Abstract:
The present invention concerns methods for efficiently supporting Voice over Internet Protocol (VoIP) on the Forward Packet Data Channel (F-PDCH) in CDMA 2000 1xEV-DV systems. Active speech in VoIP is encoded using, for example enhanced variable rate codec (EVRC), which produces 171, 80 and 16 bits per 20 ms of speech for Rate 1, Rate ½ and Rate ⅛, respectively. However, about 60% of the time a user is inactive during a speech session, so an inordinate amount of system bandwidth is comprised of rate ⅛ VoIP packets. In one embodiment of the present invention the apparatus of the present invention identifies the Rate ⅛ voice frame packets and discards them. In another embodiment of the present invention, the apparatus of the present invention identifies the Rate ⅛ voice frame packets and selects some of them for further transmission. In both embodiments the efficiency of channel utilization is increased since the amount of channel band width used to communicate relatively little information, e.g., gaps of silence, is decreased.

Description:
TECHNICAL FIELD 
     The present invention concerns apparatus and method for use in supporting Voice over Internet Protocol (“VoIP”) service in wireless telecommunications systems and more particularly concerns methods for encoding speech so that bandwidth in wireless telecommunications systems is used more efficiently. 
     BACKGROUND OF THE INVENTION 
     In communication systems there is a never-ending search to increase the efficiency of utilization of communication system assets. A typical problem in voice-based communication systems is to increase the number of conversations that can be carried in the same bandwidth. The solution to this problem has been approached from a number of different perspectives. In one such well-known solution, information theory is used to assign short symbols to encode more frequently occurring aspects of speech and relatively longer symbols to encode less frequently occurring aspects. By efficiently coding speech, more conversations can be carried in a given bandwidth. 
     Similar concerns have been encountered in new voice-based communications environment—Voice over Internet Protocol (“VoIP”) service. This invention applies to the operations of VoIP on Forward Packet Data Channel (“F-PDCH”) in CDMA2000 1xEV-DV (“1x Evolution for Data and Voice”) systems. In 1xEV-DV, the F-PDCH encoder packet (EP) size can be one of the seven possible values: 216, 408, 792, 1560, 2383, 3096, or 3864 bits. The voice payload, on the other hand, is much smaller than the EP size. For example, the Enhanced Variable Rate Codec (EVRC) produces 171, 80 and 16 bits per 20 ms for rate 1, rate ½, and rate ⅛, respectively. Active speech is encoded at rate 1 or rate ½, and background noise is encoded at rate ⅛. Typically rate ⅛ is used for about 60% of the time during a conversation due to the nature of speech in which there are frequent gaps of background noise which, when taken together, comprise a relatively large part of speech. Comparing the voice payload to the EP size, it is obvious that transmission of rate ⅛ VoIP packets on the F-PDCH is extremely inefficient, wasting a large portion of the system resources while providing minor gain to the voice quality. Bundling many rate ⅛ VoIP packets into one encoder packet can improve the packing efficiency, however, doing so will increase the overall end-to-end delay of the voice communication and adversely impact the voice quality. 
     Thus, those skilled in the art seek improved methods and apparatus for supporting VoIP service in CDMA systems, particularly apparatus and methods that use bandwidth assets more efficiently. For example, those skilled in the art seek apparatus and methods that take into consideration the fact that a large portion of speech comprises gaps of background noise that convey little or no information, and thus which need not be reproduced with a high degree of fidelity, if at all. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the limitations of the prior art. A first preferred embodiment of the present invention concerns method and apparatus for use in a wireless telecommunications system that supports voice over internet protocol service. In one method associated with the present invention, the wireless telecommunications system receives VoIP packets encoding speech wherein a portion of the VoIP packets encode background noise which comprises part of the speech; the wireless telecommunications system identifies those packets which encode background noise, and discards them. In further steps, the wireless telecommunications system performs header compression on the VoIP packets not discarded and transmits them over a wireless link to a mobile unit. 
     In a variant of the first preferred embodiment, the wireless telecommunications system receives VoIP packets wherein a portion of the VoIP packets encode background noise which comprises part of the encoded speech; the wireless telecommunications system identifies those packets which encode background noise; and then the telecommunications system retains some of the VoIP packets encoding background noise and discards the rest. 
     In a further variant of the first preferred embodiment, VoIP packets encoded using Enhanced Variable Rate Codec (“EVRC”) arrive at a Packet Data Serving Node (“PDSN”) of a wireless telecommunications system; the PDSN identifies the packets with Rate ⅛ voice frame information; the PDSN discards all of the Rate ⅛ packets; the PDSN performs IP/UDP/RTP header compression on all the Rate 1 or Rate ½ packets; and the PDSN then forwards these packets to the Packet Control Function (“PCF”) or Base Station Controller (“BSC”). 
     In still further variants of the first preferred embodiment, the PDSN selects some of the Rate ⅛ packets for transmission; performs IP/UDP/RTP header compression on the Rate ⅛ packets selected for transmission; and forwards the selected Rate ⅛ packets to the PCF or BSC. 
     In a second preferred embodiment of the present invention comprising both method and apparatus, the VoIP packets arrive at the PDSN; the PDSN performs header compression on all of the packets; the PDSN forwards them to the PCF/BSC; the PCF/BSC discards all of the Rate ⅛ packets; the Rate 1 and Rate ½ packets are transmitted to the Base Transceiver System (BTS); and the BTS then delivers the VoIP packets over the forward packet data channel to the Mobile Station (MS). 
     In variants of the second preferred embodiment, the PCF/BSC selects some of the Rate ⅛ packets for transmission; and the PCF/BSC transmits the selected Rate ⅛ packets to the Base Transceiver System. 
     Thus the embodiments of the present invention efficiently support VoIP in 1 xEV-DV systems. In particular, embodiments of the present invention discard some or all VoIP data packets corresponding to gaps of background noise in speech. As a result, the system bandwidth is used more efficiently since a greater portion of the transmitted VoIP packets contain intelligible speech as opposed to background noise. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and advantages of this invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings in which like characters refer to like elements throughout and in which: 
         FIG. 1  depicts a simplified block diagram of a CDMA 2000 1x wireless communications network suitable for use in practicing the teachings of this invention; 
         FIG. 2  depicts a conceptual block diagram of an apparatus operating in accordance with a first preferred embodiment of the present invention; 
         FIG. 3  depicts a flowchart illustrating the steps of a method operating in accordance with the first preferred embodiment of the present invention; 
         FIG. 4  depicts a flowchart illustrating the steps of an alternate method operating in accordance with the first preferred embodiment of the present invention; 
         FIG. 5  depicts a conceptual block diagram of an apparatus operating in accordance with a second preferred embodiment of the present invention; 
         FIG. 6  depicts a flowchart illustrating the steps of a method operating in accordance with the second preferred embodiment of the present invention; and 
         FIG. 7  depicts a flowchart illustrating the steps of an alternate method operating in accordance with the second preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is simplified block diagram of a wireless communication system  1 , specifically a CDMA 2000 1x network that is suitable for use in practicing the teachings of this invention. A description of  FIG. 1  will be provided in order to place this invention into a suitable technological context. However, it should be appreciated that the specific network architecture and topology shown in  FIG. 1  is not to be construed in a limiting sense upon this invention, as embodiments of this invention could be practiced in networks having an architecture and topology that differs from that shown in  FIG. 1 . Further, the general concepts of this invention may be practiced as well in a TDMA-based mobile IP network, and the invention is thus not limited for use only in a CDMA network. In general, this invention will find utility in wireless technologies that support a Voice over Internet Protocol (VoIP) functionality. As such, while reading the ensuing description it should be noted that while some aspects of the description are specific to a CDMA network, the description is not intended to be read in a limiting sense upon the implementation, use and practice of this invention. 
     The wireless communication system  1  shown in  FIG. 1  includes at least one mobile station (MS)  10 . The MS  10  may be or may include a cellular telephone, or any type of mobile terminal (MT) or mobile node (MN) having wireless communication capabilities including, but not limited to, portable computers, personal data assistants (PDAs), Internet appliances, gaming devices, imaging devices and devices having a combination of these and/or other functionalities. The MS  10  is assumed to be compatible with the physical and higher layer signal formats and protocols used by a network  12 , and to be capable of being coupled with the network  12  via a wireless link  11 . In the presently preferred embodiments of this invention the wireless link  11  is a radio frequency (RF) link, although in other embodiments the wireless link  11  could be an optical link. 
     In a conventional sense the network  12  includes a mobile switching center (MSC)  14  coupled through an IS-41 Map interface to a visitor location register (VLR)  16 . The VLR  16  in turn is coupled through an IS-41 Map interface to a switching system seven (SS-7) network  18  and thence to a home location register (HLR)  20  that is associated with a home access provider network of the MS  10 . The MSC  14  is also coupled through an A1 interface (for circuit switched (CS) and packet switched (PS) traffic) and through an A5/A2 interface (CS services only) to a first radio network (RN)  22 A. The first RN  22 A includes a base station (BS)  24 A that includes a base transceiver station (BTS) and a base station center (BSC) that is coupled through an A8/A9 interface to a Packet Control Function (PCF)  26 A. The PCF  26 A is coupled via an R-P (PDSN/PCF) interface  27  (also called an A10/A11 interface) to a first packet data service node (PDSN)  28 A and thence to an IP network  30  (via a Pi interface). The PDSN  28 A is also shown coupled to a visited access, authorization and accounting (AAA) node  32  via a Pi and a remote authentication dial-in service (RADIUS) interface, that in turn is coupled to the IP network  30  via a RADIUS interface. Also shown coupled to the IP network  30  via RADIUS interfaces are a Home IP network AAA node  34  and a Broker IP network AAA node  36 . A home IP network/home access provider network/private network Home Agent  38  is coupled to the IP network via a Mobile IPv4 interface. In accordance with RFC3220, the Home Agent  38  is a router on the home network of a mobile node (the MS  10  in this description) that tunnels datagrams for delivery to the mobile node when it is away from home, and that maintains current location information for the mobile node. 
     Also shown in  FIG. 1  is a second RN  22 B that is coupled to the first RN  22 A via an A3/A7 interface. The second RN  22 B includes a BS  24 B and a PCF  26 B and is coupled to a second PDSN  28 B. The PDSN  28 A and the PDSN  28 B are coupled together through a P-P interface  29  (PDSN to PDSN interface, defined in IS835C). It should be noted that there may be a plurality of BSs  24  connected to a single PCF  26  (defining a BS subnet), and that there may be a plurality of PCFs  26  within a given network all connected to a single PDSN  28 . 
       FIG. 2  depicts a system for carrying out a first preferred embodiment of the present invention. In  FIGS. 2 and 5 , the PDSN, PCF/BSC, and BTS are referred generically by reference characters  28 ,  26 , and  24 , respectively, to indicate that the methods and apparatus of the present invention can be practiced in systems that differ somewhat from that depicted in  FIG. 1 . As shown in  FIG. 2 , the PDSN  28  receives rate 1 voice packets  60 , rate 1 voice packets  62  and rate ⅛ voice packets  64  encoded using the Enhanced Variable Rate Codec (“EVRC”). Although the invention is described with reference to the EVRC codec, other voice codecs known to those skilled in the art can be used. In the first preferred embodiment, the PDSN detects those voice packets corresponding to rate ⅛ voice packets  64  and discards them. The PDSN then performs header compression on the rate 1 and ½ packets to create VoIP packets  70  and  72 . The rate 1 and rate ½ voice packets  70 ,  72  are then forwarded to PCF  26 , and in turn to the BTS incorporated in the BS  24 . The voice packets are then transmitted to the MS  10  over wireless link  11 . 
       FIG. 3  depicts a flowchart illustrating the steps of a method in accordance with the first preferred embodiment of the present invention. In the method, the PDSN receives rate 1, rate ½ and rate ⅛ VoIP packets at step  100 . The PDSN determines which VoIP packets correspond to rate ⅛ packets at step  110 , and discards them at step  120 . Next the PDSN performs IP/UDP/RTP header compression on the rate 1 and rate ½ packets at step  130 , and forwards them to the PCF at step  140 . Then the PCF/BSC delivers the rate 1 and rate ½ packets to the BTS for transmission on the F-PDCH. 
       FIG. 4  depicts a flowchart illustrating the steps of an alternate method in accordance with the first preferred embodiment of the present invention. At step  200 , the PDSN receives VoIP packets. In step  210 , the PDSN determines which VoIP packets correspond to rate ⅛ packets and at step  220 , the PDSN retains some of the rate ⅛ VoIP packets and discards the rest. At step  230 , the PDSN performs IP/UDP/RTP header compression on rate 1 and rate ½ packets, as well as the retained rate ⅛ packets. Next, at step  240 , the PDSN forwards the rate 1, ½ and retained ⅛ packets to the PCF. Then at step  250 , the PCF/BSC delivers the rate 1, ½ and ⅛ packets to the BTS for transmission on the F-PDCH. 
       FIG. 5  depicts a system for carrying out a second preferred embodiment of the present invention. As shown in  FIG. 5 , the PDSN  28  receives rate 1, ½ and ⅛ voice packets  60 ,  62  and  64 , respectively, and performs header compression on all of them. The rate 1, ½ and ⅛ voice packets with compressed headers  70 ,  72  and  74  are then forwarded to PCF  26 . The PCF  26  determines which VoIP packets corresponds to rate ⅛ packets  74  and discards them. The rate 1 and ½ voice packets  70  and  72  are then transmitted to the MS  10  over wireless link  11  by BTS  24 . 
       FIG. 6  depicts a flowchart illustrating the steps of a method in accordance with a second preferred embodiment of the present invention. At step  300 , the PDSN receives the VoIP (including rate 1, ½ and ⅛ packets) and at step  310  performs IP/UDP/RTP header compression on all packets. Next at step  320  the PDSN forwards all packets to the PCF. The PCF at step  330  determines which packets correspond to rate ⅛ VoIP packets, and at step  340  discards them. Finally at step  350  the PCF/BSC delivers the rate 1 and ½ packets to the BTS for transmission on the F-PDCH. 
       FIG. 7  depicts a flowchart illustrating the steps of an alternate method in accordance with a second preferred embodiment of the present invention. At step  400 , the PDSN receives rate 1, ½ and ⅛ VoIP packets. Next, the PDSN performs IP/UDP/RTP header compression on all packets at step  410 . Then at step  420  the PDSN forwards all packets to the PCF. The PCF at step  430  determines which VoIP packets are rate ⅛ packets. Next at step  440  the PCF retains some of the identified rate ⅛ packets and discards the rest. Finally at step  450  the PCF/BSC delivers the rate 1 and ½ and retained rate ⅛ packets to the BTS for transmission on the F-PDCH. 
     An embodiment of the invention is a computer memory medium tangibly embodying a program of machine-readable instructions executable by one or more digital processing apparatus to perform operations in a wireless telecommunications system for supporting voice over interne protocol. The operations comprise: receiving VoIP packets at the packet data serving node, wherein at least one VoIP packet encode background noise associated with speech; identifying the at least one VoIP packet encoding background noise; and discarding the at least one VoIP packet. 
     Another embodiment of the invention is a computer memory medium tangibly embodying a program of machine-readable instructions executable by one or more digital processing apparatus to perform operations in a wireless telecommunications system for supporting voice over internet protocol. The operations comprise: receiving VoIP packets at the packet data serving node, wherein a portion of the VoIP packets encode background noise associated with human speech; identifying the VoIP packets encoding background noise; retaining some VoIP packets encoding background noise; and discarding the remaining VoIP packets encoding background noise. 
     A further embodiment of the invention is a computer memory medium tangibly embodying a program of machine-readable instructions executable by one or more digital processing apparatus to perform operations in a wireless telecommunications system for supporting voice over internet protocol. The operations comprise: receiving VoIP packets at the packet data serving node, wherein at least one of the VoIP packets encode background noise associated with human speech; performing header compression on the VoIP packets; transmitting the VoIP packets to the packet control function; receiving the VoIP packets at the packet control function; identifying the at least one VoIP packet encoding background noise; and discarding the at least one VoIP packets. 
     Yet another embodiment of the invention is a computer memory medium tangibly embodying a program of machine-readable instructions executable by one or more digital processing apparatus to perform operations in a wireless telecommunications system for supporting voice over interne protocol. The operations comprise: receiving VoIP packets at the packet data serving node, wherein a portion of the VoIP packets encode background noise associated with speech; performing header compression on the VoIP packets; transmitting the rate VoIP packets with compressed headers to the packet control function; receiving the VoIP packets at the packet control function; identifying the VoIP packets encoding background noise; retaining some VoIP packets encoding background noise; and discarding the remaining VoIP packets encoding background noise. 
     Thus it is seen that a apparatus and method for efficiently supporting VoIP in a wireless communication system are provided by the present invention. One skilled in the art will understand that the present teachings can be applied to other wireless communications systems besides those based on CDMA principles. In addition, the VoIP packets can be encoded with other codecs besides EVRC known to those skilled in the art. Accordingly, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments; that these described embodiments are presented for the purposes of illustration and not of limitation; and that the present invention is therefore limited only by the claims which follow.