Abstract:
Operating a communication device in a half-duplex mode using only overhead channels; and substantially free running a timing reference obtained during reception to allow a timing reference value to drift during transmission.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of priority of co-pending U.S. Provisional Patent Application Ser. No. 60/653,798 entitled “Low Duty Cycle CDMA Device”, filed Feb. 16, 2005. This application also claims the benefit of priority of co-pending U.S. Provisional Patent Application Ser. No. 60/708,671 entitled “Low Duty Cycle Half-Duplex Mode Operation with Telecommunication Device”, filed Aug. 15, 2005. Benefits of priority of the filing dates of Feb. 16, 2005 and Aug. 15, 2005 are hereby claimed, and the disclosures of the Provisional Patent Applications are hereby incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     1. Field  
         [0003]     The present invention generally relates to transmission of data over telecommunication networks, and to telecommunication devices that enable such transmission. More particularly, the invention concerns a new technique for using the telecommunication device in a half-duplex mode for a low duty cycle data transmission operation.  
         [0004]     2. Background  
         [0005]     Remote monitoring of operations may involve battery-operated, wireless telecommunication devices that monitor operational status information and transmit via radio frequency signals the operational status information to a remotely situated information-processing device. Oftentimes, the operational status information can be transmitted via radio frequency signals as short messages. In such monitoring and transmission configurations, issues associated with power consumption management are an important concern.  
         [0006]     In a typical operational environment, low maintenance battery-operated monitoring/telecommunication devices are desirable to facilitate operating efficiency and to reduce maintenance costs. Therefore, it is desirable to have a monitoring/telecommunication device that can operate for an extended period of time without requiring frequent maintenance for battery replacement and the like. For example, the telecommunication device may be placed in a sleep or low-power operating mode when there is no ongoing communication with the information-processing device. A trade off is usually made between the availability of the telecommunication device for communications with the information processing device and the amount of power consumption savings that can be achieved. A telecommunication device employing a power consumption saving technique may not be able to communicate with the remotely situated information-processing device as its communication circuitry or sections thereof may be shut-off when the device is in the sleep mode in order to conserve battery power.  
         [0007]     There is therefore a need in the art for low power means of transmitting operational status information via radio frequency signals.  
       SUMMARY  
       [0008]     In one aspect, a method of operating a communication device is disclosed. The method includes operating a communication device in a half-duplex mode using only overhead channels; and substantially free running a timing reference obtained during reception to allow a timing reference value to drift during transmission.  
         [0009]     In another aspect, a communication device is disclosed. The communication device comprising: a receive chain and a transmit chain operating in a half-duplex mode to receive and transmit low duty cycle (LDC) messages using only overhead channels; and a half-duplex controller coupled to the receive chain and the transmit chain to substantially free run a timing reference obtained during reception to allow a timing reference value to drift during transmission.  
         [0010]     In another aspect, a tangible storage medium including a computer program for operating a communication device in a half-duplex mode using only overhead channels is disclosed. The program comprises executable instructions that cause a computer to: substantially free run a timing reference obtained during reception to allow a timing reference value to drift during transmission; and substantially freeze a power estimate obtained during the reception for use as a transmit power value during the transmission.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  illustrates a block diagram of one implementation of a communication device such as a CDMA communication device.  
         [0012]      FIG. 2  illustrates a block diagram of another implementation of a communication device showing a detailed configuration of tracking loops.  
         [0013]      FIG. 3  illustrates a block diagram of another implementation of a communication device showing detailed configurations of the power management and the half-duplexer.  
         [0014]      FIG. 4  illustrates one alternative implementation of the half duplexer integrated into the receive chain and the transmit chain so that the half-duplex operation is performed within the receive chain and the transmit chain with forward link and reverse link signals time sharing one antenna.  
         [0015]      FIG. 5  illustrates another alternative implementation of the half duplexer integrated into the receive chain and the transmit chain but with the forward link signal being received at antenna A and the reverse link signal being transmitted antenna B.  
         [0016]      FIG. 6  is a flowchart illustrating a method for transmitting and receiving low duty cycle (LDC) messages in a half-duplex mode in accordance with one implementation of the present invention.  
         [0017]      FIG. 7  shows a registration model in which the communication device transmits an access probe signal, including the LDC messages, during the transmit mode.  
         [0018]      FIG. 8  shows a model in which the communication device transmits an LDC message over the access probe signal.  
         [0019]      FIG. 9  shows a model in which the communication device determines whether the device is being paged by the base station.  
         [0020]      FIG. 10  illustrates a block diagram of another implementation of a communication device, which is implemented with a dual band half-duplex transceiver. 
     
    
     DETAILED DESCRIPTION  
       [0021]     The nature, objectives, and advantages of the present invention will become more apparent to those skilled in the art after considering the following detailed description in connection with the accompanying drawings.  
       Introduction  
       [0022]     In recognition of the above-stated problems associated with remote monitoring of operational status information and transmitting via radio frequency signals, the present disclosure describes several embodiments for using only overhead channels of a telecommunication network (e.g., a cellular network such as a CDMA or GSM network) in a half-duplex mode. In particular, the operational status information is transmitted from a communication device to a remotely situated information-processing device as low duty cycle (LDC) messages in a half-duplex mode.  
         [0023]     In one implementation, the communication device is a wireless telecommunication device including a CDMA communication device, and the remotely situated information-processing device is a processor located within or coupled to the CDMA network, such as a base station controller or other network controllers. In another implementation, the remotely situated information-processing device includes another communication device implemented in a peer-to-peer communication configuration.  
         [0024]     In one implementation, the overhead channels used in CDMA 2000 1× (First Evolution) include pilot, sync, and paging channels in the forward link and an access channel in the reverse link. The overhead channels used in CDMA 2000 1× EV-DO (First Evolution-Data Only) include pilot, sync, and control channels in the forward link and an access channel in the reverse link. In other implementations, the overhead channels include any non-traffic channels that provide reference, timing, system configuration, and access. In a CDMA application, traffic channels carry main information such as two-way voice signals for providing telephone conversation.  
         [0025]     The term “half-duplex mode” refers to a mode of the communication device that, for any given transmission period, is permitted to act as one of a transmitter or receiver, but the device cannot both transmit and receive in the same communication period.  
         [0026]     The term “low duty cycle messages” refers to messages transmitted intermittently or occasionally.  
         [0027]     The term “hibernate mode” refers to a mode of the communication device that places the communication device in a state of sleep and turns off all units in the communication device except for a timing device to keep track of the duration of the sleep. For low duty cycle applications, the duration of the sleep is often substantially longer than allowable under the protocol of a conventional wireless communication network.  
       Communication Device  
       [0028]      FIG. 1  illustrates a block diagram of one implementation of a communication device  100 , such as a CDMA communication device. The communication device  100  includes a half-duplex transceiver  110 , a half-duplex controller  120 , a real-time clock (RTC)  130 , a power management unit  140 , and a modem (e.g., a digital baseband processor)  150 . The half-duplex transceiver  110  includes a receive chain  112 , a transmit chain  114 , and a half duplexer  116 . Thus, units  110  and  150  in the communication device  100  are configured to enable communication over an existing communication network such as a CDMA network. In one implementation, the communication device is a fixed device. In another implementation, the communication device is a mobile device.  
         [0029]     In the illustrated implementation of  FIG. 1 , the half-duplex transceiver  110  operates in a half-duplex mode where the half duplexer  116  switches between a receive mode and a transmit mode. In one implementation, the half duplexer  116  is implemented with an RF switch. In another implementation, the half duplexer  116  is integrated into the receive chain  112  and the transmit chain  114  so that the switching between the modes is performed by the receive chain  112  and the transmit chain  114 . When the half-duplex transceiver  110  is operating in the receive mode, the half-duplexer  116  selects the received forward link signal and routes the signal to the baseband processor  150  through the receive chain  112 . Alternatively, when the half-duplex transceiver  110  is operating in the transmit mode, the half duplexer  116  receives the reverse link signal output from the baseband processor  150  through the transmit chain  114  and routes the reverse link signal to an antenna for transmission.  
         [0030]     In one implementation, the decision to switch to the transit mode is made by the communication device  100  in an asynchronous manner rather than in a synchronous manner where the receive mode to transmit mode switching is periodic and predictable. This asynchronous switching is either triggered by an event within the communication device  100  or in coordination with a network entity based on exchanged messages. The switching instances need not be locked to the basestation or network system timing.  
         [0031]     In the illustrated implementation of  FIG. 1 , the simple half duplexer  116  such as a receive/transmit RF switch replaces an RF front end of a conventional communication device including an expensive and lossy duplexer. Since the communication device  100  is operating in a half-duplex mode, certain RF blocks can be time shared between the receive chain  112  and the transmit chain  116 . Therefore, operating the communication device in a half-duplex mode allows the receive chain  112  and the transmit chain  114  to be implemented on a same silicon substrate without any interference.  
         [0032]     The half-duplex controller  120  is configured to control the mode of the half-duplex transceiver  110 . For example, when the transceiver  110  is to be operated in a receive mode, the half-duplex controller  120  enables the receive chain  112  to synchronize the communication device  100  with a network timing and to compute an open loop power estimate. When the transceiver  110  is to be operated in a transmit mode, the half-duplex controller  120  freezes the timing reference along with a frequency tracking loop (i.e., the tracking of a finger), and switches off the receive chain  112 . The half-duplex controller  120  then switches on the transmit chain  114  and enables the transmit chain  114  to transmit an access probe message at the open loop power estimate last computed by the receive chain  112 . Once the transceiver  110  is ready to be operated in a receive mode again, the half-duplex controller  120  switches the receive chain  112  on and closes the control loop for the timing reference. The transceiver  110  then listens for LDC messages on overhead channels of a telecommunication network.  
         [0033]     To enter a hibernate mode, the power management unit  140  is configured to manage the power consumption of the communication device  100  by turning off all units within the communication device  100  except for the power management unit  140  and the realtime clock (RTC)  130 . When the communication device  100  receives a command from a network controller to enter into a hibernate mode for a particular duration, the received command is sent to the power management unit  140 , which turns off power to all units except for the power management unit  140  and the RTC  130 . While the communication device  100  is in the hibernate mode, the power management unit  140  keeps track of the particular duration using the RTC  130 .  
         [0034]      FIG. 2  illustrates a block diagram of another implementation of a communication device  200  showing a detailed configuration of tracking loops. During a receive mode of the communication device  200 , tracking loops  210 ,  220 ,  230  of the receive chain  112  is active to synchronize the communication device  200  with a network timing and to compute an open loop power estimate. However, when the communication device  200  is to be operated in a transmit mode, the half-duplex controller  120  freezes the timing reference  210 , the frequency tracking loop  220 , and the last-computed open loop power estimate  230 . In a normal full duplex mode, the frequency tracking loop enables the communication device to stay locked in frequency and is used to adjust the local oscillator of the transmit chain to remove any residual frequency error of the digital receivers.  
         [0035]     Once the tracking loops are frozen, the half-duplex controller  120  switches off the receive chain  112  and switches on the transmit chain  114 . Since the frequency tracking loop  220  is frozen, the local oscillator  240  of the transmit chain  114  is allowed to drift. However, as described below, since the duration of the transmit mode is relatively short for low duty cycle applications, the drift of the local oscillator does not adversely affect the integrity of the transmitted signal. Further, since the open loop power estimate control loop  230  is frozen, the power amplifier  250  of the transmit chain  114  is set to transmit at the last computed open loop power estimate for the entire duration of the transmit mode. Again, since the duration of the transmit mode is relatively short, using the same transmit power for the entire transmit mode does not adversely affect the integrity of the transmitted signal, especially for those LDC application where the communication device  200  is fixed. In an alternative implementation, the timing reference and the power estimate may be integrated over time rather than letting the timing reference drift and maintaining the same power level (as the last power estimate calculated in receive mode) during the transmit mode.  
         [0036]      FIG. 3  illustrates a block diagram of another implementation of a communication device  300  showing detailed configurations of the power management and the half-duplexer.  
         [0037]     When the communication device  300  is to be operated in a half-duplex mode, the power management unit  140  directs the power control unit  310  to operate the receive chain  112  and the transmit chain  114  in the half-duplex mode. Therefore, when the transceiver  110  is to be operated in a receive mode, the power control unit  310  turns on power to the receive chain  112  and turns off power to the transmit chain  114 . Alternatively, when the transceiver  110  is to be operated in a transmit mode, the power control unit  310  turns on power to the transmit chain  114  and turns off power to the receive chain  112 .  
         [0038]     During the half-duplex mode, the communication device  300  can further reduces its idle state power requirements by enabling a slotted mode of operation. In a typical wireless telecommunication network such as a CDMA network, a paging channel slot is an 80-millisecond time slot within a paging slot cycle. The paging slot cycle ranges from 16 time slots (period=1.28 seconds; slot cycle index=0) to 2048 time slots (period=163.84 seconds; slot cycle index=7). Thus, in the slotted mode, the communication device  300  only monitors a selected subset of the paging channel slots for messages from a network controller.  
         [0039]     For LDC applications, however, the time between successive transmissions of messages may be significantly longer than the maximum allowable paging slot cycle period. In this case, the network controller may command the communication device  300  into a hibernate mode, where all units except for the power management unit  140  and the RTC  130  are turned off for a predetermined period of time. In one implementation, the predetermined period of time can be one second to several years.  
         [0040]     When the communication device  300  is to be operated in the hibernate mode, the communication device  300  receives a command from the network controller to enter into the hibernate mode for a predetermined period of time. The power management unit  140  receives and directs the power control unit  310  to turn off all units within the communication device  100  except for the power management unit  140  and the RTC  130 . In the hibernate mode, the communication device  300  is placed in a state of sleep for the predetermined period of time (i.e., a sleep duration) that is often substantially longer than allowable under the protocol of a conventional wireless communication network (e.g., the slot cycle index (SCI) of a CDMA cellular network). The power management unit  140  keeps track of the sleep duration using the RTC  130 .  
         [0041]     The illustrated implementation of  FIG. 3  also shows a half-duplexer implemented as an RF switch  340  to route signals to and from the antenna  342 . During the receive mode, the RF switch  340  routes the forward link signal received at the antenna  342  to the receiver  320  through the forward link front end  322 . During the transmit mode, the RF switch  340  selects the reverse link signal output from the transmitter  330  through the reverse link front end  332  and routes the reverse link signal to the antenna  342  for transmission.  
         [0042]      FIG. 4  and  FIG. 5  illustrate two alternative implementations of the half duplexer  116 .  FIG. 4  illustrates one alternative implementation  400  of the half duplexer integrated into the receive chain  412  and the transmit chain  414  so that the half-duplex operation is performed within the receive chain  412  and the transmit chain  414  with forward link and reverse link signals time sharing one antenna  420 .  FIG. 5  illustrates another alternative implementation  500  of the half duplexer integrated into the receive chain  512  and the transmit chain  514  but with the forward link signal being received at antenna A  520  and the reverse link signal being transmitted antenna B  530 .  
       Low Duty Cycle Operation in a Half-Duplex Mode  
       [0043]     Having described various structural features, some operational aspects of the present disclosure are now described.  
         [0044]      FIG. 6  is a flowchart illustrating a method for transmitting and receiving low duty cycle (LDC) messages in a half-duplex mode in accordance with one implementation of the present invention. The method involves monitoring and transmitting the LDC messages from the communication device  100  to a remotely situated information-processing device in a half-duplex mode using only overhead channels of a telecommunication network. In one example, the telecommunication network is a CDMA network.  
         [0045]     In the illustrated implementation of  FIG. 6 , when a network controller determines that the communication device  100  should be placed into a sleep state, the device  100  is transitioned into a hibernate mode, at  600 , for a particular duration as set by the network controller. As described above, the particular duration of the hibernate mode is often substantially longer than allowable under the protocol of a conventional wireless communication network such as a CDMA network. Once the communication device  100  has been in the hibernate mode for the particular duration, the power management unit  140  of the communication device  100  transitions the device  100  into an ON state of the half-duplex mode, at  602 . In some implementations, the communication device  100  can be awakened from the hibernate mode when a priority wake up message is received even though the particular duration of the hibernate mode has not elapsed since last power down.  
         [0046]     The local oscillator (LO)  350  is turned on, at  604 , and the LO frequency band is set, at  606 . The receive chain  112  is then turned on, at  608 ; the LO frequency is set to the forward link frequency, at  610 ; and the receive chain  112  receives forward link messages, at  612 . In one implementation, the received forward link messages include instructions, control information, and/or software downloads for managing the operational state of the communication device  100 . Once the data reception process has been completed, the receive chain is turned off, at  614 . In some implementations, the receive chain  112  includes a power supply and other related units (not shown).  
         [0047]     The LO frequency is then set to a reverse link frequency, at  616 , and the transmit chain  114  is turned on, at  618 . At  620 , the transmit chain  114  transmits LDC messages using only overhead channels of a telecommunication network. In one implementation, the LDC messages include operational status information including the state, condition, and/or location of the communication device  100 .  
         [0048]     For CDMA 2000 1×, the transmission of LDC messages using only the overhead channels can be implemented as short data burst (SDB) and/or short message service (SMS) over data burst messaging (DBM). For CDMA 2000 1× EVDO, the transmission of LDC messages using only the overhead channels can be implemented as Data over Signaling (DoS).  
         [0049]      FIG. 7  through  FIG. 9  illustrate signal protocols between the communication device  100  and the network using overhead channels.  
         [0050]      FIG. 7  shows a registration model in which the communication device  100  transmits an access probe signal, including the LDC messages, during the transmit mode. If there is no acknowledgement from a base station within a predetermined period of time (T AP1 ), the access probe signal is retransmitted with increased power  700 . Once the direct command acknowledgement (L2 ACK) is received from the base station, the access probe signal transmission is terminated.  
         [0051]      FIG. 8  shows a model in which the communication device  100  transmits an LDC message over the access probe signal. The access probe signal is retransmitted until the direct command acknowledgement (L2 ACK) is received from the base station. The base station then reports that the network successfully received the transmitted message, to which the communication device acknowledges the data acceptance by the base station. Finally, the base station terminates the transmission of the access probe signal once the acknowledgement is received by the base station.  
         [0052]      FIG. 9  shows a model in which the communication device  100  determines whether the device is being paged by the base station. If it is determined that the communication device  100  is being paged by the base station, the communication device acknowledges the paging using access probe signal until the transmission of the access probe signal is terminated by the base station. The base station sends the data using Data Burst Message (DBM). The communication device  100  then acknowledges the transmission from the base station using access probe signal until the transmission is terminated by the base station.  
         [0053]     Referring back to  FIG. 6 , once the message transmission process has been completed, the transmit chain  114  is turned off, at  622 . The local oscillator (LO) is then turned off, at  624 , and the process repeats by transitioning the communication device  100  into the hibernate mode again.  
       Other Embodiments  
       [0054]      FIG. 10  illustrates a block diagram of another implementation of a communication device  1000 , which is implemented with a dual band half-duplex transceiver  1010 . The communication device  1000  includes two separate transmit and receive chains to enable operation of the transceiver  1010  over two different cellular bands. In the illustrated implementation, the dual bands are represented as an 800 MHz cellular band and a 1900 MHz PCS band. However, the dual bands can be represented as any frequency bands. The diplexer  1024  splits the antenna input into two cellular bands.  
         [0055]     The PCS band is implemented with a PCS receive chain  1012 A and a PCS transmit chain  1014 A. The cellular band is implemented a cell receive chain  1012 B and a cell transmit chain  1014 B. An RF switch  1020  selects between forward and reverse link channels of the PCS band, while an RF switch  1022  selects between forward and reverse link channels of the cellular band.  
       Applications  
       [0056]     Implementations of the LDC half-duplex operation described above can be used in many different applications including asset tracking, automated meter reading, cashless payment of parking meters, traffic lights and sensors, billboards and public displays, real-time health monitoring, home/office security and alarm systems, automotive telematics, utility distribution grid monitoring, position monitoring using GPS, and other related polling applications. Message transmission for these applications can range from an average of one short messaging service (SMS) message per hour for an asset tracking application to one SMS message per month for an automated meter reading application.  
         [0057]     Those of skill in the art understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.  
         [0058]     Those of skill further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.  
         [0059]     The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.  
         [0060]     The steps of a method described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC.  
         [0061]     Moreover, the previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.