Αν. Καθηγητής Γεώργιος Ευθύμογλου

Αν. Καθηγητής Γεώργιος Ευθύμογλου
LTE Physical channels Αν. Καθηγητής Γεώργιος Ευθύμογλου Module Title

Long Term Evolution (LTE) network LTE Basic Procedures
Introduction Long Term Evolution (LTE) network LTE Basic Procedures LTE Physical channels Radio Bearers Module Title

UE-eNB connection

LTE Physical Channels P-SS: Primary synchronization signal S-SS: secondary synchronization signal PBCH: Physical Broadcast Channel PDSCH: Physical Downlink Shared Channel PDCCH: Physical Downlink Control Channel PCFICH: Physical Control Format Indicator Channel PHICH: Physical Hybrid ARQ Indication Channel PCH: Paging channel RS: Reference Signal, used both in uplink and downlink SRS: Sounding reference signal, used in uplink DMRS: Demodulation Reference Signal PRACH: Physical Random Access Channel used in uplink PUSCH: Physical Uplink Shared Channel PUCCH: Physical Uplink Control Channel

DL L1/L2 control signaling
L1/L2 control channels, are used for downlink control information (DCI), providing the terminal with the necessary information for proper reception and decoding of the downlink and uplink data transmissions Transmitted within the first part of each subframe, called control region (L=1-3 OFDM symbols) followed by data region. Number of L is determined by CFI (Control Format Indicator). Allow for UE to decode DL scheduling signaling assignment as early as possible, thus reduce the delay. If UE not scheduled, it may power down part of receiver circuitry for a part of subframe. The size of control region can be dynamic varied on per subframe basis, matching the instantaneous traffic. Corresponds to channels PCFICH, PDCCH, PHICH

DL L1/L2 control signaling
The first L (1 or 2 or 3) OFDM Symbols of each subframe. Multiple channels are located in this area. On the first OFDM symbol of each subframe is PCFICH but PCFICH takes only part of the resource blocks on the first symbol, not all. PHICH is carried by this area as well. The remaining space not occupied by PCFICH and PHICH is allocated for PDCCH. The PDCCH carries Downlink Control Information or Downlink Control Information (DCI) to indicate the resource assignment in UL or DL for one (Radio Network Temporary Identifier) RNTI .

PCFICH (Physical Control Format Indicator Channel)
It carries the number of OFDM symbols that can be used for control channels (PDCCH and PHICH). UE decode this channel to figure out how many OFDM symbols are assigned for the control channels (PDCCH and PHICH) It is 16 data subcarriers of the first OFDM symbol of the subframe. PCFICH data is carried by 4 Resource Element Groups (REGs) and these four REGs are evenly distributed across the whole band regardless of the bandwidth. The exact position of PCFICH is determined by cell ID and bandwidth.

PCFICH (Physical Control Format Indicator Channel)
The PCFICH consists of two bits of information, corresponding to the three control-region sizes of 1,2, or 3 OFDM symbols which are coded into a 32-bit codeword. The coded bits are scrambled with a cell- and subframe-specific scrambling code to randomize inter-cell interference, QPSK modulated, and mapped to 16 resource elements. As the size of the control region is unknown until the PCFICH is decoded, the PCFICH is always mapped to the first OFDM symbol of each subframe.

Physical downlink control channel (PDCCH)
The PDCCH is used to carry downlink control information (DCI) such as scheduling decisions and power-control commands. More specifically, the DCI includes: • Downlink scheduling assignments, including PDSCH resource indication, transport format, hybrid-ARQ information, and control information related to spatial multiplexing (if applicable). A downlink scheduling assignment also includes a command for power control of the PUCCH used for transmission of hybrid-ARQ acknowledgements in response to downlink scheduling assignments. • Uplink scheduling grants, including PUSCH resource indication, transport format, andhybrid-ARQ-related information. An uplink scheduling grant also includes a command for power control of the PUSCH. • Power-control commands for a set of terminals as a complement to the commands included in the scheduling assignments/grants.

Physical downlink control channel (PDCCH)
One PDCCH carries one DCI message with one of the formats described later. As multiple terminals can be scheduled simultaneously, on both downlink and uplink, there must be a possibility to transmit multiple scheduling messages within each subframe. Each scheduling message is transmitted on a separate PDCCH, and consequently there are typically multiple simultaneous PDCCH transmissions within each cell. A user may also receive multiple DCI messages in the same subframe (on different PDCCHs), for example, if it is scheduled simultaneously in uplink and downlink.

PDCCH (Ref. 1, Section ) Each user has its own control information/per subframe.

PDCCH (Ref. 1, Section ) The mapping of PDCCHs to resource elements is subject to a certain structure. This structure is based on so-called Control-Channel Elements (CCEs), which in essence is a convenient name for a set of 36 useful resource elements. The number of CCEs, one, two, four, or eight, required for a certain PDCCH depends on the payload size of the control information (DCI payload) and the channel-coding rate. Number of CCEs used for a PDCCH is referred to as the aggregation level.

PDCCH (Ref. 1, Section ) First, the PCFICH is mapped to four resource-element groups, followed by allocating the resource-element groups required for the PHICHs. The resource-element groups left after the PCFICH and PHICHs are used for the different PDCCHs in the system.

LTE Physical Channels Physical channels in the resource grid.

LTE Physical Channels Resource elements in the grid come from six types of data source: User data, Cell Specific Reference (CSR), Downlink Control Information (DCI), PSS, SSS, and BCH. For subframe 0: all the sources of data are present (BCH only in this subframe; it carries Master Information Block, MIB) For subframe 5: user data, CSR, DCI, PSS, and SSS are present. All other subframes {1, 2, 3, 4, 6, 7, 8, 9}: user data, CSR and DCI symbols are present.

Initialization Sequence
i) Power-Up Test ii) Frequency & Time and Frame Synchronization (SYNC detection) UE decodes Primary Sync and applies the primary sync sequence with the Secondary Sync code and figures out which sequence is assigned to the cell. Decodes BCH which occupies 62 subcarriers (6 RBs) at the center frequency. BCH tells the frequency information of the system (e.g., System Frequency Bandwidth) iii) Decode System Information (SI) Message iv) Select Prefered Network v) Perform RACH Process vi) RRC Connection Setup

Sync detection This Sync detection is done every 5 ms.
Three different sequences are used as the primary sync signal and there is a one-to-one mapping between each of the three sequences and the cell ID within the cell identity group. After a UE detect this cell-identity group, it can determine the frame timing. From this cell identity group, the UE also figures out which pseudo-random sequence is used for generating the reference signal in the cell. Once this timing sync gets established, UE can decode MIB and figure out SFN number since MIB carries SFN number. System Frame Number (0-1023) is needed for sync between UE and eNB.

Cell ID Detection and System Information Detection
i) Frequency Aquisition ii) Primary Sync Signal Aquisition (Slot Timing Acquired, Secondary Sync Signal Scrambling Code Acquired) iii) Secondary Sync Signal Acquisition (Frame timing Acquired, Cell Group ID sequence acquired) iv) with PSS and SSS, Cell ID can be calculated v) with Cell ID, Reference Signal Location is detected vi) If Reference Signal Location is properly decoded, MIB can be detected vii) From MIB, SFN and System BW can be detected viii) Decode PCFICH and detect how many symbols are allocated for PDCCH. ix) Decode DCI for SIB1 from PDCCH (e.g., find Public Land Mobile Network, PLMN) x) Decode SIB1 and get the scheduling information for other SIBs xi) Decode SIBs (other than SIB1)

SIB Scheduling i) MIB is transmitted at fixed cycles (every 4 frames starting from SFN 0) ii) SIB1 is also transmitted at fixed cycles (every 8 frames starting from SFN 0). iii) All other SIB are being transmitted at the cycles specified by SIB scheduling information elements in SIB1

LTE system information (SI) blocks-MIB,SIB-1,2,3,4,5,6,7,8,9,10,11
The system information (SI) is very essential and the same is broadcasted by LTE eNB over logical channel BCCH. This logical channel information is further carried over transport channel BCH or carried by DL-SCH. There are two parts in SI static part and dynamic part. Static part is called as MIB and is transmitted using BCH and carried by PBCH once every 40ms. MIB carries useful information which includes channel bandwidth, PHICH configuration details; transmit power, no. of antennas and SIB scheduling information. Dynamic part is called as SIB and is mapped on RRC SI messages (SI-1,2,3,4,5,6,7,8,9,10,11) over DL-SCH and transmitted using PDSCH at periodic intervals. SI-1 transmitted every 80ms, SI-2 every 160ms and SI-3 every 320 ms.

LTE Basic Procedures UE is Off Power On UE iii) Frequency Search iv) Timing Sync In this process, PSS and SSS will be decoded as well. v) Cell Search Normally a UE would find multiple cells in this process PCI (Physical Cell ID) detection vi) Cell Selection vii) MIB decoding MIB decoding : UE can figure out System Bandwidth and Transmission Mode in this process. MIB/PBCH is located at the 6 RBs around the center frequency in the 1st subframe. So the success of MIB decoding does not guarantee that signal quality across the whole band is good.

LTE Basic Procedures: PBCH

LTE Basic Procedures vii) Detect CSR (Cell Specific Reference Signal) and perform Channel Estimation and Equalization. In this process, UE will detect/measure reference signal across the whole system bandwidth. So RSRP/RSRQ measured at this step can be a good indicator for overall signal quality. viii) Decode PDCCH and extract DCI information for SIB. PDCCH is spread across the whole bandwidth, so the signal quality across the whole bandwidth should be good enough for this step. viii) SIB decoding (SIB1 should be decoded first and then SIB2 and then remaining SIBs) ix) Initial RACH Process x) Registration/Authentication/Attach xi) Default EPS Bearer Setup xii) Now UE is in IDLE Mode

LTE Basic Procedures xiii) (If the current cell become weak or UE moves to another cell): Cell Reselection xiv) When Paging message comes or User make a call: RACH Process xv) Setup Dedicated EPS Bearer xv) Receive data xvi) Transmit data xvii) ( If UE power is perceived too weak by the network): Network send TPC command to increase UE Tx Power xviii) (If UE power is perceived too strong by the network): Network send TPC command to decrease UE Tx Power xix) < (If UE moves to another cell region): Network and UE perform Handover procedure > xx) User stop call and UE gets into IDLE mode.

UE-eNB connection To establish a connection to an LTE network, a UE must first determine the following from the eNB base station: Complete time and frequency synchronization information Unique Cell Identity Cyclic Prefix (CP) Length Access Mode (FDD/TDD) Synchronization requirements in LTE Symbol Timing Acquisition Carrier Frequency Synchronization Sampling Clock Synchronization

Cell Search A cell search procedure is used by the UE to acquire time and frequency synchronization with a LTE cell and UE detects the physical layer Cell ID (PCI) of that cell. Two cell search procedures in LTE: initial synchronization and detecting neighbor cells in preparation for handover LTE uses a hierarchical cell search scheme similar to WCDMA. Step-1: After being powered on, UE tunes the RF and attempts to measure the wideband received power (RSSI) for specific frequencies (channels as commanded by higher layer) over a set of supported frequency bands one after another and ranks those cells based on signal strength.

Cell Search Step-2: Then it uses downlink synchronization channels, that is locally stored P-SS and S-SS to correlate with received one. UE first finds the primary synchronization signal (PSS) which is located in the last OFDM symbol of first time slot of the 1st and 5th sub-frames. This enables UE to be synchronized on sub-frame level. Primary Synchronization Signal helps for Slot Timing Detection and Physical Layer ID (0,1,2) detection. Step-3: secondary synchronization symbols are also located in the same sub-frame of P-SS but in the symbol before P-SS. From secondary SS, UE is able to obtain physical layer cell identity group number (0 to 167). It helps for Radio Frame Timing detection, find Physical Layer Cell ID, cyclic prefix length detection, FDD or TDD detection.

Cell Search LTE cell search procedure:

Primary Synchronization Signal (P-SS) Sequences
Three PSS sequences are used in LTE, corresponding to the three physical layer identities within each group of cells. • The PSS is constructed from a frequency-domain Zadoff-Chu (ZC) sequence of length 63. • Transmitted on 6th symbol of slot 0 and slot10 of each radio frame on 72 subcarriers centered around DC.

Secondary Synchronization Signal (S-SS) Sequences
• SSC1 and SSC2 are two codes with two different cyclic shifts of a single length-31 M-sequence. • Each SSS sequence is constructed by interleaving, in the frequency-domain, two length-31 BPSK-modulated secondary synchronization codes. • The two codes are alternated between the first and second SSS transmissions in each radio frame. • This enables the UE to determine the 10 ms radio frame timing from a single observation of a SSS. • Transmitted on 5th symbol of slot 0 and slot10 of each radio frame on 72 subcarriers centered around DC. PSS carries physical layer identity (NID)(2) SSS carries physical layer cell identity group (NID)(1) Cell identity is computed using (NID)cell = 3*NID(1) + NID (2) , where (NID)(1) = 0,1,.....,167 and (NID)(2) = 0,1,2

Cell search Step-4: Once UE knows the PCI for a given cell, it also knows the location of cell Reference signals - which are used for channel estimation, cell selection / reselection and handover procedures. After channel estimation using RS (reference signal), MMSE equalization is performed to remove the effect of channel impairment from the received symbols.

Network Entry Step 1: LTE UE uses PSS and SSS to determine physical layer cell identity (PCI) (1 out of 504). Step 2: After cell search procedure is completed, LTE UE decodes Master Information Block (MIB), which is transmitted on PBCH at the periodicity of 40ms. MIB is carrying 1) system bandwidth, 2) PHICH configuration, 3) SFN number. System Information (SI) Block Type 1, which is transmitted on DL-SCH at the periodicity of 80ms, is carrying PLMN IDs, tracking area code, cell identity, access restrictions, scheduling information and more. SI-RNTI is used on PDCCH to address System Information Block Type 1 and SI Messages.

Network Entry Step 3 (a) : Random access procedure is initiated by UE by sending random access preamble on PRACH. eNB responds with random access response on PDSCH. Step 3 (b) : The data transmission is scheduled on PUSCH. The contention resolution is taken care by MAC and the same is initiated to UE by eNB on DL-SCH.

. PRACH procedure [9] This shows an example of what's happening during the initial process (RACH process) after you turn on your mobile phone.

PRACH procedure [9] i) UE initiate a Random Access Procedure on the (uplink) Random Access Channel (RACH). (The location of RACH in the frequency/time resource grid the RACH is known to the mobile via the (downlink) Broadcast Channel (BCH). The random access message itself only consists of 6 bits and the main content is a random 5 bit identity). ii) Network sends a Random Access Response Message(RARM) at a time and location on the Physical Downlink Shared Channel (PDSCH) (The time and location of RARM on PDSCH can be calculated from the time and location the random access message was sent. This message contains the random identity sent by the device, a Cell Radio Network Temporary ID (C-RNTI) which will be used for all further bandwidth assignments, and an initial uplink bandwidth assignment).

PRACH procedure [9] iii) The mobile device then uses the bandwidth assignment to send a short (around 80 bits) RRC Connection Request message which includes it's identity which has previously been assigned to it by the core network. Only the step i) uses physical-layer processing specifically designed for random access. The remaining steps utilizes the same physical layer processing as used for normal uplink and downlink data transmission.

PRACH procedure [9] Accomplished by broadcasting two special signals:
Primary Synchronization Service (PSS): Used for initial synchronization. Secondary Synchronization Service (SSS): Used for handoff synchronization. These synchronization signals are transmitted twice per 10ms radio frame. If all parameters necessary for communication between the UE and the radio-access network are known to both entities (RRC_CONNECTED) UE has successfully established a synchronized connection to the eNB (IN_SYNC).

DCI (Downlink Control Indicator)
The DCI format is a predefined format in which the downlink control information is packed/formed and transmitted in PDCCH. It tells the UE how to get its data which is transmitted on PDSCH in the same subframe. DCI format transmitted in PDCCH is like a map for a UE to find and decode PDSCH from the resource grid. The DCI format gives the UE, details such as number of resource blocks, resource allocation type, modulation scheme, transport block, redundancy version, coding rate, etc. Each DCI format, when encoding is attached with a CRC that is scrambled with the a UE-RNTI to which the PDSCH is intended to. So only that UE can decode the DCI format and hence the corresponding PDSCH. The packed DCI information is the payload to the PDCCH encoding chain.

DCI carries detailed information like: "which resource block carries your data ?" and "what kind of demodulation scheme you have to use to decode data ?" and some other additional information. The receiver first decodes DCI and based on the information it gets from the DCI it can decode the real data. It means without DCI, decoding the data delivered to you is impossible. DCI has to care about just a couple of parameters like Number of RBs, the starting point of RBs and the modulation scheme It is simple: there is no configuring of these things in RRC messages.

DCI carries the following information : i) UL resource allocation (persistent and non-persistent) ii) Descriptions about DL data transmitted to the UE. L1 signaling is done by DCI and Up to 8 DCIs can be configured in the PDCCH. These DCIs can have 6 formats : 1 format for UL scheduling, 2 formats for Non-MIMO DL scheduling, 1 format for MIMO DL Scheduling and 2 formats for UL power control.

Downlink DCI Formats Format 1 – Used for scheduling a PDSCH codeword. Only a single transport block can be scheduled here using resource allocation type-0/type-1 Format 1A – Used for scheduling a PDSCH codeword. Only a single transport block can be scheduled here using resource allocation type2 (localized or distribtued) Format 1B – Used for scheduling a PDSCH codeword with Rank-1 assignment Format 1C – Very compact scheduling of a PDSCH codeword. A single transport block can be scheduled using resource allocation type2 distributed always. Format 1D – Used for scheduling Multi-user MIMO cases Format 2 – Used for scheduling of PDSCH in closed loop spatial multiplexing Format 2A – Used for scheduling of PDSCH in open loop spatial multiplexing

Uplink DCI Formats Format 0 – Used for scheduling of PUSCH (uplink grant) Format 3 – Uplink transmit power control with 2 bit power adjustment Format 3A – Uplink transmit power control with 1 bit power adjustment Allocation of resources happens in terms of CCE ( Control Channel Elements ). 1 CCE = 9 continuous REG's ( Resource element Group ) 1 REG = 4 RE ( Resource Element )

http://www.sharetechnote.com/html/DCI.html Format 0
DCI Format Usage Major Contents Format 0 UL Grant. Resource Allocation for UL Data RB Assignment,TPC,PUSCH Hopping Flag Format 1 DL Assignment for SISO RB Assignment,TPC, HARQ Format 1A DL Assignment for SISO (compact) Format 1B DL Assignment for MIMO with Rank 1 RB Assignment,TPC, HARQ,TPMI, PMI Format 1C DL Assignment for SISO (minimum size) RB Assignment Format 1D DL Assignment for Multi User MIMO RB Assignment,TPC, HARQ,TPMI,DL Power Offset Format 2 DL Assignment for Closed Loop MIMO RB Assignment,TPC, HARQ, Precoding Information Format 2A DL Assignment for Open Loop MIMO Format 2B DL Assignment for TM8 (Dual Layer Beamforming) Format 2C DL Assignment for TM9 Format 3 TPC Commands for PUCCH and PUSCH with 2 bit power adjustment Power Control Only Format 3A TPC Commands for PUCCH and PUSCH with 1 bit power adjustment Format 4 UL Assignment for UL MIMO (up to 4 layers)

DCI format is determined by 2 factors: i) RNTI Type ii) Transmission Mode Those tables from 3GPP shows the relationships between RNTI Type, Transmission Mode and DCI format.

Relations between DCI format and Layer 3 signaling message
We have to know which DCI format is required for which RRC message. Following tables from 3GPP shows the relationship between RNTI and logical channel and you would know which RRC message is carried by which logical channel. So with two step induction, you will figure out the link between RRC message and it's corresponding DCI format.

Relations between DCI format and Layer 3 signaling message
For example, if you see the "Security Mode Command" message of section of , it says Signalling radio bearer: SRB1 RLC-SAP: AM Logical channel: DCCH Direction: UE to E-UTRAN From the table, this message is using C-RNTI. Assuming TM mode in this case is TM1 and scheduling is dynamic scheduling, from Table you will figure out that this is using C-RNTI. With this RNTI Type and TM mode, if you see table 7.1-5, this case use DCI Format 1 or DCI Format 1A.

RNTI (Radio Network Temporary Identifier)
Table shows RNTI types and DCI Format that can be used for each RNTI RNTI Types DCI Format Applicable to the RNTI Type SI-RNTI, P-RNTI, RA-RNTI 1A, 1C C-RNTI, SPS C-RNTI 0, 1A, 1B, 1D, 2, 2A, 2B, 2C, 4 (2B,2C,4 is for Rel 10 or later) M-RNTI 1C TPC-RNTI 3, 3A

RNTI (Radio Network Temporary Identifier)
RNTI is a kind of 'UE ID + Channel ID' since each type of channel has its own range of RNTI value. P-RNTI : It stands for Paging RNTI. Used for Paging Message. SI-RNTI : It stands for System Information RNTI. Used for transmission of SIB messages RA-RNTI : Random Access RNTI. Used for PRACH Response. C-RNTI : Cell RNTI. Used for the transmission to a specific UE after RACH. T-CRNTI : Temporary C-RNTI. Mainly used during RACH. SPS-C-RNTI : Semi persistent Scheduling C-RNTI TPC-PUCCH-RNTI : Transmit Power Control-Physical Uplink Control Channel-RNTI TPC-PUSCH-RNTI : Transmit Power Control-Physical Uplink Shared Channel-RNTI M-RNTI : MBMS RNTI

RNTI Question: "There are a lot of different types of RNTI and I don't see any RNTI information on DCI or Higher layer signaling message. Then how can PHY layer know which RNTI it has to use to decode a data ?". Answer: "MAC or Layer 1 controller would instruct PHY on which RNTI it has to use". There is no explicit algorithm for this, MAC/L1 controller needs to figure it out "based on context". For example, if it is at the subframe where SIB is transmitted, it would instruct PHY to use SI-RNTI. if UE is in connected mode, it may instruct to use C-RNTI, TPC RNTI etc.

C-RNTI (Cell Radio Network Temporary Identifier)
The eNodeB (Evolved Node B) assigns the UE a C-RNTI to identify the UE during exchange of all information over the air. The C-RNTI is assigned during the setup of the RRC Connection (Idle Mode to Connected Mode transition) between a UE and an eNodeB and is valid only for that RRC Connection. Once the UE leaves the coverage area of an eNodeB, the RRC Connection must be moved (Inter-eNodeB Handover) and the "new" eNodeB will assign a "new" C-RNTI to the UE. The C-RNTI is an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) specific identifier and the EPC (Evolved Packet Core) Network has no visibility to it.

GUTI (Globally Unique Temporary Identifier)
The MME (Mobility Management Entity) assigns the UE a GUTI to identify the UE during all message exchanges and procedures with the EPC. The GUTI is assigned during the Attach procedure (Deregistered State to Registered State transition) between the UE and the MME and is valid only as long as the UE is attached to the MME that assigned the GUTI. Once the UE leaves the Tracking Area(s) of an MME the "Attachment" has to be moved (Inter-MME handover) and the "new" MME will assign a "new" GUTI to the UE. Embedded within the GUTI are the PLMN ID of the service provider and the MME Identity. Thus, the GUTI uniquely and globally identifies a UE attached to a specific MME in a specific Service Providers LTE Network in a specific Country. The MME may choose to periodically re-assign a "fresh" GUTI to a UE that is attached to it.

Physical Channels

PDCCH (Physical Downlink Control Channel)
Mapped to the first L OFDM symbols in every downlink subframe. Number of the symbols L for PDCCH can be 1,2, or 3. Number L of the symbols for PDCCH is specified to UE by PCFICH PDCCH carries DCIs and the DCI carries Transport format, resource allocation, H-ARQ information related to DL-SCH, UL-SCH and PCH. PDCCH also carries DCI 0 which is for UL Scheduling assignment (UL Grants). Multiple PDCCH are supported and a UE monitors a set of control channels. Modulation Scheme is QPSK. Even though PDCCH has a lot of functions, not all of them are used at the same time so PDCCH configuration should be done flexibly.

CCEs ( Control Channel Elements ) for PDCCH
Suppose L = 3 (value obtained by PCFICH) Total RE's = L * x * y L - PCFICH value x - number of subcarriers in 1 RB y - total number of RB's considering 10 MHz bandwidth Total RE's = 3 * 12 * 50 = 1800 RE's RE's for PDCCH = Total RE's - Number of RE's used for reference signals - Number of RE's used in PHICH - Number of RE's used in PCFICH CCE's available for PDCCH = RE's for PDCCH /36 as 1 CCE = 36 RE's (4 x 9).

Resource Allocation and Management Unit
i) Resource Element (RE): The smallest unit made up of 1 symbol x 1 subcarrier. ii) Resource Element Group (REG): a group of 4 consecutive resource elements (resource elements for reference signal is not included in REG) iii) Control Channel Element (CCE) : a group of 9 consecutive REG iv) Aggregation Level - a group of 'L' CCEs (L can be 1,2,4,8) v) RB (Resource Block) This is a unit of 84 resource elements which is 12 subcarrier by 7 symbols (This is with normal Cylic Prefix which is used in most of the LTE deployment. If it is with Extended Cyclic Prefix, the number of symbols within a subframe become 6 and the number of resource elements in a single RB become 72). vi) RBG (Resource Block Group) : This is a unit comprised of multiple RBs. How many RBs within one RBG differs depending on the system bandwidth.

We use these units in hierachical manner depending on whether it is for control channel or data channel. For PDCCH, the hierachy would be : RE --> REG --> CCE --> Aggregation Level

eNodeB uses the PDCCH for sending the control information for a particular UE or a group of UE's. eNodeB uses the PDCCH for some broadcast information also which is common for all the UE's. So to make that process easier eNodeB divided its CCE's into two parts which we call them as search space: Common search space :- It consists of CCE's which are used for sending the control information which is common for all the UE's . Maximum number of CCE present in common search space is 16. For Example:- Common search space CCE's are used by eNodeB for sending the control information of SIB's which is common for all UE's. UE specific search space :- CCE's belonging to UE specific space are used for sending the control information for a particular UE only. That means information present on UE specific CCE's can only be decoded by a specific UE.

Lets suppose there are total 100 CCE's eNodeB has for sending the control information combining both common space and UE specific search space. Suppose enodeB has used 85th CCE number for a UE named george for sending his control information. Now how the UE george will come to know which CCE he needs to decode for getting his information. Either he needs to scan all 100 CCE's one by one and try to find the information. This procedure will consume a lot of battery power for the UE. So to simplify this process, eNodeB has fixed some indexes for a particular UE based on the RNTI and the subframe, so now george needs to find his control information only on those specific CCE indexes.

PDCCH Format First we should be familiar with some terms used in this procedure: Aggregation Level : It is defined as the number of CCE's used for sending a control information. Its values can be 1,2,4 and 8. Suppose for UE named george eNodeB is using some DCI format whose size comes out to be 90 bits after applying the code rate. Code rate:- It is mainly a physical layer parameter for sending the information in a redundant way such that chances of UE successfully decoding it gets increased. 1 CCE = 36 RE's 1 RE = 2 bits ( For QPSK modulation) 4 bits( For 16 QAM ) 6 bits ( For 64 QAM) And eNodeB uses QPSK modulation technique for PDCCH , Number of bits in 1 CCE = 36 * 2 = 72 bits.

PDCCH Format There are four PDCCH formats available as shown below
PDCCH Format 0 : Requires 1 CCE = Aggregation Level 1 (2^PDCCH Format = 2^0 = 1) PDCCH Format 1 : Requires 2 CCE = Aggregation Level 2 (2^PDCCH Format = 2^1 = 2) PDCCH Format 2 : Requires 4 CCE = Aggregation Level 4 (2^PDCCH Format = 2^2 = 4) PDCCH Format 3 : Requires 8 CCE = Aggregation Level 8 (2^PDCCH Format = 2^3 = 8)

PDCCH Format Number of PDCCH bits for PDCCH Format 0 = 1 (CCE) x 9 (REG/CCE) x 4 (RE/REG) x 2 (bits/RE, BPSK) = 72 Number of PDCCH bits for PDCCH Format 1 = 2 (CCE) x 9 (REG/CCE) x 4 (RE/REG) x 2 (bits/RE, BPSK) = 144 Number of PDCCH bits for PDCCH Format 2 = 4 (CCE) x 9 (REG/CCE) x 4 (RE/REG) x 2 (bits/RE, BPSK) = 288 Number of PDCCH bits for PDCCH Format 3 = 8 (CCE) x 9 (REG/CCE) x 4 (RE/REG) x 2 (bits/RE, BPSK) = 576

PDCCH candidates :- Number of CCE indexes serached by a UE in a subframe for a particular search space. These values are fixed by spec as mentioned in table :- PDCCH Format In the example for UE george, eNodeb needs to send 90 bits, so it needs to use at least 2 CCE's for the control information on PDCCH. It means it will send the control information with aggregation level 2. It is also possible that enodeB uses a higher aggregation level (more number of CCE's) even if the bits transmitted on PDCCH are less. This happens when channel conditions are bad, so to provide more redundant information to UE such that it can decode the PDCCH.

PDCCH Format Search space for PDCCH Number of PDCCH candidates Type
PDCCH candidates :- Number of CCE indexes serached by a UE in a subframe for a particular search space. These values are fixed by spec as mentioned in table :- PDCCH Format Search space for PDCCH Number of PDCCH candidates Type Aggregation level Size [in CCEs] UE-specific 1 6 2 12 4 8 16 Common

PDCCH (Physical Downlink Control Channel)
Even for the same DCI with exactly same bit length, the number of physical channel bits gets different depending on which PDCCH format it is carried by. It means the Code Rate of PDCCH varies depending on which PDCCH format is used. The code rate can be adjusted depending on the channel. For example, if we use DCI Format 2A (around 40 bits) Case 1 : If we use Aggregation Level = 1 i) After Channel Coding, the bit length would be about 120 ii) After Rate Matching, it should be 72 (1 CCE) Case 2 : If we use Aggregation Level = 2 ii) After Rate Matching, it should be 144 (2 CCE)

PDCCH data processing

) PDCCH data processing When there is no UE Tx Antenna selection, CRC attachment and Masking goes as follows. (This is the point where RNTI do the most important role) RNTI is included in CRC calculation but not explicit transmitted, different RNTIs are used for different DCI message.

PDSCH-Downlink Subframe Decoding
This procedure will explain the overall procedure to decode user data (PDSCH). It assumes that Initialization, Synchronization, IB decoding, Registration is already done and UE is in connected mode. i) Process the first OFDM symbol of the first slot within a subframe. ii) Detect PCFICH channel and figure out how many symbols are used for PDCCH. iii) Decode PHICH channel (PHICH is also at the first symbol of the first slot). iv) Based on the result of step i),ii), UE will calculate CCE index for PDCCH v) Decode PDCCH and find DCI (DCI1 or DCI1A) which is destined to the UE. vi) From the DCI, figure out the locations for PDSCH which is allocated for the UE. v) Decode PDSCH

SYNCHRONIZATION SEQUENCES
There are two cell search procedures in LTE: one for initial synchronization and another for detecting neighbor cells in preparation for handover. In both cases, the UE uses two special signals broadcast on each cell: Primary Synchronization Sequence (PSS) and Secondary Synchronization Sequence (SSS). The detection of these signals allows the UE to complete time and frequency synchronization and to acquire useful system parameters such as cell identity, cyclic prefix length, and access mode (FDD/TDD). At this stage, the UE can also decode the Physical Broadcast Control Channel (PBCH) and obtain important system information.

SYNCHRONIZATION SIGNALS FRAME STRUCTURE IN FREQUENCY AND TIME

SYNCHRONIZATION SIGNALS FOR FDD
Synchronization signals are transmitted twice per 10 ms radio frame. The PSS is located in the last OFDM symbol of the 1st and 11th slot of each radio frame which allows the UE to acquire the slot boundary timing independent of the type of cyclic prefix length. The PSS signal is the same for any given cell in every subframe in which it is transmitted (the PSS uses a sequence known as Zadoff-Chu).

SYNCHRONIZATION SIGNALS FOR FDD
The location of the SSS immediately precedes the PSS – in the before to last symbol of the 1st and 11th slot of each radio frame. The UE would be able to determine the CP length by checking the absolute position of the SSS. The UE would also be able to determine the position of the 10 ms frame boundary as the SSS signal alternates in a specific manner between two transmissions The SSS uses a sequence known as M-sequences.

PSS Structure in the frequency domain
In the frequency domain, the PSS and SSS occupy the central 6 resource blocks, irrespective of the system channel bandwidth, which allows the UE to synchronize to the network without a priori knowledge of the allocated bandwidth. The synchronization sequences use 62 sub-carriers in total, with 31 sub-carriers mapped on each side of the DC sub-carrier which is not used.

SSS Structure In the frequency domain, the PSS and SSS occupy the central 6 resource blocks, irrespective of the system channel bandwidth, which allows the UE to synchronize to the network without a priori knowledge of the allocated bandwidth. The synchronization sequences use 62 sub-carriers in total, with 31 sub-carriers mapped on each side of the DC sub-carrier which is not used.

Downlink reference signal
The downlink reference signal in LTE corresponds to a set of resource elements used by the physical layer but does not carry any higher layer's information. To allow for coherent demodulation at the user equipment, reference symbols (or pilot symbols) are inserted in the OFDM time-frequency grid to allow for channel estimation.

Downlink reference signal
There are total 510 RS sequences which corresponds to 510 different and unique cell identities. The RSs are derived from the product of a two-dimensional pseudo-random sequence and a two-dimensional orthogonal sequence. 170-pseudo-random sequences corresponding to cell-identity groups 3-orthogonal sequences each corresponding to a specific cell identity within the cell identity group.

Uplink Uplink user transmissions consist of uplink user data (PUSCH),
random-access requests (PRACH), user control channels (PUCCH), and sounding reference signals (SRS). The following illustration shows part of an LTE uplink frame and contains an allocation for each type of uplink channel. User 1 has a PUSCH allocation of [RB 20, slots 4-5]. User 2 has a PUCCH allocation of [subframe 2, PUCCH index 0]. User 3 has been given an SRS allocation of subcarrier 94 to 135 in subframe 2. User 4 is transmitting in a PRACH allocation.

Uplink

Uplink Primary Uplink Control Channel (PUCCH): only one control channel transmitted by uplink which contains information including channel quality info, acknowledgements, and scheduling requests. PUCCH is assigned by subframe instead of by slot. Primary Uplink Shared Channel (PUSCH) is used by uplink users to transmit data to the base station. All subcarriers not allocated for PRACH, PUCCH, or SRS are available for assignment to users. PUSCH data is modulated using SC-FDMA. The Physical Random Access Channel (PRACH) is used by a uplink user to initiate contact with a base station. The base station broadcasts some basic cell information, including where random-access requests can be transmitted. A UE then makes a PRACH transmission asking for PUSCH allocations, and the base station uses the downlink control channel (PDCCH) to reply where the UE can transmit PUSCH.

Uplink Data Transmission Scheduling - Non Persistent Scheduling
i) UE send SR (Scehduling Request) on PUCCH ii) Network send UL Grant (DCI 0) on PDCCH iii) UE decode DCI 0 (How UE can figure out a DCI 0 information in PDCCH is allocated for it ? Simply put, it performs the blind decoding for the whole PDCCH area (PDCCH Search Space) and check if there is any DCI 0 information that has CRC value encoded with C_RNTI allocated to it). iv) UE Transmit PUSCH based on the RBs specified by DCI 0. v) Network decode the PUSCH (How network figure out which part of Uplink subframe (UL RB) is for which UE ? It is simple. eNB knows exactly knows which UE send PUSCH at which RB because network specified this location in DCI 0 at step iii) vi) Network send ACK/NACK on PHICH vii) If Network send NACK, go to [Retransmission] Procedure.

Uplink Data Transmission Scheduling - Non Persistent Scheduling
UE has ASK the network to send UL Grant (DCI 0). If network send UL Grant, then UE can send UL data as allowed by the UL Grant.

Uplink Data Transmission Scheduling - Persistent Scheduling
In persistent scheduling mode, Network send 'Grant' in DCI Format 0 for every subframe. i) Network send the first data on DL PDSCH and PDCCH which has DCI format 1 for DL Data Decoding and DCI format 0 for UL Grant. (If there is no downlink data to be transmitted, network transmits only PDCCH with DCI format 0) ii) UE decodes PCFICH to figure CFI value. iii) UE decodes PDCCH and get the information on DCI format 1 iv) Based on DCI format 1, UE decode DL data. v) UE decodes the information on DCI format 0 from PDCCH vi) UE sends ACK/NAK for DL data through UCI (UCI will be carried by PUCCH) vii) UE checks the Grant field. viii) If Grant is allowed, UE transmit the uplink data through PUSCH ix) Network decode PUSCH data and send ACK/NACK via PHICH x) UE decode PHICH and retransmit the data if PHICH carries NACK

Uplink Data Transmission Scheduling - Persistent Scheduling
Big picture of the procedure.

UPLINK REFERENCE SIGNALS
There are two types of reference signals for uplink in LTE. The first is Demodulation Reference Signals (DM-RS) which are used to enable coherent signal demodulation at the eNodeB. The second is Sounding Reference Signal (SRS) which is used to allow channel dependent (i.e. frequency selective) uplink scheduling as the DM-RS cannot be used for this purposes since they are assigned over the assigned bandwidth to a UE. The SRS is introduced as a wider band reference signal typically transmitted in the last SCFDMA symbol of a 1 ms subframe as shown in the next Figure. User data transmission is not allowed in this block which results in about 7% reduction in uplink capacity.

Uplink reference signal
Two uplink physical reference signals are used within the PHY layer and do not convey information from higher layers. Demodulation reference signal : This facilitates coherent demodulation and associated with transmission of PUSCH or PUCCH. It is transmitted in the fourth SC-FDMA symbol of the slot Sounding reference signal : This is used to facilitate frequency dependent scheduling and not associated with transmission of PUSCH or PUCCH. SRS are of two types based on periodicity. The min. periodicity of SRS is 2ms and the max. about 320ms.

UPLINK REFERENCE SIGNALS

Uplink reference signal
Reference signal type Direction Modulation Position Function DL-RS Used in the Downlink QPSK 1st and 3rd from last OFDM symbol in each slot, 6 subcarrier difference between them in the symbol These pilot subcarriers are used for channel estimation by UE DM-RS Used in the Uplink fourth SC-FDMA symbol of the slot Channel estimation SRS Used in the uplink Zadoff Chu transmitted on last SC-FDMA symbol of each subframe or once after 2 slots channel estimation

LTE Physical Uplink Shared (PUSCH) Channel
This channel is used to carry RRC signalling messages, UCI (uplink Control Information) and application data. Uplink RRC messages are carried using PUSCH. Signalling Radio Bearer (SRB) use PUSCH and each and every connection will have its unique SRB. • LTE PUSCH channel contain user information data. • The PUSCH carries both user data as well as control signal data. Control information carried can be MIMO related parameters and transport format indicators. • The control data information is multiplexed with the user information before DFT spreading module in the uplink SC-FDMA physical layer. • PUSCH supports QPSK,16QAM and 64QAM (optional). The LTE eNodeB selects suitable modulation based on adaptation algorithm (CQI-based).

LTE Physical Uplink Shared (PUSCH) Channel
. LTE Physical Uplink Shared (PUSCH) Channel UCI is transmitted using PUSCH instead of PUCCH when there is RRC and application data to be transferred at the same time instant.

LTE Physical Uplink Control Channel (PUCCH)
This LTE channel is used to carry UCI (Uplink Control Information). which include: HARQ ACK/NACK, channel quality indicators (CQI), MIMO feedback (Rank Indicator, RI; Precoding Matrix Indicator, PMI) and scheduling requests for uplink transmission. An LTE UE can never transmit both PUCCH and PUSCH during the same subframe. PUCCH consists of 1 RB/transmission at one end of the system bandwidth which is followed by another RB in the following slot at opposite end of the channel spectrum. This makes use of frequency diversity with 2dB estimated gain. A PUCCH Control Region comprises every two such RBs.

LTE Communication Channels
Logical Channels : Define what type of information is transmitted over the air, e.g. traffic channels, control channels, system broadcast, etc. Data and signalling messages are carried on logical channels between the RLC and MAC protocols. Transport Channels : Define how is something transmitted over the air, e.g. what are encoding, interleaving options used to transmit data. Data and signalling messages are carried on transport channels between the MAC and the physical layer. Physical Channels : Define where is something transmitted over the air, e.g. which REs in the DL frame. Data and signalling messages are carried on physical channels between the different levels of the physical layer.

LTE Logical,Transport and Physical channels
These channels are used by lower layers to provide services to the upper layers. As shown logical channels are of two types; one carrying control information and the other carrying traffic information. These gets mapped to transport channels as depicted in the figure.

Logical Channels Logical channels define what type of data is transferred. These channels define the data-transfer services offered by the MAC layer. Data and signalling messages are carried on logical channels between the RLC and MAC protocols. Logical channels can be divided into control channels and traffic channels. Control Channel can be either common channel or dedicated channel. A common channel means common to all users in a cell (Point to multipoint) while dedicated channels means channels can be used only by one user (Point to Point). Logical channels are distinguished by the information they carry and can be classified in two ways Logical traffic channels carry data in the user plane, while Logical control channels carry signalling messages in the control plane.

Logical Channels [Ref 6]
Following table lists the logical channels that are used by LTE: Channel Name Acronym Control channel Traffic channel Broadcast Control Channel BCCH X Paging Control Channel PCCH Common Control Channel CCCH Dedicated Control Channel DCCH Multicast Control Channel MCCH Dedicated Traffic Channel DTCH Multicast Traffic Channel MTCH

Transport channels [Ref 6]
Transport channels define how and with what type of characteristics the data is transferred by the physical layer. Channel Name Acronym Downlink Uplink Broadcast Channel BCH X Downlink Shared Channel DL-SCH Paging Channel PCH Multicast Channel MCH Uplink Shared Channel UL-SCH Random Access Channel RACH

Transport Channels Downlink and Uplink transport channels carry L2/L3 information. • It also configures LTE PHY layer. • It sends status information such as packet error and CQI to upper layers. • Also supports peer-peer signaling between higher layers. Based on broadcast,unicast or multicast concept different transport channels exist. Downlink channels include BCH (broadcast channel), DL-SCH (downlink shared channel, to multiple mobile subscribers or UEs), PCH (paging channel, used for UE DRX and broadcasted over entire cell), MCH (multicast channel, transmitted over entire cell).

Transport Channels Uplink channels include
RACH (Random Access Channel), UL-SCH(Uplink Shared Channel). Uplink PRBs (Physical Resource Blocks) are assigned to UE by eNodeB scheduler. PUSCH is used and shared by multiple UEs to carry upper layer information towards eNodeB. It will employ QPSK/16QAM/64QAM modulation types.

Physical data channels [Ref 6]
Following table lists the physical data channels that are used by LTE: Channel Name Acronym Downlink Uplink Physical downlink shared channel PDSCH X Physical broadcast channel PBCH Physical multicast channel PMCH Physical uplink shared channel PUSCH Physical random access channel PRACH

Physical channels without transport (Ref 1, 8.2.2, 8.2.3)
There are also physical channels without a corresponding transport channel. These channels, known as L1/L2 control channels, are used for downlink control information (DCI), providing the terminal with the necessary information for proper reception and decoding of the downlink data transmission, and uplink control information (UCI) used for providing the scheduler and the hybrid-ARQ protocol with information about the situation at the terminal.

DOWNLINK PHYSICAL DATA CHANNELS
Physical Broadcast Channel (PBCH): The PBCH broadcasts a limited number of parameters essential for initial access of the cell (that is, MIB). Every 40 ms the PBCH sends cell-specific system identification and access control parameters using QPSK modulation. Physical Downlink Shared Channel (PDSCH): Used to transport user data, the PDSCH is designed for high data rates. Modulation options include QPSK, 16-QAM, and 64-QAM. Physical Multicast Channel (PMCH): This channel defines the physical layer structure to carry Multimedia Broadcast and Multicast Services (MBMS). The PMCH carries multicast information, and like the PDSCH, the PMCH has multiple options for modulation including QPSK, 16-QAM, or 64-QAM. Multicast information is sent to multiple UEs simultaneously.

UPLINK PHYSICAL DATA CHANNELS
There are three physical layer channels defined for the uplink in LTE Physical Uplink Shared Channel (PUSCH): This channel carries user data. It supports QPSK and 16 QAM modulation with 64QAM being optional. Physical Random Access Channel (PRACH): This channel carries the random access preamble a UE sends to access the network in non-synchronized mode and used to allow the UE to synchronize timing with the eNodeB. Physical Uplink Control Channel (PUCCH): Control signaling comprises uplink data transmitted independently of traffic data which include HARQ ACK/NACK, channel quality indicators (CQI), MIMO feedback (Rank Indicator, RI; Precoding Matrix Indicator, PMI) and scheduling requests for uplink transmission.

Physical control channels [6]
Physical Control Channels are listed in the below table: Channel Name Acronym Downlink Uplink Physical control format indicator channel PCFICH X Physical hybrid ARQ indicator channel PHICH Physical downlink control channel PDCCH Relay physical downlink control channel R-PDCCH Physical uplink control channel PUCCH

DOWNLINK PHYSICAL CONTROL CHANNELS
Physical Downlink Control Channel (PDCCH): UEs obtain uplink and downlink resource allocations from the PDCCH. The PDCCH carries the resource assignment for UEs which are contained in a Downlink Control Information (DCI) message. t is mapped on resource elements (REs) in first 3 OFDM symbols in first slot of subframe. Physical Control Format Indicator Channel (PCFICH): The PCFICH is a value that has a range of 1 to 3. The value of the PCFICH indicates the number of OFDM symbols used for the transmission of control channel (PDCCH) information in a subframe. The PCFICH uses QPSK modulation. Physical Hybrid ARQ Indicator Channel (PHICH): The PHICH carries the HARQ ACK/NAK which indicates to the UE whether the eNodeB correctly received uplink user data carried on the PUSCH.

LTE resource grid

LTE resource grid Given 20MHz spectrum, there are 100 RBs The 6 central RBs contain PBCH, PSS/SSS, CFI and the reference signal The remaining 94 RBs contain only control and the reference signals in CFI OFDM symbols/subframe.

Compute Peak Data Rate Given 20MHz of available spectrum, there are 100 Resource Blocks available. The 6 central RBs contain PBCH, PSS/SSS, CFI and the reference signals (for a 4 antenna port configuration) while the remaining 94 RBs in the CFI=1 OFDM symbol contain only CFI (means PDCCH here) and the reference signals. Let’s recalculate the amount of data and control block for each kind of subframe in 1 RB (12 subcarriers for duration 14 OFDM symbols): Subframe (a): CFI + PBCH + PSS/SSS + reference = 1x12+6x12+12=96 control REs (1 OFDM symbol for CFI, 6=2+4 OFDM symbols for sync+PBCH) 12x14-96= 72 data resource elements Subframe (b): CFI + PSS/SSS + reference = 1x12+2x12+20= 56 control REs 12x14-64= 112 data resource elements Subframe (c): CFI + reference= 1x12+20=32 control REs 12x14-40= 136 data resource elements

Compute Peak Data Rate The overhead can be calculated as (control occupies 6 RBs/subframe): Total control= (1 subframe a)x(6x96)+(1 subframe b)x(6x56)+(8 subframe c)x(6x32) + (94x(CFI*10) subframe c)x32=32528 resource elements Total resource elements=(100x12)x(10x14)= Overhead (CFI=1)= 100 x (32528/168000)=19.36% One information symbol can be allocated in each data resource element. The transmission is done by means of 64-QAM with 6 bits per symbol. The peak rate thorughput is: Total data=(1 column a)x(6x72)+(1 column b)x(6x112)+(8 columns c)x(6x136) + (94x10 columns c)x136= resource elements Peak rate= 4 x ( symbols x 6 bits/symbol)/10ms= 325 Mbps

SRB (Signaling Radio Bearer) mapping for LTE Signaling Message
3GPP 4.2.2 Signalling radio bearers says : SRB0 is for RRC messages using the CCCH logical channel; SRB0 uses transparent mode RLC while SRB1 and SRB2 use acknowledged mode RLC. SRB1 is for RRC/NAS messages prior to the establishment of SRB2, all using DCCH logical channel; SRB2 is for NAS messages using DCCH logical channel. SRB2 has a lower-priority than SRB1 and is always configured by E-UTRAN after security activation. May be contained in RRC messages but without RRC content. Data Radio Bearers (DRB) - Carry User plane content on the air interface

Radio Bearers A bearer service is a link between two points, which is defined by a certain set of characteristics. Whenever a UE is being provided with any service, the service has to be associated with a Radio Bearer specifying the configuration for Layer-2 and Physical Layer in order to have its QOS clearly defined. Radio bearers are channels offered by Layer 2 to higher layers for the transfer of either user or control data. In other words, Layer 2 offers to the upper layers the service of information transmission between the UE and the UTRAN by means of the Radio Bearers (RBs) and Signaling Radio Bearers (SRBs). Therefore the service access points between Layer 2 and upper layers are RBs.

Radio Bearers Radio Bearers (RB) exist between RRC & PDCP which are mapped to various logical channels lying between RLC & MAC.

Radio Bearers There are 2 types of Radio Bearers (RB) in LTE: To carry signaling. There are called the SRB (Signaling Radio Bearer) To carry user data. There are associated with an EPS Bearer. The following types of Radio Bearer are defined: SRB1: RRC signaling with high priority SRB2: RRC signaling and NAS signaling (lower priority) Best Effort: also defined as the default EPS Bearer GBR: Radio Bearer with a guaranteed bit rate VoIP: Radio bearer to carry the VoIP

Radio Bearers In LA1.X implementation, the following combinations are supported: SRB1 SRB1+SRB2+Best Effort SRB1+SRB2+Best Effort + GBR SRB1+SRB2+Best Effort + VoIP SRB1+SRB2+Best Effort + Best Effort At the RRC connection, the eNodeB scheduler creates a context for theUE containing the UEBearerList. This list is limited to 4 per user in LA1.X

Radio Bearers Each bearer is identified by the LCID (Logical Channel ID) Each bearer is associated with QoS parameters like : Max bit rate and guaranteed bit rate VoIP or not H-ARQ usage

Radio Bearers A default bearer is bearer able to carry all kinds of traffic (no filter) without QoS. It is typically created during the attach procedure A dedicated bearer is a bearer to carry a specific data flow, identified by the TFT (Traffic Flow Template), with a given QoS.

References 4G LTE/LTE-Advanced for Mobile Broadband, by Erik Dahlman, Stefan Parkvall, and Johan Skold, 2011 Elsevier. LTE in a Nutshell: The Physical Layer, White paper, 2010, Telesystem Innovations. LTE Resource Guide at LTE E-UTRAN and its Access Side Protocols

Essay Assignments (report of 5 – 10 pages)
MIB – SIBs DCI CCE Index Calculation PCFICH and PHICH (L1/L2 signalling) PDCCH PDSCH RNTI Reference Signals – Downlink

LTE DCI Decoder PDSCH allocation calculator LTE OTDOA Positioning Reference Signals

Αν. Καθηγητής Γεώργιος Ευθύμογλου

Similar presentations

Presentation on theme: "Αν. Καθηγητής Γεώργιος Ευθύμογλου"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Αν. Καθηγητής Γεώργιος Ευθύμογλου

Similar presentations

Presentation on theme: "Αν. Καθηγητής Γεώργιος Ευθύμογλου"— Presentation transcript:

Similar presentations

About project

Feedback