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INTERFERENCE CHANNELS WITH COORDINATED MULTIPOINT TRANSMISSION
, 2014
"... Coordinated MultiPoint (CoMP) transmission is an infrastructural enhancement under consideration for nextgeneration wireless networks. In this dissertation, the capacity gain achieved through CoMP transmission is studied in various models of wireless networks that have practical significance. The ..."
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Coordinated MultiPoint (CoMP) transmission is an infrastructural enhancement under consideration for nextgeneration wireless networks. In this dissertation, the capacity gain achieved through CoMP transmission is studied in various models of wireless networks that have practical significance. The capacity gain is analyzed through the degrees of freedom (DoF) criterion. The DoF available for communication provides an analytically tractable way to characterize the capacity of interference channels. The considered channel model has K transmitter/receiver pairs, and each receiver is interested in one unique message from a set of K independent messages. Each message can be available at more than one transmitter. The maximum number of transmitters at which each message can be available is defined as the cooperation order M. For fully connected interference channels, it is shown that the asymptotic per user DoF, as K goes to infinity, remains at 1 2 as M is increased from 1 to 2. Furthermore, the same negative result is shown to hold for all M ≥ 2 for any message assignment that satisfies a local cooperation constraint. On the other hand, when the assumption of full connectivity is relaxed to local connectivity, and each transmitter is connected only to its own receiver as well as L neighboring receivers, it is shown that local cooperation is optimal. The asymptotic per user DoF is shown to be at least max
The SumCapacity of the Ergodic Fading Gaussian Cognitive Interference Channel
"... Abstract—This paper characterizes the sumcapacity of the ergodic fading Gaussian overlay cognitive interference channel (EGCIFC), a timevarying channel with two source–destination pairs in which a primary/licensed transmitter and a secondary/ cognitive transmitter share the same spectrum and where ..."
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Abstract—This paper characterizes the sumcapacity of the ergodic fading Gaussian overlay cognitive interference channel (EGCIFC), a timevarying channel with two source–destination pairs in which a primary/licensed transmitter and a secondary/ cognitive transmitter share the same spectrum and where the cognitive transmitter has noncausal knowledge of the primary user’s message. The throughput/sumcapacity is characterized under the assumption of perfect knowledge of the instantaneous fading states at all terminals, which are assumed to form an ergodic process. A genieaided outer bound on the sumcapacity is developed and then matched with an achievable scheme, thereby completely characterizing the sumcapacity of the EGCIFC. The power allocation policy that maximizes the sumcapacity is derived. It is shown that the sumcapacity achieving scheme for an EGCIFC is “separable ” in all regimes (i.e., coding across fading states is not necessary), as opposed to the classical interference channel. Extensions to the whole capacity region are discussed. As a capacity achieving scheme for the EGCIFC under certain channel gain conditions, and as a topic of independent interest, the ergodic capacity of a pointtopoint multipleinput–singleoutput channel with perantenna power constraints and with perfect channel state information at all terminals is also derived. Index Terms—Cognitive radio, ergodic capacity, power allocation, separability, convex optimization. I.
On the SumCapacity of the Cognitive Interference Channel with CognitiveOnly Message Sharing
"... Abstract—Motivated by the ongoing discussion of spectrum scarcity, this paper considers the Kuser cognitive interference channel with K − 1 primary/licensed users and one cognitive/secondary user who has noncausal knowledge of the messages of all primary users. This message sharing mechanism is ..."
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Abstract—Motivated by the ongoing discussion of spectrum scarcity, this paper considers the Kuser cognitive interference channel with K − 1 primary/licensed users and one cognitive/secondary user who has noncausal knowledge of the messages of all primary users. This message sharing mechanism is referred to as cognitiveonly message sharing. For certain parameter regimes, the sumcapacity of the symmetric Gaussian noise channel is characterized to within an additive constant gap from an outer bound originally derived for a channel model with cumulative message sharing, which consists of one primary user and K−1 cognitive users where cognitive transmitter i ∈ [2: K] has noncausal knowledge of the messages of the users with index less than i. The approximately optimal achievability scheme is a combination of simultaneous interference neutralization at the primary receivers, dirtypaper coding to remove the effect of interference at the cognitive receiver, and ratesplitting, where the power splits are chosen such that the signals treated as noise are received below the noise floor of the receiver. This shows that “distributed cognition ” may not be necessary in the considered network model since (approximately) the same sumcapacity can be achieved by having only one “globally cognitive ” user whose role is to manage all the interference in the network. I.
Degrees of Freedom of Interference Channel with RankDeficient Transfer Matrix
"... Abstract—We consider the interference channel with K transmitters and K receivers all having a single antenna, wherein the K ×K transfer matrix representing this channel has rank D (D < K). The degrees of freedom (DoF) of such channels are not known as the rank deficiency in the transfer matrix ..."
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Abstract—We consider the interference channel with K transmitters and K receivers all having a single antenna, wherein the K ×K transfer matrix representing this channel has rank D (D < K). The degrees of freedom (DoF) of such channels are not known as the rank deficiency in the transfer matrix creates algebraic dependencies between the channel coefficients. We present a modified version of the [CJ08] alignment scheme, to handle these dependencies while aligning interference, and state the sufficient conditions for achieving half rate per user using this scheme. The difficulties in proving these sufficient conditions are shown for K = 4 and K = 5. We also show that these sufficient conditions are not satisfied for K ≥ 6. I.