Time-division duplex (TDD) is a technique allowing a telecommunication channel using the same transmission resource (a radio channel for example), to multiplex transmission and reception over time. This technique has a definite advantage in the case where the transmission and reception rates are variable and asymmetrical. When the transmission rate increases or decreases, more or less bandwidth can be allocated. Another advantage of this technique relates to mobile terminals moving at very low speed or in a fixed position. In this case, the beamforming technique is very effective with a TDD system.TD-LTE and 5G NR networks are adopting this technique to enhance capacity by using Mid band and High Band.
The interference source and localization of the mobile communication network, especially the Time Division Duplexing (TDD) system, becomes very complicated, especially when it becomes from natural phenomena.Atmospheric ducting is a mode of propagation of electromagnetic radiation, usually in the lower layers of Earth’s atmosphere, where the waves are bent by atmospheric refraction. For TDD system Atmospheric ducting can be a major source of intra-system interfrence.
This post mainly explain the basis of atmospheric duct interfrence for the Time Division Long Term Evolution (TD-LTE) system. It will proposes a centralized scheme to avoid such kind of interference through parameter optimization.
What is Atmospheric Duct Interference ?
With the low atmospheric duct effect, electromagnetic wave can bypass the ground plane and experiences trans-horizon propagation due to its small propagation loss like propagation in the atmospheric duct. If the remote eNodeB is located at a certain height, its large-power downlink signals can reach the local eNodeB after long-distance transmission.
Because the long-distance transmission time exceeds the uplink/downlink guard interval, the downlink signals from the remote eNodeB are received by the local eNodeB in the receive timeslot of the local eNodeB, thereby interfering with uplink reception of the local eNodeB and producing remote co-channel interference. As a result, the network KPIs deteriorate mainly UL Interference and UL Throughput.
Methods and optimization for reducing the effects of atmospheric ducting interference:
Remote interference adaptive avoidance:
Due to atmospheric duct reciprocity, downlink signals of an eNodeB subject to remote interference caused by an atmospheric duct interfere with the uplink transmission of a remote eNodeB. When there is remote interference, the eNodeB periodically detects characteristic sequences in the UpPTS and uplink subframes. Based on the detection result, the eNodeB adjusts the special subframe configuration over the Uu interface and the guard period (GP) to reduce interference to the remote eNodeB. This method can be done manually by the optimizer or automatically when some features are already activate on the network.
Atmospheric duct downlink subframe shutdown:
Atmospheric duct interference is essentially the downlink interference caused by a remote eNodeB to the uplink reception of the local eNodeB. Therefore, interference to the local eNodeB can be eliminated as long as the downlink subframes of the remote eNodeB have no power output. Based on the reciprocity of atmospheric duct, downlink service scheduling in subframes 0, 1, 5, and 6 can be disabled and scheduling of some CRS resources can be stopped on the local eNodeB when atmospheric duct interference occurs. This can reduce interference to the remote eNodeB and atmospheric duct interference on the entire network.
Optimized atmospheric duct downlink subframe shutdown:
Similar to atmospheric duct downlink subframe shutdown, this function is also based on atmospheric duct reciprocity. The eNodeB periodically detects interference in a cell and automatically performs cell-level subframe shutdown when atmospheric duct interference meets the threshold requirements. This method reduces atmospheric duct interference of the local cell to the entire network, improves the radio access and handover success rates, and decreases the service drop rate of the entire network. However, this function also provides negative gains to the local cell, decreasing the cell throughput and number of users and increasing the packet loss rate.
Read also:
TTI Bundling for better VOLTE HARQ and Latency
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Tags :
5G NR
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Antenna
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Beamforming
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LTE
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