Ron Palmer

Improving the Efficiency of Field Operations

The course that a farmer follows while covering a particular field area has a significant effect on the efficiency with which chemicals, fuel, and time are consumed. In order to measure this effect the paths of several operators were monitored as they sprayed various fields. The paths were monitored by using a precise positioning system to record the co-ordinates of the spraying vehicles as they covered the relevant field areas and these co-ordinates were later analysed to determine the amount of overlapped and missed areas. From this study it was found that there is room for significant improvement in farming efficiency. It is suggested that precise tracking of predetermined efficient courses could reduce both overlapping and misses. A method of generating these field courses is presented. By using such courses to control a spraying applicator the distance travelled to cover a field could be reduced by 16% and the amount of inputs could be reduced by 10%.

A low latency architecture for computing multiplicative inverses and divisions in GF(2/sup m/)

A low latency architecture to compute the multiplicative inverse and division in a finite field GF(2/sup m/) is presented. Compared to other proposals with the same complexity, this circuit has a lower latency and can be used in error-correction or cryptography to increase the system throughput. This architecture takes advantage of the simplicity to compute powers (2/sup i/) of an element in a Galois field. The inverse of an element is computed in two stages: power calculation and multiplication. A division can be performed using only one more multiplication in the inversion circuit.

Multipath mitigation technique in RF ranging

Radio Frequency (RF) ranging systems typically use a measurement of the signals phase to provide the range. There are many problems associated with this technique in determining the range. Multipath has a dominant effect on the phase measurement, especially when a high level of accuracy is required. This paper introduces a multipath mitigation algorithm for a spread spectrum RF ranging system, employing the frequency hopping (FH) technique. Some models are built to present the mathematical relationship between the direct signals, the reflected signals, and the composite signals. The algorithm allows the precise distance of the direct path to be determined. This technique could cancel the effect of multipath in a two-ray environment

Determining wind velocity and the speed of sound with redundant transponders for a spread spectrum acoustic ranging system

Acoustic spread spectrum signals offer advantages over radio frequencies when implementing a ranging system. Global Positioning System (GPS) receivers become less accurate when shadowed by buildings and obstacles (see Nebot, E.M. and Durrant-Whyte, H., Robotics and Autonomous Systems, vol.26, p.81-97, 1999). Sound waves offer a larger bandwidth which, when used in conjunction with spread spectrum, can create better immunity to multipath interference. A drawback to transmitting acoustic signals in a ranging system is the fact that the speed of sound can vary. Its speed changes in accordance with the temperature, density and speed of the medium in which it travels. When transmitting an acoustic signal through air, the wind affects the propagation velocity. By accounting for a changing speed of sound, a more accurate acoustic ranging system can be achieved. This paper introduces an approach to calculating both the wind velocity and the propagating speed of sound by using redundant transponders.

An algorithm to determine range distance with a frequency hopping spread spectrum system

With slow frequency hopping, a propagation phase can be obtained for each frequency that is sent. The propagation phase for any single frequency yields an ambiguous range. In using the phases from a set of frequencies, it is possible to obtain a reliable, unambiguous range. This paper explains how a set of propagation delays can be used to determine a unique range distance. Multipath is taken as the only source of interference. The phase delays are calculated and plotted against the frequency. In order to find the integer part of the phase, a transition-point search method is developed; a linear regression method is applied as well. Using linear regression, a line is determined, and the intercept of this line is proportional to the range

An analysis of multipath for frequency hopping spread spectrum ranging

Frequency hopping spread spectrum (FHSS) ranging is a newly developed radio frequency (RF) technique. With slow frequency hopping, a propagation phase can be obtained for each frequency that is sent. However, each phase is corrupted with multipath, which is a major source of error in RF ranging systems. It is imperative to mitigate this effect for the purpose of achieving the highest-level of accuracy. This paper analyzes the effects of multipath to single frequency ranging and its relationship to the accuracy of the range. Three key factors, reflection coefficient, signal frequency and antenna height, were studied in an attempt to find the optimal combination. Finally, this paper gives some insight as to how the effect could be countered

An Indoor Spread Spectrum Acoustic Ranging System

The design of a spread spectrum acoustic ranging system is presented as an alternative for transmitting and receiving positioning information [1]. Six pseudonoise codes, four maximum length and two Gold codes, are tested in a high multipath indoor environment to assess the system’s accuracy. Range measurements are made in 1 m intervals from 1 to 10 m and the results are shown for a maximum length code and a Gold code which is the modulo-2 addition of two maximum length codes. The average errors are bound between 6 and 20 cm. It appears multipath interference provides the largest contribution to the range error.Copyright

A ranging algorithm that can accommodate motion for a frequency hopping (FH) spread spectrum system

With slow frequency hopping, a propagation phase can be obtained for each frequency that is sent. The propagation phase for any one frequency yields an ambiguous range. In using the phases from a set of frequencies, it is possible to obtain a reliable, unambiguous range. However if the range is changing while the set of phases is being read, the task of determining the range becomes quite difficult. The range solution is only possible if a precise velocity is known at the time of the phase readings. This paper explains how a set of propagation delays can be adjusted with the velocity to determine a unique range distance

Multichannel multipoint distribution service system synchronization using global positioning system clock

Timing and synchronization are critical in the design of any digital communications system. A communication system being studied. The multichannel multipoint distribution services (MMDS), requires a robust synchronization in order to be able to transmit a high speed data stream and to ensure data integrity. In the absence of SONET and SDH, a precise frequency from the global positioning system (GPS) is used for the system reference clock instead of crystals. This frequency and time have an accuracy that is directly and traceable continuously to the coordinates universal time (UTC). A GPS receiver locks onto the GPS frequency and locally regenerates a stable clock. A reference 10 MHz clock with TTL output was generated. This clock is used in the system for clocking and synchronization purposes. Precision timing combined with the word synchronization scheme makes the MMDS system simple, robust, low cost, and reliable.

Multi-channel multi-point distribution service system transceiver implementation

This paper presents the hardware implementation of a high-speed transceiver to be used in a multi-channel multi-point distribution system (MMDS). Based on standards specifications, various building blocks are implemented using FPGA prototypes. It has been found that data integrity protection is expensive to implement, namely the forward error correction scheme in the transceiver. This includes Reed-Solomon codec and byte interleaving to correct both random and burst errors causing by the channel. Results show a data rate of 80 Mbit/s can be achieved using FPGA prototypes. Higher data rates are expected when final ASICs are developed.