trx_toolkit/burst_fwd.py: document and refactor BurstForwarder
Instead of having all configuration variables of BurstForwarder initialized in the class heading, let's introduce two functions for initialization (resetting to defaults) of both UL/DL params. This would allow to reset a BurstForwarder instance from the control interface in follow-up patches. Let's also introduce some basic documentation for the class fields, which were defined in the heading previously. Change-Id: I6b1bf41cf22f01a7e7ecc91c625fb0d2bf4bfeac
This commit is contained in:
Vadim Yanitskiy
parent
9fd173b179
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8d70f9d9fe
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@ -4,7 +4,7 @@
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# TRX Toolkit
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# BTS <-> BB burst forwarding
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#
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# (C) 2017 by Vadim Yanitskiy <axilirator@gmail.com>
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# (C) 2017-2018 by Vadim Yanitskiy <axilirator@gmail.com>
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#
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# All Rights Reserved
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#
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@ -27,58 +27,136 @@ import random
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from data_msg import *
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class BurstForwarder:
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# Timeslot filter (drop everything by default)
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ts_pass = None
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""" Performs burst forwarding and preprocessing between MS and BTS.
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# Freq. filter
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bts_freq = None
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bb_freq = None
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== Pass-filtering parameters
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# Randomization of RSSI
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randomize_dl_rssi = False
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randomize_ul_rssi = False
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BurstForwarder may drop or pass an UL/DL burst depending
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on the following parameters:
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# Randomization of ToA
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randomize_dl_toa256 = False
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randomize_ul_toa256 = False
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- bts_freq / bb_freq - the current BTS / MS frequency
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that was set using RXTUNE control command. By default,
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both freq. values are set to None, so nothing is being
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forwarded (i.e. bursts are getting dropped).
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# Timing Advance value indicated by MS (0 by default)
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# Valid range: 0..63, where each unit means
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# one GSM symbol advance.
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ta = 0
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FIXME: currently, we don't care about TXTUNE command
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and transmit frequencies. It would be great to distinguish
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between RX and TX frequencies for both BTS and MS.
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# Timing of Arrival values indicated by transceiver
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# in units of 1/256 of GSM symbol periods. A pair of
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# base and threshold values defines a range of ToA value
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# randomization: from (base - threshold) to (base + threshold).
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toa256_dl_base = 0
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toa256_ul_base = 0
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- ts_pass - currently active timeslot, configured by the MS.
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It can be activated or deactivated using SETSLOT control
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command from the MS.
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toa256_dl_threshold = 128
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toa256_ul_threshold = 128
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FIXME: only a single timeslot can be activated!
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FIXME: there is no such list for the BTS side.
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# RSSI values indicated by transceiver in dBm.
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# A pair of base and threshold values defines a range of RSSI
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# randomization: from (base - threshold) to (base + threshold).
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rssi_dl_base = -60
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rssi_ul_base = -70
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== Preprocessing and measurement simulation
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rssi_dl_threshold = 10
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rssi_ul_threshold = 5
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Since this is a virtual environment, we can simulate different
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parameters of a virtual RF interface:
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# Path loss simulation: DL/UL burst dropping
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# Indicates how many bursts should be dropped
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# and which dropping period is used. By default,
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# period is 1, i.e. every burst (fn % 1 is always 0)
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burst_dl_drop_amount = 0
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burst_ul_drop_amount = 0
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burst_dl_drop_period = 1
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burst_ul_drop_period = 1
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- ToA (Timing of Arrival) - measured difference between expected
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and actual time of burst arrival in units of 1/256 of GSM symbol
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periods. A pair of both base and threshold values defines a range
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of ToA value randomization:
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DL: from (toa256_dl_base - toa256_dl_threshold)
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to (toa256_dl_base + toa256_dl_threshold),
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UL: from (toa256_ul_base - toa256_ul_threshold)
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to (toa256_ul_base + toa256_ul_threshold).
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- RSSI (Received Signal Strength Indication) - measured "power" of
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the signal (per burst) in dBm. A pair of both base and threshold
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values defines a range of RSSI value randomization:
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DL: from (rssi_dl_base - rssi_dl_threshold)
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to (rssi_dl_base + rssi_dl_threshold),
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UL: from (rssi_ul_base - rssi_ul_threshold)
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to (rssi_ul_base + rssi_ul_threshold).
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Please note that the randomization of both RSSI and ToA
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is optional, and should be enabled manually.
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=== Timing Advance handling
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The BTS is using ToA measurements for UL bursts in order to calculate
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Timing Advance value, that is then indicated to a MS, which in its turn
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shall apply this value to the transmitted signal in order to compensate
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the delay. Basically, every burst is transmitted in advance defined by
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the indicated Timing Advance value. The valid range is 0..63, where
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each unit means one GSM symbol advance. The actual Timing Advance value
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is set using SETTA control command from MS. By default, it's set to 0.
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=== Path loss simulation - burst dropping
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In some cases, e.g. due to a weak signal or high interference, a burst
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can be lost, i.e. not detected by the receiver. This can also be
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simulated using FAKE_DROP command on both control interfaces:
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- burst_{dl|ul}_drop_amount - the amount of DL/UL bursts
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to be dropped (i.e. not forwarded towards the MS/BTS),
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- burst_{dl|ul}_drop_period - drop every X DL/UL burst, e.g.
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1 - drop every consequent burst, 2 - drop every second burst, etc.
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"""
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def __init__(self, bts_link, bb_link):
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self.bts_link = bts_link
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self.bb_link = bb_link
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# Randomization of RSSI
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randomize_dl_rssi = False
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randomize_ul_rssi = False
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# Randomization of ToA
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randomize_dl_toa256 = False
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randomize_ul_toa256 = False
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# Init default parameters
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self.reset_dl()
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self.reset_ul()
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# Initialize (or reset to) default parameters for Downlink
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def reset_dl(self):
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# Unset current DL freq.
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self.bts_freq = None
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# Indicated RSSI / ToA values
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self.toa256_dl_base = 0
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self.rssi_dl_base = -60
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# RSSI / ToA randomization threshold
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self.toa256_dl_threshold = 0
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self.rssi_dl_threshold = 0
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# Path loss simulation (burst dropping)
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self.burst_dl_drop_amount = 0
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self.burst_dl_drop_period = 1
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# Initialize (or reset to) default parameters for Uplink
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def reset_ul(self):
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# Unset current DL freq.
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self.bb_freq = None
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# Indicated RSSI / ToA values
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self.rssi_ul_base = -70
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self.toa256_ul_base = 0
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# RSSI / ToA randomization threshold
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self.toa256_ul_threshold = 0
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self.rssi_ul_threshold = 0
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# Path loss simulation (burst dropping)
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self.burst_ul_drop_amount = 0
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self.burst_ul_drop_period = 1
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# Init timeslot filter (drop everything by default)
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self.ts_pass = None
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# Reset Timing Advance value
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self.ta = 0
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# Converts TA value from symbols to
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# units of 1/256 of GSM symbol periods
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def calc_ta256(self):
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