Interference management in wireless networks with limited channel information at the transmitters

• Main Author: Anand, Kushal
• Other Authors: Erry Gunawan
• Format: Theses and Dissertations
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Wireless communication systems
• Online Access: http://hdl.handle.net/10356/69486
• Institution: Nanyang Technological University

In this thesis, we investigate various methods of interference mitigation techniques in wireless networks under limited or imperfect channel state information (CSI) at the transmitters (CSIT). We consider various useful networks models, especially the interference channels (ICs), the X channels (XCs) and a special case of broadcast channel. Since relays can help in greatly reducing the channel feedback overhead to the source transmitters, we also consider relay-aided interference and X channels (without any CSI feedback to the source transmitters) where the relay aids in interference alignment (IA) or interference neutralization (IN) to maximize the network degrees of freedom (DoF). First of all, we consider the single-input-single-output (SISO) ICs and XCs (without relays) under hybrid CSIT framework where each transmitter has access to delayed global and limited amount of local instantaneous CSI. Construction schemes are proposed for these networks which achieve higher DoF than the completely delayed-CSIT based schemes using much smaller coding lengths. For the three and four-user SISO-IC, we design systematic space-time coding which can achieve both secure as well as higher DoF as compared to the existing schemes. Next, we propose a semi-blind interference alignment scheme for the broadcast network where one receiver has a reconfigurable antenna capable of creating staggered channel patterns while all other receivers are normal single antenna nodes. We propose a coding scheme for this model that attains a network DoF (optimal DoF in certain cases) which is higher than that achieved by TDMA, and requires reasonable coding lengths which is suitable for time-varying channels. In our third and fourth works, we design digital precoding algorithms for the relay-aided IC and XC respectively where the source transmitters are completely blind, and the precoding schemes are designed based on the CSI which is available only at the relay. For the relay-aided IC, we design the precoder at the relay and the receive filters at the receivers using the minimum-sum mean square error (MMSE) and the sum-rate maximization criteria. Suitable initialization method is proposed for the iterative precoder designs which not only achieves better BER performance than the IA algorithm but also attains the maximum network DoF while consuming much lesser relay power. Next, for the relay-assisted multi-input-multi-output (MIMO) X channel with no or limited CSI at the source transmitters, we derive the number of antennas required at the relay to achieve the maximum network DoF using interference alignment. Our proposed DoF achievability scheme attains the maximum network DoF for both time-varying and time-invariant channels and under arbitrarily low power at the relay node. Finally, the MMSE precoders are derived for the case of relay-aided $K\mbox{-user}$ SISO-X channel which show much better BER performance than the conventional IA precoder even under limited relay power. In our final work, we consider a dual-hop SISO interference channel aided by multiple relays where direct links do not exist between the transmitters and the receivers. This type of network is applicable to the situations where the relays aid in range and coverage extension. Here, we consider no CSI feedback to the source transmitters and imperfect (quantized) CSI feedback to the relays based on which the relays perform the precoding design. We derive the interference neutralization feasibility conditions and show that in order to attain the maximum network DoF, the overall relay power must scale at a certain minimum rate with respect to the source transmitters' powers. We derive the rate-loss upper bound for this type of network due to the quantized channel information at the relays. Based on our analysis, we propose bit scaling law and an adaptive bit allocation strategy for channel feedback by the relays and the receivers so that the overall rate loss is minimized. Finally, we propose a stochastically robust MMSE precoder which exploits the adaptive bit allocation and the corresponding channel quantization error statistics to significantly improve the network sum-rate compared to all other algorithms under limited channel resolution.