1. Field of the Invention
The present invention relates to a transmission method and related apparatus for a Bluetooth system, and more particularly to, a transmission method and related apparatus of allowing a slave device to actively send packets in a Bluetooth system.
2. Description of the Prior Art
A Bluetooth system is a wireless communication system, which uses piconet as a minimum network unit. The Bluetooth system allows one master device to communicate with up to seven slave devices, using time division duplexing technology. The Bluetooth system divides communication time on a physical channel into several time slots. The time slots are numbered by a clock of the master device. The even-numbered time slots are considered “Master-to-Slave” time slots. The odd-numbered time slots are considered “Slave-to-Master” time slots. On transmission timing, the master device and the slave device alternately transmit packets. The master device is allowed to transmit packets to the slave device only in the even-numbered time slots. The slave devices start Bluetooth time division duplexing to respond the packet transmission of the master device.
Nowadays, many slave devices are applied to human interface devices (HIDs), such as a keyboard, a mouse, a headset and a controller. The main function of those slave devices aims at reception of movements from the user, such as typing on a keyboard, moving a mouse, or swinging a controller. Since those movements are somewhat unpredictable, with multiple HID devices, the master device has to employ a polling operation to, one by one, check if each HID device detects any movement from the user.
Please refer to FIG. 1, which is a timing diagram of a polling operation in a Bluetooth system according to the prior art. FIG. 1 illustrates the polling between a computer (master device) and a keyboard and a mouse (two slave devices) in a piconet. On communication time, time slots K, (K+2), (K+4) . . . (K+10) are denoted as “Mast-to-Slave” time slots. Likewise, time slots (K+1), (K+3) . . . (K+11) are denoted as “Slave-to-Master” time slots. In FIG. 1, the computer polls the keyboard and the mouse by turns. First, the computer sends a polling packet PPK1 to the keyboard in the time slot K and receives a response packet from the keyboard in the time slot (K+1). Then the computer sends a polling packet PPK2 to the mouse during the time slots (K+2)-(K+4) and receives a response packet from the mouse during the time slots (K+5)-(K+6). The computer transmits packets only in the even the time slots, so the computer is not allowed to transmit a polling packet PPK3 to the keyboard until the time slot (K+8). Similarly, the keyboard cannot response to the computer until time slot (K+11) because the time slots (K+8)-(K+9) are occupied by the polling packet PPK3.
As known above, in the Bluetooth system of the prior art, transmission behavior of the slave devices are totally controlled by the master device, without transmission domination. Therefore, for transmitting the slave data, the master and slave devices have to transmit the packets back and forth, causing more radio resource consumption.