Paper 129
IEEE 802.22 WRAN: Medium Access
Control for Coexistence of Multiple
Cognitive Radio Networks – A Survey
Presented by
Deepak S. Dikhit
Co-Authors:
Dr. Arun Kumar
Dr. Amitava Mukherjee
INTRODUCTION



SPECTRUM INEFFICIENT FSA
DYNAMIC SPECTRUM ACCESS (DSA)
COGNITIVE RADIO
“Can change its transmitter parameters based
on interaction with the environment in which it operates.”

TV WHITE SPACE & CRN
COGNITIVE CYCLE
Radio
Environment
(Outside world)
Radio Stimuli
Channel-state
Estimation &
Predictive
Modeling
Receiver
Transmit Power
Control & Spectrum
Management
Transmitter
Radio Scene
Analysis
Spectrum Hole Noise-floor Statistics Traffic Statistics
ENABLING CPAPBILITIES
 COGNITIVE CAPABILITY
•Spectrum Sensing
•Spectrum Management
•Spectrum Sharing
•Spectrum Mobility
 RECONFIGURABILITY
“Re-configurability is the capability of adjusting operating
parameters for the transmission on the fly without any modifications on the
hardware components.”
•Operating Frequency
•Modulation
•Transmission Power
•Communication Technology
IEEE 802.22 WRAN STANDARD
 To
Allow Opportunistic Utilization of Unused
Spectrum :
•Time
•Frequency
•Geo-location
IEEE 802.22 WRAN
COVERAGE
IEEE 802 CLASS NETWORKS
REFERENCE ARCHITECTURE
H igher Layers:IP,A TM,1394,
etc.
SME
C on verg en ce Sub- Layer
B rid ge(e.g.,802.1d)
MA C S A P
MLME
Spectrum
Manager(B S)
/Sp ectru m
Au tomato n( CPE)
PH Y S AP
SSF
GeoLocation
MLME -P LME S AP
PLME
SME-PLME SAP
PHY
SME-MLME SAP
MAC
MULTIPLE CRN AND
COEXISTENCE
SUPERFRAME STRUCTURE
GENERAL FRAME STRUCTURE
MAC FRAME STRUCTURE
...
frame n-1
frame n
...
frame n+1
Time
10 ms
US-MAP
Ranging/BW request/UCS notification
time buffer
Burst m
Bursts
Burst 2
Burst
Burst
Burst
60 subchannels
DS-MAP
Bursts
US-MAP
Burst n
DS sub-frame
US sub-frame
(smallest US burst portion on a given subchannel= 7 symbols)
RTG
Burst
TTG
Frame Preamble
more than 7 OFDMA symbols
Burst 3
time buffer
Burst 2
Self-coexistence window (4 or 5 symbols when scheduled)
Burst 1
Burst 1
UCD
DCD
FCH
26 to 42 symbols corresponding to bandwidths from 6 MHz to 8 MHz and cyclic prefixes from 1/4 to 1/32
SLOTTED STRUCTURE OF
A MAC FRAME
...
frame n-1
Time slot 0
frame n
Time slot
frame n+1
Adaptive
Time slot N-1
N time slots
Downstream
Subframe
Upstream
Subframe
...
Time
COEXISTENCE BEACON
PROTOCOL (CBP)
CBP
Dynamic
Resource
Renting/
Offering
Adaptive on
Demand
Channel
Contention
Spectrum
Etiquette
Interferencefree
scheduling
COEXISTENCE BEACON
PROTOCOL (CBP)
CBP PACKET STRUCTURE
PREAMBLE
SCHSCH
CBP MAC PDU
SPECTRUM SHARING & CHANNEL
CONTENTION
COEXISTENCE MANAGEMENT
TECHNIQUES
 INOVATIVE CHANNEL CONTROL & MANAGEMENT
 DEVELOPING NEW MAC PROTOCOLS
 CHANGE IN PHY-LAYER: FREQUENCY HOPPING
 GAME THEORETIC APPROACH
 EMPLOYING FUZZY LOGIC
TABLE I
COMPARISON OF COEXISTENCE MODES IN IEEE 802.22 WRAN
Characteristic
SFN Mode
D-SCH Mode
Complexity and delay of
frame Negotiation
Complexity for CPE
Initialization
Delay for CPE Initialization
High
Low
High
Low
High
Low
Additional Buffer Time in the
first frame
Chained Effect
Yes
No
Yes
No
Complexity of AGC Design
No serious problem for both
Delay of BS-ID acquisition
High
Low
Overhead in DL frame
Low
High
Overhead by scheduling
SCW
Efficiency on QP Scheduling
BroadcastS
High
Low
High
Low
TABLE II
COMPARISON OF COEXISTENCE MODES IN IEEE 802.22 WRAN
Characteristic
SFN Mode
Overhead cost - Superframe preamble
1 common super-frame preamble;
comparing to normal mode with
only one BS, no additional
overhead, = 0 bps
Overhead cost - Frame
preamble
1 common frame preamble + N
frame preambles for N BSs, one
additional frame preamble for
each super frame = 9 kbps
1 common symbol, no extra
overhead = 0 bps
The size of table = 8 bit (message
type) + 8 bit (Length) + N* [4 bit
(BS index) + 48 bit (BS-ID)] = 16
+ 52N bits;
Assume the table to be transmit
every 1s, equivalent =16+52N bps
Overhead - Superframe
control header (SCH)
Overhead - BS mapping
table
D-SCH Mode
N super-frame preambles for N
BSs =N*10.5 kbps; comparing
to normal mode with only one
BS, N-1 additional super-frame
preambles =(N1)*1440/160=9(N-1) kbps
N frame preambles for N BSs,
no additional overhead = 0 bps
N SCH for N BSs, N-1 extra
SCHs = 9(N-1) kbps
BS-ID already included in SCH
=0 bps
TABLE III
COMPARISON OF COEXISTENCE MODES IN IEEE 802.22 WRAN
Characteristic
Overhead – Buffer before & after the
aggregated symbols
Overhead- Buffer after each switching
frame (assuming the frame scheduling
switches from one to another)
Overhead – Cost for MAC message
Frame_Switch_Req (8 bit message type
+ 16 bit new frame scheduling + 8 bit
switch count = 32 bits)
Overall cost
SFN Mode
D-SCH Mode
To absorb 60 km delay, half OFDM
No buffer needed = 0bps
symbol duration before and another half
after, resulting in 1 symbol in total =9
kbps
1. Maximum overhead: Assume each BS schedule at least one active SCW and N-1
passive SCWs, the maximum additional cost is 16-N symbols for N<16. Max
overhead=(16-N)*9 kbps for N<16.
2. Minimum value: all frames schedule SCWs, no additional cost. Min overhead = 0
bps
No Frame_Switch_REQ needed = 0 bps
1.
Max: frame scheduling changes
from super-frame to super-frame:
32bit/160ms*N=200N bps
2.
Med: frame scheduling changes
every 1 second on average: 32
bits/1s*N = 32N bps
3.
Low: frame scheduling changes
every 10 second on average: 32
bits/10s*N=3.2N bps
Comparing to other cost, this cost is
neglectable, take 200N bps for
calculation.
Max: (18-N)*9000+16+52N Max: (N+14)*9000 +200Nbps
bps
Min: (N-1)*18000 + 200N bps
Min: 18000+16+52N bps
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ACKNOWLEDGEMENT
We are immensely grateful to Dr. Rajat Mathur , Mr.
Charit Mathur , Ms. Ritu Mathur and Dr. A. N. Singh
for encouragement and facilitating resources needed
for this work. We are also obliged to our colleagues
Indranil Chakraborty, Shweta Tiwari, Rishab Dixit,
Chhiteesh Rai and Ambrish Tiwari for help from time
to time in preparation of this paper.