1. Multi-block OFDM for TVWS Operation
May 2010
doc.: IEEE /0608r0
May 2010
doc.: IEEE /0608r0
Multi-block OFDM for TVWS Operation
Authors:
Submission
Slide 1
Meng Wah Chia (I2R)

2. Discontinuous TVWS Channel
May 2010
doc.: IEEE /0608r0
Discontinuous TVWS Channel
CH 20
CH 22
CH 24
CH 26
CH 21
CH 23
CH 25
CH 28
CH 30
CH 27
CH 29
CH 31
The spectrum opportunity of TVWS consists of fragments of different number of available TV channels.
These TV channels may or may not be contiguous, and may even be spaced far apart (e.g. a secondary user to access CH 21, 24, 28)
The af should support the usage of multiple available channels in TVWS.
Submission
Slide 2
Meng Wah Chia (I2R)

3. May 2010
doc.: IEEE /0608r0
May 2010
doc.: IEEE /0608r0
NC-OFDM
CH 20
CH 22
CH 24
CH 26
CH 21
CH 23
CH 25
CH 28
CH 30
CH 27
CH 29
CH 31 PU PU PU
Non-Contiguous OFDM (NC-OFDM) uses an OFDM system with a large bandwidth to span over multiple TVWS channel (e.g. from CH 20 to 29).
Information about TVWS availability obtained through spectrum sensing or database access.
Nulls are transmitted on frequency bands occupied by the primary users (PU). (e.g. CH 21).
Submission
Slide 3
Meng Wah Chia (I2R)

4. May 2010
doc.: IEEE /0608r0
Multi-Block OFDM
Multi-Block OFDM uses K-OFDM systems to transmit over multiple TVWS channels.
Spectrum sensing measurements obtain information about TVWS availability.
The center frequency of each OFDM block is adjusted such that it transmits in the dedicated TVWS channel. …. +
Submission
Slide 4
Meng Wah Chia (I2R)

5. Multi-Block OFDM Receiver
May 2010
doc.: IEEE /0608r0
Multi-Block OFDM Receiver ….
The received signal is down-converted into K parallel streams.
Submission
Slide 5
Meng Wah Chia (I2R)

6. NC-OFDM vs Multi-block OFDM
May 2010
doc.: IEEE /0608r0
NC-OFDM vs Multi-block OFDM
CH 20
CH 22
CH 24
CH 26
CH 21
CH 23
CH 25
CH 28
CH 30
CH 27
CH 29
CH 31
1 OFDM
NC-OFDM is not an effective solution when:
There are many channels occupied by the PU (e.g. when CH 21 to 27 are used by the PU): Nulls on subcarriers.
The available channels are spaced far apart (e.g. only CH 21 and 29 are to be used)
Multi-block OFDM
Dynamic spectrum access of non-adjacent channels
Simultaneous access over multiple frequency
Submission
Slide 6
Meng Wah Chia (I2R)

7. Case 1: Modulation Dependent Parameters
May 2010
doc.: IEEE /0608r0
Case 1: Modulation Dependent Parameters
Preamble
Signal
Data
5 MHz
K=1
OFDM
64 μs
16 μs
16 μs
OFDM
OFDM
10 MHz
K=2
32 μs
8 μs
OFDM
OFDM
OFDM
OFDM
20 MHz
K=4
OFDM
OFDM
OFDM
OFDM
time
16 μs
4 μs
4 μs
K: Number of active OFDM units, and depends on the number of available TVWS channels
Submission
Slide 7
Meng Wah Chia (I2R)

8. Carrier Aggregation May 2010 doc.: IEEE 802.11-10/0608r0 :
OFDM 1
OFDM 2 :
OFDM K
Carrier aggregation unit assigns the data into K OFDM blocks.
Each OFDM unit has 64 subcarriers.
Let the bandwidth of the kth OFDM block be Bk.
Number of OFDM symbols transmitted by the kth block
Number of OFDM block within TLong
Number of repetition of the kth OFDM block
Longest OFDM signal duration
Submission
Slide 8
Meng Wah Chia (I2R)

9. Case 2: Modulation Dependent Parameters
May 2010
doc.: IEEE /0608r0
Case 2: Modulation Dependent Parameters
Preamble
Signal
Data
5 MHz
K=1
OFDM
64 μs
16 μs
16 μs
OFDM
OFDM ….
OFDM
10 MHz
K=2
OFDM
OFDM
OFDM ….
OFDM
32 μs
8 μs
OFDM
OFDM
OFDM ….
OFDM
20 MHz
K=4
OFDM
time
16 μs
4 μs
4 μs
Submission
Slide 9
Meng Wah Chia (I2R)

10. Carrier Aggregation May 2010 doc.: IEEE 802.11-10/0608r0 :
OFDM 1
OFDM 2 :
OFDM K
Carrier aggregation unit assigns the data into K OFDM blocks.
Each OFDM unit has 64 subcarriers.
Let the bandwidth of the kth OFDM block be Bk.
Number of OFDM symbols transmited by the kth block
Number of OFDM block within TLong
Number of data OFDM signal for the kth OFDM block
Longest OFDM signal duration
Submission
Slide 10
Meng Wah Chia (I2R)

11. May 2010
doc.: IEEE /0608r0
May 2010
doc.: IEEE /0608r0
Carrier Sensing
Due to the requirement to sense over multiple bands, we have 2 carrier sensing carrier sensing methods:
Full-sensing of bands (1,…, K).
Set carrier sensing outcome = OR (carrier sensing outcome of band 1, ..., carrier sensing outcome of band K).
Partial-sensing of bands (1,…, n, where n K).
Set carrier sensing outcome = OR (carrier sensing outcome of band 1, ..., carrier sensing outcome of band n).
Virtual Carrier Sensing:
Full sensing of bands (Sense all bands)
Partial sensing of bands (Sense one of the bands)
Submission
Slide 11
Meng Wah Chia (I2R)

12. Suppose we transmits over K-TVWS channels.
May 2010
doc.: IEEE /0608r0
Suppose we transmits over K-TVWS channels.
Multi-Block OFDM
NC-OFDM
FFT Points
(per OFDM Unit)
NSC
NSC x K
Complexity
KNSC log NSC
KNSC log (NSC K)
Receiver Complexity
K down-conversion units
1 down-conversion unit
Support for coexistence
Uses multiple OFDM centered at multiple TVWS frequencies
Transmit nulls on non-TVWS channels
General Concerns
Inefficient in contiguous band operation
Inefficient in non-contiguous band operation
Submission
Slide 12
Meng Wah Chia (I2R)

13. May 2010
doc.: IEEE /0608r0
MAC Amendments :
New Information Element (IE) in Beacon Period (BP) contains information about
Number of channels
Channel center frequencies …
TVWS Availability …
Time
This interval is large compared to the beacon interval BP
Quiet
Period BP
Beacon Interval
Submission
Slide 13
Meng Wah Chia (I2R)

14. May 2010
doc.: IEEE /0608r0
Conclusion
Proposed multi-block OFDM as an efficient TVWS PHY design, suitable when:
PU occupies most of the available bands.
Available TVWS channels are spaced far apart.
Proposed carrier aggregation and carrier sensing rules required for Multi-block OFDM.
Proposed MAC amendments for multi-block OFDM.
Information element in Beacon Period
Submission
Slide 14
Meng Wah Chia (I2R)

15. Thank You. May 2010 doc.: IEEE 802.11-10/0608r0 Submission Slide 15
Meng Wah Chia (I2R)