not achievable. A new paradigm called cooperative
communication is a viable solution. In a cooperative scenario, a single-antenna device is
assisted by another single-antenna device to relay its message to the destination or base
station. This creates a virtual multiple-input multiple-output (MIMO) system.
There exist two cooperative strategies: amplify-and-forward (AF) and decode-and-forward
(DF). In the former, the relay ampli es the noisy signal received from the source before forwarding
it to the destination. No form of demodulation is required. In the latter, the relay
rst decodes the source signal before transmitting an estimate to the destination. In this
work, focus is on the DF method. A drawback of an uncoded DF cooperative strategy is
error propagation at the relay. To avoid error propagation in DF, various relay selection
schemes can be used. Coded cooperation can also be used to avoid error propagation at
the relay. Various error correcting codes such as convolutional codes or turbo codes can
be used in a cooperative scenario. The rst part of this work studies a variation of the
turbo codes in cooperative diversity, that further reduces error propagation at the relay,
hence lowering the end-to-end error rate. The union bounds on the bit-error rate (BER) of
the proposed scheme are derived using the pairwise error probability via the transfer bounds
and limit-before-average techniques. In addition, the outage analysis of the proposed scheme
is presented. Simulation results of the bit error and outage probabilities are presented to
corroborate the analytical work. In the case of outage probability, the computer simulation
results are in good agreement with the the analytical framework presented in this chapter.
Recently, most studies have focused on cross-layer design of cooperative diversity at the
physical layer and truncated automatic-repeat request (ARQ) at the data-link layer using the
system throughput as the performance metric. Various throughput optimization strategies
have been investigated. In this work, a cross-relay selection approach that maximizes the
system throughput is presented. The cooperative network is comprised of a set of relays and
the reliable relay(s) that maximize the throughput at the data-link layer are selected to assist
the source. It can be shown through simulation that this novel scheme outperforms from
a throughput point of view, a system throughput where the all the reliable relays always
participate in forwarding the source packet.
A power optimization of the best relay uncoded DF cooperative diversity is investigated.
This optimization aims at maximizing the system throughput. Because of the non-concavity
and non-convexity of the throughput expression, it is intractable to derive a closed-form
expression of the optimal power through the system throughput. However, this can be done
via the symbol-error rate (SER) optimization, since it is shown that minimizing the SER of
the cooperative system is equivalent to maximizing the system throughput. The SER of the
retransmission scheme at high signal-to-noise ratio (SNR) was obtained and it was noted that
the derived SER is in perfect agreement with the simulated SER at high SNR. Moreover, the
optimal power allocation obtained under a general optimization problem, yields a throughput
performance that is superior to non-optimized power values from moderate to high SNRs.
The last part of the work considers the throughput maximization of the multi-relay adaptive
DF over independent and non-identically distributed (i.n.i.d.) Rayleigh fading channels,
that integrates ARQ at the link layer. The aim of this chapter is to maximize the system
throughput via power optimization and it is shown that this can be done by minimizing the
SER of the retransmission. Firstly, the closed-form expressions for the exact SER of the
multi-relay adaptive DF are derived as well as their corresponding asymptotic bounds. Results
showed that the optimal power distribution yields maximum throughput. Furthermore,
the power allocated at a relay is greatly dependent of its location relative to the source and
destination
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