1. Field of the Invention
The present invention is related to a wireless communication system, more particularly to a method of transmitting semi-persistent scheduling data in multiple component carrier system.
2. Related Art
Wireless communication systems are widely deployed in order to provide various kinds of communication services, such as voice and data. In general, the wireless communication systems are multiple access systems which can share available system resources (e.g., bandwidths and transmission power) and support communication with multiple users. The multiple access systems can include, for example, a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, and a Single Carrier Frequency Division Multiple Access (SC-FDMA) system.
In a common wireless communication system, although the bandwidth of uplink and the bandwidth of downlink are differently set up, only one carrier is taken into consideration. Even in 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), the number of carriers constituting uplink and downlink is 1, and the bandwidth of uplink and the bandwidth of downlink bandwidth are in general symmetrical to each other on the basis of a single carrier. However, it is not easy to allocate a large frequency bandwidth except some regions in the world. Accordingly, in order to efficiently use small sliced bands, a carrier aggregation technique for producing the same effect as that a logically large band is used by binding a plurality of physically non-continuous bands in the frequency domain is being developed. The carrier aggregation technique includes, for example, a technique in which system bandwidth of 100 MHz is supported by using multiple carriers.
For the effective use of limited radio resources, a base station (BS) dynamically schedules the radio resources. When there is no data packet transmitted using radio resources allocated to a user, the BS performs scheduling such that unused radio resources can be used by another user. Thus, the radio resources can be further effectively used. As such, radio resources may not be allocated to a user who does not have a data packet to be transmitted/received. In this manner, the radio resources can be dynamically allocated on a frequency domain or a time domain. Such a scheme is referred to as dynamic scheduling. Dynamic scheduling is efficient for service types such as transmission control protocol (TCP) or the signaling radio bearers (SRBs), in which the traffic is bursty and dynamic in rate.
In addition to the dynamic scheduling, semi-persistent scheduling (SPS) is defined. SPS enables radio resources to be semi-statically configured and allocated to a UE for a longer time period than one subframe, avoiding the need for specific downlink assignment messages or uplink grant messages for each subframe. SPS is useful for services such as voice over internet protocol (VoIP) for which the data packets are small, periodic and semi-static in size. For this kind of service the timing and amount of radio resources needed are predictable.
Aggregation of multiple component carriers is mainly used for higher-rate service. Therefore, it seems unnecessary that SPS is applied to over more than two carriers.