이시현 교수

In this paper, we characterize the information-theoretic capacity scaling of wireless ad hoc networks with randomly distributed nodes. By using an exact channel model from Maxwell's equations, we successfully resolve the conflict in the literature between the linear capacity scaling by Özgür and the degrees of freedom limit given as the ratio of the network diameter and the wavelength by Franceschetti In dense networks where the network area is fixed, the capacity scaling is given as the minimum

In many known examples where compress-and-forward (CF) for relay networks is capacity achieving, it is only trivially so, i.e., it falls back to hashing without quantization. A potentially better strategy is to decode as much as possible and to compress the residual information, i.e., a combination of decode-and-forward (DF) and CF (Cover and El Gamal's Theorem 7). Indeed such a strategy was shown to be optimal by Kang and Ulukus for a certain class of diamond relay networks consisting of a sour

We consider a random access network in which K nodes wish to send independent packets to an access point (AP). In this letter, a novel method of feedback construction and an adaptive retransmission protocol of collided packets are proposed, which enable efficient successive interference cancellation at the AP. We show that the optimal throughput efficiency of one is achievable by only exploiting log K bits of feedback from the AP to K nodes, while the maximum throughput efficiency of slotted ALO

In this paper, we prove a unified achievability bound that generalizes and improves random coding bounds for any combination of source coding, channel coding, joint source-channel coding, and coding for computing problems assuming blockwise node operation. As a general network setup, we consider an acyclic discrete memoryless network, where the network demands and constraints are specified by a joint-typicality constraint on the whole channel input and output sequences. For achievability, a basi

In this paper, we study the capacity scaling of wireless ad hoc networks considering the effect of a finite wavelength, which gives a unified view on two seemingly contradictory results on the capacity scaling. Recently, it was shown that the order-optimal linear throughput scaling is achievable for some networks using hierarchical cooperation (HC) by Özgür et al., but later it was proved to violate the physical limit by Franceschetti et al. The cause of such a contradiction is the idealized cha

A hierarchical cooperative multiple-input multiple-output (MIMO) transmission can greatly improve the throughput scaling in wireless networks as shown in [1]. In this paper, we analyze the effect of channel correlation on the throughput scaling in wireless networks by focusing on an achievable rate of the cooperative MIMO transmission between two clusters of nodes as a function of the number of nodes in each cluster, the physical size of each cluster, and the distance between the two clusters. C

We establish upper and lower bounds on the secrecy capacity of the degraded Gaussian diamond-wiretap channel, and identify several ranges of channel parameters where these bounds coincide with useful intuitions. Furthermore, we investigate the effect of the presence of an eavesdropper on the capacity. We consider the following two scenarios: 1) common randomness is available at the source and the two relays and 2) randomness is available only at the source, and there is no randomness at the rela

In this paper, we take a unified approach for network information theory and prove a coding theorem, which can recover most of the achievability results in network information theory that are based on random coding. The final single-letter expression has a very simple form, which was made possible by treating sources, channels, states and side information in a unified way and by combining various constraints such as cost and distortion constraints as a single joint-typicality constraint. To demo

We consider the problem of covert communication over a state-dependent channel, where the transmitter has non-causal knowledge of the channel states. Here, “covert” means that the probability that a warden on the channel can detect the communication must be small. In contrast with traditional models without noncausal channel-state information at the transmitter, we show that covert communication can be possible with positive rate. We derive closed-form formulas for the maximum achievable covert

In this paper, we propose a noisy network coding integrated with partial decode-and-forward relaying for single-source multicast discrete memoryless networks (DMN's). Our coding scheme generalizes the partial-decode-compress-and-forward scheme (Theorem 7) by Cover and El Gamal. This is the first time the theorem is generalized for DMN's such that each relay performs both partial decode-and-forward and compress-and-forward simultaneously. Our coding scheme simultaneously generalizes both noisy ne

This paper employs a deep learning method for segmenting drivable and non-drivable areas in an urban environment using the BDD (Berkeley Deep Drive) 100K image database. In particular, we propose a semantic segmentation network using an encoder module based on depth-wise separable, non-bottleneck-1D, and pyramid pooling. The BDD 100K dataset provides reference classification results of directly drivable area, alternative drivable area, and none, under different weather, time, and location condit

In this letter, we establish the secure degrees-of-freedom of the Gaussian diamond-wiretap channel with rate-limited relay cooperation, where the eavesdropper not only observes the relay transmission through another multiple access channel but also wiretaps some of communication links among relays. The legitimate parties do not know the location of wiretapped relay links nor the eavesdropper's channel state information. As an optimal relay cooperation strategy, a noise-forwarding scheme that doe

In this letter, we consider the Gaussian diamond-wiretap channel with conferencing links between relays for the following three cases: 1) both conferencing links are confidential; 2) both conferencing links are public; and 3) one conferencing link is confidential, the other link is public, and the legitimate parties do not know which link is confidential or public. For all the cases, we establish the exact secure degrees of freedom (d.o.f.). Our results show that if at least one of conferencing

In this paper, we characterize the capacity of a new class of discrete memoryless multicast networks having a tree topology. For achievability, a novel coding scheme is constructed where some relays employ a combination of decode-and-forward and compress-and-forward and the other relays perform a random binning such that codebook constructions and relay operations are independent for each node and do not depend on the network topology. For converse, a new technique of iteratively manipulating in

In this paper, we propose a noisy network coding integrated with partial decode-and-forward relaying for single-source multicast discrete memoryless networks (DMN's). Our coding scheme generalizes the partial-decode-compress-and-forward scheme (Theorem 7) by Cover and El Gamal. This is the first time the theorem is generalized for DMN's such that each relay performs both partial decode-and-forward and compress-and-forward simultaneously. Our coding scheme simultaneously generalizes both noisy ne