Demand-based power and data rate adjustments to a transmitter to optimize channel capacity and power usage with respect to data transmission traffic over a fixed-bandwidth channel

Abstract

In a communication system in which a transmitter transmits data over a communication channel of a fixed bandwidth to a receiver, the method according to which the transmit data rate is continuously adjusted to a rate which is substantially equal to a short-term average data rate. The channel capacity and / or other characteristics of the system, is continuously adjusted, through changes in transmit power, symbol rate and modulation format, to a level at which the ratio of received signal energy per bit to noise spectral density (Eb / N0) at the receiver is close to but above its minimum acceptable level, thereby matching the channel capacity and / or other characteristics of the system to the traffic. The system has further attributes which adjust the transmit data rate responsive to conditions involving at least one of data traffic levels, power reserve emergency, thermal load and message priority.

Description

BACKGROUND OF THE INVENTION[0001]This invention relates generally to wireless communication systems and more particularly to channel capacity and power management in variable rate data transmission systems transmitting over a fixed-bandwidth communication channel.[0002]The invention finds application in prior art radio frequency communication systems operating over one or more communication channels of fixed bandwidth. When such systems are used for data communication, they may be configured to communicate data at a predetermined data rate, modulation format, error-correction-coding, and other transmit waveform characteristics that determine the so called “common air interface” of the radio frequency communication system.[0003]The transmit waveform and the prevailing additive noise in the channel determine the capacity of the channel for carrying information. In selecting the transmit waveform characteristics, it is usually the objective of the network service provider to provide an...

AI Technical Summary

Benefits of technology

[0015]It is yet another object of the invention to optimize power usage by a transmitter to minimize costs of data transmission over a fixed-bandwidth communication channel.

[0018]An advantage of the described method is that it is performed continuously during the operation of the transmitter to meet a continuously varying traffic demand on the system.

[0019]Another advantage of the method is that the transmit power remains substantially at an optimum at all times, meaning that the transmit power remains at a lowest possible level, considering the current traffic demand on the channel and a necessity to maintain a data error rate below a threshold level.

Problems solved by technology

Independent of Shannon theory, another theoretical limitation governs high speed data transmission through band-limited channels; this limitation is defined by Nyquist theory.

Returning to the discussion of Nyquist theory, any attempt to transmit symbols at a rate higher than the Nyquist rate of B symbols / second, where B is the bandpass channel bandwidth, results in intersymbol interference, wherein the decision process for detecting the bits carried by each symbol is affected by the energy in adjacent symbols.

It is extremely difficult if not practically impossible to transmit symbols through a bandlimited channel at the Nyquist rate as it requires the use of ideal channel filters of bandpass bandwidth B Hz, or lowpass equivalent bandwidth B / 2 Hz, having infinitely sharp spectral roll-off.

Such filters are referred to as a “brick wall” filters and are physically unrealizable.

Prior art communication systems have not been known to use transmitter power, modulation format or error-correction coding in a dynamic manner, to match the channel capacity to the average source data rate.

Most often, a fixed channel capacity is installed, matched to the expected peak traffic load, leading to the existence of underutilized capacity during off-peak times. Some instances are known, however, such as “bandwidth on demand” systems, where channel bandwidth is used dynamically to accommodate time varying traffic.

Current systems appear to be deficient in ways of dynamically matching the channel capacity in general and transmit power in particular to actual, time variable traffic demands on the systems.

For such systems, operating costs on a “per kilobyte of traffic” basis typically reflect power usage at maximum traffic loads and are, consequently, higher than necessary because of inherent inflexibilities in adjusting the power levels and other aspects of the transmit waveform to the traffic loads on such systems.

Images