Approximate Ergodic Capacity of a Class of Fading Two-User Two-Hop Networks

IEEE Trans. Inform. Theory

Suh

2016

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An uplink-downlink two-cell cellular network is studied in which the first base station (BS) with M 1 antennas receives independent messages from its N 1 serving users, while the second BS with M 2 antennas transmits independent messages to its N 2 serving users. That is, the first and second cells operate as uplink and downlink, respectively. Each user is assumed to have a single antenna. Under this uplink-downlink setting, the sum degrees of freedom (DoF) is completely characterized as the minimum of (), where a + denotes max(0, a). The result demonstrates that, for a broad class of network configurations, operating one of the two cells as uplink and the other cell as downlink can strictly improve the sum DoF compared to the conventional uplink or downlink operation, in which both cells operate as either uplink or downlink. The DoF gain from such uplink-downlink operation is further shown to be achievable for heterogeneous cellular networks having hotspots and with delayed channel state information. Index TermsCellular networks, degrees of freedom, heterogeneous networks, interference alignment, multiantenna techniques, reverse TDD.

Section: B Previous Workmentioning

confidence: 99%

Degrees of Freedom of Uplink–Downlink Multiantenna Cellular Networks

IEEE Trans. Inform. Theory

Suh

2016

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“…Proof: We refer to Appendix I-C for the proof. Therefore, combining (10), (11), (12) and the result in Lemma 4 provides…”

Section: A Converse Of Theoremmentioning

confidence: 82%

Linear Degrees of Freedom of MIMO Broadcast Channels With Reconfigurable Antennas in the Absence of CSIT

Yang

IEEE Trans. Inform. Theory

2017

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The K-user multiple-input and multiple-output (MIMO) broadcast channel (BC) with no channel state information at the transmitter (CSIT) is considered, where each receiver is assumed to be equipped with reconfigurable antennas capable of choosing a subset of receiving modes from several preset modes. Under general antenna configurations, the sum linear degrees of freedom (LDoF) of the K-user MIMO BC with reconfigurable antennas is completely characterized, which corresponds to the maximum sum DoF achievable by linear coding strategies. The LDoF region is further characterized for a class of antenna configurations. Similar analysis is extended to the K-user MIMO interference channels with reconfigurable antennas and the sum LDoF is characterized for a class of antenna configurations. Index TermsBlind interference alignment, broadcast channels, degrees of freedom (DoF), multiple-input and multiple-output (MIMO), reconfigurable antennas. I. INTRODUCTIONRecently, there have been considerable researches on characterizing the degrees of freedom (DoF) of wireless networks. As current wireless networks become very complicated, exact capacity characterization is so difficult that many researchers have actively studied approximate capacity characterizations in the shape of DoF. The DoF is the prelog factor of capacity, providing an intuitive metric for the number of interference-free communication channels that wireless networks can attain at the high signal-to-noise ratio (SNR) regime. Hence, it is regarded as a primary performance metric for multiantenna and/or multiuser communication systems. Cadambe and Jafar recently made a remarkable progress on understanding DoF of multiuser wireless networks showing that the sum DoF of the K-user interference channel (IC) is given by K/2 [1]. An innovative methodology called interference alignment (IA) has been proposed to obtain K/2 DoF, which aligns multiple interfering signals into the same signal space at each receiver. The concept of such signal space alignment has been successfully adapted to various network environments, e.g., see [2]-[8] and the references therein. More recently, different strategies of IA were further developed in terms of ergodic IA [9]-[12] and real IA [13], [14].Note that most of the previous researches including the aforementioned IA techniques have focused on DoF of wireless networks under the assumption that each transmitter perfectly knows global channel state information (CSI). However, for many practical communication systems, acquiring the exact CSI value at transmitters is very challenging due to channel feedback delay, system overhead, and so on. Motivated by these practical restrictions, implementing IA under a more relaxed CSI condition has been actively studied in the literature. Maddah-Ali and Tse made a breakthrough in [15] demonstrating that completely outdated CSI is still useful to improve DoF of the K-user multiple-input and single-output (MISO) broadcast channel (BC). Preceded by [15], there have been a series of researches for studyin...

“…In addition, for the case in which all channel coefficients are constant, Motahari et al [23], [24] proposed a different type of IA scheme based on number-theoretic properties of rational and irrational numbers and showed that the optimal DoF of K 2 is also achievable. Later, alternative methods of aligning interference in the finite signal-to-noise regime has been also proposed in [22], [25]- [27]. The concept of IA has been successfully adapted to various network environments, e.g., see [13]- [19] and the references therein.…”

Section: A Previous Workmentioning

confidence: 99%

Degrees of Freedom of Full-Duplex Multiantenna Cellular Networks

Chae

Lim

IEEE Trans. Wireless Commun.

2018

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We study the degrees of freedom (DoF) of cellular networks in which a full duplex (FD) base station (BS) equipped with multiple transmit and receive antennas communicates with multiple mobile users. We consider two different scenarios. In the first scenario, we study the case when half duplex (HD) users, partitioned to either the uplink (UL) set or the downlink (DL) set, simultaneously communicate with the FD BS. In the second scenario, we study the case when FD users simultaneously communicate UL and DL data with the FD BS. Unlike conventional HD only systems, inter-user interference (within the cell) may severely limit the DoF, and must be carefully taken into account. With the goal of providing theoretical guidelines for designing such FD systems, we completely characterize the sum DoF of each of the two different FD cellular networks by developing an achievable scheme and obtaining a matching upper bound. The key idea of the proposed scheme is to carefully allocate UL and DL information streams using interference alignment and beamforming techniques. By comparing the DoFs of the considered FD systems with those of the conventional HD systems, we establish the DoF gain by enabling FD operation in various configurations. As a consequence of the result, we show that the DoF can approach the two-fold gain over the HD systems when the number of users becomes large enough as compared to the number of antennas at the BS. Index TermsCellular network, degrees of freedom, full duplex, interference alignment, multiantenna technique.