Adaptive modulation

In this paper we designed an adaptation module (AM) with the objective to increase the performance of a recognition system for a new user or new writing style. The developed adaptation module is added after the recognition system, and its role is to examine the output of the independent system and produce a more correct output vector close to the desired response of the user. To achieve this end, we conceive an adaptation module based on Radial Basis Function Neural Network (RBF-NN) which is built using an incremental training algorithm. Two adaptation strategies are applied for adaptation module training: increase the number of new hidden units and adjust the parameters of the nearest unit (weights and location of center) using the standard descent gradient. This new architecture is evaluated by the adaptation of two recognition systems, one for digit recognition and one for alphanumeric character recognition. The results, reported according to the cumulative error, show that the adaptation module (AM) leads to decreasing the classification error and is capable of fast adaptation to the users handwriting. Moreover, results are compared with those carried out using the weights updating strategy of the nearest center apart from the addition of new units. In fact, the adaptation module decreases an average of 50% the error rate with standard recognition systems.

Modern wireless communication demands reliable data communication at high throughput in severe channel conditions like narrowband interference, frequency selective fading due to multipath and attenuation of high frequencies. Traditional single carrier systems address this set of problems by the use of complex, computationally intensive equalization filters. The Orthogonal Frequency Division Multiplexing (OFDM) based system, as opposed to single-carrier systems, is considered to be the future of the wireless communication and is being used to achieve high data rate by overcoming severe channel conditions without the use of these complex filters. This paper discusses the problem of Adaptive Modulation scheme selection through an OFDM based system over parallel frequency selective fading channels. An adaptive coding scheme is proposed by using Generalized Concatenated Codes (GCC), which have simple structure and are designed in such a way that they are best suited for fading channels. GCC are based on binary cyclic codes. The criterion of the proposed research is to optimize the throughput of a wireless system. Depending on the quality of sub-channels an adaptive modulation selection scheme and code assigning method is proposed. The proposed research combats against channel impairments better than those used in conventional systems by exploiting individual sub-channel condition. Results show better performance in terms of higher throughput by minimizing the bit error rate.

The continuous use of Internet services and applications triggers a sustainable growth of data transfer, therefore generating a necessity to develop an efficient and scalable transport platform. A novel-networking concept -Elastic Optical Networks (EONs) -can support bandwidth-demanding traffic from an advent of new services including cloud computing and content delivery networks. In this paper, we focus on dynamic routing of anycast and unicast traffic; anycast refers to cloud computing or content traffic served by data centers. We assume that EONs support various distance-adaptive modulation formats, namely BPSK, QPSK, and m-QAM, where m belongs to {8, 16, 32 and 64}. A higher modulation format consumes less spectrum, which can lead to a smaller blocking probability (BP) in dynamic routing. However, at the same time, a higher modulation format provides a smaller transmission distance, which triggers the need to use regenerators and increases CAPEX/OPEX network costs as well as power consumption. Therefore, the main goal of our research is to find a trade-off between the BP and using extra regenerators in the context of dynamic routing of anycast and unicast traffic in EONs.

In this paper we propose a mixed reality system (MRS) and an adaptation module for rehabilitation of the upper limb after stroke through serious games. Aim of the system is to increase intensity and number of training session using the fun factor as driver. Although our system is targeting post stroke patient it is necessary to validate and test our approach with valid users at the first stage to provide patients with stable system to use. These studies and their results are described in this paper.

Many advanced data services are driving up wireless technology, which is further boosted by growth in advanced market segments. The wireless industry is evolving from a Web of independent networks into a single integrated network with multiple standards; the expectation is that WI-FI, WI-MAX and 3G will coexist to enable a host of exerting new applications and business models. This paper focuses on concepts of WI-MAX technology, which employs microwave for the transfer of data wirelessly, and it also presents its comparison with WI-FI, and 3G technologies. WI-MAX is delivering broadband wireless access to the masses and represents alternative to digital subscriber lines (DSL) and cable broadband access. WI-MAX is based on IEEE 802.16 standard and is scalable. It stands for wireless (WI) microwave access (MAX). WI-MAX will provide anywhere, anytime connectivity. Features of WI-MAX are OFDM i.e. orthogonal frequency division multiplexing, sub channelization, directional antennas and adaptive modulation, which make WI-MAX as the technology of today. The Benefit of WI-MAX technology is that the signals can be run very close to each other on wireless channels. Super narrow lanes can put a lot of traffic over them without disturbance. Many technologies currently available can only provide line of sight (LOS) coverage; the technology behind WI-MAX has been optimized to provide excelled non-line of sight (NLOS) coverage.

In this paper, we present the implementation and verification of an secured adaptive modulation system on a Software Defined Radio (SDR) development platform. The SDR platform is supported by highly productive development system emphasizing the value of a structured development process that takes the developer through modeling, system analysis, implementation and verification by bit error rate analysis. SDR platform is a massively parallel processor in which transmitter and a part of receiver is implemented on DSP processor and demodulator is implemented on FPGA. For adaptive modulator-demodulator architecture, a bit error rate analysis is presented. Result shows that for same BER, BPSK requires minimum SNR.

Due to both logistical and technical difficulties of deploying realistic underwater acoustic networks, research involving underwater networks has primarily been limited to either theoretical analysis or simulation study. For simulation, however, there exist few commonly accepted acoustic channel models, which makes simulation study less realistic. The Kauai Acomms MURI 2008 (KAM08) experiment was conducted near Hawaii in Summer 2008, which provided us with first-hand, physical measurements of realistic acoustic communications. The paper describes how the measurements of the KAM08 experiment were programmed into a custom acoustic channel model for the QualNet simulator. We also simulated a underwater networking scenario that used an adaptive modulation scheme to optimize the energy efficiency so as to demonstrate the utility of the custom acoustic channel model.

An enhanced adaptive scheme based on threshold method with a reduced complexity that combine adaptive modulation and coding with diversity combining is presented for throughput maximization in broadband code division multiple access (CDMA) satellite networks. The proposed algorithm is a modify, enhanced, and more robust version of the existing algorithms for adaptive transmission rate and modulation in CDMA networks. The rate compatible punctured turbo-coded (RCPT), which has been found to give improved throughput performance in a direct sequence (DS) CDMA is exploited. A semianalytical process and simulations were carried out. It is found that there are significant improvement in the average throughput and the bit-error performance. The proposed algorithm using adaptive coding and modulation (instead of variable spreading gain) outperforms other systems such as Selective Power Control with Active Link Protection (SPC-ALP) algorithm proposed for adaptive transmission rate and power control in CDMA networks.

This work deals with reconfigurable control functions and protocols for supporting mobile computing applications in heterogeneous wireless systems like cellular networks and WLANs. The control functions are implemented in a software module, named Reconfigurable Access module for MObile computiNg applications (RAMON), placed in mobile and/or base stations. RAMON operates on abstract models of the main communication functions of a wireless systems (e.g., transmission over the radio channel, coding end error recovery, capacity sharing and packet scheduling, handover, congestion control, etc.). RAMON algorithms are programmed with reference to the abstract models, independently of specific radio and network technologies. RAMON interactions with a specific wireless access system are conceptually defined by means of parameters that can be measured and controlled, so that the general logic of the module can be posed on top of each system within the constraints and the flexibility provided by the system itself. The implementation of this architectural paradigm requires the definition of specific software adaptation modules between RAMON and each specific system. The reconfigurability of RAMON is exploited to adapt and select the algorithms on the basis of user/application requirements. The paper describes the RAMON architectural model and its control algorithms. Specific examples of adaptation modules are also provided. A selection of performance results achieved by a simulator implementing the RAMON module, the adaptation modules and the main communication functions of UMTS, 802.11 and Bluetooth are shown.

| In wireless/mobile communications, terminals adapt their rate and transmit power or, more in general, their coding and modulation scheme, depending on the timevarying channel conditions. This paper presents, in a tutorial form, the information theoretic framework underlying such Badaptive modulation[ techniques. First, we review fading channel models, channel state information assumptions, and related capacity results. Then, we treat the case of input power constraint, where the optimal input distribution is Gaussian. Finally, we address the case of discrete modulations.

The goal for the fourth generation (4G) of mobile communications system is to seamlessly integrate a wide variety of communication services such as high speed data, video and multimedia traffic as well as voice signals. One of the promising approaches to 4G is adaptive OFDM (AOFDM). In AOFDM, adaptive transmission scheme is employed according to channel fading condition with OFDM to improve the performance. In this paper, we have considered only adaptive modulation. First we have investigated the OFDM system performance of uncoded adaptive modulation using quadrature amplitude modulation (QAM) and phase shift keying (PSK). To further enhance the system, we employ convolutional coding to OFDM system. The obtained results show that a significant improvements in terms of bit error rate (BER) and throughput can be achieved demonstrating the superiority of the adaptive modulation schemes compared to fixed transmission schemes.

Receivers for horizontally encoded LTE based MIMO-OFDM systems are considered in this paper. Adaptive modulation and coding (AMC) is used as well as precoding. The linear minimum mean square error (LMMSE), successive interference cancellation (SIC) and K-best list sphere detectors (LSD) are compared. The receivers were designed and implemented for 2×2 and 4×4 antenna systems and meet the decoding rate requirement in LTE, i.e, 210 Mb/s in 2×2 and 405 Mb/s in 4×4 antenna systems. The results show that the performance of the receivers is similar in low SNR but the performance difference increases when a higher rank transmission is used. The K-best LSD has the highest performance and complexity. A simpler receiver could be used in the low SNRs to save power and a more complex receiver in the high SNRs when a higher goodput is needed.

WiMAX (worldwide inter-operability for microwave access) is an emerging technology for global broadband wireless system offering high speed access to mobile and broadband services. It is based on IEEE 802.16e standard. This standard only deals with MAC and PHY layer specification of network architecture. Considerable research has been done on performance analysis of PHY layer model of WiMAX system over AWGN channel model. This paper attempts performance analysis of IEEE 802.16e PHY layer model over AWGN as well as SUI channel models as SUI channel models are more realistic models based on empirical results. Different modulation schemes, coding rates, and different values of cyclic prefix are considered for comparison using BER (Bit error rate) ratio and SNR (Signal to Noise ratio) as performance parameters.

WiMAX stands for Worldwide Interoperability for Microwave Access. WiMAX is based on wireless Metropolitan Area Network (MAN) standards developed by IEEE 802.16 group. It operates in the licensed exempt and licensed spectrum between 2-11 GHz and 10-66 GHz frequency ...

Earlier paper have demonstrated that the achievable throughput of OFDM systems can benefit significantly from individual modulation/transmit power selection on a per sub-carrier basis according to the actual gain of individual sub-carriers (so called dynamic OFDM scheme). Usage of such an approach requires, however, providing support for additional functionalities such as: acquisition of the sub-carrier gains, signaling of the modulation types used between sender and receiver, etc. Therefore dynamic OFDM is actively pursued for future radio interfaces, rather than considered as extension of existing OFDM based standards. In this paper we introduce a proposal on how the widely accepted IEEE 802.11a/g systems as well as the emerging IEEE 802.11n system might be extended to support the dynamic OFDM in a single-user (point-to-point) setting. The presented approach guarantees backward compatibility to legacy devices. We address these issues by presenting (a) a set of protocol modificatio...

The development of individual behavioural profiles can be powerfully influenced by stressful social experiences. Using a comparative approach, we focus on the role of social stressors for the modulation of behavioural profile during early phases of life and adolescence. For gregarious species, the stability of the social environment in which the pregnant and lactating female lives is of major importance for foetal brain development and the behavioural profile of the offspring in later life. Social instability during these critical periods of development generally brings about a behavioural and neuroendocrine masculinisation in daughters and a less pronounced expression of male-typical traits in sons. Moreover, when mothers live in a socially threatening world during this time, anxiety-like behaviour of their offspring often is elevated in adulthood. These effects of the social environment are likely to be mediated by maternal hormones and/or maternal behaviour. In addition, they can be modulated significantly by offspring genotype. We favour the hypothesis that the behavioural effects of social stress during this phase of life are not necessarily "pathological" (nonadaptive) consequences or constraints of adverse social conditions. Rather, mothers could be adjusting the offspring to their environment in an adaptive way. Adolescence is another period in which behavioural development is particularly susceptible to social influences. There is some evidence that stressful social events experienced at this time alter and canalize behaviour in an adaptive fashion, so that earlier influences on behavioural profile development can be complemented and readjusted, if necessary, to meet current environmental conditions. In terms of underlying neuroendocrine mechanism, a central role for the interaction of testosterone and stress hormones is suggested. In summary, the modulation of behavioural profiles by social stress from the prenatal phase through adolescence appears to represent an effective mechanism for repeated and rapid adaptation.

Radio link adaptivity will be a key feature of the air interfaces of future mobile communication systems. This adaptivity includes techniques such as fast scheduling, hybrid ARQ, transmit diversity and adaptive modulation and coding. The performance of adaptive modulation generally suffers from the power inefficiencies of multilevel modulation formats. This is due to the variations in bit reliabilities caused by the bit-mapping onto the signal constellation. This article presents a concept, called constellation rearrangement (CoRe), which improves the multilevel modulation power efficiency by the joint application with transmit diversity schemes. It is shown by a theoretical analysis for 16-QAM that the presented concept can equalize variations in bit reliabilities by employing different mapping rules for the transmission over the diversity branches. This significantly improves the receiver block error rate performance and, hence, the performance of the adaptive modulation and coding. This is proven by simulations at link-level in a multicarrier CDMA system for AWGN and fading channels employing turbo coded transmission.

Wireless-enabled processor modules intended for communicating low-frequency phenomena (i.e., temperature, humidity, and ambient light) have been enabled to acquire and transmit multiple biological signals in real time, which has been achieved by using computationally-efficient data acquisition, filtering, and compression algorithms, and interfacing the modules with biological interface hardware. The sensor modules can acquire and transmit raw biological signals at a rate of 32 kbps, which is near the hardware limit of the modules. Furthermore, on-board signal processing enables one channel, sampled at a rate of 4000 samples per second at 12-bit resolution, to be compressed via adaptive differential-pulse-code modulation (ADPCM) and transmitted in real time. In addition, the sensors can be configured to filter and transmit individual timereferenced "spike" waveforms, or to transmit the spike height and width for alleviating network traffic and increasing battery life. The system is capable of acquiring 8 channels of analog signals, as well as data via an asynchronous serial connection. A back-end server archives the biological data it receives via networked gateway sensors, and hosts them to a client application that enables users to browse recorded data. The system also acquires, filters, and transmits oxygen saturation and pulse rate via a COTS interface board. The system architecture can be configured for performing real-time non-obtrusive biological monitoring of humans or rodents. This work demonstrates that low-power, computational and bandwidth-constrained wirelessenabled platforms can indeed be leveraged for wireless biosignal monitoring. Microfabrication Laboratory, a 3300-sq.ft. clean room dedicated for training students in the process of micromachining MEMS and integrated circuits. His research interests are primarily in the fields of MEMS and neuroengineering. His specific projects of interest include novel ferromagnetic MEMS (e.g., MEMS magnetometers, reconfigurable frequency-selective surfaces, and implantable magnetic microactuators for biomedical applications), nanomagnetomechanical systems, chemical sensors, micromachined sensors for plasma research, wireless sensor networks, microprobes for Parkinsons disease research, implantable and flexible 3-D microelectrode arrays, dynamic modeling of 3-D microelectrodes, microelectrode arrays for high-density neural stimulation and retinal prostheses, simulating the synthetic vision provided by retinal prostheses, micromachined systems to manipulate individual cells and to perform high-impedance patch-clamp recording, microactuators to solve the hydrocephalus shunt-clogging problem, wireless neural transceivers, braincomputer interfaces, and developing neural-control strategies and systems for functional deficits (e.g., spinal cord injury, ocular motility, and deep-brain stimulation). Lastly, he is dedicated to developing and improving graduatelevel training programs in the multidisciplinary engineering fields of MEMS, nanotechnology, and neuroengineering.

Modulated phases occur in numerous functional materials like giant ferroelectrics and magnetic shape memory alloys. To understand the origin of these phases, we review and generalize the concept of adaptive martensite. As a starting point, we investigate the coexistence of austenite, adaptive 14M phase and tetragonal martensite in Ni-Mn-Ga magnetic shape memory alloy epitaxial films. The modulated martensite can be constructed from nanotwinned variants of a tetragonal martensite phase. By combining the concept of adaptive martensite with branching of twin variants, we can explain key features of modulated phases from a microscopic view. This includes phase stability, the sequence of 6M-10M-NM intermartensitic transitions, and magnetocrystalline anisotropy.

In this paper, we analyze the predictability of the communications performance of an adaptive modulation system for underwater acoustic communications. As a case study, we consider the KAM11 data set, which has been collected off the coast of Kauai Island during July 2011. We measure the signal to noise ratio at the output of the equalizer and we observe slow fluctuations over time intervals of up to six minutes. Based on an analytical model and using the estimated time correlation coefficient of subsequent values of the ...

The present work demonstrates a novel, free and opensource educational software package on wireless communications. Targeting graduate and post-graduate studies, the package covers issues of antennas and propagation, wireless channel modeling (fading, shadowing, path loss, Doppler effect), static and adaptive modulation, client mobility and network planning applied to DVB/T and indoor networks (WiFi, femtocell) settings.

The concept of adaptivity is of paramount importance in the design of future communication systems, in which a careful exploitation of the limited available resources (bandwidth, power, etc.) is required. The potential of channel-adaptive transmission has been already recognized 30 years ago, but it did not receive much interest at that time. In the last decade, the advent of feasible software radio systems, and hence, the availability of fast flexible and reconfigurable transceivers has renewed interest in adaptive techniques, which include adaptive modulation and coding, adaptive antennas and adaptive equalization techniques. This paper focuses on adaptive modulation and adaptive error control mechanisms. Basic concepts are highlighted and an overview on the achieved results and new trends in this research area are presented. Some results from information theory are also presented, which show the limitations of these techniques and motivate further research on the practical and design issues that have to be addressed to enable performance to reach close to the theoretical limit. Copyright © 2002 John Wiley & Sons, Ltd.

ABSTRACT We apply an evolutionary strategies (ES) algorithm to the problem of designing modulation schemes used in wireless communication systems. The ES is used to optimize the digital symbol to analog signal mapping, called a constellation. Typical human-designed constellations are compared to the constellations produced by our algorithms in a simulated radio environment with noise and multipath, in terms of bit error rate. We conclude that the algorithm, with diversity maintenance, find solutions that equal or outperform conventional ones in a given radio channel model, especially for those with higher number of symbols in the constellation (arity).

Detailed investigations of the transmission performance of adaptively modulated optical orthogonal frequency division multiplexed (AMOOFDM) signals converted using reflective semiconductor optical amplifiers (RSOAs) are undertaken over intensity-modulation and directdetection (IMDD) single-mode fiber (SMF) transmission systems for WDM-PONs. The theoretical RSOA model adopted for modulating the AMOOFDM signals is experimentally verified rigorously in the aforementioned transmission systems incorporating recently developed realtime end-to-end OOFDM transceivers. Extensive performance comparisons are also made between RSOA and SOA intensity modulators. Optimum RSOA operating conditions are identified, which are independent of RSOA rear-facet reflectivity and very similar to those corresponding to SOAs. Under the identified optimum operating conditions, the RSOA and SOA intensity modulators support the identical AMOOFDM transmission performance of 30Gb/s over 60km SMFs. Under low-cost optical component-enabled practical operating conditions, RSOA intensity modulators with rear-facet reflectivity values of >0.3 outperform considerably SOA intensity modulators in transmission performance, which decreases significantly with reducing RSOA rear-facet reflectivity and optical input power. In addition, results also show that use can be made of the RSOA/SOA intensity modulation-induced negative frequency chirp to improve the AMOOFDM transmission performance in IMDD SMF systems.

Wireless communications now a days has come up with revolutionary technologies with high throughputs and reliable connectivity. Due to mobility of a subscriber with respect to transmitter, received signal quality changes. To maintain constant performance with this distance change, some instant variations are to be made to make system adaptive as per mobility. For properly suited SNR and Modulation scheme, constant BER can be maintained for ensuring QoS requirements. In this paper we have shown simulation of a IEEE802.16 Wi-Max MIMO (Multiple Input Multiple Output) model with adaptive modulation and changing SNR(real time) to meet constant BER performance of system. At the end, results are plotted and from that SNR values for minimum constant BER are deduced.

In this paper, opportunistic cooperative amplify-and-forward networks in conjunction with three different adaptive policies, namely optimal simultaneous power and rate adaptation (OPRA), constant power with optimal rate adaptation (OPA) and truncated channel inversion with fixed rate (TIFR), are investigated and compared in terms of Rayleigh channel capacity where the source adapts its rate and/or power level according to channel conditions while the best relay simply amplifies and then forwards the received signals. Furthermore, the effect of diversity combining on the network is studied by investigating two cases of maximal ratio combining (MRC) and selection combining (SC) equipped at the destination. To this end, the mathematically tractable form of the upper and lower bound of the end-to-end effective signal-to-noise ratio (SNR) is provided and then used to derive the closed-form expression of the Shannon capacity. Our results are verified through comparison with Monte Carlo simulations in some representative scenarios where we also illustrate that, among them, for an arbitrary number of cooperative relays, OPRA slightly outperforms ORA, which, in turn, outperforms TIFR.

Adaptive modulation exploits the time-variant channel capacity fluctuation of fading channels using a range of different modem modes. Specifically, no information is transmitted when the instantaneous channel signal-to-noise ratio (SNR) is low, and, hence, during this period the data must be buffered, which results in delay or latency. When the instantaneous channel quality improves, 2-, 4-, 16-, and 64-level modem modes are invoked, which allows the transmission buffer to be emptied. It is shown that channel capacity gains are achieved at the cost of some latency penalty. The latency is quantified in this treatise and mitigated by frequency hopping or statistical multiplexing. The latency is increased when either the mobile speed or the channel SNR are reduced, since both of these result in prolonged low instantaneous SNR intervals. It is demonstrated that as a result of the proposed measures, typically more than 4-dB SNR reduction is achieved by the proposed adaptive modems in comparison to the conventional benchmark modems employed.

Cognitive radio (CR) and Multiple Input Multiple Output (MIMO) technologies represent emerging and promising technologies for providing high spectrum utilization, and maximizing the capacity to face the huge demand for wireless applications. In this context, a transmission scheme that exploits both CR and MIMO is presented, together with its optimization to increase the system goodput as well as to decrease the total power consumption. In this paper we present and investigate this Spatial Cognitive Technique through a Zero-Forcing BeamForming (ZFB) as well as Adaptive Modulation, where a predefined Quality of Service (QoS) is guaranteed for Primary Users (PU), while Secondary Users (SU) are serviced as long as they do not compromise the QoS to the PU. The QoS is denoted as minimum guaranteed goodput and maximum allowed Symbol Error Rate (SER) metrics. Closed form expression for the SER, goodput and total consumed power are mathematically formulated and illustrated by extensive simulations.

In this paper we propose polling based uplink scheduling schemes for TCP based applications in a multipointto-point fixed broadband IEEE 802.16 network. Our schemes adapt the transmission rates between Subscriber Stations (SSs) and the Base Station (BS) dynamically using adaptive modulation. We ensure fairness among the SSs via a credit-based approach in which an SS that misses a chance to transmit due to bad channel gets more weightage when the channel favors scheduling. We also propose a method to compute an optimal polling interval that aims to maximize slot utilization and TCP throughput. We demonstrate through exhaustive simulations that the proposed schedulers maximize link utilization, provide long-term fairness and minimize contraction of TCP congestion window. Implementation of the proposed schemes requires a cross-layer based feedback protocol stack at the BS and SSs.

In this paper, we study the performance of a channeladaptive packet transmission system over fading channels with a finite transmit buffer. This transmission scheme combines the essential features of two popular communication techniques, namely adaptive modulation and coding (AMC) and automatic repeat request. Our joint design takes into consideration the size limitation and the dynamic variation of the transmit buffer. Specifically, we introduce a novel buffer-assisted mode selection strategy for AMC in addition to the traditional channel-quality-based strategy. We also developed three buffer management schemes. Moreover, we develop a Markov-chain-based analytical framework to investigate the performance, efficiency, and complexity of this transmission system with different mode selection strategies and buffer management schemes. This general framework allows us to derive the accurate analytical expressions for the packet loss, average delay, spectral/power efficiency, and average feedback load of this system over general fading channel. The selected numerical results, together with the related discussion, illustrate the various design tradeoffs.

We propose an optimum transmitting structure consisting of adaptive modulation, space-time block coding (STBC), and transmitter beamforming for orthogonal frequency division multiplexing (OFDM) systems to improve the data throughput and error performance. Using correlative properties of multiinput multi-output (MIMO) channels, we maximize the channelto-noise ratio (CNR) based on a water-filling principle to optimally select the number of antenna beams and the power splitting ratio. The adaptive modulator employed is based on a lookup matrix adaptive bit and power allocation (LM-ABPA) scheme. As compared to non-adaptive systems, simulation results demonstrated that the proposed configuration achieves spectrally more efficient transmission under a constant error rate as well as better error rate performance under a constant data rate.

This paper deals with the analytical evaluation of the average delay, the packet-loss rate (PLR) and the throughput of a multi-user (MU) wireless system that capitalizes on a crosslayer design of adaptive modulation and coding (AMC) with automatic repeat request (ARQ). To this end, we propose a heuristic scheduling policy, which has the nice properties to effectively exploit the system resources and to be analytically tractable. Simulation results confirm the effectiveness of the proposed scheduler. Moreover, the excellent match between analytical and simulated performance allows the proposed approach to be used for cross-layer design optimization, avoiding time-consuming simulations.

Abstract: Wimax (Worldwide Interoperability for Microwave Access) is a promising technology which can offer high speed voice, video and data service up to the customer end. The aim of this paper is the performance evaluation of an Wimax system under different combinations of digital modulation (BPSK, QPSK, 4 QAM and 16 QAM) and different communication channels AWGN and fading channels (Rayleigh and Rician). And the Wimax system incorporates Reed Solomon (RS) encoder with Convolutional encoder with half ...

The paper discusses differences between the approaches to optimization of wireless analog feedback communication systems (AFCS) and digital communication systems (DCS). There is shown that "one mile zone" transmission of the analog signals can be realized by optimal AFCS more efficiently than by DCS.

A line coding format for the output code-words of a two-digit Instantaneously Adaptive Delta Modulation (2d-IADM) system is presented. These words consist of a binary and a ternary digit and, beyond the coded information for the system's analogue-to-digital conversion process, timing and digit identification information is embedded. The suggested line coding results in a DC-free ternary signal featuring split-phase bipolar alternate marks inversion, and offers a 30% effective increase of the transmitted amount of binary information plus timing and codeword frame alignment information, at a cost of a mere 18•5% additional redundancy with respect to common split-phase coding of binary digits.

A multiscale modeling project for wind energy assessment in central Nevada has been conducted. The PSU/NCAR fifth-generation Mesoscale Model (MM5) was used in conjunction with an h-adaptive finite element model and local tower data for a 1-year cycle for the central region. The MM5 results and the local tower data are used as input into the microscale h-adaptive FEM model. The h-adaptive module permits resolution down to meter levels, allowing more accurate details regarding topographic features and wind velocity vectors. Multiscale results for assessing wind energy potential are presented in the form of monthly averaged wind power density maps. Potential locations for establishing wind farms in the region are discussed. r

Adaptive modulation can improve the throughput of cooperative communications, which has been shown in previous research. So far the adaptive modulation is applied with respect to perfect transmitter side Channel State Information (CSI) in most current work. In this paper we have investigated the modulation-adaptive cooperation in Rayleigh fading channels providing imperfect CSI at senders. The adaptive modulation scheme with rate adaptation at the relay proposed in our previous work has been extended here first. Then a new adaptive modulation scheme with adaptation at both the source and relay is proposed. Simulation results show the proposed two schemes can provide significant improvement in throughput over the fixed DF relaying cooperation even with imperfect feedback; the throughput can be further improved with the proposed scheme allowing adaptive modulation at both the source and relay.

This work analyzes the average bit error rate (BER) of Multiple-Input Multiple-Output systems in transmit-correlated Rayleigh flat-fading channels. The receiver scheme is based on the minimum mean square-error criterion and the input may be precoded in order to optimize the communication. Accurate closed-form formulations for the average BER are derived.

The present paper sets out an intelligent instrument for a quantitative measurement of air quality, consisting of a some gas sensors, each of them being embedded into a adaptation module, an data processing and acquisition module provided with a microcontroller and a decision making, display and alarm system. An electronic nose composed of a high-sensitivity and low selectivity micro-sensors array,