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LTE eNB schedulers: the basics
MAC in eNB stack contains a scheduler for assigning time/frequency resource blocks to users, in downlink and uplink, compliant with 3GPP specification. It controls and prioritizes bandwidth across users.
(source: https://blog.yate.ro/2015/07/30/an-introduction-to-the-lte-mac-scheduler/)
LTE eNB schedulers: the baseline
It’s fair to UEs in the long term, but isn’t aware of network conditions (like CQI) or specific UEs needs (like VoLTE). It’s regarded as inefficient in terms of cell throughput.
The simplest scheduling algorithm is Round Robin. It assigns resource blocks cyclically to all UEs, one after another.
It provides benchmark baseline.
Start
Schedule first user
Schedule next user
All users scheduled?Yes No
LTE eNB schedulers: Proportional Fair
Properties:weighted by CQImaintains UEs throughput historyprioritizes UEs with lower throughputcell-edge users aren’t neglected
Proportional Fair algorithm is an example of achieving good cell throughput while being quite fair.
Start
Compare CQI
User withhigher CQI?
Schedule first user
Schedule next user
1st time slotfinished?
Schedule first user
Schedule next user
2nd time slotfinished?
No Yes
No
YesNo Yes
RR greedyPF
What we want:Proportional Fair
fairness & efficiencyour scheduler
fairness & efficiency<<
fairnesscell
throughputefficiency
LTE scheduling algorithms spectrum
Advanced scheduler takes into account more properties.
We aim to provide good GBR instead of raw throughput. This should make better use of resources in real-life scenarios.
Advanced scheduler
LTE eNB schedulers: implementation
But real world data → real eNB stack.
We used Small Cell Forum's Femto Application Platform Interface. Now scheduler is pluggable into any compliant stack. FAPI was enhanced to support Carrier Aggregation.EURECOM devs added partial FAPI support to OAI.We implemented Round Robin and Advanced schedulers in ANSI C, as libraries and are integrating them with OAI.
+ LTE MAC Lab → performance estimates.Models in
was a natural choice.
Standard interfaces are a Good Thing
(source: Small Cell Forum)
Advanced scheduler: estimates
Advanced scheduler: estimates
Lessons learnt
Some after-action thoughts from our devs about working with OAI:
setting up development environment for OAI is time consuming and prone to error - needs more automationit’s hard for non-Linux-savvy devs to get basic usecases working – one-click solution would be idealOAI would benefit from a simpler way to manage its configuration
To address those needs we created a new set of productivity tools, which wrap around OAI and allow for rapid deployment of basic usage scenarios, make reconfiguration easy and save a lot of time: aLTErnative.
aLTErnative walkthrough
For novices there's interactive GUI.
For power users there's script-friendly command line.
aLTErnative walkthrough
There can be multiple profiles. Each profile has separate set of configuration files (eNB, MME, HSS) and own SIM database. In one place for easy reference. Starting from clean state is as easy as creating new profile.
aLTErnative walkthrough
Adding SIMs to HSS is easy.
aLTErnative walkthrough
Making OAI's eNB and core network work is easy too.
aLTErnative walkthrough
Additionally aLTErnative offers a way to:setup your system for OAI development through a scriptgather logs and system information in a unified wayuse its components in your own applications through an API
It works on Ubuntu, can be installed and updated easily through its Software Center.
We have a lot of plans for extending aLTErnative:support for UEssupport for other open source LTE stacksnicer GUI
We believe aLTErnative has a lot to offer for OAI community.
aLTErnative
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