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Recently, reconfigurable intelligent surface (RIS) has immensely beendeployed to overcome blockage issue and widen coverage for enabling superiorperformance 6G networks. Mainly, systems use RIS as an assistant to redirectthe transmitter (TX) incident signal towards the receiver (RX) by configuringRIS elements amplitudes and phase shifts in a passive beamforming (PBF)process. Channel estimation (CE) based PBF schemes achieve optimal performance,but they need high overhead and time consumption, especially with high numberof RIS elements. Codebook (CB) based PBF solutions can be alternatives toovercome these issues by only searching through a limited reflection patterns(RPs) and determining the optimal one based on a predefined metric. However,they consume high power and time relevant to the used CB size. In this work, wepropose a direction based PBF (D-PBF) scheme, where we aim to map between theRXs directions and the codebook RPs and store this information in an updateddatabase (DB). Hence, if the matching between a coming RX and a particular RPexists, the proposed scheme will directly select this RP to configure the RISelements, otherwise, it memorizes this codeword for future searching. Finally,if the matching failed, searching through the memorized RPs will be done tofind the optimal one, then updating the DB accordingly. After a time period,which depends on the CB size, the DB will converge, and the D-PBF scheme willneed no searching to select the optimal RP. Hence, the proposed scheme needsextremely lower overhead, power, and time comparable to the CE and conventionalCB based solutions, while obtaining acceptable performance in terms ofeffective rate.

RXs Directions based Codebook Solution for Passive RIS Beamforming