September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Reliability of IEEE 802.11 WLANs in Presence of Bluetooth Radios
Jim Zyren
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Conditions for Collision
• Frequency Overlap– Probability of collision is reduced by using a narrower
occupied channel width
• Time Overlap– Probability of collision is reduced by minimizing transmit time
(ie transmit at higher data rate)
• Sufficient Interference Energy– Interference energy can be reduced by:
• spatial separation
• tighter filtering
• processing gain
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
FHSS and DSSS Power Spectral Densities
2.400 GHz
t0 t2t1
FHSS Networks are Frequency Agile2.4835 GHz
2.400 GHz
DSSS Networks typically use 3 fixed non-overlapping Channels2.4835 GHz
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
DSSS vs. Bluetooth
• Early study of impact of Bluetooth on IEEE 802.11 DSSS system– IEEE 802.11 DSSS WLAN @ 11 Mbps– Dense environment of BT piconets
• one DSSS WLAN node per 25 m2 of office space• BT piconet co-located with each DSSS node
– 0 dBm BT tx power– +20 dBm DSSS tx power
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Enterprise Environment
40 m
IEEE 802.11 AP
IEEE 802.11 STA
BT Piconet
Composite BT/DSSS Network Topology
L.O.S. , range < 8mr3.3 , range > 8m
Lpath = 20 log (4 r / ) r < 8m= 58.5 + 33 log( r/8 ) r > 8m
where: = wavelength @ 2.45 GHz (0.1224 m) r = range (m)
Simplified Propagation Model
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Impact of BT Interference Depends on Range from AP
Range to AP (m) Rx DSSS Signal(dBm)
BT InterferenceThreshold (dBm)
Radius of BTInterference (m)
# BT Interferors inRange
4 -32.3 -42.3 1.3 1
10 -41.4 -51.4 3.7 2
20 -51.4 -61.4 10.0 13
20 m4 m
10 m
IEEE 802.11 AP
IEEE 802.11 STA
BT Piconet
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
BT Piconet User ModelFunction Traffic BT Packet Structure
Paging 1 time / connection IDE-mail 15 / day @ 10 kbytes DH1
Telephony 10 calls / day @ 1 min. each HV3
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
BT Idle 1 Call 2 Calls 3 Calls 4 Calls Paging E-mail Blocked
BT Interference Condition
Pro
bab
ilit
y
R = 20m
R = 10m
R = 4m
BT Single Piconet Utilization
BT Composite Effects
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Interference Model
1.94 dwell periods
625 sec
259 sec
BT Transmission slots
1500 byte DSSS Hi Rate Packet(1210 sec)
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Thruput of DSSS WLAN vs. Piconet Load
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
1500 750 500 375 300 250 150 100 75
Packet Payload (bytes)
Th
rou
gh
pu
t (M
bp
s)
BT Idle
33% BT Load (1 call)
Paging
100% BT Load (Email)
Effects shown are for a single BT Piconet operating in close proximityto IEEE 802.11 DSSS WLAN.
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Availability Curve for DSSS WLAN (r = 4 m)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
1500 750 500 375 300 250 150 100 75
Packet Payload (bytes)
Th
rou
gh
pu
t (M
bp
s)
97.8%
99.9%
100.0%
For r = 4m, only one BT piconet is close enough to cause interference
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Availability Curve for DSSS WLAN (r =10 m)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
1500 750 500 375 300 250 150 100 75
Packet Payload (bytes)
Th
rou
gh
pu
t (M
bp
s)
95.6%
99.7%
99.9%
100.0%
At r = 10 m, 2 piconets are close enough to interfere with DSSS receiver
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Availability Curve for DSSS WLAN (r = 20 m)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
1500 750 500 375 300 250 150 100 75
Packet Payload (bytes)
Th
rou
gh
pu
t (M
bp
s)
74.9%
95.6%
98.4%
99.5%
At r = 20 m, 13 piconets are close enough to interfere with DSSS reception. IEEE802.11 Hi Rate WLAN can still provide peak THROUGHPUT (7.2 Mbps) with 75%
certainty, and 3.5 Mbps THROUGHPUT with over 99% certainty
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Average Effect Over 8 Hour Day
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
1500 750 500 375 300 250 150 100 75
Packet Payload (bytes)
Th
rou
gh
pu
t (M
bp
s)
BT Idle
R = 4m
R = 10m
R = 20m
Average Effect over 8 hour working day is shown as a function of range from DSSS node to DSSS AP.
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Summary of BT/DSSS Results
• Degree of BT interference depends on:• local propagation conditions
• density of BT piconets
• BT piconet loading
• DSSS susceptibility to BT interference increases as a function of range from DSSS node to DSSS AP
• DSSS Hi Rate systems retain high throughput and have graceful degradation in the presence of BT interference
• Based on these user models, DSSS Hi Rate WLANs are very reliable in the presence of significant BT interference
• Results are preliminary. Must be verified by lab tests.
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
IEEE 802.11 FHSS vs. Bluetooth
• Preliminary evaluation– interaction between single BT transmitter and an IEEE 802.11
FHSS link
– 0 dBm BT Tx power, +20 dBm IEEE 802.11 tx power– Impact estimated under specific BT conditions:
Bluetooth idle (establish baseline IEEE 802.11 throughput) BT telephony w/HV3 packet (33% BT piconet load) BT file transfer w/DH1 packet (100% BT piconet load) BT in PAGE mode (worst case)
– Influence of Range and receiver filtering• IF filtering determines bandwidth of susceptibility to BT
interference (about 3 MHz for IEEE 802.11 FHSS Rx)
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Rx Desense Values (2FSK)
Bluetooth IEEE 802.11 FH HomeRF
CCI -14 dB (2) --- ---
+/- 1 channel -4 dB (2) --- ---
+/- 2 channels 30 dB 30 dB 0 dB
+/- 3 channels 40 dB 40 dB 10 dB
+/- 4 channels 40 dB 40 dB 25 dB
>+/- 5 channels 40 dB 40 dB 35 dB
(1) Vales stated in terms of interference-to-signal ratio(2) Interim values. To be finalized within 18 mos. after release
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Influence of Range (1 Mbps)
Signal-to-Interference Ratio depends on:- relative BT and IEEE 802.11 Tx power- Range from IEEE 802.11 node to AP- Range from IEEE 802.11 node to BT Tx
At 1 Mbps and 0 dBm BT Tx Power:- Bandwidth of interference susceptibility is 3 MHz- BT Tx must be approximately 50% closer to node than AP (0 dBm BT Tx power, +20 dBm IEEE 802.11FH Tx Power)
802.11 FH AP
802.11 FH Node
Link Distance (D)
BT Tx Interference Range (D/2)
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Throughput of WLAN Operating @ 1Mbps (2FSK) vs BT Load
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1500 750 500 375 300 250 150 100 75
Packet Payload (bytes)
Th
rou
gh
pu
t (M
bp
s)
BT Idle
Telephony (33% BT load)
e-mail (100% BT load)
Paging
Note: Raw data rate for 2FSK = 1 Mbps
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Influence of Range (2 Mbps)
At 2 Mbps and 0 dBm BT Tx Power:- Bandwidth of interference susceptibility is 3 MHz- BT Tx must be within roughly same distance to node as AP (0 dBm BT Tx power, +20 dBm IEEE 802.11FH Tx Power)
802.11 FH Access Point
802.11 FH Node
Link Distance (D)
BT Tx
Interference Range (D)
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Throughput of WLAN Operating @ 2 Mbps (4FSK) vs BT Load
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
1500 750 500 375 300 250 150 100 75
Packet payload (bytes)
Th
rou
gh
pu
t (M
bp
s)
BT Idle
Telephony (33% BT load)
e-mail (100% BT load)
Paging
Note: Raw data rate for 4FSK = 2 Mbps
September 1999
Jim Zyren, Intersil
doc.: IEEE 802.15-073r0
Submission
Summary of FHSS/BT Results
• Narrow channel width of FHSS systems help avoid interference in frequency domain– Occupied channel for FHSS is about 1 MHz under current
FCC rules (same width for 2FSK and 4FSK)
• Slower transmission rate requires longer transmit time– increases chances BT will hop into channel during
transmission and collide (advantage for 4FSK)
• Multi-level FSK more susceptible to ACI/CCI– 4FSK transmission can be jammed by a weaker BT signal
(advantage 2FSK)