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Multi-radio & Mixed Networks. Gaurang Sardesai & Jeff Pang. Papers. UCAN: A Unified Cellular and Ad-Hoc Network Architecture , Haiyun Luo, Ramachandran Ramjee, Prasun Sinha, Li Li, Songwu Lu, ACM MOBICOM 2003, San Diego, California

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multi radio mixed networks

Multi-radio & Mixed Networks

Gaurang Sardesai

&

Jeff Pang

papers
Papers
  • UCAN: A Unified Cellular and Ad-Hoc Network Architecture, Haiyun Luo, Ramachandran Ramjee, Prasun Sinha, Li Li, Songwu Lu, ACM MOBICOM 2003, San Diego, California
  • The Pulse Protocol: Energy Efficient Infrastructure Access, Awerbuch, Holmer, Rubens, The 23rd Conference of the IEEE Communications Society (IEEE Infocom 2004)
ucan unified cellular ad hoc network
UCAN : Unified Cellular Ad-Hoc Network
  • Synergistically combine 3G and 802.11 networks
  • Service to low data users reduces cell’s aggregate throughput
  • 3G BS forwards packets to proxy clients with better channel quality who then forward it over their 802.11 interface.
  • Maintain Fairness
  • Why would you want to relay packets for others?
    • Secure crediting mechanism
motivation
Motivation
  • Ad-Hoc mode complements the Cellular infrastructure
  • Differences between WWAN and WLAN
    • Coverage area, throughput, operating mode
  • Mobile device needs two interfaces
architecture
Architecture
  • Clients monitor downlink channel conditions. If rate is low, use relays.
  • Challenges:
    • Proxy Discovery
    • Topology / Rate change
    • Why would you forward packets for someone?
proxy discovery and routing
Proxy discovery and Routing
  • When low downlink channel rate, client sends out route request message on 802.11b interface.
  • Message propagated by intermediate nodes, route established along the way.
  • Proxy client sends request to HDR BS.
  • All further frames sent through new route using tunneling
  • Every client maintains moving avg of its downlink channel quality
  • Greedy (proactive)
  • On demand (reactive)
greedy proxy discovery
Greedy Proxy Discovery
  • Nodes periodically exchange avg downlink channel rates by broadcasting NDADV
  • Route requests sent to highest rate neighbor along with TTL
  • On receipt of request, client makes entry in table , if TTL larger than 0, forward to it’s best neighbor, else sends proxy application message to HDR BS.
  • Problem?
    • May not always locate best path
on demand proxy delivery
On-demand proxy Delivery
  • When required, destination client floods RTREQ message within certain range.
  • On receipt of req, client checks sequence number and HDR channel rate
  • Update channel rate, and apply to HDR BS to become a proxy client. IF TTL >0, decrement TTL and further broadcast.
  • BS checks seq # and decide on Proxy
on demand proxy discovery
On-demand Proxy Discovery
  • Locates the best path
  • But overhead on HDR uplink
route and proxy maintenance
Route and Proxy Maintenance
  • Rates change, clients move, loops may occur
  • Path Breaks
  • Proxy maintenance w.r.t rate change
  • Routing loops
scheduling algorithm
Scheduling Algorithm
  • Proportional Fair Scheduling
  • Client with min is scheduled for round
  • Use destination client’s own downlink rate to schedule.
secure crediting
Secure Crediting
  • Why would you want to relay for someone else?
  • All intermediate clients awarded credits.
  • Problems?
    • Deletion of legitimate clients
    • Addition of Extra Clients
  • Piggyback MAC in RTREQ message
  • But do not handle two consecutive clients conspiring
take aways
Take Aways
  • Novel Idea
  • Will this work for voice networks?
  • Don’t discuss credit accounting and per packet overhead.
pulse protocol
Pulse Protocol
  • Pulse protocol sends out periodic pulse which provides routing and synchronization.
  • Pulse forms a spanning tree, and so each node has a continuously updated route towards the nearest network gateway.
  • Allows nodes to power off radio most of the time, except when required for packet forwarding.
  • Synchronous sleep protocol
working
Working
  • Flood called pulse sent at fixed pulse intervals. Originates from sources (WAP) and propagates across ad hoc component of network.
  • Routing – each node only remembers the node from where it got the flood packet with lowest metric. Loop free.
  • Synchronization
  • If node needs to send packet, make reservation in response to flood. Sets up reverse routes. Like AODV.
  • If sending, send reservation in order to keep route fresh.
  • If you don’t want to send of forward a reservation, sleep until the next pulse, as you’re not sending a reservation.
  • To reduce contention, no data packets sent during the flood.
  • All broken routes repaired simultaneously by within one pulse interval by flood.
why multiple radios
Why Multiple Radios?
  • Multiple Senders: Channel Diversity
    • Adya, et al. ‘04
  • Multiple Receivers: Path Diversity
    • Miu, et al. ‘05
    • Ferrière, et al. ‘05

Ch. 1

Ch. 11

multi radio unification protocol mup
Multi-Radio Unification Protocol (MUP)
  • Environment:
    • Community Mesh Networks
  • Goal:
    • Increase Forwarding Capacity
  • Basic Idea:
    • Give each node NICs on different channels
    • Send on channel with best quality
  • Constraints:
    • Use commodity 802.11 parts
    • Don’t modify 802.11 MAC
    • Support legacy (single channel) nodes
    • Decentralized

MUP Architecture

mup protocol overview
MUP Protocol Overview
  • Probe neighbors to discover available channels
  • Periodically measure channel quality to each neighbor
  • Select channel with best quality
  • Send packets out best channel
  • Repeat
mup protocol example

ARP

CS

CS-ACK

ARP

MAC1

MAC1,MAC2

CS-ACK

CS

A

node

A

A

C

node

C

node

A

A

C

A

1

1

1

channel

1

channel

1

1

11

channel

11

11

?

?

?

quality

?

?

?

rtt

?

2

10

quality

MUP Protocol Example

A

B

C

Legacy node

channel quality metric
Channel Quality Metric
  • RTT (see last lecture)
    • SRTT = a*RTTnew + (1-a)*SRTT
  • Lost CS messages =>
    • SRTT = 3*SRTT
  • Problems? Alternatives?
    • Self-interference can cause oscillations
    • Could use ETX from last lecture
orthogonal channels
Orthogonal Channels
  • 802.11a
    • Theory: 13
    • Practice: 7
  • 802.11b/g
    • Theory: 3
    • Practice: 1-2
  • Signal power leakage => interference
mup throughput improvement
MUP Throughput Improvement
  • 50% legacy nodes
  • 50% 2 NIC nodes
  • Simulated TCP tput
alternative stripping
Alternative: Stripping
  • MUP picks 1 best interface
  • Instead, can use all interfaces simultaneously
  • Basic Idea:
    • Use round-robin to select which NIC to send a packet on
  • Alternatives to reduce loss?
    • FEC packet combining codes (next paper)
    • Sacrifice some capacity for redundancy
mup vs stripping
MUP vs. Stripping
  • Round-robin Stripping is worse!
    • Channel load not equal => lots of out-of-order packets
  • Load-sensitive Striping gain is negligible
    • Why? Hint: only 2 channels…
mup summary
MUP Summary
  • Leverage channel diversity with multiple-radios per node
  • Use unmodified commodity parts
  • Channel selection based on SRTT metric
multi radio diversity mrd
Multi-Radio Diversity (MRD)
  • Environment:
    • AP Infrastructure Network
  • Goal:
    • Reduce AP receiver loss/error-rate
  • Basic Idea:
    • Let multiple APs hear client packets
    • Recover errors by combining multiple copies
  • Constraints:
    • Don’t change link-layer
    • APs connected on high-speed LAN
mrd protocol overview
MRD Protocol Overview
  • Client associates with one AP
  • Other APs on same channel listen passively
  • Send all received packets to MRD Combiner (MRDC):
    • See if at least one good copy
    • If not, try to recover from all bad copies
    • If can’t recover, fail and let client retransmit
mrd protocol example

MRDC

00110000

00000000

00000000

OK!

(soft selection)

MRD Protocol Example

00000000

mrd protocol example1

OK!

(frame combining)

00000000

MRDC

00110000

00000011

00110000

00000011

MRD Protocol Example

00000000

frame combining details

1. Split into blocks

2. Find bad blocks

00 11 00 10 00

3. Check all

possibilities

against CRC

in header

(bad headers

=> drop)

00 11 00 10 00

00 11 00 00 00

00 00 00 00 00

00 00 00 10 00

Frame Combining Details

received

original

00 11 00 00 00

00 00 00 00 00

00 00 00 10 00

frame combining efficiency
Frame Combining Efficiency
  • Bit errors are bursty
  • Errors at different APs are uncorrelated
  • Theory: small number of blocks will succeed most of the time
retransmissions rfa
Retransmissions: RFA
  • When does sender know tx success?
    • Soft-selection => Link-layer ACK
    • Frame-combining => ???
  • Why wait for ACK with frame combining?
    • Slow! Must wait for MRDC
  • Solution: Request for ACK
    • Sender periodically asks for ACK
    • MRDC acks all packets combined OK
  • Issues?
    • Delay => OK if short
    • Packet reordering => need to buffer
    • Overhead => piggyback RFA on data packets
mobile experiment

recovered by

soft selection

recovered by

frame combining

Mobile Experiment
mrd summary
MRD Summary
  • Leverage path diversity with multiple receivers
  • Correct errors with frame combining
  • Use delayed RFA to obtain tx status
simple packet combining spac
Simple Packet Combining (SPaC)
  • Environment:
    • Multi-hop Sensor Network
  • Goal:
    • Recover from bit errors with multiple receptions of the same packet
  • Basic Idea:
    • A node overhears packets as they are forwarded
    • When you get more than one corrupt copy of a packet, you may be able to correct the errors
spac overview

0000

0001

0000

1100

0100

Merge with

Frame Combining

0000

SPaC Overview

0000

some spac details
Some SPaC Details
  • Can recover errors with:
    • Multiple overheard packets
    • Multiple retransmissions
  • Use same idea in MRD frame combining to correct errors
multi radio discussion
Multi-Radio Discussion
  • What more general type of diversity is channel diversity?
    • Frequency diversity
    • Really just using more spectrum
  • What more general type of diversity is receiver/path diversity?
    • Space diversity
    • Is this much different from multiple antennas?
  • What other types of diversity could multiple radios exploit?
    • Technology Diversity? (802.11, GPRS, WiMax, etc.)
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