<p>dexter has uploaded this change for <strong>review</strong>.</p><p><a href="https://gerrit.osmocom.org/c/osmo-bsc/+/22855">View Change</a></p><pre style="font-family: monospace,monospace; white-space: pre-wrap;">bts.adoc: describe ACCH repetition settings<br><br>The manual currently does not mention ACCH repetition yet. Lets<br>add some info on how to set up ACCH repetition correctly.<br><br>Change-Id: I1e27ac955882497bbeefac0c830708dd18ad46b3<br>Related: SYS#5114<br>---<br>M doc/manuals/chapters/bts.adoc<br>1 file changed, 67 insertions(+), 0 deletions(-)<br><br></pre><pre style="font-family: monospace,monospace; white-space: pre-wrap;">git pull ssh://gerrit.osmocom.org:29418/osmo-bsc refs/changes/55/22855/1</pre><pre style="font-family: monospace,monospace; white-space: pre-wrap;"><span>diff --git a/doc/manuals/chapters/bts.adoc b/doc/manuals/chapters/bts.adoc</span><br><span>index 6e7a308..0adece1 100644</span><br><span>--- a/doc/manuals/chapters/bts.adoc</span><br><span>+++ b/doc/manuals/chapters/bts.adoc</span><br><span>@@ -511,6 +511,73 @@</span><br><span> <5> The rotate subset size parameter will be increased one ACC slot at a time: len=0 -> len=1 -> len=2 -> len=3</span><br><span> <6> The time until the subset size is further increased will be calculated based on current channel load</span><br><span> </span><br><span style="color: hsl(120, 100%, 40%);">+=== Configuring FACCH/SACCH repetition</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+osmo-bts supports repetition of FACCH, uplink SACCH and downlink SACCH as</span><br><span style="color: hsl(120, 100%, 40%);">+described in _3GPP TS 44.006_ <<3gpp-ts-44.006>>. When the feature is enabled</span><br><span style="color: hsl(120, 100%, 40%);">+it is applied dynamically, depending on the rf signal quality and MS</span><br><span style="color: hsl(120, 100%, 40%);">+capabilities. FACCH/SACCH repetition (or ACCH repetition) repeats the channel</span><br><span style="color: hsl(120, 100%, 40%);">+block transmission two times. This allows the transceiver to combine the symbols</span><br><span style="color: hsl(120, 100%, 40%);">+from two separate transmissions, which increases the probability that even a</span><br><span style="color: hsl(120, 100%, 40%);">+weak signal can be decoded.</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+Enabling ACCH repetition is especially recommended when using the AMR speech</span><br><span style="color: hsl(120, 100%, 40%);">+codec. AMR already provides a forward error correction that is superior to</span><br><span style="color: hsl(120, 100%, 40%);">+the forward error correction used with FACCH or SACCH. ACCH repetition is a</span><br><span style="color: hsl(120, 100%, 40%);">+good way to even out this imbalance.</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+The VTY configuration allows to enable repetition for all three channel types</span><br><span style="color: hsl(120, 100%, 40%);">+separately. For FACCH the operator has the option to restrict the repetition</span><br><span style="color: hsl(120, 100%, 40%);">+to LAPDM command frames only. Alternatively it is also possible to allow all</span><br><span style="color: hsl(120, 100%, 40%);">+LAPDM frame types for repetition. The following example shows a typical</span><br><span style="color: hsl(120, 100%, 40%);">+configuration where ACCH repetition is fully enabled.</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+.Example typical configuration of ACCH repetition parameters at VTY BTS node</span><br><span style="color: hsl(120, 100%, 40%);">+----</span><br><span style="color: hsl(120, 100%, 40%);">+OsmoBSC(config-net-bts)# repeat dl-facch all</span><br><span style="color: hsl(120, 100%, 40%);">+OsmoBSC(config-net-bts)# repeat ul-sacch</span><br><span style="color: hsl(120, 100%, 40%);">+OsmoBSC(config-net-bts)# repeat dl-sacch</span><br><span style="color: hsl(120, 100%, 40%);">+OsmoBSC(config-net-bts)# repeat rxqual 4</span><br><span style="color: hsl(120, 100%, 40%);">+----</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+It should be noted that unless the repetition is enabled explicitly, the</span><br><span style="color: hsl(120, 100%, 40%);">+repetition is turned off by default. If no threshold (see <<acch_rep_thr>>) is</span><br><span style="color: hsl(120, 100%, 40%);">+set, the default value 4 (BER >= 1.6%) will be used. The following example shows</span><br><span style="color: hsl(120, 100%, 40%);">+a minimal configuration where the repetition is only activated for FACCH LAPDM</span><br><span style="color: hsl(120, 100%, 40%);">+command frames.</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+.Example minimal configuration of ACCH repetition parameters at VTY BTS node</span><br><span style="color: hsl(120, 100%, 40%);">+----</span><br><span style="color: hsl(120, 100%, 40%);">+OsmoBSC(config-net-bts)# repeat dl-facch command</span><br><span style="color: hsl(120, 100%, 40%);">+----</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+Since it is not worthwhile to apply any repetition when the signal conditions</span><br><span style="color: hsl(120, 100%, 40%);">+are good enough to ensure a reliable transmission in one round, the operator</span><br><span style="color: hsl(120, 100%, 40%);">+has the option to set a threshold based on RXQUAL/BER at which the repetition</span><br><span style="color: hsl(120, 100%, 40%);">+is switched on. The threshold mechanism implements a hysteresis to prevent</span><br><span style="color: hsl(120, 100%, 40%);">+bouncing between repetition on and repetition off. Only when the signal quality</span><br><span style="color: hsl(120, 100%, 40%);">+is increased again by two rxqual levels, the repetition is turned off again. It</span><br><span style="color: hsl(120, 100%, 40%);">+is even possible to permanently enable repetition, regardless of the signal</span><br><span style="color: hsl(120, 100%, 40%);">+quality.</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+[[acch_rep_thr]]</span><br><span style="color: hsl(120, 100%, 40%);">+.ACCH repetition thresholds</span><br><span style="color: hsl(120, 100%, 40%);">+[%header,cols="20%,40%,40%"]</span><br><span style="color: hsl(120, 100%, 40%);">+|===</span><br><span style="color: hsl(120, 100%, 40%);">+|rxqual |enable threshold |disable threshold</span><br><span style="color: hsl(120, 100%, 40%);">+|0 |(repetition always on) |(repetition always on)</span><br><span style="color: hsl(120, 100%, 40%);">+|1 |asciimath:[BER >= 0.2%] |asciimath:[BER = 0%]</span><br><span style="color: hsl(120, 100%, 40%);">+|2 |asciimath:[BER >= 0.4%] |asciimath:[BER = 0%]</span><br><span style="color: hsl(120, 100%, 40%);">+|3 |asciimath:[BER >= 0.8%] |asciimath:[BER <= 0.2%]</span><br><span style="color: hsl(120, 100%, 40%);">+|4 |asciimath:[BER >= 1.6%] |asciimath:[BER <= 0.4%]</span><br><span style="color: hsl(120, 100%, 40%);">+|5 |asciimath:[BER >= 3.2%] |asciimath:[BER <= 0.8%]</span><br><span style="color: hsl(120, 100%, 40%);">+|6 |asciimath:[BER >= 6.4%] |asciimath:[BER <= 1.6%]</span><br><span style="color: hsl(120, 100%, 40%);">+|7 |asciimath:[BER >= 12.8%] |asciimath:[BER <= 3.2%]</span><br><span style="color: hsl(120, 100%, 40%);">+|===</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+NOTE: osmo-bsc only sets the ACCH repetition parameters via RSL. If ACCH</span><br><span style="color: hsl(120, 100%, 40%);">+repetition can be used depends on the BTS model.</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span> ==== RACH Parameter Configuration</span><br><span> </span><br><span> The following parameters allow control over how the MS can access the random</span><br><span></span><br></pre><p>To view, visit <a href="https://gerrit.osmocom.org/c/osmo-bsc/+/22855">change 22855</a>. To unsubscribe, or for help writing mail filters, visit <a href="https://gerrit.osmocom.org/settings">settings</a>.</p><div itemscope itemtype="http://schema.org/EmailMessage"><div itemscope itemprop="action" itemtype="http://schema.org/ViewAction"><link itemprop="url" href="https://gerrit.osmocom.org/c/osmo-bsc/+/22855"/><meta itemprop="name" content="View Change"/></div></div>
<div style="display:none"> Gerrit-Project: osmo-bsc </div>
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<div style="display:none"> Gerrit-Change-Id: I1e27ac955882497bbeefac0c830708dd18ad46b3 </div>
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<div style="display:none"> Gerrit-Owner: dexter <pmaier@sysmocom.de> </div>
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