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On the Optimality of Treating Interference as Noise: General Message Sets
"... Abstract — In a Kuser Gaussian interference channel, it has been shown that if for each user the desired signal strength is no less than the sum of the strengths of the strongest interference from this user and the strongest interference to this user (all values in decibel scale), then treating int ..."
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Abstract — In a Kuser Gaussian interference channel, it has been shown that if for each user the desired signal strength is no less than the sum of the strengths of the strongest interference from this user and the strongest interference to this user (all values in decibel scale), then treating interference as noise (TIN) is optimal from the perspective of generalized degrees of freedom (GDoF) and achieves the entire channel capacity region to within a constant gap. In this paper, we show that for such TINoptimal interference channels, even if the message set is expanded to include an independent message from each transmitter to each receiver, operating the new channel as the original interference channel and treating interference as noise is still optimal for the sum capacity up to a constant gap. Furthermore, we extend the result to the sumGDoF optimality of TIN in the general setting of X channels with arbitrary numbers of transmitters and receivers. Index Terms — Gaussian networks, generalized degrees of freedom (GDoF), sum capacity, treating interference as noise (TIN), X channels. I.
INTERWEAVE/UNDERLAY COGNITIVE RADIO TECHNIQUES AND APPLICATIONS IN SATELLITE COMMUNICATION SYSTEMS
, 2014
"... The demand for precious radio spectrum is continuously increasing while the available radio frequency resource has become scarce due to spectrum segmentation and the dedicated frequency allocation of standardized wireless systems. This scarcity has led to the concept of cognitive radio communication ..."
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The demand for precious radio spectrum is continuously increasing while the available radio frequency resource has become scarce due to spectrum segmentation and the dedicated frequency allocation of standardized wireless systems. This scarcity has led to the concept of cognitive radio communication which comprises a variety of techniques capable of allowing the coexistence of licensed and unlicensed systems over the same spectrum. In this context, this thesis focuses on interweave and underlay cognitive radio paradigms which are widely considered as important enablers for realising cognitive radio technology. In the interweave paradigm, an unlicensed user explores the spectral holes by means of some spectrum awareness methods and utilizes the available spectral availabilities opportunistically while in the underlay paradigm, an unlicensed user is allowed to coexist with the licensed user only if sufficient protection to the licensed user can be guaranteed. Starting with a detailed overview of the existing techniques, this thesis provides contributions in both theoretical and the practical aspects of these paradigms. This thesis is structured into two main parts as described below. One of the important capabilities required for a cognitive radio transceiver is to be able to acquire the knowledge of its surrounding radio environment in order to utilize the available spectral opportunities
Cellular Interference Alignment: OmniDirectional Antennas and Asymmetric Configurations
"... Interference alignment (IA) is one of the major theoretical breakthroughs in the information theoretic understanding of Gaussian interference channels with more than two transmitreceive pairs. Unfortunately, practical oneshot IA precoding, where alignment is obtained on a number of channel dimensi ..."
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Interference alignment (IA) is one of the major theoretical breakthroughs in the information theoretic understanding of Gaussian interference channels with more than two transmitreceive pairs. Unfortunately, practical oneshot IA precoding, where alignment is obtained on a number of channel dimensions that does not grow with the network size, provides vanishing degrees of freedom (DoFs) gain for fully connected large networks with generic channel coefficients. Achieving nontrivial DoFs gains by oneshot alignment precoding in partially connected networks remains an open problem, as it critically depends on the specific network topology. In our previous work, we introduced the concept of “Cellular IA ” for a network topology induced by hexagonal cells with sectors and nearest neighbor intersector interference. For the uplink – assuming that neighboring basestations can exchange individually decoded messages (and not received signal samples) – we proved oneshot DoFs optimality of M/2 DoFs per user when transmitters and receivers have the same number M of antennas. In this paper we extend this line of work by considering omnidirectional (nonsectorized) cells where the users have 2 antennas, and the basestations have 2, 3 or 4 antennas. For the 2 × 2 case, we show that 3/4 DoFs per user can be achieved with linear oneshot IA precoding and for the 2 × 3 and 2×4 cases, we show the achievability of 1 and 7/6 DoFs per user respectively. Our oneshot achievability schemes are highly nontrivial and make use of a networkwide interference cancellation framework that enables local decoded
IEEE TRANSACTIONS ON INFORMATION THEORY 1 On the Gaussian ManytoOne X Channel
"... Abstract—In this paper, the Gaussian manytoone X channel, which is a special case of general multiuser X channel, is studied. In the Gaussian manytoone X channel, communication links exist between all transmitters and one of the receivers, along with a communication link between each transmitter ..."
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Abstract—In this paper, the Gaussian manytoone X channel, which is a special case of general multiuser X channel, is studied. In the Gaussian manytoone X channel, communication links exist between all transmitters and one of the receivers, along with a communication link between each transmitter and its corresponding receiver. As per the X channel assumption, transmission of messages is allowed on all the links of the channel. This communication model is different from the corresponding manytoone interference channel (IC). Transmission strategies which involve using Gaussian codebooks and treating interference from a subset of transmitters as noise are formulated for the above channel. Sumrate is used as the criterion of optimality for evaluating the strategies. Initially, a 3×3 manytoone X channel is considered and three transmission strategies are analyzed. The first two strategies are shown to achieve sumrate capacity under certain channel conditions. For the third strategy, a sumrate outer bound is derived and the gap between the outer bound and the achieved rate is characterized. These results are later extended to the K ×K case. Next, a region in which the manytoone X channel can be operated as a manytoone IC without loss of sumrate is identified. Further, in the above region, it is shown that using Gaussian codebooks and treating interference as noise achieves a rate point that is within K/2 − 1 bits from the sumrate capacity. Subsequently, some implications of the above results to the Gaussian manytoone IC are discussed. Transmission strategies for the manytoone IC are formulated and channel conditions under which the strategies achieve sumrate capacity are obtained. A region where the sumrate capacity can be characterized to within K/2 − 1 bits is also identified. Finally, the regions where the derived channel conditions are satisfied for each strategy are illustrated for a 3×3 manytoone X channel and the corresponding manytoone IC. Index Terms—Interference channel, manytoone interference channel, sum capacity, X channel. I.
1Optimal Antenna Cluster Size in CellFree LargeScale DistributedAntenna Systems with Imperfect CSI and InterCluster Interference
"... tems (LDAS), the antennas are distributed over the intended coverage area. Introducing cooperation among the antennas can significantly improve the system throughput. Whereas only finiteclustersize (limited) cooperation with LDAS antennaclusters is realistic due to practical limitations. In thi ..."
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tems (LDAS), the antennas are distributed over the intended coverage area. Introducing cooperation among the antennas can significantly improve the system throughput. Whereas only finiteclustersize (limited) cooperation with LDAS antennaclusters is realistic due to practical limitations. In this paper, the impact of antenna cluster size on the downlink sum rate of frequencydivision duplex (FDD) cellfree LDAS is analyzed considering imperfect channel state information (CSI) and intercluster interference (ICLI). We investigate the optimal cluster size, in terms of maximizing the downlink sum rate with respect to the overhead of imperfect channel training and feedback. When the number of users is sufficiently large, closedform lower bounds of the ergodic sum capacity, which are leveraged to analyze the system performance, are derived by constructing different rateachieving user scheduling schemes. Both analog and digital feedback schemes are considered to evaluate the imperfect channel feedback. Based upon these, closedform expressions of the optimal cluster size for onedimensional antennatopology systems and the corresponding achievable rates are derived. The scaling law of the optimal cluster size for twodimensional antennatopology systems is also given. Numerical results demonstrate the impact of signaltonoise ratio (SNR) and the block length on the achievable rates and the optimal cluster size, which agree with our analytical results. Index Terms—Distributed largescale antenna systems, Frequencydivisionduplex, Broadcast channel, Imperfect CSI. I.
Blind Interference Alignment for Cellular Networks
"... Abstract—We propose a blind interference alignment scheme for partially connected cellular networks. The scheme cancels both intracell and intercell interference by relying on receivers with one reconfigurable antenna and by allowing users at the cell edge to be served by all the base stations in th ..."
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Abstract—We propose a blind interference alignment scheme for partially connected cellular networks. The scheme cancels both intracell and intercell interference by relying on receivers with one reconfigurable antenna and by allowing users at the cell edge to be served by all the base stations in their proximity. An outer bound for the Degrees of Freedom is derived for general partially connected networks with singleantenna receivers when knowledge of the channel state information at the transmitter is not available. It is demonstrated that for symmetric scenarios this outer bound is achieved by the proposed scheme. On the other hand, for asymmetric scenarios the achievable Degrees of Freedom are not always equal to the outer bound. However, the penalty is typically small, and the proposed scheme outperforms other blind interference alignment schemes. Moreover, significant reduction of the supersymbol length is achieved compared to a standard blind interference alignment strategy designed for fully connected networks.
On the Optimality of Treating Interference as Noise for Kuser Compound Interference Channels
"... Abstract—For the Kuser interference channel, Geng et al. identify a general condition under which power control and treating interference as noise (TIN) is optimal from the perspective of generalized degrees of freedom (GDoF). In this work, we show that for a Kuser compound interference channel, ..."
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Abstract—For the Kuser interference channel, Geng et al. identify a general condition under which power control and treating interference as noise (TIN) is optimal from the perspective of generalized degrees of freedom (GDoF). In this work, we show that for a Kuser compound interference channel, if in every possible state for each receiver, the channel satisfies the TINoptimality condition of Geng et al., then power control and TIN achieves the entire GDoF region of the compound channel. For an arbitrary compound interference channel, we find a nontrivial counterpart regular interference channel, such that the two have the same TIN region, and the GDoFoptimal power control problems for the two are equivalent. I.
On the Symmetric 2User Deterministic Interference Channel with Confidential Messages
"... Abstract—We consider 2user symmetric interference channels with confidential messages. For the linear deterministic model of this channel, we develop inner and outer bounds for the symmetric secure rate, which are shown to match and characterize the symmetric secure capacity for a wide range of ch ..."
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Abstract—We consider 2user symmetric interference channels with confidential messages. For the linear deterministic model of this channel, we develop inner and outer bounds for the symmetric secure rate, which are shown to match and characterize the symmetric secure capacity for a wide range of channel parameters. For the achievability, we present a cooperative jamming scheme based on interference alignment principle, which is optimal for all regimes where the symmetric secure capacity is established. For the converse, a tighter outer bound than all perviously existing ones is provided for the regime where the symmetric secure capacity is still open. I.
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"... Interference alignment promises that, in Gaussian interference channels, each link can support half of a degree of freedom (DoF) per pair of transmitreceive antennas. However, in general, this result requires to precode the data bearing signals over a signal space of asymptotically large diversity, ..."
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Interference alignment promises that, in Gaussian interference channels, each link can support half of a degree of freedom (DoF) per pair of transmitreceive antennas. However, in general, this result requires to precode the data bearing signals over a signal space of asymptotically large diversity, e.g., over an infinite number of dimensions for timefrequency varying fading channels, or over an infinite number of rationally independent signal levels, in the case of timefrequency invariant channels. In this work we consider a wireless cellular system scenario where the promised optimal DoFs are achieved with linear precoding in oneshot (i.e., over a single timefrequency slot). We focus on the uplink of a symmetric cellular system, where each cell is split into three sectors with orthogonal intrasector multiple access. In our model, interference is “local”, i.e., it is due to transmitters in neighboring cells only. We consider a messagepassing backhaul network architecture, in which nearby sectors can exchange already decoded messages and propose an alignment solution that can achieve the optimal DoFs. To avoid signaling schemes relying on the strength of interference, we further introduce the notion of topologically robust schemes, which are able to guarantee a minimum rate (or DoFs) irrespectively of the strength of the interfering links. Towards this end, we design an alignment scheme which is topologically robust and still achieves the same optimum DoFs.