aligned to the datasheet rev5. the variable names were changed. some of
the return values are added. values aremaster
Shoichi Sakane
parent
93213cb784
commit
c8a2f3fa17
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@ -1,8 +1,8 @@
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#!/usr/bin/env python
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# -*- coding: utf-8 -*-
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# 4.1.1.6. LoRaTM Packet Structure, SX1276/77/78/79 Datasheet
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# http://www.semtech.com/images/datasheet/sx1276_77_78_79.pdf
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# 4.1.1.6. LoRaTM Packet Structure, SX1276/77/78/79 Datasheet Rev.5 Aug 2016
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# http://www.semtech.com/images/datasheet/sx1276.pdf
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import math
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@ -18,45 +18,57 @@ def mpsrange(a, b):
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def get_toa(n_size, n_sf, n_bw=125, enable_dro=1, disable_h=0, n_cr=1,
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n_preamble=8):
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'''
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return the time on air in milisecond.
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n_size:
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PL in the fomula. PHY Payload size in byte (= MAC Payload + 5)
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n_sf: SF (12 to 7)
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n_bw: Bandwidth in kHz. default is 125 kHz for AS923.
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enable_dro:
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DE in the fomula.
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1 when the low data rate optimization is enabled.
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0 for disabled.
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LoRaWAN always use the low data optimization.
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disable_eh:
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H in the fomula.
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0 when the explicit header is enabled.
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1 when no header is present.
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LoRaWAN always use the header.
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n_cr:
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CR in the fomula, should be from 1 to 4.
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Coding Rate = (n_cr/(n_cr+1)).
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LoRaWAN takes alway 1.
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n_preamble:
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The preamble length in bit.
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default is 8 in AS923.
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Parameters:
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n_size:
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PL in the fomula. PHY Payload size in byte (= MAC Payload + 5)
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n_sf: SF (12 to 7)
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n_bw: Bandwidth in kHz. default is 125 kHz for AS923.
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enable_dro:
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DE in the fomula.
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1 when the low data rate optimization is enabled.
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0 for disabled.
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LoRaWAN always use the low data optimization.
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disable_eh:
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IH in the fomula.
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0 when the explicit header is enabled.
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1 when no header is present.
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LoRaWAN always use the header.
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n_cr:
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CR in the fomula, should be from 1 to 4.
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Coding Rate = (n_cr/(n_cr+1)).
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LoRaWAN takes alway 1.
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n_preamble:
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The preamble length in bit.
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default is 8 in AS923.
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Return:
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dict type contains below:
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r_sym: symbol rate in *second*
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t_sym: the time on air in millisecond*.
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t_preamble:
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v_ceil:
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n_payload:
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t_payload:
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t_packet: the time on air in *milisecond*.
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'''
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t_sym = math.pow(2, n_sf) / (n_bw*1000.) * 1000.
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r_sym = (n_bw*1000.) / math.pow(2,n_sf)
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t_sym = 1000. / r_sym
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t_preamble = (n_preamble + 4.25) * t_sym
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a = 8.*n_size - 4.*n_sf + 28 + 16 - 20.*disable_h
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b = 4.*(n_sf-2.*enable_dro)
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v_ceil = a/b
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nb_sym_payload = 8 + max(math.ceil(a/b)*(n_cr+4), 0)
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t_payload = nb_sym_payload * t_sym
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t_frame = t_preamble+ t_payload
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n_payload = 8 + max(math.ceil(a/b)*(n_cr+4), 0)
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t_payload = n_payload * t_sym
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t_packet = t_preamble+ t_payload
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ret = {}
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ret["r_sym"] = r_sym
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ret["t_sym"] = t_sym
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ret["n_preamble"] = n_preamble
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ret["t_preamble"] = t_preamble
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ret["v_ceil"] = v_ceil
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ret["nb_sym_payload"] = nb_sym_payload
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ret["n_payload"] = n_payload
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ret["t_payload"] = t_payload
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ret["t_frame"] = round(t_frame, 3)
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ret["t_packet"] = round(t_packet, 3)
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return ret
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@ -102,8 +114,6 @@ if __name__ == "__main__" :
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opt = parse_args()
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ret = get_toa(opt.n_size, opt.n_sf, n_bw=opt.n_bw, enable_dro=opt.v_de,
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disable_h=opt.v_h, n_cr=opt.n_cr, n_preamble=opt.n_preamble)
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ret0 = get_toa(0, opt.n_sf, n_bw=opt.n_bw, enable_dro=opt.v_de,
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disable_h=opt.v_h, n_cr=opt.n_cr, n_preamble=opt.n_preamble)
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if opt.f_verbose:
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print "PHY payload size : %d Bytes" % opt.n_size
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print "MAC payload size : %d Bytes" % (opt.n_size-5)
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@ -112,15 +122,23 @@ if __name__ == "__main__" :
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print "Low data rate opt. : %s" % ("enable" if opt.v_de else "disable")
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print "Explicit header : %s" % ("disable" if opt.v_h else "enable")
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print "CR (coding rate) : %d (4/%d)" % (opt.n_cr, 4+opt.n_cr)
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print "Symbol Rate : %.3f symbol/s" % ret["r_sym"]
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print "Symbol Time : %.3f msec/symbol" % ret["t_sym"]
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print "Preamble size : %d symbols" % opt.n_preamble
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print "Other symbol size : %d symbols" % ret["nb_sym_payload"]
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print "Symbol Time : %.3f msec" % ret["t_sym"]
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print "Packet symbol size : %d symbols" % ret["n_payload"]
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print "Preamble ToA : %.3f msec" % ret["t_preamble"]
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print "Payload ToA : %.3f msec" % ret["t_payload"]
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print "Time on Air : %.3f msec" % ret["t_frame"]
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print "Time on Air : %.3f msec" % ret["t_packet"]
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if opt.debug_level:
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print "MAC frame data rate : %.3f bps" % ((8.*(opt.n_size-5)) /
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((ret["t_frame"]-ret0["t_frame"])/1000.))
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ret0 = get_toa(0, opt.n_sf, n_bw=opt.n_bw,
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enable_dro=opt.v_de, disable_h=opt.v_h,
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n_cr=opt.n_cr, n_preamble=opt.n_preamble)
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print "PHY PL=0 ToA : %.3f msec" % (ret0["t_packet"])
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# preamble=8 cr=1? payload-len=7? crc=16 (payload) payload-crc=16
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# =? 48 ==> 6 bytes ?
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t0 = (ret["t_packet"]-ret0["t_packet"])/1000.
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print "PHY fr.dr.(48b) 7:15: %.3f bps" % ((8.*opt.n_size+48)/t0)
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print "MAC frame DR : %.3f bps" % ((8.*(opt.n_size)) /t0)
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print "Ceil(x) : %.3f" % ret["v_ceil"]
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else:
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print "%.3f" % ret["t_frame"]
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print "%.3f" % ret["t_packet"]
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