Abstract:
A packet transmission arrangement maintains a certain minimum bandwidth for a call. When a silence period is detected, the bandwidth that is allocated to the call is reduced. When a speech period is detected, the reduced bandwidth remains in force, unless there is spare capacity, in which case a full measure of bandwidth is allocated to the call.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This invention claims priority from U.S. provisional application No. 60/144,535 and from U.S. provisional application No. 60/144,469, both filed on Jul. 19, 1999. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to packet voice transmission.  
         [0003]     Communications networks currently transfer vast quantities of information in both local and wide area networks. The information typically consists of signals representing digitized voice and video as well as data that are transferred between endpoints in networks. A communication path may be established in such networks by circuit switching or by packet switching. In circuit switching, an exclusive channel is established between a sender and a receiver throughout the entire transmission until the connection is released. In packet switching, virtual circuits or channels are established between a sender and a receiver and a channel is only occupied for the duration of the packet&#39;s transmission. Such packet switching enables networks to handle the heterogeneous mix of network traffic with varying service requirements and, ideally, packet switching is scalable and can reliably establish and maintain virtual channels without any prespecified rates (so-called bandwidth on demand).  
         [0004]     There is currently a significant interest in integrating packet voice in the next generation of broadband data systems in order to provide packet telephony capabilities. The difficulty with establishing packetized voice in the conventional virtual circuit approach described above, is that either delay or clipping is suffered. That is, when a speaker goes silent and the path is released to other users, when the speaker resumes the conversation there may be a period of time during which there is no bandwidth available for the conversation. During such time, the speech signal might be stored and forwarded when bandwidth does become available, or a portion of the speech might be clipped. Neither is a desirable consequence.  
       SUMMARY OF THE INVENTION  
       [0005]     An improvement in the art is achieved with an arrangement where a certain minimum bandwidth is always maintained. When a silence period is detected, the bandwidth that is allocated to the call is reduced. When a speech period is detected, the reduced bandwidth remains in force, unless there is spare capacity, in which case a full measure of bandwidth is allocated to the call. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  depicts one environment where the principles of this invention may be practiced;  
         [0007]      FIG. 2  illustrates  5  signal frames, with slot  2  allocated to phone  10 ;  
         [0008]      FIG. 3  shows a communication interface chart for an arrangement where bandwidth needs are determined at the base station of the  FIG. 1  arrangement; and  
         [0009]      FIG. 4  shows a communication interface chart for an arrangement where bandwidth needs are determined at the base station of the  FIG. 1  arrangement. 
     
    
     DETAILED DESCRIPTION  
       [0010]      FIG. 1  shows a cellular telephony arrangement with a cell phone  10  communicating with base station  20  that includes conventional control circuitry for managing the bandwidth available to base station  20 , and for managing the calls from various cellular phones, including phone  10 . Consider, for example, a  FIG. 1  system where a cell phone communicates with a base station over a specified 200 KHz channel that comprises frames, with eight slots per block and a given number of blocks per frame (e.g., 8). To maintain synchronization among cell phones, the base station sends a frame control signal to which all cell phones synchronize. The voice signal of phone  10  is illustratively encoded by a 13 Kbps coder that adds 9 kbps of error protection and thus develops a 22 kbps signal. Under normal conditions, when the user of phone  10  is speaking, phone  10  is allocated one out of the eight slots of each block. For example,  FIG. 2  shows 5 frames, where slot  2  is allocated to phone  10 .  
         [0011]      FIG. 3  shows the communication that takes place between phone  10  and base station  20  when base station  20  includes circuitry for detecting silence periods of a cell phone user.  
         [0012]     Line  11  represents the conventional protocol employed for establishing communication between cell phone  10  and base station  20 . This includes the protocol that is engaged in when the cell phone requests service and/or when the cell phone is hailed by the base stations. In consequence of the line  11  protocol, in line  12  base station  20  specifies to phone  10  the specific frequency channel and time slot that is available to it for sending packets upstream. Thereafter, two-way communication proceeds (line  13  in  FIG. 3 ) with cell phone  10  sending information to the base station in accordance the  FIG. 2  scheme, and base station  20  broadcasting its downstream packets. This is indicated by line  13  in  FIG. 3 . For purposes of discussion, it is assumed that base station  20  has granted phone  10  its full due bandwidth; to wit, one out of eight time slots in each block of a frame.  
         [0013]     In accordance with the  FIG. 3  arrangement, base station  20  monitors the signal of phone  10  to determine whether the user has entered a silence period. This monitoring might take one of two forms. In accordance with one approach, the cell phone sends packets that represent whatever background noise exists at the microphone of phone  10 , and base station  20  includes module  21  that base station  20  couples to the signal of phone  10 . This equipment decodes the signal of cell phone  10  and ascertains whether that signal represents speech, or background noise. Module  21  is realized through conventional modules; for example, circuitry that measures the power contained in the signal. In accordance with another approach, cell phone  10  includes conventional circuitry that detects when its user has entered a silence period and, in response thereto, stops radiating power (not unlike a voice-activated tape recorder). This improves performance of the overall wireless system, in that there is less radiated power to interfere with the transmissions of other cell phones that communicate with base station  20 . Of course, the power-measuring circuitry  21  within base station  20  has an easy time of detecting a silence period when the cell phone stops radiating power altogether.  
         [0014]     When base station  20  detects a silence period associated with a phone that has a full bandwidth allocation, such as phone  10  in this example, in accordance with the principles disclosed herein that fact is communicated to control circuit  22 , and circuit  22  sends a control message  14  to cell phone  10 , instructing phone  10  that its allocated bandwidth has been reduced. Illustratively, phone  10  is instructed that only the even-numbered (or the odd-numbered) blocks of a frame, or some other specified fraction of the frame, are henceforth available to phone  10 . This control message can have the format of the control message of line  12 . The control message  12  might also instruct cell phone  10  to move to another time slot.  
         [0015]     Although in the case of a cell phone  10  that refrains from transmitting any power during silence periods the instruction to use only the even blocks of a frame has no effect on the cell phone during the silence period, the effect is felt when cell phone wishes to resume sending a speech signal. Specifically, in accordance with the principles disclosed herein, having received an instruction to use a particular pattern of time slots, when phone  10  receives a voice signal that is to be transmitted to base station  20 , it reduces the encoding rate of the speech signal to correspond to the allotted bandwidth specified by message  14 , creates packets, and modulates the packets onto the specified 200 KHz channel in the time slot of the specified blocks. This is represented by line  15  in  FIG. 3 .  
         [0016]     Thus, in accordance with the  FIG. 3  arrangement, once phone  10  enters a silence period it relinquishes some—but not all—of the communication channel capacity that had been allocated to phone  10 . More precisely, base station  20  appropriates (for other uses) some—but not all—of the communication capacity that had been allocated to cell phone  10 . Advantageously, the appropriated capacity is sufficient to satisfy the minimum needs of at least one other user, yet not so great as to impose an unduly poor Quality of Service (QoS) on cell phone  10 . For example, the appropriated capacity might be ½, or ¾ of the full bandwidth. Indeed, it is expected that base station  20  will use the channel capacity that was relinquished by phone  10 , and appropriated by base station  20 , for establishing communication for, or to, another cell phone, such as phone  23 . It is noted that, in this case, phone  23  is operating at half bandwidth.  
         [0017]     The capacity relinquished by phone  10  by going into a silence period is not recovered by phone  10 , except by the grace of base station  20 . That is, when phone  10  exits its silence period it must encode the speech signal at the lower rate that comports with the specification of message  14 . For the example above, if message  14  allots phone  10  only half the capacity, 11 Kbps are available (instead of the 22 Kbps) for communicating information to base station  10  and, thus, 6 Kbps might be used for voice coding, leaving 5 Kbps for error protection. Transmission at this half rate continues, as shown by line  15  in  FIG. 3 , at least until controller  22  detects that phone  10  is no longer in a silence period but has began transmitting a speech signal. When base station  20  realizes that cell phone  10  is in an active (non-silence) period, it enters a process that attempts to provide cell phone  10  with the full bandwidth that is due to cell phone  10 —based on the contracted QoS of cell phone  10 . If the slots previously appropriated from cell phone  10  are unoccupied, base station  20  simply sends a command message  16 , instructing cell phone  10  to resume encoding in full bandwidth. If the slots previously appropriated from cell phone  10  are occupied with a signal of cell phone  23  (i.e., with a real-time signal) and there are other slots available to which cell phone  23  can be moved, then base station  20  moves cell phone  23 , freeing up the slots previously appropriated from cell phone  10 . Thence, base station  20  sends command  16  to cell phone  10 , instructing it to resume encoding in full bandwidth. If another full bandwidth time slot is available, base station  20  sends a message  16  to cell phone  10  instructing it to move to a new slot and to encode its speech signal in full bandwidth. Message  16  advantageously has the same general format of message  14 . Once message  16  is received, phone  10  resumes communicating at the 22 Kbps rate.  
         [0018]      FIG. 4  shows the communication that takes place between phone  10  and base station  20  when base station  20  operates without module  21  and relies on phone  10  to detect periods of silence or non-silence.  FIG. 4  is basically identical to  FIG. 3 , except that phone  10  is burdened with the need to inform base station  20  when it enters a silence period, and when it entered a non-silence period. This is depicted in  FIG. 4  by messages  18  and  19 , respectively. In this arrangement, control circuitry  22  receives its information from the cell phone instead of from module  21  but, otherwise, the operation is the same.  
         [0019]     The above example discloses a simple schema for reducing the bandwidth; to wit, allotting every even (or odd) block of a frame for a phone in a silence period (½ capacity), or allotting every fourth block of a frame for a phone in a silence period (¼ capacity). It also discloses that the bandwidth that is left for the phone in a silence period should be not smaller than the minimum bandwidth that is needed by a real-time (e.g., voice) user. It further discloses that the bandwidth that is taken away from the phone in a silence period should be not smaller than the minimum bandwidth that is needed by a user. It should be recognized, however, that the first and the third of these illustrative suggestions are not required by the principles disclosed herein.  
         [0020]     It is simple and, therefore, convenient for messages  14  and  16  to communicate an instruction such as “drop to even blocks,” or “take the odd blocks of slot  2 ,” or “resume full bandwidth.” However, there is no prohibition from message  14  instructing “drop blocks  1 ,  3 - 5 .” Also, while it is advantageous to reduce the bandwidth of a phone in a silence period by an amount that is equal to a multiple of a minimum bandwidth of another cellular phone, there is no requirement that the capacity gained by reducing the channel allotted to the phone in a silence period must be allocated to another real-time user.  
         [0021]     In fact, when another phone, such as phone  23 , is assigned to the channel that is appropriated from cell phone  10  when phone  10  goes into a silence period, a number of considerations arise. First, there is the issue of phone  23  not being given a full bandwidth. Presumably, that consequence is reached because there are no free time slots available for phone  23 —if phone  23  is just beginning to communication session, or because phone  23  is in a silence period and is merely being moved. Second, when phone  10  enters a non-silence period and phone  23  occupies half of the time slots, either phone  10  or phone  23  must be moved before cell phone  10  can receive its full due bandwidth. Moreover, unless other time slots are found, both phones continue to operate at a reduced rate.  
         [0022]     While these considerations are not very significant, operation of the system is somewhat simplified by using such freed capacity primarily for non-real-time users, who are much less sensitive to capacity being granted to them during silence periods of cell phone  10 , and capacity being taken away from them during active periods of cell phone  10 .  
         [0023]     The above describes the principles of this invention but persons skilled in the art can introduce various modifications and additions without departing from the spirit and scope of the invention. For example, although the disclosure is presented in terms of cell phones communicating with a base station, that is not a limitation of this invention. Also, the method of this invention need not bother to determine whether a cell phone that is at less than full bandwidth is entering a silence period and, conversely, need not bother to determine whether a cell phone that operates at full capacity is entering an active period. Also, the above does not address the issue of an initial connection between a cell phone and base station  20  when there is no capacity for a full bandwidth connection. It should be understood by skilled artisans, however, that the principles of this invention apply, and a connection can be established at less than full bandwidth, in accordance with the above disclosure.