529 research outputs found
Fast constant weight codeword to index converter
Abstract-Constant weight codewords, in which the number of 1's is constant, are essential to combinatorial computing. For example, it is often useful to generate all subsets of a set with a fixed number of elements. In this paper, we show an efficient circuit that converts a constant weight codeword into a unique index of that codeword. This circuit is a necessary part of a circuit that uses constant weight codewords to transmit data on and off chip. Our circuit is based on the combinatorial number system in which the digits are binomial coefficients n r . Experimental results show the efficiency of our design
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Parallel data compression
Data compression schemes remove data redundancy in communicated and stored data and increase the effective capacities of communication and storage devices. Parallel algorithms and implementations for textual data compression are surveyed. Related concepts from parallel computation and information theory are briefly discussed. Static and dynamic methods for codeword construction and transmission on various models of parallel computation are described. Included are parallel methods which boost system speed by coding data concurrently, and approaches which employ multiple compression techniques to improve compression ratios. Theoretical and empirical comparisons are reported and areas for future research are suggested
Codebook Based Hybrid Precoding for Millimeter Wave Multiuser Systems
In millimeter wave (mmWave) systems, antenna architecture limitations make it
difficult to apply conventional fully digital precoding techniques but call for
low cost analog radio-frequency (RF) and digital baseband hybrid precoding
methods. This paper investigates joint RF-baseband hybrid precoding for the
downlink of multiuser multi-antenna mmWave systems with a limited number of RF
chains. Two performance measures, maximizing the spectral efficiency and the
energy efficiency of the system, are considered. We propose a codebook based RF
precoding design and obtain the channel state information via a beam sweep
procedure. Via the codebook based design, the original system is transformed
into a virtual multiuser downlink system with the RF chain constraint.
Consequently, we are able to simplify the complicated hybrid precoding
optimization problems to joint codeword selection and precoder design (JWSPD)
problems. Then, we propose efficient methods to address the JWSPD problems and
jointly optimize the RF and baseband precoders under the two performance
measures. Finally, extensive numerical results are provided to validate the
effectiveness of the proposed hybrid precoders.Comment: 35 pages, 9 figures, to appear in Trans. on Signal Process, 201
Study and implementation of a low complexity receiver using TCH codes
The use of coding in telecommunications systems reveals to be a technique with an essential
contribution to the improvement of the recovery of transmitted signals. Depending on the
circumstances to which a signal is subjected at transmission, by recurring to coding, it is
possible to attenuate the unfavorable effects that result from this process, obtaining a signal
with superior quality in comparison with a scenario where the presence of coding is absent.
This study aims to test the feasibility of a high-rate wireless communications system using
TCH codes being applied to an OFDM signal, subjected to noise components introduced by a
wireless AWGN channel, considering a free path propagation model. Due to their correlation
properties, the use of TCH codes reveals to be adequate since they allow the same codewords
to be used to realize both error correction and channel estimation, mitigating the channels
effects, leading to the realization of a receiver with lower complexity.
With the intent of performing a qualitative analysis to this system, a simple simulation is
executed in MATLAB where an OFDM signal is generated, being therefore applied various
TCH codes and, through channel estimation, obtain the BER for their respective code lengths
and, consequently, coding gains.
The results were obtained for the modulation indexes of 16, 64 and 256-QAM. These
demonstrate that the implementation of TCH codes is a viable option to reduce the rate of
recovered errors, enabling the reception of a signal with better reliability, especially for higher
code lengths and modulation indexes.O uso de codificação em sistemas de telecomunicações revela-se uma técnica com um
contributo essencial na melhoria da recuperação de sinais transmitidos. Dependendo das
circunstâncias às quais um sinal é submetido aquando a sua transmissão, com recurso à
codificação, é possível atenuar os efeitos adversos resultantes deste processo, obtendo uma
qualidade no sinal recebido superior face a um cenário com ausência da mesma.
Este estudo tem como objetivo testar a exequibilidade de um sistema de comunicações sem
fios para alto débito usando códigos TCH e aplicando-os a um sinal OFDM, sujeito a
componentes de ruído introduzidos por um canal sem fios AWGN, considerando um modelo
de propagação em espaço livre. Devido às propriedades de correlação destes códigos, a sua
utilização revela-se adequada pois permite que as mesmas palavras de código sejam utilizadas
para efetuar correção de erros, minimizando os efeitos do canal, possibilitando o
desenvolvimento de um recetor com menor complexidade.
Visando efetuar uma análise qualitativa do sistema, é realizada uma simulação simples em
MATLAB onde é gerado um sinal OFDM ao qual são aplicados diversos códigos TCH,
realizando estimação de canal com a finalidade de obter o BER para os diferentes comprimentos
dos códigos e, consequentemente, ganhos de codificação relativos aos mesmos.
Os resultados obtidos foram realizados para os índices de modulação 16, 64 e 256-QAM.
Estes demonstram que o uso destes códigos é uma opção viável para reduzir os erros detetados,
permitindo recuperar o sinal com maior fiabilidade, especialmente para comprimentos de
código e índices de modulação elevados
Fault-Tolerant Dot-Product Engines
Coding schemes are presented that provide the ability to correct and detect
computational errors while using dot-product engines for integer vector--matrix
multiplication. Both the -metric and the Hamming metric are considered
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