Riassunto analitico
Long-Term Evolution-Wireless Local Area Network (LTE-WLAN) Aggregation (LWA) has recently emerged as a promising technology within the third Generation Partnership Project (3GPP) Release 13 to efficiently aggregate LTE and WLAN at Packet Convergence Data Protocol (PDCP) layer, allowing uplink traffic to be carried on LTE and downlink traffic on both LTE and WLAN.
This removes all the contention asymmetry problems of WLAN and allows an optimum usage of both licensed and unlicensed bands on the downlink.
The dynamic usage of unlicensed spectrum by mobile network operators drastically alleviates the limitations due to spectrum scarcity in Long Term Evolution (LTE), allowing User Equipments (UEs) larger bandwidth and therefore better performance.
However, the usual legacy UE implementation, the so called “WLAN-if coverage”, leads to a poor usage of LTE and WLAN radio resources because the UE selects the WLAN access as soon as the WLAN coverage is detected even if the LTE access would provide a better service.
This thesis presents an alternative solution to the “WLAN-if coverage” implementation, a dynamic algorithm to be implemented on the eNodeB of an infrastructured environment. The main purpose of the algorithm is to dynamically tune the amount of downlink traffic on unlicensed band to use it at its maximum capability without excessively corrupting the signal received by the UE.
The eNodeB periodically checks the data delay (D) and the Wi-Fi channel occupancy (O) and splits the downlink transmission between the LTE and the Wi-Fi Channel depending on these two values, in order to keep them below a fixed threshold and at the same time fill the unlicensed band mantaining a reliable communication.
Numerical results of the thesis refer to a typical urban scenario where both cellular coverage (C2-V) and 802.11ac are available. UEs are ordinary vehicles equipped with both radio technologies.
Then, when a disruptive event occurs, e.g., a car crash, the use of combined technologies is confined only to a special vehicle, that could be an ambulance, a police car or an emergency vehicle, in order to guarantee the best possible data communication to properly manage the emergency condition. When this happens, all downlink transmission of ordinary vehicles is switched on LTE.
After a certain amount of time, the eNodeB gradually readmits downlink transmission towards ordinary vehicles keeping under control “O” and “D” values so that they do not overcome a fixed threshold.
This investigation has been performed by the development of an ns-3 based urban vehicle simulator, where mobility has been modelled using SUMO, with a variable population of ordinary cars depending on the target of each simulation and an emergency vehicle which takes over for a limited amount of time.
The algorithm has been implemented on a testbed equipped with eight Software
Defined Radios (SDRs), located in Dresden (Germany). Each SDR pair can be used to
emulate either the LTE base station and Wi-Fi Access Point, or the receiving station, i.e.,
a vehicle equipped with both LTE and 802.11 radio interfaces.
Two main configurations were implemented on the testbed to replicate in a real environment the scenario modelled in the simulator.
In the first one (Scenario A), one SDR takes on the role of the emergency vehicle and the noise generator simulates the increasing traffic on the Wifi Channel.
In the second one (Scenario B), one SDR takes on the role of the ordinary vehicle while the noise generator acts as the emergency vehicle.
The results on the testbed showed the reliability of the algorithm even in a real environment, and numerical results are quite consistent with the ones obtained with the simulator.
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Abstract
Long-Term Evolution-Wireless Local Area Network (LTE-WLAN) Aggregation (LWA) has recently emerged as a promising technology within the third Generation Partnership Project (3GPP) Release 13 to efficiently aggregate LTE and WLAN at Packet Convergence Data Protocol (PDCP) layer, allowing uplink traffic to be carried on LTE and downlink traffic on both LTE and WLAN.
This removes all the contention asymmetry problems of WLAN and allows an optimum usage of both licensed and unlicensed bands on the downlink.
The dynamic usage of unlicensed spectrum by mobile network operators drastically alleviates the limitations due to spectrum scarcity in Long Term Evolution (LTE), allowing User Equipments (UEs) larger bandwidth and therefore better performance.
However, the usual legacy UE implementation, the so called “WLAN-if coverage”, leads to a poor usage of LTE and WLAN radio resources because the UE selects the WLAN access as soon as the WLAN coverage is detected even if the LTE access would provide a better service.
This thesis presents an alternative solution to the “WLAN-if coverage” implementation, a dynamic algorithm to be implemented on the eNodeB of an infrastructured environment. The main purpose of the algorithm is to dynamically tune the amount of downlink traffic on unlicensed band to use it at its maximum capability without excessively corrupting the signal received by the UE.
The eNodeB periodically checks the data delay (D) and the Wi-Fi channel occupancy (O) and splits the downlink transmission between the LTE and the Wi-Fi Channel depending on these two values, in order to keep them below a fixed threshold and at the same time fill the unlicensed band mantaining a reliable communication.
Numerical results of the thesis refer to a typical urban scenario where both cellular coverage (C2-V) and 802.11ac are available. UEs are ordinary vehicles equipped with both radio technologies.
Then, when a disruptive event occurs, e.g., a car crash, the use of combined technologies is confined only to a special vehicle, that could be an ambulance, a police car or an emergency vehicle, in order to guarantee the best possible data communication to properly manage the emergency condition. When this happens, all downlink transmission of ordinary vehicles is switched on LTE.
After a certain amount of time, the eNodeB gradually readmits downlink transmission towards ordinary vehicles keeping under control “O” and “D” values so that they do not overcome a fixed threshold.
This investigation has been performed by the development of an ns-3 based urban vehicle simulator, where mobility has been modelled using SUMO, with a variable population of ordinary cars depending on the target of each simulation and an emergency vehicle which takes over for a limited amount of time.
The algorithm has been implemented on a testbed equipped with eight Software
Defined Radios (SDRs), located in Dresden (Germany). Each SDR pair can be used to
emulate either the LTE base station and Wi-Fi Access Point, or the receiving station, i.e.,
a vehicle equipped with both LTE and 802.11 radio interfaces.
Two main configurations were implemented on the testbed to replicate in a real environment the scenario modelled in the simulator.
In the first one (Scenario A), one SDR takes on the role of the emergency vehicle and the noise generator simulates the increasing traffic on the Wifi Channel.
In the second one (Scenario B), one SDR takes on the role of the ordinary vehicle while the noise generator acts as the emergency vehicle.
The results on the testbed showed the reliability of the algorithm even in a real environment, and numerical results are quite consistent with the ones obtained with the simulator.
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