[Back]

V. Abad:
"Energy efficient Scheduling for LTE Uplink";
Supervisor: S. Schwarz, M. Rupp; Institute of Telecommunications, 2013; final examination: 11-15-2013.

In a scenario where mobile users are exponentially growing, new generation mobile communication systems such as Long Term Evolution (LTE) have been designed to provide higher data rates and lower latencies to allow a broad number of services and applications in a mobile device. The development of new and demanding services such as video streaming, real-time gaming entails Quality of Service (QoS) support as well as capacity increase.
On the other hand, this increased number of high consuming services and components is not coming with battery developments, for that reason the energy efficiency has become a crucial issue. These mobile devices, which are battery supplied, not only have to run an increasing number of services and lots of software functions they are also equipped with high consuming components (e.g. screen, processor). Such a device requires a huge battery capacity that is not affordable with the actual battery technology. Therefore, the energy-efficiency is assumed to be the main challenge for the researchers in designing of new architectures of the new mobile communication systems.
The objective of this diploma thesis is to design an energy-efficient packet scheduling algorithm. The Packet Scheduler (PS) is in charge of the allocation of radio resources to users over the shared wireless channel. In such a scenario where different users want to transmit over a wireless channel, the PS aims to achieve spectral efficiency by using the variability of the wireless channel and the offered traffic data. The PS requires information about the instantaneous channel quality to be able to exploit time, space, frequency and multi-user diversity. Multi-user diversity is of particular interest in this thesis, it aims at exploiting the statistic independence of the channel fading by multiple users within the same cell or coverage area. It allows to allocate users which are experiencing better channel conditions.
In LTE packet schedulers play a key role in the overall system performance. The main goal of this scheduler is to fulfil the expectations of as many users in the system as possible, taking into account the QoS requirements of their respective applications and in addition, avoiding energy waste in order to extend battery life in the User Equipment (UE).
In the first part of this thesis, a comparison study between several basic schedulers is carried out in order to evaluate their performance and general characteristics. As a result of this comparison the Proportional Fair (PF) scheduler is proposed as a starting allocation scheme. The reasons for this decision are not only its well-known trade-off between fairness and throughput, but also its flexibility. The PF scheduler computes a metric, for each Resource Block (RB) and user in the current Time Transmission Interval (TTI), trying to maximize total throughput while at the same time allowing all users at least a minimal level of service. The next chapter presents a modification of the PF metric as a good energy-saving approach, which is also applied in the final resource allocation scheme design.
In the second part of the thesis, the most common traffic models are implemented and they are randomly assigned among users with certain appearance probability in order to build a traffic-mix scenario. In that scheme several PF-based schedulers are evaluated for different number of users in the system. The results show the improvements achieved with the proposed scheduler in terms of delay and throughput for high-loaded systems and the possible energy saves under low-load conditions.
The final part briefly presents the overall conclusions and two topics for future research such as the Discontinuous Reception- (DRX), Transmission (DTX) that LTE exploits and Interference Coordinated Scheduling.

In a scenario where mobile users are exponentially growing, new generation mobile communication systems such as Long Term Evolution (LTE) have been designed to provide higher data rates and lower latencies to allow a broad number of services and applications in a mobile device. The development of new and demanding services such as video streaming, real-time gaming entails Quality of Service (QoS) support as well as capacity increase.
On the other hand, this increased number of high consuming services and components is not coming with battery developments, for that reason the energy efficiency has become a crucial issue. These mobile devices, which are battery supplied, not only have to run an increasing number of services and lots of software functions they are also equipped with high consuming components (e.g. screen, processor). Such a device requires a huge battery capacity that is not affordable with the actual battery technology. Therefore, the energy-efficiency is assumed to be the main challenge for the researchers in designing of new architectures of the new mobile communication systems.
The objective of this diploma thesis is to design an energy-efficient packet scheduling algorithm. The Packet Scheduler (PS) is in charge of the allocation of radio resources to users over the shared wireless channel. In such a scenario where different users want to transmit over a wireless channel, the PS aims to achieve spectral efficiency by using the variability of the wireless channel and the offered traffic data. The PS requires information about the instantaneous channel quality to be able to exploit time, space, frequency and multi-user diversity. Multi-user diversity is of particular interest in this thesis, it aims at exploiting the statistic independence of the channel fading by multiple users within the same cell or coverage area. It allows to allocate users which are experiencing better channel conditions.
In LTE packet schedulers play a key role in the overall system performance. The main goal of this scheduler is to fulfil the expectations of as many users in the system as possible, taking into account the QoS requirements of their respective applications and in addition, avoiding energy waste in order to extend battery life in the User Equipment (UE).
In the first part of this thesis, a comparison study between several basic schedulers is carried out in order to evaluate their performance and general characteristics. As a result of this comparison the Proportional Fair (PF) scheduler is proposed as a starting allocation scheme. The reasons for this decision are not only its well-known trade-off between fairness and throughput, but also its flexibility. The PF scheduler computes a metric, for each Resource Block (RB) and user in the current Time Transmission Interval (TTI), trying to maximize total throughput while at the same time allowing all users at least a minimal level of service. The next chapter presents a modification of the PF metric as a good energy-saving approach, which is also applied in the final resource allocation scheme design.
In the second part of the thesis, the most common traffic models are implemented and they are randomly assigned among users with certain appearance probability in order to build a traffic-mix scenario. In that scheme several PF-based schedulers are evaluated for different number of users in the system. The results show the improvements achieved with the proposed scheduler in terms of delay and throughput for high-loaded systems and the possible energy saves under low-load conditions.
The final part briefly presents the overall conclusions and two topics for future research such as the Discontinuous Reception- (DRX), Transmission (DTX) that LTE exploits and Interference Coordinated Scheduling.

LTE, MIMO OFDM

http://publik.tuwien.ac.at/files/PubDat_221265.pdf

Project Head Christoph Mecklenbräuker:
Christian Doppler Lab "Funktechnologien für nachhaltige Mobilität"

Project Head Markus Rupp:
Mobile Access Research 2013