20 research outputs found

    Cooperative Downlink Multicell Preprocessing Relying on Reduced-Rate Back-Haul Data Exchange

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    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

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    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 η=5\eta=5 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

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    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

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    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/

    Distributed Antenna Systems in Fractional-Frequency-Reuse-Aided Cellular Networks

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    Técnicas de pré-codificação para sistemas multicelulares coordenados

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    Doutoramento em TelecomunicaçÔesCoordenação MulticĂ©lula Ă© um tĂłpico de investigação em rĂĄpido crescimento e uma solução promissora para controlar a interferĂȘncia entre cĂ©lulas 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 vĂĄrias abordagens sobre coordenação multicĂ©lula, dependendo da quantidade e do tipo de informação partilhada pelas estaçÔes base, atravĂ©s da rede de suporte (backhaul network), e do local onde essa informação Ă© processada, i.e., numa unidade de processamento central ou de uma forma distribuĂ­da em cada estação base. Nesta tese, sĂŁo propostas tĂ©cnicas de prĂ©-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 Ă© feito localmente em cada estação base. Os esquemas propostos sĂŁo projectados em duas fases: primeiro sĂŁo propostas soluçÔes de prĂ©-codificação para mitigar ou eliminar a interferĂȘncia entre cĂ©lulas, de seguida o sistema Ă© melhorado atravĂ©s do desenvolvimento de vĂĄrios 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. SĂŁo tambĂ©m derivados esquemas de alocação distribuĂ­dos, assumindo que um sistema multicelular pode ser visto como a sobreposição de vĂĄrios 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
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