LTE eNB Scheduler is an advanced software library realizing functions of a base station scheduler. It interacts with the LTE eNB Stack through a Small Cell Forum (former Femto Forum) compliant interface (FAPI) extended to support Carrier Aggregation. Thanks to that LTE eNB Scheduler can be used together with LTE eNB Stack or with other customer-specific eNB protocol stacks. LTE eNB Scheduler implements two configurable scheduling algorithms including an advanced channel-aware proprietary scheduling algorithm designed for performance, as well as a simple round robin scheduling algorithm designed for benchmarking.
LTE eNB Scheduler library is implemented in ISO 9899:1999 C (C99) using the latest industry standards for improved safety and performance. LTE eNB Scheduler runs on any processing environment providing threading support. For those customers who aim at integrating our LTE eNB Scheduler with their own eNB protocol stacks, we provide integration support service.
Figure 1: LTE eNB Scheduler in the eNB architecture
Figure 2: LTE eNB Scheduler main functionalities
LTE eNB Scheduler takes three main steps while assigning radio resources to users. They are presented in the Figure 3.
At the begining list of users connected to eNB is prioritized. This step allows to sort users according to their data rate requirements and retransmission needs. In the next step, the algorithm selects resources for all users by calculating their priority per each available resource block. Priority depends on queue length, packet delay, channel conditions and historical throughput.
Scheduling decision provided by the scheduler must be compliant with 3GPP specifications – resource assignment must be in specific format, it must take into account reserved resources for control/signalling region and capabilities of the user equipment. In the last step, LTE eNB Scheduler maps calculated priorities to final scheduling decision, which fulfills 3GPP requirements.
Figure 3: Main steps of scheduling algorithm.
LTE eNB Scheduler, while assigning resources, takes into account multiple factors. Thanks to this approach algorithm can be adjusted to operator’s needs – it might maximize total base station throughput, miminize user latency or increase fairness.
Table I shows a comparison of various schedulers, including our product, based on criteria of taking into account selected parameters and measures in making a scheduling decision.
(*) support for Carrier Aggregation means ability to activate/deactivate second component carrier
Results presented below show performance of a MATLAB model of LTE eNB Scheduler implemented in the system-level simulation tool – LTE MAC Lab.
Cumulative Distribution Function of total base station throughput, presented in the Figure 4, shows that LTE eNB Scheduler offers higher throughput than other scheduling algorithms. The same resources are distributed among users in a more efficient way.
Figure 4: Total base station throughput distribution
Performance of the scheduler can be analyzed also from user point of view. To show how user throughput can be increased we compare peak and edge user throughput. Peak user throughput is achieved by users with best channel conditions and it is a 90% point of user throughput distribution. Cell edge user throughput is a 10% point of user throughput distribution.
Figure 5: Peak and cell edge user throughput.
Figure 5 shows comparison of peak and cell edge user throughput between LTE eNB Scheduler and benchmark algorithms. User throughputs are normalized for peak user throughput for Proportional Fair algorithm. Using this normalization allows to show gain obtained with LTE eNB Scheduler. Our algorithm’s performance is 35% better than Proportional Fair in terms of peak user throughput without degrading cell edge user throughput.
LTE eNB Scheduler is delivered as a library compiled for desired architecture that can be further linked with the protocol stack binary.