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Throughput Optimization and Fair Bandwidth Allocation in MultiHop Wireless Local Area Networks

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WAP=6/11 3/5=63/55 1, n9=3. d=(63/55-1)/(n9/11)=8/15. Thus b9=b7=b4=11/5-8/15=5/3 ... Incremental deployment is enabled and encouraged ... – PowerPoint PPT presentation

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Title: Throughput Optimization and Fair Bandwidth Allocation in MultiHop Wireless Local Area Networks


1
Throughput Optimization and Fair Bandwidth
Allocation in Multi-Hop Wireless Local Area
Networks
INFOCOM 2006
  • Qunfeng Dong (University of Wisconsin-Madison)
  • Suman Banerjee (University of Wisconsin-Madison)
  • Benyuan Liu (University of Massachusetts-Lowell)

Slides by Ting-Yu Lin
2
Outline
  • Introduction
  • The Performance anomaly of 802.11 WLANs
    (one-hop)
  • Previously proposed one-hop/multi-hop solutions
    and limitations
  • Our multi-hop solution
  • Fairness in multi-hop WLANs
  • Max-Min Throughput Fairness
  • Max-Min Time Fairness
  • Fair bandwidth allocation in multi-hop WLAN
  • Construction and maintenance of an efficient
    tree
  • Backward compatibility
  • Evaluation
  • Summary

3
Background
  • The Performance anomaly of 802.11 WLANs
  • Channel rate diversity is prevalent in 802.11
    WLANs KNE03, TG04
  • 802.11 DCF implements Throughput-based Fairness
  • Assigns approximately equal bandwidth to each
    client
  • A low bit rate client brings down throughput of
    everyone HRBD03

Rate of 8,9 11 Mbps Rate of 5,6,7 5.5
Mbps Rate of 1,2,3,4 2 Mbps Total
Throughput 3.3 Mbps
4
Background
  • Solution 1 Time-based Fairness TG04
  • Each client receives equal time share
  • High bit rate clients are protected
  • Aggregate throughput is increased
  • However, throughput of low bit rate clients is
    decreased!

Rate of 8,9 11 Mbps Rate of 5,6,7 5.5
Mbps Rate of 1,2,3,4 2 Mbps Total
Throughput 5.2 Mbps
5
Background
  • Solution 2 Multi-AP Association Control BHL04
  • In 802.11, clients are assigned to the AP with
    the strongest RSSI
  • Often leads to unbalanced load distribution and
    idle channel
  • Throughput and fairness can be improved by
    careful association

6
Background
  • Solution 2 Multi-AP Association Control BHL04
  • In 802.11, clients are assigned to the AP with
    the strongest RSSI
  • Often leads to unbalanced load distribution and
    idle channel
  • Throughput and fairness can be improved by
    careful association

Bandwidth of client 1 1 Mbps Bandwidth of
client 2 1 Mbps Bandwidth of client 3 1
Mbps Bandwidth of client 4 1 Mbps Bandwidth of
client 5 1 Mbps
A fair default association
7
Background
  • Solution 2 Multi-AP Association Control BHL04
  • In 802.11, clients are assigned to the AP with
    the strongest RSSI
  • Often leads to unbalanced load distribution and
    idle channel
  • Throughput and fairness can be improved by
    careful association

Bandwidth of client 1 1 Mbps Bandwidth of
client 2 2 Mbps Bandwidth of client 3 2
Mbps Bandwidth of client 4 1 Mbps Bandwidth of
client 5 1 Mbps
A max-min fair association
8
Motivation Challenges
  • A common limitation of these previous techniques
  • Only use AP-client links, which often have low
    bit rates.
  • High rate P2P links between clients exist, but
    not utilized.
  • Solution 3 Multi-Hop WLAN LBB04
  • Forward traffic via high bit rate P2P links
    between clients
  • Less channel access time is needed ? increased
    throughput
  • Challenges
  • How to build an efficient multi-hop tree rooted
    at the AP?
  • How to conduct fair bandwidth allocation in a
    multi-hop topology?
  • Objective
  • Improve throughput without sacrificing fairness
    in multi-hop WLAN

9
Our Results
  • Max-min throughput fair allocation in multi-hop
    WLANs
  • No client can get more bandwidth without
    decreasing the bandwidth of clients with the same
    or less bandwidth
  • Max-min time fair allocation in multi-hop WLANs
  • No client can get more time share without
    decreasing the time share of clients with the
    same or less time share
  • Multi-hop tree construction
  • Iteratively search for a better tree topology
    such that fair bandwidth within the new tree
    leads to better client throughput

10
Fairness
  • Max-min throughput fairness
  • A feasible bandwidth allocation B is max-min
    throughput fair if
  • No client can be allocated more bandwidth without
    decreasing the bandwidth of clients with the same
    or less bandwidth
  • Max-min time fairness
  • A feasible bandwidth allocation B is max-min time
    fair if
  • For each node i in the multi-hop tree, assume the
    same amount of total bandwidth allocated to nodes
    in the sub-tree rooted at node i
  • Neither node i nor any child of it can be
    assigned more time share of node i without
    decreasing the time share of some of them with
    equal or less time share of node i
  • Gives more bandwidth to forwarding nodes and
    hence
  • Encourages clients to serve as forwarding nodes
  • Leads to more skewed bandwidth allocation but
    higher throughput

11
Methodology
Focus on the up-link direction, and solve the
bandwidth allocation within a single-AP tree first
More aggregate throughput 55/6
Aggregate throughput 44/5
12
Max-min throughput fairness (MMFA)
A bandwidth allocation B is feasible if and only
if it is feasible at every node i with
Pi
i
Qij1, j2, j3
j3
j2
j1
13
Max-min throughput fairness (MMFA)
General idea
  • Fair bandwidth allocation within a multi-hop tree
    structure is recursively done in a bottom-up
    order
  • During the bottom-up recursive process, at each
    node i, MMFA performs the pump-and-drain
    operation
  • First pump the node, i.e., allocate to the node
    a bandwidth such that it is fully loaded or even
    overloaded
  • Then drain the nodes in the sub-tree rooted at
    that node, i.e., decrease their allocated
    bandwidth such that the resulting bandwidth
    allocation is feasible and throughput fair within
    the sub-tree

14
Max-min throughput fairness (MMFA)
Detailed design
  • Each node i maintains and reports to its parent
    the following info.

15
Max-min throughput fairness (MMFA)
  • Pump

16
Max-min throughput fairness (MMFA)
  • Drain

17
  • Original case of max-min throughput fair
    allocation
  • in a single-hop WLAN

r8, r9 11 Mbps r5, r6, r7 5.5 Mbps r1, r2, r3,
r4 2 Mbps
  • 2bi/11 3bi/5.5 4bi/2 1
  • 4bi 12bi 44bi 22
  • bi 11/30
  • aggregate throughput 99/30 3.3 Mbps

18
  • Example of max-min throughput fair allocation
    using MMFA
  • in a multi-hop WLAN (all links have a 11 Mbps
    data rate)

At node 7 Pump b711 W711/112(11/11)3 gt
1 Drain n4T4nN7L71 d(3-1)/(1/11n4/11n4/1
1)22/3 b7b411-22/311/3
At node 5 Pump b511 W511/114(11/11)5 gt
1 Drain n1T1nN5L51n2 d(5-1)/(1/112(n1/1
1n1/11))44/5 b5b1b211-44/511/5
19
At node 9 Pump b911/3, B722/3
W91/3B7/11B7/115/3 gt 1 Drain
n7T7nN9L92 d(5/3-1)/(1/11n7/11n7/11)22/
15 b9b7b411/3-22/1511/5
At node 8 Pump b811/3, B533/5, B622/3
W81/323/522/343/15 gt 1 Drain
n6T6nN8L82 d(43/15-1)/(1/11n6/11n6/11)
4211/75 gt L8L8- L8L8-1 gt
b8b6b3b5b1b211/5 Drain again
W81/52(3/52/5)11/5 gt 1 d(11/5-1)/(1/115/115
/11)6/5, so 11/5-6/51
20
Finally Drain at the AP B86, B933/5 WAP6/113/
563/55 gt 1, n93 d(63/55-1)/(n9/11)8/15 Thus
b9b7b411/5-8/155/3
Aggregate throughput is maximized 11Mbps
21
Max-min time fairness
t
Pi
i
j
Tj 3
22
Max-min time-based fairness allocation (TBFA)
General idea
  • Fair bandwidth allocation within a multi-hop tree
    structure is recursively done in a bottom-up
    order
  • During the bottom-up recursive process, at each
    node i, TBFA performs the pump-and-drain
    operation
  • First pump the node, i.e., allocate to the node
    a bandwidth such that it is fully loaded or even
    overloaded
  • Then drain the nodes in the sub-tree rooted at
    that node, i.e., decrease their allocated
    bandwidth such that the resulting bandwidth
    allocation is feasible and time fair within the
    sub-tree

23
Max-min time-based fairness allocation (TBFA)
  • Pump

24
Max-min time-based fairness allocation (TBFA)
  • Drain

25
  • Original case of max-min time fair allocation
  • in a single-hop WLAN

r8, r9 11 Mbps r5, r6, r7 5.5 Mbps r1, r2, r3,
r4 2 Mbps
  • time share at each node 1/9
  • b8b911(1/9)11/9
  • b5b6b75.5(1/9)11/18
  • b1b2b3b42(1/9)2/9
  • aggregate throughput 5.2 Mbps

26
  • Example of max-min time fair allocation using
    TBFA
  • in a multi-hop WLAN (all links have a 11 Mbps
    data rate)

At node 7 subtree size G72 Time share
T77T741/2 Bp4T74/(1/111/11)11/4b4
b7111/211/2
At node 5 subtree size G53 Time share
T55T51T521/3 Bp1T51/(1/111/11)11/6b1 Bp2Bp
111/6b2 b5111/311/3
27
Drain node 7 subtree size G41 d(33/4-11/3)/(1
1G4/(1/111/11)) 5/18 Time share T77
T741/2-5/182/9 b7112/922/9,
b4(11/2)(2/9)11/9
At node 9 Time share T991/3, T972/3 Bp7T97/(1/
111/11)11/3 b9111/311/3 B711/42/1133/4
gt Bp7
28
At node 8 Time share T881/6, T861/3,
T851/2 Bp6T86/(1/111/11)11/6 lt
B633/4 Bp5T85/(1/111/11)11/4 lt B522/3
b8111/611/6
Drain node 5 G1G21 Time share
T55T51T521/3 d(22/3-11/4)/(112/(1/111/11))
5/24 Time share T55T51T521/3-5/241/8
b5111/811/8 b1b2(11/2)(1/8)11/16
Drain node 6 G31 Time share T661/2,
T631/2 d(33/4-11/6)/(11G3/(1/111/11)) 7/18
Time share T66 T631/2-7/181/9
b6111/911/9, b3(11/2)(1/9)11/18
29
Drain node 9 Time share T991/3, T972/3 with
G72 d(22/3-55/12)/(11G7/(1/111/11))1/8 Ti
me share T991/3-1/85/24 b911(5/24)55/24 Tim
e share T972/3-2(1/8)5/12 Bp7T97/(1/111/11)5
5/24 lt B711/3 Drain node 7 (continued in next
slide..)
Finally Drain at the AP Time share TAP91/3,
TAP82/3 Bp9TAP9/(1/11)11/3 lt
B922/3 Bp8TAP8/(1/11)22/3 gt B877/12 TAP8(77/1
2)/117/12 No Drain needed at node
8! TAP91-7/125/12 Bp911(5/12)55/12 lt B922/3
30
Drain node 7 Time share T77T742/9 with
G41 d(11/3-55/24)/(11G4/(1/111/11))1/12 T
ime share T77T742/9-1/125/36
b7115/3655/36 b4(11/2)(5/36)55/72
Aggregate throughput is maximized 11Mbps
31
Tree Construction
  • Start with a default WLAN topology
  • For example, a one-hop association based on RSSI
  • Iteratively search for a better tree topology
  • Such that fair bandwidth allocation within the
    new tree leads to a better client bandwidth
    vector
  • Until no better tree can be found
  • This iterative search can also be used to handle
    client arrival and client leave
  • If a client arrives, quickly associate it with
    some AP
  • For example, the AP with the strongest RSSI
  • If a client leaves, quickly associate its
    children with some AP
  • Then iteratively search for a better tree
    topology

32
  • A good multi-hop tree structure

By migrating node 3 from node 6 to node 7!
Original tree structure
Equal bandwidth share at each node 11/9 And the
aggregate throughput is also maximized 11Mbps
33
Backward Compatibility
  • Legacy client devices can work as usual
  • Upon arrival, simply associate with the AP with
    the strongest RSSI
  • Not necessary to participate in tree construction
  • Allocated bandwidth changes as the tree topology
    evolves
  • Upon leave, simply disconnect from the AP
  • No children, no additional processing needed
  • Incremental deployment is enabled and encouraged
  • Investing to upgrade client device will lead to
    perceivable boost in performance, in spite of the
    existence of other legacy client devices

34
Evaluation
  • Network settings
  • 30 clients
  • Scenario I 150m150m One AP at each corner
  • Scenario II 300m300m One AP at each corner
  • Scenario III 150m150m One AP at the center
  • Scenario IV 300m300m One AP at the center
  • Link rates
  • 0m-50m 11 Mbps
  • 50m-80m 5.5 Mbps
  • 80m-120m 2 Mbps
  • 120m-150m 1 Mbps
  • 150m N/A

35
Evaluation
36
Evaluation
37
Evaluation
38
Evaluation
39
Evaluation
40
(No Transcript)
41
Summary
  • Unpractical interference model assumed (Truth
    even though nodes are not associated with each
    other, they still interfere!).
  • The extension part to the case of multiple APs is
    weak (Trees need to be node-disjoint).
  • This work fails to address how to construct a
    good multi-hop tree structure (only simple
    iterative heuristic is suggested), which should
    play a critical component in throughput
    optimization and fairness provisioning.
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