18739199
Block spreading for MUI/ISI-resilient generalized multi-carrier CDMA with multirate capabilities
The potential increase in capacity along with the need to provide multimedia services and cope with multiuser interference (MUI) and intersymbol interference (ISI) arising due to wireless multipath propagation, motivate well multirate wideband code-division multiple-access (CDMA) systems. This paper develops an all-digital block-spread filterbank framework capable of encompassing single- or multi-rate transceivers for asynchronous or quasi-synchronous CDMA transmissions through multipath channels. Thanks to symbol blocking and through appropriate design of user codes, the resulting generalized multi-carrier (GMC) CDMA system guarantees symbol recovery irrespective of the (possibly unknown) FIR multipath channels in both downlink and uplink setups with low complexity FIR receivers. Simulations corroborate that the novel GMC-CDMA system outperforms existing multirate alternatives in the presence of asynchronism and multipath.
13893124
Lifetime Maximization of Sensor Networks Under Connectivity and k-Coverage Constraints
In this paper, we study the fundamental limits of a wireless sensor network's lifetime under connectivity and k-coverage constraints. We consider a wireless sensor network with n sensors deployed independently and uniformly in a square field of unit area. Each sensor is active with probability p, independently from others, and each active sensor can sense a disc area with radius rs. Moreover, considering the inherent irregularity of a sensor's sensing range caused by time-varying environments, we model the sensing radius rs as a random variable with mean r0 and variance r$_{\rm 0}^{\rm 2}$σ$_{s}^{\rm 2}$. Two active sensors can communicate with each other if and only if the distance between them is smaller than or equal to the communication radius rc. 
 
The key contributions of this paper are: (1) we introduce a new definition of a wireless sensor network's lifetime from a novel probabilistic perspective, called ω-lifetime (0 ≤ ω ≤ 1). It is defined as the expectation of the time interval during which the probability of guaranteeing connectivity and k-coverage simultaneously is at least ω; and (2) based on the analysis results, we propose a near-optimal scheduling algorithm, called PIS (Pre-planned Independent Sleeping), to achieve the network's maximum ω-lifetime, which is validated by simulation results, and present a possible implementation of the PIS scheme in the distributed manner.
47404061
Diversity and Multiplexing Tradeoff in General Fading Channels
The optimal tradeoff between diversity gain and multiplexing gain for multiple-inputmultiple-output (MIMO) channels has been studied recently under the independent and identically distributed (i.i.d.) Rayleigh-fading assumption. In this correspondence, this result is extended and the optimal tradeoff performance is derived for generalized fading channel conditions, including different fading types, nonidentical fading distributions, spatial correlation, and nonzero channel means. Our results include many known models as special cases and shed light on the effects of different channel parameters on the optimal tradeoff performance
750827
Outage mutual information of space-time MIMO channels
We derive analytical expressions for the probability density function (pdf) of the random mutual information between transmitted and received vector signals of a random space-time independent and identically distributed (i.i.d.) multiple-input multiple-output (MIMO) channel, assuming that the transmitted signals from the multiple antennas are Gaussian i.i.d.. We show that this pdf can be well approximated by a Gaussian distribution, and such a Gaussian approximation is based on expressions for the given pdfs mean and variance that we derive. We prove that at high signal-to-noise ratio (SNR), every factor of 2 increase in SNR leads to an increase in outage rate in the amount of min(M,N) bits, where M and N denote the number of transmit and receive antennas, respectively. A simple expression for the moment generating function (MGF) of the mutual information pdf is also provided, based on which we establish normality of the pdf, when both M and N are large, and the SNR is large.
7391513
Asymptotic performance of hybrid-selection/maximal-ratio combining over fading channels
In this letter, we study the asymptotic performance of hybrid-selection/maximal-ratio combining (HS/MRC) and postdetection HS/equal-gain combining (HS/EGC) over generalized fading channels for large average signal-to-noise ratios (ASNRs). By evaluating the asymptotic moment generating function of the HS/MRC output SNR at high ASNR, we derive the diversity and coding gains for HS/MRC for a large class of modulation formats and versatile fading conditions, including different types of fading channels and nonidentical SNR statistics across diversity branches. Our analytical results reveal that the diversity gains of HS/MRC and HS/EGC are equivalent to that of MRC, and the difference in the coding gains for different modulation formats is manifested in terms of a modulation factor defined in this letter. Some new analytical results about effects of the number of combined branches for HS/MRC and noncoherent combining loss of HS/EGC are also provided.
14892821
A Novel Real-Time MAC Protocol Exploiting Spatial and Temporal Channel Diversity in Wireless Industrial Networks
Wireless technology is increasingly finding its way into industrial communication because of the tremendous advantages it is capable of offering. However, the high bit error rate characteristics of wireless channel due to conditions like attenuation, noise, channel fading and interference seriously impact the timeliness and guarantee that need to be provided for real-time traffic. Existing wired protocols including the popular PROFIBUS perform unfavorably when extended or adapted to the wireless context. Other wireless protocols proposed either do not adapt well to erroneous channel conditions or do not provide real-time guarantees. In this paper, we present a novel real-time MAC (Medium Access Control) protocol that is specifically tailored to the message characteristics and requirements of the industrial environments. The protocol exploits both the spatial and temporal diversity of the wireless channel to effectively schedule real-time messages in the presence of bursty channel error conditions. Simulation results show that the proposed protocol achieves much better loss rate compared to baseline protocols under bursty channel conditions.
9720590
Using the compiler to improve cache replacement decisions
Memory performance is increasingly determining microprocessor performance and technology trends are exacerbating this problem. Most architectures use set-associative caches with LRU replacement policies to combine fast access with relatively low miss rates. To improve replacement decisions in set-associative caches, we develop a new set of compiler algorithms that predict which data will and will not be reused and provide these hints to the architecture. We prove that the hints either match or improve hit rates over LRU. We describe a practical one-bit cache-line tag implementation of our algorithm, called evict-me. On a cache replacement, the architecture will replace a line for which the evict-me bit is set, or if none is set, it will use the LRU bits. We implement our compiler analysis and its output in the Scale compiler. On a variety of scientific programs, using the evict-me algorithm in both the level 1 and 2 caches improves simulated cycle times by up to 34% over the LRU policy by increasing hit rates. In addition, a combination of simple hardware prefetching and evict-me works together to further improve performance.
12482658
On circulant chromatic number and circulant chromatic function
Abstract A new concept of circulant chromatic function of a graph is introduced to generalize the concept of chromatic polynomial of a graph. This is similar to the generalization from the concept of chromatic number to the concept of circulant chromatic number. We provide circulant chromatic functions for a few classes of graphs. We consider circulant chromatic functions on the graphs obtained by elementary operations on given graphs, and the relationship between the circulant chromatic number of a graph and that of its complement. We also investigate some sufficient conditions for the circulant chromatic number and the chromatic number of a graph to be equal to each other.
27067527
A faster method for modeling virtual colony
A virtual colony composed by vivid personal characters with different facial texture and body size, will strongly enhance the reality of the whole virtual environment. This paper describes a fast, economic but realistic method for modeling virtual colony. The system has two major components: photographs based human model reconstruction and anthropometry based automatic human model edit, both of them were advanced to achieve more practical and realistic purpose. To demonstrate the power of this approach, the method was applied to generate some virtual colonies.
18979975
Integrated MicroPhotonic wideband RF interference mitigation filter
MicroPhotonic broadband RF signal processors utilize true-time-delay methods to perform processing functions that cannot be achieved by conventional electronic methods. In addition to their small physical size and immunity to EMI, Photonic signal processors offer the possibility of delaying broadband RF signals with almost no loss. In this paper, we present a novel MicroPhotonic structure that integrates a photoreceiver array, a Vertical Cavity Surface Emitting Laser (VCSEL) array, and a multi-cavity optical substrate to realize a low-cost adaptive wideband RF interference mitigation filter. Results show that for a 64-cavity MicroPhotonic structure, high-resolution, tunable interference mitigation filter with a shape factor as low as 2 and passband ripples less than 0.25 dB can be realised.
26353125
On the better protection of short-frame turbo codes
Protecting short data frames by turbo coding is a challenging task because of the small interleaver size and the need for transmission efficiency. In this letter, turbo-decoding-metrics aided short cyclic redundancy check codes are applied to novel tailbiting encoded trellis codes with a twofold purpose: to stop the iterative decoding processes to achieve low-power design and to reduce fractional coding-rate loss. Significant coding gains can be achieved by actually increasing the transmission rate with a negligible increase in power consumption. Performance improvement is demonstrated over additive white Gaussian noise channels. The savings is up to 21.4% for the transmission throughput and 21.5% for the energy consumption of the turbo decoder when frame size 49 is used.