Some questions and answers on LTE Radio Interface - Part1

1. How is the UE getting information that it is scheduled?


By reading the PDCCH (this is valid for both UL scheduling grants and DL scheduling assignments).


PDCCH contains DCI(DL control information), which indicate 3 different messages:-


1. Uplink scheduling grants for PUSCH
2. Downlink scheduling assignment for PDSCH
3. TPC command for PUSCH and PUCCH


2. In which node is PDCP located and what are the tasks of that protocol?


PDCP is located in the eNodeB and handles encryption of user data streams and reordering at handover.


Each radio bearer also uses one PDCP instance. PDCP is responsible for header compression(ROHC Robust Header Compression) and ciphering/deciphering. Obviously header compression makes sense for IP diagram's, but not for signalling. Thus the PDCP entities for signalling radio bearers will usually do ciphering/deciphering only.


3. What is a resource block?


A Resource Block (RB) is a time- and frequency resource that occupies 12 subcarriers (12x15 kHz = 180 kHz) and one slot
(= 0.5 ms). RBs are allocated in pairs by the scheduler (then referred to as Scheduling Blocks).



4. What are two radio interface solutions that increase the spectrum efficiency ?


Higher order modulation:-LTE support all types of modulation schemes like QPSK,16 QAM, 64 QAM that results in high data rate
MIMO:- MIMO increase data rate by doubles in 2*2 and 4 folds in 4*4 case.


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