Power HeadRoom Report in LTE

Power Headroom Report(PHR) in LTE :- 

                             In Uplink, the UE has a maximum transmission power defined by their power class. Power Headroom indicates how much relative transmission power (With respect to UE maximum transmission power) can be further used by UE. In mathematical expression, Power Headroom can be expressed as below:

Power Headroom = UE max transmission Power - Power of PUSCH channel (Estimated or Scheduled not really transmitted).

Note:- Power Headroom Report is transmitted in same subframe in which PUSCH is transmitted.

By the mathematical expression there are 2 possibilities :

1. Power Headroom is +Ve ; Means UE is still having adequate transmission power left and thus network can assign more resource blocks to UE.

2. Power Headroom is -Ve ; Means UE did not have anymore additional power left and is transmitting at more than its maximum transmitting power already. In this case network will not assign more resource blocks to UE.

Power Headroom Report Mapping :- 
     The PHR ranges from -23.. to +40dB .

When UE send PHR ?- There are two triggering condition for UE through RRC messages( RRC configuration, RRC reconfiguration).

1. When Downlink Pathloss changed is greater than a certain threshold(in dB)
2. By some predefined periodic PHR timer (in Sub frames).

Note:- PHR can be efficiently used in UL power control to improve the throughput.

Volte call flow: Made simple

Dear Folks, today we will discuss about one of the basic things in Volte, which is Volte call flow.

The Normal Volte call flow is look like below:

We will discuss each step one by one:

Step 1: SIP Invite: Direction:- A Party---B Party
Calling party(A) informs IMS network and Called party(B) about New call. Session Description protocol(SDP) is used for carrying information such as Bandwidth and codec.

Step 2: 100 Trying: Direction:- B Party----A party
100 Trying is the response to the calling party to stop the retransmission of SIP invite. Every Node in IMS send the 100 trying message.

Step 3: 183 session in progress: Direction:- B Party----A Party
Called party informs about codec supported in response of SDP. Dedicated bearer(QCI=1) are created at both ends i.e. Calling end as well as called end.

Step 4: SIP PRACK(Provisional Response Acknowledgment):  Direction:-A Party----B Party
It is a provisional response acknowledgment to 183 session in progress message received. Calling party uses this PRACK to communicate final selected Voice codec.

Step 5: SIP 200 OK (PRACK): Direction:- B Party----A Party
Called party accepts final selected Voice codec by Calling party.

Step 6: SIP Update: Direction:- A Party----B Party
Calling party confirms the Resources to voice call.

Step 7: SIP 200 OK (Update):- Direction:- B Party----A Party
Called party confirms the resources to voice call.

Step 8: 180 Ringing:- Direction:- B Party----A Party
All pre conditions are satisfied now and called party alerts the Calling party about ringing of call.

Step 9: SIP 200 OK(INVITE): Direction:- B Party----A Party
Finally called party Answers the call. 

All About PDCCH channels in LTE

Hello folks, Back after long time. Today we will discuss about one of the most important channels in LTE i.e PDCCH.

PDCCH(Physical downlink Control Channel):- The PDCCH can be called as heart of the data transmission in LTE as its carries the control information about the data being transmitted on the current subframe and the information about the resources which UE need to used for the Uplink data. Which means for any data transmission and reception UE must need to decode the PDCCH channel.

So next important questions comes in my mind is
Information carried by PDCCH?
Where it carries the information?
And for Whom?

We will try to answers these questions one by one.

Information carried by PDCCH:- PDCCH carries a message called DCI ( Downlink Control Information ) which includes resource assignments for a UE or group of UE's. EnodeB can transmit many DCI's or PDCCH's in a subframe. 


we have following DCI formats:-


Format 0 for transmission of resources to UE for sending their uplink data, i.e Uplink grant.

Format 1 for downlink allocation of resources for Single Input Multiple Output (SIMO)case.

Format 1A for downlink allocation of resources for SIMO operation or allocating a dedicated preample signature to a UE for random access.

Format 1B for transmission control information of Multiple Input Multiple Output (MIMO) rank 1 based compact resource assignment

Format 1C for very compact transmission of PDSCH assignment

Format 1D same as format1B with additional information of power offset

Format 2 and Format2A for transmission of DL-SCH allocation for closed and open loop MIMO operation, respectively

Format 3 and format3A for transmission of TPC command for an uplink channel.

Where it carries the information?- 
Allocation of resources happens in terms of CCE ( Control Channel Elements ).



1 CCE = 9 continuous REG's ( Resource element Group )

1 REG = 4 RE ( Resource Element )

So 1 CCE = 36REs.


PDCCH uses the resources present in first n OFDM symbols where

n - Value present in PCFICH ( Number of OFDM symbols )



So the number of CCE's present to transmit the control information will be variable depending on the

1.PCFICH value

2.Bandwidth of the system from 1.4 Mhz to 20 Mhz.

3.Number of antenna ports present which in turn will effect the reference signals present.

For Whom?- 
eNodeB uses the PDCCH for sending the control information for a particular UE or a group of UE's. It means eNodeB uses the PDCCH  for some broadcast information also which is common for all the UE's. So to make that process easier eNodeB divided its CCE's into two parts which we call them as search space:


Common search space :- It consists of CCE's which are used for sending the control information which is common for all the UE's .Maximum number of CCE present in common search space is 16.
For Example:- Common search space CCE's are used by eNodeB for sending the control information of SIB's which is common for all UE's.  


UE specific search space :- CCE's belonging to UE specific space are used for sending the control information for a particular UE only. That means information present on UE specific CCE's can only be decoded by a specific UE.


Note:- eNodeB can also send the control information for a specific UE on the common search space.

We will discuss next blog that how eNodeB calculate CCE for UE. 

Different types of scheduler in LTE

Today we will discuss about the different types of schedulers in LTE.
There are mainly 3 types of schedulers in LTE, which are as below:
1. Round-Robin
2. Proportional Fair
3. Max CQI or Max C/I

We will discuss all one by one.

1. Round- Robin scheduler:- As it names suggest this type of scheduler schedules UE in a circular manner without considering the channel condition.

Pros:- Creating an equal resource share to all users.
Cons:- The UE with Sub-Optimal CQI will also allocate with PRB thus reducing the overall Cell/User throughput.

2. Proportional Fair Scheduler:- As it name suggest this scheduler tries to make balance between throughput and fairness among all the UEs. Means it tries to maximize the total throughput and at the same time tries to provides all users at least a minimal service.

Pros:- There is equal amount of trade off between throughput and fairness.
Cons:- Implementation is complex and we can not reach the highest cell throughput with this scheduler.

3. Max CQI scheduler:- As it name suggest this type of scheduler uses the strategy to assign the PRB to the user with the best channel condition means highest CQI.

Pros:- We can reach the maximum throughput.
Cons:- Cell edged UEs are starved of scheduling which leads to poor UE experiences.

So keeping in mind the throughput and fairness for users the proportional fair schedulers are most common to use.

Please do comment.. Your feedback are valuable for me.

Scheduling in LTE

Scheduling in LTE is a process in which the resources on the shared channel i.e. PDSCH and PUSCH are assigned to users on sub-frame basis. Scheduling done on the basis of below factors:
Users traffic demand, QOS requirements and estimated channel quality.


The scheduling is done by the Uplink and Downlink schedulers which both are situated in eNodeb.


The smallest time/frequency entity that the scheduler may assign is twelve sub carrier (180kHZ) in frequency domain and 1ms in time domain and this is called scheduling blocks.


Resources handled by scheduler in downlink are:

1.Physical resource blocks-PRB

2.PDCCH resource

3.DL power

4.TX Rank

5.Baseband module processing capability


Resources handled by scheduler in Uplink are:

1.PRB

2.PUCCH resources

3.Baseband module processing capability


Downlink scheduling process:

 1.UE provides a CQI report 

 2. DL scheduler assigns resources per RB based on QOS and CQI

 3.Resource allocation is transmitted in same TTI as data.


Uplink Scheduling process:

 1.UE request UL transmission via scheduling request

 2.Scheduler assigns initial resources without detailed knowledge of buffer count

 3.More detailed BSR(Buffer status report) follow in connection with data

Transmission Channels priority in scheduling:- For every cell in every TTI(1ms), the Scheduler determines the UEs that are assigned resources. Each radio bearer is given a certain scheduling priority, based on algorithms which take the QCI (QoS Class Identifier) related parameters as input.The UE with the highest priority is selected first for transmission.The different transmissions are prioritized in the following order:

Downlink:-
1.Common channels
2.HARQ retransmission of DCCH
3.Initial transmission of DCCH
4.HARQ retransmission of DTCH
5.Initial transmission of DTCH
Uplink:-
1.Transmission of random access msg3
2.HARQ retransmission
3.Initial transmission of DCCH
4.Initial transmission of DTCH.

Types of scheduling Algorithms: Below are the major types of Scheduling Algorithms:
1.Round Robin
2.Proportional Fair
3.Max C/I
4.Semi-persistant 

Will discuss in details about above scheduling algorithms in next blog.

VoLTE KPIs

Today we will discuss about the Various types of VoLTE KPIs. 
VoLTE KPI is mainly divided into three parts:

1.IMS KPI

2.EPC(Packet core) KPI

3.RAN KPI.


IMS KPI is further divided into 2 parts:- IMS Control plane KPI and IMS User Plan KPI.

IMS Control plane KPIs are as follows:

1.RSR:- Registration success rate.         

Formulae = Count of 200OK for Registration completed/Count of SIP register sent from UE excluding 401 error attempts*100

2.CSSR- Call setup success rate%           

Formulae = Count of (Normal end call+ call failed with user behaviour)/Sum of all call attempts*100

3.Call setup time:-          

Formulae= Avg of(Time(180 ringing)- Time(SIP INVITE request))


IMS User plane KPIs are as follows:

1.Mute rate(%)

Formulae= % of calls muted (samples >2 or 5s RTP loss in both direction)

2.MOS score

3.RTP packet loss %

Formulae = % of RTP packets lost in the uplink or downlink direction.

4.One way call %

Formulae = % of calls having no voice packets count for 2 or 5 Sec in either the downlink or uplink direction.


EPC(Packet core KPI):- This also classified further in 2 parts- MME generated and SGw/PGw generated.

MME generated KPI are as follows:-

1.VoLTE attach success rate% = % of PDN connect request responded successfully by MME for IMS APN.

2.VoLTE bearer Activation success rate:% of create request got successful.

3.Paging success rate%-= % of paging responses on QCI=5 received at MME.
SGw/PGw generated KPI are as follows:-
1. IMS IP Pool Utilization%


RAN KPI are as follows: 
1.Call drop rate % = % of calls getting dropped abnormally.
2.SRVCC Success Rate % = % of calls successfully transferred with SRVCC from VoLTE to legacy NW

3.Handover Success rate %(S1 and X2).

5G NR network Architecture

Below is the 5G NR architecture as per 3GPP standard.

Network nodes and their functions:

(UE)- User equipment

(gNB)- Next Generation Node Base station

Access and Mobility Management Function (AMF) – responsible for following

       – Termination of RAN Control Plane interface (NG2)

       – Termination of NAS (NG1), NAS ciphering and integrity protection

       – Mobility Management

       – Lawful intercept (for AMF events and interface to Lawful Intercept System)

       – Transparent proxy for routing access authentication and SM messages

       – Access Authentication

       – Access Authorization

       – Security Anchor Function (SEA): It interacts with the UDM and the UE, receives the       intermediate key that was established as a result of the UE authentication process; in case of USIM based authentication, the AMF retrieves the security material from the UDM

       – Security Context Management (SCM): it receives a key from the SEA that it uses to derive access-network specific keys

User plane Function (UPF) – functions are

       – QoS handling for User plane

       – Packet routing & forwarding

       – Packet inspection and Policy rule enforcement

       – Lawful intercept (User Plane)

       – Traffic accounting and reporting

       – Anchor point for Intra-/Inter-RAT mobility (when applicable)

       – Support for interaction with external DN for transport of signaling for PDU session authorization/authentication by external DN

Session Management Control Function (SMF) – supports following:

      – Session Management

      – UE IP address allocation & management (including optional Authorization).

      – Selection and control of User Plane function

      – Termination of interfaces towards Policy control and Charging functions

      – Control part of policy enforcement and QoS.

      – Lawful intercept (for Session Management events and interface to Lawful Intercept System)

      – Termination of Session Management parts of NAS messages

      – Downlink Data Notification

      – Initiator of Access Node specific Session Management information, sent via AMF over NG2 to Access Node

      – Roaming functionality

      – Handle local enforcement to apply QoS SLAs (VPLMN)

      – Charging data collection and charging interface (VPLMN)

      – Lawful intercept (in VPLMN for Session Management events and interface to Lawful Intercept System)

Data Network (DN): Operator services, Internet access or other services

Authentication Server Function (AUSF) – Performs authentication processes with the UE

Unified Data Management (UDM) – Supports:

      – Authentication Credential Repository and Processing Function (ARPF); this function stores the long-term security credentials used in authentication for AKA

      – Storing of Subscription information

Policy Control Function (PCF) – Provides:

     – Support of unified policy framework to govern network behavior

     – Policy rules to control plane function(s) that enforce them

Application Function (AF) – Requests dynamic policies and/or charging control