Sang-Woon Jeon

Aligned Interference Neutralization and the Degrees of Freedom of the 2

We show that the 2 × 2 × 2 interference network, i.e., the multihop interference network formed by concatenation of two 2-user interference channels achieves the min-cut outer bound value of 2 DoF, for almost all values of channel coefficients, for both time-varying or fixed channel coefficients. The key to this result is a new idea, called aligned interference neutralization, that provides a way to align interference terms over each hop in a manner that allows them to be cancelled over the air at the last hop.

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Previous work showed that the 2×2×2 interference channel, i.e., the multihop interference network formed by concatenation of two 2-user interference channels, achieves the min-cut outer bound value of 2 DoF. This work studies the 2×2×2 interference channel with one additional assumption that two relays interfere with each other. It is shown that even in the presence of the interfering links between two relays, the min-cut outer bound of 2 DoF can still be achieved for almost all values of channel coefficients, for both fixed or time-varying channel coefficients. The achievable scheme relies on the idea of aligned interference neutralization as well as exploiting memory at source and relay nodes.

2

We study a layered <i>K</i>-user <i>M</i>-hop Gaussian relay network consisting of <i>Km</i> nodes in the <i>m</i>^th layer, where <i>M</i> ≥ 2 and <i>K</i>=<i>K</i>₁=<i>KM</i>+1. We observe that the time-varying nature of wireless channels or fading can be exploited to mitigate the interuser interference. The proposed amplify-and-forward relaying scheme exploits such channel variations and works for a wide class of channel distributions including Rayleigh fading. We show a general achievable degrees of freedom (DoF) region for this class of Gaussian relay networks. Specifically, the set of all (<i>d</i>₁,..., <i>dK</i>) such that <i>di</i> ≤ 1 for all <i>i</i> and Σ <i>i</i>=1<i>K di</i> ≤ <i>K</i>_Σ is achievable, where <i>di</i> is the DoF of the <i>i</i>^th source-destination pair and <i>K</i>_Σ is the maximum integer such that <i>K</i>_Σ ≤ min<i>m</i>{<i>Km</i>} and <i>M</i>/<i>K</i>_Σ is an integer. We show that surprisingly the achievable DoF region coincides with the cut-set outer bound if <i>M</i>/ min<i>m</i>{<i>Km</i>} is an integer; thus, interference-free communication is possible in terms of DoF. We further characterize an achievable DoF region assuming multi-antenna nodes and general message set, which again coincides with the cut-set outer bound for a certain class of networks.

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We consider a wireless device-to-device (D2D) network in which the nodes are uniformly distributed at random over the network area and can cache information from a library of possible messages (files). Each node requests a file in the library independently at random, according to a given popularity distribution, and downloads from other nodes having the requested file in their local cache via multihop transmission. Under the classical “protocol model” of wireless ad hoc networks, we characterize the optimal throughput scaling law by presenting a feasible scheme formed by a decentralized caching policy for the parameter regimes of interest and a local multihop transmission protocol. The scaling law optimality of the proposed strategy is shown by deriving a new throughput upper bound. Surprisingly, we show that decentralized uniform random caching yields optimal scaling in most of the system interesting regimes. We also observe that caching improves the throughput scaling law of classical ad hoc networks, and that multihop improves the previously derived scaling law of caching wireless networks under one-hop transmission.

2 Interference Channel

In recent years, there has been rapid progress on understanding Gaussian networks with multiple unicast connections, and new coding techniques have emerged. The essence of multi-source networks is how to efficiently manage interference that arises from the transmission of other sessions. Classically, interference is removed by orthogonalization (in time or frequency). This means that the rate per session drops inversely proportional to the number of sessions, suggesting that interference is a strong limiting factor in such networks. However, recently discovered interference management techniques have led to a paradigm shift that interference might not be quite as detrimental after all. The aim of this paper is to provide a review of these new coding techniques as they apply to the case of time-varying Gaussian networks with multiple unicast connections. Specifically, we review interference alignment and ergodic interference alignment for multi-source single-hop networks and interference neutralization and ergodic interference neutralization for multi-source multi-hop networks. We mainly focus on the “degrees of freedom” perspective and also discuss an approximate capacity characterization.

Aligned interference neutralization and the degrees of freedom of the 2 × 2 × 2 interference channel

In this paper, we study a layered linear binary field network with time-varying channels, which is a simplified model reflecting broadcast, interference, and fading natures of wireless communications. We observe that fading can play an important role in mitigating interuser interference effectively for both single-hop and multihop networks. We propose new coding schemes with randomized ergodic channel pairing, which exploit such channel variations, and derive their achievable ergodic rates. By comparing them with the cut-set upper bound, the capacity region of single-hop networks and the sum capacity of multihop networks are characterized for some classes of channel distributions and network topologies.

Degrees of Freedom Region of a Class of Multisource Gaussian Relay Networks

We consider a relay network having K source-destination pairs. Finding the capacity region of such a network with multiple unicast sessions is in general difficult. By focusing on a special class of such networks, we show that the capacity can be found. Namely, we consider a linear finite-field channel model, which can model interference in the network. Furthermore, we assume time-varying channels. We propose a block Markov encoding and relaying scheme that exploits such channel variations. By comparing its achievable sum-rate with the general cut-set upper bound, we show the sum capacity can be characterized for a certain class of channel distributions and network topologies

Caching in wireless multihop device-to-device networks

We study a multi-source Gaussian relay network consisting of K source-destination pairs having K unicast sessions. We assume M layers of relays between the sources and the destinations. We find achievable degrees of freedom of the network. Our schemes are based on interference alignment at the transmitters and symbol extension and opportunistic interference cancellation at the relays. For K-L-K networks, i.e., 2-hop network with L relays, we show min{K,K/2 + L/(2(K − 1))} degrees of freedom are achievable. For K-hop networks with K relays in each layer, we show the full K degrees of freedom are achievable provided that K is even and the channel distribution satisfies a certain symmetry.

A Survey on Interference Networks: Interference Alignment and Neutralization

We study Please be advised that per instructions from the Communications Society this proof was formatted in Times Roman font and therefore some of the fonts will appear different from the fonts in your originally submitted manuscript. For instance, the math calligraphy font may appear different due to usage of the usepackage[mathcal]euscript. The Communications Society has decided not to use Computer Modern fonts in their publications. 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 DoFs for both FD cellular networks. The key idea of the proposed scheme is to carefully allocate UL and DL streams using interference alignment and beam forming techniques. By comparing the DoFs of the FD systems with those of the conventional HD systems, we show that the DoF can approach the two-fold gain over the HD systems, when the number of users becomes large enough compared with the number of antennas at the BS.

Capacity of a Class of Linear Binary Field Multisource Relay Networks

We consider a wireless device-to-device network, where