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.



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.



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 Multiuser MIMO transmission weight by outdated CSI cannot steer the null to multiplexing UTs whereas causes undesired IUI.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.


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.


Contributed work

Here will list my contribution since I joined CU wireless communications lab..