Chapter: 16 p 16 LTE Time-Frequency structure Downlink L1/L2 - - PowerPoint PPT Presentation

3G Evolution

Chapter: 16 p 16

Donwlink Transmission Donwlink Transmission Scheme

Department of Electrical and Information Technology

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 1

Outline

• LTE Time-Frequency structure
• Downlink L1/L2 control signaling/processing
• Downlink transport channel processing
• Multi-Antenna transmission
• MBSFN transmission

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 2

Overall Time-domain structure

• The radio frame in LTE is defined as blocks of 10 ms

E h f i id tifi d b S t F N b

• Each frame is identified by a System Frame Number

Th b i ti it i LTE i d fi d T 1/30 720 000

• The basic time unit in LTE is defined as Ts=1/30 720 000
• One OFDM symbol length excluding the CP is 66.7 Micro sec (2048.Ts)
• The symbols,subframes,frames are defined to be multiple/submultiples

The symbols,subframes,frames are defined to be multiple/submultiples

• f Ts
• Another terminology is definition of slot which is 0.5 ms long

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 3

Overall Time-domain structure

Frame structure for FDD (full and half duplex) A typical frame structure for TDD

• Subframes 1 and 6 usually provide the guard time which are split into three parts, i.e.

y p g p p , DwPTS (Downlink Pilot Time Slot), GP and UpPTS (Uplink Pilot Time Slot)

• Subframes 0,5 are always assigned for downlink and subframe 2 is always earmarked

for uplink In TDD all neighboring cells have the same downlink/uplink scheduling

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 4

• In TDD all neighboring cells have the same downlink/uplink scheduling

Time-Frequency Grid

• Subcarrier spacing of 15 KHz (7.5 KHz in MBSFN mode)
• One resource block consists of 12 consecutive subcarriers and stretches for 7
• One resource block consists of 12 consecutive subcarriers and stretches for 7

OFDM symbols (in case of short cyclic prefix)

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 5

Time-Frequency Grid

R l b i d i OFDM b l

• Resource elements, one subcarrier during one OFDM symbol
• One resource block consists of,

– 72 RE in case of normal CP – 84 RE in case of extended CP The Date 3G Evolution - HSPA and LTE for Mobile Broadband 6

Time-Frequency Grid

• The sampling rate is fs=15000.Nfft which is a multiple/submultiple of the

WCDMA/HSPA chip rate WCDMA/HSPA chip rate

• Nfft can be in any of the following,

– 128, 256, 512, 1024, 2048

• This makes it easier to have terminals supporting all these standards
• This makes it easier to have terminals supporting all these standards
• The central subcarrier (DC-subcarrier) is not used for downlink to avoid

interference (e.g. local oscialtor leakage)

• LTE physical-layer specifications allow downlink to consist of 6 up to 110

p y y p p resource blocks (BW 1MHz-20MHz)

• Note: despite the above fact the radio frequency requirements are (initially)
• Note: despite the above fact the radio frequency requirements are (initially)

defined for a limited set of transmission bandwidth (e.g. Max no. of RB is 100)

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 7

Time-Frequency Grid Cyclic Prefix (CP) Cyclic Prefix (CP)

• There are two CP modes corresponding to different system configuration
• Normal cyclic prefix is 160.Ts=5.1 Micro sec
• Extended cyclic prefix is 512.Ts=16.7 Micro sec
• Why two different CP?

– In case of larger cells with extensive delay spread, a longer CP is usually beneficial In case of larger cells with extensive delay spread, a longer CP is usually beneficial unless the performance is more affected by noise! – in MBSFN, CP not only covers the channel dispersion but also the timming difference between transmitters invloved in broadcast

• In case of normal CP, the first OFDM symbol in each slot has a somewhat

larger length so the overall slot length becomes and exact multiple of Ts larger length so the overall slot length becomes and exact multiple of Ts

• In a frame, subframes could have either/both normal or/and extended CP (e.g.

In case of MBSFN combined configuration could happen) In case of MBSFN combined configuration could happen).

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 8

Downlink Reference Signals (Pilots) (Pilots)

• To assist channel estimation reference signals are inserted at specific locations

in each resource block

• Three types of reference signal distributions are defined for LTE,

– Cell specific downlink RS (Reference Signals) are inserted in every downlink Cell specific downlink RS (Reference Signals) are inserted in every downlink subframe and span the entire downlink cell BW – UE-specific RS used in DownLink-Shared-CHannel (DL-SCH) and are intended for UE specific RS used in DownLink Shared CHannel (DL SCH) and are intended for specific terminals. They are transmitted in non-codebook-based beam forming where terminal is not aware of what precoding matrix has been applied to the data – MBSFN reference signals, as evident from the name, are used in MBSFN transmission

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 9

Cell-specific downlink RS

• The reference pilots are inserted

assuming the full BW i e 110 assuming the full BW, i.e. 110 resource blocks. Thus, the pilots in the central part of the band will always be the same fascilitates always be the same fascilitates decoding of BCH info

• Pilot pattern of each cell has a cell-

specific configuration specific configuration

• The depicted pattern is only one out
• f 6 possible frequency shifts of pilot

patterns patterns

• each cell has a specific pilot pattern

corresponding to its cell identity Th 504 ll id titi d fi d

• There are 504 cell identities defined

for LTE. Thus, each frequency shifted pilot pattern covers 84 different cell identities identities

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 10

Cell-specific downlink RS

• Smart assigning of pilot patterns in neighboring cells reduces the interference

caused on the pilot positions assiged to each individual cell This becomes caused on the pilot positions assiged to each individual cell. This becomes specially handy when pilots are power boosted to fasciliated better channel estimation

• In the so called cell search procedure (Chapter 18) the terminal detects the

physical cell identity as well as the begining of pilot sequences

• To determine the cell BW, BCH information (e.g. BW) is provided in the central

part of BW where terminal does the channel estimation without having a prior k l d f ll BW knowledge of cell BW

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 11

Cell-specific downlink RS-Multiple antenna ports antenna ports

• LTE benefits from MIMO scheme
• In specifications the term antenna port is prefered over antenna since two/multiple

physical antennas can transmit the same information and hence make one antenna port

• Each antenna port has a specific pilot pattern assigned to it. Thus, the terminal can

estimate the downlink channel corresponding to each transmit antenna independantly

• The resource elements corresponding to pilots of each antenna port don’t carry any

information for the resource blocks scheduled for other ports

• In case of 4 antenna ports the third and fourth antenna ports have less pilot density which

comes with the following pros/cons, – the reference signal overhead is reduced as an advantage – the channel estimation and tracking of channel variations degrades as a consequence Note: 4 antenna spatial multiplexing is usually used in low mobility scenarios!

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 12

Cell-specific downlink RS-Multiple antenna ports antenna ports

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 13

Cell-specific downlink RS-Multiple antenna ports antenna ports

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 14

UE-specific downlink RS

• UE-specific transmission is referred to

beam-formed transmission intended for a specific terminal/group of t i l terminals

• Just as data is beam-formed, pilots

need also beamforming as a result of which UE-specific reference signals are created

• Transmission incompassing UE-

specific RS is also called transmission using antenna port 5

• Piolts corresponding to antenna port 5

don’t collide with pilots transmitted on cell-specific RS

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 15

UE-specific downlink RS

• The terminal is informed by the network if the DL SCH is done through cell
• The terminal is informed by the network if the DL-SCH is done through cell-

specific antenna ports or antenna port 5

• The beam forming is based on non-codebook configuration in which the base

station doesn’t convey the precoding matrix to the UE/Ues

• Thus the terminal needs to know the channel experienced by the beamformed

data

• The pilots will go through the same beamforming applied to data before

transmitted to UE

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 16

MBSFN-specific RS

• Specific subframes are allocated to

carry MBSFN information carry MBSFN information

• Extended CP is used for MBSFN

transmission Piolt densit is higher in MBSFN

• Piolt density is higher in MBSFN

scheme due to higher frequency selectivity of the channel S ti l lti l i i t t d

• Spatial multiplexing is not supported

in MBSFN there is only one pilot pattern Pil t i i d

• Pilot sequence is unique and no

frequency shifted versions exist (compared to cell-specific pilot tt ) patterns)

• MBSFN broadcast/multicast is also

known as antenna port 4 transmission

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 17

Channel estimation

• UE

needs to have proper knowledge (estimate) of the channel to decode the ( ) received data

• Interpolation/extrapolation techniques can

p p q be used for channel estimation of those resource elements not carrying any pilots

• Depending on the channel condition, e.g.

amount of time dispersion, doppler shifts,

• etc. averaging can be done over multiple

pilots in time/frequency to obtain a better pilots in time/frequency to obtain a better channel estimate

• Due to limited computational power of UE

Due to limited computational power of UE as well as low power requirements, low complexity estimators are preferred which might not give the best results

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 18

Downlink L1/L2 control signaling

• L1/L2 signaling originates from

physical layer 1 and partly from MAC

• physical layer 1 and partly from MAC

layer 2

• They are placed in the beginning of

each subframe each subframe

• L1/L2 signaling can occupy 1,2 or 3

OFDM symbols. Which size to assign depends on the traffic situation as depends on the traffic situation as well as download transmission scheme

• There are many advantages to
• There are many advantages to

transmission of control signaling in the begining of each subframe,

The terminal for which the subframe is not – The terminal for which the subframe is not intended can enter idle mode and save power – The sooner control signaling appears the li d di f d t i t t earlier decoding of data region starts The Date 3G Evolution - HSPA and LTE for Mobile Broadband 19

Downlink L1/L2 control signaling

• In case of TDD subframes 1 and (GP) have a control region of length 2 OFDM
• In case of TDD subframes 1 and (GP) have a control region of length 2 OFDM
• symbols. The third OFDM symbol constitutes the primary synchronization signal

in those subframes

• In MBSFN, control region is confined to a maximum of 2 OFDM symbols (which

is located in unicast part)

• L1/L2 control signaling can be divided into three different physical channel

types,

– Physical Control Format Indicator Channel (PCFICH), infroming the terminal about the size of control region (unique in each cell) – Physical Downlink Control Channel (PDCCH),used to signal downlink scheduling assignments and uplink scheduling grants. There are typically multiple PDCCHs per cell – Physical Hybrid-ARQ Indicator Channel (PHICH), used to signal hybrid-AQR acknowledgments There are multiple PHICHs per each cell

• acknowledgments. There are multiple PHICHs per each cell

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 20

Downlink L1/L2 control signaling Resource element groups Resource element groups

• 4 consecutive resource elements make one resource element group
• 4 consecutive resource elements make one resource element group
• Considering the existence of scattered pilot signals, 2 resource element groups

can be mapped into the first OFDM symbol of each subframe

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 21

(Downlink L1/L2 control signaling)

Physical Control Format Indicator Channel (PCFICH) y ( )

• PCFICH indirectly indicates the beginning

f d t i d h l th f 2 bit

• f data region and has a length of 2 bits
• It is coded in a 32-bit code word and

scrambled with a cell/subframe specific scrambling code (which depends on the scrambling code (which depends on the physicall cell identity)

• Naturally It is always mapped to the first

OFDM symbol of each subframe (since the y ( size of control region is initially unknown)

• The four resource groups are well

seperated in frequency (one quarter of BW h) t id d f di it each) to provide good frequnecy diversity

• Starting position is defined by the physical

layer cell identity

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 22

(Downlink L1/L2 control signaling)

Physical Hybrid-ARQ Indicator Channel (PHICH) y y Q ( )

• The error rate restrictions on PHICH are much tougher than PCFICH. They are in the
• rder of 1/10000 and are operator dependant as well
• The power is regulated by radio channel quality
• For normal CP orthogonal sequences of length 4 are used while for extended CP
• rthogonal codes of length 2 are applied. Excessive time dispersion in channel destroys
• rthogonality between the orthogonal codes

In case of normal CP PHICH group size is 8 for ex CP it is 4

• In case of normal CP PHICH group size is 8, for ex. CP it is 4

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 23

(Downlink L1/L2 control signaling)

Physical Hybrid-ARQ Indicator Channel (PHICH) y y Q ( )

• To fullfill frequency diversity PHICH is spread in frequncy grid (each resource group is

To fullfill frequency diversity, PHICH is spread in frequncy grid (each resource group is

• ne third of BW away from its counter part)
• PHICH is (usually) mapped to the first OFDM symbol. Terminal will continue to decode

even if it fails to decode PCFICH properly p p y

• In the first OFDM symbol, resources are first allocated to PCFICH, PHICH and PDCCH

respectively

• To minimize the overhead, the PHICH group number, orthogonality sequence,etc. is

determined by the number of the first resource block in which uplink transmission occured

• An uplink transport block received in subframe n should be confirmed through PHICH in

subframe n+4. It is the same for TDD (taking the downlink-uplink configuration into account) account)

• PHICH configuration is determined through info provided by PBCH which is enough for

FDD but not sufficient in case of TDD (because there is also a dependancy on the uplink/downlink configuration) 1 bit indicates if it is 1 or 3 OFDM symbols and 2 bits uplink/downlink configuration). 1 bit indicates if it is 1 or 3 OFDM symbols and 2 bits indicate the amount of allocated resources (fraction of BW in terms of no. Res. Blocks)

• In case of TDD, the terminal has to blindly process PDCCHs under various PHICH

configurations to be able to retrieve the necessary system information

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 24

(Downlink L1/L2 control signaling)

Physical Downlink Control Channel(PDCCH) y ( ) PDCCH is sed to transmit DCI s ch as

• PDCCH is used to transmit DCI such as,

– Donwlink scheduling assignments including:

• PDSCH resource indication
• transport format
• control information for spatial multiplexing
• Commands for power control of PUCCH uplink physical channel

Commands for power control of PUCCH uplink physical channel – Uplink scheduling grants,

• PUSCH resource indication
• Transport format

Transport format

• Hypbrid-ARQ related info
• Command for power control of PUSCH uplink

Power control commands for a set of terminals on top of the above – Power control commands for a set of terminals on top of the above mentioned ones

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 25

(Downlink L1/L2 control signaling)

Physical Downlink Control Channel(PDCCH) y ( )

• DCI information comes in different

message sizes for various configurations of the system configurations of the system

• Message size depends on a number

f f t BW f th ll t ffi

• f factors,e.g. BW of the cell, traffic,

etc.

• A multitude of various message types

could be transmitted per subframe

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 26

(Downlink L1/L2 control signaling)

Physical Downlink Control Channel(PDCCH) y ( )

• Message type 1C,

Random access response paging transmission of system information etc – Random access response, paging, transmission of system information, etc. – QPSK only – No Hybrid-ARQ support No closed loop spatial multiplexing – No closed-loop spatial multiplexing

• Message type 1B,

– Frequnecy contiguous resource block assignment only (supports type 2)

• Message type 1A,

– Supports codebook-based beamforming – Similar to 1B but bits for signaling of a precoding matrix are added – A flag indicates if it is 1A or DCI 0 which is used for uplink scheduling grants

• Message type 1,

– Supports non-contiguous resource block allocations in frequency pp g q y

• Message type 2,

– Similar to 1 but bits for indicating the number of transmission layers for spatial multiplexing are provided p g p

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 27

(Downlink L1/L2 control signaling)

Signaling of resource block allocations g g

• Different sig. is used to reduce the overhead of transmitting one big bitmap
• Signaling for resource block allocation
• Signaling for resource block allocation,

– Type 0 – Type 1 – Type 2 Type 2

• In type 0 and type 1, the group size/subset size depends on the BW of the

channel

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 28

(Downlink L1/L2 control signaling)

Physical Downlink Control Channel(PDCCH) y ( )

• Signaling for transport block sizes:
• Signaling for transport block sizes:

– provides information regarding modulation-coding scheme, block size – Integrated in 5 bits in different DCI message formats – There are 32 combinations,

• 29 of them modulation-coding schemes
• Three others are reserved for retransmission command purposes
• The modulation-coding scheme together with the number of resource blocks

define the transport block size

• A mother table with 29 rows and 110 columns is created from which the desired

transport block sizes will be extracted

• For BW narrower than 110 resource blocks, a subset of the table is used. If the

cell BW is N the first N columns of the table are used

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 29

(Downlink L1/L2 control signaling)

Physical Downlink Control Channel(PDCCH) y ( )

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 30

Uplink schedulink grants

• Uplink scheduling grants use DCI format 0 which is very similar to DCI format
• Uplink scheduling grants use DCI format 0 which is very similar to DCI format

1A except one flag A fl i 1A di t t if it i f li k d li k

• A flag in 1A dictates if it is for uplink or downlink
• Neither spatial multiplexing nor noncontiguous resource block allocations are

supported for a single terminal

• Resource block allocation type 2 is used

Resource block allocation type 2 is used

• An uplink transmission grant recieved in donwlink subframe n is materialized in

uplink subframe n+4 Compare with PHICH uplink subframe n+4. Compare with PHICH

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 31

PDCCH processing

• CRC is calculated in conjunction with RNTI
• Rate matching is used to adjust the rate to

Rate matching is used to adjust the rate to the transmitted RB

• To map the output from the rate matching

block a structure called Control Channel Elements (CCE) is used,

– A set of 36 resource elements 9 R. Groups – Number of CCE depends on the BW, size of control region no of antenna ports as well as control region, no. of antenna ports as well as the amount of resources occupied by PHICH – Terminal needs to blindly decode the number

• f CCEs limited number of CCE

aggregations for all possible PHICH config. aggregations for all possible PHICH config. – Scrambling is done by a cell specific sequence to randomize the intercell interference – Interleaving exploits the freq. Diversity Cyclic shift is done to randomize the inter cell – Cyclic shift is done to randomize the inter cell intereferenec even more Note: Terminal has to blindly decode the format of CCEs based on a search space defined and standardized in LTE The Date 3G Evolution - HSPA and LTE for Mobile Broadband 32 p The number of attempts is 44 times per subframe

Downlink transport-channel processing

• LTE physical layer interfaces to higher

LTE physical layer interfaces to higher layers (MAC) through Transport Channels

• Similar to WCDMA/HSPA data are

delivered to the Physical Layer in the form y y

• f transport blocks,

– Single antenna single block of dynamic size Multiple antennas up to 2 transport – Multiple antennas up to 2 transport blocks of dynamic size, each block corresponds to one code word in case of spatial multiplexing (even though up to 4 layers can be used for multiplexing still the layers can be used for multiplexing still the

• no. of transport blocks in limited to 2)

– The processing chain is in many aspects similar to PCH and MCH The Date 3G Evolution - HSPA and LTE for Mobile Broadband 33

Downlink transport-channel processing

• CRC has a length of a 24 bits Helps to

CRC has a length of a 24 bits. Helps to detect errors and ask for retransmission of data

• In WCDMA both convolutional and turbo

coding could be used. In HSPA as well as LTE only turbo coding is applied

• Scrambling sequences depend on the cell

id tit d i d i ti f identity and insure randomization of interference and help better decoding on terminal side

• QPSK 16QAM and 64QAM are supported
• QPSK, 16QAM and 64QAM are supported

in LTE

• The last stage (Resource block mapping )

maps the data for each antenna port to a p p set of available resource elements grouped as resource blocks

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 34

Resource block mapping

• Data should be mapped to resource elements which are not reserved for pilot as well as

Data should be mapped to resource elements which are not reserved for pilot as well as synchronization signals

• Transmitter might consider channel conditions both in time and frequency to schedule the

resource blocks for each UE which is not always advantagous. Thus, frequency diversity y g q y y will be exploited by distributing the RB in whole BW

• Resource allocation types 0,1,2 can be used, yet

– Due to certain limitations of type 0,1 type 2 is usually prefered T h b tt f di t ib ti i f t 2 ti f Vi t l R Bl k (VRB) h b – To have a better frequency distribution in case of type 2, notion of Virtual Resource Blocks (VRB) has been introduced in LTE

• There are two different VRBs defined in LTE.Which one to use is declared to

UE through PDCCH UE through PDCCH

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 35

Resource block mapping

• Wether localized or distributed RB are used

Wether localized or distributed RB are used will be indicated on the associated PDCCH in case of type 2 E i l bl k i ill b

• Even a single resource block pair will be

scattered in PRB

An example of mapping with 25 RB pairs

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 36

Multi-Antenna transmission

• LTE supports the following multi antenna transmission schemes on top of single antenna

LTE supports the following multi antenna transmission schemes on top of single antenna transmission,

– Transmit diversity

• In case of two antenna ports diversity is achived through space frequency block coding (SFBC)

I if 4 t t b th SFBC ll F Shift T it Di it (FSTD) li d It

• In case if 4 antenna ports, both SFBC as well as Frequency Shift Transmit Diversity (FSTD) are applied . It
• perates on groups of 4 resource elements per group resource element groups were defined

– Closed-loop spatial multiplexing including codebook-based beam-forming – Open-loop spatial multiplexing

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 37

Multi-Antenna transmission Spatial Multiplexing Spatial Multiplexing

• Spatial multiplexing means transmission of multiple streams (layers) in parallel
• Spatial multiplexing means transmission of multiple streams (layers) in parallel
• In LTE the maximum number of layers is allowed to be 4 (number of antenna

t ) ports)

• Spatial Multiplexing has two forms in LTE,

– Open-loop spatial multiplexing

• Used in high mobility scenarios and cases where the extra overhead of closed-

loop multiplexing is not justified

• The precoding matrices are well-defined No information regarding the

precoding matrix is transmitted to UE – Closed-loop spatial multiplexing ,

• multiplexing relies on the feedback received from UE
• The terminals need to provide both the Rank as well as the precoding matrix to

transmitter

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 38

Multi-Antenna transmission Closed-loop Spatial Multiplexing Closed loop Spatial Multiplexing

• UE can report its desired precoding matrix (Rank

Indication) as well as number of layers to the

• transmitter. Transmitter doesn’t have to follow

UE’s suggestion though

• One or two code words are always fed to the

layer mapper. For a single antenna port, one y pp g p code word (transport block) and for two or more antenna ports two code words are used

• Code word lengths are chosen in a way such

that layers always have equal length that layers always have equal length

• Finally layers are precoded and mapped to the

physical antenna ports through a precoding matrix W In case of a single la er being mapped to a

• In case of a single layer being mapped to a

number of antenna ports, W is a column vector producing a beamformed output The Date 3G Evolution - HSPA and LTE for Mobile Broadband 39

Multi-Antenna transmission codebook-based beam-forming codebook based beam forming

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 40

Multi-Antenna transmission General beam-forming General beam forming

• Using codebook-based beam forming UE uses cell specific pilots to perform
• Using codebook-based beam forming, UE uses cell specific pilots to perform

the channel estimation I f d b k b d b f i

• In case of non-codebook based beam forming:

– UE has to use UE specific pilots for channel estimation – The pilots have to go through the same beamforming experienced by data – This transmission is also called transmission using antenna port 5 – It is only applicable in DownLink-SharedCHannel (DL-SCH)

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 41

MBSFN transmission and MCH

• Multicast/Broadcast over Single Frequency Network
• Multicast/Broadcast over Single Frequency Network
• OFDM multi-cell multicast/broadcast a possibility
• Transmissions from various cells to the terminal appear as comming from a

single node

• Benefits,

– Increased signal strength specially at the borders of the cells g g p y – Reduced ineterference for there is no interference caused by neighboring cells – Additional diversity since the radio channel consists of several transmitters Additional diversity since the radio channel consists of several transmitters beign geographically apart MCH t t h l i d f MBFSN t i i Th d t

• MCH transport channel is used for MBFSN transmission. They are mapped to

special subframes where no other Downlink data is mapped to

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 42

MBSFN transmission and MCH

• There is only one reference signal defined for MBSFN (for one antenna port)
• There is only one reference signal defined for MBSFN (for one antenna port)
• Multi-antenna diversity is not supported. It is believed that the high frequency

selectivity of the channel in itself provides enough diversity

• Since MCH is simultaneously targetting different mobile terminals, Hybrid ARQ

y g g , y is not really applicable

• MCH transport format is the same for all involved transmitters

MCH transport format is the same for all involved transmitters

• MCH scrambling is MBSFN area-specific and not cell-specific

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 43

MBSFN transmission and MCH subframe structure subframe structure

• The subframe consists of two parts

The subframe consists of two parts

• Unicast part bears the cell specific pilot

pattern pattern

• Unicast is always two OFDM symbols in

length g

• It has the same role the L1/L2 control

region has for non-MBSFN transmission

• Due to the CP length difference between

the first and second resource block, there is a gap (hole) in the subframe

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 44

Questions?

The Date 3G Evolution - HSPA and LTE for Mobile Broadband 45