Patent Publication Number: US-2007117566-A1

Title: System and method for reducing a forced neighbor cell procedure

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention concerns communications management and more particularly, management of neighbor cell measurements.  
      2. Description of the Related Art  
      In most communications systems, a number of communications stations, such as base stations, are used to relay wireless signals to mobile units, like cellular telephones, two-way radios or personal digital assistants. While a mobile unit is communicating with the base station that is currently serving it, the mobile unit will monitor certain parameters of neighboring base stations, or neighbor cells. As an example, one parameter may be signal strength measurements of the neighbor cells, and the mobile unit can constantly monitor them to determine which neighbor cell is best for a handover.  
      If the mobile unit is sending or receiving heavy amounts of data, however, the mobile unit may not have enough time to perform the neighbor cell measurements. As such, the mobile unit may build up a deficit of these measurements. Once this deficit reaches a predetermined point, the mobile unit may force itself to perform a neighbor cell measurement, at least until the measurement deficit is alleviated to an acceptable level. Unfortunately, this forced measurement, sometimes referred to as forced neighbor cell, has a detrimental effect on packet data throughput. In particular, forced neighbor cell limits throughput for users and also wastes overall channel bandwidth because any outbound data from the network to the mobile unit is not received by the mobile unit and must be resent.  
     SUMMARY OF THE INVENTION  
      The present invention concerns a method for reducing a forced neighbor cell procedure. The method can include the steps of—in a mobile unit on a communications channel—monitoring one or more neighbor cell parameters and performing a neighbor cell measurement in a selectively generated opportunity in the communications channel to reduce the possibility that the mobile unit will enter a forced neighbor cell measurement. As an example, the neighbor cell parameter can be a signal strength or an indication as to a type of data that can be exchanged.  
      In one arrangement, the communications channel can include a reservation request slot having a first subslot and a second subslot. In addition, the opportunity can be selectively generated by only selecting the first subslot of the reservation request slot for a reservation request and avoiding the second subslot for the reservation request. Avoiding the second subslot for the reservation request can create an additional window for performing the neighbor cell measurement. The communications channel can be a half-duplex communications channel having transmission and receive slots in which the transmission and receive slots may be temporally offset. The method can also include the step of counting for a predetermined number of slots and only selecting the first subslot of the reservation request slot for the reservation request and avoiding the second subslot for the reservation request if a transmission request is received during the counting of the predetermined number of slots.  
      In another arrangement, the opportunity can be selectively generated in the communications channel by modifying a channel allocation slot in the communications channel. As an example, the channel allocation slot can be a dynamic channel allocation procedure slot, and modifying the channel allocation slot can include setting a counter in the dynamic channel allocation procedure slot. Setting the counter can include setting the counter to a predetermined value to indicate that a slot map for a number of dynamic channel allocation procedure frames may not change. This number can correspond to the predetermined value. In addition, performing the neighbor cell measurement can include performing the neighbor cell measurement during dynamic channel allocation procedure slots in at least one of the dynamic channel allocation procedure frames that may not change. As an example, the channel allocation slot in the communications channel can be modified by a communications network that is communicating with the mobile unit.  
      The present invention also concerns a system for reducing a forced neighbor cell procedure. The system can include a receiver that receives wireless signals over a communications channel and a processor coupled to the receiver. The processor can be programmed to monitor one or more neighbor cell parameters and to perform a neighbor cell measurement in a selectively generated opportunity in the communications channel to reduce the possibility that the mobile unit will enter a forced neighbor cell measurement. In addition, the processor can be programmed to perform any of the processes described above.  
      The present invention also concerns a machine readable storage having stored thereon a computer program having a plurality of code sections executable by a mobile unit. The program can cause the mobile unit to perform the steps of monitoring on a communications channel one or more neighbor cell parameters and performing a neighbor cell measurement in a selectively generated opportunity in the communications channel to reduce the possibility that the mobile unit will enter a forced neighbor cell measurement. The program can also cause the mobile unit to perform any of the processes described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:  
       FIG. 1  illustrates a communications network and several mobile units in accordance with an embodiment of the inventive arrangements;  
       FIG. 2  illustrates a block diagram of a mobile unit in accordance with an embodiment of the inventive arrangements;  
       FIG. 3  illustrates a method of reducing a forced neighbor cell procedure in accordance with an embodiment of the inventive arrangements;  
       FIG. 4  illustrates a communications channel in accordance with an embodiment of the inventive arrangements;  
       FIG. 5  illustrates another method of reducing a forced neighbor cell procedure in accordance with an embodiment of the inventive arrangements; and  
       FIG. 6  illustrates another communications channel in accordance with an embodiment of the inventive arrangements. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawings, in which like reference numerals are carried forward.  
      As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.  
      The terms “a” or “an,” as used herein, are defined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The terms “including” and/or “having,” as used herein, are defined as comprising (i.e., open language). The terms “coupled” and “engagement,” as used herein, are defined as connected, although not necessarily directly, and not necessarily mechanically. The term “module” can be defined as any combination of hardware and/or software to enable an appropriate function to be performed.  
      The terms “program,” “application,” and the like as used herein, are defined as a sequence of instructions designed for execution on a computer system. A program, computer program, or application may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system. Where suitable, the term “application” may even refer to a hardware setting or component.  
      The present invention concerns a method and system for reducing a forced neighbor cell procedure. In one arrangement, the method can include the steps of—in a mobile unit on a communications channel—monitoring one or more neighbor cell parameters and performing a neighbor cell measurement in a selectively generated opportunity in the communications channel to reduce the possibility that the mobile unit will enter a forced neighbor cell measurement.  
      The communications channel can include a reservation request slot having a first subslot and a second subslot. As an example, the opportunity can be selectively generated by only selecting the first subslot of the reservation request for a reservation request and avoiding the second subslot for the reservation request. Avoiding the second subslot for the reservation request can create an additional window for the neighbor cell measurement.  
      Alternatively, the opportunity can be selectively generated in the communications channel by modifying a channel allocation slot in the communications channel. For example, the channel allocation slot can be a dynamic channel allocation procedure slot, and the channel allocation slot can be modified by setting a counter in the dynamic channel allocation procedure slot. As another example, the counter can be set to a predetermined value to indicate that a slot map for a number of dynamic channel allocation procedure frames will not change, and the number can correspond to the predetermined value. Also, the neighbor cell measurement can be performed during dynamic channel allocation procedure slots in at least one of the dynamic channel allocation procedure frames that will not change. Performing these additional neighbor cell measurements in view of these newly-generated opportunities can help prevent the build-up of a neighbor cell measurement deficit.  
      Referring to  FIG. 1 , a communications network  100  having one or more base stations  110  is shown. As is known in the art, the base stations  110  can wirelessly communicate with one or more mobile units  112 . As an example, the mobile units  112  may be iDEN radios manufactured by Motorola, Inc. of Schaumburg, Ill., which are capable of communicating in both dispatch and interconnect modes. It is understood, however, that the invention is not so limited, as the mobile units  112  can be any other device that can receive wireless signals.  
      As is also known in the art, the communications network  100  can include a plurality of cells  114 , each of which may include a base station  110 . As an example, a mobile unit  112  may be within the boundaries of a serving Cell  114   a , and the base station  110  inside the serving cell  114   a  can communicate with the mobile unit  112 . The mobile unit  112 , however, monitors one or more parameters of one or more neighboring cells  114   b  to enable a handover procedure to be conducted when necessary. As an example, the parameter can be a signal strength or an indication as to a type of data that can be exchanged with a base station  110  in a particular cell  114 , although other suitable parameters are contemplated by the inventive arrangements.  
      Referring to  FIG. 2 , an example of a block diagram of a mobile unit  112  is shown. In this example, the mobile unit  112  can include one or more of the following: a processor  210 , a memory  212 , a transmitter  214 , a receiver  216 , a user interface  218  and an antenna  220 . The processor  210  can be coupled to, control the operation of and/or receive signals or information from the memory  212 , the transmitter  214 , the receiver  216  and the user interface  218 . In addition, the transmitter  214  and the receiver  216  can be coupled to the antenna  220 , which can transmit signals to and receive signals from the base stations  110  (see  FIG. 1 ).  
      For purposes of the invention, the term processor can include any suitable number of components capable of executing instructions to perform the processes associated with the inventive arrangements. In addition, although the memory  212  is shown as a discrete component, it may actually be part of or integrated with the processor  210 . The user interface  218  can be, for example, a keypad or a display and can receive input from a user and can signal the processor  210  with such input. In addition, the memory  212  can be any suitable type of memory for storing any suitable type of data for operation of the mobile unit  112 .  
      In one arrangement, the processor  210  can be programmed to perform measurements of the neighbor cells  114   b  (see  FIG. 1 ) in windows or opportunities that are selectively created in a communications channel through over which the mobile unit  112  is communicating with a base station  110  currently serving the mobile unit  112 . By performing these measurements, the mobile unit  112  can ready itself for a handover to a neighboring base station  110  in a neighbor cell  114   b . An opportunity can be any slot or opening in a communications channel that is suitable for performing a neighbor cell measurement. There are several examples of how these opportunities can be selectively generated, and they will be presented below.  
      Referring to  FIG. 3 , a method  300  for reducing a forced neighbor cell procedure is shown. When describing the method  300 , reference will be made to  FIGS. 1, 2  and  4 . Referring to  FIG. 4 , an example of a communications channel  400  having a number of transmission slots  410  in a transmission portion  412  and receive slots  414  in a receive portion  416  are shown. It must be noted, however, that the method  300  can be practiced in any other suitable system or device. Moreover, the steps of the method  300  are not limited to the particular order in which they are presented in  FIG. 3 . The inventive method can also have a greater number of steps or a fewer number of steps than those shown in  FIG. 3 .  
      At step  310 , the method  300  can begin, and at step  312 , one or more neighbor cell parameters can be monitored in a mobile unit on a communication channel. A neighbor cell measurement can be performed in a selectively generated opportunity in the communication channel to reduce the possibility that the mobile unit will enter a forced neighbor cell measurement, as shown at step  314 . At step  316 , the opportunity can be selectively generated by only selecting a first subslot of a reservation request slot for a reservation request and avoiding a second subslot of the reservation request slot for the reservation request. Avoiding the second subslot for the reservation request can create an additional window for performing the neighbor cell measurement.  
      As an option, at step  318 , a predetermined number of slots can be counted. In particular, the first subslot of the reservation request subslot may only be exclusively selected for the reservation request with the second slot being avoided for the reservation request if a transmission request is received during the counting of the predetermined number of slots. The method  300  can then end at step  320 .  
      As an example and referring to  FIG. 4 , the communications channel  400  can be a dispatch (i.e., half-duplex) traffic channel over which signals may be either transmitted (transmission portion  412 ) or received (receive portion  414 ) at a given time. In one arrangement, the transmission slots  410  and the receive slots  414  can be offset by a predetermined amount of time, such as 4 milli-seconds. This time is measured from the end of, for example, a receive slot  414  to the beginning of a transmission slot  412 . This timing offset exists to accommodate the time needed for the mobile unit  112  to switch between transmit and receive operations.  
      Referring now to  FIGS. 1, 2  and  4 , the mobile unit  112  can be communicating with a base station  110  in the serving cell  114   a  over the communication channel  400 . The mobile unit  112  can monitor one or more parameters, such as signal strength, of one or more neighbor cells  114   b.    
      As an example, the mobile unit  112  may begin transmitting data, such as a clip of video or audio file. As is known in the art, the data being transmitted may be transmitted to the base station  110  in stages, which can be represented by blocks of data  418 . Each block of data  418  may be made of a predetermined number of slots, and the mobile unit  112  may perform a reservation request with the base station  110  to transmit another block of data  418 . For example, the first block of data  416  on the left of  FIG. 4  may be transmitted from the mobile unit  112 , and its last transmission slot  420  is shown in the transmission portion  412 . Because the communications channel  400  may be a half-duplex channel, the receive slots  414  with an “X” inserted in them can represent receive slots  414  over which no signal may be received from the base station  110  because at least a portion of the transmission slot  420  is on the communication channel  400  at that time.  
      The next available receive slot  414  in the receive portion  416  can be an availability slot  422 , which can indicate to the mobile unit  112  that the communications channel  400  is available for transmitting. The next available transmission slot  410  can be referred to as a reservation request slot  424 , which can have a first subslot  426  and a second subslot  428 . The processor  210  of the mobile unit  112  can use the reservation request slot  424  as a request to reserve the communications channel  400  to transmit, for example, the next or second block of data  418 , which is shown on the right of  FIG. 4 .  
      In one arrangement, the reservation request slot  424  may be a packet channel random access procedure (PRAP) slot. Normally, the processor  210  can randomly select either the first subslot  426  or the second subslot  428  for the reservation request. By randomly selecting the first subslot  426  or the second subslot  428 , the likelihood of a collision with a reservation request from other mobile units  112  can be reduced. In those instances where the second subslot  428  is selected, the receive slots  414  that overlap the second subslot  428  are unavailable (they are marked with an “X” and an “X/N”).  
      In accordance with one embodiment of the inventive arrangements, the processor  210  can be programmed to only select the first subslot  426  of the reservation request slot  424  when sending the reservation request. As such, selecting the second subslot  428  to send the reservation request can be avoided, which can create an additional window for a neighbor cell measurement. In particular, the first subslot  426  may only overlap one receive slot  414 , instead of the two receive slots  414  that the second subslot  428  overlaps. As such, one of the two receive slots  414  (the one designated with the “X/N”) can be used as a neighbor cell measurement slot. That is, the processor  210  can be programmed to perform a neighbor cell measurement during this newly-generated opportunity in the communication channel  400 . This additional neighbor cell measurement can help reduce a neighbor cell deficit, if one has formed, which is possible when transmitting the blocks of data  418 .  
      The processor  210  can also perform neighbor cell measurements in the receive slots  414  following the newly-generated slot, which can be designated by “N,” at least until a reservation grant  430  has been received by the mobile unit  112 . At this point, the processor  210  can instruct the transmitter  214  to begin transmitting the next block of data  418  at the next available transmission slot  410 .  
      In one arrangement, the processor  210  may be programmed to count a predetermined number of slots and to select the first subslot  426  in accordance with the discussion above only if a transmission request is received during the counting of the predetermined number of slots. For example, from the end of the last transmission slot  410  of the first block of data  418 , the processor  210  can be programmed to count, for example, ten slots. If the processor  210  receives a transmission request during this time, the processor  210  can select only the first subslot  426  for the transmission of the reservation request and can avoid the second subslot  428 . This situation is what has occurred in the example described above, as the second block of data  418  needed to be transmitted.  
      If no transmission request is received during this counting process, however, the processor  210  can be programmed to revert to the random selection of either the first subslot  426  or the second subslot  428  to transmit the reservation request. The predetermined count process is entirely optional and is by no means limited to ten slots. Nonetheless, following this procedure can strike a balance between reducing forced neighbor cell measurements and avoiding collisions through the random selection of the first subslot  426  and the second subslot  428 .  
      Referring to  FIG. 5 , a method  500  illustrating another way to reduce a forced neighbor cell procedure is shown. When describing the method  500 , reference will be made to  FIGS. 1, 2  and  6 . Referring to  FIG. 6 , an example of a communications channel  600  having a number of DCAP frames  610  is shown. It must be noted, however, that the method  500  can be practiced in any other suitable system or device. Moreover, the steps of the method  500  are not limited to the particular order in which they are presented in  FIG. 5 . The inventive method can also have a greater number of steps or a fewer number of steps than those shown in  FIG. 5 .  
      At step  510 , the method  300  can begin. Steps  512  and  514  are similar to steps  312  and  314  of the method  300  of  FIG. 3  and will not be repeated here. At step  516 , the opportunity can be selectively generated by modifying a channel allocation slot in the communications channel. At step  518 , the channel allocation slot can be a dynamic channel allocation procedure (DCAP) slot, and a counter in the DCAP slot can be set. This counter can be set to a predetermined value to indicate that a slot map for a number of DCAP frames will not change in which the number corresponds to the predetermined value, as shown at step  520 . At step  522 , the neighbor cell measurement can be performed during DCAP slots in at least one of the DCAP frames that will not change. The method  500  can stop at step  530 .  
      For example, referring to  FIG. 6 , a communications channel  600  is shown. This communications channel  600  may be a packet channel capable of carrying both voice and data. In one arrangement, the communications channel  600  can include any suitable number of DCAP frames  610 . The top communications channel  600  shown in  FIG. 6  illustrates an example of one DCAP frame  610 , while the bottom communications channel  600  shows several annotated DCAP frames  610 .  
      As an example, the DCAP frame  610  can include a suitable number of contiguous slots  612  that carry voice and/or data. In our example, the number of slots  612  can be twenty-four, which is shown in the top DCAP frame  610 , although the DCAP frames  610  can certainly contain any other suitable number of slots  612 , including multiples of twenty-four. As another example, each DCAP frame  610  can include one or more channel allocation slots or DCAP slots  614 . As is known in the art, a DCAP slot  614  in a DCAP frame  610  can inform a mobile unit  112  of the slot allocation of the next DCAP frame  610 . As a result, the mobile units  112  on the communication channel  600  may receive and process the DCAP slots  614  to determine slot allocations in upcoming DCAP frames  610 . The communications network  100  (see  FIG. 1 ) can use the DCAP slots  614  to dynamically remove slots  612  that are designated for data and assign them to non-data users, such as for interconnect or dispatch callers.  
      Referring now to  FIGS. 1, 2  and  6 , the communications network  100  can modify the DCAP slots  614  to selectively generate an opportunity for the mobile unit  112  to perform a neighbor cell measurement. As an example, this modification can be performed at the base stations  110  or at some other component of the network  100 . In one arrangement, a counter can be incorporated into the DCAP slots  614 , and the network  100  can set these counters to a predetermined value. The sets of numbers positioned above the DCAP slots  614  in  FIG. 6  can represent examples of these predetermined values. There are at least two ways that the predetermined values can be set, and they will now be presented. Those of skill in the art will appreciate, however, that the invention is not limited to these particular examples, as other alternatives for setting the counter may be used here.  
      In the first example, the slots  612  of the communications channel  600  may be carrying voice or data packets, and the network  100  can determine that the slot maps for a number of the DCAP frames  610  may not change. At this point, the mobile unit  112  can perform neighbor cell measurements in the DCAP slots  614  of at least some of the DCAP frames  610  that may not change.  
      For example, the network  100  can set the counter to a value of “3,” which is the value above the DCAP slots  614  to the left of the forward slash symbol. The mobile units  112  that receive the DCAP slots  614  with a counter value of 3 can then use the next three DCAP slots  614  to perform a neighbor cell measurement after conventionally reading a DCAP slot  614 . The DCAP slots  614  that may be used for this purpose are shown marked with “N/DCAP,” where the “N” means that the mobile stations  112  can perform a neighbor cell measurement at this DCAP slot  614 . So, in this example, the mobile unit  112  can read the first DCAP slot  614  (from the left) and can determine that neighbor cell measurements can be performed at the next three DCAP slots  614 .  
      This predetermined value can be changed at any time, and is by no means limited to a value of three. Also, it is understood that not all the mobile units  112  will conventionally read the same DCAP slot  614  and perform the neighbor cell measurements on the same three DCAP slots  614 . For example one mobile unit  112  may read the first DCAP slot  614 —labeled as “3/0”—and perform neighbor cell measurements for the next three DCAP slots  614 —labeled as “3/3,” “3/2” and “3/1,” respectively. Another mobile unit  112 , for example, may read the DCAP slot  614  labeled as “3/3” and then perform neighbor cell measurements for the next three DCAP slots  614 , or “3/2,” “3/1” and “3/0.” In either arrangement, because the mobile units  112  are informed that a certain number of DCAP slots  614  do not have to be read, additional opportunities for the mobile units  112  to perform neighbor cell measurements can be generated, thus reducing the chances that a forced neighbor cell measurement will occur.  
      In the second example, there may be an instance where the network  100  must accommodate a non-data service request, such as an interconnect or dispatch call. These types of requests are typically given priority by the network  100 , and as such, the network  100  may need to reassign slots  612  to facilitate the call. As such, the network  100  may signal the mobile units  112  that the slot maps of the data frames  614  may change. In one arrangement, the network  100  can change the setting of the counter to begin a countdown, and these values are represented by the number to the right of the forward slash above the DCAP slots  614 . As such, when a mobile unit  112  conventionally reads a DCAP slot  614 , the mobile unit  112  can determine that it should read an upcoming DCAP slot  614  in view of the change of the slot map for an upcoming DCAP frame  610 .  
      For example, if a mobile unit  112  conventionally reads the DCAP slot  614  with the counter value on the right of the forward slash being “2” (third DCAP slot  614  from the left), then the mobile unit  112  may read the DCAP slot  614  with the counter value of “0” to the right of the forward slash (fifth DCAP slot  614  from the left). This process can instruct all the mobile units  112  of the upcoming change, even though they may not all be reading the same DCAP slot  614  during the process described above. Again, it must be noted that the invention is in no way limited to these values.  
      While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.