Performance of shared-channel multihop lightwave networks

Wireless multi-hop networks are candidate communication infrastructures in developing regions because their installation cost is quite low comparing to that for conventional wired networks. Reliable and scalable dissemination mechanism is required in practical multi-hop networks. Cooperative communication is a new scheme to improve communication performance to realize a reliable dissemination mechanism. However, high mobility networks have a big issue for autonomous control for cooperative communication. Additionally, conventional cooperative schemes cannot reduce packet collisions even if packet collisions are a big degradation factor of performance in dense multi-hop networks. We have discussed a new cooperative communication scheme that employs Orthogonal Frequency-Division Multiplexing (OFDM). Our scheme can improve communication performance and reduce packet collisions based on distributed control matter. Our advance evaluation has shown a good potential of the proposed scheme to improve communication performance in multi-hop network simulations. On the contrary, the feasibility of the proposed scheme with a real hardware device was not shown. This paper evaluates the feasibility of our original cooperative communication scheme on IEEE 802.11a standard devices. Almost all conventional cooperative communication schemes require a special physical layer and a media access control mechanism. We have focused on a characteristic of OFDM, where a receiver can demodulate multiple signals within a guard interval period. The experimental evaluation has been performed with software defined radio devices (USRP B200). We have implemented multiple transmitters, a receiver and a fading simulator for each transmitter with two USRP B200 devices. The results can show that the proposed scheme works well on IEEE 802.11a standard devices and improves communication performance in practical situations. Hence, the proposed scheme will be a new candidate of cooperative communication mechanisms that can employ general consumer devices and can realize effective dissemination mechanism for multi-hop networks.

Aiming at the virtual network embedding problem under dynamic service request, Service Request Aware-based Dynamic Virtual Network Embedding (SRAD) algorithm is proposed. We first present virtual network embedding model, and then define virtual network construction cost according to the dynamic characteristic of service request. Our goal is to find the optimal reconfiguration policies by awaring service request type and changing trends, which can minimize the overall construction cost using substrate resource. Experimental results show that the proposed algorithm satisfies the service request, achieves higher success ratio and gains higher revenue/cost ratio for substrate network comparing with the existing algorithms.

We investigate the interuser interference in cellular code—division multiple access (CDMA) and timedivision multiple access (TDMA) systems and compare the two multiple access techniques at different levels of user density per cell. The study includes the interference both on the downstream channel (from base station to users) and on the upstream channel (from users to base station). The purpose is to compare the two multiple access techniques when the total bandwidth occupancy and the maximum number of users per cell are the same. The results indicate that on a nondispersive radio channel with a path loss that is proportional to the fourth power of the distance, the interuser interference is approximately 10 dB higher in CDMA. The implication of this result, which holds for both the downstream and the upstream channels, is that for the same total bandwidth and number of users per cell, TDMA gives substantially superior bit error rate (BER) performance. This is confirmed by our numerical results evaluated for both additive white Gaussian noise (AWGN) channels and memoryless flat Rayleigh fading channels. Alternatively, CDMA needs approximately 10 times more bandwidth to achieve the same signal—to—interference (S/I) ratio, a result which may seem surprising, because the fact that CDMA employs a frequency reuse factor of 1 is often given as an evidence that this technique can support a higher number of users than TDMA in a given geographic area and frequency bandwidth.

The transmission rate between two nodes is usually very low in underwater acoustic networks due to the low available bandwidth of underwater acoustic channels. Therefore, increasing the transmission parallelism among network nodes is one of the most effective ways to improve the performance of underwater acoustic networks. In this paper, we propose a new collision-free hybrid medium access control (MAC) protocol for distributed multi-channel underwater acoustic networks. In the proposed protocol, handshaking and data transmission are implemented as a pipeline on multiple acoustic channels. Handshaking is implemented using the time division multiple access (TDMA) technique in a dedicated control channel, which can support multiple successful handshakes in a transmission cycle and avoid collision in the cost of additional delay. Data packets are transmitted in one or multiple data channels, where an algorithm for optimizing the transmission schedule according to the inter-nodal propagation delays is proposed to achieve collision-free parallel data transmission. Replication computation technique, which is usually used in parallel computation to reduce the requirement of communication or execution time, is used in the data packet scheduling to reduce communication overhead in distributed environments. Simulation results show that the proposed protocol outperforms the slotted floor acquisition multiple access (SFAMA), reverse opportunistic packet appending (ROPA), and distributed scheduling based concurrent transmission (DSCT) protocols in throughput, packet delivery rate, and average energy consumption in the price of larger end-to-end delay introduced by TDMA based handshaking.

Interference neutralization (IN) is an interference management technique that allows simultaneous transmission of multiple links by nullifying their mutual interference in the air via cooperation among the transmitters. Although IN has been studied from information theoretic perspective, its potential for a general multi-hop wireless network has not been explored. The goal of this paper is to understand IN in a multi-hop wireless network from networking perspective. We first establish an IN reference model. Based on this reference model, we develop a set of feasibility constraints for a subset of links to be active simultaneously. By identifying each eligible neutralization node (called neut), we study IN in a general multi-hop network and develop a set of necessary constraints to characterize neut selection, IN, and scheduling. These constraints allow us to study the performance of multi-hop networks without the need of getting involved into onerous signal design issues at the physical layer. Finally, we apply our IN model and constraints to study a throughput maximization problem and show that the use of IN can generally increase network throughput. In particular, throughput gain is most significant when the node density increases.

In this PhD dissertation multi-rate models are examined for the performance analysis of telecommunication networks through mathematical analysis and simulation. Particular emphasis is given to optical networks. The main goal is the development of analytical models for the calculation of network performance metrics, such as blocking probabilities, transmission delay and utilization of the common channel. The proposed analytical models are distinguished according to the network technologies. Three different technologies are considered: A) Wavelength routed optical networks. B) Optical access networks. C) Wireless Internet access networks. Multi-rate loss models are proposed for the performance evaluation of wavelength routed optical networks. Firstly, the case of a single link is considered and then a mesh all-optical network is examined. In addition, analytical models are proposed for Optical Packet Switching (OPS) networks, for the case of an all-optical OPS switch and of an OPS mesh network. Multi-rate analytical models are proposed for the evaluation of the performance of Passive Optical Networks (PONs) implementing different multiple access methods. For the case of Time Division Multiple Access (TDMA) the Ethernet PON is studied, which supports multiple service-classes. Regarding the Wavelength Division Multiplexing (WDM) PONs a hybrid WDM-TDMA PON is considered and the call-level performance is evaluated. Calls are distinguished by their arrival process, which can be random or quasi random, by their bandwidth requirements, which can be fixed of elastic and by their behavior during their service, which can be calls of fixed transmission rate or calls that alternate between ON and OFF periods. Finally multi-rate loss models are proposed for the case of Optical Code Division Multiple Access (OCDMA) PONs that take into account the user activity and the presence of additive noise in the transmission channel. For the performance analysis of wireless Internet access networks analytical models are proposed, which implement the IEEE 802.11 protocol or the IEEE 802.11e protocol. The proposed analysis calculated the saturation throughput and the end-to-end packet delay as a function of the Medium Access Control (MAC) delay and the queueing delay. In all cases the accuracy of the proposed models is validated through simulation.

The wireless channel-oriented ad-hoc multi-hop broadband (W-CHAMB) is a new link layer protocol with the aim of being able to support quality of service (QoS) in multi-hop operation in fully distributed ad hoc networks. It is based on time division multiple access (TDMA) technology, operating on a single frequency channel. In this paper, we improve the prioritized access mechanism by inserting the contention phase (CP) into the access slot. Then we propose 3 new algorithms to enhance the traffic performance in the multi-hop environment: on demand time division duplex (on-demand-TDD) for achieving high channel utilization; fairness algorithm (FA) for acquiring the fairness even in a highly interfered multi-hop network; setting valid transmission time (VTT) for each traffic channel to prevent an excessive use of the traffic channel. The extensive simulations are performed by evaluating transmission control protocol (TCP) performance over W-CHAMB multi-hop networks under heavy load situations. The achievable TCP throughput, packet delay, fairness and stability have been investigated. Results exhibit the outstanding multi-hop performance of the W-CHAMB protocol

International audience

Many transmission scheduling algorithms have been proposed to maximize the spatial reuse and minimize the time division multiple access (TDMA) frame length in multihop packet radio networks. Almost all existing algorithms assume exact network topology information and require recomputations when the network topology changes. In addition, existing work focuses on single channel TDMA systems. In this paper, we propose a multichannel topology-transparent algorithm based on latin squares. This algorithm has the flexibility to allow the growth of the network, i.e., the network can add more mobile nodes without recomputation of transmission schedules for existing nodes. At the same time, a minimum throughput is guaranteed. We analyze the efficiency of our algorithm, and examine the topology-transparent characteristics and the sensitivity on design parameters by simulation.

SDN network is a dynamic, controllable, cost-effective and adaptable system. It is suitable for communication networks with high bandwidth and high dynamic characteristics. Therefore, combining SDN ideas with the new generation of LEO satellite networks can achieve more flexible monitoring and management of the network, and can make the network expansion more convenient. Joint the Depth-First-Search (DFS) idea and Dijkstra algorithm for the huge numbers of LEO mobile satellite network based on SDN is proposed to improve the computational efficiency and the reliability of calculation result. Moreover, the communication performance of space-based network based on SDN and traditional space-based network is compared and analyzed. The simulation results show that the huge numbers of LEO mobile satellite network based on SDN breaks through the performance limitations of the traditional network architecture, and it can achieve better performance of the network.

Topology control in multi-hop wireless networks is a technique used to control nodes' activities to construct a topology with an acceptable level of network connectivity while minimizing energy consumption. It can be broadly classified into two main paradigms which are State Scheduling and Transmission Power Control. Both of them have received lots of attention from many researchers for decades. According to Transmission Power Control technique, most of them take into account only one-hop neighbor information to optimize transmission power and control topology in multi-hop wireless networks. In this paper, an energy efficient topology control based on both one-hop and two-hop neighbor information is proposed to reduce energy consumption without degrading network performances. A number of simulation scenarios are constructed in this work to study energy consumption as well as other network performances that are end-to-end delay, throughput, and packet delivery ratio of the proposed algorithm.

Multi-Radio Multi-Channel Wireless Mesh Network (MRMC-WMN) has been considered as one of the key technology for the enhancement of network performance. It is used in a number of real-time applications such as disaster management system, transportation system and health care system. MRMC-WMN is a multi-hop network and allows simultaneous data transfer by using multiple radio interfaces. All the radio interfaces are typically assigned with different channels to reduce the effect of co-channel interference. In MRMC-WMN, when two nodes transmit at the same channel in the range of each other, generates co-channel interference and degrades the network throughput. Co-channel interference badly affects the capacity of each link that reduces the overall network performance. Thus, the important task of channel assignment algorithm is to reduce the co-channel interference and enhance the network performance. In this paper, the problem of channel assignment has been addressed for MRMC-WMN. We have proposed an Interference Aware, Topology, Power and Flow Control (ITPFC) Channel Assignment algorithm for MRMC-WMN. This algorithm assignes the suitable channels to nodes, which provides better link capacity and reduces the co-channel interference. In the previous work performance of the proposed algorithm has been evaluated for a network of 30 nodes. The aim of this paper is to further evaluate the performance of proposed channel assignment algorithm for 40 and 50 nodes network. The results obtained from these networks show the consistent performance in terms of throughput, delay, packet loss and number of channels used per node as compared to LACA, FCPRA and IATC Channel Assignment algorithms.

Ultraviolet (UV) networks are widely applied in complex electromagnetic environments. Designing an efficient multi-node medium access control (MAC) protocol for these networks is important. In this study, we proposed an enhanced clustering time division multiple access (TDMA) MAC protocol based on clustering and learning automata (LA). Subsequently, the effects of the network topology, class of service, and number of cluster nodes on the network performance under the proposed protocol were analyzed. Then, the protocol was compared with the TDMA protocol and clustering system. Results revealed that it obtained a better network performance, proving its suitability for multi-node UV networking.

In a multi-hop wireless network, connectivity is determined by the link that is established by the receiving signal strength computed by subtracting the path loss from the transmission power. Two path loss models are commonly used in research, namely two-ray ground and shadow fading, which determine the receiving signal strength and affect the link quality. Link quality is one of the key factors that affect network performance. In general, network performance improves with better link quality in a wireless network. In this study, we measure the network connectivity and performance in a shadow fading path loss model, and our observation shows that both are severely degraded in this path loss model. To improve network performance, we propose power control schemes utilizing link quality to identify the set of nodes required to adjust the transmission power in order to improve the network throughput in both homogeneous and heterogeneous multi-hop wireless networks. Numerical studies to evaluate the proposed schemes are presented and compared.

This paper presents the major issues in forming a cost-effective and efficient network from a set of earth stations sharing the satellite resource. The discussion is in the context of satisfying the performance requirements for transmission of data, voice, and image presented to earth stations in digital form. Multiple access techniques have significant impacts on the network economy. Although wide-band single-carrier time-division multiple access (TDMA) uses the satellite capacity efficiently and is cost-effective for networks with large traffic volumes per node, it requires expensive earth stations and is not cost-effective for networks with small traffic volumes per node. The concept of multicarrier-TDMA (MC-TDMA) is described and its economic advantage over TDMA is demonstrated for networks with dispersed points of traffic origination. Application of demand assignment to MC-TDMA is also presented. Some implementation issues are also discussed.