11313417
Correlated MIMO Rayleigh fading systems with transmit channel state information
We analyze the capacity of correlated multiple-input-multiple-output (MIMO) channels when channel state information (CSI) is available at both the transmitter and the receiver. We show that the achievable rate by using simple beamforming can approach this capacity when the MIMO channels are highly correlated. To simplify the coding/decoding and power adaption, we apply truncated channel inversion (TCI) in MIMO correlated channels and evaluate the achievable rates. The results show that in highly correlated MIMO fading channels, beamforming combined with TCI can get close to capacity. This provides a simplified near optimum coding, as beamforming with TCI requires only one code designed for the AWGN channel and one coder/decoder pair.
14744107
Reduced-complexity decoding of LDPC codes
Various log-likelihood-ratio-based belief-propagation (LLR-BP) decoding algorithms and their reduced-complexity derivatives for low-density parity-check (LDPC) codes are presented. Numerically accurate representations of the check-node update computation used in LLR-BP decoding are described. Furthermore, approximate representations of the decoding computations are shown to achieve a reduction in complexity by simplifying the check-node update, or symbol-node update, or both. In particular, two main approaches for simplified check-node updates are presented that are based on the so-called min-sum approximation coupled with either a normalization term or an additive offset term. Density evolution is used to analyze the performance of these decoding algorithms, to determine the optimum values of the key parameters, and to evaluate finite quantization effects. Simulation results show that these reduced-complexity decoding algorithms for LDPC codes achieve a performance very close to that of the BP algorithm. The unified treatment of decoding techniques for LDPC codes presented here provides flexibility in selecting the appropriate scheme from performance, latency, computational-complexity, and memory-requirement perspectives.
214797989
NiagaraCQ: a scalable continuous query system for Internet databases
Continuous queries are persistent queries that allow users to receive new results when they become available. While continuous query systems can transform a passive web into an active environment, they need to be able to support millions of queries due to the scale of the Internet. No existing systems have achieved this level of scalability. NiagaraCQ addresses this problem by grouping continuous queries based on the observation that many web queries share similar structures. Grouped queries can share the common computation, tend to fit in memory and can reduce the I/O cost significantly. Furthermore, grouping on selection predicates can eliminate a large number of unnecessary query invocations. Our grouping technique is distinguished from previous group optimization approaches in the following ways. First, we use an incremental group optimization strategy with dynamic re-grouping. New queries are added to existing query groups, without having to regroup already installed queries. Second, we use a query-split scheme that requires minimal changes to a general-purpose query engine. Third, NiagaraCQ groups both change-based and timer-based queries in a uniform way. To insure that NiagaraCQ is scalable, we have also employed other techniques including incremental evaluation of continuous queries, use of both pull and push models for detecting heterogeneous data source changes, and memory caching. This paper presents the design of NiagaraCQ system and gives some experimental results on the system's performance and scalability.
13034661
A probabilistic approach to fault-tolerant routing algorithm on mesh networks
In this paper, we propose a novel and efficient fault tolerant routing algorithm for mesh networks based on the concept of k-submesh without virtual channels and not sacrifice non-faulty nodes. Our algorithm is distributed and local information based. Due to the fact that our algorithm is designed based on k-submesh structure, we apply probabilistic analysis on the fault tolerance of our routing algorithm. Suppose that each node has an independent failure probability, we derive the probability that our routing algorithm successfully returns a fault-free routing path. For example, we formally prove that as long as the node failure probability is bounded by 0.35%, our routing algorithm succeeds in finding a fault-free routing path with high probability of 99% on mesh networks with 250000 nodes. Our algorithm runs in liner time and simulation results show that the length of the routing path constructed by our algorithm are very close to the optimal length.
8059419
Asymptotic analysis of MIMO wireless systems with spatial correlation at the receiver
With a unified approach, this paper investigates the asymptotic performance or, equivalently, the large-system properties, of various point-to-point systems with antenna-array-based multiple-input multiple-output (MIMO) channels having spatial correlations. Using the replica method originally developed for statistical physics, we provide analytical solutions to the input-output mutual information of MIMO systems: 1) at the transmit side, with arbitrary inputs, and 2) at the receive side, with either the optimum space-time joint decoding or various suboptimum spatial equalizers followed by a bank of temporal decoders. Important physical meanings revealed though the analytical solutions to those more practical combinations, such as how the input-output mutual information is affected by the channel spatial correlations, are highlighted along our derivation. Moreover, we provide a novel waterfilling algorithm to determine the data-rate-maximizing transmit signal covariance matrix when only the channel long-term spatial correlations are available at the transmitter.
14652586
A simple typed intermediate language for object-oriented languages
Traditional class and object encodings are difficult to use in practical type-preserving compilers because of the complexity of the encodings. We propose a simple typed intermediate language for compiling object-oriented languages and prove its soundness. The key ideas are to preserve lightweight notions of classes and objects instead of compiling them away and to separate name-based subclassing from structure-based subtyping. The language can express standard implementation techniques for both dynamic dispatch and runtime type tests. It has decidable type checking even with subtyping between quantified types with different bounds. Because of its simplicity, the language is a more suitable starting point for a practical type-preserving compiler than traditional encoding techniques.
16388639
Cardinality-based inference control in OLAP systems: an information theoretic approach
We address the inference control problem in data cubes with some data known to users through external knowledge. The goal of inference controls is to prevent exact values of sensitive data from being inferred through answers to online analytical processing (OLAP) queries. We present an information theoretic approach for cardinality-based inference control, which simply counts the number of cells that all queries have covered thus far to determine whether a new query should be answered. Compared to previous approaches in sum-only data cubes, our new approach has a more general framework (applies to MIN, MAX and SUM) and is more effective.