doc.: ieee 802.22-05/0094r1 submission november 2005 ying-chang liang, institute for infocomm...
TRANSCRIPT
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
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
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
Slide 14
doc.: IEEE 802.22-05/0094r1
Submission
Option B: System Parameters
November 2005
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
Slide 16
doc.: IEEE 802.22-05/0094r1
Submission
Basic TDD Frame Structure
November 2005
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
Slide 31
doc.: IEEE 802.22-05/0094r1
Submission
Shortened Block Turbo Code (SBTC) Structure
November 2005
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Variable pilot (symbol 1) 11 24 37 63 76 89 163 176 189 215 228 241
Variable pilot (symbol 2) 14 27 40 66 79 92 166 179 192 218 231 244
Variable pilot (symbol 3) 17 30 43 69 82 95 169 182 195 221 234 247
November 2005
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Windowing & Pulse Shaping
OFDMA Formulator
OFDMA Formulator
Windowing & Pulse Shaping
November 2005
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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
Ying-Chang Liang, Institute for Infocomm Research
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