Heecheol Yang

Dynamic supersymbol design of blind interference alignment for K-user MISO broadcast channels

We develop a blind interference alignment (BIA) through staggered antenna switching scheme for more realistic channel assumption. Contrary to the general assumption that the coherence time of the channel is long enough to perform BIA, when the coherence time is not long enough, channel coefficients stay constant for limited block length. Therefore, we propose a dynamic supersymbol design algorithm which can construct a supersymbol with limited block length which is determined by the coherence time of the channel. We demonstrate that the supersymbol length can be reduced significantly by aligning interferences in a hierarchical manner referred to as hierarchical BIA. Furthermore, we also show that the proposed dynamic supersymbol design algorithm achieves higher degrees of freedom than the conventional method with a given coherence time.

Degrees of freedom for K-user SISO interference channels with blind interference alignment

We derive the degrees of freedom (DoF) for K-user single-input single-output interference channels with a reconfigurable antenna at receivers, assuming linear coding strategies without channel state information at transmitters. Our DoF converse builds upon the inherent feature that channel states changing patterns of the links towards the same receiver are always identical. We prove the linear sum DoF is upper-bounded by n* K/K+n*(n*-1), n* where n* is the optimal number of preset modes among N. Moreover, we propose a linear scheme that achieves the upper-bound if K/n* is an integer. For the other cases, we give a guideline for the achievable scheme.

Hierarchical Blind Interference Alignment Over Interference Networks With Finite Coherence Time

We investigate a blind interference alignment (BIA) scheme through staggered antenna switching over various interference networks (e.g., broadcast channel, interference channel, and cellular networks) with realistic channel assumptions. In existing BIA, the coherence time of channel is assumed to be long enough, but that may not always be true in realistic scenarios. Therefore, we propose a dynamic supersymbol design method which can construct a supersymbol with limited symbol extension that is determined by the coherence time of channel. It is demonstrated that the supersymbol block length can be reduced significantly by aligning interferences in a hierarchical manner, referred to as hierarchical BIA. The key idea of hierarchical BIA is to align interferences in groups and to use the same supersymbol structure between groups, producing aligned inter-group interferences without inner-group interference. Consequently, it is observed that with a given coherence time the proposed dynamic supersymbol design that exploits hierarchical BIA achieves higher degrees of freedom than the conventional method.

Grouping based blind interference alignment for K-user MISO interference channels

We propose a blind interference alignment (BIA) through staggered antenna switching scheme with no ideal channel assumption. Contrary to the ideal assumption that channels remain constant during BIA symbol extension period, when the coherence time of the channel is relatively short, channel coefficients may change during a given symbol extension period. To perform BIA perfectly with realistic channel assumption, we propose a grouping based supersymbol structure for K-user interference channels which can adjust a supersymbol length to given coherence time. It is proved that the supersymbol length could be reduced significantly by an appropriate grouping. Furthermore, it is also shown that the grouping based supersymbol achieves higher degrees of freedom than the conventional method with given coherence time.

Topological interference management with reconfigurable antennas

We study the symmetric degrees-of-freedom (DoF) of partially connected interference networks under linear coding strategies without channel state information at the transmitters beyond topology. We assume that the receivers are equipped with reconfigurable antennas that can switch among their preset modes. In such a network setting, we characterize the class of network topologies in which half linear symmetric DoF is achievable. Moreover, we derive a general upper bound on the linear symmetric DoF for arbitrary network topologies. We also show that this upper bound is tight if the transmitters have at most two co-interferers.

Linear Degrees of Freedom of Full-Duplex Cellular Networks with Reconfigurable Antennas

In this paper, we characterize the linear degrees of freedom (DoF) of a cellular network in which the base station (BS) operates in a full-duplex (FD) mode and the users operate in a half-duplex mode. We assume that the BS and the users are equipped with reconfigurable antennas which can be switched between their preset modes. We consider two practical scenarios for different assumptions on channel state information at the transmit sides (CSIT), referred to as no CSIT and partial CSIT models. To derive the inner-bounds for two scenarios, we propose a new achievable scheme which enables interference alignment between uplink and downlink interference signals at each user via preset mode switching of reconfigurable antennas. The key concept of our scheme is to align the interference signals of uplink transmission at the downlink users, through the identical preset mode pattern over the multiple of downlink transmission periods and silence periods of the BS. We also develop an outer-bound on the linear sum DoF of the cellular network for the no CSIT model, which matches up with the inner-bound. Moreover, we also provide a natural variant of the proposed scheme when considering residual self-interference at the FD BS, which can alleviate the shortcoming of the existing self-interference cancellation techniques.

Linear Degrees of Freedom of Full-Duplex Cellular Networks With Reconfigurable Antennas

We derive the linear degrees of freedom (DoF) of a cellular network without channel state information at the transmit sides in which the base station operates in a full-duplex mode, and the base station and users are equipped with reconfigurable antennas which can switch among their preset modes. To derive an inner- bound, we propose an achievable scheme to align interferences from uplink users to downlink users via preset mode switching of reconfigurable antennas. The key concept of our scheme is to align the interfering signals of uplink transmission at the downlink users, through the identical preset mode pattern over the multiple of downlink transmissions and silences of the base station. We also develop an outer- bound on the linear sum DoF of the cellular network, which matches up with the inner-bound.

Topological Interference Management With Reconfigurable Antennas

We study the symmetric degrees-of-freedom (DoF) of partially connected interference networks under linear coding strategies without channel state information at the transmitters beyond topology. We assume that the receivers are equipped with reconfigurable antennas that can switch among their preset modes. In such a network setting, we characterize the class of network topologies in which half linear symmetric DoF is achievable. Moreover, we derive two general upper bounds on the linear symmetric DoF for arbitrary network topologies. We also demonstrate the tightness of our bounds for the class of network topologies in which all the transmitters in the network have at most two co-interferers.

Wireless power transfer techniques for cell balancing of battery management systems

Wireless power transfer techniques are being used in diverse areas such as electric cars and charging electric devices. This paper deals with cell balancing problems for battery management systems. We propose novel active cell balancing techniques with modified wireless power transfer technique. It can be used for active cell balancing, and it has the advantage of scalability of battery cell structure.