Wireless communication device and controlling method thereof

Abstract: A wireless communication device and a controlling method thereof. The wireless communication device (20) performing wireless communication includes a transceiver (21) for transmitting and receiving data externally, and a controller (23) for processing the data received from the transceiver (21), the wireless communication device (20) operating as a slave that is connected to a master (30), the controller (23) receiving a polling data addressed to the device (20) from a master (30) through the transceiver (21), and temporarily stopping the operation of the transceiver (21) during a sleep period which is determined according to the number of other slaves connected to the master (30). Since the wireless communication device (20) operated as an active slave can stop its data transmission/reception during a communication standby period, i.e., until the beginning of the next polling slot, the power consumption can be considerably reduced without affecting the communication itself.

Description: The present invention relates to a wireless communications device and a controlling method. Generally, a portable wireless communications device uses a battery for power supply. Accordingly, the device can only be used for a limited time due to the limited power of the battery. Research has been continuously performed into ways of extending the use time of portable wireless devices, and also into ways of reducing the size of the device for higher portability. For example, one body of research suggests reducing the power consumption of the individual elements used in the wireless device, thereby reducing the power consumption of the device overall. This suggestion, however, has little advantage since not much power can be saved by current technology. Meanwhile, another body of research underway is that of enhancing the charging efficiency of a battery by increasing the charging density without increasing the size of the battery, again with little success yet. Since reducing the power consumption of the individual elements, or enhancing the charging efficiency of the battery are limitative and slow in developing, various methods are currently developed to reduce power consumption by controlling the operations of the communication device. The controlling operation with respect to the communication device, for reducing power consumption, will be described below, taking Bluetooth communications as an example. Generally, Bluetooth is a communication technology for transmitting data such as voice and video data within a distance of 10m to 100m at a maximum speed of 1Mbps. The Bluetooth devices that intercommunicate according to the Bluetooth standard are communicably connected with each other by processes like Inquiry, Inquiry Scan, Page, and Page Scan, or the like. According to respective roles in a network, the devices are determined to be a master or a slave. A piconet is constructed in such a manner that more than one slave is connected to one master. A master and slaves perform bi-directional communication by a Time Division Duplex (TDD) technique. According to the Bluetooth communication standard presently available, seven slaves can be actively connected to a master in a piconet for a mutual communication therebetween. Once the slaves are connected to the master, the slaves can be operated in active, sniff, hold, or park modes. Operations of the slaves in the respective modes will be described referring to Figures 1A through 1C. First, referring to Figure 1A, when the slave is in an active mode, the master sequentially transmits data to the slaves at predetermined slot intervals according to a predetermined link order. Here, reference characters M followed by increasing numeral subscripts are master-to-slave slots for the slaves of the corresponding link order. The slave in the active mode receives data from the master during master transmission sections. If the data is addressed to the slave, the slave transmits data during the slot that is allocated after the master transmission section. In Figure 1A, reference characters S followed by increasing numeral subscripts are slave-to-master slots for the slaves of corresponding link order. In the active mode, the slave of zero link order, i.e., an active slave 0 receives the data addressed to the slave from the master, and transmits data during the slave-to-master slot (S0 in Figure 1A). Then the slave is turned to reception mode, where the slave detects if the data addressed thereto is transmitted from the master. Here, the hatched portions of Figure 1A are where the power is consumed for data transmission/reception. Since the active slave 0 needs to be operated in the reception mode even when data is transmitted from the master to the other slaves, unnecessary power is consumed. Meanwhile, the activity time of the slaves for data transmission/reception in sniff mode is less than the activity time consumed by the active slaves, and the operation of the sniff slaves is shown in Figure 1B. As shown in Figure 1B, a slave in a sniff mode, i.e., a sniff slave 1, communicates with a master after a predetermined offset (Dsniff) time and during a period of Nsniff_attempt of a sniff period (Tsniff). Meanwhile, a slave in a hold mode, i.e., a hold slave 2 temporarily holds data transmission for a hold timeout duration, the time duration agreed with the master, and is turned to the active mode. Lastly, as shown in Figure 1C, a slave in a park mode, i.e., a parked slave 3, receives a slot broadcasted from the master for a beacon instant (TB), which starts at an interval of one or more beacon instants (TB). The parked slave 3 is turned into the active mode upon receiving an unpark message in a Scan section. When an unpark message is not received, the parked slave 3 remains in a sleep mode. In order to minimize power consumption and optimize data processing by a dynamic power control using the sniff, hold, and park modes, necessary conditions for determining an optimum mode for the master and the slaves need to be regularly checked. That is, to identify necessary conditions for determining the optimum mode, such as communication traffic requested by the slaves and communication service types like voice communication or data communication, frequent communications between the master and the slaves are required. Accordingly, in addition to the time for data transmission, the time should be allocated for mode determination, and the efficiency of data transmission is deteriorated. "MAC Schedule Policies for Power Optimisation in Bluetooth: A Master Driven TDD Wireless System" IEEE Vehicular Technology Conference, New York, vol. 1 of 3, Conf. 51 15 May 2000, pages 196-200, has been identified as the closest prior art. This document discloses communication protocols designed to conserve energy at the slave stations. One of the protocols disclosed involves dynamically computing the time at which the slave is to become active with changing slot utilisation parameters. However, this protocol is based on the number of slaves in a pico-cell remaining constant. The present invention has been made with a view to solve or reduce the above-mentioned problems, and accordingly, it is an aim of embodiments of the present invention to provide a wireless communication system and a controlling method thereof, capable of reducing power consumption for unnecessary data reception, without decreasing a data transmission rate, as claimed in the appended claims. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figures 1A through 1C are timing diagrams showing an operation of a master and slaves according to connection modes in a Bluetooth communication scheme; Figure 2 is a block diagram showing a wireless communications device according to an embodiment of the present invention; Figure 3 is a timing diagram showing communication with a master when the wireless communications device of Figure 2 is operated as a slave; and Figure 4 is a flow chart showing an operation of a wireless communications device operated as an active slave according to embodiments of the present invention. Referring to Figure 2, a wireless communication device 20 includes a transceiver 21 and a controller 23. The transceiver 21 processes externally-received wireless signals such as Radio Frequency (RF) signals, and wirelessly transmits signals. The controller 23 is connected with a host through a communication interface. Here, a host is a communication terminal such as a laptop computer, cellular phone, etc. The controller 23 processes signals requested by the host and processes signals received from the transceiver 21. That is, the controller 23 transmits data (Tx_data) to the transceiver 21, and processes data (Rx_data) received from the transceiver 21. The controller 23 controls the operation of the transceiver 21. In Figure 2, signal lines recorded in Tx_enable and Rx_enable are command signal lines for directing a transmission mode, a reception mode, or an operation hold of the transceiver 21. In a wireless communication device 20 that is operated as an active slave, the controller 23 detects whether polling data is transmitted from the master 30 with an address thereto. If so, the controller 23 of the recipient slave device 20 transmits data to the master 30, and then stops the operation of the transceiver 21 to prevent power consumption during a predetermined sleep period. Here, the polling data is sequentially transmitted from the master 30 to the respective slave devices connected with each other, in a predetermined order, for data communication therebetween. The polling data contains address information of the recipient slave device. The sleep period is determined according to the information about the number of slave devices connected to the master 30, which is provided during or after a connection establishment with the master 30. In addition to the information about number of slave devices connected with each other, for a more efficient determination of the sleep period, it is preferable for the master 30 to provide connection state information that includes the number of slots allocated to the respective slave devices, and the synchronous connection types of the slave devices corresponding to the number of slots. The process of determining the sleep period will be described later in greater detail. Referring to Figure 3, operation of the wireless communications device 20 as an active slave will be described below. As shown in Figure 3 and previously described referring to Figure 1A, the master 30 sequentially transmits transmission data, i.e., polling data, in a round robin fashion. That is, the master 30 sequentially transmits the polling data according to a slave link order and at a predetermined slot interval. In Figure 3, the portions referred by a character M followed by increasing numeral subscripts (0 to N-1) are master-to-slave slots of a corresponding order. A wireless communication device 20 operated as a slave device of zero link order is an active slave device 0. Upon receipt of the polling data addressed thereto from the master 30, the active slave device 0 transmits data to the master 30 during three (3) allocated slots (S 0 ). Then, the active slave device 0 holds transmission/reception operation during an internally determined sleep period (Tsleep), and then wakes up to receive the polling data from the master 30 for the next cycle. In Figure 3, the hatched squares indicate power consumption for data transmission/reception. The sleep period should be shorter than the interval from polling data reception to the next polling data reception for the next cycle. The operation of the wireless communications device 20 as an active slave in a Bluetooth communication scheme will be described referring to Figure 4. First, during or after the connection establishment with other wireless communication devices, the wireless communications device 20 assigned as an active slave determines one of the operation parameters, i.e., a sleep period, by using the connection state information received from the master 30 (Step S100). Meanwhile, in Bluetooth communication, 1, 3, or 5 slots are available for occupation according to the respective packet types. Here, if the slave device does not know the number of slots available to the respective slave devices, the slave device cannot estimate exactly when the next polling data will be transmitted thereto. As a result, the respective slave devices have to determine the sleep period on a minimum basis, so as to wake up and be turned to the reception mode in time for the next polling data. The minimum sleep period for bi-directional communication between the master 30 and a plurality of slaves in a piconet corresponds to a doubled value of the number of slaves (Ns) being connected. Accordingly, provided that one cycle is a time period in which the slots are allocated to the respective slaves once by a Time Division Duplex (TDD) method, the minimum sleep period (Tsleep) for one slave is obtained by subtracting the number of slots allocated to one slave from the minimum number of slots allocated for one cycle. That is, the minimum sleep period (Tsleep) for one slave is obtained by Tsleep = 2*(Ns-1)* time slot. Here, the time slot corresponds to 625 µ second. Meanwhile, if information about the number of slots allocated to the respective slaves in the piconet is available, the power consumption can be considerably reduced since the sleep period of each slave can be lengthened based on an estimation of the time when the next polling data addressed thereto will be transmitted from the master 30. After the sleep period parameter is determined as above, the slave is operated in the reception mode, detecting whether the polling data is transmitted from the master 30 with the address thereto (Step S110). More specifically, the controller 23 outputs a transmission stop signal (Tx-enable=0) and a reception mode performing signal (Rx-enable=1). Here, the numbers 0 and 1 indicate operation stop and operation perform, respectively. The 'operation stop' means partially or entirely stopping the power supply to the respective elements performing the data transmission/reception. If it is determined that the polling signal addressed to the slave is received in S120, the reception mode is stopped, and the transceiver 21 performs a transmission mode (Step S130). That is, the controller 23 outputs 0 and 1 to the transceiver 21 for Rx_enable signal and Tx_enable signal, respectively. Then, data is transmitted to the master 30 during allocated slots (Step S140). After completion of the data transmission, the slave is operated in the sleep mode (Step S150). That is, the controller 23 outputs 0 through Rx_enable and Tx_enable signal lines to stop operations of the transceiver 21. The controller 23 also counts time. Next, it is determined whether the counted time by the controller 23 corresponds to the predetermined sleep period (Step S160). If the counted time corresponds to the sleep period, the slave is returned to S110 to perform the reception mode in which the slave wakes up. The steps S110 through S160 are repeated unless change requests for operation conditions occur, such as a change of the piconet connection state, i.e., change of the number of slaves connected to the piconet, receipt of an operation stop command from the host, or turn off of the power supply, or the like. Next, it is determined whether a request is made from the host or the master for changing the operational conditions (Step S170). If such a changing request is made from the host or from the master 30, the operation according to the parameter determined in S100 is ended. Wireless communication devices operated as active slaves can have, for example, a transmission/reception power of 1mW and a sleep mode power of 0mW. Let PM_ON represent a power consumption pattern according to the number of slaves when the wireless communications device 20 is operated with the minimum sleep period. Let PM_OFF represent a conventional power consumption pattern according to the number of slaves when the wireless communications device 20 as the active slave receives a polling slot addressed to the other slaves. Let PM_IDEAL represent a power consumption pattern according to the number of slaves when the wireless communication device 20 is operated with the sleep period that is accurately calculated according to an exact estimation for the next polling point. Provided that the probabilities of occupying one (1) slot is 0.8, occupying three (3) slots is 0.15, and occupying five (5) slots is 0.05, the power consumption in the operation condition of PM_ON is reduced by 15 to 24 percent from the operation condition of PM_OFF. According to the wireless communications device 20 and the controlling method thereof as described above, since the wireless communications device 20 operated as the active slave can stop its data transmission/reception during a communication standby period, i.e., until the beginning of the next polling slot, the power consumption can be considerably reduced without affecting the communication itself. In the drawings and specification, there have been disclosed typical preferred embodiment of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims: A wireless communications system comprising a first device (30) and at least two second devices (20) for performing wireless communication each of the second devices (20) comprising: a transceiver (21) for transmitting and receiving data externally; and a controller (23) for processing the data received from the transceiver (21), said controller (23) receiving polling data addressed to the second device from said first device (30) through the transceiver (21), and temporarily stopping the operation of the transceiver (21) for a sleep period; wherein if a number of slots allocated to the second device and the other second devices is not known by the second devices the controller is adapted for determining the sleep period according to the number of other second devices connected to the first device (30) and recalculating the sleep period each time the number of other second devices changes, and the controller (23) is adapted for calculating the sleep period by multiplying a predetermined time slot by double the number of the other second devices, and the first device (30) is adapted for sequentially transmitting said polling data according to a predetermined second device order, and the controller (23), upon receipt of the polling data addressed to the device (20), is adapted for stopping the operation of the transceiver (21) for the sleep period after a completion of the data transmission characterised in that where said number of slots allocated is known the first device (30) is adapted to provide connection state information that includes a number of slots allocated to the second device and the other second devices wherein the controller is adapted to calculate the sleep period using the connection state information. The device as claimed in claim 1, wherein the predetermined time slot corresponds to 625 µ second. A controlling method for a second wireless communications device (20), comprising the steps of: i) detecting whether polling data addressed to the device (20) is received from a first device (30); ii) transmitting data to the first device (30) when the polling data addressed to the second device (20) is received, and stopping a data reception from the first device for a predetermined sleep period; iii) identifying whether the sleep period has elapsed; and iv) repeating the steps i) and ii) at least once, when determining the sleep period has elapsed; further comprising, if a number of slots allocated to the second device and other second devices is not known the step of calculating the sleep period according to the number of other second devices currently connected to the first device (30) and recalculating the sleep period each time the number of other second devices changes; wherein the sleep period is calculated by multiplying the predetermined time slot by two times the number of other second devices connected to the first device (30), and wherein the first device (30) sequentially transmits said polling data according to a predetermined second device order, characterised in that , when the number of slots allocated to the second device and the other second devices is known the first device (30) provides connection state information that includes a number of slots allocated to the second device and the other second devices and the sleep period is calculated using the connection state information. The method as claimed in claim 3, wherein the time slot corresponds to 625 µ second.

Inventors: JANG KYUNG-HUN, KANG HYUN-SOOK, LEE TAE-JIN, PARK JONG-HUN, JANG, KYUNG-HUN, KANG, HYUN-SOOK, LEE, TAE-JIN, PARK, JONG-HUN
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 2001
Main classification: H04B1
IPC codes: H04B1, H04J3, H04M1, H04L12, G06F1, H04B7, H04W84, H04W52