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PUCCH Format
PUCCH (Physical Uplink Control Channel) carries a set of information called "UCI(Uplink Control Information)". (This is similar to PDCCH which carries DCI (Downlink control information)". Depending on what kind of information the UCI in PUCCH carries, PUCCH is classified into various formation as follows.
You may see a lot of different way of describing these formats depending on situation. It may be confusing at the beginning, but it would be better for you to get familiar with those different way of expression. You may want a single big table which has every details, but you will notice that those big table would be even more confusing.
So I will try to describe these formats in this page in various ways with a little bit different focus. You will see all of these are saying the same thing.. but in a little bit different perspective.
In 3GPP 36.213, section 10.1 UE procedure for determining physical uplink control channel assignment. The PUCCH format is summarized as follows.
- HARQ-ACK using PUCCH format 1a or 1b
- HARQ-ACK using PUCCH format 1b with channel selection
- Scheduling request (SR) using PUCCH format 1
- HARQ-ACK and SR using PUCCH format 1a or 1b
- CQI using PUCCH format 2
- CQI and HARQ-ACK using PUCCH format
- 2a or 2b for normal cyclic prefix
- 2 for extended cyclic prefix
Following is a tabular format of description of specification described above in 3GPP specification (36.213-10.1.1 PUCCH format information).
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PUCCH Format
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UCI information
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| Format 1 |
Scheduling Request (SR) |
| Format 1a |
1-bit HARQ ACK/NACK with/without SR |
| Format 1b |
FDD (1CC)
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2-bit HARQ ACK/NACK with/without SR (This is for MIMO, 1 bit for each transport block)
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FDD (2CC)
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4-bit HARQ ACK/NACK with channel selection |
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TDD (1CC)
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4-bit HARQ ACK/NACK |
| Format 2 |
CQI (20 coded bits) |
| Format 2 |
CQI and 1 or 2 bit HARQ ACK/NACK - 20 bits - Extended CP only
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| Format 2a |
CQI and 1 bit HARQ ACK/NACK - (20 + 1 coded bits)
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| Format 2b |
CQI and 2 bit HARQ ACK/NACK - (20 + 2 coded bits)
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| Format 3 |
FDD(up to 5CC)
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up to 10 bit HARQ ACK |
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TDD(up to 5CC)
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up to 20 bit HARQ ACK |
| Format 3 |
FDD(up to 5CC)
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11 bit corresponding to 10 bit HARQ ACK and 1 bit positive/negative SR
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TDD(up to 5CC)
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21 bit corresponding to 20 bit HARQ ACK and 1 bit positive/negative SR
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| Format 3 |
HARQ-ACK, 1-bit positive/negative SR (if any) and CSI report(s).
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| Format 4 |
more than 22 bits of UCI including HARQ-ACK, SR (if any) and periodic CSI report(s) (if any).
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| Format 4 |
more than one CSI report and SR (if any).
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| Format 5 |
more than 22 bits of UCI including HARQ-ACK, SR (if any) and periodic CSI report(s) (if any).
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| Format 5 |
more than one CSI report and SR (if any).
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Following is another tabular format of description of specification, this is intended to give you idea on the contents of HARQ and CSI.
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PUCCH Format
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Number of Bits
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UCI information
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| Format 1 |
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No Ack/Nack, SR only |
| Format 1a |
1
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SISO Ack/Nack |
| Format 1b |
FDD (1CC)
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2
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MIMO Ack/Nack |
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FDD (2CC)
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4
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MIMO Ack/Nack |
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TDD (1CC)
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4
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MIMO Ack/Nack |
| Format 2 |
20
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CSI, no Ack/Nack |
| Format 2a |
21
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CSI + SISO Ack/Nack |
| Format 2b |
22
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CSI + MIMO Ack/Nack |
| Format 3 |
FDD(up to 5CC)
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10
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Ack/Nack (up to 5CC) |
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TDD(up to 5CC)
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20
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Ack/Nack (up to 5CC)
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| Format 3 |
FDD(up to 5CC)
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11
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Ack/Nack (up to 5CC) + SR |
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TDD(up to 5CC)
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21
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Ack/Nack (up to 5CC) + SR |
NOTE : 'Number of Bits' here the bit length after PUCCH channel coding. In short, the number of ACK/NACK bits does not change by channel coding process, but the number of CSI (e.g, CQI) increases to 20 bits. See PUCCH Channel Coding page.
NOTE : Regarding how each of these format are utilized and configured in signaling, check out this tutorial of Amarisoft TechAcademy.
Important Questions about PUCCH
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Overall logics about PUCCH was relatively simple at Rel 8, but as it gets evolved the rule gets complicated and a lot of confusions start arising. A couple of questions you have to keep asking yourself about PUCCHs are
- At a certain subframe, does UE has to transmit PUCCH or PUSCH ?
- If UE has to transmit PUCCH, what kind of PUCCH format it has to transmit ? what kind of information it should carry ?
Question is simple,but the answer would get different depending on situation. To figure out the correct answer to these questions, you need to have clear understanding not only on HARQ mechanism, but also on CSI mechanism. HARQ mechanism is relatively simple, but CSI mechanism is pretty complex.. and it gets extremely complicated as it evolves
to Rel 9,10,11.
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Physical Layer Configuraion for PUCCH
If you are mostly working on higher layer signaling (e.g, RRC or NAS) and has to configure PUCCH details in RRC message, you would have some difficulties of understanding/setting physical layer configuration of PUCCH. Following topics would help you in this aspect.
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