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With the introduction of 5G technology, telecommunications industry enters a stage where remarkable changes occur. The rapid increase of traffic load combined with the emergence of new network requirements has led to the need of developing a network architecture capable of supporting a network of high efficiency, improved transmission rates and low latency. C-RAN architecture is able to meet all these challenges, while focuses on the innovation of a functional split in the Base Station (BS) where the Baseband Units - BBU is detached from the Remote Radio Heads - RRH. Its successful implementation is able to bring significant benefits where among them cost reduction, the entrance of new network requirements and services as well as enhanced network flexibility, are the ones that dominate. In this paper, we perform the analysis of this type of network through the application of specific Teletraffic Models: the Multi-rate Loss Model and the Retry Models. The Multi-rate Loss Model refers to systems that serve different types of services, whose calls are accepted by the system if only there are service units available. The Retry Models allows rejected calls to retry their connection to the system, offering a lower chance of losing calls and thus reduced network performance. The comparison of the blocking probabilities can lead us to conclusions about the efficiency of these models in a C-RAN network and then in the evaluation of the overall network performance.

5G mobile networks will be soon available to handle all types of applications and to provide service to massive numbers of users. In this complex and dynamic network ecosystem, end-to-end performance analysis and optimization will be key features in order to effectively manage the diverse requirements imposed by multiple vertical industries over the same shared infrastructure. To enable such a vision, the MARSAL project [1] targets the development and evaluation of a complete framework for the management and orchestration of network resources in 5G and beyond by utilizing a converged optical-wireless network infrastructure in the access and fronthaul/midhaul segments. At the network design domain, MARSAL targets the development of novel cell-free-based solutions. Namely, scalable and cost-efficient wireless access points deployment will be achieved by exploiting the distributed cell-free concept combined with wireless and wired serial fronthaul approaches. We will target the inclusion of these innovative functionalities in the O-RAN project. In parallel, in the fronthaul/midhaul segments MARSAL aims to radically increase the flexibility of optical access architectures for Beyond-5G cell site connectivity via different levels of fixed-mobile convergence. In the network and service management domain, the design philosophy of MARSAL is to provide a comprehensive framework for the management of the entire set of communication and computational network resources by exploiting novel ML-based algorithms of both edge and midhaul data centers, by incorporating the Virtual Elastic Data Centers/Infrastructures paradigm. Finally, at the network security domain, MARSAL aims to introduce mechanisms that provide privacy and security to application workload and data, targeting to allow applications and users to maintain control over their data when relying on the deployed shared infrastructures, while AI and Blockchain technologies will be developed in order to guarantee a secured multi-tenant slicing environment.

The convergence of fiber and wireless systems based on millimiter-wave (mmWave) bands seems to be a promising fronthaul solution for the fifth generation (5G) centralized radio access network (C-RAN) deployments. The 5G fronthaul allows the flexible splitting of functionalities between centralized and remote units but requires high data rates. These can be achieved by combining the traits of analog radio-over-fiber (RoF) communication, the wide mmWave spectrum and the availability of different functional splits. To that end, we focus on a novel RoF fronthaul architecture and evaluate its performance in terms of end-to-end packet delay under different network setups. Our simulation results show that the experienced delay is affected by the fronthaul load but remains below 100 μs in most cases.

5G New Radio's (NR) spectrum expansion towards higher bands, although critical towards achieving the envisioned 5G capacity requirements, creates the need for installing a very large number of Access Points (APs), which asserts tremendous capital burden on the Mobile Network Operators. Current centralization solutions such as the Cloud Radio Access Network (C-RAN) alleviate partially the costs of densification by moving the majority of radio processing functionalities from the Remote Radio Heads (RRHs) to the central Base Band Unit (BBU), but still require very high-speed Point-to-Point links between the BBU and each RRH mainly due to the digitized Common Public Radio Interface (CPRI) that is excessively inefficient for hauling broadband signals. In this article, we present a novel architecture that employs an analog converged Fiber-Wireless scheme in order to create a very spectrally efficient Point-to-Multipoint network capable of interconnecting a large number of APs, while allowing compatibility with mature Ethernet-based low-cost equipment. Preliminary simulation results show very low end-to-end Ethernet packet delay, well below eCPRI's 100 μs mark, even for fiber lengths up to 10 km, indicating the suitability of our solution for employment in 5G NR large-scale fronthaul networks., © 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Biased user association is a promising load balancing approach in 5G heterogeneous networks due to its effectiveness in offloading users from macro base stations (BSs) to small cell BSs. However, users that are offloaded from macro BSs to small cell BSs suffer from severe interference as they are not served by the BS that provides the strongest received power. To mitigate this interference problem, this work utilises joint transmission coordinated multipoint (JT-CoMP) to enable users that are located in the cell expansion area (CRE) to be jointly served by multiple BSs thereby increasing their signal-to-interference noise ratio (SINR) and throughput. Unlike the traditional per-tier biasing approach, this paper utilises particle swarm optimisation (PSO) to assign each small cell BS a specific biasing value with the aim of balancing and control the load among BSs while the overall throughput of the system is still maximised. Simulation results demonstrate that per-tier biasing with no JT-CoMP achieves poor performance in terms of coverage probability, average user throughput and the throughput of offloaded users since offloaded users are not served by the best downlink BS. By implementing JT-CoMP with per-tier biasing, a 5 dB JT-CoMP biasing value can improve the throughput of offloaded users and it slightly improves the average user throughput. Comparing PSO with 5 dB CoMP, results show that per-BS biasing using PSO with CoMP improves the average user throughput from 0.59 to 0.72 Mbps (22%) and the throughput of an offloaded user from 0.04 to 0.1 Mbps (+ 150%).

This paper proposes a methodology for the efficient allocation of both optical and wireless resources in an SDN/NFV-based converged optical-wireless network architecture. Our approach considers a network slicing architecture where different network slices form end-to-end logically isolated networks, each one dedicated to a different type of service with diverse requirements. The target of the proposed approach is to optimally determine the network slices so that the specific delay and bandwidth requirements of the multiple services are met, by considering both the optical and wireless network resources.

Fifth Generation (5G) Cloud-Radio Access Networks (C-RANs) are about to exploit both optical and Millimeter Wave (mmWave) technology to meet the ever-increasing traffic demands. In this new type of converged Fiber-Wireless (FiWi) systems efficient Medium Transparent-Medium Access Control (MT-MAC) protocols should be designed, able to satisfy the very strict 5G service requirements. To this end, in this paper, we propose an MT-MAC protocol for mmWave Analog Radio-over-Fiber (A-RoF) C-RANs, which employs gated service, according to which users are granted transmission windows equal to the number of bytes contained in their buffer. An analytical model is also proposed for the mean packet delay, which is verified by means of simulation for different fiber length values, network load conditions and optical capacity values. Our results not only prove the accuracy of the proposed model but also the suitability of the proposed MT-MAC protocol to meet the sub-ms delay challenge of latency-critical 5G network requirements.

In this paper, we consider a single link of fixed capacity that accommodates calls of different service-classes with different bandwidth-per-call requirements. The link behaves as a multirate loss system. Calls of each service-class arrive in the link according to a Poisson (random) or a quasi-random process and have an exponentially distributed service time. Poisson or quasi-random arriving calls are generated by an infinite or finite number of traffic sources, respectively. Service-classes are also distinguished according to the behavior of in-service calls, in elastic and adaptive service-classes. Elastic calls can compress their bandwidth by simultaneously increasing their service time. Adaptive calls tolerate bandwidth compression without affecting their service time. All calls compete for the available link bandwidth under the combination of the Threshold (TH) and the Bandwidth Reservation (BR) policies. The TH policy can provide different QoS among service-classes by limiting the number of calls of a service-class up to a predefined threshold, which can be different for each service-class. The BR policy reserves part of the available link bandwidth to benefit calls of high bandwidth requirements. The proposed models, for random or quasi-random traffic, do not have a product form solution for the determination of the steady state probabilities. However, we approximate both models by reversible Markov chains, and prove recursive formulas for the efficient calculation of the call-level performance metrics, such as time and call congestion probabilities as well as link utilization. The accuracy of the proposed formulas is verified through simulation and found to be quite satisfactory.

Fifth generation (5G) networks are expected to combine several technologies to meet the ever-increasing capacity demands. Among them, centralized-radio access network (C- RAN) architecture, enables the separation of the baseband unit (BBU) from the remote radio head (RRH) so as to achieve higher performance in terms of cost-efficiency and flexibility. Another key 5G technology is the deployment of a massive number of multiple-input multiple-output (MIMO) antennas operating at higher frequencies, i.e., at the millimeter wave (mmWave) band. However, this move towards high mmWave traffic streams make the use of the traditional interface between BBU and RRH, its main specification being the common public radio interface (CPRI), prohibitive. To that end, a novel 5G fronthaul architecture is needed, able to cope with scenarios where high fronthaul traffic is expected, e.g., in dense area networks. To ensure high performance, an efficient medium access control (MAC) protocol should be also designed for these demanding use cases. To this end, a medium transparent MAC (MT-MAC) protocol was recently proposed for fiber wireless (FiWi) fronthaul networks. Although MT-MAC was shown to achieve high performance in terms of throughput and delay for indoor scenarios, its performance under challenging outdoor scenarios is unknown. Hence, in this paper, we study the MT- MAC performance under realistic outdoor dense area network conditions and we comment on its suitability as a 5G protocol solution for FiWi fronthaul networks. Finally, further insights are given for the key parameters that should be taken into account in the design of efficient 5G protocol solutions.

In order to meet the traffic density requirement and cope with the technical challenges of hot-spot scenarios exhibiting extreme user density in very confined geographical areas, the fifth generation (5G) networks must undergo radical technological and architectural innovations that support a broad solution portfolio. This solution mix includes spectrum expansion to the millimeter Wave (mmWave) band, massive Multiple-Input Multiple-Output antennas and network densification through remote radio head deployment. Since the current Common Public Radio Interface-based mobile fronthaul cannot cope with massive mmWave multi-Gbps traffic streams, it is imperative to introduce a novel converged 5G architecture, specifically designed to facilitate mmWave access to massive amounts of users. To this end, a Medium Transparent Medium Access Control (MT-MAC) protocol has been proposed, designed to operate over a converged mmWave analog Fiber-Wireless (FiWi) fronthaul. MT-MAC allows for fast and direct negotiation of wavelength, radio frequency and time resources between the base band unit and the mmWave users, while offering fast on-demand link formation. However, its performance has not yet been evaluated under 5G heavy-traffic scenarios, as the ones previously described. Hence, in this paper, we investigate the performance of an MT-MAC-enabled fronthaul and report on its suitability for mmWave hot-spot 5G access networks.

Passive Optical Networks (PONs) are an efficient high-performance optical access solution that is able to provide huge bandwidth in a resourceful way through the incorporation of inexpensive passive elements. PONs have been widely used for the provision of high-demand services to a number of wired end-users. However, the PON configuration may be also used for the support of wireless end-users through the integration of the PON with a wireless access system. This converged network can therefore take advantage of the mobility features of the wireless network and the high-bandwidth benefits of the PON. In this article, we highlight the basic features of the existing optical-wireless access systems. Moreover, we discuss the challenges in the medium access control layer of the converged network and viable solutions for the efficient Quality of Service management support.

The authors propose a new multirate teletraffic loss model of a single link with certain capacity that accommodates different service-classes whose calls come from finite traffic sources. Calls compete for the available link bandwidth under the combination of the threshold (TH) and the bandwidth reservation (BR) policies. The TH policy can provide different quality of service among service-classes by limiting calls of each service-class up to a certain number, which is a predefined TH, which can be different for each service-class. The BR policy reserves part of the available link bandwidth to benefit calls of high bandwidth requirements. They show that the proposed model, without the BR policy, has a product form solution (PFS) and prove recursive formulas for the efficient calculation of the call-level performance metrics, such as time and call congestion probabilities as well as link utilisation. The combination of the TH and BR policies destroys the PFS of the model. However, they show that approximate but recursive formulas still exist for the efficient calculation of the call-level performance metrics. The accuracy of the proposed formulas is verified through simulation and found to be very satisfactory.

Telecom operators are racing towards upgrading their facilities and broadband services in order to meet the highly challenging 5G operational framework in dense urban landscapes. The oversubscribed sub-6 GHz wireless band is lacking the necessary bandwidth to support the envisioned 5G data rates, suggesting the transition to mm-wave bands as the only viable scenario. In conjunction with the cell densification that is required to achieve the desired frequency reuse factor, it becomes obvious that the current CPRI-based fronthaul cannot cope with massive multi-Gbps traffic streams and a paradigm shift in resource allocation and network intelligence is necessary. To this end we propose the Medium Transparent MAC protocols as the solution towards forming and managing a converged mm-wave FiWi fronthaul infrastructure. Our approach allows for directly negotiating wavelength, frequency and time resources between the centralized unit and the wireless terminals, while offering fast on-demand link formation following closely the demand fluctuation at the picocell level. In this paper we investigate the functional and physical consolidation as well as the respective performance of MT-MAC-enabled fronthaul and report on its application and suitability for mm-wave 5G access networks.

This paper describes and summarizes the notion of medium-transparency in the access control protocols. Two versions of the medium transparent MAC protocols have been presented to this day. The first is the pure Medium Transparent MAC (MT-MAC) that assigns optical capacity for equal time intervals to every RAU of the network. The second version is the Client-Weighted MT-MAC (CW-MT-MAC) that assigns wavelengths based on the number of active users that reside within each RAU, and for time proportionate to the latter, with the purpose of providing capacity fairness among the users. The CWMT- MAC exhibits improvement on user throughput and delay equalization for various network conditions such as different user distribution patterns and loads under specific wavelength availability constraints. The results conclude that the medium transparent MAC protocols can operate successfully over converged Radio-over-Fiber (RoF) networks, confirming their agility and showing that extended range 60GHz LAN areas between wireless users even without line of sight conditions can be obtained. In addition, the results show that the CW-MT-MAC alleviates the inter-user standard deviation in terms of throughput and packet delay, thus proving its enhanced user-fairness properties, highlighting its ability to serve modern applications where Packet Delay Variation is a major issue.

Facing the increasing energy demands associated with the perspective of fifth generation (5G) wireless networks, the Mobile Network Operators (MNOs) are motivated to gradually convert their traditional Radio Access Network (RAN) infrastructure to more flexible and power efficient centralized architectures, i.e., Cloud-RAN (C-RAN). Apart from their promising benefits in terms of management and network optimization, these new architectures further enable the sharing of spectrum and network elements, such as the Remote Radio Heads (RRHs) and the Baseband Units (BBUs), among multiple operators. In this paper, we introduce a novel scheme based on coalitional game theory to identify the potential room for cooperation among different MNOs that provide service to the same area. The proposed scheme sets the rules for profitable collaboration and identifies the core formation conditions (i.e., pricing) for various scenarios with different market and spectrum shares among three operators. Our results show that i) cooperation among subcoalitions of MNOs is always beneficial, yielding both higher revenues and enhanced Quality of Service (QoS) for the end users, and ii) the cooperation of all operators (grand coalition) is profitable for given user pricing in different scenarios.

This paper presents the vision of the 5G STEP-FWD project, funded by the European Commission, with the objective to propose a novel optical-wireless networking solution for the provision of high speed connectivity to end users. The features of the new architecture, based on the utilization of Ultra-Dense Wavelength Division Multiplexing Passive Optical Networks as the backhaul network, providing access to hyper dense mmWave networks, are presented in detail. Moreover, the research challenges to meet the 5G requirements in terms of low latency, spectral and energy efficiency are highlighted, followed by the description of way the project 5G STEP-FWD is going to address them.

The convergence of two popular access technologies, namely Worldwide interoperability for Microwave Access (WiMAX) and passive optical network (PON) is a promising access solution that combines the mobility feature of WiMAX and the ample bandwidth of PONs. In such a converged optical-wireless access network, the provision of quality of service (QoS) support is a challenging issue, mainly because of the different bandwidth allocation mechanisms of the two access technologies. Since the considered convergence seems to be dominant, it deserves assiduous analysis and evaluation. In this study, the authors investigate the delay performance of a converged optical-wireless network that provides QoS support by considering multiple service-classes with different priorities. In the wireless domain, the IEEE 802.16 standard is applied, whereas in the optical domain a wavelength division multiplexing ethernet PON provides connectivity to both wired and wireless users. The authors present an analytical framework for the calculation of the average end-to-end packet delay of each service-class, by developing two queuing models for each domain of the converged network. The end-to-end delay is calculated as the sum of the queuing delay in both domains, and the transmission and propagation delay in the optical domain. The accuracy of the proposed analysis has been verified by simulation and found to be quite satisfactory.

An Optical Code Division Multiple Access (OCDMA) Passive Optical Network (PON) is a highly promising PON configuration, thanks to the potential of OCDMA technology in eliminating channel contention and efficiently supporting multi-rate traffic with different QoS requirements. In this paper, we provide a mathematical framework for a call-level performance analysis of an OCDMA PON that accommodates multiple service-classes of bursty traffic with retries. Blocked calls of random arrivals may immediately retry several times, by requesting less resources (number of codewords) each time, in order to be admitted for service. The bursty nature of traffic is denoted by the fact that in-service calls may alternate between transmission and no-transmission periods. Our analysis takes into account user activity and the various components of additive noise. An approximate recursive formula is derived for the efficient calculation of call-level performance measures. The proposed analytical model is further extended to assess the performance of an OCDMA PON that provides QoS differentiation, through the utilization of multiple-weight optical codes. Both proposed models are verified through simulation and found to be absolutely satisfactory. Moreover, comparison of the new models with a model without retries shows the necessity and effectiveness of the new models.

We demonstrate for the first time an analytical model for computing the end to end packet delay of an Optical/Wireless 60GHz Radio-over-Fiber (RoF) network operating under the Medium-Transparent MAC (MT-MAC) protocol. The model takes into account contention both at the optical and the wireless layer, effectively incorporating the MTMAC mechanism for seamless and dynamic capacity allocation over both optical and wireless transmission media. Based on this model, we provide an extensive delay performance analysis of the Medium Transparent MAC protocol for various optical capacity availability scenarios, varying load conditions and optical network fiber lengths. The theoretical results are found to be in good agreement with respective simulation-based findings, confirming that the employment of Medium Transparent MAC protocols can allow for efficient incorporation of the MT-MAC scheme into the upcoming era of 5G mm-wave small-cell networks.

Full-Duplex (FD) wireless and Device-to-Device (D2D) communication are two promising technologies that aspire to enhance the spectrum and energy efficiency of wireless networks, thus fulfilling key requirements of the 5th generation (5G) of mobile networks. Both technologies, however, generate excessive interference, which, if not managed effectively, threatens to compromise system performance. To this direction, we propose two transmission policies that enhance the communication of two interfering FD-enabled D2D pairs, derived from game theory and optimization theory. The game-theoretic policy allows the pairs to choose their transmission modes independently and the optimal policy to maximize their throughput, achieving significant gains when the pairs interfere strongly with each other., Comment: 6 pages, 7 figures, IEEE Global Communications Conference 2016 (GLOBECOM), Accepted

Optical Code Division Multiple Access (OCDMA) provides increased security communications with large dedicated bandwidth to end users and simplified network control. We analyse the call-level performance of an OCDMA Passive Optical Network (PON) configuration, which accommodates multiple service-classes with finite traffic source population. The considered user activity is in accordance with the bursty nature of traffic, so that calls may alternate between active (steady transmission of a burst) and passive states (no transmission at all). Parameters related to multiple access interference, additive noise, user activity and number of traffic sources are incorporated to our analysis, which is based on a two-dimensional Markov chain. An approximate recursive formula is derived for efficient calculation of call blocking probability. Furthermore, we determine the burst blocking probability; burst blocking occurs when a burst delays its returning from passive to active state. The accuracy of the model is completely satisfactory and is verified through simulation. Moreover, we reveal the consistency and necessity of the proposed model.

The ever increasing demand of elastic and adaptive services, where in-service calls can tolerate bandwidth compression/expansion, together with the bursty nature of traffic, necessitates a proper teletraffic loss model which can contribute to the call-level performance evaluation of modern communication networks. In this paper, we propose a multirate loss model that supports elastic and adaptive traffic, under the assumption that calls arrive in a single link according to a batched Poisson process (a more “bursty” process than the Poisson process, where calls arrive in batches). We assume a general batch size distribution and the partial batch blocking discipline, whereby one or more calls of a new batch are blocked and lost, depending on the available bandwidth of the link. The proposed model does not have a product form solution, and therefore we propose approximate but recursive formulas for the efficient calculation of time and call congestion probabilities, link utilization, average number of calls in the system, and average bandwidth allocated to calls. The consistency and the accuracy of the model are verified through simulation and found to be quite satisfactory.

We study the performance of Machine-to-Machine (M2M) communications in Long Term Evolution Advanced (LTE-A) networks. The proposed analysis is applied to the random access procedure within LTE-A for the calculation of the average overall delay, by considering multiple classes of M2M devices with diverse Quality-of-Service (QoS) requirements. The QoS differentiation is expressed through different Access Class Barring (ACB) parameters and backoff times for the various QoS classes. For the packet arrival process of M2M devices we consider an ON-OFF arrival process, which is a realistic approach, especially for M2M communications in Smart Grid environments. Furthermore, the proposed analysis is suitable for smart grid communication networks, where multiple M2M gateways are installed in different points of the network. The comparison of analytical results with simulations reveals the high accuracy of the proposed analysis.

Super dense wireless cloud network (WCN) provides for a low latency and reliable multi-user communications by leveraging on advanced transmission techniques of densely deployed relays acting as a macro-relay node (so-called WCN). Cloud Access (CA) nodes are gateways to the WCN and their queued packets are flooded through a dense self-contained WCN with massively interacting relay nodes. In this paper, we address the scheduling problem of multiple CA nodes that mutually share the WCN resources to relay multiple flows under heterogeneous traffic arrival rates. We show that when the interference mitigation capability of the WCN is efficient enough, the simultaneous transmissions in all-at-once mode is the optimal solution compared to the baseline scheme. A distributed offloading mechanism is tailored in the WCN backhaul to reduce the traffic heterogeneity effect and activate the maximum possible CA nodes simultaneously. This consequently ties up the end users quality of service (QoS) at a high level of experience as shown by the numerical results.

We discuss the system-level simulation of an ultradense, multi-hop wireless network employing physical layer network coding to increase its throughput and eliminate the effect of interference between links in the network. We describe the network paradigm being developed by the DIWINE project, and the principles of physical layer network coding. The system-level simulator (SLS) operates on a packet level, and determines packet error probability for the network coded data at each relay in terms of the noise power and the signal level from each incoming link. We describe this simulation methodology and the software package used to implement it, and give numerical results for throughput versus load for a simple example network, showing that the approach developed by DIWINE outperforms a simple TDMA baseline scheme under most conditions.

It is envisioned that small cells are going to play an important role in future cellular networks. Due to limited coverage areas of small cells and increased user mobility, a proper analysis and evaluation of handoff traffic is of major importance. In this paper, we propose a novel teletraffic model for the analysis of handoff traffic in cellular CDMA networks. When the cell load is above a predefined threshold, we allow the handoff calls to reduce their bandwidth requirements in order to avoid blocking. Our model also realistically assumes a finite number of traffic sources in the cell and enables analytical determination of uplink blocking probabilities for new and handoff calls. To this end, the CDMA system has been described as a continuous-time Markov chain in order to derive an efficient recursive formula for the calculation of system state probabilities. The proposed analytical model has been validated through simulation experiments, which show good accuracy of the derived results.

Mobility Management in future cellular networks is becoming more challenging due to transition from macro only to multi-tier deployments. In this framework, the massive use of small cells rendered traditional Handover algorithms inappropriate to deal effectively with frequent Handovers, especially for fast users, in dense urban scenarios. Studies in this area focus mainly on the adjustment of the Hysteresis Margin and on the Time-to-Trigger (TTT) selection in line with the Self-Organized Networks (SON), concept. In that sense, the ability of each node to adapt its parameters to the actual scenario is considered vital for the smooth operation of the network. This work contributes to the latter by analyzing the dependence of the Handover performance on the inter-site distance between the macro cell and the small cell. Specifically, the most common KPIs (i.e. Handover, Ping Pong and Radio Link Failure probabilities) are analyzed for different inter-site distances and TTT values to provide solid basis for the TTT selection.

Passive Optical Networks (PONs) constitute a predominant point-to-multipoint architectures for an efficient and cost-effective fiber-based broadband access. We have analyzed several PON configurations, which either have been already standardized, like Wavelength Division Multiplexing - Time Division Multiplexing (WDM-TDM) PONs, or are highly promising PON technologies, like Optical Code Division Multiple Access (OCDMA) PONs. Based on Markov chains, we have developed teletraffic loss models for the call-level performance evaluation in the upstream PON direction. The PONs accommodate multiple service-classes of bursty traffic; to reflect the bursty nature of traffic and to simplify the analysis, we resort to ON-OFF traffic modeling. Call-connection requests are considered random (infinite population of traffic sources) or quasi-random (finite population of traffic sources). The main call-level performance index is the Call Blocking Probability (CBP). For the efficient CBP calculation, we result in approximate recursive formulas, whose the accuracy is completely satisfactory, as it has been verified through simulation.

Hybrid Wavelength-Time Division Multiplexing (WDM-TDM) Passive Optical Networks (PONs) become strong candidates for Next Generation PONs and, therefore, merit deep performance evaluation. In this paper, we concentrate on the performance of a Dynamic Wavelength Allocation (DWA) protocol, under multi-dimensional traffic which is modeled by a Pareto ON-OFF model; it resembles the bursty nature of traffic by considering ON and OFF transmission periods, whose duration is Pareto distributed. The investigated protocol may cause service delay to existing connections, if they will be found in state OFF, while no connection is found in state ON at the same time. In this case, the occupied wavelength is released, and a new wavelength (however, not always available, hence the delay) will be allocated to OFF connections, upon request from a connection to return to state ON. The delay caused by the so-called Delay Wavelength Release (D-WR) protocol, as well as other performance measures, are evaluated via simulation, and compared with the delay and corresponding measures of the same protocol, when the ON-OFF traffic under service has exponentially distributed ON and OFF periods.

Passive Optical Networks (PONs) are attractive fiber-based access systems providing broadband access solutions at a low cost. A hybrid Wavelength Division Multiplexing (WDM) - Time Division Multiple Access (TDMA) PON is a favorite PON configuration, in which the researchers have drawn much attention. We have analysed and proposed several protocols for dynamic wavelength allocation in a WDM-TDMA PON, by separately considering random or quasi-random input-traffic. By modelling the bursty in-service traffic as an ON-OFF model, we have proposed three protocols for random call arrivals. The same protocols have also been proposed for quasi-random call arrivals, resulting however in different evaluation conclusions (than in the case of random arriving calls). This fact gave rise to a fourth protocol, the Priority Wavelength Release (Pr-WR) Protocol, suitable for quasi-random input-traffic. According to this protocol, the service-classes accommodated in the PON are distinguished in two groups: the high and low priority groups. A connection between an Optical Node Unit (ONU) and the Optical Line Terminal (OLT) (the common link of the PON) can be terminated and the occupied wavelength is released, only when the common link is empty or holds low priority calls in state OFF. In this paper, we examine the Pr-WR protocol in the WDM-TDMA PON under a mixture of quasi-random and random arriving calls. The ON-OFF teletraffic model for the mixture of random and quasi-random arrivals is presented. We evaluate the behaviour of this protocol in comparison with the other three protocols in respect of: a) the Connection Failure Probability (due to the unavailability of a wavelength), and b) the Delay (low priority calls may delay in state OFF, until a new wavelength becomes available upon a new call arrival). For the Pr-WR Protocol, we also calculate the Call Blocking Probability (due to the restricted bandwidth of the wavelength) and the Burst Blocking Probability (burst of calls delays in state OFF, due to temporal unavailability of wavelength bandwidth). We come to safe conclusion which is favourite for the Pr-Wr protocol.

We consider a multirate access tree network accommodating K service-classes of Poisson traffic, and focus on the determination of derivatives of Call Blocking Probabilities (CBP) with respect to offered traffic-load of any service-class. Based on the derivatives, we further show how we can successfully approximate CBP for small variations of offered traffic-load.

In this paper, we consider a single link that supports both elastic and adaptive traffic of Batch Poisson arriving calls, under the Bandwidth Reservation (BR) policy, whereby we can achieve specific QoS per service-class. Arriving batches have a generally distributed batch size, and can be serviced either as a whole or in part (partial batch blocking discipline), depending on the available link bandwidth. Blocked calls are lost. Accepted calls of a batch can compress or expand their bandwidth; elastic calls expand or compress their service time accordingly, while adaptive calls do not alter their service time. This system does not have a Product Form Solution. For the efficient calculation of time and call congestion probabilities as well as link utilization, we derive approximate but recursive formulas. The accuracy of the model is completely satisfactory and is verified together with the model's consistency, through simulation. Comparison of the new model with existing models reveals its necessity.

We present a new loss model for the call-level analysis of a single link, which accommodates calls of different service-classes with elastic bandwidth requirements. Calls arrive in the link according to a Batch Poisson process, a process that can be used to model traffic, which is more 'peaked' and 'bursty' than the Poisson process. The available link bandwidth is shared to calls according to the Bandwidth Reservation policy, whereby we can guarantee certain Quality-of-Service for each service-class. In the proposed model, we assume a general batch size distribution and the Partial Batch Blocking discipline. According to this discipline, one or more calls of an arriving batch can be accepted, while the rest can be discarded, depending on the available link bandwidth. New and in-service calls tolerate bandwidth compression/expansion. The analysis of the system is based on Markov chains. Since no Product Form Solution exists, for an efficient solution, we propose an approximate reversible Markov chain. Based on it, we derive a recursive formula for the calculation of link occupancy distribution and consequently time and call congestion probabilities (important call-level performance metrics). The proposed model's accuracy and its consistency are verified by simulation and found to be quite satisfactory.

Optical packet switching is a promising all-optical network technology for future large-scale networks, due to good resource utilization and the ability to handle high data rates in a cost-efficient way. In this paper we investigate the performance of an optical packet switching network, in respect of the packet blocking probability. The network supports the wavelength conversion technique, in order to reduce packet losses. We derive an analytical model for the calculation of blocking probability, based on the reduced load approximation method. The demonstration of the accuracy of the proposed analysis is realized by comparing the analytical results with that of simulation; the results found to be quite satisfactory.

We consider a single-link loss system of capacity C bandwidth units, accommodating K service-classes of Poisson traffic with different bandwidth-per-call requirements. Calls of all service-classes compete for the available link bandwidth under the bandwidth reservation (BR) policy. The BR policy is used in teletraffic engineering in order to achieve call blocking probability (CBP) equalization among different service classes. Such a single-link loss system has been analytically described by the Erlang Multirate Loss Model under the BR policy (EMLM/BR). In this paper, we focus on the problem of determining, in an efficient analytical way, derivatives of blocking probabilities with respect to offered traffic-load of any service-class under the BR policy. We further show through an analytical formula how CBP derivatives can be used to determine approximate CBP when small variations of offered traffic-load are considered.

Future access networks will have to meet the ever increasing demand for capacity. Optical access systems are now considered as a viable alternative solution to the xDSL technologies for delivering future integrated broadband services. Nowadays, passive optical networks are the most promising and cost-effective class of fiber access systems. In this paper we develop teletraffic loss models for calculating connection failure probabilities (due to unavailability of a wavelength) and call blocking probabilities (due to the restricted bandwidth capacity of a wavelength) in hybrid TDM-WDM passive optical networks with dynamic wavelength allocation. The optical access network accommodates bursty services of ON-OFF (transmission or no transmission) type. The proposed models are derived from one-dimensional Markov chains which describe the wavelengths occupancy in the optical access network. The accuracy of the proposed models is validated by simulation and was found to be quite satisfactory.

Optical Packet Switching (OPS) is a promising technology that efficiently utilizes the raw bandwidth provided by the Wavelength Division Multiplexing (WDM) technique. OPS is expected to support the radically increasing bandwidth demands of the Next Generation Internet backbone. Since realtime applications demand various but certain levels of Quality of Service (QoS), optical networks based on OPS should provide service differentiation. In this paper we investigate the performance of an all-optical packet switch, in terms of the packet blocking probability. We analyse several QoS differentiation schemes, including wavelength conversion, packet dropping and wavelength reservation. We demonstrate the accuracy of the proposed analysis by comparing the analytical results with that of simulation; the results found to be quite satisfactory.

Passive Optical Network (PON) systems are rapidly becoming the most promising and cost-effective class of fiber access systems. In this paper we investigate the performance of a simple PON configuration, in respect of the end-to-end packet delay. The network supports multiple service-classes with priorities, in terms of the number of packets that can be transmitted in each transmission period. We calculate the mean queueing delay of a packet, by taking into account the fact that packets are serviced in batches. The queueing delay is defined through the formulation of two queuing models; an M/D/1 model for the batches, and an M/D/m model for the individual packets. We also study the effect of the packet arrival rate of different service-classes, and the effect of the distribution of the packets into a frame, on the end-to-end packet delay. The accuracy of the proposed model is validated by simulation and was found to be quite satisfactory.

We investigate the performance of the IEEE 802.11e in respect of end-to-end delay, which is estimated by the sum of queuing delay and MAC delay. The MAC delay analysis is performed based on elementary probability theory (conditional probabilities) while avoiding the complex Markov Chain method. A comprehensive study of the MAC delay is presented by providing higher moments of the MAC delay distribution. To this end, we use the Z-transform of the backoff duration. The first moment corresponds to the mean MAC delay, while the second moment corresponds to the Standard Deviation of the MAC delay; the latter depicts the jitter. We also estimate the probability mass function (pmf) of the MAC delay through the Lattice Poisson Algorithm. As far as the queuing delay is concerned, we provide the mean queuing delay by considering a queuing system with one queue per Access Category (AC) per mobile station, with a single server (the wireless medium), common to all mobile stations, and a Markov Modulated Poisson Process as input, that expresses the bursty nature of Internet traffic. The presented analytical model provides results of the mean end-to-end delay for both saturated and non-saturated channel conditions.

We study the call-level performance behavior of two Passive Optical Network (PON) configurations in the upstream direction: an Optical Code Division Multiple Access (OCDMA) PON and a hybrid Wavelength Division Multiplexing (WDM)-OCDMA PON. Each PON accommodates 2K service-classes, which are grouped in two service priorities. The latter are denoted by thresholds in accessing the PON resources. The input traffic is assumed quasi-random, (finite number of traffic sources). Our analysis results in recursive formulas for the calculation of the system state probabilities, as well as of the call blocking probabilities and connection failure probabilities. To evaluate the proposed models the analytical results are compared with simulation results. The comparison reveals that the accuracy of the proposed analysis is quite satisfactory.

The passive optical network (PON) is an attractive solution for delivering services with numerous applications, such as high-definition video, video conferencing and data traffic. In this paper we develop teletraffic loss models for calculating connection failure probabilities (due to unavailability of a wavelength) and call blocking probabilities (due to the restricted bandwidth capacity of a wavelength) in hybrid TDM-WDM PONs with dynamic wavelength allocation. We consider either stream or elastic traffic. The proposed models are derived from one-dimensional Markov chains which describe the service system in the PON. The wavelengths occupancy in the PON is also provided. The accuracy of the proposed models is validated by simulation and was found to be quite satisfactory.

The IEEE 802.11 protocol is the dominant standard for wireless local area networks (WLANs) and has generated much interests in investigating and improving its performance. The IEEE 802.11 medium access control (MAC) is mainly based on the distributed coordination function (DCF). DCF uses a carrier sense multiple access with collision avoidance (CSMA/CA) protocol in order to resolve contention between wireless stations and to verify successful transmissions. In this paper we present an extensive investigation of the performance of the IEEE 802.11b MAC protocol, in respect of end-to-end delay. The end-to-end delay analysis of the IEEE 802.11b has not been completed, because no adequate queuing delay is provided. Our delay analysis is based on Bianchi's model for the DCF, while a more comprehensive model could be used as well. We use z-transform of backoff duration to get mean value, variance and probability distribution of MAC delay. From the mean value and the variance of the MAC delay we determine the mean queuing delay in each station. Our analysis is validated by simulation results for both the Basic and RTS/CTS access mechanisms of the DCF. The accuracy of the analysis found to be quite satisfactory. We assume data rates of 1, 5.5 and 11 Mbps, in order to highlight the effect of the bit rate on delay performance for both access mechanisms.

Traffic grooming in Wavelength Division Multiplexing (WDM) optical networks is a promising technology for improving the performance and reducing the network cost. We study the blocking performance of a single-hop WDM traffic groomed optical network, by considering that different connections request service through a single optical link. In each connection the generated calls may come from a single or multiple service-classes. For the case of a single service-class we develop a novel analytical loss model to calculate Connection Blocking Probabilities (ConBP) and Call Blocking Probabilities (CBP). Also, we extend this model to support multiple service-classes. The accuracy of the calculations is verified by simulation and found to be absolutely satisfactory.

Optical access systems are now considered a feasible alternative to the predominant broadband access technologies, while, at the same time, passive optical networks (PONs) are viewed as an attractive and promising type of fiber access system. In this paper we present and analyze three basic dynamic wavelength allocation scenarios for a hybrid wavelength division multiplexing-time division multiple access (WDM-TDMA) PON. We propose new teletraffic loss models for calculating call-level performance measures, like connection failure probabilities (due to unavailability of a wavelength) and call blocking probabilities (due to the restricted bandwidth capacity of a wavelength). The PON accommodates bursty service-classes of ON-OFF traffic. The proposed models are extracted from one-dimensional Markov chains, which describe the wavelength occupancy in the PON, and two-dimensional Markov chains, which describe the bandwidth occupancy inside a wavelength. The accuracy of the proposed models is validated through simulation and is found to be quite satisfactory. Moreover, these models are computationally efficient because they are based on recursive formulas.

The authors present an extensive investigation of the performance of the IEEE 802.11 medium access control (MAC) protocol, with respect to throughput and delay. For the protocol analysis, a new model, which describes the protocol's behaviour to a great extent by incorporating and extending the existing models, is proposed. The authors also present a detailed analysis of the end-to-end delay through the study of the MAC delay and the queueing delay. The authors use the Z-transform of backoff duration to obtain the mean value, the variance and the probability distribution of the MAC delay. For the queueing analysis, first the authors consider an M/G/l queue in order to provide a first look at the queueing delay. Second, the authors modify the input process of the queue so that the packet arrival process is described by an ON- OFF model, which expresses the bursty nature of traffic. In the investigations, data rates of 1, 5.5 and 11 Mbps are assumed to highlight the effect of the bit rate on network performance for both Basic and request-to-send/ clear-to-send access mechanisms. The throughput and delay analyses are validated by simulating the distributed coordination function, whereas the models are compared with the existing models based on their results. The accuracy of the analyses was found to be quite satisfactory.

mmWave radio, although instrumental for achieving the required 5G capacity KPIs, necessitates the need for a very large number of access points, which places an immense strain on the current network infrastructure. In this article, we try to identify the major challenges that inhibit the design of the Next Generation Fronthaul Interface in two upcoming distinctively highly dense environments: in Urban 5G deployments in metropolitan areas, and in ultra-dense Hotspot scenarios. Second, we propose a novel centralized and converged analog Fiber-Wireless Fronthaul architecture, specifically designed to facilitate mmWave access in the above scenarios. The proposed architecture leverages optical transceivers, optical add/drop multiplexers and optical beamforming integrated photonics towards a Digital Signal Processing analog fronthaul. The functional administration of the fronthaul infrastructure is achieved by means of a packetized Medium Transparent Dynamic Bandwidth Allocation protocol. Preliminary results show that the protocol can facilitate Gb/s-enabled data transport while abiding to the 5G low-latency KPIs in various network traffic conditions.

©2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. In this paper, we demonstrate an analytical model for computing the end-to-end packet delay of a converged optical/wireless 60 GHz Radio-over-Fiber (RoF) network operating under the medium-transparent MAC (MT-MAC) protocol. For the calculation of the cycle times, this model considers the protocol time consumed for contention and data exchange over both optical and wireless media, a feature of the MT-MAC that effectively enables it to provide direct and seamless interaction between the RoF Central Office and the end users. This new analytical model enables us to conduct an extensive delay performance analysis of the various performance aspects of hybrid RoF networks operating under the fixed service paradigm, such as various optical capacity availability scenarios, varying load conditions, optical network ranges, transmission window lengths, and data packet sizes. The derived theoretical results present an excellent match with the respective simulation findings, providing sub millisecond latency values for a plethora of network conditions, confirming that the MT-MAC scheme can effectively be incorporated into the upcoming mm-wave 5G era.

Future mobile networks will offer high data rates based on high-capacity fronthaul. Current fronthaul design has two main components that communicate via the common public radio interface and fiber links, i.e., remote units (RUs) that implement simple signal processing and centralized baseband units (CBBUs) in high power-consuming data centers that perform complex network functions. Various functional splits between CBBUs and RUs are feasible, inducing trade-offs between centralization gains and bandwidth demands. This design lacks in capacity and flexibility, motivating the use of converged fiber-wireless (Fi-Wi) fronthaul with high-bandwidth fiber and millimeter-wave links, and splits that move functionalities to RUs reducing the delay demands. Further flexibility is offered by analog radio-over-fiber fronthaul that supports dynamic functional splitting via software-defined networking (SDN). Ensuring acceptable delay for all RUs, i.e., minimizing fronthaul grade-of-service (GoS), requires selection of CBBUs, channel bandwidth and functional splits of RUs. The split type affects fronthaul power consumption determining which fronthaul components are active and their processing power. Using a simulated annealing-based dynamic fronthaul resource allocation (DFRA) scheme, we jointly optimize GoS and power consumption in a novel SDN Fi-Wi fronthaul. Our results show that DFRA minimizes GoS and power consumption for all load levels outperforming baseline approaches.

The upcoming generation of mobile networks is expected to serve numerous mobile users with high quality-ofservice (QoS) demands, requiring high-capacity fronthaul. As the provision of fiber connections directly to the end users is not cost-efficient, the integrated fiber wireless (FiWi) fronthaul design based on wireless networking and passive optical networks (PONs) has been proposed. The FiWi design involves modern networking technologies that can accommodate the need for data rates in the Gb/s scale and low delay, such as the wavelength division multiplexing (WDM) in the optical domain and the multiple input multiple output (MIMO) communication over millimeter wave (mmWave) spectrum in the wireless domain. The co-existence of two network types requires resource management in a medium transparent manner, i.e., the sharing of the bandwidth in the wireless domain should allow the organization of the data packets in optical frames. As the traffic circulating in the FiWi fronthaul involves packets of different priorities, i.e., different QoS classes, the resource management scheme should support QoS differentiation. To this end, we propose a resource management scheme for FiWi fronthaul and we extensively study its performance in terms of experienced delay and throughput. Our simulation results demonstrate that the proposed scheme significantly reduces the delay of the high priority class., Grant numbers : SPOT5G - Single Point of attachment communications heterogeneous mobile data networks ((TEC2017-87456-P).© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.