ENB capacity depends on the eNB configuration request, which is further in compliance with the customers’ request.
Note that the capacity is also confined by the product itself with the capability restrictions of the hardware as well as the software inside.
On the other hand, it has been theoretically proofed that there is tradeoff between wireless system throughput and capacity. Fairness is therefore introduced to represent how the system handles the scheduling of different users in various wireless channel conditions. Different fairness factors lead to different results with respect of capacity in the following section.
13.1.1 ENB CAPACITY CONFIGURATIONS
Features and configuration elements impacting the eNB capacity figures are:
TDD UL/DL Bandwidth configured through parameters bandwidth. Different capacity figures are available depending on the LTE bandwidth used.
Parameter maxNbrOfUsers controls the number of users that can be admitted in a cell (users per modem).
Parameter maxNumberOfCallPerEnodeB controls the number of users that can be admitted on the eNB (users per Controller board)
From TLA6.0, there is no different between 10/20 MHz bandwidth, different DL/UL configurations and 2 antennas/8 antennas, with parameter uplinkControlChannelLUTindex setting to value 0 and CFI setting to 3. The following table is summarizing the eNB capacity figures that can be obtained.
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LTE/IRC/APP/032749 V06.03 / EN Approved Standard 28/Oct/2013 Page 158/290 TDD
bandwidth DL/UL Configuration 1/configuration2, 2/8 antennas, Special subframe 7/5
Average Scheduled #user per TTI per cell = 10 Table 13-1: TLA6.0 Capacity figures
13.1.2 ALPHAFAIRNESSFACTOR
Parameter alphaFairnessFactor tunes the alpha fairness factor (thus the behaviour) of the DL scheduler.
The scheduler is the processing entity that allocates resources to user plane and control plane traffic. Different factors such as channel quality, data pending in buffers, relative priorities in terms of QoS traffic are some key factors that are used by the scheduler to pick specific users from the active pool and allocate air-link resources to them. The overall goal is to ensure that users do get a chance to share the available bandwidth in the system, and the resources are allocated in an efficient manner while maintaining good system utilization.
Expected behaviour when changing this parameter alphaFairnessFactor = 0
Aggressive mode (α = 0) means that the scheduler prefers better radio channel conditions to normal radio channel conditions. Therefore, the scheduler provides more resources to UEs in better conditions. The better the radio conditions of the UE, the more resources (and hence the higher the data rate) it gets.
Using test procedures described in section 10.1.9, the follow results when apply the aggressive mode you should expect:
UE in Cell Edge are allocated the less PRB in average to favour UE with better radio conditions. On the other side, since the better radio condition usually brings throughput gains, this mode may have best throughput performance as compared to proportional fairness and enhanced proportional fairness.
alphaFairnessFactor = 1
Proportional Fairness (α = 1), the scheduler attempts to provide the same number of RBs to all the UEs (despite their different conditions).
Using test procedures described in section 10.1.9, the follow results when apply the proportionalfair mode you should expect:
Default Value= "1"
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LTE/IRC/APP/032749 V06.03 / EN Approved Standard 28/Oct/2013 Page 159/290 Average fairness maintained despite different radio conditions
alphaFairnessFactor = 2
Conservative mode (α = 2) shows the more Ue move away, the more PRB they are allocated, decreasing gaps between Ue Throughput but decreasing the cell Throughput as well. The scheduler attempts to allocate the resources in such a way that all the UEs eventually get the same data rate (which is not the case of the fair scheduler since different radio conditions result in different data rates even when the number of resources is the same, hence the increased fairness of the scheduler, as compared to the “regular” fair scheduler).
Using test procedures described in section 10.1.9, the follow results when apply the conservative mode you should expect:
When the UE’s is in bad radio conditions, more PRB are allocated in average to decrease throughput gaps
Average UE DL throughput per radio group (Good, Medium, Bad radio conditions), decrease compared to proportionalfair mode
In overall the final 15 UE throughput decrease compared with proportionalfair mode
alphaFairnessFactor conclusions:
Conservative mode (α = 2), shows the more UE move away, the more PRB they are allocated, decreasing gaps between UE Throughput but decreasing the cell Throughput as well.
Aggressive mode (α = 0), shows the more UE come closer, the more PRB they are allocated, increasing gaps between UE Throughput but also the cell Throughput.
Proportional Fair mode (α = 1), shows the better fairness distribution between the different radio conditions. All UE’s will have the same resources even in bad radio conditions, appropriate for commercial networks.
13.1.3 ULSCHEDPROPFAIRALPHAFACTOR
Parameter ulSchedPropFairAlphaFactor tunes the alpha fairness factor (thus the behaviour) of the UL Scheduler.
Expected behaviour when changing this parameter
ulSchedPropFairAlphaFactor = 1 KPI Impact:
Throughput – Low values increase the throughput in the near&mid-cell condition at expense of cell edge users.
Capacity - Low values increase the cell overall throughput at expense of cell edge users.
Default Value= "0.5"
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LTE/IRC/APP/032749 V06.03 / EN Approved Standard 28/Oct/2013 Page 160/290 Aggressive mode (α = 1), Yields a maximum C/I scheduler. The scheduler provides more resources to UEs in better conditions. The better the radio conditions of the UE, the more resources (and hence the higher the data rate) it gets.
Using test procedures described in section 11.1.3, the follow results when apply the aggressive mode you should expect:
ULS choice only depends on spectrum efficiency => unpredictable fairness behaviour TCP flow control increases BO of favoured Ues and decrease BO of others
ulSchedPropFairAlphaFactor = 0.5
Proportional Fair (α = 0.5), Yields a fair scheduler. The scheduler attempts to provide the same number of RBs to all the UEs (despite their different conditions).
Using test procedures described in section 11.1.3, the follow results when apply the proportional fair mode you should expect:
PRB used in UL => decreased in degraded radio when Ue reach maximum path loss (PHR limitation) Fairness no more significant between Cell edge group and the others conditions, since UE is at maximum path loss.
ulSchedPropFairAlphaFactor = 0
Conservative mode (α = 0), yields an increased fairness scheduler. The scheduler attempts to allocate the resources in such a way that all the UEs eventually get the same data rate (which is not the case of the fair scheduler since different radio conditions result in different data rates even when the number of resources is the same, hence the increased fairness of the scheduler, as compared to the “regular” fair scheduler).
Using test procedures described in section 11.1.3, the follow results when apply the conservative mode you should expect:
Average Ue Throughput per radio group => differences decreased compared to proportional Fair mode
Cell Throughput decreased compared to proportional Fair mode
The more UE are in bad radio, the more PRB they are allocated in average to decrease Throughput gaps.
ulSchedPropFairAlphaFactor conclusions:
Conservative mode (α = 0), does not show any improvement compared to proportional fair results, as shown in simulations results as well.
Proportionalfair mode (α = 0.5), fairness no more significant between Cell edge and the other radio conditions, since UE is at maximum path loss. More PRB bandwidth used in this configuration compared with the other. Better configuration for commercial networks.
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LTE/IRC/APP/032749 V06.03 / EN Approved Standard 28/Oct/2013 Page 161/290 Aggressive mode (α = 1), is not a significant test since throughput between users are not
predictable. This mode is not recommended for customer deployment.