Abstract:
In a code division multiple access (CDMA) system a dispatch call is established between two mobile units ( 10 ) and ( 12 ). The system includes a CDMA 2000 system providing for the dispatch data services. This requires that messages and bearer traffic are processed by radio link protocol. The CDMA 2000 system supports the FCH and DCCH channels. If the speaker&#39;s forward link is link limited, ( 26 ), then a DCCH channel is assigned to the speaker, ( 28 ). If the speaker&#39;s reverse link is link limited then a FCH channel is assigned to the speaker. In addition if there is a low battery level of the speaker, an FCH channel is assigned to the speaker, ( 30 ). When the speaker changes, ( 40 ), the FCH and DCCH channels for the speaker and listener are switched dynamically, ( 44 - 48 ).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention pertains to providing data services and more particularly to providing data, voice and dispatch services over code division multiple access 2000 (CDMA 2000) system.  
           [0002]    Providing data services over CDMA 2000 requires that the voice bearer traffic be transmitted through radio link protocol (RLP). Radio link protocol provides for two types of channels, a FCH channel which is the only type of channel for providing voice services and a DCCH channel.  
           [0003]    For the DCCH, full frames of data must be transmitted. That is, if less than a full frame of bits are to be transmitted, then the frame must filled (padded) with unneeded bits in order to send a full frame. For the DCCH channel, when there is no data to send, only power control information is sent at approximately 800 bits per second.  
           [0004]    For the FCH, full, half, eighth (&amp; possibly quarter) rate frames of data may be transmitted. That is, the frame rate is generally the lowest rate frame which is large enough to carry the payload. The rest of the frame is then filled (padded) with unneeded bits in order to send the frame rate selected. For the FCH channel, when there is no data to send, power control information and an eighth rate frame is sent. Thus, when the FCH has no bearer data to send, it sends more power (generates more interference and drains more battery if a MS is sending it) than a DCCH would. If no bearer data is to be sent, then a FCH channel requires about ⅛ the power of a full frame rate frame plus the power required to send the power control information. In contrast, the DCCH only needs to send the power required to send the power control information when there is no bearer traffic to send.  
           [0005]    In many systems, the RF link from the system to the mobile user (forward link) become RF interference limited when the system link is loaded with symmetric traffic. Typically, about eighty percent (80%) of the bits sent in a data call are sent on the forward link. This tends to also result a forward link interference limited system. As a result the forward link tends to become interference limited. Since data traffic is a growing percentage of the total traffic in modern systems, the forward link is expected to continue to be the limiting link in the typical system. However, it is possible, that in some systems, the reverse (mobile to base station link) can become the limiting link.  
           [0006]    Accordingly, it is highly desirable to provide a data transmission, voice and dispatch services over CDMA 2000 while adding a minimum of interference to the interference limited links; regardless of the type of service provided. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a block diagram of a mobile to mobile dispatch call via CDMA 2000 infrastructure.  
         [0008]    [0008]FIGS. 2 and 3 are a flow chart of a detection of a dispatch call origination in accordance with the present invention.  
         [0009]    [0009]FIG. 4 is a flow chart of a dispatch call that has stopped transmitting in accordance with the present invention.  
         [0010]    [0010]FIG. 5 is a flow chart of a dispatch call in which the listener has requested to become the speaker in accordance with the present invention.  
         [0011]    [0011]FIG. 6 is a flow chart of a dispatch call that roams from one cell to another cell in accordance with the present invention.  
         [0012]    [0012]FIGS. 7 and 8 are a flow chart of a voice call (non-dispatch call) in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    [0013]FIG. 1 is a block diagram of a mobile to mobile dispatch call using CDMA 2000 standards. Mobile transceiver  10  connects through base station  11  to mobile transceiver  12 . Between mobile  10  and base station  11 , a speaker air link  104  provides for the data transmission from the mobile  10  to the base station  11 . Base station  11  is coupled to mobile  12  via the listener&#39;s over the air link  116 . The speaker at mobile  10  is coupled to vocoder  101  which transmits the voice to RLP input buffer  102 . Buffer  102  feeds the RLP transmitter  103  which transmits the data over the speaker air link  104  to base station  11 . The speaker may be a conventional voice speaker or may include a constant bit rate audio or video source.  
         [0014]    At base station  11 , the RLP code  111  receives the incoming data and transmits it to the RLP resequencing queue  112 . The RLP resequencing queue orients the data in logical sequence and transmits it through chat server  113  to RLP input buffer  114 . Input buffer  114  then drives RLP transmitter  115  to transmit the data via the listener air link  116  to mobile  12 .  
         [0015]    The listener air link  116  couples base station  11  to mobile  12 . The data transmitted via the listener air link  116  is received by RLP code  121 . The data is then logically oriented by RLP resequencing queue  122 . The data is then transmitted to a vocoder input buffer  123  and finally is converted to voice by vocoder  124  and transmitted to the listener associated with mobile  12 .  
         [0016]    Both mobiles  10  and  12  include battery level detectors. Mobile  10  includes battery level detector  125  which is coupled to RLP transmitter  103  and transmits an indication of the battery level for mobile  10 . Similarly, mobile  12  includes a battery level detector  126  and when mobile  12  is in a transmission mode, battery level detector  126  transmits an indication of the battery level to base station  11 .  
         [0017]    [0017]FIGS. 2 and 3 depict an origination of a dispatch call. A dispatch call origination is detected by the base station, block  22 . Next, the base station detects whether the speaker&#39;s air link  104  is more forward or reverse interference limited. That is, whether the transmitting or receiving link of mobile  10  or example, is more limited, block  24 . Next, block  26  determines whether the speaker&#39;s forward link (up link with respect to the base station) is interference limited. If the speaker&#39;s forward link is interference limited, the base station  12  assigns a DCCH channel to the speaker, block  28 .  
         [0018]    If the speaker&#39;s forward link is not limited, the speaker&#39;s reverse link is more limited or if the battery level detector  125  for example, has detected a low battery level. In that case, the reverse link is limited and the base station assigns a FCH channel to the speaker, block  30 .  
         [0019]    Next, block  32  detects whether each listener&#39;s link is more forward or reverse interference limited. If a listener&#39;s forward link is link limited, block  34  transfers control to block  36  via the YES path. Block  36  assigns a FCH channel to the listener&#39;s forward link. If the listener&#39;s forward link is not link limited, block  34  transfers control to block  38  via the NO path. Block  38  determines that the listener&#39;s link is reverse link limited and assigns a call a DCCH channel.  
         [0020]    Next, it is determined whether the speaker has changed. If the speaker has changed, block  40  transfers control to block  42 . If the speaker has not changed, control is transferred to block  50  and the method is continued. If the speaker has changed, block  40  transfers control to block  42  via the YES path.  
         [0021]    Block  42  determines whether the previous speaker had been assigned a DCCH channel. If the previous speaker had been assigned a DCCH channel, block  42  transfers control to block  44  via the YES path. Block  44  changes the previous speaker&#39;s channel to an FCH channel and changes the previous listener&#39;s channel to a DCCH channel. The process then continues with block  50 .  
         [0022]    If the previous speaker did not have a DCCH channel, block  42  transfers control to block  46  via the NO path. Block  46  changes the previous speaker&#39;s channel to a DCCH channel. Then, block  48  changes the previous listener&#39;s channel to a FCH channel and continues the process at block  50 .  
         [0023]    Block  50  determines whether an existing dispatch call (data) needs to make an interconnect call (voice call). That is, whether a data transmission call needs to make a basic voice call. If an interactive call is requested, block  50  transfers control to block  52  via the YES path. Block  52  determines whether the existing channel is a DCCH channel. If the channel is a DCCH channel, then the DCCH channel is switched to a FCH channel, block  54 . The switch from the DCCH channel to the FCH channel occurs with a single message from the switching network. The switching is performed by the network without tearing down the existing traffic channel which implies a lower delay. The process is then ended. If the channel is not a DCCH channel, then a FCH channel is already in use and block  52  simply ends the process via the NO path.  
         [0024]    If the call is not a dispatch call requesting an interconnect call, block  50  transfers control via the NO path to end the process. FIG. 4 depicts a dispatch call that has stopped, that is, a speaker has released the push to talk button of the mobile  10 , for example. It is determined whether a dispatch call has stopped by block  60 . If the dispatch call has stopped, block  60  transfers control to block  62  via the NO path. Block  62  determines whether the link is more forward or reverse interference limited. If the link is forward link interference limited, block  64  transfers control to block  66  via the YES path. Block  66  assigns the link a FCH channel and ends the process.  
         [0025]    If the link is not forward link interference limited, block  64  transfers control to block  68  via the NO path. Block  68  determines whether the link is reverse link interference limited. If the link is reverse link interference limited, block  68  transfers control to block  70  via the YES path. Block  70  assigns the reverse link a DCCH channel and ends the process. If block  68  has not detected that the reverse link is interference limited, control is transferred and the process is ended.  
         [0026]    [0026]FIG. 5 depicts the procedure for a listener who presses the talk button and is subsequently granted by the system the ability to speak. Block  80  detects that a listener has pressed the talk button and is granted the permission by the system to talk. Block  82  determines whether the link is more forward or reverse interference limited.  
         [0027]    If the link is more forward link interference limited, block  84  transfers control via the YES path to block  86 . Block  86  assigns the forward link a DCCH channel and ends the process. If the link was not forward link interference limited block  84  transfers control to block  88  via the NO path. Block  88  determines whether the link is reverse interference limited. If it is, control is transferred from block  88  to block  90 . Block  90  assigns a FCH channel to the link and ends the process. If the reverse link is not interference limited, block  88  simply ends the process.  
         [0028]    [0028]FIG. 6 depicts a flow chart of a dispatch call which moves from one cell to another. When a dispatch caller moves to a new cell, a detection is made by the base station of any differences in the interference to the caller from the previous cell in which the caller was located, block  100 .  
         [0029]    Block  102  determines whether the caller is not the speaker, control is transferred to block  110 . If the caller is the speaker, block  102  transfers control to block  104  via the YES path. Block  104  determines whether the speaker&#39;s link is more forward or reverse interference link limited. If the speaker&#39;s link is more reverse link limited, the reverse link is assigned an FCH channel, block  106 . Control is then transferred to block  110 . If the speaker&#39;s link is more forward link limited, block  108  assigns a DCCH channel to the speaker&#39;s forward link and transfers control to block  110 .  
         [0030]    Block  110  detects whether each listener&#39;s link is more forward or reverse interference limited. If each listeners link is more forward link interference limited, block  112  transfers control to block  114  via the YES path. Block  114  assigns a FCH channel to the listener&#39;s forward link and ends the process. If the link is not more forward link interference limited, block  112  transfers control to block  116  via the NO path.  
         [0031]    Block  116  determines whether the reverse link is interference link limited. If it is, block  116  transfers control to block  116  via the YES path. Block  118  assigns a DCCH channel to the listener&#39;s reverse link and ends the process. If the reverse link is not more interference link limited, the process is simply ended by block  116 .  
         [0032]    [0032]FIGS. 7 and 8 depict a flow chart of a non-dispatch call, voice call, processed by the arrangement describing the present invention. Traffic is observed over the forward link by block  120  which estimates the number of full, half and eighth rate frames that would have been sent over the link if a FCH channel was used. Next, for the forward link, an estimate of the number of full, half and eighth rate frames that would have been sent over the link if a DCCH channel was used, is made by block  122 .  
         [0033]    For the reverse link, an estimate is made of the number of full, half and eighth rate frames that would have been sent over the link if a FCH channel was used, block  124 . Then, for the reverse link an estimate is made of the number of full, half and eighth rate frames that would have been sent over the reverse link if a FCH channel was used, block  126 .  
         [0034]    Next, a determination is made whether the forward or reverse link is RF interference limited, block  128 . Block  130  determines whether there is any benefit to be obtained over RF interference by switching channels. If not, block  130  continues the process at block  140 .  
         [0035]    If there is benefit to be obtained by minimizing the RF interference over the links to the mobile, block  130  transfers control to block  132  via the YES path. Block  132  switches the channels of the forward link. That is, if the forward link was using a FCH channel, a switch is made to a DCCH channel; or if a DCCH channel was used for the forward link, the base station switches the channel to a FCH channel.  
         [0036]    Similarly, for the reverse link, the channels are switched by block  134 . If a FCH channel was used for the reverse link, the base station switches the channel to a DCCH channel; or if a DCCH channel was used for the reverse link, the base station switches the reverse channel to a FCH channel.  
         [0037]    Next, block  136  examines the historical channel activity using the estimates for FCH and DCCH made above in steps  120  through  126 , to determine whether there is a preferred channel type indicated by previous calls to or from that particular mobile to determine what channel type to assign. There may be no previous history with this mobile or insufficient data in which case the channel type will be left as previously set in steps  132  and  134 .  
         [0038]    Lastly, block  138  insures that the channel type assigned to the mobile minimizes the RF impact, that is, the total number of bits sent without error per minute. Then the process is then continued at block  140 .  
         [0039]    Block  140  determines whether the call is an interconnect (voice) call that is requesting a dispatch (data) call service. If not, block  140  simply ends the process via the NO path. If so, block  140  transfers control to block  142 . Block  142  detects that a speaker has pressed the dispatch service button and is granted the permission by the system. Block  144  determines whether the link is more forward or reverse interference limited.  
         [0040]    If the link is more forward link interference limited, block  146  transfers control via the YES path to block  148 . Block  148  assigns the forward link a DCCH channel and ends the process. If the link was not forward link interference limited block  146  transfers control to block  150  via the NO path. Block  150  determines whether the link is reverse interference limited. If it is, control is transferred from block  150  to block  152 . Block  152  assigns a FCH channel to the link and ends the process. If the reverse link is not interference limited, block  150  simply ends the process.  
         [0041]    Historically, is IS-95 CDMA systems, these systems were generally forward link limited when loaded with symmetric traffic. In data calls roughly 80% of the bits are sent over the forward link. This would tend to force systems to be forward link limited. As dispatch services become significant system services then it is also possible that cells in the cell system would become reverse link limited if a large number of mobiles were speaking at the same time. With dynamic FCH/DCCH channel switching as embodied in the present invention, problems of forward and reverse link limitations are minimized while the CDMA system provides a relatively high quality of service.  
         [0042]    Although the preferred embodiment of the invention has been illustrated, and that form described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the present invention or from the scope of the appended claims.