Loren Carrasco

Using Two-Dimensional Markov Models and the Effective-Capacity Approach for Cross-Layer Design in AMC/ARQ-Based Wireless Networks

This paper proposes a novel framework for the cross-layer analysis and design of wireless networks combining adaptive modulation and coding (AMC) at the physical layer with an automatic repeat request (ARQ) protocol at the data-link layer. Most previous works rely on first-order amplitude-based finite-state Markov chains (AFSMCs) to model the physical layer. It is shown that these models present several deficiencies that could compromise the design of higher layer protocols. Thus, a physical-layer first-order 2-D Markov model using both the amplitude and the rate of change of the fading envelope is presented. Based on this multidimensional physical-layer Markov model, the quality-of-service (QoS) performance at the data-link layer is investigated through the use of two different approaches. The first one relies on an analytical framework based on a discrete-time Markov chain (DTMC) that jointly describes the statistical behavior of the arrival process, the queueing system, and the physical layer. The second one is based on the effective-bandwidth and effective-capacity theories. Both the DTMC-based and the effective-bandwidth/capacity-based approaches are analyzed and compared in combination with our proposed physical-layer first-order 2-D Markov model in a cross-layer design aiming to satisfy the required average packet loss probability constraint by maximizing the average throughput of the system. Numerical results show that our proposed framework represents a significant improvement over previous models.

Reverse Link Performance of a DS-CDMA System With Both Fast and Slow Power Controlled Users

In this paper the performance of the reverse link of a multicell DS-CDMA system with coexisting open-loop and closed-loop power controlled users transmitting heterogeneous traffic is analyzed. Real-time and non-real-time traffic performance expressions are obtained. The analysis includes a different channel coding scheme for each traffic type selected in accordance to their specific QoS requirements. Moreover, the study takes into account the effect of frequency-selective Nakagami-m fading with arbitrary parameters, correlated log-normal shadowing, power control imperfections and selection-based macroscopic diversity. How the power control imperfections, the number of resolvable paths, or the proportion of simultaneous open-loop and closed-loop power controlled users affect the reverse link capacity of the system is discussed in detail. Analytical results are also given for systems with different processing gains and for propagation environments with different multipath intensity profile (MIP) distributions.

Cross-Layer Optimization of Adaptive Multi-Rate Wireless Networks Using Truncated Chase Combining HARQ

A cross-layer performance analysis of a wireless network using adaptive modulation and coding at the physical layer and a truncated Chase combining hybrid automatic repeat request (HARQ-CC) scheme for error control at the data link layer is developed. Based on a Markov chain queueing model, analytical expressions for performance metrics such as throughput, average packet delay and packet loss rate are derived and then used to formulate a constrained optimization problem to maximize the system throughput under the prescribed Quality-of-Service constraints. Numerical results reveal that HARQ-CC consistently outperforms the classical Type-I Hybrid forward error correction/automatic repeat request schemes.

Effect of Slow Power Control Error on the Reverse Link of OSTBC DS-CDMA in a Cellular System With Nakagami Frequency-Selective MIMO Fading

In this paper, the performance of a multicell orthogonal space-time block-coding direct-sequence code-division-multiple-access system with base station diversity is studied for the reverse link in terms of bit error rate, taking into account the effects of frequency-selective Nakagami-m fading with arbitrary parameters, correlated lognormal shadowing, power control imperfections, selection-based macroscopic diversity, and space-time rake receiver diversity. How the transmitter and receiver antenna configuration setups, the number of rake fingers, and the number of resolvable paths affect the reverse-link capacity of the system is discussed in detail. Analytical results are also given for systems with different processing gains and for propagation environments with different multipath intensity profile distributions

Cross-layer modeling of AMC/ARQ-based wireless networks with outdated CSI

State-of-the-art wireless communications standards combine (hybrid) automatic repeat request (HARQ) protocols at the data link control (DLC) layer with adaptive modulation and coding (AMC) strategies at the physical layer. Most previous work on cross-layer modeling of these networks assumes the availability of ideal channel state information (CSI). However, in practical systems the CSI used to perform link adaptation may be outdated. This paper presents a generalized cross-layer multidimensional discrete-time Markov chain (DTMC)-based queuing model that jointly exploits the capabilities of ARQ and AMC, by explicitly accounting for imperfections in the AMC scheme caused by the delay in the CSI feedback channel. Based on the stationary state probability distribution of the proposed multidimensional DTMC, closed-form analytical expressions for performance metrics such as average throughput, queue length, packet delay and packet loss rate are derived, and an analysis of the impact of using outdated CSI on these performance parameters is presented.

A Two-Dimensional Markov Model for Cross-Layer Design in AMC/ARQ-Based Wireless Networks

Nowadays, there are lots of research efforts focusing on cross-layer designs combining adaptive modulation and coding (AMC) with an automatic repeat request (ARQ) protocol. One of the main drawbacks of these research works is that they rely on first-order amplitude-based finite-state Markov chains (AFSMC) to model the wireless fading channel. Furthermore, most of the analytical models used in these works present several deficiencies that could compromise the design of cross-layer protocols. To overcome the aforementioned problems, in this paper we propose a novel cross-layer analytical framework that is based on both the use of a first-order two-dimensional Markov model and a judicious implementation of the AMC threshold searching algorithm used in the transmission mode (TM) selection. This threshold search is designed independently from the channel model and is able to discriminate between useful and useless TMs. To exploit the joint impact on QoS performance measures of both AMC and ARQ we present a formulation of an AMC/ARQ cross-layer design as a constrained optimization problem.

Cross-layer design of multi-rate wireless networks based on link layer truncated ARQ

A Markov chain-based queueing model is developed for a cross-layer performance analysis of a wireless network based on adaptive modulation and coding (AMC) at the physical layer and truncated automatic repeat request (ARQ) error control at the data link layer. This model generalizes previous results by using a first-order two-dimensional Markov chain to model the wireless fading channel. Furthermore, it allows each frame at the physical layer to contain an arbitrary number of packets from the data link layer and still ensuring that, concerning the acknowledged packets, the transmit buffer operates in first-in first-out (FIFO) mode. Analytical expressions for performance metrics such as throughput, average packet delay and packet loss rate, both due to buffer overflow and due to exceeding the maximum number of allowed retransmissions, are derived. These expressions are then used to formulate a constrained optimization problem to maximize the system throughput under the prescribed QoS constraints.

Scheduling algorithms for 4G wireless networks

Scheduling algorithms are fundamental components in the process of resource management in mobile communication networks with heterogeneous QoS requirements such as delay, delay jitter, packet loss rate or throughput. The random characteristics of the propagation environment and the use of complex physical layers in order to combat this random behavior further complicates the design of simple, efficient, scalable and fair scheduling algorithms. This paper presents the main criteria used in the design of scheduling algorithms for 3G/4G mobile communications networks and provides a survey of scheduling mechanisms proposed for use in TDMA and CDMA based systems.

W-CDMA MAC protocol for multimedia traffic support

This paper proposes a multimedia MAC protocol to be used at the top of the new generation W-CDMA air interfaces. The protocol is highly interrelated with the power control functionality in order to extract the maximum capacity and flexibility out of the CDMA scheme. Moreover the protocol includes a complete set of QoS mechanisms to ensure the correct and fair coexistence of very different traffic types.

A New MAC Protocol Ensuring the Multimedia Traffic QoS for CDMA Networks

This paper describes the CDMAC, a new Medium Access Control (MAC)protocol for multimedia traffic in CDMA wireless networks. Theprotocol intends to extract the maximum capacity and flexibilityout of the CDMA scheme and at the same time guarantee the expectedQoS of different service types. CDMAC is able to maintain QoSrequirements thanks to the shaping, policing and trafficdifferentiation performed by the scheduler. Moreover, an iterativealgorithm, applied at the beginning of each frame, is used to findthe optimal power vector for all mobiles present in the system,which maximize the system capacity. The basic constraint of thecapacity maximization process is that the BER QoS of eachconnection should be fulfilled. Finally a distributedimplementation, feasible in a practical scenario, is presented.