With all the hype created around IMS and LTE, operators have started questioning network vendors if they are supporting RAN specific features for VoLTE. TTI bundling is one of the features among many others that can help VoIP (VoLTE) calls in LTE.
TTI Bundling is LTE feature to improve coverage at cell edge or in poor radio conditions. UE has limited power in uplink (only 23dBm for LTE) which can result in many re transmissions at cell edge (poor radio). Re transmission means delay and control plan overhead which may not be acceptable for certain services like VoIP. To understand TTI bundling one need to have the basic idea of Hybrid Automatic Repeat Request (HARQ) and Transmission Time interval (TTI).
TTI Bundling is LTE feature to improve coverage at cell edge or in poor radio conditions. UE has limited power in uplink (only 23dBm for LTE) which can result in many re transmissions at cell edge (poor radio). Re transmission means delay and control plan overhead which may not be acceptable for certain services like VoIP. To understand TTI bundling one need to have the basic idea of Hybrid Automatic Repeat Request (HARQ) and Transmission Time interval (TTI).
HARQ
HARQ is a process where data at mac layer is protected against noisy wireless channels through error correction mechanism. There are couple of different versions of HARQ but in LTE we have a type known as 'Incremental Redundancy Hybrid ARQ'. When receiver detects erroneous data, it doesn't discard it. On the other hand, sender will send the same data again but this time, with different set of coded bits. The reciever will combine the previously recieved erroneous data with newly attempted data by the sender. This way the chances of successfully decoding the bits improve every time. This will repeat as long as the receiver is not able to decode the data. The advantage of this method is that with each re-transmission, the coding rate is lowered. Whereas in other types of HARQ, it might use the same coding rate in every re-transmission
TTI
TTI is LTE smallest unit of time in which eNB is capable of scheduling any user for uplink or downlink transmission. If a user is receiving downlink data, then during each 1ms, eNB will assign resources and inform user where to look for its downlink data through PDCCH channel. Check the following figure to understand the concept of TTI
Now coming to TTI Bundling ...
HARQ is a process where receiver combines the new transmission every time with previous erroneous data. There is one drawback however, that it can result in delay and too much control overhead in case of poor radio conditions if the sender has to attempt many transmissions. For services like VoIP this means bad end user experience. Well, there is another way- Instead of re-transmitting the erroneous data with new set of coded bits, why not send few versions (redundancy versions) of the same set of bits in consecutive TTI and eNB sends back Ack when it successfully decodes the bits. I hope the figure below will make it clear. This way we are avoiding delay and reducing control plane overhead at mac layer
Good Explanation. Made it very simple to follow.
ReplyDeleteGood explanation. Does TTI bundling happen only in DL ? Or only in UL ? Or is equally applicable to both?
ReplyDeleteGood explanation. Does TTI bundling happen only in DL ? Or only in UL ? Or is equally applicable to both?
ReplyDeleteOk here is what I understand
DeleteSince UE has very limited power in uplink (23dbm LTE) this means that at cell edge there can be many re transmissions in uplink due to poor radio conditions. Re transmission means control plane overhead and specially the delay which is not acceptable for services like VoIP. So if we use TTI bundling with HARQ process we can avoid delay . So the basic idea of TTI bundling is to improve performance of VoIP applications at cell edge and therefore it happens only in uplink
Hope this helps
For TTI Bundling, is there a HARQ ID used for retransmission
ReplyDeleteThanks for the chart on explaining it visually. But will it be better to modify the example of TTI Bundling case to 4 TTI since till R11, 36.321 defined below?
ReplyDelete7.5 TTI_BUNDLE_SIZE value
The parameter TTI_BUNDLE_SIZE is 4.
Or is there any misunderstanding from my side?
Very useful :) Thx
ReplyDeletethank you. nice explanation. Could you please explain how PDCCH usage goed down because of TTI bundling?
ReplyDeleteBeautiful teaching. Many thanks
ReplyDeleteEasy to understand, Thank you!
ReplyDeleteGood explanation. Easy to follow. Thank You
ReplyDeleteGood expaination
ReplyDeleteWhy are the durations of the TTIs all common, or equal? ?There must be some technical reason why they are not varied
ReplyDeleteThis comment has been removed by the author.
ReplyDeletethanks for sharing this valuable information ...
ReplyDeleteSimple and easy to understand.
ReplyDeleteGreat Article. Thank you for sharing! Really an awesome post for every one.
ReplyDeleteHybrid DFT Spread OFDM Digital Filter Multiple Access PONs for Converged 5G Networks Project For CSE
Measuring Web Latency and Rendering Performance Method, Tools, and Longitudinal Data set. Project For CSE
Minimum Connected Dominating Set Under Routing Cost Constraint in Wireless Sensor Networks With Different Transmission Ranges. Project For CSE
Network Slicing Games Enabling Customization in Multi Tenant Mobile Networks Project For CSE
Reinforcement Learning for Self Organization and Power Control of Two Tier Heterogeneous Networks Project For CSE
i was just browsing along and came upon your blog. just wanted to say good blog and this article really helped me.
ReplyDeleteCheap RX Medicine for sale
I’d have to check with you here. Which is not something I usually do! I enjoy reading a post that will make people think. Also, thanks for allowing me to comment!
ReplyDeleteSmall World
Fasttrack.ucoz.net
I am very enjoyed for this blog. Its an informative topic. It help me very much to solve some problems. Its opportunity are so fantastic and working style so speedy.
ReplyDeleteDmt vape pen for sale
Aw, this was a really nice post. In idea I would like to put in writing like this additionally – taking time and actual effort to make a very good article… but what can I say… I procrastinate alot and by no means seem to get something done.
ReplyDeleteMappery.com
Information
I’d have to check with you here. Which is not something I usually do! I enjoy reading a post that will make people think. Also, thanks for allowing me to comment!
ReplyDeleteLudomanistudier.dk
Information
Click Here
Yes i am totally agreed with this article and i just want say that this article is very nice and very informative article.I will make sure to be reading your blog more. You made a good point but I can't help but wonder, what about the other side? !!!!!!THANKS!!!!!!
ReplyDeletebuy weed 24/7
Thank you for very usefull information..
ReplyDeletebuy smart buds online
Superbly written article, if only all bloggers offered the same content as you, the internet would be a far better place..
ReplyDeleteMarijuana for sale in Adelaide
This is a great post. I like this topic.This site has lots of advantage.I found many interesting things from this site. It helps me in many ways.Thanks for posting this again.
ReplyDeletebuy weed online
Great post, you have pointed out some excellent points, I as well believe this is a very superb website.
ReplyDeletemoon rocks for sale
i am always looking for some free stuffs over the internet. there are also some companies which gives free samples.
ReplyDeleteBuy marijuana online
Nice post. I learn something more challenging on different blogs everyday. It will always be stimulating to read content from other writers and practice a little something from their store. I’d prefer to use some with the content on my blog whether you don’t mind. Natually I’ll give you a link on your web blog. Thanks for sharing.
ReplyDeleteCareer.habr.com
Information
Click Here
You should take part in a contest for one of the best blogs on the web. I will recommend this site!
ReplyDeleteFairygodboss.com
Information
Click Here
You have a great blog here! would you like to make some invite posts on my blog?
ReplyDeleteClick Here
Visit Web
Support.advancedcustomfields.com
Hello! I just would like to give a huge thumbs up for the great info you have here on this post. I will be coming back to your blog for more soon.
ReplyDeleteLongisland.com
Information
Click Here
You can easily buy crack cocaine online from our online store and get it safely delivered. We are a renowned supplier of such kind of products.
ReplyDeleteI am often to blogging and i really appreciate your content. The article has really peaks my interest. I am going to bookmark your site and keep checking for new information.
ReplyDeleteOver-blog.com
Website
Your place is valueble for me. Thanks!
ReplyDeleteTrailblazer.me
Information
Click Here
Visit Web
I wish more authors of this type of content would take the time you did to research and write so well.I am very impressed with your vision and insight. Buy liquid ket online
ReplyDeleteYour article has piqued a lot of positive interest.I can see why since you have done such a good job of making it interesting. Latest Indian Defense News Analysis
ReplyDeleteThis is the right blog for anyone who wants to find out about this topic. You realize so much its almost hard to argue with you (not that I actually would want…HaHa). You definitely put a new spin on a topic thats been written about for years. Great stuff, just great!
ReplyDeleteUlule.com
Information
Click Here
Visit Web
This comment has been removed by the author.
ReplyDeletevery interesting post.this is my first time visit here.i found so mmany interesting stuff in your blog especially its discussion..thanks for the post!
ReplyDeleteOrder Adderall 30mg Online