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B-6. Performance Analysis

B-6.1 Process Loading Estimates

Loading estimates, based on benchmark tests or empirical techniques, have been generated for the four main subprocesses within the Process Telemetry function. Both nominal processing loads and non-nominal processing loads will be derived. The latter scheme might be required if there were a large number of discrete (1-bit) measurands; a complex wavetrain; complex derived measurands, EU conversions, or limit check algorithms; a format change or anomalous vehicle; and a large number of tabular measurand displays.

Sync/Extract Telemetry. In determining the processing load for this function, the following assumptions are made:

* Frame/Packet Synchronization is accomplished with a front-end card and there is no processor load.

* Format ID and Embedded Determination requires negligible processor load to detect the wavetrain format ID and load the appropriate processing format. Processor memory is also assumed to be sufficient to hold all applicable formats that could occur in the vehicle downlink.

* The average nominal measurand size is 8 bits (per Section B-2), and the average non-nominal measurand size is 4 bits.

* Extraction using a software decommutation method requires 15 instructions/measurand (nominal) and 20 instructions/measurand (non-nominal).

The Telemetry Extract processing load is described by the following equation:

Nominal LTE = ((M + S1)/8 meas/sec) * (15 instr/meas) / (1.83 SPECint92/MIPS * 106)

Non-Nominal LTE = ((M + S1)/4 meas/sec) * (20 instr/meas) / (1.83 SPECint92/MIPS * 106)

where: LTE = Telemetry Extract load (SPECint92)

M = Mission/sensor telemetry rate (bps)

S1 = SOH telemetry rate (bps)

Convert Measurands. In determining the processing load for this function, the following assumptions are made:

* Formation of derived measurands and all EU and limit check algorithms for SOH data require 37.5 instructions/measurand (nominal). This factor is derived from an AFSCN study, wherein timing measurements were performed for different sets of telemetry operations on a 20 MIPS processor. Measurands were processed at a rate of 2.5M measurands/second, and a total load of 93.75 MIPS was measured. This load, when divided by the measurand rate, results in the processing factor of 37.5 instructions/measurand. For the non-nominal case, the factor is estimated to be 25% higher (46.8 instructions/measurand).

* A data quality check of each wavetrain is assumed to require an additional conditional algorithm, such as a CRC algorithm for error checking, plus a logical operation to associate synchronization status with a measurand. Using data from the above AFSCN study, the resulting load is 26.25 MIPS at 2.5M measurands/second, which translates to a Data Quality factor of 10.5 instructions/measurand/wavetrain (nominal). For the non-nominal case, the factor is estimated to be 25% higher (13.125 instructions/measurand/wavetrain).

The total Telemetry Conversion load is described by the following equation:

Nominal LTC = (((S1 + S2)/8 meas/sec) * (48 instr/meas)) + (M/8 meas/sec * 10.5 instr/meas))

(1.83 SPECint92/MIPS) * 106

Non-Nominal LTC = (((S1 + S2)/4 meas/sec) * (59.9 instr/meas)) + (M/4 meas/sec * 13.1 instr/meas))

(1.83 SPECint92/MIPS) * 106

where: LTC = Telemetry Conversion load (SPECint92)

M = Mission/sensor telemetry rate (bps)

S1 = SOH telemetry rate (bps)

S2 = Embedded SOH telemetry rate, e.g. in mission stream

Monitor Telemetry. In determining the processing load for this function, the following assumptions are made:

* 5% of measurands in the SOH wavetrain change in a nominal vehicle situation, and there is an average of 1 monitor rule for every 3 measurands

* 100% of measurands in the SOH wavetrain change in a non-nominal vehicle situation, and three measurands can be evaluated within a single expert system rule

* Benchmark tests have shown a typical performance load of 270 rules/sec/SPECint92 for several popular COTS rule based expert systems used for monitoring telemetry data

The Telemetry Monitor load is described by the following equation:

Nominal LTM = (((S1 + S2)*(0.05)/8 meas/sec) / 3 meas/rule) / (270 rules/sec/SPECint92)

Non-Nominal LTM = (((S1 + S2)/4 meas/sec) / 3 meas/rule) / (270 rules/sec/SPECint92)

where: LTM = Telemetry Monitor load (SPECint92)

S1 = SOH telemetry rate (bps)

S2 = Embedded SOH telemetry rate, e.g. in mission stream

Display SV Health and Status. In determining the processing load for this function, the following assumptions are made:

* In the nominal case, only 1% of SOH measurands are displayed on any format, either foreground or background, and there is only one active format

* In the non-nominal case, 10% of SOH measurands are displayed on any format, either foreground or background, and there are 5 active formats

* Display processing load for graphical display of telemetry data using a popular COTS product has been measured at 250 measurands/sec/SPECint92

The Telemetry Display load is described by the following equation:

Nominal LTD = D * ((S1 + S2)*(0.01)/8 meas/sec) / (250 meas/sec/SPECint92)

Non-Nominal LTD = D * ((S1 + S2)*(0.1)/4 meas/sec) / (250 meas/sec/SPECint92)

where: LTD = Telemetry Display load (SPECint92)

D = Number of active display formats

S1 = SOH telemetry rate (bps)

S2 = Embedded SOH telemetry rate, e.g. in mission stream