|
|
|
|
|
|
DTCH/DL-SCH PHY processing
Below diagram shows simplistic view of DTCH processing at PHY [36.212:5.3.2].
|
MAC
DTCH
(Transport block)
|
|
|
PHY
CRC
attachment
|
|
Segmentation
& CRC attach
for coding
|
|
Channel
coding
|
|
Rate
matching
|
|
|
Modulation
|
|
To OFDM
modulation
|
|
Fig 1.3.4
Let us look at redundancy added each stage.
For DTCH, 24 bit CRC is added to transport block [36.212:5.3.2.1]. Before channel coding is applied, transport block is segmented if more than 40 bits [36.212:5.1.2]. Each segment is appended with 24 bit CRC, which acts as a code block. DL-SCH use Turbo 1/3 coding [36.212:5.1.3]. Each code block goes through Turbo 1/3 coding and interleaving, generating 3 streams - each of size (code block size + 4) bits. Rate matching collects bits from these streams, forms virtual circular buffer and then - based on redundancy version, resource assignment, and modulation scheme - chooses certain number of (consecutive) bits for transmission. Modulation does not add to overhead.
|
|
|
|
|
|
|
|
|
|
|
