Abstract: A public cordless telephone system includes an arrangement for informing a public handset unit when it is within the reception range of a public base unit even though all communication channels are then occupied or all public base units in the reception area are then busy communicating with other handset units. In operation, each public base unit while communicating with any public handset unit inserts in the communication channel it is then occupying spectrum energy such as is provided either by a pilot signal or a frequency shift keying (FSK) signal. By providing this additional spectrum energy along with normal voice signal energy in the communication channel, a public handset unit while searching for an available channel and interrogating this channel will be able to determine, even though the channel is occupied, that there is a public base unit within its reception range.

Abstract: A cordless telephone public base unit employed in a public telephone system in close proximity with other public base units effectively avoids contention with these other base units for access to a cordless telephone handset unit generating a service request. Contention between the public base unit and the other public base units is resolved by assigning a specific one of a plurality of times during which the base unit may respond to the service request from the handset unit. The time in which the base unit responds to the service request may advantageously be determined by a randomly generated number, the received signal strength of the service request or a combination of these two parameters. Once access to the handset unit is acquired by a base unit and communications between these two units is established on a communications channel, all other handset units and base units are prevented from interfering with the communications between these two units.

Abstract: In a public cordless telephone system, a cordless telephone handset unit requests and establishes a communications link with a public base unit served by a desired local service provider whenever possible. By generating a service request containing a specific carrier request code, the handset unit selectively identifies an available public base unit served by the desired local service provider and then establishes a communications link with this base unit. In response to receiving the service request from the handset unit, all public base units operated by the chosen service provider respond by providing a first acknowledgment signal. All other public base units respond by providing a second acknowledgment signal. When both such signals are received, the handset unit responds only to the first acknowledgment signal and establishes a communications link with the first base unit providing this signal.

Abstract: The sensitivity of an optically-based touch screen is substantially impro by adaptively establishing the detection threshold based on the peak trapped light measured over a number of frames on the screen being painted. In accordance with one feature of the invention, the peak trapped light from a target area painted on the screen is compared with a priorly established threshold as a way of determining that a target area is being touched by the user. In accordance with another feature of the invention, the threshold is modified in a way that compensates for possible erroneous touch indications due, for example, to bright spots on the screen.