Link/Network Layer: MIMO, Cognitive Radio; Energy Management of Radio Resource Control (RRC)

Link/Network Layer:MIMO, Cognitive Radio; Energy Management of

Radio Resource Control (RRC)

Y. Richard Yang

11/15/2012

2

Outline

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

Admin.

Project meeting slots to be posted on classesv2

3

4

Recap: Constraints in Capacity Analysis

transmission successful if there

are no other transmitters within a

distance (1+)r of the receiver

Interference constraint a single half-duplex

transceiver at each node

Radio interface constraint

T

b

nWTbh

1 2)(

21

)(

1

2 16)(

WTr

T

b

bh

h

hb

receiver

sender

r(1+)r

5

Recap: Capacity Bound

n

ii

n

ii xnx

1

2

2

1

Note:

Let L be the average (direct-line) distance for all T end-to-end bits.

T

b

bh

h

hbrTL

1

)(

1

T

b

bh

h

hb

T

b

T

b

bh

h

hb rbhrTL

1

)(

1

2

11

)(

1

)()(

nWTWTWTn

TL

816

2 2

nW

L

8rate*distance capacity:

6

Improving Wireless Mesh Capacity

transmission successful if there

are no other transmitters within a

distance (1+)r of the receiver

Interference constraint a single half-duplex

transceiver at each node

Radio interface constraint

T

b

nWTbh

1 2)(

21

)(

1

2 16)(

WTr

T

b

bh

h

hb

nW

L

8

rate*distance capacity:

Reduce LIncrease

W

Approx.optimal

Multipletransceivers

Reduceinterf. area

7

Outline

Admin. and recap Improve mesh capacity

Reduce L (infrastructure “blackholes”, mobility for delay tolerant networks)

MIMO: Use multiple antennas

Multiple Input Multiple Output (MIMO)

4x4 MIMO http://www.quantenna.com/qac-2300rdk.html

LTE

Kindle Fire HD

8

MIMO Basics

9

1

2

1

2

2221122

2211111

xhxhy

xhxhy

11h

12h

21h

22h

Solve two variables from two equations.

Using MIMO for more Concurrency: Motivation

10

Assume tx1 is sending to rx1

Can tx2 transmit in 802.11 using carrier sensing?

No Transmission in current 802.11n

MIMO Benefit: Concurrency using Interference Nulling

tx2: for every symbol q,transmits q on first antenna and aq on second antenna.

11

11h 21h31h

interference at rx1:

qhh )( 3121

if tx2 picks 31

21

hh

NO interference at rx1.

Problem

- rx2 hears p from tx1

- Can rx2 decode?

12

11h 21h31h

Decoding at rx2: Observation

- for different symbols p from tx1, the received signal at rx2 moves along a 1-d vector

13

11h 21h31h

phph

hy tx1

13

12

1txh

- rx2 can estimate channels h12, h13 from preamble

Perp. Of tx1 space

Decoding at rx2: Removing tx1 signal by Projection

- rx2 projects received signal orthogonal to

14

11h 21h31h

phph

hy tx1

13

12

1txh

projection space

Decoding at rx2: Projection Details

- rx2 picks w2 and w3:

to compute

15

11h 21h31h

projection space

3322 ** ywyw

Decoding at rx2: Projection Details

16

11h 21h31h

=>

qhhw

hhw

ywyw

)](

)([

33233

32222

3322

Summary: MIMO allows concurrency w/ interference nulling.

Problem of Only Nulling

17

Assume both tx1 and tx2 are transmitting.

If only nulling, tx3 cannot

transmit

nulli

ng

Solution: MIMO using Interference Alignment

18

Assume both tx1 and tx2 are transmitting.

Key idea: rx2 ignores interference from tx1 by projection. If tx3 aligns tx3 -> rx2 interference along the same direction as that oftx1 -> rx2, then rx2 can remove it too.

nulli

ng

MIMO with Nulling and Alignment

19

tx3 picks ’, ’, ’

rx2 sees:

1txh

Because rx2 projects to orthogonal to , nointerference from tx3 to rx2

20

Outline

Admin. and recap Improve mesh capacity

Reduce L (infrastructure “blackholes”, mobility for delay tolerant networks)

MIMO: Use multiple antennas Cognitive radio: use unlicensed spectrum

Spectrum Allocation Chart

21

Unlicensed Spectrum

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

Problem of Using Unlicenced

Unlicensed spectrum may have occupants and is fragmented

Requirement: Coexistence with dynamic and unknown narrowband devices in the unlicensed spectrum

23

Zigbee 802.11a Others

UnlicensedSpectrum

Zigbee 802.11a Others

UnlicensedSpectrum

1. Operate below noise-level Limits range

Wideband

Existing Solutions

Zigbee 802.11a Others

UnlicensedSpectrum

1. Operate below noise-level Limits range

2. Pick a contiguous unoccupied band Limits throughput

Wideband

Existing Solutions

Zigbee 802.11a Others

UnlicensedSpectrum

1. Operate below noise-level Limits range

2. Pick a contiguous unoccupied band Limits throughput

Wideband

Sacrifice Throughput or Range!

Existing Solutions

Zigbee 802.11a Others

UnlicensedSpectrum

Cognition: Detect unoccupied bandsAggregation: Weave all unoccupied bands into one link

Wideband

Swift: Cognitive Aggregation

Research Issues

How to detect available frequency bands?

How to operate across chunks of non-contiguous frequencies?

How do sender and receiver establish communication when their perceived available frequency bands differ?

Aggregating Non-Contiguous Bands

Leverage OFDMDivides frequency band into multiple sub-bands that can be treated independently

Transmitter: Puts power and data only in OFDM bands not occupied by narrowband devicesReceiver: Extracts data only from OFDM bands used by transmitter

Frequency band

Cognition: How to detect occupied bands?

Unlicensed Can’t assume known narrowband devices Typical solution: Power threshold

Ideal ThresholdNarr

ow

ban

d

Pow

er

in d

Bm

Baseband Frequencies (MHz)

Faraway 802.11

Cognition: How to detect occupied bands?

Unlicensed Can’t assume known narrowband devices Typical solution: Power threshold

Ideal ThresholdNarr

ow

ban

d

Pow

er

in d

Bm

Baseband Frequencies (MHz)

Faraway 802.11

Problem: No Single Threshold Works Across All Locations

Ideal Threshold

Narr

ow

ban

d

Pow

er

in d

Bm

Baseband Frequencies (MHz)

Faraway 802.11

Nearby 802.11

Unlicensed Can’t assume known narrowband devices Typical solution: Power threshold

Cognition: How to detect occupied bands?

Adaptive Sensing

Intuitively: Poke the narrowband device, putting power in ambiguous bandsIf the narrowband device reacts, back away

Reasonable for unlicensed spectrum, which operates as best-effort

Unlicensed devices typically react to interferenceCarrier sense in 802.11, TCP backoff, etc.

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

Adaptive Sensing: Alg

Narrowband Reaction

Detection Metric

Carrier Sense (e.g.,802.11): Will not transmit when sensing a SWIFT packet

Probability of narrowband power immediately after a SWIFT packet

Back-off (e.g., TCP, MAC): Will send less often

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

ConservativeThreshold

Wideband

• Start with a conservative choice of bands• Keep tightening as long as narrowband is

unaffected

Adaptive Sensing in Action

Wideband

Metric

Estimate Normal Behavior

Adaptive Sensing in Action

Wideband

Metric

Tighten

Sense

Test: Same as Normal

Adaptive Sensing in Action

Wideband

Metric

Tighten

Sense

Test: Different from Normal

Adaptive Sensing in Action

Wideband

Metric

Loosen

Sense

Test: Same as Normal

Adaptive Sensing in Action

Wideband Throughput and Range

Baseline that operates below the noise of 802.11

Wideband Throughput and Range

Other Work

Cognitive Radios802.22, KNOWS, CORVUS, DIMSUMNet etc.

Wideband systemsIntel, Chandrakasan et al., Mishra et al., Sodini et al.

45

Outline

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

management

46

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

BTSMS

RACH (request signaling channel)

AGCH (assign signaling channel)

SDCCH (request call setup)

SDCCH (assign TCH)

SDCCH message exchange

Communication

call setup from an MS

47

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.

48

RRC State Management in UMTS

Given the large overhead to set up radio resources, UMTS implements RRC state machine on mobile devices for data connection

Channel Radio Power

IDLE Not allocated

Almost zero

CELL_FACH

Shared, Low Speed

Low

CELL_DCH Dedicated, High

Speed

High

Courtesy: Erran Li.

49

RRC of a Large Commercial 3G Net

Promo Delay: 2 Sec

DCH Tail: 5 sec

FACH Tail: 12 sec

DCH: High Power State (high throughput and power consumption)FACH: Low Power State (low throughput and power consumption)IDLE: No radio resource allocated

Tail Time: waiting inactivity timers to expire

50

RRC Effects on Device/Network

FACH and DCH

Wasted Radio Energy 34%

Wasted Channel Occupation Time 33%

51

Case Study: Pandora Streaming

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

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

52

Case Study: Fox News

Problem: Scattered bursts due to scrollingRecommendation: Group transfers of small thumbnail

images in one burst

Problem: Scattered bursts due to scrollingRecommendation: Group transfers of small thumbnail

images in one burst

53

Case Study: BBC News

Scattered bursts of delayedFIN/RST Packets

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

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

54

Case Study: Google Search

Search three key words.ARO computes energy consumption for three phases

I: Input phase S: Search phase T: Tail Phase

UL PacketsDL Packets

Bursts

RRC States

Usr Input

Problem: High resource overhead of query suggestions and instant searchRecommendation: Balance between functionality and resource when

battery is low

Problem: High resource overhead of query suggestions and instant searchRecommendation: Balance between functionality and resource when

battery is low

55

RRC State Transitions in LTE

56

RRC State Transitions in LTE

RRC_IDLE

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

RRC state transitions in LTE

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

57Cellular Networks and Mobile Computing (COMS

6998-11)Courtesy: Junxian Huang et al.

RRC state transitions in LTE

Continuous

ReceptionSend/receive a packet

Promote to RRC_CONNECTED

Send/receive a packetPromote to

RRC_CONNECTED

Reset Ttail

58Cellular Networks and Mobile Computing (COMS

6998-11)Courtesy: Junxian Huang et al.

RRC state transitions in LTE

Ttail stopsDemote to RRC_IDLE

DRX

Ttail

expiresTtail

expires

59Cellular Networks and Mobile Computing (COMS

6998-11)Courtesy: Junxian Huang et al.

60

Summary

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