Research
Blind Adaptive Array for Spatial Spectrum Sharing
Blind Adaptive Array Algorithms
Spectrum superposing is an ultimate form of spectrum usage to resolve the frequency resource exhaustion especially in microwave band.
If all wireless communication systems use the same frequency channel, inter-system interference (ISysI) severely degrades spectral efficiency. Blind adaptive array (BAA) is one of the promising approaches to suppress ISysI without any a priori information of interference such as CSI. Although lots of BAA algorithms have been developed, they has some limitations in their applicable region.
By attracted this promising feature, a novel semi-blind approach has been proposed: CSI-aided blind adaptive array (BAA) interference suppression. This solution is the most offensive way canceling out ICI as well as IUI even in non-cooperative manner.
K. Maruta, K. Senoo, D. Hisano, Y. Nakayama, K. Nishimori, “Interference Gaussianization: Time-Domain Inter-Symbol Spreading for Blind Adaptive Array Signal Source Identification,” IEEE Access, Vol. 9, pp.89539-89553, June 2021.
K. Maruta, C-J. Ahn, “Stabilised Blind Interference Suppression of Constant Modulus-based Adaptive Array over Rayleigh Fading Channels by Initial Antenna Selection,” IET Microwaves, Antennas & Propagation, Volume 13, Issue 11, p. 1876-1882, September 2019.
K. Maruta, J. Mashino, T. Sugiyama, “Blind Interference Suppression Scheme by Eigenvector Beamspace CMA Adaptive Array with Subcarrier Transmission Power Assignment for Spectrum Superposing,” IEICE Transactions on Communications, Vol.E98-B, No.06, pp.1050-1057, June 2015.
Massive MIMO
Semi-blind Uplink Interference Suppression
Although the massive MIMO can extremely enhance the system capacity by spatially multiplexing a number of user terminals (UTs), its upper limit is forced due to limited number of orthogonal pilot sequences.
It causes inter-cell interference (ICI) between pilot signals resulting in pilot contamination and worsens estimation accuracy of CSI in addition to the additive noise effect; inter-user interference (IUI) cannot be well suppressed as well as ICI.
Massive MIMO has a potentiality for interference suppression by exploiting its excess degree of freedom (DoF) being larger than the total number of accommodating/interfering UTs.
By attracted this promising feature, a novel semi-blind approach has been proposed: CSI-aided blind adaptive array (BAA) interference suppression. This solution is the most offensive way canceling out ICI as well as IUI even in non-cooperative manner.
K. Maruta, C-J. Ahn, “Multi Modulus Signal Adaptation for Semi-Blind Uplink Interference Suppression on Multicell Massive MIMO Systems,” IEICE Transactions on Communications, Vol. E104-B, No. 2, pp. 158-168, February 2021. [RCS Technical Committee Recommended Paper]
K. Maruta, C-J. Ahn, “Improving Semi-Blind Uplink Interference Suppression on Multicell Massive MIMO Systems: A Beamspace Approach,” IEICE Transactions on Communications, Vol.E102-B, No. 8, pp.1503-1511, August 2019.
K. Maruta, C-J. Ahn, “Uplink Interference Suppression by Semi-Blind Adaptive Array with Decision Feedback Channel Estimation on Multicell Massive MIMO Systems,” IEEE Transactions on Communications, vol. 66, no. 12, pp. 6123-6134, December 2018.
Null Space Expansion
In multiuser MIMO downlink, UTs are always suffering from channel aging due to their mobility. Multiuser MIMO transmission weight by outdated CSI cannot steer the null to multiplexing UTs whereas causes undesired IUI.
Exploiting excessive DoF brought by massive antenna arrays, base station (BS) additionally perform null-steering with the use of past estimated CSIs. It can expand the null space around multiplexing UTs and suppressed IUI can be maintained even at the mobility situation.
N. Funaki, K. Maruta, C-J. Ahn, “Dimensionality Reduction of Interference Subspace for Multiuser Massive MIMO Null-Space Expansion,” Digital Signal Processing, Vol. 114, 103063, July 2021.
K. Arai, K. Maruta, C-J. Ahn, “Uplink Null-Space Expansion for Multiuser Massive MIMO in Time-Varying Channels Under Unknown Interference,” IEEE Access, Vol. 8, pp. 224292-224305, December 2020.
T. Iwakuni, K. Maruta, A. Ohta, Y. Shirato, T. Arai, M. Iizuka, “Experimental Verification of Null-Space Expansion for Multiuser Massive MIMO via Channel State Information Measurement,” IEICE Transactions on Communications, Vol.E101-B, No.3, pp.877-884, March 2018.
T. Iwakuni, K. Maruta, A. Ohta, Y. Shirato, T. Arai, M. Iizuka, “Null-Space Expansion for Multiuser Massive MIMO Inter-User Interference Suppression in Time Varying Channels,” IEICE Transactions on Communications, Vol.E100-B, No.5, pp.865-873, May 2017. [IEICE Best Paper Award]
Wireless Multihop Network
Efficient Relay Protocol
Multuhop relay is a practical means to rapidly enhance wireless communication coverage in a simple and cost-effective manner. For its relaying scheme, CSMA/CA is the possible candidate. Such distributed coordination function, however, frequently causes collision due to co-channel intra/inter-path interference which results in excessive re-transmission or packet loss.
High efficient relay protocol is one of the topic of interest, e.g. intermittent periodic transmit (IPT) wherein the core (master) node periodically transmit out data packets so as to avoid intra/inter-path interference. Another approach is to reduce transmission opportunity; wireless network coding (WNC) which can superimpose bi-directional traffic forwarding.
K. Maruta, H. Furukawa, “Highly Efficient Multi Channel Packet Forwarding with Round Robin Intermittent Periodic Transmit for Multihop Wireless Backhaul Networks,” Sensors, Vol. 17, No. 11: 2609, November 2017.
K. Maruta, J. Mashino, N. Otsuki, T. Sugiyama, “System Throughput Improvement by Optimizing Timeout for Wireless Network Coding and Frame Aggregation on CSMA/CA Bidirectional Two-Hop Relaying Prototype,” IEEJ Transactions on Electrical and Electronic Engineering, Vol.11, No.S1, pp.S115–S121, June 2016.