For the fully connected K user wireless interference channel where coefficients are time-varying and drawn from a continuous distribution, sum capacity is characterized as C(SNR)=K/2log(SNR)+o(log(SNR)) . Thus, almost surely has K/2 degrees of freedom. Achievability based on idea alignment. Examples also provided channels with constant (not time-varying) exactly achieved by alignment at all SNR values.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Cognitive radios hold tremendous promise for increasing spectral efficiency in wireless systems. This paper surveys the fundamental capacity limits and associated transmission techniques different network design paradigms based on this promising technology. These are unified by definition of a cognitive radio as an intelligent communication device that exploits side information about its...

We provide an overview of the extensive results on Shannon capacity single-user and multiuser multiple-input multiple-output (MIMO) channels. Although enormous gains have been predicted for such channels, these predictions are based somewhat unrealistic assumptions about underlying time-varying channel model how well it can be tracked at receiver, as transmitter. More realistic dramatically impact potential MIMO techniques. For channels there multiple theoretic definitions and, each...

Recent results establish the optimality of interference alignment to approach Shannon capacity networks at high SNR. However, extent which can be aligned over a finite number signalling dimensions remains unknown. Another important concern for schemes is requirement global channel knowledge. In this work, we provide examples iterative algorithms that utilize reciprocity wireless achieve with only local knowledge each node. These also numerical insights into feasibility are not yet available...

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We provide achievability as well converse results for the degrees of freedom region a multiple-input multiple-output (MIMO) <emphasis><formula formulatype="inline"><tex>$X$</tex></formula></emphasis> channel, i.e., system with two transmitters, receivers, each equipped multiple antennas, where independent messages need to be conveyed over fixed channels from transmitter receiver. The inner and...

Recent results establish the optimality of interference alignment to approach Shannon capacity networks at high SNR. However, extent which can be aligned over a finite number signalling dimensions remains unknown. Another important concern for schemes is requirement global channel knowledge. In this work we provide examples iterative algorithms that utilize reciprocity wireless achieve with only local knowledge each node. These also numerical insights into feasibility are not yet available in theory.

The degrees of freedom MIMO interference networks with constant channel coefficients are not known in general. Determining the feasibility a linear alignment solution is key step toward solving this open problem. Our approach paper to view problem as system bilinear equations and determine its solvability by comparing number variables. To end, we divide problems into two classes - proper improper. An called if does exceed Otherwise, it Examples presented support intuition that for generic...

In this correspondence, we consider the problem of maximizing sum rate a multiple-antenna Gaussian broadcast channel (BC). It was recently found that dirty-paper coding is capacity achieving for channel. order to achieve capacity, optimal transmission policy (i.e., transmit covariance structure) given conditions and power constraint must be found. However, obtaining when employing computationally complex nonconvex problem. We use duality transform into well-structured convex multiple-access...

In this correspondence, we show that the exact number of spatial degrees freedom (DOF) for a two user nondegenerate (full rank channel matrices) multiple-input-multiple-output (MIMO) Gaussian interference with M1, M2 antennas at transmitters 1, 2 and N1, N2 corresponding receivers, perfect knowledge all is min{M1 + M2, N1 max(M1, N2), max(M2, N1)}. A constructive achievability proof shows zero forcing sufficient to achieve available DOF on MIMO channel. We also through an example...

We provide inner bound and outer for the total number of degrees freedom <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> user multiple-input multiple-output (MIMO) Gaussian interference channel with xmlns:xlink="http://www.w3.org/1999/xlink">M</i> antennas at each transmitter xmlns:xlink="http://www.w3.org/1999/xlink">N</i> receiver if coefficients are time-varying drawn from a continuous distribution. The bounds tight when ratio [(max( ,...

In the private information retrieval (PIR) problem, a user wishes to retrieve, as efficiently possible, one out of K messages from N non-communicating databases (each holds all messages) while revealing nothing about identity desired message index any individual database. The theoretic capacity PIR is maximum number bits that can be privately retrieved per bit downloaded information. For and databases, we show (1+1/N+1/N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML"...

We solve the transmitter optimization problem and determine a necessary sufficient condition under which beamforming achieves Shannon capacity in linear narrowband point-to-point communication system employing multiple transmit receive antennas with additive Gaussian noise. assume that receiver has perfect channel knowledge while only of either mean or covariance coefficients. The is modeled at as matrix complex jointly random variables zero known (covariance information), nonzero white...

We explore the degrees of freedom M times N user wireless X networks, i.e., networks transmitters and receivers where every transmitter has an independent message for receiver. derive a general outer bound on region these networks. When all nodes have single antenna channel coefficients vary in time or frequency, we show that <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">total</i> number xmlns:xlink="http://www.w3.org/1999/xlink">X</i> network...

Cognitive radios are promising solutions to the problem of overcrowded spectrum. In this article we explore throughput potential cognitive communication. Different interpretations radio that underlay, overlay, and interweave transmissions user with those licensed users described. Considering opportunistic communication as a baseline, investigate improvements offered by overlay methods. Channel selection techniques for access such frequency hopping, tracking, coding presented. The trade-off...

While the best known outerbound for K user interference channel states that there cannot be more than K/2 degrees of freedom, it has been conjectured in general constant with any number users only one degree freedom. In this paper, we explore spatial freedom per orthogonal time and frequency dimension wireless where coefficients take distinct values across slots but are fixed time. We answer five closely related questions. First, show can achieved by design, i.e. if nodes allowed to choose...

This work studies linear interference networks, both wired and wireless, with no channel state information at the transmitters (CSIT) except a coarse knowledge of end-to-end one-hop topology network that only allows distinction between weak (zero) significant (non-zero) channels further coefficients' realizations. The capacity (wired) DoF (wireless) are found to be bounded above by an index coding problem for which antidote graph is complement given graph. problems shown equivalent under...

Cognitive radios are promising solutions to the problem of overcrowded and inefficient licensed spectrum. In this work we explore throughput potential cognitive communication. We summarize different radio techniques that underlay, overlay interweave transmissions user with those users. Recently proposed models for based on technique described. For technique, present a 'two switch' model develop inner outer bounds secondary capacity. Using two switch model, investigate inherent tradeoff...

Private information retrieval (PIR) is the problem of retrieving as efficiently possible, one out K messages from N non-communicating replicated databases (each holds all messages) while keeping identity desired message index a secret each individual database. The theoretic capacity PIR (equivalently, reciprocal minimum download cost) maximum number bits that can be privately retrieved per bit downloaded information. T-private generalization to include requirement even if any T collude,...

It has been conjectured by Hø-Madsen and Nosratinia that complex Gaussian interference channels with constant channel coefficients have only one degree-of-freedom regardless of the number users. While several examples are known achieve more than 1 degree-of-freedom, these special cases span a subset measure zero. In other words, for almost all coefficient values, it is not if achievable. this paper, we settle Høst-Madsen-Nosratinia conjecture in negative. We show at least 1.2...

We propose a blind interference alignment scheme for the vector broadcast channel where transmitter is equipped with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> antennas and there are xmlns:xlink="http://www.w3.org/1999/xlink">K</i> receivers, each reconfigurable antenna capable of switching among preset modes. Without any knowledge coefficient values at transmitters only mild assumptions on coherence structure we show that...

The main contribution of this paper is the insight that transmitters' knowledge channel coherence intervals alone (without any values coefficients) can be surprisingly useful in a multiuser setting, illustrated by idea blind interference alignment introduced work. Specifically, we explore five network communication problems where possibility alignment, and consequently total number degrees freedom (DoF) with uncertainty at transmitters, are unknown. These share common property each case best...

The high repair bandwidth cost of ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> , xmlns:xlink="http://www.w3.org/1999/xlink">k</i> ) maximum distance separable (MDS) erasure codes has motivated a new class that can reduce over conventional MDS codes. In this paper, we address xmlns:xlink="http://www.w3.org/1999/xlink">d</i> exact codes, which allow for any single failed node to be repaired exactly with access arbitrary set survivor...

It is shown that in the K-user interference channel, if for each user desired signal strength no less than sum of strengths strongest from this and to (all values decibel scale), then simple scheme using point-to-point Gaussian codebooks with appropriate power levels at transmitter treating as noise (TIN) every receiver (in short, TIN scheme) achieves all points capacity region within a constant gap. The generalized degrees freedom (GDoF) under condition polyhedron, which be fully achieved...