Field
The following description relates to an apparatus and transmission method for transmitting communication signals at the maximum data transmission rate within a range to satisfy the specific absorption rate (SAR) regulations associated with electromagnetic wave exposure from a portable device.
Discussions of Background
With the development of data communication and display technologies, portable devices (for example, smartphones and tablet PCs) which enable data communication have become a necessity for modern people. Such portable devices operate based on electronic components and thus expose users to electromagnetic waves. Recently, as the harmfulness of electromagnetic waves to the human body has become an issue, specific absorption rate (SAR) regulations for portable devices have been established. SAR regulations use energy absorbed per unit time and mass as an index, and regulate the rate of absorption of electromagnetic wave energy by a biological tissue, and is measured in W/kg. In the Republic of Korea, the limit SAR value for portable devices is set at 1.6 W/kg, and since April 2002, a SAR limit value for the human body has been introduced to protect the human body against electromagnetic waves absorption. Therefore, SAR values of portable devices have been required to be tested and the sale of portable devices with a SAR value higher than the limit value has been prohibited. In the Republic of Korea, the government has further proposed amendments to heighten the SAR regulations. In the amended SAR regulations, Body SAR regulations which require measuring SARs of the six sides of a portable device have been added, and a grading system has also been implemented.
As illustrated in FIG. 1, a circuit switched fall-back (CSFB) type portable device is designed to perform communication only in a single frequency band through a main antenna 30 even when two different frequency bands are supported. For example, the portable device is designed such that in a case where transmission of a voice signal 11 is requested while transmission of a data signal 12 is performed, a channel regarding the transmission of the data signal 12 is disconnected by a switch 20, a channel regarding the transmission of the voice signal 11 is connected by the switch 20, and the main antenna 30 performs communication only in a single frequency band. Since the existing SAR regulations only required SAR measurement at a human's head, for a CSFB type portable device, the SAR regulations could be easily satisfied by positioning the main antenna 30 at a position farthest from the head.
However, the CSFB type portable device has a disadvantage that communication in a certain frequency band may be interrupted. In the above example, transmission of voice signal 11 is interrupted by communication of the data signal 12. Therefore, the simultaneous voice and LTE (SVLTE) technology which simultaneously enables transmission and reception in two or more frequency bands has been introduced. However, since the SVLTE technology uses a CDMA network and a LTE network at the same time, there is a limit in improving data transmission rates. Accordingly, the SVLTE technology has been further developed into LTE carrier aggregation (CA) technology which performs transmission and reception simultaneously using two LTE networks.
Referring to FIG. 2, a portable device which uses the LTE CA technology has a diplexer 20 inserted instead of a switch as shown in FIG. 1. The diplexer 20 filters each signal, and may transmit two LTE signals 11, 12 in different frequency bands by simultaneously filtering the two LTE signals. Accordingly, voice communication and data communication can be simultaneously performed over the LTE network, and thus data signals can be continuously received without interruption even during voice communication.
Since strength of electromagnetic waves increase as the power of transmission signals increase, in order for the LTE CA type portable device to comply with the SAR regulations, the power of a signal associated with a certain frequency band may need to be limited. For example, if the transmission power of the voice signal 11 is equal to or higher than a predetermined magnitude (for example, 20 dBm or higher), even if a base station commands the portable device to transmit the data signal 12 at its maximum magnitude (for example, 23 dBm), the portable device may need to control the magnitude of the transmission power of the data signal 12 to be set at a predetermined magnitude (for example, 19 dBm) or less.
The LTE CA type portable device has problems that in a poor electromagnetic wave environment, the data transmission rate may decrease, the signal quality of data communication may be degraded, and/or the communication may be interrupted. To resolve these problems, considering the fact that the electromagnetic wave absorption rate can be decreased by increasing the distance between the transmission antennas, a transmission method using a plurality of transmission antennas may be considered. However, since multipurpose antennas such as a GPS, Bluetooth, and Wi-Fi all need to be integrated in the portable device, there is a limit in satisfying the SAR regulations by increasing the distance between the multiple antennas.