# A Review on Millimeter-Wave Hybrid Beamforming for Wireless Intelligent Transport Systems
## 3 An In-Depth Analysis of the mmWave Hybrid Beamforming Landscape
### Duplex  
Full-duplex communication is beneficial for hybrid beamforming, as it significantly boosts system performance. * **Full-Duplex with CSI** Full-digital precoders are used to obtain the baseband precoder and RF beamformer in HBF systems. The mm-wave frequency band is suitable for this hybrid beamforming full-duplex. In order to reduce the amount of self-interference, the RF beamformer weight, precoder, and combiner matrices for both the transmitter and the receiver are developed simultaneously. After the whole digital solution is acquired, the beamformer, precoder, and combiner matrices are generated using an iterative procedure that is based on the ideal simplified condition of perfect channel state information (CSI). Then, the HBF solution is derived from the digital response using the least-squares approach [65]. * **Full-Duplex with RF Chain having Dynamic Range** A mixed beamforming architecture enables a mm-wave receiver to operate in full-duplex mode, establishing simultaneous in-band connections and communications with two devices. This design offers beam alignment schemes and codebook-based analog beamforming. For full-duplex system studies, such as those including beamforming-based approaches and analog and/or digital self-interference cancelation, it is helpful to determine the amount of self-interference reduction required at various locations in the receiver. The goal of this effort should not be to provide a fully operational mm-wave  
Figure 11: Fully connected architecture [64]. Figure 10: Subconnected architecture with switches [64]. system; rather, it is meant to demonstrate a design technique that takes into account certain practical aspects. This approach has the potential to be a gold standard for systems limited to a certain dynamic range and those that function in the real world [66]. * **Full-Duplex with Limited Dynamic Range** With the advent of full-duplex (FD) radio, which allows for simultaneous transmission and reception on the same frequency band, data speeds are increased by a factor of up to two. An improved weighted sum rate (WSR) in a single-cell mm-wave multiple-input multiple-output (MIMO) FD system is the goal of a novel hybrid beamforming (HYBF) design. The HYBF technique is unique in that it considers not only the overall sum-power restrictions but also the actual per-antenna power limits. Users of the uplink (UL) and FD BS have their demands satisfied by a novel optimum power distribution approach that takes into account interference, self-interference (SI), and LDR noise. A completely digital half-duplex (HD) system with varying amounts of LDR noise and RF chain numbers may reach the maximum gain for a multi-user (MU) mm-wave FD system. This layout outperforms the HD method using a small number of RF chains across the board when it comes to LDR noise. An advantage of this design is that it allows for amplitude control at the analog stage [67]. * **Sensing and Full-Duplex Communication** The capacity of Integrated Sensing and Communication (ISAC) to enhance spectrum efficiency via the sharing of hardware and spectrum to facilitate simultaneous sensing and communication activities has garnered significant attention in recent years. One important technique that might aid ISAC usage is in-band full-duplex (FD), which can transmit and receive data simultaneously. A large-scale MIMO base station (BS) node communicates with a downlink (DL) multi-antenna user using a hybrid analogue and digital (A/D) beamforming process. When using the BS receiver, the DL user may pick up radar objects inside its coverage area by using the same waveform [68]. * **Full-Duplex with Power Management** Due to the elimination of the necessity for two distinct channels for data transmission and reception, hybrid beamforming and combining for mm-wave full-duplex MIMO interference channel full-duplex (FD) communication has the potential to revolutionize wireless communications.