I assume that you're looking for a basic answer, rather than a detailed technical description of how these values are computed. CQI is Channel Quality Indicator. PMI stands for Pre-coding Matrix Indicator, and RI is Rank Indicator. These three values are computed on the fly in LTE systems and used to try to optimize resource allocation among the various user end devices (UEs) that are requesting service. More efficient use of resources means that a system can serve more users at once. Therefore, it is highly desirable that the values reflect as accurately as possible the quality of the LTE access channel, that is, the accuracy of the transfer of bits in each direction over the wireless (RF) channel. Constraints on the processor power available to compute these values and constraints on the length of time the values remain accurate (ie, limits to the delay in getting a value) make it difficult to optimize resource allocation. The computation becomes more complex if the UE is moving, since the RF conditions will change as the user moves and will changes faster the faster the user moves (walking vs driving, say).

There are different proposals for computing these values, and you should refer to the appropriate LTE standard or one of the various papers that describe methods of computation for more information.

One paper that I found while Googling this topic was by Stefan Schwarz, Christian Mehlfuhrer and Markus Rupp, Calculation of the Spatial Preprocessing and Link

Adaption Feedback for 3GPP UMTS/LTE. The pdf is available on line (http://tinyurl.com/m43rwm2). Their article describes their particular computation method, but gives some information on the general technique as well.

see the following

http://www.sharetechnote.com/html/Handbook_LTE_CQI_PMI_RI_ReportingConfiguation.html

Hi Leigh,

Thanks for quick response. Can you please explain how these values (cqi,pmi and ri will be decoded on eNB side ). I think UE report all these three value in 20 bits, which we see in eNB side on L1 layer but how these three parameter used to be extracted from this 20 bit value.

Thanks in advance

Hi, Abhishek,

I am not up on the details of how these values are computed and encoded for LTE. I will say however, based on my experience with the encoding of similar QoE values in GSM and CDMA: you can't take the values off the bit stream at face value. Aside from parsing the bit stream, you may need to add a constant added or the values might be difference values or something. So make sure you understand what the numbers represent (RSSI or whatever) before you try to use them. Seddick's note above looks like a good place to start. Good luck!

These parameters typically calculated on the UE and transmitted on the PUCCH (see size of bits based on using Format 1/1a/1b or Format 2/2a/2b in TS 36.211) are used for closed-loop link adaptation. Initial investigation looked at several algorithms to implement link evaluation, like Effective Exponential SNR Mapping (EESM), Mean Instantaneous Capacity (MIC), Received Block Information Rate (RVIR) and Mean Mutual Information per Bit (MMIB). See:

[1] "PER Prediction for PHY Mode Selection in OFDM Communication Systems", Proc of Globecom, Nov. 2003;

[2] 3GPP TR 25.892, v1.10 (2004-03);

[3] Ericsson, "Effective SNR mapping for modeling frame error rates in multiple-state channels," 3GPP2-C30-20030429-010, April 2003;

[4] Ericsson, "System-level evaluation of OFDM further consideration," 3GPP TSG-RAN-1 35 Document R1-03-1303, Lisbon, Portugal, Nov 2003.

Hi,

In PUCCH Format 2/2a/2b CSI (CQI,PMI,RI) bits are coded by Reed-Muller code into 20bits per subframe. In the book 'LTE-The UMTS Long Term Evolution: Stefania Sesia, Issam Toufik, Matthew Baker,' I read that in PUCCH Format 2 extended CP subject, the largest number of information bits supported by the block code is 13, corresponding to 11 CSI bits and 2 ACK/NACK bits (for two codeword transmission in downlink).

The length of the CQI is 4bit, RI 1or 2 bits(depending on number of transmission layer and eNb antenna ports), PMI is 2,1 or 4 bits (depending on rank and number of eNb antenna ports) am I true?

I want to learn how max number of CSI bits can be 11 bit? and is this value valid for only extended CP?

Thanks in advance.

CQI,PMI and RI in LTE and 5G are used in link adaptation to update the modulation and the coding scheme and the format of each transport block TB.