Variable-rate System Research Articles

The Adoption of New Technologies in Dryland Farming Regions of Idaho, Washington, and Oregon

In the last 30 years several advanced technologies including guidance systems, auto-steer systems, variable fertilizer rate systems, and section controllers have become mainstream in modern irrigated agriculture. Although these technologies have become widely accepted under irrigated conditions in the United States, their adoption under dryland conditions has lagged. The purpose of this study was to document the adoption of these technologies in the dryland inland areas of northern Idaho, eastern Washington, and northeastern Oregon. Three mail-based surveys conducted 15 years apart in 1981, 1996, and 2011 were used to document adoption. All of the Dillman-based surveys received grower responses in excess of 50%. In 2011, guidance systems, auto steer systems, section controllers, and variable rate application systems were used by 46.8, 36.6, 25.5, and 20.4% of the survey respondents, respectively. The use of these technologies was less than 2% in 1981 and less than 10% in 1996. The factors of annual precipitation zone, grower age, number of years farmed, and farm size all had an impact on the use of modern technology. In general, variable rate systems were more popular in the drier areas. Younger farmers were more likely to have adopted the new technologies, and new technology use was more widespread on the larger farms. This article is important because it contains a 30-year history of how quickly modern technologies have been adopted in northern Idaho and eastern Washington. This article is unique because medium-term production changes (20–40 years) are seldom documented by a single research/extension program in production agriculture.

DEVELOPMENT OF A PRECISION FARMING SYSTEM FOR TURKISH FARMERS

The objective of this paper is to explain the information about a precision farming system which has been developed for Turkish farmers. The developed system includes a variable rate controller for centrifugal fertiliser spreaders, an application map software and an autonomous steering system for tractors. The variable rate controller for the centrifugal fertiliser includes stepper motors used to adjust the distributed fertiliser amount. An electronic control system was designed to control stepper motors in addition to a DGPS system, which was used to determine positioning. The application map software was used to provide communication between the variable rate system and the stepper motor, computer and DGPS. In order to develop a variable rate controller, a toothed axle was fitted to the stepper motor. A variable rate controller was developed to combine cereal sowing machines. This system includes step motors for each seed metering unit as well as PIC, PDA and GPS receivers. The software was developed to create an application map and send signals to control units. Furthermore, an automated steering system was developed by a private Turkish company. Preliminary test results of this system were successful. The system is still being tested.

A Novel Multi-carrier Order Division Multi-access Communication System Based on TDCS with Fractional Fourier Transform Scheme

In this paper, we propose a novel fractional Fourier transform (FrFT) based multi-carrier order division multi-access communication system, in which each user is uniquely identified by an FrFT order. Transform domain communication system (TDCS) with FrFT scheme is also proposed to synthesize the wide-band baseband waveforms in all FrFT domains with different users' FrFT orders, which enhances the interference avoidance capability of this system under most of interference. Therefore, multiple independent data streams can be transmitted by using FrFT---OFDM in the same time and different FrFT domains. However, chirp bases, as the new kind of carriers with different modulated rates, are merely mutually approximately orthogonal. There is a problem of energy leakage between multiple chirp carriers, which possibly causes the multiple chirp carriers inter-shielding to influence the FrFT---OFDM demodulation performance. An efficient allocation algorithm of multiple chirp carriers by presetting the carrier parameters is proposed to solve this problem. Based on MC-CDMA, a variable bit rate system structure is proposed for TDCS with FrFT scheme under different channel environments. In order to simplify the process of modulation and demodulation of TDCS with FrFT scheme, a whole new cyclic shift key modulation mode in FrFT domain is also proposed. Both theories and simulations confirm strictly the validity of the proposed system.

Performance Comparison of M-QAM Communications for (S + N) and (S/N) Channel State Estimation Schemes

Channel estimation at the receiver side is essential for adaptive modulation schemes, prohibiting low complexity systems from using variable rate (VR) and/or variable power transmissions. This problem can be solved using variable-rate M-QAM modulation scheme for communications over fading channels in the absence of channel gain estimation at the receiver. It is shown that signal plus noise (S + N) sampling value can serve as a much better criterion compared to signal-to-noise ratio (S/N) for determining modulation order in VR systems. In this way, low complexity transceivers use VR transmissions to improve spectrum efficiency under an error performance constraint. Two kinds of fading channels: Weibull fading and α–μ fading are considered. Spectrum efficiency of (S + N) based systems are compared to that of S/N systems and the advantage of (S + N) scheme over (S/N) scheme is shown. The symbol error rates of two schemes are also studied. As an application, the proposed VR modulation scheme is shown to work with a maximum ratio combining diversity receiver.

A Robust Variable Sampling Time BLDC Motor Control Design Based uponμ-Synthesis

The variable sampling rate system is encountered in many applications. When the speed information is derived from the position marks along the trajectory, one would have a speed dependent sampling rate system. The conventional fixed or multisampling rate system theory may not work in these cases because the system dynamics include the uncertainties which resulted from the variable sampling rate. This paper derived a convenient expression for the speed dependent sampling rate system. The varying sampling rate effect is then translated into multiplicative uncertainties to the system. The design then uses the popular μ-synthesis process to achieve a robust performance controller design. The implementation on a BLDC motor demonstrates the effectiveness of the design approach.

Variable Rate Transmission Schemes for CI/MC-CDMA System

In this paper, two multirate transmission schemes have been proposed for carrier interferometry multicarrier code division multiple access (CI/MC-CDMA) system. System models for wide range of data rates are discussed based on orthogonal property of CI codes of any length. Non-contiguous CI codes have been introduced for multirate CI/MC-CDMA. Advantage of frequency diversity in non-contiguous allocation improves the performance of variable rate system over frequency selective channel. It is shown that non-contiguous allocation allows more number of very high data rate users compared to contiguous allocation with some increased complexity at iterative receiver.

Opportunistic Multiple Relay Selection with Diverse Mean Channel Gains

We consider multiple relay selection for proactive relaying with diverse mean channel gains on different links. We consider a variable rate system where the transmission rate is maximized based on an end-to-end (e2e) channel gain. We consider two relay selection methods and provide an efficient algorithm for selecting an optimal set of active relay nodes, with a cardinality constraint on the set. An approximation to the statistical behavior of the e2e performance for the two relay selection methods is derived. Our results show benefits from using multiple relays when different links exhibit different mean channel gains.

Variable-rate M-PSK communications without channel amplitude estimation

Channel estimation at the receiver side is essential to adaptive modulation schemes, prohibiting low complexity systems from using variable rate and/or variable power transmissions. Towards providing a solution to this problem, we introduce a variable-rate (VR) M-PSK modulation scheme, for communications over fading channels, in the absence of channel gain estimation at the receiver. The choice of the constellation size is based on the signal-plus-noise (S+N) sampling value rather than on the signal-to-noise ratio (S/N). It is analytically shown that S+N can serve as an attractive simpler criterion, alternative to S/N, for determining the modulation order in VR systems. In this way, low complexity transceivers can use VR transmissions in order to increase their spectral efficiency under an error performance constraint. As an application, we utilize the proposed VR modulation scheme in equal gain combining (EGC) diversity receivers.

Evaluation of Application Accuracy and Performance of a Hydraulically Operated Variable-Rate Aerial Application System

An aerial variable-rate application system consisting of DGPS (Differential Global Positioning System)-based guidance, an automatic flow controller, and a hydraulically controlled pump was evaluated for response to rapidly changing flow requirements and accuracy of application. Spray deposition position error was evaluated by direct field observation of water-sensitive paper (WSP) cards while traveling east to west and north to south across rate change boundaries. Data from the flow controller and a custom-built flowmeter monitor were used to evaluate flow controller error and variable-rate system error while making applications to a series of four management zones (28, 47, 56, and 37 L ha-1; each 81 m long). Observations of WSP showed that average spray deposition position error magnitude was 5.0 m when traveling east to west and 5.2 m when traveling north to south. Statistical analysis indicated that direction of travel had a non-significant effect on the magnitude of spray deposition position error. Flow controller error and variable-rate system error were evaluated from data collected while making applications to a series of four management zones (each zone required approximately 1.2 s) with application rates of 28, 47, 56, and 37 L ha-1. Areas under time plots of required and actual flow rates were compared and indicated flow controller error ranging from -1.0% to 2.1%. Variable-rate system error due to rate change timing was evaluated by comparing required rates from the system to required rates from the prescription. Area under time plots of these variables showed that average rate timing error for six application passes ranged from -9.1% to 1.4% with an average of -3.04%. Considering the speed at which changes have to be made for aircraft typically flying at 65 m s-1, the hydraulically operated variable-rate system performed well for location accuracy of deposition, response to changing flow rates, and accuracy of application amounts for the prescription.

Relevance vector machines based modelling and optimisation for collaborative control parameter design: a case study

A new collaborative control parameter design strategy is proposed for economic plant control process. The relevance vector machines (RVMs) and genetic algorithms (GAs) are combined to generate the optimal control index table for controllers. More specifically, the probabilistic model based on RVMs is utilised to describe the non-linear behaviours according to the experimental dataset. The evolution-based optimisation model based on GAs is used for collaborative design of the optimum control parameter combinations. A variable-rate fertilising system is presented as an application case for collaborative generation of control index table with the combined accuracy, energy saving and fertilising-consistency optimisation objectives. The experimental results show the effectiveness of the proposed hybrid approach.

V-BLAST-Based Virtual MIMO for Distributed Wireless Sensor Networks

A virtual multiple-input multiple-output (MIMO) communications architecture based on vertical Bell Laboratories layered space-time (V-BLAST) receiver processing is proposed for wireless sensor networks (WSNs). The proposed scheme does not require transmitter-side node cooperation unlike previously proposed virtual MIMO schemes. The energy and delay efficiencies of the proposed virtual MIMO scheme are derived for networks with both single-and multiple-antenna data gathering nodes (DGNs). Numerical results show the significant energy savings offered by the proposed method. These results also indicate that rate optimization over transmission distance is not essential as in virtual MIMO systems based on Alamouti scheme. In most scenarios, a fixed-rate virtual MIMO system with 4-quadrature amplitude modulation can achieve performance very close to that of an optimized, variable-rate system. In the case of single-antenna DGNs, the proposed scheme typically incur larger delay values compared to traditional single-input single-output communication, making it a good candidate for energy-starved but delay-tolerant WSNs.

Hard Fairness Versus Proportional Fairness in Wireless Communications: The Single-Cell Case

We consider a wireless communication system formed by a single cell with one base station and K user terminals. User channels are characterized by frequency-selective fading due to small-scale effects, modeled as a set of M parallel block-fading channels, and a frequency-flat distance-dependent path loss. We compare delay-limited systems with variable-rate systems under fairness constraints, in terms of the achieved system spectral efficiency C (bit/s/Hz) versus E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b </sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . The considered delay-limited systems impose "hard-fairness": every user transmits at its desired rate on all blocks, independently of its fading conditions. The variable-rate system imposes "proportional fairness" via the popular Proportional Fair Scheduling (PFS) algorithm, currently implemented in 3G wireless for data (delay-tolerant) applications. We find simple iterative resource allocation algorithms that converge to the optimal delay-limited throughput for orthogonal (frequency-division multiple access (FDMA)/time-division multiple access (TDMA)) and optimal (superposition/interference cancellation) signaling. In the limit of large K and finite M we find closed-form expressions for C as a function of E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . We show that in this limit, the optimal allocation policy consists of letting each user transmit on its best subchannel only. Also, we find a simple closed-form expression for the throughput of PFS in a cellular environment, that holds for any K and M. Finally, we obtain closed-form expressions for C versus E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> in the low and high spectral efficiency regimes. The conclusions of our analysis in terms of system design guidelines are as follows: a) if hard fairness is a requirement, orthogonal access incurs a large throughput penalty with respect to the optimal (superposition coding) strategy, especially in the regime of high spectral efficiency; b) for high spectral efficiency, PFS does not provide any significant gain and may even perform worse than the optimal delay-limited system, despite the fact that the imposed fairness constraint is laxer; c) for low to moderate spectral efficiency, the stricter hard-fairness constraint incurs in a large throughput penalty with respect to PFS

On the Expected Rate of Slowly Fading Channels With Quantized Side Information

We study a multiple-layer variable-rate system employing quantized feedback to maximize the expected rate over a single-input single-output slowly fading Gaussian channel. The transmitter uses partial channel-state information, which is obtained via an optimized resolution-constrained feedback link, to adapt the power and to assign code layer rates, subject to different power constraints. To systematically design the system parameters, we develop a simple iterative algorithm that successfully exploits results in the study of parallel broadcast channels. We present the necessary and sufficient conditions for single-layer coding to be optimal, irrespective of the number of code layers that the system can afford. Unlike in the ergodic case, even coarsely quantized feedback is shown to improve the expected rate considerably. Our results also indicate that with as little as one bit of feedback information, the role of multilayer coding reduces significantly

Uniformity testing of variable-rate center pivot irrigation control systems

As water supplies become limited, agricultural water use needs to become more efficient to maintain current productivity levels. The efficiency of center pivot and linear move irrigation systems can be increased by matching the amount and rate of water application to specific soil conditions that vary in the field. Such site-specific application can be achieved by variable-rate control systems. Although such systems are being developed, their effects on center pivot and linear move uniformity have not been documented. The uniformity along the length of a center pivot and a linear move irrigation system was measured at two system movement speeds and three variable-rate settings. One variable-rate system is commercially available using pneumatically actuated solenoid valves to turn groups of sprinklers ON and OFF at fractions of a minute corresponding to the cycle rate, for example a 50% cycle rate is 30 s ON and 30 s OFF. The other variable-rate system used commonly available electric solenoid valves to accomplish the same task. Overall, the coefficient of uniformity and low quarter distribution uniformity averaged 93% and 0.90, respectively for the center pivot irrigation system; 84% and 0.74 for the linear move system. The results were not significantly (P > 0.05) affected by wind speed, cycling rate, or system movement speed. The type of nozzle did influence the uniformity because of the distinctly different application characteristics of rotator, fixed plate, and wobbling low pressure sprinklers. Thus, the variable-rate technologies tested under the conditions presented in this paper had at least as good uniformity as the center pivot and linear move systems when functioning in non-variable-rate mode.

MIMO Systems With Adaptive Modulation

Adaptive modulation (AM) schemes in multiple input multiple output (MIMO) systems with a perfect or imperfect channel state information (CSI) at both the transmitter and receiver were investigated. Under an average transmit power and instantaneous bit error rate (BER) constraint, the transmit parameters including the subchannel transmit power and/or spectral efficiency are optimally adapted in the spatial and/or temporal domain to maximize the average spectral efficiency (ASE). Two categories, the continuous rate and discrete rate, of adaptive systems were considered, where the derived asymptotic closed form expressions for the former provided much insight into the latter. Analytical and numerical results showed that a full multiplexing gain was achieved in variable rate variable power (VRVP) systems and variable rate (VR) systems. Variable power (VP) systems with unequal numbers of transmit and receive antennas also achieved the full multiplexing gain, unlike VP systems with equal number of transmit and receive antennas. The effect of CSI imperfection on the ASE and BER was evaluated for VR systems and closed form expressions for the ASE and BER were obtained. They prove to be a useful tool to assess the system performance without taking time consuming AM MIMO system simulations.

The Impact of Interest Rates and The Housing Market on The UK Economy

The Chancellor has asked Professor David Miles to examine the UK market for longer‐term fixed rate mortgages. This paper by Adrian Cooper, which is part of a study commissioned by the Miles Review, presents the results of a series of simulations using the OEF Model of the UK economy to investigate the contribution of the housing market to macroeconomic volatility and the implications of changing the structure of mortgage finance from the current variable rate system linked to short‐term interest rates to a fixed rate system linked to long rates. The main findings are that the housing market has been a contributor to past volatility in the UK economy, and that moving to a fixed rate structure would reduce the impact of a change in interest rates on key macroeconomic indicators.

The Repo Auctions of the European Central Bank and the Vanishing Quota Puzzle*

AbstractUntil June 2000 the European Central Bank (ECB) used fixed rate tenders for its weekly repo auctions. A switch to variable rate tenders became necessary due to massive overbidding by banks. In this paper we introduce a stylized game among banks to investigate this overbidding phenomenon. Our results confirm the weakness of the fixed rate tender format and indicate that the ECB's liquidity management has significantly improved since the switch to the variable rate system. Yet recent episodes of rate cut expectations suggest that the ECB's practice of setting a minimum bid rate should be abandoned in favor of a more symmetric interest rate target.

PDF optimized parametric vector quantization of speech line spectral frequencies

A computationally efficient, high quality, vector quantization scheme based on a parametric probability density function (PDF) is proposed. In this scheme, the observations are modeled as i.i.d realizations of a multivariate Gaussian mixture density. The mixture model parameters are efficiently estimated using the expectation maximization (EM) algorithm. A low complexity quantization scheme using transform coding and bit allocation techniques which allows for easy mapping from observation to quantized value is developed for both fixed rate and variable rate systems. An attractive feature of this method is that source encoding using the resultant codebook involves very few searches and its computational complexity is minimal and independent of the rate of the system. Furthermore, the proposed scheme is bit scalable and can switch seamlessly between a memoryless quantizer and a quantizer with memory. The usefulness of the approach is demonstrated for speech coding where Gaussian mixture models are used to model speech line spectral frequencies. The performance of the memoryless quantizer is 1-3 bits better than conventional quantization schemes.

Multirate optical fast frequency hopping CDMA system using power control

This paper addresses the problem of real-time multimedia transmission in fiber-optic networks using code division multiple access (CDMA). We present a multirate optical fast frequency hopping CDMA (OFFH-CDMA) system architecture using fiber Bragg gratings (FBGs). In addition, we argue that, in multimedia applications, different services have different quality of service (QoS) requirements; hence, the user only needs to use the minimum required power to transmit the signal, such that the required signal-to-interference ratio (SIR) is met. We show that a variable bit rate optical communication system with variable QoS can be implemented by way of power control with great efficiency. Present-day multirate optical CDMA systems concentrate on finding the code structure that supports a variable rate system, neglecting the importance of the transmission power of active users on the multiple access interference (MAI) and, therefore, on the system capacity. We assign different power levels to each rate through a power control algorithm using variable optical attenuators, which minimizes the interference and, at the same time, provides variable QoS constraints for different traffic types. Although we are using a code family that preserves good correlation properties between codes of different lengths, simulations show a great improvement in the system capacity when power control is used.

MMSE receivers for multirate DS-CDMA systems

Minimum-mean squared error (MMSE) receivers are designed and analyzed for multiple data rate direct-sequence code-division multiple-access (DS-CDMA) systems. The inherent cyclostationarity of the DS-CDMA signal is exploited to construct receivers for asynchronous multipath channels. Multiple- and single-bandwidth access are treated for both single and multicarrier scenarios. In general, the optimal receiver is periodically time-varying. When the period of the optimal receiver is large, suboptimal receivers are proposed to achieve a lower complexity implementation; the receivers are designed as a function of the cyclic statistics of the signals. In multiple chipping rate systems, the complexity of receivers for smaller bandwidth users can also be controlled by changing their front-end filter bandwidth. The effect of front-end filter bandwidth on receiver performance and system capacity is quantified for a variable chipping rate system. Analysis and simulation show that significant performance gains are realized by the periodically time-varying MMSE receivers over their time-invariant counterparts.