A Secure Waveform Format for Interference Mitigation in Heterogeneous Uplink Networks

In heterogeneous networks (HetNets), providing reliable and secure transmission uplinks to combat the potential interference is a major challenge. We address the multi-tier uplink interference issue, inspired by the secure waveform design in spatial and spectral domains to improve the system reliability and capacity. A system combining a beamforming (BF) technique based on uniform circle array and a frequency-hopping (FH) technique has been developed under an orthogonal frequency division multiplex (OFDM) scheme (i.e., OFDM/FH-BF system). The modified receiver structure is designed for the hopped multicarrier signals. The convergence of the adaptive FH-BF system, which is critical for supporting highly mobile users in HetNets, is investigated. The combined effects of FH and BF techniques on system performance, in terms of output signal-to-interference-plus-noise ratio and bit-error-rate (BER), are fully studied. The simulation results show that the proposed OFDM/FH-BF system converges in a reasonably low number of snapshots, which meets the strict requirement for serving rapidly moving users. The combination of BF and FH techniques can offer reliable uplinks by mitigating the potential interference. In particular, at the cell edge with multiple interferers K, the FH technique becomes the dominant anti-interference approach and the BER decreases with increasing size of the frequency slots set q.