Zubia Ishrat

Two-hop relay networks for critical industries require high reliability within a limited spectrum. The lower hop between densely populated user equipment (UE) and the relay nodes (RNs) is assumed to have low spectral efficiency due to the inexpensive low-powered UEs equipped with omnidirectional antennas in non-line-of-sight (NLOS) conditions. Thus, spectrally efficient frequency reuse (FR) in the upper hop between RNs and base stations (BSs) is pivotal in enhancing the two-hop relay network’s uplink coverage and capacity. To achieve this objective, we propose the deployment of higher order sectorisation (HOS) at BS and directional antennas (DAs) at RNs in the upper hop and propose rotational (RFR), double (DFR), and triple (TFR) frequency reuse schemes. These schemes allow FR by exploiting the orientation of the DAs at RNs and are compared with conventional distance-based FR. Furthermore, an optimisation method is formulated to partition the limited bandwidth between the two hops to increase the average end-to-end uplink capacity while using the proposed FR schemes on the upper hop. When evaluating system performance with HOS at BSs (upper hop) and RNs (lower hop) in irregular cellular layout, the statistical evaluation of uplink interference becomes computationally expensive. To tackle this issue, we developed a semi-analytical model to efficiently compute the statistical distribution of uplink interference with reduced time and complexity. It is shown that this model is an accurate tool for performance assessments, which also validate the end-to-end two-hop capacity improvements up to 73% and 110% using the proposed DFR and TFR schemes, respectively.

We evaluate the performance of a low-power narrowband system utilising higher-order sectorisation (HOS) at the base stations (BS) and directional antennas (DA) at fixed user equipment (UE). We use a specific rotational frequency reuse scheme (RFR) for directional UEs and extend it for HOS (3, 6 and 12 sectors) by considering antenna orientations for interference avoidance. We propose two novel schemes for directional UEs with a cluster size less than one, named double frequency reuse (DFR) and triple frequency reuse (TFR). These schemes are tested and compared to conventional frequency reuse (CFR) through simulations in a realistic geographic terrain. The simulation results indicates that the proposed schemes are helpful to achieve higher capacity while using different BS and UE antenna beamwidths. It is shown that scheme RFR provides a performance enhancement compared to CFR only with wider UE antenna beamwidths. The implementation of DFR achieves reduced outage probability and offers a large increase in average spectral efficiency per cell (ASE) of up to 84.8-81.6% in 6 and 12 sectored system. The scheme TFR provides a maximum ASE of up to 149-153% in 6 and 12 sectored system. However, in a six-sectored system, TFR only meets the coverage criteria with a narrow beamwidth antenna of 20°.