Kaushik Josiam

Feasibility study on full-duplex wireless millimeter-wave systems

To enable simultaneous transmit and receive operations on the same frequency band, also known as full duplex, on adjacent panels of a millimeter wave (mmWave) base station (BS), we benchmark the amount of leakage interference from the transmitter to the receiver. We construct a self-interference channel model consisting of line-of-sight (LOS) leakage and non-LOS (NLOS) reflections from nearby clusters. From simulations, we further show that due to antenna beamforming in mmWave systems, the LOS leakage interference is subdued, whereas the NLOS leakage is amplified. For some BS designs, the NLOS leakage is likely to be the dominant interference. It impacts system designs in two ways. First, the worst case interference can still saturate the receiver chain and would require analog and digital cancellation in addition to the isolation provided by antenna beamforming. Second, due to the delay associated with NLOS reflective components, the cancelers would need to accommodate a large dynamic delay.

Low complexity RF beam search algorithms for millimeter-wave systems

We consider a millimeter wave communication system with multiple RF beam-forming chains each capable of forming beams in different spatial directions. The optimal codebook-based RF beam search algorithm has an exponential complexity in both the number of RF chains at the transmitter and at the receiver, which is infeasible in practice. To enable implementations that scale with increasing number of RF chains, we propose a class of RF beam search algorithms with varying complexities that iteratively search for the capacity maximizing RF beams over subsets of RF chains. The performances of the two linear variations of the proposed algorithm, jointly linear and separately linear, are evaluated in a millimeter wave cellular setting that involves reference symbol transmission from the mobile station to the base station. We show that, for a 2 × 2 system, using the proposed algorithms achieves a computation savings of about 86% with minimal performance loss.

Intelligent coding in relays

Recently, we have seen a lot of industry activity that explores alternative architectures based on a multihop relay model for future wireless networks. This type of relay-based architecture is incited by an expected tenfold increase in peak data rates and two times increase in spectral efficiency of the future beyond third generation (3G) and fourth generation (4G) systems relative to the current 3G systems.

A practical perspective on cooperative relaying in cellular systems

Relays are used to forward data from the source to the destination. There are scenarios wherein a relay is the only means for the data to reach the destination. In this paper, we will focus on scenarios wherein one or more relays are used to forward data to the destinations when the destination is already in the coverage area of the source. This latter scenario has been studied under the term cooperative relaying, as a scheme that primarily aids in improving the throughput within a given coverage area. Our goal is to take previously postulated studies and evaluate achievable cooperative relaying gains in more realistic settings. In discussing the gains, we first identify the practical constraints and study the implications of adding such constraints on the gains that can be extracted from cooperative relaying.