Carmen B. Rodríguez-Estrello

System-Level Analysis of Mobile Cellular Networks Considering Link Unreliability

Traditionally, system-level performance evaluation of mobile wireless communication networks has been addressed by only considering resource insufficiency, whereas the effect of an unreliable wireless channel has largely been ignored because of the complexity that its inclusion entails. To fill this void, a general analytical model for the system-level performance evaluation of mobile wireless networks taking into account both resource insufficiency and link unreliability is proposed in this paper. The effect of link unreliability is captured through the appropriate probabilistic characterization of the ldquounencumbered call-interruption time.rdquo Additionally, useful functional relationships between the call-interruption processes of the proposed analytical model and some system-level parameters that can easily be obtained from statistics collected at base stations (BSs) are derived. For the sake of generality, the involved time variables (i.e., cell dwell time, unencumbered call-interruption time, and channel holding time) are considered generally distributed. Then, general and easily computable mathematical expressions for many useful performance metrics under more realistic considerations are obtained. The analytical model proposed here is able to provide new and important insights into the dependence of system performance on link unreliability. Such understanding of this teletraffic engineering issue is vital for planning, designing, dimensioning, and optimizing mobile cellular networks for present and future wireless communication systems beyond the third generation.

Queueing analysis of mobile cellular networks considering wireless channel unreliability and resource insufficiency

A queueing model for the system level performance evaluation of mobile cellular networks considering both resource insufficiency and wireless channel unreliability is proposed and mathematically analyzed. The proposed mathematical approach is based on the use of simple call interruption processes to model the effect of wireless channel unreliability. More importantly, this paper develops a system level teletraffic model for the performance evaluation considering that channel holding times for new and handed off calls are general (but not necessary identically) distributed random variables. Additionally, an approximated one-dimensional recursive approach based on the well known Kauffman-Roberts formula is proposed for the case when the channel holding time variables can be adequately characterized by Hyper-Exponential distributions. Also, the case when the channel holding time variables are Mixed-Erlang distributed, a distribution having universal approximation capability, is analyzed. Thus, our teletraffic model allows obtaining more general, realistic, and easily computable analytical results.

System Level Model for the Wireless Channel Unreliability in Mobile Cellular Networks

In this paper, a new system level approach for the wireless channel unreliability modeling is proposed. Firstly, in order to characterize the call interruption process due to the wireless channel unreliability, the Gilbert-Elliot model is used to obtain the probability distribution of the interruption time. Then, it is shown that link unreliability can be adequately modeled by considering a Poissonian call interruption process. This allows simplifying system level mathematical analysis and easily identifying the factors that mainly influence the performance of mobile cellular networks. For the characterization of the interruption process in real cellular networks, it is enough to know some few system level statistics that can be easily obtained at base stations. Then, with the proposed call interruption modeling, an elegant teletraffic analysis for the performance evaluation of mobile cellular networks considering both wireless link unreliability and resource insufficiency is developed.

System Level Performance Metrics in Mobile Wireless Communication Networks Considering Both Resource Insufficiency and Link Unreliability

Teletrafflc modeling of mobile communication networks has been commonly addressed by considering only resource insufficiency, while the effect of the unreliability nature of wireless channels has been largely ignored because of the complexity involved in its study. To fill this void, a general analytical model for the system level performance evaluation of mobile wireless networks taking into account both resource insufficiency and link unreliability is proposed and mathematically analyzed in this paper. In the mathematical analysis, for the sake of generality, the involved time variables (i.e., cell dwell time, unencumbered call interruption time, and channel holding time) are considered to have a general probability distribution. Then, original and easily computable mathematical expressions for many fundamental system level performance metrics are derived. The proposed analytical model allows obtaining more general and realistic results.

Waiting time analysis for an OFDMA wireless cellular system with finite buffering and AMC

In this paper, the waiting time analysis for an OFDMA wireless cellular system with finite buffering and Adaptive Modulation and Coding (AMC) is addressed. When AMC is considered, several concentric regions within cells serving users with different data rates are differentiated. Phase type (PHT) distribution functions are used to model the conditional cumulative distribution function of the waiting time for users in the different coverage regions. The representation of the conditional waiting time distribution through PHT distributions allows expressing cumulative distribution function (CDF) as a linear combination of negative exponential distributions. The analytical method proposed here captures the exact behavior of the waiting time and the obtained solution is based on matrix analytic derivation, which allows evaluating system performance for any size of buffer and any number of coverage regions.

Approximated Calculations of Connection Level Access Waiting Time Distribution in OFDMA-Based Wireless Cellular Systems with AMC

In this paper, two analytical approaches to approximately calculate the access (at connection level) waiting time distribution for an OFDMA-based wireless cellular system with finite buffering under First-Come, First-Served (FCFS) discipline and Adaptive Modulation and Coding (AMC) are proposed. It has been demonstrated in previous published works that access waiting time is a random sum of random variables with the same distribution but random mean. Therefore, the computational complexity for the numerical evaluation of the access waiting time probability distribution increases exponentially with the size of the buffer and the number of coverage regions. In order to reduce the computational complexity, the use of negative exponential distribution is proposed to approximate the whole access waiting time distribution for certain conditions of traffic load. Moreover, an efficient way to calculate its parameter through the Littles theorem is proposed. A more general approach is based on the central limit theorem (CLT). In particular, it considers that the conditional access waiting time of a service request queued in the a given position can be adequately approximated by a Gaussian distribution. The proposed approximation approaches are numerically evaluated and compared against the exact mathematical analysis in terms of the cumulative distribution function. Numerical results show that the maximum percentage error between the both approximated CDFs is smaller than 10% relative to the exact analysis under certain conditions.

On the system-level statistical characterization of link unreliability in cellular networks

In this paper, statistical characterization of link unreliability in cellular networks at system level is addressed. Traditionally, system-level performance evaluation of mobile wireless communication networks has been performed by considering only resource insufficiency, while the effect of unreliable wireless channel has been largely ignored. Recently, a new system level analytical approach to capture the effect of both link unreliability and radio resource insufficiency in mobile wireless networks was proposed. In that model, the effect of unreliable wireless channel is captured through the appropriate statistical characterization of the unencumbered call interruption time (UCIT). The present paper shows how the probability distribution function of unencumbered call interruption time can be derived from either few system level statistics that can be easily obtained at base stations or link level statistics. Numerical results clearly show that UCIT should be modeled as a general distributed random variable to adequately capture the effect of link unreliability.