Y. Richard Yang
11/15/2012




Admin. and recap
Improve mesh capacity



Reduce L (infrastructure “blackholes”, mobility for delay tolerant networks)
MIMO: Use multiple antennas
Cognitive radio: use more spectrum
Radio resource management for energy management of mobile devices
2


Project meeting slots to be posted on classesv2
3

Recap: Constraints in Capacity Analysis

Radio interface constraint a single half-duplex transceiver at each node
Interference constraint
 transmission successful if there are no other transmitters within a distance
(1+ D )r of the receiver

T b


1 h ( b )

WT n
2
(1+ D )r receiver r sender

T b h ( b  )

1 h

1
( r b h
)
2 
16 WT
 D 2
4

Recap: Capacity Bound Note:

 i n 

1 x i


2
 n i n 

1 x i
2
Let L be the average (direct-line) distance for all

T end-to-end
T h ( bits.
b )


TL
 b


1 h

1 r b h

TL

 b h ( T  b

1 h

1
) r b h

 b

 T

1 h ( b )
 b h ( T  b

1 h

1
)
( r b h
)
2

TL

WTn
2
16 WT
 D 2

8

WT
D n rate*distance capacity:

L

8

W
D n
5

Improving Wireless Mesh Capacity

Radio interface constraint
Multiple a single half-duplex transceiver at each node transceivers
Reduce interf. area
Interference constraint
 transmission successful if there are no other transmitters within a distance
(1+ D )r of the receiver

T  h ( b )

WT n
2 rate*distance capacity:
Approx.
optimal

L


T b h ( b  )

1 h

1
( r b h
)
2 
16 WT
 D 2
Increase
W
8

W
D n
6



Admin. and recap
Improve mesh capacity


Reduce L (infrastructure “blackholes”, mobility for delay tolerant networks)
MIMO: Use multiple antennas
7

Multiple Input Multiple Output (MIMO)

4x4 MIMO
 http://www.quantenna.com/qac-2300rdk.html

LTE

Kindle Fire HD
8

x
1 h
11 y
1
1
1 h
12 h
21 y
2
2
2 h
22 x
2 y y
1
2

 h
11 x h
12 x
1
1
 h
21 x
2
 h
22 x
2
Solve two variables from two equations.
9

Using MIMO for more Concurrency:
Motivation
No Transmission in current 802.11n
Assume tx1 is sending to rx1
Can tx2 transmit in 802.11 using carrier sensing?
10

MIMO Benefit: Concurrency using
Interference Nulling h
11 h
21 h
31 tx2: for every symbol q, transmits q on first antenna and aq on second antenna. interference at rx1:
( h
21
  h
31
) q if tx2 picks    h
21 h
31
NO interference at rx1.
11

Problem h
11 h
21 h
31
rx2 hears p from tx1
Can rx2 decode?
12

Decoding at rx2:
Observation h
11 h
21 h
31
for different symbols p from tx1, the received signal at rx2 moves along a
1-d vector tx 1
 y


 h h
12
13
 h

 p

 h tx 1 p
Perp. Of tx1 space
rx2 can estimate channels h12, h13 from preamble
13

Decoding at rx2:
 y

Removing tx1 signal by Projection

 h
12 h
13

 p

 h tx 1 p
rx2 projects received signal orthogonal to
 h tx 1 h
11 h
21 h
31 projection space
14

Decoding at rx2:
Projection Details h
11 h
21 h
31
- rx2 picks w2 and w3: w
2
* h
12
+ to compute w
3
* h
13
=
0 w
2
* y
2
 w
3
* y
3 projection space
15

Decoding at rx2:
Projection Details h
11 h
21 h
31 w
2
* h
12
+ w
3
* h
13
=
0
=> w
2
 y
2
 w
3
[ w
2
( h
22 y
3
  h
32
)
 w
3
( h
23
  h
33
)] q
Summary: MIMO allows concurrency w/ interference nulling.
16

Problem of Only Nulling
If only nulling, tx3 cannot transmit
Assume both tx1 and tx2 are transmitting.
17

Solution: MIMO using Interference Alignment
Key idea: rx2 ignores interference from tx1 by projection. If tx3 aligns tx3 -> rx2 interference along the same direction as that of tx1 -> rx2, then rx2 can remove it too.
Assume both tx1 and tx2 are transmitting.
18

MIMO with
Nulling and Alignment tx3 picks  ’ ,  ’ ,  ’ rx2 sees:
Because rx2 projects to orthogonal to , no interference from tx3 to rx2
 h tx 1
19



Admin. and recap
Improve mesh capacity



Reduce L (infrastructure “blackholes”, mobility for delay tolerant networks)
MIMO: Use multiple antennas
Cognitive radio: use unlicensed spectrum
20

21


Opportunity: unlicensed spectrum is large and has low utilization

US unlicensed freq:
• 2.400-2.4835 G
• 902-928 M
• 5.800-5.925G
• 5.15-5.25 G (200 mw)
• 5.25-5.35 (1 w)
• 5.725-5.825 (4w)
22


Unlicensed spectrum may have occupants and is fragmented
Zigbee 802.11a
Others
Unlicensed
Spectrum

Requirement: Coexistence with dynamic and unknown narrowband devices in the unlicensed spectrum
23

1. Operate below noise-level
Limits range
Wideband
Zigbee 802.11a
Others
Unlicensed
Spectrum

1. Operate below noise-level
Limits range
2. Pick a contiguous unoccupied band
Limits throughput
Wideband
Zigbee 802.11a
Others
Unlicensed
Spectrum

1. Operate below noise-level
Limits range
2. Pick a contiguous unoccupied band
Limits throughput
Wideband
Zigbee 802.11a
Others

Cognition: Detect unoccupied bands
Aggregation: Weave all unoccupied bands into one link
Wideband
Zigbee 802.11a
Others
Unlicensed
Spectrum


How to detect available frequency bands?

How to operate across chunks of noncontiguous frequencies?

How do sender and receiver establish communication when their perceived available frequency bands differ?

Aggregating Non-Contiguous Bands
Leverage OFDM
Divides frequency band into multiple sub-bands that can be treated independently
Frequency band
Transmitter: Puts power and data only in
OFDM bands not occupied by narrowband devices
Receiver: Extracts data only from OFDM bands used by transmitter

Cognition: How to detect occupied bands?
Unlicensed  Can’t assume known narrowband devices
Typical solution: Power threshold
180
150
120
90
60
30
0
Faraway 802.11
Baseband Frequencies (MHz)
Ideal Threshold

Cognition: How to detect occupied bands?
Unlicensed  Can’t assume known narrowband devices
Typical solution: Power threshold
180
150
120
90
60
30
0
Faraway 802.11
Baseband Frequencies (MHz)
Ideal Threshold
Problem: No Single Threshold Works Across All Locations

Cognition: How to detect occupied bands?
Unlicensed  Can’t assume known narrowband devices
Typical solution: Power threshold
210
180
150
120
90
60
30
0
Nearby 802.11
Faraway 802.11
Ideal Threshold

Unlicensed devices typically react to interference
Carrier sense in 802.11, TCP backoff, etc.
Intuitively:
Poke the narrowband device, putting power in ambiguous bands
If the narrowband device reacts, back away
Reasonable for unlicensed spectrum, which operates as best-effort

Continuously sense the medium when not sending a packet
Detect appearance of narrowband device when narrowband power exceeds noise level
Detect reaction from changes in narrowband power profile

Narrowband Reaction
Carrier Sense (e.g.,802.11):
Will not transmit when sensing a SWIFT packet
Back-off (e.g., TCP, MAC):
Will send less often
Detection Metric
Probability of narrowband power immediately after a SWIFT packet
Inter-arrivals of narrowband power
Autorate: Will use lower modulation, increasing packet size
Duration of narrowband power
Look for statistically significant change in metric using standard tests (e.g. t-test)

Adaptive Sensing in Action


Start with a conservative choice of bands
Keep tightening as long as narrowband is unaffected
Conservative
Threshold

Adaptive Sensing in Action
• Start with a conservative choice of bands
• Keep tightening as long as narrowband is unaffected
Wideband

Adaptive Sensing in Action
Wideband
Metric
Estimate Normal Behavior
Time

Adaptive Sensing in Action
Tighten
Wideband
Metric
Sense
Test: Same as Normal
Time

Adaptive Sensing in Action
Tighten
Wideband
Metric
Sense
Test: Different from
Normal
Time

Adaptive Sensing in Action
Loosen
Wideband
Metric
Sense
Test: Same as Normal
Time

450
400
350
300
250
200
150
100
50
0
Baseline
3 6 9 12
Distance (m)
15
Baseline that operates below the noise of 802.11
18 21

450
400
350
300
250
200
150
100
50
0
Baseline
SWIFT
3 6 9 12
Distance (m)
15 18 21

Other Work
Cognitive Radios
802.22, KNOWS, CORVUS, DIMSUMNet etc.
Wideband systems
Intel, Chandrakasan et al., Mishra et al.,
Sodini et al.




Admin. and recap
Improve mesh capacity
Radio resource management for energy management
45

Recall: GSM Logical Channels and Request

Many link layers use a hybrid approach


Mobile device uses random access to request radio resource
The device holds the radio resource during a session
MS call setup from an MS
BTS
RACH (request signaling channel)
AGCH (assign signaling channel)
SDCCH (request call setup)
SDCCH message exchange
SDCCH (assign TCH)
Communication
46

Radio Resource Control Setup for Data in 3G
RRC connection setup: ~ 1sec +
Radio Bearer Setup: ~ 1 sec
Figure source: HSDPA/HSUPA for UMTS: High Speed Radio Access for Mobile Communications. John Wiley and Sons, Inc., 2006.
Source: Erran Li.
47


Given the large overhead to set up radio resources, UMTS implements RRC state machine on mobile devices for data connection
Channel
IDLE Not allocated
CELL_FAC
H
Shared,
Low Speed
CELL_DCH Dedicated,
High Speed
Radio
Power
Almost zero
Low
High
Courtesy: Erran Li.
48

DCH Tail: 5 sec
FACH Tail: 12 sec
Promo Delay: 2 Sec
Tail Time: waiting inactivity timers to expire
DCH : High Power State (high throughput and power consumption)
FACH : Low Power State (low throughput and power consumption)
IDLE : No radio resource allocated
49

Wasted Radio Energy
Wasted Channel Occupation Time
FACH and DCH
34%
33%
50

Problem : High resource overhead of periodic audience measurements (every 1 min)
Recommendation : Delay transfers and batch them with delay-sensitive transfers
51

Problem : Scattered bursts due to scrolling
Recommendation : Group transfers of small thumbnail images in one burst
52

Problem : Scattered bursts of delayed FIN/RST packets
Recommendation : Close a connection immediately if possible, or within tail time
Scattered bursts of delayed
FIN/RST Packets
53

UL Packets
DL Packets
Bursts
Usr Input
RRC States
Search three key words.
ARO computes energy consumption for three phases
I : Input phase S : Search phase T : Tail Phase
Problem : High resource overhead of query suggestions and instant search
Recommendation : Balance between functionality and resource when battery is low
54

55

RRC_IDLE
• No radio resource allocated
• Low power state:
11.36mW average power
• Promotion delay from
RRC_IDLE to
RRC_CONNECTED: 260ms
56

RRC_CONNECTED
• Radio resource allocated
• Power state is a function of data rate:
• 1060mW is the base power consumption
• Up to 3300mW transmitting at full speed
Cellular Networks and Mobile Computing (COMS 6998-
11)
Courtesy: Junxian Huang et al.
57

Continuous
Reception
Reset Ttail
Cellular Networks and Mobile Computing (COMS 6998-
11)
Courtesy: Junxian Huang et al.
58

DRX
Ttail stops
Demote to
RRC_IDLE
Cellular Networks and Mobile Computing (COMS 6998-
11)
Courtesy: Junxian Huang et al.
59


App developers may not be aware of interactions with underlying network radio resource management

A good topic to think about as a part of your project
60