一种电台中FPGA的可靠初始化逻辑设计

在机载通信领域,由于飞机体积、重量及功耗等要求,往往需要在一个独立电台设备上实现多种通信模式,同时受限于电台的成本、功耗等因素,通常各种通信模式功能依靠FPGA的动态加载来实现。实际工程中发现,当FPGA动态加载时,由于各版本的加载时间、复位管理、时钟管理、接口时序等不一致,非常容易出现偶发的加载后功能异常,此类问题现象随机,极难定位,很容易耗费大量的人力、物力及时间。为解决上述矛盾,提出一种适合在电台中使用的FPGA初始化逻辑设计,保证不同版本的FPGA加载后能稳定工作,提升电台工作的可靠性与稳定性。实践表明,该方法简单、可靠,具有非常强的工程推广意义。     

一种用于分组数据可靠传输的Ⅱ型混合ARQ方法

本文基于码率匹配截短Turbo码和“码字校验交替重传”方案，提出了一种新的Ⅱ型混合ARQ方法，并将其应用于移动通信系统的分组数据业务中。仿真结果和分析表明，综合系统性能和复杂性两方面考虑，该方法不失为一种实现分组数据可靠传输的最佳解决方案。     

Parity-based loss recovery for reliable multicast transmission

We investigate how forward error correction (FEC) can be combined with automatic repeat request (ARQ) to achieve scalable reliable multicast transmission. We consider the two scenarios where FEC is introduced as a transparent layer underneath a reliable multicast layer that uses ARQ, and where FEC and ARQ are both integrated into a single layer that uses the retransmission of parity data to recover from the loss of original data packets. To evaluate the performance improvements due to FEC, we consider different loss rates and different types of loss behavior (spatially or temporally correlated loss, homogeneous or heterogeneous loss) for up to 10⁶ receivers. Our results show that introducing FEC as a transparent layer below ARQ can improve multicast transmission efficiency and scalability. However, there are substantial additional improvements when FEC and ARQ are integrated     

一种安全数据库体系结构的设计

较为详细地分析了安全数据库实现的模型和技术，重点论述了多级安全数据库中的强制访问控制和基于角色的访问控制模块的实现方案及其关键技术；并在此基础上设计出了一种安全级别至少为Bl的安全数据库体系结构。     

A reliable relay selection scheme for SSK modulation in cooperative communication systems

Space shift keying (SSK) modulation is a scheme in which the indices of active transmit antennas play an essential role in carrying information bits. In SSK modulation, the communication channel acts as modulating unit. Therefore, using the conventional relay selection schemes based on channel coefficients are impossible in cooperative systems using SSK modulation. In this paper, we propose a novel relay selection scheme that is applicable in cooperative systems using SSK modulation. The proposed scheme is based on calculating and measuring the Euclidean distances between received signal and all active or inactive channel coefficients. The proposed relay selection scheme is applied for a cooperative communication system with multiple relay nodes and a direct link between source and destination. The analytical expressions are derived to calculate the average bit error rate over Rayleigh fading channels. The analytical and simulation results show that this relay selection scheme can provide a full cooperative diversity order, for SSK modulation. In addition, we show that this scheme can be used at destination as a signal selection method, to select the best received signal from different paths. The analytical results are validated using Monte Carlo simulation studies.     

Clock recovery circuits with instantaneous locking

Clock recovery circuits based on matched gated oscillators are proposed. Lock is acquired on the first data transition, even with non-return-to-zero line coding and with instantaneous and arbitrarily large phase shifts of the incoming signal. Simulated results of a fully integrated 650 Mbit/s clock recovery circuit designed in an existing 0.9 mu m CMOS technology are also presented.<>     

First low-cost failure recovery for reliable real-time multimediacommunication

Transmission of multimedia data over a packet-switched network typically requires resource reservation to guarantee an acceptable level of performance (e.g., throughput or delay). In this article we address the problem of how to make such real-time communication reliable. First of all, it is essential to bound the duration of service disruption caused by failures to a reasonably small value. Considering the large volume of multimedia data, minimizing the fault-tolerance overhead is also important. Furthermore, as more applications with different dependability requirements share the same network, the level of dependability for a given application should be “customizable”, depending on the criticality of the application. We first survey the existing approaches, and then present our scheme which is developed in accordance with three design goals: fast failure recovery, low fault-tolerance overhead, and per-connection reliability guarantee. Our scheme provides an integrated solution covering such issues as connection establishment, failure detection, runtime failure recovery, and resource reconfiguration     

A design technique for reliable networks under a nonuniform trafficdistribution

Many network-reliability analysis techniques define and compute a variety of reliability measures. Most techniques assume that network connectivity is the only determining factor in network reliability; and merely analyze an existing network structure but do not provide any methodology for reliable design. This paper presents a heuristic design algorithm to enhance the reliability of existing communication networks by modifying their topology. This algorithm improves the reliability of the least reliable node (reliability is the probability that messages transmitted from a given node reach their destination). To use this algorithm on large networks, a reliability analysis method is developed which determines approximate network reliability values in linear-time when an upper bound is placed upon the in-degree of all network nodes. The heuristic network design algorithm uses this approximate reliability analysis technique to place additional links. The goal of this link placement is to improve the reliability of the least-reliable node. The placement of additional links is a function of both the traffic distribution and the connectivity of the network. This process continues until either a desired level of network reliability is achieved or a maximum number of additional links has been added. A unique feature of this design strategy is that it has quadratic time-complexity when the maximum in-degree of all network nodes is limited     

A design space exploration scheme for data-path synthesis

In this paper, we examine the multicriteria optimization involved in scheduling for data-path synthesis (DPS). The criteria we examine are the area cost of the components and schedule time. Scheduling for DPS is a well-known NP-complete problem. We present a method to find nondominated schedules using a combination of restricted search and heuristic scheduling techniques. Our method supports design with architectural constraints such as the total number of functional units, buses, etc. The schedules produced have been taken to completion using GABIND as written by Mandal et al., and the results are promising     

A multiple clocking scheme for low-power RTL design

This paper presents a resource allocation technique to design low-power register-transfer-level datapaths. The basis of this technique is to use a multiple clocking scheme of n nonoverlapping clocks, by dividing the frequency f of a single clock into n cycles, to partition the circuit into n disjoint modules and assign each module to a distinct clock, and to operate each module only during its corresponding duty cycle, thus clocking each module by a frequency f/n to reduce power. However, the overall effective frequency of the circuit remains f, i.e., the single clock frequency. Further power reduction is also obtained by tradeoffs between voltage, power, and delay across multiple clock partitions. Power savings up to 50% of the proposed multiple clocking scheme in comparison to single gated clock designs are also reported     

A forwarding scheme for reliable and energy-efficient data delivery in cluster-based sensor networks

This letter proposes a novel forwarding scheme for reliable and energy-efficient data delivery in the cluster-based sensor networks. While multiple nodes in a cluster receive a packet, only one node among them is elected to send the acknowledgement back and then to broadcast it to the next cluster. With the binary exponential backoff algorithm for the election, the proposed scheme is more reliable and energy-efficient than existing forwarding schemes for the cluster-based sensor networks.     

Timing recovery scheme for CV-CCMA receiver

The authors describe a baud-rate timing recovery scheme for a multiuser technique known as complex valued collaborative coding multiple access (CV-CCMA). This synchronisation scheme is suitable for digital signal processing implementation and integrates efficiently within the overall reception system. The timing function is directly derived from the samples of the received signal and adaptively employs the complex gain coefficients which are estimated by the detection process. The statistical performance of this timing function is derived by simulation for various values of E_b/N₀. It is shown that it has a low variance at the desired sampling instant     

A reliable cooperative spectrum detection scheme in cognitive radio networks

Reliable spectrum detection of the primary user (PU) performs an important role in the cognitive radio network since it’s the foundation of other operations. Spectrum sensing and cognitive signal recognition are two key tasks in the development of cognitive radio (CR) technology in both commercial and military applications. However, when the CR terminals receiving signals have little knowledge about the channel or signal types, these two tasks will become much more difficult. In this paper, we propose a reliable cooperative spectrum detection scheme, which combines the cooperative spectrum sensing with distributed cognitive signal recognition. A novel improved cooperative sensing algorithm is achieved by using a credibility weight factor and the “tug-of-war” rule, which is based on the double threshold detection and Dempster–Shafer theory, to determine whether the PU signals exist. In this scheme, cognitive signal recognition can be used to identify the signal type when the PU signal is present. During the cognitive signal recognition processing, the CR terminals make local classification of the received signals by using Daubechies5 wavelet transform and Fractional Fourier Transform, and send their recognition results to the globe decision making center. A distributed processing uses these cognitive terminals’ local results to make final decisions under the Maximum Likelihood estimation algorithm. Simulation results show that the proposed method can achieve good sensing probability and recognition accuracy under the Additive White Gaussian Noise channel.     

Control plane design for reliable optical networks

The application of an IP-based control plane to optical networks has opened up new opportunities and challenges for network designers. Although much work has been done on standardization of protocols for IP networks, the applicability of these protocols to controlling optical networks and the overall reliability of optical networks needs further investigation. This article provides a detailed discussion of a number of subtle protocol design and implementation issues that were not addressed in early standardization efforts or published papers     

Delay-aware reliable broadcast scheme based on power control for VANETs简

In vehicular Ad-hoc network（VANET）, many multi-hop broadcast schemes are employed to widely propagate the warning messages among vehicles and the key is to dynamically determine the optimal relay vehicle for retransmission. In order to achieve reliable and fast delivery of warning messages, this paper proposes a delay-aware and reliable broadcast protocol（DR-BP） based on transmit power control technique. First, a comprehensive model is derived to evaluate the transmission in vehicle-to-vehicle communications. This model considers the wireless channel fading, transmission delay and retransmissions characters occurring in the physical layer/medium access control（PHY/MAC） layer. Then, a local optimal relay selection mechanism based on the above model is designed. In DR-BP scheme, only the vehicle selected as the optimal relays can forward warning messages and the transmit power is time-varying. Finally, extensive simulations verify the performance of DR-BP under different traffic scenarios. Simulation results show that DR-BP outperforms the traditional slotted 1-persistence（S1P） and flooding scheme in terms of packets delivery ratio and transmission delay.     

不同网络制式下QQ业务性能分析及优化方案

本文对不同网络制式下QQ业务的性能进行分析并提出相应优化方案.QQ类业务具有小数据分组、不连续传输等特征,对移动通信网络的信令面与业务面资源产生了较大的占用与浪费.不同网络制式下,由于资源分配机制不同,QQ业务对网络的影响不同,针对其的优化机制也有所不同,本文分析了2G (GSM)、3G(TD-SCDMA)及B3G (...     

A design concept for reliable mobile radio networks with frequency hopping signaling

The design of a packet radio network must reflect the operational requirements and environmental constraints to which it is subject. In this paper, we outline those features that distinguish the High Frequency (HF) Intra Task Force (ITF) Network from other packet radio networks, and we present a design concept for this network that encompasses organizational structure, waveform design, and channel access. Network survivability is achieved through the use of distributed network control and frequency hopping spread-spectrum signaling. We demonstrate how the execution of the fully distributed Linked Cluster Algorithm can enable a network to reconfigure itself when it is affected by connectivity changes such as those resulting from jamming. Additional resistance against jamming is provided by frequency hopping, which leads naturally to the use of code division mutiple access (CDMA) techniques that permit the simultaneous successful transmission by several users. Distributed algorithms that exploit CDMA properties have been developed to schedule contention-free transmissions for much of the channel access in this network. Contention-based channel access protocols can also be implemented in conjunction with the Linked Cluster network structure. The design concept presented in this paper provides a high degree of survivability and flexibility, to accommodate changing environmental conditions and user demands.     

Protocol design for scalable and reliable group rekeying

We present the design and specification of a protocol for scalable and reliable group rekeying together with performance evaluation results. The protocol is based upon the use of key trees for secure groups and periodic batch rekeying. At the beginning of each rekey interval, the key server sends a rekey message to all users consisting of encrypted new keys (encryptions, in short) carried in a sequence of packets. We present a scheme for identifying keys, encryptions, and users, and a key assignment algorithm that ensures that the encryptions needed by a user are in the same packet. Our protocol provides reliable delivery of new keys to all users eventually. It also attempts to deliver new keys to all users with a high probability by the end of the rekey interval. For each rekey message, the protocol runs in two steps: a multicast step followed by a unicast step. Proactive forward error correction (FEC) multicast is used to reduce delivery latency. Our experiments show that a small FEC block size can be used to reduce encoding time at the server without increasing server bandwidth overhead. Early transition to unicast, after at most two multicast rounds, further reduces the worst-case delivery latency as well as user bandwidth requirement. The key server adaptively adjusts the proactivity factor based upon past feedback information; our experiments show that the number of NACKs after a multicast round can be effectively controlled around a target number. Throughout the protocol design, we strive to minimize processing and bandwidth requirements for both the key server and users.     

A novel reliable and secure communication scheme for cognitive radio networks using concatenated kernel codes

Cognitive radio networks have emerged as a possible solution for the spectrum scarcity problem. Cognitive radio networks involve heterogeneous entities as part of it for facilitating spectrum sharing. Ensuring reliability and security in such scenario is inevitable for the licensed users (primary users) as well as for the unlicensed users (secondary users). To address the challenges of reliable and secure communication for the secondary users, in this paper, a novel reliable and secure communication framework is proposed. A class of group codes called concatenated kernel codes is used to achieve reliability and techniques of fundamental cutset and fundamental circuit to achieve security in terms of authentication of sender. It is shown that the proposed communication framework provides reliability mitigating the continuous interference of primary users and security by defending against the cryptanalytic attacks such as replay attack, related key attack, and man‐in‐the‐middle attacks. The theoretical basis of the proposed framework is validated, and its performance is evaluated through simulations.     

一种实用的DF协作无线传感器网络跨层设计

针对前向译码（DF）协作无线传感器网络的特点和要求,探讨基于分集合并和差错控制两种技术的实用跨层设计方案。首先,研究支持DF中继协议的协作传感器网络在目的节点采用等增益合并（EGC）的检测方案。通过和传统的最大比合并（MRC）方案以及最近提出的协作MRC方案综合比较,说明等增益合并是一个具有良好性能的实用方案。然后,把物理层的EGC和数据链路层的自动请求重传（ARQ）结合起来,再进行系统分析。最后,基于EGC和截断ARQ提出一种实用跨层设计方案。