FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] RADIO COMMUNICATION BASE STATION APPARATUS AND RADIO COMMUNICATION METHOD USED FOR MULTI-CARRIER COMMUNICATION; PANASONIC CORPORATION, A CORPORATION ORGANIZED AND EXISTING UNDER THE LAWS OF JAPAN WHOSE ADDRESS IS 1006, OAZA KADOMA, KADOMA-SHI, OSAKA, 571-8501, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. DESCRIPTION Technical Field The present invention relates to a radio transmitting apparatus and radio transmitting method. Background Art In mobile communication systems represented by a cellular communication system or radio LAN (Local Area Network) system, random access areas are provided in the transmission domain. When a terminal station (hereinafter "UE") implements an association request to a base station (hereinafter "BS") at first, or when a UE implements a new band assignment request in a centralized control system where, for example, the BS assigns transmission time and transmission frequency band to the UE , random access areas are provided in the uplink. Here, a base station is also referred to as an "access point" or "Node B." Further, in systems adopting TDMA (Time Division Multiple Access), which is currently standardized in 3GPP RAN LTE, when the initial association request is implemented (i.e. , when the 2 power supply of a UE is activated, and further when handover is performed, when communication is not performed for a predetermined period or when the transmission timing synchronization in the uplink is not established such a case where synchronization is lost due to the channel condition), a random access is utilized in the first process of acquiring uplink transmission timing synchronization, implementing an association request to the BS or implementing a band assignment request (i.e., resource request). Unlike other channels to be scheduled, reception error and retransmission occur with respect to random access bursts (hereinafter "RA bursts") transmitted in a random access area (hereinafter "RA slot") due to signature sequence collision (i.e., transmitting the same signature sequence by a plurality of UEs using the same RA slot) or due to interference between signature sequences. When RA burst collision and reception error occur, the processing delay by acquiring uplink transmission timing synchronization including RA bursts and processing delay for association request processing to BS, increase. Therefore, a reduced collision rate of signature sequences and improved detection performance of signature sequences are required. As a method of improving detection 3 performance of signature sequences, studies are underway to generate signature sequences from a GCL (Generalized Chirp Like) sequence or Zadoff-Chu sequence of low autocorrelation characteristics and low cross-correlation characteristics between sequences. In the WCDMA (Wideband-Code Division Multiple Access) system disclosed in Non-Patent Document 1, to prevent collision of preambles and identify transmitted preambles, a reduced collision rate of signatures is realized by providing a plurality (sixteen kinds) of signature sequences that can be transmitted and providing fifteen RA slots that can be selected randomly in twenty milliseconds. Further, in BS, by using code sequences of good autocorrelation characteristics and good cross-correlation characteristics between signature sequences as described above, it is possible to separate and detect individual signature sequences. Here, a preamble refers to a signal sequence which is known between the transmitting apparatus and the receiving apparatus and which forms the random access channel. Generally, a random access channel is comprised of signal sequences of good autocorrelation characteristics and cross-correlation characteristics. Further, a signature refers to individual components of a preamble 4 pattern, and, here, assume that a signature sequence is equivalent to a preamble pattern. Further, in the technique disclosed in Non-Patent Document 2, a reduced collision rate of signature sequences and improved detection performance are realized by classifying the initial cell access including RA burst transmission into the processing to start from the network side (i.e., BS side) and the processing to start from the UE side and reporting paging information including system information related to RA burst transmission by RA burst transmission from the network side to the UE. To be more specific, Non-Patent Document 2 discloses including uplink ("UL") interference information and dynamic persistent level parameter showing the retransmission time interval or the like, in paging information reported in the downlink, and reporting the paging information to a plurality of UEs one by one or at a time using PCH's (paging channels). The UE having received the paging information uses the UL interference information to set RA burst transmission power. Further, it is possible to control the error rate of RA burst transmissions and the time intervals of RA burst transmissions using the UL interference information and dynamic persistent level parameter, so that the UE can 5 control the priority of RA burst transmissions and select a more effective signature sequence. Non-Patent Document 1: 3GPP TS 25.214V6.7.1(6.Random access procedure), December, 2 00 5 TSG-RAN Working Group 2 #49, Seoul, Korea, Nov. 7-11, 2005 Non-Patent Document 2: R2-052769, LG Electronics, "Initial access for LTE" 3GPP TSG RAN WG1/2 Joint Meeting, Athens, Greece, March 27-31, 2006 Disclosure of Invention Problem to be Solved by the Invention However, with the technique disclosed in Non-Patent Document 1, in systems adopting TDMA or TDMA-FDMA, many selectable RA slots are provided, and, consequently, the domain assigned for user data transmission decreases and throughput of the overall system degrades significantly. Further, with the technique disclosed in Non-Patent Document 2, although improved detection performance of RA burst transmission is expected in the access steps to start from the network side, retransmission time intervals are controlled to reduce the collision rate of RA burst transmissions, and, consequently, the processing delay to complete RA burst transmissions increases. 6 It is therefore an object of the present invention to provide a radio transmitting apparatus and radio transmitting method for improving throughput and enabling faster initial access processing including RA burst transmission. Means for Solving the Problem The radio transmitting apparatus of the present invention employs a configuration having: an assigning section that, when a group of signature sequences that are orthogonal to each other or have low cross correlations to each other is a signature group, assigns signature sequences for use in an initial random access transmission by a radio communication terminal apparatus, from a same signature group in one or more signature groups; a control channel generating section that generates a control channel including identification information of the assigned signature sequences; and a transmitting section that transmits the generated control channel to the radio communication terminal apparatus. The radio transmitting method of the present invention includes: an assigning step of, when a group of signature sequences that are orthogonal to each other or have low correlations to each other is a signature group, assigning signature sequences for 7 use in an initial random access transmission by a radio communication terminal apparatus, from a same signature group in one or more signature groups; a control channel generating step of generating a control channel including identification information of the assigned signature sequences; and a transmitting step of transmitting the generated control channel to the radio communication terminal apparatus. it is faster burst Advantageous Effect of the Invention According to the present invention, possible to improve throughput and enable initial access processing including RA transmission. Brief Description of Drawings FIG.l is a block diagram showing the configuration of a base station apparatus according to Embodiments 1 and 2 of the present invention; FIG.2 illustrates a signature table formed with Zadoff-Chu sequences in detail; FIG. 3 is a block diagram showing the configuration of a terminal station apparatus according to Embodiments 1 and 2 of the present invention■ 8 FIG-4 is a sequence diagram showing the random access procedure between the BS shown in FIG.l and the UE shown in FIG.2; FIG.5 illustrates the operations of the signature sequence assignment control section shown in FIG.l; FIG. 6 illustrates the number of transmittable RAs per RA slot according to mutual interference power between signature sequences of the initial RA; FIG.7 illustrates a report method of signature IDs ; FIG. 8 illustrates a signature table according to Embodiment 2 of the present invention; FIG.9 illustrates the operations of a signature sequence assignment control section according to Embodiment 2 of the present invention; and FIG. 10 illustrates the number of RAs that can be transmitted per RA slot according to mutual interference power between signature sequences of the initial RA. Best Mode for Carrying Out the Invention Embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. However, in the embodiments, components having the same function will be assigned 9 the same reference numerals and overlapping explanations will be omitted. (Embodiment 1) FIG. 1 is a block diagram showing the configuration of base station apparatus 100 according to Embodiment 1 of the present invention. In this figure, a plurality of signatures generated from a single Zadoff-Chu sequence form a single group (hereinafter "signature group"), and signature table storage section 101 stores a plurality of signature groups generated from a plurality of different Zadoff-Chu sequences. Further, the signature table will be described later in detail. [0 020] Signature sequence assignment control section 102 acquires the identity of the UE targeted for paging from the higher layer (not shown), while reading out a signature sequence from signature table storage section 101 and assigning the read signature sequence to the UE of the paging target. Further, according to a detection result outputted from signature sequence detecting section 115, which will be described later, signature sequence assignment control section 102 decides whether or not to retransmit RA bursts. Signature sequence assignment control section 102 will be described later in detail. Further, signature table storage section 101 and signature sequence assignment 10 control section 102 function as an assigning means. Paging information processing section 103 is provided with paging information generating section 104, coding section 105 and modulating section 106, and functions as a control channel generating means. Paging information generating section 104 generates a paging channel (i.e., downlink control channel) including the signature ID (and RA slot information if necessary) outputted from signature sequence assignment control section 102 and paging control information (i.e., information such as the identity of the UE and others reported by paging) inputted from the higher layer (not shown). The generated paging channel is outputted to coding section 105. Coding section 105 encodes the paging channel outputted from paging information generating section 104, and modulating section 106 modulates the encoded paging channel by a modulation scheme such as BPSK and QPSK. The modulated paging channel is outputted to multiplexing section 110. DL data transmission processing section 107 is provided with coding section 108 and modulating section 10 9, and performs transmission processing of DL transmission data. Coding section 108 encodes the DL transmission data, and modulating section 109 modulates the encoded DL transmission data by a modulation scheme such as BPSK and QPSK, and outputs 11 the modulated DL transmission data to multiplexing section Ho . Multiplexing section 110 time-multiplexes, f requency-riiUi tip l exes , spatial-multiplexes or code-multiplexe^ the paging channel outputted from modulating section 106 and the DL transmission data transmitter from modulating section 10 9, and outputs the multiplex signal to RF transmitting section 111. RF transmitting section 111 performs predetermined transmission processing such as D/A conversion, filtering and up-conversion on the multiplex signal outputted from multiplexing section 110, and transmits the signal after radio transmission processing from antenna 112. RF receiving section 113 performs predetermined receiving processing such as down-conversion and A/D conversion on the signal received via antenna 112, and outputs the signal after radio receiving Processing to demultiplexing section 114. Demultiplexing section 114 demultiplexes the signal outputted from RF receiving section 113 into RA slots and UL data slots, and outputs the demultiplexed RA slots to signature sequence detecting Section 115 and the demultiplexed UL data slots to IJL data receiving processing section 116 and demodulating section 117. Signature sequence detecting section 115 12 performs preamble waveform detection processing such as correlation processing on the RA slots outputted from demultiplexing section 114 using the signatures stored in signature table storage section 101, and detects whether or not a signature sequence was transmitted. The detection result is outputted to signature sequence assignment control section 102. UL data receiving processing section 116 is provided with demodulating section 117 and decoding section 118, and performs UL data receiving processing. Demodulating section 117 corrects the channel response distortion of the UL data outputted from demultiplexing section 114 and identifies the signal points by hard decisions or soft decisions depending on the modulation scheme. Decoding section 118 performs error correcting processing on a result of the signal point identification in demodulating section 117, and outputs UL received data. Here, Zadoff-Chu sequences forming the signature table will be explained. First, a Zadoff-Chu sequence of the sequence length N is calculated by following equation 1 when N is an even number, and calculated by following equation 2 when N is an odd number. [1] [2] , where n is 0, 1, 2 , ..., N- 1 , q is an arbitrary integer, and k is coprime to N and is a positive integer less than N. [0031] Further, a cyclic-shifted Zadoff-Chu sequence generated by cyclically shifting the above-noted Zadoff-Chu sequence in units of shift amount A, that is, the sequence replacing n by (n+mA)mod N is shown in equation 3 when N is an even number, and is shown in equation 4 when N is an odd number. [3] [4] -.(Equation 4) ,where n is 0, 1, 2, ..., N-l, q is an arbitrary integer, k is coprime to N and is a positive integer less than N, m is 0, 1, ..., M-l, and M is the biggest integer not exceeding N/A. The cross-correlation is ideally zero in detection period t that is in the range of 0=t