Apparatus, method and program to optimize battery life in a wireless device

The battery life of batteries of a mobile device operating in a wireless network is optimized by dynamically changing symbol rates and bits per symbol and selecting one for communicating based upon the source providing power to the mobile device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless networks in general and in particular to power management in devices operating in said wireless networks.

2. Prior Art

The use of wireless devices and wireless networks as a means for accessing remote office computers, the Internet or communicating with other wireless devices is well known in the prior art. The popularity of wireless devices has increased significantly due in part to the fact that they can be used wherever one chooses to use them and there is a wireless network to make the interconnection.

Because of this synergism it is almost impossible to separate wireless devices from wireless networks. Stated another way, when one uses wireless devices a wireless network is also used whether the user is aware or not aware of the wireless network. In this regard the wireless network, if not already, is becoming a standard part of mobile technology. When compared with wired networks wireless networks may have functional advantages. For example, their availability for use anywhere; without the need for cables to be attached.

In spite of these advantages, there are also disadvantages. Probably the most striking disadvantage is that a wireless network imposes significant energy drain on the mobile device battery. The battery drain phenomenon occurs because when the mobile device is wirelessly connected to the wireless network it must continuously receive and transmit high power radio signals. As a consequence it is believed that wireless network may reduce battery life>(greater than) 50%.

Most prior art attempts to solve this problem either adjust radio power or place mobile units in low power, also called sleep, mode. It seems as if the prior art solution could adversely affect the throughput of the mobile device.

In view of the above there is a need to provide a more effective and efficient method and apparatus that address the battery drain phenomenon and at the same time does not adversely affect throughput of the mobile device.

SUMMARY OF THE INVENTION

The present invention provides apparatus and method that extend battery life by dynamically changing symbol rate and bits per symbol. As a consequence power consumption is reduced without reducing throughput.

In particular the mobile unit is provided with three power rails, namely: battery, DC and Auxiliary (Aux). A power type detector monitors the power rails to determine which one is supplying power to the mobile unit. If power is provided by DC or Aux maximum symbol rate with low number of bits per symbol is requested of the Access Point. The Access Point which is capable of operating at different symbol rates will grant the request if it is capable of operating at the requested symbol rate. If the request is granted both Access Point and mobile device switch to the agreed to symbol rate to communicate.

If power is provided by battery, the battery power is tested; if greater than 50% a lower symbol rate with higher number of bits per symbol is requested of the Access Point by the mobile unit. If the Access Point supports the requested symbol rate and number of bits per symbol and if granted both Access Point and mobile unit switch to communicate at the agreed symbol rate.

If the battery power is less than 50% the minimum symbol rate and max number of bits per symbol is requested and if granted by the Access Point both Access Point and mobile unit switch and communicate at the agreed symbol rate.

One of the interesting observations is that by transmitting at lower symbol rates battery life increases. The increase in battery life occurs because the transmitter chip set requires less current when running at a slower symbol rate. The throughput is maintained at the slower symbol rate by increasing the number of bits per symbol.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a schematic for a network in which the present invention is implemented. The network100includes wireless LAN106and wired LAN110. The wireless LAN106operates in accordance with IEEE 802.11 specification for wireless networks. The wires LAN110is preferably an ethernet LAN running at 100 Mbps. Access Point102is shown connected to ethernet LAN110while a wireless node or device108is shown positioned within signal range, delineated by dash lines104, of Access Point102. With client device108being in the operating range of Access Point102, the client device108is able to transmit and receive information to and from Access Point102.

FIG. 2shows a block diagram of the Access Point (AP) according to the teachings of the present invention. Elements inFIG. 2that are similar to elements inFIG. 1are identified with like numerals and will not be discussed further. The Access Point200includes controller202, wireless LAN adapters222,238. . . N and wired LAN adapter212. The wireless LAN adapters222,238. . . N provides a wireless LAN interface to controller202whereas wired LAN adapter212provides a wired LAN interface to the ethernet LAN110. As will be discussed in greater detail hereinafter each of the adapters222,238. . . N (N being total number of wireless adapters) operates (transmit/receive) at different symbol rate and different bit rate. As a consequence the Access Point can communicate with mobile devices running at adjustable symbol rate and adjustable bit rate. The controller202is coupled by bus232to wireless LAN adapters222,238. . . N and by bus234to wired LAN adapter212. The controller202includes memory204, interface flow control logic206, program storage208, and microprocessor210. The named components204,206,208and210are interconnected as shown inFIG. 2. The program storage208stores control program (firmware) that microprocessor210runs or executes to support the wired and wireless networks. The data store204is used to temporarily hold data that is being transferred between wireless network and the wired network110. The interface flow control logic206controls the movement of data from controller202to the wireless adapters222,238. . . N and to wired adapter212.

In an alternate embodiment a single wireless adapter that supports multiple concurrent channels which can change symbol rate and bit rate dynamically could be used in the Access Point.

The LAN adapter212provides the LAN interface to ethernet LAN110. Wired LAN adapter212includes Controller214, TX FIFO220, RX FIFO216and Physical Layer218. Controller214provides MAC (medium access control) functions for the LAN adapter212. Controller214is connected to TX FIFO220and RX FIFO216. The TX FIFO220holds data to be transmitted onto the ethernet LAN whereas the RX FIFO216receives data from ethernet LAN110. TX FIFO220and RX FIFO216are connected to Physical Layer218. The Physical Layer218provides physical function to the adapter which includes conversion of digital to analog signals compliant with ethernet specification, provides physical connection to network110, etc.

Still referring toFIG. 2, each of the wireless LAN adapters, such as wireless LAN adapter222is designed to run protocols specified by IEEE 802.11b wireless LAN specification. In addition, each of the wireless adapters runs at a different symbol rate and a different bit rate. The wireless LAN adapter222or238. . . N includes RF Transceiver224, TX FIFO230, RX FIFO228and Controller226. The named components are connected as shown in the figure. The Controller226provides interface function and is commonly known as medium access control (MAC). The MAC is connected to the TX FIFO230which holds data to be subsequently transmitted to the wireless network. Likewise, the RX FIFO228holds data that is received from the wireless network. The RF Transceiver224and power amplifier antenna240converts digital signals to radio frequency energy compliant with 802.11b specification. The RF Transceiver and power amplifier antenna240also receives radio frequency signals and converts them to digital signals. As a consequence the RF Transceiver and power amplifier antenna240includes both a transmitting subsystem and a receiver subsystem. The transmitting subsystem handles data which is transmitted into the wireless network106whereas the receiving subsystem manages data received from the wireless network106. RF transceivers and power amplifier antenna240are well known in the prior art and further discussions are not warranted. It should be noted components on wireless adapters238. . . N are not shown but are identical to the components described for wireless adapter222. The primary difference between the multiple wireless adapters222,238. . . N is that each one operates on a different channel at different symbol rates and different bit rates. It should be noted that 802.11 specification defines 14 channels in the 2.4 Ghz band.

FIG. 3shows a block diagram of the structure for a client device such as a portable computer or like device. The client300includes peripheral component interface (PCI) bus controller308to which DASD312, keyboard/mouse314, flash program storage316and memory controller304are connected. The function of PCI bus controller308includes arbitrating between the attached devices and enabling those devices to access the memory306and DASD312. The microprocessor302is coupled through the memory controller304to the memory306. The memory controller304controls the memory306. The flash program storage316contains initialization program or bios that is used to establish the client in an operating state when it is first turned on.

Still referring toFIG. 3, PCI expansion bus310connects video controller318and wireless adapter322to the PCI bus controller308. The video controller318is connected to a video display320. The video controller318manages the information to be displayed on the video display320. The wireless adapter322provides the wireless LAN interface that allows a client to communicate via radio waves to an Access Point. As a consequence, the wireless adapter322includes power amplifier/antenna344coupled to RF Transceiver330which is connected to TX FIFO328and RX FIFO326. Controller324couples TX FIFO328and RX FIFO326to the PCI bus310. The Controller324performs the MAC functions that allow the wireless adapter322to interface with the PCI bus and process data according to the protocols set forth in IEEE 802.11 standard for wireless network. The RF Transceiver330includes both the transmitting section and a receiving section that function in a way similar to that of previously described RF Transceiver224. A symbol and bit rate generator341that generates variable symbols based upon the power source on which the mobile device is running is also provided. A circuit diagram for symbol generator341is shown inFIG. 4. Even though the symbol generator is shown as part of the controller324this should not be construed as a limitation on the invention. In the actual design it can be mounted anywhere the designer chooses within the mobile device.

Still referring toFIG. 3, the present invention allows the client device300to maintain a constant data throughput as it changes to lower power modes to control battery life. To this end the client device300includes a power subsystem including power supply334with an input to be coupled to AC power source332and two output power rails labeled Aux Power336and DC Power338. A battery340is connected to DC Power338and generates an output labeled Battery Power342. Aux Power336is available whenever client device300is connected to external power supply334. DC Power338is provided whenever client device300is connected to power supply334and powered on. DC power is always provided to battery340. Battery power342is available as long as battery340has charge. Power Type Detector (PTD)345monitors Aux Power336, DC Power338and Battery Power342and sets a bit in Power Source Register344to indicate the source that is providing power to client device300. PTD345could be a PLA (Program Logic Array) or other combinatorial logic designed in accordance to the flowchart set forth inFIG. 6and described hereinafter. As will be discussed herein the type of power being used will determine the symbol rate and bit rate selected and used by the client device to transmit data. The symbol rate selected is stored in symbol rate register344.

FIG. 4shows a block diagram of the circuit that generates the variable symbol rate. Phase lock loop400generates the base timing waveform. The output of phase lock loop400is provided to adder circuit402which adds the fundamental frequency pulse (not shown) to obtain the frequency of the desired symbol rate. The output of adder circuit402provides the timing for the Eye Pattern generation in block404. The Eye Pattern generation changes the timing into a differential pair and with windows for data inclusion and set transition periods as illustrated inFIG. 5. There are various other methods know to one skilled in the art to generate symbol rate for a client device such as a portable computer or like device.

FIG. 5shows a graphical representation of adjustable symbol rates and adjustable bits per symbol according to the teachings of the present invention. InFIG. 5symbols are represented by the envelopes whereas bit rates are represented by solid dots within each envelope. As a consequence in graph502the symbol rate is 1× and the bit rate is 4 bits per symbol. In graph504the symbol rate is 1.3× and the bit rate is 3 bits per symbol. In graph506the symbol rate is 2× and the bit rate is 2 bits per symbol. In graph508the symbol rate is 4× and the bit rate is 1 bit per symbol. It should be noted that in graph500as the symbol rate increases the bit rate decreases and vice versa. By transmitting data in accordance with the relationship between the bit rate and symbol rate shown inFIG. 5constant throughput is maintained as the power supply to the mobile device changes from high to low thus conserving battery life.

FIG. 6shows a flowchart for the logic used in power type detector345(FIG. 3) to determine what source is providing power to the mobile device. As stated herein the symbol rate and bit rate of the client device is based upon the power source providing power to the client device. The program starts in block600and descends into block602whereat the output from AUX power336(FIG. 3) is checked. If the response is positive the program enters604and sets the “AUX” bit in power source register344. If in block602the result is negative the program descends into606where it checks the output from DC power source338. If the result is positive the program enters block608where it sets a bit for DC power in power source register344. If the check from606is negative the mobile device must be running on battery power and the program descends into610where the battery power bit is set in power source register344. After setting one of the bits in the power source register the program loops back to block600where it repeats the process previously described.

FIG. 7shows a flowchart of a program executed in the mobile device to establish a connection between the mobile device and an Access Point. The program begins in700and descends into702whereat the mobile device scans for Access Points within range. The scanning can be accomplished by having the client device listen for beacons from Access Points or having client device attempt to ping various networks. After determining which Access Points are within range the client device compares the available Access Points to Access Point preference list, block704. The preference list is usually preloaded into the mobile unit The program then descends into block706where it checks for a match. If there is no match the program loops back to702and repeats the steps previously described. If a match occurs in706the program descends into708where it connects to the first available Access Point probably the one that matches the highest one on its preference list of available access points.

FIG. 8is a flowchart for a program executed on the mobile device to determine the symbol rate at which the mobile device will communicate with a selected Access Point. The program starts in800and descends into802where it checks the power source register to determine what type of power is being used in the portable device. The program then descends into804. If the setting is AUX power the program exits along the Y path into block806whereat the mobile device requests maximum symbol rate from the Access Point. The program then loops back to802. If the AUX bit in the power source register is not set the program exits block804along the N path into block808. In block808the program checks if the DC power bit in the power source register is set. If the bit is set the program exits along the Y path into block810where the program requests maximum symbol rate from the Access Point. The program then loops back to802. If in block808the response is negative the program exits along the N patch into812. It should be noted that if the power is neither AUX power or DC power then it must be battery power. In block812the program tests to see if the battery power is greater than 50% of maximum power available from the battery. If it is the program exits block812along the Y path into814whereat a lower symbol rate is requested from the Access Point. The program then loops back to block802. If in block812the battery power is less than 50% the program exits along the N path into block816where it requests minimum symbol rate and loops back to802. With respect toFIG. 5minimum symbol rate would be graph502while maximum symbol rate would be graphed508.

FIG. 9shows a flowchart for a program executed in the Access Point to accept or deny a symbol rate requested by a mobile device. The program starts in900and descends into902where it waits for a requested symbol rate. As discussed inFIG. 8the requested symbol rate would be received from a mobile unit within the operational range of the Access Point. Having received a requested symbol rate from a mobile unit the program descends into904where it makes a determination as to whether or not it can support or not support the requested symbol rate. If it cannot support the requested symbol rate the program exits along the No (N) path into908and issues a deny response. If in904the Access Point can support the requested symbol rate the program exits along the Yes (Y) path into906where the Access Point selects a wireless adapter with a symbol rate that matches the requested symbol rate. Thereafter, communication between the mobile device and Access Point is carried out using the agreed to symbol rate.

In summary, once a mobile unit registers with the Access Point the mobile unit determines the symbol rate based upon the power source to which the mobile unit is attached. It then negotiates with the Access Point to see if the Access Point can support that symbol rate. If the Access Point does support the symbol rate the communication between the Access Point and the mobile is consummated using the agreed upon symbol rate.

In view of the foregoing it will be evident to a person skilled in the art that various modifications may be made within the spirit and the scope of the present invention as hereinafter defined by the appended claims and that the present invention is thus not limited to the example provided.