Lte Handover Fundamentals 2w3r3m

LTE-parameter-Optimization 10/14/2014

LTE MEASUREMENT HANDOVER HANDOVER INTRA E-UTRAN (X2)

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LTE MEASUREMENT HANDOVER HANDOVER EVENTS

Event Type Event A1 Event A2 Event A3 Event A4 Event A5 Event B1 Event B2

Description Serving becomes better than threshold Serving becomes worse than threshold Neighbour becomes offset better than serving Neighbour becomes better than threshold Serving becomes worse than threshold1 and neighbour becomes better than threshold2 Inter RAT neighbour becomes better than threshold Serving becomes worse than threshold1 and inter RAT neighbour becomes better than threshold2

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LTE MEASUREMENT HANDOVER HANDOVER EVENTS A1

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LTE MEASUREMENT HANDOVER HANDOVER EVENTS A2

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LTE MEASUREMENT HANDOVER HANDOVER EVENTS A3

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LTE MEASUREMENT HANDOVER HANDOVER EVENTS A4

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LTE MEASUREMENT HANDOVER HANDOVER EVENTS A5

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LTE MEASUREMENT HANDOVER HANDOVER EVENTS B1

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LTE MEASUREMENT HANDOVER HANDOVER EVENTS B2

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LTE MEASUREMENT HANDOVER Speed dependent scaling of measurement parameters

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LTE MEASUREMENT HANDOVER

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Automatic Neighbor Relation (ANR) LTE is the first cellular standard to take advantage of self-organizing network (SON) functionality One of the first SON features to be defined was automatic neighbor relation (ANR) Over the past few years, this has become a challenging and time consuming task not only because of new technology deployments such as LTE, but also due to provisioning 2G (GSM, CDMA) and 3G (WCDMA, HSPA, 1xEV-DO) cells

Back to basics Physical cell ID (PCI), which identifies a cell that is served by an eNB The PCI is derived from the primary and secondary synchronization signal There are, in total, 504 unique PCIs being used throughout the entire LTE network. That relatively small number results in PCI reuse at some point The 3rd Generation Partnership Project (3GPP), the standardization body behind LTE, has specified additional identities to retain the ability to uniquely identify an eNB (and its associated cells) in an operator’s LTE network ECI (E-UTRAN Cell Identifier, ECGI- E-UTRAN Cell Global Identifier) are some of them. All these identities—PCI, ECI, and ECGI—play an important role in the definition and execution of ANR functionality

ANR-SIB Neighbor list is actually information acquired while reading system information in the form of SIBs. For LTE, these SIBs are primarily Type 4 and 5. Other SIBs provide neighbor list information for legacy radio access technologies, short RAT. SIB Type 4 lists the LTE intra-frequency neighbor cells—cells on the same carrier frequency, but with a different cell identity. SIB Type 5 provides neighboring LTE cells on a different frequency band (interfrequency)

Why do we need Neighbors? How are they derived?? The initial list of cells provided by SIBs 4 and 5 are based on simulations performed with network planning tools. The coverage prediction models used by these software tools by nature simulate real-life conditions and therefore leave room for error, as conditions and the environment may change. However, a missing neighbor in the neighbor relation table (NRT) is a common reason for call and connection drops due to failed handovers. Handovers are network controlled—that is, the network decides about the target cell. An up-to-date NRT is therefore essential for successful handover Carriers are required to perform drive tests to optimize neighbor lists manually for all technologies during the operational phase of a network. With the anticipated massive deployment of small cells, including picocells and femtocells, as part of heterogeneous networks (HetNets), this task will become even more challenging if not impossible. An automated way to determine neighbor relations is absolutely essential from an operational point of view, especially for LTE

ANR procedure and device

ANR procedure and device In the general ANR procedure, the eNB instructs the LTE terminal to take quality measurements of neighboring cells on a periodic basis—on the same frequency, for instance. While doing so, the device may detect a PCI that is not listed in the neighbor list. When sending the measurement report to the network, the device uses the cell identity to indicate the cell it is reporting, including the newly detected cell with a PCI of 27. After receiving the measurement report, the eNB instructs the terminal to report the ECGI, while reading the BCCH of that cell. In the next step, the UE reports the example ECGI of 46, which the eNB will use to update its neighbor relation table (NRT). This table contains for each cell the neighbor relation (NR), determined by the target cell identifier (TCI), which comprises ECGI and PCI

Attributes of TCI For each TCI, three attributes will be set: no remove, no handover, and no X2. The first (“no remove” command) stipulates that the eNB shall not remove this cell from the NRT. The second (“no handover” command) stipulates that no handover shall be initiated to this cell. The Third (“no X2” command) excludes the establishment of the logical X2 interface to this identified cell and its serving eNB. The operation and maintenance (OAM) center controls the listed attributes. It is the only authority that can delete entries from the NRT

ANR procedure and device ANR enables intra-frequency and inter-frequency neighbor cell detection for LTE. For Inter-frequency, the network needs to inform the device about which frequencies to measure. It also requires the scheduling of measurement gaps, which enables the terminal to retune its receiver to the instructed frequencies and take the required signal quality measurements. This is the reason why long DRX( Discontinous reception) cycle required for ANR. After the device reports the newly detected PCI, the network also will instruct it to report its ECGI. As previously discussed, the ECGI consists of the ECI and the PLMN identity. Both IDs are transmitted within SIB Type 1, which has a fixed periodicity in LTE of 80 ms. Standard measurement gaps do not provide enough time to successfully detect and decode SIB Type 1 for the newly detected cell. Only the long DRX cycle permits the device to derive the PLMN identity as well as the ECI, enabling the ECGI report back to the network FGI (Feature Group Indicator) bits 17 to 19 determine if the device can perform periodical measurements for intra-LTE (intra- and inter-frequency; bit 17, 18) or for inter-RAT (bit 19),i,.e., 3G/WCDMA

ANR procedure and device