chapter 17 – outline 17 · 2009. 5. 14. · 17.5 pusch frequency hopping • hopping based on...

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

17Uplink transmission scheme

3G Evolution - HSPA and LTE for Mobile Broadband

Chapter:

3G Evolution

Department of Electrical and Information TechnologyTelmo Santos


Chapter 17 – Outline

• The Uplink physical resource

• Uplink reference signals

• Uplink L1/L2 control signaling

• Uplink transport-channel processing

• PUSCH frequency hopping


17.1 The uplink physical resource

DFT size limited to productsof integers of 2,3 or 5

• Based on DFTS-OFDM transmission– Low-PAR ’single-carrier’ transmission– Flexible bandwidth assignment– Orthogonal multiple access in time and frequency



• Frequency domain structure– Flexible bandwidth: 6–110 resource blocks (1–20 MHz )

No unused DC-subcarrieris defined for uplink



• Time domain structure– Normal CP: 5.1us (1.5Km) 1 slot = 7 OFDM symbols– Extended CP: 16.7us (5Km) 1 slot = 6 OFDM symbols


17.2 Uplink reference signals

• Uplink demodulation reference signals (DRS)– Necessary for demodulation

of PUSCH and PUCCH– Time multiplexed

(downlink: frequency multiplexed)



• Uplink DRS should have the following properties– 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-amplifier

efficiency.

Sounds contradicting? maybe not...

Zadoff-Chu sequences:

Constant power in both thefrequency and the time domain



• So why are we not using Zadoff-Chu sequences directly?– 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 >= 36:we use cyclic extensions of shorter prime-length sequences (freq.domain)

• For sequence lengths of 12 or 24:30 QPSK-based sequences were found from computer search

A minimum of 30 sequencesmust exist for each length!



• Phase-rotated reference-signal sequences

Root sequence (in time-domain):

Phase-rotated sequences:

Frequency domainphase rotation

Time domaincyclic shift=

and thegood thing is:

They are perfectlyorthogonal!



• Possible uses for phase-rotated (orthogonal) reference-signal sequences

PUCCH PUSCH

and are different phase rotations

• Multiple mobile terminals within a cell simultaneously use the same frequency resource

eNodeB

user

• Reduced intercell interference(requires good time alignment between neighour cells uplink transmission)



• Reference-signal assignment to cells– At least we must have 30 sequences per sequence length.

Length <= 60 Length => 72

Bandwidth measured in numberof resource blocks must be

a product of 2, 3 or 5!

In a given time slot, the uplink reference-signalsequences in a cell are taken from one group,

which can be:fixed group assignment or group hopping



• Reference-signal assignment to cells (cont.)– Fixed group assignment

– Group hoppingThe 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).



• Uplink sounding reference signals (SRS)– 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)



• Uplink sounding reference signals (SRD)– 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



• Uplink sounding reference signals (SRD)– 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.


17.3 Uplink L1/L2 control signaling

• It consist of– Hybrid ARQ acknowledgements– Reports of channel conditions to help downlink scheduling– Scheduling requests for UL-SCH transmissions

≠ from downlink• Other characteristics– 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)



• Uplink L1/L2 control signaling on PUCCH

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



• PUCHH format 1– 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



• PUCHH format 1– 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



• PUCHH format 1 – Scheduling requests– 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 schedulingrequest mechanism. No collisions!

Every terminal is given a reserved resource on which it can transmit arequest for uplink.



• PUCHH format 2– Channel status reports

PUCHH format 2 is capable of multipleinformation bits per subframe

Per subframe we have: • 4 symbols for channel estimation• 10 symbols for QPSK mod

Rotation angles are also hopping to randomizeinter-cell interference



• Simultaneous transmission of multiple feedback reports– Hybrid-ARQ acknowledgement and channel-status report



• Resource-block mapping for PUCCH– Multiple resource block pairs can be used to increase the control-signaling

capacity.

PUCCH format 2 is put on theedges of the cell bandwidth

PUCCH format 1 and 2multiplexed over different

phase rotations



• Uplink L1/L2 control signaling on PUSCH– 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


17.4 Uplink transport-channel processing

There is no multi-antenna-mapping function as in the

downlink


17.5 PUSCH frequency hopping

• Subband-based hopping according to cell-specific hopping/mirroing patterns– What is provided in the scheduling grant is the virtual resource.– Example of hopping pattern:

Reserved for PUCCH

subband #0

Cell-specificpattern

slot 1slot 2

Period of the patterns corresponds to 1 frame

subband #3


17.5 PUSCH frequency hopping

• Hopping based on explicit hopping information in the scheduling grantThe 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


18LTE access procedures

Chapter:

3G Evolution

Department of Electrical and Information TechnologyTelmo Santos


Chapter 18 – Outline

• Aquisition and cell search

• System Information

• Random access

• Paging


18.1 Acquisition and cell search

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 communicate

and operate properly within the cell.

• Overview of LTE cell search– 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).



• Overview of LTE cell search

There are 2 signals transmitted in the downlink:– Primary Synchronization Signal (PSS)– Secondary Synchronization Signal (SSS)

Different position useful to detect the duplex scheme



• Overview of LTE cell search

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.



• PSS sctructure– The 3 PSSs are 3 Zadoff-Chu sequences



• SSS sctructure– 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 frequency interleaving of two

length-31 m-sequences


18.2 System information

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



• MIB and BCH transmission



• MIB and BCH transmission

In case of FDD, the BCH follows right after the PSS and SSS



• System-Information Blocks– The main part of the system information is included in different System

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

• SIB1, info on wether the terminal is allowed to camp on the cell(period = 80 ms)

• SIB2, info on uplink bandwidth, random access parameter and power control(period = 160 ms)

• SIB3, info on cell-reselection(period = 320 ms)

• SIB4-SIB8, info on neighbor-cell, LTE or not(period = 640 ms)


18.3 Random access


18.3 Random access

• Step 1: Random-access preamble transmission– PRACH time-frequency resources


18.3 Random access

• Step 1: Random-access preamble transmission– Preamble structure and sequence selection


18.3 Random access

• Step 1: Random-access preamble transmission– PRACH power setting:

Power ramping is allowed for each unsuccessfull random access attempt.

– Preamble sequence generationAgain, Zadoff-Chu sequences are used


18.3 Random access

• Step 1: Random-access preamble transmission– Preamble detection

This is basically an efficient correlation operation implemented

in the frequency domain


18.3 Random access

• Step 2: Random-access response

• Step 3: Terminal identification

• Step 4: Contention resolution


18.4 Paging

• 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


That’s it!

chapter 17 – outline 17 · 2009. 5. 14. · 17.5 pusch frequency hopping • hopping based on...

Documents