1. Field of the Invention
The present invention relates generally to the technical field of mobile communications, and specifically to a mobile communications system, a base station apparatus, a user apparatus, and a method using next generation mobile communications technology.
2. Description of the Related Art
Communications schemes to succeed such schemes as wideband code division multiple access (W-CDMA), high-speed downlink packet access (HSDPA), and high-speed uplink packet access (HSUPA) (i.e., LTE: Long Term Evolution) are being investigated in a W-CDMA standardization body, 3GPP. As radio access schemes in the LTE, OFDM (orthogonal frequency division multiplexing) for downlink and SC-FDMA (Single-Carrier Frequency Division Multiple Access) for uplink are viewed as promising (See Non-patent document 1, for example.)
The OFDM scheme is a multi-carrier transmission scheme for dividing a frequency band into multiple narrow frequency bands (sub-carriers) and putting data on the respective sub-carriers to transmit the data. It is expected that densely lining up the sub-carriers on the frequency axis while having them in an orthogonal relationship would make it possible to achieve high-speed transmission and improve the utilization efficiency of the frequency.
The SC-FDMA scheme is a single-carrier transmission scheme for dividing a frequency bandwidth per terminal, and transmitting using different frequency bands among multiple terminals. This scheme is preferable from the points of view of wider coverage and reduced power consumption of the terminal, as interference between the terminals may be reduced in a simple and effective manner and variation in transmit power may be reduced.
In LTE systems, one or more resource blocks are allocated to a mobile station to conduct communications in both downlink and uplink. The resource blocks are shared among a large number of mobile stations within the system. A base station apparatus determines which one of the multiple mobile stations a resource block is to be allocated to per sub-frame (1 ms in LTE) (This process is called scheduling). In downlink, the base station apparatus transmits, to the mobile station selected in the scheduling, a shared channel in one or more resource blocks. In uplink, the selected mobile station transmits a shared channel, to the base station apparatus, in one or more resource blocks.
Then, in a communications system using the above-mentioned shared channel, it is necessary to signal which user apparatus the above-mentioned shared channel is allocated to per sub-frame (1 ms in LTE. Also may be called TTI (time transmission interval)). In LTE, a control channel used for the signaling is called a physical downlink control channel (PDCCH) or a downlink (DL) L1/L2 control channel. Information on the physical downlink control channel includes Downlink Scheduling Information, ACK/NACK (Acknowledgement/Negative acknowledgement information), Uplink Scheduling Grant, Overload Indicator, and Transmission Power Control Command Bit, for example. (See Non-patent document 2, for example.) The ACK/NACK (Acknowledgement/Negative acknowledgement information) may be called Physical Hybrid ARQ Indicator Channel (PHICH). The PHICH may be defined as a different physical channel having a parallel relationship with respect to the PDCCH, not being included in the PDCCH.
The downlink scheduling information and uplink scheduling grant correspond to information for signaling which user apparatus the shared channel is allocated to. The downlink scheduling information may include, with respect to the downlink shared channel, downlink resource block allocation information, UE ID, the number of streams, information on precoding vector, data size, modulation scheme, information on HARQ (hybrid automatic repeat request), etc. The downlink scheduling information may be called downlink assignment information or a downlink scheduling grant. Moreover, uplink scheduling information includes, with respect to the uplink shared channel, uplink resource allocation information, UE ID, data size, modulation scheme, uplink transmit power information, information on demodulation reference signal in uplink MIMO, etc. The uplink scheduling information and uplink scheduling grant may collectively be called downlink control information (DCI).
Now, mobile telephone, wave astronomy, satellite communications, aviation and sea radar, earth resources survey, and wireless LAN that use radio waves generally divide frequency bands to be utilized to prevent interference by each other, Moreover, within frequency bands allocated to mobile telephone systems, multiple systems exist with a frequency band for each system being separated, for example.
For example, FIG. 1 shows how a frequency band between 1884.5 MHz and 1980 MHz is utilized. In FIG. 1, 1920 to 1980 MHz is allocated to IMT-2000 (International Mobile Telecommunication-2000) UL (Uplink), within which W-CDMA (UTRA FDD) system is operational from 1940 to 1980 MHz. Moreover, PHS systems are operational at a band of frequency which is smaller than 1920 MHz, or more specifically at a band of frequency from 1884.5 to 1919.6 MHz.
The above-described 1920 to 1980 MHz corresponds to UTRA FDD Band I Uplink in 3GPP.
In other words, in systems utilizing radio waves, frequency bands to be utilized are separated to prevent intersystem interference. However, a transmitter which radiates radio waves ends up radiating unwanted emissions (below called adjacent channel interference) in a band outside an own-system frequency band. Thus, multiple neighboring systems end up interfering with each other even if frequency bands are separated. Thus, there is going to be a large detrimental effect on a neighboring system if the power level of the unwanted emissions is large.
In order to prevent the detrimental effect on the neighboring system due to such adjacent channel interference, characteristics of the adjacent-channel interference and spurious emission are specified in each system. For example, in a 3GPP W-CDMA system, TS25.104 6.6 Output RF spectrum emissions (see Non-patent document 3) exists as a requirement for base station adjacent channel interference and spurious emission, while TS25.101 6.6 Output RF spectrum emissions (see Non-patent document 4) exists as a requirement for mobile station adjacent channel interference and spurious emission.
Below the requirements for mobile station adjacent channel interference and spurious emission will further be described in detail.
For example, a requirement for adjacent channel leakage power ratio (ACLR) in the above-described Non-patent document 4 specifies that an amount of interference with another system which exists infrequency bands 5 MHz and 10 MHz away from a system in question is suppressed to no more than a predetermined threshold, and is specified in a relative value. For example, for a specified value of ACLR for the frequency band 5 MHz away (separation) of 33 dB and a transmit power of 21 dBm, an amount of interference that is leaking from the system in question into the frequency band 5 MHz away must be suppressed to no more than −12 dBm.
Moreover, a requirement for spurious emission to the PHS band in the above-described Non-patent document 4 specifies suppressing to no more than −41 dBm per 300 kHz, which specifying is in an absolute value.
In general, a region for which the requirement for ACLR is applied is set to be a region in which system bandwidth of the system in question is multiplied by 2.5, while a region for which the requirement for spurious emission is applied is set to be the other region. FIG. 2 illustrates the region for which the requirement for ACLR is applied and the region for which the requirement for spurious emission is applied. The value of 2.5 is set based on the fact that a spectrum of a unwanted emissions to outside the system bandwidth is proportional to the transmit bandwidth.
Now, in order to suppress the unwanted emissions to outside the above-mentioned system bandwidth, a mobile station needs to be provided with a highly linear power amplifier. Thus, taking into account the cost or size of the mobile station, reducing the above-mentioned unwanted emissions or meeting the above-described requirements for ACLR and for spurious emission may be difficult. Then, in the above-mentioned Non-patent document 4, it is specified to reduce the maximum transmit power in order to suppress the cost or size of the mobile station. For example, in a Release 5 specification, it is specified to reduce the maximum transmit power based on the amplitude ratio of uplink DPDCH and DPCCH. Moreover, in the Release 6 specification, it is specified for the mobile station to calculate a value of a Cubic metric, and reduce the maximum transmit power based on the Cubic metric value. Reducing the maximum transmit power makes it possible to further suppress the cost or size of the mobile station.    Non-patent document 1: 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA,” June 2006    Non-patent document 2: R1-070103, Downlink L1/L2 Control Signaling Channel Structure: Coding    Non-patent document 3: 3GPP TS25.104 v6.13.0    Non-patent document 4: 3GPP TS25.101 v6.13.0