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ABSTRACT: This paper presents a MAC-PHY cross-layer semianalytical model allowing the goodput performance evaluation of open- and closed-loop link adaptive schemes in WLAN environments based on IEEE 802.11n. Without loss of generality, this paper considers the well-known open-loop automatic rate fallback (ARF) algorithm and a closed-loop fast link adaptation (FLA) algorithm based on exponential effective SNR mapping (EESM). In contrast to previous works, the channel conditions are not assumed to be ideal and users are allowed to use different transmission modes. Results are presented demonstrating the accuracy of the proposed model. Moreover, results serve to show the superiority of closed-loop over open-loop techniques, specially when the number of stations contending for the medium grows.
Communications (ICC), 2011 IEEE International Conference on; 07/2011
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ABSTRACT: To provide heterogeneous quality-of-service (QoS) guarantees to applications, most wireless communications standards combine the error-correcting capability of hybrid automatic repeat request (HARQ) protocols at the data link control layer with the adaptation ability of adaptive modulation and coding (AMC) strategies at the physical layer. In this paper, a novel cross-layer multidimensional discrete-time Markov chain (DTMC)-based queuing model is developed to jointly exploit the capabilities of HARQ and AMC. The analytical DTMC-based model, which generalizes and extends previous results on this topic, stems from a comprehensive consideration of packet multimedia traffic sources modeled as discrete-batch Markovian arrival processes, finite queue-length systems, truncated HARQ protocols, AMC strategies, and a wireless channel first-order 2-D Markov model that relies on the amplitude and rate of change of the fading envelope. Based on the stationary state probability distribution of this multidimensional DTMC, closed-form analytical expressions for performance metrics such as throughput, average packet delay, and packet loss rate, which were caused either by buffer overflow or by exceeding the maximum number of allowed retransmissions, are derived. Furthermore, the proposed analytical framework is used to formulate multidimensional and simplified 2-D constrained optimization problems aiming at maximizing the system throughput under prescribed QoS constraints. Computer simulation results are carried out to verify the validity of the proposed analytical model and to quantify the performance gain due to cross-layer optimization and the use of truncated HARQ protocols.
IEEE Transactions on Vehicular Technology 04/2011; · 1.92 Impact Factor
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ABSTRACT: 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.
Global Telecommunications Conference (GLOBECOM 2010), 2010 IEEE; 01/2011
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ABSTRACT: This paper considers the use of precoding in MIMO-OFDM systems based on deterministic channel state information at the transmitter (CSIT). The proposed technique combats subcarrier fading using a linear spreading of the source information in the spatial and frequency domains. Unlike previous works, it is assumed that the receiver does not necessarily has to rely on linear processing, allowing in this way more powerful receiver strategies. In particular, it is shown that a detector based on the maximum likelihood (ML) criterion brings along important performance benefits. Different spreading strategies are evaluated in terms of their performance and ML detection complexity. It can be observed that spreading the information and optimising the system over a group of subcarriers (rather than on a per subcarrier-basis or all subcarriers together) extracts virtually all the diversity the wireless channel can provide while remaining computationally feasible. Simulation results are presented within the context of the new WLAN standard IEEE 802.11n in order to illustrate the practicality of the proposed technique.
Wireless Days (WD), 2010 IFIP; 11/2010
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ABSTRACT: Recent research has shown that code-division multiplex orthogonal frequency-division multiplex (CDM-OFDM) significantly improves the robustness of conventional OFDM against subcarrier fading. In particular, the combination of CDM with multiple transmit antennas has been shown to be very effective in the context of IEEE 802.11n. In this paper another distinctive feature of the forthcoming WLAN standard, namely, the existence of a feedback channel, is exploited to implement a frequency diversity adaptive technique. In the proposed method the receiver estimates an effective diversity order of the underlying wireless channel and feeds it back to the transmitter, which then uses it to appropriately dimension the CDM component. At the same time, the receiver can switch between iterative or noniterative processing depending on the CDM dimension of the forthcoming packets. Results show that this adaptivity can bring along important reductions in complexity without compromising error performance.
Global Telecommunications Conference, 2009. GLOBECOM 2009. IEEE; 01/2010
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ABSTRACT: Wireless architectures combining the use of spatial division multiplexing (SDM) and space-time block coding (STBC) have begun to appear in the latest communications standards. In recent years, different detection strategies for these schemes have been proposed which can be broadly categorised as group-based or direct-detection techniques. While the former class aims at separating the different STBC streams and then apply conventional simple Alamouti decoding, the latter type directly estimates the transmitted symbols without fully exploiting the Alamouti structure. Previous publications have shown that direct-detection outperform group-based detectors with the penalty of a higher computational complexity. This letter presents a unified view of the detection strategies for hybrid SDM/STBC systems and presents two new families of group-based detectors. It is shown that linear group detection, when properly implemented, attains the same performance as linear direct detectors at a significant lower complexity.
IEEE Transactions on Communications 12/2009; · 1.68 Impact Factor
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ABSTRACT: 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.
IEEE Transactions on Vehicular Technology 11/2009; · 1.92 Impact Factor
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ABSTRACT: Code-division multiplex orthogonal frequency-division multiplex (CDM-OFDM) has received considerable attention due to its superior resilience against subcarrier fading in comparison with conventional OFDM. More recently, group-orthogonal CDM-OFDM (GO-CDM-OFDM) has been considered as a suitable method to extract additional frequency diversity of the wireless channel by splitting the available subcarriers into (orthogonal) groups and applying optimum detection at the receiver on a per-group basis. One critical parameter of this scheme is the group size as it can effectively act like a complexity-performance trading knob. In this work an adaptive technique to dynamically adjust the group size as a function of the instantaneous operating scenario is presented. It is shown that this adaptivity can bring along important reductions in complexity without compromising error performance.
IEEE Signal Processing Letters 11/2009; · 1.39 Impact Factor
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ABSTRACT: Multicarrier and multiple transmit/receive antenna have become two key technologies underpinning most of the current development and research efforts towards ubiquitous high-throughput wireless communications. Both techniques can be used to increase the link throughput and/or to improve its robustness against channel fading and noise. This paper presents a unified bit error rate analysis for a particular flavour of multicarrier, namely, group-orthogonal code-division multiplex (GO-CDM), in combination with multiple Tx/Rx antennas. This system can be shown to encompass many of current wireless architectures and the analysis is general enough to incorporate the effects of channel frequency selectivity and Tx and/or Rx antenna correlation. The main outcome of this paper is a general analytical framework suitable to study the effects of the different types of diversity in multicarrier systems. More particularly, it is shown how GO-CDM can play an important role in improving the performance of MIMO-OFDM systems.
Signal Processing Advances in Wireless Communications, 2009. SPAWC '09. IEEE 10th Workshop on; 07/2009
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ABSTRACT: 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.
Cross Layer Design, 2009. IWCLD '09. Second International Workshop on; 07/2009
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ABSTRACT: This paper considers the use of cross-layer MIMO fast link adaption (FLA) algorithms in the context of IEEE 802.11n. An FLA technique based on packet error rate (PER) that makes use of the exponential effective SNR mapping (EESM) is proposed. Additionally, a bit error rate (BER) based FLA scheme is proposed that simplifies the calibration procedure without any significant performance degradation. Results show that both, PER- and BER-based, FLA techniques select the modulation and coding scheme (MCS) in a close to optimum fashion in the sense of maximising the data throughput while satisfying a prescribed packet error rate (PER) target. Channel estimation errors have also been considered, revealing the importance of good channel estimators in order for FLA strategies to work satisfactorily.
Cross Layer Design, 2009. IWCLD '09. Second International Workshop on; 07/2009
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ABSTRACT: Among the many varieties of multicarrier, code-division multiplex orthogonal frequency-division multiplex (CDM-OFDM) has received considerable attention due to its superior resilience against subcarrier fading in comparison with conventional OFDM. More recently, group-orthogonal CDM-OFDM (GO-CDM-OFDM) has been considered as a suitable method to extract the maximum frequency diversity of the wireless channel by splitting the available subcarriers into (orthogonal) groups and applying optimum detection at the receiver on a per-group basis. One critical parameter of this scheme is the group size as it can effectively act like a complexity-performance trading knob. In this work an adaptive technique to dynamically adjust the group size as a function of the instantaneous operating scenario is presented. It is shown how this adaptivity can bring along important reductions in complexity without compromising error performance.
Cross Layer Design, 2009. IWCLD '09. Second International Workshop on; 07/2009
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ABSTRACT: In this paper, a novel framework for the cross-layer 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 is proposed. In order to achieve this goal, the physical-layer service process is first modeled as a multidimensional finite-state Markov chain. Then, based on this multidimensional Markov model, the QoS performance at the data-link layer is characterized using the effective capacity approach. Queueing analysis using this effective capacity function is finally used in a cross-layer design approach aiming to satisfy the required average packet loss probability constraint by maximizing the average throughput of the system. Numerical examples are provided to show the advantages of our approach compared to other approaches using first-order amplitude-based finite state Markov models.
Vehicular Technology Conference, 2009. VTC Spring 2009. IEEE 69th; 05/2009
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ABSTRACT: The combination of spatial division multiplexing (SDM) and space-time block coding (STBC) is able to yield high-throughput and robust wireless communications (e.g. IEEE 802.11n). In the most common configuration, known as double space time transmit diversity (DSTTD), two Alamouti encoded streams are transmitted in parallel. In this paper we introduce an improved multicarrier hybrid STBC/SDM scheme whereby the transmitted symbols are spread onto different subcarriers. A computationally efficient and near optimal receiver architecture is presented which is able to exploit the additional diversity. Simulations results using the IEEE 802.11n framework configured to operate in DSTTD mode demonstrate the performance gains of our approach.
Radio and Wireless Symposium, 2009. RWS '09. IEEE; 02/2009
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ABSTRACT: In this correspondence, we present a new unified bit-error-rate analysis of group-orthogonal multicarrier (GO-MC) systems for both uplink and downlink segments when using a maximum-likelihood (ML) multiuser and multisymbol detector, respectively. The proposed analysis is based on the union bound, and it is general enough to allow each of the transmitted symbols in the group to come from a different modulation alphabet and have different received power. Monte Carlo simulation results are also presented to assess the accuracy of the derived analytical expressions. A very good agreement between analytical and simulation results can be appreciated, highlighting the usefulness of our approach in the assessment and planning of generalized GO-MC systems.
IEEE Transactions on Vehicular Technology 02/2009; · 1.92 Impact Factor
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ABSTRACT: 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.
Global Telecommunications Conference, 2008. IEEE GLOBECOM 2008. IEEE; 01/2009
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ABSTRACT: Group-orthogonal multicarrier code-division multiple access (GO-MC-CDMA) has been proposed as an attractive multiplexing technique for the uplink segment of wireless systems. More recently, a variant of this scheme has also been proposed for the downlink. This paper presents a unified bit error rate (BER) performance analysis of group-orthogonal wireless systems when using maximum likelihood (ML) multiuser/multisymbol detection covering both link directions. Valuable design rules regarding the number of subcarriers per group and the selection of spreading codes are derived. Simulations results using realistic system parameters and ETSI BRAN channel models are also presented which serve to validate the analytical results.
IEEE Transactions on Communications 11/2008; · 1.68 Impact Factor
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ABSTRACT: 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.
IEEE Transactions on Wireless Communications 05/2008; · 2.59 Impact Factor
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ABSTRACT: This paper presents novel detection strategies for hybrid systems combining spatial division multiplexing (SDM) and space- time block coding (STBC). Group-based approaches in which STBC streams are individually targeted as well as direct approaches where the STBC structure is not taken into account in the detection process are considered. We introduce two types of group-based detectors and compare their performance with that of previous group-based and direct proposals in both, coded and uncoded setups, showing the superiority of one of our proposals (linear). Despite the generality of the proposed receivers, the presented simulations results focus on the IEEE 802.1 In wireless local area network (WLAN) as this is one of the first commercial standards to explicitly support hybrid SDM/STBC systems.
Smart Antennas, 2008. WSA 2008. International ITG Workshop on; 03/2008
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ABSTRACT: This paper proposes the use of group-orthogonal frequency diversity combined with space-time block coding (STBC) to improve the performance of IEEE 802.11n wireless networks (WLANs). The extra diversity is achieved by using code-division multiplexing whereby each symbol is transmitted on more than one subcarrier. At reception, following the STBC decoding, a maximum likelihood-based turbo receiver is used to take full advantage of the available diversity. The performance of the proposed scheme is investigated over the two different operating bandwidths specified in 802.11n, (20 or 40 MHz) and with different number of transmit antennas. Simulation results using the current IEEE 802.11n specifications serve to illustrate the benefits of the proposed scheme under realistic conditions.
Wireless Communications and Networking Conference, 2008. WCNC 2008. IEEE; 01/2008
