双载频在WCDMA网中的应用

在3G网络部署和扩容过程中,经常使用多载波基站。基于基站的资源架构和多载波基站,可以快速实现3G网络的平滑扩容。因此,多载波基站成为3G移动通信网络扩容的主要实现方式之一。本文介绍了WCDMA中双（多）载频技术在一些场合中的应用和组网策略。     

利用DSP实现多载波调制的研究

介绍了利用DSP（数字信号处理器）实现多载波调制的技术。分析了利用多载波调制提高数据传输速率的原因,并比较了多种多载波调制方法,选择O-QAM（正交复用QAM）方法,讨论了O-QAM的原理和实现以及在调制解调器中的实际应用。研究结果表明利用DSP实现多载波调制技术的原理和实现方法正确,提高了超短波通信中的数据传输速率。     

Rate, Sub-Carrier, and Power Allocations for Multi-Carrier CDMA with LMMSE Multiuser Detection

Multi-carrier code-division-multiple-access (MC-CDMA) is a promising transmission technique for high-speed wireless multimedia communication in frequency-selective fading channels. In this letter, allocations of physical transmission rate, sub-carrier, and power are proposed for a MC-CDMA system that applies multi-code (MC)/variable-spreading-length (VSL) multi-rate access to minimize total transmitted power, where we consider users have different data rate and BER.requirements and LMMSE multiuser detection is used in the receivers. We derive transmission rate capacity and propose a simple admission control criterion that linearly relates the code length, data rate and BER requests of all users. The proposed iterative allocation algorithm jointly allocates the sub-carrier power of each user and solves the sub-carrier allocation problem     

Performance of Multiband Complex-Wavelet-Based MC-CDMA System with Space-Time Coding over Nakagami-m Fading Channels

Space-time coding technique and Multi-carrier CDMA (MC-CDMA) technique have received much interest due to their high frequency spectrum efficiency and high data rate transmission. On the basis of analyzing the two technique principle, utilizing the optimized multiband complex wavelet as multi-carrier basis function, we propose an MC-CDMA system based on multiband complex wavelet and space-time coding for downlink and investigate the system bit error rate (BER) performance over Nakagami-m fading channel. The system has much higher spectrum efficiency and data rate due to no need any cyclic prefix (CP) when compared to the conventional MC-CDMA system. Moreover, the application of space-time coding technique improves the ability against fading channel effectively and perfects the downlink performance further. Simulation results show that the proposed multiband complex-wavelet-based MC-CDMA (MBCW-MC-CDMA) system performs better than conventional MC-CDMA system and real wavelet-packet-based MC-CDMA system due to its superior ability against interferences. Especially, the space-time coded MBCW-MC-CDMA system has superior performance, and it outperforms single antenna MBCW-MC-CDMA and conventional MC-CDMA with space-time coding.     

Comparisons of system architectures for microwave-photonics transmissions at 60 GHz

We report here on different system architectures for a wireless link operating in the 60 GHz range, which has a high potential for use in short range and highly secure high data rate applications. The millimetre wave around 60 GHz is generated by photonic heterodyning or microwave-photonics using radio-over-fibre concept of transmission. Low error transmission using two techniques at data rates up to 4.2 Gb/s is experimentally demonstrated.     

Estimation of system reliability using a "non-constant failurerate" model

One of the most controversial techniques in the field of reliability is reliability-prediction methods based on component constant-failure-rate data for the estimation of system failure rates. This paper investigates a new reliability-estimation method that does not depend upon constant failure rates. Many boards were selected from the Loughborough University field-reliability database, and their reliability was estimated using failure-intensity based methods and then compared with the actual failure intensity observed in the field. The predicted failure-intensity closely agrees with the observed value for the majority of a system operating lifetimes. The general failure intensity method lends itself very easily to system-reliability prediction. It appears to give an estimate of the system-reliability throughout the operating lifetime of the equipment and does not make assumptions, such as constant failure rate, which can be detrimental to the validity of the estimate. The predictions seem, on present evidence, to track the observed behavior well, given the uncertainties that are evident in the field. The failure intensity method should be investigated further to see if it is feasible to estimate the system reliability throughout its lifetime and hence provide a more realistic picture of the way in which electronic systems behave in the field     

一种基于带通RAKE接收机的多载波解调方法

ＣＤＭＡ２０００采用多载波和直接序列扩频两种方式来达到提供宽带数据业务的目的。针对ＣＤＭＡ２０００前向信道的三载波调制方式,提出了一种基于带通ＲＡＫＥ接收机的多载波解调方法。这种方法避开了设计多比特的基带数字滤波器,从而大大降低了实现的复杂度。文章首先分析了三载波的调制结构。根据ＲＡＫＥ接收机的原理,推导出相应的带通ＲＡＫＥ接收机模型并给出解调结构,最后,用ＳＰＷ软件对此模型进行仿真并给出了传真结     

Constraints on the bit rates in direct detection opticalcommunication systems using linear or soliton pulses

The effects of stimulated Raman scattering (SRS) and the self-frequency shift on soliton communication systems are analyzed. These effects impose stringent limitations on the maximum data rates that can be carried in such systems. The limitations arise as soliton amplitude or frequency fluctuations are translated into pulse position jitter after propagation along a fiber. Estimates of the maximum data rates in single-channel and multichannel soliton systems are obtained and are compared with data rates in linear direct detection systems. A single-channel soliton system can, in principle, carry data at a rate of between two and ten times faster than a simple, direct-detection, linear system. In a multichannel system, using data channels at different wavelengths, the advantages of using solitons are reduced     

多载波CDMA的三种方案及其特性比较

多载波扩频码分多址系统是一种消除符号间干扰的有效技术。它结合了OFDM和CDMA的优点,在高速数据传输时,其抗符号间干扰的性能明显优于传统的单载波CDMA系统。本文首先分析了三种多载波CDMA方案的基本原理,然后对它们的系统特性进行了比较。     

Subscriber loop transmission using low operating current light emitting diodes subjected to temperature extremes

A unique edge-emitting LED has been developed that has characteristics particularly attractive for use in loop transmission equipment. At low operating currents of 20-25 mA, sufficient optical power is launched into a Single-mode fiber to transmit data rates typical of the present day loop plant, 1.5-45 Mbit/s. In the system experiments reported here, 45-Mbit/s data was transmitted 12.9 km while operating the LED at a low drive current of 20-mA peak and at temperatures from -20 to +70°C. These experiments and related analyses confirm that the LED offers a reliable, low cost, and easy to use alternative to diode lasers and high drive current LED's in the telephone loop plant.     

A comparison of the implementation and annual operating costs of IDR and TDMA in the intelsat system

The outcome of a preliminary systems cost study which compares the cost of operating INTELSAT intermediate data rate (IDR) and time division multiple access (TDMA) stations under various conditions is reported. The differences in the annual cost of operating the two candidate methods over the range of 1 to 1000 terrestrial channels are derived under the conditions of no CME, DSI only and the use of DCME. For DCME the effect of one, two, three and four destinations per DCME is considered. The results show that while the initial cost of the TDMA equipment is higher than with IDR, the annual cost of operating the systems is dominated by the space segment costs. For this reason the greater bandwidth efficiency, inherent multidestinational capability and ease of capacity expansion of the TDMA system give it a lower annual operating cost, even at fairly moderate earthstation capacities (e.g. for DCME with two destinations TDMA becomes cheaper than IDR for capacities in excess of about 300 channels). There are attributes of both systems which will also influence the network planners' decision. The IDR system is modular in that costs associated with implementation are incurred more gradually than with the TDMA system. Furthermore, IDR is to a great extent an extrapolation of the current FDM/FM/FDMA practice. However, since the equipment costs are small compared to the space segment charges, it may prove advantageous to adopt the lowercost system as soon as possible. In addition, the TDMA system offers significant long-term advantages of low-cost expansion and the ability to reconfigure the system with minimal or no loss of traffic.     

基于FPGA的实时峰均比抑制算法

为了克服多载波传输系统具有较高峰均比（PAPR）的固有缺点,介绍了PAPR的定义和目前国内外几种主要降低PAPR的技术。针对现行的PAPR抑制算法复杂度高,实时性差,改变信号频谱分布的缺点,提出了一种基于现场可编程门阵列的实时PAPR抑制算法实现方法。该方法在对原有的PAPR抑制算法进行改进的基础上,根据等效缩比原理,使用XILINX公司的Virtex-5芯片予以实现。实验结果表明,本方法是实时、有效、可行的。     

Feasibility study for worldwide videotex interworking

Results are presented of a study of the feasibility realizing a real-time information retrieval service operating between different worldwide videotex systems by means of gateway facilities that use conversion of data syntax and processing of the videotex information structure. Two separate evaluations were carried out, both using response time as the performance criterion. One was for communication processes at both of two gateways, and the other was for data syntax conversion at the local host. Both approaches are considered as kernel functions in the gateway system. The results of each evaluation were favorable in the sense that response time for the total system using gateways compared favorably to the response time in direct videotex access over the packet-switched public data network     

Performance analysis of an MC-CDMA broadcasting system under highpower amplifier non-linearities .I. System proposal

Multi-carrier modulation (MCM) schemes have been under developed as an effective way to improve channel capacity utilization under multipath interference and selective fading reception for next generation two-way wireless communication systems. However, in the application of one-way broadcasting there is a great need for a new system that cannot only operate in a multipath environment, but also can reuse scarce spectral resources and employ cost-effective high-power amplifiers. For this research, an MCM system referred to as multi-carrier code division multiple access (MC-CDMA) was developed to characterize the primary broadcasting concern of operating under high power amplifier (HPA) nonlinearities. We cover MC-CDMA background, its application to broadcasting, the expected performance limits, and modeling approach     

Uplink Arrays for the Deep Space Network

Deep-space communication and navigation is faced with two challenges in the future: (1) the potential retirement of the largest antennas of NASA's Deep Space Network and (2) an anticipated need for increasing ground system capacity so as to support higher data rates to and from missions operating at remote locations in the solar system, as well as in anticipation of a larger number of simultaneously flying missions. In the transmitting, or uplink, direction, one approach to increasing the effective transmitted power is to array multiple antennas. This is attractive mainly because it promises a lower construction cost than equivalent (large) single antenna systems. In addition, it has the potential for increasing the reliability of the uplink and reducing maintenance costs. This paper introduces the concept of uplink arraying by examining technological challenges and possible solutions to them. Arraying principles are presented and error sources described. The main challenge is to maintain carrier phase alignment among the antennas, and this must be done by periodic calibration. Presently, two calibration methods are being developed at the Jet Propulsion Laboratory as part of an uplink arraying demonstration effort. These methods are briefly discussed.     

Region-based scalable self-recovery for salient-object images

Self-recovery is a tamper-detection and image recovery methods based on data hiding. It generates two types of data and embeds them into the original image: authentication data for tamper detection and reference data for image recovery. In this paper, a region-based scalable self-recovery (RSS) method is proposed for salient-object images. As the images consist of two main regions, the region of interest (ROI) and the region of non-interest (RONI), the proposed method is aimed at achieving higher reconstruction quality for the ROI. Moreover, tamper tolerability is improved by using scalable recovery. In the RSS method, separate reference data are generated for the ROI and RONI. Initially, two compressed bitstreams at different rates are generated using the embedded zero-block coding source encoder. Subsequently, each bitstream is divided into several parts, which are protected through various redundancy rates, using the Reed-Solomon channel encoder. The proposed method is tested on 10 000 salient-object images from the MSRA database. The results show that the RSS method, compared to related methods, improves reconstruction quality and tamper tolerability by approximately 30% and 15%, respectively.     

A Novel Digital Control Technique for Brushless DC Motor Drives

Brushless DC (BLDC) motor drives are continually gaining popularity in motion control applications. Therefore, it is necessary to have a low cost, but effective BLDC motor speed/torque regulator. This paper introduces a novel concept for digital control of trapezoidal BLDC motors. The digital controller was implemented via two different methods, namely conduction-angle control and current-mode control. Motor operation is allowed only at two operating points or states. Alternating between the two operating points results in an average operating point that produces an average operating speed. The controller design equations are derived from Newton's second law. The novel controller is verified via computer simulations and an experimental demonstration is carried out with the rapid prototyping and real-time interface system dSPACE.     

Conversion of 60‐, 30‐, 10‐, and 5‐Minute Rain Rates to 1‐Minute Rates in Tropical Rain Rate Measurement

In this study, several methods to convert rain rate data for various time intervals to one‐minute rates are compared. High‐resolution tipping bucket precipitation records for seven locations in a tropical region are analyzed and compared using these conversion models. The Segal, Chebil, and Burgueno methods give the smallest average errors below 10% at different integration times.     

Joint synchronization and SNR estimation for turbo codes in AWGN channels

Turbo codes are sensitive to both (timing) synchronization errors and signal-to-noise ratio (SNR) mismatch. Since turbo codes are intended to work in environments with very low SNR, conventional synchronization methods often fail. This paper investigates blind symbol-timing synchronization and SNR estimation based on oversampled data frames. The technique is particularly suitable for low-rate turbo codes operating in additive white Gaussian noise at low SNR and modest data-transfer rates, as in deep space, satellite, fixed wireless, or wireline communications. In accordance with the turbo principle, intermediate decoding results are fed back to the estimator, thereby facilitating decision-directed estimation. The analytical and simulated results show that with three or more samples per symbol and raised cosine-rolloff pulse shaping, performance approaches that of systems with perfect timing and SNR knowledge at the receiver.     

COVID-19 discrimination framework for X-ray images by considering radiomics,selective information,feature ranking,and a novel hybrid classifier

In medical imaging procedures for the detection of coronavirus, apart from medical tests, approval of diagnosis has special significance. Imaging procedures are also useful for detecting the damage caused by COVID-19. Chest X-ray imaging is frequently used to diagnose COVID-19 and different pneumonias. This paper presents a task-specific framework to detect coronavirus in X-ray images. Binary classification of three different labels (healthy, bacterial pneumonia, and COVID-19) was performed on two differentiated data sets in which corona is stated as positive. First-order statistics, gray level co-occurrence matrix, gray level run length matrix, and gray level size zone matrix were analyzed to form fifteen sub-data sets and to ascertain the necessary radiomics. Two normalization methods are compared to make the data meaningful. Furthermore, five feature ranking approaches (Bhattacharyya, entropy, Roc, t-test, and Wilcoxon) are mentioned to provide necessary information to a state-of-the-art classifier based on Gauss-map-based chaotic particle swarm optimization and neural networks. The proposed framework was designed according to the analyses about radiomics, normalization approaches, and filter-based feature ranking methods. In experiments, seven metrics were evaluated to objectively determine the results: accuracy, area under the receiver operating characteristic (ROC) curve, sensitivity, specificity, g-mean, precision, and f-measure. The proposed framework showed promising scores on two X-ray-based data sets, especially with the accuracy and area under the ROC curve rates exceeding 99% for the classification of coronavirus vs. others.