Abstract:
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.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to wireless networks in general and in particular to power management in devices operating in said wireless networks.  
           [0003]    2. Prior Art  
           [0004]    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.  
           [0005]    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.  
           [0006]    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&gt;(greater than) 50%.  
           [0007]    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.  
           [0008]    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  
         [0009]    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.  
           [0010]    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.  
           [0011]    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.  
           [0012]    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.  
           [0013]    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.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The invention as well as a preferred mode of use, further objects and advantages thereof will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0015]    [0015]FIG. 1 shows a schematic of a wired and wireless network in which the present invention is implemented.  
         [0016]    [0016]FIG. 2 shows a block diagram of an Access Point (AP) according to the teachings of the present invention.  
         [0017]    [0017]FIG. 3 shows a block diagram of a mobile device according to the teachings of the present invention.  
         [0018]    [0018]FIG. 4 shows a schematic of the circuit that generates the symbol rate according to the teachings of the present invention.  
         [0019]    [0019]FIG. 5 shows a schematic of the adjustable symbol rate and adjustable bit rate according to the teachings of the present invention.  
         [0020]    [0020]FIG. 6 shows a flowchart for the logic used to detect the power source that is being used by the mobile unit.  
         [0021]    [0021]FIG. 7 shows a flowchart of the process used by the mobile device to connect to an Access Point.  
         [0022]    [0022]FIG. 8 shows a flowchart of a process by which the mobile device requests a desired symbol rate from the Access Point.  
         [0023]    [0023]FIG. 9 shows a flowchart of a process used by the Access Point to accept or deny a requested symbol rate. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    [0024]FIG. 1 shows a schematic for a network in which the present invention is implemented. The network  100  includes wireless LAN  106  and wired LAN  110 . The wireless LAN  106  operates in accordance with IEEE 802.11 specification for wireless networks. The wires LAN  110  is preferably an ethernet LAN running at 100 Mbps. Access Point  102  is shown connected to ethernet LAN  110  while a wireless node or device  108  is shown positioned within signal range, delineated by dash lines  104 , of Access Point  102 . With client device  108  being in the operating range of Access Point  102 , the client device  108  is able to transmit and receive information to and from Access Point  102 .  
         [0025]    [0025]FIG. 2 shows a block diagram of the Access Point (AP) according to the teachings of the present invention. Elements in FIG. 2 that are similar to elements in FIG. 1 are identified with like numerals and will not be discussed further. The Access Point  200  includes controller  202 , wireless LAN adapters  222 ,  238  . . . N and wired LAN adapter  212 . The wireless LAN adapters  222 ,  238  . . . N provides a wireless LAN interface to controller  202  whereas wired LAN adapter  212  provides a wired LAN interface to the ethernet LAN  110 . As will be discussed in greater detail hereinafter each of the adapters  222 ,  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 controller  202  is coupled by bus  232  to wireless LAN adapters  222 ,  238  . . . N and by bus  234  to wired LAN adapter  212 . The controller  202  includes memory  204 , interface flow control logic  206 , program storage  208 , and microprocessor  210 . The named components  204 ,  206 ,  208  and  210  are interconnected as shown in FIG. 2. The program storage  208  stores control program (firmware) that microprocessor  210  runs or executes to support the wired and wireless networks. The data store  204  is used to temporarily hold data that is being transferred between wireless network and the wired network  110 . The interface flow control logic  206  controls the movement of data from controller  202  to the wireless adapters  222 ,  238  . . . N and to wired adapter  212 .  
         [0026]    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.  
         [0027]    The LAN adapter  212  provides the LAN interface to ethernet LAN  110 . Wired LAN adapter  212  includes Controller  214 , TX FIFO  220 , RX FIFO  216  and Physical Layer  218 . Controller  214  provides MAC (medium access control) functions for the LAN adapter  212 . Controller  214  is connected to TX FIFO  220  and RX FIFO  216 . The TX FIFO  220  holds data to be transmitted onto the ethernet LAN whereas the RX FIFO  216  receives data from ethernet LAN  110 . TX FIFO  220  and RX FIFO  216  are connected to Physical Layer  218 . The Physical Layer  218  provides physical function to the adapter which includes conversion of digital to analog signals compliant with ethernet specification, provides physical connection to network  110 , etc.  
         [0028]    Still referring to FIG. 2, each of the wireless LAN adapters, such as wireless LAN adapter  222  is 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 adapter  222  or  238  . . . N includes RF Transceiver  224 , TX FIFO  230 , RX FIFO  228  and Controller  226 . The named components are connected as shown in the figure. The Controller  226  provides interface function and is commonly known as medium access control (MAC). The MAC is connected to the TX FIFO  230  which holds data to be subsequently transmitted to the wireless network. Likewise, the RX FIFO  228  holds data that is received from the wireless network. The RF Transceiver  224  and power amplifier antenna  240  converts digital signals to radio frequency energy compliant with 802.11b specification. The RF Transceiver and power amplifier antenna  240  also receives radio frequency signals and converts them to digital signals. As a consequence the RF Transceiver and power amplifier antenna  240  includes both a transmitting subsystem and a receiver subsystem. The transmitting subsystem handles data which is transmitted into the wireless network  106  whereas the receiving subsystem manages data received from the wireless network  106 . RF transceivers and power amplifier antenna  240  are well known in the prior art and further discussions are not warranted. It should be noted components on wireless adapters  238  . . . N are not shown but are identical to the components described for wireless adapter  222 . The primary difference between the multiple wireless adapters  222 ,  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.  
         [0029]    [0029]FIG. 3 shows a block diagram of the structure for a client device such as a portable computer or like device. The client  300  includes peripheral component interface (PCI) bus controller  308  to which DASD  312 , keyboard/mouse  314 , flash program storage  316  and memory controller  304  are connected. The function of PCI bus controller  308  includes arbitrating between the attached devices and enabling those devices to access the memory  306  and DASD  312 . The microprocessor  302  is coupled through the memory controller  304  to the memory  306 . The memory controller  304  controls the memory  306 . The flash program storage  316  contains initialization program or bios that is used to establish the client in an operating state when it is first turned on.  
         [0030]    Still referring to FIG. 3, PCI expansion bus  310  connects video controller  318  and wireless adapter  322  to the PCI bus controller  308 . The video controller  318  is connected to a video display  320 . The video controller  318  manages the information to be displayed on the video display  320 . The wireless adapter  322  provides the wireless LAN interface that allows a client to communicate via radio waves to an Access Point. As a consequence, the wireless adapter  322  includes power amplifier/antenna  344  coupled to RF Transceiver  330  which is connected to TX FIFO  328  and RX FIFO  326 . Controller  324  couples TX FIFO  328  and RX FIFO  326  to the PCI bus  310 . The Controller  324  performs the MAC functions that allow the wireless adapter  322  to interface with the PCI bus and process data according to the protocols set forth in IEEE 802.11 standard for wireless network. The RF Transceiver  330  includes both the transmitting section and a receiving section that function in a way similar to that of previously described RF Transceiver  224 . A symbol and bit rate generator  341  that generates variable symbols based upon the power source on which the mobile device is running is also provided. A circuit diagram for symbol generator  341  is shown in FIG. 4. Even though the symbol generator is shown as part of the controller  324  this 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.  
         [0031]    Still referring to FIG. 3, the present invention allows the client device  300  to maintain a constant data throughput as it changes to lower power modes to control battery life. To this end the client device  300  includes a power subsystem including power supply  334  with an input to be coupled to AC power source  332  and two output power rails labeled Aux Power  336  and DC Power  338 . A battery  340  is connected to DC Power  338  and generates an output labeled Battery Power  342 . Aux Power  336  is available whenever client device  300  is connected to external power supply  334 . DC Power  338  is provided whenever client device  300  is connected to power supply  334  and powered on. DC power is always provided to battery  340 . Battery power  342  is available as long as battery  340  has charge. Power Type Detector (PTD)  345  monitors Aux Power  336 , DC Power  338  and Battery Power  342  and sets a bit in Power Source Register  344  to indicate the source that is providing power to client device  300 . PTD  345  could be a PLA (Program Logic Array) or other combinatorial logic designed in accordance to the flowchart set forth in FIG. 6 and 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 register  344 .  
         [0032]    [0032]FIG. 4 shows a block diagram of the circuit that generates the variable symbol rate. Phase lock loop  400  generates the base timing waveform. The output of phase lock loop  400  is provided to adder circuit  402  which adds the fundamental frequency pulse (not shown) to obtain the frequency of the desired symbol rate. The output of adder circuit  402  provides the timing for the Eye Pattern generation in block  404 . The Eye Pattern generation changes the timing into a differential pair and with windows for data inclusion and set transition periods as illustrated in FIG. 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.  
         [0033]    [0033]FIG. 5 shows a graphical representation of adjustable symbol rates and adjustable bits per symbol according to the teachings of the present invention. In FIG. 5 symbols are represented by the envelopes whereas bit rates are represented by solid dots within each envelope. As a consequence in graph  502  the symbol rate is 1× and the bit rate is 4 bits per symbol. In graph  504  the symbol rate is 1.3× and the bit rate is 3 bits per symbol. In graph  506  the symbol rate is 2× and the bit rate is 2 bits per symbol. In graph  508  the symbol rate is 4× and the bit rate is 1 bit per symbol. It should be noted that in graph  500  as 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 in FIG. 5 constant throughput is maintained as the power supply to the mobile device changes from high to low thus conserving battery life.  
         [0034]    [0034]FIG. 6 shows a flowchart for the logic used in power type detector  345  (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 block  600  and descends into block  602  whereat the output from AUX power  336  (FIG. 3) is checked. If the response is positive the program enters  604  and sets the “AUX” bit in power source register  344 . If in block  602  the result is negative the program descends into  606  where it checks the output from DC power source  338 . If the result is positive the program enters block  608  where it sets a bit for DC power in power source register  344 . If the check from  606  is negative the mobile device must be running on battery power and the program descends into  610  where the battery power bit is set in power source register  344 . After setting one of the bits in the power source register the program loops back to block  600  where it repeats the process previously described.  
         [0035]    [0035]FIG. 7 shows 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 in  700  and descends into  702  whereat 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, block  704 . The preference list is usually preloaded into the mobile unit The program then descends into block  706  where it checks for a match. If there is no match the program loops back to  702  and repeats the steps previously described. If a match occurs in  706  the program descends into  708  where it connects to the first available Access Point probably the one that matches the highest one on its preference list of available access points.  
         [0036]    [0036]FIG. 8 is 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 in  800  and descends into  802  where it checks the power source register to determine what type of power is being used in the portable device. The program then descends into  804 . If the setting is AUX power the program exits along the Y path into block  806  whereat the mobile device requests maximum symbol rate from the Access Point. The program then loops back to  802 . If the AUX bit in the power source register is not set the program exits block  804  along the N path into block  808 . In block  808  the 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 block  810  where the program requests maximum symbol rate from the Access Point. The program then loops back to  802 . If in block  808  the response is negative the program exits along the N patch into  812 . It should be noted that if the power is neither AUX power or DC power then it must be battery power. In block  812  the 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 block  812  along the Y path into  814  whereat a lower symbol rate is requested from the Access Point. The program then loops back to block  802 . If in block  812  the battery power is less than 50% the program exits along the N path into block  816  where it requests minimum symbol rate and loops back to  802 . With respect to FIG. 5 minimum symbol rate would be graph  502  while maximum symbol rate would be graphed  508 .  
         [0037]    [0037]FIG. 9 shows 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 in  900  and descends into  902  where it waits for a requested symbol rate. As discussed in FIG. 8 the 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 into  904  where 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 into  908  and issues a deny response. If in  904  the Access Point can support the requested symbol rate the program exits along the Yes (Y) path into  906  where 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.  
         [0038]    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.  
         [0039]    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.