Relaying%20in%20network%20with%20multiple%20sources%20has%20aspects%20not%20present%20in%20the%20relay%20networks:

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Relaying in Networks with Multiple Communicating
Pairs Interference Forwarding
Ivana Maric, Ron Dabora and Andrea Goldsmith
Summary
Channel Model
Motivation
Introduction
ACHIEVEMENT DESCRIPTION

• Relaying in network with multiple sources has
  aspects not present in the relay networks
• Relaying messages to one destination increases
  interference to others
• Relays can jointly encode messages from multiple
  sources
• There are many relevant encoding strategies
• Encoding strategies for networks with multiple
  sources are not well understood and developed
• Current approach multihop routing
• Time shares between data streams (no joint
  encoding)
• Does not exploit broadcast or interference
• We consider smallest network that captures
  relaying for multiple sources the interference
  channel with a relay
• Previous work
• Sridharan, Vishwanath, Jafar and Shamai ISIT,
  2008
• Rates and degrees of freedom when the relay is
  cognitive
• Sahin and Erkip Asilomar 2007, CTW 2008

Various relaying strategies for forwarding
information to intended receivers have been
proposed Capacity of networks are still unknown
one of the key reasons we dont know how to
handle and exploit interference

• In relay networks
• Relays forward data for a single
  source-destination pair
• Cooperative strategies are well developed and
  known to bring gains
• Cooperative strategies exploit the broadcast
  nature of wireless medium
• In networks with multiple sources
• The center issue is coping with interference
  created by simultaneous transmissions
• Networks with multiple sources contain broadcast,
  multicast, relay and interference channel
  elements as their building blocks

ASSUMPTIONS AND LIMITATIONS To
demonstrate interference forwarding gains, we
considered scenario in which the relay can
observe the signal from only one source and can
thus forward only one of the two messages MAIN
RESULT We determined conditions under which
having a relay enhance the interference improves
the performance. We also obtained capacity in the
special case HOW IT WORKS The relay forwards
a message to a receiver that is not interested
in that message, thus increasing the interference
at that receiver. This allows the receiver to
decode and cancel the interference, and decode
its message in the clear channel

• Compare the rates to outer bounds
• Further develop strategies for forwarding in the
  presence of interference
• Consider more general scenarios in which
  interference enhancement needs to be combined
  with other relaying strategies
• Apply this strategy to larger networks

END-OF-PHASE GOAL
STATUS QUO

• Two messages

• Rates

In networks with multiple sources, relays can
help beyond forwarding useful information, by
increasing interference at the receivers. This
allows receivers to decode the interference and
cancel it prior to decoding their desired messages

• Decoding

• Encoding

COMMUNITY CHALLENGE
NEW INSIGHTS

• We present new relaying strategy interference
  forwarding

Prize level Capacity results for networks with
multiple sources
We proposed a new relaying strategy for networks
with multiple sources. We showed that it can
improve the rate performance and that it achieves
capacity in a certain scenario.
Capacity Result
Gaussian Channels
Assumptions
Achievable Rates

• We define strong interference conditions as

• The presence of the relay changes the strong
  interference conditions
• The relay can push a receiver into the strong
  interference regime where decoding of interfering
  message is optimal
• We evaluated these results for the Gaussian
  channels

• Theorem Any rate pair (R1,R2) that satisfies

(2)
satisfied for any distribution p(x1)p(x2,x3)p(y1,y
2x1,x2,x3)
?
(1)

• Conditions (2) are analogous to the strong
  interference conditions derived by Costa and El
  Gamal for the interference channel
• Conditions (2) imply that the flow of
  information from each source to the non-intended
  receiver is better than to the intended receiver
• Consequently, receivers can decode the undesired
  messages for free and hence experience no
  interference

• To illustrate gains from interference forwarding,
  we consider the special case (shown in Figures)
• The relay cannot observe signal sent from source
  1
• Then, it can only forward message W2 thus
  improving rate R2
• From the perspective of the other receiver, the
  relay is interference forwarding
• Can relay help also receiver 1 and improve rate
  R1?

for any distribution p(x1)p(x2,x3)p(y1,y2x1,x2,x3
)
Noise Powers

• The channel degradedness condition

• Rates in the Thm. are achieved by
• Single-user encoding at the encoder 1 to send W1
• Decode-and-forward at the encoder 2 and the
  relay to send message W2

(3)

• Theorem When (2)-(3) hold, rates (1) are the
  capacity region.
• In strong interference, decoding both messages is
  optimal

Insights and Future Work
Comparison with Rate Splitting
Numerical Results for Gaussian Channel
Conclusions

• Without the relay, the channel reduces to the
  interference channel (IC)
• The best known rates for IC are achieved with
  rate splitting

• Demonstrated gains from interference forwarding
• Interference forwarding
• Can improve the performance through
  interference cancellation
• Can hurt the receiver by increasing interference
• Achieves capacity in a special scenario of
  strong interference
• It pushes receiver in strong interference
  regime where the receiver can decode both
  messages
• We determined conditions under which decoding
  interference is optimal
• Interference forwarding
• Can be realized through decode, compress
  -and-forward
• Can be combined with other encoding schemes

• Insights
• When relaying for multiple sources
• Jointly encode messages (network coding approach)
• Exploit broadcast
• Forward messages and interference
• Future work
• Develop and evaluate transmission strategies that
  unify above approaches
• Analyze the general case of the interference
  channel with a relay
• Further develop strategies for relaying in the
  presence of interference

• Without the relay interference channel in
  strong interference
• With relay, h130 no interference forwarding
• With relay, h13gt0 interference forwarding
• Interference forwarding enlarges the rate region
• It facilitates interference cancellation

• In the case when the relay can only use
  interference forwarding, can the relay still
  help?
• We compare the rates achieved with and without
  the relay

• Proposition When

strong relay-rcvr1 link
strong source2-relay link
for any distribution p(x1)p(x2,x3)p(y1,y2x1,x2,x3
)
interference forwarding outperforms rate
splitting (no relaying).