A hierarchical channel selection scheme for macro/micro cellular networks

Hierarchical channel allocation schemes for cellular networks offer a promising approach to solve the pressing problem of increasing the cellular servicing capacity in spite of the limited radio spectrum available. We propose a hierarchical channel selection scheme for handling handoffs and new calls in micro/macro cellular systems. The scheme is intended to improve the performance and quality of service of these systems by increasing the cell channel utilization, reducing the handoff blocking probability and improving the responsive to new calls. The proposed scheme is based on several design enhancements including an overflow buffer, which is used for handoff calls that cannot be immediately switched to a micro cell channel. The application of this overflow buffer is made feasible by the availability of the umbrella coverage of the macro cell. A modified Guard Channel policy is proposed in conjunction with the overflow buffer for the purpose of giving handoff requests higher priority without the aggressive blocking of new calls. Load balancing rules aimed at the careful selection of micro and macro cell channels are developed. Handoff and new call requests are classified into few categories and control techniques for handling each category are defined. Each allocation for a new channel requires a check on the load factor of the cell. A detailed simulation model was developed to evaluate the hierarchical scheme, refine its design, and compare its performance with four of the schemes previously proposed in the literature. The simulation tests were performed under different tele traffic conditions and parameter values. The performance comparison results obtained by our extensive tests have shown that the proposed scheme consistently reduces the average handoff dropping rate, increases the new call acceptance rate and enhances the throughput of the cellular system

Teletraffic Performance of Hierarchical Cellular Network in Different Populations of Slow Mobile Generated Traffics

Ever since the first analogue mobile cellular was launched 15 years ago, the growth of and demand for the cellular communications have never reached its saturation stage. The technological change from analogue to digital and now the merging of cellular mobile and personal communications system (peS) have already taken place. All of these changes will tremendously increase in the number of mobile communication users which leads to serious Quality of Service (QoS) problems. The objective of layered network architecture comprising a hierarchical layer of different cell sizes is to provide increased capacity and alternate routes for calls that may be otherwise blocked when parts of the network are congested. Thus, this configuration results in higher traffic capacity and improves the quality of service (QoS) of the network. Today, teletraffic problems present a much greater challenge than when the first analogue mobile cellular was launched. The coming of hierarchical network makes it even more challenging to the network designers to design the hierarchical network structure that is able to cope with the huge growth of traffic and provide acceptable QoS to the customers at the same time. In this study two types of cell sizes were used whereby the upper layers are of large cell radius known as macrocells and the lower layers are of small cells radius size known as microcells. The hierarchical structure of cells serves two purposes. Firstly, the cells of small and large radius provide a more economically efficient system for higher and lower traffic densities, respectively, and secondly the subscribers of lower and higher mobility can efficiently be served in small and large cell radius, respectively. Two types of users' mobility patterns within the layers were included in the model. They were fast mobile low traffic density users travelling at the speed of 9 m/s and slow mobile high traffic density moving at the speed of 1.5 m/s. These basically represent the vehicular and pedestrian traffic respectively. Three models for two different categories of slow mobile high traffic densities known as independent model, semi-interactive and fully-interactive model were simulated. They were analysed for 50% and 70% slow mobile high traffic densities

Analysis of hierarchical cellular networks with mobile base stations

In this paper. we develop and evaluate a hierarchical cellular architecture for totally mobile wireless networks (TMWNs). Extensive performance tests were conducted to evaluate the performance of a two-tier system and compare its throughput, handoff blocking rate and new call success rate with those obtained by a one-tier model. Our tests have shown that when the total number of channels is kept the same, the two-tier system outperformed the one-tier counterpart under all load conditions. Under the constraint of equal power consumption, the two-tier system still achieved improvement over the one-tier system. especially at light and medium load levels. The improvement of the two-tier system over the one-tier system was observed to diminish as the degree of randomness in the mobility model is reduced scenarios where the one-tier system outperforms the two-tier system are given. Load balancing schemes based on the concept of reversible handoffs are introduced and their performance improvements are analyzed. Comparison results on the percentage of terminal coverage are presented. An analytical model to compute the new call and handoff blocking probabilities in TMWN is given and evaluated. The model extends the Markov chain approach previously used in hierarchical architectures with stationary base stations and uses a corrected derivation for the handoff blocking probability

Queueing Networks for Vertical Handover

PhDIt is widely expected that next-generation wireless communication systems will be heterogeneous, integrating a wide variety of wireless access networks. Of particular interest recently is a mix of cellular networks (GSM/GPRS and WCDMA) and wireless local area networks (WLANs) to provide complementary features in terms of coverage, capacity and mobility support. If cellular/ WLAN interworking is to be the basis for a heterogeneous network then the analysis of complex handover traffic rates in the system (especially vertical handover) is one of the most essential issues to be considered. This thesis describes the application of queueing-network theory to the modelling of this heterogeneous wireless overlay system. A network of queues (or queueing network) is a powerful mathematical tool in the performance evaluation of many large-scale engineering systems. It has been used in the modelling of hierarchically structured cellular wireless networks with much success, including queueing network modelling in the study of cellular/ WLAN interworking systems. In the process of queueing network modelling, obtaining the network topology of a system is usually the first step in the construction of a good model, but this topology analysis has never before been used in the handover traffic study in heterogeneous overlay wireless networks. In this thesis, a new topology scheme to facilitate the analysis of handover traffic is proposed. The structural similarity between hierarchical cellular structure and heterogeneous wireless overlay networks is also compared. By replacing the microcells with WLANs in a hierarchical structure, the interworking system is modelled as an open network of Erlang loss systems and with the new topology, the performance measures of blocking probabilities and dropping probabilities can be determined. Both homogeneous and non-homogeneous traffic have been considered, circuit switched and packet-switched. Example scenarios have been used to validate the models, the numerical results showing clear agreement with the known validation scenarios

A Price Based Spectrum Sharing Scheme in Wireless Cellular Networks

Radio frequency spectrum scarcity has become a high priority research area over the past few years. The huge increase of network subscribers with multimedia applications coupled with underutilization of radio frequency spectrum motivates the search for other measures to address the scarcity of radio frequency spectrum. This work investigates on a price based spectrum sharing scheme for connection-oriented traffic in wireless cellular networks as a solution to address the scarcity of radio frequency spectrum. Dynamic pricing approach is applied with traffic overflows into neighbor networks. Performance evaluations of the scheme at steady state using MATLAB simulations reveal significant gains to the quality of service. Application of the scheme to highly loaded network traffic improves both network revenue and traffic channel utilizations. Keywords?Pricing, spectrum sharing, traffic overflows, Quality of service, channel utilizations, Wireless cellular networks

State-Dependent Bandwidth Sharing Policies for Wireless Multirate Loss Networks

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

Performance Evaluation in Single or Multi-Cluster C-RAN Supporting Quasi-Random Traffic

In this paper, a cloud radio access network (C-RAN) is considered where the remote radio heads (RRHs) are separated from the baseband units (BBUs). The RRHs in the C-RAN are grouped in different clusters according to their capacity while the BBUs form a centralized pool of computational resource units. Each RRH services a finite number of mobile users, i.e., the call arrival process is the quasi-random process. A new call of a single service-class requires a radio and a computational resource unit in order to be accepted in the C-RAN for a generally distributed service time. If these resource units are unavailable, then the call is blocked and lost. To analyze the multi-cluster C-RAN, we model it as a single-rate loss system, show that a product form solution exists for the steady state probabilities and propose a convolution algorithm for the accurate determination of congestion probabilities. The accuracy of this algorithm is verified via simulation. The proposed model generalizes our recent model where the RRHs in the C-RAN are grouped in a single cluster and each RRH accommodates quasi-random traffic

Modeling of voice data integrated traffic in 3G mobile cellular network, Journal of Telecommunications and Information Technology, 2007, nr 2

The most important feature of 3G mobile cellular network is introduction of voice data integrated service under multilayered cell environment to support overflow traffic of lower layered cells by upper ones. This paper deals with traffic model of three layered cells, i.e., micro cell, macro cell and satellite cell. Here a new call admission control is introduced for three layered cell of 3G mobile cellular network. State transition chain is designed for theoretical analysis of above mentioned traffic. Blocking probability of data call, new voice call and handover failure of voice call, probability of utilization of micro cell channel, macro cell channel and satellite cell channel are analyzed against different traffic parameters and yield logical results