Asynchronous Communication System Research Articles

Space-Time Two Dimensional RAKE Receiver in Cooperative Communications Systems with Interference Cancellation Technique

In this paper, space-time two dimensional RAKE receiver was introduced into the asynchronous cooperative communication systems, and a high-performance RAKE receiving algorithm was proposed. Firstly, the transmitted signal was estimated by traditional space-time RAKE receiver, and then, decision feedback technique was investigated into the new algorithm, where each multipath component in the received signal was composed using the estimated results of the transmitted signal and then cancelled successively from the received signal, so the inter symbol interference in the received signal which was generated by the multipath fading channel was eliminated, and the line of sight (LOS) component in the received signal was obtained. Finally, the LOS component was combined together by the space-time block code combining rule to obtain the spatial diversity gain. Based on that, the iterative decision feedback architecture was further employed, where one stage stands for the process from multipath components reconstitution to space time combination, and the performance of the new scheme can be improved effectively by the multiple decision feedback stages. Computer simulations show that the new algorithm can improve the performance of traditional space-time RAKE dramatically when SNR is higher than 5 dB in asynchronous cooperative communication systems.

Real-Time Control of a Video Game Using Eye Movements and Two Temporal EEG Sensors.

EEG-controlled gaming applications range widely from strictly medical to completely nonmedical applications. Games can provide not only entertainment but also strong motivation for practicing, thereby achieving better control with rehabilitation system. In this paper we present real-time control of video game with eye movements for asynchronous and noninvasive communication system using two temporal EEG sensors. We used wavelets to detect the instance of eye movement and time-series characteristics to distinguish between six classes of eye movement. A control interface was developed to test the proposed algorithm in real-time experiments with opened and closed eyes. Using visual feedback, a mean classification accuracy of 77.3% was obtained for control with six commands. And a mean classification accuracy of 80.2% was obtained using auditory feedback for control with five commands. The algorithm was then applied for controlling direction and speed of character movement in two-dimensional video game. Results showed that the proposed algorithm had an efficient response speed and timing with a bit rate of 30 bits/min, demonstrating its efficacy and robustness in real-time control.

An Interference Cancellation Space-Time RAKE Receiver in Asynchronous Cooperative Communications Systems

Space-time two dimensional RAKE receiver was introduced into asynchronous and cooperative communication system, and a high-performance RAKE receiving algorithm was proposed. In this algorithm, the transmitting signals were estimated coarsely by traditional space-time rake receiver, then each multipath signal was reconstructed using the estimated result as well as the channel impulse response, and then eliminated successively from reception signals, so it can eliminate Inter Symbol Interference of receiver signals which generate by multipath fading, and the line of sight (LOS) component in the received signal was obtained, and finally, the space-time combination was carried out to the LOS component, and the spatial diversity was achieved. This algorithm can effectively reduce the bit error rate of the asynchronous cooperative communication system. Simulation result shows that the new algorithm can improve the performance of traditional space-time RAKE when SNR is higher than 5dB dramatically.

Efficient Space-Time Two Dimensional RAKE Receiver in Asynchronous Cooperative Communications Systems with Full Diversity

A high-performance space-time two dimensional RAKE receiving algorithm was proposed in asynchronous cooperative communication system. the transmitting signals were estimated coarsely by traditional space-time rake receiver, then on the basis of that we introduce feedback technology, each multipath signal of transmitted signals was composed by the decision results, and then every multipath component in the received signal can be obtained by eliminating the composed multipath signals from the received signal. Finally, the multipath components were combined by space-time combination and multipath combination rules accordingly, so spatial as well as multipath diversities were achieved. Simulation results show that the new scheme can reduce the bit error rate dramatically compare with traditional space-time RAKE in asynchronous cooperative communication system.

Low complexity timing estimation and resynchronization for asynchronous bidirectional communications with multiple antenna relay

SummaryIn this paper, we consider an asynchronous bidirectional communication system over flat fading channels in which the two source nodes are not perfectly synchronized. A low complexity pilot aided timing estimation and resynchronization scheme is proposed to combat the fractional asynchronous delay between the two source nodes. In the proposed scheme, cyclic prefixed single carrier block transmission is implemented at the two sources and frequency domain orthogonal pilots are transmitted to the relay simultaneously. After timing and channel estimation at the relay, a fractionally spaced frequency domain equalizer is employed at the relay to resynchronize the received mixed signals. With the proposed resynchronization scheme, the data detection at the two sources is the same as in a perfect synchronized system, because the two asynchronous signals are already resynchronized at the relay node. Simulation results show that the performance gap between the proposed scheme and the perfect synchronized system is within 1 dB when there are four antennas at the relay. Copyright © 2014 John Wiley & Sons, Ltd.

Spectral Efficiency of Asynchronous MC-CDMA With Frequency Offset Over Correlated Fading

Multiple-access interference (MAI) and intercarrier interference (ICI) due to a carrier frequency offset are two major factors that deteriorate the performance of multicarrier code-division multiple access (MC-CDMA) in wireless communications. This paper presents a new mathematical analysis for the spectral efficiency of asynchronous MC-CDMA communication systems over a frequency-selective Rayleigh fading environment. It employs accurate statistical models for MAI and ICI that account for the correlation between adjacent subcarriers to derive a new simple expression. An approximate expression for the spectral efficiency is also provided, which reduces complexity.

Research on Various Algorithms in Asynchronous Network Communication System

This paper discusses an in-depth analysis of various encryption technologies, such as RSA, DES, SHA-1, improves DES algorithm and combines their advantages, then put forward a new communication security model based on various algorithms. Thus increasing the security of asynchronous network communication system.

SPREAD SPECTRUM COMMUNICATION SYSTEM WITH SEQUENCE SYNCHRONIZATION UNIT USING CHAOTIC SYMBOLIC DYNAMICS MODULATION

In this paper, we propose a new asynchronous multiuser communication system based on spread spectrum and chaotic symbolic dynamics modulation. By combining spread spectrum and chaotic modulation, the proposed system provides increased security by reducing the probability of detection while allowing multiuser transmissions. The sequence synchronization of chaos communication system is studied. A time acquisition technique based on serial search is proposed to achieve synchronization. An analysis is carried out to determine the probability of detection, the probability of false alarm and the bit error rate of the system. Simulation results show that the proposed system can achieve sequence synchronization under low signal-to-noise ratios, and also confirm our analytically computed expressions.

Joint CFO and Channel Estimation for Asynchronous Cooperative Communication Systems

This letter addresses the joint maximum likelihood carrier frequency offset (CFO) and channel estimation for asynchronous cooperative communication systems. We first present a space-alternating generalized expectation-maximization (SAGE) based iterative estimator (SAGE-IE). Then a low-complexity approximate SAGE-IE (A-SAGE-IE) is developed. Our proposed algorithms decouple the multi-dimensional optimization problem into many one-dimensional optimization problems where the CFO and channel coefficients of each relay-destination link can be determined separately. Simulations indicate that, even though timing offsets are present, the proposed estimators can asymptotically achieve the Cramer-Rao bround (CRB) for the perfectly timing synchronized case.

An asynchronous communication system based on the hyperchaotic system of 6th-order cellular neural network

This paper proposes a novel asynchronous communication scheme. Based on this scheme, a model using the hyperchaotic system of 6th-order Cellular Neural Network (CNN) is designed. This scheme enhances the security of asynchronous communication compared to the conventional ones. It is noteworthy that the proposed communication scheme does not depend on synchronization, and almost all chaotic systems can be involved in this scheme. Numerical simulations show the effectiveness of this scheme.

The weakest failure detector to implement a register in asynchronous systems with hybrid communication

This paper introduces an asynchronous crash-prone hybrid system model. The system is hybrid in the way the processes can communicate. On the one side, a process can send messages to any other process. On another side, the processes are partitioned into clusters and each cluster has its own read/write shared memory. In addition to the model, a main contribution of the paper concerns the implementation of an atomic register in this system model. More precisely, a new failure detector (denoted MΣ) is introduced and it is shown that, when considering the information on failures needed to implement a register, this failure detector is the weakest. To that end, the paper presents an MΣ-based algorithm that builds a register in the considered hybrid system model and shows that it is possible to extract MΣ from any failure detector-based algorithm that implements a register in this model. The paper also (a) shows that MΣ is strictly weaker than Σ (which is the weakest failure detector to implement a register in a classical message-passing system) and (b) presents a necessary and sufficient condition to implement MΣ in a hybrid asynchronous communication system.

Asynchronous cooperative communication systems: A survey on signal designs

Cooperative communications is a promising technique for future high speed wireless communications. These systems may be formulated as virtual multi-input multi-output (MIMO) systems where spatial/cooperetive diversity is a key advantage. However, different from MIMO systems, one of the major challenges for cooperative communications systems is that the cooperative transmissions in cooperative systems may be neither time nor frequency synchronized, since the transmissions are from multiple cooperative nodes at different locations. The existing signal designs for co-located MIMO systems may not be able to collect the cooperative diversity in cooperative communications systems. This paper gives an overview of recent research efforts on combating the time and frequency asynchronism of the cooperative communication network. We focus on the signal designs (or space-time codings/modulations) to achieve full cooperative diversity, and summarize some of the resent distributed space-timing coding and space-frequency coding techniques to combat timing errors and frequency offsets, and in the meantime to achieve full cooperative diversity, in both one-way and two-way cooperative networks.

Asynchronous anti-noise hyper chaotic secure communication system based on dynamic delay and state variables switching

This Letter designs an asynchronous hyper chaotic secure communication system, which possesses high stability against noise, using dynamic delay and state variables switching to ensure the high security. The relationship between the bit error ratio (BER) and the signal-to-noise ratio (SNR) is analyzed by simulation tests, the results show that the BER can be ensured to reach zero by proportionally adjusting the amplitudes of the state variables and the noise figure. The modules of the transmitter and receiver are implemented, and numerical simulations demonstrate the effectiveness of the system.

HYPERTENSION MANAGEMENT IN URBAN UNDERSERVED PATIENTS USING AN INTERNET COMMUNICATION SYSTEM

Background: Inadequate control of blood pressure (BP) contributes to excess cardiovascular disease (CVD) risk, especially in underserved communities. Patient-centered care (PCC) tools that involve home monitoring of BP and Internet or telephone-based communication with a care provider may improve BP control and lower CVD risk. We compared the effectiveness of an Internet and telephone-based telemedicine communication system (T) to usual care (UC) from a primary care provider (PCP) in managing patients with hypertension. Methods: 242 hypertensive subjects (JNC VII- Stage I and II, 16% white, 80% African American, 4% others, 62% female, age 60 ± 12 years) with systolic blood pressure >140 mmHg from two medical center were randomized to T (50%), or UC (50%). 166 patients completed 6-month followup. T patients reported their weight, BP, steps/day, cigarettes/day, twice weekly via an Internet or IVR (interactive voice response) phone system to our clinical center. Patients randomized to UC alone served as control. Monthly blood pressure summaries were sent to all T subjects and to their primary care providers. Results: All patients had blood pressure above 140 mmHg; 26% had diabetes, 39% - hyperlipidemia, and 19% were smokers. There was no significant difference between T and UC in initial blood pressure, height, weight and waist circumference. After 6-months follow-up, reduction of systolic BP was greater in the T group (-18 ± 18 mmHg) compared to UC (-13 ± 18mmHg) and trended to be significantly different (p=0.067). There were no significant differences between groups when comparing age, sex, BMI, fasting blood glucose, total cholesterol, HDL, and LDL. Conclusions: The results suggest that frequent web or telephone based communications can be effective in improving BP control in patients with Stage I or stage II HTN. This asynchronous, Internet and telephone based communication system can be an important component of a patient centered care program to augment PCP management and strengthen patient to provider relationships in the setting of chronic hypertension.

비동기 협력 통신 시스템에서 낮은 릴레이 복잡도를 갖는 새로운 Alamouti 전송 기법

본 논문에서는 직교 주파수 분할 다중화 기법을 이용하는 비동기 협력 통신 시스템에서 낮은 릴레이 복잡도를 갖는 새로운 Alamouti 시공간 전송 기법을 제안한다. 기존 기법은 릴레이 노드에서의 상수 곱 연산 외에도 추가적인 시간 반전 연산을 필요로 하므로 릴레이 노드에서의 시스템 복잡도가 크다는 문제점을 가지고 있다. 이와 달리 제안한 기법은 소스 노드에서의 간단한 심볼 조합과 릴레이 노드에서의 상수 곱만을 이용하여 목적지 노드에서 Alamouti 부호 구조를 획득함으로써 2차 다이버시티 이득을 달성한다. 모의실험 결과를 통하여 제안한 기법이 2차 다이버시티 이득을 달성하며, 릴레이 노드의 복잡도를 줄이면서도 기존 기법과 동일한 비트오류율 성능을 갖는 것을 확인한다. In this paper, we propose a novel Alamouti space-time transmission scheme for orthogonal frequency division multiplexing (OFDM) based asynchronous cooperative communication systems with low relay complexity. The conventional scheme requires an additional operation likes time-reversal at the relay nodes besides the simple multiplications at the relay nodes, which result in increasing the complexity of relay nodes. Unlike the conventional scheme, exploiting the simple combination of the symbols at the source node and the simple multiplications at the relay nodes, the proposed scheme achieves the second order diversity gain by obtaining the Alamouti code structure at the destination node. Simulation results show that the proposed scheme achieves the second order diversity gain and has the same bit error rate performance as the conventional scheme.

Theoretical performance for asynchronous multi-user chaos-based communication systems on fading channels

In this paper, we present a study of the bit error rate (BER) performance of chaos-based DS-CDMA system over an m-distributed fading channel. In this system, the perfect synchronization between receiver and transmitter is assumed. The transmitted bit energy after spreading by chaotic signal is not considered as constant in order to evaluate with precision the BER for such system. The performance of chaos-based DS-CDMA system is examined first in mono-user case. An approximation of the received bit energy by a known distribution leads to an accurate analytical BER expression. This BER computation approach is generalized for asynchronous multi-user case. The performance of DS-CDMA system using Gold sequence is compared and discussed to chaos-based DS-CDMA system. A perfect match between simulations and analytical BER expressions confirms the exactitude of our approach.

Oblique Strategies for Ambient Journalism

Alfred Hermida recently posited ‘ambient journalism’ as a new framework for para- and professional journalists, who use social networks like Twitter for story sources, and as a news delivery platform. Beginning with this framework, this article explores the following questions: How does Hermida define ‘ambient journalism’ and what is its significance? Are there alternative definitions? What lessons do current platforms provide for the design of future, real-time platforms that ‘ambient journalists’ might use? What lessons does the work of Brian Eno provide–the musician and producer who coined the term ‘ambient music’ over three decades ago? My aim here is to formulate an alternative definition of ambient journalism that emphasises craft, skills acquisition, and the mental models of professional journalists, which are the foundations more generally for journalism practices. Rather than Hermida’s participatory media context I emphasise ‘institutional adaptiveness’: how journalists and newsrooms in media institutions rely on craft and skills, and how emerging platforms can augment these foundations, rather than replace them.

From TV to Twitter: How Ambient News Became Ambient Journalism

Scholars have applied the term "ambient" to journalism to describe the omnipresent nature of news in society through the proliferation of one-way media into public spaces. This approach is based on a one-directional model of mass media where the audience is framed as the receptor of communication. However this paper suggests that we need to reassess the meaning of ambient as applied to news and journalism due to the participatory and interactive characteristics of the networked digital media. The Internet has changed the relationship between journalists and audiences from a one-way, asymmetric model of communication to a more participatory and collective system, where citizens have the ability to participate in the news production process. This paper argues that ambient news has evolved into ambient journalism – an awareness system that offers diverse means to collect, communicate, share and display news and information, from both professional and non-professional sources.

Dynamic Reservation Scheme of Physical Cell Identity for 3GPP LTE Femtocell Systems

A large number of phone calls and data services will take place in indoor environments. In Long Term Evolution (LTE), femtocell, as a home base station for indoor coverage extension and wideband data service, has recently gained significant interests from operators and consumers. Since femtocell is frequently turned on and off by a personal owner, not by a network operator, one of the key issues is that femtocell should be identified autonomously without system information to support handover from macrocell to femtocell. In this paper, we propose a dynamic reservation scheme of Physical Cell Identities (PCI) for 3GPP LTE femtocell systems. There are several reserving types, and each type reserves a different number of PCIs for femtocell. The transition among the types depends on the deployed number of femtocells, or the number of PCI confusion events. Accordingly, flexible use of PCIs can decrease PCI confusion. This reduces searching time for femtocell, and it is helpful for the quick handover from macrocell to femtocell. Simulation results show that our proposed scheme re- duces average delay for identifying detected cells, and increases network capacity within equal delay constraints. The 3rd Generation Partnership Project (3GPP) is work- ing on the standardization of asynchronous communication systems. This technology is being enhanced gradually en- suring higher user data rate, bigger system capacity, and lower cost. The wideband CDMA (WCDMA) system is standardized with 3GPP release 99/4 which is being de- ployed in the world. Release 5 is related to High Speed Downlink Packet Access (HSDPA), and it improves the downlink packet transmission speed theoretically up to 14.4 Mbps. High Speed Uplink Packet Access (HSUPA) is enhanced up to 5.76 Mbps in uplink, and it is standardized with the Release 6. We simply mention both HSDPA and HSUPA as High Speed Packet Access (HSPA). In release 7, High Speed Packet Access Evolution (eHSPA, HSPA+) is standardized. eHSPA is based on the HSPA network with a simple upgrade, and it supports more bandwidth efficiency and lower latency. The maximum data rate is 28.8 Mbps in downlink and 11.5 Mbps in uplink (1). How- ever, users still require further system improvements. The technology is dramatically enhanced in release 8, where the standard of Long Term Evolution (LTE) is currently being established. The main objectives of LTE are higher data rates, lower latency, increased capacity, enhanced coverage, and an optimized system for the packet switching network (2). LTE also considers a femtocell, which is referred to as a home base station for an indoor coverage extension and overall network performance enhancement (3). Recently, LTE-Advanced standard targeting of 1Gbps for low mobil- ity is being discussed in release 9. We look into general features and requirements of fem- tocells. Important issues related to access control are de- scribed, followed by our contributions and organization of the paper.

Integrated Networks: National and International Online Experiences

There is an increasing impression among online geography educators that interaction can be developed based on specific teaching and learning methods. The authors developed a practical research study to investigate this issue. The study was based on advanced graduate courses in geography at Beijing Normal University and Texas State University. International interaction was complemented by online collaboration among the US local group. Both synchronous and asynchronous communication systems were used, which spanned two platforms. Results of this experience indicate that teaching and learning methods must be enhanced by a flexible online learning model and extensive organizational support in order to increase interaction and reach a certain level of cooperation.