OpenRaiser/Intern-Atlas huggingface dataset:
Performance of a Concurrent Link SDMA MAC under Practical PHY Operating Conditions
Venue: arXiv cs.NI 2010
Year: 2010

Space Division Multiple Access (SDMA) based Medium Access Control (MAC) protocols have been proposed to enable concurrent communications and improve link throughput in Multi-Input Multi-Output (MIMO) Ad Hoc networks. For the most part, the works appearing in the literature make idealized and simplifying assumptions about the underlying physical layer as well as some aspects of the link adaptation protocol. The result is that the performance predicted by such works may not necessarily be a good predictor of actual performance in a fully deployed system. In this paper we look to introduce elements into the SDMA MAC concept that would allow us to better predict their performance under realistic operating conditions. Using a generic SDMA-MAC we look at how the network sum throughput changes with the introduction of the following: $(a)$ use of the more practical MMSE algorithm instead of the zero-forcing or SVD based nulling algorithms used for receive beamnulling; $(b)$ impact of channel estimation errors; $(c)$ introduction of link adaptation mechanism specifically designed for concurrent SDMA MACs; $(d)$ incorporation of TX beamforming along with RX beamnulling. Following on the transmission window during which concurrent transmissions are allowed by the MAC, we qualify the impact of each of these four elements in isolation. At the conclusion, the performance of a system that incorporates elements $a-d$ is presented and compared against the baseline system, showing an improvement of up to 5x in the overall network sum throughput.
The Cardinality of an Oracle in Blum-Shub-Smale Computation
Venue: arXiv cs.LO 2010
Year: 2010

We examine the relation of BSS-reducibility on subsets of the real numbers. The question was asked recently (and anonymously) whether it is possible for the halting problem H in BSS-computation to be BSS-reducible to a countable set. Intuitively, it seems that a countable set ought not to contain enough information to decide membership in a reasonably complex (uncountable) set such as H. We confirm this intuition, and prove a more general theorem linking the cardinality of the oracle set to the cardinality, in a local sense, of the set which it computes. We also mention other recent results on BSS-computation and algebraic real numbers.
NP-Logic Systems and Model-Equivalence Reductions
Venue: arXiv cs.LO 2010
Year: 2010

In this paper we investigate the existence of model-equivalence reduction between NP-logic systems which are logic systems with model existence problem in NP. It is shown that among all NP-systems with model checking problem in NP, the existentially quantified propositional logic (\exists PF) is maximal with respect to poly-time model-equivalent reduction. However, \exists PF seems not a maximal NP-system in general because there exits a NP-system with model checking problem D^P-complete.
Computational Complexity of Iterated Maps on the Interval (Extended Abstract)
Venue: arXiv cs.MS 2010
Year: 2010

The exact computation of orbits of discrete dynamical systems on the interval is considered. Therefore, a multiple-precision floating point approach based on error analysis is chosen and a general algorithm is presented. The correctness of the algorithm is shown and the computational complexity is analyzed. As a main result, the computational complexity measure considered here is related to the Ljapunow exponent of the dynamical system under consideration.
Emergence of Complex-Like Cells in a Temporal Product Network with Local Receptive Fields
Venue: arXiv cs.NE 2010
Year: 2010

We introduce a new neural architecture and an unsupervised algorithm for learning invariant representations from temporal sequence of images. The system uses two groups of complex cells whose outputs are combined multiplicatively: one that represents the content of the image, constrained to be constant over several consecutive frames, and one that represents the precise location of features, which is allowed to vary over time but constrained to be sparse. The architecture uses an encoder to extract features, and a decoder to reconstruct the input from the features. The method was applied to patches extracted from consecutive movie frames and produces orientation and frequency selective units analogous to the complex cells in V1. An extension of the method is proposed to train a network composed of units with local receptive field spread over a large image of arbitrary size. A layer of complex cells, subject to sparsity constraints, pool feature units over overlapping local neighborhoods, which causes the feature units to organize themselves into pinwheel patterns of orientation-selective receptive fields, similar to those observed in the mammalian visual cortex. A feed-forward encoder efficiently computes the feature representation of full images.
Centrality Metric for Dynamic Networks
Venue: arXiv cs.CY 2010
Year: 2010

Centrality is an important notion in network analysis and is used to measure the degree to which network structure contributes to the importance of a node in a network. While many different centrality measures exist, most of them apply to static networks. Most networks, on the other hand, are dynamic in nature, evolving over time through the addition or deletion of nodes and edges. A popular approach to analyzing such networks represents them by a static network that aggregates all edges observed over some time period. This approach, however, under or overestimates centrality of some nodes. We address this problem by introducing a novel centrality metric for dynamic network analysis. This metric exploits an intuition that in order for one node in a dynamic network to influence another over some period of time, there must exist a path that connects the source and destination nodes through intermediaries at different times. We demonstrate on an example network that the proposed metric leads to a very different ranking than analysis of an equivalent static network. We use dynamic centrality to study a dynamic citations network and contrast results to those reached by static network analysis.
Spectrum Sharing in Cognitive Radio with Quantized Channel Information
Venue: arXiv cs.IT 2010
Year: 2010

We consider a wideband spectrum sharing system where a secondary user can share a number of orthogonal frequency bands where each band is licensed to an individual primary user. We address the problem of optimum secondary transmit power allocation for its ergodic capacity maximization subject to an average sum (across the bands) transmit power constraint and individual average interference constraints on the primary users. The major contribution of our work lies in considering quantized channel state information (CSI)(for the vector channel space consisting of all secondary-to-secondary and secondary-to-primary channels) at the secondary transmitter. It is assumed that a band manager or a cognitive radio service provider has access to the full CSI information from the secondary and primary receivers and designs (offline) an optimal power codebook based on the statistical information (channel distributions) of the channels and feeds back the index of the codebook to the secondary transmitter for every channel realization in real-time, via a delay-free noiseless limited feedback channel. A modified Generalized Lloyds-type algorithm (GLA) is designed for deriving the optimal power codebook. An approximate quantized power allocation (AQPA) algorithm is also presented, that performs very close to its GLA based counterpart for large number of feedback bits and is significantly faster. We also present an extension of the modified GLA based quantized power codebook design algorithm for the case when the feedback channel is noisy. Numerical studies illustrate that with only 3-4 bits of feedback, the modified GLA based algorithms provide secondary ergodic capacity very close to that achieved by full CSI and with only as little as 4 bits of feedback, AQPA provides a comparable performance, thus making it an attractive choice for practical implementation.
Good Codes From Generalised Algebraic Geometry Codes
Venue: arXiv cs.IT 2010
Year: 2010

Algebraic geometry codes or Goppa codes are defined with places of degree one. In constructing generalised algebraic geometry codes places of higher degree are used. In this paper we present 41 new codes over GF(16) which improve on the best known codes of the same length and rate. The construction method uses places of small degree with a technique originally published over 10 years ago for the construction of generalised algebraic geometry codes.
Performance of RCPC-Encoded V-BLAST MIMO In Nakagami-m Fading Channel
Venue: arXiv cs.NI 2010
Year: 2010

Multiple Input Multiple Output (MIMO) wireless communication link has been theoretically proven to be reliable and capable of achieving high capacity. However, these two advantageous characteristics tend to be addressed separately in many major researches. Researches on various approaches to attain both characteristics in a single MIMO system are still on-going and an established approach is yet to be concluded. To address this problem, in this paper a Vertical Bell Laboratories Layered Space-Time (V-BLAST) MIMO enhanced with Rate-Compatible Convolutional (RCPC) codes with Zero Forcing (ZF) and Minimum Mean Squared Error (MMSE)-based detection is proposed. The analytical BER of the system is presented and numerically analyzed. The system performance is analyzed in Nakagami-m fading channel, which provides accuracy and flexibility in matching the signals statistics compared to other fading models. The complexity which arises in the calculations of the RCPC codes parameters is significantly reduced by using equivalent convolutional codes. Results show that the use of high-rate code allows for bandwidth efficiency and at the same time does not severely degrades the system performance. It is also shown that the MMSE-based system outperforms the conventional ZF-based system especially in the low Eb/N0 region and in severe fading conditions.
Rectangular and Circular Antenna Design on Thick Substrate
Venue: arXiv cs.OH 2010
Year: 2010

Millimeter wave technology being an emerging area is still very undeveloped. A substantial research needs to be done in this area as its applications are numerous. In the present endeavor, a rectangular patch antenna is designed on thick substrate and simulated using SONNET software, also a novel analysis technique is developed for circular patch antenna for millimeter wave frequency. The antenna is designed at 39 GHz on thick substrate and has been analyzed and simulated.The results of the theoretical analysis are in good agreement with the simulated results.
Mutual Coupling Reduction in Two-Dimensional Array of Microstrip Antennas Using Concave Rectangular Patches
Venue: arXiv cs.OH 2010
Year: 2010

Using concave rectangular patches, a new solution to reduce mutual coupling and return loss in two-dimensional array of microstrip antennas is proposed. The effect of width and length concavity on mutual coupling and return loss is studied. Also, the patch parameters as well as the amounts of width and length concavity are optimized using an enhanced genetic algorithm. Simulation results show that the resulting array antenna has low amounts of mutual coupling and return loss.
Novel method for planar microstrip antenna matching impedance
Venue: arXiv cs.OH 2010
Year: 2010

Because all microstrip antennas have to be matched to the standard generator impedance or load, the input impedance matching method for antenna is particularly important. In this paper a new methodology in achieving matching impedance of a planar microstrip antenna for wireless application is described. The method is based on embedding an Interdigital capacitor. The fine results obtained by using a microstrip Interdigital capacitor for matching antenna impedance led to an efficient method to improve array antenna performance. In fact, a substantial saving on the whole surfaces as well as enhancement of the gain, the directivity and the power radiated was achieved.
Mechanism for Learning Object retrieval supporting adaptivity
Venue: arXiv cs.CY 2010
Year: 2010

In todayâs world designing adaptable course material requires new technical knowledge which involves a need for a uniform protocol that allows organizing resources with emphasis on quality and Learning. This can be achieved by bundling the resources in a known and prescribed fashion called Learning objects. Learning Objects are composed of two aspects namely "Learning" and "Object". The Learning aspect of Learning objects refers to Education. Since Education is a process so the primary aim of learning objects tends to be facilitating acquisition, assessment and conversion of content into Learning objects while fostering the assimilation of these Learning objects into learning modules and instruction. The Object part of Learning objects relates to the Digital Electronic format of the resources i.e. to say that it deals with the physical resource that forms the Learning objects. The objects in LOs are analogous to objects used in object-oriented modeling (OOM). The analogy helps visualize how LOs will be packaged, processed and transported across the digital library as well as utilized in course building. OOM concepts such as encapsulation, classification, polymorphism, inheritance and reuse can be borrowed to describe the operations on LOs in the digital library. Thus, the aim of this paper is threefolds. Firstly, to discuss the background of this research and the concept of Learning Objects. Secondly, to provide a framework for adaptive mechanism for the retrieval of Learning Objects and thirdly to highlight the benefits that this new proposed framework shall bring.
Variational Program Inference
Venue: arXiv cs.AI 2010
Year: 2010

We introduce a framework for representing a variety of interesting problems as inference over the execution of probabilistic model programs. We represent a "solution" to such a problem as a guide program which runs alongside the model program and influences the model program's random choices, leading the model program to sample from a different distribution than from its priors. Ideally the guide program influences the model program to sample from the posteriors given the evidence. We show how the KL- divergence between the true posterior distribution and the distribution induced by the guided model program can be efficiently estimated (up to an additive constant) by sampling multiple executions of the guided model program. In addition, we show how to use the guide program as a proposal distribution in importance sampling to statistically prove lower bounds on the probability of the evidence and on the probability of a hypothesis and the evidence. We can use the quotient of these two bounds as an estimate of the conditional probability of the hypothesis given the evidence. We thus turn the inference problem into a heuristic search for better guide programs.
`Q-Feed' - An Effective Solution for the Free-riding Problem in Unstructured P2P Networks
Venue: arXiv cs.NI 2010
Year: 2010

This paper presents a solution for reducing the ill effects of free-riders in decentralised unstructured P2P networks. An autonomous replication scheme is proposed to improve the availability and enhance system performance. Q-learning is widely employed in different situations to improve the accuracy in decision making by each peer. Based on the performance of neighbours of a peer, every neighbour is awarded different levels of ranks. At the same time a low-performing node is allowed to improve its rank in different ways. Simulation results show that Q-learning based free riding control mechanism effectively limits the services received by free-riders and also encourages the low-performing neighbours to improve their position. The popular files are autonomously replicated to nodes possessing required parameters. Due to this improvement of quantity of popular files, free riders are given opportunity to lift their position for active participation in the network for sharing files. Q-feed effectively manages queries from free riders and reduces network traffic significantly
Low Power Shift and Add Multiplier Design
Venue: arXiv cs.AR 2010
Year: 2010

Today every circuit has to face the power consumption issue for both portable device aiming at large battery life and high end circuits avoiding cooling packages and reliability issues that are too complex. It is generally accepted that during logic synthesis power tracks well with area. This means that a larger design will generally consume more power. The multiplier is an important kernel of digital signal processors. Because of the circuit complexity, the power consumption and area are the two important design considerations of the multiplier. In this paper a low power low area architecture for the shift and add multiplier is proposed. For getting the low power low area architecture, the modifications made to the conventional architecture consist of the reduction in switching activities of the major blocks of the multiplier, which includes the reduction in switching activity of the adder and counter. This architecture avoids the shifting of the multiplier register. The simulation result for 8 bit multipliers shows that the proposed low power architecture lowers the total power consumption by 35.25% and area by 52.72 % when compared to the conventional architecture. Also the reduction in power consumption increases with the increase in bit width.
A novel technique for image steganography based on Block-DCT and Huffman Encoding
Venue: arXiv cs.MM 2010
Year: 2010

Image steganography is the art of hiding information into a cover image. This paper presents a novel technique for Image steganography based on Block-DCT, where DCT is used to transform original image (cover image) blocks from spatial domain to frequency domain. Firstly a gray level image of size M x N is divided into no joint 8 x 8 blocks and a two dimensional Discrete Cosine Transform (2-d DCT) is performed on each of the P = MN / 64 blocks. Then Huffman encoding is also performed on the secret messages/images before embedding and each bit of Huffman code of secret message/image is embedded in the frequency domain by altering the least significant bit of each of the DCT coefficients of cover image blocks. The experimental results show that the algorithm has a high capacity and a good invisibility. Moreover PSNR of cover image with stego-image shows the better results in comparison with other existing steganography approaches. Furthermore, satisfactory security is maintained since the secret message/image cannot be extracted without knowing decoding rules and Huffman table.
Full vectoring optimal power allocation in xDSL channels under per-modem power constraints and spectral mask constraints
Venue: arXiv cs.IT 2010
Year: 2010

In xDSL systems, crosstalk can be separated into two categories, namely in-domain crosstalk and out-of-domain crosstalk. In-domain crosstalk is also refered to as self crosstalk. Out-of-domain crosstalk is crosstalk originating from outside the multi-pair system and is also denoted as external noise (alien crosstalk, radio frequency interference,...). While self crosstalk in itself can easily be canceled by a linear detector like the ZF detector, the presence of external noise requires a more advanced processing. Coordination between transmitters and receivers enables the self crosstalk and the external noise to be mitigated using MIMO signal processing, usually by means of a whitening filter and SVD. In this paper, we investigate the problem of finding the optimal power allocation in MIMO xDSL systems in the presence of self crosstalk and external noise. Optimal Tx/Rx structures and power allocation algorithms will be devised under practical limitations from xDSL systems, namely per-modem total power constraints and/or spectral mask constraints, leading to a generalized SVD-based transmission. Simulation results are given for bonded VDSL2 systems with external noise coming from ADSL2+ or VDSL2 disturbing lines, along with a comparison between algorithms with one-sided signal coordination either only at the transmit side or the receive side.
I/O Efficient Algorithms for Matrix Computations
Venue: arXiv cs.DS 2010
Year: 2010

We analyse some QR decomposition algorithms, and show that the I/O complexity of the tile based algorithm is asymptotically the same as that of matrix multiplication. This algorithm, we show, performs the best when the tile size is chosen so that exactly one tile fits in the main memory. We propose a constant factor improvement, as well as a new recursive cache oblivious algorithm with the same asymptotic I/O complexity. We design Hessenberg, tridiagonal, and bidiagonal reductions that use banded intermediate forms, and perform only asymptotically optimal numbers of I/Os; these are the first I/O optimal algorithms for these problems. In particular, we show that known slab based algorithms for two sided reductions all have suboptimal asymptotic I/O performances, even though they have been reported to do better than the traditional algorithms on the basis of empirical evidence. We propose new tile based variants of multishift QR and QZ algorithms that under certain conditions on the number of shifts, have better seek and I/O complexities than all known variants. We show that techniques like rescheduling of computational steps, appropriate choosing of the blocking parameters and incorporating of more matrix-matrix operations, can be used to improve the I/O and seek complexities of matrix computations.
Using Grid Files for a Relational Database Management System
Venue: arXiv cs.DB 2010
Year: 2010

This paper describes our experience with using Grid files as the main storage organization for a relational database management system. We primarily focus on the following two aspects. (i) Strategies for implementing grid files efficiently. (ii) Methods for efficiency evaluating queries posed to a database organized using grid files.
Exploiting the Temporal Logic Hierarchy and the Non-Confluence Property for Efficient LTL Synthesis
Venue: arXiv cs.LO 2010
Year: 2010

The classic approaches to synthesize a reactive system from a linear temporal logic (LTL) specification first translate the given LTL formula to an equivalent omega-automaton and then compute a winning strategy for the corresponding omega-regular game. To this end, the obtained omega-automata have to be (pseudo)-determinized where typically a variant of Safra's determinization procedure is used. In this paper, we show that this determinization step can be significantly improved for tool implementations by replacing Safra's determinization by simpler determinization procedures. In particular, we exploit (1) the temporal logic hierarchy that corresponds to the well-known automata hierarchy consisting of safety, liveness, Buechi, and co-Buechi automata as well as their boolean closures, (2) the non-confluence property of omega-automata that result from certain translations of LTL formulas, and (3) symbolic implementations of determinization procedures for the Rabin-Scott and the Miyano-Hayashi breakpoint construction. In particular, we present convincing experimental results that demonstrate the practical applicability of our new synthesis procedure.