[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Most of the signal processing that we will study in this course involves local operations on a signal, namely transforming the signal by applying linear combinations of values in the neighborhood of each sample point. You are familiar with such operations from Calculus, namely, taking derivatives and you are also familiar with this from optics namely blurring a signal. We will be looking at sampled signals only. Let's start with a few basic examples. Local difference Suppose we have a 1D image and we take the local difference of intensities, DI(x) = 1 2 (I(x + 1) − I(x − 1)) which give a discrete approximation to a partial derivative. (We compute this for each x in the image.) What is the effect of such a transformation? One key idea is that such a derivative would be useful for marking positions where the intensity changes. Such a change is called an edge. It is important to detect edges in images because they often mark locations at which object properties change. These can include changes in illumination along a surface due to a shadow boundary, or a material (pigment) change, or a change in depth as when one object ends and another begins. The computational problem of finding intensity edges in images is called edge detection. We could look for positions at which DI(x) has a large negative or positive value. Large positive values indicate an edge that goes from low to high intensity, and large negative values indicate an edge that goes from high to low intensity. Example Suppose the image consists of a single (slightly sloped) edge:

http://ieeexplore.ieee.org/iel5/5/31307/01456462.pdf

Linear systems

Device-to-Device (D2D) communication has emerged as a promising technology for optimizing spectral efficiency in future cellular networks. D2D takes advantage of the proximity of communicating devices for efficient utilization of available resources, improving data rates, reducing latency, and increasing system capacity. The research community is actively investigating the D2D paradigm to realize its full potential and enable its smooth integration into the future cellular system architecture. Existing surveys on this paradigm largely focus on interference and resource management. We review recently proposed solutions in over explored and under explored areas in D2D. These solutions include protocols, algorithms, and architectures in D2D. Furthermore, we provide new insights on open issues in these areas. Finally, we discuss potential future research directions.

A Survey of Device-to-Device Communications: Research Issues and Challenges

One of the most engaging challenges for mobile operators today is how to manage the exponential data traffic increase. Mobile data offloading stands out as a promising and low-cost solution to reduce the burden on the cellular network. To make this possible, we need a new hybrid network paradigm that leverages the existence of multiple alternative communication channels. This entails significant modifications in the way data are handled, affecting also the behavior of network protocols. In this paper, we present a comprehensive survey of data offloading techniques in cellular networks and extract the main requirements needed to integrate data offloading capabilities into today's mobile networks. We classify existing strategies into two main categories, according to their requirements in terms of content delivery guarantees: delayed and nondelayed offloading. We overview the technical aspects and discuss the state of the art in each category. Finally, we describe in detail the novel functionalities needed to implement mobile data offloading in the access network, as well as current and future research challenges in the field, with an eye toward the design of hybrid architectures.

/pdf/data-offloading-techniques-in-cellular-networks-a-survey-4iwi5hn095.pdf

Data Offloading Techniques in Cellular Networks: A Survey

Direct communication between two or more devices without the intervention of a base station, known as device-to-device (D2D) communication, is a promising way to improve performance of cellular networks in terms of spectral and energy efficiency. The D2D communication paradigm has been largely exploited in non-cellular technologies such as Bluetooth or Wi-Fi but it has not yet been fully incorporated into existing cellular networks. In this regard, a new proposal focusing on the integration of D2D communication into LTE-A has been recently approved by the 3GPP standardization community as discussed in this paper. In cellular networks, D2D communication introduces several critical issues, such as interference management and decisions on whether devices should communicate directly or not. In this survey, we provide a thorough overview of the state of the art focusing on D2D communication, especially within 3GPP LTE/LTE-A. First, we provide in-depth classification of papers looking at D2D from several perspectives. Then, papers addressing all major problems and areas related to D2D are presented and approaches proposed in the papers are compared according to selected criteria. On the basis of the surveyed papers, we highlight areas not satisfactorily addressed so far and outline major challenges for future work regarding efficient integration of D2D in cellular networks.

In-Band Device-to-Device Communication in OFDMA Cellular Networks: A Survey and Challenges

Modified projection approach for robust adaptive array beamforming

This article first reviews the proximity discovery techniques used in most device-to-device communication systems. The associated issues when applied to a cellular network and the potential solutions are then addressed. We propose a unified discovery design for full, partial, and off-network coverage scenarios. We discuss the advantages and disadvantages of packet and signature-based discovery schemes. We present a signature-based discovery design as a conceptual example for cellular applications. Through this example, we demonstrate that a cellular network can benefit from the information provided by the device discovery that a traditional cellular system lacks so that resources, interference, and connection selection can be more efficiently managed under a unified cellular network centric architecture.

Proximity discovery for device-to-device communications over a cellular network

Zadoff-Chu (ZC) sequences have been used as random access sequences in modern wireless communication systems, replacing the conventional pseudo-random-noise (PN) sequences due to their superior autocorrelation properties. An analytical framework quantifying the ZC sequence's performance and its fundamental limitation as a random access sequencein the presence of frequency offset between the transmitter and the receiver is introduced. We show that a ZC sequence's perfect autocorrelation properties can be severely impaired by the frequency offset thereby limiting the overall performance of the random access signals formed from these sequences. First, we derive the autocorrelation function of these random access sequences as a function of the frequency offset. Next, we introduce the concept of critical frequency offsets and the spectrum associated with a ZC sequence set to characterize the frequency offset properties of the random access signals. Finally, we demonstrate that the frequency offset immunity of a ZC sequence set can be controlled by shaping the spectrum of the ZC sequence set.

Analysis of the Frequency Offset Effect on Random Access Signals

An adaptive digital beamforming technique with compressed sensing (CS) for sparse receiving arrays is proposed. Because of the angle sparseness of arriving signals, CS theory can be adopted to sample receiving signals. Then, receiving signals from absent elements on the antenna aperture can be reconstructed by using CS method. Adaptive digital beamforming algorithms are adopted to form antenna beam, whose main lobe is steered to the desired direction and nulls steered to the directions of interference.

Adaptive beamforming with compressed sensing for sparse receiving array

A single-feed tri-band circularly polarized (CP) annular slot antenna is presented. The antenna structure is composed of two non-concentric annular slots that are fed by an L-shaped series step impedance microstrip line configuration. The proposed antenna is designed to operate at the L1 & L2 bands of the Global Positioning System (GPS) and the frequency band of the Compass Navigation Satellite System (CNSS). The measured results show that the impedance bandwidths are good for all bands. And the radiation patterns with good CP characteristics are obtained at the three resonant frequencies.

Weixing Sheng

Papers

Modified projection approach for robust adaptive array beamforming

Proximity discovery for device-to-device communications over a cellular network

Analysis of the Frequency Offset Effect on Random Access Signals

Adaptive beamforming with compressed sensing for sparse receiving array

Tri-Band Circularly Polarized Annular Slot Antenna for GPS and CNSS Applications