421 research outputs found
Interference Mitigation Through Limited Receiver Cooperation: Symmetric Case
Interference is a major issue that limits the performance in wireless
networks, and cooperation among receivers can help mitigate interference by
forming distributed MIMO systems. The rate at which receivers cooperate,
however, is limited in most scenarios. How much interference can one bit of
receiver cooperation mitigate? In this paper, we study the two-user Gaussian
interference channel with conferencing decoders to answer this question in a
simple setting. We characterize the fundamental gain from cooperation: at high
SNR, when INR is below 50% of SNR in dB scale, one-bit cooperation per
direction buys roughly one-bit gain per user until full receiver cooperation
performance is reached, while when INR is between 67% and 200% of SNR in dB
scale, one-bit cooperation per direction buys roughly half-bit gain per user.
The conclusion is drawn based on the approximate characterization of the
symmetric capacity in the symmetric set-up. We propose strategies achieving the
symmetric capacity universally to within 3 bits. The strategy consists of two
parts: (1) the transmission scheme, where superposition encoding with a simple
power split is employed, and (2) the cooperative protocol, where
quantize-binning is used for relaying.Comment: To appear in IEEE Information Theory Workshop, Taormina, October
2009. Final versio
Interference Mitigation Through Limited Receiver Cooperation
Interference is a major issue limiting the performance in wireless networks.
Cooperation among receivers can help mitigate interference by forming
distributed MIMO systems. The rate at which receivers cooperate, however, is
limited in most scenarios. How much interference can one bit of receiver
cooperation mitigate? In this paper, we study the two-user Gaussian
interference channel with conferencing decoders to answer this question in a
simple setting. We identify two regions regarding the gain from receiver
cooperation: linear and saturation regions. In the linear region receiver
cooperation is efficient and provides a degrees-of-freedom gain, which is
either one cooperation bit buys one more bit or two cooperation bits buy one
more bit until saturation. In the saturation region receiver cooperation is
inefficient and provides a power gain, which is at most a constant regardless
of the rate at which receivers cooperate. The conclusion is drawn from the
characterization of capacity region to within two bits. The proposed strategy
consists of two parts: (1) the transmission scheme, where superposition
encoding with a simple power split is employed, and (2) the cooperative
protocol, where one receiver quantize-bin-and-forwards its received signal, and
the other after receiving the side information decode-bin-and-forwards its
received signal.Comment: Submitted to IEEE Transactions on Information Theory. 69 pages, 14
figure
Capacity Theorems for the Fading Interference Channel with a Relay and Feedback Links
Handling interference is one of the main challenges in the design of wireless
networks. One of the key approaches to interference management is node
cooperation, which can be classified into two main types: relaying and
feedback. In this work we consider simultaneous application of both cooperation
types in the presence of interference. We obtain exact characterization of the
capacity regions for Rayleigh fading and phase fading interference channels
with a relay and with feedback links, in the strong and very strong
interference regimes. Four feedback configurations are considered: (1) feedback
from both receivers to the relay, (2) feedback from each receiver to the relay
and to one of the transmitters (either corresponding or opposite), (3) feedback
from one of the receivers to the relay, (4) feedback from one of the receivers
to the relay and to one of the transmitters. Our results show that there is a
strong motivation for incorporating relaying and feedback into wireless
networks.Comment: Accepted to the IEEE Transactions on Information Theor
Incremental Relaying for the Gaussian Interference Channel with a Degraded Broadcasting Relay
This paper studies incremental relay strategies for a two-user Gaussian
relay-interference channel with an in-band-reception and
out-of-band-transmission relay, where the link between the relay and the two
receivers is modelled as a degraded broadcast channel. It is shown that
generalized hash-and-forward (GHF) can achieve the capacity region of this
channel to within a constant number of bits in a certain weak relay regime,
where the transmitter-to-relay link gains are not unboundedly stronger than the
interference links between the transmitters and the receivers. The GHF relaying
strategy is ideally suited for the broadcasting relay because it can be
implemented in an incremental fashion, i.e., the relay message to one receiver
is a degraded version of the message to the other receiver. A
generalized-degree-of-freedom (GDoF) analysis in the high signal-to-noise ratio
(SNR) regime reveals that in the symmetric channel setting, each common relay
bit can improve the sum rate roughly by either one bit or two bits
asymptotically depending on the operating regime, and the rate gain can be
interpreted as coming solely from the improvement of the common message rates,
or alternatively in the very weak interference regime as solely coming from the
rate improvement of the private messages. Further, this paper studies an
asymmetric case in which the relay has only a single single link to one of the
destinations. It is shown that with only one relay-destination link, the
approximate capacity region can be established for a larger regime of channel
parameters. Further, from a GDoF point of view, the sum-capacity gain due to
the relay can now be thought as coming from either signal relaying only, or
interference forwarding only.Comment: To appear in IEEE Trans. on Inf. Theor
Recommended from our members
Capacity of interference networks : achievable regions and outer bounds
textIn an interference network, multiple transmitters communicate with multiple receivers using the same communication channel. The capacity region of an interference network is defined as the set of data rates that can be simultaneously achieved by the users of the network. One of the most important example of an interference network is the wireless network, where the communication channel is the wireless channel. Wireless interference networks are known to be interference limited rather than noise limited since the interference power level at the receivers (caused by other user's transmissions) is much higher than the noise power level. Most wireless communication systems deployed today employ transmission strategies where the interfering signals are treated in the same manner as thermal noise. Such strategies are known to be suboptimal (in terms of achieving higher data rates), because the interfering signals generated by other transmitters have a structure to them that is very different from that of random thermal noise. Hence, there is a need to design transmission strategies that exploit this structure of the interfering signals to achieve higher data rates. However, determining optimal strategies for mitigating interference has been a long standing open problem. In fact, even for the simplest interference network with just two users, the capacity region is unknown. In this dissertation, we will investigate the capacity region of several models of interference channels. We will derive limits on achievable data rates and design effective transmission strategies that come close to achieving the limits. We will investigate two kinds of networks - "small" (usually characterized by two transmitters and two receivers) and "large" where the number of users is large.Electrical and Computer Engineerin
Cooperative Protocols for Relay and Interference Channels with Half-Duplex Constraint
Enabling cooperation among nodes of a wireless network can significantly reduce the required
transmit power as well as the induced intra-network interference. Due to the practical
half-duplexity constraint of the cooperating nodes, they are prohibited to simultaneously
transmit and receive data at the same time-frequency resource. The purpose of this
dissertation is to illustrate the value of cooperation in such an environment. To understand
how to cooperate efficiently, information theory is employed as a useful tool, which not only
determines the fundamental limits of communication (i.e., capacity) over the considered
network, but also provides insights into the design of a proper transmission scheme for that
network.
In this thesis, two simple but yet important types of wireless networks, namely Relay
Channel, and Interference Channel are studied. In fact, these models constitute building
blocks for larger networks. The first considered channel is a diamond-shaped relay channel
consisting of a source, a destination, and two parallel relays. The second analyzed channel
is an interference channel composed of two transmitter-receiver pairs with out-of-band
transmitter cooperation, also referred to as conferencing encoders. While characterizing
the capacity of these channels are difficult, a simpler and a more common approach is to
find an achievable scheme for each channel that ensures a small gap from the capacity for
all channel parameters.
In chapter 2, the diamond relay channel is investigated in detail. Because of the half-duplex
nature of the relays, each relay is either in transmit or receive mode, making
four modes possible for the two-relay combination, specifically, 1) broadcast mode (both
relays receive) 2,3) routing modes (one relay transmits, another receives) 4) multiple-access
mode (both relays transmit). An appropriate scheduling ( i.e., timing over the modes) and
transmission scheme based on the decode-and-forward strategy are proposed and shown
to be able to achieve either the capacity for certain channel conditions or at most 3.6 bits below the capacity for general channel conditions. Particularly, by assuming each
transmitter has a constant power constraint over all modes, a parameter Δ is defined,
which captures some important features of the channel. It is proven that for Δ=0 the
capacity of the channel can be attained by successive relaying, i.e., using modes 2 and 3
defined above in a successive manner. This strategy may have an infinite gap from the
capacity of the channel when Δ≠0. To achieve rates as close as 0.71 bits to the capacity,
it is shown that the cases of Δ>0 and Δ<0 should be treated differently. Using new
upper bounds based on the dual problem of the linear program associated with the cut-set
bounds, it is proven that the successive relaying strategy needs to be enhanced by an
additional broadcast mode (mode 1), or multiple access mode (mode 4), for the cases of Δ0, respectively. Furthermore, it is established that under average power
constraints the aforementioned strategies achieve rates as close as 3.6 bits to the capacity
of the channel.
In chapter 3, a two-user Gaussian Interference Channel (GIC) is considered, in which
encoders are connected through noiseless links with finite capacities. The setup can be
motivated by downlink cellular systems, where base stations are connected via infrastructure
backhaul networks. In this setting, prior to each transmission block the encoders
communicate with each other over the cooperative links. The capacity region and the
sum-capacity of the channel are characterized within some constant number of bits for
some special classes of symmetric and Z interference channels. It is also established that
properly sharing the total limited cooperation capacity between the cooperative links may
enhance the achievable region, even when compared to the case of unidirectional transmitter
cooperation with infinite cooperation capacity. To obtain the results, genie-aided upper
bounds on the sum-capacity and cut-set bounds on the individual rates are compared with
the achievable rate region. The achievable scheme enjoys a simple type of Han-Kobayashi
signaling, together with the zero-forcing, and basic relaying techniques
- …