Haejoon Jung

Experimental range extension of concurrent cooperative transmission in indoor environments at 2.4GHz

Concurrent cooperative transmission (CCT) is a cooperative transmission (CT) technique where multiple radios transmit diversity versions of the same message at the same time. Through array gain and diversity gain, CCT achieves a signal-to-noise (SNR) advantage, which can be used for better link reliability and transmission range extension. CCT range extension can enable broadcasting with fewer hops, balance energy in wireless sensor networks, and overcome network partitions. However, there are few experimental studies of CT range extension in the literature. In this paper, we consider two-hop directional range extension and two-hop coverage area extension as function of relay cluster topology. In particular, we measure average packet error rate (APER), which is averaged over multipath fading. We estimate path loss and shadowing parameters from the APER, and compare outage rate contours based on the log-distance path loss model to the measured APERs.

Multi-Packet Opportunistic Large Array Transmission on Strip-Shaped Cooperative Routes or Networks

The Opportunistic Large Array (OLA) is one type of cooperative transmission, which provides fast and reliable broadcasts and unicasts in multi-hop networks. While the existing literature on OLAs assumes one-shot transmission with a single packet, we analyze multi-packet OLA transmission within a single flow along strip-shaped networks or OLA-based cooperative routes. When multiple packets are transmitted from the same source using the same channel before the previous packet has cleared the network, which is called spatial pipelining, intra-flow interference is produced by OLAs transmitting co-channel packets. Using the continuum assumption (approximated by high density networks), the authors optimize the throughput. This paper theoretically shows spatial pipelining over strip networks is always feasible for path loss exponent α≥2, which is not true for disk-shaped networks. Moreover, the impacts of system parameters are analyzed, and the upper bound of the optimal packet spacing (the lower bound of the optimal throughput) is derived. Also, spatial pipelining in finite networks is studied with numerical results, which confirm the theoretical analysis.

On cooperative transmission range extension in multi-hop wireless ad-hoc and sensor networks

Range extension is a promising feature offered by cooperative transmission (CT), also known as virtual multiple-input-single-output (VMISO). Many authors have considered how the diversity and array gains from CT may benefit a wireless multi-hop network, when the gains are used for increasing link reliability and reducing transmit power. However, relatively less attention has been given to the benefits of CT range extension and few testbed implementations of CT have been demonstrated. In this paper, we focus on how CT range extension can impact the lower three layers, especially medium access control (MAC) and routing for ad hoc and sensor multi-hop networks (AHSMNs). We assume cooperators decode and forward the packets. Various analytical models, performance analyses, and experimental results using software-defined radios in an indoor office environment are discussed. For wireless sensor networks (WSNs), we review CT range extension at the network layer, to eliminate the energy hole that forms around sink nodes in non-CT networks, and we review cooperator selection and duty cycle scheduling algorithms at Layer 2, to maximize the lifetime of a multi-hop WSN. For ad hoc networks, we emphasize a family of lightweight broadcasting and unicasting protocols based on a simple form of CT called the opportunistic large array (OLA). Experimental results, including OLA-based unicast routing and diversity order effects in two-hop CT networks, are discussed.

Multi-Packet Interference in Opportunistic Large Array Broadcasts over Disk Networks

The Opportunistic Large Array (OLA) is a simple form of cooperative transmission, in which a group of single-antenna nodes decode the same packet, then a short time later relay the packet simultaneously in orthogonal or space-time coded channels. The authors have previously shown that OLA transmissions can be adequately synchronized so they appear to a receiver as having come from a conventional array with co-located antennas doing transmit diversity. OLAs have been considered as a basis for rapid single-packet broadcasting in multi-hop networks, however, there are few studies that consider OLA broadcasting of multiple co-channel packets. Using the continuum assumption (approximated by high density networks), we focus on broadcast throughput optimization, as determined by the packet insertion rate at the source. We consider spatial pipelining, which means broadcasting a packet before the previous co-channel packet has cleared the network. We show theoretically that for infinitely large networks the feasibility of spatial pipelining depends on the path loss exponent. For finite networks, we study the propagation behavior of spatially pipelined packets using numerical analysis.

SNR penalty from the path-loss disparity in virtual multiple-input-single-output (VMISO) link

Cooperative transmission (CT), in which spatially separated wireless nodes collaborate to form a virtual antenna array or virtual multiple-input-multiple-output (VMISO) link, is an effective technique to mitigate multi-path fading by spatial diversity. In this paper, we study the disparities in path losses between the randomly placed relay nodes in a transmit cluster and the destination nodes. Many authors assume that the elements in a virtual antenna array are co-located, even though they are spread out. In this paper, we show that a signal-to-noise-ratio (SNR) penalty of up to 3dB should be included when making this assumption. By the high-SNR approximation of the outage rates, we show that the performance degradation caused by the path-loss disparity can be characterized equivalently by log-normal shadowing. Moreover, we derive the upper and lower bounds of the real outage probabilities in closed forms based on the log-normal shadowing model, by which we can estimate the SNR penalty of the co-located assumption.

Analysis of spatial pipelining in Opportunistic Large Array broadcasts

The Opportunistic Large Array (OLA) is a simple form of cooperative transmission, in which a group of single-antenna nodes decode the same packet, then a short time later relay the packet simultaneously in orthogonal channels. The authors have previously shown that OLA transmissions can be adequately synchronized so they appear to a receiver as having come from a real array antenna doing transmit diversity. OLAs have been considered as a basis for rapid single-packet broadcasting in multi-hop networks, however, there are few studies that consider the long range, intra-flow interference produced by OLAs transmitting previous packets from the same source. We show that the broadcast throughput from a single source is always degraded if the source transmits a packet before previous co-channel packets have finished propagating across the network. The infinite disc case is treated theoretically, while the finite disc case is treated numerically.

Connectivity Analysis of Millimeter-Wave Device-to-Device Networks with Blockage

We consider device-to-device (D2D) communications in millimeter-wave (mm Wave) for the future fifth generation (5G) cellular networks. While the mm Wave systems can support multiple D2D pairs simultaneously through beamforming with highly directional antenna arrays, the mm Wave channel is significantly more susceptible to blockage compared to microwave; mm Wave channel studies indicate that if line-of-sight (LoS) paths are blocked, reliable mm Wave communications may not be achieved for high data-rate applications. Therefore, assuming that an outage occurs in the absence of the LoS path between two wireless devices by obstructions, we focus on connectivity of the mm Wave D2D networks. We consider two types of D2D communications: direct and indirect schemes. The connectivity performances of the two schemes are investigated in terms of (i) the probability to achieve a fully connected network and (ii) the average number of reliably connected devices . Through analysis and simulation, we show that, as the network size increases, and decrease. Also, and decrease, when the blockage parameter increases. Moreover, simulation results indicate that the hybrid direct and indirect scheme can improve both and up to about 35% compared to the nonhybrid scheme.

Analysis of intra-flow interference in Opportunistic Large Array transmission for strip networks

The Opportunistic Large Array (OLA), a simple form of concurrent cooperative transmission that extends range, is known to provide fast and reliable broadcasting of a single packet on both disk- and strip-shaped networks. This paper studies multi-packet OLA transmission within a single flow along a strip-shaped network, which also models an OLA-based cooperative route in a large multi-hop network. One packet makes interference on many other packets in the same flow, which generally retards OLA sizes for all packets, and can cause some packets to die off. However, by using the continuum and deterministic channel assumptions, which correspond to high node density, the authors show that multi-packet transmission can be made reliable and throughput can be optimized, by selecting the correct inter-packet spacing.

Outage Analysis of Multihop Wireless Backhaul Using Millimeter Wave under Blockage Effects

We consider multihop millimeter-wave (mm-Wave) wireless backhaul communications, by which small cell base station (SBS) clusters can connect to a macrocell base station (MBS). Assuming the mm-Wave wireless backhaul links suffer from outage caused by obstacles that block the line-of-sight (LoS) paths, we derive the statistics of a perhop distance based on the blockage model using stochastic geometry and random shape theory and analyze the multihop outage probability using the statistics of a perhop distance. We also provide an optimal number of hops to minimize the end-to-end outage performance between the MBS and the destination SBS cluster when the end-to-end distance is given.

Characterization of Path-Loss Disparity in Virtual Multiple-Input-Single-Output Links

Cooperative transmission (CT) is an effective technique to achieve spatial diversity in fading environments, where spatially separated wireless nodes collaborate to form a virtual antenna array or virtual multiple-input-multiple-output (VMISO) link. Many authors model the path loss of the VMISO link as though the elements in the virtual antenna array are colocated, even though they are spread out. In this paper, we show that the spreading causes a signal-to-noise-ratio (SNR) penalty of up to 3 dB. Moreover, in the high SNR regime, we show that the performance degradation caused by the path-loss disparity can be characterized equivalently by log-normal distribution. We use these two observations to propose a new CT link model, expressed in closed form as an outage probability based on the log-normal shadowing model. The quality of the model is evaluated by a statistical test based on Kolmogorov-Smirnov method.