Abstract:
A system determines if a primary paging channel should be received based on an examination of a quick paging channel. A first QPCH symbol is examined ( 102 ) and the normalized pilot energy is determined ( 104 ). If the normalized pilot energy is above a first threshold ( 106 ), the symbol is demodulated and the QPCH-symbol-to-pilot-energy ratio is determined ( 110 ) and compared against another threshold ( 114 ). If the normalized pilot energy is below the first threshold, the system proceeds to the second QPCH symbol immediately. Based on the two comparisons, a second QPCH signal is examined ( 108 ) or the system sleeps ( 116 ). If the second signal is examined, and if its normalized pilot energy is high enough, it also is demodulated and the ratio of the sum-of-the-combined-QPCH-symbols to the sum-of-the-combined-pilot-energies is determined ( 122 ). If this ratio exceeds a threshold ( 124 ), the primary paging channel is processed ( 120 ); otherwise the system sleeps ( 116 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to wireless communications systems. Specifically, the present invention relates to receivers for demodulating quick paging channels in communications systems employing more than one paging channel to facilitate offline processing. 
     2. Description of the Related Art 
     Wireless communications systems are employed in a variety of demanding applications ranging from search and rescue to Internet applications. Such applications require reliable, cost-effective, and space-efficient communications systems with accompanying wireless phones having maximum battery life and associated standby time. 
     Cellular telecommunications systems, such as Code Division Multiple access (CDMA) communications systems, are often characterized by a plurality of mobile stations (e.g. cellular telephones, mobile units, wireless telephones, or mobile phones) in communication with one or more Base Station Transceiver Subsystems (BTS&#39;s). Signals transmitted by the mobile stations are received by a BTS and often relayed to a Mobile Switching Center (MSC) having a Base Station Controller (BSC). The MSC, in turn, routes the signal to a Public Switched Telephone Network (PSTN) or to another wireless phone. Similarly, a signal may be transmitted from the Public Switched Telephone Network to a wireless phone via a base station or BTS and an MSC. 
     Wireless communications networks often employ various channels, such as paging channels and traffic channels, as disclosed in the IS-95 cellular telephone standard, to facilitate communications between a wireless phone and a BTS. Paging messages are transmitted over a paging channel by a BTS to an associated wireless phone to indicate an incoming call. When a wireless phone detects a paging message, a sequence of service negotiation messages is transmitted between the wireless phone and an associated BTS to establish a traffic channel. A traffic channel typically supports voice and data traffic. 
     Conventionally, a wireless telephone continuously monitors the paging channel for pages indicative of incoming calls. The receiver of the wireless phone remains on while signal processing circuitry within the wireless phone demodulates the paging channel to determine if a page was sent. Unfortunately, the receiver draws excess power, which significantly limits phone battery life. 
     Systems for minimizing wireless phone power consumption are often employed in the wireless phone and/or accompanying network to extend phone battery life, i.e., standby time. To improve standby time, some newer wireless phones operate in slotted mode. In slotted mode, the receiver of the wireless phone is periodically activated in accordance with predetermined paging slots established in accordance with the IS-95 telecommunications standard. An associated BTS transmits pages during the paging slots. Wireless phone standby time is extended by periodically powering-up the receiver and demodulating the paging channel rather than continuously demodulating the full paging channel as done previously. 
     Unfortunately, paging channel messages are often long and require extensive processing, which increases phone power consumption and reduces battery life and associated standby time. Furthermore, the design of such systems and the associated paging channels necessitates redundant processing of the lengthy paging channel messages to detect incoming calls. This further reduces phone battery life. 
     Further increases in phone standby time are achieved via a relatively new addition to the IS-95 telecommunications standard known as offline processing. In a wireless communications network employing offline processing, a pair of Quick Paging Channel (QPCH) symbols is periodically transmitted to the wireless phone. The quick paging channel symbols, i.e., quick pages, indicate the presence or absence of an incoming call to be established on a forthcoming traffic channel (F-CCCH). The QPCH symbols arrive in pairs at 9600 bits per second (bps) or 4800 bps. The time slots at which the QPCH symbols are transmitted from an associated BTS are known by the wireless phone, which periodically powers-up the receiver at corresponding time slots. 
     In a wireless phone employing offline processing, the wireless phone receiver powers-up, samples the QPCH, then immediately powers-down the receiver and processes the QPCH sample offline (when the receiver is off). Subsequent analysis of the QPCH sample or samples indicates whether the wireless phone should power-up the receiver and demodulate the paging channel to receive an incoming page associated with an incoming call. Use of the QCPH helps minimize receiver activation time and the instances of complete paging channel demodulation, enabling a reduction in wireless phone power consumption and an associated extension in phone battery life. Unfortunately, existing systems and methods for demodulating the QPCH and deciding whether or not to process the subsequent full paging channel based on the QPCH are undesirably large, expensive, consume excess power, and are generally inefficient. Furthermore, existing systems often fail to effectively employ the first symbol or both symbols of the QPCH as needed to effectively determine whether to process the forthcoming full paging channel. 
     Hence, a need exists in the art for an efficient and cost effective system and method for receiving and processing quick paging channel symbols to determine whether or not to process the forthcoming full paging channel. There exists a further need for an efficient system and method that selectively employs either one or both symbols of each quick paging channel slot, in accordance with the existing signal environment, to most efficiently and reliably detect the presence of an incoming page via minimal requisite hardware. 
     SUMMARY OF THE INVENTION 
     The need in the art is addressed by the efficient system for determining if a primary paging channel should be received and processed of the present invention. In the illustrative embodiment, the inventive system is adapted for use with a wireless communications device in a wireless communications system employing quick paging channel. The system includes a first mechanism for receiving an electromagnetic signal having pilot signal and quick paging signal components. A second mechanism ascertains whether a second symbol of the quick paging channel signal should be immediately analyzed based on a first quality parameter and a first decision metric associated with a first symbol of the quick paging signal and provides a first indication in response thereto. The first decision metric is representative of a value of the first symbol. A third mechanism determines, via the second symbol, whether the primary paging channel should be immediately processed based on a second quality parameter and a second decision metric associated with the second symbol. The third mechanism provides a second indication in response thereto when the first indication indicates that the second symbol should be immediately analyzed. 
     In a specific embodiment, the first quality parameter and the second quality parameter are based on a portion of the pilot signal associated with the first symbol and the second symbol, respectively. The first and second quality parameters are normalized pilot energies that are indicative of a quality of a signal environment in which the electromagnetic signal is propagating. The first decision metric is determined in accordance with the following metric (D 1 ):          D   1     =       Q                   P   1         E     pilot                 1                                
     where D 1  is the first decision metric; QP 1  is the dot product, cross product, or a combination thereof (depending on the mode of the transmission) of the first symbol with an estimate of the pilot signal associated with the first symbol; and E pilot1  is an energy of the pilot signal associated with the first symbol. 
     The second decision metric is the demodulation symbol (D) defined in accordance with one of the following equation:          D   =         Q                   P   1       +     Q                   P   2             E     pilot                 1       +     E     pilot                 2             ,                          
     where QP 2  is the dot product, cross product, or a combination thereof (depending on the mode of the mobile station) of the second symbol with an estimate of the pilot signal associated with the second symbol, and E pilot2  is an energy of the second portion of the pilot signal. 
     The novel design of the present invention is facilitated by the first mechanism and the second mechanism, which strategically process the first quick paging channel symbol and/or the second paging channel signal as needed. This avoids sometimes unnecessary processing of the second quick paging channel symbol, yet provides for a maximum probability of successful detection of a forthcoming primary paging channel and reduces or eliminates instances of redundant processing of the primary paging channel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of an exemplary wireless communications system constructed in accordance with the teachings of the present invention. 
     FIG. 2 is a more detailed diagram of the mobile station of FIG. 1 showing a unique quick paging channel (QPCH) combiner and QPCH detector constructed in accordance with the teachings of the present invention. 
     FIG. 3 is a flow diagram of a method implemented by the mobile station of FIG. 2 via the QPCH combiner, the QPCH memory, and the QPCH detector of FIG.  2 . 
    
    
     DESCRIPTION OF THE INVENTION 
     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
     FIG. 1 is a block diagram of an exemplary wireless communications system  10  for which the present invention is adapted. The system  10  includes a Mobile Switching Center (MSC)  12  having a Base Station Controller (BSC)  14 . A Public Switched Telephone Network (PSTN)  16  routes calls from telephone lines and other networks and communications devices (not shown) to and from the MSC  12 . The MSC  12  routes calls from the PSTN  16  to and from a first BTS  18  and a second BTS  20  associated with a first cell  22  and a second cell  24 , respectively. The BTS&#39;s  18  and  20  are often called cell controllers. 
     The MSC  12  routes calls between the BTS&#39;s  18  and  20 . The first BTS  18  directs calls to the first mobile station  26  within the first cell  22  via a first communications link  28 . The communications link  28  is a two-way link having a forward link  30  and a reverse link  32 . Typically, when the BTS  18  has established voice communications with the mobile station  26 , the link  28  is characterized as a traffic channel. While only two BTS&#39;s  18  and  20  are shown in FIG. 1, more BTS&#39;s or fewer BTS&#39;s may be employed without departing from the scope of the present invention. 
     When the mobile station  26  moves from the first cell  22  to the second cell  24 , the mobile station  26  is handed off to the second BTS  20 . Handoff typically occurs in an overlap region  36  where the first cell  22  overlaps the second cell  24 . In a soft handoff, the mobile station  26  establishes a second communications link  34  with the target BTS  20  in addition to the first communications link  28  with the source BTS  18 . During a soft handoff, both the first link  28  and the second link  34  are maintained simultaneously. After the mobile station  26  has crossed into the second cell  24 , it may drop the first communications link  28 . In a hard handoff, the communications link  34  is not established. When the mobile station  26  moves from the first cell  22  to the second cell  24 , the link  28  to the source BTS  18  is dropped and a new link is formed with the target BTS  20 . 
     FIG. 2 is a more detailed diagram of the wireless phone, i.e., mobile station  26  of FIG. 1 showing a unique Quick Paging Channel (QPCH) combiner (demodulation symbol (D) computer)  40  and QPCH detector  42  constructed in accordance with the teachings of the present invention. For clarity, various components are omitted from FIG. 2, such as Intermediate Frequency (IF) to baseband converters, mixers, downconverters, oscillators, timers, power supplies, and amplifiers, however those skilled in the art will know where and how to implement the additional requisite components. 
     The mobile station  26  includes a transceiver  44  having an antenna  46  that is connected to a duplexer  48 . The duplexer  48  is connected to an input of a CDMA receiver section  50  and to an output of a CDMA transmitter  52 . A baseband processor  54  is connected to the CDMA transceiver  44  and includes a controller  56 , a sample Random Access Memory (RAM)  58 , an interpolator  60 , a searcher  62 , a received energy estimator  64 , a despreader/decover circuit  66 , a Pilot Estimator (pilot filter)  68 , a pilot energy computation circuit  70 , a demodulator  72 , the QPCH combiner  40 , the QPCH page detector  42 , a Viterbi decoder  74 , QPCH memory  80 , and an encoder  76 . 
     The controller  56  is connected to a bus  78  that provides control input to the CDMA transmitter  52  and the CDMA receiver  50 . An output of the CDMA receiver  50  is a digital receive signal that is provided as input to the sample RAM  58  of the baseband processor  54 . An output of the sample RAM  58  is input to the interpolator  60 . An output of the interpolator  60  is connected to inputs of the searcher  62 , and the despreader/decover circuit  66 . An output of the searcher  62  represents peaks corresponding to candidate pilot signals, which are input to the controller software/circuitry  56 . A pilot output of the despreader/decover circuit  66  represents a pilot signal estimate(s) that has k in-phase (I pilot     k   ) and quadrature (Q pilot     k   ) signal components, one I pilot     k   , and Q pilot     k    component for each k th  multipath signal component. The pilot output of the despreader/decover circuit  66  provides input to the pilot estimator (pilot filter)  68 . The output of the pilot estimator  68  represents a filtered pilot estimate(s) and is input to the demodulator  72  and the pilot energy computation circuit  70 . An output of the pilot energy computation circuit  70  is connected to an input of the QPCH combiner  40 . The searcher  62  detects peaks corresponding to pilots. The peaks are provided to software running on the controller  56 , which then provides them to the combiner  40  for combining after application-specific processing. 
     Traffic/data channel, primary (full) paging channel, and QPCH channel outputs of the despreader/decover circuit  66  are input to the demodulator  72 . A dot product, cross product, and/or a (dot product+cross product) output, and a QPCH page output of the demodulator  72  are provided as input to the QPCH combiner  40 . The (dot product+cross product) output may be omitted and the sum computed in the QPCH combiner  40  rather than in the demodulator  72  without departing from the scope of the present invention. 
     Traffic and primary paging channel outputs of the demodulator  72  are provided as input to the Viterbi decoder  74  after further processing via subsystems (not shown) such as scaling circuits and de-interleaving circuits (see IS-95 specifications). An output of the decoder  74  is connected to an input of the controller  56 . The QPCH combiner  40  communicates with the page detector  42 , an output of which is connected to an input of the controller  56 . A QPCH memory  80  receives inputs from the QPCH combiner  40  and the controller software/circuitry  56  and provides output to the page detector  42 . 
     In operation, CDMA signals received via the antenna  46  are directed to the CDMA receiver  50  via the duplexer  48 . The CDMA receiver  50  includes radio frequency to intermediate frequency conversion circuitry (not shown) for mixing the received radio frequency signals (Rx) to intermediate frequency signals. Automatic Gain Control (AGC) circuitry (not shown) adjusts the total power of the received signal to a predetermined value. Additional frequency conversion circuitry (not shown) mixes the intermediate frequency signals to analog baseband signals, which are then converted to digital base band signals via an analog-to-digital converter (not shown). The digital baseband signals include In-phase (I), Quadrature (Q), and noise signal components. 
     Similarly, the CDMA transmitter  52  includes frequency conversion circuitry (not shown) for converting digital input signals (having in-phase and quadrature signal components) output from the encoder  76  to analog radio frequency signals in preparation for transmission via the antenna  46 . 
     The sample RAM  58  in the baseband processor  54  samples the digital baseband signals received from the CDMA receiver  50  at predetermined time slots. The sample RAM  58  maintains the samples in a buffer (not shown) for use by offline processing circuitry as discussed more fully below. The predetermined time slots at which the sample RAM  58  performs sampling of the received signal are determined in accordance with IS-95 telecommunications standards. The sample RAM  58  may be selectively bypassed when the mobile station  26  is not operating in slotted mode via an enable signal received from the controller  56 . Other systems and methods for selectively bypassing the sample RAM  58  may be employed without departing from the scope of the present invention. 
     The length of the signal sample taken by the sample RAM  58  is directly related to the size of the sample RAM  58 . The sample RAM  58  samples the signal environment, i.e., the received signal, to gather sufficient information pertaining to a QPCH of the received signal to facilitate offline processing. As discussed more fully below, the unique design of the present invention helps minimize the required size of the sample RAM  58 . 
     An output of the sample RAM  58  is connected to the interpolator  60 . The interpolator  60  upconverts a digital signal output from the sample RAM  58  to a higher digital frequency. In the present specific embodiment, the rate of the digital signal output from the sample RAM  58  is equivalent to the rate of the received digital signal, which is twice the chip rate. The interpolator  60  converts the rate of the digital signal to eight times the chip rate (CHIP×8). Those skilled in the art will appreciate that the exact rates of digital signals employed by the mobile station  26  are application-specific and may be determined by one skilled in the art to meet the needs of a given application. 
     When the sample RAM  58  has sampled the received signal, the interpolator  60  provides an up-converted digital signal having in-phase and quadrature signal components to the searcher  62  and the despreader/decover circuit  66 . The searcher  62  analyzes the received digital signal and outputs candidate pilot peaks (one peak for each multipath component) to the controller software/circuitry  56 . 
     In one embodiment of the present invention, the searcher  62  is implemented in accordance with the teachings of the U.S. Provisional Patent Application No. 60/176,478, entitled “EFFICIENT SYSTEM AND METHOD FOR FACILITATING QUICK PAGING CHANNEL DEMODULATION VIA AN EFFICIENT OFFLINE SEARCHER IN A WIRELESS COMMUNICATIONS SYSTEM”, filed Jan. 17, 2000, assigned to the assignee of the present invention and incorporated herein by reference. Alternatively, the searcher  62  may be implemented as a pilot despreader that may be constructed by one skilled in the art with access to the present teachings, without departing from the scope of the present invention. 
     The pilot estimator  68  may be implemented as a Finite Impulse Response Filter (FIR) or an Infinite Impulse Response Filter (IIR). The pilot estimator  68  filters noise from the noisy pilot signal provided by the searcher  62  and provides a pilot signal estimate ({circumflex over (P)}) in response thereto. The pilot signal estimate {circumflex over (P)} includes in-phase (I pilot     k   ) and quadrature (Q pilot     k   ) signal components associated with the k th  pilot multipath signal component and is represented by the following vector ({circumflex over (P)} k ): 
     
       
           {circumflex over (P)}   k =( I   pilot     k     , Q   pilot      k   ),  [1] 
       
     
     An additional subscript, such as 1 or 2 is added to specify whether a given signal component corresponds to a first symbol or a second symbol, respectively, of a slot of a received QPCH signal. For example, {circumflex over (P)} 1     k   =(I pilot1     k   , Q pilot1     k   ) refers to the k th  multipath pilot estimate associated with the first QPCH symbol. A pilot signal is associated with or corresponds to a QPCH symbol when the pilot signal is received approximately simultaneously with the QPCH symbol (if there is one) and is provided in the same signal sample of the sample RAM  58 . 
     The pilot signal estimate {circumflex over (P)} k  is provided to the demodulator  72  and the pilot energy computation circuit  70 . The pilot energy computation circuit  70  squares the pilot signal estimate {circumflex over (P)} k  and provides an estimate of the energy (E pilot     k   ) of the k th  pilot multipath signal component to the QPCH combiner  40 . The pilot energy E pilot     k    includes a first component E pilot1     k    associated with the first QPCH symbol of a QPCH slot and a second component E pilot2     k    associated with the second QPCH symbol of the QPCH slot. The QPCH combiner  40  includes an integrator (not shown) for summing the pilot energies E pilot1     k    and E pilot2     k    over the k pilot multipaths to yield E pilot1  and E pilot2 , respectively, in accordance with the following equations:                  E     pilot                 1       =       ∑   k          E     pilot                   1   k             ,           [   2   ]                   E     pilot                 2       =       ∑   k          E     pilot                   2   k             ,           [   3   ]                                
     where E pilot1     k    is the pilot energy associated with the k th  multipath signal component of the first QPCH symbol of a QPCH slot, and E pilot2     k    is the pilot energy associated with the k th  multipath signal component of the second QPCH symbol of the QPCH slot. 
     The despreader/decover circuit  66  includes a pseudo-noise despreader (not shown) and an M-ary Walsh decover circuit (not shown) for decovering a pilot channel, a data channel, a primary paging channel, and a QPCH from the received signal output from the interpolator  60 , if they exist in the received signal. M is 64 in the present embodiment. The decovered channels are provided to the demodulator  72 . 
     The demodulator  72  computes the dot product, cross product, or both (depending on the modulation format of the QPCH) between a QPCH signal received from the despreader/decover circuit  66  and the pilot estimate {circumflex over (P)} k  output from the pilot estimator  68 . In the present specific embodiment, the QPCH signal includes a slot having a first symbol and a second symbol defined in accordance with the IS-95 telecommunications standard. 
     The dot product (dot 1 ) of the first QPCH symbol (QPCH 1 ) with the corresponding pilot estimate {circumflex over (P)} 1     k    is defined in accordance with the following equation:                  dot   1     =       ∑   k          (         I     pilot                   1   k              I     QPCH                   1   k           +       Q     pilot                   1   k              Q     QPCH                   1   k             )         ,           [   4   ]                                
     where k is the number of available multipath components of the received signal; I pilot1     k    is the in-phase component of the pilot estimate associated with k th  multipath component of the first QPCH symbol of the slot; I QPCH1     k    is the in-phase component of the k th  multipath component of the first QPCH symbol; Q pilot1     k    is the quadrature component of the k th  multipath component of the pilot estimate associated with the first QPCH symbol; and Q QPCH1     k    is the quadrature component of the k th  multipath component of the first QPCH symbol of the QPCH signal. 
     Similarly, the dot product (dot 2 ) of the second QPCH symbol (QPCH 2 ) with the corresponding pilot estimate {circumflex over (P)} 2     k    is defined in accordance with the following equation:                  dot   2     =       ∑   k          (         I     pilot                   2   k              I     QPCH                   2   k           +       Q     pilot                   2   k              Q     QPCH                   2   k             )         ,           [   5   ]                                
     where the individual symbols are similar to those defined above for equation (4) but are associated with the second QPCH symbol of a slot rather than the first QPCH symbol of the slot. 
     Additional details of quick paging channels employed for the purposes of offline processing are disclosed in U.S. Pat. No. 6,111,865, issued Aug. 29, 2000, entitled DUAL CHANNEL SLOTTED PAGING, assigned to the assignee of the present invention and incorporated herein by reference. Further QPCH details are disclosed in copending U.S. patent application Ser. No. 09/252,846, filed Feb. 19, 1999, entitled A METHOD AND APPARATUS FOR MAXIMIZING STANDBY TIME USING A QUICK PAGING CHANNEL, assigned to the assignee of the present invention and incorporated herein by reference. 
     The demodulator  72  computes the first dot product (dot 1 ) associated with the first QPCH symbol, the second dot product (dot 2 ) associated with the second QPCH symbol, and/or the cross products cross 1  and cross 2  associated with the first and second QPCH symbols, respectively, and provides the results to the QPCH combiner  40 . The cross products cross 1  and cross 2  are defined in accordance with the following equations:                  cross   1     =       ∑   k          (         I     pilot                   1   k              Q     QPCH                   1   k           -       Q     pilot                   1   k              I     QPCH                   1   k             )         ,           [   6   ]                   cross   2     =       ∑   k          (         I     pilot                   2   k              Q     QPCH                   2   k           -       Q     pilot                   2   k              I     QPCH                   2   k             )         ,           [   7   ]                                
     where the individual symbols are as defined above for equations (4) and (5). 
     Whether the demodulator  72  computes dot products and/or cross products is application-specific and depends on the mode of the system  26 . For example, in 1 Multi-Carrier (1×MC) systems without Orthogonal Transmit Diversity (OTD) (1×MC non OTD), the demodulator  72  computes dot and cross products in accordance with equations (4) through (9) and outputs dot 1 +cross 1  and dot 2 +cross 2  to the QPCH combiner  40 . In 3 Multi-Carrier (3×MC) systems and in 1×MC systems with OTD, the demodulator  72  outputs dot products, cross products, or sums of dot and cross products depending on the needs of a given application. With reference to the present teachings, the appropriate demodulator output may be determined by one ordinarily skilled in the art to meet the needs of a given application. The additions of the dot and cross products (dot 1 +cross 1  and dot 2 +cross 2 ) may be performed in the QPCH combiner  40  without departing from the scope of the present invention. 
     The output of the demodulator  72  that is input to the QPCH combiner  40  is denoted QP 1  for outputs associated with the first QPCH symbol of a slot and QP 2  for outputs associated with the second QPCH symbol of a slot. Various outputs of the demodulator  72  for various system modes are summarized in the following table: 
     
       
         
               
               
               
             
           
               
                   
                                                       TABLE 1 
               
               
                   
                   
               
               
                   
                 Mode 
                 Quick Page Calculation (QP) 
               
               
                   
                   
               
             
             
               
                   
                 1xMC non OTD 
                 QP 1  = dot 1  + cross 1 , 
               
               
                   
                   
                 QP 2  = dot 2  + cross 2   
               
               
                   
                 1xMC OTD, or 3xMC 
                 QP 1  = dot 1 , cross 1 , or dot 1  + cross 1   
               
               
                   
                   
                 QP 2  = dot 2 , cross 2 , or dot 2  + cross 2   
               
               
                   
                   
               
             
          
         
       
     
     Alternatively, another combinative function of the pilot estimate and the first and second QPCH symbols may be provided to the QPCH combiner  40  in addition to or instead of the dot and/or cross products, without departing from the scope of the present invention. 
     The demodulator  72  may also provide a data/traffic signal, if available, to the Viterbi decoder  74  when the mobile station  26  is handling a call or other type of traffic channel. The decoder  74  may then decode the data/traffic signal, which may represent voice or another type of data, and forward the decoded signal to the controller  56 . The controller  56  employs various hardware and/or software modules (not shown) to route the decoded signals to a microphone or to another software or hardware function (not shown). 
     The QPCH combiner  40  computes a first decision parameter (CSI 1 ), which is the normalized pilot energy, and is described by the following equation:                  CSI   1     =       E     pilot                 1           I   ^       o                 1           ,           [   8   ]                                
     where CSI 1  is the normalized pilot energy associated with the first QPCH symbol of a slot; E pilot1  is the energy of the portion of the pilot signal summed over all multipath components and received simultaneously with the first QPCH symbol; Î o1  is the total energy of the portion of the received signal, including noise and interference, received simultaneously with the first QPCH symbol. 
     Similarly, the QPCH combiner  40  computes, as needed, a second decision parameter CSI 2  for the second QPCH symbol of a slot in accordance with the following equation:                  CSI   2     =       E     pilot                 2           I   ^       o                 2           ,           [   9   ]                                
     where the symbols are as described above for equation (10) but are associated with the second QPCH symbol of a slot. 
     In the present specific embodiment, Î o1  and Î o2  are predetermined via AGC circuitry and Gain Control Amplifiers (GCA&#39;s) (not shown) in the CDMA receive chain  50 , however, Î o1  and Î o2  may be estimated via energy estimators or determined via other mechanisms without departing from the scope of the present invention. 
     A third decision parameter D 1  is a novel decision metric representative of the value of the first QPCH symbol of the QPCH slot that is described by the following equation:                  D   1     =       Q                   P   1         E     pilot                 1           ,           [   10   ]                                
     where QP 1  and E pilot1  are as described above. Note that the decision parameter D 1  is not a function of Î o1  since received signals are gain controlled (via AGC circuitry) to a specific target level. 
     The QPCH combiner  40  sums the parameters CSI 1  and D 1  over all available multipath components and provides the results to the page detector  42  when requested by the page detector  42 , which behaves in accordance with a unique method of the resent invention as discussed more fully below. With access to the present teachings, those skilled in the art may build a QPCH combiner and page detector suitable for use with the present invention. 
     The QPCH combiner  40  employs the Quick Paging (QP) values QP 1  and QP 2 , the pilot energy estimates E pilot1  and E pilot2 , and received signal energy estimates Î o1  and Î o2  associated with the first and second QPCH symbols, respectively, to compute the demodulation symbol, i.e., decision metric D, when requested by the page detector  42 , in accordance with the following equation:                D   =         Q                   P   1       +     Q                   P   2             E     pilot                 1       +     E     pilot                 2             ,           [   11   ]                                
     where D incorporates both the first symbol and the second symbol of the received QPCH slot and is representative of the value, either on or off, of the QPCH page corresponding to the slot. The remaining parameters are as described above. 
     The page detector  42  selectively compares parameters CSI 1 , CSI 2 , D 1 , and D to predetermined thresholds to determine whether the mobile station  26  should subsequently power-up the CDMA receiver  50  to receive and process a forthcoming full page sent via the primary paging channel, as discussed more fully below. When the page detector  42  determines that a forthcoming full page should be received and processed based on one or more comparisons of the above parameters (CSI 1 , CSI 2 , D 1 , and D) with predetermined thresholds, an appropriate indication is sent to the controller  56  indicating that the CDMA receiver  50  should be activated in accordance with IS-95 standards to receive and demodulate an immediately forthcoming primary paging channel. The controller  56  then activates the CDMA receiver  50  and places the sample RAM  58  in bypass mode via control signals delivered via the bus  78  at a time corresponding to a slot during which the primary paging channel is to be received. The decoder  74  is automatically enabled via signaling information contained in the received signal. 
     When the mobile station  26  receives the full page on the primary paging channel, the page is despread via the despreader/decover circuit  66 , combined over multipath components via the demodulator  72 , and provided to the decoder  74 , where the page is decoded. Constituent page information is forwarded from the decoder  74  to the controller  56 . Software and/or hardware circuitry known in the art (not shown) within the controller  56  interprets the page. If the page indicates an incoming call associated with a forthcoming traffic channel, the controller  56  issues appropriate control commands to various modules within the mobile station  26  to prepare the mobile station  26  to handle the forthcoming traffic channel. 
     If the primary paging channel should not be processed based as determined from one or more of the parameters CSI 1 , CSI 2 , D 1 , and D, then an indication specifying that a full page on the primary paging channel is not forthcoming is sent to the controller  56 . The controller  56  then powers-down the transceiver section  44  and enters the mobile station  26  into a sleep state as defined in the IS-95 telecommunications standards. The QPCH is On-Off Keying (OOK) modulated, and the values of D 1  and D help indicate the presence or absence (on or off, respectively) of a forthcoming paging channel. 
     The mobile station  26  is equipped with a unique system, as discussed more fully below, substantially implemented via the QPCH combiner  40 , page detector  42 , and associated memory  80 , to facilitate the successful establishment of a traffic channel between the mobile station  26  and an associated wireless communications system (see FIG. 1) when a page is sent to the mobile station  26  via the wireless communications system indicating the presence of a forthcoming call. 
     FIG. 3 is a flow diagram of a method  100  implemented by the mobile station  26  of FIG. 2 via the QPCH combiner  40  and QPCH detector  42  of FIG.  2 . With reference to FIGS. 2 and 3, in an initial receiving step  102 , a digital received signal is output from the interpolator  60 . The received signal includes a pilot signal component and a QPCH signal component that includes a first QPCH symbol of a QPCH slot. The pilot estimator  68  outputs pilot signal components, corresponding to the first QPCH symbol, from the digital received signal and provides the pilot signal components to the pilot energy computation circuit  70 , which computes and sums the pilot energies over all available multipaths in accordance with equation (2) to yield E pilot1 . The resulting pilot energy E pilot1  is an estimate of the energy of the pilot signal associated with the first QPCH symbol. Subsequently, control is passed to a signal quality step  104 . 
     In the signal quality step  104 , a normalized pilot energy (CSI 1 ) associated with the first QPCH symbol is computed, which is a value representative of a quality of a portion of the digital received signal containing the first QPCH symbol. The CSI 1  is computed by dividing the pilot energy E pilot1  associated with the first symbol by the total energy of the received signal I o1  associated with the portion of the digital received signal containing the first QPCH symbol as defined in equation (8). Subsequently, control is passed to a first erasure-checking step  106 . 
     In the first erasure-checking step  106 , CSI 1 =E pilot1 /I o1  is compared to a predetermined erasure threshold T erasure  that is stored in the QPCH memory  80 . If CSI 1  is less than T erasure , then erasure is declared. When erasure is declared for the first symbol, the signal environment through which the received signal is propagating is determined to be of insufficient quality to rely on the value of the first metric (D 1 ) to determine whether to receive and process a forthcoming primary paging channel. 
     In the present specific embodiment, the predetermined erasure threshold T erasure  is stored in the QPCH memory  80  associated with the page detector  42 . Alternatively, the erasure threshold T erasure  may be provided by the controller  56  via a bus (not shown) and dynamically computed in response to a changing signal environment as indicated via the pilot energy output from the pilot energy computation circuit  70  and input to the controller  56 . 
     When erasure is declared in the first erasure-checking step  106 , control is passed to a second symbol step  108 . Otherwise, control is passed to a first demodulation step  110 . 
     In the first demodulation step  110 , the demodulator  72  provides the dot product (dot 1 ) between the first symbol of the QPCH page and the associated pilot signal (see equation (2)) to the QPCH combiner  40 . The pilot energy computation circuit  70  provides the energy of the pilot signal (E pilot1 ) associated with the first QPCH symbol to the QPCH combiner  40 . The QPCH combiner  40  then computes the first metric D 1  in accordance with equation (6). Subsequently, control is passed to a first on-off checking step  114 . 
     In the first on-off-checking step  114 , the first decision metric D 1  is compared to a first on-off threshold T 1/10 . If D 1  is less than T 1/10 , then control is passed to a sleep step  116 , where the transceiver  44  is powered-down and the mobile station  26  is placed in a sleep state. If D 1  is greater than T 1/10 , then control is passed to the second symbol step  108 . 
     In the second symbol step  108 , steps  102  and  104  are performed for the second QPCH symbol of the QPCH slot corresponding to the QPCH page of the received signal to yield values for QP 2  (see table (1)) and E pilot2 . The QPCH combiner  40  then computes CSI 2  by dividing QP 2  by E pilot2 . Subsequently, control is passed to a second erasure-checking step  118 . 
     In the second erasure-checking step  118 , CSI 2  is compared to the erasure threshold T erasure , which may be different from the corresponding erasure threshold employed in the first erasure-checking step  106  without departing from the scope of the present invention. If CSI 2  is less than T erasure , then control is passed to a primary paging step  120 , where the forthcoming primary paging channel is received and processed in accordance with IS-95 telecommunications standards. Otherwise, control is passed to a second demodulation step  122 . 
     In the second demodulation step  122 , the second symbol of the QPCH slot is processed via the QPCH combiner  40  in response to control commands received from the QPCH detector  42  to yield the decision metric D in accordance with equations (11). Those skilled in the art will appreciate that both the controller may provide such control commands  56  and the QPCH combiner  40  or only the controller  56  instead of by the QPCH combiner  40  without departing from the scope of the present invention. 
     Subsequently, control is passed to a second on-off-checking step  124 , where D is compared to a combined on-off threshold T 0/1combined . If D is larger than the combined on-off threshold T 0/1combined , then control is passed to the primary paging step  120 , where the forthcoming primary paging channel is received and processed. Otherwise, control is passed to the sleep step  116  and the mobile station  26  is placed in a sleep state. Hence, the present invention exploits diversity without compromising standby time. 
     The exact values of the various thresholds, such as the erasure threshold T erasure , the on-off threshold T 1/0 , and the combined on-off threshold T 0/0combined  are application-specific and may be determined by one skilled in the art to meet the needs of a given application. 
     Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications, and embodiments within the scope thereof. 
     It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.