Radiocommunication system using time-division digital frames

What is claimed is:

1. A radiocommunication system for performing bidirectional simultaneous communication, comprising:

a base station having transmitting means for dividing each of a plurality of digital frames into a plurality of time slots and assigning a plurality of consecutive channel numbers to the time slots of each digital frame, each including a bit and frame synchronization field, an address field, a control field, a transmit information field, and a frame check and correct sequence field, and transmitting the time-division digital frames as a radio signal of a first frequency, and receiving means for receiving a radio signal of a second frequency; and

a plurality of terminal stations each having receiving means for receiving the radio signal of the first frequency transmitted from the transmitting means of said base station and transmitting means for selecting at least one of said channels in said plurality of time-division digital frames to which said plurality of consecutive channel numbers are added and each of which has a frame structure which is the same as the frame structure of each of said time-division digital frames received from said base station, and transmitting the time-division digital frame of the selected channel to said base station as a radio signal of the second frequency.

2. A radiocommunication system according to claim 1, in which said base station further includes adding means for generating free channel identification information representing unused channels at the second frequency and adding the free channel identification information to each of said digital frames which are to be transmitted from said base station to each terminal station.

3. A radiocommunication system according to claim 2, in which each terminal station further includes detecting means for detecting unused channels at the second frequency on the basis of the free channel identification information contained in each of the digital frames transmitted from the transmitting means of said base station, to determine which of said channels is to be selected.

4. A radiocommunication system according to claim 1, in which each of the digital frames further includes a frame count field in which the channel number is contained.

5. A radiocommunication system according to claim 1, in which the transmit information field has a plurality of data blocks each of which comprises data of one byte.

6. A radiocommunication system according to claim 5, in which one data block of said transmit information field serves as control information between said base station and said terminal stations, and said one data block performs communication of the control information between said terminal stations and said base station while said base and terminal stations are transmitting target data using data blocks other than said one data block.

7. A radiocommunication system according to claim 1, in which said terminal stations perform bit and frame synchronization on the basis of said bit and frame synchronization field in the time-division digital frames transmitted from said base station.

8. A radiocommunication system according to claim 1, in which a transmission speed of data from said base station to said terminal stations depends upon the number of channels selected in the first frequency, and a transmission speed of data from said terminal stations to said base station depends upon the number of channels selected in the second frequency.

9. A radiocommunication system for performing bidirectional simultaneous communication, comprising:

a first terminal station having transmitting means for dividing each of a plurality of digital frames into a plurality of time slots and assigning a plurality of consecutive channel numbers to the time slots of each digital frame, each including a bit and frame synchronization field, an address field, a control field, a transmit information field, and a frame check and correct sequence field, selecting at least one of the channels in the time-division digital frames, and transmitting the time-division digital frame of the selected channel as a radio signal of a first frequency;

a second terminal station having transmitting means for adding said plurality of consecutive channel numbers, which are periodically repeated, to said plurality of time-division digital frames, selecting at least one of the channels other than said selected at least one of the channels in the time-division digital frames, and transmitting the time-division digital frame of the selected channel as a radio signal of a first frequency;

a base station having receiving means for receiving and separating the time-division digital frames transmitted from said first and second terminals for each of the channels and recognizing channel numbers added to the channels selected by said first and second terminal stations, transmitting means for adding said plurality of consecutive channel numbers, which are periodically repeated, to said plurality of time-division digital frames, selecting a digital frame of the same channel as the channel selected by said first terminal station, transmitting the time-division digital frame of the selected channel to said first terminal station as a radio signal of a second frequency, selecting a digital frame of the same channel as the channel selected by said second terminal station, and transmitting the time-division digital frame of the selected channel of said second terminal station as a radio signal of the second frequency; and

interface means provided on said base station, for transmitting and receiving digital data to and from a digital network to insert data or control information into the time-division digital frame.

10. A radiocommunication system for performing bidirectional simultaneous communication, comprising:

a base station having transmitting means for dividing each of a plurality of digital frames into a plurality of time slots and assigning a plurality of consecutive channel numbers to the time slots of each digital frame, each including a bit and frame synchronization field, an address field, a control field, a transmit information field, and a frame check and correct sequent field, and transmitting the time-division digital frames as a radio signal of a first frequency, and receiving means for receiving a radio signal of a second frequency; and

a plurality of terminal stations each having receiving means for receiving the radio signal of the first frequency transmitted from the transmitting means of said base station, and recognizing and separating each channel from each digital frame, and transmitting means for selecting at least one of said channels in said plurality of time-division digital frames to which said plurality of consecutive channel numbers are added and each of which has a frame structure which is the same as the frame structure of each of said time-division digital frames received from said base station, and transmitting the time-division digital frame of the selected channel of said base station as a radio signal of the second frequency;

wherein the receiving means of said base station receives the time-division digital frames of the second frequency transmitting from the terminal stations and separates the time-division frames for each of the channels.

11. A radiocommunication system for performing bidirectional simultaneous communication, comprising:

a first terminal station having transmitting means for dividing each of a plurality of digital frame into a plurality of time slots and assigning a plurality of consecutive channel numbers to the time slots of each digital frame, each including a bit and frame synchronization field, an address field, a control field, a transmit information field and a frame check and correct sequence field, selecting at least one of the channels in the time-division digital frames, and transmitting the time-division digital frame of the selected channel as a radio signal of a first frequency;

a second terminal station having transmitting means for adding said plurality of consecutive channel numbers, which are periodically repeated, to said plurality of time-division digital frames, each including the bit and frame synchronization field, the address field, the control field, the transmit information field and the frame check and correct sequence field, selecting at least one of the channels other than said selected at least one of the channels in the time-division digital frames, and transmitting the time-division digital frame of the selected channel as a radio signal of the first frequency;

a base station having receiving means for receiving and separating the time-division digital frames transmitted from said first and second terminals for each of the channels and recognizing channel numbers added to the channels selected by said first and second terminal stations, transmitting means for adding said plurality of consecutive channel numbers, which are periodically repeated, to said plurality of time-division digital frames, each including the bit and frame synchronization field, the address field, the control field, the transmit information field and the frame check and correct sequence field, selecting a digital frame of the same channel as the channel selected by said first terminal station, transmitting the time-division digital frame of the selected channel to said first terminal station as a radio signal of a second frequency, selecting a digital frame of the same channel as the channel selected by said second terminal station, and transmitting the time-division digital frame of the selected channel to said second terminal station as a radio signal of the second frequency; and

interface means provided on said base station, for transmitting and receiving digital data to and from a digital network to insert data or control information into the time-division digital frame.

12. A radiocommunication system according to claim 11, in which said base station further includes adding means for generating free channel identification information representing unused channels at the second frequency and adding the free channel identification information to each of said digital frames which are to be transmitted from said base station to each terminal station.

13. A radiocommunication system according to claim 12, in which each terminal station further includes detecting means for detecting unused channels at the second frequency on the basis of the free channel identification information contained in each of the digital frames transmitted from the transmitting means of said base station, to determine which of said channels is to be selected.

14. A radiocommunication system according to claim 11, in which each of the digital frames further includes a frame count field in which the channel number is contained.

15. A radiocommunication system according to claim 11, in which the transmit information field has a plurality of data blocks each of which comprises data of one byte.

16. A radiocommunication system according to claim 11, in which said terminal stations perform bit and frame synchronization on the basis of said bit and frame synchronization field in the time-division digital frames transmitted from said base station.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiocommunication system and, more particularly, to a radiocommunication system using time-division digital frames.

2. Description of the Related Art

In general, in places where many people work, such as large office buildings, factory sites and hospitals, many employees do their respective tasks, at different sections. Each employee is engaged in a task with a transceiver, so that he or she may make contact with another employee, or the office, to exchange information if needed.

In such places, not only speech communication but also communication of digital data, such as image data, is frequently performed. Speech communication can be performed by transceivers carried by employees. On the other hand, digital data communication is carried out using communication equipment such as facsimile terminal equipment, data terminal equipment or computers, which are mutually connected through normal telephone lines or private data lines provided within office buildings and factory sites. Thus, for local communication in office buildings or factory sites, different communication equipment is needed for each type of information to be transmitted.

In the radiocommunication system of an office building or factory site, in order for many employees to communicate with a base station simultaneously, the number of required transmission frequencies must at least correspond to the number of employees. Hence, when the number of employees increases, the number of radio frequencies available in the radiocommunication system must also be increased. If the number of employees increases too much, however, the number of communication channels would be inadequate, and thus sufficient radiocommunication service could not be provided.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a radiocommunication system which permits radiocommunication of various types of digital information, such as speech, images and digital data, and realizes many communication channels by the use of a single radio frequency on a time-division basis.

According to the present invention there is provided radiocommunication system comprising: a first radiocommunication device having transmission section for adding channel identification information to each of a plurality of digital frames, arranging the digital frames on a time division basis and transmitting the time-division digital frames as a radio signal of a first frequency; and a second radiocommunication device having receiving section for receiving the radio signal transmitted from the transmitting means of the first radiocommunication device and separating the digital frames for each channel in accordance with the channel identification information.

In the radiocommunication system, channel identification information is added to each of a plurality of digital frames and the digital frames are transmitted on a time division basis as a radio signal of a first frequency. Thus, signals on a plurality of channels are transmitted simultaneously by the radio signal of the first frequency. Therefore, many communication channels are realized by the use of a same radio frequency band, permitting the effective use of frequencies.

In addition, proper selection of the number of channels to be transmitted simultaneously can achieve a desired data transmission rate. For this reason, the data transmission rate can be selected according to the type of data to be communicated. Further, by using the data for D channel of an integrated service digital network (ISDN) so as to fit the ISDN interface, another information can be transmitted simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a time-division digital frame used with a radiocommunication system of the present invention;

FIG. 2 illustrates the contents of a frame count field included in the digital frame of FIG. 1;

FIG. 3 is a schematic diagram illustrating the communication principle of a radiocommunication system according to an embodiment of the present invention;

FIGS. 4A through 4D are timing diagrams for explaining the operation of transmitting and receiving the time-division digital frame in the radiocommunication system shown in FIG. 3;

FIG. 5 illustrates in block form an example of a specific arrangement of radio terminal equipment used in the radiocommunication system shown in FIG. 3;

FIG. 6 is a block diagram of the main part of the transmitting circuit of the radio terminal equipment shown in FIG. 5;

FIG. 7 is a block diagram of the main part of the receiving circuit in the radio terminal equipment shown in FIG. 5;

FIG. 8 illustrates in block form another specific arrangement of the radio terminal equipment used in the radiocommunication system of FIG. 3; and

FIG. 9 is a block diagram of an example of the radio base station used in the radiocommunication syste of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, some uses of the radiocommunication system of the present invention will be described.

As described above, in large office buildings, hospitals, factory sites and other places where many personnel work, communication of a large amount of information is required at all times. The radiocommunication system of the present invention is intended to realize communication at such places by means of portable or easily carried radio transmitter-receivers. At such places, communication of image data from facsimile terminal equipment, and digital data from data terminal equipment and computer equipment, as well as communication by speech, is performed frequently. Such communication is effected through normal telephone lines or private data lines at present, and exclusive communication equipment is utilized exclusively, for each type of data. The radiocommunication system of the present invention is intended to realize a digital version of such communication equipment and permit wireless communication between communication apparatuses.

The digital version of communication equipment and wireless communication would have a great effect on the promotion of the efficiency and facility of work in large office buildings, hospitals, factory sites and another places. For example, in hospitals, diagnostic data could be written into or read from a computer system easily and instantly as well as speech communication. In factories, the transmission of control data to a malfunctioning device situated in a dangerous place, and the reception of monitor data related to the operation of the malfunctioning device could be effected easily and safely. When applied to the integrated service digital network (ISDN), the radiocommunication system of the present invention permits transmission of simple moving images, thus enabling a portable telephone and television conference system to be realized.

Referring now to FIG. 1, a time-division digital frame, which is used with the radiocommunication system according to the invention and conforms to HDLC (High Level Data Link Control procedure), comprises bit and frame synchronization fields F, an address field A, a control field C, a frame count field FC, a transmit information field I and a frame check and correct sequence field FCS. The bit and frame synchronization field F, address field A and control field C contain eight bits each. The frame count field FC contains six bits. The transmit information field I contains nine data blocks each of eight bits (one byte). The frame check and correct sequence field FCS contains 11 bits.

The digital frame is 121 bits in length and has a cycle of 500 .mu.s. The bit rate of the digital frame is thus 242 Kbits per second where no time division is used. For error correction of the digital frame data, use is made of a fire code (M=4, code length=105 bits, information bit length=94 bits, error correcting capability=4 bits).

Note that, instead of using the fire code, a block code or convolution code may be used as an error correction code. In such a case, however, the code length and the error correcting capability will be different.

Next, the function of each field of the digital frame will be described.

Bit and frame synchronization field F

The bit and frame synchronization field F is a bit sequence used to establish synchronization and the start and finish of a digital frame and is inserted at the beginning and end of the frame. One of the synchronization field F positioned at the end of the preceding frame, and the synchronization field F positioned at the start of the next frame, may be omitted to use the remaining field for both frames because digital frames are transmitted continuously. The bit and frame synchronization frame F may have a bit pattern of, for example, "01111110". Also, a bit pattern such as "1010 . . . " and a frame synchronization pattern of a PN code or the like may be combined for use as the bit and frame synchronization field F.

Address field A

Address field A contains information representing a source address and a destination address of a time-division digital frame. In the present embodiment, of eight bits of address field A, the high-order two bits are used for an address to identify base station equipment and the low-order six bits are used for an address to identify a radio terminal equipment unit. If the address field A needs more than eight bits, it may be expanded according to the number of the base station and radio terminal units involved in the radiocommunication system, or a part of the information field I may be used for transmission of address information.

Control Field C

The control field C is a bit sequence adapted for transmission of control information between the base station unit and a radio terminal unit and contains control information conforming to HDLC.

Frame count field FC

The frame count field FC is a bit sequence adapted to use digital frames on a time-division basis. A specific arrangement of the frame count field FC will be described below with reference to FIG. 2.

As shown in FIG. 2, the frame count field FC contains 2-bit transmission channel identification information TCH representing the channel number of a digital frame to be transmitted. The 2-bit transmission channel identification information TCH is a binary code for representing any of channel 0 to channel 3 over which a digital frame is transmitted between the base station and a terminal unit.

The frame count field FC further contains 4-bit free channel identification information RCH for identifying a busy condition of each of the four channels 0 to 3 which are used for transmission from terminal units to the base station. The four bits of the free channel identification information RCH represent, from left to right, the busy condition of the channel 0 (CH0), channel 1 (CH1), channel 2 (CH2) and channel 3 (CH3). The free channel identification information RCH is set by the base station. For example, a "1" is set in a bit position corresponding to a busy channel and a "0" is set in a bit position for a free channel.

The free channel identification information RCH is used in order for the base station to inform each of the terminal units of a free channel or free channels. Hence, each digital frame transmitted from the base station to terminal units contains both the transmission channel identification information TCH and free channel identification information RCH. On the other hand, digital frames transmitted from terminal units to the base station may contain only the transmission channel identification information TCH. That is, the free channel identification channel RCH is not necessarily required. Where the number of channels is increased to eight, each of the transmission channel identification information TCH and the free channel identification information RCH has three bits. The 3-bit free channel identification information RCH is used to indicate the first free channel. In this case, the rate of transmission on each channel will be 18 Kbits per second.

In the frame count field FC of FIG. 2, the transmission channel identification information TCH is set to "01" and the free channel identification information RCH is set to "1010". The "01" of the transmission channel identification information TCH means that a digital frame containing this information belongs to the channel 1 (CH1) and the "1010" of the free channel identification information RCH indicates that the channel 0 (CH0) is busy, the channel 1 (CH1) is not busy, the channel 2 (CH2) is busy and the channel 3 (CH3) is not busy in communication between terminal units and the base station.

Transmit information field I

The transmit information field I is a bit sequence of information to be transmitted, and is comprised of nine blocks, each of eight bits (one byte). When, therefore, digital data is transmitted using all four channels and all the nine blocks of the transmit information field I for each channel, the information transmission rate will be given by 8 (bits).times.9 (blocks).times.5 (.mu.s).times.10.sup.2 =144 Kbits per second. This transmission rate is adapted to 2B+D (64 Kbits/s.times.2+16 Kbits/s=144 Kbits/s) regulated as the international standardized interface in the integrated services digital network (ISDN). Here one of nine blocks is provided for D channel of ISDN. As a concrete example, 64 Kbits/s.times.2 =128 Kbits/s (B channel) may be used for transmission of moving images and speech, and 16 Kbits/s (D channel) may be used for transmission of still images (facsimile images), to thereby permit simultaneous transmission of moving images, speech and still images.

The standard information transmission rate in normal data transmission over telephone lines is 64 Kbits/s. Such a transmission rate can be achieved by using two channels of the four channels and transmitting a transmit information field I having a total of 16 blocks on the two channels. In this case, it will be possible to use the remaining two blocks, each provided for the D channel, for communication of control information between the terminal unit and the network, or communication between terminal units.

For transmission of band-compressed information of speech or the like at a transmission rate of 32 Kbits/s, a single channel will suffice. Also, another data transmission can be made simultaneously with 4 Kbits/s, accommodating the D channel.

In this way, information transmission at a transmission rate of 144 Kbits/s or less can be achieved by the selective use of the four channels. In this case, the information transmission rate per channel is 32 Kbits/s+4 Kbits/s. To use two channels or more for high speed transmission of a piece of information, it is required to use channels which are continuous in time.

Frame check and correct sequence FCS

The frame check and correct sequence FCS is a bit sequence for detecting and correcting errors in data transmission and is composed of an 11-bit fire code in the present embodiment. The range of correction of errors by the fire code is all the bits in the digital frame data except for the bit and frame synchronization fields F.

The principle of radiocommunication using the digital frame of FIG. 1 will be described below with reference to FIG. 3.

In FIG. 3 is illustrated a radiocommunication system comprising a base station unit P1 and two radio terminal units T1 and T2. Each of the terminal units T1 and T2 is provided with a radio transmitter unit Tx and a radio receiver unit Rx. Base station unit P1 has a radio transmitter unit Tx' and a radio receiver unit Rx'.

Here there is illustrated a case where a single frequency is used for transmission and a single frequency for reception, that is, a carrier frequency of f1 is used for transmission from the base station to the terminal units and a carrier frequency of f2 is used for transmission from the terminal units to the base station.

By way of example, in FIG. 3, a two-way communication is carried out between base station P1 and terminal unit T1 via channel 0 (CH0), and a two-way communication is carried out between base station P1 and terminal unit T2 via channel 1 (CH1) and channel 2 (CH2).

Next, with reference to FIGS. 4A through 4D, a description will be given of the process of request-to-call from each of terminal units T1 and T2 to base station P1 and the process of response from base station P1 to each of terminal units T1 and T2, which are required to permit two-way communication between base station P1 and each of terminal units T1 and T2.

Base station P1 always transmits a radio signal of a carrier frequency of f1 to each of terminal units T1 and T2 to enable them to establish bit and frame synchronization even when actual information transmission is not made. The digital frame transmitted by the radio signal is shown in FIG. 4A.

As shown in FIG. 4A, base station P1 repeatedly transmits four time-division digital frames corresponding to respective channels CH0 to CH3 in sequence. In this case, the frame count fields FC of the four digital frames have their high-order two bits, or transmission channel identification information TCH, set to "00", "01", "10" and "11" corresponding to channels CH0 to CH3. The low-order four bits of the frame count field FC of each digital frame, namely, the free channel identification information RCH, is set to "0000". This means that all the channels CH0 to CH3 are not used at carrier frequency f1 transmitted from base station P1 to terminal units T1 and T2, and at carrier frequency f2 transmitted from terminal units T1 and T2 to base station P1. As shown in FIGS. 4A to 4D, in carrier frequencies f1 and f2, the same channel number is assigned to the digital frames in the same time-slot.