In this paper we consider a cloud radio access network (C-RAN) architecture where the baseband signal processing servers, named baseband units (BBUs) are separated from the remote radio heads (RRHs). The RRHs form a single cluster while the BBUs form a centralized pool of data center resources. Each RRH of the C-RAN accommodates bursty traffic which is expected to play a dominant role in 5G networks. We approximate bursty traffic via the compound Poisson process according to which batches of calls, with a generally distributed batch size, occur at time points that follow a negative exponential distribution. Each call of a new batch is treated separately from the other calls of the same batch. A new call requires a computational resource unit from the centralized pool of BBUs and a radio resource unit from the serving RRH. If both units are available, then the call is accepted in the RRH for an exponentially distributed service time. Otherwise, call blocking occurs. We model this C-RAN as a loss system and show that the steady state probabilities have a product form solution (PFS). Based on the PFS, we propose an efficient convolution algorithm for the accurate calculation of the main performance measures which are time and call congestion probabilities. The accuracy of this algorithm is verified via simulation.

The authors study the downlink of an orthogonal frequency division multiplexing (OFDM) based cell that services calls from different service‐classes with various resource requirements. They assume that calls arrive in the cell as batches according to a compound Poisson process. They consider that the batch size is generally distributed while each call of a batch is treated separately from the other calls of the same batch, according to the complete sharing policy. To determine the most important performance metrics, i.e. congestion probabilities and resource utilisation in this OFDM‐based cell, they model it as a multirate loss model, show that the steady‐state probabilities can be determined via a product form solution (PFS) and propose recursive formulas which reduce the complexity of the calculations. In addition, they study the bandwidth reservation (BR) policy which can be used for the reservation of subcarriers in order to favour service‐classes whose calls have high subcarrier requirements. The existence of the BR policy destroys the PFS of the steady‐state probabilities. However, they show that there exist recursive formulas for the determination of the various performance measures. Simulation verifies the accuracy of the proposed formulas.

The authors consider a low earth orbit (LEO) mobile satellite system (MSS) that accepts new and handover calls of multirate service‐classes. New calls arrive in the system as batches, following the batched Poisson process. A batch has a generally distributed number of calls. Each call is treated separately from the others and its acceptance is decided according to the availability of the requested number of channels. Handover calls follow also a batched Poisson process. All calls compete for the available channels under the complete sharing policy. By considering the LEO‐MSS as a multirate loss system with ‘satellite‐fixed’ cells, it can be analysed via a multi‐dimensional Markov chain, which yields to a product form solution (PFS) for the steady‐state distribution. Based on the PFS, they propose a recursive and yet efficient formula for the determination of the channel occupancy distribution, and consequently, for the calculation of various performance measures including call blocking and handover failure probabilities. The latter are much higher compared to the corresponding probabilities in the case of the classical (and less bursty) Poisson process. Simulation results verify the accuracy of the proposed formulas. Furthermore, they discuss the applicability of the proposed model in software‐defined LEO‐MSS.

We consider a reference cell of fixed capacity in a wireless cellular network while concentrating on next-generation network architectures. The cell accommodates new and handover calls from different service-classes. Arriving calls follow a random or quasi-random process and compete for service in the cell under two bandwidth sharing policies: 1) a probabilistic threshold (PrTH) policy or 2) the multiple fractional channel reservation (MFCR) policy. In the PrTH policy, if the number of in-service calls (new or handover) of a service-class exceeds a threshold (difference between new and handover calls), then an arriving call of the same service-class is accepted in the cell with a predefined state-dependent probability. In the MFCR policy, a real number of channels is reserved to benefit calls of certain service-classes; thus, a service priority is introduced. The cell is modeled as a multirate loss system. Under the PrTH policy, call-level performance measures are determined via accurate convolution algorithms, while under the MFCR policy, via approximate but efficient models. Furthermore, we discuss the applicability of the proposed models in 4G/5G networks. The accuracy of the proposed models is verified through simulation. Comparison against other models reveals the necessity of the new models and policies.

In the recent years, mobile cellular networks are undergoing fundamental changes and many established concepts are being revisited. New emerging paradigms, such as Software-Defined Networking (SDN), Mobile Cloud Computing (MCC), Network Function Virtualization (NFV), Internet of Things (IoT), and Mobile Social Networking (MSN), bring challenges in the design of cellular networks architectures. Current Long-Term Evolution (LTE) networks are not able to accommodate these new trends in a scalable and efficient way. In this paper, first we discuss the limitations of the current LTE architecture. Second, driven by the new communication needs and by the advances in aforementioned areas, we propose a new architecture for next-generation cellular networks. Some of its characteristics include support for distributed content routing, Heterogeneous Networks (HetNets) and multiple Radio Access Technologies (RATs). Finally, we present simulation results which show that significant backhaul traffic savings can be achieved by implementing caching and routing functions at the network edge.

In this paper, we propose a multirate teletraffic loss model of a single link with certain bandwidth capacity that accommodates Poisson arriving calls, which can tolerate bandwidth compression (elastic traffic), under the threshold policy. When compression occurs, the service time of new and in-service calls increases. The threshold policy provides 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. Due to the bandwidth compression mechanism, the steady state probabilities in the proposed model do not have a product form solution. However, we approximate the model by a reversible Markov chain, and prove recursive formulas for the calculation of call blocking probabilities and link utilization. The accuracy of the proposed formulas is verified through simulation and found to be very satisfactory.

Software-defined networking (SDN) has gained a tremendous attention in the recent years, both in academia and industry. This revolutionary networking paradigm is an attempt to bring the advances in computer science and software engineering into the information and communications technology (ICT) domain. The aim of these efforts is to pave the way for completely programmable networks and control-data plane separation. Recent studies on feasibility and applicability of SDN concepts in cellular networks show very promising results and this trend will most likely continue in near future. In this work, we study the benefits of SDN on the radio resource management (RRM) of future-generation cellular networks. Our considered cellular network architecture is in line with the recently proposed Long-Term Evolution (LTE) Release 12 concepts, such as control-data plane split, heterogeneous networks (HetNets) environment, and network densification through deployment of small cells. In particular, the aim of our RRM scheme is to enable the macro base station (BS) to efficiently allocate radio resources for small cell BSs in order to assure quality-of-service (QoS) of moving users/vehicles during handoffs. We develop an approximate, but very time- and space-efficient algorithm for radio resource allocation within a HetNet. Experiments on commodity hardware show algorithm running times in the order of a few seconds, thus making it suitable even in cases of fast moving users/vehicles. We also confirm a good accuracy of our proposed algorithm by means of computer simulations.

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.

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.

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 present a new model, named Wireless Finite Connection-Dependent Threshold Model, for the call-level analysis of W-CDMA networks that support both elastic and stream traffic. Calls generated by service-classes of finite source population (quasi-random call arrival process) compete for their acceptance to a W-CDMA cell, under the complete sharing policy. An arriving call can be accepted with one of several contingency Quality-of-Service (QoS) requirements, depending on the resource availability in the cell; the latter is indicated by thresholds. We present an approximate but recurrent formula for the efficient calculation of the system state probabilities; consequently, the call blocking (time congestion) probabilities and other performance metrics in the uplink direction are provided. The model's accuracy is verified by simulation and found to be quite satisfactory. Moreover, the proposed model performs much better than the corresponding model of infinite number of sources.

The call-level performance modelling and evaluation of 3G cellular networks is important for the proper network dimensioning and efficient use of the network resources, such as bandwidth and power. In the case of the wideband code division multiple access (W-CDMA) cellular networks, this task is complicated, not only because of the so called soft blocking, the multiple access interference (MAI) and the heterogeneous traffic, but also due to the handoff process. In this paper, we propose a new teletraffic model for the call-level analysis of handoff traffic in the uplink of W-CDMA networks where multiple services with finite number of traffic sources are accommodated. Parameters related to the soft blocking and MAI are included into the model. The proposed model is described by a discrete time Markov chain. An efficient recurrent formula for the calculation of the system state probabilities is derived. Based on this formula, blocking probabilities of both new and handoff calls are determined. The accuracy of the proposed model is evaluated through simulation and is found to be very satisfactory. Moreover, we show the necessity of distinguishing the handoff traffic from the new traffic, in respect of blocking probabilities.

We propose a new teletrafflc model for the calculation of link occupancy distribution and determine the call blocking probabilities and link utilization in a single-link multi-rate loss system. We considerKdifferent service-classes, either of elastic or of adaptive type, that compete for the available link bandwidth under the complete sharing policy. Calls arrive to the link with several contingency bandwidth requirements that depend on thresholds, which indicate the total link occupied bandwidth. It is possible for a call, while in service with a certain bandwidth to reduce it, in order for new calls to be accepted in the link. The accuracy of the new model is verified by simulation results. Moreover, the proposed model performs much better than the existing model for elastic and adaptive traffic.

We propose a new teletraffic model, named Wireless Engset Multi-rate Loss Model (W-EnMLM) for the call-level analysis of W-CDMA networks, supporting heterogeneous service-classes of finite population of traffic sources. Quasi- random arriving calls (generated by mobile users), compete for their admission to a W-CDMA cell under the Complete bandwidth Sharing (CS) policy. We present an approximate but recurrent formula for the efficient calculation of the system state probabilities and the call blocking probabilities in the uplink direction. The accuracy of the proposed model is verified by simulation results and found to be completely satisfactory. Moreover, the proposed model performs much better than the corresponding model of infinite number of traffic sources.

We consider an ON-OFF traffic model of a single link which accommodates service-classes of finite population. Calls arrive according to a quasi-random process and, if accepted, enter the system via state ON; then calls may alternate between ON-OFF states. When a call is transferred to state OFF, it releases the bandwidth held in state ON, while when it tries to return to state ON it re-requests its bandwidth. If it is available a new ON-period (burst) begins; otherwise burst blocking occurs and the call remains in state OFF. We prove that the proposed finite source ON-OFF model (f-ON-OFF) has a product form solution and provide an accurate recursive formula for the call blocking probabilities calculation. For the burst blocking probabilities calculation we propose an approximate formula. Finally, we generalize the f-ON-OFF model to include a mixture of service-classes of finite and infinite number of sources. Simulation results validate our analytical methodology.

The call-level QoS assessment in ATM networks remains an open issue, due to elastic services. We consider the coexistence of available bit rate (ABR) services with QoS guarantee services in a virtual path (VP) link and evaluate the call blocking probabilities (CBP). To this end, firstly, we review two extensions of the Erlang multirate loss model and examine their applicability on ABR services. In the first extension, the retry models, blocked calls can retry with reduced resource requirements and increased arbitrary mean residency requirements. In the second extension, the threshold models, request sizes and residency times are state dependent. For both models, we present expressions for efficient calculation of the final CBP. Secondly, we propose the connection-dependent threshold model, which resembles the threshold models, but the state dependency is individualized among call connections. Finally we evaluate the above-mentioned models by comparing them based on the resultant CBP. Our investigation shows that the retry models can hardly approach the behavior of ABR services, while the threshold models perform better than the retry models. The proposed connection-dependent threshold model performs much better than the threshold models. Simulation results validate the proposed model.

This paper presents a model for large-scale hierarchical networks which leads to an almost optimal path bandwidth (PB) allocation, under constraints posed by the installed bandwidth in the transmission links of the network. The PB allocation procedure consists of three phases. In the first phase, a suitable decomposition of the whole network takes place, in which the hierarchical network is split to a set of sub-networks of just one level. In the second phase, the optimization algorithm developed for one-level telecommunication networks is applied to each subnetwork to define the optimal PB allocation. The optimization criterion is to minimize the worst call blocking probability (CBP) of all switching pairs of the sub-network. In the third phase, composition of the sub-networks takes place in a successive way which leads to the final PB allocation. As the hierarchical network is built up from optimized sub-networks, it is considered that it has an almost optimal PB allocation. The proposed PB allocation scheme is explained by means of an example.

The paper presents a centralized virtual path bandwidth (VPB) control scheme for ATM networks which satisfies mainly three specifications: a) optimality during a medium-term control interval, b) fast time response so as to absorb the medium-term traffic fluctuations, and c) easy implementation. The paper mainly points at the impact of direct, on-line traffic measurements on bandwidth control. The control objective is to rearrange the installed bandwidth of the virtual paths according to the offered traffic so as to minimize the maximum call blocking probability of the whole network. Network simulation shows that a sophisticated VPB controller which relies on simple measurements of the offered traffic can substantially improve the performance of an ATM network. The necessary bandwidth rearrangement time is also examined by simulation.>