A radio communication system comprising: a base station; and a plurality of radio communication apparatuses (21 - 25) including first-type and second-type radio communication apparatuses, the first-type radio communication apparatuses being able to autonomously perform data communication without a user operation, and the second-type radio communication apparatuses performing data communication in response to a user operation; wherein the base station is configured to: when the plurality of radio apparatuses belong to a same cell, classify at least some of the plurality of radio communication apparatuses into a plurality of groups including first and second groups, and assign to the first group (21, 22) a first signal sequence that has a property of being orthogonal to a signal sequence obtained by cyclically shifting the first signal sequence, and assign to the second group (23, 24) a second signal sequence that has a property of being orthogonal to a signal sequence obtained by cyclically shifting the second signal sequence, the second signal sequence being different from the first signal sequence and from the signal sequence obtained by cyclically shifting the first signal sequence; and wherein each of the plurality of radio communication apparatuses is configured to: when the radio communication apparatus belongs to the first group, perform spread modulation on data using the first signal sequence or the signal sequence obtained by cyclically shifting the first signal sequence, and transmit the data to the base station, and when the radio communication apparatus belongs to the second group, perform spread modulation on data using the second signal sequence or the signal sequence obtained by cyclically shifting the second signal sequence, and transmit the data to the base station; and wherein the base station classifies the first-type radio communication apparatuses (21 - 24) into the plurality of groups, and does not classify the second-type radio communication apparatuses into any of the groups. a base station; and a plurality of radio communication apparatuses (21 - 25) including first-type and second-type radio communication apparatuses, the first-type radio communication apparatuses being able to autonomously perform data communication without a user operation, and the second-type radio communication apparatuses performing data communication in response to a user operation; wherein the base station is configured to: when the plurality of radio apparatuses belong to a same cell, classify at least some of the plurality of radio communication apparatuses into a plurality of groups including first and second groups, and assign to the first group (21, 22) a first signal sequence that has a property of being orthogonal to a signal sequence obtained by cyclically shifting the first signal sequence, and assign to the second group (23, 24) a second signal sequence that has a property of being orthogonal to a signal sequence obtained by cyclically shifting the second signal sequence, the second signal sequence being different from the first signal sequence and from the signal sequence obtained by cyclically shifting the first signal sequence; and when the plurality of radio apparatuses belong to a same cell, classify at least some of the plurality of radio communication apparatuses into a plurality of groups including first and second groups, and assign to the first group (21, 22) a first signal sequence that has a property of being orthogonal to a signal sequence obtained by cyclically shifting the first signal sequence, and assign to the second group (23, 24) a second signal sequence that has a property of being orthogonal to a signal sequence obtained by cyclically shifting the second signal sequence, the second signal sequence being different from the first signal sequence and from the signal sequence obtained by cyclically shifting the first signal sequence; and wherein each of the plurality of radio communication apparatuses is configured to: when the radio communication apparatus belongs to the first group, perform spread modulation on data using the first signal sequence or the signal sequence obtained by cyclically shifting the first signal sequence, and transmit the data to the base station, and when the radio communication apparatus belongs to the second group, perform spread modulation on data using the second signal sequence or the signal sequence obtained by cyclically shifting the second signal sequence, and transmit the data to the base station; and when the radio communication apparatus belongs to the first group, perform spread modulation on data using the first signal sequence or the signal sequence obtained by cyclically shifting the first signal sequence, and transmit the data to the base station, and when the radio communication apparatus belongs to the second group, perform spread modulation on data using the second signal sequence or the signal sequence obtained by cyclically shifting the second signal sequence, and transmit the data to the base station; and wherein the base station classifies the first-type radio communication apparatuses (21 - 24) into the plurality of groups, and does not classify the second-type radio communication apparatuses into any of the groups.