Transmission apparatus, reception apparatus, mobile communications system and transmission control method

The present invention relates to a transmission apparatus, a reception apparatus, a communications system and a transmission control method.

A fourth generation (4G) mobile communications method which is the next generation of IMT-2000 (International Mobile Telecommunications 2000) is under development. The fourth generation (4G) method is expected to flexibly support various environments from a multi-cell environment including a cellular system to an isolated cell environment such as a hotspot area and an indoors area, and increase frequency utilization efficiencies in both cell environments.

In the fourth generation communications method, the following radio access methods have been proposed for a link from a mobile station to a base station (referred to as an up-link, hereinafter). As single-carrier transmission methods, a DS-CDMA (Direct Sequence Code Division Multiple Access) method, an IFDMA (Interleaved Frequency Division Multiple Access) method, and a VSCRF-CDMA (Variable Spreading and Chip Repetition Factors-CDMA) method have been proposed, for example. As multi-carrier methods, an OFDM (Orthogonal Frequency Division Multiplexing) method, a Spread OFDM method, an MC-CDMA (Multi-Carrier Code Division Multiple Access) method, and a VSF-Spread OFDM (Variable Spreading Factor Spread OFDM) method have been proposed.

The single-carrier method provides high power efficiency because peak power is lower in terms of consumption power in a terminal, which reduces back-off of a transmission power amplifier.

As an example of the single-carrier methods, the VSCRF-CDMA method is explained with reference to FIG. 1 (See patent-related document 1).

A spreading portion 1 includes a code multiplication portion 2, a repetitive synthesis portion 8 connected to the code multiplication portion 2, and a phase shift portion 10 connected to the repetitive synthesis portion 8.

The code multiplication portion 2 multiplies a transmission signal by a spreading code. For example, a multiplier 4 multiplies the transmission signal by a channelization code defined under a predetermined code spreading ratio SF. In addition, a multiplier 6 multiplies the transmission signal by a scramble code.

The repetitive synthesis portion 8 compresses the spread transmission signal in a time-wise manner and performs chip repetition a predetermined number of times (CRF times). The transmission signal to which the repetition has been applied presents a comb-shaped frequency spectrum. When the repetition number CFR is equal to one, the repetitive synthesis portion 8 has the same configuration and operations in the usual DS-CDMA method.

The phase shift portion 10 deviates (or shifts) a phase of the transmission signal by a predetermined frequency established specifically for each mobile station.

In the VSCRF-CDMA method, when the CRF is greater than 1, for example, equal to 4, a comb-shaped frequency spectrum utilized by each user is arranged in a distributed manner over the entire band, as shown in FIG. 2A. In this case, a user-specific frequency offset is smaller than an allocated bandwidth.

On the other hand, when CRF is equal to 1, the spectrum utilized by each user is arranged over a block, as shown in FIG. 2B. In this case, the user-specific frequency offset is greater than the allocated bandwidth.

In addition, there has been proposed a radio access method where a comb-shaped frequency spectrum in the frequency domain is obtained (See non-patent documents 1, 2).

A transmission apparatus 30 to which the radio access method is applied includes a FFT portion 12 to which a spread data sequence is input, a rate conversion portion 14 connected to the FFT portion 12, a frequency domain signal generation portion 16 connected to the rate conversion portion 14, an IFFT portion 18 connected to the frequency domain signal generation portion 16, a GI addition portion 20 connected to the IFFT portion 18, and a filter 22 connected to the GI addition portion 20, as shown in FIG. 3.

The fast Fourier transformation (FFT) portion 12 divides the spread data sequence every Q chips into blocks and performs a fast Fourier transformation, thereby transforming the blocks into the frequency domain. As a result, Q single-carrier signals are obtained in the frequency domain. By the way, the spread data sequence corresponds to an output signal of the multiplier 6 in the spreading portion 1 explained with reference to FIG. 1.

The rate conversion portion 14 repeats a predetermined number of times, for example, CRF times the Q counts of the single-carrier signals. As a result, the number of the single-carrier signals generated is N_sub=Q×CRF.

The frequency domain signal generation portion 16 shifts each single-carrier signal on the frequency axis so that the spectrum becomes comb-shaped. For example, when a process corresponding to CRF=4 is carried out, three zeros are arranged between every single-carrier signal. As a result, the comb-shaped frequency spectra explained with reference to FIGS. 2A and 2B are formed.

The IFFT portion 18 performs a fast inverse Fourier transformation on the comb-shaped spectra obtained by shifting each single-carrier signal on the frequency axis.

The guard interval addition portion 20 adds guard intervals to a signal to be transmitted. The guard intervals are obtained by replicating a portion of the top or end of a symbol to be transmitted. The filter 22 performs a band limitation on the transmission signal.

On the other hand, the multi-carrier method, which has a long symbol, can provide an improved reception quality in a multi path environment by providing the guard intervals.

As an example, the OFDM method is explained with reference to FIG. 4.

FIG. 4 is a block diagram of a transmission portion used in a transmission apparatus of the OFDM method.