Hyukjoon Kwon

Interference mitigation in MIMO interference channel via successive single-user soft decoding

This paper examines a practical way of mitigating interference in multi-input multi-output (MIMO) interference channel when each user is constrained to use a point-to-point code. It was recently shown that the capacity region of interference channel with point-to-point codes can be established by a combination of two schemes: treating interference as noise and joint decoding. In practice, a straightforward implementation of a joint decoding receiver could be significantly more complex than treating interference as noise. Thus, as a low-complexity approach to joint decoding, this paper proposes a successive single-user soft decoding receiver, which performs interference-aware detection with a priori log-likelihood ratio (LLR) and single-user soft decoding for every user successively. The proposed receiver is compared with a receiver treating interference as noise and a receiver performing interference-aware detection without a priori LLR and single-user decoding for the desired user only. Simulation results show that the proposed receiver significantly outperforms these existing receivers.

Successive Interference Cancellation via Rank-Reduced Maximum A Posteriori Detection

This paper proposes a codeword-based iterative detection and decoding (IDD) algorithm for multiple-input multiple-output (MIMO) systems. In the proposed algorithm, multiple streams in a codeword are jointly detected at the rank-reduced (RR) maximum a posteriori (MAP) receiver and inter-stream interference is mitigated with successive interference cancelation (SIC). Thus, the algorithm is abbreviated to RR-MAP-SIC. Recent wireless standards such as Long-Term Evolution require the system to encode data bits per codeword, not per stream. As a result, conventional SIC algorithms could lose joint information among streams in a codeword because different streams of the same codeword are treated as interference. Instead, the proposed RR-MAP-SIC minimizes the loss of joint information by using the rank-reduced MAP detector. In addition, this paper compares the detector complexity of RR-MAP-SIC and investigates how the probability of symbol error is changed in terms of the covariance of the residual interference. As the number of iterations increases, the covariance is reduced so that the error events also decrease. Lastly, the extrinsic information transfer (EXIT) chart is used to analyze the performance of RR-MAP-SIC. Simulation results demonstrate the superiority of RR-MAP-SIC over the conventional algorithm and numerically verify the EXIT chart analysis.

Si-based optical I/O for optical memory interface

Optical interconnects may provide solutions to the capacity-bandwidth trade-off of recent memory interface systems. For cost-effective optical memory interfaces, Samsung Electronics has been developing silicon photonics platforms on memory-compatible bulk-Si 300-mm wafers. The waveguide of 0.6 dB/mm propagation loss, vertical grating coupler of 2.7 dB coupling loss, modulator of 10 Gbps speed, and Ge/Si photodiode of 12.5 Gbps bandwidth have been achieved on the bulk-Si platform. 2x6.4 Gbps electrical driver circuits have been also fabricated using a CMOS process.

Interference-Aware Interference Mitigation for Device-to-Device Communications

This paper proposes a way of applying interference- aware interference mitigation algorithms to device- to-device (D2D) communications in cellular networks for system throughput improvement. One of main purposes for using D2D communications is to offload throughput passing through a base station in cellular networks. In this sense, interference management between cellular and D2D signals is inevitable for both cellular and D2D mobile stations (MSs). Recently, interference-aware interference mitigation algorithms have been proposed in a theoretical aspect as well as a practical aspect. These algorithms operate based on interference information given at a MS, which can be obtained via network assistance or blind estimation. This paper explains how interference- aware algorithms can be applied to D2D communications in cellular networks. Moreover, this paper analyzes the throughput performance by deriving the rate upper-bounds. Simulation results demonstrate that the system throughput can be significantly improved while not losing the performance of a cellular MS too much.

Interference-Aware Interference Cancellation Using Soft Feedback via Network Assistance

This paper proposes an interference-aware interference cancellation (IAIC) algorithm that effectively mitigates inter-cell interference. In modern cellular networks, a serving signal could be disrupted due to interfering signals transmitted from neighbor cells in proximity to the serving cell. In order to overcome the disturbance of interfering signals, the recent 3GPP standard specification has explored a way of using network assistance, called network-assisted interference cancellation and suppression (NAICS). IAIC is in the same research direction of NAICS such that decoding an interfering signal as well as a serving signal is enabled via network assistance. Hence, IAIC is able to decode both signals as in a multiple access channel (MAC). However, a serving signal is only of concern while all decoded signals are of concern in a MAC. Using this characteristic, IAIC can be implemented as a practical solution. This paper demonstrates that the performance of IAIC is superior as well as requiring less complexity.

Symbol-level combining for hybrid ARQ on interference-aware successive decoding

This paper proposes a symbol-level combining (SLC) scheme for hybrid automatic-repeat-request (HARQ), being used with an interference-aware successive decoding (IASD) algorithm [1]. Recently, it is revealed that the capacity in an interference channel over point-to-point codes can be achieved by combining two schemes: one is jointly decoding an interfering signal with a serving signal and the other is treating it as noise. Due to its high computational complexity, joint decoding can be practically replaced with successive decoding as suggested in [1]. However, when HARQ is enabled, it has been not well defined how interference should be handled at each transmission. Since interference is changed at each transmission, it is not helpful to store the information of interfering signals. Instead, the proposed scheme employes the decoded information of interfering signals in order to convert an interference channel to a point-to-point channel. The proposed scheme only requires a fixed size of memory and does not increase the detector complexity of IASD with respect to the number of retransmission. Simulation results demonstrate the superiority of the proposed scheme to the optimal SLC scheme at the conventional receiver.

Blind Decoding of Control Channel for Other Users in 3GPP Standards

This paper explores the blind decoding of control channels for obtaining other user identities in 3GPP specification, such as high-speed packet access and long-term evolution. The reliable decoding of control channels with user identities is crucial to mitigate inter-cell interference as well as multi-user interference. This paper exploits a method of user identity filtering followed by a method of user identity detection based on the traffic persistency, which is common to all standards. Hence, the proposed methods are applicable to all the standards regulated by 3GPP specification. In particular, this paper analyzes the proposed other user identity detection algorithm under the random coding. Simulation results show that the proposed method is reliable even at low SNRs and is also aligned with the analysis.

Successive Interference Cancelation via Rank-Reduced Maximum Likelihood Detection

This paper proposes a codeword-based iterative detecting and decoding (IDD) algorithm using a rank- reduced maximum likelihood (ML) detector with pre- whitened interference over multiple-input multiple- output (MIMO) channels. This iterative algorithm operates on the principle of successive interference cancelation (SIC) where all the layers per codeword are decoded together at each iteration. The recent wireless standard requires to encode data bits per codeword, not per layer at multiple antennas. Thus, SIC algorithms based on layer-separating detectors could lose joint information between layers in a single codeword. Instead, the proposed algorithm minimizes this loss by using rank-reduced ML detectors over soft feedback. Simulations are performed on a space-time bit-interleaved coded modulation over Rayleigh fading channels, and demonstrate the proposed SIC algorithm is superior to comparable iterative and non-iterative IDD algorithms.