Downlink joint rate and power allocation in cellular multirate WCDMA systems

This paper proposes a novel dynamic joint rate and power control procedure for downlink data transmission in a multicell variable spreading factor wideband code-division multiple-access (WCDMA) system where the different users have similar quality-of-service requirements in terms of the signal-to-interference ratio (SIR). Two variations of the dynamic joint rate and power allocation procedure, namely, Algorithm-1 and Algorithm-2, are presented. The performances of these two schemes are compared to the performance of the optimal dynamic link adaptation for which the rate and power allocation is found by an exhaustive search. The optimality criterion is the maximization of the total radio link level capacity (or sum-rate capacity) in terms of the average number of radio link level frame transmitted per adaptation interval under constrained SIR and power limit in the base station transmitter. The proposed schemes have linear time complexity as compared to the exponential time complexity of the optimal scheme and achieve better radio link level throughput fairness compared to the optimal link adaptation scheme with a moderate loss in total throughput. Performance evaluation is carried out under random and directional micromobility models with uncorrelated and correlated long-term fading, respectively, in a cellular WCDMA environment for both the homogeneous (or uniform) and the nonhomogeneous (or nonuniform) traffic load scenarios.     

Dynamic rate adaptation and integrated rate and error control in cellular WCDMA networks

Optimal dynamic rate allocation among mobile stations for variable rate packet data transmission in a cellular wireless network is an NP-complete problem; therefore, suboptimal solutions to this problem are sought for. In this paper, three novel suboptimal dynamic rate adaptation schemes, namely, peak-interference-based rate allocation, sum-interference-based rate allocation, and mean-sense approximation-based rate allocation, are proposed for uplink packet data transmission in cellular variable spreading factor wide-band code division multiple access (WCDMA) networks. The performances of these schemes are compared to the performance of the optimal dynamic link adaptation for which the rate allocation is found by an exhaustive search. The optimality criterion is the maximization of the average number of radio link level frames transmitted per frame time under constrained signal-to-interference-plus-noise ratio (SINR) at the base station receiver. Two different error control alternatives for variable rate packet transmission environment are presented. We demonstrate that the dynamic rate adaptation problem under constrained SINR can be mapped into the radio link level throughput maximization problem with integrated rate and error control. Performance evaluation is carried out under random and directional micromobility models with uncorrelated and correlated long-term fading, respectively, in a cellular WCDMA environment for both the homogeneous (or uniform) and the nonhomogeneous (or nonuniform) traffic load scenarios.     

A Novel Analytical Framework for Integrated Cross-Layer Study of Call-Level and Packet-Level QoS in Wireless Mobile Multimedia Networks

We present a novel integrated analytical framework for analyzing the quality-of-service (QoS) performance measures in a wireless mobile multimedia network. The framework integrates physical, radio link, and network layer parameters and protocols to analyze the call-level and packet-level performances. In the network layer, call admission control (CAC) is responsible for deciding whether an incoming call can be accepted or not so that the performances of the ongoing calls do not deteriorate below the acceptable level. Also, an adaptive channel allocation (ACA) scheme is used to maximize the utilization of the radio resources. In the data link layer, queue management and error control are used for non-real-time loss-sensitive traffic. In the physical layer, a finite state Markov channel (FSMC) is used to model channel fading, and adaptive modulation is used for rate adaptation according to channel quality. Various call-level and packet-level QoS measures for real-time, non-real-time, and best-effort traffic are obtained. The analytical results are validated by extensive simulations. Examples of the applications of the presented analytical framework are also provided     

Adaptive Fair Subcarrier/Rate Allocation in Multirate OFDMA Networks: Radio Link Level Queuing Performance Analysis

This paper presents a semi-analytical methodology for radio link level performance analysis in a multirate "orthogonal frequency-division multiple-access" (OFDMA) network with adaptive fair rate allocation. Multirate transmission is assumed to be achieved through adaptive modulation, and fair rate allocation is based on the principle of generalized processor sharing to allocate the subcarriers adaptively among the users. The fair rate allocation problem is formulated as an optimization problem with the objective of maximizing system throughput while maintaining fairness (in terms of transmission rate) among the users. The "optimal" fair rate allocation is obtained by using the "Hungarian method." A heuristic-based approach, namely the "iterative approach," that is more implementation friendly is also presented. The throughput performance of the iterative fair rate allocation is observed to be as good as that of optimal fair rate allocation and is better than that of the static subcarrier allocation scheme. Also, the iterative fair allocation provides better fairness compared to that for each of the optimal and the static subcarrier allocation schemes. To this end, a queuing model is formulated to analyze radio link level performance measures such as packet dropping probability and packet transmission delay under the above rate allocation schemes. In this formulation, packet arrivals are modeled by the discrete Markov modulated Poisson process, which is flexible to model different types of traffic arrival patterns. The proposed framework for radio link level performance analysis of multirate OFDMA networks is validated by extensive simulations. Also, examples on the application of the proposed model for connection admission control and quality-of-service provisioning are illustrated     

Dynamic random access code assignment for prioritized packet data transmission in WCDMA networks

We propose a measurement-based dynamic random access (RA) code assignment procedure for prioritized packet data transmission in wideband code-division multiple access (WCDMA) networks. This dynamic adaptation process is based on analytical performance results derived for random packet access under Rayleigh fading in WCDMA networks. The performance of the proposed measurement-based RA code assignment procedure with three different adaptation methods is evaluated by using computer simulations. The performance of the proposed scheme is compared with those of a retransmission control-based and static channel allocation-based prioritized packet access scheme. An integrated (physical layer and link layer) delay-throughput performance model is presented for finite population RA WCDMA systems. The proposed dynamic RA code assignment procedure can be used in an adaptive quality of service (QoS) framework for dynamically adjusting the QoS of prioritized RA data traffic in the evolving WCDMA-based differentiated services wireless Internet protocol networks.     

Channel-quality-based opportunistic scheduling with ARQ in multi-rate wireless networks: modeling and analysis

In this paper, we develop a novel framework for analyzing radio link level performance for opportunistic scheduling with automatic repeat request (ARQ)-based error control in multi-rate wireless networks. The multi-rate transmission is assumed to be achieved through adaptive modulation and coding (AMC) to adjust the transmission rate according to the channel condition. The residual error effect due to each AMC setting is counteracted by means of a limited persistence ARQ protocol. The novelty of the proposed analytical framework lies in the fact that we are able to derive complete statistics (in terms of probability mass function) for both short-term and long-term performance measures such as system throughput, per-flow throughput, inter-success delay under both uncorrelated and correlated wireless channels. These performance measures can also be obtained in case of non-identical channels for different users. Analytical results are validated through simulations and the impacts of channel behavior on the different radio link level performance metrics are investigated.     

Analysis of TCP performance under joint rate and power adaptation in cellular WCDMA networks

To improve the spectral efficiency while meeting the radio link level quality of service requirements such as the bit-error-rate (BER) requirements for the different wireless services, transmission rate and power corresponding to the different mobile users can be dynamically varied in a cellular wideband code-division multiple-access (WCDMA) network depending on the variations in channel interference and fading conditions. This paper models and analyzes the performance of transmission control protocol (TCP) under joint rate and power adaptation with constrained BER requirements for downlink data transmission in a cellular variable spreading factor (VSF) WCDMA network. The aim of this multilayer modeling of the WCDMA radio interface is to better understand the interlayer protocol interactions and identify suitable transport and radio link layer mechanisms to improve TCP performance in a wide-area cellular WCDMA network.     

Integrated scheduling and link adaptation for heterogeneous networks: design and performance analysis

ABSTRACT

This paper presents novel integrated scheduling and link adaptation (ISLA) schemes for links which have a common spectrum and possibly different rates and reliability constraints. We consider the problem of weighted sum average rate maximisation of wireless links. In an orthogonal transmission system, a link is selected using instantaneous signal-to-noise (SNR) of all the links, and its rate and power are set in a jointly optimised manner. To demonstrate the effectiveness of the proposed approach, we analyse ISLA schemes with continuous rate adaptation using constant or adaptive transmission powers. ISLA schemes are designed in similar settings for practical discrete rate-adaptive systems using adaptive modulation and coding. To this end, a design framework is presented, which relies on a partitioning of space of links’ SNRs into regions, similar to structured vector quantisation. Within this framework, a particular ISLA design with high performance and polynomial complexity is suggested. The proposed schemes are designed before the start of the transmission, based on closed-form solutions, and can easily be applied to multiple access or broadcast networks. We also analyse several schemes for comparison, which employ modified Round-Robin, opportunistic scheduling or online generalised scheduling. Numerical results demonstrate how the proposed ISLA schemes outperform the benchmark schemes and effectively meet various user requirements.¹     

Reservation-based bandwidth allocation in a radio ATM network

The comparative performance of a number of reservation-based bandwidth sharing policies that could be used to maximize the link utilization and/or offer equally fair or preferential treatment to a class of supported users, is examined in the context of a radio asynchronous transfer mode local-area network (ATM LAN). Our analytical results, based an a recursion for the link occupancy distribution originally suggested by Kaufman (1981) and Roberts (1981) independently and subsequently extended to include finite source population models, are further extended in the cases of equal sharing of the resources with retries, and a dynamic sharing mechanism in which, when the available capacity is exceeded, weighted reductions for the active users' rates and queueing are employed. Next, examining the application of the above sharing schemes in an indoor radio environment, we apply switched diversity and a Reed-Solomon-based forward error correction (FEC) scheme to recover radio-related (Rayleigh fading) packet losses. The performance and the effects of the fading-mitigating switched-antenna-diversity mechanism and the required on a packet-basis coding protection are taken into account in order to establish the actual radio link throughput under the above conditions     

Performance characteristics of cellular systems with different link adaptation strategies

In this paper, the theoretical performance of cellular systems with different types of link adaptation is analyzed. A general link and system performance analysis framework is developed to enable the system-level performance characteristics of the various link adaptation strategies to be studied and compared. More specifically, this framework is used to compare the downlink performance of fully loaded cellular systems with fixed power and modulation/coding, adaptive modulation/coding (AMC), adaptive power allocation (APA) with system-level AMC, and water-filling (WF). Performance is studied first for idealized methods, and then for cases where some practical constraints are imposed. Finally, a hybrid link adaptation scheme is introduced and studied. The hybrid scheme is shown to overcome most of the performance loss caused by the practical constraints. Moreover, the hybrid scheme, as opposed to WF, enables the system to be tuned to meet the most important performance objective for the system under consideration, such as coverage reliability, capacity, or data rate distribution. The algorithms and the framework presented in this paper can be used to improve the link adaptation performance of modern cellular systems such as HSDPA.     

Joint resource reconfiguration and robust routing for cognitive radio networks: a robust optimization approach

Cognitive radio (CR) networks comprise a number of spectrum agile nodes with the capability of spectrum detection. Applying techniques of spectrum sharing in CR networks can achieve the efficient utilization of network resources. Usually, data rates of user sessions are time varied because of the dynamic behaviors of CR networks. It is expected that the occurrence of link outage should be avoided and incorporated into the routing design under conditions of increasingly crowded spectrum. This paper proposes an integral framework, which considers these two correlated schemes (resource reconfiguration and robust routing) simultaneously. For that, the resource reconfiguration scheme is developed for the efficient usage of network resources and aims at reducing the occupancy of licensed bands. The link outage, resulting from random session rate, is confined within an acceptable range by using strategy of virtual ‘network portfolio’. A robust optimization approach is proposed to guarantee reliable data transmission among possible interfering links. Both these two items (resource reconfiguration and robust routing) are formulated in a framework of cross‐layer optimization. The evolutionary process of CR network states is provided in simulations, where the results show that the joint design proposal can achieve the least interferences among different licensed users while realizing robust routing. Copyright © 2013 John Wiley & Sons, Ltd.     

Adaptive modulation systems for predicted wireless channels

When adaptive modulation is used to counter short-term fading in mobile radio channels, signaling delays create problems with outdated channel state information. The use of channel power prediction will improve the performance of the link adaptation. It is then of interest to take the quality of these predictions into account explicitly when designing an adaptive modulation scheme. We study the optimum design of an adaptive modulation scheme based on uncoded M-quadrature amplitude modulation, assisted by channel prediction for the flat Rayleigh fading channel. The data rate, and in some variants the transmit power, are adapted to maximize the spectral efficiency, subject to average power and bit-error rate constraints. The key issues studied here are how a known prediction error variance will affect the optimized transmission properties, such as the signal-to-noise ratio (SNR) boundaries that determine when to apply different modulation rates, and to what extent it affects the spectral efficiency. This investigation is performed by analytical optimization of the link adaptation, using the statistical properties of a particular, but efficient, channel power predictor. Optimum solutions for the rate and transmit power are derived, based on the predicted SNR and the prediction error variance.     

Performance of a cellular network based on frequency hopping with dynamic channel allocation and power control

A frequency- and time-division multiple-access (F-TDMA)-based mobile radio system using both dynamic channel allocation (DCA) and frequency hopping (FH) is investigated. We propose a new interference adaptive DCA (IA-DCA) algorithm that is suitably designed for a network implementing FH. The role played by the power control algorithm in this DCA-FH context is also investigated. We compare the performance of our proposal to that of fixed channel allocation (FCA) with and without FH and the well-known IA-DCA schemes investigated in the literature in the absence of FH. The performance results show that interesting synergic effects can be obtained in terms of forced termination and user satisfaction probability by using both DCA and FH. The results we show in the paper have been achieved by means of a system-level simulation tool which takes propagation, user mobility, interference, traffic, and channel allocation into account. The advantages of using FH are accounted for by using a suitable analytical model that gives the frame error rate as a function of the carrier-to-interference ratio and the number of hopping frequencies, at link level; this model is taken from the literature where it was presented for FCA, and here it is modified in order to be applicable to the DCA case.     

Queue-aware uplink bandwidth allocation and rate control for polling service in IEEE 802.16 broadband wireless networks

IEEE 802.16 standard defines the air interface specifications for broadband access in wireless metropolitan area networks. Although the medium access control signaling has been well-defined in the IEEE 802.16 specifications, resource management and scheduling, which are crucial components to guarantee quality of service performances, still remain as open issues. In this paper, we propose adaptive queue-aware uplink bandwidth allocation and rate control mechanisms in a subscriber station for polling service in IEEE 802.16 broadband wireless networks. While the bandwidth allocation mechanism adaptively allocates bandwidth for polling service in the presence of higher priority unsolicited grant service, the rate control mechanism dynamically limits the transmission rate for the connections under polling service. Both of these schemes exploit the queue status information to guarantee the desired quality of service (QoS) performance for polling service. We present a queuing analytical framework to analyze the proposed resource management model from which various performance measures for polling service in both steady and transient states can be obtained. We also analyze the performance of best-effort service in the presence of unsolicited grant service and polling service. The proposed analytical model would be useful for performance evaluation and engineering of radio resource management alternatives in a subscriber station so that the desired quality of service performances for polling service can be achieved. Analytical results are validated by simulations and typical numerical results are presented.     

Understanding Link Behavior of Non-intrusive Wireless Body Sensor Networks

The wireless body sensor network (BSN) is used to detect and transmit physiological data such as vital signs by using radio wave communication. It offers a large saving potential for future healthcare applications because hospitalization of patients with chronic diseases can be kept at a minimum. The radio wave communication on the human body is impacted by the dielectric properties, the posture, and the movement of the body. Under these conditions a highly dynamic link-state and link quality are observed. In this paper we present a study of the link layer behavior of wireless BSNs operating at 2.45 GHz. We report on a wearable body-centric network operation in realistic environments from which we characterize the wireless channels based on a novel test framework. Our test framework uses a 200 ms time resolution for sampling of the wireless links between on-body sensor nodes. We record the received signal strength indicator and link quality indicator values as well as the packet delivery statistics in real-time. Based on recorded experiments we quantify the potential packet delivery performance and energy gain that can be obtained by using dynamic routing and adaptive transmission power schemes, respectively. Subsequently we formulate a set of requirements for the next revision of our prototype wireless BSN developed at Aarhus University School of Engineering in Denmark.     

High-speed power-efficient indoor wireless infrared communication using code combining .I

While use of power-efficient signaling schemes appears to be effective at compensating for the inherent high path-loss associated with pure diffuse infrared links, it begins to lose its effectiveness as the data rate is increased. At very high data rates, intersymbol interference (ISI) can result in a very high and sometimes irreducible power penalty, preventing the system from operating at a low bit-error probability. We use a link design employing a multibeam transmitter in conjunction with a narrow field-of-view (FOV) direction diversity receiver. The design goal is to eliminate the effect of ISI so that power-efficient signaling schemes such as pulse-position modulation (PPM) can be employed at very high data rates. We also use high-rate Reed-Solomon codes to further increase the power efficiency of PPM signals. The proposed system can be made rate-adaptive through varying modulation level L and/or code rate R without increasing the complexity significantly. This provides a dynamic range large enough to allow efficient utilization of available bandwidth, i.e., to allow portable terminals to communicate at their highest permitted data rate, without sacrificing the quality of service. It is shown that a bit error rate not exceeding 10/sup -9/ can be achieved within the link coverage area with 99% probability at bit rates up to a few hundreds of megabits per second, using transmitted power levels well below 1 W.     

Downlink Radio Resource Allocation for Multi-Cell OFDMA System

This paper presents a radio resource control (RRC) scheme for OFDMA systems where dynamic resource allocation is realized at both a radio network controller (RNC) and base stations (BSs). The scheme is semi-distributed in the sense that the RRC decision is split between RNC and BSs. RNC makes decision on which channel is used by which BS at super-frame level and BSs then make decision on which user is assigned to which channel at frame-level. Two optimization problems for RNC and BSs are formulated and computationally efficient algorithms that perform the function of interference avoidance and traffic/channel adaptation are developed. Numerical analysis is performed under several cell configurations to show tradeoffs between sector interference suppression and dynamic interference avoidance. The results indicate that with reasonable signaling overhead, the protocol and the associated algorithms yield excellent performance for both real-time and non real-time services, even under fast fading     

High-availability free space optical and RF hybrid wireless networks

We introduce hybrid free-space optical and RF wireless links as potential technology for designing next-generation broadband wireless networks. We present various design challenges and potential solutions for real-time link performance characterization and adaptation for enhanced performance during adverse weather conditions. First, we introduce the hybrid wireless architecture and emphasize its significant role in achieving ubiquitous carrier-grade wireless connectivity. Second, we propose a link monitoring scheme that accurately reflects the performance of optical wireless links under various weather conditions. In addition, we examine the role of known link performance restoration schemes - power and data rate control. Third, we propose two novel link restoration schemes that efficiently utilize the hybrid architecture: dynamic load switching and multihop routing. Finally, the article describes an elaborate field testbed based on the hybrid architecture and various link restoration techniques. The dynamic load switching scheme is shown to have a profound impact on the overall hybrid link availability. The results, recorded from the experiments during extreme weather conditions, validate the impact of the hybrid architecture concept and conclusively prove the availability and reliability of the architecture in achieving sustained highspeed wireless connectivity.     

Selective maximum-likelihood symbol-by-symbol detection for multidimensional multicode WCDMA with precoding

To faciliate high-rate uplink transmission, a novel selective maximum-likelihood (SML) detection is realized on a set of parallel multicode (MC) channels as a result of MC wideband code-division multiple-access (WCDMA) signaling with precoding. Multidimensional (MD) signaling can be combined with MC to further increase the data rate with fixed spreading factor per symbol. In connection with this MDMC signaling, the proposed SML detection achieves significantly improved symbol-error probability, compared with other detection methods, both without soft sequential decoders for a tractable analysis.