Patent Publication Number: US-6219559-B1

Title: Two-way communication system for performing dynamic channel control

Description:
PRIOR APPLICATION 
     This application is a continuation of U.S. application Ser. No. 08/617,703 filed Apr. 1, 1996 by Hill et al., entitled “Two-Way Communication System for Performing Dynamic Channel Control” which is a continuation-in-part of U.S. patent application Ser. No. 08/493,041 U.S. Pat. No. 5,606,729 filed Jun. 21, 1995 and granted Feb. 25, 1997 by D&#39;Amico et al., entitled “Method and Apparatus for Implementing a Received Signal Quality Measurement in a Radio Communication System.” 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to two-way communication systems, and in particular to two-way communication systems performing dynamic channel control. 
     BACKGROUND OF THE INVENTION 
     Current two-way non-real-time communication systems utilize two-way messaging between a base transceiver and a plurality of selective call transceivers. When selective call transceivers experience communication problems due to noise interference, the base transceiver continues to attempt communication with the troubled selective call transceivers until a predetermined number of retries is exhausted. 
     Noise interference found in communication systems include co-channel interference, adjacent channel interference, and inherent noise in the receiver circuits of the selective call transceivers. Co-channel interference occurs from communication cells utilizing the same communication frequency. Adjacent channel interference is caused by power that is coupled between adjacent frequency channels. 
     In severe cases, selective call transceivers within the two-way communication system that experience noise interference cannot receive messages until the interference subsides, or the users of the selective call transceivers move to another location where the interference is less substantial. This situation usually results in message latencies that are inconsistent with customer expectations. 
     Thus, what is needed is a two-way communication system that dynamically adjusts signal quality of signals received by selective call transceivers experiencing noise interference. In particular, it is desirable that the noise interference be measured in such a manner that maintains system capacity as high as possible, while at the same time improving communication with selective call transceivers experiencing noise interference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an electrical block diagram of a two-way communication system according to the present invention. 
     FIG. 2 is an electrical block diagram of elements of a fixed portion of the two-way communication system according to the present invention. 
     FIG. 3 is an electrical block diagram of a selective call transceiver according to the present invention. 
     FIG. 4 is a coverage diagram of the two-way communication system comprising a plurality of coverage zones grouped in coverage zone clusters according to the present invention. 
     FIGS. 5 and 6 are first and second embodiments of a timing diagram of a plurality of predetermined synchronized signal quality measurement slots transmitted with the analog voice message according to the present invention. 
     FIG. 7 is a timing diagram representing instantaneous sampling of a plurality of values of pilot carrier power during transmission of the analog voice message, and the measurement thresholds used to determine the quality of the received analog voice message according to the present invention. 
     FIG. 8 is a timing diagram of elements of an outbound protocol and an inbound protocol of the fixed and portable portions of the two-way communication system according to the present invention. 
     FIGS. 9 and 10 are flow charts of the controller operation according to the present invention. 
     FIG. 11 is a flow chart of the selective call transceiver operation according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is an electrical block diagram of a communication system according to the present invention. The two-way communication system comprises a base transceiver  102  and a portable portion  104 . The base transceiver  102  includes a plurality of base stations  116 , for communicating with the portable portion  104 , utilizing conventional radio frequency (RF) techniques well known in the art, and coupled by communication links  114  to a controller  112  which controls the base stations  116 . As will be explained in more detail in connection with FIG. 4, a base transceiver  102  includes a plurality of base transmitters centrally controlled by the controller  112 . According to the present invention, signal quality adjustment of signals to be received by subscriber units (also called “selective call transceivers” herein) is made by the controller with respect to one or more base transmitters that either communicate with the subscriber unit or that affect the signal quality of signals received by the subscriber unit (for example co-channel interferers). 
     The hardware of the controller  112  is a combination of the Wireless Messaging Gateway (WMG™) Administrator! paging terminal, and the RF-Conductor!™ message distributor manufactured by Motorola, Inc. The hardware of the base stations  116  is a combination of the Nucleus® Orchestra! transmitter and RF-Audience!™ receivers manufactured by Motorola, Inc. It will be appreciated that other similar hardware can be utilized for the controller  112  and the base stations  116 . 
     Each of the base stations  116  transmits RF signals to the portable portion  104  comprising a plurality of selective call transceivers  122  via a transmitting antenna  120 . The base stations  116  each receive RF signals from the plurality of selective call transceivers  122  via a receiving antenna  118 . The RF signals transmitted by the base stations  116  to the selective call transceivers  122  (outbound messages) comprise selective call addresses identifying the selective call transceiver  122 , and data or voice messages originated by a caller. The RF signals transmitted by the selective call transceivers  122  to the base stations  116  (inbound messages) comprise positive acknowledgments (ACKs) which indicate the message was received reliably by the selective call transceiver  122 , or negative acknowledgments (NAKs) which indicate the selective call transceiver  122  did not receive the message reliably. 
     A detailed description of inbound acknowledge-back messaging is more fully described in U.S. Pat. No. 4,875,038 issued Oct. 17, 1989 to Siwiak et al., which is hereby incorporated herein by reference. 
     The controller  112  is coupled by telephone links  101  to a public switched telephone network (PSTN)  110  for receiving selective call originations therefrom. Selective call originations comprising voice and data messages from the PSTN  110  can be generated, for example, from a conventional telephone  111  coupled to the PSTN  110  in a manner that is well known in the art. 
     Voice messages transmitted by the base stations  116  utilize mixed signaling techniques. A voice message includes a digital message portion and an analog message portion. The digital message portion includes at least the addressing information which is used to identify the selective call transceiver  122 , and a message vector identifying the location of the analog message. 
     The outbound and inbound messages are, for example, similar to Motorola&#39;s well-known InFLEXion™ digital selective call signaling protocol. This protocol utilizes well-known error detection and error correction techniques and is therefore tolerant to bit errors occurring during transmission, provided that the bit errors are not too numerous in any one code word. 
     Outbound channel transmissions of the digital message portion transmitted by the base stations  116  utilize two and four-level frequency shift keyed (FSK) modulation, operating at sixteen hundred or thirty two hundred symbols-per-second (sps), depending on traffic requirements and system transmission gain. Outbound channel transmissions of the analog message portion transmitted by the base stations  116  utilize single side band (SSB) transmission. A voice message comprises an upper side band (USB), a lower side band (LSB) and a pilot carrier. It will be appreciated that, alternatively, a voice message can comprise the pilot carrier and a single one of the sidebands. A detailed explanation of the preferred analog voice messaging system can be found in application Ser. No. 08/395,747 filed Feb. 28, 1995 by Leitch et al., which is hereby incorporated herein by reference. 
     Inbound channel transmissions from the selective call transceivers  122  to the base stations  116  utilize four-level FSK modulation at a rate of eight hundred bits per second (bps). Inbound channel transmissions occur during predetermined data packet time slots synchronized with the outbound channel transmissions. The outbound and inbound channels operate on separate carrier frequencies utilizing frequency division multiplex (FDM) techniques well known in the art. A detailed description of FDM techniques is more fully described in U.S. Pat. No. 4,875,038 issued to Siwiak et al. It will be appreciated that, alternatively, the outbound and inbound channels can operate on a single carrier frequency using time division duplex (TDD) techniques as described more fully in U.S. Pat. No. 5,168,493 issued to Nelson et al. It will be further appreciated that, alternatively, other signaling protocols, modulation schemes, and transmission rates can be utilized for either or both transmission directions. 
     FIG. 2 is an electrical block diagram of elements of the base transceiver  102  according to the present invention. The base transceiver  102  comprises portions of the controller  112  and the base stations  116 . The controller  112  comprises a processing system  210  for directing operation of the controller  112 . The processing system  210  is coupled through a transmitter controller  204  to a base transmitter  202  via the communication links  114 . The communication links  114  use conventional means well known in the art, such as a direct wire line (telephone) link, a data communication link, or any number of radio frequency links, such as a radio frequency (RF) transceiver link, a microwave transceiver link, or a satellite link, just to mention a few. 
     The base transmitter  202  transmits two and four-level FSK data messages to the selective call transceivers  122  during a digital message portion. A lower sideband (LSB), upper sideband (USB) and a pilot are transmitted by the base transmitter during the analog message portion for voice messages. The processing system  210  is also coupled to at least one base receiver  206  through a receiver interface  208  via the communication links  114 . The base receiver  206  demodulates four-level FSK and is collocated with the base stations  116 , as implied in FIG. 2, but can be positioned remote from the base stations  116  to avoid interference from the base transmitter  202 . The base receiver  206  is for receiving one or more acknowledgments (ACKs or NAKs) from the selective call transceivers  122 . 
     The processing system  210  is also coupled to an input interface  218  for communicating with the PSTN  110  through the telephone links  101  for receiving selective call originations. In order to perform the functions (to be described below) necessary in controlling the elements of the controller  112 , as well as the elements of the base stations  116 , the processing system  210  includes a conventional computer system  212 , and conventional mass storage media  214 . The conventional mass storage media  214  includes, for example, subscriber user information such as, addresses for selective call transceivers  122 , programming options, and signal quality measurements received from the selective call transceivers  122  as will be described below. The conventional computer system  212  is programmed by way of software included in the conventional mass storage media  214 . 
     The conventional computer system  212  comprises a plurality of processors such as, for example, VME Sparc™ processors manufactured by Sun Microsystems, Inc. These processors include memory such as dynamic random access memory (DRAM), which serves as a temporary memory storage device for scratch pad processing such as, for example, storing messages originated by callers using the PSTN  110 , processing acknowledgments received from the selective call transceivers  122 , and for protocol processing of messages destined for the selective call transceivers  122 , just to mention a few. The conventional mass storage media  214  is a conventional hard disk mass storage device. 
     It will be appreciated that other types of conventional computer systems  212  can be utilized, and that additional computer systems  212  and mass storage media  214  of the same or alternative type can be added as required to handle the processing requirements of the processing system  210 . 
     FIG. 3 is an electrical block diagram of the selective call transceiver  122  according to the present invention. The selective call transceiver  122  comprises a transmitter antenna  302  for transmitting RF signals to the base stations  116  and a receiver antenna  305  for intercepting RF signals from the base stations  116 . The transmitter antenna  302  is coupled to a transmitter  304  that utilizes conventional techniques well known in the art. Similarly, the receiver antenna  305  is coupled to a receiver  306  for receiving RF signals from the base stations  116 . The RF signals received from the base stations  116  use conventional two and four-level FSK. The RF signals transmitted by the selective call transceiver  122  to the base stations  116  use four-level FSK. 
     Radio signals received by the receiver  306  produce demodulated information at the output. The demodulated information is coupled to the input of a processor  310 , which processes outbound messages. Similarly, inbound acknowledgment messages are processed by the processor  310  and delivered to the transmitter  304  for transmission. A conventional power switch  308 , coupled to the processor  310 , is used to control the supply of power to the transmitter  304  and the receiver  306 , thereby providing a battery saving function. 
     To perform the necessary functions of the selective call transceiver  122 , the processor  310  includes a microprocessor  316 , a RAM  312 , a ROM  314 , an EEPROM  318 , and a digital to analog converter (DAC)  311 , and an analog to digital converter (ADC)  313 . The RAM  312 , the ROM  314 , and the EEPROM  318  comprise the elements of a memory of the processor  310 . The microprocessor  316  is similar to the DSP 56100  digital signal processor (DSP) manufactured by Motorola, Inc. It will be appreciated that other similar processors can be utilized for the microprocessor  316 , and that additional processors of the same or alternate type can be added as required to handle the processing requirements of the processor  310 . It will be appreciated that other types of memory, e.g., EEPROM or FLASH, can be utilized for the ROM  314 , as well as the RAM  312 . It will be further appreciated that the RAM  312  and the ROM  314 , singly or in combination, can be integrated as a contiguous portion of the microprocessor  316 . 
     The microprocessor  316  is programmed by way of the ROM  314  to process received outbound messages, and in response thereto for creating and formatting inbound messages. During outbound message processing, the microprocessor  316  samples the demodulated signal generated by the receiver  306  by way of the ADC  313 . The microprocessor  316  then decodes an address in the demodulated data of the outbound message, compares the decoded address with one or more addresses stored in the EEPROM  318 , and when a match is detected, the microprocessor  316  proceeds to perform a signal quality measurement on the signals of the outbound message transmitted by the base transmitter  202 . 
     A preferred method for performing signal quality measurements is disclosed in co-pending and commonly assigned U.S. application Ser. No. 08/493,041 filed Jun. 21, 1995 by D&#39;Amico et al., entitled “Method and Apparatus for Implementing a Received Signal Quality Measurement in a Radio Communication System,” which is incorporated herein by reference. A description of relevant portions of this method is provided herein. 
     Specifically, the ROM  314  includes a power measurement element  315  which instructs the microprocessor  316  in the procedure for performing signal quality measurements during message processing. It will be appreciated that, alternatively, a hardware power measurement element  303  included in the receiver  306  can be used to replace the software implemented power measurement element  315 . The hardware power measurement element  303  is one or more received signal strength indicators (RSSI) functionally similar to, for example, the MC13135 RSSI device manufactured by Motorola, Inc. Note each RSSI device measures the mean RMS signal power for the pilot carrier and USB or LSB signals. 
     Once the signal quality measurement has been determined, the selective call transceiver  122  proceeds to send a NAK response message to the base stations  116  along with the signal quality measurement data if the quality of signals measured by the selective call transceiver  122  are below a predetermined minimum quality threshold. For signal quality measurements above the minimum quality threshold, the selective call transceiver  122  sends an ACK to the base stations  116 . In an alternative embodiment, the ACK message is accompanied with the signal quality measurement data. Subsequently, the selective call transceiver  122  processes the outbound message sent by the base station  116 . 
     In yet another alternative embodiment, the selective call transceiver  122  can transmit signal quality measurement data during any inbound message transaction. This transaction could be, for example, an unscheduled inbound message transaction initiated by the selective call transceiver  122  in response to a communication request by the user of the selective call transceiver  122  with the base transceiver  102 . 
     Once the microprocessor  316  has processed the message, it stores the message in the RAM  312 , and a call alerting signal is generated to alert a user that a message has been received. The call alerting signal is directed to a conventional audible or tactile alerting device  322  for generating an audible or tactile call alerting signal. In addition, the microprocessor  316  is programmed to send the ACK or NAK depending on the quality of the received message. To send the acknowledgment, the microprocessor  316  utilizes the DAC  311  to modulate the transmitter with the FSK data corresponding to the acknowledgment messages. 
     The message can be accessed by the user through user controls  320 , which provide functions such as lock, unlock, delete, read, etc. More specifically, by the use of appropriate functions provided by the user controls  320 , the message is recovered from the RAM  312 , and then displayed on a display  324 , e.g., a conventional liquid crystal display (LCD), or played out audibly, in the case of a voice message, by the combination of an audio amplifier  326  and a speaker  328 . 
     FIG. 4 is a coverage diagram of the two-way communication system comprising a plurality of coverage zones  402  grouped in coverage zone clusters  404  according to the present invention. The coverage zone clusters  404  comprise twelve coverage zones  402 . It will be appreciated that, alternatively, more or less coverage zones  402  can be used in the coverage zone clusters  404 . Each coverage zone  402  within the coverage zone cluster  404  includes a base station  116  (e.g., BS 1 ). In this example, base station  116  BS 1  within the coverage zone  402  has a corresponding set of base stations  116  BS 2 , BS 3 , BS 4 , BS 5 , BS 6 , and BS 7  within coverage zones  402  of different coverage zone clusters  404  which transmit messages utilizing the same subchannel frequency. 
     Thus, base stations  116  BS 2 , BS 3 , BS 4 , BS 5 , BS 6 , and BS 7  are first tier co-channel interferers of BS 1 . The co-channel interference is shown with solid arrows pointed into BS 1  from each of the base stations  116  BS 2 , BS 3 , BS 4 , BS 5 , BS 6 , and BS 7 . In addition to co-channel interference, transmissions from BS 1  also suffer from adjacent channel interference (shown with a dashed arrow) from base stations  116  in other coverage zones  402  which utilize adjacent subchannel frequencies. Additionally, ambient noise (shown with a dashed arrow) such as, for example, Gaussian white noise spread throughout the two-way communication system also contributes to the degradation of signals transmitted by BS 1 . From the point of view of a selective call transceiver  122  located within the coverage zone  402  of BS 1 , transmitted signals from BS 1  are further degraded by the inherent noise of the receiver  306 . It is expected that co-channel interference is the most significant contributor to the degradation of signals transmitted by BS 1 . 
     Normally in mixed signaling systems utilizing digital and analog transmission of voice messages, distortion in the transmitted message can be detected in the digital message portion with error detection or correction codes well known in the art. For the analog message portion, however, distortion in the transmitted message cannot readily be detected without some form of a signal quality measurement. FIG. 5 is a timing diagram of a first embodiment of a plurality of predetermined synchronized signal quality measurement (SQM) slots transmitted with an analog voice message in accordance with the present invention. 
     An analog voice message comprises one or more voice fragments. Within each voice fragment an SQM period is reserved for measurements that assist in predicting the signal quality of a received analog voice message. The SQM period comprises SQM slots (SQM 1  through SQM 8  shown by way of example). The SQM slots are transmitted proximate the voice fragment, e.g., before or after the voice fragment and within the same protocol frame as the voice fragment. It will be appreciated that the SQM slots can be transmitted in other positions as well, such as within the voice fragment. 
     The SQM period is 30 ms in duration, and the SQM slots are 7.5 ms in duration. It will be appreciated that, alternatively, the SQM period and SQM slot duration can be of greater or lesser length than specified depending on the application. Each SQM slot represents analog transmission of an USB, or a LSB and an associated pilot carrier. In addition, each base station  116  is assigned to a side band corresponding to each SQM slot (BS 1 , through BS 7  shown by way of example). The SQM slot assigned to each base station  116  is defined as a home silence slot. Base stations  116  BS 1 , BS 3 , BS 5 , and BS 7  are assigned to the USB silence slots while base stations  116  BS 2 , BS 4 , and BS 6  are assigned to the LSB silence slots. In this example, there is no base station  116  represented by SQM 8 , thus all base stations  116  transmit a tone in SQM 8 , as described further below. 
     In the first embodiment of the present invention, the base stations  116  transmit a tone (e.g., 1 KHz) in all SQM slots excluding their home silence slot. In this embodiment only SQM slots  1  through  8  are utilized. In this method, a selective call transceiver  122  in the coverage zone  402  of BS 1  in the SQM slot assigned to BS 1  receives a tone signal from BS 2  through BS 8 . Similarly, in the silence slot assigned to BS 2  the selective call transceiver  122  receives a tone signal from BS 1 , BS 3 , BS 4 , BS 5 , BS 6 , and BS 7 , and so on. Transmitting tones in this manner provides a selective call transceiver  122  located in the coverage zone  402  of BS 1  a method for measuring the co-channel interference from first tier co-channel interferers (i.e., BS 2  through BS 7 ), as well as co-channel interference from higher tiers. 
     This method is applied throughout the two-way communication system for all coverage zones  402  and coverage zone clusters  404  simultaneously prior to the transmission of an analog voice message. However, base stations  116  which do not intend to transmit a voice frame remain silent for all tone slots, and thus do not contribute as co-channel interferers during the measurement process. During the simultaneous transmission of all coverage zones  402  and associated coverage zone clusters  404  in the two-way communication system, the selective call transceiver  122  within the coverage zone  402  of BS 1 , for example, measures noise interference comprising co-channel interference and adjacent channel interference, and receiver noise. Noise interference may also be referred to as interference plus noise (I+N). 
     The selective call transceiver  122  is also programmed to determine the home silence slot in cases where the home silence slot location is not provided in the outbound message. In order to determine the home silence slot, the processor  310  of the selective call transceiver  122  is programmed to first measure the mean RMS pilot power P mx  corresponding to each SQM slot (P m1  through P m4 ), and the mean RMS power of the interference plus noise (I+N) for each SQM slot (I m1  through I m8 ), all expressed in milli-watts. During the demodulation process of the LSB and USB signals, the processor  310  of the selective call transceiver  122  is programmed to divide the side band signals by the mean RMS power of the pilot, thus normalizing variations in the received signals. 
     However, during conditions which degrade the pilot carrier mean power (e.g., fading) dividing the side bands by the mean RMS power of the pilot signal results in an increase of the I+N intercepted by the selective call transceiver  122 . For this reason, during detection of the home silence slot, the demodulated signal is multiplied by the mean pilot power of its corresponding SQM slot resulting in the products P m1 I m1 , P m1 I m2 , P m2 I m3 , P m2 I m4 , P m3 I m5 , P m3 I m6 , P m4 I m7 , and P m4 I m8 . This removes the normalization step, and results in a true comparison of the mean RMS power of the I+N for each SQM slot. 
     Since BS 1  does not transmit a tone in its home silence slot, the lowest product of P mx I mx  identifies the home silence slot, which for this example is P m1 I m1  for a selective call transceiver  122  residing in the coverage zone  402  of BS 1 . Once the home silence slot has been identified, the processor  310  of the selective call transceiver  122  is programmed to determine a signal quality threshold (T), expressed in dBm, which follows the expression T=S d −(V m −I m )+P m , where S d  is a predetermined minimum desired signal to interference plus noise ratio, expressed in dB, of the signal received by the selective call transceiver  122 , where V m  is a predetermined normal mean RMS power of the analog voice message portion, expressed in dBm, where I m  is the noise interference mean RMS power of the home silence slot (in this example, I m1 ), expressed in dBm, and wherein P m  is the mean RMS pilot power measured during the SQM period (in this example, P m1 ) expressed in dBm. The value of S d  is received over-the-air (OTA), and is considered a quality factor defined by the system provider of the two-way communication system. The value of V m  is factory programmed into the selective call transceiver  122 . Thus, S d  and V m  are constants.          T   =         S   d     ·     I   m     ·     P   m         V   m         ,                   
     where S d  is a dimensionless ratio, and T, I m , P m , and V m  are expressed in milli-watts. As discussed above, Sd and Vm are constants, thus the remaining variable for the above equation is I m . For this reason, an increase in I m  results in an increase of T, and a decrease in I m  results in a decrease of T. The threshold equation for T implies that the greater the measured noise interference, the more pilot signal power is required in the received signal to compensate for the higher noise interference. In contrast, the lower the measured noise interference, the less pilot signal power is required in the received signal. Since the mean RMS pilot power is expected to track with the mean RMS power of the side bands, T provides a signal quality means to determine the quality of a received signal. 
     FIG. 6 is a timing diagram of a second embodiment of a plurality of predetermined synchronized signal quality measurement (SQM) slots transmitted with an analog voice message in accordance with the present invention. In the second embodiment of the present invention, the base stations  116  transmit a tone (e.g., 1 KHz) only in a home tone slot. In this arrangement, a selective call transceiver  122 , unaware of the location of its home tone slot, is programmed to measure the mean RMS power of the pilot P mx  corresponding to each SQM slot (P m1 , P m2 , P m3 , P m4 , and P mq ), and the mean RMS power of the noise interference I mx  of each tone slot (I m1 , I m2 , I m3 , I m4 , I m5 , I m6 , I m7 , I m8 , and I mq ), all expressed in milli-watts. 
     As was done above, each component of I mx  is multiplied with its corresponding P mx  to remove the effects of the normalization step (i.e., P m1 I m1 , P m1 I m2 , P m2 I m3 , P m2 I m4 , P m3 I m5 , P m3 I m6 , P m4 I m7 , P m4 I m8 , and P mq I mq ). Note, since no tones from any base stations  116  are transmitted during the quiet slots no co-channel interference is present, thus I mq  represents primarily the noise component of I+N at the selective call transceiver  122 . Since BS 1  transmits a tone in its home tone slot, the highest product of P mx I mx  identifies the home tone slot, which for this example is P m1 I m1  for a selective call transceiver  122  residing in the coverage zone  402  of BS 1 . Once the home tone slot has been identified, the selective call transceiver  122  is programmed to determine the total noise interference (I mt ) of its coverage zone  402  which follows the expression:          I     m   t       =         ∑     x   =   1     N              I     m   x       ×     P     m   x           P     m   q           -       (     N   -   1     )          I     m   q                           
     For a selective call transceiver  122  located in the coverage zone  402  of BS 1 , N=7 (i.e., I mx  for BS 2  through BS 8 ), and I m1  is excluded from the calculation. The term I mx * P mx /P mq  moves the normalization reference from P mx  to P mq . Since each I mx  includes a noise component comprising ambient noise, adjacent channel interference from other two-way communication systems, and inherent noise from the receiver  306 , the summation of the I mx  terms adds a set of unnecessary noise components (in this example, 6 additional noise terms). The term (N−1)*I mq  removes the additional noise components since I mq  is essentially the noise term present at the selective call transceiver  122 . 
     Once I mt  has been determined, the processor  310  of the selective call transceiver  122  is programmed to determine a signal quality threshold (T), expressed in dBm, which follows the expression T=S d −(V m −I mt )+P mq , where S d  is a predetermined minimum desired signal to (noise) interference, expressed in dB, of the signal received by the selective call transceiver  122 , where V m  is a predetermined normal mean RMS power of the analog voice message portion, expressed in dBm, where I mt  is the determined total noise interference mean RMS power, expressed in dBm, and wherein P mq  is the mean RMS pilot power measured during the quiet slot, expressed in dBm. The function of this equation follows the description given above for the first embodiment. 
     The equation for T can also be expressed as:          T   =         S   d     ·     I   m     ·     P   m         V   m         ,                   
     where S d  is a dimensionless ratio, I mt , P mq , and V m  are expressed in milli-watts. 
     The first and second embodiments discussed above, utilize methods for determining the home tone slot and quiet slot which required multiplication of the noise interference I mx  with its corresponding pilot signal P mx . This procedure removes the normalization introduced by the demodulator. It will be appreciated that, alternatively, this procedure can be avoided by having the demodulator not divide the signal received from the tone slots by the pilot carrier during signal quality measurements. This reading can be utilized to quicken the determination of the home tone slot and quiet slot (second embodiment only). In addition, the equations for T can be determined such that the pilot term is no longer necessary. 
     FIG. 7 is a timing diagram representing instantaneous sampling of a plurality of values of pilot carrier power during reception of the analog voice message, and the measurement thresholds used to determine the quality of the received analog voice message according to the present invention. The signal  406  represents instantaneous sampling of pilot carrier power. As discussed above, T represents the signal quality threshold tested against the received signal. P avg  represents the mean RMS power calculated over a voice fragment, expressed in dBm. To account for fading P avg  is subtracted by a fade margin (M f ) which follows the expression 
     
       
           M   f =min (6, P   f [3+12 /R   f ]), 
       
     
     expressed in dB. This formula is empirically derived. It will be appreciated that, alternatively, another formula derived analytically and/or empirically can be used. R f  represents the number of fades per second more than 13 dB below the threshold T. P f  represents the percent of samples more than 13 dB below the threshold T. FIG. 7 shows two fade crossings (pointed to by arrows) resulting in a fading rate of 
     
       
           R   f =(2/fragment duration), in seconds. 
       
     
     Only two regions of the pilot power samples fall 13 dB below the threshold T. Thus P f  equals the total number of samples 13 dB below T divided by the total sample count over a fragment duration, times one hundred. The fade margin equation is limited to 6 dB, that is, P f [3+12/R f ] is capped at 6 dB. 
     The calculated M f  is subtracted from P avg  as shown in FIG. 7, thus bringing P avg  closer to the threshold T (i.e., adding a stricter requirement of the quality of the receive signal). As long as P avg −M f  is greater than the threshold T the fragment is deemed of acceptable quality as shown by this example. Once the fragment has been processed, the selective call transceiver  122  saves the fragment in the RAM  312 , and transmits an ACK to the controller  112  confirming a reliable transaction for the fragment. If P avg −M f  falls below the threshold T, then the selective call transceiver  122  discards the fragment, and transmits a NAK to the controller  112  negating the transaction. 
     Once the controller  112  receives the NAK from the selective call transceiver  122  it reconstructs the fragment and re-transmits it to the selective call transceiver  122 . In the case where multiple fragments are processed by the selective call transceiver  122 , some of which pass the threshold test, and others which fail the threshold test, the ACK and NAK messages include sufficient information to identify the fragments which need re-transmission and those which do not. 
     It will be appreciated that the selective call transceiver  122  can also be programmed to differentiate between co-channel and adjacent channel interference by comparing the measured interference of the home tone slot to the silence slot. If the levels are approximately the same and above a predetermined level, this indicates that adjacent channel interference is the major source of interference. If the home tone slot is higher, this indicates co-channel interference is the major source of interference. 
     The selective call transceiver  122  can further be programmed to differentiate between co-channel or adjacent channel interference and receiver noise interference by comparing the interference level to a predetermined level in the receiver  306 . If the measured interference level is above this predetermined level, the major source of interference is predominately co-channel or adjacent channel interference. 
     FIG. 8 is a timing diagram of elements of an outbound protocol and an inbound protocol of the base transceiver  102  and portable portion  104  of the two-way communication system according to the present invention. The signaling format operating on the outbound and inbound channels operates on independent frequencies utilizing FDM as described above. Using FDM transmission the outbound RF channel transmission is depicted during an outbound transmission time interval  502 , while the inbound RF channel transmission is depicted during an inbound transmission time interval  504 . The outbound transmission time interval  502  and the inbound transmission time interval  504  are subdivided by a time boundary  503 . The time boundary  503  depicts a point in time before which the outbound transmissions must cease and after which the inbound transmissions can commence. 
     The elements of the outbound protocol comprise an outbound sync  506 , a selective call address  510 , a message vector  512  and an outbound message  514 , while the inbound protocol comprises an inbound sync  516  and an inbound message  518 . The outbound sync  506  provides the selective call transceiver  122  a means for synchronization utilizing techniques well known in the art. The selective call address  510  identifies the selective call transceiver  122  for which the outbound message  514  is intended. The message vector  512  points in time within the signal format to the position of the outbound message  514  to be received by the selective call transceiver  122 . 
     In addition, the message vector  512  includes an SQM information field  508 . The SQM information field  508  comprises an enable code word  520 , and a desired signal to interference plus noise constant S d 522 . The enable code word  520  enables or alternatively disables the signal quality measurement performed by the corresponding selective call transceiver  122 . S d    522  provides the constant needed in determination of the threshold T equation discussed above. 
     The system provider of the two-way communication system defines the desired dB level for S d . In an alternative embodiment of the present invention, the SQM information field  508  also includes an SQM id 524 . The SQM id    524  is used to identify the home silence/tone slot assigned to the coverage zone  402  in which the selective call transceiver  122  is known to be located, which precludes the need to search for the home silence/tone slot. It will be appreciated that, alternatively, the SQM information field  508  can also be located in any other appropriate portion of the outbound message stream within the outbound transmission time interval  502 . Moreover, the signal to be measured and adjusted for is alternatively a digital signal transmitted using various FM or AM communication techniques. The outbound message  514  comprises an SQM period  526  and an analog voice message  528 . The SQM period  526  utilized for the determination of the threshold T, as described above. 
     Inbound messages are transmitted during scheduled time slots. The inbound sync  516  provides the base stations  116  a means for synchronization utilizing techniques well known in the art. The inbound message  518  comprises a pager identifier (ID)  830 , a response message  532 , and a signal quality measurement data (SQM)  534 . The pager ID  830  is, for example, the address of the selective call transceiver  122  included in the EEPROM  318 . The response message  532  is either an ACK or NAK message depending on the quality of signals received from the base transceiver  102  during outbound message reception. 
     The SQM data  534  is the signal quality measurement data sampled by the processor  310 . The signal quality measurement data  534  is transmitted to the base stations  116  with NAK messages. As an alternative, the signal quality measurement data can also be sent with ACK responses. 
     In an alternative embodiment, the inbound protocol allows for messages to be transmitted during unscheduled time slots. These time slots are intermixed with the scheduled time slots. The unscheduled time slots comprise the same elements as the scheduled time slots. During unscheduled inbound messaging, the selective call transceiver  122  is programmed for one of two mode. 
     In a first mode, the selective call transceiver  122  is programmed to transmit SQM data  534  in the unscheduled inbound message, while in a second mode the selective call transceiver  122  is programmed not to send SQM data  534 . These programming modes are controlled by the base transceiver  102  by way of conventional over-the-air programming. Unscheduled and scheduled inbound transmissions including SQM data  534  are used by the base transceiver  102  for creating an SQM historical database, as will be described below. 
     FIGS. 9 and 10 depict overall operation  800  of the controller  112  according to the present invention. The operation  800  begins with step  802  where the processing system  210  of the controller  112  sends a simulcast “Where aRe yoU (WRU)” message to the selective call transceivers  122 . In step  804  the processing system  210  waits for responses from the selective call transceivers  122 . If a group of response messages received are ACKs, then processing system  210  proceeds to step  810  where it creates a first group of ACK&#39;d selective call transceivers  122 . If there is a group of selective call transceivers  122  which do not respond within a predetermined time, determined in step  806 , then the processing system  210  proceeds to step  808  where it creates a second group of non-responsive selective call transceivers  122  listed as out-of-range. Communication with this group is attempted at a later time. 
     In step  812  the processing system sends a simulcast “Where To Listen” (WTL) frame to the first group of selective call transceivers  122  specifying the point in time where the outbound message  408  will be transmitted to the selective call transceivers  122 . In step  814  the processing system  210  sends the outbound messages to the first group of selective call transceivers  122  utilizing the first frequency reuse plan, the first base transmitter power plan, and the first channel frequency plan. A base power plan is the power level of the base transmitter communicating with the selective call transceiver, and/or the power levels of nearby base transmitters. A frequency reuse plan involves those base transmitters that could contribute to co-channel interference of the selective call transceiver at a current location of the selective call transceiver. For example, base transmitters B 2 -B 7  in FIG. 4 are potential co-channel interferers (indeed first tier interferers) with respect to a selective call transceiver in communication with base transmitter B 1 . The first frequency reuse plan provides the highest system capacity available for communicating with the selective call transceivers  122 . However, as is well known to one of ordinary skill in the art, the greater capacity derived from a frequency reuse plan results in greater levels of noise interference in the two-way communication system. The first channel frequency plan determines the channel frequency of the base transmitter in communication with the selective call transceiver  122  for receiving outbound messages transmitted by the base transmitter. A new channel frequency, if necessary to reduce the signal-to-noise interference level caused by adjacent channel interference, is transmitted to the selective call transceiver to enable it to properly tune to the new frequency. 
     Two prevalent noise interferences are co-channel and adjacent channel interference. Co-channel interference is caused by multiple coverage areas utilizing the same communication frequency. In two-way communication systems, coverage areas utilizing the same communication frequency are placed by design as far apart as possibly allowed by the frequency reuse plan. However, when co-channel interference remains a problem, an adjustment of the frequency reuse plan resulting in an increase in the signal-to-interference ratio helps to substantially reduce this interference. 
     Adjacent channel interference is caused by power that is coupled between adjacent frequency channels. By adjusting the channel frequency plan, that is, assigning a different channel frequency to the selective call transceiver  122  for receiving outbound messages, adjacent channel interference can be substantially reduced for those selective call transceivers  122  experiencing this problem. A third form of interference nearly always present in the two-way communication system is transceiver noise inherent in the selective call transceivers  122 . By adjusting the base transmitter power plan, the selective call transceivers  122  receive a stronger RF signal that compensates for inherent noise in the selective call transceiver  122 . It can be appreciated that adjusting the base transmitter power plan may also affect co-channel and adjacent channel interference at the selective call transceiver. 
     The selective call transceivers  122  are programmed to measure these three forms of interference during message transmission with the methods described above, and are further programmed to include this measurement data in the SQM data  534  field when responding on the inbound channel. 
     In step  816  the processing system  210  waits for responses from the selective call transceivers  122 . If a group of response messages received are ACKs, then processing system  210  discontinues processing for that group of selective call transceivers  122 . If there is a group of selective call transceivers  122  which do not respond within a predetermined time, determined in step  818 , and/or a group of selective call transceivers  122  responding with NAKs, then the processing system  210  proceeds to step  820  of FIG. 10 where it creates a third group of NAK&#39;d and/or non-responsive selective call transceivers  122 . Note the NAK messages include SQM data  534  from the failed outbound message(s) transmitted in step  814 . 
     In step  822  the processing system  210  adjusts signal quality of signals received by the third group of selective call transceivers  122  based on the SQM historical data accumulated by the processing system  210  from previous communication cycles. The adjustment of the signal quality of signals received by the third group of selective call transceivers  122  is based on several possible courses of action. In accordance with one course of action, the processing system  210  is programmed to adjust a power plan transmitted by the at least one base transmitter  202  in accordance with the SQM data  534  stored in the memory of the computer system  212 . The power plan is the radio frequency (RF) power levels transmitted by the plurality of base transmitters  202  in the two-way communication system. The adjusted power plan results in a second power plan utilized for communicating with the third group of selective call transceivers  122 . 
     In a second course of action, the processing system  210  is programmed to adjust a frequency reuse plan transmitted by a plurality base transmitters  202  in accordance with the SQM data  534  stored in the memory of the computer system  212 . The adjusted frequency reuse plan results in a second frequency reuse plan affecting those base transmitters that are potential co-channel interferers with the selective call transceiver  122 , and utilized for communicating with the third group of selective call transceivers  122 . In a third course of action, the processing system  210  is programmed to adjust both the frequency reuse plan and the power plan transmitted by the plurality base transmitters  202  in accordance with the SQM data  534  stored in the memory of the computer system  212 . In a fourth course of action, the processing system  210  is programmed to the adjust channel frequency plan of the selective call transceiver  122  experiencing adjacent channel interference, thereby removing the adjacent channel interference, in accordance with the SQM data  534  stored in the memory of the computer system  212 . The adjusted channel frequency plan results in a second channel frequency plan utilized for communicating with the third group of selective call transceivers  122 . 
     Step  822  includes any of the four courses of action described above, as well as others useful to achieve desired signal qualities throughout a coverage area. In step  824  the processing system  210  sends outbound messages to the third group of selective call transceivers  122  utilizing the second frequency reuse plan, the second base transmitter power plan, and/or the second channel frequency plan derived in step  822 . In step  826  the processing system  210  waits for responses from the third group of selective call transceivers  122 . If a group of response messages received are ACKs, then processing system  210  discontinues processing for that group of selective call transceivers  122 . If there is a group of selective call transceivers  122  which do not respond within a predetermined time, determined in step  828 , and/or a group of selective call transceivers  122  respond with NAKs, then the processing system  210  proceeds to step  830  where it creates a fourth group of NAK&#39;d and/or non-responsive selective call transceivers  122  listed as out-of-range, and stores received SQM data transmitted by those selective call receivers. Communication with this group is attempted at a later time. 
     It will be appreciated that, alternatively, the processing system  210  can be programmed to resend a WRU message along with a WTL message to the third group of selective call transceivers  122  to account for selective call transceivers  122  that may have relocated to other coverage areas in the two-way communication system. To accomplish this, the processing system would repeat steps  802  through  812  prior to sending outbound messages in step  824  to the third group of selective call transceivers  122 . 
     It will be further appreciated that, alternatively, the processing system  210  can be programmed to use any number of frequency reuse plans, base transmitter power plans, and/or channel frequency plans such as, for example, yet a third frequency reuse plan, a third base transmitter power plan, and/or third channel frequency plan to attempt communication with the fourth group of selective call transceivers  122 . It will be further appreciated that, alternatively, the processing system  210  can be programmed to use any number of frequency reuse plans, base transmitter power plans, and/or channel frequency plans for any group of selective call transceivers  122  such as, for example, the first group of selective call transceivers  122 . The selection of the frequency reuse plan, the base transmitter power plan, and/or channel frequency plan is determined by the processing system  210  in accordance with a historical database of SQM data derived from a history of transmission cycles between the selective call transceivers  122  and the base transceiver  102 . 
     It will be further appreciated that communication transactions between the base transceiver  102  and the selective call transceivers  122  in the two-way communication system of the present invention is non-real-time. It will also be appreciated that the two-way communication system of the present invention is unlike prior art real-time systems such as cellular telephony, where the two-way cellular subscriber units conform to the cellular system environment (i.e., noise interference) rather than the cellular system conforming to the environment of the cellular subscriber units as is done by the present invention. 
     FIG. 11 is a flow chart  900  of the selective call transceiver  122  operation according to the present invention. The flow chart  900  begins with step  902  where the selective call transceiver  122  waits for a message from the base transceiver  102 . In step  904  the processor receives WRU and WTL frames from the base transceiver  102 . In step  906  the processor  310  of the selective call transceiver  122  measures signal quality of the signals of the outbound message received from base transceiver  102  in accordance with the methods described above. 
     The processor  310  is programmed for measuring several types of interference. First, the at least one selective call transceiver  122  is programmed for measuring adjacent channel interference based on the signals received from the at least one base transmitter  202 , and for generating adjacent channel interference data included in the SQM data  534  to be transmitted to the base transceiver  102 . Secondly, the selective call transceiver  122  is programmed for measuring co-channel interference based on the signals received from the base transmitter  202 , and for generating co-channel interference data included in the SQM data  534  to be transmitted to the base transceiver  102 . 
     The selective call transceiver  122  is still further programmed for measuring noise interference of the receiver  306  based on the signals received from the base transmitter  202 , and for generating receiver noise data included in the SQM data  534  to be transmitted to the base transceiver  102 . The selective call transceiver  122  is yet further programmed for measuring co-channel interference, adjacent channel interference, and receiver  306  noise interference based on the signals received from the base transmitter  202 , and for generating co-channel interference data, adjacent channel interference data and receiver noise interference data included in the SQM data  534  to be transmitted to the base transceiver  102 . 
     Once the signal-to-interference measurement is made, the processor  310  proceeds to step  908  where it determines whether the signal-to-interference measurement is greater than a predetermined threshold stored in the memory of the selective call transceiver  122 . If the signal-to-interference measurement is less than the predetermined threshold, then the processor  310  proceeds to step  910  where it sends via the transmitter  304  a NAK response message  532  with the SQM data  534  to the base transceiver  102 , and returns to step  902  where the processor  310  awaits for a re-transmitted outbound message. If the signal-to-interference measurement is greater than the predetermined threshold, then the processor  310  proceeds to step  912  where it sends via the transmitter  304  an ACK response message  532  together with the SQM data  534  (or alternatively without the SQM data  534 ) to the base transceiver  102 . In step  914  the processor  310  alerts the user of the selective call transceiver  122  of the incoming message by way of the alerting device  322 . In step  916  the user receives via the display or audio system the message by invoking functions provided by the user controls  320 . 
     Thus, the present invention provides a greatly improved two-way communication system for performing noise interference measurement and control of the quality of signals transmitted by the base transceiver to be received by a selective call transceiver. In particular, the two-way communication system transmits signals that are measured by the selective call transceivers to derive a signal quality measurement. The signal quality measurement is then transmitted to the base transceiver for analysis on how to best improve signal quality of signals to be received by those selective call transceivers experiencing interference. The base transceiver can accumulate SQM data to generate a historical SQM database for dynamically reconfiguring the two-way communication system by, for example, adjusting the frequency reuse plan, the base transmitter power plan, and/or the channel frequency plan.