1. System Description and Operation Principles for IEEE 802.22 WRANs
November 2005
doc.: IEEE /0094r0
January 2006
System Description and Operation Principles for IEEE WRANs
IEEE P Wireless RANs Date:
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Ying-Chang Liang, Institute for Infocomm Research
Y.-C. Liang, Inst. for Infocomm Research

2. November 2005
doc.: IEEE /0094r0
January 2006
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
Sensing Mechanism using two-step sensing approach
Frame structure for non-continuous sensing
Block spreading for additional multiple access
Ying-Chang Liang, Institute for Infocomm Research
Y.-C. Liang, Inst. for Infocomm Research

3. WRANs Operate in the VHF/UHF TV bands using cognitive radio technology
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

4. Two-Layer OFDMA How? Advantages:
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

5. OFDMA A group of subcarriers is defined as a subchannel
January 2006
OFDMA
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
Ying-Chang Liang, Institute for Infocomm Research

6. OFDMA January 2006 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
Ying-Chang Liang, Institute for Infocomm Research

7. Scalable Design Each CPE supports one TV channel usage
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

8. Variable Bandwidths within one TV Channel
January 2006
Variable Bandwidths within one TV Channel
Parameters
Values
Channel bandwidth
1.25 MHz
2.5 MHz
5 MHz
7.5 MHz
Sampling frequency*
MHz
MHz
MHz
MHz
Sampling interval
0.7 μs
0.35 μs
0.175 μs μs
FFT size
256
512
1024
1536
Subcarrier spacing
kHz
Useful OFDMA symbol interval
179.2 μs
* Oversampling factor of 8/7
Ying-Chang Liang, Institute for Infocomm Research

9. Support Variable TV Channel Bandwidths of 6, 7 & 8MHz
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

10. Option A for Variable TV Bandwidth
January 2006
Option A for Variable TV Bandwidth
TV channel bandwidth
8 MHz
7 MHz
6 MHz
Sampling frequency
7.5MHz*8/7 = MHz
FFT size
1536
Number of useful subcarriers
1249
1145
937
Data/pilot subcarriers per subchannel
48/4
Number of subchannels 24 22 18
Ying-Chang Liang, Institute for Infocomm Research

11. Option A with Variable CP Length
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

12. Option A: Minimum Peak Rates
January 2006
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
No of subchannels per user 2
Minimum peak rates
1.513 Mbps
(QPSK, ¾ rate, 1/16 CP factor)
504 kbps
(QPSK, ½ rate, 1/16 CP factor)
Ying-Chang Liang, Institute for Infocomm Research

13. Option B for Variable TV Bandwidth
January 2006
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 =
8/7*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)
Ying-Chang Liang, Institute for Infocomm Research

14. Option B: System Parameters
January 2006
Option B: System Parameters
Ying-Chang Liang, Institute for Infocomm Research

15. TDD as the Duplex Mode Why TDD? Drawback of TDD Our proposals
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

16. Basic TDD Frame Structure
January 2006
Basic TDD Frame Structure
Ying-Chang Liang, Institute for Infocomm Research

17. DL Subframe DL Preamble
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

18. January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

19. Adaptive TDD Frame Structure
January 2006
Adaptive TDD Frame Structure
Near-by users are allowed to transmit earlier than far-away users
Reduced BS TTG for increased throughput
Ying-Chang Liang, Institute for Infocomm Research

20. CPE3 is the nearest user while CPE2 and CPE4 are the farthest user.
January 2006
Adaptive TDD S1 S2 S3 S4 S5 S6 S7 S8 S9
CPE1 G
pre
data
CPE2
CPE3
CPE4
CPE5
time
CPE3 is the nearest user while CPE2 and CPE4 are the farthest user.
Ying-Chang Liang, Institute for Infocomm Research

21. Channel Sensing and Adaptive TDD
January 2006
Channel Sensing and Adaptive TDD
TTG2
TTG1 BS
DL Subframe
Sense
UL 1
UL 2
TRS
Tss
CPE1
DL Subframe
Sense
UL 1
DL1
DS1
Tss
SSRTG
DL1
CPE2
DL Subframe
Sense
UL 2
DL2
DS2
Tss
SSRTG
DL2
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
Ying-Chang Liang, Institute for Infocomm Research

22. Other Channel Sensing Options
January 2006
Sensing Duration
= 100 ~ 200 us
Sensing Frequency
= 200~300Hz
Other Channel Sensing Options
CPE Sensing
BS Sensing
Ying-Chang Liang, Institute for Infocomm Research

23. Other Channel Sensing Options
January 2006
Other Channel Sensing Options
Sensing Duration
= 100 ~ 200 us
Sensing Frequency
= 200~300Hz
CPE Sensing
(at distributed subcarrier positions)
BS Sensing
(at distributed subcarrier positions)
Ying-Chang Liang, Institute for Infocomm Research

24. Channel Sensing Using Null Subcarriers
January 2006
Channel Sensing Using Null Subcarriers
Ying-Chang Liang, Institute for Infocomm Research

25. OFDMA Transmitter for BS
January 2006
OFDMA Transmitter for BS
Preamble
Pilot
Data 1
Randomizer
FEC
Interleaver
Symbol
Pre-transform
Mapper
Two-layer
OFDMA
Windowing
Encoder .
& Pulse .
Shaping .
Formulator
Data K
Randomizer
FEC
Interleaver
Symbol
Pre-transform
Encoder
Mapper
Ying-Chang Liang, Institute for Infocomm Research

26. OFDMA Transmitter for CPE
January 2006
OFDMA Transmitter for CPE
Preamble/
Pilot
Data
Randomizer
FEC
Interleaver
Symbol
Pre-transform
OFDMA
Windowing
Encoder
Mapper .
Formulator
& Pulse .
Shaping .
Zeros
Ying-Chang Liang, Institute for Infocomm Research

27. January 2006
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.
Ying-Chang Liang, Institute for Infocomm Research

28. FEC Encoder: Convolutional Code (CC)
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

29. FEC Encoder: Block Turbo Code (BTC)
January 2006
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)
Ying-Chang Liang, Institute for Infocomm Research

30. Parity Check Matrices for Hamming Codes
January 2006
Parity Check Matrices for Hamming Codes
N’ = 15
K’ = 11
N’ = 31
K’ = 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.
Ying-Chang Liang, Institute for Infocomm Research

31. Shortened Block Turbo Code (SBTC) Structure
January 2006
Shortened Block Turbo Code (SBTC) Structure
Ying-Chang Liang, Institute for Infocomm Research

32. Data Payload for One Subchannel: SBTC
January 2006
Data Payload for One Subchannel: SBTC
Modulation
Scheme
QPSK
8PSK
16-QAM
64-QAM
Coded
Bytes
Encoding
Rate
~1/2
~2/3
~3/4
~5/6
Allowed
Data
(Bytes) /
No of
symbols
6/1
9/1 12
16/2
20/2
16/1
20/1 24
16/3
25/3
25/2
25/1 36
23/4
35/4
23/2
35/2 48
31/5 60
40/6
40/4
40/3
40/2 72
Ying-Chang Liang, Institute for Infocomm Research

33. January 2006
Interleaver
s: 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
Ying-Chang Liang, Institute for Infocomm Research

34. Localized or distributed mapping Applicable to both UL and DL
January 2006
Pre-Transforms
P/S
IFFT
(size N)
S/P
Transform
(size M)
Cyclic Prefix
Localized or distributed mapping
Applicable to both UL and DL
Ying-Chang Liang, Institute for Infocomm Research

35. Pre-Transforms Transform matrix: Uplink
January 2006
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
Interleaved FDMA
Localized FDMA
Ying-Chang Liang, Institute for Infocomm Research

36. Adaptive Modulation and Coding (AMC)
January 2006
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)
Ying-Chang Liang, Institute for Infocomm Research

37. Variable Throughput (1.25MHz, Downlink)
January 2006
Variable Throughput (1.25MHz, Downlink)
Modulation
Code rate
Data rate (in Mpbs) for different CP factor
3/8
1/4
1/8
1/16
QPSK
0.779
0.857
0.952
1.008
2/3
1.039
1.143
1.270
1.345
1.169
1.286
1.429
1.513
5/6
1.299
1.587
1.681
16-QAM
1.558
1.714
1.905
2.017
2.078
2.286
2.540
2.689
2.338
2.571
2.857
3.025
2.597
3.175
3.361
64-QAM
3.117
3.429
3.810
4.034
3.507
3.857
4.286
4.538
3.896
4.762
5.042
256-QAM
4.156
4.571
5.079
5.378
4.675
5.143
5.714
6.050
5.195
6.349
6.723
minimum downlink peak rate
Ying-Chang Liang, Institute for Infocomm Research

38. Variable Throughput (1.25MHz, Uplink)
January 2006
Variable Throughput (1.25MHz, Uplink)
Modulation
Code rate
Data rate (in Mpbs) for different CP factor
3/8
1/4
1/8
1/16
BPSK
0.195
0.214
0.238
0.252
2/3
0.260
0.286
0.318
0.336
0.292
0.321
0.357
0.378
5/6
0.325
0.397
0.420
QPSK
0.390
0.429
0.476
0.504
0.520
0.571
0.635
0.672
0.584
0.643
0.714
0.756
0.649
0.794
0.840
16-QAM
0.779
0.857
0.952
1.008
1.039
1.143
1.270
1.345
1.169
1.286
1.429
1.513
1.299
1.587
1.681
64-QAM
1.194
1.559
1.715
1.905
2.017
1.754
1.929
2.143
2.269
1.948
2.381
2.521
minimum uplink peak rate
Ying-Chang Liang, Institute for Infocomm Research

39. Transmit Power Control (TPC)
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

40. Preamble and Pilot Design
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

41. DL Preamble The first OFDMA symbol of DL subframe
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

42. January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

43. Pre-Equalization for Uplink
January 2006
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
s(k,n): modulated symbol for user k at subcarrier n
B(k): subcarrier index set for user k
p(k,n): power constraint factor such that (C(k) is the power for user k)
Ying-Chang Liang, Institute for Infocomm Research

44. January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

45. DL Pilot Subcarrier Allocation (N =256)
January 2006
DL Pilot Subcarrier Allocation (N =256)
Fixed pilot
Variable pilot (symbol 0)
Variable pilot (symbol 1)
Variable pilot (symbol 2)
Variable pilot (symbol 3)
Ying-Chang Liang, Institute for Infocomm Research

46. January 2006
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.
Ying-Chang Liang, Institute for Infocomm Research

47. Multiple Antenna Technologies
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

48. Cyclic Delay Transmission
January 2006
Cyclic Delay Transmission
Frequency diversity
achieved by FEC !
Ying-Chang Liang, Institute for Infocomm Research

49. Space-Frequency Coding (SFC)
January 2006
Space-Frequency Coding (SFC)
Subcarrier 1
Subcarrier 2
Ant 1
S(1)
-S*(2)
Ant 2
S(2)
S*(1)
Ying-Chang Liang, Institute for Infocomm Research

50. Switched-beam Beamforming + CDT/STBC
January 2006
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
Base
CPE 1
Ying-Chang Liang, Institute for Infocomm Research

51. Interference Avoidance to Primary Users (PUs)
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

52. Delay Spread Reduction
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

53. Basic Transmit Beamforming (BTB)
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

54. Advanced Transmit Beamforming (ATB)
January 2006
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.
Ying-Chang Liang, Institute for Infocomm Research

55. ATB Reflector 1 Or repeater CPE Reflector 2 Local scatters
January 2006
ATB
Reflector 1
Or repeater
Reflector 2
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
By adjusting timings D1 and D2, the overall delay of the channel can be changed.
Ying-Chang Liang, Institute for Infocomm Research

56. ATB: Channel Shortening and Lengthening
January 2006
ATB: Channel Shortening and Lengthening
Ying-Chang Liang, Institute for Infocomm Research

57. January 2006
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
Base
CPE 1
CPE 2
Ying-Chang Liang, Institute for Infocomm Research

58. Random Beamforming for MIMO
January 2006
Random Beamforming for MIMO BS
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
Ying-Chang Liang, Institute for Infocomm Research

59. Random Beamforming for MIMO
January 2006
Random Beamforming for MIMO
Pilot
Data … Pp
Sp(n)
xp(n) H1
Q1H
u1(n)
y1(n)
z1(n) . HM
QMH
uM(n)
yM(n)
zM(n)
Sk(n)
xk(n) Hk
QkH
uk(n)
yk(n)
zk(n)
Pilot mode
Data mode: User k is scheduled for transmission
DFE
Ying-Chang Liang, Institute for Infocomm Research

60. Random Beamforming: Pilot Mode
January 2006
Random Beamforming: Pilot Mode
CPE BS
Random beamformer
generator
ZF-GDFE receiver
Training
sequences
Random
beamformer
SINR measurement
SINR calibration
using power control
Proportional fairness
scheduling
Feedback requested rate
& power allocations
Ying-Chang Liang, Institute for Infocomm Research

61. Sectorization Each cell is divided into multiple sectors
January 2006
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
Ying-Chang Liang, Institute for Infocomm Research

62. Inter-Sector Diversity
January 2006
Inter-Sector Diversity
Ying-Chang Liang, Institute for Infocomm Research

63. Sensing Mechanism Two-step sensing
November 2005
doc.: IEEE /0094r0
January 2006
Sensing Mechanism
Two-step sensing
Step 1: energy detection
If EP > TH1, then decide that PU present
If EP < TH2, then decide that PU absent
If TH2≤EP≤TH1, then proceed to step 2
Step 2: cyclostationary detection
Compute SCD at selected cyclic frequencies
If average energy of SCD, EC > TH3, then decide PU present
Tentative decisions perform at the sensing unit. Decision fusion performed at the decision unit.
Ying-Chang Liang, Institute for Infocomm Research
Y.-C. Liang, Inst. for Infocomm Research

64. Frame Structure for Non-continuous Sensing
January 2006
Frame Structure for Non-continuous Sensing
Distributed (non-continuous) sensing
Super frame = n * frames DL
Frame 0
Frame 1
Frame n UL
Sensing
DL/S/UL
Ying-Chang Liang, Institute for Infocomm Research

65. OFDMA with Block Spreading
January 2006
OFDMA with Block Spreading
Transmitter (frequency domain implementation)
P/S
IFFT
(size = NFFT)
Mapped Symbols from SS
Cyclic Prefix
Block Spread
Ying-Chang Liang, Institute for Infocomm Research

66. OFDMA with Block Spreading
January 2006
OFDMA with Block Spreading
Transmitter (time domain implementation)
Mapped Symbols from SS
Phase Rotation
Cyclic Prefix
Block Spread
Repetition
Ying-Chang Liang, Institute for Infocomm Research

67. OFDMA with Block Spreading
January 2006
OFDMA with Block Spreading
OFDM Block
Spreading Code c1
P/S CP CP
Block 1 c2 CP CP CP
Block 2
Block 1
Block K cK CP
Block K
Ying-Chang Liang, Institute for Infocomm Research

68. OFDMA with Block Spreading
January 2006
OFDMA with Block Spreading
Reference Receiver
FFT
Frequency domain Processing
Received Signal
Remove cyclic Prefix
Block Despread
Ying-Chang Liang, Institute for Infocomm Research

69. OFDMA with Block Spreading
January 2006
OFDMA with Block Spreading
Block de-spreading in Reference Receivers
P/S c1 CP CP CP CP
Block 1
Block K cK CP
Ying-Chang Liang, Institute for Infocomm Research

70. MAC Enhancement January 2006
Ying-Chang Liang, Institute for Infocomm Research

71. January 2006
References
[1] IEEE Wireless RAN, Functional Requirements for the WRAN Standard, IEEE /0007r46, October 2005.
[2] IEEE IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems, 2004.
[3] ETSI EN V1.5.1 ( ) Digital Video Broadcasting (DVB): Framing structure, channel coding and modulation for digital terrestrial television
Ying-Chang Liang, Institute for Infocomm Research