Franklin P. Antonio

Faster line segment intersection

Publisher Summary This chapter presents an algorithm to determine whether two line segments in 2-D space intersect or not and to determine the point of intersection. Rapid calculation of line segment intersections is important because this function is often called a primitive many number of times in the inner loops of other algorithms. To develop the algorithm, it is convenient to use vector representation. The chapter describes C implementation as one that involves calculation of the intersection point coordinates where the segments are found to intersect. The C implementation uses integer arithmetic. Calculation of the intersection point involves operations that are cubic in the input coordinates so that the limitation to input coordinates in the range [0, 1023] or other similar-sized range avoids overflow on 32-bit computers. When line segments do not intersect, input coordinates in the range [0, 16383] can be handled.

A novel adaptive predistortion technique for power amplifiers

One of the main concerns in wireless communication systems is high-power amplifier (HPA) efficiency as this has a direct impact on size, power consumption, and cost. At the same time, HPA linearity is critical for linear modulation schemes. Nonlinear devices introduce intermodulation products to a bandlimited waveform resulting in violation of emission specifications. This paper explores an adaptive predistortion algorithm that compensates for the nonlinear distortion of an HPA by predistorting the input waveform. Predistortion is applied in the form of digital gain and phase changes that are functions of instantaneous input waveform amplitudes. Measured out-of-band emission levels are used as a metric for the convergence of the algorithm. Upon convergence, the combined nonlinearities of predistortion and the HPA cancel, effectively producing a linear device. The use of waveform predistortion improves the overall efficiency by allowing amplifier operation closer to the saturation point.

OmniTRACS: a commercial Ku-band mobile satellite terminal and its applicability to military mobile terminals

The technical characteristics of the OmniTRACS system are described. This system is the first operational mobile Ku-band satellite communications system and provides two-way message and position determination service to mobile terminals using existing Ku-band satellites. Interference to and from the system is minimized by the use of spread-spectrum techniques, together with low-power, low-data-rate transmissions. The applicability of this technology to implement a military mobile terminal operating over existing SHF satellites is also presented. Features discussed include the return- and forward-link modulating signals, the return-link power density, and the mobile-terminal hardware.<<ETX>>