Doc.: IEEE 802.22-05/0094r1 Submission November 2005 Ying-Chang Liang, Institute for Infocomm...

November 2005

Ying-Chang Liang, Institute for Infocomm Research

Slide 1

doc.: IEEE 802.22-05/0094r1

Submission

System Description and Operation Principles for IEEE 802.22 WRANs

IEEE P802.22 Wireless RANs Date: 2005-11-07

Name Company Address Phone email Ying-Chang Liang [email protected]

Wing Seng Leon [email protected]

Yonghong Zeng [email protected]

Changlong Xu [email protected]

Ashok Kumar Marath

[email protected]

Anh Tuan Hoang [email protected]

Francois Chin [email protected]

Zhongding Lei

Institute for Infocomm Research

21 Heng Mui Keng Terrace, Singapore 119613

65-6874-8225

[email protected]

Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22.

Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at [email protected].>

November 2005


Slide 2

doc.: IEEE 802.22-05/0094r1

Submission

Abstract• OFDMA as the basic multiple-access scheme for both uplink and downlink• Pre-transform for uplink to reduce peak-to-average power ratio (PAPR)• TDD as the duplex mode, with adaptive guard time control to maximize the

system throughput • Distributed channel sensing using guard interval between dowlink subframe

and uplink subframe• The CPEs support the usage of single TV channel with variable channel

bandwidth (6, 7 & 8MHz)• The BS supports the usage of multiple TV channels, either contiguous or

discontiguous • Scalable bandwidth ranging from 1.25 MHz to 7.5 MHz for each CPE• Preamble and pilot design to avoid interference to primary users• Shortened block Turbo codes (SBTC) with special parity check matrix design• Supporting transmit power control (TPC) and adaptive modulation and

coding (AMC) • Adaptive antennas for interference avoidance and channel shortening• Transmit diversity, random beamforming and virtual MIMO • Cellular deployment and sectorization for enhanced channel capacity

November 2005


Slide 3

doc.: IEEE 802.22-05/0094r1

Submission

WRANs

• Operate in the VHF/UHF TV bands using cognitive radio technology – Sensing before using

– No fixed spectrum available

• Co-exist with primary users, e.g. wireless microphone– Primary users have higher priority in channel usage

• Coverage range as large as 100 km– Large delay spread

– Long propagation delay

November 2005


Slide 4

doc.: IEEE 802.22-05/0094r1

Submission

Two-Layer OFDMA

• How?– 1st Layer: FDMA -- User allocation to TV channels– 2nd Layer: OFDMA -- Multiple access within each TV

channel

• Advantages:– Provide user orthogonality– Most suitable for irregular spectrum (discontiguous TV

channels, partial TV channel)– Exploit multiuser diversity

November 2005


Slide 5

doc.: IEEE 802.22-05/0094r1

Submission

OFDMA

Tb Tc

Ts

Subchannel 1 Subchannel 2 Subchannel K

Guard bands Guard bands

• A group of subcarriers is defined as a subchannel

• Each user is allocated with one or more subchannels

• Localized subchannel vs distributed subchannel

• Localized subchannel preferable for avoiding interference to primary users

November 2005


Slide 6

doc.: IEEE 802.22-05/0094r1

Submission

OFDMA

usedN

N

Bf

b

c

T

TC

Parameters Description

B Chanel bandwidth

N FFT size

Number of used subcarriers, including DC subcarrier

Oversampling factor

Subcarrier spacing

Tb Useful symbol duration

Tc Cyclic prefix duration

Ts =Tc+Tb OFDMA symbol duration

Cyclic prefix factor

November 2005


Slide 7

doc.: IEEE 802.22-05/0094r1

Submission

Scalable Design

• Each CPE supports one TV channel usage– OFDMA

– Scalable bandwidth ranging from 1.25 MHz to 7.5 MHz

– Scalable for 6 MHz, 7MHz and 8MHz TV channels

• BS supports the usage of multiple TV channels, either contiguous or discontiguous – Two-layer OFDMA for BS

November 2005


Slide 8

doc.: IEEE 802.22-05/0094r1

Submission

Variable Bandwidths within one TV Channel

Parameters Values

Channel bandwidth

1.25 MHz 2.5 MHz 5 MHz 7.5 MHz

Sampling frequency*

1.4286 MHz 2.8571 MHz 5.7143 MHz 8.5714 MHz

Sampling interval 0.7 μs 0.35 μs 0.175 μs 0.1167 μs

FFT size 256 512 1024 1536

Subcarrier spacing

5.5804 kHz

Useful OFDMA symbol interval

179.2 μs

* Oversampling factor of 8/7

November 2005


Slide 9

doc.: IEEE 802.22-05/0094r1

Submission

Support Variable TV Channel Bandwidths of 6, 7 & 8MHz

• Option A: Fixed sampling frequency– Adding variable number of nulls

• Option B: Variable sampling frequency– Keeping same number of useful subcarriers

November 2005


Slide 10

doc.: IEEE 802.22-05/0094r1

Submission

Option A for Variable TV Bandwidth

TV channel bandwidth 8 MHz 7 MHz 6 MHz

Sampling frequency 7.5MHz*8/7 = 8.5714 MHz

FFT size 1536

Number of useful subcarriers

1249 1145 937

Data/pilot subcarriers per subchannel

48/4 48/4 48/4

Number of subchannels 24 22 18

November 2005


Slide 11

doc.: IEEE 802.22-05/0094r1

Submission

Option A with Variable CP Length

CP factor 1/16 1/8 1/4 3/8 *

CP length 11.2 μs 22.4 μs 44.8 μs 67.2 μs

OFDMA symbol interval

190.4 μs 201.6 μs 224 μs 246.4 μs

* optional, to support repeater applications

November 2005


Slide 12

doc.: IEEE 802.22-05/0094r1

Submission

Option A: Minimum Peak Rates

Downlink Uplink

Channel bandwidth 1.25 MHz

Total No of subcarriers 256

No of used subcarriers 209

No of subchannels 4

No of data subcarriers per subchannel 48

No of pilot subcarriers per subchannel 4

No of subchannels per user 4 2

Minimum peak rates1.513 Mbps

(QPSK, ¾ rate, 1/16 CP factor)

504 kbps(QPSK, ½ rate, 1/16 CP

factor)

November 2005


Slide 13

doc.: IEEE 802.22-05/0094r1

Submission

Option B for Variable TV Bandwidth

TV channel bandwidth 8 MHz 7 MHz 6 MHz

Sampling Frequency

8/7*8 =9.14MHz

8/7*7 =8 MHz

8/7*6 =6.86 MHz

FFT size 1024 / 2048

Number of useful subcarriers

864 / 1728

CP length (28 / 14 / 7 us) / (56 / 28 / 14 us)

Spectrum efficiency(With ~1/16 CP factor)

78%

Number of subchannels

27 (32 / 64 subcarriers per subchannels)

November 2005


Slide 14

doc.: IEEE 802.22-05/0094r1

Submission

Option B: System Parameters

November 2005


Slide 15

doc.: IEEE 802.22-05/0094r1

Submission

TDD as the Duplex Mode

• Why TDD?– Difficult to identify paired spectrum for FDD

• Drawback of TDD– Large BS TTG due to long propagation delay

• Our proposals– Adaptive guard time control to increase system

throughput

– A sensing slot allocated for distributed channel sensing after DL subframe

November 2005


Slide 16

doc.: IEEE 802.22-05/0094r1

Submission

Basic TDD Frame Structure

November 2005


Slide 17

doc.: IEEE 802.22-05/0094r1

Submission

DL Subframe • DL Preamble

– transmitted in the first OFDMA symbol of the TDD frame– used by CPEs for time synchronization, frequency synchronization and

channel estimation • FCH contains the Downlink Frame Prefix (DLFP) which specifies:

– used subchannel bitmap, ranging channel indication, coding scheme for DL/UL-MAP, DL/UL-MAP length

• DL-MAP specifies:– Frame duration (in # of OFDMA symbols) and frame number– Subchannel allocation for each DL burst (subchannel and symbol offsets).– Coding/modulation scheme used for each DL burst

• UL-MAP specifies:– Subchannel allocation for each UL burst (subchannel and symbol offsets)– Coding/modulation scheme for each UL burst– UL-subframe start time for each burst (relative to the beginning of the

frame) due to the use of adaptive TDD

November 2005


Slide 18

doc.: IEEE 802.22-05/0094r1

Submission

UL Subframe

• Preamble is not necessary if pre-equalization is done at CPEs

• Otherwise, the first OFDMA symbol of a UL burst is designed as the UL preamble

• One subchannel can be assigned for ranging and BW request

• A sensing slot after DL subframe is designed for BS and all CPEs to sense the primary users

• Adaptive TDD is proposed to reduce required BS TTG

November 2005


Slide 19

doc.: IEEE 802.22-05/0094r1

Submission

Adaptive TDD Frame Structure

• Near-by users are allowed to transmit earlier than far-away users

• Reduced BS TTG for increased throughput

November 2005


Slide 20

doc.: IEEE 802.22-05/0094r1

Submission

Adaptive TDD

timeCPE3 is the nearest user while CPE2 and CPE4 are the farthest user.

S1 S2 S3 S4 S5 S6 S7 S8 S9

CPE1 G G pre G data G data G data G data G data G data G data

CPE2 G G G pre G data G data G data G data G data G data

CPE3 G pre G data G data G data G data G data G data G data G data

CPE4 G G G pre G data G data G data G data G data G data

CPE5 G G pre G data G data G data G data G data G data G data

November 2005


Slide 21

doc.: IEEE 802.22-05/0094r1

Submission

Channel Sensing and Adaptive TDD

T ss = n * Tb, n = 1, 2, 3…TTG1 > TRS + Tss

TTG2 – TTG1 = k * Ts, k = 1, 2, 3…

A sensing slot after DL subframe for BS and CPEs to sense the channel

DL Subframe

DL2

DL Subframe

DL Subframe UL 2

SSRTG

TRS

Sense

Tss

Sense

Tss

Sense

Tss

UL 1

SSRTG

TTG1

TTG2

UL 2UL 1

DL2

DL1 DL1

CPE2

CPE1

BS

DS1

DS2

November 2005


Slide 22

doc.: IEEE 802.22-05/0094r1

Submission

Other Channel Sensing Options Sym 0 Sym 1 Sym K Sym K+1 Sym 27

Downlink Pilot and Shared Control Symbol

Guard interval for switching + Sensing

Downlink Data OFDMA Symbols

Guard interval for switching + Sensing

Uplink Data OFDMA Symbols

Freq. Sub- carriers

Sym 2

Uplink Pilot and Shared Control Symbol

BS SensingCPE Sensing

Sensing Duration = 100 ~ 200 us

Sensing Frequency= 200~300Hz

November 2005


Slide 23

doc.: IEEE 802.22-05/0094r1

Submission

Sym 0 Sym 1 Sym K Sym K+1 Sym 13

Downlink Pilot / Shared Control / SensingSymbol

Downlink Data OFDMA Symbols Uplink Data OFDMA Symbols

Freq. Sub- carriers

Uplink Pilot / Shared Control / SensingSymbol

Other Channel Sensing Options

BS Sensing(at distributed subcarrier positions)

CPE Sensing(at distributed subcarrier positions)

Sensing Duration = 100 ~ 200 us

Sensing Frequency= 200~300Hz

November 2005


Slide 24

doc.: IEEE 802.22-05/0094r1

Submission

Channel Sensing Using Null Subcarriers

`

Pilot subcarrier

Control subcarrier

Null subcarrier (Sensing)

Configuration II

Configuration I

November 2005


Slide 25

doc.: IEEE 802.22-05/0094r1

Submission

OFDMA Transmitter for BS

.

.

.

Data K

Data 1

Preamble Pilot

Two-layerOFDMA

Formulator

Windowing

& Pulse Shaping

Randomizer

FEC

Encoder

Interleaver

Symbol Mapper

Pre-transform

Randomizer

FEC

Encoder

Interleaver

Symbol Mapper

Pre-transform

November 2005


Slide 26

doc.: IEEE 802.22-05/0094r1

Submission

OFDMA Transmitter for CPE

.

.

.

Data

Randomizer

FEC

Encoder

Interleaver

Symbol Mapper

Preamble/ Pilot

OFDMA Formulator

Zeros

Windowing & Pulse Shaping

Pre-transform

November 2005


Slide 27

doc.: IEEE 802.22-05/0094r1

Submission

Randomizer

• Only information bits are randomized but preambles are not randomized

• Information of sub-channel offset and symbol offset are used to initialize the state of the randomizer for different data block.

MSB LSB

Data in Data out

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

MSB b 14 b 13 b 12 b 11 b 10 b 9 b 8 b 7 1 1 b 4 b 3 b 2 b 1 b 0

b 7 b 6 b 5 b 4 b 3 b 2 b 1 b 0 b 4 b 3 b 2 b 1 b 0

LSB

MSB

Symbol offset (8LSB) Subchannel offset (5LSB)

MSB LSB LSB

November 2005


Slide 28

doc.: IEEE 802.22-05/0094r1

Submission

FEC Encoder: Convolutional Code (CC)

• Native code: – Rate ½ with constraint length: 7

– Generator polynomials: 171oct, 133oct

• Other coding rates through puncturing– 2/3, ¾, 5/6

November 2005


Slide 29

doc.: IEEE 802.22-05/0094r1

Submission

FEC Encoder: Block Turbo Code (BTC)

• Component code – Extended Hamming code

• Native code: (16,11), (32,26) and (64,57)

• Other code rate through shortening

– Parity check code• (8,7) and (16,15)

November 2005


Slide 30

doc.: IEEE 802.22-05/0094r1

Submission

Parity Check Matrices for Hamming Codes

154111000

111000

110110

101101

315111000

111000

111000

110110

101101

636111000

111000

111000

111000

110110

101101

N’ = 15K’ = 11

N’ = 31K’ = 26 N’ = 63

K’ = 57

Special parity check matrix design simplifies the decoding complexity.The syndrome value gives the error position, thus, look-up table is not needed.

November 2005


Slide 31

doc.: IEEE 802.22-05/0094r1

Submission

Shortened Block Turbo Code (SBTC) Structure

November 2005


Slide 32

doc.: IEEE 802.22-05/0094r1

Submission

Data Payload for One Subchannel: SBTC

Modulation Scheme QPSK 8PSK 16-QAM 64-QAM

CodedBytes

Encoding Rate

~1/2 ~2/3 ~3/4 ~5/6 ~1/2 ~2/3 ~1/2 ~2/3 ~3/4 ~5/6 ~1/2 ~2/3

Allowed Data

(Bytes) /No of

symbols

6/1 9/1 12

16/2 20/2 16/1 20/1 24

16/3 25/3 16/2 25/2 16/1 25/1 36

23/4 35/4 23/2 35/2 48

31/5 60

40/6 40/4 40/3 40/2 72

November 2005


Slide 33

doc.: IEEE 802.22-05/0094r1

Submission

Interleavers: half of the number of coded bits per subcarrier

k: the index of the coded bit before the first permutation

i: index after the first and before the second permutation

j: index after the second permutation

Ncbps: number of coded bits per encoded block

• First permutation (Block interleaver) i = (Ncbps/16) (k mod 16) + floor(k/16) k = 0,1,…,Ncbps – 1

• Second permutation (Interleaving within the modulated symbol)

j = s × floor(i / s) + (i + Ncbps – floor(16i / Ncbps)) mod s i = 0,1,… Ncbps – 1

November 2005


Slide 34

doc.: IEEE 802.22-05/0094r1

Submission

Pre-Transforms

IFFT

(size N)

0

0

00

00

0

0

P/S Cyclic Prefix

S/P Transform(size M)

Localized or distributed mapping

Applicable to both UL and DL

November 2005


Slide 35

doc.: IEEE 802.22-05/0094r1

Submission

Pre-Transforms• Transform matrix:

– DFT matrix multiplied by diag(1, α, …, α M-1), α = exp(-jπ/2M) or 1

– Walsh-Hadamard matrix

– Identity matrix

• Uplink– Single carrier system if DFT matrix is used

– Localized FDMA vs Interleaved FDMA

– Low PAPR

A B C

Frequency

A B CA B C

Frequency

ABCABCABCABC

Interleaved FDMA ABC

Frequency

ABCABCABCABCABC

Frequency

Localized FDMA

November 2005


Slide 36

doc.: IEEE 802.22-05/0094r1

Submission

Adaptive Modulation and Coding (AMC)

• Modulation schemes:– Downlink: QPSK, 16-QAM, 64-QAM, 256 QAM

– Uplink: BPSK, QPSK, 8-PSK, 16-QAM, 64 QAM

• Code rates (CC and BTC):– 1/2, 2/3, 3/4, 5/6

– Convolutional Codes (CC) and Block Turbo Codes (BTC)

November 2005


Slide 37

doc.: IEEE 802.22-05/0094r1

Submission

Variable Throughput (1.25MHz, Downlink)

min

imu

m d

own

link

peak

rate

Modulation Code rate Data rate (in Mpbs) for different CP factor

3/8 1/4 1/8 1/16

QPSK

½ 0.779 0.857 0.952 1.008

2/3 1.039 1.143 1.270 1.345

¾ 1.169 1.286 1.429 1.513

5/6 1.299 1.429 1.587 1.681

16-QAM

½ 1.558 1.714 1.905 2.017

2/3 2.078 2.286 2.540 2.689

¾ 2.338 2.571 2.857 3.025

5/6 2.597 2.857 3.175 3.361

64-QAM

½ 2.338 2.571 2.857 3.025

2/3 3.117 3.429 3.810 4.034

¾ 3.507 3.857 4.286 4.538

5/6 3.896 4.286 4.762 5.042

256-QAM

½ 3.117 3.429 3.810 4.034

2/3 4.156 4.571 5.079 5.378

¾ 4.675 5.143 5.714 6.050

5/6 5.195 5.714 6.349 6.723

November 2005


Slide 38

doc.: IEEE 802.22-05/0094r1

Submission

Variable Throughput (1.25MHz, Uplink)

min

imu

m u

plin

k p

eak rate

Modulation Code rate Data rate (in Mpbs) for different CP factor

3/8 1/4 1/8 1/16

BPSK

½ 0.195 0.214 0.238 0.252

2/3 0.260 0.286 0.318 0.336

¾ 0.292 0.321 0.357 0.378

5/6 0.325 0.357 0.397 0.420

QPSK

½ 0.390 0.429 0.476 0.504

2/3 0.520 0.571 0.635 0.672

¾ 0.584 0.643 0.714 0.756

5/6 0.649 0.714 0.794 0.840

16-QAM

½ 0.779 0.857 0.952 1.008

2/3 1.039 1.143 1.270 1.345

¾ 1.169 1.286 1.429 1.513

5/6 1.299 1.429 1.587 1.681

64-QAM

½ 1.194 1.286 1.429 1.513

2/3 1.559 1.715 1.905 2.017

¾ 1.754 1.929 2.143 2.269

5/6 1.948 2.143 2.381 2.521

November 2005


Slide 39

doc.: IEEE 802.22-05/0094r1

Submission

Transmit Power Control (TPC)

• Objectives of TPC

– Maintaining the reliability of communication when there are changes in channel and propagation conditions.

– Conserving power while reducing interference.

• Transmitters must support monotonic TPC with range of up to 30 dB, 1 dB steps, and ± 0.5 dB accuracy.

• Transmit power control will be supported on link-by-link basis

November 2005


Slide 40

doc.: IEEE 802.22-05/0094r1

Submission

Preamble and Pilot Design

DL preamble Time synchronization, frequency synchronization and channel

estimation

UL preamble channel estimation

DL and UL pilot allocations in each OFDMA symbol for channel parameter estimation and tracking

Preamble and pilot design avoiding interference to primary users

November 2005


Slide 41

doc.: IEEE 802.22-05/0094r1

Submission

DL Preamble

• The first OFDMA symbol of DL subframe– Periodic with period N/2 in time domain

– The locations of active subcarriers are: 2k, k=0,1,…,N/2-1.

• If the subcarrier coincides with the DC or a guard subcarrier, or a subcarrier used by a primary user, set the value on the subcarrier to zero.

• Use a PN sequence to generate the values for the active subcarriers. – Low PAPR consideration

– Each cell uses a different PN

November 2005


Slide 42

doc.: IEEE 802.22-05/0094r1

Submission

UL Preamble

• UL preamble may be not necessary if pre-equalization is done at CPE, otherwise, a preamble is needed for channel estimation

• Each user sends a user dependent preamble to the BS to aid the estimation of channels at the BS.– Constructed from the basic preamble by setting all the

subcarriers which are not allocated to the user as null subcarriers

• If the subcarrier is used by a primary user, set the value on the subcarrier to zero.

• Use a PN sequence to generate the values for the active subcarriers– Low PAPR consideration – Each cell uses a different PN

November 2005


Slide 43

doc.: IEEE 802.22-05/0094r1

Submission

Pre-Equalization for Uplink

• The wireless channel usually changes slowly, we can use the channel estimated based on the downlink preamble to do pre-equalization for uplink.

• Let H(k,n) be the frequency domain channel response for user k at subcarrier n. The pre-equalized signal for user k is

– where

where s(k,n): modulated symbol for user k at subcarrier nB(k): subcarrier index set for user kp(k,n): power constraint factor such that (C(k) is the

power for user k)

),(

),(),(),(

nkH

nksnkpnkd )(kBn

)(n)H(k,

n)n)s(k,p(k,2

B(k)n

kC

November 2005


Slide 44

doc.: IEEE 802.22-05/0094r1

Submission

DL Pilot

• There are N/16 pilot subcarriers spread over the whole spectrum

• Two types of pilots– Fixed-location pilots: Subcarrier locations for the fixed location pilots remain

unchanged in every OFDMA symbol.

– Variable-location pilots: subcarrier locations for the variable location pilots change in every four OFDMA symbols.

• N/64 fixed-location pilots (1 for each subchannel)– Locations: 52k+1 and N/2+(3N/32)+52k+1, k=0,1,…,N/128-1.

• (N/16-N/64) variable-location pilots (3 for each subchannel)– Locations: 13k+3(L mod 4)-5 and N/2+(3N/32)+13k+3(L mod 4)-5, k=0,1,

…,N/32-1 (k is not divisible by 4). (L is the OFDMA symbol index.)

• In all cases, if the pilot subcarrier coincides with a subcarrier used by a primary user, set the value on the pilot subcarrier to zero

November 2005


Slide 45

doc.: IEEE 802.22-05/0094r1

Submission

DL Pilot Subcarrier Allocation (N =256)

Fixed pilot 1 53 153 205

Variable pilot (symbol 0) 8 21 34 60 73 86 160 173 186 212 225 238




November 2005


Slide 46

doc.: IEEE 802.22-05/0094r1

Submission

UL Pilot

• The subcarriers are first divided into clusters with each cluster having 13 subcarriers.

• Each cluster has one pilot subcarrier.

• The pilot location is varying in three OFDMA symbols. – The location in a cluster is: 4(L mod 3)+3, L is the OFDMA

symbol index.

• If the pilot subcarrier coincides with a subcarrier used by a primary user, set the value on the pilot subcarrier to zero.

November 2005


Slide 47

doc.: IEEE 802.22-05/0094r1

Submission

Multiple Antenna Technologies

• Transmit diversity– Robustness to fading effect

• Transmit beamforming– Range extension

– Interference avoidance

– Delay spread reduction

• Spatial multiplexing– Increased throughput for dedicated users

• Virtual MIMO and random beamforming– Increased system throughput

November 2005


Slide 48

doc.: IEEE 802.22-05/0094r1

Submission

Cyclic Delay Transmission

Ant 2

Ant 1

X2

X1

FEC Interleaver MOD IFFT

CP

CP Cyclic Delay

T

Composite channel

delay

delay

delay

h1

h2

he Frequency diversityachieved by FEC !

November 2005


Slide 49

doc.: IEEE 802.22-05/0094r1

Submission

Space-Frequency Coding (SFC)

Data Symbols

h2

h1

Tx Ant 2

Tx Ant 1

Rx Ant

Add CP

OFDMA

Formulator

SFC Encoder

Add CP

OFDMA

Formulator

Subcarrier 1 Subcarrier 2

Ant 1 S(1) -S*(2)

Ant 2 S(2) S*(1)

November 2005


Slide 50

doc.: IEEE 802.22-05/0094r1

Submission

Switched-beam Beamforming + CDT/STBC

• Downlink transmission (Localized)• Two eigenbeams (switched beams) transmitted at a time • Data transmitted at one beam cyclic delayed version at

another beam• Achieve diversity and beamforming gain simultaneously

CPE 1

Base

November 2005


Slide 51

doc.: IEEE 802.22-05/0094r1

Submission

Interference Avoidance to Primary Users (PUs)

• Beamforming to avoid interference to PU– Use geographic knowledge of

the primary user

– Frequency planning

• CPE2 uses frequencies unoccupied by PU for communication

• Frequencies occupied by PU can be allocated to CPE1& CPE3

PU coverage

Base station

Primary user (PU) CPE 1

CPE 2

CPE 3

November 2005


Slide 52

doc.: IEEE 802.22-05/0094r1

Submission

Delay Spread Reduction

• For channels with large delays– Repeater applications

– Large cell size

• Solutions– Basic transmit beamforming (BTB) and advanced transmit

beamforming (ATB)

– Exploits spatial domain as different reflectors usually have different direction of departure (DOD) w.r.t. transmitter

November 2005


Slide 53

doc.: IEEE 802.22-05/0094r1

Submission

Basic Transmit Beamforming (BTB)

• In DL, beamformer only directs transmission to the path/cluster with the strongest gain per user.

• Other directions are suppressed – reducing overall delay

• Frequency domain beamforming for each user (subchannel) – different directions

.

.

.

Ant NT

Ant 1

.

.

.

User K

User 1

MOD Frequency Domain

Beamformer

MOD

Frequency Domain

Beamformer


OFDMA Formulator

OFDMA Formulator


November 2005


Slide 54

doc.: IEEE 802.22-05/0094r1

Submission

Advanced Transmit Beamforming (ATB)

• More than one beam transmitted per user in DL.

• If overall channel delay in excess of CP length, relatively delay of each beam may be adjusted to suit CP length.

• Can also be used to increase delay diversity

• A repeater behaves like an additional delay path with known direction – can use ATB to mitigate extra delay introduced by repeater.

November 2005


Slide 55

doc.: IEEE 802.22-05/0094r1

Submission

ATB

By adjusting timings D1 and D2, the overall delay of the channel can be changed.

Reflector 1Or repeater

Reflector 2Or repeater

CPE

Local scatters

Beam 1

Beam 2

Delay 1 T1 = τ1+ D1

Delay 2 T2 = τ2+ D2

Overall Delay|T1-T2| +δ

Pre-alignment& beamforming

Stream 1

Stream 2

November 2005


Slide 56

doc.: IEEE 802.22-05/0094r1

Submission

ATB: Channel Shortening and Lengthening

τ1 δ

τ2 δ

τ1 δ

τ2 δ delay

delay

delay

delay

δ |T1-T2|

delay

Shortening

Lengthening

hc

τ1 + D1

(a)

(b)

τ2+D2

November 2005


Slide 57

doc.: IEEE 802.22-05/0094r1

Submission

Virtual MIMO

• Uplink

• Multiple Antennas at BS and single antenna at each CPE

• Multiple CPEs share the same physical channel

• Spectrum efficiency increase linearly with CPE number if the CPE number is less than the number of BS antennas

CPE 1

CPE 2

Base

November 2005


Slide 58

doc.: IEEE 802.22-05/0094r1

Submission

Random Beamforming for MIMO

• Randomly pick up one beamforming matrix, it will hit somebody if there are many users within the cell!

• When the user is hit and scheduled, it seems that the BS knows the CSI of that user.

• Equal rate for all data streams using TPC

• Multiuser diversity gain

BS

November 2005


Slide 59

doc.: IEEE 802.22-05/0094r1

Submission

Random Beamforming for MIMO

Pilot Data Pilot Data …

Pp

Sp(n) xp(n)H1

Q1H

u1(n)

y1(n)

z1(n)

.

.

.HM

QMH

uM(n)

yM(n)

zM(n)

Pp

Sk(n) xk(n)Hk

QkH

uk(n)

yk(n)

zk(n)

Pilot mode

Data mode: User k is scheduled for transmission

DFE

DFE

DFE

November 2005


Slide 60

doc.: IEEE 802.22-05/0094r1

Submission

Random Beamforming: Pilot Mode

Random beamformergenerator

BS CPE

Training sequences

Random beamformer

ZF-GDFE receiver

SINR measurement

SINR calibrationusing power control

Feedback requested rate & power allocations

Proportional fairness scheduling

November 2005


Slide 61

doc.: IEEE 802.22-05/0094r1

Submission

Sectorization

• Each cell is divided into multiple sectors

• Each sector is covered by one sector or more antennas

• Frequency reuse 1 except sector edge users

• Inter-sector diversity is achieved for sector edge users using CDT or STBC

• If designed properly, sector-specific scrambling codes can be used to achieve frequency diversity

November 2005


Slide 62

doc.: IEEE 802.22-05/0094r1

Submission

Inter-Sector Diversity

.

.

.

Sector 2 antenna

Data K2

Data 1

.

.

.

Data K1

Data 1

FEC Encoder

Interleaver

Symbol Mapper

Preamble/ Pilot

OFDMA Formulator

FEC

Encoder

Interleaver

Symbol Mapper

CP

CP

FEC

Encoder

FEC

Encoder

Interleaver

Interleaver

Symbol Mapper

Symbol Mapper

OFDMA Formulator

Sector 1 antenna

Symbol Mapper

Interleaver

FEC

Encoder

Sector edge users

Scrambling Codes for Sector 2

Scrambling Codes for Sector 1

November 2005


Slide 63

doc.: IEEE 802.22-05/0094r1

Submission

References

[1] IEEE 802.22 Wireless RAN, Functional Requirements for the 802.22 WRAN Standard, IEEE 802.22-05/0007r46, October 2005.

[2] IEEE 802.16-2004. IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems, 2004.

[3] ETSI EN300 744 V1.5.1 (2004-11) Digital Video Broadcasting (DVB): Framing structure, channel coding and modulation for digital terrestrial television

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Doc.: IEEE 802.22-05/0094r1 Submission November 2005 Ying-Chang Liang, Institute for Infocomm...

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