Digital Transmission Scheme Research Articles

Surface electrode switching of a 16-electrode wireless EIT system using RF-based digital data transmission scheme with 8 channel encoder/decoder ICs

A Radio Frequency (RF) based digital data transmission scheme with 8 channel encoder/decoder ICs is proposed for surface electrode switching of a 16-electrode wireless Electrical Impedance Tomography (EIT) system. A RF based wireless digital data transmission module (WDDTM) is developed and the electrode switching of a EIT system is studied by analyzing the boundary data collected and the resistivity images of practical phantoms. An analog multiplexers based electrode switching module (ESM) is developed with analog multiplexers and switched with parallel digital data transmitted by a wireless transmitter/receiver (Tx/Rx) module working with radio frequency technology. Parallel digital bits are generated using NI USB 6251 card working in LabVIEW platform and sent to transmission module to transmit the digital data to the receiver end. The transmitter/receiver module developed is properly interfaced with the personal computer (PC) and practical phantoms through the ESM and USB based DAQ system respectively. It is observed that the digital bits required for multiplexer operation are sequentially generated by the digital output (D/O) ports of the DAQ card. Parallel to serial and serial to parallel conversion of digital data are suitably done by encoder and decoder ICs. Wireless digital data transmission module successfully transmitted and received the parallel data required for switching the current and voltage electrodes wirelessly. 1mA, 50kHz sinusoidal constant current is injected at the phantom boundary using common ground current injection protocol and the boundary potentials developed at the voltage electrodes are measured. Resistivity images of the practical phantoms are reconstructed from boundary data using EIDORS. Boundary data and the resistivity images reconstructed from the surface potentials are studied to assess the wireless digital data transmission system. Boundary data profiles of the practical phantom with different configurations show that the multiplexers are operating in the required sequence for common ground current injection protocol. The voltage peaks obtained at the proper positions in the boundary data profiles proved the sequential operation of multiplexers and successful wireless transmission of digital bits. Reconstructed images and their image parameters proved that the boundary data are successfully acquired by the DAQ system which in turn again indicates a sequential and proper operation of multiplexers as well as the successful wireless transmission of digital bits. Hence the developed RF based wireless digital data transmission module (WDDTM) is found suitable for transmitting digital bits required for electrode switching in wireless EIT data acquisition system.

Binary tree approach for data hiding based on histogram modification

This paper presents a new approach for data hiding scheme for the secure digital data transmission. Here we present the modification to histogram by considering the differences of the pixels which can be used for increasing data hiding capacity. We also show-off how different images affect the performance of this proposed method.

Wireless multicarrier digital transmission via weyl-heisenberg frames over time-frequency dispersive channels

The issue of multicarrier transmission with high spectral efficiency and low interference over time-frequency (TF) dispersive channels is addressed in this paper. Specifically, we propose a digital signal transmission scheme employing overcomplete Weyl-Heisenberg (W-H) frames as modulation pulses. The proposed W-H frame transmission scheme, which relaxes the conventional orthogonality/biorthogonality constraints for perfect transmultiplexing, can be viewed as a generalization of the orthogonal frequency division multiplexing (OFDM) and nonorthogonal (biorthogonal) frequency division multiplexing (NOFDM). With this new transmission scheme, one can not only achieve higher spectral efficiency effectively but also design the pulse shape more flexibly to combat the impact of the propagation channel. In order to optimally mitigate the intersymbol interference (ISI) and interchannel interference (ICI) caused by the wireless channel, the selections of the Gaussian pulse shape and T-F grid parameters are addressed jointly from the viewpoint of minimum energy perturbation for several typical channel scattering functions. Simulation results are presented to study the performance of the proposed system. It is shown that the proposed overcomplete W-H frame transmission system with a lower-order constellation is more robust against the TF dispersive channels than the incomplete Riesz basis system employing a higher-order constellation with the same spectral efficiency.

On the Distortion SNR Exponent of Some Layered Transmission Schemes

We consider the problem of joint source-channel coding for transmitting K samples of a complex Gaussian source overT bK uses of a block-fading multiple-input multiple-output (MIMO) channel with M transmit and N receive antennas. We consider the case when we are allowed to code over L blocks. The channel gain is assumed to be constant over a block and channel gains for different blocks are assumed to be independent. The performance measure of interest is the rate of decay of the expected mean-squared error with the signal-to-noise ratio (SNR), called the distortion SNR exponent. We first show that using a broadcast strategy similar to that of Gunduz and Erkip, but with a different power and rate allocation policy, the optimal distortion SNR exponent can be achieved for 0 les b les (|N - M| + 1)/ min(M,N) and for b > MNL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . This is the first time the optimal exponent is characterized for 1/min(M, N) < b < (|N - M| + 1)/min(M, N). Then, we propose a digital layered transmission scheme that uses both time layering and superposition. The new scheme is at least as good as currently known schemes for the entire range of bandwidth expansion factors b, whereas at least for some M, N, and b, it is strictly better than the currently known schemes.

Simplified receiver design for STBC binary continuous phase modulation

Existing space-time codes have focused on multiple- antenna systems with linear modulation schemes such as phase- shift keying and quadrature amplitude modulation. Continuous phase modulation (CPM) is an attractive scheme for digital transmission because of its constant envelope which is needed for power efficient transmitters. Recent research has shown that space-time coded CPM can achieve transmit diversity to improve performance while maintaining the compact spectrum of CPM signals. However, these efforts mainly combine space- time coding (STC) with CPM to achieve spatial diversity at the cost of a high decoding complexity. In this paper, we design space-time block codes (STBC) for binary CPM with modulation index h = 1/2 and derive low-complexity receivers for these systems. The proposed scheme has a much lower decoding complexity than STC CPM with the Viterbi decoder and still achieves near-optimum error performances.

Evaluation of coverage area for a wide line-of-sight indoor optical free-space communication system employing coherent detection

The application of coherent detection to indoor optical free-space communications is considered here. Analytical expressions are derived for a wide line-of-sight (W-LOS) optical link which determine the coverage area and the required photo-detection area given different binary digital transmission schemes and a given bit rate. The coverage area is maximised for systems using both metal–semiconductor–metal (MSM) and PIN photo-detectors. Results show that MSM photo-detectors, due to their inherently lower capacitance per unit photo-detection area, result in a greater coverage area than their PIN counterparts. To demonstrate the viability of implementing coherent detection indoors, a 200 Mb/s LOS optical link which uses coherent detection is also reported.

Signal shaping for peak-power and dynamics reduction in transmission schemes employing precoding

Precoding, i.e., nonlinear pre-equalization, at the transmitter side has been proved to be a very efficient strategy for channel equalization in single-carrier digital transmission schemes. It enables the application of coded modulation in a seamless fashion. A drawback of precoding is that the signal at the input of the decision device exhibits a huge dynamic range. Based on dynamics shaping, a combined precoding/shaping technique introduced in the paper by Fischer et al. (1995), a new shaping strategy is developed in this paper. This technique enables a flexible tradeoff among: (1) reduction of the average transmit power; (2) avoidance of peaks in the transmit signal in order to facilitate line driver implementation; and (3) restriction of the maximum amplitude at the receiver side to a prescribed value. Over a wide range, all three demands can be met simultaneously. As the scheme is fully compatible with Tomlinson-Harashima (1971, 1972) precoding, it can replace the precoder even in existing and standardized schemes. Simulation results for a typical digital subscriber line scenario show the achievable gains.

Vorhersage und Messung der Bitfehlerrate in COFDM-Gleichwellennetzen

For the digital terrestrial transmission scheme Digital Audio Broadcasting (DAB) and Digital Video Broadcasting (DVB-T), the prediction of the Bit Error Rate (BER) for a specific reception area is a characteristic variable. State-of-the-art methods to determine the BER for Coded Orthogonal Frequency Division Multiplex (COFDM) are either restricted to some typical propagation scenarios with simple echo profiles or they use general statistic channel models, which allow an analytical derivation of the BER. These methods and scenarios are suitable to investigate the general system behavior or to simulate different competing transmission schemes. For radio network planning they are not appropriate. This is mainly due to the very general results, which have no direct link to the actual propagation situation. Based on detailed qualitative and quantitative investigations of all relevant disturbance factors for DAB and DVB-T, this paper presents a new and very fast BER calculation method, which uses the results of wave propagation prediction models. The approach is verified by measurements in the L-band in an operational DAB network.

Digital transmission scheme for ISDB-T and reception characteristics of digital terrestrial television broadcasting system in Japan

We introduce a transmission scheme for ISDB-T, and proposes a soft-decision decoding technique for ISDB-T receivers to improve the reception performance under multipath distortion and interference from analog television signals. We propose two techniques that apply estimated the channel frequency response for each carrier to the derivation of soft-decision metrics in 64QAM-OFDM. We present Viterbi soft-decision decoding characteristics by these proposed techniques for AWGN transmission paths, multipath conditions. We also propose a soft-decision technique that erases the data of carriers exhibiting large disturbance.

High performance satellite networks

The high performance satellite communications networks of the future will have to be interoperable with terrestrial fiber cables. These satellite networks will evolve from narrowband analogue formats to broadband digital transmission schemes, with protocols, algorithms and transmission architectures that will segment the data into uniform cells and frames, and then transmit these data via larger and more efficient synchronous optional (SONET) and asynchronous transfer mode (ATM) networks that are being developed for the information “superhighway”. These high performance satellite communications and information networks are required for modern applications, such as electronic commerce, digital libraries, medical imaging, distance learning, and the distribution of science data. In order for satellites to participate in these information superhighway networks, it is essential that they demonstrate their ability to: (1) operate seamlessly with heterogeneous architectures and applications, (2) carry data at SONET rates with the same quality of service as optical fibers, (3) qualify transmission delay as a parameter not a problem, and (4) show that satellites have several performance and economic advantages over fiber cable networks.

Power and bandwidth efficient digital communication using turbo codes in multilevel codes

AbstractThe recently proposed Turbo codes are applied to bandwidth efficient modulation schemes via multilevel coding. For this purpose, Turbo codes are extended for a wide range of fine tunable rates by puncturing. A straightforward derivation of iterative Turbo decoding and the concept of extrinsic information is presented. New design rules for multilevel codes with arbitrary component codes and codeword lengths are derived from information theory. Simulation results show that application of Turbo codes to properly designed multilevel coding schemes leads to digital transmission schemes with high power and bandwidth efficiency.

Coded Modulations for Fading Channels: An Overview

AbstractIt is by now well known that combined channel coding and digital modulation (in short coded modulation) yield power and bandwidth efficient digital transmission schemes for the Gaussian channel. These schemes perform closer to channel capacity than those where coding and modulation are treated separately. More recently, coded modulation methods have been investigated for transmission over Rayleigh fading channels. It has been discovered that systems optimized for the Gaussian channel are not optimum for fading channels. This is primarily due to the importance of built‐in time diversity of the coded modulation scheme for fading channels.In this paper we give a brief overview of recent developments in signal design for Rayleigh fading channels. Mainly schemes based on phase shift keying are presented. Theoretical guidance for design and identification of the most important system parameters are given. A couple of detailed examples of code designs and their error probability performance are also given. Optimum and suboptimum receivers are discussed. An overview of analytical performance analysis tools, as well as code designs for both trellis coded modulation and block coded modulation is included in the paper. Methods for unequal error protection are given. Potential application areas are identified. An extensive reference list is supplied.

Pseudo-analog speech transmission in mobile radio communication systems

A low-complexity pseudo-analog speech transmission scheme is proposed for portable communications. It uses a speech coder based on adaptive differential pulse code modulation (ADPCM) in combination with a multilevel digital modulation technique such as M-ary DPSK or M-ary FSK and features low quantization noise, bandwidth efficiency, and robustness to transmission errors. A nonsymmetric M-ary DPSK scheme called skewed M-ary DPSK is proposed to enhance the noisy channel performance. Comparison to conventional analog FM and a digital speech transmission scheme using adaptive predictive coding and forward error correction (FEC) based on convolutional coding shows that the pseudo-analog system has the best objective signal-to-noise ratio performance under most channel conditions. Informal subjective evaluations rate the digital system superior to the pseudo-analog scheme for bad channels and conversely for good channels. It is concluded that the pseudo-analog system can be designed with low delay and high speech quality for good channels with high spectral efficiency. >

Novel satellite digital video TDMA system for business video communications

The authors propose a satellite video signal transmission system that uses a time division multiple access (TDMA) scheme for digital video signal transmission and a code division multiple access (CDMA) scheme for voice signal transmission from a video signal reception-only earth station (backward voice signal transmission). The adoption of a TDMA scheme makes it possible to transmit video signals from various places and to communicate in multipoint-to-(multi)point mode. For backward voice channel transmission from video signal reception-only earth stations, a superposed CDMA voice signal transmission over TDMA video signals by using the same transponder is proposed. The employment of high coding gain forward error correction and development of a cochannel interference cancellation technique have made it possible for the proposed system to transmit a practical number of voice channels. The performance of the proposed system has been experimentally evaluated and the results show the proposed scheme can transmit about 20 CDMA voice channels simultaneously. >

A Compatible Multiplexing Technique for Anisochronous and Isochronous Digital Data Traffic

This concise paper reports the result of a study on a multiplexing scheme for digital data transmission and switching which can handle both anisochronous and isochronous data traffic of various mix, mainly in one digital channel of PCM primary multiplex level (e.g., 1544 kbits/s) and corresponding time-division switch (TDSW) of data-switching equipment. The study aims to determine a unified scheme which is economical and flexible for intercity heavy-traffic data links, to accommodate a wide range of data speeds. The paper describes various multiplexing schemes and analyzes their features in terms of frame structure, synchronization time, error-correction capability, compatibility with signaling, hardware complexity, etc. A bit-interleaved multiplexing scheme is chosen as suitable and is applied in a laboratory model of a digital data switching system, the DDX-1 System.

A Baseband Hybrid Digital Transmission Scheme

A baseband hybrid digital transmission scheme is studied, and it is shown that the low- and high-frequency cutoffs in analog repeaters extremely degrade signal waveforms. Solutions studied are a combination of dc-constrained coding and modification of amplitude-frequency characteristics for low-frequency distortion, and a combination of flat amplitude equalization and simple phase equalization for high-frequency distortion. It is shown that these solutions reduce waveform distortions by a factor of ten. A solution of the control problem for automatic gain control (AGC) is also presented.

Queuing Analysis of Satellite Networks

This paper models satellite communications systems by means of bipartite graphs. It assumes stochastic inputs and time delay is the factor of interest. The paper formulates the model and describes the routing and digital transmission schemes, assuming the network links to be synchronized. Messages may be transmitted only in the synchronized time slots, on a first-come first-served basis. The queuing problem is discussed for the single branch and for the satellite network cases, and approximate solutions are obtained for the case of satellites with finite memories.

Precoding for Multiple-Speed Data Transmission

In certain applications, because of noise, compatibility, or other considerations, it is desirable that a data transmission system have the flexibility to operate at multiple speeds. In this paper, a precoding scheme for multiple-speed digital or analog data transmission is presented. The scheme has a flexibility which allows the data rate and overall channel characteristics to be changed simultaneously by simply changing the data format and some resistive elements. There is no change in the filters, the equalization, the transmitter signaling interval, or the receiver sampling time. By using partial response channels, a number of commonly used data rates are easily obtained, using a physically realizable precoder and correlator. With correct timing and the use of orthonormal siginals, the signal-to-noise ratio is maximized at each data rate for bandlimited white noise under the constraints of fixed line signal power and no intersymbol interference. Timing error is considered in a two-speed transmission scheme, and the selection of a precoding matrix using eye opening as the criterion is studied. This study clearly demonstrates the advantage of changing the overall channel characteristics when changing the data rate. Eye openings obtained are equal to or larger than those of two conventional schemes transmitting at the same data rates.