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 (E b /N 0 ) 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.

1. In a method of data communications between a transmitter and a receiver, utilizing modulated radio frequency carriers having a modulation format including a symbol rate, and further utilizing a fixed bandwidth communication channel having a channel capacity, the said data communications occurring at a transmit data rate for data received by the transmitter as input data messages at an average source data rate, a method of dynamically adjusting the channel capacity, comprising the steps of:
 changing the transmit data rate corresponding to the channel capacity in response to indicated changes in the average source data rate so as keep the transmit data rate marginally above the average source data rate with a margin that is substantially constant for all values of average source data rate; and  
 changing the channel capacity in response to any change in the transmit data rate to maintain a ratio of signal energy per bit to a noise power spectral density at the receiver at a level at which a bit error rate at the receiver is maintained substantially at but below a threshold value, and wherein changes to the channel capacity are made through adjustments to the transmit power, symbol rate and modulation format.  
 
     
     
       2. The method of  claim 1 , wherein the modulation format of the carrier is MPSK, and wherein the phase encoding is one of coherent and differential at a plurality of symbol rates and a plurality of modulation orders. 
     
     
       3. The method of  claim 2 , wherein the modulation format adjustment includes adjusting the modulation order. 
     
     
       4. The method of  claim 1 , wherein the receiver is able to determine the symbol rate. 
     
     
       5. The method of  claim 1 , wherein the receiver is able to determine a modulation order. 
     
     
       6. The method of  claim 5 , wherein receiver determines the modulation order by performing the steps of:
   performing an amplitude histogram of the inphase  ( I )  and quadrature  ( Q )  complex baseband samples of the receive signal; and        selecting a particular modulation order through pattern matching between the receive signal histograms and a set of reference histograms.     
     
     
       7. The method of  claim 5 , wherein receiver determines the modulation order by performing the steps of:
   demodulating the receive signal with an MPSK demodulator of the highest permitted modulation order;        recording the average number of signal constellation hits over a predetermined length of time; and        identifying constellation points that have been transmitted based on the steps of demodulating and recording.     
     
     
       8. The method of  claim 1 , wherein the transmitter and the receiver are in a store- and - forward communication system of messages having a determinable length and received in intervals at message arrival times, the method further comprising the steps of:      determining an average source data rate based on counting the total length of all messages received in a predetermined period of time; and        determining the level of current data traffic based on the average source data rate.     
     
     
       9. The method of  claim 1 , further comprising the steps of:
   temporarily suspending changing the transmit data rate in response to changes in data traffic levels;        increasing the transmit data rate to a maximum established transmit data rate during a period when a message of urgency is received for transmission by the transmitter and transmit data rate is not already at such maximum established transmit data rate;        increasing the channel capacity to a maximum allocated level commensurate and simultaneously with any such increase in the transmit data rate.     
     
     
       10. The method of  claim 1 , further comprising the steps of:
   temporarily suspending changing the transmit data rate in response to changes in data traffic levels;        decreasing the transmit data rate to a predetermined minimum transmit data rate during a period when a power reserve indicator signals that resources for operating the transmitter have become limited and the transmit data rate is not already at such predetermined minimum established transmit data rate; and        decreasing the transmit power to a minimum transmit power level commensurate and simultaneously with any such decrease in the transmit data rate to the predetermined transmit data rate whereby consumption of the limited power resources is reduced.