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Multi-User Diversity in Single-Radio OFDMA Ad Hoc Networks Based on Gibbs Sampling. Marzieh Veyseh J.J. Garcia-Luna-Aceves Hamid R. Sadjadpour. Motivation. Channel 1. Channel 1. Concurrency Frequency Code Space. Channel 3. fc3. fc4. fc5. fc1. fc2. Code 1. Channel 1. Code 3.

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Multi-User Diversity in Single-Radio OFDMA Ad Hoc Networks Based on Gibbs Sampling

Marzieh Veyseh

J.J. Garcia-Luna-Aceves

Hamid R. Sadjadpour


Motivation
Motivation

Channel 1

Channel 1

Concurrency

  • Frequency

  • Code

  • Space

Channel 3

fc3

fc4

fc5

fc1

fc2

Code 1

Channel 1

Code 3

Code 2

Code 3

Code 1

fc

fc

fc

fc


Motivation1
Motivation

t1

Adaptivity

  • Time

  • Frequency, through different modulations…

    Diversity

    To use fading in our advantage and to improve rate…

  • MIMO

  • OFDAM-Multiuser diversity

t2

t3

t5

t1

t3

t4


Ofdma
OFDMA

Subchannel i

Subchannel 3

Subchannel 1

Subchannel 2

Subchannel 4

fc

  • Proposed for infrastructure-based OFDMA networks

  • We think that utilizing OFDMA in ad hoc networks gives us the ability to achieve our goals:

    • Concurrency: multiple nodes use different portions of BW

    • Diversity: multi-user diversity

    • Adaptivity: subchannels can have different sizes


  • Ofdma synchronization
    OFDMA Synchronization

    C-Tx

    C-Tx

    • In an ad hoc multi-transmitter scenario to avoid loss of orthogonality at a common neighbor to multiple transmitters, a quasi-synchronousnetwork is required.

    • Quasi-synchronous : transmitter start sending data at the same time

    • Multi-transmission synchronization achieved via control message exchanges


    Previous work
    Previous work

    • Not much work on protocols for OFDMA for ad hoc networks

    • CTRMA: In our previous work, we assigned non-overlapping channels unique within the two hop neighborhood based on some priority order. [OFDMA Based Multiparty Medium Access Control in Wireless Ad Hoc Networks, ICC, 09])

    • CBD: We added diversity when distributing the assigned subchannels among neighbors[Cross-Layer Channel Allocation Protocol for OFDMA Ad Hoc Networks, Globecom 10]


    Gibbs sampling

    GSA

    Gibbs Sampling

    a

    C-Tx_1

    C-Rx

    Goal:

    • Maximize concurrency

      • Design a MAC that assigns subchannels to each directional link on-demand and based on the present interference, and node’s needs

    • Maximize diversity

      • Subchannel selection should be done based on minimizing fading

      • Gibbs sampling previously used to distribute

        channels among multiple

        802.11 Aps :

        min direct interference

    C-Tx_2

    C-Rx

    b


    Gibbs sampling1
    Gibbs Sampling

    • Graph , and state X…want to find


    GSA

    Gibbs Subchannel Assignment (GSA)

    • We propose to use Gibbsian method by defining a new energy model and a MAC protocol that works to select subchannels (Schannel) for each communicating link.

    b

    u

    v

    C-Tx (c)

    C-Tx (a)

    C-Rx

    Subchannel k


    MDMA

    a

    c

    Freq

    C-Tx

    b

    d

    RTM-T

    Control

    FreeTx Schannel_1

    FreeTx Schannel_2

    time


    MDMA

    MDMA

    a

    c

    Freq

    C-Tx

    b

    d

    RTM-T

    Control

    FreeTx Schannel_1

    Pilot

    FreeTx Schannel_2

    Pilot

    time


    MDMA

    a

    c

    Freq

    C-Tx

    SINR(k)>Thr

    a b c d

    v

    b

    d

    e

    RTM-T

    Control

    CTR

    FreeTx Schannel_1

    Pilot

    FreeTx Schannel_2

    Pilot

    time


    MDMA

    a

    c

    Freq

    C-Tx

    a b c d

    b

    d

    RTM-T

    Control

    CTR

    FreeTx Schannel_1

    Pilot

    Data: C-Tx->a

    Broadcast

    FreeTx Schannel_2

    Pilot

    Data: C-Tx->b

    Broadcast

    time


    MDMA

    c

    a

    Freq

    C-Rx

    b

    d

    RTM-R

    Control

    FreeRx Schannel_1

    FreeRx Schannel_2

    time


    MDMA

    c

    a

    Freq

    C-Rx

    b

    d

    RTM-R

    Control

    a b c d

    FreeRx Schannel_1

    CTT

    a b c d

    FreeRx Schannel_2

    CTT

    time


    MDMA

    c

    a

    Freq

    C-Rx

    b

    d

    STT

    RTM-R

    Control

    a b c d

    FreeRx Schannel_1

    CTT

    a b c d

    FreeRx Schannel_2

    CTT

    time


    MDMA

    c

    a

    Freq

    C-Rx

    b

    d

    STT

    RTM-R

    Control

    a b c d

    FreeRx Schannel_1

    Data: a->C-Rx

    CTT

    a b c d

    FreeRx Schannel_2

    CTT

    Data: b->C-Rx

    time


    Analysis

    Range =

    a

    v

    v

    u

    Average =4


    Analysis

    1.3

    v

    v

    a

    u


    Analysis result
    Analysis Result

    Analytically GSA is outperforming ideal scheduling

    2.6 times


    Matlab Simulations

    Simulations

    a

    C-Tx

    b

    u

    c


    Matlab Simulations

    Simulations

    A

    B

    A

    B

    C

    B

    A


    Matlab Simulations

    MDMA

    • GSA increases concurrency comparing to CBD

    2.3 times

    63%


    Qualnet Simulations

    MDMA

    1.6 times


    Conclusion

    Conclusion

    • Previous cross-layer MAC fail to effectively utilize OFDMA

    • We improved our previous works by

      • Utilizing Gibbs method

      • Increasing two-hop neighbor concurrency

      • Attaining diversity

    • Our analysis and simulations proved that MDMA’s performance with the same BW is

      • 1.6 times better than CBD

      • 2.2 times better than CTRMA

      • 2.4 times better than traditional multi-channel networks

    • Future work

      • Mobility

      • 802.11n OFDMA



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