Jaeweon Kim

Prototyping real-time full duplex radios

In this article, we present a real-time full duplex radio system for 5G wireless networks. Full duplex radios are capable of opening new possibilities in contexts of high traffic demand where there are limited radio resources. A critical issue, however, in implementing full duplex radios in real wireless environments is being able to cancel self-interference. To overcome the selfinterference challenge, we prototype our design on a software-defined radio platform. This design combines a dual-polarization antenna-based analog part with a digital self-interference canceler that operates in real time. Prototype test results confirm that the proposed full duplex system achieves about 1.9 times higher throughput than a half duplex system. This article concludes with a discussion of implementation challenges that remain for researchers seeking the most viable solution for full duplex communications.

An energy efficient source coding and modulation scheme for wireless sensor networks

A direct sequence code division multiple access (DS-CDMA) system combined with modified minimum energy (MME) coding is proposed and analyzed. The MME coding improves energy savings and error performance of minimum energy (ME) coding by partitioning a codeword into several subframes and using indicator bits. The results show that the proposed system clearly outperforms DS-CDMA systems with or without ME coding in terms of energy consumption and bit error rate. This indicates that combining MME coding and DS-CDMA is an attractive choice for wireless sensor networks.

Multi-code multicarrier CDMA: performance analysis

A novel multi-code multicarrier code division multiple access (MC-MC-CDMA) system is proposed and analyzed in a frequency selective fading channel. By allowing each user to transmit multiple orthogonal codes, the proposed MC-MC-CDMA system can support various data rates, as required by next generation standards, and achieve spreading gain in the time domain. Multicarrier CDMA provides robustness to multipath and spreading in the frequency domain. The bit error rate of the system is analytically derived in frequency selective fading, with Gaussian noise and multiple access interference. The results show that the proposed MC-MC-CDMA system clearly outperforms both single-code multicarrier CDMA (MC-CDMA) and single-carrier multi-code CDMA in a fixed bandwidth allocation. This indicates that MC-MC-CDMA should be seriously considered for next generation cellular systems.

Cooperative Spectral Covariance Sensing under Correlated Shadowing

This paper investigates the theoretical limits of white space sensing in a cognitive radio (CR) network limited by channel correlation. In a log-normal shadowing channel, the received signal power is correlated based on the distance between the sensors and this makes sensing the presence of a signal difficult, even with several cooperative sensors. In the proposed system, each sensor uses the spectral covariance sensing (SCS) algorithm to detect the primary signal and then sends its decision statistic to the base station (BS). The BS, using the Neyman Pearson log-likelihood ratio test, makes the final decision. We analyze the probability of a false alarm (PFA) and compare it with that of the cooperative energy detector. We show that an asymptotic lower bound on the PFA is an order of magnitude lower than that of the energy detector. We also demonstrate improvements in the cooperation gain in terms of the effective number of independent sensors, and the required number of sensors for a given detection metric. The results of this paper show that cooperative SCS detection has far better white space sensing properties than cooperative energy detection in correlated channels.

Physical layer authentication using controlled inter symbol interference

Spectrum security and enforcement is one of the major challenges that need to be addressed before cognitive radios (CR) can be widely deployed for opportunistic spectrum sharing. One of the mechanisms needed to carry out spectrum enforcement is the authentication or identification of transmitters. We propose a novel scheme for authenticating transmitters at the physical layer called partial response signaling with authentication (PRSA). Our results indicate that PRSA is superior to the prior art in terms of detection performance.

Full Dimension MIMO (FD-MIMO): Demonstrating Commercial Feasibility

Massive multi-input multi-output (MIMO) is shown to significantly increase spectral efficiency by exploiting a large number of antennas to support high-order multiuser MIMO. In 3GPP Release-13, a full-dimension MIMO (FD-MIMO) technology was introduced to address practical aspects for massive MIMO in cellular systems; extensive simulations show 2–4 times capacity gain compared with current LTE systems. FD-MIMO has been identified as one of the key 5G technologies and is being continuously improved in 3GPP new radio standards. However, several practical challenges such as interference mitigation among MIMO streams for a large number of users with limited channel feedback, hardware limitations, such as calibration errors that limit the precoding capabilities need to be addressed carefully. A proof of concept (PoC) base-station and user equipment (UE) prototype has been designed to validate the potential of FD-MIMO technology and demonstrate commercial implementation feasibility. In this paper, we present theory and architecture behind an FD-MIMO prototype and share the field test results with LTE-based UEs in a multi-user MIMO setup. We also analyze the impact of transmitter and receiver calibration errors on the performance of the FD-MIMO system.