Variable-rate System Research Articles

A 2.4-kbps variable-bit-rate ADP-CELP speech coder

Based on ADP-CELP (Adaptive Density Pulse Code Excited Linear Prediction), in which the sound source is expressed in terms of an adaptive density pulse train model, a variable-rate ADP-CELP system is proposed in which one mode out of four, with different bit rate depending on the nature of the short section speech signal, is selected for each frame. The coding method in each mode is designed to be adapted to the nonspeech section, nonsound section, steady speech section, and nonsteady speech section. The bit rates are 0.53, 2.67, 3.17, and 4.1 kbps. In the variable-rate ADP-CELP system, the variation of the spectral envelope is used as a guideline so that a high sound quality and low bit rate are attempted by means of the speech/nonspeech classification method to accurately distinguish the speech section and nonspeech section even under a background noise environment and of the interpolation vector quantization method that can reduce the coding volume for the pitch period to one-half without degrading the quality. In the variable-rate ADP-CELP system, the average rate is less than 2.4 kbps in the case of sound rate of 60% and the corresponding quality is more than the half-rate standard system (3.45 kbps) of domestic digital cellular telephones. © 2000 Scripta Technica, Electron Comm Jpn Pt 3, 83(7): 32–41, 2000

A multicarrier allocation (MCA) scheme for variable-rate 3Gwireless systems

High spectral efficiency and flexible data rate access are the main focus of future wireless networks. Multiple channel allocation schemes have the potential of achieving this goal. By assigning multiple slots and/or multiple carriers to one user, it is possible to provide a flexible data rate with quite low complexity. In this article we propose a simple allocation scheme where each user is assigned a fixed group of carriers. These carriers are adaptively used depending on the interference situation within the system. The system performance in terms of average throughput is investigated for two different types of allocation schemes: a fully centralized scheme and a distributed one that uses frequency diversity as a mean of improving the user link quality. The obtained results show that both schemes improve the system throughput over single carrier allocation without affecting the capacity of the system in terms of number of users per cell.

EVALUATION OF A FLOW CONTROL SYSTEM FOR SITE-SPECIFIC HERBICIDE APPLICATIONS

An electronic flow control system for site-specific herbicide applications was tested for steady stateperformance. The control system used spray nozzles coupled with solenoid valves, regulated using pulse-widthmodulation at 10 Hz and duty cycles of 10 to 100% to control the flow rate. The controller could vary the nozzle flow ratein the ratio of up to 9.5 to 1 without a significant change in the spray pattern. Droplet size distribution of the variable ratesystem was fairly constant at duty cycles of 25 to 100%. The Volume Median Diameter (VMD) at a duty cycle of 10% wassignificantly different from the rest. Response delay was small and suitable for high-speed herbicide applications. Theuniformity of spray deposition along the orthogonal direction (along travel direction) decreased dramatically as the dutycycle decreased and travel speed increased. The variable flow nozzle could be used on existing sprayers for maintainingthe application rate as the speed changes by controlling the flow rate. For local sensor based site-specific herbicideapplication, the controller has to be modified to overcome banded spray deposition at high travel speed and low dutycycle combinations.

Variable rate QAM for mobile radio

Quadrature amplitude modulation (QAM) schemes which vary the number of modulation levels in accordance with the mobile radio fading channel variations are investigated. Important parameters considered are the fading rate and the block size used. We describe how the adaptive QAM modems can be employed and consider their use in a DECT-like TDD packet structure. System performance in the presence of cochannel interference is also considered. Simulations show that the variable rate system has about 5 dB improvement in channel SNR over a fixed 16-level QAM system for BER's between 10/sup -2/ and 10/sup -5/ and channel SNR's between 25 and 40 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A study on a high density digital video disc player

A prototype of a high density digital video disc player which employs a variable bit rate system has been developed. It can reproduce high quality video signal with a maximum data rate of 7.5 Mbps for 2 hours.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance analysis of trellis coded biorthogonal sequences in a variable rate system

AbstractFor digital communication systems with a given binary modulation scheme and variable information rate, a coding technique is described which employs a particular structure of trellis code. It consists of a convolutional encoder followed by a mapper which selects biorthogonal codewords. Based upon the state diagram of the system, performance is evaluated and then compared to that of more conventional solutions. Beside having good performance, this approach is very modular, i.e. its structure easily adapts to different information rates. Furthermore, it allows the time synchronization system to work at lower signal‐to‐noise ratios.

Efficient communications using the meteor-burst channel

This work presents the results of a theoretical study of the meteor-burst channel which illustrates its time-varying bursty nature. In addition, the authors describe an innovative approach to data transmission over meteor-burst systems, i.e. the use of the feedback adaptive variable rate (FAVR) system which allows the maximum amount of information to be transmitted over each meteor-burst channel. For underdense meteor channels the FAVR performance is compared to an optimum system, i.e. a system capable of changing its bit rate instantaneously to channel conditions so as to maintain a constant SNR in each bit, and to a constant optimum rate/burst system. It is shown that when compared to an optimum rate per burst system, FAVR can result in a throughput increase exceeding a factor of 10. It is also shown that FAVR can approach the optimum system performance, although for practical purposes, it appears that 83-88% of optimum is attainable.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

QAM: the modulation scheme for future mobile radio communications?

With spectral congestion increasing, and plans announced to dramatically increase the number of mobile telephone users over the coming decade, many approaches are being considered to reduce the bandwidth requirements of each user. One approach is the use of quadrature amplitude modulation (QAM), a particular form of multilevel modulation where each symbol contains several bits of information. The use of QAM for mobile radio applications is considered and it is shown that this form of multilevel modulation can offer an attractive solution to current bandwidth restrictions in microcellular networks. An advanced variable-rate system is also considered and hardware development of a QAM modem discussed.

High Data Rate Meteor-Burst Communications

The meteor burst communications channel offers a largely untapped means of communications that can alleviate congestion in many existing communications systems. It also provides some interesting advantages over other beyond-line-of-sight systems, including lower susceptibility to atmospheric perturbations, a limited footprint, and relatively low cost. Past system applications have been quite limited, however, due to the random nature of the meteor burst phenomenon which has resulted in relatively low throughput and lengthy wait-times.This paper presents the results of an experimental study of the meteor burst channel which illustrates its time-varying bursty nature. In addition, the authors describe an innovative approach to data transmission over meteor burst systems, ie, the use of the Feedback Adaptive Variable Rate (FAVR) system which allows the maximum amount of information to be transmitted over each meteor burst channel.For underdense meteor channels the FAVR performance is compared to an optimum system, ie, a system capable of changing its bit rate instantaneously to channel conditions so as to maintain a constant SNR in each bit, and to a constant optimum rate/burst system. It is shown that for such a system FAVR can result in a throughput increase exceeding a factor of 10.

Performance of Modified-Fano Algorithm in Adaptive-Variable-Rate Transmission System over Fading Channels

Ideas of feedback, adaptive transmission and coding have been combined to improve the performance of communication systems over the Rayleigh fading channel with slow and flat fading assumption. The coded variable-rate transmission systems employ the Fano and the modified Fano algorithms for decoding [1]. The simulation study of the uncoded variable-rate bipolar signalling with continuous rate adaptation over an infinite range shows that such a system can completely nullify the effect of fading. A four-rate uncoded systems is only 0.5 dB inferior and the two-rate coded system with either Modified-Fano or Fano decoding is only 0.4 dB inferior to the ideal infinite rate systems at a BER of 10-5. The increase in the average rate of transmission of both coded and uncoded variable rate systems is found to degrade the error performance. For the coded systems both the Fano and Modified-Fano algorithms provide the similar error performance but the Modified-Fano decoder provides the throughput advantage over the Fa...

Variable-rate deposit insurance: A re-examination

This paper investigates the impact of variable-rate deposit insurance on the financial and real sectors of the economy and its role as an absorber of bankruptcy risk within these sectors. A variable-rate system raises the cost of funds to the real sector and increases probability of bankruptcy of the borrowing firms. When such bankruptcies occur, society experiences a dead weight loss. We argue that appropriate deposit insurance pricing must weigh the social costs connected with both financial firm failure and real-sector bankruptcy.

Adaptive Variable-Rate Communication System for Fading Channels

Diversity techniques have been in use since long for communication over fading channels. Alternatively, adaptive feedback techniques have been suggested to improve the performance of communication ...

Quality of service and bandwidth efficiency of cellular mobile radio with variable bit-rate speech transmission

The performance of an adjustable source/channel codec in a cellular mobile-radio environment is investigated. The speech transmission rate and the amount of forward error correction change in response to changing channel conditions. The channel rate is constant at 32 kb/s, and when the channel is good all of these bits are used for speech transmission. In intermediate and poor channels the speech rate is 24 or 16 kb/s, and the remaining channel symbols are used for forward error correction. Relative to conventional transmission this approach offers an improved grade of service. For example, the outage rate (the proportion of "poor or worse" communications) goes from nine percent with fixed-rate to three percent with variable-rate transmission. Alternatively, this improved grade of service can be exchanged for higher bandwidth efficiency. The fixed-rate system (with nine percent outage) has 23 users per cell. With 52 users per cell the outage of the variable-rate system is only six percent.

A Simple Buffer Control for Variable-Rate Communication Systems

Transmission of data with receiver-controlled bit rate is an effective way to reduce the effect of signal-to-noise ratio (SNR) fluctuations, as in a fading channel. All previous publications on this subject ignore the critical topic of buffer size. This concise paper summarizes the results of the first study of the effect of finite buffers on a variable-rate system for fading channels.

Should Variable Policy Loan Interest Rates Be Adopted?

The final report of the Presidents' Committee on Financial Structure and Regulation has recommended that serious consideration be given by the life insurance industry to changing a long standing practice of making loans available to policyholders at fixed interest rates, usually 5 or 6 percent. The proposal is to switch to a variable interest rate system under which borrowing rates in life insurance would change with market interest rates. This system has been widely adopted abroad. A major advantage claimed for the proposed system would be to slow down the disintermediation process which has caused some life insurers to lose substantial amounts of investible funds when market rates of interest exceed the fixed rates. It is argued in this paper that the variable interest system might have more disadvantages than advantages for the life insurance industry and for policyowners; it would be no panacea for many of the ills about which certain members of the industry are complaining. For a variety of reasons, discussed below, life insurance companies in the United States have been concerned with the problems caused by the fact that most life insurance policies now specify fixed rates of interest applicable to policy owners who borrow on policies with cash values. In periods of tight money and high open market interest rates, this has produced substantial increases in policy loans and has tended to disrupt the direction of the normal flows of capital through life insurance companies. In the recent report of the Hunt Commission,'' developed after two years of Mark R. Greene, Ph.D., is Distinguished Professor of Insurance in the University of Georgia. Dr. Greene is a Past President of A.R.I.A. This paper was submitted in October, 1972. The author acknowledges with appreciation the helpful comments and criticisms of an earlier draft of this paper by Mr. Abram T. Collier and E. N. Wadsworth of New Enaland Life Insurance Co., and to Dr. John W. Eilert of the professional staff of the Life Insurance Association of America. 1 The report of the President's Commission on study and investigation, specific recommendations on life insurance structures were made, which included one to amend state laws to allow life insurers to issue policies containing flexible policy loan interest rates, subject to appropriate usury laws establishing interest rate maximums. In justifying this recommendation, the