Abstract:
To make more efficient use of power resources, a mobile device adjusts the power necessary for receiving and/or transmitting data in response to signal quality. As the quality of received signals change, the device alters the power used to transmit and/or receive signals. When signal quality is poor, more power is used to receive the signal to maintain device functionality. When signal quality is strong, less power can be used while still maintaining device performance. This preserves device functionality while allowing the device to conserve power when possible.

Description:
BACKGROUND 
       [0001]    1. Field of Art 
         [0002]    The present invention generally relates to the field of power management in mobile communication devices, and more specifically, to adjusting power consumption based on received signal quality. 
         [0003]    2. Description of the Related Art 
         [0004]    Mobile communication devices such as mobile phones, smartphones, personal digital assistants and handheld computers are becoming increasingly more powerful and functional devices while their size decreases. Many mobile communication devices are now multifunction devices, able to be controlled with one hand, with multiple device roles including: personal digital assistant (PDA), cellular phone, portable media player, voice recorder, video recorder, global positioning system (GPS), camera, and/or electronic file storage. Similarly, portable computer functionality has continued to increase while the computers become thinner and lighter. This combination of increased functionality and reduced size has made mobile device use more prevalent. 
         [0005]    Additionally, advancements in both wireless Internet coverage and wireless network capabilities have made a broad range of data, such as electronic files, image files, audio files and video files, more accessible to mobile communication devices, including portable computers. Network improvements have also allowed electronic data to be accessed from virtually all locations. Thus, the improvements in both wireless network access and portable device design and functionality has increased the use of portable communication devices for data modification, event scheduling and other common tasks. 
         [0006]    However the increased functionality and reduced size of mobile devices has made power consumption an increasingly important characteristic of mobile devices. Particularly, the decreased size of mobile devices has limited the space available for batteries or other power sources while the increased functionality of mobile devices has increased the overall power required for the devices. Thus, it is increasingly important for portable devices to efficiently use their limited power supplies. In particular, improved power management systems can increase the operational time of mobile communication devices without reducing their functionality or increasing their size to accommodate larger power supplies. 
         [0007]    Therefore, there is a need for efficient power management techniques for mobile communication devices. 
       SUMMARY 
       [0008]    Various embodiments of the invention allow the power used by a mobile communication device to be adjusted based on the quality of communication signals received wirelessly by the mobile device. Since power is consumed when data is transmitted and/or received by a mobile device, adjusting the power required for transmission or reception decreases the overall power consumed by the device. To achieve this power adjustment, the mobile communication device adjusts the power used for transmission or reception based on the signal quality of the received signal. In this way, less power is used when a received signal has high quality as less processing is necessary to make the received signal useable. 
         [0009]    In one implementation, a signal is received and a signal quality, such as a signal-to-noise ratio or a bit error rate, of the received signal is computed. The computed signal quality is then used to adjust the power provided for reception and/or transmission. In one approach, the signal quality is compared with a threshold value and the power is adjusted depending on whether the signal quality is above or below the threshold value. 
         [0010]    In one implementation, a mobile communication device includes a receiving signal path, a power supply subsystem and a signal characterization module. The power supply subsystem provides power to the receiving signal path and/or to a transmitting signal path. The signal characterization module is coupled between the receiving signal path and the power supply subsystem. Based on a signal quality of a wireless communication signal received by the receiving signal path, the signal characterization module adjusts the power provided by the power supply subsystem to the receiving signal path and/or to the transmitting signal path. For example, for received signals with a higher signal-to-noise ratio, the power supply subsystem may provide less power to an analog-to-digital converter in the receiving signal path. This may result in a lower resolution analog-to-digital conversion, but which resolution is still sufficient given the higher signal-to-noise ratio of the incoming signal. 
         [0011]    Other aspects of the invention include devices that implement power saving techniques such as those described above, components for these devices, and systems using these devices or techniques. Further aspects include methods and processes corresponding to all of the foregoing. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    The disclosed embodiments have other advantages and features which will be more readily apparent from the following detailed description and the appended claims, when taken in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a block diagram of a data communication network suitable for use with the invention. 
           [0014]      FIG. 2  is a block diagram of a transceiver according to one embodiment of the invention. 
           [0015]      FIG. 3  is a flowchart of adjusting power consumption according to one embodiment of the invention. 
           [0016]      FIG. 4  is a flowchart of a method for computing signal quality according to one embodiment of the invention. 
           [0017]      FIG. 5  is a block diagram of a baseband processor according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The Figures and the following description relate to preferred embodiments of the present invention by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of the claimed invention. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. 
         [0019]    Generally, the following examples allow the power used to receive and/or transmit data to be adjusted in response to the quality of a received data signal. When the received signal is high-quality, the power used to receive the signal is reduced. For example, in one implementation, when the received signal is converted from an analog signal to a digital signal, the number of bits comprising the digital signal is decreased when the received signal quality is high. Because the received signal quality is high, this resolution reduction does not detract from device performance but does reduce device power consumption. Similarly, when the received signal quality is low, the power used to receive the signal is increased. For example, when the receive signal is converted from an analog signal to a digital signal, the number of bits comprising the digital signal is increased. Although this resolution increase requires more power, it maintains device functionality. Because the power used varies with signal quality, the device is configured to only consume as much power is necessary to maintain its performance level (e.g., a specific bit error rate). Corresponding power adjustments can also be made for data transmission. 
         [0020]      FIG. 1  shows a data communication network  100  suitable for use with the invention. The data communication network  100  includes a base station  110  and one or more mobile stations  120  (i.e., mobile communication devices). The base station  110  and mobile stations  120  include transceivers  130  for wirelessly transmitting and receiving data between the devices. In some applications, the data communication network  100  is a wireless network compliant with the IEEE 802.16 standard, the IEE 802.11 standard or any other time division duplexing (TDD) format. For convenience,  FIG. 1  shows transceivers  130  but devices  110  and  120  could be configured with only transmitters or only receivers if bidirectional communication is not required. 
         [0021]    The data communication network  100  typically uses symbols to represent data to be transmitted and uses multicarrier modulation to transmit the symbols. For example, the data communication network  100  could transmit data symbols using orthogonal frequency-division multiplexing (OFDM), binary phase-shift keying (BPSK), or other modulation methods. Multicarrier modulation techniques, such as ODFM divide the data stream to be transmitted into several parallel data streams, each containing less data than the original data stream. The available frequency spectrum is then divided into several sub-channels and each reduced data stream is transmitted by using a modulation scheme such as BPSK, phase-shift-keying (PSK), or quadrature amplitude modulation (QAM) to modulate each sub-channel. 
         [0022]    The base station  110  and mobile station  120  include transceivers  130  for transmitting and receiving wireless communications signals that contain these data symbols. The transceiver  130  transmits wireless communication signals and receives wireless communication signals to be processed from other devices. In certain applications, the transceiver  130  includes an antenna capable of transmitting and receiving wireless signals, such as those compliant with the IEEE 802.16 standard, IEEE 802.11a/b/g standard or other wireless communication formats. However, the transceiver  130  can be any device capable of wirelessly transmitting and receiving signals. When transceiver  130  transmits or receives data, it draws power from the corresponding base station  110  or mobile station  120 . By varying this power consumption responsive to signal quality, the base station  110  or mobile station  120  is able to operate longer without requiring a larger power supply. A more detailed description of the structure of the transceiver  130  is provided in conjunction with  FIG. 2 . 
         [0023]      FIG. 2  shows a variable-power consumption transceiver  130  in accordance with an embodiment of the invention. In this example, the transceiver  130  includes a receiving signal path  210 , a signal characterization module  220 , a scalable power supply subsystem  230  and a transmitting signal path  240 . The receiving signal path  210  receives a wireless communication signal  205  and processes the received signal to recover the data encoded on the signal. In the case of RF communications, the complete receiving signal path  210  might include an RF antenna to provide gain and/or directionality, an RF front end to convert the received RF signal to baseband form, and a baseband processor to recover the encoded data. The baseband processor could include an analog-to-digital converter (ADC) which converts baseband analog signals to digital signals, and additional data processing elements (such as DSPs, processors and associated clocks and storage). The receiving signal path  210  can use various designs to implement the ADC, such as direct conversion, delta-sigma, pipeline, delta-encoded or other suitable converter architectures. 
         [0024]    The signal characterization module  220  is coupled to the receiving signal path  210  and processes the received signal to determine the quality of the received wireless communication signal  205 . The signal characterization module  220  may use the raw wireless communication signal  205  directly or may use the received signal after it has been partially or fully processed by the receiving signal path  210 . 
         [0025]    The signal characterization module  220  can be implemented in many ways. For example, it may be structured as a software process and/or a firmware application. The software and/or firmware can be structured to operate on a general purpose microprocessor or controller, a specialized processor or controller, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) or a combination thereof In addition to processing capability, the signal characterization module  220  typically also includes a memory module (or other storage) that stores instructions and/or data for execution or other use by a processor. In some implementations, the memory module stores data describing the signal strength of the received wireless communication signal  205  and data describing the noise affecting the network  100 . The signal characterization module  220  can be implemented as part of the scalable power supply subsystem  230 . 
         [0026]    The scalable power supply subsystem  230  provides power to the receiving signal path  210  and/or to the transmitting signal path  240 . The amount of power provided is adjusted by the signal characterization module  220 , based on the signal quality of the wireless communication signal  205 . For example, when signal quality is high, power consumption is reduced by reducing the number of signal processing operations performed. In one implementation, the scalable power supply subsystem  230  is a voltage source capable of altering the voltage output in response to control signals from the signal characterization module  220 . In another approach, the scalable power supply subsystem  230  is a voltage regulator module or other device capable of dynamically adjusting the voltage output. In many mobile communication devices, for example in many handheld devices, the power supply subsystem  230  is battery-powered. 
         [0027]    In some cases, the transceiver  130  further includes a transmitting signal path  240  which receives a data signal  235  for transmission to another device as wireless communication signal  245 . The transmitting signal path  240  often is the reverse of the receiving signal path  210 . For example, it might include a baseband process (with data processing elements and digital-to-analog converter), followed by an RF front end and antenna. The transmitting signal path  240  can use various designs to implement the digital-to-analog converter, such as pulse width modulation, delta-sigma, R-2R ladder, segmented or other suitable converter architectures. The signal characterization module  220  may also (or alternately) adjust the power provided by power supply subsystem  230  to transmitting signal path  240  based on the received signal quality. 
         [0028]    For convenience, the terms “receiving signal path” and “transmitting signal path” will be used to refer both to the entire signal paths and to portions of the entire signal path. For example, the term “receiving signal path” includes the entire path from antenna to RF front end to ADC to subsequent processing, but it also includes just the ADC alone or just the subsequent processing alone or just the ADC in combination with the subsequent processing. 
         [0029]      FIG. 3  shows a method for adjusting power responsive to signal quality according to an embodiment of the invention. In the example of  FIG. 3 , the receiving signal path  210  receives  310  a wireless communication signal (which could be either the directly transmitted signal  205  or a signal derived from it). The signal quality of the received signal is then computed  320 . 
         [0030]    A common measure of signal quality is signal-to-noise ratio. In one approach, a signal strength is estimated based on reception of the wireless communication signal  205 . The noise strength is estimated based on reception without a wireless communication signal  205 . The signal-to-noise ratio is determined by taking the ratio of the estimated signal strength and estimated noise strength. Alternatively, the signal quality computation  320  can be a bit-error-rate estimate of the received signal, a signal-plus-noise-plus-distortion to noise-plus-distortion (SINAD) ratio or other metric indicating signal parameters relative to noise parameters. The noise energy can be a fixed value or can be dynamically adjusted as network  100  conditions change. In one implementation, during the signal quality computation  320 , a new value for noise energy is also computed and stored for subsequent computations  320 .  FIG. 4 , described below, illustrates an example algorithm for computing  320  signal quality. However, other algorithms, such as computing a ratio of received signal energy to noise energy, can be used to determine  320  the received signal quality. 
         [0031]    In step  330  of  FIG. 3 , the computed signal quality (e.g., SNR) is compared to a threshold value. If the computed signal quality is high (e.g., when it exceeds a threshold value), the power provided by the scalable power supply subsystem  230  is decreased  340 . Conversely, if the computed signal quality is low (e.g., when it falls below a threshold value), the power provided by the scalable power supply subsystem  230  is increased  340 . 
         [0032]      FIG. 4  shows an algorithm for computing  320  signal quality according to an embodiment of the invention. The receiving signal path  210  generates outputs. If a communication signal is present, then the output represents signal. If no communication signal is present, then the output represents noise. In this way, signal strength and noise strength can be estimated. 
         [0033]    In the approach of  FIG. 4 , the signal characterization module  220  stores estimates of signal strength and noise strength, which are updated as follows. The strength of a signal received by the receiving signal path  210  is detected  410 . It is then determined  420  whether the detected signal strength exceeds the current estimate of the noise strength. The initial estimate of the noise strength can be preset to a reference value. If the received signal strength does not exceed the current estimate of the noise strength, then the received signal is assumed to be noise only (no valid signal) and the estimate of noise strength is updated  450 . 
         [0034]    If the detected signal strength exceeds the current estimate of noise strength, then either the noise strength has increased or the detected signal includes a valid signal. It is then determined  430  whether the detected signal is a valid signal (i.e., conforms to the protocol for wireless communication between base station and mobile station). This typically can be achieved by the data processing section of the receiving signal path  210 . 
         [0035]    If the received signal is not a valid signal, then it is assumed to be noise and the stored noise strength is updated  450  to reflect the higher noise level. Alternatively, if the received signal is a valid signal, then the current estimate of the signal strength is updated  440 . In one approach, the signal strength is updated  440  by subtracting the estimated noise strength from the strength of the detected signal and using the resulting value as the estimate of the signal strength. This value can also be used to determine  330  whether the provided power should be increased or decreased. Alternatively, the signal quality may be updated  440  by storing the strength of the received valid signal, by calculating a parameter based on the received valid signal, or by any other method deriving a representation of signal quality from detected signal strength. 
         [0036]      FIG. 5  is a block diagram of a baseband processor according to another embodiment of the invention. In this example, the mobile stations  120  and base station  110  communicate via RF wireless links. In various applications, the RF wireless links are compliant with the IEEE 802.16 standard, the IEE 802.11 standard or any other time division duplexing (TDD) format. The mobile stations typically have transceivers that include an RF antenna, an RF front-end subsystem, a baseband processor subsystem and a media access control (MAC) subsystem.  FIG. 5  shows only the baseband processor subsystem, which interfaces on the lefthand side to the RF front-end subsystem and interfaces on the righthand side to the MAC subsystem. In one implementation, the baseband processor is implemented on a single chip. 
         [0037]    In this example, the receiving signal path  210  includes an analog-to-digital converter  512 , a sample rate converter  514  and a receiving datapath  516  (which implements additional data processing, such as decoding and error checking). The transmitting signal path  240  includes a transmitting datapath  546 , a sample rate converter  544  and a digital-to-analog converter  542 . The power supply subsystem  230  is a scalable voltage supply. The signal characterization module  220  characterizes SNR for the received signal. 
         [0038]    The SNR module  220  adjusts the power provided by supply  230  according to the SNR of the received signal. More specifically, the power adjustment changes the effective resolution of the ADC  512  and/or the DAC  542 . In one approach, lower signal quality (i.e., lower SNR) results in a higher voltage supplied to the ADC  512 , thus increasing its resolution. For example, when the signal quality falls below a specified threshold, the ADC resolution might increase from a minimum of 6 bits to a maximum of 10 bits. In one implementation, the ADC  512  always generates 10 bits for the sample rate converter  514  but, when the effective resolution is 6 bits, then four of the 10 bits are always 0. In this case, the circuitry in the remainder of the receiving signal path  210  that would normally process these four bits (which are now all 0) may also be switched off (or to a power saving mode). Because reducing ADC resolution decreases the power required to operate the transmitting signal path  210 , power consumption is decreased but device functionality is preserved because the received signal has sufficient strength to offset the lower resolution of the ADC  512 . For example, reducing the resolution of a 10-bit ADC  512  or a 10-bit DAC  542  by one bit results in a 10%-20% power savings by reducing the computational complexity. Alternatively, a clock rate for data operations (e.g., “add,” “multiply,” “read,” etc.) is modified responsive to signal quality. 
         [0039]    For example, in a system designed so that a quadrature phase shift keying (QPSK) signal with a signal-to-noise ratio (SNR) of 10 dB can be correctly demodulated and decoded, ADC  512  or DAC  542  resolution can be reduced as long as the quantization noise does not degrade SNR below 10 dB. Hence, in the above-described example, if a signal having an SNR of 50 dB is received, the ADC  512  and/or DAC  542  resolution is reduced. Although the reduction in resolution increases the quantization noise in the system, as long as the quantization noise does not degrade signal SNR below 10 dB, the signal can be correctly detected and demodulated. 
         [0040]    In one configuration, a similar process is used to increase or decrease the resolution of the DAC  542  to adjust the wireless communication signal transmitted by the transceiver, resulting a lower-power RF signal. For example, a 10 bit DAC  542  uses a voltage range of 0-1.5V while a 10-bit DAC where the two most significant bits are 0, effectively an 8-bit DAC  542 , uses a voltage range of 0-0.5V. Hence, when multiplied by the same gain value, the 8-bit DAC  542  output results in a reduced-power RF signal. 
         [0041]    Power adjustment can occur at various stages of operation, for example during initial handshake between base station and mobile station, while idling (e.g., if a cell phone is on but not actively being used) or during active use (i.e., during the period when the mobile communications device is either receiving or transmitting wirelessly to the base station). 
         [0042]    As used herein, “coupled” is intended to mean both coupled directly (without intervening elements) and coupled indirectly (with intervening elements). Upon reading this disclosure, those of skill in the art will appreciate still additional alternative structural and functional designs for a system and a method for adjusting power consumption in response to variations in signal quality through the disclosed principles herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the present invention is not limited to the precise construction and components disclosed herein and that various modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus of the present invention disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims.