Lauri Pirttiaho, Contents: NMP/Oulu - pudn.comread.pudn.com/downloads48/sourcecode/comm/161337/WCDMA...

1 © NOKIA 3gppl1.PPT/ 27-Sep-2000 / [email protected]

Lauri Pirttiaho, NMP/Oulu Contents:

• General about radio communications systems • 3GPP WCDMA L1, the physical layer structure • Transmitting and receiving • Channels • Codings • Procedures Not included: • diversity techniques, ARQ, power control, device classes etc.


Radio communications system

• The Purpose of physical radio link is to establish a reasonably reliable radio communication path between the communicating system.

• In commercial systems some drivers for further development are:

• The capacity, or number of users serviced by the system. • The data rate, or the qualities perceived by one user.

• Physical radio link carries information from one system to another in a form of electromagnetic waves.

• The receiver is interfered by • signals from other systems, and • ever present physical noises.


Multiple Access Methods • Multiple access refers to how different users access the

system simultaneously.

time

frequ

ency

FDMA

time

frequ

ency

TDMA

time

frequ

ency

Code

CDMA


Duplexing Methods • Duplexing refers to how one user can establish a two way

communications link with the system.

time

frequ

ency

• Frequency division duplex (FDD)

• (Full duplex in analog systems)

time

frequ

ency

• Time division duplex (TDD)

• (Half duplex in analog systems)


Structure of the Physical Layer

RF

L1 Protocol

BB

RRC

MAC


The UMTS FDD Frequencies

The first allocation of the UMTS FDD system (ITU regions 1 & 3) is:

• 1920 — 1980 MHz up-link • 2110 — 2170 MHz down link • duplex distance 190 MHz The radio channel structure: • 5 MHz channel spacing • 200 kHz channel raster • UTRA absolute radio frequency channel number (UARFCN):

(channel number = 5 x frequency in MHz)


Modulation and Filtering

Modulation method: • Chip frequency 3.84 MHz • QPSK

Filter

Filter

π/2

I

Q

Filtering: • Pulse shaping before modulation • RRC with frequency domain roll-off

0.22


WCDMA TX: Spreading

• Channelization within one frequency is achieved by representing bits as sequences of chips.

0 1 0 1 1 0


WCDMA TX: Spreading

• The sequences are quasi-orthogonal between the channels. • Combination of:

• Bit long orthogonal sequences (Walsh sequences), and • Frame long pseudo noise sequences (Gold sequences)

I

Q


WCDMA TX: Spreading

• The complex symbols are scrambled by complex sequences formed of truncated Gold sequences.

Bits Pairing

Odd Bits

Walsh code

Even Bits

Q

I

(I,Q) Pair to

Complex (I + jQ)

Complex Gold code

Chips

• The transmitted bits are paired, spread to a chip sequences using Walsh sequences and mapped to complex symbols.


WCDMA RX

The receiver also needs to remove: • Noise • Interference from other channels and frequencies • Multi path propagation interference (fading)

Receiving a CDMA transmission requires: • Demodulation and filtering of the chip sequence. • Correlating with the scrambling and spreading codes to detect

the channel contents (chip sequence to bit sequence).


WCDMA RX: Rake

• Inter symbol interference due to multipath propagation.


Chips Delay Chips

WCDMA RX: Rake

• Correlating the received chip stream with sequences delayed by the propagation time differences.

Scrambling sequence

Spreading Sequence

Integrate & dump

Chips Delay Chips

Scrambling sequence

Spreading Sequence

Integrate & dump

Chips Delay Chips

Scrambling sequence

Spreading Sequence

Integrate & dump

Com

bining

Bits


Error Correction and Detection

Convolutional codes, K = 9

G0 = 561 G1 = 753

G0 = 557 G1 = 663 G2 = 711

Turbo code: PCCC, 2 x K=3 RCC's

Interleaver

CRC check sum: gCRC24(D) = D24 + D23 + D6 + D5 + D + 1 gCRC16(D) = D16 + D12 + D5 + 1 gCRC12(D) = D12 + D11 + D3 + D2 + D + 1 gCRC8 (D) = D8 + D7 + D4 + D3 + D + 1


WCDMA FDD Transport Channels L1 provides the upper layers a variety of transport channels: • Common channels

• BCH, the broadcast channel for system and cell information • PCH, the paging channel • FACH, the forward access channel for down-link

connectionless random access communication. • RACH, the random access channel for up-link random

access communication. • CPCH, the common packet channel for higher volume up-

link packet communication. • DSCH, the down-link shared channel for improving down

link peak communication throughput. • Dedicated channels

• DCH, the dedicated channel, for CS communication.


Dedicated channels

Dedicated channels

Common channels

Common channels WCDMA FDD Physical Channels

CPICH

PCCPCH PSCH

SSCH

SCCPCH

AP-AICH

AICH

PICH

CD/CA-ICH

CSICH

PDSCH

DPCCH DPDCH

DPDCH DPCCH

PRACH

PCPCH

BCH

PCH, FACH

DCH

DCH

RACH

CPCH

DSCH


WCDMA FDD Frame and Slot Structure

Frame: 10 ms, 38400 chips

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Slot: 2/3 ms, 2560 chips (example of DL DPCH)

Data TPC Data TFCI Pilots


Synchronization

...Established

Identify scrambling code from CPICH

Identify code group & frame sync from SSCH

Acquire slot sync from PSCH

Synchronization...

PSCH

PCCPCH

CPICH

SSCH

PCCPCH (carries BCH)


Establishing Radio Link

• Cell information • From BCH, tells parameters needed for establishing

communication

• Paging • From PCH when PICH indicates there is paging coming

• RACH/FACH • RACH/AICH up-link using slotted aloha protocol • reply on FACH

• DCH • Will carry both communication and control data • Paging during DCH comes on the DCCH


Soft & Hard Hand-over

Frequency A Frequency B



Node B 1 Node B 2 Node B 3


WCDMA/GSM Hand-over

GSM coverage area

WCDMA coverage area


WCDMA/GSM Hand-over

Lauri Pirttiaho, Contents: NMP/Oulu - pudn.comread.pudn.com/downloads48/sourcecode/comm/161337/WCDMA...

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