Battery conservation for downhole telemetry

A method of conserving battery energy used in transmitting signals carrying data from a downhole location, using a transmission system where a predetermined set of data is to be transmitted once during a predetermined period, the method comprising the steps of:

• transmitting at least one signal during said period to transmit the set of data;
• selecting the time of transmission of said at least one signal;
• and
• representing at least some of the data to be transmitted in terms of the time of transmission of said at least one signal.

A computer readable data carrier carrying a program comprising code portions which when loaded and run on computer means cause the computer means to execute the steps of:

• a) obtaining information regarding the data size of a predetermined set of data to be sent over a channel during a predetermined period, which set of data is to be sent using the steps of transmitting at least one signal during said period, selecting the time of transmission of said at least one signal, and representing at least some of the data to be transmitted in terms of the time of transmission of said at least one signal;
• b) obtaining information regarding the transmission characteristics of the channel over which the data is to be transmitted;
• and
• c) selecting at least one of:
• 1) the number of signals to send during the predetermined period;
• 2) the duration of each signal;
• 3) the power of each signal;
• and
• 4) the quantization of the predetermined period, so as to allow transmission of the required data during the predetermined period whilst minimising the battery energy used.

A method of generating a modulation scheme to conserve battery energy used by a downhole device in sending data items from a set of predetermined data items during a predetermined period, the method comprising the steps of:

• selecting a data transmission period within the predetermined period and dividing the data transmission period into equal length time slots;
• and
• selecting a plurality of unique signal arrangements and associating each signal arrangement with a respective one of the predetermined data items;
• wherein each unique signal arrangement has an associated pattern of pulses distributed in the time slots and the unique signal arrangements are selected so as to one of control and minimize, across the whole group of associated pulses, the mean number of pulses per associated pattern of pulses.