Variable Data Rates Research Articles

Modeling and performance analysis of optical WDM node architecture using SRR protocol

In order to enhance the data transport capability and overall throughput of an optical wavelength division multiplexing (WDM) system, a proper node architecture design is necessary. In the present paper a simple node architecture model based on media access control protocols for bursty data traffic of variable time slot duration and data rate has been proposed to decrease the packet loss probability and to increase the efficiency of an optical WDM system using synchronous round robin (SRR) protocol. An appropriate mathematical model has been derived to evaluate performance of the proposed node architecture. It has been observed that the network performance is well controlled through implemented model and the corresponding network design parameters.

Prototype of a secure wireless patient monitoring system for the medical community

Many medical applications set new demands on sensor network designs. They often involve highly variable data rates, multiple receivers and security. Most existing sensor network designs do not adequately support these requirements, focusing instead on aggregating small amounts of data from nodes without security. In this paper, we present a software design for medical sensor networks. This framework provides a set of protocols and services specifically tailored for this application domain. It includes a secure communications model, an interface for periodic collection of sensor data, a dynamic sensor discovery protocol and protocols that monitor and save up to 70% of the energy of a node. The framework is built in TinyOS and a JAVA based user interface is provided to debug the framework and display the measured data. An extensive evaluation of the framework of a 6-node sensor test-bed is presented, measuring scalability and robustness as the number of sensors and the per node data rate are varied. The results show that the proposed framework is a scalable, robust, reliable and secure solution for medical applications.

BER Analysis of Multi-Code Multi-Carrier CDMA Systems in Multipath Fading Channel

This paper proposes a Multi-Code Multi-Carrier Code Division Multiple Access (CDMA) scheme for next generation wireless communication systems. This system retains the advantages of Multi-Carrier CDMA in combating multipath and rejecting interference, and provides variable and adaptive data rates through the use of Multi-Code scheme. The rate adaptation algorithm proposed computes the user data rate as a function of the instantaneous channel condition and application dependent data rates. Exploiting the channel information improves the effective data rate and overall capacity of the system. The performance improvement of the proposed system to the Multi-Code CDMA system is shown through simulations. Walsh-Hadamard, Gold and Kasami codes are explored as possible choices for the multiple codes in the system.

Secure Variable Data Rate Transmission

A novel secure variable data rate (SVDR) transmission method is presented along with an architecture for implementing the SVDR transmission. This method reduces transmission overhead requirements by allowing both parties to maintain the initialization vector information locally rather than by obtaining it from the received packet. The only requirement this method places on the transmission is to maintain the sequence. This brief shows a 70% reduction in the overhead for transmitting this sequence information with a window size of 10 and seven priority levels.

A 67.5 dB SFDR Full-CMOS VDSL2 CPE Transmitter and Receiver with Multi-Band Low-Pass Filter

This paper presents a full-CMOS transmitter and receiver for VDSL2 systems. The transmitter part consists of the low-pass filter, programmable gain amplifier (PGA) and 14-bit DAC. The receiver part consists of the low-pass filter, variable gain amplifier (VGA), and 13-bit ADC. The low pass filter and PGA are designed to support the variable data rate. The RC bank sharing architecture for the low pass filter has reduced the chip size significantly. And, the 80 Msps, high resolution DAC and ADC are integrated to guarantee the SNR. Also, the transmitter and receiver are designed to have a wide dynamic range and gain control range because the signal from the VDSL2 line is variable depending on the distance. The chip is implemented in 0.25 ㎛ CMOS technology and the die area is 5 ㎜ × 5 ㎜. The spurious free dynamic range (SFDR) and SNR of the transmitter and receiver are 67.5 ㏈ and 41 ㏈, respectively. The power consumption of the transmitter and receiver are 160 ㎽ and 250 ㎽ from the supply voltage of 2.5 V, respectively.

An adaptive receiver of joint data and channel estimation for meteor burst communications

AbstractIn view of the characteristics of the meteor burst channel, the variable rate data transmission should be adopted to improve the system average throughput, which results in channel tracing and equalization problems at the receiver. Although the joint data and channel estimation of maximum likelihood sequence detection performing the principle of per‐survivor processing (PSP) is considered as an optimal detection scheme, its great computational complexity is a major problem and can hardly agree with the decreasing of the meteor channel. Based on the estimation of the system parameters, an adaptive state reduction of the PSP (ASRP) algorithm with only a few states in the trellis diagram is employed, while these states are chosen by the time‐varying threshold according to the exponential decay of meteor channels. It is shown that, ASRP can make a good tradeoff between the performance and the computational complexity, and provides reliable data transmission for adaptive modulation and coding of the meteor burst communication system. Computer simulation results and performance analysis are also included to support our developments. Copyright © 2010 John Wiley & Sons, Ltd.

A Time Slicing Adaptive OFDM System for Mobile Multimedia Communications

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Multi-Symbol Encapsulated-Orthogonal Frequency Division Multiplexing (MSE-OFDM) is an adaptive OFDM system which was proposed earlier to meet the overwhelming needs of spectrum-efficient wireless communication systems. In this technique, one cyclic prefix (CP) is used for multiple OFDM symbols. The motivation for MSE-OFDM is to mitigate two major inherited disadvantages of OFDM system at the same time i.e., the sensitivity to carrier frequency offset (CFO) and high peak to average power ratio (PAPR). In this paper, we propose a new time slicing technique where the cyclic prefix is replaced with the precoded pseudo-random sequence for MSE-OFDM system. Therefore it is possible to multiplex multiple data streams using this technique with dynamic data rates for mobile multimedia communications. It also overcomes disadvantages with other techniques such as high sensitivity to frequency offset inherited with Orthogonal Frequency Division Multiple Access (OFDMA) system and complex equalization problem with conventional Single Carrier-Frequency Division Multiple Access (SC-FDMA). Therefore this technique can be used for both uplink and downlink transmissions of mobile multimedia communications with variable data rates. With those inherent advantages of proposed time slicing technique which is compatible to DVB-H standard, power saving for mobile receivers is enabled and therefore extended battery life can be guaranteed which is very important for the mobile users. </para>

Passive-Set-Position-Modulation Framework for Interactive Robotic Systems

In this paper, we propose a novel framework, passive set-position modulation (PSPM), which enables us to connect a (continuous-time) robot's position to a sequence of slowly updating/sparse (discrete-time) set-position signal via the simple (yet frequently used in practice) spring coupling with damping injection, while enforcing passivity of the closed-loop robotic system. The PSPM modulates the original set-position signal in such a way that the modulated signal is as close to the original signal as possible (i.e., maximum information recovery for better performance), yet only to the extent permissible by the available energy in the system (i.e., passivity constraints). We present its algorithm and theoretically show its passivity and performance. We also show how this PSPM can be applied for two applications, with some experimental results: Internet teleoperation with varying delay and packet loss; and haptics with slow and variable-rate data update.

Performance analysis of SAC based non-coherent optical CDMA system for OOC with variable data rates under noisy environment

Performance analysis of SAC based non-coherent optical CDMA system for OOC with variable data rates under noisy environment

Quality-Based OVSF Code Assignment and Reassignment Strategies for WCDMA Systems

In third-generation code division multiple access (3G CDMA) mobile cellular systems, orthogonal variable spreading factor (OVSF) codes are applied in downlink to maintain the orthogonality between different channels. Since the number of available codes is limited, efficiently utilizing OVSF codes becomes an important issue. The code assignment and reassignment problem focuses on the subject of minimizing the number of code relocations. Previous works were based on some assumptions, including fixed service data rates and a code-limited system capacity. In this paper, we investigate this issue from a different perspective, by applying variable service data rates and an interference-limited system capacity. We have proposed three OVSF code assignment and reassignment strategies for this scenario, including sparse-first, sparse-first/rightmost, and modified sparse-first/rightmost, with a view to achieving the best service quality. The proposed strategies are well evaluated and compared with other strategies, based on the number of code reassignments, service quality, and throughput, via simulation. It is found that our proposed strategies outperform others under the scenario with variable service data rates and an interference-limited system capacity.

Flexible and reliable transmission techniques for scale-free UWB system

The speedy dissemination of digital consumer electronics devices within home and personal area causes increments of multimedia communication and advent of entertainment networking. This feature of communication requires variable data-rate and reliable transmission. In order to meet the various demands, in this paper, the multiband orthogonal frequency division multiplexing (MBOFDM) ultra-wideband (UWB) system by exploiting a time domain spreading factor and multiple-access scheme is proposed for variable data-rate transmission from 20kbps to 960Mbps in wireless communication. This article presents the basic structure and main functions of the variable data-rate (VR)-UWB system. With an emphasis on a proposed idea, we address the multiple-access in MB-OFDM system and apply adaptive bit allocation schemes to OFDMA system. It is shown in this article that scale-free UWB can accept multiple users and provide variable data-rate as well as support reliable transmission, while most conventional studies focus on the fixed rate transmission. The proposed system will be promising solution in ubiquitous environment to support multimedia traffic with various rates.

Novel Pilot-Free Adaptive Modulation for Wireless OFDM Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Orthogonal frequency-division multiplexing (OFDM) is the ubiquitous contemporary technology adopted for digital audio/video broadcasting, as well as wireless local and metropolitan area networks. Since the wireless multimedia services often have different quality-of-service requirements and their performance is sensitive to the channel conditions, the conventional fixed OFDM modulation scheme might not be a satisfactory solution nowadays. In this paper, we introduce a novel pilot-free adaptive modulation scheme, which is bandwidth efficient and allows variable data rates, for the future robust OFDM systems. We design a number of modulation modes in a combination of different constellation sizes and different polynomial cancellation coding (PCC) methods to combat the crucial intercarrier interference (ICI) problem. Instead of estimating the channel quality based on the overhead pilot symbols, we propose to directly estimate the signal-to-noise ratio (SNR) free of using any pilot. Moreover, our scheme offers more modulation modes than some other existing adaptive modulation methods, which are simply based on different constellation sizes. According to the Monte Carlo simulations, the empirical results show that our adaptive modulation scheme, in most channel conditions <formula formulatype="inline"><tex>$(\hbox{SNR} \geq 13\ \hbox{dB})$</tex></formula>, not only can satisfy the predetermined bit-error-rate (BER) requirement <formula formulatype="inline"><tex>$(\hbox{BER} \leq 10^{-4})$</tex></formula> but also can dynamically enhance the throughputs in the rather clean environments with high SNR values. </para>

Two-Layer Spreading CDMA: An Improved Method for Broadband Uplink Transmission

This paper proposes and investigates a novel code-division multiple-access (CDMA) system. This two-layer spreading CDMA (TLS-CDMA) system can combat multiple-access interference (MAI) and multipath interference (MPI) simultaneously and effectively in a multiuser scenario over frequency-selective fading channels. Moreover, a two-layer cell-specific scrambling code is proposed for the TLS-CDMA system in the uplink transmission to efficiently suppress other-cell interference (OCI) in a multicell environment. The proposed TLS-CDMA system allows the two-layer spreading factors to be adapted to the cell structure, the channel conditions, and the number of active users to support variable data rate transmission among multiple users. The superior performance of the TLS-CDMA system over other uplink transmission systems, such as cyclic prefix CDMA (CP-CDMA) and multicarrier CDMA (MC-CDMA), is also illustrated using performance analysis and simulation results.

Modeling and simulation of WDM optical networks under traffic control protocols

A proper node architecture design capable to support different network protocol enhances the data transport capability of a wavelength division multiplexed system. In the present paper a simple node architecture model has been developed to simulate the node throughput based on media access control protocols for bursty data traffic of variable time slot duration and data rate. An appropriate mathematical model has been derived to evaluate different types of traffic reservation protocols used in WDM networks. It has been observed that the network performance is well controlled through implemented protocols and network design parameters.

Impact of transmit power on throughput performance in wireless ad hoc networks with variable rate control

In this paper, the capacity of ad hoc networks employing pure aloha MAC protocol is studied under the effect of different transmission power levels and variable data rate control. The data rate of a certain link is related to SINR, and SINR is, in turn, related to transmitted power and link distance. The increasing of power conducts a high data rate, while results in a high interference of the network. Consequently, the optimum power that yields maximum network throughput is a tradeoff between transmission rate and network interference. Mathematical models for analysis of ad hoc networks capacity is presented, and a revised expression to approximate the capture probability of the network is also proposed. It is demonstrated that the optimal transmission power, thus the optimal range, which maximize the throughput of the network by theoretical and simulation results.

Joint coding and embedding techniques for multimedia images

Hiding data in digital images is a technique for secret data communication. It involves embedding important data into a cover image in digital form with minimal perceptible degradation. In this paper, we first propose an improved data hiding method for side-match vector quantization (SMVQ) compressed images, which utilizes the codeword-pairing procedure to modulate the index code of each image block. In order to take it a step further and obtain a larger embedding capacity, we remodel the first proposed method into a new one with the power of variable-rate data embedding through the use of a multiple-base notational system. According to the experimental results, the two proposed methods are indeed capable of providing a larger embedding capacity without causing noticeable distortions of stego-images in comparison with previous methods. Moreover, our methods also maintain a low compression bit-rate without auxiliary data.

Efficient integration OVSF code management strategies in UMTS

The key feature of the third-generation (3G) wireless communication networks is the ability to dynamically support a variety of multimedia service. In order to satisfy the requirements of multimedia services with variable data rates, the orthogonal variable spreading factor (OVSF) codes, adopted by the third-generation partnership project technical specifications, are used as channelization codes. This paper presents a fast and efficient code word generation method for multiple codes assignment system. Our code word generation method can find the optimal code word under the constraint of an assigned code amount, under the constraint of a maximal resource waste ratio, and under the constraint of realistic situation of the current residual codes. The computational complexity of the code word generation method is bounded by the amount of the assigned OVSF code, and by the layers of the OVSF code tree. From the simulation results, we show that using two or three codes or the resource waste ratio is ⩽40% is sufficient to achieve a high level of performance.

Genetic approach for dynamic OVSF code allocation in 3G wireless networks

Orthogonal variable spreading factor (OVSF) codes provide variable data rate transmissions for different bandwidth requirements in 3G WCDMA networks. In order to effectively utilize limited OVSF resources, many works in the literature have focused on dynamic code assignment (DCA) schemes. This paper investigates genetic algorithm (GA) based approach for dynamic OVSF code assignment in WCDMA networks. Different from existing conventional code assignment (CCA) and dynamic code assignment schemes, population is adaptively constructed according to existing traffic density in the OVSF code-tree. In order to improve the ability of the GA, we employ so-called “ dominance & diploidy” structure to adapt to changing traffic conditions. Performances of these two methods are evaluated in terms of blocking probability and spectral efficiency, and also compared with CCA and DCA. The simulation results show that the GA, especially with diploid structure, provides reduced code blocking probability and improved spectral efficiency in the system when compared to the CCA and DCA schemes. In addition to these, different GA operators are also tested under varying traffic loads to increase the overall system performance.

Walsh code assignment and data structure for variable data rate communications

In digital communication systems, variable-length Walsh codes, also called orthogonal variable spreading factor codes, are used to support simultaneous variable-rate data transmission. This paper describes algorithms for dynamic variable- length Walsh code assignment. Optimal assignment criterion is derived and an efficient data structure for maintaining variable- length Walsh codes is introduced. The benefits of code reallocation are also studied. Performance is evaluated via simulation.

Differential UWB Communications With Digital Multicarrier Modulation

As a high-rate alternative of impulse radio (IR) ultrawideband (UWB) communications, analog and digital multicarrier UWB radios with coherent detection have been introduced. In this paper, we investigate digital multicarrier differential (MCD) modulation and demodulation schemes for UWB communications. In our approach, the differential encoding and decoding are carried out across multiple digital carriers in the frequency domain. Hence, channel estimation is bypassed by using neighboring carriers as reference carriers. Compared with the transmitted reference TR-UWB which relies on delaying and correlating the received signal segments in time domain, our MCD-UWB avoids the need for analog delay elements. In addition, our digital-carrier based approach does not incur any spectrum expansion. We also show that our approach enables variable data rates, and remains operational even in the presence of severe interframe interference (IFI). In addition, the small spacing between differentially encoded carriers ensures that the data rate is not limited by the channel coherence bandwidth. Furthermore, our schemes are flexible in providing variable-rate transmissions. Simulations are also carried out to corroborate our theoretical analysis.