20 research outputs found
Cooperative Downlink Multicell Preprocessing Relying on Reduced-Rate Back-Haul Data Exchange
Different-complexity multicell preprocessing (MCP) schemes employing distributed signal-to-interference leakageplus-noise ratio (SILNR) precoding techniques are proposed, which require reduced back-haul data exchange in comparison with the conventional MCP structure. Our results demonstrate that the proposed structures are capable of increasing the throughput achievable in the cell-edge area while offering different geographic rate profile distributions, as well as meeting different delay requirements
Imperfect Digital Fibre Optic Link Based Cooperative Distributed Antennas with Fractional Frequency Reuse in Multicell Multiuser Networks
The achievable throughput of the entire cellular area is investigated, when employing fractional frequency reuse techniques in conjunction with realistically modelled imperfect optical fibre aided distributed antenna systems (DAS) operating in a multicell multiuser scenario. Given a fixed total transmit power, a substantial improvement of the cell-edge area's throughput can be achieved without reducing the cell-centre's throughput. The cell-edge's throughput supported in the worst-case direction is significantly enhanced by the cooperative linear transmit processing technique advocated. Explicitly, a cell-edge throughput of bits/s/Hz may be maintained for an imperfect optical fibre model, regardless of the specific geographic distribution of the users
Error probability and capacity analysis of generalised pre-coding aided spatial modulation
The recently proposed multiple input multiple output (MIMO) transmission scheme termed as generalized pre-coding aided spatial modulation (GPSM) is analyzed, where the key idea is that a particular subset of receive antennas is activated and the specific activation pattern itself conveys useful implicit information. We provide the upper bound of both the symbol error ratio (SER) and bit error ratio (BER) expression of the GPSM scheme of a low-complexity decoupled detector. Furthermore, the corresponding discrete-input continuous-output memoryless channel (DCMC) capacity as well as the achievable rate is quantified. Our analytical SER and BER upper bound expressions are confirmed to be tight by our numerical results. We also show that our GPSM scheme constitutes a flexible MIMO arrangement and there is always a beneficial configuration for our GPSM scheme that offers the same bandwidth efficiency as that of its conventional MIMO counterpart at a lower signal to noise ratio (SNR) per bit
Cell-centric and user-centric multi-user scheduling in visible light communication aided networks
Visible Light Communication (VLC) combined withadvanced illumination has been expected to become an integralpart of next generation heterogeneous networks at the time ofwriting, by inspiring further research interests. From both theCell-Centric (CC) and the User-Centric (UC) perspectives, variousVLC cell formations, ranging from fixed-shape regular cellswith different Frequency Reuse (FR) patterns and merged cellsemploying advanced transmission scheme to amorphous userspecificcells are investigated. Furthermore, different Multi-UserScheduling (MUS) algorithms achieving Proportional Fairness(PF) are implemented according to different cell formations.By analysing some critical and unique characteristics of VLC,our simulation results demonstrate that, the proposed MUSalgorithms are capable of providing a high aggregate throughputand achieving modest fairness with low complexity in most of thescenarios considered.<br/
Técnicas de pré-codificação para sistemas multicelulares coordenados
Doutoramento em TelecomunicaçÔesCoordenação Multicélula é um tópico de investigação em råpido
crescimento e uma solução promissora para controlar a interferĂȘncia entre
células em sistemas celulares, melhorando a equidade do sistema e
aumentando a sua capacidade. Esta tecnologia jĂĄ estĂĄ em estudo no LTEAdvanced
sob o conceito de coordenação multiponto (COMP). Existem
vårias abordagens sobre coordenação multicélula, dependendo da
quantidade e do tipo de informação partilhada pelas estaçÔes 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
distribuĂda em cada estação base.
Nesta tese, são propostas técnicas de pré-codificação e alocação de
potĂȘncia considerando vĂĄrias estratĂ©gias: centralizada, todo o
processamento Ă© feito na unidade de processamento central; semidistribuĂda,
neste caso apenas parte do processamento Ă© executado na
unidade de processamento central, nomeadamente a potĂȘncia alocada a
cada utilizador servido por cada estação base; e distribuĂda em que o
processamento é feito localmente em cada estação base. Os esquemas
propostos são projectados em duas fases: primeiro são propostas soluçÔes
de prĂ©-codificação para mitigar ou eliminar a interferĂȘncia entre cĂ©lulas,
de seguida o sistema é melhorado através do desenvolvimento de vårios
esquemas de alocação de potĂȘncia. SĂŁo propostas trĂȘs esquemas de
alocação de potĂȘncia centralizada condicionada a cada estação base e com
diferentes relaçÔes entre desempenho e complexidade. São também
derivados esquemas de alocação distribuĂdos, assumindo que um sistema
multicelular pode ser visto como a sobreposição de vårios sistemas com
uma Ășnica cĂ©lula. Com base neste conceito foi definido uma taxa de erro
mĂ©dia virtual para cada um desses sistemas de cĂ©lula Ășnica que compĂ”em
o sistema multicelular, permitindo assim projectar esquemas de alocação
de potĂȘncia completamente distribuĂdos.
Todos os esquemas propostos foram avaliados em cenĂĄrios realistas,
bastante prĂłximos dos considerados no LTE. Os resultados mostram que
os esquemas propostos sĂŁo eficientes a remover a interferĂȘncia entre
cĂ©lulas e que o desempenho das tĂ©cnicas de alocação de potĂȘncia
propostas Ă© claramente superior ao caso de nĂŁo alocação de potĂȘncia. O
desempenho dos sistemas completamente distribuĂdos Ă© inferior aos
baseados num processamento centralizado, mas em contrapartida podem
ser usados em sistemas em que a rede de suporte nĂŁo 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