this is a new episode of our series 5g
explained in this video we discuss
initial acquisition procedures including
cell search decoding of the broadcast
channel and a random access channel we
look at the phases of cell search and
the role of the primary and secondary
synchronization signals then we look at
P BCH decoding to retrieve the master
information block and how this procedure
supports beam sweeping recovering the
SSB time index is a crucial step in
decoding the MIB we will discuss the
next piece of information aue accesses
after the MIB the system information
block type 1 or si b1
finally we will look at the random
access channel and procedure the
synchronization signal block provides
the ue with the ability to perform frame
and simple synchronization which means
the ue can discover the presence of a
downlink 5g signal and then start making
sense of it after presence and timing
have been established the ue decodes the
broadcast channel and reads the content
of a master information block a sight
piece of information that can be
gathered is the SSB index which helped
determine a suitable beam for
communication between the gene OB and ue
i would use illustrations from the NR
synchronization procedure example in
MathWorks 5g toolbox to explain this
process in detail as we saw in the
episode of is 5g explained series about
the synchronization signal block there
are three possible primary
synchronization sequences the ue
typically runs 3 correlators in parallel
to detect one of the three possible
sequences once a peak is detected two
pieces of information have been gained
which PSS is being transmitted and the
timing of ESS B note that at this point
gue cannot tell which one of yes SB
occurrences it has detected this will
come later
here we can see that the Yui has been
able to detect all 8 SS bees that were
sent although the second one is the one
with the highest SNR it will be selected
for the rest of the procedure also the
PSS corresponding to index 0 in blue is
clearly recognized as the one
transmitted in this cell the other 2 in
orange and red do not show any peek
there are three hundred thirty six
possible secondary synchronization
sequences but at this point the timing
of the SSS is known so those
correlations must be run only once this
stage determines which SSS was sent the
main piece of information gathered at
the env stage is the physical cell ID
which is three times the sss plus the p
SS a value between 0 and 1007 this step
shows a very clear peak for sequence
number 34 as a result the physical cell
ID in this cell is 3 times 34 + 0 or 102
- the matlab code shows the simple
process to determine the SS s there's a
loop that tries out all 336
possibilities and identifies the SS s
with maximum correlation each SSB comes
with a realization of the physical
broadcast channel and associated dmrs
the knowledge of cell ID is important to
demodulate the BCH button enables the UE
to generate the right dmrs for channel
estimation once the BCH has been
demodulated the master information block
and the SSB index unknown the next few
slides explained the different steps for
BCH demodulation each occurrence of a PB
CH has a different dmrs which depends on
the SSB block index the ue receiver
hence tries out all 4 or 8 possible
versions of a DMR s and determines which
one was sent for
SSB received in doing so the Yui
determines the SSB index if they are up
to eight possible occurrences as you may
remember from the episode about the
synchronization signal block for carrier
frequency under 725 gigahertz or fr1 it
can be up to 8 code currencies while
that number is 64 for fi2 or a
millimeter wave transmission this means
that another piece of information is
needed to uniquely determine the SSB
index for fi2 transmission as you may
remember from the video of this 5g
explained series about synchronization
signal block for far to the MIB carries
3 bits for time index those 3 bits along
with the knowledge of which dmrs was
used let the UE determine one of 64
possible SSB indexes here we see a more
detailed view of the procedure thus far
dmrs search leads to channel estimation
and noise estimation along with the SSB
indexed or 3 bits thereof depending on
the carrier frequency the SSB resource
elements are equalized and decoded
yielding the master information block
you can find a complete MATLAB code for
this procedure as part of math words 5g
toolbox although the standard doesn't
mandate it explicitly
it is widely expected that each SSB
occurrence will be being formed with a
different pattern this enables the
genome B to scan the space and target
the energy in successive directions
remember that with millimeter wave
frequencies beams become narrower but
the 5g standard specifies up to 64
possible occurrences instead of 8 this
means that it is possible to use a high
directivity antenna pre coder to extend
PVC edge coverage here a few blocks are
shown each targeting a few degrees in
spades
the code on the right shows how to
generate those beamforming vectors with
MathWorks phaser a system toolbox notice
I have a more concrete look at the
process of BCH decoding and beam search
with an example built with math works
well G toolbox we artificially paused
the simulation after each SSB
transmission as it otherwise would be
too fast to command alive you can see
the gene OB with an array of transmit
antenna heat transmitted the first
occurrence of SSB with a beam toward the
size of a space in front of it the UE is
located at around 20 degrees of the
horizontal but we assume there is no
direct line-of-sight the only path
between the genome B and the UE is that
one bounce of the wall shown in blue the
urea received this first transmission
with low energy the second transmission
leads to a similar result a correlation
amplitude and so do the following ones
until the seventh transmission where the
main beam covers the location of the
reflection in this case the received
energy is much higher and once all
transmissions are complete the UE can
clearly identify the SSB with the most
suitable beamforming as a side note
we'll talk about Raj in a few slides but
it is worth noting at this point that if
the Eno The Associated occasions or
transmission time opportunities with a
particular SSB index it can expect Raj
that are received at a particular time
instant to be coming from a ue had
picked that SSB index as the strongest
as the G nobody knows which mean forming
was used for that particular s has been
indexed you can perform receive
beamforming using the same pattern at
that given time instant to maximize the
probability of receiving the ranch
this can be seen as the initial step in
establishing beamforming
between the Gino B and the UE the next
piece of information the UE looks for is
the system information block one cause
si b1 as we saw in the episode about
synchronization signal block the master
information block includes all elements
needed to locate and decode the SI b1
note that the si b1 is carried by the dl
SCH which is the same channel that
carries data packets
once the UE has decoded the si v1 it has
all the information it needs to request
access to the network the other random
access procedure there are two possible
lengths for the ROG preamble the long
preamble at 839 and a short one at 139
the long preamble is used for these
large cells as the timing uncertainty is
larger because of longer propagation
delays left for the long preamble is
limited to subs 6 gigahertz 5g
transmission the short preamble applies
to all possible 5g frequencies we're not
going into all the detail of a different
ROG formats here but it is good to be
aware that different formats exist which
vary in number of OFDM symbols cyclic
prefix length and God times the
information about which format to use is
carried by the SIV one we want to
conclude this section about acquisition
procedures with a simplified overview of
the random access procedure the ue makes
its presence known to the network by
sending a Raj the G note B replies by
sending a Raj access response
carried by the PDS eh it contains a
timing advance for the UE to adjust its
timing a temporary rnt I or Radio
Network temporary identifier and a
scheduling grant for the UE to
acknowledge the access response
the Yui is able to discover and decode
the access response because their
response uses a reserved rnt I called
the RA rnt I referred to the episode
about downing control information for a
discussion about the use of our NT is to
identify control information at this
point there could be several us that
sent the same request at the same time
and the Geno be can't tell which ue or
you ease it is talking to so the
response to the ROG access response is a
contention resolution message which is
sent via the PU SCH or data carrying
channel using the scheduling around
provided in the access response in the
final step the Gino B acknowledges the
contention resolution message by sending
back the device identity in a message
encrypted with the temporary RN TI the
UE that recognizes its device identity
knows that it has been acknowledged by
the G note B and uses the temporary RN t
i from now on this concludes this
episode of the 5g explained series on
initial acquisition procedures