Masters Thesis: 4G/5G Baseband Dev. - Improve Down Link Throughput with DL Sub Symbol Times shi i Stockholm

1.  Implement a mechanism for individual adjustment of the timing of the FDD/TDD LTE downlink frame structure for each cell that is being served by the base station.

2. Implement a mechanism to avoid collisions between Random Access Messages in uplink subframes and the data in subsequent downlink subframes.

3. Implement a mechanism that will align the FDD/TDD LTE uplink cells served by the base station to the same symbol timing.

4. Evaluate how well the CRS shift method will interact with other interference mitigation techniques such as the Ericsson Lean Carrier method and CRS IC.

5. Investigate the cause of any potential performance issues and propose/implement a solution if it can be found.

6. Verification of the feature is performed by "over the air" testing by car. Lab measurements may also be a complement or an alternative to the OTA testing.

Development Environment:

This Baseband Digital Signal processing task will be implemented in Ericsson’s state of the art multi-core Flex ASIC platform. Programming work will be performed in C language.

This thesis work aims at addressing the problem of mitigating the interference generated by CRS interference by shifting the timing alignment of the DL frame structure between cells by a fraction of a full OFDM symbol. The use of different time shifts between cell neighbors has the effect of distributing the CRS interference power into two OFDM symbols instead of a single OFDM symbol in the victim cell. In the traditional configuration where the same time alignment is used in all DL cells that is served by the same eNB the CRS would be distributed over one OFDM symbol only. By distributing the CRS interference over two OFDM symbols instead of a single OFDM symbol the earlier described negative impact on the decoding performance can be significantly reduced and the DL throughput is significantly improved.

When a UE attempts to connect to a cell it first listens to the primary and secondary synchronization channels transmitted in DL by the eNB. The UE use these signals to synchronize its internal timing against the transmission timing of LTE frame structure of the cell. After having completed the synchronization towards the LTE DL frame structure of the cell the UE transmits a Random-Access message (PRACH) also referred to as message 1. The PRACH is sent on a physical resource that is specified in the DL broad cast information. At the detection of PRACH the time of arrival of the PRACH is measured by the eNB. Since the eNB is aware of that PRACH must be transmitted at the beginning of an UL subframe it can use this information to calculate the propagation delay between the UE and the eNB. The propagation delay corresponds to the initial timing misalignment between the UL and DL frame structures. If the eNB detects what it believes is a valid PRACH, a message 2 signal is sent back to the UE, in response. The message 2 message includes information that commands the UE to adjust its initial UL transmission timing for subsequent UL transmissions.

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Primary country and city: Sweden (SE) || || Stockholm || 21097

Req ID: 220901