LTE Self Learned Notes – Part 1

PCI : Physical Cell ID

As the terminology implies, Physical Cell ID is an indentification of a cell at physical layer. It has similar role as Primary Scrambling Code of UMTS cell.

This physical cell ID is determined by Primary Sync Signal (PSS) and Secondary Sync Signal (SSS) as described below :

RSRP : Reference Signal Received Power

RSRP is the short form of Reference Signal Received Power and it is equivalent to UMTS CPICH Received Signal Code Power (RSCP)

SINR : Signal Interference Noise Ratio

SINR define as below :

RF Conditions of LTE (Quick view)

MIMO : Multiple Input Multiple Output

Consist based on several TM (Transmission Modes), as can be seen below :

LTE Transmission

modeMIMO Scheme

Mode-1 single antenna transmissionMode-2 transmit diversityMode-3 open loop codebook based pre-codingMode-4 closed loop codebook based pre-codingMode-5 multiuser MIMO version of transmission mode-4

Mode-6single layer special case of closed loop codebook

based pre-coding

Mode-7release 8 non codebook based pre-coding

supporting only single layer, based on beamforming

Mode-8release 9 non codebook based pre-coding

supporting upto 2 layers.

Mode-9release 10 non codebook based pre-coding

supporting upto 8 layers

MME : Mobility Management Entity

MME critical function as can be seen below :

- Network Access Control: MME manages authentication and authorization for the UE. It also facilitates UE access to the network to gain IP connectivity.

- Radio Resource Management: MME works with the HSS and the RAN to decide the appropriate radio resource management strategy (RRM) that can be UE-specific.

- Mobility Management: One of the most complex functions MME performs. Providing seamless inter-working has multiple use cases such as Inter-eNB and Inter-RAT, among others. The use

cases become more complex depending on a change in MME, S-GW, P-GW or inter-working across other wireless networks.

- Roaming Management: MME supports outbound and inbound roaming subscribers from other LTE/EPC systems and legacy networks.

- UE Reach-ability: MME manages communication with the UE and HSS to provide UE reach-ability and activity-related information.

- Tracking Area Management: Allocates and reallocates a tracking area identity list to the UE.- Lawful Intercept: Since MME manages the control plane of the network, MME can provide the

whereabouts of a UE to a law enforcement monitoring facility.- Load Balancing Between S-GWs: Directs UEs entering an S-GW pool area to an appropriate S-

GW. This achieves load balancing between S-GWs.

MME location in LTE network architecture as can be seen below :

ANR : Automatic Neighbour Relation

The ANR function resides in the eNB and manages the conceptual Neighbour Relation Table (NRT). Located within ANR, the Neighbour Detection Function finds new neighbours and adds them to the NRT. ANR also contains the Neighbour Removal Function which removes outdated NRs. The Neighbour Detection Function and the Neighbour Removal Function are implementation specific.

An existing Neighbour cell Relation (NR) from a source cell to a target cell means that eNB controlling the source cell knows the ECGI/CGI and Physical Cell Identifier (PCI) of the target cell and has an entry in the NRT for the source cell identifying the target cell.

For each cell that the eNB has, the eNB keeps a NRT. For each NR, the NRT contains the Target Cell Identifier (TCI), which identifies the target cell. For E-UTRAN, the TCI corresponds to the E-UTAN Cell Global Identifier (ECGI) and Physical Cell Identifier (PCI) of the target cell.

The ANR function relies on cells broadcasting their identity on global level, E-UTRAN Cell Global Identifier (ECGI) and allows O&M to manage the NRT. O&M can add and delete NRs. It can also change the attributes of the NRT. The O&M system is informed about changes in the NRT.

Intra-LTE/frequency ANR:

The eNB serving cell with ANR function, instructs each UE to perform measurements on neighbor cells, as a part of the normal call procedure. The eNB may use different policies for instructing the UE to do measurements, and when to report them to the eNB.

When UE discovers new cell’s ECGI, the UE reports the detected ECGI to the serving cell eNB. In addition the UE reports the tracking area code and all PLMN IDs that have been detected. The eNB adds this neighbour relation to NRT.

Inter-RAT/Inter-frequency ANR:

The eNB serving cell with ANR function can instruct a UE to perform measurements and detect cells on other RATs/frequencies .during connected mode. The eNB may use different policies for instructing the UE to do measurements, and when to report them to the eNB.

The UE reports the PCI of the detected cells in the target RATs/frequencies. When the eNB receives UE reports containing PCIs of cell(s), eNB may instruct the UE to read the CGI and the RAC of the detected neighbour cell in case of GERAN detected cells and CGI, LAC and, RAC in case of UTRAN detected cells. For the Interfrequency case, the eNB may instruct the UE to read the ECGI, TAC and all available PLMN ID(s) of the inter-frequency detected cell.

The eNB updates its inter-RAT/inter-frequency Neighbour Relation Table after receiving relevant info from UE.