Abstract:
A portable digital communications system is provided that signals the communications recipient of a worsening wireless link with communication partners. In audio communication systems, static is introduced as the alert signal, along with the decoded data that was transmitted. Static gives the communications recipient a qualitative feeling of the wireless link status. In response to the static signal, communications recipients move their positions to improve the link. In a video communications system, static and/or “snow” are introduced as the alert signal to give the recipient a qualitative feeling of the wireless link status. The invention allows the warning signal to be mixed with the decoded data, mixed with simulated data generated to replace incorrectly decoded data, or presented without data. In addition, static is introduced in response to averaging schemes to more closely simulate the performance of static and/or “snow” in an analog receivers. A method for signaling the recipient of a digital communication of a worsening wireless link is also provided.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates generally to wireless communication devices, and more particularly to a system and method for intuitively indicating the signal quality of a wireless communications link. 
     Most wireless communication devices are mobile stations, such as handheld telephones that are used by pedestrians, or individuals traveling in automobiles. A mobile station can contact another mobile station, or a fixed position relay station, to communicate with other users in the communication system. Typically, a mobile station is free to roam. That is, a mobile station is allowed to operate as it travels through a variety of geographical regions. Often, communication networks are broken up into cells, such as in cellular telephone networks. These cells correspond approximately to geographical regions inside the communication network. As a mobile station, or cellular telephone moves through geographical regions it will change cells, communicating with proximate cells as it moves. 
     The geographical area in which communications are exchanged with a wireless communications device is typically called a coverage area. The coverage area of a cellular system is limited by a number of parameters. The presence of nearby tall buildings, mountains, or hillsides, shadow (block) radio frequency (RF) signals between a mobile station and a communicating base station. Coverage is also limited by multi-path interference, or the arrival of echoed copies of the same communication at two different periods in time. Operator-configurable system parameters also effect the coverage area. These parameters include the positioning of base station antennas, the selection of which base station communicates with the mobile station, and the transmit power levels of the mobile station and the base station. Co-channel interference between multiple mobile stations and base stations, using the same radio frequency in adjoining cells, also limits the coverage area. 
     Because of fierce competition between wireless communication providers, and the user&#39;s expectation that cellular networks should provide the same level of performance as fixed wireline networks, system operators are active in adjusting system parameters to achieve the optimum performance. In many cases, system parameters are adjusted on a daily basis. Users find that certain so called “dead spots”, or locations where communications are frequently dropped or cannot be initiated, remain constant. Other “dead spots” come and go as the side effects of optimizations performed in the network. For example, a cell-site antenna may be re-aimed to provide a stronger signal to one coverage area at the expense of a weaker signal in a second coverage area. 
     Traditionally, the most qualitative assessment of a fixed line telephone link has been the listener&#39;s perception of noise mixed with the intended signal. More recently, analog cellular telephone users have come to rely upon the background static noise as a qualitative assessment of the quality of the communication link. That is, the degree of static that an analog phone user hears tends to be a good indication of whether the call is likely to be dropped, and if the call is dropped, how likely it will be that a new call can be initiated from the same location. The ability to initiate a new call is critical since higher RF signal levels are generally required for initiating a call, as opposed to maintaining an existing call. 
     Since a majority of the cellular telephones currently in existence are handheld, pedestrian or automobile users play an active role in determining the reliability of their communication link. That is, wireless telephone users often adjust their location to improve the quality of the radio link, thereby reducing the likelihood that the call will be dropped. For this reason, one sees wireless telephone users placing calls near windows or exterior doors where the base station signal is strongest. When calls are dropped, users rely upon their memory of static levels to select the optimum location for initiating a new call. 
     Presently, second generation cellular telephone systems are being deployed. These systems generally use digital schemes instead of the previously used analog techniques. In addition, digital broadcast television and pager systems are currently in development. Generally, these systems allow operators to support more users with the same limited bandwidth. These digital systems also provide new customer services, resistance to eavesdropping and fraud, and longer battery life. Digital systems also provide a more consistent audio quality. It is believed that in the future, digital systems will replace analog systems. 
     FIG. 1 illustrates the perceived audio quality of an analog versus digital radio link. In an analog system, the audio quality is highly correlated to the radio link quality. In a digital system, this is not necessarily the case. Digital cellular systems rely upon compression techniques to reduce the transmitted bandwidth requirements. In addition, coded bits are added to the data stream to allow the receiving entity to detect and correct minor errors in the wireless radio communication link. As shown in FIG. 1, when the radio link is good, the received digital cellular speech is perceived as lower in quality than analog speech. This is due to the losses attributable to speech compression. However, as the radio link quality decreases, the ability of the digital system to correct certain errors, results in the maintenance of speech quality at a level which eventually exceeds that of the analog system. At some point, the link becomes so poor that even the digital system&#39;s error correction scheme is no longer effective. In practice, such a poor link is shown to be inadequate for maintaining digital, as well as analog communications. 
     Near “dead spots”, a digital telephone may be on the verge of dropping a call, and yet, the user will have little warning that communication is on the verge of interruption. The user of an analog cellular telephone in a similar situation would be warned of a perilous communication link due to the presence of familiar static mixed in with the intended signal. Because the users of digital telephones are unaware of perilous communication links, they are unable to take measures to improve the link. That is, they are unaware that they should change position to improve the communication link. Interspersed muted audio frames are the only sign that some segments of the digital communication have been so poorly received that they are lost. However, in high ambient noise environments, such as typically encountered by a handheld telephone user, it is very difficult to detect these warning signs. In fact, it is only possible to detect these muted frames when the other party is speaking continuously. If the transmitting party is in a quiet setting with no background noise and is not speaking, it is impossible for the digital cellular telephone user to determine if speech frames are being muted. 
     It would be advantageous if a digital cellular telephone user had a real time indication of the quality of the wireless communications. With such an indicator, telephone users could adjust their location to avoid missing a communication, thereby reducing the chances of having a call dropped. 
     It would be advantageous if a digital cellular telephone user had an intuitive indicator of the quality of a wireless communications link. 
     It would also be advantageous if a digital cellular telephone user had a static noise warning to indicate the state of the radio link quality so that they could move positions as analog cellular telephone users do. 
     It would be advantageous if wireless video receivers had an intuitive, real time, indication of the state of the communication link quality. It would likewise be advantageous if that indicator was a snow-like visual degradation and static sound similar to that of an analog television signal. 
     Accordingly, in a wireless communication system including a plurality of intercommunicating transceivers to send and receive messages of digitally encoded information, a method of indicating the signal quality of a received message is provided. Alternately, the system includes a plurality of receivers to receive messages of digitally encoded information. The method comprises the steps of: a) estimating the quality of the received message to derive a signal quality estimate and; b) activating an indicator in response to the signal quality estimate in step a), whereby a transceiver user is warned of a poor communications link. 
     It is an aspect of the invention that the indicator activated in step b) is a static noise sound, whereby the presence of static gives the transceiver user an intuitive sense of the received message signal quality. It is another aspect of the invention to include the further step, following step a), of averaging the estimated signal quality of messages received over a plurality of predetermined first periods of time to create an average signal quality estimate; and activating the indicator in step b) in response to the average signal quality estimate, to present the warning indicator to the user over a predetermined number of predetermined second periods of time. A static noise pattern presented to the user closely simulates the characteristics of an analog receiver. 
     It is an aspect of the invention that the signal quality estimated in step a) is responsive to the following received message quality data: 
     1. received message signal strength, which provides a measurement of carrier power of a received message; 
     2. block decoder status, which indicates whether received messages are successfully decoded into information; and 
     3. path metric data, which provides a measurement of the corrections required to decode message information. The signal quality is, therefore, based on carrier power, the amount of lost information, and the amount of corrected information. 
     In one preferred embodiment, the communication system is a GSM cellular phone network with intercommunicating mobile station telephones, in which the signal quality estimated in step a) is also responsive to the following network-controlled message quality data: 
     4. mobile station transmitter carrier power level, which provides an indication of signal quality as measured by a communicating base station; 
     5. timing advance, which provides a measurement of how far a mobile station is from a communicating base station; and 
     6. the status of the discontinuous transmission (DTX) function. The message quality standards are adjusted in response to the increased sensitivity of the transceiver to message errors when DTX mode is in use. 
     In another preferred embodiment of the invention the communication system is a digital television signal broadcast to digital televisions, and the signal quality estimated in step a) is also responsive to the detection of the loss of sequential broadcast frames. The warning indicator in step b) is a snow-like visual degradation, whereby the user sees an intuitive warning that the received message quality is poor. 
     A wireless communication system including a plurality of intercommunicating transceivers to send and receive messages of digitally encoded information is also provided. Alternately, the system includes a plurality of receivers to receive messages of digitally encoded information. The system for indicating the signal quality of a received message comprises a signal quality estimator including inputs to accept received message quality data, and an output to provide a signal quality estimate in response to the received quality data. The system also comprises an indicator having an input operatively connected to the output of the signal quality estimator to accept the signal quality estimate, and an output, to warn of poor signal quality, which is activated in response to the signal quality estimate. The indicator warns a user of a poor communications link. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a graph illustrating the perceived audio quality of an analog versus digital communication system (prior art). 
     FIG. 2 is a flow diagram illustrating steps in the method of indicating the signal quality of a received message. 
     FIG. 3 illustrates the receipt of a wireless message of digitally encoded information (prior art). 
     FIG. 4 illustrates a received message during a time period of poor signal quality, and demonstrates the warning indicator feature of the invention. 
     FIG. 5 illustrates a received message during a time period of moderately poor signal quality, and demonstrates another aspect of the warning feature of the invention. 
     FIG. 6 illustrates a received message during a time period of poor signal quality, demonstrating the extrapolated information function (prior art). 
     FIG. 7 illustrates a received message during a time period of poor signal quality, demonstrating the extrapolation and indicator functions of the invention. 
     FIG. 8 illustrates a received message during a time period of poor signal quality, demonstrating the indicator averaging function of the present invention. 
     FIG. 9 is a block diagram of the system of the present invention system for indicating the signal quality of a received message. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a graph illustrating the perceived audio quality of an analog versus digital communication system (prior art). The radio link quality is represented on a continuum from 0 to 100 percent along the horizontal axis. At 100 percent the radio, or wireless, link is perfect. The vertical axis is perceived audio quality which is also represented along a continuum from 0 to 100 percent. An analog receiver trace  10 , and a digital receiver trace  12  are drawn in FIG.  1 . When the radio link quality is high, as in the region of radio link quality represented by reference designator  14 , the perceived audio quality of an analog receiver is superior to that of a digital receiver. This perceived quality difference is due to compression schemes and error correction formats which reduce the information bandwidth. In the region of radio link quality represented by reference designator  16 , the perceived audio quality of the digital receiver is superior to that of the analog. In the region of radio and quality represented by reference designator  18 , the perceived audio quality of the digital receiver is still superior to that of the analog receiver, however, the slope between perceived excellent quality and lost communication is very steep. The present invention provides an indication to the user of a digital receiver that they are operating with a radio link quality in the area represented by reference designator  18 , or possibly in the area represented by reference designator  16 . This warning gives the digital receiver user an opportunity to change location, and thus improve the radio link quality. 
     FIG. 2 is a flow diagram illustrating steps in the method of indicating the signal quality of a received message. Step  20  provides a wireless communication system including a plurality of intercommunicating transceivers to send and receive messages of digitally encoded information. Alternately, step  20  provides a wireless communication system including a plurality of receivers to receive messages of digitally encoded information. Step  22  estimates the quality of the received message to derive a signal quality estimate. Step  23  activates an indicator in response to the signal quality estimate in Step  22 . Step  24  is a product: either a transceiver, or a receiver, which warns the user of a poor communications link. 
     It is an aspect of the invention that the communications system includes a mobile station, a typical communication system includes a plurality of portable, handheld receivers, or transceivers, having a size and weight small enough to be manipulatable by the user. Because of the mobile station&#39;s small size, the user has the option of changing the location of the mobile station in response to an indicator warning that the received message signal is poor. 
     Various types of indicators are used to warn the user of poor received message quality. In one aspect of the invention, the indicator activated in Step  23  is tactile, the user feels a warning that the received message quality is poor. An example of a tactile indicator is a vibrator, so that the user feels a vibration in the communications equipment as a warning. Alternately, the indicator activated in Step  23  is visual display, whereby the user sees a warning that the received message quality is poor. Typical visual indicators include video, LED, and gauge type displays to give either a qualitative or quantitative reading of signal quality. 
     In a preferred embodiment of the invention, the indicator activated is an audio signal, whereby the user hears a warning that the received message quality is poor. Since many communications involve audio information, the listener is sensitive to audio signals and, therefore, likely to hear an audio warning. Preferably, the audio indicator activated in Step  23  is a static noise sound, whereby the presence of static gives the user an intuitive sense of the received message signal quality. Since analog communication equipment emits static when the signal is poor, static tends to be an intuitive warning signal. 
     It is an aspect of the invention that Step  22  includes comparing the signal quality estimate to a predetermined first minimum quality level. Step  23  includes activating the indicator as follows: 
     1) when the signal quality estimate is greater than, or equal to, the first minimum quality level, the indicator is not activated; 
     2) when the signal quality estimate is less than the first minimum quality level, the indicator is activated, whereby the user is warned of a message quality below a specified standard. 
     It is an aspect of the invention that the method includes further steps. Step  25  decodes the received message into information useful to the user, and Step  26  presents the information decoded in Step  25  to the user. In one preferred embodiment, the information decoded in Step  25  is auditory, and the warning indicator in Step  23  is a static noise, whereby communications simulate an analog wireless telephone to give the user an intuitive feeling of signal quality. 
     A variety of factors regarding a received message are measured and compared to derive a signal quality level. Likewise, the first minimum quality level is a determination built upon a number of factors in the reception of a signal. In the simplest aspect of the invention, the signal quality is calculated from a predetermined scale of values, and compared against a set first quality value. The alarm is triggered as the result of a value comparison. For example, in a simple aspect of the invention the first minimum quality level is the block decoder status, or whether the information in a frame of data bits is decoded. Whenever the block decoder status for a frame is bad, the static warning indicator is turned on. In a more sophisticated aspect of the invention, the values of signal quality are allowed to slide based on situation specifics and a history of recent performance. Likewise, the first minimum quality level is a value that slides based on relative relationships and situation specifics. The simple aspect of the invention is suitable for a hardware implementation, while more sophisticated methods of calculating the signal quality estimate and first minimum level are more easily implemented through software based embodiments of the invention. For example, as in the simple system, static is turned on when the block decoder status is bad. In a more complicated system, the static warning is also turned on, in some situations, when the block decoder status is good, but the path metric (number of corrections made) is high. 
     FIG. 3 illustrates the receipt of a wireless message of digitally encoded information (prior art). Trace  30  represents the receipt of a wireless message after the carrier signal has been removed. In addition, the signal has already been converted from modulation format, i.e., a digital modulation format, into audio information. For the purposes of clarity, the received signal, or audio information sent by a communicating transmitter, is represented as a sine wave. Actual audio and video signals are significantly more complicated than received message  30 , and to the untrained observed appear as random noise. The processed and demodulated received message is presented as communicated information  32 . Thus, the signal represented by trace  30  has already been processed several times by the receiver, and has already been subject to some signal quality analysis for the purpose of calculating a signal quality estimate. 
     Received message  30  is divided into predetermined first periods of time. The block decoder status of received message  30  during time period  34  is good, so the transmitted information is decoded. Likewise, communicating information  32  is divided into predetermined second periods of time. For the purposes of clarity, received message  30  and communicated information  32  are shown as being operated from the same clock. A time delay, or decoder latency, exists between received message  30 , received in time period  34 , and its presentation to the user as communicated information  32  in time period  36 . The delay is due to the process of decoding and correcting the digitally encoded received message  30 . For the purposes of clarity, the delay is shown as one time period. In most systems, the time delay between traces  30  and  32  is fixed. Alternately, traces  30  and  32  are asynchronous timed, and the delay between traces is either larger or smaller than one first, or second, time period. That is, received message  30  and communicated information  32  are managed with different clocks so that there is no correlation between the time periods of trace  30  and  32 . 
     In a GSM cellular telephone, time period  34  is typically 20 milliseconds (ms), and 456 bits of digitally coded information are packed into a time period, or frame. A segment of time  38 , within time period  34 , represents the time allotted for the receipt of a single bit of data. 
     FIG. 4 illustrates received message  30  during a time period  34  of poor signal quality, and demonstrates the warning feature of the invention. In some aspects of the invention, for example, the block decoder status of received message  30  during frame  34  is bad, and no transmitted information is decoded. Since the information processed by the receiver is not properly decoded, the entire frame of data is withheld. Prior art digital receivers typically operate by presenting no communicated information  32  during time period  36  (i.e., muting the received audio), when no received information  30  is obtained, or decoded, during time period  34 . 
     Referring again to FIG. 2, the signal quality estimate made in Step  22  is less than the first minimum quality level and the indicator is activated. The indicator signal is represented by trace  40  (FIG. 4) and the timing of the signal substantially matches communicated information trace  32 . That is, the signal quality estimate made for received message  30  during time period  34 , is displayed in time period  36 . Once again, indicator signal  40  is shown as operating with the same clock as traces  30  and  32 . Alternately, the timing of indicator signal may be different from that of traces  30  and  32 . In time period  36 , following first period  34 , received message  30  is successfully decoded, and the signal quality estimate is greater than the first minimum quality level. Therefore, decoded information is presented as communicated information  32  in time period  42 , after the processing delay. Indicator  40  is not activated in time period  42 . Indicator signal  40  can be used to turn on a tactical, visual, or audio warning. 
     FIG. 4 illustrates a static signal  44  superimposed upon the communicated information  32  presented in time period  36 , in response to received massage  30  received during time period  34 . Static signal  44  is added to communicated information  32  during the entire time period  36 . Since no decoded information is presented, the user hears only static during time period  36 . Alternately, indicator  40  is triggered just during parts of time period  36  so that static signal  44  is only superimposed during parts of time period  36 . Alternately indicator  40  and static  44  are triggered over multiple time periods so that static  44  is superimposed on communicated information over multiple time periods, i.e., periods  36  and  42 . In some systems suitable for GSM, an error rate of 15% is likely to cause the lack of information, or bad block decoder status, in received message  30  during time period  34 . Alternately, even if received message  30  of time period  34  is successfully decoded, the message may be of poor enough signal quality that a decision is made to overlay static  44 , with the decoded information as communicated information  32  during time period  36  to warn the user, see FIG.  5 . 
     Referring again to FIG. 2, it is an aspect of the invention that Step  22  includes comparing the signal quality estimate to a predetermined second minimum quality level. The information decoded in Step  25  is presented to the user in Step  26  as follows: 
     1) when the signal quality estimate in Step  22  is greater than, or equal to, the second minimum quality level, the decoded information is presented; and 
     2) when the signal quality estimate in Step  22  is less than the second minimum quality level, the decoded information is not presented, whereby the user is not presented with communicated information when the received message quality is below a specified standard. In some systems suitable for GSM, for example, the second minimum quality level is a 15% error rate. 
     FIG. 4 illustrates the use of the signal quality estimate with the first and second minimum quality levels. Since the signal quality estimate is less than the first minimum quality level, the static warning is triggered. That is, static is presented as communicated information  32  during time period  36 . Since the signal quality estimate is below the second quality estimate, the decoded information is not presented as communicated information  32  during time period  36 . In this aspect of the invention the first and second minimum quality levels are substantially equal. 
     FIG. 5 illustrates received message  30  during a time period  34  of moderately poor signal quality, and demonstrates another aspect of the warning feature of the invention. The signal quality estimate made in Step  22  is greater than a second minimum quality level, so that decoded information is presented as communicated information  32  in time period  36 . However, in this aspect of the first and second minimum quality levels are not equal, so that decoded information and static  44  are presented as communicated information  32  during time period  36 . In a more sophisticated aspect of the invention, the factors in triggering the static warning and presenting the decoded information are not necessarily the same. The warning and decoding circuits are independent. That is, the two quality determination systems may use different quality inputs, or weight the same quality inputs differently. Also, since the decoding function occurs relatively early in the message receive process, in some aspects of the invention, the decoder circuitry provides outputs that are signal quality inputs for the warning indicator measurement system. Thus, the calculation of whether to present static  44  and decoded information as communicated information  32  are both independent and interrelated. For example, FIG. 4 indicates a situation where the signal quality is low and the quality indicator for both static indicator  44  and decoded information are below their minimum values, i.e., the block decoder status is bad, and the first and second minimum quality levels are defined as a bad block decoder status. In another example, FIG. 5 represents a case where the signal quality is above the second minimum. The decoded information is presented, but since the quality estimate is below the first minimum, static  44  is triggered. For example, in one aspect of the invention the first minimum is a bad block decoder status, and the second minimum is a bad path metric. When received message  30  has a good block decoder status and a bad path metric in time period  34 , then both static and the decoded information are presented to the listener as communicated information  32  in time period  36 . 
     Referring to FIG. 2, it is an aspect of the invention that step  22  includes comparing the signal quality estimate to a predetermined third minimum quality level. Step  26  includes presenting extrapolated information and decoded information as follows: 
     1) when the signal quality estimate is greater than, or equal to, the third minimum quality level in step  22 , decoded information is presented; and 
     2) when the signal quality estimate is less than the third minimum quality level in step  22 , extrapolated information is presented, whereby the user is presented with extrapolated information when the message information is not properly received. 
     FIG. 6 illustrates received message  30  during a time period  34  of poor signal quality, demonstrating the extrapolated information function (prior art). During time period  34 , when the signal quality estimate of received message  30  is less than the third minimum quality level, an extrapolated information trace  46  is turned on. The extrapolated information itself is represented by trace  48 . Extrapolated information, in some aspects of the invention, is a repetition of the information presented to the user during the previous time segment. Alternately, extrapolated information is a more sophisticated attempt to supply the user with actual data, or at least supply information that the user does not find annoying. Extrapolated information is dependent on amount of time, or decoded bits, since good information has been received. That is, extrapolated information can more accurately mimic decoded information immediately after good decoded information has been received. If decoded information is not received for a long period of time, then extrapolated information is typically just non-annoying information or silence. As with the other signals, the timing of traces  46  and  48  has been shown to be synchronous with traces  30  and  32  for the purposes of clarity. Alternately, traces  46  and  48  are asynchronous with traces  30  and  32 . 
     The information demodulated, or decoded, in response to received message  30  during time period  34  is not presented as communicated information  32  during time period  36 . Rather, extrapolated information  48  is presented as communicated information during time period  36 . During time period  36 , received message  30  is properly recovered. The signal quality estimate is greater than the third minimum quality level, and the decoded information is presented as communicated information  32  during time period  42 . FIG. 6 illustrates a situation where the second and third minimum quality levels are substantially equal. Alternately, the second and third quality levels are not equal so that a signal quality estimate between the second and third levels causes no information, either decoded or extrapolated, to appear on communicated information trace  32  during time period  36 . In another alternative, the second and third minimum quality levels overlap so that demodulated and extrapolated information are both presented in a mixture on communicated information trace  32  during time period  36 . 
     FIG. 7 illustrates received message  30  during a time period  34  of poor signal quality, demonstrating the extrapolation and indicator functions of the invention. FIG. 7 is a combination of FIGS. 4-6. For the purposes of clarity, the first, second, and third minimum quality levels are approximately equal. During time period  34 , the signal quality estimate is below first, second, and third minimum quality levels. Indicator signal  40 , static  44 , and extrapolated information  48  are generated, so that static  44 , is superimposed upon extrapolated information  48 , and presented as communicated information during time period  36 . Alternately, the first, second, and third minimum quality levels are not equal so that the muting, indicator, and extrapolated information turn on at different times. As mentioned above in the discussion of FIG. 5, in more sophisticated aspects of the invention, the calculation of signal quality is carried out by separate systems for the calculation of first and second minimum quality levels. This same analysis also applies to the calculation of when to present extrapolated information  48 , and the definition of the third minimum quality level. Also, the calculation systems are likely to be interrelated. The extrapolation circuitry is likely to be heavily dependent on the decoded information circuitry, since extrapolated information is likely to be based on decoded data from prior periods of time. In other alternatives of the invention, the various signals of FIG. 7 are clocked asynchronously. 
     Referring to FIG. 2, one aspect of the invention includes the further steps, following Step  22 . Step  27  averages the estimated signal quality of messages received over a plurality of predetermined first periods of time to create an average signal quality estimate. Step  28  activates the indicator in Step  23  in response of the average signal quality estimated in Step  27 , to present the warning indicator to the user over a predetermined number of predetermined second periods of time. The static noise patterns presented to the user closely simulate the characteristics of an analog receiver. 
     FIG. 8 illustrates received message  30  during a time period  34  of poor signal quality, demonstrating the indicator averaging function of the present invention. As in FIGS. 3 through 7 above, the quality of the message received during first time period  34  is poor, the block decoder status is bad. In response, warning indicator  40  is triggered during time period  36 . However, in addition to being triggered in time period  34 , indicator  40  is also triggered in time period  42 . Therefore, static  44  is presented to the user as communicated information in time periods  36  and  42 . As in FIGS. 3-7, received message  30 , and communicated information  32  are arbitrarily shown in a synchronous relationship for the purposes of clarity. The signal quality estimate is averaged over portions of a first time period, a single time period, or over several first time periods. Likewise, depending on the method used to calculate the average, indicator  40  is presented to the user over a portion of a second time period, a single time period, or several second time periods. 
     Static warning indicator  44 , activated above, has a predetermined indicator signal amplitude, a predetermined indicator signal duration, a predetermined indicator signal spectral content, and a predetermined time domain shape, which vary in response to the average signal quality estimate. FIG. 8 illustrates that indicator signal  40  has a ramp shape in time period  42 , so that less of static noise  44  is presented in the communicated information in time period  42 . A linear relationship between indicator signal  40  and amplitude of static presented as communicated information  32  is shown presented in FIG.  8 . 
     In another alternative aspect of the invention, indicator signal  40  during time period  42  is a pulse having a smaller amplitude than in time period  36 . As a result, the static presented as communicated information  32  during time period  42  is of a smaller amplitude than the static presented as communicated information  32  during time period  36 . A reduction in static is performed, in some aspects of the invention, to provide a warning, averaged over a plurality time periods, in response to a single frame of received message  30  having a low signal quality. Sometimes this averaging effect gives the digital receiver a more “analog feel”, and is more pleasing to the ear of the listener. In other variations the amplitude of the static presented as communicated information  32  is responsive to the quantitative value of signal quality estimate (see FIG.  9 ), the difference between the signal quality estimate and the first minimum quality level, or the amplitude of indicator  40 . For example, when the signal quality of received message  30  is low during time period  34 , and medium during time period  36 , then the static amplitude of communicated information  32  is high during time period  36 , and medium during time period  42 . 
     The length of time that static is presented as communicated information  32  varies in many aspects of the invention. The average signal quality estimate is calculated according to a variety of mathematical algorithms including the averaging of many time periods together, and an average that includes past history of the signal quality estimate mixed together with the instantaneous signal quality. The indicator signal also takes a variety of forms, including simply being off and on, and having amplitudes and shapes to mix the static signal  44 , or other indicators, into communicated information  32 . In addition, the spectral content of static signal  44  is manipulated in response to average signal quality estimate to, for example, have a frequency content corresponding to different levels of signal quality. 
     The extrapolation and muting functions are also used with the average signal quality estimate. FIG. 8 illustrates the signal quality estimate being below the second minimum quality level in time period  34  so that no decoded information is presented as communicated information  32  during time period  36 . Alternately, decoded information and extrapolated information signal  48  (FIG. 7) are responsive to the average signal quality estimate, so that the amplitude, duration, spectral content, and time domain shape vary as indicator signal  40 , described above. 
     Referring again to FIG. 2, it is an aspect of the invention that the signal quality estimated in Step  22  is responsive to received message quality data such as the received message signal strength, which provides a measurement of carrier power of a received message. The carrier power of a received message must have a threshold above the basic noise level for a message to be received properly. Received carrier power impacts radio link quality as shown in FIG.  1 . While the received carrier power may vary greatly before the perceived quality level of digital phone is compromised, a weakening of the received message signal strength may also be used to indicate that the user is about to suffer degraded communications. Indirectly, received signal strength provides an indication of signal quality. 
     It is an aspect of the invention that the signal quality estimated in Step  22  is responsive to block decoder status, which indicates whether received messages are successfully decoded into information, and path metric data, which provides a measurement of the corrections required to decode message information. The signal quality is based on the amount of lost information, and the amount of corrected information. 
     Referring to FIG. 3, each received message  30 , before demodulation, includes several data bits, for example, data bit  38 . Several of the bits are not strictly information, some are code bits added so that the receiver is able to recover corrupted bits in the received message. “Raw” speech is converted into digital information at 64 kilobits per second (kb/sec). To save bandwidth, digital wireless telephones compress the 64 kb/sec data into 13 kb/sec by removing inherent redundancy. Most of the redundant information is restorable by the receiver. Error protection bits are added to the 13 kb/sec of information, resulting in 23.8 kb/sec of “protected” speech being transmitted. The coded bits are use to detect, and then correct, corrupted information bits. 
     Unfortunately, error protection schemes are not always capable of correcting every incorrectly received bit of data. In one popular digital cellular system, the decoding algorithms begin to loose the ability to correct bit errors when the error rate increases beyond 15 percent. At approximately a 15 percent error ratio, communicated information, mixed with errors, is presented to the listener. Even when the information is discernible, its presentation to the user is often annoying. Generally, the manufacturers of communication equipment make a design decision as to what percentage of error bits will be tolerated before the communicated information is muted. That is, decoded information containing error bits above a predetermined number is not presented to the user in the fear that this communicated information, at least partially, contains corrupted information and errors. 
     Block decoder status is information generated by a receiver in response to whether each block of coded information received, has been successfully decoded, or whether it has been unsuccessfully decoded due to the presence of too many bit errors. The presence of information blocks having so many errors as to prevent correction, is a strong indicator of poor signal quality. 
     Path metric data is a finer measurement of received signal quality than the block decoder data. The path metric data measures how many bits of a received message received during a certain period of time actually required correction. For example, as a user begins to receive a message of poor signal quality, the decoded information being presented perfectly to the user will initially be perfect. That is, even when there is a high path metric, or many bit corrections, the block decoder status is initially good. However, a high path metric may be an indication that the user will soon be required to change positions in order to maintain adequate communication. 
     It is an aspect of the invention that the communication system is a GSM cellular phone network with intercommunicating mobile station telephones. Referring to FIG. 2, the signal quality estimated in Step  22  is also responsive to the following network-controlled message quality data: 
     mobile station transmitter carrier power level, which provides an indication of signal quality as measured by a communicating base station; 
     timing advance, which provides a measurement of how far a mobile station is from a communicating base station; and 
     the status of the discontinuous transmission (DTX) function, whereby the message quality standards are adjusted in response to the increased sensitivity of the transceiver to message errors when DTX mode is in use. 
     In a typical cellular telephone network, the base station determines the carrier power level and timing advance used by the mobile station. A high mobile station transmitter carrier power level indicates that the mobile station is being poorly received at the base station. Likewise, when the base station orders the mobile station to advance the timing of all transmissions to the base station, this is an indication that the mobile station is a far distance from the base station, and that the signal quality, as measured by the base station, is poor. 
     The DTX function is initiated by the base station in some cellular telephone systems. The DTX function attempts to save mobile station battery power by ordering the mobile station not to transmit when there is no information. That is, when DTX mode is in use, the mobile station does not transmit background noise for periods of time when the user is not speaking. However, the DTX mode makes the loss of transmitted messages more critical, since redundant messages are no longer being sent. Therefore, it is typical to adjust the signal quality to more heavily weight the frame loss count when DTX mode is in use. 
     In one preferred embodiment of the invention, the communication system is a digital television signal broadcast to digital televisions. The signal quality estimated in Step  22  is responsive to the detection of the loss of sequential broadcast frames, as well as receiver carrier power, block decoder data, and path metric data. 
     In one aspect of the invention, the information decoded in Step  25  is a video signal having both visual and auditory signal components. The warning indicator in Step  23  is a snow-like visual degradation, such as experienced when the cable, or antenna, signal to an analog television is weak. Thus, the user sees an intuitive warning that the received message quality is poor. In another aspect of the invention the indicator signal in Step  23  is static noise whereby the user hears an intuitive warning that the received message quality is poor. In another aspect of the invention the warning indicator signal in Step  23  is both a static noise and a snow-like visual degradation, whereby the user experiences the familiar characteristics of analog television to warn of poor received message quality. The use of static and snow-like visual degradation in response to poor signal quality is perceived of as more leasing to a user than solid color blocks or screens that continue to hold the last decoded message, which are typically used in the prior art. 
     FIG. 9 is a block diagram of the system of the present invention system for indicating the signal quality of a received message. The system is used in a wireless communication, or telephone, system including a plurality of intercommunicating transceivers, or mobile station telephones, to send or receive messages of digitally encoded information. Alternately, the system indicates the signal quality of a received message used in a wireless communication system including a plurality of receivers to receive message of digitally encoded information. A signal quality estimator  70  includes inputs  72  through  82  to accept received message quality data. Signal quality estimator  70  includes an output  84  to provide a signal quality estimate in response to the received quality data accepted at inputs  72  through  82 . The system also includes an indicator  86  having an input operatively connected to output  84  of signal quality estimator  70  to accept the signal quality estimate. Indicator  86  has an output  88 , to warn of poor signal quality, which is activated in response to the signal quality estimate on line  84 . Indicator  86  warns a transceiver, receiver, or mobile station telephone user of a poor communications link. In one aspect of the invention, the receiver includes separate information decoder, information extrapolation, and indicator warning systems. The systems, even though they are interrelated, independently determine whether they are triggered, and the resulting outputs are mixed and presented to the user. FIG. 9 is a simplified version of such a system. 
     In one aspect of the invention, the system includes a mobile station, having a size and weight small enough manipulable by the user. The user has the option of changing the location of the mobile station in response to an indicator warning that the received message signal quality is poor. 
     In one aspect of the invention indicator  86  is a visual display, whereby the user sees a warning that the received message quality is poor. In another aspect of the invention indicator  86  is a tactile device, whereby the user feels a warning that the received message quality is poor. Alternately, indicator  86  is an auditory generator, whereby the user hears a warning that the received message quality is poor. 
     Signal quality estimator  70  includes an input  90  to accept a predetermined first minimum quality level. Signal quality estimator  70  provides a signal quality estimate on line  84  as follows: 
     1) when the signal quality estimate is greater than, or equal to, the first minimum quality level on line  90 , indicator  86  is provided with a signal that does not activate indicator  86 ; and 
     2) when the signal quality estimate is less than the first minimum quality level on line  90 , indicator  86  is provided with a signal on line  84  that activates indicator  86 . The user is warned of received message quality below a specified standard. 
     Signal quality estimator  70  includes an input  74  responsive to block decoder status, which indicates whether received messages are successfully decoded into information. Signal quality estimator  70  includes an input  76  responsive to path metric data, which provides a measurement of the corrections required to decode message information. Further, signal quality estimator  70  has an input  72  responsive to receive message signal strength, which provides a measurement of the carrier power of a received message. The signal quality estimate output on line  84  is based on carrier power, the amount of information lost, and the amount of corrected information. 
     In one preferred embodiment, the communication system is GSM cellular phone network of intercommunicating mobile station telephones. Signal quality estimator  70  includes inputs responsive to the following network-controlled message quality data: mobile station transmission carrier power level on line  78 , which provides an indication of the signal quality as measured by a communicating base station; timing advance on line  80 , which provides a measurement of how far a mobile station is from the communicating base station; and the status of the discontinuous transmission (DTX) function on line  82 , so that the message quality standards are adjusted in response to the increased sensitivity of the transceiver to message errors when DTX mode is in use. 
     In another preferred embodiment, a communication system is a digital television signal broadcast to digital televisions. Signal quality estimator  70  includes an input, not shown, responsive to the detection of the loss of sequential broadcast frames. 
     It is an aspect of the invention that signal quality estimator  70  averages the received message quality data input over a plurality of predetermined first periods of time to provide a signal quality estimate average output on line  84  that is an average of the signal quality. Warning indicator  86  is activated during a predetermined number of predetermined second periods of time in response to the signal quality estimate average. Indicator  86  is activated in response to a pattern of received message quality. 
     It is an aspect of the invention that warning indicator  86  is a static noise generator having an input operatively connected to signal quality estimator output  84  to accept the signal quality estimate, and an output  88  to provide a static warning. The user, hearing the static, has an intuitive sense of the received message quality. Static generator  86  includes a static noise source  92  having an output  94  to provide static noise. Static generator  86  includes a mixer circuit  96  to control the amplitude of static warning output  88 . Mixer  96  has two inputs and an output, a first input operatively connected to signal quality estimator output  84  to accept the signal quality estimate, and a second input operatively connected to static noise source output  94  to accept static noise. Mixer  96  controls the amplitude of the static noise in response to the signal quality estimate to generate static warning output on line  88 , whereby the user hears louder static when the received message is of poorer quality. 
     In one preferred embodiment of the invention, the encoded information transmitted by the communicating partner is audio, whereby a digital radio telephone user has an intuitive warning of signal quality that is similar to that of an analog wireless phone. That is, the user of an audio communications product is accustomed to hear static as an indicator of link quality. 
     It is an aspect of the invention that the system further comprises a receiver  98  having an input  100  to accept received wireless messages, and an output  102  to provide digitally encoded messages. The system also comprises a decoder circuit  104  to decode digital information, having an input operatively connected to receiver output  102  to accept a digitally encoded message, and an output  106  to provide decoded information. The system further comprises an adder circuit  108  to combine the decoded information on line  106  with the static warning on line  88 . Adder circuit  108  has a first input operatively connected to static noise generator output  88  to accept the static warning, a second input operatively connected to decoder circuit output  106  to accept decoded information, and an output  110  to provide communicated information to the user as a combination of decoded information with an indication of signal quality. The combination of static with decoded information gives the user an intuitive sense of the received message quality. 
     It is an aspect of the invention that signal quality estimator  70  includes an input  112  to accept a predetermined second minimum quality level. As noted above, decoder circuit  104  has an input operatively connected to signal quality estimator output  84 . Decoder circuit  104  is responsive to the signal quality estimate on line  84  to provide decoded information as follows: 
     1) when the signal quality estimate on line  84  is greater than, or equal to, the second minimum quality level on line  112 , decoded information is provided on line  106  to adder circuit  108 ; and 
     2) when the signal quality estimate on line  84  is less than the second minimum quality level on line  112 , no decoded information is provided on line  106  to adder circuit  108 . The user is not presented with decoded information when a received message quality below a specified standard. 
     It is an aspect of the invention that adder circuit  108  includes an input  114  to accept extrapolated information. Signal quality estimator  70  includes an input  116  to accept a predetermined third minimum quality level. The system further comprises an extrapolator circuit  118  having an input operatively connected to signal quality estimator output  84  to accept the signal quality estimate, and an input operatively connected to decoder output  106  to accept decoded information. 
     Extrapolator circuit  118  has an output operatively connected to adder circuit input  114  to provide extrapolated information. Extrapolator  118  is responsive to the signal quality estimate on line  84  as follows: 
     1) when the signal quality estimate on line  84  is greater than, or equal to, the third minimum quality level on line  116 , no extrapolated information is provided to adder circuit  108 ; and 
     2) when the signal quality estimate on line  84  is less than the third minimum quality level on line  116 , extrapolated information is provided to adder circuit  108 . The user is presented with extrapolated information in response to the received message quality. 
     In one preferred embodiment of the invention the encoded information is video, having visual and audio signal components, and warning indicator output  88  is static noise, whereby the user has an intuitive warning of signal quality to help adjust reception of the message. In another aspect of the invention, warning indicator output  88  is snow-like visual distortion, whereby a user has an intuitive warning of signal quality to help adjust reception of the message. In another aspect of the invention the warning indicator output  88  is both static noise and snowSMT like visual distortion, whereby the user has an intuitive warning of signal quality similar to that of an analog television. 
     Alternately, signal quality estimator  70  may provide three different signal quality estimates (not shown) to static noise generator  86 , decoder  104 , and extrapolator circuit  118 . These three signal quality estimates are responsive, respectively, to first quality level on  90 , second quality level on line  112 , and third quality level on line  116 . Thus, the triggering of indicator  86 , muting of the decoder  104 , and triggering of extrapolator  118  are performed at different estimates of signal quality. As another alternative, two minimum quality levels are equal, the second and third levels for example. Then, the warning indicator is activated when the signal quality is below the first minimum quality level, and when the signal quality level is below the second (third) quality level, extrapolated information is presented instead of decoded information. When the first, second and third quality levels are the same, the same signal quality estimate  84  is provided to indicator  86 , decoder  104 , and extrapolator  118 . 
     FIG. 9 depicts the invention configured with electrical and mechanical elements. Alternately, many of the functions shown in FIG. 9, and mentioned above, are enabled through the use of software routines. Software routines perform comparison, averaging, extrapolation, mixing, adding, and calculation, and are well known in the art. 
     New types of communication systems are currently in development, and the ones presently in existence are being improved to incorporate the performance enhancement features of digital systems. In addition, the price and size of the units in many of these communication systems allow them to be portable, handheld, and even pocket size. While the presence of static in a telephone signal, or snow in a television picture, is typically experienced as an annoyance by the user, they also provide the user with a non-quantitative measurement of signal quality. The more static a received message has, the poorer the signal quality. A user motivated to receive a high quality signal knows enough to change location in response to the presence of static. Because of the superior performance of digital systems in environments where a wireless link, or radio frequency, message is poor, users are not aware that they may be perilously close to loosing a message. The system and method of the present invention gives the user of the digital communication products a warning of poor wireless message quality. The use of static provides the user with an intuitive sense of measurement quality that people have inherently learned from decades of using analog communication products. 
     Although a preferred embodiment of the invention is applicable to digital cellular phones, the invention is also applicable to digital paging systems, and digital television broadcast systems. Other modifications and variations within the scope of the present invention will occur to those skilled in the art.