237 research outputs found
MLTE Algorithm for Multicast Service Delivery in OFDMA Networks
Dispensing and overseeing radio resources to the multi-cast transmissions in OFDMA (orthogonal-frequency division-multiple-access) systems is testing exploration issue tended to by this paper. A sub-grouping technique, which separates the subscribers into subgroups as indicated by the accomplished channel quality, is considered to defeat the throughput confinements of conventional multicast data conveyance schemes. A low complexity algorithm intended to work with diverse resource allocation strategies, is additionally proposed to diminish the computational complexity of the subgroup development issue. Reproduction results, did by considering the long term evolution system taking into account OFDMA, affirm the adequacy of the proposed arrangement, which accomplishes a close ideal execution with a restricted computational load for the system. In this paper we are introducing the MLTE for improve the MBPS speed for fix network coverage at uniform and sparse.
DOI: 10.17762/ijritcc2321-8169.150713
SYNCHRONIZATION AND RESOURCE ALLOCATION IN DOWNLINK OFDM SYSTEMS
The next generation (4G) wireless systems are expected to provide
universal personal and multimedia communications with seamless connection
and very high rate transmissions and without regard to the users’ mobility and
location. OFDM technique is recognized as one of the leading candidates to
provide the wireless signalling for 4G systems. The major challenges in
downlink multiuser OFDM based 4G systems include the wireless channel, the
synchronization and radio resource management. Thus algorithms are required
to achieve accurate timing and frequency offset estimation and the efficient
utilization of radio resources such as subcarrier, bit and power allocation.
The objectives of the thesis are of two fields. Firstly, we presented the
frequency offset estimation algorithms for OFDM systems. Building our work
upon the classic single user OFDM architecture, we proposed two FFT-based
frequency offset estimation algorithms with low computational complexity.
The computer simulation results and comparisons show that the proposed
algorithms provide smaller error variance than previous well-known algorithm.
Secondly, we presented the resource allocation algorithms for OFDM
systems. Building our work upon the downlink multiuser OFDM architecture,
we aimed to minimize the total transmit power by exploiting the system
diversity through the management of subcarrier allocation, adaptive
modulation and power allocation. Particularly, we focused on the dynamic
resource allocation algorithms for multiuser OFDM system and multiuser
MIMO-OFDM system. For the multiuser OFDM system, we proposed a lowiv
complexity channel gain difference based subcarrier allocation algorithm. For
the multiuser MIMO-OFDM system, we proposed a unit-power based
subcarrier allocation algorithm. These proposed algorithms are all combined
with the optimal bit allocation algorithm to achieve the minimal total transmit
power. The numerical results and comparisons with various conventional nonadaptive
and adaptive algorithmic approaches are provided to show that the
proposed resource allocation algorithms improve the system efficiencies and
performance given that the Quality of Service (QoS) for each user is
guaranteed.
The simulation work of this project is based on hand written codes in the
platform of the MATLAB R2007b
Non-convex Optimization for Resource Allocation in Wireless Device-to-Device Communications
Device-to-device (D2D) communication is considered one of the key frameworks to provide suitable solutions for the exponentially increasing data tra c in mobile telecommunications. In this PhD Thesis, we focus on the resource allocation for underlay D2D communications which often results in a non-convex optimization problem that is computationally demanding.
We have also reviewed many of the works on D2D underlay communications and identi ed some of the limitations that were not handled previously, which has motivated our works in this Thesis.
Our rst works focus on the joint power allocation and channel assignment problem in the D2D underlay communication scenario for a unicast single-input and single-output (SISO) cellular network in either uplink or downlink spectrums. These works also consider several degrees of uncertainty in the channel state information (CSI), and propose suitable measures to guarantee the quality of service (QoS) and reliability under those conditions. Moreover, we also present a few algorithms that can be used to jointly assign uplink and downlink spectrum to D2D pairs. We also provide methods to decentralize those algorithms with convergence guarantees and analyze their computational complexity. We also consider both cases with no interference among D2D pairs and cases with interference among D2D pairs. Additionally, we propose the formulation of an optimization objective function that combines the network rate with a penalty function that penalizes unfair channel allocations where most of the channels are assigned to only a few D2D pairs.
The next contributions of this Thesis focus on extending the previous works to cellular networks with multiple-input and multiple-output (MIMO) capabilities and networks with D2D multicast groups. We also present several methods to accommodate various degrees of uncertainty in the CSI and also guarantee di erent measures of QoS and reliability.
All our algorithms are evaluated extensively through extensive numerical experiments using the Matlab simulation environment. All of these results show favorable performance, as compared to the existing state-of-the-art alternatives.publishedVersio
Técnicas de pré-codificação para sistemas multicelulares coordenados
Doutoramento em TelecomunicaçõesCoordenação Multicélula é um tópico de investigação em rápido
crescimento e uma solução promissora para controlar a interferência entre
células em sistemas celulares, melhorando a equidade do sistema e
aumentando a sua capacidade. Esta tecnologia já está em estudo no LTEAdvanced
sob o conceito de coordenação multiponto (COMP). Existem
várias abordagens sobre coordenação multicélula, dependendo da
quantidade e do tipo de informação partilhada pelas estações base, através
da rede de suporte (backhaul network), e do local onde essa informação é
processada, i.e., numa unidade de processamento central ou de uma forma
distribuída em cada estação base.
Nesta tese, são propostas técnicas de pré-codificação e alocação de
potência considerando várias estratégias: centralizada, todo o
processamento é feito na unidade de processamento central; semidistribuída,
neste caso apenas parte do processamento é executado na
unidade de processamento central, nomeadamente a potência alocada a
cada utilizador servido por cada estação base; e distribuída em que o
processamento é feito localmente em cada estação base. Os esquemas
propostos são projectados em duas fases: primeiro são propostas soluções
de pré-codificação para mitigar ou eliminar a interferência entre células,
de seguida o sistema é melhorado através do desenvolvimento de vários
esquemas de alocação de potência. São propostas três esquemas de
alocação de potência centralizada condicionada a cada estação base e com
diferentes relações entre desempenho e complexidade. São também
derivados esquemas de alocação distribuídos, assumindo que um sistema
multicelular pode ser visto como a sobreposição de vários sistemas com
uma única célula. Com base neste conceito foi definido uma taxa de erro
média virtual para cada um desses sistemas de célula única que compõem
o sistema multicelular, permitindo assim projectar esquemas de alocação
de potência completamente distribuídos.
Todos os esquemas propostos foram avaliados em cenários realistas,
bastante próximos dos considerados no LTE. Os resultados mostram que
os esquemas propostos são eficientes a remover a interferência entre
células e que o desempenho das técnicas de alocação de potência
propostas é claramente superior ao caso de não alocação de potência. O
desempenho dos sistemas completamente distribuídos é inferior aos
baseados num processamento centralizado, mas em contrapartida podem
ser usados em sistemas em que a rede de suporte não permita a troca de
grandes quantidades de informação.Multicell coordination is a promising solution for cellular wireless systems
to mitigate inter-cell interference, improving system fairness and
increasing capacity and thus is already under study in LTE-A under the
coordinated multipoint (CoMP) concept. There are several coordinated
transmission approaches depending on the amount of information shared
by the transmitters through the backhaul network and where the
processing takes place i.e. in a central processing unit or in a distributed
way on each base station.
In this thesis, we propose joint precoding and power allocation techniques
considering different strategies: Full-centralized, where all the processing
takes place at the central unit; Semi-distributed, in this case only some
process related with power allocation is done at the central unit; and Fulldistributed,
where all the processing is done locally at each base station.
The methods are designed in two phases: first the inter-cell interference is
removed by applying a set of centralized or distributed precoding vectors;
then the system is further optimized by centralized or distributed power
allocation schemes. Three centralized power allocation algorithms with
per-BS power constraint and different complexity tradeoffs are proposed.
Also distributed power allocation schemes are proposed by considering
the multicell system as superposition of single cell systems, where we
define the average virtual bit error rate (BER) of interference-free single
cell system, allowing us to compute the power allocation coefficients in a
distributed manner at each BS.
All proposed schemes are evaluated in realistic scenarios considering LTE
specifications. The numerical evaluations show that the proposed schemes
are efficient in removing inter-cell interference and improve system
performance comparing to equal power allocation. Furthermore, fulldistributed
schemes can be used when the amounts of information to be
exchanged over the backhaul is restricted, although system performance is
slightly degraded from semi-distributed and full-centralized schemes, but
the complexity is considerably lower. Besides that for high degrees of
freedom distributed schemes show similar behaviour to centralized ones
Novel feedback and signalling mechanisms for interference management and efficient modulation
In order to meet the ever-growing demand for mobile data, a number of different technologies
have been adopted by the fourth generation standardization bodies. These include multiple access
schemes such as spatial division multiple access (SDMA), and efficient modulation techniques
such as orthogonal frequency division multiplexing (OFDM)-based modulation. The
specific objectives of this theses are to develop an effective feedback method for interference
management in smart antenna SDMA systems and to design an efficient OFDM-based modulation
technique, where an additional dimension is added to the conventional two-dimensional
modulation techniques such as quadrature amplitude modulation (QAM).
In SDMA time division duplex (TDD) systems, where channel reciprocity is maintained, uplink
(UL) channel sounding method is considered as one of the most promising feedback methods
due to its bandwidth and delay efficiency. Conventional channel sounding (CCS) only conveys
the channel state information (CSI) of each active user to the base station (BS). Due to
the limitation in system performance because of co-channel interference (CCI) from adjacent
cells in interference-limited scenarios, CSI is only a suboptimal metric for multiuser spatial
multiplexing optimization. The first major contribution of this theses is a novel interference
feedback method proposed to provide the BS with implicit knowledge about the interference
level received by each mobile station (MS). More specifically, it is proposed to weight the
conventional channel sounding pilots by the level of the experienced interference at the user’s
side. Interference-weighted channel sounding (IWCS) acts as a spectrally efficient feedback
technique that provides the BS with implicit knowledge about CCI experienced by each MS,
and significantly improves the downlink (DL) sum capacity for both greedy and fair scheduling
policies. For the sake of completeness, a novel procedure is developed to make the IWCS pilots
usable for UL optimization. It is proposed to divide the optimization metric obtained from the
IWCS pilots by the interference experienced at the BS’s antennas. The resultant new metric, the
channel gain divided by the multiplication of DL and UL interference, provides link-protection
awareness and is used to optimize both UL and DL. Using maximum capacity scheduling criterion,
the link-protection aware metric results in a gain in the median system sum capacity of
26.7% and 12.5% in DL and UL respectively compared to the case when conventional channel
sounding techniques are used. Moreover, heuristic algorithm has been proposed in order to
facilitate a practical optimization and to reduce the computational complexity.
The second major contribution of this theses is an innovative transmission approach, referred
to as subcarrier-index modulation (SIM), which is proposed to be integrated with OFDM. The
key idea of SIM is to employ the subcarrier-index to convey information to the receiver. Furthermore,
a closed-form analytical bit error ratio (BER) of SIM OFDM in Rayleigh channel
is derived. Simulation results show BER performance gain of 4 dB over 4-QAM OFDM for
both coded and uncoded data without power saving policy. Alternatively, power saving policy
maintains an average gain of 1 dB while only using half OFDM symbol transmit power
Optimize Power Allocation Scheme to Maximize Sum Rate in CoMP with Limited Channel State Information
Extensive use of mobile applications throws many challenges in cellular systems like cell edge
throughput, inter cell interference and spectral e�ciency. Many of these challenges have been
resolved using Coordinated Multi-Point (CoMP), developed in the Third Generation Partnership
Project for LTE-Advanced) to a great extent. CoMP cooperatively process signals from base sta-
tions that are connected to various multiple terminals (user equipment (UEs)) at transmission and
reception. This CoMP improves throughput, reduces or even removes inter-cell interference and
increases spectral e�ciency in the downlink of multi-antenna coordinated multipoint systems.
Many researchers addressed these issues assuming that BSs have the knowledge of the common
control channels dedicated to all UEs and also about the full or partial channel state information
(CSI) of all the links. From the CSI available at the BSs, multiuser interference can be managed
at the BSs. To make this feasible, UEs are responsible for collecting downlink CSI. But, CSI
measurement (instantaneous and/or statistical) is imperfect in nature because of the randomly
varying nature of the channels at random times. These incorrect CSI values available at the BSs
may, in turn, create multi-user interference. There are many techniques to suppress the multi-user
interference, among which the feedback scheme is the one which is gaining a lot of attention. In
feedback schemes, CSI information needs to be fed back to the base station from UEs in the uplink.
It is obvious, the question arises on the type and amount of feedback need to be used. Research
has been progressing in this front and some feedback techniques have been proposed. Three basic
CoMP Feedback schemes are available. Explicit or statistical channel information feedback scheme
in which channel information like channels's covariance matrix of the channel are shared between the
transmitter and receiver. Next, implicit or statistical channel information feedback which contains
information such as Channel quality indication or Precoding matrix indicator or Rank indicator. 1st
applied to TDD LTE type structure and 2nd of feedback scheme can be applied in the FDD system.
Finally, we have UE which tranmit the sounding reference signal (CSI). This type of feedback scheme
is applied to exploit channel reciprocity and to reduce channel intercell interference and this can be
applied in the TDD system. We have analyzed the scenario of LTE TDD based system. After this,
optimization of power is also required because users at the cell edge required more attention than
the user locating at the center of the cell. In my work, it shows estimated power gives exponential
divercity for high SNR as low SNR too.
In this method, a compression feedback method is analyzed to provide multi-cell spatial channel
information. It improves the feedback e�ciency and throughput. The rows and columns of the
channel matrix are compressed using Eigenmode of the user and codebook based scheme speci�ed
in LTE speci�cation. The main drawback of this scheme is that spectral e�ciency is achieved with
the cost of increased overheads for feedback and evolved NodeB (eNB). Other factor is complexity
of eNodeB which is to be addressed in future work
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