Kiyeon Kim

The Feasibility of Interference Alignment for Full-Duplex MIMO Cellular Networks

The feasibility condition of interference alignment (IA) for full-duplex (FD) multiple-input multiple-output (MIMO) cellular networks is considered. A necessary condition and a sufficient condition on the IA feasibility are established, characterizing the optimal sum degrees of freedom (DoF) for a broad class of network topologies. The necessary and sufficient condition is shown specially for a class of symmetric network topologies. The results demonstrate that FD operation at the base station with appropriate IA is able to improve the sum DoF than the conventional half-duplex operation.

Generalized Inverse Aided PAPR-Aware Linear Precoder Design for MIMO-OFDM System

We propose a linear precoding scheme for a single user multiple-input-multiple-output orthogonal frequency division multiplexing (OFDM) system to minimize peak to average power ratio (PAPR) by using redundant spatial resources at the transmitter through a singular-value-decomposition-based generalized inverse. The proposed precoder based on the generalized inverse is composed of two parts. One is for minimizing PAPR, and the other is for obtaining the multiplexing gain. Moreover, the proposed precoder contains a scalar parameter α that quantifies the received signal-to-noise power ratio (SNR) loss at the cost of PAPR reduction. Even in cases of small SNR loss, the proposed scheme dramatically reduces PAPR. Furthermore, simulation results show that we can obtain a PAPR close to 1 by using dozens of transmission antennas with small SNR loss.

A Single Feedback Based Interference Alignment for Three-User MIMO Interference Channels with Limited Feedback

Conventional interference alignment (IA) for a MIMO interference channel (IFC) requires global and perfect channel state information at transmitter (CSIT) to achieve the optimal degrees of freedom (DoF), which prohibits practical implementation. In order to alleviate the global CSIT requirement caused by the coupled relation among all of IA equations, we propose an IA scheme with a single feedback link of each receiver in a limited feedback environment for a three-user MIMO IFC. The main feature of the proposed scheme is that one of users takes out a fraction of its maximum number of data streams to decouple IA equations for three-user MIMO IFC, which results in a single link feedback structure at each receiver. While for the conventional IA each receiver has to feed back to all transmitters for transmitting the maximum number of data streams. With the assumption of a random codebook, we analyze the upper bound of the average throughput loss caused by quantized channel knowledge as a function of feedback bits. Analytic results show that the proposed scheme outperforms the conventional IA scheme in term of the feedback overhead and the sum rate as well.

Performance Analysis of Random Beamforming for MIMO Broadcast Channel: Outage Probability Approach

Random beamforming has been considered as a practical scheme for MIMO BC system while achieving asymptotically optimal growth rate. However, this advantage is in terms of average sum rate performance, which is less meaningful when the quality of service is considered in system design. In this paper, we study the outage probability performance of random beamforming for both single receive antenna and multiple receive antenna with ZF receiver cases to consider the quality of service issues such as required data rate and outage probability itself. For single receive antenna case, the outage probability is lower bounded along with SNR due to its interference-limited nature. When multiple receive antennas are deployed at each user, the outage probability achieves the diversity of the number of users, but it has power penalty as much as the multiplexing gain. We also show exploiting multiple antennas at each user achieves larger multiplexing gain for given required data rate and outage probability. However, in low SNR regime, using single receive antenna reduces receiver complexity while achieving little performance degradation compared to multiple receive antenna case.

The Feasibility of Interference Alignment for MIMO Interfering Broadcast—Multiple-Access Channels

The feasibility conditions of interference alignment (IA) are analyzed for interfering broadcast-multiple-access channels in which one cell operates as downlink but the other cell operates as uplink. Under a general multiple-input and multiple-output antenna configuration, a necessary condition and a sufficient condition for one-shot linear IA are established, i.e., linear IA without symbol or time extension. In various example networks of interest, the optimal sum degrees of freedom (DoFs) are characterized by the derived necessary condition and sufficient condition. For symmetric DoF within each cell, a sufficient condition is established in a more compact expression, which yields the necessary and sufficient condition for a class of symmetric DoFs. An iterative construction of transmit and receive beamforming vectors is further proposed, which provides a specific beamforming design satisfying one-shot IA. Simulation results demonstrate that the proposed IA not only achieves larger DoF, but also significantly improves the sum rate over the single-cell operation in the practical signal-to-noise ratio regime.

Two stages power allocation for band aggregated single carrier-FDMA with Zeroforcing-FDE

In this paper we derive the power loading method for Band Aggregation (BA) Single Carrier-Frequency Division Multiple Access (SC-FDMA) with Zero-Forcing Frequency Domain Equalizer (ZF-FDE). In previous research [6], they derive the optimal power allocation for SC-FDMA with single band, however, this result cannot directly be extended to multiple bands. Thus, we proposed sub-optimal the two stages power loading scheme for SC-FDMA with ZF-FDE in multiple bands. First, we optimize the total powers of each band and then powers of each sub-carrier are optimized by using optimal power in the first step. Simulation results show that the proposed power control is particularly effective in improving the achievable data rate at low Signal to Noise Ratio (SNR).