Abstract:
Power control of mixed voice and data transmissions is disclosed. A voice signal is transmitted at a dynamically-adjusted voice transmit power capped at a maximum voice transmit power limit. Concurrently, data bursts are transmitted on top of the voice signal. Data noise is inserted between the data bursts transmissions. The data burst and inserted data noise are transmitted at a dynamically-adjusted data transmit power based on the voice transmit power to restrict the rate of change of the data transmit power until a maximum data transmit power limit is reached.

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. §120 
       [0001]    The present application for patent is Continuation of patent application Ser. No. 11/241,288 entitled “Method for Power Control for Mixed Voice and Data Transmission” filed Sep. 30, 2005, currently pending, which claims priority to U.S. Pat. No. 7,130,288, filed Jan. 24, 2001, both of which are assigned to the assignee hereof and hereby expressly incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention generally relates to the field of wireless communication systems. More specifically, the invention relates to downlink, i.e. from the base station to a set of terminal units, mixed voice and data transmission for code division multiple access communication systems. 
         [0004]    2. Background 
         [0005]    In a code division multiple access (“CDMA”) communication system, such as IS-95, or CDMA2000, or WCDMA (wideband CDMA), transmission can be provided for voice communication and data communication simultaneously by transmitting voice and data signals across one or more communication channels. Certain types of signal transmission, for example, voice and certain types of low data rate data transmissions are degraded by delays in transmission. Certain types of data signal transmission, on the other hand, are tolerant of delays in transmission. For example, because the data is tolerant of delay, the data can be grouped into packets and scheduled for transmission. Furthermore, a delayed packet need not be dropped, and transmission errors can be corrected by simply retransmitting a packet at a later time, i.e. rescheduling the packet. Large amounts of packet data information can be transmitted efficiently in short “bursts” of data at high power and high data rate. Conventional voice/data transmission treats voice and data communications similarly by setting up a communication link at a pre-determined data rate, and attempting to transmit voice and data information without exceeding a certain frame error rate. With conventional low data rate voice/data transmission, changes in the data rate generally do not involve significant changes in the overall transmit power; this is because low data rate connections only use a fraction of the total power available at the base station. By way of contrast, transmission of high speed packet data may require frequent extreme changes in data rate which typically involve large changes in power level. Since high data rate transmission uses a significant fraction of the total base station transmit power, the overall base station transmit power level could be significantly affected by the variation in the power used for high data rate transmissions. 
         [0006]    In the present application, voice signal transmission and other signal transmission which is degraded by delays in transmission, as well as conventional data transmission where changes in the data rate are infrequent and relatively minor and changes in transmission power levels are small relative to the total base station transmit power, are referred to as “voice”. Data signal transmission, such as high speed packet data, which can be tolerant of delays in transmission and can be scheduled, and typically is transmitted in short “bursts” at high power and high data rate, as well as any signal transmission where changes in the data rate are frequent and extreme and changes in transmission power levels are relatively large, are referred to as “data”. 
         [0007]    In order to efficiently accommodate these different types of signal transmission simultaneously, i.e., mixed voice and data transmission, different approaches may be followed. One approach is to specify a different part of the frequency spectrum, i.e. a different “band” of frequencies or frequency band, for each type of signal. Another approach is to multiplex the voice and data signals together through time division. With the time division approach, some of the time available for transmitting the signals is allotted to voice signals and some of the time available for transmitting the signals is allotted to data signals. For example, in a GSM+GPRS system (Global System for Mobile combined with Generalized Packet Radio System) some time slots normally used for regular GSM voice transmission are instead used for packet data transmission. One approach, used as an example in the present application, is code division multiple access (CDMA), which allows multiple signals to be transmitted at the same time on the same frequency band. 
         [0008]    In CDMA systems each user&#39;s signal is separated from other users&#39; signals by modulating the transmission signal with a distinct spreading code sequence. The modulation of the transmission signal spreads its spectrum so that the bandwidth of the encoded transmission signal is much greater than the original bandwidth of the user&#39;s information. For this reason CDMA is also referred to as “spread spectrum” modulation or coding. Each user uniquely encodes its information into a transmission signal using the spreading code sequence. The intended receiver, knowing the spreading code sequence of the user, can decode the transmission signal to recover the information. 
         [0009]    By way of background, in CDMA communications, the user&#39;s signal is spread to allow many users to simultaneously use the same bandwidth without significantly interfering with one another. One means of spreading is the application of distinct “orthogonal” spreading codes or functions, such as Walsh functions, to each user&#39;s signal. “Orthogonality” refers to lack of correlation between the spreading functions. In a given spread spectrum communication system using Walsh functions (also called Walsh code sequences), a pre-defined Walsh function matrix having n rows of n chips each is established in advance to define the different Walsh functions to be used to distinguish different user&#39;s signals. As an example, for a given sector (or cell in the WCDMA terminology), each downlink channel is assigned a distinct Walsh function. In other words, communications between a base station and each user are coded by a distinct Walsh code sequence in order to separate each user from the others. 
         [0010]    The base station transmits signals to all users in a sector so that the Walsh codes are time synchronized in order to achieve orthogonality between the different signals. Effectiveness of the orthogonal spreading codes is affected by the phenomenon of “multipath”. Simply stated, multipath is interference caused by reception of the same signal over multiple paths, that is, multiple copies of the signal arrive after different path delays. Due to the loss of time synchronization, the orthogonality between different user signals is lost. Interference due to loss of orthogonality through multipath can be averaged by the use of other types of spreading codes such as pseudo-noise (“PN”) sequences, for example. The autocorrelation properties of PN sequences can be used to improve rejection of multipath interference. However, due to the loss of orthogonality through multipath, there is greater interference between the signals of different users, referred to as “intra-cell interference”, including interference of a user&#39;s own signal with itself, also referred to as “self-interference”. 
         [0011]    In a multi cell system, there can be interference caused by user signals transmitted by the base station in one cell interfering with the user signals transmitted in another cell, also referred to as “inter-cell interference”. The transmit power of the base station transmitters is controlled so as to minimize the amount of power transmitted into neighboring cells in order to limit inter-cell interference. Extreme fluctuations in transmit power can exacerbate the effects of inter-cell interference, as well as intra-cell interference between users including self-interference, described above. 
         [0012]      FIG. 1  illustrates an example of the effect of data transmission on power control for multiple voice and data users within the same cell in a CDMA or spread spectrum communication system.  FIG. 1  shows graph  100 , having power axis  101  plotted against time axis  102 . The transmit power for a typical voice user varies in time according to single user voice power curve  104 . The aggregate transmission power for all the voice users within the cell is shown as Pv  106  in graph  100 . Aggregate voice power Pv  106  varies in time as shown in graph  100 . Power is allocated in addition to aggregate voice power Pv  106  for data burst transmissions  108 ,  109 , and  110 . The maximum available signal transmission power that can be allocated for the total of aggregate voice and data signal transmissions is maximum power limit Pmax  112 , shown in graph  100  as a horizontal solid line and also indicated by “Pmax.” The data and voice aggregate transmission power is shown as Pv+d  114  in graph  100 . Data and voice aggregate power Pv+d  114  within the cell varies in time as shown in graph  100 . As seen in graph  100 , Pv+d  114  remains below maximum power limit Pmax  112 . 
         [0013]      FIG. 1  shows an example of the effect that data signal transmission can have on power control for a single user in terms of changes to single user voice power curve  104 . As a result of data burst transmission  108 , interference can be increased, due to the intra-cell effects outlined above, for the single user whose power allocation is represented by single user voice power curve  104 . To balance the increased interference, power allocation can be increased for the single user leading to local power peak  105  in single user voice power curve  104 . In a conventional voice/data transmission system, changes in power allocation between users tend to balance out, by occurring randomly in time, leaving only a minor effect on aggregate voice power Pv  106 . However, the effect of data burst transmission  108  is simultaneous for many users in the cell, so there is a relatively large effect on aggregate voice power Pv  106 , shown as increase  116  in aggregate voice power Pv  106 . 
         [0014]    Continuing with  FIG. 1 , at the end of data burst transmission  108 , interference is reduced for the users within the cell. Thus, the power control system at the base station will decrease the power allocation to the users, leading to decrease  117  in aggregate voice power Pv  106 . In a mixed voice and data communication system, the power control system must be able to respond quickly to changes in interference. Thus, decrease  117  in aggregate voice power Pv  106  may be more than needed in view of subsequent data burst transmission  109 . In other words, the reaction of the base station&#39;s power control system leading to decrease  117  “undershoots” the equilibrium value for stable system performance. As a result, then, of data burst transmission  109 , which again causes an increase in interference for the users, the base station&#39;s power control system increases the power allocation for the users, leading to increase  118  in aggregate voice power Pv  106 . Once again, increase  118  in aggregate voice power Pv  106  may be more than needed. In other words, the reaction of the power control system leading to increase  118  “overshoots” the equilibrium value for stable system performance. 
         [0015]    Thus, as shown in  FIG. 1 , when data signal transmission is mixed with voice signal transmission in a wireless communication system, the different signal characteristics of voice and data transmissions lead to problems with power control for users within the same cell. The signal characteristics of data communications, namely that data transmission typically occurs in bursts, tends to cause disruptions in power control which do not occur with the relatively continuous signal characteristics of voice communications. For example, over-allocation and under-allocation of power to each user and to the aggregate of all users within a cell can disrupt communications and severely degrade the quality of the communication links. In addition, the system becomes subject to large swings in the total power output, as shown by the large variations in the level of data and voice aggregate power Pv+d  114 , which indicates the total power output of the system. 
         [0016]      FIG. 2A ,  FIG. 2B , and  FIG. 2C  illustrate an example of some of the effects of data transmission on power control for users in neighboring cells in a CDMA or spread spectrum communication system.  FIG. 2A  shows a diagram of cells for exemplary cellular spread spectrum communication system  200  comprising several cells including cell  203 , labeled “cell # 0 ” and cell  206 , labeled “cell # 1 .” Despite the use of power control within each cell, out-of-cell terminal units cause interference which is not under the control of the receiving base station within the cell. Thus, for example, power control within cell  203  can be affected by interference from the transmission to terminal units in cell  206  and vice versa. 
         [0017]    For example, in a mixed voice and data communication system, transmission of data within cell  203  can cause interference in a neighboring cell such as cell  206 . The interference in cell  206  causes increased power allocation to terminal units in cell  206 , which is in turn seen as increased interference in cell  203 . The increased interference in cell  203  can cause increased power allocation in cell  203 , which originally transmitted the data burst. Thus, there is a complete cycle of interaction between the power allocation in cell  203  and cell  206 , which resembles a positive feedback loop. The cycle of interaction between the power allocation in cell  203  and cell  206  can lead to higher power consumption than necessary in both cells. The increased power consumption in cell  203  and cell  206  can be seen as increased interference by other neighboring cells, so that the positive feedback effect spreads power control problems from cell  203  and cell  206  to other cells in the system. 
         [0018]    An example of feedback effect between two cells only, cell  203  and cell  206 , is shown in detail in  FIG. 2B  and  FIG. 2C .  FIG. 2B  shows graph  230 , having power axis  231  plotted against time axis  232 . The total transmit power for voice users within cell  203  is shown as aggregate voice power Pv  236  in graph  230 . Aggregate voice power Pv  236  varies in time as shown in graph  230 . Power for data burst transmission  237  is allocated in addition to aggregate voice power Pv  236 . Maximum power limit Pmax  234  that is allocated for the total of aggregate voice and data transmissions in cell  203  is indicated in graph  230  by horizontal solid line Pmax  234 . 
         [0019]      FIG. 2C  shows graph  260 , having power axis  261  plotted against time axis  262 . Time axis  262  of graph  260  is aligned vertically with time axis  232  of graph  230  so that points on time axis  262  in graph  260  align vertically below the simultaneous points on time axis  232  in graph  230 . The total transmit power for voice users within cell  206  is shown as aggregate voice power Pv  266  in graph  260 . Aggregate voice power Pv  266  varies in time as shown in graph  260 . Maximum power limit Pmax  264  that is allocated for the total of aggregate voice and data transmissions in cell  206  is indicated in graph  260  by horizontal solid line Pmax  264 . 
         [0020]    Continuing with  FIG. 2B  and  FIG. 2C , graph  230  of  FIG. 2B  shows that the total transmit power within cell  203  is represented by aggregate voice power curve Pv  236 , up until transmission of data burst  237 . During data burst  237 , the total transmit power within cell  203  is substantially equal to Pmax  234 . After data burst  237 , the total transmit power within cell  203  is again represented by aggregate voice power curve Pv  236 . Similarly, graph  260  of  FIG. 2C  shows that the total transmit power within cell  206  is represented by aggregate voice power curve Pv  266 . As discussed above, the power increase in cell  203 , from Pv  236  to approximately Pmax  234 , during data burst  237  is seen as increased interference by the users within cell  206 . The increased interference in cell  206  leads to higher power allocation by the power control system in cell  206 . The higher power allocation is reflected in increase  267  in aggregate voice power curve Pv  266 . Conversely, increase  267  in aggregate voice power in cell  206  is seen as increased interference by the users within cell  203  and leads to higher power allocation by the power control system in cell  203 . The higher power allocation by the power control system in cell  203  is reflected in increase  238  in aggregate voice power curve Pv  236 . 
         [0021]    The feedback process continues back and forth between cell  203  and  206  and can lead to a cell allocating the maximum transmit power available, as shown, for example, by maximum  268  in aggregate voice power curve Pv  266 . When all available transmit power has been allocated, such as at maximum  268  shown in graph  230  of  FIG. 2C , additional users can be denied access to the communication system. To the extent that additional users would have been able to access the communication system, system performance has been degraded. Further the communication link quality for the current users may also be degraded. As pointed out above, the effect can spread from cell to cell and is not restricted to the first pair of cells. Thus,  FIG. 2A ,  FIG. 2B , and  FIG. 2C  illustrate an example of some of the effects between cells of data transmission on power control in a CDMA or spread spectrum communication system. 
         [0022]    As noted above, mixed transmission of voice and data in a CDMA or spread spectrum communication system can subject the system to large swings or variations in the amount of transmission power consumed. For example, such large variation is shown in  FIG. 1  by aggregate power curve Pv+d  114 . As shown in  FIG. 1 , Pv+d  114  varies from approximately one half of limit of maximum power Pmax  112  to substantially all of Pmax  112 . Such large variation, comprising 50% of the maximum power, would be typical for mixed voice and data communication systems where half of the available power is allocated for voice transmission and half of the available power is allocated for data transmission. As seen in  FIG. 1  and in  FIG. 2A ,  FIG. 2B , and  FIG. 2C , the large variation can lead to over-allocation and under-allocation of power to each user and to the aggregate of all users within one cell or several cells in the communication system. The resulting instability of power control in the communication system can cause serious degradation of system performance including access problems and degradation of communication link quality for the users. 
         [0023]    Thus, there is a need in the art for transmitting mixed voice and data signals without causing abrupt large variations in power consumption. There is also a need in the art for transmitting mixed voice and data signals without causing sudden large reactions in power control. Further, there is need in the art for transmitting mixed voice and data signals without causing undue interference within a cell. Moreover, there is a need in the art for transmitting mixed voice and data signals without causing undue interference between cells. 
       SUMMARY 
       [0024]    The present invention is directed to a method for power control for mixed voice and data transmission. According to various embodiments of the invention, mixed voice and data signals are transmitted without causing abrupt large variations in power consumption or sudden large reactions in power control. Further, mixed voice and data signals are transmitted without causing undue interference within a cell or between cells. 
         [0025]    In one aspect of the invention, a “voice noise power” is added to an aggregate voice power which is the total voice power used by all users in a cell. The voice noise power is transmitted in addition to the aggregate voice power in order to maintain the total of the aggregate voice power and voice noise power at a pre-determined voice power limit. Since the aggregate voice power and the voice noise power are substantially maintained at a relatively steady level, i.e. at the voice power limit, power fluctuations within a cell and also in the neighboring cells are significantly diminished. The voice noise power can be, for example, artificial voice noise which is orthogonally coded or PN coded. In one embodiment, the voice power limit can be increased or decreased to further improve control over power consumption during voice and data transmission. 
         [0026]    Further, in order to maintain the power consumed by data transmission at a desired level, data noise is transmitted after transmission of a data burst, or in between data bursts, by inserting a pre-determined amount of artificial data into the gaps in data transmission. The data noise is transmitted in addition to the data bursts in order to maintain the total power consumed during data transmission at a desired level. For example, the data noise can be transmitted as artificial noise or dummy data, which is orthogonally coded or PN coded. Since the total power consumed during data transmission is substantially maintained at a desired level, power fluctuations within a cell and also in the neighboring cells are significantly diminished. In one embodiment, the desired level for data transmission power consumption can be increased or decreased to further improve control over power consumption during voice and data transmission. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  illustrates an example of power control for mixed voice and data transmission within one cell in a spread spectrum communication system. 
           [0028]      FIG. 2A  illustrates an example diagram of geographical layout of cells for a spread spectrum communication system. 
           [0029]      FIG. 2B  illustrates an example of power control graphed as a function of time for cell number  0  of  FIG. 2A . 
           [0030]      FIG. 2C  illustrates an example of power control graphed as a function of time, over the same time period as  FIG. 2B , for cell number  1  of  FIG. 2A . 
           [0031]      FIG. 3  illustrates an example of power control graphed as a function of time in accordance with one embodiment for a spread spectrum communication system. 
           [0032]      FIG. 4  also illustrates an example of power control graphed as a function of time in accordance with another embodiment for a spread spectrum communication system. 
           [0033]      FIG. 5  illustrates an example of power control graphed as a function of time in accordance with yet another embodiment for a spread spectrum communication system. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The presently disclosed embodiments are directed to a method for power control for mixed voice and data transmission. The following description contains specific information pertaining to the implementation of the present invention. One skilled in the art will recognize that the present invention may be implemented in a manner different from that specifically discussed in the present application. Moreover, some of the specific details of the invention are not discussed in order not to obscure the invention. The specific details not described in the present application are within the knowledge of a person of ordinary skill in the art. 
         [0035]    The drawings in the present application and their accompanying detailed description are directed to merely example embodiments of the invention. To maintain brevity, other embodiments of the invention which use the principles of the present invention are not specifically described in the present application and are not specifically illustrated by the present drawings. 
         [0036]      FIG. 3  illustrates an example of power control in a CDMA communication system in accordance with one embodiment. The general principles of CDMA communication systems, and in particular the general principles for generation of spread spectrum signals for transmission over a communication channel is described in U.S. Pat. No. 4,901,307 entitled “Spread Spectrum Multiple Access Communication System Using Satellite or Terrestrial Repeaters” and assigned to the assignee of the present invention. The disclosure in that patent, i.e. U.S. Pat. No. 4,901,307, is hereby fully incorporated by reference into the present application. Moreover, U.S. Pat. No. 5,103,459 entitled “System and Method for Generating Signal Waveforms in a CDMA Cellular Telephone System” and assigned to the assignee of the present invention, discloses principles related to PN spreading, Walsh covering, and techniques to generate CDMA spread spectrum communication signals. The disclosure in that patent, i.e. U.S. Pat. No. 5,103,459, is also hereby fully incorporated by reference into the present application. Further, the present invention may utilize time multiplexing of data and various principles related to “high data rate” communication systems, and the present invention can be used in a “high data rate” communication systems, disclosed in U.S. patent application entitled “Method and Apparatus for High Rate Packet Data Transmission” Ser. No. 08/963,386 filed on Nov. 3, 1997, and assigned to the assignee of the present invention. The disclosure in that patent application is also hereby fully incorporated by reference into the present application. 
         [0037]    Referring back to  FIG. 3 , graph  300  shows power axis  301  plotted against time axis  302 . Aggregate voice power Pv  304  for all the voice users within the cell is shown in graph  300  as solid curve  304 . Aggregate voice power Pv  304  varies in time as shown in graph  300 . Voice power limit Pv,max  306  is the maximum voice power allocated for the aggregate of voice signal transmissions. Voice power limit Pv, max  306  is shown in graph  300  as horizontal double-dotted-dashed line  306 . Extra voice power is allocated in addition to aggregate voice power Pv  304 , so that the total voice power transmitted at any time is substantially equal to voice power limit Pv, max  306 . The extra voice power, which “fills in” the gap between Pv  304  and Pv, max  306 , can be provided, for example, by transmitting some additional information which is encoded using orthogonal codes just as if the additional power were being provided for additional users. In the embodiment shown in  FIG. 3 , no useful information is transmitted, so the extra voice power is transmitted as artificial noise. It is manifest that useful information can be transmitted using the extra voice power, the details of which are apparent to a person of ordinary skill in the art, and thus are not described here. The artificial noise is shown in  FIG. 3  as voice noise power  308 , and also indicated with the word “noise.” Voice noise power  308  is encoded using, for example, orthogonal codes as if voice noise power  308  originated as an ordinary user signal. Thus, other users within the cell can still recover their own signal using spread spectrum despreading techniques such as orthogonal codes despite added voice noise power  308 . In other words, the users within the cell are “protected” from voice noise power  308  by the use of orthogonal codes or PN codes or other means of spreading voice noise power  308 . 
         [0038]    Continuing with  FIG. 3 , power is allocated in addition to voice power limit Pv,max  306  for transmission of data bursts  310 ,  312 , and  314 . Total power Pv+d  316  is the total of aggregate voice power Pv  304  plus the power allocated for voice noise power  308  plus the power allocated for transmission of data bursts  310 ,  312 , and  314 . Thus, total power Pv+d  316  may also be stated as the total of Pv, max  306  plus the power allocated for data burst transmissions. Data power Pdata  324  is the power used for transmission of data bursts  310 ,  312 , and  314 . Thus, by definition: 
         [0000]        Pv+d=P data+ Pv ,max. 
         [0000]    Total power Pv+d  316  is shown in graph  300  as dotted-dashed, stepped line  316 . Total power Pv+d  316  varies in time as shown in graph  300 . The maximum available signal transmission power that can be allocated for the total of aggregate voice, artificial noise, and data transmissions is maximum total power limit Pmax  318 , shown in graph  300  as horizontal solid line  318  and also indicated by “Pmax”. As seen in graph  300 , Pv+d  316  remains below maximum power limit Pmax  318 . 
         [0039]    As discussed above, transmission of data signals typically occurs in bursts, in contrast to transmission of voice signals, where the average power level for a number of users is relatively even. Thus, relatively large amounts of data are transmitted in bursts at high bit rates separated by periods of relative inactivity, or quiet, in which the data bit rate is low or data transmission ceases entirely. For example, after data burst  310  and before data burst  312 , and again after data burst  312  and before data burst  314 , there is no data available for transmission, i.e. there are gaps in the data transmission. In order to prevent total power Pv+d  316  from suddenly dropping, additional data power is transmitted when there are gaps in data transmission to maintain the power consumed by data transmission, data power Pdata  324 , at a desired level. Accordingly, total power Pv+d  316  is maintained at a desired level. 
         [0040]    The additional data power, which “fills in” the gap between data burst  310  and data burst  312 , and the gap between data burst  312  and data burst  314 , can be provided, for example, by transmitting some additional information which is encoded using orthogonal codes just as if the additional power were being provided for additional data users. In the embodiment shown in  FIG. 3 , no useful data is transmitted, so the additional data power is transmitted as artificial noise or dummy data. The artificial noise is shown in  FIG. 3  as data noise  320 , and data noise  322 . Data noise  320  and data noise  322  are encoded, for example, using orthogonal codes as if data noise  320  and data noise  322  originated as ordinary data signals. Thus, users within the cell can still demodulate their own signals without undue interference from data noise  320  and data noise  322 . In other words, the users within the cell are “protected” from data noise  320  and data noise  322  by the use of orthogonal codes or PN codes or other means of spreading data noise  320  and data noise  322 . 
         [0041]      FIG. 3  shows an example interaction of mixed voice and data signal transmission with power control in accordance with one embodiment. The amount of data power, Pdata  324 , allocated to data burst  310  is controlled as a percentage of voice power limit Pv, max  306  rather than allocating the full amount of power which might be required to transmit data burst  310  as quickly as possible. For initial data burst  310 , Pdata  324  is limited, for example, to 10% of Pv, max  306 . Then, for example, for subsequent data burst  312 , Pdata  324  is increased or adjusted upward by pre-determined amounts of 5% of Pv, max  306  as required to transmit the data at a reasonable rate. For example, Pdata  324  can be increased subject to specific conditions relating to the amount of data noise and actual data that have recently been transmitted. For example, the condition can be that the actual data transmitted, i.e. the amount of data transmitted in data burst  310 , is 95% or more of the total power transmitted and that the data noise transmitted is 5% or less of the total power transmitted. Conversely, Pdata  324  can be decreased or adjusted downward by pre-determined amounts, for example, when the actual data transmitted is 50% or less of the total power transmitted and the data noise transmitted is 50% or more of the total power transmitted. In general, the pre-determined and pre-defined amounts for the adjustments can be any amounts between 0% and approximately 15%; 5% and 10% are used only as examples for illustrative purposes. For subsequent data burst  314 , no further adjustments of Pdata  324  are required. As seen in the equation Pv+d=Pdata+Pv, max, total power Pv+d  316  is limited by the pre-determined increases in Pdata  324 . 
         [0042]    As shown in  FIG. 3 , filling Pv, max  306  with voice noise  308 ; increasing total power Pv+d  316  by pre-determined amounts; and filling in Pv+d  316  by inserting data noise such as data noise  320  between consecutive data bursts  310  and  312  have the effect of eliminating large swings, overshoots, and instability in the allocation of aggregate voice power Pv  304 . For example, filling in Pv+d  316  by inserting data noise such as data noise  320  between consecutive data bursts  310  and  312  prevents the overreactions of the power control system to large sudden changes in data power level, discussed in connection with  FIG. 1 , by eliminating such large sudden changes when there are gaps in the data transmission. As a result, aggregate voice power Pv  304  changes smoothly. Increasing total power Pv+d  316  by pre-determined amounts also results in eliminating large sudden changes when there are transitions from “quiet periods” to transmitting data bursts or when there are large increases in the rate or amount of data being transmitted by the communication system. Moreover, filling Pv, max  306  with voice noise  308  prevents the feedback effect between cells discussed in connection with  FIG. 2  by keeping the voice power, “seen” by other cells as noise, at a constant level, i.e. Pv, max  306 . Keeping the voice power at a constant level further prevents large swings in the voice power, such as those seen in  FIG. 2C , and thus prevents reactions of neighboring cells to those swings. As a result, the intra-cell power control problems discussed above in connection with  FIG. 1  are avoided, and the inter-cell power control problems discussed above in connection with  FIG. 2  are also avoided. 
         [0043]      FIG. 4  illustrates another example of power control in a CDMA communication system in accordance with one embodiment.  FIG. 4  shows graph  400 , having power axis  401  plotted against time axis  402 . Aggregate voice power Pv  404  for all voice users within the cell is shown in graph  400  as solid curve  404 . Aggregate voice power Pv  404  varies in time as shown in graph  400 . Voice power limit Pv,max  406  is the maximum voice power allocated for the aggregate of voice signal transmissions. Voice power limit Pv, max  406  is shown in graph  400  as double-dotted-dashed, stepped line  406 . Extra voice power is allocated in addition to aggregate voice power Pv  404 , so that the total voice power transmitted at any time is substantially equal to voice power limit Pv, max  406 . The extra voice power is voice noise power  408 , which “fills in” the gap between Pv  404  and Pv, max  406 . As discussed above, voice noise power  408  is typically provided by transmitting artificial noise which is coded or spread the same way as other user signals so that the users within a cell can recover their own signal using spread spectrum despreading techniques despite added voice noise power  408 . 
         [0044]    When no useful information is transmitted using voice noise power  408 , it is to the advantage of the system to minimize the amount of power consumed by voice noise power  408 .  FIG. 4  shows an example of adapting voice power limit Pv, max  406  in accordance with one embodiment. Adapting voice power limit Pv, max  406  has the effect of reducing the amount of power consumed by transmission of voice noise power  408 , for example, in comparison with voice noise power  308  in the example shown in  FIG. 3 . Adaptation of voice power limit Pv, max  406  can be achieved in many ways. For example, voice power limit Pv, max  406  can be adjusted to pre-set levels in response to a change in usage in order to reflect periods of greater or lesser usage. Usage can be measured according to various criteria. For example, usage can be measured as the percentage utilization of the total system capacity based on the number of users actually using the system at a particular time compared to the maximum number of users the system can accommodate. As another example, usage can be measured as the percentage utilization of available transmit power by comparing the value of aggregate voice power Pv  404  to the value of maximum power limit Pmax  418 , described below. The response to change in usage can be dynamic, or the response can be scheduled for certain times of day. Voice power limit Pv, max  406  can be set to a higher limit at the beginning of a “busy hour”, for example, and then reset to a lower limit at the end of the busy hour. 
         [0045]    Continuing with  FIG. 4 , power is allocated in addition to voice power limit Pv,max  406  for transmission of data bursts  410 ,  412 , and  414 . Total power Pv+d  416  is the total of aggregate voice power Pv  404  plus the power allocated for voice noise power  408  plus the power allocated for transmission of data bursts  410 ,  412 , and  414 . Thus, total power Pv+d  416  may also be stated as the total of Pv, max  406  plus the power allocated for data burst transmissions. Data power Pdata  424  is the power used for transmission of data bursts  410 ,  412 , and  414 . Thus, by definition: 
         [0000]        Pv+d=P data+ Pv ,max. 
         [0000]    Total power Pv+d  416  is shown in graph  400  as dotted-dashed, stepped line  416 . Total power Pv+d  416  varies in time as shown in graph  400 . The maximum available signal transmission power that can be allocated for the total of aggregate voice, artificial noise, and data transmissions is maximum total power limit Pmax  418 , shown in graph  400  as horizontal solid line  418  and also indicated by “Pmax”. As seen in graph  400 , Pv+d  416  remains below maximum power limit Pmax  418 . 
         [0046]    As discussed above, transmission of data typically occurs in bursts. In order to prevent total power Pv+d  416  from suddenly dropping, additional data power is transmitted when there are gaps in the data transmission to maintain the power consumed by data transmission, data power Pdata  424 , at a desired level. Accordingly, total power Pv+d  416  is maintained at a desired level. The additional data power, which “fills in” the gap between data burst  410  and data burst  412 , and the gap between data burst  412  and data burst  414 , is data noise  420  and data noise  422 . As discussed above, data noise  420  and data noise  422  can be provided by transmitting artificial noise or dummy data, which is coded or spread the same way as other user data signals. Thus, the users within the cell can recover their own signal using spread spectrum despreading techniques despite added data noise  420  and data noise  422 . 
         [0047]      FIG. 4  also shows an example interaction of mixed voice and data signal transmission with power control in accordance with one embodiment. The amount of data power, Pdata  424 , allocated to data burst  410  is controlled as a percentage of voice power limit Pv, max  406  rather than allocating the full amount of power which might be required to transmit data burst  410  as quickly as possible. For initial data burst  410 , Pdata  424  is limited, for example, to 10% of Pv, max  406 . Then, for example, for subsequent data burst  412 , Pdata  424  is increased by pre-determined amounts of 5% of Pv,max  406  as required to transmit the data at a reasonable rate. For example, Pdata  424  can be increased subject to specific conditions relating the amount of data noise and actual data that have recently been transmitted. For example, the condition can be that the actual data transmitted, i.e. the amount of data transmitted in data burst  410 , is 95% or more of the total power transmitted and that the data noise transmitted is 5% or less of the total power transmitted. In general, the pre-determined and pre-defined amounts for the adjustments can be any amounts between 0% and approximately 15%; 5% and 10% are used only as examples for illustrative purposes. For subsequent data burst  414 , no further adjustments of Pdata  424  are required. As seen in the equation Pv+d=Pdata+Pv, max, total power Pv+d  416  is limited by the pre-determined increases in both Pdata  424  and Pv, max  406 . 
         [0048]    As shown in  FIG. 4 , adapting voice power limit Pv, max  406 ; filling Pv, max  406  with voice noise  408 ; increasing total power Pv+d  416  by pre-determined amounts; and filling in Pv+d  416  by inserting data noise such as data noise  420  between consecutive data bursts  410  and  412  have the effect of eliminating large swings, overshoots, and instability in the allocation of aggregate voice power Pv  404 . For example, filling in Pv+d  416  by inserting data noise such as data noise  420  between consecutive data bursts  410  and  412  prevents the overreactions of the power control system to large sudden changes in data power level, discussed in connection with  FIG. 1 , by eliminating such large sudden changes when there are gaps in the data transmission. As a result, aggregate voice power Pv  404  changes smoothly. Increasing total power Pv+d  416  by pre-determined amounts also results in eliminating large sudden changes when there are transitions from “quiet periods” to transmitting data bursts or when there are large increases in the rate or amount of data being transmitted by the communication system. Moreover, filling Pv, max  406  with voice noise  408  prevents the feedback effect between cells discussed in connection with  FIG. 2  by limiting the voice power, “seen” by other cells as noise, to slow, smooth, gradual changes, i.e. Pv, max  406  is constrained to pre-defined adjustments. Limiting the voice power to gradual changes further prevents large swings in the voice power, such as those seen in  FIG. 2C , and thus prevents reactions of neighboring cells to those swings. 
         [0049]    As a result, the intra-cell power control problems discussed above in connection with  FIG. 1  are avoided, and the inter-cell power control problems discussed above in connection with  FIG. 2  are also avoided. Furthermore, adaptation of voice power limit Pv, max  406  improves the efficiency and the economy of power control in the communication system by minimizing the amount of extra power used for voice noise filling. 
         [0050]      FIG. 5  illustrates a further example of power control in a CDMA communication system in accordance with one embodiment.  FIG. 5  shows graph  500 , having power axis  501  plotted against time axis  502 . Aggregate voice power Pv  504  for all voice users within the cell is shown in graph  500  as solid curve  504 . Aggregate voice power Pv  504  varies in time as shown in graph  500 . Voice power limit Pv,max  506  is the maximum voice power allocated for the aggregate of voice signal transmissions. Voice power limit Pv, max  506  is shown in graph  500  as double-dotted-dashed, stepped line  506 . Extra voice power is allocated in addition to aggregate voice power Pv  504 , so that the total voice power transmitted at any time is substantially equal to voice power limit Pv, max  506 . The extra voice power is voice noise power  508 , which “fills in” the gap between Pv  504  and Pv, max  506 . As discussed above, voice noise power  508  is typically provided by transmitting artificial noise, which is coded or spread the same way as other user signals. Thus, the users within a cell can recover their own signal using spread spectrum despreading techniques despite added voice noise power  508 . 
         [0051]    When no useful information is transmitted using voice noise power  508 , it is to the advantage of the system to minimize the amount of power consumed by voice noise power  508 .  FIG. 5  shows an example of adapting voice power limit Pv, max  506  in accordance with one embodiment. Adapting voice power limit Pv, max  506  has the effect of reducing the amount of power consumed by transmission of voice noise power  508  in comparison with the case in which a voice power limit, such as voice power limit Pv, max  306  shown in  FIG. 3 , is not adapted. Adaptation of voice power limit Pv, max  506  can be achieved in many ways. For example, voice power limit Pv, max  506  can be adjusted to pre-set levels in response to a change in usage or at certain times of the day in order to reflect periods of greater or lesser usage. Voice power limit Pv, max  506  can be set to a higher limit at the beginning of a “busy hour”, for example, and then reset to a lower limit at the end of the busy hour. 
         [0052]    Continuing with  FIG. 5 , power is allocated in addition to voice power limit Pv,max  506  for transmission of data bursts  510 ,  512 , and  514 . Total power Pv+d  516  is the total of aggregate voice power Pv  504  plus the power allocated for voice noise power  508  plus the power allocated for transmission of data bursts  510 ,  512 , and  514 . Thus, total power Pv+d  516  may also be stated as the total of Pv, max  506  plus the power allocated for data burst transmissions. Data power Pdata  524  is the power used for transmission of data bursts  510 ,  512 , and  514 . Thus, by definition: 
         [0000]        Pv+d=P data+ Pv ,max. 
         [0000]    Total power Pv+d  516  is shown in graph  500  as dotted-dashed, stepped line  516 . Total power Pv+d  516  varies in time as shown in graph  500 . The maximum available signal transmission power that can be allocated for the total of aggregate voice, artificial noise, and data transmissions is maximum total power limit Pmax  518 , shown in graph  500  as horizontal solid line  518  and also indicated by “Pmax”. As seen in graph  500 , Pv+d  516  remains below maximum power limit Pmax  518 . 
         [0053]    As discussed above, transmission of data typically occurs in bursts. In order to prevent total power Pv+d  516  from suddenly dropping, additional data power is transmitted when there are gaps in the data transmission to maintain the power consumed by data transmission, data power Pdata  524 , at a desired level. Accordingly, total power Pv+d  516  is maintained at a desired level. The additional data power, which “fills in” the gap between data burst  510  and data burst  512 , is data noise  520 . Similarly, data noise  522  is transmitted to maintain the level of total power Pv+d  516  after the end of data burst  512 , although there is no data burst transmitted subsequent to the transmission of data noise  522 . It is wasteful, however, to continue transmission of data noise  522  for very long if there is no subsequent data to transmit or if the data transmission rate has fallen low enough that substantially less power should be allocated to data transmission. In other words, data power Pdata  524  should be reduced or adjusted to a lower level. 
         [0054]    Therefore, data noise  522  is transmitted subject to specific conditions relating the amount of data noise and actual data that have recently been transmitted. For example, the condition can be that the data noise transmitted is equal to or greater than the actual data transmitted. Then, if the amount of data noise  522  is equal to or greater than the amount of data transmitted in data burst  512 , then data power Pdata  524  will be reduced or decreased by a pre-determined amount to a lower level. For example, the pre-determined amount can be equal to 10% of voice power limit Pv, max  506 .  FIG. 5  shows data noise  523  transmitted at a level of data power Pdata  524 , which is reduce by 10% of voice power limit Pv, max  506  from the level of data noise  522 . In general, the pre-determined and pre-defined amounts for the adjustments can be any amounts between 0% and approximately 15%, and 5% and 10% are used as examples only for illustrative purposes. 
         [0055]    As no further data is transmitted, data power Pdata  524  continues to be reduced, for example, by a pre-determined amount equal to 10% of voice power limit Pv, max  506  for each reduction, during the transmission of data noise  523 . Thus, the example in  FIG. 5  shows a “stepped” appearance for data noise  523 . In addition, the example of  FIG. 5  shows voice power limit Pv, max  506  being reduced by amounts equal to approximately 10% of voice power limit Pv, max  506  during the transmission of data noise  523 . Thus, total power Pv+d  516 , which is the sum of data power Pdata  524  and voice power limit Pv, max  506 , is shown in graph  500  as decreasing during the transmission of data noise  523  in response to both the reductions in voice power and in data power. As seen in the equation Pv+d=Pdata+Pv, max, total power Pv+d  516  is limited by the pre-determined decreases in both Pdata  524  and Pv, max  506 . 
         [0056]    Data noise  520 , data noise  522 , and data noise  523  can be provided by transmitting artificial noise or dummy data, which is coded or spread the same way as other user data signals, as discussed above. Thus, the users within the cell can recover their own signals using spread spectrum despreading techniques despite added data noise  520 , data noise  522 , and data noise  523 . 
         [0057]    As shown in  FIG. 5 , adapting voice power limit Pv, max  506 ; filling Pv, max  506  with voice noise  508 ; reducing data power Pdata  524  in pre-determined amounts; and filling in Pv+d  516  by inserting data noise such as data noise  520  between consecutive data bursts  510  and  512  or by inserting data noise such as data noise  523  when reducing data power Pdata  524  have the effect of eliminating large swings, overshoots, and instability in the allocation of aggregate voice power Pv  504 . For example, filling in Pv+d  516  by inserting data noise such as data noise  520  between consecutive data bursts  510  and  512  prevents the overreactions of the power control system to large sudden changes in data power level, discussed in connection with  FIG. 1 , by eliminating such large sudden changes when there are gaps in the data transmission. As a result, aggregate voice power Pv  504  changes smoothly. Reducing total power Pv+d  516  by pre-determined amounts also results in eliminating large sudden changes when there are transitions from transmitting data bursts to “quiet periods” or when there are large decreases in the rate or amount of data being transmitted by the communication system. Moreover, filling Pv, max  506  with voice noise  508  prevents the feedback effect between cells discussed in connection with  FIG. 2  by limiting the voice power, “seen” by other cells as noise, to slow, smooth, gradual changes, i.e. Pv, max  506  is constrained to pre-defined adjustments. Limiting the voice power to gradual changes further prevents large swings in the voice power, such as those seen in  FIG. 2C , and thus prevents reactions of neighboring cells to those swings. 
         [0058]    As a result, the intra-cell power control problems discussed above in connection with  FIG. 1  are avoided, and the inter-cell power control problems discussed above in connection with  FIG. 2  are also avoided. Furthermore, adaptation of voice power limit Pv, max  506  improves the efficiency and the economy of power control in the communication system by minimizing the amount of extra power used for voice noise filling. In addition, limiting and reducing data power Pdata  524 , improves the efficiency and the economy of power control in the communication system by minimizing the amount of extra power used for data noise filling. 
         [0059]    It is appreciated by the above detailed disclosure that the invention provides a method and system of power control for mixed voice and data transmissions in a CDMA communication system. Although the invention is described as applied to communications in a CDMA system, it will be readily apparent to a person of ordinary skill in the art how to apply the invention in similar situations where power control for mixed voice and data signal transmission is needed. 
         [0060]    From the above description, it is manifest that various techniques can be used for implementing the concepts of the present invention without departing from its scope. Moreover, while the invention has been described with specific reference to certain embodiments, a person of ordinary skill in the art would recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. For example, the voice noise filling presented in one embodiment described here can be omitted so that data power is allocated directly on top of voice power without departing from the method of data noise filling and smoothly allocating data power presented in one embodiment described here. Also, for example, different techniques can be employed for measuring interference, transmitting artificial voice noise and artificial data noise, and adjusting the power allocated to the transmitted signal. Further, the type of information used for voice noise and data noise filling and the type of coding or spreading used may differ from that presented in one embodiment described here. The described embodiments are to be considered in all respects as illustrative and not restrictive. It should also be understood that the invention is not limited to the particular embodiments described herein, but is capable of many rearrangements, modifications, and substitutions without departing from the scope of the invention. 
         [0061]    Thus, a method for power control for mixed voice and data transmission has been described.