Speeding up execution

Question

I am working on a MIMO channel emulator. The system has a large number of blocks which have to finish execution within the coherence time of the channel, which is a fraction of a milli second. However due to the complexity of some of the operations, I have had to use Matlab scripts to execute them. Now the entire cblock takes around half a second to run, which is far from my goal. Is the invocation of Matlab slowing down the operation? How do I speed up the execution to finish within the coherence time?
Thanks

Answer 1

There are quite a few things you can do to speed up your program.  A factor of 3 to 5 is probably acheivable.  Who knows how much more?
1. You have some duplicated code and a lot of unnecessary code.
2. You do a lot of things the hard and slow way.
3. I do not have Matlab so I cannot test the speed of the scripts.  Since they call Matlab to run the scripts, I suspect the process is slower, even if Matlab can do the calculation faster.
4. Wires running behind other objects and right to left make a LV program hard to read.
5. At least one part probably does not work.  The code executes but may not produce the result you expect.
OK. Specifics.
1. You have constants 6 and 20 several places in the code.  If your system ever changes you will need to find and change all of them.  It is usually better to have one of each and wire them to all the places used.  No speed penalty but a lot of work troubleshooting if something needs to be changed.
2a. Using the Continuous Random.vi to generate 1 sample, as an array, then indexing the sample out takes about 3 times longer than using the Random Number (the Dice) from the Numeric palette.  It also produces uniformly distributed random numbers between 0 and 1. There are 8 or 9 of these constructions in your program.  Add about 200 ns each time one is called.
2b. Express VIs are almost always slower than using LV primitve functions.  The Angle Spread calculation (multiply, add, power of 10) is 260 ns slower on my computer. The Random Delays (ln(x)) is about 250 ns slower.
2c. Expression nodes are slower than using LV primitve functions.  The simple i+1 in a for loop takes 4.3 ns compared to 1.6 ns for the +1 primitive in the Numeric palette. Calculating the subpath offsets in a Formula Node takes 1 us compared to 280 ns with a case structure. Since it never changes, it should be calculated once, outside the loop. Then the time does not matter but you save a microsecond on every iteration.
5. The AoD sorting: step 6 involves equality comparison of floating point values.  This will often produce a false value for inputs which may be very close due to the finite representation of numbers in binary. Using the >0 test or In Range and Coerce?, depending on exactly what you are trying to do is probably a better method.
Lynn