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  • LTE Physical layer Interview Que and Ans 21-30


    21. Radio Channel Processing step?

    Ans. This section describes a well-known structure, relevant to a couple of physical channel.
         The base-band signal representing a downlink physical channel is described in terms of the subsequent steps:
    • scrambling of coded bits in each of the code words to be transmitted on a physical channel
    • Modulation of scrambled bits to generate complicated values for modulated symbols
    • Mapping of the complex-valued modulation symbols onto one or numerous transmission layers
    • Pre coding of the complex-valued modulation symbols on every layer for transmission on the antenna ports
    • Mapping of complex-valued modulation symbols for every antenna port to resource elements
    • Generate complex-valued time-domain OFDM signal for every antenna port

    Radio-Channel-Processing-step-in-lte

    22. Describe Master Information Block (MIB)? System Frame Number (SFN) and PHICH?

    Ans. For more information of MIB click here and read Que.12 Answer.
    For more information of SFN click here and read Que.15 & Que.19 Answer.
    For more information of PHICH click here and read Que.30 Answer.

    23. Describe PBCH and its position in Frame Structure and what Information Carried by PBCH?

    Ans. PBCH stands for Physical Broadcast Channel. In lte PBCH have fixed position on Tslot 1 starting 4 ofdm symbols.
        Total 240 bits PBCH reserve in Downlink Frame Structure.
        PBCH carry MIB information.
        PBCH present in every radio frame, sub-frame 0 and Tslot 1.

    24. Describe PCFICH? its position in Frame Structure and Information Carried by PCFICH?

    Ans. PCFICH stands for Physical Control Format Indicator Channel.
    PCFICH provides the information how many ofdm symbols using by PDCCH.
    It works on Resource Element Group [REG].
    1 REG == 4RE
    if PDCCH reserve 1 ofdm symbol than PCFICH have 4 REG. Location at PRB 0,1,3 and 4th.

    25. Describe PDCCH? its position in Frame Structure and Information Carried by PDCCH?

    Ans. PDCCH stands for Physical Downlink Control Channel.
    PDCCH position may varying as per traffic available on eNodeB
    For e.g. in 1.4 MHz PDCCH can use ofdm symbols 1, 2, 3.
    Reaming 3, 5,10,15,20 MHz bandwidth PDCCH can use ofdm symbols 0, 1, 2.
    PDCCH present in every frame every sub frame starting ofdm symbols.

    26. Describe PDSCH? its position in Frame Structure and Information Carried by PDSCH?

    Ans. PDSCH stands for Physical Downlink Shared Channel.
    PDSCH present in every radio frame, every sub-frame.
    PDSCH carry user related data.

    27. Define PUCCH? its position in Frame Structure and Information Carried by PUCCH?

    Ans. PUCCH stands for Physical Uplink Control Channel.
    PUCCH-and-PUSCH-in-lte
    Frame time and slot time in Uplink is the same as the downlink. And the useful resource block structure is also equal both in uplink and downlink. 7 symbols in one slot is equal in both uplink and downlink.

    A little bit of differences you would note would be the location of the each channel. Normally in downlink case, a channel has a tendency to lie across the entire bandwidth but the channels within the uplink slot seem to be more localized. For example, PUCCH is located most effective at the lowest and highest result in frequency domain and reference indicators additionally localized in time area or both time domain and frequency area.

    28. Define PUSCH? its position in Frame Structure and Information Carried by PUSCH?

    Ans. PUSCH stands for Physical Uplink Shared Channel.
    The above Que.27 image had shown the PUSCH position in uplink frame structure.
    PUSCH carry user data in uplink direction.
    ENodeB give resources to ue on DCI format 0, ue use allocated resource for transmitting their data in uplink direction.

    29. What Modulation Technique are using in all Physical-Channel?

    Ans. Modulation techniques are provided in DCI in downlink direction from eNodeB to ue.
    And UCI in uplink direction from UE to ENodeB.
    Total DCI formats are using Pdcch channel and UCI are using in Pucch channel.

    30. What is REG?

    Ans. The Resource Element Group is a group of 4 consecutive resource elements.
    PCFICH, PDCCH and PHICH resource elements are counts by how many REG present in a radio frame.

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