| Summary: | 碩士 === 國立中正大學 === 通訊工程研究所 === 107 === Abstract
The mobile communication system changes decade after decade. The next generation of mobile communication aims to provide users with better service experience and can be applied in various scenarios, such as enhanced mobile broadband (eMBB), large Massive Machine Type Communications (MMTC), Ultra-Reliable and Low Latency Communications (URLLC). Therefore, the 5th Generation Mobile Communication New Radio (5G-NR) must satisfy these diverse requirements, such as instantaneous traffic burst, ultra-high throughput, and ultra-low latency.
On the other hand, when adjacent TRPs(Transmission Reception Point, TRP) operate in different transmission directions in heterogeneous TDD slot configurations for accommodating their diverse traffic load, additional Cross-Link Interference(CLI) happens. This will seriously degrade the transmission quality for nearby base stations or user equipments. There are many strategies mitigating CLI, such as link adaptation, scheduling coordination, beam coordination, hybrid time division duplex (Hybrid TDD), and advanced receiver. This thesis proposed an approach on link adaptation to mitigate CLI.
Heterogeneous time slot configuration TDD system means that there are at least two different TDD configurations among base stations in the simulation environment. , where each base station selects one in these different TDD configurations based on its downlink/uplink traffic ratio, but also possibly resulting in CLI in adjacent TRPs.
First of all, the mechanism proposed in this thesis will establish a Victim UE-Aggressor UE pair list through some UE-UE measurements. When the base stations have the Victim UE-Aggressor UE pair list, the CLI mitigation method can be implemented through the coordination between the base stations.
While transmission proceeds, the victim UE will feedback two channel quality indicators in two cases of subframes. One is without aggressor UE interference, and the other is with aggressor UE interference. Therefore, two modulations and coding selections can be obtained through these two types of feedback.
Finally, based on the transmission direction and traffic notification of aggressor, corresponding modulation and coding thus can be adaptively selected to possibly mitigate the effect of CLI from aggressor UE and improve system performance, such as user error rate, user packet delay, and user packet retransmission times and DL Cell Spectral Efficiency.
Using the method proposed in this thesis, there are a total of 18 victim user devices, of which 55% error rate and downlink base station spectral efficiency are improved, 44% retransmission times are reduced, but 78% of victim user device packet delays increases. From the results, the method used in this thesis has a limited improvement. About 55% of the victim users have system performance gains, and the remaining victim devices may have system performance loss.
The contributions of this thesis are: (1) Effort on a complete observation and description of UE-UE interference, (2) Description of the relationship between UE-UE interference and the degree of spectrum benefit in downlink serving cells, (3) Proposing a method with adaptive modulation and coding scheme selection to mitigate the effect of UE-UE interference and improve DL cell spectral efficiency.
Keywords: Heterogeneous time slot configuration TDD, link adaptation, UE-UE Abstract
The mobile communication system changes decade after decade. The next generation of mobile communication aims to provide users with better service experience and can be applied in various scenarios, such as enhanced mobile broadband (eMBB), large Massive Machine Type Communications (MMTC), Ultra-Reliable and Low Latency Communications (URLLC). Therefore, the 5th Generation Mobile Communication New Radio (5G-NR) must satisfy these diverse requirements, such as instantaneous traffic burst, ultra-high throughput, and ultra-low latency.
On the other hand, when adjacent TRPs(Transmission Reception Point, TRP) operate in different transmission directions in heterogeneous TDD slot configurations for accommodating their diverse traffic load, additional Cross-Link Interference(CLI) happens. This will seriously degrade the transmission quality for nearby base stations or user equipments. There are many strategies mitigating CLI, such as link adaptation, scheduling coordination, beam coordination, hybrid time division duplex (Hybrid TDD), and advanced receiver. This thesis proposed an approach on link adaptation to mitigate CLI.
Heterogeneous time slot configuration TDD system means that there are at least two different TDD configurations among base stations in the simulation environment. , where each base station selects one in these different TDD configurations based on its downlink/uplink traffic ratio, but also possibly resulting in CLI in adjacent TRPs.
First of all, the mechanism proposed in this thesis will establish a Victim UE-Aggressor UE pair list through some UE-UE measurements. When the base stations have the Victim UE-Aggressor UE pair list, the CLI mitigation method can be implemented through the coordination between the base stations.
While transmission proceeds, the victim UE will feedback two channel quality indicators in two cases of subframes. One is without aggressor UE interference, and the other is with aggressor UE interference. Therefore, two modulations and coding selections can be obtained through these two types of feedback.
Finally, based on the transmission direction and traffic notification of aggressor, corresponding modulation and coding thus can be adaptively selected to possibly mitigate the effect of CLI from aggressor UE and improve system performance, such as user error rate, user packet delay, and user packet retransmission times and DL Cell Spectral Efficiency.
Using the method proposed in this thesis, there are a total of 18 victim user devices, of which 55% error rate and downlink base station spectral efficiency are improved, 44% retransmission times are reduced, but 78% of victim user device packet delays increases. From the results, the method used in this thesis has a limited improvement. About 55% of the victim users have system performance gains, and the remaining victim devices may have system performance loss.
The contributions of this thesis are: (1) Effort on a complete observation and description of UE-UE interference, (2) Description of the relationship between UE-UE interference and the degree of spectrum benefit in downlink serving cells, (3) Proposing a method with adaptive modulation and coding scheme selection to mitigate the effect of UE-UE interference and improve DL cell spectral efficiency.
Keywords: Heterogeneous time slot configuration TDD, link adaptation, UE-UE Interference, adaptive MCS selection scheme, DL Cell Spectral Efficiency.
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