M. Carmen Aguayo-Torres

Capacity with Explicit Delay Guarantees for Generic Sources over Correlated Rayleigh Channel

This work analyzes the joint influence of channel fading and the data outsourcing process in the QoS metrics of a wireless system. As a first contribution, expressions of the channel effective bandwidth function (also known as effective capacity) for time-correlated Rayleigh fading under different adaptive rate policies are obtained. This result allows us to analytically evaluate the maximum constant information rate that can be transmitted over the channel under a probabilistic delay constraint. Later, this Capacity with Probabilistic Delay Constraint CDt, ε is generalized for systems with non-constant sources and simple closed-form expressions able to capture the influence of source processes in the probability of over-delay are given. Figures on how much the maximum allowable rate decreases for shorter allowable delays or for more changing rate sources are shown and the expected delay violation is compared to simulations in order to validate our results.

On finite state Markov chains for Rayleigh channel modeling

The use of finite state Markov chains (FSMC) for the simulation of the Rayleigh channel has been generalized in the last years. Several parameters influence the construction of the chain. The chain can be defined in terms of the complex channel response, the envelope of the received signal or the Signal to Noise Ratio. Moreover the partition method has to be selected among various options. This paper presents an evaluation of the FSMC, including a novel partition method that makes a uniform division of the density function of the desired signal and a comparison with other methods of generation of the fading channel. First and second order statistics and other performance parameters are examined in order to shed more light on the advantages and limitations of the Markov modeling.

Qos modeling for performance evaluation over evolved 3g networks

The end-to-end Quality of Service (QoS) must be ensured along the whole network in order to achieve the desired service quality for the end user. In hybrid wired-wireless networks, the wireless subsystem is usually the bottleneck of the whole network. The aim of our work is to obtain a QoS model to evaluate the performance of data services over evolved 3G radio links. This paper focuses on the protocols and mechanisms at the radio interface, which is a variable-rate multiuser and multichannel subsystem. Proposed QoS models for such scenario include selective retransmissions, adaptive modulation and coding, as well as a cross-layer mechanism that allows the link layer to adapt itself to a dynamically changing channel state. The proposed model is based on a bottom-up approach, which considers the cumulative performance degradation along protocol layers and predicts the performance of different services in specific environments. Numerical parameters at the physical layer resemble those proposed for 3GPP Long Term Evolution (LTE). By means of both analytical (wherever possible) and semi-analytical methods, streaming service quality indicators have been evaluated at different radio layers.

Multiuser capacity for heterogeneous QoS constraints in uncorrelated Rayleigh channels

In this work, we derive analytical expressions for the maximum attainable user rate by accomplishing a probabilistic delay constraint in an uncorrelated Rayleigh channel. These rates are derived for two representative scheduling schemes, round robin (RR) and best channel (BC) allocation, but presented tools can be applied to any scheduling policy. On the basis of the effective bandwidth theory, the result follows the same procedure as, where the capacity with probabilistic delay constraint CD t ,¿ was defined as the maximum source rate that may be supported in a single-user wireless system with a probability ¿ of exceeding certain delay bound Dt. The extension to a multiuser system and the evaluation of the user rates show to what extent the throughput maximization of BC allocation is attained at the expense of fairness, whereas in the RR scheduling both the differences among users and the total system capacity are smaller. Simulations are finally performed in order to validate our results.

A Real-Time End-to-End Testbed for Evaluating the Performance of Multimedia Services

In this paper, we describe a real-time testbed used to assess the end-to-end performance for multimedia services. This testbed uses network performance indicators to emulate the behavior of any network type (fixed, cellular, etc.). Application performance indicators can be evaluated by running a multimedia service on top of the emulated network. A user is able to experience real-time the subjective quality of any multimedia service running over whatever network. In this paper, we describe the testbed architecture and evaluate the performance of streaming services over future wireless networks, based on 3GPP Long Term Evolution (LTE).

Analysis of Delay Constrained Communications over OFDM Systems

Ergodic capacity is not a suitable information-theoretic measure for delay sensitive applications over fading channels. On the other hand, delay-limited capacity becomes zero for Rayleigh channels. In this case, the Capacity with Probabilistic Delay Constraint becomes useful. In [1], the maximum constant source rate that may be supported in a wireless system with a probability Ɛ of exceeding certain delay bound Dt, CDt, Ɛ was evaluated for a Rayleigh channel. This contribution extends that work to an OFDM system over a generic Rayleigh frequency selective channel. An analytical expression of the capacity CDt, Ɛ is obtained and figures on how much the maximum allowable rate decreases for higher time or frequency correlation in the channel response are shown. Finally, the expected delay violation is compared to simulations in order to validate our results.

A Framework to Evaluate Fairness in Fractional Frequency Reuse Based Cellular Networks

The focus in Mobile communication networks has been addressed to high data rate networks that offer high quality of service. Long Term Evolution Advanced (LTE-A) technology has been the first to completely fulfill 4G requirements. However, performance gains remain limited due to severe interference levels. For this reason, the Inter-Cell Interference (ICI) problem is one of the main challenges in LTE-A systems. In order to deal with this ICI problem, in this paper we propose a novel framework to analyze the fairness of several scheduling techniques when Fractional Frequency Reuse (FFR) schemes are used. We evaluate the system performance of a typical FFR-based LTE-A scenario. Performance results show the optimum values of the Signal to Interference plus Noise Ratio and partition bandwidth for frequency reuse that maximizes the spectral efficiency. Fairness evaluation has been done in terms of the Gini index, showing a trade-off between spectral efficiency and fairness among users. In that sense, the proposed Truncated-Equal Transmission Rate scheduling policy is able to adjust this trade-off by means of a parameter

Fairness and Rate Coverage of Symmetric Transmission over Heterogeneous Cellular Networks under Diverse Coupling and Association Criteria

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