TWO WAY RADIO WITH A TRANSMITTER HAVING RF POWER CONTROL
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2001-Nov-21
This invention is a two way portable radio with selectable RF output power levels. Today's FM portable radios are designed for performance under worst case fringe area coverage conditions. The portable transmit- ter is designed for coverage at that worst case level and consequently transmits excessive RF output power under actual user conditions ( 9dB excess power for 50% of the time). Furthermore, those transmitters that do have power control capability and could potentially utilize power control do not exhibit substantial current drain reductions with RF power cutback because of inefficient RF power amplifier designs, This invention is a portable twoway radio having the capability of cutting back transmitter RF output power in response to signalling from a companion unit which determines the signal strength received by the companion unit. The portable unit further exhibits at least two RF output power lsvels where the efficiency is high. Therefore, reduced power operation with the consequent substantial battery energy savings is accomplished in response to actual signal strength fed back from a companion unit. The companion unit may be a base station or another similar portable unit. The system works as follows. A first portable unit transmits a signal initially at full power. The companion station receiver detects and measures the average signal strength of the portable radio transmitted signal, determines whether sufficient margin exists be tween the received signal strength and the signal strength level required for reliable communications. If sufficient margin exists, that is if the portable transmitter signal strength is in excess by a predetermined amount (more than 9dB in this example) a signal is transmitted to the portable commanding a (9dB) power reduction. The portable may listen for this signal in "holes" during its own transmit time, or during its own receive cycle. The feasibility of having 4OmSec receive "holes" during transmit, and "hole filling" to maintain audio quality have been successfully demonstrated by the mobile radio research group. Figure 1 shows a portable (or base station) receiver and transmitter in block diagram form im- plementing the invention. The receiver is shown capable of measuring signal strength of a received signal at signal point S. The signal may be just enough for reliable communications (level A), or sufficiently strong (level M) and with enough margin to be a candidate for power cut back. That measured signal strength information and a status of the transmitter (full power or transmitting low power) is sent to the other (companion) portable unit. The companion portable may then cut back its own transmitter power based on the reported signal strength and may request that first unit reduce its RF power level based on its own measurement of the first unit's signal strength. Thus, portable to portable or portable to base operation is accommodated.