Variable Data Rate Transmission Research Articles

Dynamically tuneable pre‐modulation filter for an airborne PCM/FM telemetry system

In the conventional airborne telemetry system, the pre-modulation filter with a multi-pole active Bessel filter is preferred to use in Pulse Code Modulator (PCM)/FM transmission. In the existing system, it is not possible to change the cut-off frequency for different data rates dynamically as required in the launch scenario of a long-range aerospace vehicle. In general, aerospace vehicle has multiple propellant stages to travel a desired trajectory path. Each stage gets separated from the vehicle at different instances. Each stage measurement plan is defined and correspondingly the PCM format is generated with an optimum data rate. Hence, the telemetry system is required to transmit variable data rates at various instances of a long-range aerospace vehicle from launch point to end point of a vehicle. This can be addressed by designing a dynamically tuneable pre-modulation (DTPM) filter. Here, a suitable DTPM filter scheme is proposed to mitigate variable data rate transmission in the telemetry system. The scheme is analysed as per IRIG-106 standard and simulated using MATLAB. The same has been modelled using VHDL and implemented targeting 28 nm technology Xilinx Zynq FPGA device.

An Efficient Model of DSSS System Using Multirate and Data Rate Transition Techniques

In this paper, an analytical and simulated approach has been developed for evaluating the performance of Bit Error Rate (BER) of Direct Sequence Spread Spectrum (DSSS). It is also demonstrated in this paper that how BER can be minimised using Rate Transition techniques. The work uses effective spreading sequence to achieve variable data rate transmission. In this research work, blind detection of the user signal has been considered assuming the receiver has prior knowledge of the user’s spreading code and is synchronised by using increased matched filter gain. Thus, it is not required to control the information to be transmitted along with the user signal. An attempt has also been made to show that how bandwidth utilisation has been halved using multirate techniques. This innovative research findings make use of implementing an efficient DSSS with reduced BER.

An Efficient Dynamic Orthogonal Variable Spreading Factor Code Allocation Approach in WCDMA through Modified Adaptive Genetic Algorithm

Orthogonal Variable Spreading Factor (OVSF) codes would give variable data rate transmissions for different bandwidth supplies in Wideband CDMA (WCDMA) networks. These OVSF codes are used for the channelization of codes in WCDMA. In WCDMA, effective utilization of OVSF codes has become an active area of research as the number of codes is very limited. It is a fact that the successor and predecessor codes of OVSF cannot be used simultaneously when a specific code is used in OVSF as their encoded sequences become indistinguishable. Consequently, OVSF code tree has inadequate number of available codes. Thus, this research study uses Adaptive Genetic Algorithm (AGA) 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 existing technique in order to improve the ability of the GA, ＂dominance and diploidy＂ structure is employed to adapt to changing traffic conditions. Because in SGA algorithm cannot convergence if the new user is included into the existing OVSF code tree while SGA is running to find optimum OVSF code tree, SGA cannot adapt its structure to this unexpected variation. This problem can be overcome by the Modified Adaptive Genetic Algorithm (MAGA). Performance of the proposed MAGA approach is evaluated in terms of blocking probability and spectral efficiency and is compared with SGA, D&D GA.

Variable rate data transmission by size of constellation and symbol duration adaptation

In variable rate modulation, maximisation of data rate can be achieved either by fixing the symbol rate with an adaptive control of the constellation size, or by fixing the constellation size and changing the symbol duration. It is proved that for joint optimal control of both types, they should be used separately: the constellation size changes under a constant maximal symbol rate, and when these opportunities have been exhausted the symbol rate adaptation should be used.

Multiple access interference and multipath interference analysis of orthogonal complementary code‐based ultra‐wideband systems over multipath channels

SUMMARYIn order to alleviate multiple access interference and multipath interference of ultra‐wideband (UWB) system, we propose the orthogonal complementary code (OCC)‐based direct‐sequence UWB system and offset‐stacking (OS)‐UWB system. OCC has perfect partial autocorrelation and cross‐correlation characteristics. With the application of OCC in UWB system, we can obtain better performance in multiple access interference and multipath interference. The proposed OS‐UWB structure can also achieve variable data rate transmission because of its innovative OS spreading technique. Theoretical analysis and simulation results show that the proposed UWB system can achieve excellent performance and outperform the unitary code‐based direct‐sequence UWB system. Copyright © 2013 John Wiley & Sons, Ltd.

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.

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.

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.

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.

Effective Admission Policy for Multimedia Traffic Connections over Satellite DVB-RCS Network

Thanks to the great possibilities of providing different types of telecommunication traffic to a large geographical area, satellite networks are expected to be an essential component of the next-generation internet. As a result, issues concerning the designing and testing of efficient connection-admission-control (CAC) strategies in order to increase the quality of service (QoS) for multimedia traffic sources, are attractive and at the cutting edge of research. This paper investigates the potential strengths of a generic digital-video-broadcasting return-channel-via-satellite (DVB-RCS) system architecture, proposing a new CAC algorithm with the aim of efficiently managing real-time multimedia video sources, both with constant and high variable data rate transmission; moreover, the proposed admission strategy is compared with a well-known iterative CAC mainly designed for the managing of real-time bursty traffic sources in order to demonstrate that the new algorithm is also well suited for those traffic sources. Performance analysis shows that, both algorithms guarantee the agreed QoS to real-time bursty connections that are more sensitive to delay jitter; however, our proposed algorithm can also manage interactive real-time multimedia traffic sources in high load and mixed traffic conditions.

An optimum combining and concatenated-RAKE for dual-antenna mobile terminals in UMTS

The downlink of UMTS employs variable spreading factor and multicode to support variable data rate transmissions. In multicode and low spreading factor scenarios, interpath interference (IPI) among code channels is a principle factor that needs to be taken into consideration in system design. For example, the RAKE receiver with conventional maximum-ratio-combining suffers greatly from the presence of IPI. We present a new receiver structure that effectively incorporates an optimum combining scheme and dual-antenna diversity to enhance system performance.

Variable rate transmission and blind rate detection for coherent DS-CDMA mobile radio

A variable rate data transmission and blind rate detection scheme is proposed for coherent DS-CDMA mobile radio. The data to be transmitted is first transformed into a QPSK symbol sequence, then multiplied by the rate-matched repetition code of ‘1, –1’, and finally spread over a wide bandwidth. At the receiver, the received signal is despread by a matched filter and non-coherent rate detection is applied. The despread signal sample sequence is then multiplied by a repetition code of detected rate to recover the original transmitted QPSK symbol sequence. The probability of rate detection error for a three-rate case is evaluated by computer simulations in a two-path Rayleigh fading channel.

Variable rate data transmission with blind rate detection for coherent DS-CDMA mobile radio

A variable rate data transmission and blind rate detection scheme is proposed for coherent DS-CDMA mobile radio. The data to be transmitted is first transformed into a QPSK symbol sequence, then multiplied by the rate-matched repetition code of '1, -1'. And finally spread over a wide bandwidth. At the receiver, the received signal is despread by a matched filter and non-coherent rate detection is applied. The despread signal sample sequence is then multiplied by a repetition code of detected rate to recover the original transmitted QPSK symbol sequence. The probability of rate detection error for a three-rate case is evaluated by computer simulations in a two-path Rayleigh fading channel.

Optimal nonuniform signaling for Gaussian channels

Variable-rate data transmission schemes in which constellation points are selected according to a nonuniform probability distribution are studied. When the criterion is one of minimizing the average transmitted energy for a given average bit rate, the best possible distribution with which to select constellations points is a Maxwell-Boltzmann distribution. In principle, when constellation points are selected according to a Maxwell-Boltzmann distribution, the ultimate shaping gain ( pi e/6 or 1.53 dB) can be achieved in any dimension. Nonuniform signaling schemes can be designed by mapping simple variable-length prefix codes onto the constellation. Using the Huffman procedure, prefix codes can be designed that approach the optimal performance. These schemes provide a fixed-rate primary channel and a variable-rate secondary channel, and are easily incorporated into standard lattice-type coded modulation schemes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>