Techlte Blog
LTE Advance

LTE Advanced

Hi All,Please go through the Topics covered by techlteworld. Happy Learning .>Carrier Aggregation (CA) LTE Advanced 

Admin

August 08, 2021

20 Min Read

LTE Advance

LTE Protocol Stack

LTE Protocol stack is divided into Three Layers.Layer 1 (Physical Layer)Layer 2 (PDCP,MAC,RLC Layers)Layer 3 (NAS and RRC Layers)Protocol StackFunctions of each Layer.NAS: 3GPP TS 24.301EPS bearer managementAuthenticationPaging originationEPC connection management-IDLE mobility handlingSecurity mode controlTracking area updatePDN connectivity and dysconnectivity procedure.RRC:  3GPP TS 36.331RRC protocol layer exists in UE & eNodeb.It is part of LTE air interface control plane.Broadcast of System Information related to the non-access stratum (NAS) and access stratum (AS)PagingEstablishment, maintenance and release of an RRC connection between the UE and E-UTRANMobility functionsQoS management functions.UE measurement reporting and control of the reporting.Recovery from radio link failurePDCP: 3GPP TS  36.323PDCP protocol layer exists in UE & eNodebHeader compression and decompression of IP data packet.Transfer of user data.Maintenance the PDCP sequence number.Security of data.Ciphering and Integrity Protection.Transfer of control plane data.RLC: 3GPP TS 36.322Concatenation, Segmentation and reassembly of RLC SDUs.Retransmission of RLC PDUs (Only for AM data transfer)Reordering of RLC data PDUs (Only for UM and AM data transfer.Protocol error detection and recovery.MAC: 3GPP TS  36.323Prioritization among various data streams for a given UE.Error Correction trough HARQ.Mapping between logical channels and transport channels.Transport format selection.Padding.Physical layerEncode raw data before modulation.Measure the air interface to know the channel quality.Link adaptation.Power control.

Admin

August 07, 2021

20 Min Read

LTE Advance

LTE Subcarriers, Modulation And Frame Structure

LTE Subcarriers, modulation and Frame structureLTE subcarrier is the smallest independent part of an LTE signal.The smallest defined piece of an LTE signal is a single subcarrier is RE (Resource Element).Modulation scheme used in LTE.QPSK16QAM64QAMLTE Frame Structure in FDDEach LTE downlink subcarrier operates in 10 ms long frames.Each frame is made up of 10 subframes, each 1 ms.Each subframe contains 2 slots, each 0.5 ms.Each slot carries seven modulated symbols, which could be QPSK, 16QAM, or 64QAM.Generic Frame Sequences:Resource BlockIn the frequency domain, 12 subcarriers form one physical resource block (180kHz * 0.5ms). The resource block size is the same for all bandwidths.2 RB(Resource Block) = 1 Scheduling Block(SB)1 Scheduling Block(SB)=1 TTI =1 SubframeScalable Bandwidth:LTE channel bandwidth can be 1.4, 3, 5, 10, 15, 20 MHz.The wider bandwidth the higher throughput.

Admin

August 07, 2021

20 Min Read

LTE Advance

LTE Synchronization Signals (PSS And SSS)

Initial AcquisitionIn frequency Acquisition we will getBand Information (Supported Band Info)EARFCN Information (Defined EARFCN)PLMN InformationNeed to knowPLMN and EARFCN information will be provided by SIM.Band Information will be provided by Phone (system file).Now work of UE is to obtain time and frequency synchronization.So the first signal to be detected is PSS then SSS in Time domain and frequency domain.From PSS and SSS the PCI ID decoding will be done.PSS (Primary Synchronization Signals)PSS is used for Slot Synchronization.Position of PSS in time domain (1st Subframe,1st Timeslot,7th OFDM Symbol).Periodicity -5 ms.In frequency domain across the 7th OFDM symbol depending of variable bandwidth.PSS is decoded on Centre frequency, where minimum 6RB is required i.e 62 subcarrier.If it will 1.4 Mhz it will be across the bandwidth.Centre frequency is required because it is having higher gain.PSS Information ElementsSubframe Number.Cell number, PSS records.PSS Indices. (0,1,2)Peak Position.SSS (Secondary Synchronization Signals)SSS is used for Frame Synchronization.Position of SSS in time domain (1st Subframe,1st Timeslot,6th OFDM Symbol).Periodicity -5 ms.In frequency domain SSS is decoded on Centre frequency, where minimum 6RB is required i.e 62 subcarrier.If it will 1.4 Mhz it will be across the bandwidth.SSS Information ElementsEARFCN.Cell ID number.Frame Boundary Information.Cyclic PrefixNumber of Barred/detected cell.

Admin

August 07, 2021

20 Min Read

LTE Advance

LTE CSFB (Circuit Switch Fall Back)

CSFBTo make a voice call there are mainly two solutions:CSFBIMS based Volte CallThere are pre conditions for CSFB:When UE is in LTE RAT it should be registered with MSC .UE is not directly connected to MSC .MME is connected to MSC via SGs interface.SGs Interface:SGs interface is between MME and MSC.LA Update is transferred by MME to MSC over SGsThere must be MME-MSC/VLR SGs association which is created at below occasion:During Combined EPS and IMSI attach.During Combined TA and LA Update.Combined EPS and IMSI attach procedure:In Attach request message UE send IE Type : combined EPS and IMSI attach.Note : EPS –PS Domain.          IMSI-CS Domain. Pre Conditions:Message in UE Log:CSFB Call flowType of CSFB implementation done in the network.1.Blind CSFB2.Measurement Based CSFB3.RIM or Flash CSFB.Note : When in legacy network (3G/2G) the UE can have PS data sessions. PS data is supported in 2G network only when DTM (Dual Transfer Mode) is supported. When UE supports DTM it can have both voice and data simultaneously.What happens after VOICE Call get over:If RAT is 2GUE will remain in 2G until data transfer completed or resume data flow after call completion.UE go to LTE without resuming data flow.If RAT is 3GUE can wait for data transfer to complete before cell reselection to LTE.UE go to LTE cell during ongoing data flow.

Admin

August 07, 2021

20 Min Read

LTE Advance

What Is CPRI & ECPRI ?

While the CU/DU split adds a lot of extra flexibility in how services are deployed, there is still an area of cost that needs to be optimized is the RU. Today, the interface between the BBU and RU in 4G LTE is proprietary to mobile equipment vendors. It is based on the Common Public Radio Interface (CPRI ) interface, but this is not an open interface today as there are dependencies in the implementation of BBUs and RRHs that require both to be sourced from the same vendor. In addition, it is a costly bottleneck as it is based on transport of digital radio signals directly over a point-to-point optical fiber. CPRI is adequate when RAN architectures are based on macro-cells alone, but becomes a major cost when a point-to-point fiber connection needs to be made between multiple micro-cell RUs to BBUs installed 20 km away. As the amount of data to be transmitted increases, the cost of the interface also increases. This is because the CPRI interface requires a constant bit rate no matter the load and there is therefore no possibility for statistical multiplexing.In 2017/18 an update to this interface called enhanced CPRI (eCPRI ) was introduced. The eCPRI interface uses Ethernet as the L2 interface, which allows existing solutions for control, management and synchronization to be used. Ethernet allows packet-based switching and statistical multiplexing of several RU connections onto a single backhaul fiber. This vastly improves the cost of deploying micro-cells.Let’s discuss CPRI & eCPRI in detail below:CPRI: Common Public Radio InterfaceCPRI Transport The CPRI is an industry forum defining a publicly available specification for the interface between a radio equipment control (REC) and a radio equipment (RE) in wireless networks. CPRI specifies a digitized serial interface between a base station referred to as REC in CPRI terminology and an RRH or RE. The specifications cover the userplane, the control-plane transport mechanisms, as well as the synchronization schemes. The specification supports both electrical and optical interfaces as well as point-to-point, star, ring, daisy-chain topologies.The CPRI interface provides a physical connection for I/Q samples transport as well as radio unit management, control signaling, and synchronization such as clock frequency and timing synchronization.Antenna Carrier: CPRI transports I/Q samples to/from a particular antenna port and RF carrier. This is called an antenna-carrier (AxC) and is the amount of digital baseband (I/Q) user-plane data necessary for either reception or transmission of only one carrier at one independent antenna element.Antenna Carrier group: Itis an aggregation of multiple Antenna Carrier streams with the same sample rate, the same sample width, and the same destination.Antenna Carrier Container: Itconsists of a number of Antenna Carriers and is a part of a basic CPRI frame.Data is organized into basic frames of 16 words. The first word of each basic frame is the control word. Each word can be 8, 16, or 32 bits, depending on the width of the I/Q samples. The width of the word depends on the CPRI line rate. For example, in an LTE system, if I =16 bits and Q = 16 bits, then one Antenna carrier is 32 bits.Each 256 basic frames make up a hyperframe and 150 hyperframes are needed to transport an LTE 10 ms frame. Data in a basic frame is encoded with 8B/10B encoding, that is, 8 bits of data are encoded in 10 bits. The extra bits are used to detect link failures. Some of the CPRI rates support 64B/66B encoding scheme and this extension is used to detect sync header impairments and link failures.One of the CPRI technical requirements defines the clock frequency accuracy of RRH as 0.002 ppm. This requirement states that the maximum impact of jitter from the CPRI fronthaul on the frequency accuracy of RRH should be less than  0.002 ppm.ECPRI:eCPRI Transport The concepts of CPRI-over-Ethernet and replacing the TDM-like CPRI format with Ethernet messaging both hold the promise of reducing the bandwidth requirements of CPRI transport and making fronthaul affordable and available to all mobile operators.eCPRI, introduces improved transport efficiency to match the speed and bandwidth requirements of 5G fronthaul networks.The main advantages of the eCPRI protocol include support of functional split option 7, flexible bandwidth scaling according to user-plane traffic, and the use of mainstream transport technologies, which makes it possible carrying eCPRI and other traffic simultaneously in the same switched network.As shown in figure below, in eCPRI, the radio base station is divided into two building blocks: eCPRI radio equipment control (eREC) and eCPRI radio equipment (eRE), which are physically separated and are connected via a transport network. The eREC implements part of the physical layer functions and higher layer functions of the air interface, whereas the eRE contains the remaining part of the physical layer functions and the analog RF functions. Userplane data, control and management, and synchronization signals (i.e., synchronization data used for frame and timing alignment) are packetized, multiplexed, and transferred over the transport network which connects eREC(s) and eRE(s). The eCPRI does not rely on specific transport network and data-link-layer protocols, thus any type of network can be used for eCPRI.eCPRI Protocol planes: This method typically involves the transmission and reception of eCPRI messages.C&M Plane: Control and management data flow for the operation, administration and maintenance of nodes.User Plane: Data flows covered by user plane as:Data flow to be transferred from radio base station to user equipment and vice versa.Other eCPRI flows not covered by others flows and protocol planes.Real time control data.Synchronization Plane: As eCPRI is being used in Open RAN architecture and nodes are from different OEM’s So Synch plane has been introduced to maintain the data flow for synchronization timing information between nodes.The main difference between eCPRI and CPRI can be summarized by looking at their respective characteristicsCPRI characteristics• It is intrinsically a point-to-point interface.• There is a master port and a slave port connected directly by optical/electrical cable (s) as a hop.• Networking functions are application layer functions and not supported by the CPRI interface itself. .• Supported logical connections include point-to-point (one REC to one RE) and point-to-multipoint (one REC to several REs).• Redundancy, QoS, security, etc. are REC/RE functions.eCPRI characteristics• An eCPRI network consists of eCPRI nodes (eRECs and eREs), transport network, as well as other network elements including grand master for timing and EMS/NMS for management.• There is no longer a master port/slave port classification at physical level• The eCPRI layer is above the transport networking layer.• The eCPRI layer does not depend on a specific transport network layer (TNL) topology.• The transport network may include local network and local switches provided by the eREC/eRE vendors.• Supported logical connections include point-to-point (one eREC to one eRE), point-to-multipoint (one eREC to several eREs), multipoint-to-multipoint (eRECs to eREs, eRECs to eRECs, eREs to eREs).• Redundancy, QoS, security, etc. are mainly transport network functions; eCPRI nodes need to implement proper TNL protocols to support these capabilities.

Admin

August 07, 2021

20 Min Read