Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-07-22
2001-10-02
Trost, William (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000
Reexamination Certificate
active
06298242
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to a wireless communication system, and more specifically, to a method and apparatus for reducing frame error rate (FER) in a wireless communications system.
II. Related Art
When delivering data over a wireless link that has a relatively poor FER (for example, greater than 1%), many methods of retransmitting data exist for achieving as low a FER as a data service demands. For example, a cyclic redundancy check (CRC) can be performed at a receiving end of a link to check the integrity of a block of data. CRC is a well known method of establishing that data was correctly received in data communications. A CRC character is generated at a transmitting device and appended to a data block. The receiving end makes a similar calculation and compares its results with the added CRC character. If there is a difference, the receiving end requests retransmission of the data block.
For example, the use of protocols such as Automatic Retransmission reQuest (ARQ) can be used for retransmission of data blocks. In ARQ, the transmitting device encodes an error-detection field (for example, a CRC field) based on the contents of a data block. The receiving end recalculates the check field and compares it with that received. If they match, an acknowledgment (ACK) is transmitted back to the transmitting device. If they don't match, a negative acknowledgment (NAK) is returned, and the transmitting device retransmits the message.
The above discussed method is satisfactory for transmitting many types of data. However, these methods of achieving low FER cause increased latency due to the retransmission of data blocks. Such increased latency is not acceptable when transmitting certain types of data, such as real time digitized voice, or any other type of latency sensitive data. More specifically, the retransmission of data blocks causes delay times that are both higher on average and have greater variance than the requirements for many latency sensitive systems.
What is needed is a method and apparatus for delivering data having low FER without having increased latency. In other words, there is a need for a method and apparatus for reducing FER without relying on the retransmission of data blocks.
SUMMARY OF THE INVENTION
The present invention is directed toward a method and apparatus for controlling a signal transmission power. The method of the present invention includes the steps of demodulating a received signal to produce a demodulated signal and distorting the demodulated signal to produce a distorted demodulated signal. The demodulated signal can be distorted by, for example, adding noise. A signal quality measurement, such as signal-to-noise ratio, is then determined based on the distorted demodulated signal rather than the demodulated signal. An adjustment in the transmission power is then requested based on the signal quality measurement of the distorted demodulated signal.
In one embodiment of the present invention, the determined signal quality measurement is compared to a threshold and an adjustment in the transmission power is then requested based on the results of the comparison. The threshold represents a desired minimum signal quality level at which signals should be received. Some quality measurement functions, such as SNR, have values that are proportional to signal quality. That is, they increase with increasing quality and decrease with decreasing quality. Therefore, an increase in transmission power is requested if these signal quality measurements fall below the threshold, and a decrease in power can be requested if the signal quality measurements exceed the threshold. Other functions, based on error events, have values that are inversely proportional to signal quality, and decrease in value with increased signal quality and visa versa. In this situation, a decrease in transmission power is requested if the measurement falls below the threshold, and an increase in power is requested if the measurement exceeds the threshold.
In one embodiment, the method of the present invention further includes the steps of decoding the demodulated signal to produce decision data and decoding the distorted demodulated signal to produce distorted decision data. A second signal quality measurement or a measure of “error events,” is then determined based on said distorted decision data (rather than the decision data). The threshold, used in determining whether to increase or decrease transmission power, is adjusted based on the second signal quality measurement.
In one embodiment where the signal is transmitted by a base station and received by a user terminal, the steps of the present invention are performed by the user terminal, and the transmission power at the base station is being controlled.
In another embodiment where the signal is transmitted by a gateway and received by a user terminal using a satellite, the steps of the present invention are performed by the user terminal, and the transmission power of the gateway is being controlled.
In still another embodiment where the signal is transmitted by a user terminal and received by a base station, it is the transmission power at the user terminal that is being controlled.
In a further embodiment, the signal is transmitted by a user terminal and received by a gateway via a satellite, the steps of the present invention are performed by the gateway, and the transmission power of the user terminal is being controlled.
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Ogrod Gregory D.
Perez-Gutierrez Rafael
Qualcomm Inc.
Trost William
Wadsworth Philip R.
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