WO2004054171A1

WO2004054171A1 - Wireless multi-channel transmitting and receiving system and method of the same

Info

Publication number: WO2004054171A1
Application number: PCT/KR2003/000680
Authority: WO
Inventors: Saekwon Chang; Youngjun Chang
Original assignee: Kyungwoo Systech Inc.
Priority date: 2002-12-06
Filing date: 2003-04-04
Publication date: 2004-06-24
Also published as: KR100509223B1; KR20040049484A

Abstract

This invention is related to a radio multi-channel transmitting and receiving system and a method of the same by which a user can select a language and easily listen to a message composed of the selected language among radio multi-channel transmitting signals which are transmitted after being assigned contents composed of multi-language to each frame, and multi-language voice informations can be delivered in various galleries, international meeting hall, tourist resort and so on. Also, this invention, as a radio multi-channel transmitting and receiving system and a method of the same using HDMA (Hybrid Division Multiple Access) method mixed more than 2 methods of the various multiplex transmitting and receiving methods, is related to a Hand-off function, by which a user can automatically listen to a message transmitted from the nearest transmitter among various transmitters where many transmitters are simultaneously operating in gallery and exhibition etc., of the system.

Description

WIRELESS MULTI-CHANNEL TRANSMITTING AND RECEIVING SYSTEM AND METHOD OF THE SAME

Technical Field

The present invention relates to a system and method for transmitting and receiving multiple radio channels that can enable a user to select a desired language and listen to content based upon the selected language from a radio multi-channel transmission signal carrying multichannel contents assigned to frames, and that can conveniently deliver voice information created in multiple languages in a variety of galleries, international meeting halls, tourist resorts, etc.

Background Art

Conventional methods for transmitting and receiving multiple radio channels perform multiplexing operations on the basis of time division multiple access (TDMA), frequency division multiple access (FDMA), code division multiple access (CDMA), etc. However, the present invention provides a method and system for transmitting and receiving multiple radio channels using a hybrid division multiple access (HDMA) technique in which at least two of the TDMA, FDMA and CDMA techniques, etc. are mixed. The present invention is associated with a handoff in a radio multi-channel transmitting and receiving system that can allow a user to receive a signal automatically transmitted from the nearest one of a plurality of transmitters in a state in which the plurality of transmitters simultaneously operate as in galleries, exhibition fairs, etc.

Further, the present invention provides a method in which CDMA and TDMA characteristics are combined, and relates to a handoff in a system and method for transmitting and receiving multiple radio channels. Furthermore, the present invention applies "Polarity alternated pulse width/code division multiple access (PW/CDMA)-based modulating and demodulating technology", which was issued on March 30, 2001, as Korean Patent No. 0293128, that improves the method in which the CDMA and TDMA characteristics are combined, to the system and method of the present invention.

Disclosure of the Invention

When voice information (that is also referred to as "contents") created in multiple languages needs to be delivered to the public, a conventional method for delivering content on a language-by-language basis has a problem in that time loss can be significant due to a standby time before content based upon a desired language is provided. A method for enabling a listener to select a language on a content-by- content basis by means of a wired receiving device and listen to content based upon the selected language via a receiver such as a headset or etc. limits the scope of activities of the listener. It is inconvenient that the public cannot simultaneously use the content based upon the selected language in the conventional method. There is a problem in that a language selection operation and an operation for wearing or taking off the receiver such as the headset or etc. must be repeatedly performed when the listener moves to various locations, within a gallery for example.

When the user must manually input a desired information number into a mobile terminal storing all contents required for guidance in another conventional method, he or she can listen to desired information. Furthermore, there is another conventional method for automatically providing corresponding voice information when a signal transmitter having a unique number is near to a predetermined location. In this case, because every mobile terminal equipped with a built-in large capacity memory must store all necessary contents, the inconvenience and economic problems due to a collective creation and correction operation for the larger amount of contents can be incurred. These problems can be significantly addressed if content can be broadcast by radio and a listening operation for the broadcast content can be performed by means of a predetermined terminal.

However, a radio frequency channel is assigned on an available language-by-language basis and content based upon a desired language channel is selected and received from transmitted channel contents in a conventional analog type radio guidance broadcast technique being a kind of FDMA. In this case, there are problems in that the number of types of transmittable contents (or the number of transmitters) is small and the technique is available only in an environment in which other electronic waves can be cut off in the course of transmission between the transmitters. Conventional technical elements relating to FDMA or TDMA include channels (frequencies and time slots) corresponding to a multiplication of an amount of information to be transmitted and the number of languages. Thus, as the number of contents increases, not only technical implementation is impossible, but also an operation for automatically selecting and receiving different contents based upon designated languages cannot be appropriately carried out. To overcome these drawbacks, the conventional technology uses the same frequency on a language-by-language basis and arranges the transmitters based upon the different contents to be sufficiently distanced from one another so that a signal from any one of the transmitters cannot reach another transmitter, in order for crosstalk between the transmitters to be avoided. Alternatively, the conventional technology may use a limited method in which the transmitters are arranged in areas separated by radio wave cut-off walls so that these drawbacks can be overcome, but this form of the conventional technology cannot be applied to transmitting dense contents.

Therefore, the present invention has been made in view of the above problems, and it is one object of the present invention to provide a system and method for transmitting and receiving multiple radio channels that can automatically receive content based upon a previously designated language from one frequency signal carrying frames corresponding to voice information created in one or more languages sent by a transmitter, and that can send, by means of one or more transmitters, a multiplexed signal containing contents created in the multiple languages and data forming a preamble using a synchronous code designated in each transmitter or different synchronous codes of the transmitters in a variety of international meeting halls, museums, galleries, etc., and that can enable a receiver to selectively or automatically receive specific content created in a specific language using the synchronous code contained in the preamble of data containing the specific content that a user desires to listen to, such that a large amount of contents created in one or more languages can be effectively transmitted using a limited bandwidth.

Furthermore, it is another object of the present invention to provide a system and method for transmitting and receiving multiple radio channels that can automatically select content from the nearest transmitter located within a radio wave receivable distance in an environment in which a plurality of transmitters that transmit one frequency signal carrying voice information, respectively, are densely clustered. In accordance with the first aspect of the present invention, the above and other objects can be accomplished by the provision of a radio multichannel transmitting and receiving system for carrying out a radio transmission and reception operation for multiplexed data based upon digitally coded and compressed multiple channels, comprising: at least one transmitter comprising: an input signal processor for processing an input signal received from an external device; a modem for multiplexing the input signal and forming a frame of each channel containing a preamble based upon a designated synchronous code; a high frequency module for transmitting frames consecutively transmitted from the modem through a specific frequency and scanning all available frequencies; and a central processing unit (CPU) for controlling the processor, the modem and the module; and at least one receiver comprising: a high frequency module for receiving a signal from the transmitter; a modem for demodulating the signal received by the high frequency module; a codec for decoding the demodulated signal; an output unit for externally outputting the decoded signal from the codec; a user interface of a receiving side for selecting a received channel desired by a user from the multiplexed signal; and W

a CPU for controlling the module, the modem, the codec, the output unit and the user interface, measuring received signal strength intensity (RSSI) values of synchronized signals received by the high frequency module, producing a weighted moving average (S) value on a signal-by-signal basis 5 using the measured RSSI values, selecting a frequency signal having a largest

S value from the received signals, commanding the modem to receive the selected frequency signal, carrying out a handoff to another frequency other than a currently active frequency if the S value of the currently active frequency is smaller than a threshold value and the S value of another 10 frequency other than the currently active frequency is larger than a threshold value, and commanding the modem to receive a handoff signal. Preferably, the transmitter may further comprise: a flash memory for storing a signal inputted from the input signal processor in a coded and compressed format; and 15 a user interface of a transmitting side for selecting and inputting one of a download mode and a transmission mode according to the user's request. Preferably, the transmitter's input signal processor may comprise: a universal serial bus (USB) port for receiving a coded and compressed signal from an external personal computer (PC); or 20 a codec for coding and compressing a voice signal inputted tlirough a microphone in real time.

Preferably, the mode for the transmitter or receiver multiplexes a signal based upon polarity alternated pulse width/code division multiple access (PW/CDMA); and 25 the multiplexed channel contains language channels configured by voice data created in multiple languages.

Preferably, the transmitter's modem may form a frame preamble using a different synchronous code for each transmitter.

In accordance with the second aspect of the present invention, the 30 above and other objects can be accomplished by the provision of a radio multi-channel transmitting method using the above-described radio multichannel transmitting and receiving system, comprising the steps of:

(a) scanning all available frequencies;

(b) selecting a frequency having a low RSSI value according to a result of the scanning and deciding a transmission frequency;

(c) reading data inputted from an input signal processor;

(d) multiplexing the read data and forming a frame of each channel containing a preamble based upon a designated synchronous code; and (e) transmitting a multiplexed frame if a current time is a frame transmission period for transmitting data, receiving a signal of the frequency decided at the step (b) to determine whether the RSSI value is low if a current time is not a frame transmission period for transmitting data, and re- deciding the transmission frequency if the RSSI value is high. In accordance with the third aspect of the present invention, the above and other objects can be accomplished by the provision of a radio multichannel transmitting method using the above-described radio multi-channel transmitting and receiving system, comprising the steps of: (a) scanning all available frequencies; (b) selecting a frequency having a low RSSI value according to a result of the scanning and deciding a transmission frequency;

(c) reading data inputted from an input signal processor or data stored in a flash memory;

(d) multiplexing the read data and forming a frame of each channel containing a preamble based upon a designated synchronous code;

(e) transmitting a multiplexed frame if a current time is a frame transmission period for transmitting data, receiving a signal of the frequency decided at the step (b) to determine whether the RSSI value is low if a current time is not a frame transmission period for transmitting data, and re- deciding the transmission frequency if the RSSI value is high; and

(f) storing a signal from an external input signal processor in the flash memory if an operating mode selected by a user interface is a download mode rather than a transmission mode.

Preferably, the step (d) may comprise the step of: multiplexing data based upon polarity alternated pulse width/code division multiple access (PW/CDMA) and configuring a multiplexed channel as language channels of voice data created in multiple languages. Preferably, the step (d) may further comprise the step of: forming a frame preamble using a different synchronous code previously designated on each transmitter.

In accordance with the fourth aspect of the present invention, the above and other objects can be accomplished by the provision of a radio multichannel receiving method using the above-described radio multi-channel transmitting and receiving system, comprising the steps of:

(a) scanning all transmitted frequencies;

(b) selecting a reception frequency using an RSSI value on each frequency synchronized with a previously designated synchronous code and a weighted moving average (S) value between RSSI values, on the basis of a result of the scanning;

(c) determining whether a frame of multiplexed data of a signal scanned and received according to the reception frequency corresponds to a channel selected by a user interface, re-receiving a signal of the reception frequency if the frame of multiplexed data does not correspond to the selected channel, and reading demodulated data from a modem to transmit the read data to a codec if the frame of multiplexed data corresponds to the selected channel; and

(d) decoding the transmitted data by means of the codec and outputting the decoded data to an external output unit. Preferably, the radio multi-channel receiving method may further comprise the step of: (e) performing the handoff, the step (e) comprising the steps of:

(e-1) scanning frequencies other than a current reception frequency and selecting a candidate frequency; and (e-2) determining whether a handoff must be performed using RSSI values of the candidate frequency selected at the step (e-1) and an active frequency and an S value between the RSSI values, performing the step (b) if the handoff must be performed, and scanning the active frequency to perform the step (c) if the handoff does not need to be performed. Preferably, the step (e) may further comprise the steps of: determining whether an S value for a currently active frequency is stable for a first predetermined time and determining whether an S value for a candidate frequency is stable for a second predetermined time; determining whether the S value for the currently active frequency is smaller than a first threshold value and determining whether the S value for the candidate frequency is larger than a second threshold value; and performing the step (b) only if the S value for the currently active frequency is stable for the first predetermined time, the S value for the candidate frequency is stable for the second predetermined time, the S value for the currently active frequency is smaller than the first threshold value, and the S value for the candidate frequency is larger than the second threshold value.

Preferably, the step (c) may comprise the step of: if the frame of multiplexed data corresponds to the selected channel, decoding the multiplexed data on the basis of polarity alternated pulse width/code division multiple access (PW/CDMA), and the channel selected by the user interface is one of language channels configured by voice data created in multiple languages. Preferably, the step (e) may further comprise the step of: selecting a reception frequency using a previously designated synchronous code according to the result of the scanning, scanning frequencies other than a current reception frequency using a previously designated synchronous code when another channel is selected by a user interface, and performing the step (b).

Brief Description of the Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating the configuration of a master module for transmitting contents in a radio multi-channel transmitting/receiving device in accordance with the present invention;

FIG. 2 is a block diagram illustrating the configuration of a terminal module for receiving contents in the radio multi-channel transmitting/receiving device in accordance with the present invention;

FIG. 3 is a schematic diagram illustrating a format of content frames transmitted received in the radio multi-channel transmitting/receiving device in accordance with the present invention;

FIG. 4 is a flowchart illustrating a transmission procedure in a radio multi-channel transmitting/receiving method in accordance with the present invention;

FIG. 5 is a flowchart illustrating a reception procedure in the radio multi-channel transmitting/receiving method in accordance with the present invention;

FIG. 6 is a flowchart illustrating a procedure for determining whether a handoff must be performed in a receiver in the radio multi-channel transmitting/receiving method in accordance with the present invention;

FIGS. 7 A to 7D are views illustrating the examples of radio multichannel transmitting/receiving devices in accordance with present invention;

FIG. 8 is a graph illustrating a typical relationship between a received signal strength intensity (RSSI) value of a signal from a transmitter and a distance between the transmitter and the receiver;

FIG. 9 is a graph illustrating a relationship between a weighted moving average value between signals obtained for a handoff, an RSSI value and a distance between the transmitter and the receiver in accordance with the present invention; and

FIG. 10 is a graph illustrating the RSSI value of a time varying signal from the transmitter at a specific distance.

Best Mode for Carrying Out the Invention

Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings.

FIG. 1 is a block diagram illustrating the configuration of a master module for transmitting contents in a radio multi-channel transmitting/receiving device in accordance with the present invention. In

FIG. 1, an external input signal processor 130 includes a universal serial bus

(USB) port 134 connected to an external personal computer (PC), etc. or a W

10

codec 132 coupled to a microphone 131. The external input signal processor 130 can include both the USB port 134 and the codec 132.

In detail, data, coded and compressed/processed by an extemal PC, stored (downloaded) in a built-in flash memory via the USB port 134 (i.e., a 5 serial communication interface), streaming-coded and compressed/processed data consecutively transmitted via the USB port 134 from the PC, or data coded and compressed/processed from a voice signal inputted from the microphone 131 by the codec 132 is transmitted to a modem 120 on a frame- by-frame basis. The transmitted voice data is modulated according to a

10 transmission technique based upon a time division multiple access (TDMA), frequency division multiple access (FDMA) or code division multiple access (CDMA) technique. The modulated data is transmitted to a radio frequency (RF) module 110 according to a designated frame format, a synchronous code and timing. The RF module 110 carries out a frequency shift keying (FSK)

15 modulation operation with a designated frequency and transmits a result of the

FSK modulation operation via an antenna (ANT) 100.

FIG. 2 is a block diagram illustrating the configuration of a terminal module for receiving contents in the radio multi-channel transmitting/receiving device in accordance with the present invention.

20 Multiplexed data is extracted from a high frequency signal inputted via an antenna (ANT) 200 on the basis of a frequency designated by an RF module 210. The extracted data is transmitted to a modem 220. The modem 220 demodulates the coded and compressed data from a transmitter into original data. Then, channel data of a corresponding frame is transmitted to a decoder

25 230. The decoder 230 decodes the channel data into an analog signal and outputs the analog signal to a receiver 260.

In accordance with the preferred embodiment of the present invention, the RF modules 110 and 210 use the Bluetooth specification, and uses some of a maximum number of 79 frequencies as available frequencies in

30 a case where an industrial, scientific and medical (ISM) band of 2.402 ~ 2.480 GHz is divided into 1 MHz bandwidth units. In this case, transmission power is in a range of Class 1 ~ Class 3 (0 ~ 20 dBm) and reception sensitivity corresponds to -70 dBm or below.

In accordance with the preferred embodiment of the present W

11

invention, the modems 120 and 220 are implemented by an application specific integrated circuit (ASIC) on a single chip capable of performing a function of modulating and demodulating a signal appropriate for a transmission technique, a function of setting a frame format and additional 5 functions. These modems use a structure for multiplexing a TDMA-based element and a CDMA-based element so that data can be transmitted.

In a TDMA-based structure, a time axis is divided into units^' of frames. A frame includes a lock time field 300 for an RF phase locked loop (PLL), a preamble field 310 for frame synchronization, a message field 330

10 for transmitting data, and an end of frame (EOF) field 340. The length (or time period) of each field and the synchronous code used can be controlled by software.

In a CDMA-based structure, data to be transmitted is spread by a multiplexing orthogonal code having the length of 64 chips, a maximum

15 number of 16 independent internal channel signals are combined, a power level is constantly binarized, and a message is transmitted. When all frames are transmitted, 10 Kbps per internal channel are used, a data rate necessary for transmitting 16 channels is a maximum of 160 Kbps, and a chip rate is 1 Mbps.

20 An available frequency and an operating mode (including transmission, reception and scanning modes) associated with frames are designated and operated by the modem. The transmitter and receiver must perform a timing/synchronization operation when a multiplexed signal based upon the CDMA is demodulated, and the transmitter and receiver use the same

25 synchronous preamble code. In each frame, the synchronization with the transmitter is performed within a 1/8 chip in relation to a plurality of preamble signals having the length of 64 chips using a correlator.

This method can maintain the synchronous timing irrespective of the precision of a clock oscillator of the transmitting/receiving system, and can

30 ignore other synchronous code signals. Furthermore, the modem provides a received signal strength intensity (RSSI) value of a received frequency and a synchronous signal state value so that quality of transmission can be determined.

FIG. 3 is a schematic diagram illustrating a format of content frames in accordance with a preferred embodiment of the present invention. In detail, each frame has a length of 2 ms. Furthermore, five frames including one control frame 331 and four data frames 332, 333, 334 and 335 configure one cycle 350 and have a period of 10 ms. The synchronization between the transmitter and receiver is continuously maintained by preamble signals of all frames. The control frame 331 is assigned to maintain synchronization with another transmitter or to be later used as protocol information associated with an operating standard. The four frames 332, 333, 334 and 335 corresponding to four extemal channels are used for transmitting and receiving voice information.

In particular, where the polarity alternated pulse width/code division multiple access (PW/CDMA) is used as an example, 20-bit data in each of 16 internal channels is spread by 64 chips of a multiplexing orthogonal code in a message part on a bit-by-bit basis and a summing operation is carried out. Then, binary data corresponding to a total of 1280 chips (20 x 64) truncated to a single level is transferred to the RF module. Where this is expressed as a data transmission rate, a total of 320 bits (20 bits x 16 channels) is transmitted in a frame of each cycle, and hence a transmission rate corresponding to 32 Kbps per frame (where one second = 100 cycles) is obtained. In accordance with the present invention, a transmission rate of coded and compressed data is selected as 16 or 32 Kbps. When 4-language contents are simultaneously transmitted so that the selected transmission rate can match a modem transmission rate, compressed data of 32 Kbps (e.g., Moving Picture Experts Group (MPEG) data) is assigned to each of frames 2, 3, 4 and 5 and the assigned data is transmitted. A receiving terminal transmits, to a decoder, data of a frame corresponding to a selected language so that the decoder can carry out real-time voice data demodulation.

Where a simultaneous transmission based upon at least 4 languages is performed for simultaneous interpretation in an intemational meeting hall, voice quality can be slightly degraded. In this case, coded and compressed data of 16 Kbps can be assigned to 8 channels of 16 internal channels associated with the frames 2, 3, 4 and 5, and the assigned data is transmitted. The receiving terminal transmits, to a decoder, internal 8-channel data corresponding to frames based upon the selected language so that a correct voice data demodulation operation can be carried out.

More preferably, at least two transmitters use different synchronous codes previously designated on a transmitter-by-transmitter basis, and contents based upon 4 languages are transmitted to each transmitter. In order for the present invention to implement high voice quality within a limited bandwidth range according to a radio transmission, compressed data (e.g., compressed data based upon the MPEG standard) can be implemented in voice quality corresponding to a radio broadcast at the transmission rate of 16 Kbps ~ 32 Kbps. Furthermore, a transmission frame format is set for a voice data demodulation operation based upon the real-time transmission so that the transmission rate of data can correctly match that of a communication interval.

FIG. 4 is a flowchart illustrating the transmission procedure of a transmitting module in a radio multi-channel transmitting/receiving device. After the transmitting module is first initialized (at step 410), 79 available frequencies of the ISM band are scanned twice or more (at step 420). It is determined whether empty frequencies are present (at step 430). If the empty frequencies are present, one of the empty frequencies is decided to be a transmission frequency F_A (at step 440). It is determined whether streaming transmission has been selected through a user interface (e.g., a selection switch). If streaming transmission has been selected (at step 450), data from the USB or voice data from the microphone via the codec is read (at step 460). On the other hand, if streaming transmission has not been selected, data stored in the flash memory is read (at step 451). It is determined whether a current time corresponds to a transmission period for frames corresponding to data to be transmitted (at step 470). If a current time corresponds to a transmission period for frames corresponding to data to be transmitted, the data is transmitted (at step 480). On the other hand, if a current time does not correspond to a transmission period for frames corresponding to data to be transmitted, the transmitter receives its own frequency FA decided on a scanning operation for all frequencies (at step 471). It is determined whether the RSSI of the frequency is low and it is determined whether or not the frequency is good (at step 481). At this point, since the transmitter is in a state in which no frame has been transmitted, the low RSSI corresponds to a good frequency. Since the high RSSI corresponds to a frequency previously used by another radio device, a scanning operation is performed for all frequencies and empty frequencies must be searched for (at the above step 430). If a download mode is not selected by the user interface (e.g., the selection switch between the download mode and a transmission mode), a transmission/reception operation is repeated. On the other hand, if the download mode is selected (at step 490), the flash memory stores new data through the USB from the PC (at step 491). That is, the download mode is an operating mode used for enabling the user to carry out an upgrade operation using the new data in the flash memory. The operating mode is set as the transmission mode at normal times.

As described above, the transmitter based upon the transmitting module associated with FIG. 4 transmits contents tlirough an optimal empty frequency so that the receiver can receive high quality contents. In the transmitting module in accordance with the present invention, a preamble of a frame to be transmitted by the transmitter is formed by one synchronous code previously designated or ^*by a synchronous code (GC) previously designated on at least one transmitter.

FIG. 5 is a flowchart illustrating the reception procedure of a receiving module in the radio multi-channel transmitting/receiving device.

After the receiving module is first initialized (at step 510), 79 available frequencies of the ISM band are scanned (at step 520). A candidate frequency Fc having the largest RSSI value according to the frame synchronization based upon a previously designated synchronous code is decided (at step 530). If the candidate frequency is not detected, all frequencies are scanned again (at step 520). An active frequency F_A is replaced by the candidate frequency Fc (at step 540). The active frequency F_A is scanned (at step 550). It is determined whether or not a received frame (e.g., any one of voice data units created in Korean, English, Japanese and Chinese languages) is desired by the user (at step 560). If no desired frame has been received, the active frequency F_A is repeatedly received until the desired frame is received (at step 561). On the other hand, if the desired frame has been received, data of the received frame is sent to the decoder (at step 570). After the data is sent to the decoder, a frequency FQ other than the active frequency F_A is scanned, the synchronization operation is set, and the best candidate frequency is selected as Fc (at step 580). A handoff is prepared to change the active frequency (at step 590). At this time, the candidate frequency can further increase frequency scan efficiency by further increasing the number of scanning operations in comparison with other frequencies. If a weighted moving average value between RSSI values of the candidate frequency satisfies a handoff requirement, the handoff is performed and the active frequency is replaced by the candidate frequency (at the above step 540). In FIGS. 4 and 5, F_A denotes an active frequency, Fc denotes a candidate frequency, and Fo denotes another frequency. A difference between the candidate frequency and another frequency depends upon an RSSI value difference. A frequency having the largest RSSI value among the scanned another frequencies is set as the candidate frequency. A scanning operation means an operation for receiving frames having different synchronous (code and timing) signals.

The method for enabling all transmitting/receiving devices to multiplex and transmit voice information based upon one or more languages though one frequency using the same synchronous code (e.g., gold code (GC)) has been described above as an example. More preferably, the present invention further includes a structure configured by a plurality of transmitters using different synchronous codes previously designated on a language-by- language basis and a receiver for carrying out a frequency scanning operation using a synchronous code corresponding to a language selected by a user interface where contents based upon at least four languages need to be simultaneously transmitted in the simultaneous interpretation in the intemational meeting hall, etc.

The flowcharts for the transmitting and receiving methods of the above-described transmitting and receiving devices correspond to an asynchronous technique in which respective transmitters perform transmission operations according to different synchronous timings. The synchronous technique for enabling the transmitters to carry out the transmission operations synchronously is different from the asynchronous technique in that one transmitter carries out a transmission operation in synchronization with the neighboring transmitter according to a control frame and a receiver carries out a synchronous reception operation in place of the scanning operation at a time other than a corresponding frame time.

However, those skilled in the art will appreciate that the transmitting/receiving modules in accordance with the present invention can be implemented through the modification or correction also where the synchronous technique is used or different synchronous codes are used. Of course, the transmitting/receiving modules are included in the accompanying claims. The receiving module associated with FIG. 5 determines a reception state of the best candidate frequency Fc of synchronized frequencies, compares the candidate frequency with a currently active frequency F_A, and determines whether the handoff must be performed.

Before a detailed description is given of FIG. 6, a technical ground associated with means for determining the handoff in the present invention will first be described. The handoff is similar to a function for enabling communication to be performed by automatically switching a traffic channel from one base station to another base station when a mobile station moves to various locations. The handoff used in the present invention is significantly different from the conventional handoff in terms of transmission structures.

The receiving terminal of the present invention sequentially receives frequencies other than the currently active frequency and monitors RSSI values and synchronous states. An RSSI value and a chip error rate (CER) provided by the modem must be used so that a better frequency in other transmission signals can be automatically switched and a signal from the nearest transmitter can be received where a current signal is degraded to below a defined value due to movement. However, as a value difference is instantly significantly varied because of various peripheral states, a special processing algorithm is needed so that the handoff can be appropriately determined. The RSSI value of a received signal is inversely proportional to a distance in relation to a log function. The RSSI value can instantly vary by approximately 30 dB with respect to the same distance due to the movement of a transmitting/receiving device, an antenna's direction, attenuation by various peripheral objects such as a human body, etc. or fading of a reflected wave (refer to the moving obstacle shown in FIG. 10).

Thus, the present invention uses moving average and exponential smoothing so that a difference between measured values according to states and the affection of instant variation can be removed. An average value A between "m" RSSI values is produced in each time period. A final weighted moving average (S) value is calculated from all weighted moving average values and a weight value w.

1 " Average between RSSI values : A_n = — • ^ RSSI_t

"* l=n-m

Weighted moving average : S_n = w A_n + (1 - w) • S_n__i

A_n : current average, m : number of data units

S_n : current S value, S_n__λ : previous S value, w : weight value

As the number m of data units or a weight value w increase, instant variation can be more easily and quickly mitigated. However, since a reaction delay increases where the number m of data units or a weight value w is overly large, m = 5 ~ 15 and w = 0.05 ~ 0.15 are used, and more preferably m = 8 and w = 0.1 are used.

Because the S value can be abruptly varied due to movement, the antenna's direction and an obstacle such as a human body, etc., a handoff function becomes very unstable. To improve this problem, the handoff determination must be performed only when the S value associated with an active frequency FA and a candidate frequency Fc is stable for a predetermined time or more. A stable state time means a persistence time for which a current value is within a range of (a previous value ± one bit) in consideration of an integer calculation error. As shown in FIG. 10, a stable flag value is in a high level state for a predetermined time or more, that is, for approximately 0.5 ~ 1 sec, in accordance with the preferred embodiment of the present invention. FIG. 6 is a flowchart illustrating a procedure for determining whether a handoff must be performed in a radio multi-channel receiver.

In FIG. 6, the variables are defined as follows. A: Time for which SA is maintained in stable state, i.e., 0.5 ~ 1 sec

Tc: Time for which Sc is maintained in stable state, i.e., 0.5 ~ 1 sec S_A : Lowest threshold value of FA when handoff is unnecessary

S_CL: Lowest threshold value of Fc capable of serving as F_A

The threshold value corresponds to approximately 50 ~ 70% of the S value (corresponding to 1.5 ~ 2.5 m) when the distance between the transmitter and receiver is 50 cm. In this case, S_C > S_A + (2 ~ 5%) must be satisfied so that a consecutively repeated handoff can be avoided.

At a handoff determination time point as the S value and the stable state persistence time value are calculated every time a reception or scanning operation is performed, it is determined whether a stable time of SA associated with the active frequency is smaller than T_A (at step 610). If the stable time of S_A associated with the active frequency is smaller than T_A, a currently active frequency FA is maintained (at step 660). On the other hand, if the stable time of SA associated with the active frequency is TA or above, it is determined whether a stable time of Sc is Tc or above (at step 620). If the stable time of Sc is smaller than Tc, the currently active frequency F_A is maintained (at the above step 660). On the other hand, if the stable time of Sc is Tc or above, SA is compared with SAL (at step 630). If S_A is SAL or above, the currently active frequency F_A is maintained. On the other hand, if SA is smaller than SA_L, S_C of the candidate frequency is compared with S_CL (at step 640). If Sc is S_CL or below, the currently active frequency F_A is maintained (at the above step 660). On the other hand, if Sc is larger than S_CL, the active frequency F_A is replaced with the candidate frequency Fc (at step 650).

In brief, only when the stable time of SA associated with the active frequency is T_A or above, the stable time of Sc is Tc or above, S_A is smaller than SA_L and Sc is larger than S_{C »} the active frequency FA is replaced with the candidate frequency Fc. Otherwise, the currently active frequency F_A is maintained.

According to these determinations, a stable handoff can be implemented in various states.

FIGS. 7A to 7D are views illustrating the examples of radio multichannel transmitting/receiving devices in accordance with present invention.

FIG. 7A is a view illustrating the case where a signal from a personal computer (PC) 720 is transmitted through a universal serial bus (USB) port 134, a stored signal is transmitted after a voice input signal inputted through a microphone 131 is stored in a flash memory, or the voice input signal inputted tlirough the microphone 131 is immediately transmitted.

FIG. 7B is a view illustrating the case where data inputted through the PC 720 or the microphone 131 is transmitted in real time.

FIG. 7C is a view illustrating the case where contents based upon at least four languages are transmitted using one synchronous code by one transmitter usable in the intemational meeting hall, etc.

FIG. 7D is a view illustrating the case where contents based upon at least four languages are transmitted using N synchronous codes by N transmitters usable in the intemational meeting hall, etc. as in FIG. 7C.

Furthermore, the radio multi-channel transmitting/receiving system can include a plurality of receivers (not shown) as well as a plurality of transmitters in accordance with the embodiment of the present invention. FIG. 8 is a graph illustrating a typical relationship between an RSSI value of a signal from a transmitter and a distance between the transmitter and the receiver. As the distance between the transmitter and the receiver increases, the RSSI value is exponentially reduced.

FIG. 9 is a graph illustrating a relationship between a weighted moving average value between signals obtained for a handoff, an RSSI value and a distance between the transmitter and the receiver in accordance with the present invention. In FIG. 9, it can be found that a weighted moving average value matches an actual RSSI value.

FIG. 10 is a graph illustrating the RSSI value of a signal varying with a time from the transmitter at a specific distance. Where a moving obstacle is present, the RSSI value is abruptly reduced as time goes by, and hence a stable flag value is varied from a high level to a low level. A state in which the stable flag value is high indicates a stable state, and a state in which the stable flag value is low indicates an unstable state.

Industrial Applicability

As apparent from the above description, the present invention provides a system and method for transmitting and receiving multiple radio channels that can enable a plurality of transmitters to transmit voice information created in various languages and that can enable at least one receiver to automatically carry out a handoff to a frequency for the nearest transmitter. In comparison with the conventional radio transmitting and receiving system and method, the system and method of the present invention can be used in an environment in which the transmitters are closely crowed. The receiver of the present invention can include only essential components for receiving contents transmitted from the transmitters. Because the receiver of the present invention does not need to store all contents as in a conventional receiver in an environment in which the plurality of transmitters are conventionally located in galleries, the present invention can implement a cost-effective, light-weight receiver. As a handoff is automatically performed in accordance with the present invention, a user does not need to operate a switch, such that the present invention can provide convenience.

Claims

W21Claims:

1. A radio multi-channel transmitting and receiving system for carrying out a radio transmission and reception operation for multiplexed data based upon digitally coded and compressed multiple channels, 5 comprising: at least one transmitter comprising: an input signal processor for processing an input signal received from an external device; a modem for multiplexing the input signal and forming a frame of 10 each channel containing a preamble based upon a designated synchronous code; a high frequency module for transmitting frames consecutively transmitted from the modem through a specific frequency and scanning all available frequencies; and 15 a central processing unit (CPU) for controlling the processor, the modem and the module; and at least one receiver comprising: a high frequency module for receiving a signal from the transmitter; a modem for demodulating the signal received by the high 20 frequency module; a codec for decoding the demodulated signal; an output unit for externally outputting the decoded signal from the codec; a user interface of a receiving side for selecting a received channel 25 desired by a user from the multiplexed signal; and a CPU for controlling the module, the modem, the codec, the output unit and the user interface, measuring received signal strength intensity (RSSI) values of synchronized signals received by the second high frequency module, producing a weighted moving average (S) value on a signal-by- 30 signal basis using the measured RSSI values, selecting a frequency signal having a largest S value from the received signals, commanding the modem to receive the selected frequency signal, carrying out a handoff to another frequency other than a currently active frequency if the S value of the currently active frequency is smaller than a threshold value and the S value of another frequency other than the currently active frequency is larger than a threshold value, and commanding the modem to receive a handoff signal.

2. The radio multi-channel transmitting and receiving system as set forth in claim 1 , wherein the transmitter further comprises: a flash memory for storing a signal inputted from the input signal processor in a coded and compressed format; and a user interface of a transmitting side for selecting and inputting one of a download mode and a transmission mode according to the user's request.

3. The radio multi-channel transmitting and receiving system as set forth in claim 1, wherein the transmitter's input signal processor comprises: a universal serial bus (USB) port for receiving a coded and compressed signal from an extemal personal computer (PC); or a codec for coding and compressing a voice signal inputted through a microphone in real time.

4. The radio multi-channel transmitting and receiving system as set forth in any one of claims 1 to 3, wherein the mode for the transmitter or receiver multiplexes a signal based upon polarity altemated pulse width/code division multiple access (PW/CDMA); and wherein the multiplexed channel contains language channels configured by voice data created in multiple languages.

5. The radio multi-channel transmitting and receiving system as set forth in claim 4, wherein the transmitter's modem forms a frame preamble using a different synchronous code based upon each transmitter.

6. A radio multi-channel transmitting method using the radio multichannel transmitting and receiving system set forth in claim 1, comprising the steps of:

(a) scanning all available frequencies; (b) selecting a frequency having a low RSSI value according to a result of the scanning and deciding a transmission frequency;

(c) reading data inputted from an input signal processor;

(d) multiplexing the read data and forming a frame of each channel containing a preamble based upon a designated synchronous code; and

(e) transmitting a multiplexed frame if a current time is a frame transmission period for transmitting data, receiving a signal of the frequency decided at the step (b) to determine whether the RSSI value is low if a current time is not a frame transmission period for transmitting data, and re- deciding the transmission frequency if the RSSI value is high.

7. A radio multi-channel transmitting method using the radio multichannel transmitting and receiving system set forth in claim 2, comprising the steps of:

8. The radio multi-channel transmitting method as set forth in claim 6 or 7, wherein the step (d) comprises the step of: multiplexing data based upon polarity altemated pulse width/code division multiple access (PW/CDMA) and configuring a multiplexed channel as language channels of voice data created in multiple languages.

9. The radio multi-channel transmitting method as set forth in claim 8, wherein the step (d) further comprises the step of: forming a frame preamble using a different synchronous code previously designated on each transmitter.

10. A radio multi-channel receiving method using the radio multichannel transmitting and receiving system set forth in claim 1, comprising the steps of:

(a) scanning all transmitted frequencies; (b) selecting a reception frequency using an RSSI value on each frequency synchronized with a previously designated synchronous code and a weighted moving average (S) value between RSSI values, on the basis of a result of the scanning;

(d) decoding the transmitted data by means of the codec and outputting the decoded data to an external output unit.

11. The radio multi-channel receiving method as set forth in claim 10, further comprising the step of: (e) performing the handoff, the step (e) comprising the steps of:

(e-1) scanning frequencies other than a current reception frequency and selecting a candidate frequency; and

(e-2) determining whether a handoff must be performed using RSSI values of the candidate frequency selected at the step (e-1) and an active frequency and an S value between the RSSI values, performing the step (b) if the handoff must be performed, and scanning the active frequency to perform the step (c) if the handoff does not need to be performed.

12. The radio multi-channel receiving method as set forth in claim 11, wherein the step (e) further comprises the steps of: detem ining whether an S value for a currently active frequency is stable for a first predetermined time and determining whether an S value for a candidate frequency is stable for a second predetermined time; determining whether the S value for the currently active frequency is smaller than a first threshold value and determining whether the S value for the candidate frequency is larger than a second threshold value; and performing the step (b) only if the S value for the currently active frequency is stable for the first predetermined time, the S value for the candidate frequency is stable for the second predetermined time, the S value for the currently active frequency is smaller than the first threshold value, and the S value for the candidate frequency is larger than the second tlireshold value.

13. The radio multi-channel receiving method as set forth in any one of claims 10 to 12, wherein the step (c) comprises the step of: if the frame of multiplexed data corresponds to the selected channel, decoding the multiplexed data on the basis of polarity altemated pulse width/code division multiple access (PW/CDMA), and wherein the channel selected by the user interface is one of language channels configured by voice data created in multiple languages.

14. The radio multi-channel receiving method as set forth in any one of claims 10 to 12, wherein the step (e) further comprises the step of: selecting a reception frequency using a previously designated synchronous code according to the result of the scanning, scanning frequencies other than a current reception frequency using a previously designated synchronous code when another channel is selected by a user interface, and performing the step (b).