BACKGROUND

Technical Field

The present invention relates to a sequence allocation method and a sequence allocating apparatus for allocating a Zadoff-Chu sequence or GCL sequence to a cell.

Description of the Related Art

Mobile communication systems represented by a cellular communication system or wireless radio LAN (i.e., local area network) systems are provided with a random access region in their transmission regions. This random access region is provided in an uplink transmission region when a terminal station (hereinafter, “UE”) sends a connection request to a base station (hereinafter, “BS”) for the first time, or when a UE makes a new band allocation request in a centralized control system where a BS or the like allocates transmission times and transmission bands to UEs. The base station may be referred to as an “access point” or “Node B.”

Furthermore, in a system using TDMA (i.e., time division multiple access) such as the 3GPP RAN LTE, which is currently undergoing standardization, when a connection request is made for the first time (which takes place not only when a UE is powered on but also when uplink transmission timing synchronization is not established such as when handover is in progress, when communication is not carried out for a certain period of time, and when synchronization is lost due to channel conditions, and so on), random access is used for a first process of acquiring uplink transmission timing synchronization, connection request to a BS (i.e., association request) or band allocation request (i.e., resource request).

A random access burst (hereinafter, “RA burst”) transmitted in a random access region (hereinafter, “RA slot”), unlike other scheduled channels, results in reception errors and retransmission due to collision between signature sequences (situation in which a plurality of UEs transmit the same signature sequence using the same RA slot) or interference between signature sequences. Collision of RA bursts or the occurrence of reception errors increases processing delays in the acquisition of uplink transmission timing synchronization including RA bursts and processing of association request to the BS. For this reason, a reduction of the collision rate of signature sequences and improvement of detection characteristics of signature sequences are required.

As the method for improving the detection characteristics of signature sequences, generation of a signature sequence from a GCL (i.e., generalized chirp like) sequence having a low auto-correlation characteristic and also a low inter-sequence cross-correlation characteristic or Zadoff-Chu sequence is understudy. A signal sequence, constituting a random access channel and known between transmitter and receiver, is referred to as a “preamble” and a preamble is generally comprised of a signal sequence having better auto-correlation and cross-correlation characteristics. Furthermore, a signature is one preamble pattern, and suppose the signature sequence and preamble pattern are synonymous here.

Non-Patent Documents 1 to 3 use a Zadoff-Chu sequence or GCL sequence, whose sequence length N is a prime number, as an RA burst preamble. Here, adopting a prime number for sequence length N makes it possible to use N−1 sequences with optimal auto-correlation characteristics and cross-correlation characteristics, and optimizes (makes a correlation amplitude value √N constant) cross-correlation characteristics between any two sequences of the available sequences. Therefore, the system can allocate any sequence out of the available Zadoff-Chu sequences to each cell as a preamble.

Non-Patent Document 1: R1-062174, Panasonic, NTT DoCoMo “Random access sequence comparison for E-UTRA”

Non-Patent Document 2: R1-061816, Huawei, “Expanded sets of ZCZ-GCL random access preamble”

Non-Patent Document 3: R1-062066, Motorola, “Preamble Sequence Design for Non-Synchronized Random Access”

BRIEF SUMMARY

Problems to be Solved by the Invention

However, since the Zadoff-Chu sequence or GCL sequence is a complex code sequence where each element making up the sequence is a complex number, a correlation circuit (matched filter) necessary for code detection on the receiving side requires complex multiplication for each element of the sequence, which involves a large amount of calculation and also increases the circuit scale. Furthermore, when the number of different Zadoff-Chu sequences or GCL sequences used in one cell increases, it is necessary to perform correlation calculations corresponding in number to sequences for preamble detection, and this results in the amount of calculation and circuit scale proportional to the number of sequences allocated.

It is an object of the present invention to provide a sequence allocation method and a sequence allocating apparatus that reduces the amount of calculation and circuit scale of the correlation circuit on the receiving side in a system in which a plurality of different Zadoff-Chu sequences or GCL sequences are allocated to one cell.

Means for Solving the Problem

The sequence allocation method of the present invention includes an allocating step of allocating a combination of sequence numbers of Zadoff-Chu sequences or GCL sequences allocated to one cell, having a relationship that the absolute values of the amplitudes of the coefficients of the real part and the imaginary part of each element of the sequence are equal.

The sequence allocating apparatus of the present invention adopts a configuration including a sequence allocating section that allocates combinations of sequence numbers of Zadoff-Chu sequences or generalized chirp like sequences to be allocated to one cell, the combinations of sequence numbers holding a relationship that absolute values of amplitudes of coefficients of real parts and imaginary parts of elements in the sequences are equal and a reporting section that has correspondences between the combinations of sequence numbers and indexes of the combinations, and reports an index corresponding to a combination of sequence numbers allocated.

Advantageous Effect of the Invention

The present invention provides an advantage of reducing the amount of calculation and circuit scale of the correlation circuit on the receiving side in a system in which a plurality of different Zadoff-Chu sequences or GCL sequences are allocated to one cell.

