MXPA97006531A - System for voice messages and method for enabling the use of modulation components - Google Patents

Abstract

The present invention relates to a method for transmitting a message to a receiver comprising the steps of: temporarily separating the message into first and second message parts that are contiguous parts of the message in time, orthogonally modulating first and second orthogonal components with the first and second parts of the message, respectively for generating first and second orthogonally modulated components, and simultaneously transmitting the first and second orthogonally modulated components

Description

SYSTEM FOR VOICE MESSAGES AND METHOD TO MAKE EFFICIENT THE USE OF ORTHOGONAL MODULATION COMPONENTS Field of the Invention The invention relates to paging systems and more preferably to a voice paging system and a method for using components in an orthogonal modulation scheme.

Background of the Invention In a radio frequency (RF) communication system suitable for transmitting voice messages to portable receivers or other receivers, for example selective call receivers (eg pagers), single sideband modulation techniques are used for spectrum efficiency reasons . Today, only one of the upper or lower sidebands is used to transmit information to the receiver. The demodulation and reconstruction of a message that is sent entirely through the upper or lower sideband requires the receiver to sample the component in phase (I) and the component of quadrature.

(Q) of the signal for the duration of the message on the channel. Both sidebands are recovered, but the message is contained in only one of the sidebands. The information from the other sideband is discarded.

The fact that only one of the sidebands actually transmits the message is an inefficient use of "air" time that produces "traffic" inefficiencies in the assigned radio frequency band. In addition, this is an inefficient use of the processor power of the receiver and unnecessarily consumes battery power in a portable receiver device.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram of a selective call communication system according to the invention. Fig.2 is a diagram illustrating a subchannel spectrum according to the invention. Fig.3 is a block diagram of a transmitter according to the present invention. Fig. 4 is a diagram of a compandor module in the transmitter according to the invention. Fig. 5 is a block diagram of an orthogonal modulator according to the invention. Fig.6 is a block diagram of another orthogonal modulator according to the invention.

Fig.7 is a diagram illustrating the pulse response of a Hilbert filter according to the invention. Fig.8 is a polyphase diagram of the interpolation module of the transmitter according to the invention.

Fig.9 is a diagram of a pulse response of an interpolation filter in the interpolation module. Fig.10 is a block diagram illustrating the use of a time inverter module in the transmitter according to the invention. Fig.11 is a graph illustrating a voice message. Fig.12 is a diagram illustrating a digital representation of the voice message shown in Fig.11. Figs. 13 and 14 are diagrams illustrating representations of two halves of the voice message of the Fig.11 Figs.15-17 are time diagrams illustrating an example of a signaling protocol according to the present invention. Fig.18 is a block diagram of a receiver according to the present invention.

Detailed Description of the Drawings With reference to Fig. 1, an electrical block diagram of a radio communication system 100 according to the preferred embodiment of the invention is shown. The radio communication system 100 comprises a message input device, for example a conventional telephone 101, a fax machine 120 or a terminal for messages 122, connected through a conventional switched telephone network (PSTN) 108 by telephone connections conventional ones 110 with a system controller 102. The system controller 102 controls the operation of a number of radio frequency transmitters / receivers 103, through one or more telephone connections 116, which are generally twisted pair telephone cables and can also include radiofrequency, microwave, or other connections of high quality. The system controller 116 encodes and decodes incoming and outgoing telephone addresses in formats that are compatible with the terrestrial message switching computers. The system controller 102 also functions to encode and program outgoing messages, which may include information such as analog voice messages, digital numeric messages and response orders, for transmission. by the radiofrequency transmitters / receivers 103 to a number of selective call receivers 106, also called selective call radios to indicate that these devices have transmission capacity or "acknowledgment". The system controller 102 further functions to decode incoming messages, including response and non-request messages, received by the radio frequency transmitters / receivers 103 from the number of selective call receivers 106.

Examples of response messages are acknowledgments and designated response messages. An acknowledgment is a response to an outgoing message initiated in the system controller 102. An example of an outgoing numeric message intended for a selective call radio 106 is a numeric pager message that entered from the telephone 101. An example of a Outgoing analog message destined to a selective call radio 106 is a voice pager message that entered from the telephone 101. For these examples, the acknowledgment indicates the successful reception of the outgoing analog or numerical message. A designated response message is a message sent from a selective call radio in response to an order included in an outgoing message from the system controller 102. An example of a message from. The designated response is a message initiated by the selective call radio 106, but which is not transmitted until another designated response command is received from the system controller 102. The designated response command, in turn, is sent by the system controller 102 after an incoming message for requesting permission to transmit the designated response message is transmitted from selective calling radio 106 to system controller 102. Response messages are preferably transmitted at a designated time within the outgoing message or order, but alternatively they can be transmitted using an unscheduled protocol, for example an ALOHA or segmented ALOHA protocol, which are known in the art. An unsolicited message is an incoming message transmitted by a selective calling radio 106 without having received an outgoing message that needs a response. An example of an unsolicited message is an incoming message from a selective calling radio 106 which notifies the radio communication system 100 that the selective calling radio 106 is within range of the radio communication system 100. An unsolicited message it can include a request for transmission of a de-nominated response and can include data as numerical data. Non-requested messages are transmitted using an ALOHA or segmented ALOHA protocol. Incoming messages and. projections are included in incoming radio signals transmitted from, and incoming radio signals received by, a conventional antenna 104 coupled with the incoming radio signal transmitter / receiver 103. The radio communication system 100 is also characterized as comprising an amount of fixed sites 115, each fixed site comprises the system controller 102, one of the radio frequency transmitters / receivers 103, the communication connection 116 which couples the system controller 102 with the radio frequency transmitter / receiver 103 and the antenna 104.

It should be noted that the system controller 102 is capable of operating in a distributed transmission control environment that allows the mixing of cellular coverage, multiple transmission, satellite or other coverage schemes involving a number of radiofrequency transmitters / receivers 103, conventional antennas 104, to provide reliable radio signals within a geographical area as large as a worldwide network.

Each of the selective call radios 106 assigned for use in the radio communication system 100 has at least one address assigned to it which is a unique selective call address. The selective call address allows the transmission of a message from the system controller 102 only to the destination selective call radio 106.

In accordance with the present invention, voice messages are transmitted in a number of subchannels. Fig.2 illustrates a single sub-channel. In a preferred embodiment, there are three subchannels in a radiofrequency (RF) channel and the radiofrequency channel has a width of, for example, 25 kHz. Alternatively, seven subchannels can be used in a 50 kHz channel and it is easy to notice for one skilled in the art that other subchannel numbers can be used according to the channel bandwidth. The subchannels are separated by 6250 Hz. Each subchannel has a 500 bandwidth, a sideband 510 and a pilot carrier 520. As will be evident hereafter, the sidebands 500 and 510 are used to carry portions of a single message, or two separate messages. The spectrum allocation for voice in a subchannel is 2500 Hz, which contains the voice bandwidth of 300 to 2800 Hz.

Fig.3 illustrates the transmission process 600 according to the present invention by which messages and particularly analog voice messages are transmitted. This process is preferably executed by the transmitter / receiver 103, but is alternatively executed by the system controller 102. In any case, the transmitted information is ultimately incorporated into a signaling protocol which will be described hereinafter together with Figs.15-17.

An incoming voice message S (n) is received through a telephone line, for example, by the system controller 102. If, for example, the telephone line is an IT line, then the voice is coded using code modulation. 64 kbps pulses (PCM) and is converted into linear 16-bit PCM at a sampling rate of 8 kHz by the A / D converter 605. Regardless of the type, a voice message on a conventional analog telephone line is digitized by the A / D 605 converter in an appropriate digitized format. Then, the digitized voice information is processed by the low pass filter (BPF) 610 which filters out frequencies outside the typical voice spectrum of 300-2800 Hz. The filtered digitized voice information then passes through an automatic gain control module (AGC). ) 620 to compensate for the variability of the amplitudes of the input voice, generating fluctuations, for example, when a person speaks in a telephone handset of a telephone, cordless telephone, cell phone, etc. The AGC 620 module improves intelligibility and also ensures that the pilot carrier energy that is added is always below a certain fraction of a signal energy present in the transmitted signal. An AGC scheme that has a fast attack time constant of approximately 2.5 meseg, for example, and a bridging time constant of 2 seconds, for example, is useful for keeping the voice power constant in a wide range range of voice samples without distorting voice characteristics. These parameters do not try to be limiting.

The digitized voice information is compressed in time scale with a compressor in time scale 630. Any number of compression schemes in time scale is useful. The digitized voice information is then passed through the compass (compressor-expander) of amplitude 640, which the compande (compresses-expands) in a ratio of 2: 1 dB for example to protect it from channel noise.

An orthogonal modulation scheme is used that compresses first and second orthogonal modulation components. According to an embodiment of the invention, the first and second orthogonal modulation components are used to carry segments of a single voice message. According to another embodiment, the first and second orthogonal components are used to carry the first and second separate voice messages. In another embodiment, the first and second orthogonal modulation components are for example upper or lower sidebands 500 and 510, respectively, or the phase (I) and quadrature-phase (Q) components (also called "channels"), respective. Furthermore, regardless of which scheme is used, the invention contemplates the orthogonal modulation of the first and second components with first and second message parts, respectively, to generate first and second orthogonally modulated components.

A speech separator module 650 is used if the first and second orthogonal modulation components are to carry a single message. The call of the voice separator module 650 are the first and second message parts that temporarily make up the speech signal S (n). The voice message parts are marked Sa (n) and Sb (n), respectively. However, two separate messages have to be modulated in the first and second orthogonal modulation components, the voice separator module 650 is not used and the two voice messages Si (n) and S2 (n) are each processed in parallel with each other. the 600-640 and 600 '-640' modules (equal to the 600-640 modules, but not shown) before advancing to the following modules.

The single voice message S (n) is temporarily separated into the first and second message parts Sa (n) and Sb (n) with the voice separation module 650. The voice separation module 650, in case of digital information, separates a table of numbers representing the processed voice message S (n) in two, at a point, eg. zero intersection or another convenient temporal event, at some point near the temporary midpoint of the voice message S (n).

Then, the voice message parts Sa (n) and Sb (n) (or voice messages SI (n) and S2 (n) as the case may be) are passed through an orthogonal modulator 660 which modulates the message parts of voice in first and second orthogonal modulation components. The orthogonal modulator 660 is described in more detail hereinafter.

Then the pilot carrier is summed by an adder 705 to the result of the orthogonal modulator 660. The pilot carrier has an amplitude of approximately 0.15 times the maximum amplitude in the speech information.

Before this point in the transmitter processing, the modules operate at a sample rate of for example 8 kHz. When it is finally converted into analog information, the images appear in multiples of 8 kHz.

To eliminate these images, you will need an anti-image filter. Accordingly, to avoid this need, the processed signal is interpolated with an interpolator module 710 at a sample rate of 26 kHz so that the images are separated by 16 kHz. Once converted into analog information, the analog filter is used to delete images.

The results of the interpolator are then converted from digital to analog using a 16-bit D / A converter module 720. The analog output of the D / A converter module 720 is then passed through an appropriate 730 analog (anti-image) reconstruction filter to eliminate all the images, leaving only the baseband SSB signal.

A quadrature amplitude modulation module (QAM) 740 is coupled with the result of the reconstruction filter 730 for modulation of the SSB signal to the appropriate sub-channel that is transmitted through an antenna 750.

Fig. 4 illustrates in detail the amplitude compansor module 640. As is known in the art, amplitude compression (expansion-compression) involves intensifying low amplitude components and compressing high amplitude components of a signal. This protects the low amplitude components from the channel noise effect and thus provides better intelligibility and quality.

The amplitude compass 640 generates a control voltage factor c2 (n) by computing the average absolute value of the signal averaged for N samples. This is achieved by using two mobile average filters. The first moving average filter 641 computes the average absolute value of N incoming samples and the second moving average filter 642 computes the average of N samples of the average absolute values obtained from the result of the first moving average filter 641.

In delay module 643, the incoming signal is delayed by N-1 samples and the compared signal of amplitude of output is computed with the equation: (Factor of Gain of Compressor of Delayed Sample X) / (Control Voltage c2 (n)) 12 In the implementation shown in Fig.C, N = 48 and the Gain Factor = 0.140625XN. Preferably and although it is not shown in Fig. 4, the signal of compacted amplitude is filtered low pass again with a low pass filter of 300-2800 Hz to eliminate harmonies that would be introduced due to the compansion. A filter similar to the BPB 610 is useful.

Figs. 5 and 6 illustrate two examples of implementations of the orthogonal modulator 600. In Fig. 5, the voice message parts modulate upper and lower sidebands, while in Fig. 6, the message parts modulate components I and Q.

First, in Fig. 5, orthogonal modulator 660 comprises first and second Hilbert transformation modules 670 and 680, respectively. The Hilbert 670 and 680 transformation modules each comprise a Hilbert filter of 33 intakes 672 and 682, respectively, a delay module of 16 samples 674 and 684, respectively and a multiplier 676 and 686 respectively. The 33-shot Hilbert filters 672 and 682 generate the Q components and the 16-sample delay modules 674 and 684 generate the I components. The multipliers 676 and 686 generate 90 degree phase shifts as needed for the Q component. The upper sideband I + j * Q is generated with the adder 685 and the lower sideband (-j * Q is generated with the adder 695.

In Fig.6, however, a different configuration of the orthogonal modulator is shown. In this configuration, the orthogonal modulator 660 'includes a delay module 700, similar to the delay module 674, and a Hilbert filter 701 similar to the filter 672. The voice message part Sa (n) (or Si (n) ) is passed through the delay module 700 and the message part Sb (n) (or S2 (n)) is passed through the Hilbert filter 701. The result of the Hilbert filter is coupled with the multiplier 702 for a displacement of 90 degree phase. In the adder 703, the result of the delay module 700 is added to the result of the multiplier 702. Therefore, the result of the adder 703 comprises the message part Sa (n) modulated in the component I and the message part Sb ( n) modulated in the Q component; or in the case of the second embodiment, the message part SI (n) modulated in the component I and the message part S2 (n) modulated in the component Q.

Fig.7 illustrates, for example, a pulse response of the 33-shot Hilbert filters 672, 682 and 701.

Fig.8 is a polyphasic representation of an example of a suitable interpolator module 710, known in the art and Fig.9 is a pulse response of the interpolator module 710. As shown in Fig.9, every alternate sample is zero, which reduces computational complexity. In addition, the frequency response of the filter has a bandpass at 0-3kHz and an attenuation of 60 dB at 5600 Hz. In Fig.8, H0 (z2) = ho + z-1h2 + z "2h4 + ...; and H? = Z_1 [h? + Z_1h3 + z ~ 2h5 + ...]. Taking advantage of the alternating zeros in the answer of impulse and the polyphasic representation, the computations are reduced to 6 multiples per sample at a sampling rate of 16 kHz for a channel (I or Q), which constitutes a substantial improvement with respect to the multiplications per sample at 16 kHz in a direct implementation.

Optionally none, one or both message parts are inverted in time before modulation with orthogonal modulator 660 (or 660 '). Fig. 10 illustrates a time inverter module 800 that couples with the result of the voice separator 650 if a single message is transmitted, or with the result of the amplitude comparator 640, if two message parts are transmitted. The time inverter module 800 temporarily inverts the message part so that it is transmitted backward in time. In the case of the digital implementation of the invention, the time inverter module 800 reads a sequence of numbers from last to first, from the result to the voice separator 650 or to the amplitude comparator 640. For example, the time inverter modulator 800 is a software shuffler that decreases from the highest Index downward as will be described hereafter.

By inverting the message parts in time, the voice information "encodes" and therefore has a low level of security or privacy because the part inverted in time of the voice signal will not be "readable" or intelligible to a receiver that casually monitors the channel. Therefore, only receivers that, a priori, know that the transmitted voice information is inverted in time can demodulate and make the transmitted signal intelligible. It will be appreciated that the decision to invest in time not to invest in time can be made within a signaling protocol on a frame-by-frame basis in a previously arranged sequence known in the transmitter and in the receiver. An example of a sequence known to the transmitter and the receiver is the binary coded address of the selective call receiver. In addition, in the case where channels I and Q are remodulated, the simultaneous superposition of spectra in the channel of two voice parts, one or both, inverted in time, obscure the intelligibility for a receiver that casually monitors.

With reference to Figs.11-14, an example of transmission of a message according to the invention is shown. As shown in Fig.11, a voice message Vm is shown having a time duration Tm. When sampling and scanning with the A / D converter module 605, the voice message S (n) is defined by a sequence of digital numbers 1 through N which are digital representations of the samples shown in Fig.12. The digital representation of the voice message Vm is separated in two by the speech separator 650. A preferred point for separating the voice message is at the zero point in time Ts. Therefore, the digital value of the sample k is the value of the voice message in time Ts. The first message part Sa (n) comprises the digital values for the samples 1 to k and the second message part Sb (n) comprises the digital values for the samples k + 1 to N, as shown in Figs. 13 and 14, respectively. Either or both of the first and second message parts are optionally inverted and the parentheses in Figs. 13 and 14 indicate the order of the digital values if each message part is inverted in time.

If the upper and lower sidebands 500 and 510 are used to transport the message parts, the sideband 500 is formed with one of the message parts, for example the first part using the Hilbert 670 transformation module. The upper lateral portion conveying the first message part is represented by the expression ISa + jQsa- Similarly, the lower lateral band conveying the second message part (inverted in time or not) is represented by the expression Isb-jQst > / generated by the Hilbert transformation module 680. Therefore, with reference to Fig.2, the first and second message parts Sa (n) and Sb (n) are transported by the upper and lower side bands 500 and 510. Accordingly, a voice message having a time duration Tm is transmitted in half the time the message is transported by the upper sideband 500 and the other half is transported by the lower sideband 510.

As will be evident hereafter, the receiver usually detects both sidebands, especially if the receiver uses digital signal processing, but ignores one of the sidebands. If the message is compressed in time at the output, both sidebands can be used to transmit a message in the middle of the transmission time or "air". Moreover, the receiver receives the same message in half the time, consuming less power because the power consumption coding circuit is activated only half the time.

Similarly, the upper and lower sidebands 500 and 510 optionally transports two separate messages. In this case, the message one SI (n) is represented as Isi + jQsi and the message two S2 (n) is represented as IS2-jQs2 in the output of the Hilbert transformation modules 670 and 680, respectively.

In the case of paging systems, the voice message portions are transmitted according to a protocol. A protocol of this type is shown in Figs.15-17. With reference to Fig.15, a time diagram is shown illustrating features of an exemplary transmission coding format of an outgoing signaling protocol used by the radio transmission system 100 of Fig. 1 and including details of a control box 330, according to the embodiment of the invention. The control boxes 330 are also classified as digital frames 330.

The signaling protocol is subdivided into time divisions, which are one hour 310, one cycle 320, tables 330,430, one block 340 and one word 350. Up to fifteen cycles identified exclusively of 4 minutes are transmitted every hour. Up to twenty-eight frames identified exclusively of 1,875 seconds including control frames 330 and analog frames 430 (described below with reference to Fig.8) are transmitted in each of the cycles 320. Normally, the one hundred twenty-eight frames are transmitted. A synchronization and frame information signal 331 that lasts one hundred fifteen milliseconds and 11 blocks identified exclusively one hundred sixty milliseconds 340 are transmitted in each of the control boxes 330. The bit rates of 3200 bits per second (bps) or 6400 bps are usable during each control board 330. The bit rate during each control board 330 is transmitted to the selective call radios 106 during the synchronization signal 331. When the bit rate is 3200 bps, 16 words of 32 uniquely identified bits are included in each block 340, as shown in Fig.6. When the bit rate is 6400 bps, 32 exclusively identified 32-bit words (not shown) are included in each block 340. In each 32-bit word, at least 11 bits are used for the detection and correction of errors and errors. bits or less are used for information, in a manner known to one skilled in the art. The bits and words 350 in each block 340 are transmitted in an interleaved fashion using techniques known to one skilled in the art to improve the error correction capability of the protocol.

The information is included in each control box 330 in the information fields, which comprise frame structure information in a block information field (BI) 332, one or more selective call addresses in an address field (AF) 333, and one or more vectors in a vector (VF) field 334. The vector field 334 begins at the vector boundary 334. Each vector in the vector field 334 corresponds to one of the addresses in the address field 333 The boundaries of the information fields 332,333,334 are defined with the information field of block 332 and information fields 333,334 which are variable, according to factors such as the type of system information included in the synchronization field and information of frame 331 and the number of addresses included in the address field 333, and the number and type of vectors included in the vector field 334.

With reference to Fig.16, there is shown a time diagram illustrating features of the transmission format of the outgoing signaling protocol used by the radio communication system of Fig.l, and including details of a voice frame 430, according to the preferred embodiment of the invention. The voice frames 430 are also classified here as analog frames 430. The durations of the hour 310, cycle 320 and frame 330,430 protocol divisions are identical to those described with respect to a control frame of Fig.15. Each analog frame 430 has an anterior portion 435 and an analog portion 440. The information in the synchronization signal and frame information 331 is the same as the synchronization signal 331 in a control frame 330. As described herein, the part previous 435 is modulated in frequency and the analog part 440 of table 430 is modulated in amplitude. The analog part 440 is that part that carries the voice message parts through an orthogonal modulation component. Fig. 16 shows that the radio communication system includes three subchannels, each of which has a pilot subcarrier similar to that described in Fig. 1 and to which voice message parts can be assigned for transmission.

According to the preferred embodiment of the present invention, the transition part 444 includes the amplitude-modulated pilot subcarriers for at least three sub-channels 441, 442 and 443. Each sub-channel 441, 442 and 443 includes an upper sideband signal and a sideband signal. shown in Fig. 1 and also has associated therewith a channel I and a channel Q. In the example illustrated in Fig. 16, the upper sideband signal 500 includes a message part 415, which is a first part of a first voice message and in the lower sideband 510 is a second part of for example the same first voice message.

With reference to Fig.17, a time diagram illustrating a control board 330 and two analog frames 430 of the outgoing signaling protocol used by the radio communication system of Fig. 1 shown in accordance with the preferred embodiment is shown. of the invention. The diagram in Fig.8 shows an example of a zero chart that is a control box 330. Four directions 501,502,503,504 and four vectors 518,521,522,523 are shown in a zero box. Two addresses 501,502 include a selective calling radio address 106, while the other two addresses 503,504 are for a second and third selective calling radio 106. Each address 501,502,503,504 is uniquely associated with one of the vectors 518,521,522,523 by the inclusion of a pointer within each direction that indicates the position of the protocol (ie where the vector starts and how long it lasts) associated vector. According to the preferred embodiment of this invention the vector position is provided by identifying the number of words 350 after the vector boundary 335 at which the vector starts and the vector length, in words. It will be appreciated that the relative positions of the directions and vectors are independent of each other. The relationships indicated by the pointers are illustrated with arrows.

In the example shown in Fig.17, the control frame vectors 518, 521, 523 are associated only with one message part in one of the sub-channels 441 or 442. Specifically, the vector 518 points towards the upper sideband 500 of the sub-channel 441 and vector 522 points to lower sideband 510 of sub-channel 441. Similarly, vector 521 points to both sidebands of sub-channel 442. That is, the case of sub-channel 441, the example shows that two different message parts are transported by the upper and lower sidebands. In the case of sub-channel 442, two halves of a message part are transported by the upper and lower sidebands. Therefore, the control frame vectors 518, 521, 523 include information within them to indicate that the sub-channel (ie, which radio frequency) should look at a voice frame message and also information to indicate whether two separate messages are to be retrieved from the sub-channel or if the first and second halves have to be recovered.

In terms of signaling protocol, the method for transmitting first and second messages to a receiver that can be pointed according to the invention consists in orthogonally modulating first and second orthogonal components with first and second messages, respectively, to generate first and second orthogonally modulated components and simultaneously transmitting the first and second orthogonally modulated components in a protocol including address information corresponding to an address of a receiver to which it can be pointed and suitable synchronization information to drive the receiver to which it can be signaled to enter a mode suitable for simultaneously demodulating the first and second components orthogonally modulated at a particular time in accordance with the synchronization information.

One use for the realization where two different messages are transmitted simultaneously by upper and lower sidebands (or I and Q channels), respectively, is that where one message is a direct voice paging message and the other is a mail message of voice, which is stored in the pager.

Turning now to Fig.18, the selective call receiver 106 includes at least one antenna 840, a quadrature amplitude demodulator (QAM) 850, an FM demodulator 860, a decoder / controller 870 and a sound amplifier 872, a loudspeaker 874, an alarm 876, a display 878 and controls 880. The demodulator QAM 850 executes QAM demodulation in the signal detected by the antenna 840 in order to recover the voice messages. The FM demodulator 860 performs FM demodulation recovery data and other non-analog messages. The result of the FM 860 demodulator is a limited data signal (digital data) which is coupled with the decoder / controller 870 and includes the signaling protocol information decoded by the decoder / driver 870 and is responsible for displaying or storing data messages, locating the sub-channel to demodulate voice messages, triggering the 876 alarm, etc.

The voice messages are retrieved through a series of processing modules that operate on the I and Q channel output of the QAM 850 demodulator. The processing modules are shown in 900-960 and are implemented for example with factory elements in a digital signal processor, or software stored in the decoder / controller 870. In the latter case, the processing modules would be executed by the decoder / controller 870.

If the message parts are modulated in the I and Q components, the message parts are retrieved directly from the output of the QAM 850 demodulator. If either or both message parts were inverted in time in the transmission, the recovered message parts are they reverse back in the correct sequence with the time reversal modules 900 and 910. Accordingly, the message part SI (n) is taken at the output of the inversion module at time 900 and the message part S2 (n) it is taken at the exit of the investment module in time 910.

In contrast, if the message parts were modulated in the upper and lower sidebands, then the component I is passed through the delay module 920 and the Q component is passed through the Hilbert transformation module 930. The summing module 940 sum the result of the modules 920 and 930 and the summing module 950 subtracts the result of the module 930 to the result of the delay module 920. The recovered message parts are passed through the investment modules in time 900 and 910 and were inverted in time in the broadcast.

The message parts Sa (n) and Sb (n) are processed with the time sequencing adder 960 which temporarily combines the message parts Sa (n) and Sb (n) to reconstruct the original message S (n).

It should be understood that the additional functions of time decompression and amplitude decompression are preferably executed to "undo" these processes executed in the modulation. Therefore, although not specifically shown in Fig. 18, the time decompression and amplitude decompression modules are coupled to the output of the time sequencing adder 960, for example. Another post-demodulation processing suitable for improving the quality of the recovered signal is provided according to the invention.

The foregoing description is given as an example only and is not intended to limit the invention in any way except as set forth in the following claims.

Claims (10)

1. A method for transmitting a message to a receiver comprising the following steps: temporarily separating the message into first and second message parts that are contiguous parts of the message in time; modulating orthogonally first and second orthogonal components with the first and second message parts, respectively, to generate orthogonally modulated first and second components; and simultaneously transmitting the first and second orthogonally modulated components.

2. The method of claim 1 wherein the step of orthogonally modulating comprises generating a component in phase and a quadrature component where the in-phase component is modulated with the first message part and the quadrature component is modulated with the second message part.

3. The method of claim 1 wherein the step of orthogonally modulating comprises generating bands. upper and lower side, where the upper side band is modulated with the first message part and the lower side band is modulated with the second part of the message.

4. The method of claim 1 wherein the first and second message parts comprise a single voice message.

5. A method for transmitting first and second portions of a message to a receiver comprising the following steps: orthogonally modulating first and second components with first and second message parts, respectively, to generate first and second orthogonally modulated components, the first and second parts of messages are contiguous parts in time; and simultaneously transmitting the first and second orthogonally modulated components in a protocol including address information corresponding to an address of a receiver and synchronization information suitable for driving the receiver to enter a suitable mode for simultaneously demodulating the first and second orthogonally modulated components at a particular instant of time according to the synchronization information.

6. The method of claim 5, wherein the step of orthogonally modulating comprises generating an in-phase component and a quadrature component, wherein the in-phase component is modulated with the first part of the message and the quadrature component is modulated with the second part of the message.

7. The method of claim 5 wherein the step of orthogonally modulating comprises generating upper and lower sidebands, wherein the upper sideband is modulated with the first part of the message and the lower sideband is modulated with the second part of the message.

8. A method for receiving a transmitted signal comprising first and second components comprising the following steps: demodulating the transmitted signal to obtain first and second message part of the first and second orthogonally modulated components, respectively, the first and second message parts are parts of contiguous messages in time of a single message; and sequencing the first and second message parts to combine them in time to generate a single message composed of first and second message parts.

9. The method of claim 8 which also comprises the step of inverting in time at least one of the first and second message portions before placing them in temporal sequence.

10. The method of claim 8 wherein the first and second portions are digital signals and which also comprises the step of converting the first and second message parts into analog signals.