a perspective on network interference and multiple access control

A Perspective on Network Interference and Multiple Access Control

Michael J. NeelyUniversity of Southern California

May 2008

Capacity Region

1 Wireless Link = AWGN Channel 1 Wireless Link = ON/OFF Channel

“information theory” “queueing theory”

+Symbols

C = log(1 + SNR)

Packet Arrivals Pr[ON]=p

C = p packets/slotCapacity: Capacity:

Mathematical Models for a Wireless System (two meaningful perspectives)

-Symbol-by-symbol transmission

-Capacity optimizes bit rate over all coding of symbols (Shannon Theory)

-Slot-by-slot packet transmission

-Capacity is obvious (Basic Queueing Theory)

N-User Gauss. Broadcast Downlink N-User Downlink (Fading Channels)

bitsbits

ON/OFF

-Symbol-by-symbol transmission

-Capacity is a REGION of achievable bit rates

-Optimizes coding of symbols

-Opportunistic scheduling

-Observe ON/OFF channels, decide which queue to serve (“collision free” = easy)

-Capacity is a REGION of achievable rates

N-User Gauss. Broadcast Downlink N-User Downlink (Fading Channels)

bitsbits

ON/OFF

Capacity Region:all (1,…, N) s.t. Capacity Region: all (1,…, N) s.t.

for all subsets K of users.

[Tassiulas & Ephremides 93](degraded Gauss. BC)

N-Node Static Multi-Hop Network(multiple sources and destinations)

-Symbol-by-Symbol Transmissions-Optimize the coding

Capacity = ???

-Optimize Scheduling/Routing-General Interference Sets

Capacity = Known Exactly (Multi-Commodity Flow Subject to “Graph Family” Link Constraints)

[Backpressure, Tassiulas, Ephremides 92]

N-Node MANET

“info theory” “queueing theory”

Capacity = ???

N-Node MANET

Capacity = Known Exactly

[Neely, Modiano, et. al. JSAC 05, IT 05]

-Ergodic Mobility-Optimize the Scheduling/Routing-General Channel Interference Models (SINR, Collision Sets, etc.)

N-Node MANET

Capacity = ???

N-Node MANET

Capacity = ???

N-Node MANET

Capacity = ???

N-Node MANET

Capacity = ???

N-Node MANET

Capacity = ???

N-Node MANET

Capacity = ???

N-Node MANET

Capacity = ???

N-Node MANET

Capacity = ???

N-Node MANET

Capacity = ???

N-Node MANET

Capacity = ???

N-Node MANET

Capacity Region

The Theory: Generalized Max-Weight Matches, Backpressure

Georgiadis, Neely, Tassiulas, Foundations and Trends in Networking, 2006.http://www-rcf.usc.edu/~mjneely/pdf_papers/NOW_stochastic_nets.pdf

General Interference Models

Multi-hop

Max: [Wl(t)C(I(t), S(t)) - VCostl(t)]

Control Action Topology State

Capacity Region

Multi-hop

Capacity Region

Multi-hop

Capacity Region

*Max: Wl(t)C(I(t), S(t))

*[Neely Thesis 03] *[Georgiadis, Neely, Tassiulas, NOW F&T 2006] http://www-rcf.usc.edu/~mjneely/pdf_papers/NOW_stochastic_nets.pdf

*Maximizing to within a factor yields -factor throughput region!

Multi-hop

The Issues: (A comparison to info theory)

-Capacity log(1+SNR) known exactly

-Randomized Coding can achieve capacity but… …Complexity and Delay!

-Shannon Created the Challenge:

Prompted years of research in thedesign of efficient, low complexityCodes that perform near capacity(analytically or experimentally) was the research.

Turbo-codes work well experimentally!

-Capacity Region characterized exactly (in terms of optimization)

-Randomized Scheduling can achieve full Capacity… [Tassiulas 98] [Modiano, Shah, Zussman 2006] [Erylimaz, Ozdaglar, Modiano 07] [Shakkottai 08] [Shah 08] [Jiang, Walrand 08], etc.

-But Complexity and Delay is the Challenge! [Neely et al. 02], [Shah, Kopikare 02], etc.

Final Slide: Two Suggested Approaches: 1) The Analogy:

Information Theory ==> Design of Codes to work well in practice, Turbo Codes

Network Queue Theory ==> Design of practical MAC Scheduling Protocols, Implementation, “Turbo” Multiple Access

Eg: *[Bayati, Shah, Sharma 05] (uses iterative detection theory) [Modiano, Shah, Zussman 2006], [Erylimaz, Ozdaglar, Modiano 07] [Shakkottai 08], [Shah 08], [Jiang, Walrand 08],etc.

2) “Beyond Links”: Combine PHY layer and Networking

MIMO [Kobayashi, Caire 05]Cooperative Comms [Yeh, Berry 05]Network Coding [Ho, Viswanathan 05], [Lun, Medard 05]Multi-Receiver Diversity [Neely 06] broadcasting

a perspective on network interference and multiple access control

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