Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/30—Monitoring; Testing of propagation channels
  • H04B17/309—Measuring or estimating channel quality parameters
  • H04B17/318—Received signal strength
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/20—Monitoring; Testing of receivers
  • H04B17/23—Indication means, e.g. displays, alarms, audible means
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/06—Receivers
  • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
  • H04B1/1027—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal

Definitions

• This invention relates to communications systems, and more particularly to mobile radiotelephone communications systems which communicate with terrestrial base stations or orbiting satellites.
• Radio communications systems are increasingly being used for wireless mobile communications.
• Radio communications systems use mobile radiotelephones which communicate with terrestrial base stations or orbiting satellites.
• An example of a mobile radiotelephone communications system is a cellular telephone system.
• Cellular telephone systems are wide area communications networks which utilize a frequency reuse pattern.
• the design and operation of an analog cellular telephone system is described in an article entitled "Advanced Mobile Phone Servi ce” by Blecher, IEEE Transactions on Vehicular Technology, Vol. VT29, No. 2, May 1980, pp. 238-244.
• the analog mobile cellular system is also referred to as the "AMPS" system.
• TDMA Time- Division Multiple Access
• EIA Electronics Industries Association
• TIA Telecommunications Industries Association
• ADC American Digital Cellular
• GSM Global System for Mobile communications
• mobile radiotelephones include an antenna and a transceiver for receiving radiotelephone communications via the mobile radiotelephone antenna.
• the antenna is typically mounted on the vehicle body.
• the antenna typically projects from the housing of the handportable radiotelephone.
• Proper orientation of the antenna relative to the radiotelephone communications signal is important for clear reception without distortion or dropouts.
• often a slight reorientation of the antenna produces a marked improvement in radiotelephone reception.
• handportable phones suffer a loss of signal strength when the transmission is being received from the other side of the user's head. Head blockage can cause 6dB loss of signal.
• antenna orientation is so important in a mobile radiotelephone, many mobile radiotelephones provide a display of the received signal strength of the radiotelephone communications signal, which can prompt the user to reorient the antenna. Moreover, the quality of the received signal in an analog or uncoded digital mobile radiotelephone system tends to degrade gradually with increasing misalignment of the antenna. Thus, the noise level tends to gradually increase, which can prompt the user to reorient the antenna, by moving the vehicle or the handportable radiotelephone, in order to reduce this noise . It is now common to employ digital speech coding and/or digital error correction coding in radio communications systems, in order to improve communications efficiency.
• This digital coding permits communications at good quality down to very low signal- to-noise ratios as low as 2dB or less, with very sharp cutoff below this threshold.
• the graceful degradation of analog FM or uncoded systems is lost and is replaced with an abrupt cutoff below a threshold.
• poor orientation can cause the signal strength to fall below the threshold so that communications abruptly cease. The decrease in signal strength is not accompanied by an increase in noise level which could prompt antenna reorientation.
• a mobile radiotelephone which injects an audible alignment signal, which is a function of the orientation of the radiotelephone antenna, into the audible radiotelephone communications.
• the audible alignment signal prompts the radiotelephone user to reorient the radiotelephone antenna for improved alignment relative to the source of the radiotelephone communications.
• the received radiotelephone communications have a received signal strength which is a function of the location of the radiotelephone antenna.
• an audible alignment signal which is a function of the received signal strength of the radiotelephone communications, is injected into the audible radiotelephone communications.
• the audible alignment signal can be a direct function of received signal strength, or it can be a function of another parameter which indirectly depends on signal strength, such as distortion or noise level.
• the audible alignment signal is preferably artificial noise which is injected into the radiotelephone loudspeaker along with the radiotelephone communications signal, and thereby restores subjective graceful degradation behavior to the received radiotelephone communications. By artificially restoring subjective graceful degradation behavior, the present invention prompts the user to reorient the radiotelephone antenna for receiving radiotelephone communications.
• a mobile radiotelephone includes means for receiving radiotelephone communications, including an antenna and a radio transceiver.
• Signal strength indicating means is responsive to the receiving means for producing a signal strength indication which is a function of the signal strength of the received radiotelephone communications. As described above, the signal strength indication may be a direct or indirect function of signal strength.
• Acoustic transducing means which typically includes one or more loudspeakers or earspeakers and which may include voice codecs and other circuitry, is responsive to the receiving means and to the signal strength indicating means to produce an audible signal which combines the received radiotelephone communications and the signal strength indication, such that an audible signal strength indication is provided along with audible radiotelephone communications.
• the present invention is particularly useful in digital coded mobile radiotelephones or other mobile radiotelephone systems wherein the receiving means is an abrupt cutoff receiving means, which produces an audible radiotelephone communications signal when a received signal strength of a radiotelephone communications signal is above a threshold and which suppresses or cuts off the audible radiotelephone communications signal when the received signal strength is below the threshold.
• the signal strength indicating means produces a warning signal which is a function of the received strength of the radiotelephone communications signal to indicate that the received signal strength is approaching the threshold.
• the signal strength indicating means preferably comprises means for producing artificial noise which increases as a function of the decrease in the received signal strength of the radiotelephone communications signal, to thereby indicate that the received signal strength is degrading or approaching the threshold.
• the artificial noise increases as a function of the decrease of the received signal strength from a received signal strength which is above the threshold to a received signal strength which is below the threshold, to thereby indicate that the received signal strength is approaching the threshold and has passed through the threshold.
• audible indications that increase in intensity with increase in signal strength may also be used.
• the artificial noise level can still prompt the user as to antenna reorientation which will restore communications.
• the artificial noise can be any signal which is different from the received radiotelephone communications and which changes as a function of antenna orientation.
• the artificial noise may be broadband white noise or pink noise, a single sinusoidal frequency or multiple sinusoidal frequencies which change in amplitude or frequency as the signal strength decreases.
• the artificial noise may be a periodic signal, such as a click or chirp, the repetition periodicity of which changes as a function of changes in the received signal strength of the radiotelephone communications signal, to indicate that the received signal strength is degrading or approaching the threshold. This changing periodicity signal may sound like a radio tuning indication.
• the artificial noise may also be a synthesized voice message such as the audible word "move", which increases in amplitude or frequency as the received signal strength decreases.
• the present invention is also particularly useful with mobile radiotelephone systems which use automatic power control at the transmitter (terrestrial base station or satellite) .
• These transmit power control systems cause the transmitter to increase its power in response to an indication from the mobile radiotelephone that the mobile radiotelephone is receiving a low signal strength.
• This automatic power control system provides an even sharper threshold because it prevents signal degradation for slow decreases in received signal strength which the automatic power control system can track, until no more power can be provided.
• a transmit power indicating signal is transmitted by the transmitter along with radiotelephone communications.
• the audible alignment signal is also made responsive to the transmit power indicating signal which is received by the radiotelephone, to thereby produce a signal strength indication which is a function of the signal strength of the received radiotelephone communications and of the transmit power of the received radiotelephone communications.
• the present invention prompts a user to reorient the radiotelephone antenna for better reception by injecting an audible artificial noise signal into the audible radiotelephone communications. The user can be prompted to reorient the antenna before audibly degraded communications is reached. Improved mobile radiotelephone communications are thereby provided.
• Figure 1 is a block diagram of a mobile radiotelephone wherein the present invention may be used.
• FIG 2 is a block diagram of a receive Digital Signal Processor (DSP) which produces an alignment signal according to the present invention.
• Figure 3 illustrates operations for producing a first alignment signal according to the present invention.
• DSP Digital Signal Processor
• Figure 4 illustrates operations for producing a second alignment signal according to the present invention.
• Figure 5 is a block diagram of received signal processing according to a second embodiment of the invention.
• Figure 6 is a block diagram of a demodulator according to the second embodiment of the invention.
• Mobile radiotelephone 100 may be a vehicular mobile radiotelephone but is preferably a handportable mobile radiotelephone.
• Mobile radiotelephone 100 typically receives radiotelephone communications 150 from a terrestrial base station 155 or an orbiting satellite (not shown) .
• Figure 1 is a simplified representation of a dual-mode cellular radiotelephone which is described in greater detail in U.S. Patent Application Serial No. 07/967,027, entitled "Mul ti -Mode Signal Processing" by coinventor Paul . Dent and Bj ⁇ rn Ekelund and assigned to the parent company of the present assignee, the disclosure of which is hereby incorporated herein by reference .
• antenna 145, radio transceiver 140 and receive Digital Signal Processor (DSP) 125 function as means for receiving radiotelephone communications 150.
• Receive DSP 125 processes the signal which is received from the radio transceiver 140 via DSP interface 135 and produces a digital audio signal which can be applied to voice codec 115 for transmission over an acoustic transducer such as a loudspeaker 110.
• Transmit DSP 120 receives a digitized voice signal from microphone 105 via voice codec 115 and provides this signal to DSP interface 135 for transmission by radio transceiver 140 and antenna 145.
• Microcontroller 130 controls some or all of the components of the mobile radiotelephone 100. The design of mobile radiotelephone 100 is well known to those having skill in the art and need not be described further herein.
• the present invention is preferably embodied, in part, as a stored program which executes on the receive DSP 125, which may be, for example, a Texas Instruments Inc.
• Instruments C53 Digital Signal Processor may also be embodied, in part, as a stored program executing on microcontroller 130 or on another processor. Alternatively, custom logic designs, or combinations of software and hardware may be used. In an analog radiotelephone system, analog components may be used.
• receive DSP 125 includes communications signal producing means 210 which produces a digital received radio communications (voice) signal 250 from the radiotelephone communications which is received from DSP interface 135.
• Communications signal 250 is applied to voice codec 115 for conversion to an analog signal, which is supplied to loudspeaker 110 to produce audible radiotelephone communications.
• Communications signal processing means 210 may include digital speech decoding and error correction functions to produce an abrupt cutoff receiver using techniques well known to those having skill in the art.
• receive DSP 125 also includes alignment signal producing means 220.
• Alignment signal producing means 220 may receive an indication of received signal to noise ratio from DSP interface 135.
• radio transceiver 140 may produce a received signal strength indication signal.
• receive DSP 125 or microcontroller 130 may generate a received signal strength indication signal from the received radio communications. The generation of a received signal strength signal is well known to those having skill in the art and need not be described further.
• Alignment signal producing means 220 produces an alignment or warning signal 240 which is a function of the received signal strength of the radiotelephone communications signal .
• the alignment signal 240 is injected into the audible radio communications signal by combining the digital received radio communications signal 250 and the alignment signal 240 at summer 230.
• Summer 230 produces a combined signal 260 which is provided to voice codec 115 for conversion to an analog signal and broadcast over loudspeaker 110.
• the radio communications signal 250 and alignment signal 240 need not be combined, but rather may be separately provided to one or more loudspeakers or earpieces 110, as long as an audible alignment signal is injected into the audible radiotelephone communications.
• alignment signal producing means 220 and summer 260 form injection means for injecting an audible alignment signal which is a function of the orientation of the radiotelephone antenna, into the audible radiotelephone communications.
• Acoustic transducing means, such as loudspeaker 110 and voice codec 115 are responsive to receive digital processor 125 to produce an audible signal which combines the received radiotelephone communications signals 250 and the alignment signal
• an alignment signal (Block 220 of Figure 2)
• a signal is produced which increases as a function of decreasing received signal strength.
• an artificial noise signal is generated and is scaled or amplified by the signal which is produced at Block 310. Accordingly, artificial noise is produced whose amplitude increases as a function of decreasing received signal strength, thus providing an artificial indication of gradual degradation of signal strength.
• the amplified artificial noise is injected into the audible radiotelephone communications.
• the artificial noise signal can be white noise, pink noise or any other kind of broadband noise, or may be single or multiple frequency noise such as sinusoidal noise or multiple sinusoids whose amplitudes increase or decrease with a reduction of received signal strength.
• an audible indication which increases with signal strength is chosen to have "pleasing" characteristics, such as a musical major chord, while an audible indication that increases with worsening signal would be given "non- pleasing" characteristics, such as white noise or a discord.
• the artificial noise signal preferably becomes audible above the threshold and becomes stronger as the received signal strength passes through the threshold and drops to below the threshold, to prompt the user to reorient the radiotelephone antenna to restore communications.
• a second embodiment 220' of alignment signal producing 220 of Figure 2 will now be described.
• a first signal is produced which increases as a function of decreasing received signal strength, as was already described in connection with Block 310.
• a second signal is produced which increases as a function of increasing transmit power.
• the base station 155 ( Figure 1) or satellite increases its transmit power in response to an indication that the mobile radiotelephone 100 is receiving a less than desired signal strength, and decreases its transmit power in response to an indication that the mobile radiotelephone 100 is receiving a greater than desired signal strength.
• an indication of the base station or satellite transmit power is provided in downlink transmissions of radiotelephone communications 150 which are received by the mobile phone.
• a second signal is produced which increases as a function of increasing transmit power from the network. The audible indication is thus controlled by feedback from the network prompting the user to reorient his antenna in order to improve either up- or downlink.
• the first and second signals are combined to produce a third signal which varies as a function of the first and second signals.
• the third signal will increase as a function of decreasing received signal strength but will also increase as a function of increasing transmit power. Accordingly, when transmit power is increased, the alignment signal will increase to prompt the user to reorient the antenna so that the transmitter can produce lower transmit power.
• the alignment signal is produced.
• the artificial noise signal is a periodic signal such as a sine wave or clicks, the frequency of which is varied based on the value of the third signal.
• this variable frequency artificial noise signal provides a tuning indication wherein, for example, higher frequency indicates lower signal strength and higher transmit power.
• the artificial noise is injected into the radiotelephone communications.
• the present invention produces an audible alignment signal which is a function of the orientation of the radiotelephone antenna (and also possibly the transmit power of the base station or satellite) which indicates alignment or misalignment of the radiotelephone antenna for reception of the radiotelephone communications.
• the user is then prompted to reorient the antenna so that the alignment signal decreases.
• the invention provides a graceful degradation indication which can be used in analog systems to provide a graceful degradation indicator before actual system noise begins to intrude, and can be used in digital systems which employ coding to indicate that a cutoff threshold is about to be approached, or has been passed.
• the user is prompted to reorient the antenna and restore a high quality signal .
• Figure 5 illustrates a different partitioning of the block diagram of receive signal processing in either a radiotelephone or a transmitter (terrestrial base station or satellite) .
• Figure 5 is a functional partitioning corresponding to Figure 1 which is a hardware partitioning.
• Receive DSP 125 processes the converted received signal to perform demodulation and error-correction decoding functions 500 to obtain digital symbols representing coded speech.
• the coded speech is further decoded in DSP 125 and converted to analog speech by CODEC 115, which functions are designated as Block 510 in Figure 5.
• Block 500 also decodes command messages and passes them to control processor 130.
• Block 500 also produces a signal quality indication representing the probability that decoded bits passed to speech decoding 510 are error free.
• Speech decoder 510 may include the ability to ignore bits indicated to be unreliable and to output default speech sounds or otherwise conceal the effect of erroneous bits by a process known as "speech parameter interpolation" .
• Error concealment may include outputting "comfort noise” during periods of unreliable signal. The comfort noise avoids abruptly cutting off all acoustic output which gives the undesirable impression of "chopped" speech.
• the demodulation and decoding function 500 can additionally output a signal representing the radio noise which was removed in the decoding process, as will now be described.
• a Viterbi sequential maximum likelihood sequence estimator includes a State Memory 65 for storing a number of hypotheses of a received symbol sequence together with a path metric for each that is representative of cumulative probability. Processing comprises using a transmitter model 60 which may include a model of the propagation channel learned from processing a known bit sequence called a training sequence or syncword. The latter information is embodied in the Reference Vector Arrays in State Memory 65.
• Transmitter model 60 computes an expected signal value corresponding to a new bit hypothesis on the assumption, for each state in turn, that the previous hypotheses are true.
• the expected signal value is compared with the received signal value in comparator 61 to obtain the difference.
• the difference is a measure of the error between the hypothesis and the actual received signal sample, which error is only due to radio noise in the case that the hypothesis is correct.
• the mismatch indication is added to the previous path metric corresponding to the tested hypothesis to obtain a new cumulative mismatch or path metric .
• Adder 62 forms the new path metric from a state having a leftmost bit in the Current Hypotheses memory equal to binary '0', while adder 64 forms the new path metric for a corresponding Current Hypothesis which differs only in the leftmost bit position being a binary ' 1' .
• Comparator 63 compares the two new path metrics and selects the lower one and all corresponding contents of the associated state memory to become the new contents of a state memory, with a left shift of the leftmost bit (which will be a 0 or a 1 according to which state gave the lower path metric) out of Current Hypotheses and into Already Processed part of the memory.
• the comparator 61 computes the difference between a hypothesized signal value and an actually received signal value, which difference will be due only to radio noise in the case the hypothesized signal value is true. Instead of discarding this computed difference, an embodiment of the present invention records the differences alongside each data symbol in the Already Processed part of the state memory. When error correction coding produces several transmitted samples per original data bit to be transmitted, transmitter model 60 will likewise produce several signal samples for comparison and comparator 61 will test these plural samples to obtain several differences. These differences are normally combined as a sum of squares to obtain the mismatch indication before being discarded.
• the differences are saved in the state memory 65 against each processed bit decision.
• the saved differences from one state are allowed to overwrite the saved differences of another state when one of two compared hypotheses is selected to survive by the Viterbi process.
• the final bit decisions made by the Viterbi MLSE processor are those which minimize the sum square differences. Accordingly, the residual errors are likely to be due only to radio noise and not to incorrect bit decisions.
• the saved differences are therefore equal to the received radio noise and may be output to speech decoder 510. Speech coder 510 can add the radio noise samples to the audio signal so that the user will hear an exact representation of the radio noise characteristics varying proportionally with signal-to-noise ratio and not "chopped" by the abrupt threshold of the decoding process.
• Digital radiotelephones that employ digitization of speech signals often incorporate error detection codes as well as error correction coding.
• a Cyclic Redundancy Check (CRC) code is often appended to the most perceptually important bits in a digital speech transmission.
• CRC check fails, the erroneous bits are prevented from causing unwanted acoustic artifacts by various error concealment strategies also known as "deburping" .
• Such deburping can preserve useful speech qualities when the CRC fails as much as 5% of the time. Detection of CRC failure for more than 5% of the time can be used as a trigger to automatically add the audible signal quality indication to the telephone output in order to cause the user to take corrective action.
• the embodiment described above illustrates that noise representations arbitrarily close to the true radio noise can be extracted in principle from a demodulation and decoding process, and artificially reintroduced into an audio signal to give a true indication of rising or falling signal quality, independent of the thresholding characteristics of the demodulator.
• the path metric is proportional to the mean square of the radio noise and may be used to scale the audible indication according to the square of the radio noise, or indeed according to any power of the radio noise level .
• the audible indication thereby scaled can be a prestored audio waveform, if it is desired to reduce the complexity of the demodulation and decoding process.
• a waveform may be chosen to be a "displeasing" sound when it is indicative of falling signal quality.
• a "pleasing" waveform such as a major musical chord can be used when it is scaled inversely, i.e. by dividing it with a power of the path metric, so that its intensity increases with rising signal quality.
• a combination of a displeasing sound that increases with noise level and a pleasing sound that increases with signal level may also be employed, but at least the "pleasing" sound should be audible when the user selects the "audible tuning indication" to be enabled, so that he can prevent it from causing distraction during a voice conversation with otherwise good signal- to-noise ratio.
• the network may send command messages as previously described to controller 130 in order to remotely turn on or off an audible indication to realign the antenna.
• a command may be issued by the network either based on a signal strength measured by the mobile phone and transmitted as a signal strength report to the network, or may be based on a signal strength measured by the network receiver receiving the mobile phone's transmission, or a combination of both.
• mobile phones do not receive continuously in standby mode but wake up only in a so- called sleep-mode slot which is preassigned by the network to each mobile unit. This may only occur at 1 second intervals for example.
• the network knows when the mobile receiver will be awake and call alerts to that receiver are transmitted only at those times. Sampling the received signal only at one second intervals may be a little too slow to provide the user with a signal quality indication on standby that he can optimize by moving the antenna position.
• the user can be required to enable the audible indication by depressing a button, which, when the phone is in standby mode, can temporarily cause the receiver to operate continuously or at least sufficiently frequently to measure signal strength for the purposes of aligning the antenna.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Quality & Reliability (AREA)
• Mobile Radio Communication Systems (AREA)

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• 1997
  • 1997-03-07 EP EP97908929A patent/EP0895678A2/de not_active Withdrawn
  • 1997-03-07 CN CNB97193004XA patent/CN1135755C/zh not_active Expired - Fee Related
  • 1997-03-07 AU AU20716/97A patent/AU722052B2/en not_active Ceased
  • 1997-03-07 KR KR1019980707145A patent/KR100349192B1/ko not_active IP Right Cessation
  • 1997-03-07 WO PCT/US1997/003558 patent/WO1997034381A2/en not_active Application Discontinuation
  • 1997-03-07 JP JP9532694A patent/JP2000506699A/ja not_active Ceased
  • 1997-03-07 BR BR9708051A patent/BR9708051A/pt not_active IP Right Cessation

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