Top 5 LTE Interview Questions & Best Answers

00:27:26
https://www.youtube.com/watch?v=GLBdbv7ZuRg

Ringkasan

TLDRIn this video, the speaker shares insights and tips on how to excel in job interviews, particularly focusing on technical interviews related to LTE (Long-Term Evolution) networks. Drawing from a decade of experience conducting interviews, the speaker highlights the importance of distinguishing oneself by delivering detail-oriented answers with depth and technical expertise. The key topics discussed include common LTE interview questions such as optimizing call drop rates, understanding LTE handover events, and PCI planning rules. For each topic, the speaker emphasizes the importance of not only knowing the theoretical definitions but also being able to provide practical examples and detailed explanations that exhibit a strong grasp of the subject matter. For instance, when discussing LTE KPI (Key Performance Indicators) related questions, candidates should be able to identify various causes of call drops and suggest specific optimization actions. Similarly, when it comes to PCI planning rules, one should be able to explain the rationale behind these rules and their practical implications. The video also delves into topics such as LTE network entry call flow and downlink throughput optimization. The speaker recommends approaching each question with a structured method, identifying the bottleneck, and suggesting comprehensive optimization strategies. Overall, the video underlines that a candidate's ability to convey deep technical knowledge and present thorough, structured answers will set them apart in competitive interviews.

Takeaways

  • 🔹 Tips for acing interviews with a focus on LTE topics.
  • 🔍 Detail-oriented and depth in answers can set candidates apart.
  • 📊 Common questions include call drop rate optimization.
  • 📚 Understanding and explaining LTE events like handover is key.
  • 🛠 Demonstrate technical knowledge by providing examples.
  • 🚦 Highlight bottlenecks and their solutions in throughput optimization.
  • 📏 Explain PCI planning rules with rationale and impact.
  • 🔄 Discuss end-to-end LTE processes like network entry flow.
  • 📈 Stress on identifying bottlenecks in throughput issues.
  • 🗣 Candidates are advised to prepare structured answers.

Garis waktu

  • 00:00:00 - 00:05:00

    The speaker introduces a session about tips for acing job interviews, emphasizing the significance of standing out. Having conducted over 100 interviews, the speaker promises to share insights that captivate interviewers. Many resources offer generic interview answers, but the goal is to deliver unique and technical responses that make applicants memorable to interviewers. Today's focus is on LTE KPI questions like call drop rates.

  • 00:05:00 - 00:10:00

    The importance of understanding the LTE call drop rate optimization is highlighted. Common answers about radio quality improvements aren't enough; instead, interviewees should demonstrate detailed knowledge of causes and solutions for signal drops. By discussing specifics like RLCD transmissions, out-of-sync drops, and handover execution drops, interviewees can showcase their technical depth, essential for impressing interviewers in telecom roles.

  • 00:10:00 - 00:15:00

    A strong example in interviews involves going beyond definitions of LTE handover events like A1, A2, etc., by providing examples and crafting mobility strategies on the spot. This demonstrates in-depth understanding and quick problem-solving abilities. Extending the technical explanation to include LTE PCI planning rules showcases awareness about the impact of subnet configurations, impressing interviewers with a detailed, knowledgeable approach.

  • 00:15:00 - 00:20:00

    Discussing the LTE network call flow from the earliest signals to ERC and NAS signaling illustrates comprehensive understanding. Starting with the primary synchronization signal, the speaker describes the complete network entry process, emphasizing how starting from scratch showcases a candidate's thorough knowledge. Describing each step and its significance assures interviewers of the candidate's expertise and sets them apart from others.

  • 00:20:00 - 00:27:26

    Addressing LTE downlink performance, the speaker stresses identifying throughput bottlenecks before optimization. Examples include interference issues, congestion types, and solutions like readjustments, load balancing, or spectrum refarming to improve efficiency. Highlighting such detailed analysis and problem-solving strategies reflects a high level of technical expertise, assuring interviewers of a candidate's capability to enhance network performance.

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Mind Map

Pertanyaan yang Sering Diajukan

  • What are the top questions usually asked in LTE interviews?

    Questions about LTE KPI like call drop rates, LTE handover events, PCI planning rules, network entry call flow, and downlink throughput optimization are commonly asked.

  • How can one stand out in an interview?

    To stand out, provide detailed, example-based answers demonstrating deep technical knowledge and understanding of various processes and concepts.

  • What is a common question related to LTE KPI?

    A common question is how to optimize the LTE call drop rate.

  • How should you answer a question about call drop rates?

    Provide detailed explanations including multiple causes of call drops, corresponding actions, and optimizations, such as improving radio quality and adjusting handover success rates.

  • What strategy is suggested for explaining LTE handover events in an interview?

    Explain definitions with examples, showing understanding of mobility strategy and technical depth in handover processes.

  • What should you consider when discussing PCI planning in LTE?

    Beyond listing rules, discuss the basis and impact of PCI rules, like avoiding same PCI use in nearby cells, and understanding interference issues.

  • Why is it important to talk about backhaul issues in LTE optimization questions?

    Identifying backhaul issues can indicate a candidate's comprehensive understanding of LTE performance bottlenecks and their solutions.

  • What is key in optimizing LTE downlink throughput?

    Identifying the bottleneck first, such as interference or congestion, and then discussing specific optimization actions.

  • How can one effectively demonstrate knowledge in LTE technical interviews?

    Provide thorough, structured answers that cover end-to-end processes and reflect deep technical understanding.

  • What does understanding LTE handover events involve?

    It involves knowing the definitions of events, such as a1, a2, a3, etc., and explaining with practical examples.

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Gulir Otomatis:
  • 00:00:00
    hi guys
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    today we are going to have an
  • 00:00:03
    interesting topic it's going to be an
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    exciting one
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    many of you have requested for that so
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    let's start
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    today i'm going to tell you some tips
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    and tricks about how you can ace an
  • 00:00:14
    interview how you can stand out from the
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    crowd how how you can be unique
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    um now why it's important um of course
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    any everyone wants to get a job right uh
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    everyone wants to do good in the
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    interviews so
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    i have been taking interviews for over
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    the last 10 years i've taken more than
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    100 interviews
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    so i can tell you what an interviewer is
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    looking for and
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    how
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    you can stand out from the crowd and how
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    you can make sure that you are the
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    eligible one for the for that position
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    now
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    uh what i have seen is that there are
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    many uh
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    videos there are many sessions there are
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    many there's a lot of documentation
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    about uh interview questions but most of
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    them they will show you the interview
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    questions but not the answers even if
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    they have the answers they will not
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    really show you the
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    the answers that will really make you
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    stand out so you will see answers that
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    are the generic description or
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    definition of the of the event or of the
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    the question
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    at hand but you won't really see
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    something that will
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    make you
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    you know the one that will make sure
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    that the interviewer thinks that this is
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    the guy i'm looking for so what i'm
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    doing gonna do today is that i'm gonna
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    tell you
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    the top questions
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    that you should be having in nearly all
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    the interviews um when you go for an
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    interview and i will tell you how you
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    can answer in such a way that
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    your answer will be the most unique one
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    and it should be it will have the most
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    uh technical depth to it so so let's
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    start let's start i think if we can
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    start with it uh you can get an idea
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    what i'm talking about
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    for instance
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    there would always be a question about
  • 00:02:01
    an lte kpi
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    either accessibility or call drop rate
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    so
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    most of the time i've seen that the call
  • 00:02:09
    drop rate is uh one of the the most
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    important questions and one of the most
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    uh go-to questions for interviewers
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    because this question really can tell
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    you uh you about the about the person
  • 00:02:21
    about his optimization skills
  • 00:02:23
    so if the interviewer asks you how to
  • 00:02:27
    optimize lte call drop rate so what's
  • 00:02:30
    the most easiest answer that many people
  • 00:02:33
    give you many people reply in a very
  • 00:02:35
    simple way that you need to improve
  • 00:02:37
    radio quality and
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    you need to improve handover success
  • 00:02:42
    rate and things like that but what we
  • 00:02:45
    what we really want to see is the depth
  • 00:02:47
    of the knowledge and where that where
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    you can show that is that you can
  • 00:02:51
    actually tell the interviewer that there
  • 00:02:54
    can be multiple causes which can cause a
  • 00:02:56
    drop and then you can tell first three
  • 00:02:59
    or four causes and then there are
  • 00:03:01
    corresponding possible actions and
  • 00:03:04
    optimization actions that you can take
  • 00:03:06
    to reduce the impact of that specific
  • 00:03:08
    cause
  • 00:03:09
    so let's take an example for instance so
  • 00:03:11
    you can tell that there can be if you
  • 00:03:14
    they can be one of the cause that a
  • 00:03:16
    major cause that causes the drops in lte
  • 00:03:19
    is the rlcd transmission so it can be
  • 00:03:21
    downlink it can be uplinked if it is
  • 00:03:23
    downlink rlcd transmission it is a radio
  • 00:03:26
    induced drop and you can improve it by
  • 00:03:29
    improving downlink radio quality or you
  • 00:03:32
    can also reduce the impact of this drop
  • 00:03:35
    by increasing the downlink rlcd
  • 00:03:37
    transmission count
  • 00:03:40
    if you have an uplink rlcd transmission
  • 00:03:42
    drop that usually is packed under mme
  • 00:03:46
    this is another important difference you
  • 00:03:48
    need to understand that
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    you need to show that to the interviewer
  • 00:03:52
    that you understand that
  • 00:03:54
    the e note b initiated drops and the mme
  • 00:03:57
    initiated drops are different and you
  • 00:04:00
    understand that the mme initiated drops
  • 00:04:02
    are actually most of the time the uplink
  • 00:04:05
    drops which the enob is not aware of now
  • 00:04:08
    i have explained this in detail in my
  • 00:04:10
    lte call drop video so if you want to
  • 00:04:12
    refer to that you can
  • 00:04:14
    i don't want to go into those details
  • 00:04:15
    over here but the point to understand is
  • 00:04:18
    that this downlink rlcd transition drop
  • 00:04:21
    this falls in tender radio while the
  • 00:04:24
    uplink rs3 transmission drops usually
  • 00:04:26
    fall under mme and to improve that you
  • 00:04:29
    can increase the uplink rlc retransmit
  • 00:04:31
    count as well
  • 00:04:33
    similarly we have out of sync drops so
  • 00:04:35
    if you have out of sync drops in the
  • 00:04:37
    network again if you improve downlink
  • 00:04:39
    radio quality they will improve but you
  • 00:04:42
    can also reduce their impact and already
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    improve the kpi by increasing the n310
  • 00:04:47
    and t310 values so that is something
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    that you know the interviewer will know
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    that for each kind of drop you know that
  • 00:04:55
    not just the drawing radio quality or
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    uploading radio quality you know
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    something else as well because when
  • 00:05:00
    you're optimizing it's difficult to go
  • 00:05:03
    and do radio quality optimization in
  • 00:05:05
    detail but you need to know the tips and
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    tricks like these ones which are quick
  • 00:05:10
    ones that you can do n310 and t310 timer
  • 00:05:13
    values to improve the this kind of drop
  • 00:05:16
    rate
  • 00:05:17
    another one is the hand over execution
  • 00:05:19
    drops so if you have handover failures
  • 00:05:22
    and they are causing drops then what you
  • 00:05:24
    can do is that you can go and check at
  • 00:05:26
    neighbor levels
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    and check which if there is let's say
  • 00:05:29
    one or two neighbors which are the cause
  • 00:05:31
    of this drops you can blacklist those
  • 00:05:33
    top neighbors
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    but if
  • 00:05:36
    it is being caused
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    due to a neighbor being very far away
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    then you can just increase the cell
  • 00:05:42
    range of that neighbor and that should
  • 00:05:43
    also solve the issue
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    if you have no response drops this is a
  • 00:05:48
    kind of drop where the e note b has sent
  • 00:05:50
    an rrc message rrc command but the ue
  • 00:05:54
    does not respond back with the rrc
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    reconfiguration complete for instance in
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    this case you will have a drop you can
  • 00:06:00
    check if the rfc signaling response
  • 00:06:02
    timer is very low you can increase that
  • 00:06:05
    or you can take a cell trace and then
  • 00:06:07
    identify if it is being caused by a
  • 00:06:10
    specific rfcv configuration message or a
  • 00:06:13
    specific user type so
  • 00:06:15
    these are the kind of things that you
  • 00:06:18
    need to show to the interviewer that you
  • 00:06:21
    know
  • 00:06:22
    much more in detail and you have much
  • 00:06:24
    more depth when in comparison to other
  • 00:06:27
    candidates
  • 00:06:28
    let's take another example another very
  • 00:06:30
    common question is can you explain the
  • 00:06:33
    lte handover events
  • 00:06:35
    now
  • 00:06:36
    mostly the
  • 00:06:37
    candidates just will tell you definition
  • 00:06:39
    of each even a1 a2 a3 a4 a5 and these
  • 00:06:43
    are the definitions
  • 00:06:45
    this is not the wrong answer answer is
  • 00:06:47
    correct but what makes you stand out
  • 00:06:50
    what makes you stand out would be that
  • 00:06:52
    if you also explain this with an example
  • 00:06:55
    so for instance you can say that
  • 00:06:57
    a3 start with a3 if i use an intra
  • 00:07:00
    frequency handover i use a3 event and a3
  • 00:07:04
    means that the target cell has to be
  • 00:07:06
    better by an offset so it means that if
  • 00:07:08
    my rsrp is -100 and target rsrp is minus
  • 00:07:13
    96 if a3 is 4 db then i will do an intra
  • 00:07:17
    frequency handover
  • 00:07:19
    a3 can also be used for inter frequency
  • 00:07:21
    handling but mostly for inter frequency
  • 00:07:24
    we use this a4 or a5
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    now
  • 00:07:27
    a1 a2 a4 a5 they come into play together
  • 00:07:31
    a2 is used that if
  • 00:07:34
    i go below and the a2 threshold i will
  • 00:07:38
    start to measure other inter frequency
  • 00:07:40
    cells
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    so let's take an example that a2 is
  • 00:07:43
    minus 110
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    so if i go below minus 110 i will start
  • 00:07:48
    looking for other inter frequency cells
  • 00:07:52
    where which should where i can hand over
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    so
  • 00:07:55
    that means i need a threshold that to
  • 00:07:58
    find out if the other interfrequency
  • 00:08:00
    cell is good that is where the event a4
  • 00:08:02
    comes into play so if event a4 is minus
  • 00:08:05
    106
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    that means if my own rsrp is below 100
  • 00:08:10
    minus 110 and the target cell
  • 00:08:13
    which is the inter frequency cell has an
  • 00:08:15
    rsrp of minus 106 and or higher
  • 00:08:19
    force in minus 105 then i should do an
  • 00:08:22
    inter frequency handover
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    similarly if i don't use a4 and i use a5
  • 00:08:28
    a5 has two thresholds
  • 00:08:30
    threshold one and threshold two
  • 00:08:32
    threshold one is that the user needs to
  • 00:08:34
    be below threshold one on the serving
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    cell
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    and the target cell should be above
  • 00:08:38
    threshold 2 to do a a5 handover so again
  • 00:08:41
    if my rsrp is minus 111
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    so i am below threshold 1 of my 110
  • 00:08:47
    and the target cell has rsrp of my 105
  • 00:08:50
    which is above this threshold 2 so i
  • 00:08:52
    will have an a5 handover
  • 00:08:55
    similarly if i am below
  • 00:08:57
    a2 but
  • 00:08:59
    none of the a4 or a5 thresholds are met
  • 00:09:01
    and the user goes back
  • 00:09:03
    in good radio conditions then i need to
  • 00:09:06
    stop measurements because measurements
  • 00:09:08
    they take away lots of resources and
  • 00:09:11
    they impact the user's
  • 00:09:13
    throughput and also battery life as well
  • 00:09:16
    so that is why we have a1 so if i go
  • 00:09:20
    above minus 108 let's say this is if
  • 00:09:22
    that's my a1 or minus 108
  • 00:09:26
    if i go above that then it would mean
  • 00:09:29
    that i should stop all measurements that
  • 00:09:32
    is what the a1
  • 00:09:35
    is used for you really so um again
  • 00:09:39
    this is not the only answer of course
  • 00:09:41
    you can think of better answers as well
  • 00:09:43
    but this is how i visualize that if we
  • 00:09:46
    answer in this way we have told the
  • 00:09:48
    interviewer that not only do i know the
  • 00:09:50
    definitions i can quickly make a
  • 00:09:53
    mobility strategy as well right on
  • 00:09:56
    uh on the go right so if you give these
  • 00:10:00
    examples these values you what you have
  • 00:10:02
    done is that you have made a mobility
  • 00:10:04
    strategy right on the spot so this shows
  • 00:10:07
    that uh you your depth your technical
  • 00:10:10
    depth your technical experience is much
  • 00:10:14
    more complex is much higher comparison
  • 00:10:16
    to in comparison to other candidates
  • 00:10:20
    so another one which is nearly there in
  • 00:10:23
    all the lte interviews is the lte pci
  • 00:10:26
    planning rules now again
  • 00:10:29
    normally people just list the rules
  • 00:10:31
    which is you don't use same pci in the
  • 00:10:34
    same geographical location pci mod 3 pcm
  • 00:10:38
    or 30 but
  • 00:10:40
    what's important is to understand the
  • 00:10:42
    basis behind that and the impact of each
  • 00:10:46
    rule if you violate this rule how much
  • 00:10:49
    of an impact will there be
  • 00:10:52
    so for instance
  • 00:10:53
    you talk about the same pci rule you
  • 00:10:55
    tell the user that it the interviewer
  • 00:10:58
    that you should not use the same pci
  • 00:11:00
    within the geographical location but or
  • 00:11:03
    within the vicinity of the cell but you
  • 00:11:05
    need to tell what is this vicinity
  • 00:11:09
    so
  • 00:11:10
    the best scenario would be that every
  • 00:11:12
    cell has a cell radius or cell range so
  • 00:11:14
    you should ensure that the same pci
  • 00:11:18
    comes into play comes is being reused
  • 00:11:20
    after two times the cell radius but that
  • 00:11:23
    is not really not possible in dense
  • 00:11:25
    urban areas in the cities because there
  • 00:11:27
    are too many sites so in that case what
  • 00:11:30
    you can do is that you can
  • 00:11:32
    make sure that
  • 00:11:34
    it should not be there within the
  • 00:11:37
    neighbors so that we do not have pci
  • 00:11:39
    confusion and pci collision if you if
  • 00:11:42
    that is the minimum that's the minimum
  • 00:11:43
    you can do but if you have pci confusion
  • 00:11:46
    then you have a poor hand over success
  • 00:11:48
    rates so
  • 00:11:50
    that is uh then you can use this kind of
  • 00:11:52
    criteria uh to use it to identify the
  • 00:11:55
    geographical location where the pca
  • 00:11:56
    should not be reused
  • 00:11:58
    then comes the pci mod 3.
  • 00:12:01
    now why is it important because the pci
  • 00:12:04
    tells you the location of the lte
  • 00:12:06
    reference signals
  • 00:12:07
    and for for a 2tx or 4tx system
  • 00:12:11
    every third pci has the same reference
  • 00:12:14
    signal location
  • 00:12:15
    that means that the reference signals
  • 00:12:17
    will collide with each other
  • 00:12:19
    they will
  • 00:12:21
    they will have interference with each
  • 00:12:23
    other if we use pci mod 3
  • 00:12:26
    in the areas where the cells are
  • 00:12:27
    overlapping
  • 00:12:29
    similarly if you have one tx size
  • 00:12:33
    then the pci
  • 00:12:35
    every six pci overlaps so in that case
  • 00:12:38
    the pcm mod 6 rule applies
  • 00:12:41
    and the pci mod 30 that is used for
  • 00:12:44
    uplink so every 30th pci it has the same
  • 00:12:48
    reference signals for uplink same
  • 00:12:50
    sequence is used so that means that you
  • 00:12:52
    will have higher interference for uplink
  • 00:12:55
    uh or you can say that if the e note b
  • 00:12:57
    will have more difficulty in decoding
  • 00:12:59
    the uplink if you have a pcm mod 30
  • 00:13:03
    being used uh within the within the same
  • 00:13:05
    cells within the adjacent self
  • 00:13:08
    so that is uh what each pci rule
  • 00:13:12
    actually implies so you if you tell this
  • 00:13:14
    in this detail then
  • 00:13:17
    the interviewer will know that not only
  • 00:13:20
    do you know the rules you also know the
  • 00:13:22
    impact of these rules and you know the
  • 00:13:24
    basis behind them so that is something
  • 00:13:27
    that is
  • 00:13:28
    going to make sure that you stand out
  • 00:13:30
    again
  • 00:13:32
    another one that is there in
  • 00:13:34
    it can be in different flavors you can
  • 00:13:36
    ah you can the interior can ask you
  • 00:13:37
    about the lte network entry call flow
  • 00:13:40
    lte attach call flow network entry steps
  • 00:13:44
    accessibility call flow but uh more or
  • 00:13:46
    less this is there in nearly all
  • 00:13:50
    the interviews now
  • 00:13:52
    usually people start from the rrc
  • 00:13:54
    connection request which is over here
  • 00:13:57
    but what i prefer
  • 00:13:59
    is that if the user starts from the
  • 00:14:02
    scratch with the pss because this if you
  • 00:14:05
    start from here and you move all the way
  • 00:14:08
    towards the
  • 00:14:09
    edap setup this shows that you know end
  • 00:14:12
    to end this shows that your knowledge is
  • 00:14:14
    end to end you understand
  • 00:14:16
    from the start till end and this also
  • 00:14:20
    shows that you you are knowledge hungry
  • 00:14:22
    because most of the people will simply
  • 00:14:25
    start from rfc connection request and
  • 00:14:27
    will not even talk about all of this
  • 00:14:30
    again that starting from here is not
  • 00:14:32
    incorrect as well that's also okay the
  • 00:14:34
    answer is still gonna be fine but it
  • 00:14:37
    will not be something that will
  • 00:14:39
    make that will really make you stand out
  • 00:14:42
    it will not be something that will uh
  • 00:14:44
    tell the interviewer that this candidate
  • 00:14:47
    is unique so if you start from this test
  • 00:14:50
    from the start that the ue first of all
  • 00:14:53
    it reads the primary synchronization
  • 00:14:55
    signal the pss which gives it a slot
  • 00:14:59
    level synchronization and center
  • 00:15:02
    frequency information
  • 00:15:03
    then it reads the secondary
  • 00:15:05
    synchronization signal which is the sss
  • 00:15:08
    and that tells it about the cp length
  • 00:15:11
    the cyclic prefix length it gives it's a
  • 00:15:13
    symbol level synchronization it tells
  • 00:15:16
    you whether the the frame structure is
  • 00:15:18
    tdd or fdd it also gives you sub frame
  • 00:15:21
    information
  • 00:15:23
    and with the combination of pss and ssss
  • 00:15:25
    together
  • 00:15:27
    the ue can decode the pci as well
  • 00:15:30
    and pci tells the ue about the location
  • 00:15:33
    of the reference signals and the pc
  • 00:15:35
    pitch
  • 00:15:37
    now after this would just just
  • 00:15:39
    behind the pss we have the pbch
  • 00:15:42
    so the ue decodes the pbch which carries
  • 00:15:45
    the master information block the mib
  • 00:15:49
    and this gives you information about
  • 00:15:50
    system bandwidth
  • 00:15:52
    frame number
  • 00:15:53
    ph and the number of tx
  • 00:15:56
    now when you have information about ph
  • 00:15:59
    pc fetch and reference signals then all
  • 00:16:02
    the other
  • 00:16:03
    symbols or ref source elements in that
  • 00:16:06
    in the first symbol they are they belong
  • 00:16:09
    to pdcch that means that after this you
  • 00:16:12
    can read the pdc ch as well
  • 00:16:14
    and from the pdcch you look for the si
  • 00:16:18
    rnti so the pcc it will tell you where
  • 00:16:21
    the sieve one is located
  • 00:16:23
    and then you read the save one it tells
  • 00:16:25
    you about multiple parameters but it
  • 00:16:28
    also tells you about qrx level min
  • 00:16:31
    so
  • 00:16:32
    that tells you the minimum
  • 00:16:35
    rsrp that you need to access the cell so
  • 00:16:38
    how do you get the rsrp
  • 00:16:40
    you have already know where the
  • 00:16:41
    reference signals are you read the
  • 00:16:43
    reference signal so you get the rsrp and
  • 00:16:46
    if the rsrp is above qrx level min you
  • 00:16:49
    try to attach or connect to the cell now
  • 00:16:52
    the next thing you need to do you need
  • 00:16:53
    to do ratch now the rash parameters they
  • 00:16:56
    come from sieve two so say one also
  • 00:16:59
    tells you about the other sieves so you
  • 00:17:01
    read the sieve too and you get the raj
  • 00:17:03
    information based on this one the ue it
  • 00:17:08
    generates the preamble and it sends the
  • 00:17:10
    preamble to the e node b this is
  • 00:17:13
    also called the message one which is the
  • 00:17:15
    premium which carries the preamble now
  • 00:17:16
    once the energy gets the preamble it
  • 00:17:19
    responds back with the message to which
  • 00:17:21
    is also called random access response or
  • 00:17:23
    rar
  • 00:17:25
    and that carries the timing at once
  • 00:17:28
    so now the ue knows its timing at once
  • 00:17:31
    it
  • 00:17:32
    fixes its timing and sends rash message
  • 00:17:35
    3 which is also
  • 00:17:37
    known as rrc connection request an rfc
  • 00:17:40
    connection request carries the ue id if
  • 00:17:43
    the ui is already connected before it
  • 00:17:45
    will know it's timzy value so it this
  • 00:17:47
    this rrc connection request will carry
  • 00:17:49
    the timzy
  • 00:17:50
    if it does not know it's timzy it will
  • 00:17:52
    carry a random ue id
  • 00:17:54
    it also carries the course code so if
  • 00:17:57
    the ue is
  • 00:17:58
    let's say wants to send something send
  • 00:18:01
    some data the course code will be mo
  • 00:18:03
    data if the ue is just a signaling
  • 00:18:06
    message it will be ammo signaling
  • 00:18:08
    similarly if it is an incoming call it
  • 00:18:11
    will be empty access
  • 00:18:12
    from here you can find out
  • 00:18:14
    what kind of
  • 00:18:16
    this connection is as well
  • 00:18:18
    then the enodb sends an rfc connection
  • 00:18:20
    setup
  • 00:18:21
    in response to the rfc connection
  • 00:18:23
    request this carries the srb1 which is a
  • 00:18:26
    signaling radio beta 1 configuration so
  • 00:18:29
    once the ue gets that then the ue uses
  • 00:18:32
    this configuration applies it on itself
  • 00:18:35
    and then responds with rrc connection
  • 00:18:37
    setup complete
  • 00:18:38
    now if it is a let's say an attached
  • 00:18:40
    message then the attached message will
  • 00:18:43
    carry some nas signaling non access
  • 00:18:46
    stratum signaling so the rrc connection
  • 00:18:48
    setup complete is the message which
  • 00:18:51
    carries that nas signaling
  • 00:18:53
    now the e node b needs to now transfer
  • 00:18:56
    this nas signaling to the core to the
  • 00:18:58
    mme and that was done using the s1
  • 00:19:01
    initial ue message so inode b sends this
  • 00:19:04
    message to the mme the core and it
  • 00:19:07
    carries the nas message now the core
  • 00:19:10
    when it looks into this message it
  • 00:19:11
    responds with s1 initial context setup
  • 00:19:14
    request
  • 00:19:15
    now the core might respond with some
  • 00:19:17
    other messages as well but the most
  • 00:19:19
    common message which is the erab setup
  • 00:19:21
    message is this one in response to s1
  • 00:19:24
    initial ui message so this message it
  • 00:19:27
    carries the qos information like the qci
  • 00:19:30
    erev id
  • 00:19:32
    mbr values and once the node b gets this
  • 00:19:35
    information it transfers this message to
  • 00:19:38
    the
  • 00:19:39
    huey using rrc reconfiguration messages
  • 00:19:42
    and over here it also sends the security
  • 00:19:44
    mode command as well
  • 00:19:46
    so with this message rsvd configuration
  • 00:19:48
    message it sets up the data radio bearer
  • 00:19:51
    and the signaling radio beta 2 srb2 and
  • 00:19:54
    also the security information which is
  • 00:19:56
    in the smc message the security mode
  • 00:19:58
    command so once this is completed ue
  • 00:20:02
    will respond
  • 00:20:03
    back with security mode complete and rs3
  • 00:20:05
    configuration complete the enode b will
  • 00:20:07
    then send s1 initial context setup
  • 00:20:11
    response to the mme indicating that the
  • 00:20:14
    betas are set up and this is where we
  • 00:20:16
    say the e-wrap setup is completed and
  • 00:20:18
    over the over the nas messages we can
  • 00:20:20
    also do the attach complete uh or
  • 00:20:24
    after this message
  • 00:20:26
    and
  • 00:20:27
    we can say that the ue is now
  • 00:20:28
    successfully connected to the
  • 00:20:30
    lte network and we can say that this is
  • 00:20:33
    the end of our call flow or and we can
  • 00:20:36
    also end our answer here as well so what
  • 00:20:38
    we have done here is that we have taken
  • 00:20:40
    this network entry steps and
  • 00:20:43
    we have given an answer that is
  • 00:20:46
    from the start the first thing the ue
  • 00:20:48
    does it starts over here and we have
  • 00:20:50
    taken it all the way uh to the until the
  • 00:20:53
    end where the edap setup is done and we
  • 00:20:56
    have also explained
  • 00:20:58
    what each individual message is carrying
  • 00:21:01
    so it is
  • 00:21:02
    it is something that
  • 00:21:03
    is
  • 00:21:04
    giving a lot of depth to the answer
  • 00:21:08
    and definitely if the interviewer goes
  • 00:21:11
    through this kind of depth
  • 00:21:13
    the interview will know that this guy
  • 00:21:16
    is different from others
  • 00:21:20
    another one which is uh which is the
  • 00:21:22
    most common question and it is
  • 00:21:24
    asked in
  • 00:21:25
    nearly every interview that is how to
  • 00:21:28
    optimize
  • 00:21:29
    lte downlink through performance just
  • 00:21:32
    now
  • 00:21:32
    again
  • 00:21:34
    simple answers you can improve radio
  • 00:21:37
    quality carrier aggregation a couple of
  • 00:21:40
    features
  • 00:21:41
    but
  • 00:21:42
    the most important thing that i
  • 00:21:45
    think is important for
  • 00:21:47
    optimization is to identify the
  • 00:21:49
    bottleneck first so uh
  • 00:21:51
    you can answer that with
  • 00:21:54
    this scenario that first i need to
  • 00:21:56
    identify what is the bottom lag that is
  • 00:21:59
    causing the load throughput so if i say
  • 00:22:01
    that the throughput is being low
  • 00:22:04
    throughput is being caused because of
  • 00:22:06
    low cqi and low mcs
  • 00:22:09
    and even the ta timing advanced value is
  • 00:22:11
    also low that means the users even near
  • 00:22:14
    the cell have bad radio quality so that
  • 00:22:17
    means they it is more of an interference
  • 00:22:19
    scenario it is a low si and r scenario
  • 00:22:22
    so in those kind of scenarios physical
  • 00:22:24
    optimization like down tilts can help
  • 00:22:28
    features like lean carriers can help
  • 00:22:30
    reference signal d boosting can help
  • 00:22:33
    because the reference signals are
  • 00:22:34
    de-boosted they reduce the interference
  • 00:22:36
    noise
  • 00:22:37
    there are also features like coordinated
  • 00:22:39
    multi-point or
  • 00:22:41
    adaptive or single frequency network
  • 00:22:43
    which used to combine two cells into one
  • 00:22:46
    cell together at the cell edge they also
  • 00:22:49
    reduce interference a lot these kind of
  • 00:22:51
    features
  • 00:22:52
    are
  • 00:22:53
    there when you have an interference
  • 00:22:55
    limited uh issues interference limited
  • 00:22:58
    cells where you have low throughput
  • 00:23:00
    because of high interference or low sinr
  • 00:23:04
    another one is the congestion now the
  • 00:23:06
    congestion can be on the data channel in
  • 00:23:09
    this case you have high resource block
  • 00:23:11
    utilization so in this case either you
  • 00:23:14
    add more cells that will add more
  • 00:23:15
    capacity you can add more carriers that
  • 00:23:17
    can add more capacity or you enable load
  • 00:23:20
    balancing features so you
  • 00:23:23
    make sure that all the carriers are
  • 00:23:25
    equally loaded if one carrier is less
  • 00:23:27
    loaded you can use load balancing to
  • 00:23:29
    push users to that one you can enable
  • 00:23:32
    carrier aggregation so
  • 00:23:34
    it should already be there but lte carry
  • 00:23:36
    aggregation should improve your overall
  • 00:23:38
    throughput and capacity
  • 00:23:41
    if you have a control congestion that is
  • 00:23:43
    a pdcch
  • 00:23:45
    congestion and you can see that you have
  • 00:23:48
    high pdcc utilization
  • 00:23:51
    in that case what you need is that you
  • 00:23:53
    need to expand the pdc ch capacity so
  • 00:23:56
    increase the cfi that means
  • 00:23:58
    number of symbols required or allocated
  • 00:24:01
    to pdcch if you increase that if there's
  • 00:24:03
    only one symbol make it two with the two
  • 00:24:05
    symbols make it three they're already
  • 00:24:07
    three make it adaptive so in that case
  • 00:24:10
    what happens is that you can improve
  • 00:24:12
    your
  • 00:24:13
    pdc ch capacity another thing you can do
  • 00:24:16
    is that you can reduce your aggregation
  • 00:24:18
    levels so the uh if the pcc is using
  • 00:24:21
    high aggregation levels then it will be
  • 00:24:23
    congested very quickly for instance if
  • 00:24:26
    you are using the highest aggregation
  • 00:24:27
    level you and you have one symbol you
  • 00:24:29
    might only you be able to allocate one
  • 00:24:31
    or two uis
  • 00:24:32
    in that slot in that subframe but if you
  • 00:24:35
    reduce the irrigation level to let's say
  • 00:24:37
    four or two you can now um
  • 00:24:40
    transmit
  • 00:24:41
    four or eight users for instance in the
  • 00:24:44
    same subframe so in this case you can
  • 00:24:46
    increase your pgch capacity
  • 00:24:50
    excuse me
  • 00:24:52
    another issue could be backhaul issues
  • 00:24:54
    so backhaul issues
  • 00:24:55
    are something that we can't really do
  • 00:24:57
    but if how to find out that is important
  • 00:25:00
    so
  • 00:25:01
    from the rand perspective if you have
  • 00:25:03
    low slot usage
  • 00:25:05
    or if you have
  • 00:25:07
    high
  • 00:25:08
    single
  • 00:25:10
    last tdi usage
  • 00:25:11
    then that means that you have you can
  • 00:25:14
    have
  • 00:25:15
    some backhaul issues or or your core
  • 00:25:17
    issues so in that case you need to
  • 00:25:19
    increase the backhoe capacity so the
  • 00:25:21
    important thing is to add yet you should
  • 00:25:23
    be able to identify
  • 00:25:25
    possible backhaul capacity issues from
  • 00:25:28
    your
  • 00:25:29
    own analysis on the rant side
  • 00:25:31
    now another one could be
  • 00:25:33
    simple poor coverage in this case what
  • 00:25:36
    will happen is that you will see high
  • 00:25:37
    path loss and high ta timing advanced
  • 00:25:40
    counters so in this case you know that
  • 00:25:42
    users are very far away so in this case
  • 00:25:45
    you can up tilt
  • 00:25:47
    you can increase your power
  • 00:25:49
    or you can move users to the lower
  • 00:25:52
    frequency bands so if you are using
  • 00:25:54
    let's say a higher band like 2600 and
  • 00:25:57
    you can see that it is the users are
  • 00:25:59
    camping in very poor coverage and their
  • 00:26:01
    throughput is very very low and you and
  • 00:26:03
    you have tried up tilting you've tried
  • 00:26:05
    increasing the power but nothing is
  • 00:26:07
    really helping you can offload the cell
  • 00:26:09
    edge users to a lower band for instance
  • 00:26:12
    the 1800 band or 2100 band or 800 band
  • 00:26:15
    so that in in that band because a lower
  • 00:26:18
    band they will have more higher rsrp and
  • 00:26:21
    more coverage so it will be uh
  • 00:26:24
    it will end up users having better
  • 00:26:26
    throughputs in comparison to uh what
  • 00:26:28
    they're getting on the higher uh
  • 00:26:30
    higher frequency band
  • 00:26:32
    so these are the factors uh but if you
  • 00:26:35
    talk about throughput for per bottleneck
  • 00:26:39
    and you explain the optimization actions
  • 00:26:42
    and the identifying factors for each of
  • 00:26:44
    the bottleneck type then that is
  • 00:26:46
    something that gives a structure to your
  • 00:26:48
    answer and it also tells
  • 00:26:50
    the interviewer that
  • 00:26:52
    your knowledge and your depth is much
  • 00:26:55
    more and you have done that your
  • 00:26:57
    experience is much much higher so it
  • 00:27:00
    gives you the edge that you're looking
  • 00:27:02
    for and
  • 00:27:03
    if you try to answer them in these kind
  • 00:27:06
    of structural ways
  • 00:27:08
    you should be able to
  • 00:27:10
    land yourself a job pretty quickly so
  • 00:27:13
    that's all from my side
  • 00:27:15
    to let me know if you have any questions
  • 00:27:17
    or any other questions that you want me
  • 00:27:18
    to cover that will also be good so best
  • 00:27:21
    of luck
  • 00:27:22
    have a nice day
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