Making transmission schedules immune to topology changes inmulti-hop packet radio networks

Transmissions scheduling is a key design problem in packet radio networks, relevant to TDMA and CDMA systems. A large number of topology-dependent scheduling algorithms are available, in which changes of topology inevitably require recomputation of transmission schedules. The need for constant adaptation of schedules to mobile topologies entails significant, sometime insurmountable, problems. These are the protocol overhead due to schedule recomputation, performance penalty due to suspension of transmissions during schedule reorganization, exchange of control message and new schedule broadcast. Furthermore, if topology changes faster than the rate at which new schedules can be recomputed and distributed, the network can suffer a catastrophic failure. The authors propose a robust scheduling protocol which is unique in providing a topology transparent solution to scheduled access in multi-hop mobile radio networks. The proposed solution adds the main advantages of random access protocols to scheduled access. Similarly to random access it is robust in the presence of mobile nodes. Unlike random access, however, it does not suffer from inherent instability, and performance deterioration due to packet collisions. Unlike current scheduled access protocols, the transmission schedules of the proposed solution are independent of topology changes, and channel access is inherently fair and traffic adaptive     

Application layer QoS optimization for multimedia transmission over cognitive radio networks

In cognitive radio (CR) networks, the perceived reduction of application layer quality of service (QoS), such as multimedia distortion, by secondary users may impede the success of CR technologies. Most previous work in CR networks ignores application layer QoS. In this paper we take an integrated design approach to jointly optimize multimedia intra refreshing rate, an application layer parameter, together with access strategy, and spectrum sensing for multimedia transmission in a CR system with time varying wireless channels. Primary network usage and channel gain are modeled as a finite state Markov process. With channel sensing and channel state information errors, the system state cannot be directly observed. We formulate the QoS optimization problem as a partially observable Markov decision process (POMDP). A low complexity dynamic programming framework is presented to obtain the optimal policy. Simulation results show the effectiveness of the proposed scheme.     

Access probability optimization for streaming media transmission in heterogeneous cellular networks

FemtoCaching technology, aiming at maximizing the access probability of streaming media transmission in heterogeneous cellular networks, is investigated in this paper. Firstly, five kinds of streaming media deployment schemes are proposed based on the network topology and the relationship between users and streaming media. Secondly, a matching algorithm for adaptive streaming media deployment is proposed, where the FemtoCaching can be adjusted dynamically. Thirdly, a joint problem is formulated combined with the channel assignment, the power allocation, and the caching deployment. To address this problem, we propose a joint optimization algorithm combining matching algorithm and genetic algorithm to maximize the access probability of streaming media transmission. Simulation experiments demonstrate that: (1) the average access probability of all users accessing streaming media in the network based on the proposed algorithm compared with recent works can be greatly improved, and (2) the performance increases with increasing the number of channels and the storage capacity of micro base stations, but decreases with increasing the number of users.

     

Fast code-rate optimization for robust image transmission over lossy packet networks

In this paper, we propose an efficient method for the allocation of Reed-Solomon codes to source symbols, for unequal loss protection. The proposed formulation recasts the multivariate optimization problem into a univariate one, dramatically reducing the computational complexity. Results are shown for image transmission over lossy packet networks, employing the JPEG2000 and SPIHT encoders. The proposed algorithm exhibits performance equivalent to previous methods, while providing a significant complexity reduction.     

Optimal WDM schedules for optical star networks

We consider single-hop wavelength-division multiplexed networks in which the transmitters take a nonzero amount of time, called tuning latency, to tune from one wavelength to another. For such networks, we show that, under certain conditions on the traffic matrix, there exist polynomial-time algorithms that produce the optimal schedule. Further, the tuning latency is masked in the length of the optimal schedule. Using Chernoff-Hoeffding bounds, we show that the condition on the traffic matrix is satisfied with high probability when the wavelength reuse factor is large, i.e., the number of nodes is large compared to the number of wavelengths. Simulation results show the dramatic improvement in the performance of the network using our algorithm as compared with other heuristics     

A distributed cooperative relaying optimization scheme for secondary transmission in Cognitive Radio networks

In Cognitive Radio (CR) networks, cooperative communication has been recently regarded as a key technology for improving the spectral utilization efficiency and ensuring the Quality of Service (QoS) for Primary Users (PUs). In this paper, we propose a distributed joint relay selection and power allocation scheme for cooperative secondary transmission, taking both Instantaneous Channel State Information (I-CSI) and residual energy into consideration, where secondary source and destination may have different available spectrum. Specifically, we formulate the cognitive relay network as a restless bandit system, where the channel and energy state transition is characterized by the finite-state Markov chain. The proposed policy has indexability property that dramatically reduces the compu-tation and implementation complexity. Analytical and simulation results demonstrate that our pro-posed scheme can efficiently enhance overall system reward, while guaranteeing a good tradeoff between achievable date rate and average network lifetime.     

Analysis and optimization of adaptive multicopy transmission ARQprotocols for time-varying channels

This paper outlines an efficient method to concurrently optimize a multiplicity of design variables for continuous selective-repeat (SR) and go-back-N (GBN) automatic repeat request (ARQ) strategies, both in noiseless and noisy feedback channels. For these ARQ protocols, we adapt either the number of identical message blocks sent in each transmission (in the case of GBN scheme) or the number of copies of a block retransmitted to handle a NACKed codeword (for the SR protocol) dynamically to the estimated channel condition. The channel state information is obtained by counting the contiguous acknowledgment (ACK or NACK) messages. Exploiting the asymptotic properties of the steady state probability expressions, we show analytically that the optimum solution indeed lies in the infinite space. Subsequently, a simple expression to estimate the suboptimal design parameters is suggested. Our approach of minimizing the mean-square error function yields to a quantitative study of the appropriateness of the selected parameters. Exact analytical expressions that allows us to compute the throughput crossover probability between any two arbitrary multicopy transmission modes are derived. The results provide fundamental insights into how these key parameters interact and determine the system performance     

PLC-RF无线传输网络中的能效最优设计方法

针对电力线通信（PLC）和射频（RF）无线通信混合传输的室内通信场景,提出了一种基于角度信息的信道状态信息（AI-CSI）的能效优先传输方案。首先,Wi-Fi无线网络和PLC网络分别作为主网络和次级网络,并且采用认知无线电技术来提高频谱效率的情况下,建立次级网络总能效最大化为目标函数的优化问题。其次,为了求解该问题,通过基于AI-CSI的迫零波束成形方法,获得波束成形权矢量,并进一步提出Dinkelbach与拉格朗日乘子法相结合的优化方法,进行最优的功率分配。最后,计算机仿真结果不仅验证了所提方案的有效性和优越性,而且分析了中继天线数和用户个数等典型参数对系统能效带来的影响,从而为实际系统设计提供了参考和依据。     

Throughput optimization using simultaneous sensing and transmission in energy harvesting cognitive radio networks

A three‐dimensional continuous‐time Markov model is proposed for an energy harvesting cognitive radio system, where each secondary user (SU) harvests energy from the ambient environment and attempts to transmit data packets on spectrum holes in an infinite queuing buffer. Unlike most previous works, the SU can perform spectrum sensing, data transmission, and energy harvesting simultaneously. We determine active probability of the SU transmitter, where the average energy consumption for both spectrum sensing and data transmission should not exceed the amount of harvested energy. Then, we formulate achievable throughput of secondary network as a convex optimization problem under average transmit and interference energy constraints. The optimal pair of controlled energy harvesting rate and data packet rate is derived for proposed model. Results indicate that no trade‐off is available among harvesting, sensing/receiving, and transmitting. The SU capability for self‐interference cancelation affects the maximum throughput. We develop this work under hybrid channels including overlay and underlay cases and propose a hybrid solution to achieve the maximum throughput. Simulation results verify that our proposed strategy outperforms the efficiency of the secondary network compared to the previous works.     

传感信号在接入网中传输的技术分析

文章提出了光纤通信网与传感网融合的设想,即利用已有光纤接入网的通信信道,让传感网络发出的传感信号在光纤接入网中传输.首先分析了这种设想的可行性,然后提出了按固定帧复用的方式对传感信号和通信信号进行耦合,并根据已有光纤接入网的结构建立了该系统的网络基本结构,重点分析了传感信号与通信信号复用时的时隙及带宽分配问题.     

Digital video transmission for broadband networks

The information society to come is characterized by a large information flow in the integrated broadband network. Today it is the distribution of TV programmes that requires high transmission capacity. This leaves the cable operator with a problem. How should the CATV network of today be constructed? It must fulfil the need for distribution now and it must be prepared for new services to come. Some aspects of the above problem are discussed in this paper. It is emphasized that digital techniques as well as optical fibre transmission should be included in a modern cable network. The Danish DOCAT network concept is presented as one way to accomplish this. DOCAT combines optical fibre transmission in the trunk network with conventional coaxial techniques in the subscriber network.     

Analysis and optimization of duty-cycle in preamble-based random access networks

Duty-cycling has been proposed as an effective mechanism for reducing the energy consumption in wireless sensor networks (WSNs). Asynchronous duty-cycle protocols where the receiver wakes up periodically to check whether there is a transmission and the sender transmits preambles to check if the receiver is awake are widely used in WSNs due to the elimination of complex control mechanisms for topology discovery and synchronization. However, the intrinsic simplicity of the asynchronous mechanism has the drawback of smaller energy saving potential that requires the optimization of the duty cycle parameters. In this paper, we propose a novel method for the optimization of the duty-cycle parameters in preamble-based random access networks based on the accurate modeling of delay, reliability and energy consumption as a function of listen time, sleep time, traffic rate and medium access control (MAC) protocol parameters. The challenges for modeling are the random access MAC and the sleep policy of the receivers, which make it impossible to determine the exact time of data packet transmissions, and thus difficult to investigate the performance indicators given by the delay, reliability and energy consumption to successfully receive packets. An analysis of these indicators is developed as a function of the relevant parameters of the network and it is used in the minimization of the energy consumption subject to delay and reliability requirements. The optimization provides significant reduction of the energy consumption compared to the previously proposed protocols in the literature.     

Design of transmission and multiplexing systems for broadbandpacket networks

Dynamic time-division multiplexing (DTDM) is a flexible network transport technique capable of handling both continuous and bursty traffic effectively. By using three different multiplexing architectures in the network, DTDM permits graceful evolution of the existing circuit switching network into a flexible broadband packet communications network supporting integrated voice, data, and video traffic. The first multiplexing stage uses a packet assembler to multiplex different broadband services into a common DTDM-format serial bit stream. The second multiplexing stage uses a statistical packet multiplexer to concentrate network traffic for more efficient use of transmission facilities. The third multiplexing stage uses a synchronous time-division multiplexer for high-speed point-to-point transparent transmission. The multiplexer uses a simple tributary synchronization scheme based on positive and negative block justification, which combines the concept of controlled-slip and bit-stuffing techniques while maintaining information integrity. A generic CMOS LSI chip has been designed for use in the three-stage multiplexing system     

Analysis and optimization of a cross-layer adaptation mechanism for real-time applications in wireless networks

The theoretical analysis of a cross-layer mechanism for improving the quality of service of real-time applications in wireless networks is presented. The mechanism coordinates adaptations of the modulation order at the Physical layer and the media encoding mode at the Application layer, to improve packet loss rate, throughput and mean delay. With the use of Continuous Flow Modeling, the system is considered as a “fluid” queue with inflow and outflow rates representing its traffic generation and service rates, respectively. Each data source is modeled as a Markov chain, from the steady-state of which the optimal adaptation thresholds of the cross-layer mechanism are derived. Extensive performance evaluation results show that the optimized operation of the mechanism attains a significant performance improvement compared to both the sub-optimal case, and a legacy system, which adjusts the modulation order and encoding mode separately and independently of each other.     

GPON-based transmission hierarchy for metro ring networks

Nowadays, almost all of metro network operators face the challenge that how to give a uniform support to multiple client networks, and meanwhile increase traffic's transmission efficiency. In an attempt to address this problem, here we first propose a gigabit passive optical network (GPON) based transmission hierarchy (GTH) for metro networks, by modifying the frame structures and application scenarios of traditional GPON technology. Then we study the GTH technology by analyzing the network operating principles and dynamic bandwidth allocation mechanisms. In order to evaluate GTH's performance, we build a simulation testbed for metro ring networks, and compare GTH with multi-service transport platform (MSTP) and technologies of packet transport network (PTN). Simulation results show that for transmission efficiency, GTH outperforms MSTP and is comparable to PTN. Furthermore, each time point of network expansion in GTH networks is further than it is in MSTP and PTN networks.     

Iterative transmitter and receiver optimization for CDMA networks

Optimization of the capacity of a single-cell code-division multiple-access (CDMA) system, both from the perspective of the maximum number of users that can be served at a required quality of service level and from the information theoretic perspective, has been recently shown to be achieved by the same joint transmit and receive strategies. We propose an alternating minimization based iterative algorithm that updates the transmitters and the corresponding receivers of the users. The algorithm is suitable for online implementation, and the objective function is suitable for extension to multicell networks, both of which are in contrast with the previously proposed algorithms. We show that the algorithm is provably convergent to the optimum signature sequences and the corresponding receivers.     

光纤传输网脆弱性分析与对策研究

光纤传输网具有独特的优势,但也有特殊的脆弱性.随着光纤通信技术的快速发展和广泛应用,光纤传输网的安全性显得越来越重要.文章按照分层的观点,介绍了光纤传输网的安全分层结构,分析了光纤传输网不同层面的脆弱性和所受攻击的类型及方法,并针对各层可能受到的安全威胁, 研究了相关的安全对策.     

Cooperative and opportunistic transmission for wireless ad hoc networks

Moving toward 4G, wireless ad hoc networks receive growing interest due to users' provisioning of mobility, usability of services, and seamless communications. In ad hoc networks fading environments provide the opportunity to exploit variations in channel conditions, and transmit to the user with the currently "best" channel. In this article two types of opportunistic transmission, which leverage time diversity and multi-user diversity, respectively, are studied. Considering the co-channel interference and lack of a central controller in ad hoc networks, the "cooperative and opportunistic transmission" concept is promoted. For opportunistic transmission that exploits time diversity, it is observed that the inequality in channel contention due to the hidden terminal phenomenon tends to result in energy inefficiency. Under this design philosophy, we propose a distributed cooperative rate adaptation (CRA) scheme to reduce overall system power consumption. Taking advantage of the time-varying channel among different users/receivers and being aware of the potential contention among neighboring transmissions, we propose a QoS-aware cooperative and opportunistic scheduling (COS) scheme to improve system performance while satisfying QoS requirements of individual flows. Simulation results show that by leveraging node cooperation, our proposed schemes, CRA and COS, achieve higher network throughput and provide better QoS support than existing work     

ADV-MAC: Analysis and optimization of energy efficiency through data advertisements for wireless sensor networks

Several Medium Access Control (MAC) protocols have been proposed for wireless sensor networks with the objective of minimizing energy consumption. For example, Sensor-MAC (S-MAC) was proposed to reduce energy consumption by introducing a duty cycle. However, S-MAC cannot handle variable loads because of its static duty cycle. Timeout-MAC (T-MAC) introduced an adaptive duty cycle to handle variable traffic loads. However, nodes that do not take part in data exchange waste energy because of continuous renewal of their timeout values. To eliminate this energy waste, we propose ADV-MAC, a MAC protocol for wireless sensor networks that introduces the concept of advertising for data contention. ADV-MAC minimizes the energy lost in idle listening while maintaining an adaptive duty cycle to handle variable loads. Additionally, ADV-MAC enables energy efficient MAC-level multicasting. We derive an analytical model for the packet delivery ratio and the energy consumption of the protocol. We verify the analytical model with simulations and use the model to choose an optimal value of the advertisement period. Simulations show that the optimized ADV-MAC provides substantial energy gains (50–70% less than T-MAC and S-MAC for the scenarios investigated) while faring as well as T-MAC in terms of packet delivery ratio and latency.