Cellular radio communication system, base station, radio terminal and radio communication method

A base station which uses OFDMA (Orthogonal Frequency Division Multiple Access) scheme for communication to radio terminals, comprising:

• a reception section configured to receive classification information for classifying the radio terminals respectively under any one of a plurality of groups from the radio terminals;
• a group determining section configured to determine groups under which the radio terminals are to be classified based on the classification information received;
• a channel determining section configured to determine frequency channels to assign to the radio terminals;
• a slot distribution section configured to distribute slots which are time frame of constant length to the groups;
• a slot format storage configured to store slot formats for the groups, defining an arrangement of at least one pilot symbol for synchronization, at least one pilot symbol for transmission path estimation and data symbols for transmitting transmission data;
• a notification section configured to notify each of the radio terminals of control information representing a slot format of the group under which the radio terminal is classified, the frequency channel assigned to the radio terminal and positions of slots distributed to the group under which the radio terminal is classified;
• a slot creation section configured to create slot data at each slot position, including a plurality of symbol based on transmission data directed to radio terminals which belong to the group to which the slot position is assigned, information of the frequency channels assigned to the radio terminals in the group, data for synchronization specified beforehand, data for the transmission path estimation specified before hand and a slot format associated with the group;
• an OFDM modulation section configured to OFDM-modulate the respective symbols included in the slot data created to generate a plurality of OFDM symbols;
• and
• a transmission section configured to transmit the plurality of OFDM symbols as OFDM slot data.

A radio terminal which uses OFDMA (Orthogonal Frequency Division Multiple Access) scheme for communication from a base station, comprising:

• a classification information creation section configured to create classification information for requesting classifying into any one of a plurality of group;
• a transmission section configured to transmit the classification information created to the base station;
• a reception section configured to receive OFDM slot data as a plurality of OFDM symbols from the base station;
• and
• a control information acquisition section configured to acquire control information from the base station, wherein the control information indicates (A) a slot format associated with a group classified into by the base station which defines an arrangement of at least one pilot symbol for synchronization, at least one pilot symbol for transmission path estimation and data symbols for transmitting transmission data, (B) a frequency channel assigned by the base station, and (C) positions of slots which are time frame of constant length, distributed to said group;
• an OFDM demodulation section configured to perform a fast Fourier transform on the respective OFDM symbols in the OFDM slot data received at slot positions indicated in the control information to separate the each OFDM symbol into a plurality of subcarriers respectively, and carry out synchronization processing, transmission path estimation processing and demodulation processing according to the slot format indicated in the control information using subcarriers which belong to the frequency channel indicated in the control information.

A radio communication method in which an OFDMA (Orthogonal Frequency Division Multiple Access) scheme is used for communication from a base station to radio terminals, comprising:

• transmitting classification information for classifying the radio terminals respectively under any one of a plurality of groups from the radio terminals to the base station;
• determining groups under which the radio terminals are to be classified based on the classification information;
• determining frequency channels to assign to the radio terminals;
• distributing slots which are time frame of constant length to the groups;
• notifying each of the radio terminals of the control information representing a slot format of the group under which the radio terminal is classified, the channel assigned to the radio terminal and positions of slots distributed to the group under which the radio terminal is classified, wherein the slot format defines an arrangement of at least one pilot symbol for synchronization, at least one pilot symbol for transmission path estimation and data symbols for transmitting transmission data;
• creating slot data including a plurality of symbol in each slot position based on transmission data directed to radio terminals which belong to the group to which the slot position is assigned, information of the frequency channel assigned to radio terminals in the group, data for synchronization specified beforehand, data for the transmission path estimation specified before hand, and a slot format associated with the group;
• OFDM-modulating the respective symbols included in the slot data to generate a plurality of OFDM symbols;
• transmitting the plurality of OFDM symbols as OFDM slot data, from the base station to the radio terminals belonging to the group;
• receiving the OFDM slot data transmitted from the base station at radio terminals;
• receiving the control information transmitted from the base station at radio terminals;
• performing a fast Fourier transform on the respective OFDM symbols in the OFDM slot data at slot positions indicated in the control information to separate the each OFDM symbol into a plurality of subcarriers;
• and
• carrying out synchronization processing, transmission path estimation processing and demodulation processing according to the slot format indicated in the control information using subcarriers which belong to the frequency channel indicated in the control information.