Adaptive Code Modulation Research Articles

Energy-Efficient Cross-Layer Optimization for Wireless Sensor Networks

In this paper, we propose a cross-layer design combining adaptive modulation coding (AMC) and automatic repeat request (ARQ) to minimize the bit energy consumption under both packet loss rate and retransmission delay constraints. We analyze the best constellation size of M-ary square quadrature amplitude modulation (MQAM) in different distance, and give advice on retransmission limits under different packet loss rates. The impacts of path loss fading and additive white Gaussian noise (AWGN)are taken into consideration. The computation of energy consumption includes the circuit, transmission and retransmission energies at both transmitter and receiver sides. Numerical results are obtained to verify the validity of our design. We also show that the retransmission benefit varies with the packet loss rate constraint.

Proportional Fair Scheduling Gains for AMC-Aware Systems under Heterogeneous Radio Conditions

This letter provides exact analytical expressions and simpler, but still effective, approximations for the multiuser diversity gains associated with Proportional Fair (PF) opportunistic scheduling. The impact of Adaptive Modulation & Coding (AMC) and of heterogeneous user populations with different radio conditions on the downlink are taken into account. The analysis is applicable to all major fading models and is based on the notion of the scheduling gain, a quantity that captures throughput and fairness aspects relevant to a user served under a considered scheduling policy as part of a heterogeneous group of users. Exploitation of relevant characteristics in the AMC rate function gives rise to two distinct regimes, corresponding to regular and very high average SNR conditions. All users in each of these regimes have approximately equal PF scheduling gains.

Capacity maximisation in eigen-multiple-input multiple-output using adaptive modulation and Reed–Solomon coding

Eigen-multiple-input multiple-output (MIMO) with water-filling gives the maximum information-theoretic capacity, but realising this maximisation is not straightforward because practical factors are omitted. Adaptive modulation and error coding are combined for finding the maximum practicable capacity (throughput of correctly detected bits) in eigen-MIMO. Quadrature amplitude modulation (QAM) is the logical choice of modulation and here Reed–Solomon (RS) coding is used. RS coding has the advantages of algorithmic simplicity, low-memory requirements, and decoder complexity, and its unique closed-form error probability makes it possible to obtain an optimal power allocation, signal constellation size(s), and code rate(s) on the eigenchannels, for the maximum practicable capacity. The proposed adaptive scheme is applied to two architectures for the encoders/decoders (CODECs): outer coding, where a single CODEC is deployed for the overall serial data; and inner coding, where there is a CODEC for each eigenchannel. The optimal power allocation is different to the water-filling used for the information-theoretic capacity. Also, simple and accurate approximations are found for the bit-error rate (BER) of a single Rayleigh channel and of a 2×2 system. Finally, a selection procedure between different system configurations is presented for obtaining the highest practicable capacity subject to either average or instantaneous output BER.

Multiuser Resource Allocation with Adaptive Modulation and LDPC Coding for Heterogeneous Traffic in OFDMA Downlink

We describe an optimization technique for multiuser resource allocation assuming adaptive modulation and coding (AMC) in OFDMA radio downlink communications. The resource allocation process is based on the dual solution of a weighted sum-rate maximization problem. In particular, to realistically address IP-based video and data communications, the set of considered constraints include the number of bits actually present in the different transmission buffers. Furthermore, we propose an innovative AMC solution, based on M-QAM modulation and LDPC codes, jointly working with the scheduler and capable to maximize the throughput while guaranteeing a given set of performance requirements. A simple weight adaptation algorithm is introduced to properly tune the trade off between opportunistic transmissions and fairness among users. Several simulation results are presented to validate the proposed approach and a comparison with more traditional schemes is provided. In particular, we show that a good trade off between user fairness and opportunistic exploitation of the radio channel can be reached with the proposed strategies, improving the communication quality for both real-time video and non real-time data applications.

Adaptive Bit-Interleaved Coded Modulation Based on the Expurgated Bound for Mobile Radio OFDM Systems Aided by Fading Prediction

Adaptive bit-interleaved coded modulation (ABICM) is attractive for rapidly varying mobile radio channels due to its robustness to imperfect channel state information (CSI). A novel ABICM method that exploits the expurgated bound to maintain the target bit error rate (BER) for diverse CSI conditions is proposed and evaluated for an adaptive mobile radio orthogonal frequency division-multiplex (OFDM) system aided by the long-range fading prediction. It is demonstrated that ABICM is much less sensitive to prediction errors than adaptive modulation techniques that do not employ interleaving. However, reliable fading prediction is still necessary for ABICM to achieve high spectral efficiency for practical channel conditions.

A Strategy to Reduce the Signaling Requirements of CQI Feedback Schemes

Resource allocation in OFDMA systems involves the application of adaptive modulation/coding (AMC). AMC provides the flexibility to match the modulation-coding scheme (MCS) to each user's channel co...

Dynamic multidimensional optical networking based on spatial and spectral processing

The recent introduction of optical OFDM and spatial MIMO techniques has led to considerable increases in spectral efficiency and aggregate throughput for future optical networks. However, these spatial and spectral domains can also be exploited for next-generation elastic optical networking. In this paper, we introduce the first hierarchy for dynamic multidimensional spatial and spectral optical networking and complement it with adaptive coded-modulation to form the basis of a novel elastic networking concept.

A dual-channel cross-layer architecture for underwater acoustic networks

The performance of underwater acoustic networks( UAN) is affected by the node device constraints of memory, processing power, battery life time and network topology variation. To improve the performance and to utilize scarce resource can be obtained with a Cross-layer design. Cross-layer design, one of the key technique in underwater communication networks, overcomes the disadvantages of the strictly layered networks such as nonoptimality and inflexibility. It enables the system to utilize the limited resources more sufficiently, especially in no central control, rapid changes topology of underwater networks, and achieves better performance. This paper discusses the benefits of cross-layer underwater acoustic networks and related work, introduces a representative cross-layer architecture, named dual-channel cross-layer architecture, to promote the overall system performance for underwater networks. In addition, three cross-layer solutions, node adaptive modulation and channel coding, joint design of MAC a...

An occupancy-based and channel-aware multi-level adaptive scheme for video communications over wireless channels

Abstract Video streaming over wireless channels is challenged with the time-varying nature of the underlying channels and the stringent requirements of video applications. In particular, video streaming has strict requirements on bandwidth, delay, and loss rate while wireless channels are dynamic and error-prone by nature. In this article, we propose a novel multilevel adaptive scheme that is designed to mitigate the challenges facing video streaming over unreliable channels. This is done while preventing potential playback discontinuities and guaranteeing a graceful degradation of the rendered video quality. Scalable video coding, adaptive modulation, and adaptive channel coding are integrated to achieve the objectives of the proposed scheme. If adaptive modulation and channel coding are not enough to guarantee the on-time delivery of decodable video frames, we adopt scalable coding. Simulation results show that the proposed adaptive scheme achieves an improvement of about 2.5 dB in the peak signal-to-noise ratio over a nonadaptive one. In addition, the proposed scheme reduces the number of starvation instances by 50 and 90% in the cases of Stop-and-Wait and Go-Back-N automatic repeat requests, respectively.

Image-based Position Estimation and Adaptive Modulation Coding in Vehicular Communication

Vehicle position estimation is a key technology for Inter-Vehicle Communications, while template matching can be used to get information of vehicular position. In the paper, a simplified template matching, namely area-based template match is considered. A vehicular communication system designed for wireless data application is proposed where a camera is fixed in a vehicle which is served as a base station. By means of comparison between the outline area of vehicular image and reference templates, the base station can obtain the position estimation of the vehicle. The reference templates can be pre-calculated from a group of field experiment data. Based on supervised learning, we develop an image-based vehicle position estimation method and evaluate its effect on an adaptive coding modulation scheme. The computer simulation results show that in the wireless fading channel with the OFDM physical model, compared with fixed modulation coding scheme, the studied adaptive modulation and coding (AMC) scheme taking account of the position estimation can gain greater throughput.

Simulation of IEEE 802.16j Mobile WiMAX Relay Network to Determine the Most Efficient Zone to Deploy Relay Station

An IEEE 802.16j mobile WiMAX relay network is a next-generation mobile wireless broadband network that uses adaptive modulation coding. When a mobile station is shadowed by a building and thus has a bad-quality channel to the base station, such a relay design can help it achieve a higher throughput from/to the base station. It's not known what modulation zone QPSK½, QPSK¼ or 16QAM½ it should be from base station to relay station to achieve better throughput. Simulation was made with NCTUns. This paper analyzes which modulation zone is most efficient for relay stations to be deployed to achieve maximum network throughput. The number of subscriber stations impact to the network throughput with slot load in one frame and optimal relay stations number connected to one base station. Ill. 7, bibl. 10, tabl. 3 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.112.6.451

Modeling and analysis of applying adaptive modulation coding in wireless multicast and broadcast systems

Traditional wireless communications only utilize fixed-rate multicast and broadcast. In other words, only the most robust modulation and coding scheme can be applied for data transmission. Such a scheme fails to sufficiently exploit the potential gains of multicast and broadcast, resulting in bandwidth waste. To overcome such a problem, investigating the rate adaptation of multicast and broadcast wireless systems is the primary task. Unlike the traditional wireless systems, this paper presents an analytical model with rate adaptation for both multicast and broadcast. Adaptive modulation and coding are applied to achieve rate adaptation. We construct a stochastic model by using Finite State Markov chains for the multicast broadcast system modeling. The model's outputs are shown to approximate to the results of our system level simulations. The model derives the performance of rate adaptation in multicast and broadcast. With the deduced modeling results, we can predict the system throughput providing the channel states, and the modulation and coding schemes variations.

A combined resource management and admission control scheme for optimizing uplink performance of M-WiMAX systems

According to the AMC (Adaptive Modulation-Coding) mechanism of the M(obile)-WiMAX, the amount of data per modulation symbol depends on the perceived Signal-to-Noise Ratio, while, based on the OFDMA (Orthogonal Frequency Division Multiple Access) technique, each communication entails multiple concurrent transmissions. Therefore, in the uplink case, where each terminal has a maximum power limitation, the assignment of additional subcarriers does not always correspond to a proportional datarate increment, since the power dispersion over a larger set of symbols can cause the transition to a lower AMC level. In this framework, the present paper introduces a novel RRM (Radio Resource Management) algorithm that dynamically alters the number of subcarriers to be allocated to each connection so as to achieve spectrum saving via augmenting the bits per symbol ratio. Furthermore, in order to mitigate the extensive fluctuations imposed by the novel RRM scheme, an adequate minimum-complexity CAC (Connection Admission Control) scheme is proposed, which succeeds in accurately estimating the bandwidth requirements of the active flows by incorporating theoretical calculations along with a sampling process. It is proven analytically as well as through simulations that the new combined RRM-CAC strategy increases substantially the system capacity, without violating the Quality-of-Service guarantees.

Closed-form analysis of adaptive coded modulation over Rician shadowed fading channels

A simple analytical framework is presented for the performance analysis of adaptive coded modulation (ACM) over Rician shadowed fading channels. Obtained results find applicability in the prediction of the average spectral efficiency and the average bit error rate achievable by practical ACM schemes in satellite communications systems.

A hybrid CAC algorithm for maximizing downlink capacity of M-WiMAX systems

Due to the implementation of an Adaptive Modulation-Coding (AMC) mechanism in the 802.16e physical layer, each connection's bandwidth requirements cannot be statically computed, but they derive as a function of the terminals' instantaneous Signal-to-Noise Ratio (SNR). Therefore, the Connection Admission Control (CAC) mechanism fails to establish an efficient policy that would optimally exploit the system's resources. In this respect, the present paper formulates initially an adequate method for statistically calculating the average capacity of a Mobile-WiMAX system, according to the distribution of the several attenuation factors that affect the signal along the propagation path. In parallel, based on the processing of the terminal's SNR samples, a sophisticated algorithm for filtering out any misleading measurements is developed. This second method aims at predicting the upcoming Modulation-Coding state of every connection, so as to acquire a short-term view of its spectrum demands. Finally, all the above info collected from both the estimation methods is utilized by the CAC procedure in order to perform an as accurate as possible computation of the resource availability. As a result, this hybrid approach succeeds in maximizing the network revenue through significantly increasing the number of concurrently serviced connections while guaranteeing their Quality of Service (QoS) standards.

Analysis of SIP Transfer Delay in Multi-Rate Wireless Networks

In this letter, we analyze the SIP transfer delay over multi-rate wireless networks where different transmission modes based on adaptive modulation code are supported. We consider a Nakagami m fading channel at the physical layer and automatic repeat request at the data link layer. Extensive simulation results are given to validate the analytical results and to demonstrate the effects of message sizes and channel conditions.

Adaptive Opportunistic Multicast Scheduling Over Next-Generation Wireless Networks

This paper considers the problem of opportunistic multicast scheduling in wireless time-division multiplexing systems with adaptive modulation and channel coding. The problem is first formulated and an effective scheduling scheme is proposed to maximize the multicast throughput while a desired packet error rate is guaranteed. The proposed scheme dynamically selects multicast rates by considering the configuration of the multicast group and instantaneous network states, and thus it can adapt well to network conditions. Extensive simulation results conclusively demonstrate that, compared to the worst-user multicast scheduling, the proposed approach can increase the wireless channel efficiency by large margins, especially when the channel is operating in a lower signal-to-noise ratio region and/or when the multicast group size increases. Besides, the simulations show that the proposed approach can work well in systems with imperfect channel estimation.

On Performance Evaluation of Different QoS Mechanisms and AMC scheme for an IEEE 802.16 based WiMAX Network

WiMAX is an emerging broadband wireless access system based on IEEE 802.16 specification which defines PHY and MAC layer for both fixed and mobile profiles. The WiMAX system effectively supports wide variety of broadband wireless access (BWA) technologies (including high speed internet and multimedia access) with high Quality of service (QoS) requirements. To support flexibility, efficiency and various requirements of QoS over a range of different applications and environments several provisioning and mechanisms are provided in the standard. In this paper various QoS provisions are analyzed for different application traffics. The effect of Adaptive Modulation Coding (AMC) mechanism on the QoS performance of WiMAX network is also studied. The results obtained show that these provisions and mechanisms enhance the QoS performance of the network in terms of throughput, packet loss and delay.

Performance analysis of variable-power adaptive modulation in space-time block coded MIMO diversity systems

In this paper, the performance analysis of multi-antenna MIMO systems with variable-power (VP) adaptive modulation and space-time coding is presented. The fading gain value is partitioned into a number of regions by which we decide the transmission power according to the region the fading gain falls in. The optimum fading gain region boundaries (switching thresholds) for maximizing spectrum efficiency (SE) under a target BER and average power constraint are derived. It is shown that the Lagrange multiplier in the constrained SE optimization will be unique if the existence condition for multi-antenna systems is satisfied, and is unique for single antenna systems. A practical iterative calculation method based on Steepest Descent Algorithm for finding the Lagrange multiplier is proposed. With the switching thresholds, the closed-form expressions of the SE and average BER, respectively for VP system and constant-power (CP) system are achieved. Simulation results for SE and average BER are in good agreement with the theory analysis. The results show that VP adaptive modulation with space-time coding provides better SE than the counterpart with CP under a target BER and average power constraint.

An optimal power-throughput tradeoff study for MIMO fading ad-hoc networks

In this paper, we study optimal tradeoffs of achievable throughput versus consumed power in wireless ad-hoc networks formed by a collection of multiple antenna nodes. Relying on adaptive modulation and/or dynamic channel coding rate allocation techniques for multiple antenna systems, we examine the maximization of throughput under power constraints as well as the minimization of transmission power under throughput constraints. In our examination, we also consider the impacts of enforcing quality of service requirements expressed in the form of channel coding block loss constraints. In order to properly model temporally correlated loss observed in fading wireless channels, we propose the use of finite-state Markov chains. Details of fading statistics of signal-to-interference-noise ratio, an important indicator of transmission quality, are presented. Further, we objectively inspect complexity versus accuracy tradeoff of solving our proposed optimization problems at a global as oppose to a local topology level. Our numerical simulations profile and compare the performance of a variety of scenarios for a number of sample network topologies.