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.