JPH03280630A - Digital signal transmitting method - Google Patents

Abstract

PURPOSE:To attain digital communication with high quality in fading by skipping a signal with a low level due to fading and implementing the communication based on a signal with a high reception level. CONSTITUTION:An information signal is processed into a frame, the transmission speed at a radio block is selected a little higher than the information speed to apply time compression and a super-frame is formed by using some frames as the unit. Moreover, a frame freely designated is formed in the super-frame, the location of the frame is designated for a decreased level based on level fluctuation information detected from the past level measurement of the frame, no communication is implemented at the frame location but the communication is implemented at other frames with a high level. Thus, digital mobile communication with high quality is implemented in fading without giving economical and capacity load onto a base station and a portable equipment while ensuring the real time of the communication.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a digital signal transmission method in digital mobile communications, in which communication is performed in areas where the reception level is high, other than the fading drop areas.

(2) Prior art and its problems In land mobile communications, the reception level fluctuates as the mobile station moves. This fluctuation is called Rayleigh fading because it follows a Rayleigh distribution, and its speed fo (H2) is defined by the moving speed V (m/5ec) and the radio frequency wavelength λ (m
), then fD=V/λ −−−−−−−−−−−−−・
-・-・・・・−-, (11) Since the depth of the drop in level reaches several tens of dB, the communication quality in the drop portion significantly deteriorates, resulting in a situation where communication is impossible. In conventional digital mobile communication systems, in order to cope with this deterioration, the following methods are used: ■ Perform communication while selecting a communication channel whose level has not dropped (high level) from among multiple wireless communication channels by using diversity reception; Diversity transmission is performed on the transmitting side to reduce the number of errors; ■Using an error correction code and interleaving method, errors in the dropped portion are dispersed within the code length of the interleave size and error correction is applied; ■Communication Methods such as dividing the information into packets and retransmitting the packets that hit the drop-off portion are used.Whether or not the method (■) provides excellent characteristics regardless of the fading speed has been investigated by improving the receiving system. It is necessary to prepare multiple base station antenna systems, which is a burden on the miniaturization and economicalization of mobile stations.Method (2) requires a burden on the transmitting side equipment, especially multiple base station antenna systems.
There are problems in terms of station space and cost. Method (2) requires a long interleaving length when the speed of the mobile station is slow, which causes a problem of large information delay, and if the moving speed is slow, sufficient effects cannot be obtained. Method (2) basically cannot perform real-time transmission and is not suitable for voice transmission. In digital mobile communications, which will be the mainstay of future digital mobile communications, real-time communications (
conditions such as: (1) the mobile phone must be small and inexpensive; the area of the base station must be small in order to reduce the required transmission power of the mobile phone, and the base station must therefore be simple; All of the above methods had some drawbacks.

(3) Object and Features of the Invention The object of the present invention is to overcome these difficulties and realize a high-quality digital mobile communication system in a fading environment.

For this reason, the present invention frames an information signal and
By compressing time by making the transmission speed of the wireless section slightly higher than the information speed and configuring a superframe with several frames as a unit, one frame that can be freely specified and used within the superframe is created. Based on the level fluctuation information detected from level measurement in past frames, the frame position is applied to the part where the level drops, and communication is not performed at the corresponding frame position, but only in other frame parts where the level is high. This ensures real-time communication while also providing economical and
This system is characterized by ensuring high quality communication without imposing a capacity burden and even when moving speeds are slow.

(Structure and operation of the invention) FIG. 1 is a diagram illustrating the relationship between the super frame and level fluctuation of the invention. The superframe length is set to less than half the fading period expected from the moving speed of the mobile device, so that multiple level drops do not occur within a superframe. That is, the fading period is T, and the superframe length is T.

Then, T, ≦T, /2 −・−・−−−−−−1−−・−・
T8 is set so as to satisfy the relationship -.=.-(2). On the other hand, regarding the subframe length Tfub,
The more the drop in level is absorbed, the greater the effect, or if it is taken too long, the transmission efficiency will drop (.So, if the width of the drop in level corresponding to the minimum allowable level is T, then Td≦T,... −m−−・−・−−11−−−
−−−−・−T * u so as to satisfy the relationship (3)
Set b. Note that the transmission rate at this time is η1. Then, if there is one spare subframe, η,, = (T, -T, ub)/T, -・----
1 (41). Therefore, (2), (3)
, From equation (4), the subframe length T t b is T,≦T. ,≦(1−η,h)(T+/2)−
Set to satisfy (5). To predict a drop in level and notify the communication partner, set the level at which to start measuring the slope of level fluctuations, measure the level in subframe units of the received signal at your own station, and calculate the slope and subframe length T, 1. The level drop position is predicted based on the relationship between The corresponding spare subframe of the station received signal is skipped. In addition, if a drop in level fluctuation is not predicted within the superframe, a predetermined position, for example, the first
The last subframe in the superframe shown in the figure is regularly skipped as a spare subframe. In this case, since the communication quality of the spare subframe at this regular skip position is good, dummy bits such as synchronization signals and check signals are inserted to make effective use of the spare subframe. By using such a configuration and procedure, it is possible to avoid the depressed portions of level fluctuations where the communication quality is poor, and to realize communication only in the portions where the reception level is high and where the communication quality is good. In addition,
The larger T is from equation (5) (that is, the slower the fading speed is, the slower the moving speed is from equation ( )), the greater the selection range of subframe length T g u b or superframe length T. I know it will increase.

FIG. 2 is a diagram illustrating the frame structure of the present invention. When one spare subframe is used, the digital information signal to be transmitted is framed into frames (T, /T, . . . -1) that are one less than the number of subframes in the superframe and read into the buffer memory. In the example shown in FIG. 2, the super frame has a length of eight characters, and the number of subframes in the super frame is nine. Information in each frame is speed-converted from the buffer memory and read out in accordance with a skip request from the communication partner.

Read speed f. is f, where f is the information signal input to the buffer. =f, /ηlb (η1. is the transmission efficiency expressed by equation (4)). That is, the time is compressed by a factor of 1/η. The read transmission information signal is reframed together with a synchronization signal related to the subframe, a control signal such as a skip request to the other party, and is transmitted in a superframe. For the spare subframe, a dummy hit is inserted in addition to the control signal, and the spare subframe is incorporated into the superframe.

FIG. 3 is a diagram illustrating a frame structure when the present invention is applied to a TDMA mobile communication system. The TDMA frame length is taken as the subframe length, and the superframe length and subframe length are set so as to satisfy the relationships explained in FIGS. 1 and 2. That is, the digital information signal to be transmitted is
Convert the MA frame length into a frame, compress the time, and then convert it into a TDMA frame.
The #hm signal is added to configure the local subframe. Third
In the example shown in the figure, the digital information signal to be transmitted has a TDMA frame length, and as in the example shown in FIG.
Reading is performed by compressing the time so that there are nine subframes including TDMA control signals and information signals in a superframe. The subframe of the local station is further time-compressed together with the subframe of the other station to form a TDMA frame and transmitted. FIG. 3 shows an example in which six stations constitute a TDMA frame (6-channel multiplexed TDMA transmission), and the own station signal is transmitted through the second slot. A control signal related to a skip request is defined as one of the TDMA control signals to ensure efficient use of TDMA control slots. In FIG. 3, for ease of understanding, the reading speed of the buffer memory is calculated by combining the own station TDMA control signal and the information signal, and
Set it to 0, read it once, and then read TDMA again.
This is an example of time compression to the transmission speed (six times speed conversion due to six channel multiplexing), but the information signal is read from the buffer memory at the TDMA transmission speed from the beginning, and the TDMA
An efficient method is to directly configure a TDMA frame together with a control signal.

FIG. 4 shows an example of the configuration of the present invention. The information transmission a to be sent is read into the buffer memory/frame formation circuit A in a frame according to the control signal d from the control unit, and is read from the control unit based on the control signal (reception) h sent from the other party of communication. A control signal d indicating whether or not to use the spare subframe of
The time is compressed and read out for each frame according to the following. The read information signal is a control signal (sent) to the other party of the communication including a skip request made by the control unit based on the level information g from the received level detection/processing circuit E by the frame (multiplexing) circuit B. The signal C is reframed together with e to form a subframe, and is further transmitted to the communication partner by a modulator/transmitter C as a signal C having a superframe structure in which a plurality of subframes are units. On the other hand, on the receiving side, a receiver/demodulator F receives and demodulates the signal from the communication partner. The demodulated signal i is separated into an information signal j and a control signal (reception) h by a frame (separation) circuit G.
is a control signal (
Reception) h is input to the control unit as described above. Further, the reception level f is input to the reception level detection/processing circuit E, the slope of the level fluctuation is measured to predict the position of the level drop, and the above-mentioned level information g is generated and input to the control section. The buffer circuit re/def seaming circuit H reads (received) h into the information signal j for each subframe in accordance with the control signal l indicating whether to skip or not, which is generated by the control unit based on the level information g, The received information signal k is read out with time expansion at , and the received information signal k is reproduced.

(Effects of the Invention) By employing the digital signal transmission method according to the present invention as described above, it is possible to avoid communication in the depressed portion of level fluctuation where the communication quality is significantly degraded, and to perform communication in the high level portion. It is possible to achieve high quality communication,
In addition, since signal processing is simple in the baseband, the slower the signal transmission movement, the greater the flexibility in selecting superframe lengths, subframe lengths, etc., without placing an economical or capacity burden on base stations or mobile stations. Since this increases the effectiveness, it becomes possible to economically construct a high-quality mobile phone system in combination with the above-mentioned effects. Note that since this signal transmission method is independent from conventional quality improvement methods such as diversity and error correction, even higher quality signal transmission can be achieved by combining these methods.

[Brief explanation of drawings]

FIG. 1 is a time chart for explaining the relationship between super frame and level fluctuation in the present invention, FIG. 2 is a time chart for explaining the frame structure in the present invention, and FIG. 3 is a time chart for explaining the frame structure in the present invention. A time chart for explaining the frame structure when applied to a DMA mobile communication system,
FIG. 4 is a block diagram showing a configuration example of the present invention. A... Buffer memory/frame formation circuit, B... Reframe (multiplex) circuit, C... Modulator/transmitter, D
...control unit, E...reception level detection/processing circuit, F
...Receiver/demodulator, G...Reframe (separation) circuit, H...Buffer circuit re/def seam circuit, a
...Information signal (transmission Lb...information signal read from A, C...output signal of B, d...read/read control signal (transmission), e...control signal (transmission) ), f...
Reception level, g...level information, h...control signal (
i...demodulated signal, j...information signal separated by G, k...information signal (reception).

Claims (2)

[Claims] (1) In a digital mobile communication system in which a control signal is added to an information signal divided at regular intervals to constitute a subframe, and a plurality of subframes constitute a superframe, the subframe in the superframe is The number of frames is set to be one or more spare subframes greater than the number of subframes necessary to transmit information, and the position of the level drop is predicted from the fluctuation trend of the received level, and the When a drop in level is predicted within the superframe, notifying the other party in a control slot of a subframe immediately before the subframe that the subframe including the drop position will be the spare subframe;
The other party shall not send an information signal in the subframe that includes the position of the level drop, and if the level drop is not predicted within the superframe or the number of subframes in which the level drop is predicted is less than the number of spare subframes. If the number is low, a dummy bit is inserted into the spare subframe, and communication is performed in a subframe other than the spare subframe in the superframe. (2) In the TDMA mobile communication system, an information signal framed with a TDMA frame length is time-compressed, a TDMA control slot is added to form a subframe, and multiple subframes are combined into a TD.
A superframe with a length that is an integral multiple of the MA frame is constructed, one or more spare subframes are created that can be used freely, and each subframe is placed in the TDMA slot assigned to the own station as an input information signal to the own station. The control signal for the spare subframe is defined and used as one of the control signals used in the control slot in the TDMA slot, and the position of the drop in level is predicted from the fluctuation trend of the received level. If a drop in the level is predicted within a superframe, the other party is notified in the control slot of the subframe immediately before the subframe that the subframe containing the drop position will be used as a backup subframe, and the other party is notified of the level drop. An information signal is not sent in a subframe that includes a drop position, and if a drop in level is not predicted within the superframe, or if the number of subframes in which a drop in level is predicted is less than the number of spare subframes, the A digital signal transmission method characterized by inserting dummy bits into subframes and performing communication in subframes other than spare subframes within a superframe.