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<h1>GPRS Coding Schemes</h1>

<p>GPRS provides four coding schemes, from CS-1 to CS-4, offering
data rates from 9.05 to 21.4 kbit/s per channel. By using PCU1 and 16 kbit/s
Abis links, it is possible to support CS-1 and CS-2.</p>


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<p>Coding scheme CS-1 is always used in unacknowledged RLC
mode, except with PCU2 where it is also possible to use other
CSs in unacknoledged RLC mode.</p>


<p>In acknowledged mode of operation, RLC data blocks are
acknowledged, and both CS-1 and CS-2 are supported. Each TBF can use either
a fixed coding scheme (CS-1 or CS-2), or Link Adaptation (LA). The link adaptation
algorithm is based on the RLC BLER (Block Error Rate). Retransmitted RLC data
blocks must be sent with the same coding as was used initially.</p>


<p>CS-3 and CS-4 are supported in BSS11.5. See <em>Coding
Schemes CS-3 and CS-4</em> for details.</p>
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