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require 'pp'
# parameters
minutes = 30 # how long to run the sim
packet_size_bytes = 25
packet_size_bits = packet_size_bytes * 8
channels = [ 12, 11, 10, 9, 8, 7, 6 ]
channel_bits_per_second = [ 0.293 * 1000, 0.537 * 1000, 0.976 * 1000, 1.757 * 1000, 3.125 * 1000, 5.468 * 1000, 9.375 * 1000 ]
channel_time_per_packet = channel_bits_per_second.map{ |bps| packet_size_bits / bps }
# print out header for our TSV output
puts "packets_per_minute\t#{channels.join("\t")}\tall"
# let's gather some data points, based on a few packets/min settins
(100..1000).step(100) do | packets_per_minute |
# generate random packets over the total time
packets = []
( 1..packets_per_minute * minutes ).each do |i|
channel = ( rand() * 7 ).to_i # uniformly pick a random channel
start_time = rand() * 60 * minutes # pick a start time
end_time = start_time + channel_time_per_packet[ channel ] # compute the end time
# store this packet as a json object
packets << { channel: channel, start_time: start_time, end_time: end_time, collision: false }
end
# pair all packets to see which collide
(0..packets.size - 2).each do |i|
(i+1..packets.size - 1).each do |j|
packet1 = packets[ i ]
packet2 = packets[ j ]
if packet1[ :channel ] == packet2[ :channel ] # we need to be on the same channel
if( # and we need some overlap in our packet windows
(
( packet1[ :end_time ] > packet2[ :start_time ] ) &&
( packet1[ :end_time ] < packet2[ :end_time ] )
) ||
(
( packet2[ :end_time ] > packet1[ :start_time ] ) &&
( packet2[ :end_time ] < packet1[ :end_time ] )
)
)
packets[ i ][ :collision ] = true
packets[ j ][ :collision ] = true
end
end
end
end
# count errors, per channel
error_counter = [ 0, 0, 0, 0, 0, 0, 0 ]
all_channels_error_counter = 0
channel_counter = [ 0, 0, 0, 0, 0, 0, 0 ]
all_channels_counter = 0
packets.each do | packet |
error_counter[ packet[ :channel ] ] += 1 if packet[ :collision ]
all_channels_error_counter += 1 if packet[ :collision ]
channel_counter[ packet[ :channel ] ] += 1
all_channels_counter += 1
end
# print out these counts as error rates
print "#{packets_per_minute}"
(0..6).each do | counter |
print "\t#{error_counter[ counter ].to_f / channel_counter[ counter ]}"
end
print "\t#{all_channels_error_counter.to_f / all_channels_counter}"
puts
end
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