Communication terminal device, base station device and radio communication system in which a random access channel is accessed by employing an initial access code randomly selected from a selected group of initial access codes

A base station apparatus using a random access channel (RACH), the apparatus comprising:

• a receiving section that receives data transmitted for contention based initial access from a radio terminal apparatus using a random access channel (RACH), the radio terminal apparatus comprising a receiving section that receives a pilot signal transmitted from the base station apparatus, a measuring section that measures a reception power of the pilot signal, a selecting section that selects, based on the reception power measured by the measuring section, one code group among a plurality of code groups into which codes for contention based initial access before a connection to the base station apparatus is established are divided, the code groups being respectively associated with different ranges of reception powers at the radio terminal apparatus, and a transmitting section that performs a transmission to the base station apparatus for the contention based initial access via the RACH using a code randomly selected from codes of the selected one code group, whereby the selected one code group to which said code belongs provides an indication to the base station apparatus of radio condition at the radio terminal apparatus, wherein a range of a lower reception power is narrower than a range of a higher reception power such that a larger number of codes are included in a code group associated with a lower reception power than a code group associated with a higher reception power, and no code group is associated with a reception power that is less than a given value;
• an assigning section that assigns the codes to the groups which are respectively associated with the different reception powers and each of which provides an indication of radio condition at the radio terminal apparatus;
• and
• a transmitting section that transmits data to the radio terminal apparatus based on the code used in the received data.

A base station apparatus using a random access channel (RACH), the apparatus comprising:

• a transmitting section that transmits a pilot signal to a radio terminal apparatus;
• and
• a receiving section that receives data transmitted for contention based initial access before a connection of the radio terminal apparatus to the base station apparatus is established from the radio terminal apparatus using a code, which is randomly selected by said radio terminal apparatus from codes of one of groups which is selected based on a reception power of the pilot signal at the radio terminal apparatus, codes being grouped into the groups respectively associated with different ranges of reception powers of the pilot signal, and the selected one group to which the selected code belongs provides an indication to the base station apparatus of radio condition at the terminal apparatus, wherein:
• said transmitting section further transmits data to the radio terminal apparatus based on the code used in the data transmitted for the contention based initial access,
• wherein a range of a lower reception power is narrower than a range of a higher reception power such that a larger number of codes are included in a code group associated with a lower reception power than a code group associated with a higher reception power, and no code group is associated with a reception power that is less than a given value.

A radio communication system using a random access channel (RACH) comprising a base station and a terminal, wherein:

• said terminal comprises:
• a receiving section that receives a pilot signal;
• a measuring section that measures a reception power of the pilot signal;
• a selecting section that selects, based on the reception power measured by the measuring section, one code group among a plurality of code groups into which codes for contention based initial access before a connection to the base station apparatus is established are divided, the code groups being respectively associated with different ranges of reception powers at the radio terminal apparatus;
• and
• a transmitting section that transmits data for the contention based initial access via the RACH using a code randomly selected from codes of the selected one code group, whereby the selected one code group to which said code belongs provides an indication to the base station apparatus of radio condition at the radio terminal apparatus;
• and said base station comprises:
• a transmitting section that transmits the pilot signal;
• and
• a receiving section that receives from said terminal the data transmitted for the contention based initial access,
• wherein a range of a lower reception power is narrower than a range of a higher reception power such that a larger number of codes are included in a code group associated with a lower reception power than a code group associated with a higher reception power, and no code group is associated with a reception power that is less than a given value.

A method for radio communication using a random access channel (RACH), the method comprising:

• receiving a pilot signal, which is transmitted from a base station apparatus, at a radio terminal apparatus;
• measuring a reception power of the pilot signal;
• selecting, based on the reception power, one code group among a plurality of code groups into which codes for contention based initial access before a connection to the base station apparatus is established are divided, the code groups being respectively associated with different ranges of reception powers at the radio terminal apparatus;
• and
• performing a transmission to the base station apparatus for the contention based initial access via the RACH using a code randomly selected from codes of the selected one code group, whereby the selected one code group to which said code belongs provides an indication to the base station apparatus of radio condition at the radio terminal apparatus,
• wherein a range of a lower reception power is narrower than a range of a higher reception power such that a larger number of codes are included in a code group associated with a lower reception power than a code group associated with a higher reception power, and no code group is associated with a reception power that is less than a given value.