Please help with my doubt.
Assume there is initial access of UE to the network. At step 2 of RA Procedure eNB sends RA Response. RAR is transmitted on PDSCH. To let UE know about that transmission eNB must configure control channel. As far as I can see, either DCI format 1A or DCI format 1C might be used for that purpose. Is there more precise criteria, which format should be used for scheduling of RAR?
Thanks in advance.
Format 1C is not used for RARs; it's mostly intended for MCCH (Multicast Control Channel) information.
Thanks for reply. Could you please suggest where to look for more explanations? It's hard for me to figure out directly from specification. In the same time, there are some books. For example, "LTE for 4G mobile broadband" by Farooq Khan at p. 384 states:
"DCI format 1C is used for highly compact assignments where transmissions on DL-SCH use QPSK modulation and distributed virtual resource blocks. This format carries scheduling assignment of system information (SI), random access response and paging. "
Next, in "LTE – The UMTS Long Term Evolution" by Stefania Sesia et al. at p. 196 it is stated:
DCI Format 1A is used for compact signalling of resource assignments for single codeword PDSCH transmissions, and for allocating a dedicated preamble signature to a UE for contention-free random access.
DCI Format 1C is used for very compact transmission of PDSCH assignments. When format 1C is used, the PDSCH transmission is constrained to using QPSK modulation. This is used, for example, for signalling paging messages and some broadcast system information messages.
Then, in "4G: LTE/LTE-Advanced for Mobile Broadband" by Erik Dahlman, Stefan Parkvall, Johan Skold at p. 181 we find:
DCI format 1C is used for various special purposes such as random-access response, paging, and transmission of system information. Common for these applications is simultaneous reception of a relatively small amount of information by multiple users.
I should not say this information is controversial, but its definitely far from being clear and easy to understand. So still I wonder, whether both DCI 1A and 1C can be used for RAR scheduling at eNB discretion, or there are some more restriction, which escaped from my attention.
Please comment. Thanks in advance.
Well, seems I've found something. As per
TS 36.523-3 V8.1.0, p. 41
Two types of DCI combinations are
identified as default formats for the signalling and protocol test.
DCI combination 1
format 1A, resource allocation type 2 localised, for all DL scheduling types.
DCI combination 2
format 1C, resource allocation type 2 distributed, for scheduling of
format 1 resource allocation type 0, for UE dedicated scheduling.
Because document itself is titled as "User Equipment (UE) conformance specification; Part 3: Test Suites", I guess, both combinations are correct, while preference of one over another left open.
My response was based on the current version of 36.212, where the formats are described. Section 18.104.22.168.3: "DCI format 1A is used for the compact scheduling of one PDSCH codeword and random access procedure initiated by a PDCCH order." Section 22.214.171.124.4: "DCI format 1C is used for very compact scheduling of one PDSCH codeword and notifying MCCH change." I suppose technically the one PDSCH codeword could be a RAR, but I don't think that's the intent.
Hello, I also has a doubt.
How to decide DCI format1A or DCI format1C when scheduling System information Blocks?
CRC of DCI formt1a, DCI format 1c can be scrambled by SI-RNTI, and I think both of them can schedule SI messages. But which one can be choosed when UE transimit SI messages?
If DCI format0 is used, how many PRBs assigned to transmit SI messages in PDSCH?
Thanks in advance!
System Information (SI) messages are only sent on the downlink; they are never sent on the uplink.