Impact of MAC Scheduling algorithms on throughput in a Multi UE scenario

In this example we understand how the scheduling algorithm affects the UDP download throughput of a multi-user (UE) system where the UE’s are at different distances from the gNB. Open NetSim, Select Examples ->5G NR ->Scheduling then click on the tile in the middle panel to load the example as shown in below screenshot

Graphical user interface, application Description automatically generated

Figure 4‑31: List of scenarios for the example of Scheduling

The following network diagram illustrates, what the NetSim UI displays when you open the example configuration file.

Figure 4‑32: Network set up for studying the Scheduling

Round Robin#

Settings done in example config file

  1. Set grid length as 4000m from Environment setting.

  2. Set distance as follows.

    1. gNB_7 to UE_8 = 300m

    2. gNB_7 to UE_9 = 600m, and

    3. gNB_7 to UE_10 = 900m

  3. Go to Wired link properties and set the following properties as shown below Table 4‑21.

Wired Link Properties
Uplink_Speed 5000Mbps
Downlink_Speed 5000Mbps
Uplink and downlink BER 0.0000001

Table 4‑21: Wired Link Properties

  1. Go to gNB properties à Interface (5G_RAN), set the following properties as shown below Table 4‑22.
Properties
DataLink Layer Properties
Scheduling Type ROUND_ROBIN
Physical Layer Properties
CA_Type INTER_BAND_CA
CA_Configuration CA_2DL_1UL_n39_n41
CA1
Numerology 2
Channel Bandwidth 40 MHz
CA2
Numerology 2
Channel Bandwidth 100 MHz
Outdoor_Scenario URBAN_MACRO
LOS_NLOS_Selection USER_DEFINED
LOS_Probabillity 0
Pathloss Model 3GPPTR38.901-7.4.1
Shadow Fading Model None
Fading _and_Beamforming NO_FADING_MIMO_UNIT_GAIN
O2I Building Penetration Model Low Loss Model

Table 4‑22: gNB >Interface (5G_RAN) >Physical layer properties

  1. Set Tx_Antenna_Count as 2 and Rx_Antenna_Count as 1 in gNB properties.

  2. Set Tx_Antenna_Count as 1 and Rx_Antenna_Count as 2 in all the UEs.

  3. Go to Application properties and set the following properties as shown below Table 4‑23.

Application Properties
Application 1 Application 2 Application 3
Application Type CBR CBR CBR
Source_Id 12 12 12
Destination_Id 8 9 10
QoS UGS UGS UGS
Transport Protocol UDP UDP UDP
Packet_Size 1460Bytes 1460Bytes 1460Bytes
Inter_Arrival_time 10μs 10μs 10μs
Start_Time 1s 1s 1s

Table 4‑23: Application properties

  1. Plots are enabled in NetSim GUI.

  2. Run Simulation for 1.5s, after simulation completes go to metrics window and note down throughput value from application metrics.

Proportional Fair#

Settings done in example config file:

  1. Set all the properties as configured in Round Robin example and go to gNB properties à Interface (5G_RAN) à Data Link Layer properties, set Scheduling type as PROPORTIONAL_FAIR.

  2. Run Simulation for 1.5s, after simulation completes go to metrics window and note down throughput value from application metrics.

Max Throughput#

Settings done in example config file:

  1. Set all the properties as configured in Round Robin example and go to gNB properties à Interface (5G_RAN) à Data Link Layer properties, set Scheduling type as MAX_THROUGHPUT.

  2. Run Simulation for 1.5s, after simulation completes go to metrics window and note down throughput value from application metrics.

Fair Scheduling#

Settings done in example config file:

  1. Set all the properties as configured in Round Robin example and go to gNB properties à Interface (5G_RAN) à Data Link Layer properties, set Scheduling type as FAIR_SCHEDULING.

  2. Run Simulation for 1.5s, after simulation completes go to metrics window and note down throughput value from application metrics.

Result: We first run the scenario with each of the UEs downloading a single application in standalone basis. This gives the maximum achievable rate per node. The results are below.

Distance from gNB (m) Application Id Throughput (Mbps)
300 1 759.50
600 2 233.06
900 3 80 .66

Table 4‑24: UE throughputs if they were run standalone (without the other UEs downloading data)

We then run the same simulation with all the three UEs simultaneously downloading data.

Throughput (Mbps)
Scheduling Application 1 Application 2 Application 3 Aggregate
Round Robin 223.90 61.90 17.37 303.17
Proportional Fair 665.24 3.59 0 668.83
Max Throughput 672.13 0.00 0.00 672.13
Fair Scheduling 37.025 37.189 37.329 111.54

Table 4‑25: UDP download throughputs for different scheduling algorithms when all three 3 UEs simultaneously downloading data

The PHY rate is decided based on the SNR. A UE closer to the gNB will get a higher date rate than a UE further away. In this example the distances from the gNB are such that UE10_Distance > UE9_Distance > UE8_Distance.

In Round Robin PRBs are allocated equally among all three nodes. However, throughputs are in the order UE8 > UE9 > UE10 because of their distances from the gNB. The individual throughputs seen by each of the UEs is exactly $\frac{1}{3}$ of the throughput as shown in Table 4‑24.

In proportional fair scheduling the resource allocation is such that nearer UEs get proportionally higher allocation (based on CQI) when compared to further away UEs. In Max throughput scheduling the PRBs are allocated such that the system gets the maximum download throughput.

Fair scheduling provides strict fairness, and this results in all applications seeing equal throughput.