Rate Maximization under Partial CSIT for Multi-Stage/Hybrid BF under Limited Dynamic Range for OFDM Full-Duplex Systems
Résumé
This paper considers a bidirectional full-duplex Multi-Input Multi-Output (MIMO) OFDM system. The limited dynamic range (LDR) noise model takes into account the hardware impairments in the radio frequency (RF) chain and is thus more practical. Hence we propose a beamforming (BF) design
which takes into account the LDR noise characteristics and also is robust to imperfections in the estimated channel. At the transmit side, we introduce a two stage beamformer (BF) with an inner BF of lower dimension and an outer BF of higher dimension, both BFs being at the digital (baseband) side. The inner BF in OFDM domain handles directive transmission, while the outer BF in time domain handles self interference (SI). At the receive side, we propose a hybrid combiner which involves an analog phase shifter based BF, with fewer RF chains compared to the number of receive antennas and a digital (baseband) BF in OFDM domain. The analog BF helps reduce SI before analogto-digital conversion (ADC). All the BFs are optimized using maximization of the expected weighted sum rate (WSR) which is solved using an alternating minorization approach. The proposed multi-stage BF architecture has multiple advantages including SI reduction during OFDM cyclic prefixes, with uplink (UL) or downlink (DL) possibly using different numerology or being asynchronous, allowing proper ADC operation.