Abstract:
A method for communication includes deploying a half-duplex terminal in a wireless full-duplex communication network configured to permit simultaneous transmission of downlink paging messages and uplink access messages between a base station and full-duplex mobile terminals in the network. The half-duplex terminal is assigned paging channel slots in a cyclical sequence of the paging channel slots, so that the base station transmits the downlink paging messages to the half-duplex terminal only during the assigned paging channel slots. The half-duplex terminal is controlled so that the half-duplex terminal transmits the uplink access messages only during an interval bounded by the assigned paging channel slots occurring in successive cycles in the sequence.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/794,233, entitled, “HALF-DUPLEX TERMINAL OPERATION IN A FULL DUPLEX NETWORK” filed on Apr. 21, 2006, which is assigned to the assignee hereof and which is expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to wireless communication, and specifically to reducing the complexity and cost of wireless communication devices.  
       BACKGROUND OF THE INVENTION  
       [0003]     Cellular communication networks are designed for full-duplex operation, in which terminals (such as cellular telephones) can both receive and transmit signals simultaneously. Cellular network standards thus assume terminals have full-duplex capability and permit simultaneous downlink and uplink transmissions to and from any given terminal. In other words, terminals must generally be capable of receiving and decoding a downlink signal from a base station in the course of making an uplink transmission.  
         [0004]     Cellular push-to-talk (PTT) is a new class of mobile telephone service that enables instant one-to-one and one-to-many half-duplex communications on cellular telephones, emulating “walkie talkie” operation. In half-duplex operation, a terminal can either receive or transmit, but cannot both receive and transmit at the same time. An open PTT-over-cellular (PoC) standard is emerging under the auspices of the Open Mobile Alliance (OMA). Generally, PoC is implemented as an add-on feature of full-duplex cellular telephones and requires that participating telephones listen continuously for signals on a channel that is allocated for PTT service.  
       SUMMARY OF THE INVENTION  
       [0005]     Half-duplex terminal operation is sufficient for many applications of wireless communication networks, particularly applications that involve only digital messaging and do not use voice channels. As noted above, however, commonly-deployed wireless networks, such as cellular networks, are configured for full-duplex operation and thus require terminals to support full-duplex standards. As full-duplex circuitry adds to the cost of the terminal, it would be desirable to produce a true half-duplex terminal that is nonetheless compatible with full-duplex network standards.  
         [0006]     In some wireless networks, such as cellular networks, a base station may transmit a downlink paging message to a terminal in an assigned time slot. The terminal may also contact the base station by transmitting an uplink access message. Embodiments of the present invention enable a half-duplex terminal to operate in such a wireless network by ensuring that the terminal will transmit uplink access messages only during intervals between its assigned downlink paging time slots. Thus, the terminal will operate in transmit mode only during the intervals between paging time slots, and is available at all other times to receive downlink messages.  
         [0007]     This approach ensures that the half-duplex terminal will not miss any downlink paging messages sent by the base station, so that the paging and access channels can be used to carry data messages reliably in half-duplex mode. The base station, however, need not be aware that the terminal is not full-duplex enabled, and embodiments of the present invention can thus be implemented without changes to existing network infrastructure or standards.  
         [0008]     There is therefore provided, in accordance with an embodiment of the present invention, a method for communication, including deploying a half-duplex terminal in a wireless full-duplex communication network, which is configured to permit simultaneous transmission of downlink paging messages and uplink access messages between a base station and full-duplex mobile terminals in the network; assigning to the half-duplex terminal paging channel slots in a cyclical sequence of the paging channel slots, so that the base station transmits the downlink paging messages to the half-duplex terminal only during the assigned paging channel slots; and controlling the half-duplex terminal so that the half-duplex terminal transmits the uplink access messages only during an interval bounded by the assigned paging channel slots occurring in successive cycles in the sequence.  
         [0009]     In some embodiments, the paging messages and access messages are transmitted on signaling channels of the network, and the half-duplex terminal is configured to monitor the paging messages only during the assigned slots. Additionally or alternatively, controlling the half-duplex terminal includes transmitting a sequence of the uplink access messages separated by variable intervals, and determining the variable intervals responsively to the assigned paging channel slots.  
         [0010]     In a disclosed embodiment, the communication network is configured to operate in accordance with a CDMA network standard.  
         [0011]     There is also provided, in accordance with an embodiment of the present invention, a half-duplex wireless communication terminal for deployment in a wireless full-duplex communication network configured to permit simultaneous transmission of downlink paging messages and uplink access messages between a base station and full-duplex mobile terminals in the network, the terminal including a receiver operative to receive the downlink paging messages from the base station, a transmitter coupled in parallel with the receiver in a half-duplex configuration and is operative to the transmit uplink access messages to the base station, and a controller coupled to control the receiver so as to receive the downlink paging messages during assigned paging channel slots in a cyclical sequence of the paging channel slots during which the base station transmits the downlink paging messages to the terminal, and to control the transmitter so as to transmit the uplink access messages only during an interval bounded by the assigned paging channel slots occurring in successive cycles in the sequence.  
         [0012]     There is additionally provided, in accordance with an embodiment of the present invention, a wireless communication network including a base station configured to simultaneously transmit downlink paging messages and receive uplink access messages to and from full-duplex mobile terminals in the network, and a terminal that includes a receiver operative to receive the downlink paging messages from the base station a transmitter coupled in parallel with the receiver in a half-duplex configuration and is operative to transmit the uplink access messages to the base station, and a controller coupled to control the receiver so as to receive the downlink paging messages during assigned paging channel slots in a cyclical sequence of the paging channel slots during which the base station transmits the downlink paging messages to the terminal, and to control the transmitter so as to transmit the uplink access messages only during an interval bounded by the assigned paging channel slots occurring in successive cycles in the sequence.  
         [0013]     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a block diagram that schematically illustrates a cellular communication system, in accordance with an embodiment of the present invention; and  
         [0015]      FIG. 2  is a timing diagram that schematically illustrates transmission times of paging and access probe messages, in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0016]      FIG. 1  is a block diagram that schematically illustrates a cellular communication system  30 , in accordance with an embodiment of the present invention. System  30  is built around a cellular telephone network  32 , but may comprise, alternatively or additionally, a personal communication system (PCS) or any other suitable public or private wireless network. Although the present embodiment is described hereinbelow with reference to aspects of cdma2000 cellular network standards, alternative embodiments of the present invention may be adapted for use with other wireless standards and protocols, such as cdmaone, 1xEVDO, UMTS, GSM or any other suitable standard. All of these standards provide for full-duplex communications between wireless terminals and base stations in the network.  
         [0017]     A wireless half-duplex terminal  34  communicates over the air with a base station  42  in accordance with the protocols mandated by network  32 . Uplink messages transmitted from terminal  34  to base station  42  are modulated, upconverted, filtered and amplified by a transmitter  36  to produce an uplink radio signal. Downlink messages transmitted from base station  42  to terminal  34  are received, downconverted, filtered, demodulated and otherwise processed by a receiver  38 . The receiver and transmitter are coupled in parallel in a half-duplex hardware configuration, as is known in the art. The operations of transmitter  36  and receiver  38  are managed by a controller  40 , so as to comply with the applicable network protocols while operating in half-duplex mode.  
         [0018]     In the present embodiment, terminal  34  is designed for use in an application that involves digital messaging only, rather than voice communications, and which requires that the cost and power consumption of the terminal be minimized. Messages are carried between the terminal and base station  42  over signaling channels, i.e., the common paging (downlink) and access (uplink) channels, without using network traffic channels. One example of such an application is wireless tracking, in which terminal  34  is attached to a person or object and periodically transmits its location to an application server  44  in network  32 . In such an application, terminal  34  can communicate with base station  42  over a common channel (i.e., a signaling channel), and half-duplex communication is sufficient to meet the application requirements. Other applications that can benefit from the low cost and low power consumption of such a half-duplex terminal will be apparent to those skilled in the art and are considered to be within the scope of the present invention.  
         [0019]     The half-duplex communication model is useful, inter alia, in applications in which mobile wireless terminals operate in a hibernation cycle alternating between a hibernation mode and a wake mode. For example, terminal  34  may be a low-duty-cycle (LDC) device, which may be used in a variety of position tracking, tagging, telemetry and similar applications. LDC terminals operate in a hibernation cycle, whereby each terminal wakes-up to receive and transmit data for only a small percentage of the time. This low-duty-cycle operation minimizes the utilization of the air interface and further reduces energy consumption by the terminal. On the other hand, if a half-duplex LDC terminal, during its brief waking period, transmits an uplink access message while the base station is transmitting a downlink paging message, the terminal may fail to receive the downlink paging message. This potential problem is resolved by embodiments of the present invention.  
         [0020]     Communication between base station  42  and terminals (mobile stations) in network  32  can be initiated by either the base station or the terminal. The base station may initiate a connection by transmitting a downlink paging message addressed to the terminal. The terminal may initiate a connection by transmitting an uplink access message to the base station. (The terms “paging” and “access” are taken from the terminology that is commonly used in CDMA network standards, but should be understood to refer generally to equivalent downlink and uplink signaling messages that are used in other types of wireless networks, as well.) The paging and access messages themselves may be used to carry data messages (such as SMS messages) between the base station and the terminal.  
         [0021]     Since network  32  is designed for full-duplex operation, there is no restriction in the network standards on the relative timing of the paging and access messages. In other words, a terminal may send an access message at any time, regardless of when the base station may transmit a paging message, and the access and paging messages may therefore overlap in time. Full-duplex terminals are capable of receiving the paging message notwithstanding the overlap. If base station  42  transmits a paging message to half-duplex terminal  34  while the terminal is transmitting an access message, however, the paging message will be lost.  
         [0022]      FIG. 2  is a timing diagram that schematically illustrates a method used by terminal  34  in avoiding overlap of access and paging messages, in accordance with an embodiment of the present invention. As noted above, this embodiment uses features of cdma2000, which are described in standards promulgated by the 3rd Generation Partnership Project 2 “3GPP2” (available at www.3gpp2.org), including particularly  Medium Access Control  ( MAC )  Standard for cdma 2000  Spread Spectrum Systems  (specification C.S0003-0, version 3.0, 2001) and  Upper Layer  ( Layer  3)  Signaling Standard for cdma 2000  Spread Spectrum Systems  (specification C.S0005-0, Version 1.0, 1999), which are incorporated herein by reference.  
         [0023]     Section 2.6.2.1.1.1.1 of specification C.S0005-0 describes a slotted mode, which may be used by terminals in the cdma2000 network. In order to conserve power, terminals are permitted to operate in the slotted mode while in an idle state. In this mode, the terminal monitors the paging channel only during certain assigned slots. In the example shown in  FIG. 2 , terminal  34  operates in accordance with a slot cycle  50  consisting of sixteen paging channel slots (each of which is  80  ms long), and is assigned to receive paging messages during one slot  52  in each cycle. The length of the slot cycle and the slot assigned to the terminal in each cycle are identified in messages exchanged between the terminal and the base station, using functions specified in the standard, which depend, inter alia, on the hard-coded electronic serial number of the terminal. Thus, in this example, there will be a known interval of 1.2 sec between the end of the assigned slot  52  in one cycle  50  and the beginning of the assigned slot in the next cycle. Controller  40  of terminal  34  is programmed to operate in accordance with the applicable parameters.  
         [0024]     The procedure by which terminals may access the base station in the cdma2000 network is described in section 2.2.2.2.2.1.3 of specification C.20003-0. To access the base station, the terminal transmits a sequence of access messages, referred to in the standard as “probes,” of gradually increasing power, separated by certain time intervals. (The entire sequence of access probes is referred to as an “access attempt.”) One access probe  54  is shown in  FIG. 2 . The duration and timing of the access slots during which terminals may transmit access probes are defined by configuration parameters that are transmitted by the base station in an Access Parameters Message. In cdma2000, for example, the duration of each access slot may be between 80 and 520 ms. The interval between successive probes is determined by the transmitting terminal, based on the access slots defined by the base station. In the worst case, the duration of the probe (520 ms) is nearly half the length of the slot cycle in the present example. Thus, there is a high probability that the probe will overlap with the receive slot that the terminal is supposed to monitor. Even typical access slot lengths of 100-200 ms still give significant overlap probability.  
         [0025]     In order to avoid this eventuality, in an embodiment of the present invention, controller  40  determines when to transmit probe  54  based on the known timing of slots  52 . In other words, the controller times the probe transmission so that probes will be transmitted only during access slots that fall in the interval between the paging channel slots assigned to terminal  34  in successive cycles  50 . Thus, as shown in  FIG. 2 , the possibility of overlapping transmission and reception is eliminated. Although this pattern of probe transmission places certain constraints on the timing of access probes transmitted by terminal  34 , it can still be randomized sufficiently to avoid any ill effect on network performance. In any case, only terminal  34  deviates in its behavior from the standard, while base station  42  operates without change in full compliance with applicable standards.  
         [0026]     Although the exemplary embodiment shown in  FIG. 2  and described above uses certain specific timing parameters, the methods of this embodiment may likewise be applied using other timing parameters permitted by cdma2000 standards, as well as in the context of other wireless network types and standards that use slotted downlink transmission. It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.