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LTE Video Presentations

OFDM Time Frequency Multiplexing

Rohde & Schwarz‘s presentations provide an excellent introduction to LTE. The presentations are accompanied with an audio narration. The topics covered are covered:

  1. LTE Introduction
    • Motivations for LTE
    • LTE market and background
    • Requirements
    • Evolution path to LTE
  2. LTE Parameters and Downlink Modulation
    • LTE parameters and frequency bands
    • What is OFDMA?
    • OFDMA multiple access and downlink frame structure
    • OFDMA transmit and receive chains
  3. OFDMA and Downlink Frame Structure Details
    • Downlink OFDMA time-frequency multiplexing
    • LTE Spectrum Flexibility and Bandwidth
    • FDD downlink frame structure detailed
    • TDD frame structure
  4. SC-FDMA and LTE Uplink
    • Introduction to SC-FDMA and uplink frame structure
      • Marriage of single carrier transmission and FDMA
    • Uplink SC-FDMA tranmsit and receive chains
    • Peak to Average Power Ratio (PAPR) comparison with SC-FDMA and OFDMA
  5. Network and Protocol Architecture
    • LTE/SAE network architecture
    • EPC -Evolved Packet Core
    • Base Station control plane and user plane protocol stacks
    • EPC protocol stacks
  6. Channel Mapping and UE Categories
    • Logical and transport channel mapping in downlink and uplink
    • LTE UE Categories
  7. Initial Cell Search and Cell Selection
    • Downlink physical channels and signals
    • Cell Search and Selection in LTE
      • Primary synchronization signal
      • Secondary synchronization signal
      • Reference signals
  8. System Information
    • Downlink reference signal details
    • Master Information Block on PBCH
    • System Information on DL-SCH
  9. Random Access Procedures and EPS Bearer Setup
    • Random access preamble transmission to eNodeB
    • Random access response from eNodeB
    • Resource allocation and contention resolution
    • Signaling on PDCCH
    • Hybrid ARQ
    • RRC Connection Setup and EPS Bearer Setup
  10. Uplink Channels and Signals
    • Uplink physical channels and signals
    • PU-SCH: Physical Uplink Shared Channel
    • Uplink assignment signaling on PDCCH
    • Uplink frequency hopping
    • PUCCH
  11. LTE Mobility and MIMO Introduction
    • Intra MME Handover over the X2 interface
    • RRC States
    • MIMO Basics
      • Transmit diversity
      • Spatial multiplexing
      • Beamforming
  12. Downlink and Uplink MIMO in LTE
    • Downlink MIMO modes
      • Transmit diversity
      • Spatial multiplexing
      • Cyclic delay diversity
      • Beam forming
    • Spatial multiplexing downlink transmitter chain
      • Code book based precoding
    • Uplink MIMO
      • Uplink transmit antenna selection
      • Multi-user MIMO
  13. eNodeB and UE Performance Requirements
    • eNodeB modulation quality measurements
    • eNodeB performance requirements
    • UE performance requirements
  14. UE Certification and Field Trials
    • LTE terminal testing stages
    • LTE terminal certification
    • LTE field trial scenarios
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PSTN subscriber to IMS subscriber call flow

IP Multimedia Subsystem is the new IP based signaling system for setting up multimedia sessions. We have already covered the call flow for an IMS subscriber calling another IMS subscriber. Here we will look at the call flow of a regular PSTN subscriber calling an IMS user.

PSTN to IMS call flow

PSTN subscriber to IMS subscriber call flow

This call flow covers the handling of a CS network originated call with ISUP. In the diagram the MGCF requests seizure of the IM CN subsystem side termination and CS network side bearer termination. When the MGCF receives an answer indication, it requests the IM-MGW to both-way through-connect the terminations. Originating and terminating end initiated call releases are also covered.

The following sequence is covered:

  1. ISUP IAM Handling and Initial IM-MGW and MGCF (Mn) Interactions
  2. Initial Handshake between MGCF and IMS CSCF Servers
  3. Mn Interactions for Codec selection
  4. ISUP ACM related interactions on Mn interface
  5. IMS Answer to ISUP ANM Handling
  6. Conversation Mode
  7. Call Release:
    • Calling PSTN Subscriber Initiated Call Release
    • Called Subsciber Initiates Call Release

Link: PSTN subscriber to IMS call flows

Focus on different aspects of the call flow

PSTN to IMS call is a very complex flow. The main sequence flow is supplemented with flows that focus on a particular aspect of the flow. A snapshot of one such diagrams is shown here:PSTN subscriber to IMS subscriber - Terminating S-CSCF interactions

Link: PSTN subscriber to IMS call flows


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Rules for managing header file includes in C++

C++ header file include rulesC++ header file management can be very frustrating:

  • Changing the the order of header files often results in difficult to track compilation errors
  • C++ project compilations take a long time due to complex header file inclusions

Here are a few rules to remedy this:

  • A header file should be included only when a forward declaration would not do the job.
  • The header file should be so designed that the order of header file inclusion is not important.
    • This is achieved by making sure that x.h is the first header file in x.cpp
  • The header file inclusion mechanism should be tolerant to duplicate header file inclusions.

An example of illustrates the header file inclusion rules:

Header file

#ifndef _a_h_included_
#define _a_h_included_
#include "abase.h"
#include "b.h"

// Forward Declarations
class C;
class D;

class A : public ABase
{
  B m_b;
  C *m_c;
  D *m_d;

public:
  void SetC(C *c);
  C *GetC() const;

  void ModifyD(D *d);
};
#endif

Source file

#include "a.h"
#include "d.h"

void A::SetC(C* c)
{
  m_c = c;
}

C* A::GetC() const
{
  return m_c;
}

void A::ModifyD(D* d)
{
  d->SetX(0);
  d->SetY(0);
  m_d = d;
}

For details, refer to: C++ Header File Include Rules