159 research outputs found
Multicast Scheduling and Resource Allocation Algorithms for OFDMA-Based Systems: A Survey
Multicasting is emerging as an enabling technology
for multimedia transmissions over wireless networks to support several groups of users with flexible quality of service (QoS)requirements. Although multicast has huge potential to push the limits of next generation communication systems; it is however one of the most challenging issues currently being addressed. In this survey, we explain multicast group formation and various
forms of group rate determination approaches. We also provide a systematic review of recent channel-aware multicast scheduling and resource allocation (MSRA) techniques proposed for downlink multicast services in OFDMA based systems. We study these enabling algorithms, evaluate their core characteristics, limitations and classify them using multidimensional matrix. We cohesively review the algorithms in terms of their throughput maximization, fairness considerations, performance complexities,
multi-antenna support, optimality and simplifying assumptions. We discuss existing standards employing multicasting and further highlight some potential research opportunities in multicast systems
Recent advances in radio resource management for heterogeneous LTE/LTE-A networks
As heterogeneous networks (HetNets) emerge as one of the most promising developments toward realizing the target specifications of Long Term Evolution (LTE) and LTE-Advanced (LTE-A) networks, radio resource management (RRM) research for such networks has, in recent times, been intensively pursued. Clearly, recent research mainly concentrates on the aspect of interference mitigation. Other RRM aspects, such as radio resource utilization, fairness, complexity, and QoS, have not been given much attention. In this paper, we aim to provide an overview of the key challenges arising from HetNets and highlight their importance. Subsequently, we present a comprehensive survey of the RRM schemes that have been studied in recent years for LTE/LTE-A HetNets, with a particular focus on those for femtocells and relay nodes. Furthermore, we classify these RRM schemes according to their underlying approaches. In addition, these RRM schemes are qualitatively analyzed and compared to each other. We also identify a number of potential research directions for future RRM development. Finally, we discuss the lack of current RRM research and the importance of multi-objective RRM studies
An Analytical Framework for Heterogeneous Partial Feedback Design in Heterogeneous Multicell OFDMA Networks
The inherent heterogeneous structure resulting from user densities and large
scale channel effects motivates heterogeneous partial feedback design in
heterogeneous networks. In such emerging networks, a distributed scheduling
policy which enjoys multiuser diversity as well as maintains fairness among
users is favored for individual user rate enhancement and guarantees. For a
system employing the cumulative distribution function based scheduling, which
satisfies the two above mentioned desired features, we develop an analytical
framework to investigate heterogeneous partial feedback in a general
OFDMA-based heterogeneous multicell employing the best-M partial feedback
strategy. Exact sum rate analysis is first carried out and closed form
expressions are obtained by a novel decomposition of the probability density
function of the selected user's signal-to-interference-plus-noise ratio. To
draw further insight, we perform asymptotic analysis using extreme value theory
to examine the effect of partial feedback on the randomness of multiuser
diversity, show the asymptotic optimality of best-1 feedback, and derive an
asymptotic approximation for the sum rate in order to determine the minimum
required partial feedback.Comment: To appear in IEEE Trans. on Signal Processin
Policy-Based Radio Resource Management in Multicast OFDMA Systems
Η ασύρματηφασματική αποδοτικότητα είναι ένας, όλο και περισσότερο, σημαντικός
παράγοντας εξαιτίας της ταχείας ανάπτυξης των ασύρματων υπηρεσιών ευρείας
ζώνης. Η σχεδίαση ενός συστήματος με πολλά φέροντα, όπως είναι ένα σύστημα
OFDMA,επιτρέπει στα συστήματα να έχουν υψηλή χωρητικότητα για να ικανοποιήσουν
τις απαιτήσεις των υπηρεσιών ευρείας ζώνης.Αυτή η αυξημένη χωρητικότητα των
συστημάτων μπορεί να βελτιστοποιηθεί περαιτέρω εκμεταλλευόμενοι καλύτερα τα
χαρακτηριστικά των ασύρματων καναλιών. Ηθεμελιώδηςιδέα ενός σχήματος κατανομής
πόρων είναι η αποτελεσματική κατανομή των διαθέσιμων ασύρματων πόρων, όπως
είναι οι υποφορείς και η ισχύς εκπομπής, μεταξύ των χρηστών του συστήματος.
Σχετικά με τα προβλήματα της κατανομής πόρων σε ασύρματα συστήματα
τηλεπικοινωνιών βασισμένα στην τεχνική OFDMA, η περισσότερη έρευνα
επικεντρώνεται στην αναζήτηση πολιτικών ανάθεσης υποφορέων και ισχύος. Οι
διαθέσιμες τεχνικές της βιβλιογραφίας δεν μπορούν να εφαρμοστούν όπως είναι σε
συστήματα πολυεκπομπής. Επιπλέον, οι υπάρχουσες τεχνικές δεν μπορούν να
εφαρμοστούν αμετάβλητες σε πραγματικά συστήματα στα οποία υπάρχει μεγάλος
αριθμός OFDMυποφορέων, καθώς η υπολογιστική πολυπλοκότητα είναι πολύ μεγάλη.
Ο βασικός στόχος της παρούσας διπλωματικής εργασίας είναι η πρόταση ικανών
μηχανισμών κατανομής των διαθέσιμων υποφορέων σε ασύρματα συστήματα
πολυεκπομπής χρησιμοποιώντας την τεχνολογία OFDMA. Πιο συγκεκριμένα, σχετικά με
τα συστήματα πολυεκπομπής, θεωρούμε ότι τόσο ο σταθμός βάσης όσο και κάθε
χρήστης είναι εφοδιασμένοι με μοναδική κεραία και η μονάδα κατανομής δεν είναι
ο υποφορέας, όπως στα συμβατικά συστήματα OFDMA, αλλά μία ομάδα
γειτονικώνυποφορέων, η οποία ονομάζεται τεμάχιο, με σκοπό τη μείωση της μεγάλης
υπολογιστικής πολυπλοκότητας.
Ένας αποτελεσματικός αλγόριθμος προτείνεται του οποίου ο στόχος είναι η
μεγιστοποίηση του συνολικού ρυθμού μετάδοσης δεδομένων με περιορισμούς στη
συνολική διαθέσιμη ισχύ, στο BERανά τεμάχιο και στους αναλογικούς περιορισμούς
μεταξύ των ρυθμών μετάδοσης δεδομένων των ομάδων χρηστών. Η προσομοίωση και η
ανάλυση της πολυπλοκότητας που παρουσιάζονται, υποστηρίζουν τα πλεονεκτήματα
της κατανομής πόρων σε συστήματα πολυεκπομπήςOFDMA τα οποία βασίζονται σε
κατανομή τεμαχίων και έχουν ως στόχος την εξασφάλιση της αναλογικότητας μεταξύ
των ρυθμών μετάδοσης δεδομένων των ομάδων χρηστών.Wireless spectral efficiency is increasingly important due to the rapid growth
of demand for high data rate wideband wireless services. The design of a
multi-carrier system, such as an OFDMA system, enables high system capacity
suited for these wideband wireless services. This system capacity can be
further optimized with a resource allocation scheme by exploiting the
characteristics of the wireless fading channels. The fundamental idea of a
resource allocation scheme is to efficiently distribute the available wireless
resources, such as the subcarriers and transmission power, among all admitted
users in the system.
Regarding the problems of resource allocation in OFDMA-based wireless
communicationsystems, much of the research effort mainly focuses on finding
efficient power controland subcarrier assignment policies. With systems
employing multicast transmission,the available schemes in literature are not
always applicable. Moreover, the existing approachesare particularly
inaccessible in practical systems in which there are a large numberof OFDM
subcarriers being utilized, as the required computational burden is
prohibitivelyhigh.
The ultimate goal of this Thesis is therefore to propose affordable mechanisms
toflexibly and effectively share out the available resources in multicast
wireless systems deployingOFDMA technology. Specifically, according to
multicast system, it is assumed thatboth the BS and each user are equipped
witha single antenna and the allocation unit is not the subcarrier,as in
conventional OFDMA systems, but a set of contiguoussubcarriers, which is called
chunk, in order to alleviate the heavy computational burden.
An efficient algorithmis proposed whose aim is to maximize the total throughput
subject to constraints on totalavailable power,BER over a chunk, and
proportional data rates constraints among multicast groups. Simulation and
complexity analysis are provided to support thebenefits of chunk-based resource
allocation to multicast OFDMA systems with targeting proportional data rates
among multicast groups
Statistical Analysis and Optimization of a Fifth-Percentile User Rate Constrained Design for FFR/SFR-Aided OFDMA-Based Cellular Networks
Interference mitigation strategies are deemed to play a key role in the
context of the next generation (B4G/5G) of multicellular networks based on
orthogonal frequency division multiple access. Fractional and soft frequency
reuse (FFR, SFR) constitute two powerful mechanisms for intercell interference
coordination that have been already adopted by emerging cellular deployments as
an efficient way to improve the throughput performance perceived by cell-edge
users. This paper presents a novel optimal fifth-percentile user rate
constrained design for FFR/SFR-based networks that, by appropriately
dimensioning the center and edge regions of the cell, rightly splitting the
available bandwidth among these two areas while assigning the corresponding
transmit power, allows a tradeoff between cell throughput performance and
fairness to be established. To this end, both the cumulative distribution
function of the user throughput and the average spectral efficiency of the
system are derived assuming the use of the ubiquitous proportional fair
scheduling policy. The mathematical framework is then used to obtain numerical
results showing that the novel proposed design clearly outperforms previous
schemes in terms of throughput fairness control due to a more rational
compromise between average cell throughput and cell-edge ICIC
Busy burst technology applied to OFDMA–TDD systems
The most significant bottleneck in wireless communication systems is an ever-increasing disproportion
between the bandwidth demand and the available spectrum. A major challenge in
the field of wireless communications is to maximise the spatial reuse of resources whilst avoiding
detrimental co-channel interference (CCI). To this end, frequency planning and centralised
coordination approaches are widely used in wireless networks. However, the networks for the
next generation of wireless communications are often envisioned to be decentralised, randomly
distributed in space, hierarchical and support heterogeneous traffic and service types. Fixed
frequency allocation would not cater for the heterogeneous demands and centralised resource
allocation would be cumbersome and require a lot of signalling. Decentralised radio resource
allocation based on locally available information is considered the key.
In this context, the busy burst (BB) signalling concept is identified as a potential mechanism
for decentralised interference management in future generation networks. Interference aware
allocation of time-frequency slots (chunks) is accomplished by letting receivers transmit a BB
in a time-multiplexed mini-slot, upon successful reception of data. Exploiting channel reciprocity
of the time division duplex (TDD) mode, the transmitters avoid reusing the chunks
where the received BB power is above a pre-determined threshold so as to limit the CCI caused
towards the reserved chunks to a threshold value. In this thesis, the performance of BB signalling
mechanism in orthogonal frequency division multiple access - time division duplexing
(OFDMA-TDD) systems is evaluated by means of system level simulations in networks operating
in ad hoc and cellular scenarios. Comparisons are made against the state-of-the-art centralised
CCI avoidance and mitigation methods, viz. frequency planning, fractional frequency
reuse, and antenna array with switched grid of beams, as well as decentralised methods such as
the carrier sense multiple access method that attempt to avoid CCI by avoiding transmission on
chunks deemed busy. The results demonstrate that with an appropriate choice of threshold parameter,
BB-based techniques outperform all of the above state-of-the-art methods. Moreover,
it is demonstrated that by adjusting the BB-specific threshold parameter, the system throughput
can be traded off for improving throughput for links with worse channel condition, both
in the ad hoc and cellular scenario. Moreover, by utilising a variable BB power that allows a
receiver to signal the maximum CCI it can tolerate, it is shown that a more favourable trade-off
between total system throughput and link throughput can be made. Furthermore, by performing
link adaptation, it is demonstrated that the spatial reuse and the energy efficiency can be traded
off by adjusting the threshold parameter. Although the BB signalling mechanism is shown to
be effective in avoiding detrimental CCI, it cannot mitigate CCI by itself. On the other hand,
multiple antenna techniques such as adaptive beamforming or switched beam approaches allow
CCI to be mitigated but suffer from hidden node problems. The final contribution of this thesis
is that by combining the BB signalling mechanism with multiple antenna techniques, it is
demonstrated that the hybrid approach enhances spatial reusability of resources whilst avoiding
detrimental CCI.
In summary, this thesis has demonstrated that BB provides a flexible radio resource mechanism
that is suitable for future generation networks
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