1. Field of the Invention
The present invention relates to a method and apparatus for communicating with seven or more terminals efficiently in a Bluetooth Wireless Personal Area Network (W-PAN), and more particularly, to a communication method and apparatus utilizing the sniff mode to allow a terminal to be in a sleep state for a Sniff Interval Time (SIT) and then be converted into an active mode for a service period in order to communicate such that a master can efficiently communicate with seven or more slaves using conventional seven Active Member Addresses (AM_ADDR).
2. Description of the Background
A Bluetooth system is a wireless communication technique in which short-range devices such as a computer, mobile phone, a headset, a printer, a PDA, a notebook, electric home appliances, etc. are connected using a wireless connection network to enable duplex communication even without a complicated wire. The Bluetooth system is highlighted as a principal element for mobile communications, owing to its advantages such as low-priced equipment and wide-ranging applications. In recent years, service of the Bluetooth system have centered on mobile phones, headsets, etc. using the Bluetooth protocol.
Communications between Bluetooth devices is based on a master-slave connection utilizing a synchronized frequency jumping pattern and clock. The Bluetooth device that establishes the frequency jump sequence from which to request a connection and maintains the master clock is called the “master.” The Bluetooth device that synchronizes to the frequency jump sequence of the master and maintains time synchronization with the master clock by implementing an internal offset of its own clock in response to a connection request is called a “slave”.
Bluetooth devices in a standby mode can detect the addresses and approximate clock offset values of other Bluetooth devices through an inquiry and inquiry scan process. Once identified, a connection between Bluetooth devices (nodes) can be constructed through a paging and paging scan process in which the frequency jumping pattern is established.
A connection between one master and one or more slaves is called “piconet”, and each of the slaves is distinguished using a 3-bit Active Member Address (AM_ADDR). FIG. 1 is a view illustrating a piconet consisting of one master and several slaves in a conventional Bluetooth system. As shown in FIG. 1, the 3-bit active addressing scheme limits a piconet to one master and seven slaves in active mode.
Accordingly, in one piconet, only seven slaves can perform communications at a given time, and excess slaves over and above the seven addressable are allocated a Park Member Address (PM_ADDR) and an Access Request Address (AR_ADDR) from the master. These devices then release their Active Member Address (AM_ADDR) for use by other devices and enter a parking mode. They are then considered to be in a sleep state and this procedure is called “parking”.
When a parked slave again requires to communicate with the master the Access Request Address is used to transmit the access request message to the master through a beacon channel. The master receives the access request message and checks its communication resources to determine if an Active Member Address (AM_ADDR) is or can be made available. If so, it then accepts the call. This procedure is called “un-parking”.
A Bluetooth piconet utilizes a Time Division Duplex (TDD) scheme controlled by the master to communicate with the member slaves. The master transmits a data packet or a control packet to the slave indicating that the slave has been allocated the subsequent time slot to transmit its data packet to the master.
The process of transmitting a data or control packet by the master to the slave in order to allocate a time slot to the slave is called “polling”. If a slave polled by the master has data to be transmitted, the data packet is transmitted in response. If no data exists to be transmitted by the slave, a null packet is transmitted.
As described above, the conventional Bluetooth system cannot, in one piconet, provide service for more than seven slaves. In one Bluetooth piconet, if communication with more than seven Bluetooth devices is required, two conventional methods are used.
In a first method, described above, a slave in active mode is converted into parking mode and the returned Active Member Address (AM_ADDR) is then allocated to a new slave so as to provide service. This method has a drawback in that one or more active slaves are forcibly interrupted and placed in park mode thereby resulting in deteriorating the quality of service. Further, this conventional method has another drawback in that service delays are lengthened and the efficiency of a throughput is decreased due to the long delay time for the parking or the un-parking of slaves.
In another method of communicating with more than seven slaves, a Scatternet is used. A connection between multiple piconets is called “Scatternet” and is created when a device resides as a slave on one piconet and a master on another. This conventional method has the drawback that, for various reasons such as the fact that the present Bluetooth standard does not define a detailed protocol for this service, it is not yet possible to implement.