Number Of Frequency Slots Research Articles

Selective Resource Offloading in Cloud-Edge Elastic Optical Networks

With the rapid development of Internet of Things (IoT), IoT mobile devices host more computation-intensive and real-time applications, such as face recognition, online gaming, and augmented reality/virtual reality services. This paper mainly addresses the problems of the selective resource offloading in order to achieve resource optimization in cloud-edge elastic optical networks (CE-EONs). We firstly propose two integer linear program (ILP) models to minimize both the end-to-end (E2E) latency and the total number of frequency slots by considering the latency sensitivity, followed by introducing three corresponding heuristic approaches, namely resource priority offloading (RPO), distance priority offloading (DPO), and coordinated distance and resource offloading (DRO). For comparison, we also introduced an existing resource offloading (ERO) approach in CE-EONs. On one hand, simulation results show that the DRO approach greatly approximated to the optimized solutions of ILP models in the static traffic scenario. Meanwhile, the DRO approach achieves the better performance in terms of average E2E latency. On the other hand, the proposed DRO approach can significantly reduce the blocking probability owing to much improved spectrum efficiency and achieves a graceful tradeoff between the computing resources and E2E latency compared to the RPO, DPO, and ERO approaches in the dynamic traffic scenario.

Link load prediction in an optical network with restoration mechanisms

Knowledge about the future link load is an essential issue for optical network operators, especially in the case of network failure and the restoration of affected traffic. In this paper, we study the dynamic operation of an optical network in its normal non-failure state and the situation of a link failure followed by the restoration process. Data obtained during the simulation are used for link load prediction. We propose dynamic methods for multistep link load prediction. The analyzed link load is expressed in two ways: the bitrate of the overall traffic allocated to the link and the number of frequency slots occupied. The proposed prediction methods are expanded to include additional mechanisms that improve the forecasting quality expressed by the mean absolute percentage error metric. We evaluate developed methods on a dataset collected using a representative European network topology with realistic traffic containing diverse types of network transmissions. In broad numerical experiments, we prove the high prediction quality of regression algorithms aided by the proposed additional features.

Optimal Quasi-Orthogonal FH Sequences With Adaptive Array Receiver for Massive Connectivity in Asynchronous Multi-Cluster Networks

This paper is concerned with the enabling of massive connectivity in a multi-cluster network. In order to tackle significant amount of interference imposed by inter- and intra-cluster users, we consider a frequency-hopping (FH) system where an improved quasi-orthogonal hopping pattern, called optimal strong no-hit-zone FH sequence (SNHZ-FHS) set, is adopted in each cluster. We propose a flexible construction of SNHZ-FHS sets and derive their Hamming correlation values at different access delays. Since the maximum number of supportable users under traditional FH networks is strictly limited by the number of frequency slots, we investigate the design of a novel class of adaptive array beam-forming (BF) receiver in which SNHZ-FHS patterns (i.e., SNHZ-FH/BF) are reused over asynchronous multi-cluster uplink channels. Extensive numerical comparisons show that our proposed SNHZ-FH/BF system provides an effective means for attaining higher user capacity as well as remarkable capability of interference suppression.

Spectrum Reconstruction Algorithm based on Resource Partition Allocation in Elastic Optical Networks

In order to solve the problem of spectrum fragment in elastic optical networks, a spectrum reconstruction algorithm based on resource partition allocation is proposed in this paper. Services are classified according to the different frequency of the services that occupy different number of frequency slots in the networks. Region division of spectrum resources is made according to the type of services and services are allocated in the corresponding spectrum partitions. When defragmenting in the networks, we reconstruct the spectrum for different regions with comprehensively considering the factors in time domain and frequency domain, integrating current resources and preventing the generation of spectrum fragment in the future. Simulation results show that the algorithm can reduce the degree of network fragmentation and reduce traffic blocking.

Adaptive modulation allocation algorithm in elastic optical networks

SummaryThis paper introduces a new way to allocate the modulation format and improves the energy efficiency in elastic optical networks. For every connection request, both the quality of transmission and quality of service requirements are investigated. The allocation of modulation formats is based on both the physical distance and the required number of frequency slots. To improve the energy efficiency, Yen's algorithm is executed for every connection requested, and the lightpath with the lowest power consumption is selected. Numerical results were compared with adaptive modulation algorithms presented in the existing literature. The energy efficiency was improved by up to 27%, the used bandwidth available was reduced by up to 60%, and the blocking probability was decreased by 30% using our proposed adaptive algorithm.

A Secure Intelligent Spectrum Control Strategy for Future THz Mobile Heterogeneous Networks

In order to improve communication efficiency, applying THz communication to MHNs is envisioned as a promising approach. However, the security of THz MHNs is rarely discussed and urgently needs attention. For the purpose of effectively resolving the exposed security issues in THz MHNs, in this article, an intelligent spectrum control strategy in a THz network is proposed, and an intelligent spectrum control sequence is generated, which has the characteristics of adaptive frequency slot number, wide gap, and orthogonality. Extensive theoretical analyses prove that this sequence outperforms the sequences available in uniformity, randomness, and Hamming correlation. Simulation results indicate that the proposed strategy has great anti-attack capability and high throughput, and that the BER of THz communication with the proposed strategy can be increased two orders of magnitude in a complex electromagnetic environment. By using the proposed strategy, the security and reliability of future THz MHNs can be ensured.

Quasi Path Restoration: A post-failure recovery scheme over pre-allocated backup resource for elastic optical networks

Abstract Spectrum conflict during primary and backup routes assignment in elastic optical networks results in increased resource consumption as well as high Bandwidth Blocking Probability. In order to avoid such conflicts, we propose a new scheme, Quasi Path Restoration (QPR), where we divide the available spectrum into two: (1) primary spectrum (for primary routes allocation) and (2) backup spectrum (for rerouting the data on link failures). QPR exhibits three advantages over existing survivable strategies such as Shared Path Protection (SPP), Primary First Fit Backup Last Fit (PFFBLF), Jointly Releasing and re-establishment Defragmentation SPP (JRDSSPP), and Path Restoration (PR): (1) the conflict between primary and backup spectrum during route assignment is completely eliminated, (2) upon a link failure, connection recovery requires less backup resources compared to SPP, PFFBLF, and PR, and (3) availability of the same backup spectrum on each link improves the recovery guarantee. The performance of our scheme is analyzed with different primary backup spectrum partitions on varying connection-request demands and number of frequency slots. Our results show that QPR provides better connection recovery guarantee and Backup Resources Utilization (BRU) compared to bandwidth recovery of PR strategy. In addition, we compare QPR with Shared Path Protection and Primary First-Fit Backup Last Fit strategies in terms of Bandwidth Blocking Probability (BBP) and average frequency slots per connection request. Simulation results show that BBP of SPP, PFFBLF, and JRDSPP varies between 18.59% and 14.42%, while in QPR, BBP ranges from 2.55% to 17.76% for Cost239, NSFNET, and ARPANET topologies. Also, QPR provides bandwidth recovery between 93.61% and 100%, while in PR, the recovery ranges from 86.81% to 98.99%. It is evident from our analysis that QPR provides a reasonable trade-off between bandwidth blocking probability and connection recoverability.

Mixed Channel Traffic Grooming for IP Over EON with SBPP-Based Cross-Layer Protection

We consider mixed channel traffic grooming in a shared backup path protected IP over elastic optical network (EON) and develop an auxiliary graph-based heuristic algorithm to share common optical channels between working and protection IP traffic flows. We compare integrated protection (i.e., cross-layer protection capacity sharing) with nonintegrated protection (i.e., overlay protection) to show how cross-layer sharing improves capacity utilization. Using simulations, network performance is evaluated in terms of the maximum number of frequency slots (FSs) used, the spare capacity redundancy, and the number of transponders required for a static traffic demand. For a dynamic traffic demand, the bandwidth blocking probability (BBP) is also obtained. It is found that the proposed mixed channel traffic grooming scheme can reduce both the BBP and the number of transponders required while improving the spectral efficiency compared to a system using dedicated channel traffic grooming. Integrated protection is also found to be more efficient than overlay protection under comparable conditions. We also observe that only a limited number of transponders per node and a limited number of FSs per transponder are sufficient to achieve good performance for an IP over EON with mixed channel traffic grooming and cross-layer spare capacity sharing.

A multicast contention resolution scheme based on shared spectrum converter for elastic optical switching node

The replication and forwarding of multicast traffic make spectrum contention probability significantly increase in elastic optical switching node. Spectrum conversion is considered as a very appealing solution to resolve spectrum contention without additional delay and traffic reordering at the receiver. In this paper, we propose a multicast switching node architecture configured with limited range spectrum converter (LRSC) and full range spectrum converter (FRSC) for elastic optical switching node. The proposed optical node architecture adopts a group of feedback shared LRSCs and a small number of output shared FRSCs to resolve optical multicast contention in frequency domain. To reduce the bandwidth blocking probability and node cost, a double weights maximal clique scheduling algorithm is designed. The number of frequency slots required by the traffic and the number of used LRSCs are considered as two weights, and graph coloring algorithm is introduced to select the scheduling scheme which uses the minimum number of LRSCs for achieving the maximum total number of frequency slots of output traffics. Simulation results show that the proposed node architecture and scheduling algorithm greatly improve the bandwidth blocking probability performance with relatively lower node cost.

Spectrum-space-divided spectrum allocation approaches in software-defined elastic optical networks

Recently, the architecture of elastic optical network (EON) has been proposed as a candidate solution to accommodate both huge bandwidth requirements and flexible connections in next generation optical networks. In order to improve the spectrum efficiency, we propose different spectrum-space-divided approaches and develop two integer linear programming (ILP) models and several spectrum-space-divided spectrum allocation approaches with and without dedicated-path protection in software-defined elastic optical networks (SD-EONs). Simulation results show that the ILP models achieve better performance in terms of the number of frequency slots and hop counts than the proposed spectrum-space-divided spectrum allocation approaches with and without dedicated-path protection under the static scenario of connection requests. Furthermore, we apply the spectrum-space-divided spectrum allocation approaches with and without dedicated-path protection to reduce the blocking probability and to improve spectrum efficiency under the dynamic connection requests compared to the traditional first-fit spectrum allocation approach in SD-EONs.

Optimal Selection of Encode Rate and the Number of Frequency Slots in ISA-MAC

Optimal Selection of Encode Rate and the Number of Frequency Slots in ISA-MAC

Optimal Selection of Encode Rate Applied in Food ISA-MAC System

This study bases on earlier ideal named food ISA-MAC system (Instantaneous Spectrum Availability MAC). In actual system, it’s a quite attractive character that one can access the channel as he wants and focus on the optimal encode rate and the number of frequency slots of food ISA-MAC system. Take the probability of no-error channel transmission and the normalized throughput of the system as constrained condition, an analysis come out and be taken as a guide for reality design which is found on the mathematic model and the capability of error detection and correction and can be adapted to CSMA, ALOHA using FH similar to food ISA-MAC system which is designed for fulfilling the requirement of accessing at any moment.

Routing and Spectrum Assignment for Dual Failure Path Protected Elastic Optical Networks

We present the design of a dual failure protected elastic optical network (EON) for different sharing capabilities of protection lightpaths. Routing and spectrum assignment (RSA) is considered for such a network so as to minimize the maximum number of frequency slots (FSs) used. The key principles for protection resource sharing among the first and the second protection lightpaths are identified for dedicated 1:1:1, mixed 1:1:1, 1+1:1, and 1+1+1 protection. Both integer linear programming (ILP) models and spectrum window plane (SWP)-based heuristic algorithms are proposed for RSA in dual failure protected EONs. Simulation results indicate that, apart from being efficient, the proposed SWP-based heuristic algorithm not only performs close to the ILP model but also does much better than a benchmark adaptive routing algorithm. We find that 1:1:1 protection technique performs better in terms of the maximum number of FSs used and the spare capacity redundancy than both the 1+1:1 and 1+1+1 techniques. In addition, the mixed 1:1:1 case outperforms the dedicated 1:1:1 case both in minimizing the maximum number of link FSs used and its spare capacity redundancy.

Multi- Spectrum Bands Allocation for Time-Varying Traffic in the Flexible Optical Network

The flexible optical networks are the promising solution to the exponential increase of traffic generated by telecommunications networks. They combine flexibility with the finest granularity of optical resources. Therefore, the flexible optical networks position themselves as a better solution than conventional WDM network. In the operational phase, traffic of connections fluctuates. In fact, the user’s need is not the same during day periods. Such traffic may experiment evidence of rising working hours, end of months or years and decreases during the night or on holidays. This variation requires the expansion or contraction of the number of frequency slots allocated to a connection to match the exact needs of the moment. The expansion of the traffic around the reference frequency of connection may lead to blockage because it must share frequency slots with neighboring connections in compliance with the constraints of continuity, contiguity, and non-overlapping. In this study, we offer a technique for allocating frequency slots for time-varying traffic connections. We share out the additional traffic load on different spectrum paths by respecting the constraint of time synchronization related to the differential delay to reduce the blocking rate due to traffic fluctuation.

Cognitive Frequency Hopping Sequences

Since the immutable conventional Frequency hopping (FH) sequence cannot keep high FHcommunication reliability in complex electromagnetic environment, we propose an algorithm that cangenerate high-performance Cognitive frequency hopping sequence (CFHS) for Cognitive frequencyhopping (CFH) system. By employing the pseudo-random perturbation mapping, the CFHS is generated byremapping the block cipher FH sequence with the adaptive frequency slot number and frequency gap.The CFHS inherits the great integrated performance and its parameters could change with theelectromagnetic environment. The statistics properties of Markov and uniformity are analyzed basedon the Markov process theory and probability theory. Simulation results show that CFHS outperformsthe widely-used FH sequences on the performance of uniformity, randomness, Hamming correlation,complexity and sensitivity. The proposed CFHS could be extensively applied in high reliable CFHsystem.

Generation and characterization of orthogonal FH sequences for the cognitive network

The existing orthogonal frequency hopping (FH) sequence cannot support the high throughput and high spectrum efficient cognitive FH (CFH) network due to its small family size, high computational complexity and short period. To overcome these disadvantages, this paper investigates the generation of the orthogonal FH sequence and analyzes its multiple accessibility performance based on the CFH frequency division multiple-access (FDMA) network model. By the random mapping and cyclical shift replacement (CSR) scheme, a large family size of orthogonal FH sequence with dynamic frequency slot number is generated. In this case, the external interference could be eliminated by avoiding the interfered frequencies, and blocking mutual interference incurred for the packet by the orthogonal frequencies. Moreover, the theoretical relationships of the throughput and transmission delay with respect to the user number and the packet arrival rate are given, which shows that our proposed orthogonal FH sequence could support high throughput and short packet transmission delay in CFH-FDMA network. The simulation results validate our theoretical analysis of the CFH-FDMA network performance, and show that our proposed sequence outperforms the widely used no hit zone FH sequences in terms of uniformity, randomness, Hamming correlation, complexity and sensitivity, etc.

Analysis of asynchronous frequency hopping multiple‐access network performance based on the frequency hopping sequences

In this study, the authors investigate the impact of the frequency-hopping (FH) sequence on the packet transmission performance of the asynchronous frequency-hopping multiple-access (FHMA) network. According to the model of the asynchronous FHMA network given in this study, the authors analyse the impact of the two important FH sequence factors – uniformity and frequency slot number – on the correct transmission probability and the packet transmission frequency efficiency. According to the non-collision probability analysed in this study, the uniformity of the FH sequence is an important issue to determine the correct packet transmission probability. Moreover, based on the definition of the packet transmission frequency efficiency given in this study, the optimal frequency slot number employed to obtain the maximum frequency efficiency is obtained. By employing three typical FH sequences, the simulation results are also included, which validates the theoretical analysis about the packet transmission performance of the asynchronous FHMA network.

Spectrum-Aware Survivable Strategies With Failure Probability Constraints Under Static Traffic in Flexible Bandwidth Optical Networks

This paper addresses the problem of spectrum-aware survivable strategies with failure probability constraints under static traffic in flexible bandwidth optical networks. The joint failure probability between primary and backup paths must be below the maximum tolerable joint failure probability for each traffic demand. We develop integer linear program (ILP) models for dedicated-path protection and shared-path protection in order to minimize the total number of frequency slots consumed, and we also propose a spectrum-aware dedicated protection (SADP) algorithm and a spectrum-aware shared protection (SASP) algorithm. Simulation results show that the ILP model solutions consume minimum number of frequency slots, but lead to higher average joint failure probability compared to the SADP and SASP algorithms. Moreover, both the SADP and SASP algorithms achieve a better performance in terms of total number of frequency slots consumed as compared to a conventional dedicated-path protection algorithm and a conventional shared-path protection algorithm, respectively, but lead to higher average joint failure probability.

Optimal Design for Shared Backup Path Protected Elastic Optical Networks Under Single-Link Failure

This paper considers the network protection technique of shared backup path protection (SBPP) in comparison with 1 + 1 path protection for elastic optical networks. We develop integer linear programming (ILP) models to minimize both the required spare capacity and the maximum number of link frequency slots (FSs) used. We consider transponder tunability that corresponds to the condition of whether or not the same set of FSs is required to be used for both the working and protection lightpaths. We also apply the bandwidth squeezed restoration technique to obtain the maximum restoration levels for the affected service flows, subject to a limited FS capacity on each fiber link. Our studies show that the proposed SBPP technique requires much lower spare capacity compared to the traditional 1 + 1 path protection approach. The flexibility of allowing the working and protection lightpaths to use different sets of FSs (i.e., with full transponder tunability) has the advantage of reducing both the number of FSs needed and the spare capacity redundancy required.

Novel Node-Arc Model and Multiiteration Heuristics for Static Routing and Spectrum Assignment in Elastic Optical Networks

We consider an elastic optical network and study the static routing and spectrum assignment (RSA) problem aiming to minimize the maximum number of frequency slots required to accommodate all lightpath demands. We introduce a novel node-arc integer linear programming (ILP) model, which jointly decides optimal routes and assigned spectra for lightpaths between all source-destination pairs. To reduce the total number of variables, and therefore lower the computational complexity, our new node-arc model extends previous work by representing the spectrum assigned to each lightpath by two variables (i.e., the starting and ending boundary frequency slot indexes). To achieve scalability, we also develop an efficient spectrum-window-based greedy heuristic algorithm, and further propose three multiiteration-based algorithms that consider the effect of demand-serving sequences. Analytical and numerical results show that comparing with an existing approach, our solution to the RSA problem based on the new node-arc ILP model achieves a significant computational complexity improvement. Further numerical results demonstrate that the proposed multiiteration algorithms obtain solutions closer to optima than existing algorithms.