26,325 research outputs found
Simple I/O-efficient flow accumulation on grid terrains
The flow accumulation problem for grid terrains takes as input a matrix of
flow directions, that specifies for each cell of the grid to which of its eight
neighbours any incoming water would flow. The problem is to compute, for each
cell c, from how many cells of the terrain water would reach c. We show that
this problem can be solved in O(scan(N)) I/Os for a terrain of N cells. Taking
constant factors in the I/O-efficiency into account, our algorithm may be an
order of magnitude faster than the previously known algorithm that is based on
time-forward processing and needs O(sort(N)) I/Os.Comment: This paper is an exact copy of the paper that appeared in the
abstract collection of the Workshop on Massive Data Algorithms, Aarhus, 200
Engineering Parallel String Sorting
We discuss how string sorting algorithms can be parallelized on modern
multi-core shared memory machines. As a synthesis of the best sequential string
sorting algorithms and successful parallel sorting algorithms for atomic
objects, we first propose string sample sort. The algorithm makes effective use
of the memory hierarchy, uses additional word level parallelism, and largely
avoids branch mispredictions. Then we focus on NUMA architectures, and develop
parallel multiway LCP-merge and -mergesort to reduce the number of random
memory accesses to remote nodes. Additionally, we parallelize variants of
multikey quicksort and radix sort that are also useful in certain situations.
Comprehensive experiments on five current multi-core platforms are then
reported and discussed. The experiments show that our implementations scale
very well on real-world inputs and modern machines.Comment: 46 pages, extension of "Parallel String Sample Sort" arXiv:1305.115
Cache-Oblivious VAT-Algorithms
The VAT-model (virtual address translation model) extends the EM-model
(external memory model) and takes the cost of address translation in virtual
memories into account. In this model, the cost of a single memory access may be
logarithmic in the largest address used. We show that the VAT-cost of
cache-oblivious algorithms is only by a constant factor larger than their
EM-cost; this requires a somewhat more stringent tall cache assumption as for
the EM-model
Wireless Communications in the Era of Big Data
The rapidly growing wave of wireless data service is pushing against the
boundary of our communication network's processing power. The pervasive and
exponentially increasing data traffic present imminent challenges to all the
aspects of the wireless system design, such as spectrum efficiency, computing
capabilities and fronthaul/backhaul link capacity. In this article, we discuss
the challenges and opportunities in the design of scalable wireless systems to
embrace such a "bigdata" era. On one hand, we review the state-of-the-art
networking architectures and signal processing techniques adaptable for
managing the bigdata traffic in wireless networks. On the other hand, instead
of viewing mobile bigdata as a unwanted burden, we introduce methods to
capitalize from the vast data traffic, for building a bigdata-aware wireless
network with better wireless service quality and new mobile applications. We
highlight several promising future research directions for wireless
communications in the mobile bigdata era.Comment: This article is accepted and to appear in IEEE Communications
Magazin
- …