9,702 research outputs found
The Fed's entry into check clearing reconsidered
No full textCheck collection systems ; Federal Reserve System
Low-density parity-check codes and their rateless relatives
No full textThis survey guides the reader through the extensive open literature that is covering the family of low-density parity-check LDPC codes and their rateless relatives. In doing so, we will identify the most important milestones that have occurred since their conception until the current era and elucidate the related design problems and their respective solutions
Multilevel structured low-density parity-check codes for AWGN and Rayleigh channels
No full textWe propose a novel class of protograph low-density parity-check (LDPC) codes having a combinatorial rather than a random structure, which are termed multilevel-structured (MLS) LDPC codes. It is demonstrated that they posses a strikingly simple structure and, thus, benefit from reduced storage requirements, hardware-friendly implementations, and low-complexity encoding. Our simulation results provided for both additive white Gaussian noise (AWGN) and uncorrelated Rayleigh (UR) channels demonstrate that these advantages accrue without compromising the attainable bit error ratio (BER) and block error ratio (BLER) performance, when compared with their previously proposed more complex random-construction-based counterparts, as well as with other structured codes of the same length
Three-stage turbo MBER Multiuser beamforming receiver using irregular convolutional codes
No full textBased on extrinsic information transfer (EXIT) charts, the convergence behavior of a three-stage serially concatenated multiuser beamforming receiver is presented. This system uses a linear minimum bit error rate (BER) multiuser detector as the inner module. Due to the nonrecursive nature of this inner module, a unity-rate memory-1 recursive precoder is placed in front of the channel to provide the required recursive structure. Irregular convolutional codes (IRCCs) are constructed to be used as the outer code to achieve near-capacity performance. Our simulations show that this system outperforms the traditional two-component iterative structure and is capable of significantly educing the error floor
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On multi-user EXIT chart analysis aided turbo-detected MBER beamformer designs
No full textThis paper studies the mutual information transfer characteristics of a novel iterative soft interference cancellation (SIC) aided beamforming receiver communicating over both additive white Gaussian noise (AWGN) and multipath slow fading channels. Based on the extrinsic information transfer (EXIT) chart technique, we investigate the convergence behavior of an iterative minimum bit error rate (MBER) multiuser detection (MUD) scheme as a function of both the system parameters and channel conditions in comparison to the SIC aided minimum mean square error (SIC-MMSE) MUD. Our simulation results show that the EXIT chart analysis is sufficiently accurate for the MBER MUD. Quantitatively, a two-antenna system was capable of supporting up to K=6 users at Eb/N0 = 3dB, even when their angular separation was relatively low, potentially below 20º. <br/
Quasi-cyclic Generalized LDPC codes with low error floors
No full textIn this paper, a novel methodology for designing structured generalized LDPC (G-LDPC) codes is presented. The proposed design results in quasi-cyclic G-LDPC codes for which efficient encoding is feasible through shift-register-based circuits. The structure imposed on the bipartite graphs, together with the choice of simple component codes, leads to a class of codes suitable for fast iterative decoding. A pragmatic approach to the construction of G-LDPC codes is proposed. The approach is based on the substitution of check nodes in the protograph of a low-density parity-check code with stronger nodes based, for instance, on Hamming codes. Such a design approach, which we call LDPC code doping, leads to low-rate quasi-cyclic G-LDPC codes with excellent performance in both the error floor and waterfall regions on the additive white Gaussian noise channel
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Political Parties and Web 2.0: The Liberal Democrat Perspective
No full textPolitical parties have been criticised for their limited use of interactivity via their Internet presences,
largely it is suggested because they seek to control their online messages. This article will consider
interactivity from the perspective of a political party, the Liberal Democrats, using their Freedom
Bill online campaign as a case study. We suggest that the Liberal Democrats use ‘weak interactivity’
because of internal policymaking concerns, and their belief that as a political party they are
promoting their ideas, not co-creating a new product. Thus we suggest interaction should be closer
to a formal consultation than a face-to-face dialogue
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