KR20020037342A - Method and apparatus supporting tdd/tty modulation over vocoded channels - Google Patents

Abstract

The present invention is directed to a method and apparatus used to encode / decode low activity communication signals (such as board tones) in transmission over communication system 100. Communication system 100 may include any number of wireless links. Once the system 100 recognizes a low activity signal transmission request, each vocoder used to encode / decode a signal in the system 100 performs a unique encoding / decoding process. In one embodiment, frames containing errors that adversely affect the signal are sent to the vocoder and the "soft bits" contained in the frame are used to determine the original signal transmitted. In another embodiment, the encoding of the signal includes encoding the signal using redundancy into an encoded signal that is spread over multiple vocoder frames.

Description

METHOD AND APPARATUS SUPPORTING TDD / TTY MODULATION OVER VOCODED CHANNELS}

Many deaf people use communication terminals that are specially structured and designed to allow them to communicate over standard telephone lines. The devices, referred to as communication devices for deaf (TDDs) or text telephone yokes (TTYs), are collectively referred to as TDD in the application. In general, TDD includes a keyboard and display connected to a telephone via a modem (modulator / demodulator). The modem is embedded in the TDD and directly connected to a telephone line or by a sound connector to a conventional telephone handset. The TDD may transmit information in coded tones over the telephone line to other TDDs connected to opposite ends of the telephone line via another modem. Tones are referred to as low activity communication because the frequency and amplitude envelope remain relatively constant.

Codes and protocols widely used in the prior art in TDD communications are unique. Code sets and communications protocols (TDD protocols), known as Baudots, have historically developed when many deaf communication devices were based on mechanical or electromechanical devices rather than electronic devices. Thus, the TDD protocol consists of a set of constraints that are no longer relevant to current devices. Such constraints serve to form a code protocol and a communication network of users and devices operating under the protocol, which is somewhat outdated.

In general, TDD communication is performed with 50 boards (45.5 boards in some countries) representing 6 characters per second. Other protocols currently available for TDD communications incorporate higher baud rates such as ASCII (US Standard Code Information Exchange). Regardless, the standard TDD communication character set consists of five bits of characters. The letters are similar to the letters of the alphabet representing words or thoughts. One character is grouped into overhead information bits before transmission, and each group of bits transmitted has a duration or unit interval of 22 milliseconds. For example, under the conventional TDD protocol, the group of bits to be transmitted is 8 bits (start bit (one source or zero bit), 5 bits representing a character and at least 1 and 1/2 bits indicating a stop point of the transmission group). ).

Compared with current communication systems, TDD transmissions are slow. The bigger problem is that the TDD signal is nearly constant. Such slow speed monotonic signals can be significantly damaged in digital communication systems, in particular communication systems including wireless links, which transmit higher activity signals at very high speeds. An example of such a communication system is a code division multiple access (CDMA) system with a large wireless subscriber unit. Each subscriber unit has a transceiver and communicates within the system through a satellite repeater or ground station, referred to as a cell. Each cell contains a physical plant called a base station. One cell covers a limited geographical area and routes calls sent by the subscriber unit through the mobile switching center between communication networks. As the subscriber moves to the geographic area of the new cell, the routing of the subscriber call can continue through the new cell by a process called "handoff".

A subscriber unit, generally referred to as a cell phone, transmits a signal received by a base station. This signal is relayed to the mobile switching center, which routes the signal to a public switched telephone network (PSTN) that includes a telephone line or other subscriber unit. Similarly, the signal may be transmitted from the PSTN to the subscriber unit via the base station and the mobile switching center.

The interface between the subscriber unit and the base station is called the air interface. The Telecommunications Industry Association (TIA) provided a standard for handling CDMA calls on the air interface named "IS-95 Mobile Station-Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular Systems." Addendum to IS-95 is provided in the Communications Service Bulletin (TSB). The standard IS-95 + TSB74 contains the service negotiation provisions on the air interface and is incorporated herein by reference.

Service negotiation is important for successfully performing communications, particularly low activity TDD communications, through digital communication systems. Another problem with modern systems, including one of the problems mentioned above, is that a vocoder (a device used in a system to encode a voice or TDD analog signal into a digital signal and decode the digital signal into a voice or TDD analog signal) The difficulty is in processing the low rate monotonic signals described by the TDD protocol. In current systems, low activity communication signals, such as TDD communications, can be processed and ignored by vocoder with background noise or signal interference.

Accordingly, there is a need for a technique such as the present invention that can be easily integrated into existing communication systems and can reduce frame error rates by implementing protocols used by vocoder while transmitting low activity communication signals.

The present invention should be compatible with wireless communication modulation systems, such as CDMA systems, which serve large system users. A detailed discussion of the CDMA system and technology used in the multiple access communication system is disclosed in U.S. Pat. 4,901, 307 "spread spectrum multiple access communication systems using satellite or terrestrial repeaters." In addition, the present invention should also be compatible with other modulation systems and techniques used in other types of communication systems, such as time division multiple access (TDMA), frequency division multiple access (FDMA), and amplitude modulation (AMPS) schemes.

FIELD OF THE INVENTION The present invention relates to the field of communications devices for deaf communications (TDDs) or text telephone yokes (TTYs). More specifically, the present invention relates to a standard vocoder motion modulation method that enables reliable transmission of TDD / TTY signals in a communication system. The communication system can include a wireless link.

1A is a block diagram illustrating hardware components and interconnections of a communication system incorporating a wireless link in accordance with an embodiment of the present invention.

1B is a block diagram of a vocoder capable of executing the encoding and decoding method of the present invention coupled to a recognition apparatus of the prior art in accordance with an embodiment of the present invention.

2 illustrates a typical conventional TDD communication device used in accordance with one embodiment of the present invention.

3 shows the traffic channel frame format for rate set 1 used by the variable rate vocoder.

4 is a flowchart of a method according to an embodiment of the present invention.

5 shows a block diagram of a wireless communication system constructed in accordance with one embodiment of the present invention.

6 shows a block diagram of a wireless communication system constructed in accordance with one embodiment of the present invention.

7 is a flowchart of a method of controlling a transmit power level between a base station and a mobile station.

In general, the present invention relates to a low activity communication modulation method by a communication system using an encoded signal and an increased transmit power level. More specifically, the present invention relates to a method of using encoding and decoding characterized for low activity communication signals to minimize the frame error rate of the transmitted signal. The present invention also provides a method of decoding a low activity signal by looking at the "soft bit" contained in an error frame or a frame adjacent to the error frame to determine the content of the original frame.

Certain embodiments of the disclosed subject matter provide a native decoding method for TDD signals encoded using standard encoding protocols. In one embodiment, the decoder can compare the vocoded frame from the known TDD signal and the frame containing the transmission error (error frame) and determine the vocoded frame most similar to the transmitted frame. In yet another embodiment, the decoder may examine the adjacent frame to determine the vocoded frame most similarly transmitted but erroneous upon receipt. In yet another embodiment, the decoder may be modulated to include a signal enhancer or repeater that "erases" erroneous bits in the transmitted frame before the decoding method is applied to the transmitted frame. It will also be appreciated that while TDD communications are discussed through the present invention, other slow or low activity communications may also be transmitted using the present invention.

Yet another embodiment of the present invention provides the decoding method discussed above but generates vocoder parameters different from the standard vocoder parameters. When a TDD signal is received, the encoder switches to the "board encoding mode", informs the decoder of the protocol changeover, and uses channel coding redundancy to improve the decoder, which determines that the TDD signal is sent correctly even if it is contained in poor quality frames. . This version of the invention replaces standard vocoder parameters with more spaced vocoder "symbols", thus making it easier to distinguish tones.

Another version of the present invention provides a method of encoding a TDD signal in a vocoder frame using redundancy but over multiple vocoder frames. When a frame is lost, the information is interleaved over an "N" frame so that the decoder can extract the necessary information from adjacent frames to determine the content of the lost frame.

Another version of the present invention combines the above-mentioned encoding and decoding method of the present invention with a method of controlling the transmission power level to provide a cost effective system. Modulating the design of a standard vocoder chipset in a mobile station is expensive and can hinder the implementation of the above-mentioned encoding and decoding methods. However, the communication system may be implemented such that the above-mentioned method is used at the base station of the system rather than the mobile station. The frame error rate for the low activity communication signal transmitted from the base station to the mobile station's unmodulated vocoder can be minimized using a method of controlling the transmit power level.

The present invention provides many advantages for the user. One advantage is that TDD messages can be transmitted using a digital transmission medium having a wireless link. Another advantage is that the TDD device can be connected to a mobile device or subscriber unit, such as a digital cellular telephone, connected to a communication system by a wireless link. The present invention also provides a number of other advantages and advantages, which will become more apparent after a review of the following detailed description of the invention.

The characteristics, objects, and advantages of the present invention will become more apparent to those skilled in the art after reviewing the following detailed description with reference to the drawings in which like reference numerals are used.

1-7 illustrate examples of various methods and apparatus of the present invention. To facilitate the description but not to limit the invention, the examples are described as a TDD communication device mounted in a digital communication system incorporating a radio link, an example of which is described below.

Hardware Elements and Interconnect

1 illustrates one type of communication system 100 including a radio link and a TDD communication device (TDD) 200 as used in the present invention. As shown in detail in FIG. 2, TDD generally includes a keyboard and display connected to a telephone via a modem (modulator / demodulator). The modem is built into the TDD and is either connected directly to the telephone line or connected to a regular telephone handset by an acoustic coupler. The TDD may transmit information in coded tones over the telephone line to another TDD, such as TDD 102 shown in FIG. 1 connected to the other end of the telephone line via another modem.

In a digital communication system using a wireless link, the TDD 200 may be connected to the subscriber unit 104 used in the communication system 100 to transmit a received signal. A typical embodiment of the subscriber unit 104 is a digital signal phone such as the Q-800 manufactured by Shemcom, which is generally referred to as a cell phone. Subscriber unit 104 as shown in FIG. 1 includes a recognition device 106 communicatively coupled to its circuitry. The hardwire 108 may be used to connect the TDD 200 to the subscriber unit 104 via the recognition device 106, or a device port may be used. The recognition device and device port were filed on July 13, 1998, entitled "Methods and Devices for Establishing TDD / TTY Services Over Vocoded Channels", which are assigned to the assignee of the present invention and incorporated herein by reference. Patent Application No. 09 / 114,344.

The device port may be configured to receive low activity communication device attachments such as plugs, connectors or receivers. The items are currently commonly used to connect telephone and computer equipment and are readily available to electronics suppliers. The device port interfaces with an attachment to connect a low activity communication device (not shown), such as TDD 200, to subscriber unit 104 of communication system 100. The device port allows information to be exchanged between the low activity communication device and the subscriber unit 104. Regardless of whether device ports or fixed wiring are used, recognition device 106 allows system 100 to recognize whether a TDD signal should be transmitted.

Referring to FIG. 1, after the recognition device 106 receives a low activity communication signal, the signal is processed by the subscriber unit 104. Originally, the transmitted signal is configured to have the information contained in the low activity signal. Since the communication system 100 recognized that the low activity signal was transmitted, the system is adapted to make the transmission readable. For example, an analog signal received from analog circuitry 228 shown in FIG. 2 is generally a signal that includes digitization of the signal, transmit power level setting to prevent signal fading during transmission, signal compression and filtering, or " Voice "processing. This function may be performed by a circuit (not shown) of the subscriber unit 104 including the vocoder. Depending on the received signal, a variable data rate vocoder (generally referred to herein as a vocoder) may flexibly determine and negotiate a service within communication system 100 to provide successful transmission and signal decoding. The negotiation involves forming values for a number of parameters such as the data rate, transmit power, and compression technique that the vocoder uses. A more detailed discussion of signal processing for transmission in communication systems is referred to as "IS-95" and is incorporated herein by reference Electronic Industry Association named "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular Systems". Other transmission standards that appear in standard TIA / EIA / IS-95-A, including standard vocoder protocols are known in the art.

However, when a low activity signal is received, the vocoder may identify the signal as a noise, pause, or signal that is not intended to be transmitted. In short, the vocoder does not know which service to use because the vocoder cannot identify the received low activity signal. By recognizing the system 100 that the low activity signal is transmitted, the vocoder will establish the service requested to transmit and decode the signal as optimally as possible.

After the low activity communication signal has been processed and the service determined, the signal may be transmitted over the wireless link 114 using the antenna 112. The digitized signal is received by another antenna 116 at a remote location, such as base station 118, and processed by base station circuitry (not shown) that includes vocoder 120. Several base station circuit arrangements for communication systems are known in the art and can be understood through the TIA / EIA / IS-95-A referenced above. By processing the signal after reception, a low activity signal that reflects the information contained in the transmitted low activity signal may be transmitted to the low activity device 102 via the communication link 120. The second recognition device 106 is shown connected to the base station 118. This provides the low activity signal sent from the low activity communication device 102 back to the TDD communication device 200.

Communication link 120 is shown in two diagonal lines to emphasize that base station 118 cannot be directly connected to low activity device 102. Base station 118 is connected to a standard PSTN switching center commonly used by telephone companies to coordinate telephone calls and low activity device 102 is connected to a PSTN. In yet another embodiment, a second mobile station (not shown) coupled to the low activity communication device 102 may be linked to the base station 118. Moreover, the communication system may comprise the above mentioned mobile switching center.

2 is a schematic block diagram of a conventional TDD device 200, standard or enhanced TDD circuit, operating in accordance with the present invention. In the TDD device of FIG. 2, the keyboard 202 is provided to a user who can input data characters. The output of the keyboard 202 is connected to the processor 204 used to control the circuit elements included in FIG. Characters received or transmitted by the processor 204 are also displayed on the display 206. Optionally, the same character received or transmitted may be reproduced through a device such as printer 208. Some TDD devices may not have a printer, even if they are standards for TDD with some kind of image display to allow users to view typed and received characters. The keyboard 202 serves as an input source of data characters for the processor 204 while the display 206 and printer 208 are used as local destinations for the data stream characters.

Processor 204 may be connected by a suitable data and address bus used in this type of application in the art. In FIG. 2, bus 210 connects read only memory (ROM) 212 to non-volatile random access memory (NVRAM) 214. Suitable control lines 216 and 218 are coupled from the processor 204 to the ROM 212 and NVRAM 214 providing bidirectional control of the unit. The ROM 212 permanently stores not only data used by the program but also a program instructing the operation of the processor 204. For example, specific character strings may be stored for inter-machine communication and synchronization of two TDDs in enhanced mode of operation. The NVRAM 214 is a floating storage location for data entering and exiting the TDD device 200, and is used as a buffer for quickly storing standard messages input by the user through the keyboard 202. Other circuit structures may be used that combine the microprocessor 202 and the ROM 212 and NVRAM 214 of a single integrated circuit.

Connected to the processor 204 in FIG. 2 is a telephone keypad 220 that allows entry of a telephone number dialed by the processor 202 through the communication system 100. The standard telephone handset 224 is placed on a telephone receiver 226 incorporating a switch (not shown) that indicates that the handset 224 is in use and is therefore separated from the telephone receiver 226.

Processor 204 is coupled to communication system 100 via analog circuitry 228. The connection is shown as a fixed wiring connection 230, but may be any type of connection capable of linking the analog circuit 228 and the communication system 100. Analog circuitry 228 provides a connection between handset and processor 202 while allowing board tones and dialing tones to be received by communication system 100. Analog circuitry 228 provides an interface of voice information between handsets 224. The analog circuit 228 of the TDD device 200 is connected to the communication system 100 using a connector such as the device discussed above.

Regardless of the particular technique described above, those skilled in the art will appreciate that the apparatus discussed above can be implemented in other architectures of communication systems without departing from the scope of the present invention. As a specific example, multiple subscriber unit 104 may be linked to base station 118, or low activity communication device 200 may be integrated in subscriber unit 104.

action

After the TDD signal is received, the vocoder used by the system 100 during signal processing recognizes or detects whether a low activity signal has been received for transmission and uses a 1/8 data rate traffic channel frame format to transmit the signal. It is available. However, the application of the following method for quarter data rate to full data rate traffic channel transmission can be achieved as described below.

3 shows a conventional variable data rate vocoder frame format for a traffic channel using data rate set 1. The variable data rate vocoder generates frames every 20 milliseconds using code excitation linear prediction (CELP) techniques known in the art. The frame may be formatted in full data rate, 1/2, 1/4 or 1/8 data rate format according to voice activity. If a baud tone is received, the variable data rate vocoder will detect low activity and use the 1/8 data rate format, thus presuming that the currently used vocoder can detect that the signal is being transmitted. In general, board signals are treated as noise and are generally ignored.

Full data rate refers to that each bit included in each frame is not repeated. A half data rate transmits the same number of bits per frame, but each bit is repeated once per frame, ie each unique bit appears twice in the frame. The quarter data rate refers to each unique bit appearing four times per frame. The more information bits are transmitted more repeatedly, the less total information is transmitted per frame. At full data rate, the signal is transmitted at higher power, because a given bit is transmitted only once. This full data rate power level is referred to as the reference power in this application. Since the bits are repeated at a lower data rate, a reduced power level is used because power for each repeating bit is accumulated over the frame. Assuming a fixed minimum power is used for transmission, full data rate transmission will include more frame errors than half data rate transmission of the same information.

In general, the power level is set based on the selected frame error rate (FER) for the transmitted signal received at the remote station, referred to as the destination of the transmitted signal, such as the subscriber unit. When a low activity signal is transmitted, the preferred FER is chosen because the current method increases the actual FER. This selected FER range is between 0.1 and 1.0% error rate, but can be larger or smaller if necessary to preserve the transmission signal quality. Preferably, 0.2% FER is preferred for low activity signals.

In the present invention, by implementing a specialized encoding and decoding method, the frame error rate can be controlled. In this environment, the disclosed technique, which falls short of the desired FER to adjust the transmit power level (in this case FER is the total number of erroneous frames even after reconstruction of the vocoder frame information), can also be used with specialized encoding and decoding techniques. have. In general, the vocoder will be fixed at full data rate and the transmit power will be increased to transmit low activity signals. It will be appreciated that the required growth rate is much smaller than the growth rate required when current encoding / decoding techniques cannot be implemented.

A. Decoder Using Soft Bits

In one embodiment, when a TDD call is received, the system 100 recognizes or detects the call type. System 100 processes a call from TDD unit 200 for transmission using standard processing techniques known in the art. If a frame is received at a remote point, for example base station 118, the call is decoded using the present invention. If a frame error occurs in the physical layer, that is, if the frame does not pass the checksum described in IS-95, the frame is still sent to vocoder 120 for decoding. Sending error frames to the vocoder is not done in the standard IS-95 implementation. The bits included in the error frame are referred to as "soft bits" because they are not all faulty and information can be collected from the bits individually to reconstruct the information contained in the error frame. .

However, upon recognizing or detecting that a TDD call has been received, the vocoder decoder of the present invention observes the received vocoder parameter and compares the error frame by comparing the parameters with the "symbols" of the TDD modulated signal or tone appearing in the vocoder parameter interval. Process. The decoder compares the vocoder parameters of the stored vocoded TDD tones with the received vocoder parameters. This comparison allows to determine which TDD signal was most similarly received.

For example, suppose that the vocoder indication of the board tone of "0" appears in sequence of sixteen "0", and assume that the indication of the board tone of "1" appears in sixteen "1". This method considers these indications as speech parameter spacing symbols. In the following example, the three layers are identified as follows.

Vocoder frame boundary conditions: | -voc frame 'N'-|

Board tone boundary condition: | -baudot 'X'-|, and

Received vocoder parameter: 000000000000000 or

11111111111111111

Assume that the vocoder decoder receives the following parameters.

The decoder recognizes the board tone boundary condition and recognizes that the reception parameter for the second board '0' is closer to '0' than to '1'. The decoder modulates the estimated error bit before determining and decoding the board tone '0'. For the next baud tone '1', the decoder recognizes that the vocoder parameter is closer to '1' than to '0' and thus modulates the bits. The decoder uses the following sequence to generate the currently corrected TDD signal.

This example shows an error variation to occur at frame boundary conditions, which is not always the case. If this variation is commonly classified within a frame, the following alternative versions of the present invention can be used.

When the vocoder decoder receives an error frame in which error bits are included in the frame, the vocoder may watch for adjacent non-error or "good" frames to reconstruct the error frame. Adjacent frames will contain some of the board tones lost in the error frame. For example, assume that the following signal has been received.

The vocoder parameter for the second baud tone '0' is too ambiguous to make an accurate decision on the tone because the number of '0's is almost equal to the number of' 1 'of the vocoder frame parameters. To make a better decision, the vocoder looks at the next adjacent frame (voc frame 3) and determines if the tone continues to appear as '0' in this frame. Therefore, the decoder determines that the board half-tone of the vocoder frame 2 will be the board '0' tone.

As shown in the flowchart of FIG. 4, after it is determined whether a low activity signal is received at task 402, 404, the decoder continues to monitor and update the receiving board tone boundary condition of task 408. Otherwise, no low activity signal is processed using conventional methods. If an error frame is received as detected in the physical layer, the frame is assigned an indicator N and the vocoder checks the error frame at task 410. As the frame parameters are fairly pronounced, if a "reliable" decision can be made, considering whether the frame is a board '0' or '1', the error frame is modulated to reflect the decision parameter. The reliable decision is within the predicted probability of obtaining the original frame parameter. For the purposes of the present invention, the preferred probability is in the range of 51% certainty. Once the modulation is made, the method returns to task 402 and determines the next signal.

If no reliable decision is made as shown in task 412, the vocoder checks the next contiguous frame N + 1 or, optionally, N-1. If the frame is good at task 416, then a decision to modulate the erroneous frame is made at task 418 based on frame N + 1 or, optionally, parameters contained within frame N-1. If the next contiguous frame is none good, then the next most reliable decision is made based on the parameters contained in the next contiguous frame N + 1.

B. Encoders and Decoders Using Soft Bits

Decoder implementation in an embodiment of the invention is similar to that described above. However, in order to further reduce the error rate and to improve the accuracy and reliability of the decoded signal, the encoder also takes advantage of the "soft bit".

When the vocoder encoder detects that a board tone is being sent, the encoder switches to the "board tone encoding mode". In this mode, the encoder determines whether the tone received for encoding is '0' or '1'. The encoder then sends the decision to the decoder, which uses the vocoder frame, but uses channel coding redundancy to improve the number of times the decoder determines the appropriate board tone. Even if the decoder receives the tone of the error frame, the decoder can more accurately determine the transmitted tone based on the previous decision.

In the simple example, when the encoder detects that the board '1' is being sent, the encoder sends a series of ones to the decoder. This series can be any length, but if necessary it must be of sufficient length for the decoder to operate as described in section A. The version of the present invention replaces the standard vocoder parameters with more spaced (ie more distinguishable) vocoder "symbols", thus making it easier to determine between two tones even when the frame is in error.

C. Encoders and Decoders Without Soft Bits

The embodiment of the present invention is another version of the method described in sections A and B, but the decoder is not given a soft bit from any error vocoder frame to process.

In this case, if the vocoder encoder detects a '1' or '0' board tone, the vocoder also encodes the tone of the vocoder frame using redundancy, but the encoding can be done over several vocoder frames. '1' and '0' are interleaved over M frames so that if one frame is lost, the decoder can extract the necessary information from the adjacent frame. The following example shows interleaving occurring over four frames, but any number of frames may be used. Suppose the encoder detects the next baud tone for transmission.

110

The encoder encodes the following frame for transmission to the decoder.

In this example, the vocoder frame parameter for each frame is segmented when four bits represent the detected board tones in a particular vocoder frame. All 16 bits represent the detected board tones from the last four vocoder frames.

| Board for frame N-3 | Board for frame N-2 | Board for frame N-1 | Board for frame N |

To describe a board tone that does not correspond to a vocoder frame boundary condition, the present invention utilizes the following 4-bit sequence, where XXYY represents the 'X' board code where the code of the current vocoder frame carries the 'Y' board code. It is reflected.

D. Modulated Vocoder with Increased Transmit Power

In another embodiment, the enormous cost of modulating the chipset of the mobile station to achieve the encoding and decoding process described above in sections A, B and C is usefully minimized.

The encoding and decoding methods of sections A, B and C can be usefully achieved by using standard vocoders that communicate with signal enhancers such as estimators or repeaters or other devices capable of performing signal enhancement functions. In addition, the method of section A, B or C can be achieved through the use of a modulated vocoder. Those skilled in the art will appreciate that the vocoder may be modulated to incorporate the functionality of the signal enhancer, i.e. to estimate whether the error bit received by the communication unit was originally sent as '0' or '1'.

The system of FIG. 5 illustrates one embodiment of the present invention. Transmission from base station 550 to mobile station 510 is referred to as the forward link and transmission from mobile station 510 to base station 550 is referred to as the reverse link. On the reverse link, the unmodulated vocoder 520 of the mobile station 510 encodes the board signal into standard vocoder parameters and sends the vocoder parameters to the base station 550. Modulated vocoder 560 receives the encoded board signal and enhances the board signal to recover error bits. Thereafter a flawless version of the board signal is generated. In the forward link, the unmodulated vocoder 580 of the base station 550 encodes the board signal using standard vocoder parameters and transmits the vocoder parameters to the mobile station 510. The modulated vocoder 530 receives the encoded board signal and augments the board signal to recover error bits.

However, using signal enhancers or modulated vocoders on the forward and reverse links to achieve the decoding method discussed in sections A, B, and C is costly to produce. In another embodiment of the present invention, the frame error rate of the system can be reduced by using a signal enhancer of the base station on the reverse link and using a power control technique to adjust the signal transmission power level from the base station to the mobile station on the forward link. Can be.

In the reverse link of the communication system of FIG. 6, base station 655 reconstructs the original board signal contained within the vocoder encoded frame according to the method discussed in sections A, B, and C. FIG. However, in the forward link, U. S. Patent Application No. entitled " Method and Apparatus for Establishing TDD / TTY Service over Vocoded Channel " At 09 / 114,344, base station 655 transmits the encoded board signal using power control technology.

7 is a flowchart of a method of controlling transmission power between a base station and a mobile station. The method begins at task 702, where the board signal is received by the mobile station 605. After the signal is received, the vocoder used by mobile station 605 during signal processing is fixed at task 704 at full data rate. In this embodiment, the transmit power is not reduced from the transmit power used by the communication system for full data rate transmission at task 710. The power level is generally set based on the FER selected for the transmitted signal received at the mobile station 605. When the board signal is transmitted, the preferred FER is chosen because the actual character error rate of the board signal is 9 to 10 times the FER. The chosen FER range is an error rate between 0.1% and 1.0%, but may be smaller if necessary to preserve the quality of the transmitted signal. Preferably, 0.2% FER is preferred for board signal transmission. If the FER exceeds the selection range of task 712, mobile station 605 informs base station 655 that system adjustments are required to reduce the FER in a conventional manner during task 706. Thus, an adjustment is made at task 708. This adjustment generally includes increasing the transmit power for full data rate transmission, but also includes adjusting other known parameters to reduce the FER. If the FER is acceptable at task 712, signal transmission can continue at task 714 and flexible adjustments to the communication system continue over transmission of the entire transmission signal 710. Otherwise, when the transmission of the board signal ends, the vocoder is unlocked and the communication system returns to normal operation.

Other embodiments

While preferred embodiments of the invention have been shown, those skilled in the art will clearly appreciate that various modifications and changes can be made without departing from the spirit and scope of the invention, and the invention is limited only by the following claims.

Claims (17)

A method of transmitting a perceived low activity communication signal in a communication system comprising a mobile station and a base station, the method comprising: Transmitting the original frame represented by the original bit sequence; Receiving a first transmission frame comprising a first transmission bit sequence sequenced substantially the same as the original bit sequence; Enhancing the first transmitted bit sequence to produce an enhanced bit sequence; And Processing the enhanced bit sequence to obtain additional information used to identify the original bit sequence in the original frame. The method of claim 1, wherein processing the enhanced bit sequence comprises: Comparing the enhanced bit sequence with a known low activity communication signal bit sequence; Determining whether the enhanced bit sequence is statistically reliable; If the enhanced bit sequence is statistically reliable, modulating the enhanced bit sequence to identify the original bit sequence in the original frame. The method of claim 1, wherein the enhanced bit sequence is labeled with frame N, The step of processing the enhanced bit sequence, Comparing the enhanced bit sequence with a known low activity communication signal bit sequence to produce a comparison result; If the comparison result appears to be statistically reliable, modulating the enhanced bit sequence based on the comparison result to reflect the known low activity communication signal bit sequence; If the result of the comparison is not statistically reliable, processing the frame N + 1 adjacent to frame N to determine if frame N + 1 contains a predetermined error; If the frame N + 1 has no error, Determining a low activity communication signal defined by a bit sequence contained in the frame N + 1; And And modulating the enhanced bit sequence of frame N based on the bit sequence included in frame N + 1. 4. The method of claim 3, wherein the comparison result is statistically reliable if the probability of causing the known low activity communication signal bit sequence to reflect the original bit sequence is greater than 51%. 2. The method of claim 1, wherein transmitting the original frame is performed by a mobile station and receiving the first transmission frame by a base station. 2. The method of claim 1, further comprising the step of replacing a standard vocoder encoding / decoding parameter used by multiple vocoders with a vocoder code, wherein the sequenced bits included in the vocoder code are included in the sequenced vocoder parameter. Further spaced apart by bits, wherein the replacing step is performed before the transmitting step. 7. The method of claim 6, wherein replacing the standard vocoder parameters comprises: Informing the first vocoder that a low activity communication signal is to be transmitted; Encoding the low activity communication signal with a first vocoder, The second vocoder determines whether the bit is 0 or 1, and the encoding step uses channel coding redundancy in the information bit field of the original frame to improve the likelihood that the first vocoder will decode the original frame. And informing the first vocoder that a low activity signal is transmitted. 7. The method of claim 6, wherein processing the enhanced bit sequence comprises: Comparing the enhanced bit sequence with a known low activity communication signal bit sequence; And And modulating the enhanced bit sequence based on the comparison to identify the original bit sequence. A method of transmitting a perceived low activity communication signal in a communication system comprising a mobile station and a base station, the method comprising: Transmitting from the mobile station a first original frame represented by the first original bit sequence; Receiving a first transmission frame at a base station, wherein the first transmission frame comprises a first transmission bit sequence that is sequenced identically to the first original bit sequence, Enhancing a first transmitted bit sequence in the base station to produce an enhanced bit sequence; Transmitting the enhanced bit sequence to a first vocoder in the base station; Processing the enhanced bit sequence with the first vocoder to obtain side information used to identify the first original bit sequence of the first original frame; And Transmitting a second original frame from the base station at an increased transmit power level. 10. The method of claim 9, wherein transmitting the second original frame from a base station at increased transmit power comprises: Fixing all vocoders used to process the second original frame at full data rate; And Transmitting the second original bit sequence at an increased transmit power level to maintain a minimum target frame error rate relative to the second original bit sequence. The method of claim 9, wherein the enhanced bit sequence is labeled frame N and processing the enhanced bit sequence comprises: Comparing the enhanced bit sequence with a known low activity communication signal bit sequence to produce a comparison result; If the comparison results show statistical credibility, Modulating the enhanced bit sequence based on the comparison result to reflect the known low activity communication signal bit sequence; If the comparison result is not statistically reliable, Processing the frame N + 1 adjacent to frame N to determine if frame N + 1 contains a predetermined error; If the frame N + 1 has no error, Determining a low activity communication signal defined by a bit sequence contained in the frame N + 1; And And modulating the enhanced bit sequence of frame N based on the bit sequence included in frame N + 1. 12. The method of claim 11, wherein the comparison result appears to be statistically reliable if the known low activity communication signal bit sequence has a 51% probability of reflecting the original bit sequence. 12. The method of claim 11, wherein transmitting the second original frame from a base station at an increased transmit power level comprises: Fixing all vocoders used to process the second original frame at full data rate; And Transmitting the second original bit sequence at an increased transmit power level to maintain a minimum target frame error rate relative to the second original bit sequence. 14. The method of claim 13, wherein the minimum target frame error rate is less than 1.0%. An apparatus for transmitting a low activity communication signal in a communication system, Means for encoding an original frame of the low activity communication signal into an original bit sequence; Means for transmitting the original bit sequence; Means for receiving a first transmission frame comprising a first transmission bit sequence; And Means for enhancing the first transmit bit sequence with a signal enhancer to produce a defect free signal. The method of claim 15, Means for comparing the enhanced bit sequence with a known low activity communication signal bit sequence; Means for determining whether the enhanced bit sequence is statistically reliable; Means for checking statistical reliability of the enhanced bit sequence; And Means for modulating the enhanced bit sequence to identify an original bit sequence within the original frame. An apparatus for transmitting a perceived low activity communication signal in a communication system, A vocoder that encodes the low activity communication signal into an original bit sequence; A transmitter for transmitting the original bit sequence; A receiver receiving a first transmission frame comprising a first transmission bit sequence; And And a signal enhancer for enhancing the first transmit bit sequence to produce a defect free signal.