Patent Application
20070268875
All the objects, advantages, and novel features of the invention will become more apparent from the following detailed descriptions when taken in conjunction with the accompanying drawings.
Although the invention has been explained in relation to several preferred embodiments, the accompanying drawings and the following detailed descriptions are the preferred embodiment of the present invention. It is to be understood that the following disclosed descriptions will be examples of present invention, and will not limit the present invention into the drawings and the special embodiment.
The present invention according to the Bluetooth standard presents a mechanism for avoiding the failure problem in the process of the role exchange due to noise or other effects. Now referring to the
By definition of Bluetooth system, all devices are on the same level and any Bluetooth device can be a Master or a Slave. The only rule is that the one first sending request of connecting is called the master and the other one is the slave, which is assigned during Piconet forming. It depends on the application that the master and the slave can exchange sometimes.
When the two Bluetooth devices are connected with each other, a physical channel is built in the baseband, in which a Time Division Duplex (TDD) scheme is used for transmitting signals between the master and the slave. The master sends out the data during even time slot and the slave must listen for the master before it may send out the information.
The role exchange procedure starts at a first time point t1. A first slave 310 asks role exchange and transmits a FHS packet to a first master 320. Then, the first master 320 sends a confirm packet back. Even though the first slave 310 did not receive the confirm packet due to noise or other factors, the first master 320 has exchanged as a second slave 340 at the second time point t2. The first slave 310, which did not receive the confirm packet from the first master 320 does not know whether the first master 320 received a FHS packet or not and transmits a plurality of FHS packet. The first slave 310 exchanges as a second master 330 automatically at the second time point t3, which can avoid the failure of role exchange procedure.
After the time point t3, the master and slave exchange as a new slave and master, respectively and then the second master 330 sends a poll packet. After the second slave 340 receives the poll packet, an empty packet will be sent back to the second master 330 to finish the role exchange process.
The first slave 310 asks role exchange to be a master, transmits a FHS packet to a first master 320, and comprises the following steps of: the first master 320 transmitting a confirm packet to the first slave 310.
In general, the first time point t1 is less than t2, and the second time point t2 is less than the third time point t3. The third time point t3 can be set between 0.625 ms-20 ms, and is preferred a multiple of 0.625 ms. However it is noted that the third time point t3 needs to be less than a role exchange time, 20 ms.
The number of re-transmitting a FHS packet from the first slave 310 is 2-6 times, and the optimized number is 3. If the first slave 310 receives the confirm packet from the first master 320 before re-transmitting the maximum number of FHS packets, the first slave 310 can exchange as the second master 330.
The packet transmission does not occupy the full time slot of 625 μs in length, ie, 1600 slots/sec. Bluetooth adopts the mechanism for frequency hopping, which hops from one time slot to another channel and divides 2.45 GHz band into 79 channels of 1 MHz to transmit data.
The master can only send at even-numbered time slot and the slave can only send at odd-numbered time slot. Packets transmitted by the master may span over one, three, or up to five time slots.
The FHS including three parts of access code, header, and payload is the same as packets at other intervals ( wherein synchronous connect orientation, SCO, and asynchronous connect link, ACL). A confirm packet consists of access code and is used during the pre-connection. A confirm packet is a powerful information machine since it carries information of access codes indicating where to go or to come from. A null packet consists of access code and header and does not need to receive any feedback message. A poll packet has the same structure as the null packet but it requires a response.
In summary, the present invention provides a role exchange method for Bluetooth wireless communication, which avoids the failure problem of role exchange as connecting with Bluetooth devices and reinforces the weakness in the Bluetooth scheme by using the mechanism for re-transmitting packets and exchanging role. Because of sufficient stability of connecting and being connected, the users can feel satisfied.
Although the invention has been explained in relation to its preferred embodiment, it is not used to limit the invention. It is to be understood that many other possible modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the invention as hereinafter claimed.
