In a mobile communication system, a single base station (i.e., Node-B) communicates with at least one mobile station over a radio frequency (RF) channel. In a system for transmitting a packet over a multiple sub-carrier, a base station receives the packet over a wired Internet, and transmits the received packet to each mobile station according to a predetermined communication scheme. In this case, downlink scheduling takes a role in determining when the base station transmits data, what frequency bandwidth the base station uses and which mobile station the base station transmits data to. The base station receives data from the mobile station using a pre-determined communication scheme, demodulates the received data, and transmits the demodulated packet to the wired Internet.
Uplink scheduling takes a role in determining when the mobile station transmits data, what frequency bandwidth the mobile station uses and which base station the mobile station transmits data to. Typically, a mobile station having a good channel condition can transmit/receive data using much more frequency resources during a longer time.
In communication system for performing communication using at least two carriers, communication resource includes a time-domain resource and a frequency-domain resource, and the time-domain resource and the frequency-domain resource can be defined in predetermined units. For example, a resource block composed of N sub-carriers and M time units (e.g., M sub-frames) can be defined (where, N or M may be set to an integer>1)
FIG. 1 shows an example of the resource block.
Referring to FIG. 1, each square indicates a single resource block. The single resource block comprises the set of a predetermined number of sub-carriers transmitted within a predetermined time.
In a downlink, the base station allocates the resource block to a selected mobile station according to a predetermined scheduling rule, and transmits data to the mobile station using the allocated resource block.
In an uplink, the base station allocates the resource block to the selected mobile station according to a predetermined scheduling rule, and transmits data to the base station using the resource block.
A method for controlling a packet-reception failure is classified into an automatic repeat request (ARQ) and a hybrid automatic repeat request (HARQ).
In the ARQ, if a transmitter receives an acknowledgement (ACK) signal after transmitting a packet (or a frame), it transmits a new packet. Otherwise, if the transmitter receives a negative acknowledgement (NACK) signal, it re-transmits the packet.
If a receiver receives a packet and successfully decodes the received packet, it transmits an ACK signal. Otherwise, if the receiver fails to decode the packet, it transmits a NACK signal, deletes the received packet from a buffer, and waits for a re-transmission packet.
In the HARQ, if a transmitter receives an acknowledgement (ACK) signal after transmitting a packet, it transmits a new packet. Otherwise, if the transmitter receives a negative acknowledgement (NACK) signal, it re-transmits the packet to which a FEC (Forward Error Correction) coding is applied.
Therefore, if the decoding process for the received packet is successfully performed, the receiver transmits the ACK signal. Otherwise, it transmits the NACK signal and stores the received packet in a buffer. Upon receipt of the re-transmission packet according to the NACK signal, the receiver combines the re-transmission packet with the stored packet, and decodes the combined result, to increase a successful reception rate.
The HARQ can be classified into a synchronous HARQ and an asynchronous HARQ according to re-transmission timing.
In case of the synchronous HARQ, if a first transmission of a packet fails, a re-transmission of the packet is executed at a specific time determined by the system. For example, if the system is designed to re-transmit the packet at intervals of a fourth time unit after the first transmission failure, there is no need to inform the receiver of any information about re-transmission time. Therefore, if the transmitter receives the NACK signal, it re-transmits the packet at intervals of four time units.
In case of the asynchronous HARQ, re-transmission time information is scheduled. Therefore, the re-transmission time corresponding to the NACK signal is changed according to a variety of factors such as a channel condition.
The HARQ can be classified into a channel-adaptive HARQ and a channel-non-adaptive HARQ on the basis of specific data indicating whether channel condition information is reflected or not in determining an amount of resources for re-transmission.
The channel-non-adaptive HARQ uses a same number of resource blocks determined in a first transmission to modulate a re-transmission packet. For example, if the transmitter transmits data using 8 resource blocks for a first transmission, it re-transmits the data using the 8 resource blocks in the same manner of the first transmission.
The channel-adaptive HARQ changes the number of resource blocks to modulate a re-transmission packet according to channel conditions. For example, although the transmitter transmits data using 8 resource blocks for a first transmission, it re-transmits the data using 8 or less resource blocks according to channel condition.
A synchronous HARQ, an asynchronous HARQ, a channel-non-adaptive HARQ, and a channel-adaptive HARQ method are combined to acquire four type HARQ control methods. Representative examples of the four type HARQ control methods are an as synchronous channel-adaptive HARQ and a synchronous channel-non-adaptive HARQ.
The asynchronous channel-adaptive HARQ adaptively changes a re-transmission timing and an amount of resources according to channel condition, such that it can more efficiently re-transmit desired data. However, the asynchronous channel-adaptive HARQ has a disadvantage in that it inevitably increases overhead.
The synchronous channel-non-adaptive HARQ fixes a re-transmission timing and an amount of resources required for the re-transmission, such that almost no overhead is required for the re-transmission. However, the synchronous channel-non-adaptive HARQ has a disadvantage in that it inevitably deteriorates re-transmission efficiency.
A system for transmitting a signal using at least two carriers allocates radio resources in units of a resource block composed of the set of a predetermined number of sub-carriers transmitted within a fixed time. In case that the radio resources are allocated in resource block units, method of allocating radio resources efficiently to a mobile station that performs re-transmission is needed.