4 research outputs found
Bilayer Low-Density Parity-Check Codes for Decode-and-Forward in Relay Channels
This paper describes an efficient implementation of binning for the relay
channel using low-density parity-check (LDPC) codes. We devise bilayer LDPC
codes to approach the theoretically promised rate of the decode-and-forward
relaying strategy by incorporating relay-generated information bits in
specially designed bilayer graphical code structures. While conventional LDPC
codes are sensitively tuned to operate efficiently at a certain channel
parameter, the proposed bilayer LDPC codes are capable of working at two
different channel parameters and two different rates: that at the relay and at
the destination. To analyze the performance of bilayer LDPC codes, bilayer
density evolution is devised as an extension of the standard density evolution
algorithm. Based on bilayer density evolution, a design methodology is
developed for the bilayer codes in which the degree distribution is iteratively
improved using linear programming. Further, in order to approach the
theoretical decode-and-forward rate for a wide range of channel parameters,
this paper proposes two different forms bilayer codes, the bilayer-expurgated
and bilayer-lengthened codes. It is demonstrated that a properly designed
bilayer LDPC code can achieve an asymptotic infinite-length threshold within
0.24 dB gap to the Shannon limits of two different channels simultaneously for
a wide range of channel parameters. By practical code construction,
finite-length bilayer codes are shown to be able to approach within a 0.6 dB
gap to the theoretical decode-and-forward rate of the relay channel at a block
length of and a bit-error probability (BER) of . Finally, it is
demonstrated that a generalized version of the proposed bilayer code
construction is applicable to relay networks with multiple relays.Comment: Submitted to IEEE Trans. Info. Theor
Multi-Way Relay Networks: Orthogonal Uplink, Source-Channel Separation and Code Design
We consider a multi-way relay network with an orthogonal uplink and
correlated sources, and we characterise reliable communication (in the usual
Shannon sense) with a single-letter expression. The characterisation is
obtained using a joint source-channel random-coding argument, which is based on
a combination of Wyner et al.'s "Cascaded Slepian-Wolf Source Coding" and
Tuncel's "Slepian-Wolf Coding over Broadcast Channels". We prove a separation
theorem for the special case of two nodes; that is, we show that a modular code
architecture with separate source and channel coding functions is
(asymptotically) optimal. Finally, we propose a practical coding scheme based
on low-density parity-check codes, and we analyse its performance using
multi-edge density evolution.Comment: Authors' final version (accepted and to appear in IEEE Transactions
on Communications
Cancelamento de interferência em sistemas celulares distribuídos
Doutoramento em Engenharia ElectrotécnicaO tema principal desta tese é o problema de cancelamento de interferência
para sistemas multi-utilizador, com antenas distribuídas. Como tal, ao iniciar,
uma visão geral das principais propriedades de um sistema de antenas
distribuídas é apresentada. Esta descrição inclui o estudo analítico do impacto
da ligação, dos utilizadores do sistema, a mais antenas distribuídas.
Durante essa análise é demonstrado que a propriedade mais importante do
sistema para obtenção do ganho máximo, através da ligação de mais antenas
de transmissão, é a simetria espacial e que os utilizadores nas fronteiras das
células são os mais bene ciados. Tais resultados são comprovados através
de simulação. O problema de cancelamento de interferência multi-utilizador
é considerado tanto para o caso unidimensional (i.e. sem codi cação) como
para o multidimensional (i.e. com codi cação). Para o caso unidimensional
um algoritmo de pré-codi cação não-linear é proposto e avaliado, tendo
como objectivo a minimização da taxa de erro de bit. Tanto o caso de
portadora única como o de multipla-portadora são abordados, bem como o
cenário de antenas colocadas e distribuidas. É demonstrado que o esquema
proposto pode ser visto como uma extensão do bem conhecido esquema
de zeros forçados, cuja desempenho é provado ser um limite inferior para
o esquema generalizado. O algoritmo é avaliado, para diferentes cenários,
através de simulação, a qual indica desempenho perto do óptimo, com baixa
complexidade. Para o caso multi-dimensional um esquema para efectuar
"dirty paper coding" binário, tendo como base códigos de dupla camada é
proposto. No desenvolvimento deste esquema, a compressão com perdas de
informação, é considerada como um subproblema. Resultados de simulação
indicam transmissão dedigna proxima do limite de Shannon.This thesis focus on the interference cancellation problem for multiuser distributed
antenna systems. As such it starts by giving an overview of the
main properties of a distributed antenna system. This overview includes, an
analytical investigation of the impact of the connection of additional distributed
antennas, to the system users. That analysis shows that the most
important system property to reach the maximum gain, with the connection
of additional transmit antennas, is spatial symmetry and that the users at
the cell borders are the most bene ted. The multiuser interference problem
has been considered for both the one dimensional (i.e. without coding) and
multidimensional (i.e. with coding) cases. In the unidimensional case, we
propose and evaluate a nonlinear precoding algorithm for the minimization
of the bit-error-rate, of a multiuser MIMO system. Both the single-carrier
and multi-carrier cases are tackled as well as the co-located and distributed
scenarios. It is demonstrated that the proposed scheme can be viewed as an
extension of the well-known zero-forcing, whose performance is proven to be
a lower bound for the generalized scheme. The algorithm was validated extensively
through numerical simulations, which indicate a performance close
to the optimal, with reduced complexity. For the multi-dimensional case, a
binary dirty paper coding scheme, base on bilayer codes, is proposed. In the
development of this scheme, we consider the lossy compression of a binary
source as a sub-problem. Simulation results indicate reliable transmission
close to the Shannon limit