this is a new episode in our series 5d explained in this video we discussed a
blink data transmission in 5g new radio
we will look at the uplink shared channel chain which includes LDPC coding
the physical uplink shared channel chain including the optional transform
precoding and the different types of PD SDH mapping the uplink share channel or
ul SCH is the channel that carries user data it has a structure very similar to
the downlink share channel with CRC code block segmentation the use of LDPC a key
difference with LTE and read matching the output of a coding chain is a code
word contrary to the downlink share channel
it is limited to four layers which means that uplink transmissions always use a
single code word the coded data is then mapped to the physical uplink channel or
PU SDH here you can see how every stage of the uplink shared channel processing
is mapped to functions it mathworks fuzzy toolbox you can recognize CRC
encoding code block segmentation LDPC coding and rate matching here again the
chain is similar to the downlink chain with two notable differences the first
one is the presence of transform precoding a DFT operation which is what
turns OFDM modulation into single carrier OFDM or
SC OFDM sometimes known by another name DFT spread OFDM or DFT as OFDM transform
precoding is optional which means that the uplink supports both regular OFDM
and as see OFDM the second difference is that pre coding is specified on the
uplink and we will see it can be of two types I just mentioned transform
precoding is an optional step scfdma provides
nor PAPR which means that less back off is needed on the power amplifier
this helps with you ease that are in larger cells or have limited power
modulation schemes in the OFDM case are the same as for the downlink ranging
from QPSK to 256 QAM when transport recording is enabled an additional
modulation scheme PI over to BPSK is also available to help with very low SNR
transmission in a large cell or with no power layer mapping on the uplink uses
the same mechanism as on the downlink mechanism that is discussed in another
episode of this 5g explained series with one big difference there can be a
maximum of 4 layers for that reason the uplink always includes a single codeword
the single codeword is mapped to n layers with ant between 1 and 4 by
mapping input blocks of n input bits to n layers as shown here pre coding is the
operation mapping layers to antenna ports as mentioned earlier there are 2
precoding modes codebook based and non kobu B's precoding for no include
book-based precoding the ue determines the precoding matrix based on
measurements it performs on downlink signals typically the channel State
Information reference signals for codebook base precoding the ue simply
applies the precoding matrix specified by the gene would be here we have a
closer look at the non codebook base pre coding scheme this is the mode where the
ue makes its own decision about which precoding matrix to use as just
mentioned the ue determines a suitable precoding matrix from LCS IRS
measurements it then applies the proposed precoding matrix to the SRS or
sounding reference signal the gene will be then informs the UE of which subset
of the beamforming vectors can use finally the UE can apply
selected beamforming vectors - psdh transmission in summary in that mode
where the you it does propose a precoding matrix the gene will be can
still veto some of the beamforming vectors which will reduce the number of
layers for transmission for codebook base precoding the gene would be
determines the precoding matrix based either on downing measurements for TDD
or on uplink measurements of sounding reference signals he then sends the pre
coding information to the UE in the downlink control message for uplink and
the UE simply looks up the matrix in a series of tables the different tables
for different number of layers as well as for transmission with or without
transform precoding the whole process of channel sounding and precoding is
described in detail in another episode of this 5g explained video series Buse H
symbols are mapped to the resource grid using one of two mapping types a or B
these are the same mapping types as for PD SC H on the downlink mapping a is
meant for allocations that start at the beginning of a slot the demodulation
reference signal is then mapped to symbol 2 or 3 mapping type B is meant
for locations that start partway through the slot in which case the dmrs is
mapped to the first symbol of the allocation this concludes this episode
of the 5g explain video series on uplink data transmission