A method performed by a first wireless communication apparatus, the method comprising: distributing frequency tones of a resource unit, in the following also referred to as RU, over a distribution bandwidth as a distributed-tone RU, in the following also referred to as dRU, ; generating a plurality of subcarrier indices for the distributed-tone RU such that a distribution of the distributed-tone RU is symmetric to a direct-current, in the following also referred to as DC, tone along an axis of subcarrier indices ; and communicating wirelessly with a second wireless communication apparatus using the distributed-tone RU in a 6GHz low-power indoor in the following also referred to as LPI, system ; characterized in that the generating of the plurality of subcarrier indices comprises providing a set of subcarrier indices for a 26-tone dRU in a table such that, for a larger-sized dRU with more than 26 tones, the generating of the plurality of subcarrier indices further comprises generating another set of subcarrier indices for the larger-sized dRU from the table and using a dRU hierarchical structure with or without one or more extra tones as padding, wherein: subcarrier indices for a 52-tone dRU are generated from corresponding two 26-tone dRUs, subcarrier indices for a 106-tone dRU are generated from either corresponding four 26-tone dRUs or corresponding two 52-tone dRUs with two extra tones as padding, subcarrier indices for a 242-tone dRU are generated from corresponding two 106-tone dRUs and one 26-tone dRU with four extra tones as padding, and subcarrier indices for a 484-tone dRU are generated from corresponding two 242-tone dRUs. distributing frequency tones of a resource unit, in the following also referred to as RU, over a distribution bandwidth as a distributed-tone RU, in the following also referred to as dRU, ; generating a plurality of subcarrier indices for the distributed-tone RU such that a distribution of the distributed-tone RU is symmetric to a direct-current, in the following also referred to as DC, tone along an axis of subcarrier indices ; and communicating wirelessly with a second wireless communication apparatus using the distributed-tone RU in a 6GHz low-power indoor in the following also referred to as LPI, system ; characterized in that the generating of the plurality of subcarrier indices comprises providing a set of subcarrier indices for a 26-tone dRU in a table such that, for a larger-sized dRU with more than 26 tones, the generating of the plurality of subcarrier indices further comprises generating another set of subcarrier indices for the larger-sized dRU from the table and using a dRU hierarchical structure with or without one or more extra tones as padding, wherein: subcarrier indices for a 52-tone dRU are generated from corresponding two 26-tone dRUs, subcarrier indices for a 106-tone dRU are generated from either corresponding four 26-tone dRUs or corresponding two 52-tone dRUs with two extra tones as padding, subcarrier indices for a 242-tone dRU are generated from corresponding two 106-tone dRUs and one 26-tone dRU with four extra tones as padding, and subcarrier indices for a 484-tone dRU are generated from corresponding two 242-tone dRUs. subcarrier indices for a 52-tone dRU are generated from corresponding two 26-tone dRUs, subcarrier indices for a 106-tone dRU are generated from either corresponding four 26-tone dRUs or corresponding two 52-tone dRUs with two extra tones as padding, subcarrier indices for a 242-tone dRU are generated from corresponding two 106-tone dRUs and one 26-tone dRU with four extra tones as padding, and subcarrier indices for a 484-tone dRU are generated from corresponding two 242-tone dRUs. <EOS>