3GPP Long Term Evolution

1. 23/7/2015 3GPP Long Term Evolution (LTE): Transport Block Size and Code rate
http://4g-lte-world.blogspot.mx/2012/12/transport-block-size-code-rate-protocol.html 1/6
LTE is a standard for wireless communication based on 3GPP technologies, promising high­speed data for mobile phones and data terminals
3GPP Long Term Evolution (LTE)
Home LTE Frequency Bands 3GPP releases summary Quiz Useful Links About Me
Sunday, December 23, 2012
Transport Block Size and Code rate
Since the size of transport block is not fixed, often a question comes to mind as to how transport block size is calculated in LTE.
Back Ground
If we only consider "Uplink direction" and we assume that the UE is already attached to the network, then data is first received by PDCP
(Packet data compression protocol) layer. This layer performs compression and ciphering / integrity if applicable. This layer will pass on
the data to the next layer i.e. RLC Layer which will concatenate it to one RLC PDU.
RLC layer will concatenate or segment the data coming from PDCP layer into correct block size and forward it to the MAC layer with its
own header. Now MAC layer selects the modulation and coding scheme configures the physical layer. The data is now in the shape of
transport block size and needed to be transmitted in 1ms subframe.
Now how much bits are transferred in this 1ms transport block size?
It depends on the MCS (modulation and coding scheme) and the number of resource blocks assigned to the UE. We have to refer to the
Table 7.1.7.1­1 and Table 7.1.7.2.1­1 from 3GPP 36.213
Lets assume that eNB assigns MCS index 20 and 2 resource blocks (RBs) on the basis of CQI and other information for downlink
transmission on PDSCH. Now the value of TBS index is 18 as seen in Table 7.1.7.1­1
Transport Block size
Recent Posts Widget
RSRP, RSSI and
RSRQ
Nokia Networks
Technology Vision
2020
Overview of LTE 3GPP
releases
Recent Posts
Join this site
with Google Friend Connect
Members (207) More
»
Already a member? Sign in
Followers
5 Más Siguiente blog»

2. 23/7/2015 3GPP Long Term Evolution (LTE): Transport Block Size and Code rate
http://4g-lte-world.blogspot.mx/2012/12/transport-block-size-code-rate-protocol.html 2/6
After knowing the value of TBS index we need to refer to the Table 7.1.7.2.1­1 to find the accurate size of transport block (Only portion
of the table is shown here while for the complete range of values refer to 3gpp document
36.213 http://www.quintillion.co.jp/3GPP/Specs/36213­920.pdf)
Now from the Table 7.1.7.2.1­1 the value of Transport block size is 776 bits for ITBS = 18 and NPRB=2
In simple words, code rate can be defined as how effectively data can be transmitted in 1ms transport block or in other words, it is the
ratio of actual amount of bits transmitted to the maximum amount of bits that could be transmitted in one transport block
code rate = (TBS + CRC) / (RE x Bits per RE)
where
TBS = Transport block size as we calculated from Table 7.1.7.2.1­1
CRC = Cyclic redundancy check i.e. Number of bits appended for error detection
RE = Resource elements assigned to PDSCH or PUSCH
Bits per RE = Modulation scheme used
While we know the values of TBS, CRC and bits per RE (modulation order), it is not easy to calculate the exact amount of RE used for
Code Rate
29,282
Pageviews last month
Live Traffic Feed
Live Traffic Feed
Real-time view · Get Feedjit
A visitor from Chennai,
Tamil Nadu viewed
"3GPP Long Term
Evolution (LTE): Primary
and secondary
synchronization signals
(PSS & SSS) in LTE" 9
hrs 42 mins ago
A visitor from India
viewed "3GPP Long
Term Evolution (LTE):
System information block
2 (SIB2) in LTE" 9 hrs 43
mins ago
A visitor from India
viewed "3GPP Long
Term Evolution (LTE):
Master Information Block
(MIB) in LTE" 9 hrs 43
mins ago
A visitor from Moscow,
Moscow City viewed
"3GPP Long Term
Evolution (LTE): ICIC
and eICIC" 9 hrs 45 mins
ago
A visitor from Moscow,
Moscow City viewed
"3GPP Long Term
Evolution (LTE)" 9 hrs 45
mins agoA visitor from Kaluga
viewed "3GPP Long
Term Evolution (LTE):
System information block
► 2015 (5)
► 2014 (1)
► 2013 (5)
▼ 2012 (20)
▼ December (1)
Transport
Block
Size and
Code
rate
► November (1)
► October (4)
► July (1)
► June (7)
► May (6)
Blog Archive
The views expressed in
this blog are my own and
in no way reflect the
views of my employer. I
hope this sharing of
knowledge will not only
be beneficial to others,
but a great learning
experience for myself
too. This is just to get a
much better insight of
the LTE world.
Adnan Basir
About This Blog

3. 23/7/2015 3GPP Long Term Evolution (LTE): Transport Block Size and Code rate
http://4g-lte-world.blogspot.mx/2012/12/transport-block-size-code-rate-protocol.html 3/6
Posted by Adnan Basir
PDSCH or PUSCH since some of the REs are also used by control channels like PDCCH, PHICH etc
In our case, lets assume that 10% of RE's are assigned for control channels then
TBS = 776
CRC = 24
RE = 2 (RB) x 12 (subcarriers) x 7 (assuming 7 ofdm symbols) x 2 (slots per subframe) x 0.9 (10% assumption as above) = 302 REs
Bits per RE = 6 (Modulation order from table 7.1.7.1­1)
So
code rate = (776 + 24) / (302 * 6 ) = 0.4
+5 Recommend this on Google
Replies
Reply
18 comments:
Venkat December 29, 2012 at 1:02 PM
How is CRC bits caliculated to 24 bits in above example? please put some light on this as well.
Reply
Adnan Basir December 31, 2012 at 8:44 AM
Hi Venkat please refer to 3gpp 36.212 section 5.1.1 for details
villi johns February 10, 2013 at 2:28 AM
check here you will get some thing great lte topics i got very good help from him to complete my lte project
http://www.teletopix.org/category/4g­lte
Reply
Srikanto Bormon June 23, 2013 at 11:01 PM
I like it extremely varied and provide information that helps you in finding new information. pleased to meet­ Transportation
Warfare
Medical
Clothing
Communication
Entertainment
Electric
Financial
Food Preparation
Green Technology

4. 23/7/2015 3GPP Long Term Evolution (LTE): Transport Block Size and Code rate
http://4g-lte-world.blogspot.mx/2012/12/transport-block-size-code-rate-protocol.html 4/6
Replies
Reply
Replies
Reply
Software
Instruments
Office
Reply
Rachel Johnson October 13, 2013 at 12:06 PM
Please visit website www.telecomtube.com
for telecom jobs. Thanks
Reply
Tetru Eunor November 18, 2013 at 4:32 PM
I don't get it. Seriously . I don't get it.
Reply
Adnan Basir November 25, 2013 at 11:23 AM
what was not clear toyou ? :)
Tetru Eunor December 23, 2013 at 5:10 PM
Is the coding rate fixed ?
I mean for different CFI and different transmission modes you get different number of REs per RB hence different
coding rate.
So the coding rate is not fixed.
孟祥雲 October 22, 2014 at 4:58 AM
This comment has been removed by the author.
孟祥雲 October 22, 2014 at 5:01 AM
I found a helpful site for details about CFI
http://www.sharetechnote.com/html/Handbook_LTE_CFI.html
It mentions that the number of REs used for control channel is not fixed.
The ratio might be different according to your scenario. (i.e. system bandwidth etc.)
While in some cases, the CFI = 1 makes the REs / PRB = 150/(84x2) = 0.8928 ... , so the assumption of 10% ratio
reserving for control channels is approximately correct in most cases.
Finally, the coding rate might not be fixed with this consideration.
Hap Rojas December 2, 2013 at 2:19 PM
How does a packet travels between the internet gateway ­ PGW ­... to the UE. Since all is managed by IP how does the headers
change along the way.
Reply
Ron February 24, 2014 at 4:55 PM
When a location update procedure is carried out, PDP­context is activated.
The headers change all the way because the IP address of different entities at different layers is different. Thus, MME
for example would have 2 unique IP address, one on layer 2 and one on layer 3, and each entity has its unique IP
address.
It is due to this reason, the headers change when a packet is transferred from one entity to the other... (The packets
travels in tunnels. AT the end point of the tunnel, due to PDP context, corresponding to the next tunnel's IP
destination, the values are changed.)
Please correct me if wrong

5. 23/7/2015 3GPP Long Term Evolution (LTE): Transport Block Size and Code rate
http://4g-lte-world.blogspot.mx/2012/12/transport-block-size-code-rate-protocol.html 5/6
Newer Post Older PostHome
Subscribe to: Post Comments (Atom)
Enter your comment...
Comment as: Google Account
Publish
Preview
Create a Link
Bernoulli's Corner March 6, 2014 at 4:12 PM
Reply
This comment has been removed by the author.
Mark S March 6, 2014 at 4:15 PM
Can anyone explain why Itbs = 6 and Nrb = 1, the TB size is larger than the surrounding TB sizes including Nrb=2. This doesn't
make any sense. It is also exactly the same size as Itbs=16. Could this be a typo?
Reply
Nitesh April 7, 2014 at 6:53 PM
Great!
Reply
Luv Singh May 29, 2014 at 8:43 AM
why MCS 29 , 30 & 31 are needed ??
Reply
Álvaro Durán Martínez June 20, 2014 at 2:20 AM
Great summary
Reply
Akbar Birbal May 23, 2015 at 4:15 PM
Watch free Sports Channels online | USA Tv Channels | UK Tv Channels | Spain Tv Channels | Watch USA Tv Series online |
Adult 18+ Tv Channel | Watch High Quality Live Streaming online
www.nowwatchtvlive.me
www.tvtoss.com
www.zigstream.com/
www.128kbps.me
Reply
Links to this post
You may reproduce the content of this website only if you provide this website as original source. Awesome Inc. template. Powered by

6. 23/7/2015 3GPP Long Term Evolution (LTE): Transport Block Size and Code rate
http://4g-lte-world.blogspot.mx/2012/12/transport-block-size-code-rate-protocol.html 6/6