Abstract:
The present invention is a novel and improved method and system for communicating a frame of information according to a discontinuous transmit format. In particular, the present invention describes a method of transmitting eighth rate speech or data frames employing transmit gating and energy scaling which simultaneously reduces the battery usage of a variable rate wireless communication device, increases the capacity of the reverse link and provides reliable communication of the eighth rate frames. In the present invention, four methods are presented for transmitting an eighth rate data frame in which half of the frame is gated out and the remaining data is transmitted at nominal transmission energy to accomplish the aforementioned goals. In addition, a power control system in which identifies forward link power control bits that .1have been gated out by the remote station and inhibits adjustment of the transmission energy in response to that identification is disclosed.

Description:
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates to communications. More particularly, the present invention relates to a novel and improved method and apparatus for transmitting variable rate data in a wireless communication system. 
     II. Description of the Related Art 
     The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA) and frequency division multiple access (FDMA) are known in the art. However, the spread spectrum modulation techniques of CDMA have significant advantages over these modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS”, assigned to the assignee of the present invention, and incorporated by reference herein. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM”, assigned to the assignee of the present invention and incorporated by reference herein. 
     CDMA by its inherent nature of being a wideband signal offers a form of frequency diversity by spreading the signal energy over a wide bandwidth. Therefore, frequency selective fading affects only a small part of the CDMA signal bandwidth. Space or path diversity is obtained by providing multiple signal paths through simultaneous links from a mobile user through two or more cell-sites. Furthermore, path diversity may be obtained by exploiting the multipath environment through spread spectrum processing by allowing a signal arriving with different propagation delays to be received and processed separately. Examples of path diversity are illustrated in U.S. Pat. No. 5,101,501 entitled “METHOD AND SYSTEM FOR PROVIDING A SOFT HANDOFF IN COMMUNICATIONS IN A CDMA CELLULAR TELEPHONE SYSTEM”, and U.S. Pat. No. 5,109,390 entitled “DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM”, both assigned to the assignee of the present invention and incorporated by reference herein. 
     A method for transmission of speech in digital communication systems that offers particular advantages in increasing capacity while maintaining high quality of perceived speech is by the use of variable rate speech encoding. The method and apparatus of a particularly useful variable rate speech encoder is described in detail in U.S. Pat. No. 5,414,796, entitled “VARIABLE RATE VOCODER”, assigned to the assignee of the present invention and incorporated by reference herein. 
     The use of a variable rate speech encoder provides for data frames of maximum speech data capacity when the speech encoder is providing speech data at a maximum rate. When the variable rate speech encoder is providing speech data at a less than maximum rate, there is excess capacity in the transmission frames. A method for transmitting additional data in transmission frames of a fixed predetermined size, wherein the source of the data for the data frames is providing the data at a variable rate, is described in detail in U.S. Pat. No. 5,504,773, entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION”, assigned to the assignee of the present invention and incorporated by reference herein. In the above mentioned patent application a method and apparatus is disclosed for combining data of differing types from different sources in a data frame for transmission. 
     In frames containing less data than a predetermined capacity, power consumption may be lessened by transmission gating a transmission amplifier such that only parts of the frame containing data are transmitted. Furthermore, message collisions in a communication system may be reduced if the data is placed into frames in accordance with a predetermined pseudorandom process. A method and apparatus for gating the transmission and for positioning the data in the frames is disclosed in U.S. Pat. No. 5,659,569, entitled “DATA BURST RANDOMIZER”, assigned to the assignee of the present invention and incorporated by reference herein. 
     A useful method of power control of a mobile in a communication system is to monitor the power of the received signal from the wireless communication device at a base station. In response to the monitored power level, the base station transmits power control bits to the wireless communication device at regular intervals. A method and apparatus for controlling transmission power in this fashion is disclosed in U.S. Pat. No. 5,056,109, entitled “METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE SYSTEM”, assigned to the assignee Of the present invention and incorporated by reference herein. 
     In a communication system that provides data using a QPSK modulation format, very useful information can be obtained by taking the cross product of the I and Q components of the QPSK signal. By knowing the relative phases of the two components, one can determine roughly the velocity of the wireless communication device in relation to the base station. A description of a circuit for determining the cross product of the I and Q components in a QPSK modulation communication system is disclosed in U.S. Pat. No. 5,506,865, entitled “PILOT CARRIER DOT PRODUCT CIRCUIT”, assigned to the assignee of the present invention and incorporated by reference herein. 
     There has been an increasing demand for wireless communications systems to be able to transmit digital information at high rates. One method for sending high rate digital data from a wireless communication device to a central base station is to allow the wireless communication device to send the data using spread spectrum techniques of CDMA. One method that is proposed is to allow the wireless communication device to transmit its information using a small set of orthogonal channels. Such a method is described in detail in co-pending U.S. patent application Ser. No. 08/886,604, entitled “HIGH DATA RATE CDMA WIRELESS COMMUNICATION SYSTEM”, assigned to the assignee of the present invention and incorporated by reference herein. 
     In the just-mentioned application, a system is disclosed in which a pilot signal is transmitted on the reverse link (the link from the wireless communication device to the base station) to enable coherent demodulation of the reverse link signal at the base station. Using the pilot signal data, coherent processing can be performed at the base station by determining and removing the phase offset of the reverse link signal. Also, the pilot data can be used to optimally weigh multipath signals received with different time delays before being combined in a rake receiver. Once the phase offset is removed, and the multipath signals properly weighted, the multipath signals can be combined to decrease the power at which the reverse link signal must be received for proper processing. This decrease in the required receive power allows greater transmission rates to be processed successfully, or conversely, the interference between a set of reverse link signals to be decreased. 
     While some additional transmit power is necessary for the transmission of the pilot signal, in the context of higher transmission rates the ratio of pilot signal power to the total reverse link signal power is substantially lower than that associated with lower data rate digital voice data transmission cellular systems. Thus, within a high data rate CDMA system, the E b /N 0  gains achieved by the use of a coherent reverse link outweigh the additional power necessary to transmit pilot data from each wireless communication device. 
     However, when the data rate is relatively low, a continuously-transmitted pilot signal on the reverse link contains more energy relative to the data signal. At these low rates, the benefits of coherent demodulation and reduced interference provided by a continuously-transmitted reverse link pilot signal may be outweighed by the decrease in talk time and system capacity in some applications. 
     SUMMARY OF THE INVENTION 
     The present invention is a novel and improved method and system for communicating a frame of information according to a discontinuous transmit format. In particular, the present invention describes a method of transmitting eighth rate speech or data frames employing transmit gating and energy scaling which simultaneously reduces the battery usage of a variable rate wireless communication device, increases the capacity of the reverse link and provides reliable communication of the eighth rate frames. In the present invention, four methods are presented for transmitting an eighth rate data frame in which half of the frame is gated out and the remaining data is transmitted at nominal transmission energy to accomplish the aforementioned goals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein: 
     FIG. 1 is a functional block diagram of an exemplary embodiment of the transmission system of the present invention embodied in wireless communication device  50 ; 
     FIG. 2 is a functional block diagram of an exemplary embodiment of modulator  26  of FIG. 1; 
     FIGS. 3A-3G illustrate the energy used to transmit the variable rate frames t for four different data rates and including four alternative embodiments for transmitting an eighth rate frame; 
     FIG. 4 is a functional block diagram of selected portions of a base station  400  in accordance with the present invention; 
     FIG. 5 is an expanded functional block diagram of an exemplary single demodulation chain of demodulator  404  of FIG. 4; and 
     FIG. 6 is a block diagram illustrating the forward link power control mechanism of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a functional block diagram of an exemplary embodiment of the transmission system of the present invention embodied in wireless communication device  50 . It will be understood by one skilled in the art that the methods described herein could be applied to transmission from a central base station (not shown) as well. It will also be understood that various of the functional blocks shown in FIG. 1 may not be present in other embodiments of the present invention. The functional block diagram of FIG. 1 corresponds to an embodiment that is useful for operation according to the TIA/EIA Standard IS-95C, also referred to as IS-2000. Other embodiments of the present invention are useful for other standards including Wideband CDMA (WCDMA) standards as proposed by the standards bodies ETSI and ARIB. It will be understood by one skilled in the art that owing to the extensive similarity between the reverse link modulation in the WCDMA standards and the reverse link modulation in the IS-95C standard, extension of the present invention to the WCDMA standards is easily accomplished. 
     In the exemplary embodiment of FIG. 1, the wireless communication device transmits a plurality of distinct channels of information which are distinguished from one another by short orthogonal spreading sequences as described in the aforementioned U.S. patent application Ser. No. 08/886,604. Five separate code channels are transmitted by the wireless communication device: 1) a first supplemental data channel  38 , 2) a time multiplexed channel of pilot and power control symbols  40 , 3) a dedicated control channel  42 , 4) a second supplemental data channel  44  and 5) a fundamental channel  46 . The first supplemental data channel  38  and second supplemental data channel  44  carry digital data which exceeds the capacity of the fundamental channel  46  such as facsimile, multimedia applications, video, electronic mail messages or other forms of digital data. The multiplexed channel of pilot and power control symbols  40  carries pilots symbols to allow for coherent demodulation of the data channels by the base station and power control bits to control the energy of transmissions of the base station or base stations in communication with wireless communication device  50 . Control channel  42  carries control information to the base station such as modes of operation of wireless communication device  50 , capabilities of wireless communication device  50  and other necessary signaling information. Fundamental channel  46  is the channel used to carry primary information from the wireless communication device to the base station. In the case of speech transmissions, the fundamental channel  46  carries the speech data. 
     Supplemental data channels  38  and  44  are encoded and processed for transmission by means not shown and provided to modulator  26 . Power control bits are provided to repetition generator  22  which provides repetition of the power control bits before providing the bits to multiplexer (MUX)  24 . In multiplexer  24  the redundant power control bits are time multiplexed with pilot symbols and provided on line  40  to modulator  26 . 
     Message generator  12  generates necessary control information messages and provides the control message to CRC and tail bit generator  14 . CRC and tail bit generator  14  appends a set of cyclic redundancy check bits which are parity bits used to check the accuracy of the decoding at the base station and appends a predetermined set of tail bits to the control message to clear the memory of the decoder at the base station receiver subsystem. The message is then provided to encoder  16  which provides forward error correction coding upon the control message. The encoded symbols are provided to repetition generator  20  which repeats the encoded symbols to provide additional time diversity in the transmission. Following repetition generator certain symbols are punctured according to some predetermined puncturing pattern by puncturing element (PUNC)  19  to provide a predetermined number of symbols within the frame. The symbols are then provided to interleaver  18  which reorders the symbols in accordance with a predetermined interleaving format. The interleaved symbols are provided on line  42  to modulator  26 . 
     Variable rate data source  1  generates variable rate data. In the exemplary embodiment, variable rate data source  1  is a variable rate speech encoder such as described in aforementioned U.S. Pat. No. 5,414,796. Variable rate speech encoders are popular in wireless communications because their use increases the battery life of wireless communication devices and increases system capacity with minimal impact on perceived speech quality. The Telecommunications Industry Association has codified the most popular variable rate speech encoders in such standards as Interim Standard IS-96 and Interim Standard IS-733. These variable rate speech encoders encode the speech signal at four possible rates referred to as full rate, half rate, quarter rate or eighth rate according to the level of voice activity. The rate indicates the number of bits used to encode a frame of speech and varies on a frame by frame basis. Full rate uses a predetermined maximum number of bits to encode the frame, half rate uses half the predetermined maximum number of bits to encode the frame, quarter rate uses one quarter the predetermined maximum number of bits to encode the frame and eighth rate uses one eighth the predetermined maximum number of bits to encode the frame. 
     Variable rate date source  1  provides the encoded speech frame to CRC and tail bit generator  2 . CRC and tail bit generator  2  appends a set of cyclic redundancy check bits which are parity bits used to check the accuracy of the decoding at the base station and appends a predetermined set of tail bits to the control message in order to clear the memory of the decoder at the base station. The frame is then provided to encoder  4 , which provides forward error correction coding on the speech frame. The encoded symbols are provided to repetition generator  8  which provides repetition of the encoded symbol. Throughput repetition generator  8  is punctured with certain symbols by puncturing element  9  according to a predetermined puncturing pattern in order to provide a predetermined number of symbols within the frame. The symbols are then provided to interleaver  6 , which reorders the symbols in accordance with a predetermined interleaving format. The interleaved symbols are provided on line  46  to modulator  26 . 
     In the exemplary embodiment, modulator  26  modulates the data channels in accordance with a code division multiple access modulation format and provides the modulated information to transmitter (TMTR)  28 , which amplifies and filters the signal and provides the signal through duplexer  30  for transmission through antenna  32 . 
     In the exemplary embodiment, variable rate data source  1  sends a signal indicative to the rate of the encoded frame to control processor  36 . In response to the rate indication, control processor  36  provides control signals to transmitter  28  indicating the energy of the transmissions. 
     In IS-95 and cdma2000 systems, a 20 ms frame is divided into sixteen sets of equal numbers of symbols, referred to as power control groups (PCGs). The reference to power control is based on the fact that for each PCG, the base station receiving the frame issues a power control command in response to a determination of the sufficiency of the received reverse link signal at the base station. 
     FIGS. 3A-3C illustrate the transmission energy versus time (in PCGs) for the three transmission rates- full, half, and quarter. In addition, FIGS. 3D-3G illustrate four separate alternative embodiments for the transmission at eighth rate frames in which half of the time no energy is transmitted. Because there is much redundancy introduced into the frames that are of less than full rate, the energy at which the symbols are transmitted may be reduced in approximate proportion to amount of additional redundancy in the frame. 
     In FIG. 3A, for full rate frame  300 , each power control group PCG0 through PCG15 transmitted at energy E. For the sake, of simplicity the frames are illustrated as being transmitted at an equal energy for the duration of the frame. One skilled in the art will understand the energy will vary over the frame and that what is represented in FIGS. 3A-3G can be thought of as the baseline energy at which the frames would be transmitted absent external effects. In the exemplary embodiment, remote station  50  responds to closed loop power control commands from the base station and from internally generated open loop power control commands based on the received forward link signal. The responses to the power control algorithms will causes the transmission energy to vary over the duration of a frame. 
     In FIG. 3B, for half rate frame  302 , the energy is equal to half the predetermined maximum level, or E/2. This is represented in FIG. 3B The interleaver structure is such that it distributes the repeated symbols over the frame in such a way to attain maximum time diversity. 
     In FIG. 3C for quarter-rate transmission  304 , the frame is transmitted at approximately one-quarter of the predetermined maximum level, or E/4. 
     In the exemplary embodiment, during the transmission of full rate, half rate and quarter rate frames, the pilot signal is continuously transmitted. However, in FIGS. 3D-3G transmitter  28  gates the transmission of half of the frame. In the preferred embodiment, during the periods in which the traffic channel transmissions are gated off, the pilot channel is also gated off to reduce battery consumption and increase reverse link capacity. In each of the embodiments, the frames are transmitted at a 50% duty cycle in which half of the time the energy of the transmission is gated off. During the period in which the frame is transmitted, the energy is scaled to approximately the energy at which a quarter rate frame is transmitted E/4. However, the inventors have through extensive simulation, determined the preferred average or baseline energy at which the eighth rate frames should be transmitted for each of the alternative embodiments for transmitting eighth rate frames. These energies have been computed to maximize battery savings and reverse link capacity while maintaining the level of reliability of transmission. 
     In the first embodiment, illustrated in FIG. 3D, the frame is transmitted such that it is gated off at alternating 1.25 ms. intervals. Thus, transmitter  28  is initially gated off for the first 1.25 ms. The second power control group (PCG1) is transmitted then with energy E 1  during the second 1.25 ms. The third power control group (PCG2) is gated off. In this embodiment, all the odd PCGs (1, 3, 5, 7, 9, 11, 13, 15) are transmitted while all the even PCGs (0, 2, 4, 6, 8, 10,12, 14) are gated off. The puncturing structure discards half of the repeated symbols and provides approximately four versions of each transmitted symbol. In the preferred first embodiment, the symbols are transmitted at an average or baseline energy of 0.385E In the preferred embodiment, the gating of transmitter  28  is performed such that the last portions of the frame are not gated off. This is preferred because it allows for meaningful closed power control commands to be sent by the receiving base station to assist in reliable transmission of the subsequent frame. 
     In the second embodiment, which is the preferred embodiment of the present invention, illustrated in FIG. 3E, the frame is transmitted such that it is gated off at alternating 2.5 ms. intervals. The transmission method illustrated in FIG. 3E represents the preferred embodiment, because it results in optimum battery savings and reverse link capacity. During the first 2.5 ms. interval (PCG0 and PCG1) transmitter  28  is gated off. Then, transmitter  28  is gated on for next 2.5 ms (PCG2 and PCG3) and so on. I this embodiment PCGs 2, 3, 6, 7, 10, 11, 14, 15 are gated on, while PCGs 0, 1, 4, 5, 8, 9, 12, 13 are gated off. The puncturing structure is such that it discards exactly half of the repeated symbols during gate off in this embodiment. In the preferred second embodiment, the symbols are transmitted at an average or baseline energy of 0.32E. 
     In the third embodiment, illustrated in FIG. 3F, the frame is transmitted such that it is gated off at alternating 5.0 ms. intervals. During the first 5.0 ms. interval (PCG014 PCG3), transmitter  28  is gated off. Then, in the next 5.0 ms interval PCGs 4, 5, 6, 7 are transmitted and so on. In this embodiment PCGs 4, 5, 6, 7, 12, 13, 14, 15 are transmitted, while PCGs 0, 1, 2, 3, 8, 9, 10, 11 are gated off. The puncturing structure is such that it discards exactly half of the repeated symbols during gate off in this embodiment. In the preferred third embodiment, the symbols are transmitted at an average or baseline energy of 0.32E. 
     In the fourth embodiment, illustrated in FIG. 3G, the frame is transmitted such that it is gated off during the first 10 ms. In the next 10 ms interval PCGs 8 through 15 are transmitted. In this embodiment PCGs 8, 9, 10, 11, 12, 13, 14, 15 are transmitted, while PCGs 0, 1, 2, 3, 4, 5, 6, 7 are gated off. The interleaver structure is such that it discards exactly half of the repeated symbols during gate off in this embodiment. In the preferred second embodiment, the symbols are transmitted at an average or baseline energy of 0.335E. 
     FIG. 2 illustrates a functional block diagram of an exemplary embodiment of modulator  26  of FIG.  1 . The first supplemental data channel data is provided on line  38  to spreading element  52  which covers the supplemental channel data in accordance with a predetermined spreading sequence. In the exemplary embodiment, spreading element  52  spreads the supplemental channel data with a short Walsh sequence (++−). The spread data is provided to relative gain element  54  which adjusts the gain of the spread supplemental channel data relative to the energy of the pilot and power control symbols. The gain adjusted supplemental channel data is provided to a first summing input of summing element  56 . The pilot and power control multiplexed symbols are provided on line  40  to a second summing input of summing element  56 . 
     Control channel data is provided on line  42  to spreading element  58  which covers the supplemental channel data in accordance with a predetermined spreading sequence. In the exemplary embodiment, spreading element  58  spreads the supplemental channel data with a short Walsh sequence (++++++++−−−−−−−−). The spread data is provided to relative gain element  60  which adjusts the gain of the spread control channel data relative to the energy of the pilot and power control symbols. The gain adjusted control data is provided to a third summing input of summing element  56 . 
     Summing element  56  sums the gain adjusted control data symbols, the gain adjusted supplemental channel symbols and the time multiplexed pilot and power control symbols and provides the sum to a first input of multiplier  72  and a first input of multiplier  78 . 
     The second supplemental channel is provided on line  44  to spreading element  62  which covers the supplemental channel data in accordance with a predetermined spreading sequence. In the exemplary embodiment, spreading element  62  spreads the supplemental channel data with a short Walsh sequence (+−). The spread data is provided to relative gain element  64  which adjusts the gain of the spread supplemental channel data. The gain adjusted supplemental channel data is provided to a first summing input of summer  66 . 
     The fundamental channel data is provided on line  46  to spreading element  68  which covers the fundamental channel data in accordance with a predetermined spreading sequence. In the exemplary embodiment, spreading element  68  spreads the fundamental channel data with a short Walsh sequence (++++−−−−++++−−−−). The spread data is provided to relative gain element  70  which adjusts the gain of the spread fundamental channel data. The gain adjusted fundamental channel data is provided to a second summing input of summer  66 . 
     Summing element  66  sums the gain adjusted second supplemental channel data symbols and the fundamental channel data symbols and provides the sum to a first input of multiplier  74  and a first input of multiplier  76 . 
     In the exemplary embodiment, a pseudonoise spreading using two different short PN sequences (PN I  and PN Q ) is used to spread the data. In the exemplary embodiment the short PN sequences, PN I  and PN Q , are multiplied by a long PN code to provide additional privacy. The generation of pseudonoise sequences is well known in the art and is described in detail in aforementioned U.S. Pat. No. 5,103,459. A long PN sequence is provided to a first input of multipliers  80  and  82 . The short PN sequence PN I  is provided to a second input of multiplier  80  and the short PN sequence PN Q  is provided to a second input of multiplier  82 . 
     The resulting PN sequence from multiplier  80  is provided to the respective second inputs of multipliers  72  and  74 . The resulting PN sequence from multiplier  82  is provided to respective second inputs of multipliers  76  and  78 . The product sequence from multiplier  72  is provided to the summing input of subtractor  84 . The product sequence from multiplier  74  is provided to a first summing input of summer  86 . The product sequence from multiplier  76  is provided to the subtracting input of subtractor  84 . The product sequence from multiplier  78  is provided to a second summing input of summer  86 . 
     The difference sequence from subtractor  84  is provided to baseband filter  88 . Baseband filter  88  performs necessary filtering on the difference sequence and provides the filtered sequence to gain element  92 . Gain element  92  adjusts the gain of the signal and provides the gain adjusted signal to upconverter  96 . Upconverter  96  upconverts the gain adjusted signal in accordance with a QPSK modulation format and provides the unconverted signal to a first input of summer  100 . 
     The sum sequence from summer  86  is provided to baseband filter  90 . Baseband filter  90  performs necessary filtering on difference sequence and provides the filtered sequence to gain element  94 . Gain element  94  adjusts the gain of the signal and provides the gain adjusted signal to upconverter  98 . Upconverter  98  upconverts the gain adjusted signal in accordance with a QPSK modulation format and provides the upconverted signal to a second input of summer  100 . Summer  100  sums the two QPSK modulated signals and provides the result to transmitter  28 . 
     Turning now to FIG. 4, a functional block diagram of selected portions of a base station  400  in accordance with the present invention. Reverse link RF signals from the wireless communication device  50  (FIG. 1) are received by receiver (RCVR)  402 , which downconverts the received reverse link RF signals to a baseband frequency. In the exemplary embodiment, receiver  402  down converts the received signal in accordance with a QPSK demodulation format. The baseband signal is then demodulated by demodulator  404 . Demodulator  404  is further described with reference to FIG. 5 below. 
     The demodulated signal is provided to accumulator  405 . Accumulator  405  sums the symbol energies of the redundantly transmitted PCGs of symbols. The accumulated symbols energies are provided to de-interleaver  406  which reorders the symbols in accordance with a predetermined de-interleaving format. The reordered symbols are provided to decoder  408  which decodes the symbols to provide an estimate of the transmitted frame. The estimate of the transmitted frame is then provided to CRC check  410  which determines the accuracy of the frame estimate based on the CRC bits included in the transmitted frame. 
     In the exemplary embodiment, base station  400  performs a blind decoding on the reverse link signal. Blind decoding describes a method of decoding variable rate data in which the receiver does not know a priori the rate of the transmission. In the exemplary embodiment, base station  400  accumulates, deinterleaves and decodes the data in accordance with each possible rate hypothesis. The frame selected as the best estimate is based on quality metrics such as the symbol error rate, the CRC check and the Yamamoto metric. 
     An estimate of the frame for each rate hypothesis is provided to control processor  414  and a set of quality metrics for each of the decoded estimates is also provided. Quality metrics that may include the symbol error rate, the Yamamoto metric and the CRC check. Control processor selectively provides one of the decoded frames to the remote station user or declares a frame erasure. 
     Turning now to FIG. 5, an expanded functional block diagram of an exemplary single demodulation chain of demodulator  404 , described in FIG. 4 is shown. In the preferred embodiment, demodulator  404  has one demodulation chain for each information channel. The exemplary demodulator  404  of FIG. 5 performs complex demodulation on signals modulated by the exemplary modulator  26  of FIG.  1 . As previously described, receiver (RCVR)  402  downconverts the received reverse link RF signals to a baseband frequency, producing I and Q baseband signals. Despreaders  502  and  504  respectively despread the I and Q baseband signals using the long code from FIG.  1 . Baseband filters (BBF)  506  and  508  respectively filter the I and Q baseband signals. 
     Despreaders  510  and  512  respectively despread the I and Q signals using the PN I  sequence of FIG.  2 . Similarly, despreaders  514  and  516  respectively despread the Q and I signals using the PN Q  sequence of FIG.  2 . The outputs of despreaders  510  and  512  are combined in combiner  518 . The output of despreader  516  is subtracted from the output of despreader  512  in combiner  520 . 
     The respective outputs of combiners  518  and  520  are then Walsh-uncovered in Walsh-uncoverers  522  and  524  with the Walsh code that was used to cover the particular channel of interest in FIG.  2 . The respective outputs of the Walsh-uncoverers  522  and  524  are then summed over one Walsh symbol by accumulators  530  and  532 . 
     The respective outputs of combiners  518  and  520  are also summed over one Walsh symbol by Walsh chip summing elements  526  and  528 . The respective outputs of Walsh chip summing elements  526  and  528  are then applied to pilot filters  534  and  536 . Pilot filters  534  and  536  generate an estimation of the channel conditions by determining the estimated gain and phase of the pilot signal data  40  (see FIG.  1 ). The output of pilot filter  534  is then complex multiplied by the respective outputs of accumulators  530  and  532  in complex multipliers  538  and  540 . Similarly, the output of pilot filter  536  is complex multiplied by the respective outputs of accumulators  530  and  532  in complex multipliers  542  and  544 . The output of complex multiplier  542  is then summed with the output of complex multiplier  538  in combiner  546 . The output of complex multiplier  544  is subtracted from the output of complex multiplier  540  in combiner  548 . Finally, the outputs of combiners  546  and  548  are combined in combiner  550  to produce the demodulated signal, input to accumulator  405 , described in FIG.  4 . 
     A second aspect of the present invention is directed toward controlling forward link transmission energy in the face of potentially gated reverse link transmissions. Forward link performance is affected when the reverse link is in gated mode of operation. Forward link power control bit is punctured into reverse link pilot based on which the base station increases or decreases transmission power. Therefore when the reverse link is gated off 50% of the time, the actual forward link power control command is sent at 400 Hz instead of 800 Hz. However, the base station does not know a priori whether the mobile station is gated off. Therefore, in normal operation the base station will increase the power during the interval when mobile station is gated off. Stimulation shows that there is a performance degradation of about 1 dB when the base station is ignorant of the mobile station&#39;s transmission mode, rather than when the base station has knowledge that the mobile station is in gated mode and reacts to forward link power control commands that are sent on the reverse link pilot (400 Hz). Therefore, there should be a method by which the base station can detect the mobile station&#39;s transmission mode (gated/non gated). 
     One method of doing this is by defining a forward link power control bit erasure decision region. That is, when the dot product magnitude (summed over all combining fingers) is less than a threshold, decide erasure and keep forward power unchanged. In this way, the base station will react effectively to 400 Hz forward link power control sent over the reverse link pilot in the gated mode. 
     As described above, in the exemplary embodiment, the forward power control symbols are multiplexed into the pilot symbol stream. The demodulated pilot and power control symbols are provided to demultiplexer  412 , which separates out the power control bit energies and provides the power control bit energies to control processor  414 , as described in FIG.  4 . 
     Control processor  414  also receives the power control bit energies for other fingers of the reverse link signal provided from remote station  50 . From the summed energies from the different demodulated fingers, control processor  414  generates commands for controlling the transmission energy of the forward link signal and provides those commands to transmitter (TMTR)  420 . In the present invention control processor  414  detects when the reverse link frame has gated out the power control bits by comparing the summed energies of those bits to a threshold and if the summed energy is less than a threshold amount inhibiting closed loop power control response. 
     Forward link traffic data for transmission to the remote station  50  described in FIG. 1 is provided to forward traffic processing element  416 , which formats the data and encodes and interleaves the resultant frame of data. The processed frame of data is provided to modulator  418 . Modulator  418  modulates the data for transmission on the forward link. In the exemplary embodiment, the forward link signal is modulated in accordance with a CDMA modulation format and in particular with a cdma2000 or IS-2000 modulation format. 
     The modulated signal is provided to transmitter  420 , which upconverts, amplifies and filters the signal for transmission. The energy at which the signal is transmitted is determined in accordance with the control signal from control processor  414 . 
     FIG. 6 illustrates the operation performed by control processor  414 . The uncovered pilot and power control symbols from Walsh chip summing elements  526  and  528 , described in FIG. 5, are provided to demultiplexers  600  and  602 , which separate out the multiplexed power control symbol energies. The power control bit symbol energies from all of the fingers being demodulated are summed in finger combiner  604 . The summed energy is provided to threshold comparator  606 , which compares the summed energy to a predetermined threshold and outputs a signal indicative of the comparison. 
     If the energy of the power control bits is below the threshold value, then power control processor  608  determines that the forward link power control bit has been gated out and inhibits adjustment of the forward link transmission energy. If the energy of the power control bits is above the threshold value, then power control processor  608  determines that the forward link power control bit has not been gated out and adjusts the forward link transmission energy in accordance with the estimated value of the received power control bit. 
     The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.