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In this paper, a new network model is proposed to improve the performance of the secondary channel in cognitive radio networks (CRNs) based ambient backscatter communication systems. This model is considered as a cooperative system with multi-secondary transmitter (ST) and multi-relay. The ST backscatters data to both the secondary receiver (SR) and relay. Also it harvests energy from the signal emitted by the primary transmitter (PT) during the busy period. The relay activated by the ST user forwards the information from ST to SR. During the idle period, the PT broadcast is interrupted and ST also performs active data transmission using the energy it has harvested. We aim to maximize the number of data transmitted to the SR. Therefore, how long the ST will perform backscattering, energy harvesting and active data transmission is a problem to be solved. In such cooperative systems with multiple users, the solution of the problem becomes more complex. Therefore, the system model has been mathematically modeled and transformed into an optimization problem, considering that users are transmitting data using time division multiple access (TDMA) and non-orthogonal multiple access (NOMA) techniques. Numerical results showed that higher data rates were achieved in NOMA. Additionally, It has been seen that the proposed model performs better when compared to the existing approaches in the literature, where the ST can only harvest energy and transmit data actively or only transmit data with ambient backscatter communication. [ABSTRACT FROM AUTHOR]

Today hollow-core optical fibers (HCF) are on the verge of surpassing the attenuation benchmark of silica single-mode optical fibers used in optical communication. Compared to solid-core optical fibers, HCFs exhibit ultra-low nonlinearity, high damage threshold, low latency and temperature insensitivity, making them ideal candidates for high-speed data communication, high-resolution sensing, high-power delivery and precise interferometry. The main challenges of low insertion loss, suppressed back-reflections and fundamental mode coupling must be addressed to incorporate HCFs into existing fiber-optic systems to fully exploit their potential. This paper provides an overview of the HCF history, from early papers in the 1980s, over the invention of photonicbandgap HCFs, to the recent achievements with antiresonant HCFs. Then light guiding mechanisms are presented and key HCF properties are discussed. Interconnection techniques to standard optical fibers are compared with respect to possible HCF applications. Fusion splicing results are presented with an alternative interconnection solution based on a modified fiber-array technique newly developed by our team. Finally, cutting-edge HCF applications that take advantage of our HCF interconnection, are discussed. [ABSTRACT FROM AUTHOR]

In light of the increasing requirement for the electromagnetic spectrum, the integration of radar and communication is widely concerned because of its miniaturizing equipments and high efficiency of spectrum. To address the issue that the communication information in integration signal for radar and communication affects its detection performance. A novel integration signal is proposed in this paper. Inspired by the high communication efficiency of shaped octal phase-shift keying (S8PSK) and high spectral efficiency of the three-section integration waveform (k-CPM-LFM), we generate a new type of modulation h-CPM by introduction of a precoding method with low complexity and a time-varying modulation index h, which is used to encode communication data into LFM radar waveform to form a novel integration waveform h-CPM-LFM. Numerical results show that the designed waveform is at least 10 dB less spectrum extension than other integration waveforms when carrying large amounts of communication information and has excellent BER performance under the condition of strong out-of-band interference. Ambiguity function analysis shows that the waveform has excellent detection performance comparable to LFM. [ABSTRACT FROM AUTHOR]

This paper presents a method for phase noise impact compensation in 60 GHz OFDM receivers and provides the results of performance evaluation using OFDM PHY parameters defined in the IEEE 802.11ay standard. It is shown that the phase noise in 60 GHz band has a critical impact on the OFDM performance for high data rate transmission employing high order modulation constellations. The proposed compensation method combines time domain algorithm predicting the linear average phase trend on the OFDM symbol duration and estimation in frequency domain of phase noise spectrum realization and convolution with correction filter response. Both algorithms use Maximum A Posteriori Probability (MAP) estimation approach to find the optimal solution and are applied successively. The proposed algorithms have moderate implementation complexity which is especially important for high speed 11ay hardware modem architecture. The performance of the proposed algorithms is evaluated in the frequency flat and frequency selective channels with phase noise model adopted in the IEEE 802.11ay. [ABSTRACT FROM AUTHOR]

In this paper, a novel compressed sensing (CS) acquisition and joint recovery of spatiotemporal correlated signals algorithm is presented for effective data collection and precise sensors data streams reconstruction in wireless sensor networks. The CS-based proposed method utilizes an iterative re-weighted €i -minimization and a (2 regularization to increase the reconstruction accuracy with a small number of required data transmission. Moreover, we develop an alternating direction method of multipliers based algorithm to efficiently solve the resulting optimization problem. Numerical experiments are conducted on several test signals with a variety of sampling ratios. The experimental results verify the effectiveness of the proposed scheme in terms of reconstruction accuracy and consumption time compared with the state of the art algorithms. [ABSTRACT FROM AUTHOR]

The paper focuses on designing precoding matrices in multi-cell multiple-input multiple-output (MIMO) simultaneous wireless information and power transfer networks (SWIPT) where the sets of users are selected for data transmission in each time slot and the unselected users are dedicated to energy harvesting. The precoding design for the SWIPT problem is formulated as a general multi-objective maximization problem, in which the sum-rate (SR) and sum harvested energy (SHE) are maximized simultaneously under the transmit power constraints. Since the objective function of the maximization problem is not concave in the design matrix variables, it is difficult to directly obtain the optimal solutions. To tackle this challenge, we recast the SR function into one more amenable by applying the connection between the minimum mean square error and achievable data rate. In addition, to deal with the non-concavity of the harvested energy function, we derive its concave minorant. Then, we develop an efficient iterative algorithm based on alternating optimization (AO) to obtain the optimal precoders. We also analyze the convergence and computational complexity of the proposed algorithm. Finally, by numerical simulation results we investigate the trade-offs between the SR and SHE. [ABSTRACT FROM AUTHOR]

In this paper, for an interference alignment (IA) based network, a time splitting scheme for transmitting training and data symbols is optimized. The time allocated for transmitting training symbol will affect the precision of channel estimation (CE) and thus the achievable rate as well as the duration for data symbol transmission. With the least square (LS) and relaxed minimum mean square error (RMMSE) CE algorithm, the lower bounds of achievable rate are carefully derived, respectively. Then we formulate an optimization problem to maximize the lower bounds of achievable rate by optimizing the time splitting factor (TSF). The existence of optimum is first proved. Then, regarding the complexity of solution, Taylor expansion is adopted to find the approximated optimal TSF. Numerical results are presented to show the optimal TSF can achieve larger lower bound of achievable rate over other fixed TSFs due to its adaptivity to the channel characteristics and its statistics of CE errors. Numerical results also validate that the approximation just brings out some small and acceptable errors on the system rate. In addition, RMMSE CE algorithm shows better performance than LS CE because RMMSE considers noise statistics as modification. [ABSTRACT FROM AUTHOR]

HTTP adaptive streaming is a widely used method for delivering the video content to its final recipients. The visual quality of the streamed video content is being adaptively changed according to network conditions to offer the user a smooth playback, which is even more important for mobile connection like LTE. In this paper, we focus on the encoding of the video content and on the segmentation of the video to be used in DASH based service. We used long sequences with duration up to 2.5 hours to simulate a real life situation. We investigate the influence of the GOP length on the final DASH segment size and evaluate the performance of AVC and HEVC when used in DASH. We used several fixed values of GOP length and one special case of scene change based GOP creation. Our results showed, that such an adaptive segmentation mode brings up to 11% bitrate savings with preserving comparable quality and lower fluctuations in absolute size of the DASH segments. [ABSTRACT FROM AUTHOR]

Energy drainage is a critical issue in sensor networks which is aggravated further by the incorporation of Cognitive Radio (CR). Radio Frequency Energy Harvesting (RF-EH) is a prominent method for mitigating energy constraints while providing potentially perpetual lifetime. However, its inclusion in Cognitive Radio Sensor Networks (CRSNs) instigates various Medium Access Control (MAC) layer challenges. Effective communication in a way to avoid collisions in the presence of multiple Primary Users (PUs) and CR nodes willing to access electromagnetic spectrum and EH are the significant challenges. In this paper, a MAC protocol for CRSNs which overcome challenges above is proposed. In our protocol, the CR nodes use Dedicated Common Control Channel (DCCC) for control information exchange among CR nodes and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol to access channel and avoid collisions. RF-EH technique is also incorporated to prolong the network lifetime. The proposed work is a state of the art MAC protocol in which CR nodes can communicate and harvest energy as well. Performance of the proposed protocol is evaluated in terms of throughput, harvested energy and lifetime of CRSNs by considering different parameters which include PU activities, number of CR nodes, number of flows and packet size. Simulations are performed on Network Simulator (NS-2). [ABSTRACT FROM AUTHOR]

This paper considers sparsity-aware adaptive compressed sensing acquisition and the joint reconstruction of intra- and inter-correlated signals in the wireless sensor networks via distributed compressed sensing. Due to the different sparsity order of the finite-length signals, we develop an adaptive sensing framework based on the sparsity order, in which sensor readings are sampled according to its own sparsity order measure. On the decoder side, utilizing a distributed compressive sensing scheme, a joint reconstruction method is proposed to recover signal ensemble even in imperfect data communication. Moreover, we explore that by adapting the sampling rate of the sensed signals, not only the whole required number of measurements is reduced, but also the reconstruction performance is significantly improved. Numerical experiments verify that our proposed algorithm achieves higher reconstruction accuracy with a smaller number of required transmission, and with lower complexity as compared to those of the state of the art CS methods. [ABSTRACT FROM AUTHOR]

This paper works with the simulation of T-CONT allocation and delay analysis in passive optical networks PON. Building our networks with the PON technology we can achieve increased data rates, however we need to ensure that the idle gaps between the particular transmissions are minimal. The primary method for the upstream time slot allocation in passive optical networks is via Multi Point Control Protocol. The baseline standard of this protocol clearly defines the use o f the REPORT and GATE control messages. The two optical network elements used here, the optical network unit ONT and the optical line termination OLT, located at the central office CO, can be scheduled to allocate the time slots. Using the control messages, a more accurate scheduling algorithm can be developed, hence we can directly improve the utilization of the bandwidth as well. In this work, we introduce the basic topology of the passive optical networks, how PON works and what basic principles o f bandwidth allocation have been applied. Subsequently, we suggest a selection of methods for time slot allocation and we make an analysis on the achieved results. Our main focus is on the system load, transfer delay and the analysis of the effectivity. [ABSTRACT FROM AUTHOR]

This paper deals with the latest digital TV standard DVB-SH (Digital Video Broadcasting - Satellite to Handhelds) with focus on utilization of its advantages for the next generation of mobile TV broadcasting. The whole paper consists of two parts. In this first part, after the brief introduction to DVB-SH and related last works review, the simulation model of DVB-SH-A, which is using terrestrial configuration with OFDM transmission mode, is presented. The work is especially focused on the description of new type of forward error correction and system configuration of the DVB-SH-A mode. For the analysis and simulation of the transmission, the original scheme of turbo encoder was modified in this paper. Application for simulation of the transmission in mobile and portable fading transmission channels was developed in MATLAB. Dependences of BER on C/N ratio for all types of payload modulation are compared with focus on mobile TV services availability. Finally, the achieved results are evaluated and clearly discussed. [ABSTRACT FROM AUTHOR]

This paper addresses a cognitive radio (CR) network scenario where a relay is assigned to mitigate interference to primary users (PUs). We develop an average probability of successful secondary transmission (PSST) to introduce relay in the CR network. The power allocation is done using dual domain concept to maximize the system throughput as well as maintaining interference to an acceptable level and this approach is implemented in our paper that has a higher convergence rate. Furthermore, we propose an alternative approach that maintains a high throughput and at the same time reduces the computational complexity significantly. A detailed analysis is done before simulation. The simulated results validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance the system,s performance. A? a MIMO system, it is expected that the mentioned diversity-multiplexing tradeoff exists in a MIMO radar, too. In this paper, this tradeoff is studied and verified in MIMO radars with widely separated antennas. In more details, it will be shown that increasing dependency between transmit-receive links results in higher diversity gain and lower multiplexing gain, and vice versa. Then, the optimal tradeoff is introduced, i.e., the conditions that the MIMO radar system should have, so that the diversity-multiplexing tradeoff is at its optimum point, are driven. [ABSTRACT FROM AUTHOR]

Wireless-powered cellular networks (WPCNs) are currently being investigated to exploit the reliability and improve battery lifetime of mobile users. This paper investigates the energy harvesting structure of the full-duplex relaying networks. By using the time switching based relaying (TSR) protocol and Amplify-and-Forward (AF) model in delay-limited transmission scheme, we propose the closed-form expression of the outage probability and then calculate the optimal throughput. An important result can be taken obviously that the time fraction in TSR, the position of relay, the noise as well as the energy conversation impacting on the outage probability as well as the optimal throughput. By Monte Carlo simulation, the numerical results indicate an effective relaying strategy in full-duplex cooperative systems. Finally, we provide fundamental design guidelines for selecting time fraction in TSR that satisfies the requirements of a practical relaying system. [ABSTRACT FROM AUTHOR]

Inter-carrier interference and multiple access interference due to carrier frequency offset (CFO) are two major factors that deteriorate the performance of orthogonal frequency division multiple access (OFDMA) and multicarrier code division multiple access (MC-CDMA) in wireless communication. This paper presents a new mathematical analysis for spectral efficiency of OFDMA communication systems over a frequency selective Rayleigh fading environment in the presence of multiple users. It also compares the spectral efficiency performance of OFDMA and MC-CDMA at different load, signal-to-noise ratio, CFO and delay spread conditions. MC-CDMA is found to be more resilient to CFO in general, however, OFDMA performs better at high load. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate probability of non-zero secrecy capacity of multi-hop relay networks over Nakagamim fading channels in presence of hardware impairments. In the considered protocol, a source attempts to transmit its data to a destination by using multi-hop randomize-and-forward (RF) strategy. The data transmitted by the source and relays are overheard by an eavesdropper. For performance evaluation, we derive exact expressions of probability of non-zero secrecy capacity (PoNSC), which are expressed by sums of infinite series of exponential functions and exponential integral functions. We then perform Monte Carlo simulations to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents an efficient parallel processing architecture using multi-core Digital Signal Processor (DSP) to improve the capability of real-time imaging for Frequency Modulated Continuous Wave Synthetic Aperture Radar (FMCW SAR). With the application of the proposed processing architecture, the imaging algorithm is modularized, and each module is efficiently realized by the proposed processing architecture. In each module, the data processing of different cores is executed in parallel, also the data transmission and data processing of each core are synchronously carried out, so that the processing time for SAR imaging is reduced significantly. Specifically, the time of corner turning operation, which is very time-consuming, is ignored under computationally intensive case. The proposed parallel architecture is applied to a compact Ku-band FMCW SAR prototype to achieve real-time imageries with 34 cm × 51 cm (range × azimuth) resolution. [ABSTRACT FROM AUTHOR]

Accurately estimating node density in Vehicular Ad hoc Networks, VANETs, is challenging and crucial task. Various approaches exist, yet none takes advantage of physical layer parameters in a distributed fashion. This paper describes a framework that allows individual nodes to estimate the node density of their surrounding network independent of beacon messages and other infrastructure-based information. The proposal relies on three factors: 1) a discrete event simulator to estimate the average number of nodes transmitting simultaneously; 2) a realistic channel model for VANETs environment; and 3) a node density estimation technique. This work provides every vehicle on the road with two equations indicating the relation between 1) received signal strength versus simultaneously transmitting nodes, and 2) simultaneously transmitting nodes versus node density. Access to these equations enables individual nodes to estimate their real-time surrounding node density. The system is designed to work for the most complicated scenarios where nodes have no information about the topology of the network and, accordingly, the results indicate that the system is reasonably reliable and accurate. The outcome of this work has various applications and can be used for any protocol that is affected by node density. [ABSTRACT FROM AUTHOR]

This paper proposes the interleaving gain in two different distributed turbo-coding schemes: Distributed Turbo Codes (DTC) and Distributed Multiple Turbo Codes (DMTC) for half-duplex relay system as an extension of our previous work on turbo coding interleaver design for direct communication channel. For these schemes with half-duplex constraint, the source node transmits its information with the parity bit sequence(s) to both the relay and the destination nodes during the first phase. The relay received the data from the source and process it by using decode and forward protocol. For the second transmission period, the decoded systematic data at relay is interleaved and re-encoded by a Recursive Systematic Convolutional (RSC) encoder and forwarded to the destination. At destination node, signals received from the source and relay nodes are processed by using turbo log-MAP iterative decoding for retrieving the original information bits. We demonstrate via simulations that the interleaving gain has a large effect with DTC scheme when we use only one RSC encoder at both the source and relay with best performance when using Modified Matched S-Random (MMSR) interleaver. Furthermore, by designing a Chaotic Pseudo Random Interleaver (CPRI) as an outer interleaver at the source node instead of classical interleaves, our scheme can add more secure channel conditions. [ABSTRACT FROM AUTHOR]

A novel three-pole tunable bandpass filter using varactor-loaded quarter-wavelength combline and asymmetric half-wavelength resonators is proposed in this paper. A nearly constant 3-dB absolute bandwidth is 150 ± 13 MHz (10.7%>~6.9% fractional bandwidth) within the tuning range of 1.4-2.0 GHz (42.8%). The filter is designed on a Rogers substrate with εr = 2.2 and h = 1 mm with its insertion loss varying from 3.6 dB to 2.8 dB and return loss better than 10 dB over the entire tuning range. The creation of two transmission zeros near the passband edges is analyzed by the even-odd-method. By using dissimilar resonators, the proposed tunable filter could obtain > 33 dB rejection levels at the second harmonics. The measured results show good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

This paper presents application of the low Duty Cycle Ratio (DCR) modulations: isochronous Digital Pulse Position Modulation (DPPM) and anisochronous Digital Pulse Interval Modulation (DPIM) in backscatter based passive RFID communication system. The proposed modulations are compared to commonly used Amplitude Shift Keying (ASK) modulation. Low DCR modulations are customized for data transmission through inductively coupled link between reader and the tag operating at frequency of 13.56 MHz. The RFID system is mathematically for mulated and the performances of the tag are evaluated for each modulation. Observed parameters are modulation depth of backscattered signal, voltage-current characteristics of tag rectifier circuit and ripple of rectifier output voltage. The application of proposed low DCR modulation techniques improves the performance of the RFID system by up to 250%. [ABSTRACT FROM AUTHOR]

This paper analyzes a digital interface and bus system modeling and optimization of the SEOSAR/PAZ Earth Observation satellite. The important part of the satellite is an X-band Synthetic Aperture Radar instrument that integrates 384 Transmit/Receive Modules located in 12 antenna panels 7.5 m away from the central processor and controlled by a synchronous 10 Mbps bidirectional serial protocol. This type of mid-range point-to-multipoint transmission is affected by bit errors due to crosstalk, transmission line attenuation and impedance mismatches. The high-speed data communication network has been designed to optimize the transmission by using a simulation model of the data distribution system which takes into account the worst-case scenario and by developing a lab-scaled prototype which exhibits BER of 10-11 for an interfering signal of 10 Vpp. The result is a point-to-multipoint bidirectional transmission network optimized in both directions with optimal values of loads and equalization resistors. This high-speed data transmission subsystem provides a compact design through a simple solution. [ABSTRACT FROM AUTHOR]

This paper is concerned with a rate-splitting based transmission strategy for the two-user symmetric Gaussian interference channel that contains common messages only. Each transmitter encodes its common message into multiple layers by multiple codebooks that are drawn .from one separate code book, and transmits the superposition of the messages corresponding to these layers; each receiver decodes the messages from all layers of the two users successively. Two schemes are proposed for decoding order and optimal power allocation among layers respectively. With the proposed decoding order scheme, the sum-rate can be increased by rate-splitting, especially at the optimal number of rate-splitting, using average power allocation in moderate and weak interference regime. With the two proposed schemes at the receiver and the transmitter respectively, the sum-rate achieves the inner bound of HK without time-sharing. Numerical results show that the proposed optimal power allocation scheme with the proposed decoding order can achieve significant improvement of the performance over equal power allocation, and achieve the sum-rate within two bits per channel use (bits/channel use) of the sum capacity. [ABSTRACT FROM AUTHOR]

The distributions of random variables are of interest in many areas of science. In this paper, ascertaining on the importance of multi-hop transmission in contemporary wireless communications systems operating over fading channels in the presence of cochannel interference, the probability density functions (PDFs) of minimum of arbitrary number of ratios of Rayleigh, Rician, Nakagami-m, Weibull and α-μ random variables are derived. These expressions can be used to study the outage probability as an important multi-hop system performance measure. Various numerical results complement the proposed mathematical analysis. [ABSTRACT FROM AUTHOR]

The primary challenge in wireless communication with energy harvesting devices is to efficiently utilize the harvesting energy such that the data packet transmission could be supported. This challenge stems from not only QoS requirement imposed by the wireless communication application, but also the energy harvesting dynamics and the limited battery capacity. Traditional solar predictable energy harvesting models are perturbed by prediction errors, which could deteriorate the energy management algorithms based on this model. To cope with these issues, we first propose in this paper a non-homogenous Markov chain model based on experimental data, which can accurately describe the solar energy harvesting process in contrast to traditional predictable energy models. Due to different timescale between the energy harvesting process and the wireless data transmission process, we propose a general framework of multiple timescale Markov decision process (MMDP) model to formulate the joint energy scheduling and transmission control problem under different timescales. We then derive the optimal control policies via a joint dynamic programming and value iteration approach. Extensive simulations are carried out to study the performances of the proposed schemes. [ABSTRACT FROM AUTHOR]

The paper describes a novel method for simple estimation of jitter contained in a received digital signal. The main objective of our research was to enable a non-invasive measurement of data link properties during a regular data transmission. To evaluate the signal quality we estimate amount of jitter contained in the received signal by utilizing internal signals of a data recovery circuit. The method is a pure digital algorithm suitable for implementation in any digital integrated circuit (ASIC or FPGA). It is based on a blind-oversampling data recovery circuit which is used in some receivers instead of a traditional PLL-based clock and data recovery (CDR) circuit. Combination of the described jitter measurement block and the data recovery block forms a very efficient input part of the digital receiver. In such a configuration it is able to simultaneously perform both data communication (data recovery) and signal quality estimation (jitter measurement). The jitter measurement portion of the receiver requires no special connection of the received data signal. Thus the measured signal is not influenced by the measurement circuitry at all. To verify the method we performed a measurement on a laboratory free-space optics link. Results of the measurement are satisfactory and can be used for on-line channel analysis. [ABSTRACT FROM AUTHOR]

The wireless channel of High-Speed Railway communication system is rapidly time-varying. The orthogonal frequency division multiplexing transmitting over this channel will be exposed to the intercarrier interference caused by large Doppler spread. The sectorised antenna can be employed for Doppler mitigation and obtaining Doppler diversity gain. In this paper the performance of this directional antenna is analyzed. The preferable partition scheme for the omnidirectional antenna and the optimal Doppler compensation frequency are addressed firstly. The uncorrelated property of the signal received from the different sectorised antennas is demonstrated originally which can be utilized for Doppler diversity gain. Finally, it is proved by the simulation results that this architecture will allows us to achieve remarkable performance under high-mobility conditions. [ABSTRACT FROM AUTHOR]

Video transmitted over unreliable environment, such as wireless channel or in generally any network with unreliable transport protocol, is facing the losses of video packets due to network congestion and different kind of noises. The problem is becoming more important using highly effective video codecs. Visual quality degradation could propagate into subsequent frames due to redundancy elimination in order to obtain high compression ratio. Since the video stream transmission in real time is limited by transmission channel delay, it is not possible to retransmit all faulty or lost packets. It is therefore inevitable to conceal these defects. To reduce the undesirable effects of information losses, the lost data is usually estimated from the received data, which is generally known as error concealment problem. This paper discusses packet loss modeling in order to simulate losses during video transmission, packet losses analysis and their impacts on the motion vectors losses. [ABSTRACT FROM AUTHOR]

Orthogonal frequency-division multiplexing (OFDM) is well-known as a high-bit-rate transmission technique, but the Doppler frequency offset due to the high speed movement destroys the orthogonality of the subcarriers resulting in the intercarrier interference (ICI), and degrades the performance of the system at the same time. In this paper a novel OFDM channel estimation algorithm with ICI mitigation based on the ICI self-cancellation scheme is proposed. With this method, a more accurate channel estimation is obtained by comb-type double pilots and then ICI coefficients can be obtained to mitigate the ICI on each subcarrier under the assumption that the channel impulse response (CIR) varies in a linear fashion. The theoretical analysis and simulation results show that the bit error rate (BER) and spectral efficiency performances are improved significantly under high-speed mobility conditions (350 km/h - 500 km/h) in comparison to ZHAO's ICI self-cancellation scheme. [ABSTRACT FROM AUTHOR]

This paper deals with Peak to Average Power Ratio (PA PR) characteristics and the theory of variable spreading factor orthogonal frequency and code division multiplexing (VSF-OFCDM) systems. Comparison and evaluation of PAPR of VSF-OFCDM systems with various 2D spreading factors (SF) are done in time and in frequency domain. The simple PAPR reduction approach based on random chip interleaving is also evaluated. [ABSTRACT FROM AUTHOR]

Many existing steganographic methods hide more secret data into edged areas than smooth areas in the host image, which does not differentiate textures from edges and causes serious degradation in actual edge areas. To avoid abrupt changes in image edge areas, as well as to achieve better quality of the stego-image, a novel image data hiding technique by adaptive Least Significant Bits (LSBs) substitution is proposed in this paper. The scheme exploits the brightness, edges, and texture masking of the host image to estimate the number k of LSBs for data hiding. Pixels in the noise non-sensitive regions are embedded by a k-bit LSB substitution with a lager value of k than that of the pixels in noise sensitive regions. Moreover, an optimal pixel adjustment process is used to enhance stego-image visual quality obtained by simple LSB substitution method. To ensure that the adaptive number k of LSBs remains unchanged after pixel modification, the LSBs number is computed by the high-order bits rather than all the hits of the image pixel value. The theoretical analyses and experiment results show that the proposed method achieves higher embedding capacity and better stegoimage quality compared with some existing LSB methods. [ABSTRACT FROM AUTHOR]

The presented paper deals with the link adaptation algorithms in mobile radio access networks based on Wideband Code Division Multiple Access (WCDMA). The mobile radio channel has a significant impact on the transmitted signal between User Equipment (UE) and Base Station (BS). The character of environment (e.g. number of received reflections) and increasing UE velocity cause unfavorable signal fadings, which have a major impact on the received signal. Due to this fact and the principle of WCDMA, fast power adaptation is essential for mobile radio access networks based on WCDMA. The prediction of mobile radio channel near-future state is one of the possible approaches how to span its unfavorable state. According to this assumption, we have improved the basic link adaptation algorithm (used to control properties of transmitter) to predictor based link adaptation algorithm. This contribution comprises the performance of basic link adaptation algorithm and predictor based algorithms, which support both variable (multi-bit) and fixed (singlebit) power steps to modify transmitter output power level. The link adaptation algorithms were simulated under various average UE velocities in urban environment. New algorithms were designed to increase the efficiency of data transmission in uplink direction.\\ [ABSTRACT FROM AUTHOR]

Due to implementation complexity the transform domain channel estimation based on training symbols or comb-type pilots has been paid more attention because of its efficient algorithm FFT/IFFT However in a comb-type OFDM system, the length of the channel impulse response is much smaller than the pilot number. In this case, the comb-pilot transform domain channel estimation only works as interpolation like the Least Squares (LS) algorithm, but loses the noise suppression function. In this paper we propose a novel frequency diversity channel estimation method via grouped pilots combining. With this estimator, not only the channel frequency response on non-pilot subcarriers can he interpolated, but also the noise can be better suppressed. Moreover, it does not need prior statistical characteristics of the wireless channel. [ABSTRACT FROM AUTHOR]

This paper deals with RC active biquad working in the so-called current mode (CM). The design approach uses only three transconductors (OTA) with the minimum necessary number of outputs and with only three passive grounded elements. The proposed filter has simple circuit configuration providing all standard transfer functions such as high-pass (HP), band-pass (BP), low-pass (LP), band-reject (BR) and all-pass (AP). Electronic tuning and independent adjusting of the quality factor and bandwidth of BP filter is possible. The presented circuits are verified by PSpice simulations utilizing OTAs on transistor level of abstraction. The linear parasitic effects of the real active elements in each suggested circuit are briefly discussed Experimental verification is also given. Designed networks can be used in many applications such as antialiasing filters, in high-speed data telecommunication systems, for signal processing in the cable modems, in regulation and measurement techniques etc. [ABSTRACT FROM AUTHOR]

In this paper we proposed a smart interference rejection filter in TH-PPM UWB system, which improves the system's error probability for an order of magnitude in case of high power OFDM interference. The smart filter is based on an adaptive transversal filter. Based on the fulfillment of certain conditions, the filter activates or deactivates some parts of it. [ABSTRACT FROM AUTHOR]

In the mobile radio environment, signals are usually impaired by fading and multipath delay phenomenon. In such channels, severe fading of the signal amplitude and inter-symbol-interference (ISI) due to the frequency selectivity of the channel cause an unacceptable degradation of error performance. Orthogonal frequency division multiplexing (OFDM) is an efficient scheme to mitigate the effect of multipath channel. Since it eliminates ISI by inserting guard interval (GI) longer than the delay spread of the channel. In general, the GI is usually designed to be longer than the delay spread of the channel, and is decided after channel measurements in the desired implementation scenario. However, the maximum delay spread is longer than GI, the system performance is significantly degraded. The conventional time-frequency interferometry (TFI) for OFDM does not consider time-variant channel with large delay spread. In this paper, we focus on the large delay spread channel and propose the ISI and inter-carrier-interference (ICI) compensation method for TFI-OFDM. [ABSTRACT FROM AUTHOR]

This paper presents an efficient tune-domain coarse frequency offset (FO) synchronizer (TCFS) for multi-band orthogonal frequency division multiplexing (MB-OFDM) systems effective for practical ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different carrier FOs and different channel responses in different bands to keep the analysis and simulation compatible for practical multi-band UWB scenario. Performance of the algorithm is studied by means of bit error rate (BER) analysis of MB-OFDM system. We derive the Cramer Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive white Gaussian noise and UWB channel model (CM) environments, CM1-CM4. Both analysis and simulation show that TCFS can estimate coarse carrier FO more efficiently in UWB fading channels for MB-OFDM applications compared to the other reported results in literature. Also, computational complexity of the proposed algorithm is analyzed for its usability evaluation. [ABSTRACT FROM AUTHOR]

In wideband wireless communication systems the RAKE receiver is commonly used to collect the resolvable multipath energy and counter the effects of fading through diversity. However, in channels with large delay and energy spread, its high complexity still remains a major issue. This motivates the study and application of computationally efficient finger placement algorithms that significantly reduce the receiver complexity with a reasonable performance loss. In this paper, a low-complexity maximum likelihood RAKE receiver, the Suboptimum - Maximum Power Minimum Correlation (S-MPMC) RAKE is proposed. The allocation of its first two fingers is based on the received signal correlation properties. Their positions determine also the placement of the rest of the fingers. Simulation results are provided to show the operation of the receiver and demonstrate its performance. Comparisons with relevant methods are performed to corroborate the merits of the proposal. The balance on the performance and the complexity of the technique makes it suitable for use in commercial wideband communication systems. [ABSTRACT FROM AUTHOR]