97 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
On Cooperative Multiple Access Channels with Delayed CSI at Transmitters
We consider a cooperative two-user multiaccess channel in which the
transmission is controlled by a random state. Both encoders transmit a common
message and, one of the encoders also transmits an individual message. We study
the capacity region of this communication model for different degrees of
availability of the states at the encoders, causally or strictly causally. In
the case in which the states are revealed causally to both encoders but not to
the decoder we find an explicit characterization of the capacity region in the
discrete memoryless case. In the case in which the states are revealed only
strictly causally to both encoders, we establish inner and outer bounds on the
capacity region. The outer bound is non-trivial, and has a relatively simple
form. It has the advantage of incorporating only one auxiliary random variable.
We then introduce a class of cooperative multiaccess channels with states known
strictly causally at both encoders for which the inner and outer bounds agree;
and so we characterize the capacity region for this class. In this class of
channels, the state can be obtained as a deterministic function of the channel
inputs and output. We also study the model in which the states are revealed,
strictly causally, in an asymmetric manner, to only one encoder. Throughout the
paper, we discuss a number of examples; and compute the capacity region of some
of these examples. The results shed more light on the utility of delayed
channel state information for increasing the capacity region of state-dependent
cooperative multiaccess channels; and tie with recent progress in this
framework.Comment: 54 pages. To appear in IEEE Transactions on Information Theory. arXiv
admin note: substantial text overlap with arXiv:1201.327
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
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