Abstract: An interactive input system comprises at least one imaging device capturing images of a region of interest, a plurality of radiation sources, each providing illumination to the region of interest and a controller coordinating the operation of the radiation sources and the at least one imaging device to allow separate image frames based on contributions from different radiation sources to be generated.

Abstract: This invention is a wireless network based on orthogonal frequency division multiplexing (OFDM) and simple terminals. In a conventional OFDM system, the signal processing hardware is divided equally between the base station and the terminal. In this invention, most of the complex signal processing hardware is shifted to the base station, making the terminal a simpler and more power-efficient device. To send information to the base station, the terminal transmits a series of QPSK symbols that make up an OFDM-code. The code is designed to distribute the signal's energy into a number of OFDM sub-carriers which can be detected and combined within the base station's OFDM receiver. Other users transmit the same OFDM-codes within the same bandwidth and at the same time, but with slightly offset carrier frequencies. Because of the nature of OFDM, the codes from different users remain orthogonal, even in a multipath radio environment.

Abstract: This disclosure covers a method of equalization for a high speed, indoor wireless local area network. The invention is designed so that the terminal equipment is as simple as possible while the hardware required for adaptive filtering, antenna diversity and frequency diversity is implemented almost entirely at the base station. The system uses pre-equalization for the downlink and post-equalization for the uplink. Antenna diversity and adaptive rate frequency diversity are used together to reduce the effects of frequency selective multipath fading to ensure that the equalizer can correct the distortion introduced by the radio channel.

Abstract: This invention modulates voice signals so that the radio waves behave the same in the radio medium as sound waves would in the acoustic medium. This is accomplished by segmenting the voice signal and compressing the segments in time before transmitting them through the radio channel. If the compression factor is correct, the distortion sounds natural to the ear because the characteristics of the radio channel match those normally encountered in the acoustic channel. The radio signal will then inherit many of the good properties of acoustic voice signals including resistance to flat fading and tolerance of frequency selective fading.

Abstract: The invention is a radio terminal that co-ordinates with similar terminals around it to form a time division multiple access (TDMA) network. No base station or special devices are needed to manage the network. The terminals autonomously establish the critical functions that form the backbone of the network including routing and synchronization. Once established, any terminal can send radio messages through the network using any modulation format, analogue or digital, that meets the network's bandwidth, timing, and power specification. Terminals are able to reach destinations beyond their range by routing signals through neighboring terminals. The routing algorithm is simplified considerably by exploiting the broadcast nature of radio waves and allowing the signal to take more than one path through the network at the same time.

Abstract: A synchronizing apparatus for a differential OFDM receiver that simultaneously adjust the radio frequency and sample clock frequency using a voltage controlled crystal oscillator to generate a common reference frequency. Timing errors are found by constellation rotation. Subcarrier signals are weighted by using complex multiplication to find the phase differentials and then the timing errors. The reference oscillator is adjusted using the timing errors. Slow frequency drift may be compensated using an integral of the timing error. Frequency offset is found using the time required for the timing offset to drift from one value to another.

Abstract: A synchronizing apparatus for a differential OFDM receiver that simultaneously adjust the radio frequency and sample clock frequency using a voltage controlled crystal oscillator to generate a common reference frequency. Timing errors are found by constellation rotation. Subcarrier signals are weighted by using complex multiplication to find the phase differentials and then the timing errors. The reference oscillator is adjusted using the timing errors. Slow frequency drift may be compensated using an integral of the timing error. Frequency offset is found using the time required for the timing offset to drift from one value to another.