3g evolution

7/29/2019 3G Evolution

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May 13, 2009 13G Evolution - HSPA and LTE for Mobile Broadband

Uplink transmission scheme

3G Evolution - HSPA and LTE for Mobile Broadband

Department of Electrical and Information Technology

Telmo Santos



DFT size limited to products

of integers of 2,3 or 5

Low-PAR single-carrier transmission

Flexible bandwidth assignment

Orthogonal multiple access in time and frequency


Flexible bandwidth: 6110 resource blocks (120 MHz )

No unused DC-subcarrier

is defined for uplink


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Time domain structure Normal CP: 5.1us (1.5Km) 1 slot = 7 OFDM symbols

Extended CP: 16.7us (5Km) 1 slot = 6 OFDM symbols


Necessary for demodulation

of PUSCH and PUCCH

Time multiplexed

(downlink: frequency multiplexed)


Limited power variations in the frequency domain to allow for similar

channel-estimation quality for all frequencies.

Limited power variations in the time domain to allow for high power-amplifierefficiency.

Sounds contradicting? maybe not...

Zadoff-Chu sequences:

Constant power in both the

frequency and the time domain


Prime-length ZC sequences are preferred to maximize the number of

possible number of sequences. But, the reference-signals length must be a

multiple of 12.

For short sequence lengths, relatively few sequences would be available.

36

31 (30 diff. seq.)

For sequence lengths :

we use cyclic extensionsof shorter prime-length sequences (freq.domain)

For sequence lengths of :

30 QPSK-based sequences were found from computer search

A minimum of 30 sequences

must exist for each length!


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Root sequence (in time-domain):

Phase-rotated sequences:

Frequency domain

phase rotation

Time domain

cyclic shift=

and the

good thing is:

They are perfectly

orthogonal!


PUCCH PUSCH

and are different phase rotations

Multiple mobile terminals within a

cell simultaneously use the samefrequency resource

eNodeB

user

Reduced intercell interference

(requires good time alignment

between neighour cells uplink

transmission)


At least we must have 30 sequences per sequence length.

Length 72

Bandwidth measured in number

of resource blocks must bea product of 2, 3 or 5!

In a given time slot, the uplink reference-signal

sequences in a cell are taken from one group,which can be:

fixed group assignment or group hopping


Fixed group assignment

Group hopping

The group hopping pattern is defined from the cell identity.

Sequence hoppingOptional scheme to be used for sequence lengths corresponding to 6 resource

blocks and above

PUCCHSequence group given by the

physical layer cell identity

modulo 30.

Cell identity ranges from 0 to 503.

PUSCHSequence group is explicitly signaled

as part of the cell system

information.

This enables the possibility for neighour cells

to share the same sequence group (slide 9).


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These are transmitted to allow for the network to estimate the uplink

channel quality at different frequencies. Not necessarily transmitted together with any physical channel.

Transmitted in regular intervals, from

2ms (every second subframe)

160ms (every 16th subframe)


SRS should cover the bandwidths of interest for the frequency-domain

scheluding.

To avoid collision between SRS and PUSCH

transmissions, no terminals use the last DFTS-OFDM

symbol of those subframes for PUSCH.

Always a multiple of 4 RB


Also based on Zadoff-Chu sequences.

Sequence mapped to every second subcarrier

Different rotations require the

span of the same bands.

Different combinations allow

the span of different bands.


Hybrid ARQ acknowledgements

Reports of channel conditions to help downlink scheduling

Scheduling requests for UL-SCH transmissions

from downlink Information on uplink indicating the UL-SCH transport-format

(it has already been defined by eNodeB).

It is always transmitted regardless if the terminal has been

assigned uplink resources for UL-SCH or not.

No simultaneoustransmission of UL-SCH

Simultaneoustransmission of UL-SCH

(transmission over PUCCH) (transmission over PUSCH)


5/12


Resources are transmitted on the

edges of the available cell bandwidth

Reasons to use the edges of the spectrum Maximize frequency diversity

Not to block the assignment of very large bandwidths to a single terminal


Hybrid ARQ acknowledgements

Scheduling requests

3 symbols for channel estimation

4 symbols for BPSK/QPSK mod

Terminals can be separated by rotated

sequences and cover sequences


Inter-cell interference exists from the non orthogonal neighboring

sequences.

Considerig:

6 rotations (out of 12)

3 cover sequences

we get 18 possible terminals.

This helps randomizing the inter-cell interference

Cell A Cell B


Occurrences of hybrid-ARQ ack. are well known to the eNodeB

However, the need for uplink resources for a certain terminal is in principle

unpredicatble by eNodeB

LTE provides a contention-free scheduling

request mechanism. No collisions!

Every terminal is given a reserved resource on which it can transmit a

request for uplink.


6/12


Channel status reportsPUCHH format 2 is capable of multiple

information bits per subframe

Per subframe we have:

4 symbols for channel estimation

10 symbols for QPSK mod

Rotation angles are also

hopping to randomize

inter-cell interference


Hybrid-ARQ acknowledgement and channel-status report


Multiple resource block pairs can be used to increase the control-signaling

capacity.

PUCCH format 2 is put on the

edges of the cell bandwidth

PUCCH format 1 and 2

multiplexed over different

phase rotations


Control signaling is time multiplexed with the data on the PUSCH.

Hybrid-ARQ ack. is given

special attention due to

its importance

Hybrid-ARQ ack. is

simply punctured into the

coded UL-SCH bit stream

Rate matching not

needed


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There is no multi-antenna-

mapping function as in the

downlink


What is provided in the scheduling grant is the virtual resource.

Example of hopping pattern:

Reserved

for PUCCH

subband #0

Cell-specific

pattern

slot 1

slot 2

Period of the patterns

corresponds to 1 frame

subband #3


The scheduling grant contains:

Information about the resource to use in the first slot (as for non-hopping) Offset of the resource to use in the second slot, relative to the first


LTE access procedures

Department of Electrical and Information Technology

Telmo Santos


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To initiate the communication with an LTE network a terminal needs first to:

Find and aquire synchronization to a cell within the network

Receive and decode the cell system information, needed to communicateand operate properly within the cell.

Cell search is a continuous process required by mobile terminals to support

mobility. It consists of

Acquire frequency and symbol synchronization to a cell.

Aquire frame timing of the cell, that is, determine the start of the downlink frame.

Determine the physical-layer cell identity of the cell.

There are 504 different identities and their are divided into 168 cell-identity groups (3

identities per group).


There are 2 signals transmitted in the downlink:

Primary Synchronization Signal (PSS)

Secondary Synchronization Signal (SSS)

Different position useful to

detect the duplex scheme


After detecting and identifying the PSS the terminal has:

5ms timing of the cell and also the position of the SSS

the cell identity within the cell-identity group (3 alternatives)

From the SSS the terminal finds the following

Frame timing

The cell-identity group (168 alternatives)

The terminal can now decode the BCB transport channel which cotains the most

basic system information.


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The 3 PSSs are 3 Zadoff-Chu sequences


The values applicable for SSS2 should be different from the values

applicable for SSS1 to allow frame-timing detection from a single SSS.

Based on frequencyinterleaving of two

length-31 m-sequences


The system information includes:

Information about the downlink and uplink bandwidths

Uplink/Downlink configuration in case of TDD

Parameters related to random-access transmission and uplink power control,

etc.

It can be derivered by two different mechanisms relying on different

transport channels

Master Information Block (MIB)

using BCH

System Information Block (SIB)

using DL-SCH



10/12


In case of FDD, the BCH follows

right after the PSS and SSS


The main part of the system information is included in different System

Information Blocks (SIB), transmitted during DL-SCH. Eight different SIBsexist:

, info on wether the terminal is allowed to camp on the cell

(period = 80 ms)

, info on uplink bandwidth, random access parameter and power

control

(period = 160 ms)

, info on cell-reselection

(period = 320 ms)

, info on neighbor-cell, LTE or not

(period = 640 ms)

May 13, 2009 393G Evolution - HSPA and LTE for Mobile Broadband May 13, 2009 403G Evolution - HSPA and LTE for Mobile Broadband


11/12



PRACH power setting:

Power ramping is allowed for each unsuccessfull random access attempt.

Preamble sequence generation

Again, Zadoff-Chu sequences are used


This is basically an efficient

correlation operation implementedin the frequency domain



12/12


The terminal is allowed to sleep with no receiver processing most of the

time and to briefly wake up at predefined time intervals to monitor

paging information from the network


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