17 Chapter: The Uplink physical resource Uplink reference - - PowerPoint PPT Presentation

May 13, 2009 1 3G Evolution - HSPA and LTE for Mobile Broadband

17

Uplink transmission scheme

3G Evolution - HSPA and LTE for Mobile Broadband

Chapter:

3G Evolution

Department of Electrical and Information Technology Telmo Santos

May 13, 2009 2 3G Evolution - HSPA and LTE for Mobile Broadband

Chapter 17 – Outline

• The Uplink physical resource
• Uplink reference signals
• Uplink L1/L2 control signaling
• Uplink transport-channel processing
• PUSCH frequency hopping

May 13, 2009 3 3G Evolution - HSPA and LTE for Mobile Broadband

17.1 The uplink physical resource

DFT size limited to products

• f 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

May 13, 2009 4 3G Evolution - HSPA and LTE for Mobile Broadband

17.1 The uplink physical resource

• Frequency domain structure

– Flexible bandwidth: 6–110 resource blocks (1–20 MHz )

No unused DC-subcarrier is defined for uplink

May 13, 2009 5 3G Evolution - HSPA and LTE for Mobile Broadband

17.1 The uplink physical resource

• Time domain structure

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

May 13, 2009 6 3G Evolution - HSPA and LTE for Mobile Broadband

17.2 Uplink reference signals

• Uplink demodulation reference signals (DRS)

– Necessary for demodulation

• f PUSCH and PUCCH

– Time multiplexed (downlink: frequency multiplexed)

May 13, 2009 7 3G Evolution - HSPA and LTE for Mobile Broadband

17.2 Uplink reference signals

• 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 the frequency and the time domain

May 13, 2009 8 3G Evolution - HSPA and LTE for Mobile Broadband

17.2 Uplink reference signals

• 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 sequences must exist for each length!

May 13, 2009 9 3G Evolution - HSPA and LTE for Mobile Broadband

17.2 Uplink reference signals

• Phase-rotated reference-signal sequences

Root sequence (in time-domain): Phase-rotated sequences: Frequency domain phase rotation Time domain cyclic shift = and the good thing is: They are perfectly

• rthogonal!

May 13, 2009 10 3G Evolution - HSPA and LTE for Mobile Broadband

17.2 Uplink reference signals

• 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)

May 13, 2009 11 3G Evolution - HSPA and LTE for Mobile Broadband

17.2 Uplink reference signals

• Reference-signal assignment to cells

– At least we must have 30 sequences per sequence length. Length <= 60 Length => 72 Bandwidth measured in number

• f resource blocks must be

a 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

May 13, 2009 12 3G Evolution - HSPA and LTE for Mobile Broadband

17.2 Uplink reference signals

• Reference-signal assignment to cells (cont.)

– Fixed group assignment – Group hopping

The group hopping pattern is defined from the cell identity.

– Sequence hopping

Optional scheme to be used for sequence lengths corresponding to 6 resource blocks and above

PUCCH

Sequence group given by the physical layer cell identity modulo 30. Cell identity ranges from 0 to 503.

PUSCH

Sequence 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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17.2 Uplink reference signals

• 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)

May 13, 2009 14 3G Evolution - HSPA and LTE for Mobile Broadband

17.2 Uplink reference signals

• 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

May 13, 2009 15 3G Evolution - HSPA and LTE for Mobile Broadband

17.2 Uplink reference signals

• 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.

May 13, 2009 16 3G Evolution - HSPA and LTE for Mobile Broadband

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 simultaneous transmission of UL-SCH Simultaneous transmission of UL-SCH (transmission over PUCCH) (transmission over PUSCH)

May 13, 2009 17 3G Evolution - HSPA and LTE for Mobile Broadband

17.3 Uplink L1/L2 control signaling

• 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

May 13, 2009 18 3G Evolution - HSPA and LTE for Mobile Broadband

17.3 Uplink L1/L2 control signaling

• 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

May 13, 2009 19 3G Evolution - HSPA and LTE for Mobile Broadband

17.3 Uplink L1/L2 control signaling

• 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

May 13, 2009 20 3G Evolution - HSPA and LTE for Mobile Broadband

17.3 Uplink L1/L2 control signaling

• 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 scheduling request mechanism. No collisions! Every terminal is given a reserved resource on which it can transmit a request for uplink.

May 13, 2009 21 3G Evolution - HSPA and LTE for Mobile Broadband

17.3 Uplink L1/L2 control signaling

• PUCHH format 2

– Channel status reports

PUCHH 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

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17.3 Uplink L1/L2 control signaling

• Simultaneous transmission of multiple feedback reports

– Hybrid-ARQ acknowledgement and channel-status report

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17.3 Uplink L1/L2 control signaling

• Resource-block mapping for PUCCH

– 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

May 13, 2009 24 3G Evolution - HSPA and LTE for Mobile Broadband

17.3 Uplink L1/L2 control signaling

• 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

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17.4 Uplink transport-channel processing

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

May 13, 2009 26 3G Evolution - HSPA and LTE for Mobile Broadband

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-specific pattern slot 1 slot 2 Period of the patterns corresponds to 1 frame subband #3

May 13, 2009 27 3G Evolution - HSPA and LTE for Mobile Broadband

17.5 PUSCH frequency hopping

• Hopping based on explicit hopping information in the

scheduling grant

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

May 13, 2009 28 3G Evolution - HSPA and LTE for Mobile Broadband

18

LTE access procedures

Chapter:

3G Evolution

Department of Electrical and Information Technology Telmo Santos

May 13, 2009 29 3G Evolution - HSPA and LTE for Mobile Broadband

Chapter 18 – Outline

• Aquisition and cell search
• System Information
• Random access
• Paging

May 13, 2009 30 3G Evolution - HSPA and LTE for Mobile Broadband

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). May 13, 2009 31 3G Evolution - HSPA and LTE for Mobile Broadband

18.1 Acquisition and cell search

• 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

May 13, 2009 32 3G Evolution - HSPA and LTE for Mobile Broadband

18.1 Acquisition and cell search

• 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.

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18.1 Acquisition and cell search

• PSS sctructure

– The 3 PSSs are 3 Zadoff-Chu sequences

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18.1 Acquisition and cell search

• 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

May 13, 2009 35 3G Evolution - HSPA and LTE for Mobile Broadband

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

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18.2 System information

• MIB and BCH transmission

May 13, 2009 37 3G Evolution - HSPA and LTE for Mobile Broadband

18.2 System information

• MIB and BCH transmission

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

May 13, 2009 38 3G Evolution - HSPA and LTE for Mobile Broadband

18.2 System information

• 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)

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18.3 Random access

May 13, 2009 40 3G Evolution - HSPA and LTE for Mobile Broadband

18.3 Random access

• Step 1: Random-access preamble transmission

– PRACH time-frequency resources

May 13, 2009 41 3G Evolution - HSPA and LTE for Mobile Broadband

18.3 Random access

• Step 1: Random-access preamble transmission

– Preamble structure and sequence selection

May 13, 2009 42 3G Evolution - HSPA and LTE for Mobile Broadband

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 generation Again, Zadoff-Chu sequences are used

May 13, 2009 43 3G Evolution - HSPA and LTE for Mobile Broadband

18.3 Random access

• Step 1: Random-access preamble transmission

– Preamble detection

This is basically an efficient correlation operation implemented in the frequency domain

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18.3 Random access

• Step 2: Random-access response
• Step 3: Terminal identification
• Step 4: Contention resolution

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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

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That’s it!