Calculation of Spectral Efficiency for Estimating Spectrum Requirements of IMT‐Advanced in Korean Mobile Communication Environments

In this paper, we analyze the algorithm of the methodology developed by ITU for the calculation of spectrum requirements of IMT‐Advanced. We propose an approach to estimate user density using traffic statistics, and to estimate spectrum efficiencies using carrier‐to‐interference ratio distribution and capacity theory as well as experimental data under Korean mobile communication environments. We calculate the IMT‐Advanced spectrum requirements based on the user density and spectral efficiencies acquired from the new method. In the case of spectral efficiency using higher modulation and coding schemes, the spectrum requirement of IMT‐Advanced is approximately 2700 MHz. When applying a 2×2 multiple‐input multiple‐output (MIMO) antenna system, it is approximately 1500 MHz; when applying a 4×4 MIMO antenna system, it is approximately 1050 MHz. Considering that the development of new technology will increase spectrum efficiency in the future, the spectrum requirement of IMT‐Advanced in the Korean mobile communication environment is expected to be approximately 1 GHz bandwidth.     

校园调频广播系统设计与安装方法

校园调频广播系统作为一种电化教学手段和教学辅助设施,有助于广大学生进行课外听力训练,提高听力水平。对如何构建校园调频广播系统进行了分析,阐述了系统选择、连接和使用等问题。     

圆极化和水平极化天线在调频广播的应用对比分析

本文介绍了水平极化和圆极化两种天线的特点和参数,通过当地发射台安装的两副不同极化天线,在相同环境条件下收测其覆盖场强,将收测的数据进行对比,分析了两副天线的覆盖效果,并据此对调频广播发射天线的更新换代提出建议.     

Energy and spectral efficiency trade‐off for the downlink OFDM‐distributed antenna systems

This paper investigates an energy efficient optimization scheme for the downlink multiuser OFDM‐distributed antenna systems. We adopt a multicriteria optimization method to offer a systematic study on the relationship between spectral efficiency (SE) and energy efficiency (EE). First, we transform the energy efficient optimization problem with high complexity into a simpler downlink multiuser OFDM problem. Then, using the weighted sum method in multicriteria optimization, an optimal energy efficient scheme is presented to allocate the available power to balance the trade‐off between SE and EE efficiently. Simulation results demonstrate that the energy efficient scheme is effective, and there existed a trade‐off between SE and EE in the downlink multiuser OFDM‐distributed antenna systems. Copyright © 2013 John Wiley & Sons, Ltd.     

Application of ANFIS Power Control for Downlink CDMA‐Based LMDS Systems

Rain attenuation and intercell interference are two crucial factors in the performance of broadband wireless access networks such as local multipoint distribution systems (LMDS) operating at frequencies above 20 GHz. Power control can enhance the performance of downlink CDMA‐based LMDS systems by reducing intercell interference under clear sky conditions; however, it may damage system performance under rainy conditions. To ensure robust operation under both clear sky and rainy conditions, we propose a novel power‐control scheme which applies an adaptive neuro‐fuzzy inference system (ANFIS) for downlink CDMA‐based LMDS systems. In the proposed system, the rain rate and the number of users are two inputs of the fuzzy inference system, and output is defined as channel quality, which is applied in the power control scheme to adjust the power control region. Moreover, ITU‐R P.530 is employed to estimate the rain attenuation. The influence of the rain rate and the number of users on the distance‐based power control (DBPC) scheme is included in the simulation model as the training database. Simulation results indicate that the proposed scheme improves the throughput of the DBPC scheme.     

A New Directional Coupler Design with High Directivity for PCS and IMT‐2000

This paper proposes a new design of directional couplers with high directivity for personal communication services (PCS) and International Mobile Telecommunications‐2000 (IMT‐2000). The directional coupler is used to check and verify the power, frequency, and antenna reflection of a signal at transmission stations for mobile communications. The performance requirements of directional couplers are a strong coupling to reduce the effect on the transmitted power and high directivity to suppress the interference of the reflected signals and reduce the errors in communication. So far, various architectures have been proposed to gain high directivity, and there have been many studies used to obtain a strong coupling. However, conventional architectures for high directivity and strong coupling have a directivity of only about 20 dB, and there have been difficulties to achieve the higher directivity of 30 dB suitable for PCS and IMT‐2000. This paper proposes a new architecture of directional couplers based on a grounding composed of strip lines, and compares the test results of this directional coupler with conventional ones. The results show that the proposed directional coupler has a directivity of more than 30 dB and is adequate for PCS and IMT‐2000.     

One‐to‐All Broadcasting of Odd Networks for One‐Port and All‐Port Models

Odd networks were introduced in the context of graph theory. However, their potential as fault‐tolerant multiprocessor networks has been shown. Broadcasting is one of the most important communication primitives used in multiprocessor networks. In this letter, we introduce efficient one‐to‐all broadcasting schemes of odd networks for one‐port and all‐port models. We show the broadcasting time of the former is 2d?2 and that of the latter is d–1. The total time steps taken by the proposed algorithms are optimal.     

OFDM‐Based STBC with Low End‐to‐End Delay for Full‐Duplex Asynchronous Cooperative Systems

We propose a new space‐time block coding (STBC) for asynchronous cooperative systems in full‐duplex mode. The orthogonal frequency division multiplexing (OFDM) transmission technique is used to combat the timing errors from the relay nodes. At the relay nodes, only one OFDM time slot is required to delay for a pair‐wise symbol swap operation. The decoding complexity is lower for this new STBC than for the traditional quasi‐orthogonal STBC. Simulation results show that the proposed scheme achieves excellent performances.     

Comparison of multicast/broadcast services in Long Term Evolution Advanced and IEEE 802.16m networks

This paper performs a comparison of multicast/broadcast services (MBS) support in Long Term Evolution Advanced (LTE‐A) and Worldwide Interoperability for Microwave Access (WiMAX) IEEE 802.16m. Firstly, the main technical features of both standards concerning MBS operation are presented. It is shown that WiMAX offers higher unicast/MBS multiplexing flexibility as it supports both frequency and time multiplexing schemes, whereas LTE‐A only includes time multiplexing. Besides, only WiMAX supports multi‐antenna transmission. Next, the results of two simulation‐based assessments are presented. In the former, it is considered a scenario with all cells transmitting the same MBS service. The effect of inter‐site distance (ISD) on the maximum MBS data rate is evaluated. Results show that WiMAX configurations outperform LTE‐A for small ISD. This is because WiMAX provides a higher number of resources dedicated to data transmission for the same bandwidth. Furthermore, some WiMAX configurations support two spatially multiplexed data streams. With higher ISDs, LTE‐A outperforms single‐stream WiMAX configurations. In the second assessment, a MBSFN area surrounded by interfering cells is considered to compare unicast/MBS multiplexing performance. The higher maximum MBS data rate is achieved in WiMAX with time division multiplexing, which is precisely the only alternative included in LTE‐A. Copyright © 2012 John Wiley & Sons, Ltd.     

Coexistence of OSCR‐Based IR‐UWB System with IEEE 802.11a WLAN

Impulse radio (IR) is a competitive candidate for ultra‐wideband (UWB) systems. In this letter, we evaluated the coexistence of an IR‐UWB system based on an orthogonal sinusoidal correlation receiver (OSCR) with an IEEE 802.11a WLAN through a detailed simulation. The coexistence performance of the two systems is characterized in terms of the receiver's bit‐error rates. Then, some approaches to interference mitigation are discussed.     

Feasibility of Coexistence of Mobile‐Satellite Service and Mobile Service in Cofrequency Bands

Interference scenarios and methodologies between a terrestrial mobile service (MS) system and mobile‐satellite service (MSS) system in a co‐channel environment are established. Taking into account a practical deployment situation for both systems, we perform computational simulation of interference in terms of carrier‐to‐interference ratio (C/I) and interference‐to‐noise ratio (I/N) to evaluate the cofrequency interference from an MS system into an MSS system, and from an MSS system into an MS system, respectively. The methodology and results can be used as a guide when planning the deployment of MSS and MS systems with no unacceptable interference impact between them.     

Broadcasting and Communication Convergent Network Based on MPEG‐21: Design and Implementation of Multimedia Service Framework

In this paper, we present a practical implementation of the MPEG‐21 multimedia framework for broadcasting and communication convergent services. MPEG‐21 standard technology was exploited to build a convergent service framework. Using this framework, a service model and several scenarios have been successfully designed and implemented. In addition, interoperability, which is the main objective of a multimedia framework, especially in a convergent environment consisting of heterogeneous networks and various types of devices, has been addressed in detail. The experimental results show that the implemented test bed provides a next‐generation multimedia service; that is, universal multimedia access (UMA), meeting the requirements of a broadcasting and communication convergent environment.     

The character of power output from utility‐scale photovoltaic systems

Power produced by utility‐scale solar photovoltaic (PV) systems has fluctuations on both short and long time scales. Power spectral density (PSD) analysis provides information on the character of these power fluctuations. Examination of the correlation and step size of the power output between several PV sites within a multi‐site system allows assessment of geographic diversification for addressing intermittency. Both techniques provide insight into the characteristics of firm power and/or demand response required to accommodate large‐scale PV deployment. Copyright © 2007 John Wiley & Sons, Ltd.     

Binary‐offset‐carrier modulation techniques with applications in satellite navigation systems

An important aspect in designing the modulation scheme for various satellite systems, such as the modernized GPS and Galileo, is to obtain good spectral properties and suitable spectral shaping. For example, in the future satellite navigation systems, some of the main goals are: low interference with the existing GPS signals, good root‐mean‐square (RMS) bandwidth, good time resolution (in order to allow the separation between channel paths and to decrease the synchronization errors) etc. Starting from the recently proposed cosine‐ and sine‐BOC modulation families for GPS and Galileo systems, we introduce a new, generalized family, denoted here by double‐BOC (DBOC) modulation. We derive and analyze the properties of the power spectral densities (PSD) and autocorrelation functions (ACF) of the DBOC modulation with various orders, we show its relationship with BPSK, sine‐ and cosine‐BOC modulations, and we illustrate via several examples how to choose optimally the parameters of this new modulation family, according to different optimization criteria. The examples are targeting at applications such as the design of suitable modulations for Galileo open service (OS) and public regulated service (PRS) signals, but the authors believe that the DBOC concept might be useful to other satellite‐based applications, when the available bandwidth is large enough. Copyright © 2006 John Wiley & Sons, Ltd.     

Limiter discriminator detection of narrow‐band duobinary FSK in a land mobile channel

Error rates (BER) for narrow‐band duobinary FM with discriminator detection and integrate and dump (LDI) post‐detection filtering in land mobile channel characterized by fading and Doppler frequency shift are obtained. The fading process is assumed to be much slower than data rate, allowing the fading process to be analysed in a quasistatic manner as it passes through the narrow‐band filter. A simulation model was constructed using the signal processing simulator, and the simulated error rate results are shown to agree well with the calculated error rate results. Copyright © 2004 John Wiley & Sons, Ltd.     

Network planning for Type 1 and Type 1a relay nodes in LTE‐Advanced networks

In this paper, the planning problem of multiple evolved Node Bs (eNBs) and two types of relay nodes is defined base on linear programming. Type 1 relay nodes are placed in the center of eNB, and Type 1a relay nodes are deployed at cell edge. Three algorithms are proposed to investigate the Type 1a relay node placement and communication interference. All algorithms are designed on the basis of graph theory and analyzed in planning case and simulation results. The ultimate goal is to maximize the average throughput of all served users with minimum communication interference. Results showed that the proposed interference coordination algorithm not only provides the lowest construction cost with slightly fewer numbers of served users but also eliminates the communication interference with the highest average throughput. Most importantly, it achieves the best communication quality for next generation mobile networks. Copyright © 2015 John Wiley & Sons, Ltd.     

UbiFOS: A Small Real‐Time Operating System for Embedded Systems

The ubiquitous flexible operating system (UbiFOS) is a real‐time operating system designed for cost‐conscious, low‐power, small to medium‐sized embedded systems such as cellular phones, MP3 players, and wearable computers. It offers efficient real‐time operating system services like multi‐task scheduling, memory management, inter‐task communication and synchronization, and timers while keeping the kernel size to just a few to tens of kilobytes. For flexibility, UbiFOS uses various task scheduling policies such as cyclic time‐slice (round‐robin), priority‐based preemption with round‐robin, priority‐based preemptive, and bitmap. When there are less than 64 tasks, bitmap scheduling is the best policy. The scheduling overhead is under 9 µs on the ARM926EJ processor. UbiFOS also provides the flexibility for user to select from several inter‐task communication techniques according to their applications. We ported UbiFOS on the ARM9‐based DVD player (20 kB), the Calm16‐based MP3 player (under 7 kB), and the ATmega128‐based ubiquitous sensor node (under 6 kB). Also, we adopted the dynamic power management (DPM) scheme. Comparative experimental results show that UbiFOS could save energy up to 30% using DPM.     

Mitigation of the moving radio interferences in the OFDM‐based power line communication channels in China

Under some special environments in China, there exist moving radio radiations with high transmission powers that can degrade the performance of the power line communications systems significantly. Such radiations overlap with the OFDM‐based signals in time and frequency domains, and hence, it is very difficult to mitigate directly if not possible. The paper introduced the fractional Fourier transform trying to deal with such moving radio interferences. When using the fractional Fourier transform to separate signals and noises/interferences, the fractional order plays a key role, but there is no method to obtain its optimal value in the published papers. In the paper, like for the time‐frequency representations, we defined the second moments of the fractional Fourier transform of the signal. The fractional order, corresponding the maximum of the second moments, is the one used to separate the OFDM signals and the moving radio interferences, which is modelled as the Doppler signals in our scheme. The proposed method can mitigate the moving radio interferences significantly by applying the proposed method to the simulated OFDM signals and the measurements data. The results also show that the system's BERs can be improved from 10⁻² to 10⁻⁵ for lower signal‐noise‐rate (SNR), and from 10⁻⁴ to 10⁻⁹ for high SNRs. Copyright © 2014 John Wiley & Sons, Ltd.     

System of Systems Approach to Formal Modeling of CPS for Simulation‐Based Analysis

This paper presents a system‐of‐systems (SoS) approach to the formal modeling of a cyber‐physical system (CPS) for simulation‐based analysis. The approach is based on a convergence technology for modeling and simulation of a highly complex system in which SoS modeling methodology, hybrid systems modeling theory, and simulation interoperation technology are merged. The methodology maps each constituent system of a CPS to a disparate model of either continuous or discrete types. The theory employs two formalisms for modeling of the two model types with formal specification of interfaces between them. Finally, the technology adapts a simulation bus called DEVS BUS whose protocol synchronizes time and exchange messages between subsystems simulation. Benefits of the approach include reusability of simulation models and environments, and simulation‐based analysis of subsystems of a CPS in an inter‐relational manner.