JPH0448297B2

JPH0448297B2 -

Info

Publication number: JPH0448297B2
Application number: JP62005911A
Authority: JP
Inventors: Akio Saburi
Original assignee: Nippon Electric Co Ltd
Current assignee: NEC Corp
Priority date: 1987-01-16
Filing date: 1987-01-16
Publication date: 1992-08-06
Also published as: JPS63175529A

Description

[Brief explanation of the drawing]

第１図は本発明の制御回路構成を示すブロツク
図、第２図ａ及びｂは夫々複数搬送波TDMA通
信方式の原理図、第３図は本発明を適用する方式
の原理図、第４図は本発明に使用するバースト・
タイム・プラン活用回路の一例のブロツク図、第
５図はバースト・タイム・プラン活用回路の他の
一例のブロツク図、第６図は本発明に使用する減
衰器回路の一例のブロツク図、第７図は減衰器回
路の他の一例のブロツク図、第８図は本発明の中
心となる減衰器制御回路の構成のブロツク図であ
る。２０……データ・バースト、４０……搬送波、
３２……地球局装置、３４……通信端局装置、３
６……地上回線接続装置、１０２……地上回線、
１１０……制御情報、２０２……記憶回路、２０
４……フレーム周期カウンター、２１０……減衰
器、、２１２……発振器、２１６……減衰器制御
回路、６０６……バースト分離回路、６０８……
復調器。 Figure 1 is a block diagram showing the control circuit configuration of the present invention, Figures 2a and b are principle diagrams of a multi-carrier TDMA communication system, Figure 3 is a principle diagram of a system to which the present invention is applied, and Figure 4 is a diagram showing the principle of a system to which the present invention is applied. Burst used in this invention
FIG. 5 is a block diagram of another example of the burst time plan utilization circuit. FIG. 6 is a block diagram of an example of the attenuator circuit used in the present invention. This figure is a block diagram of another example of the attenuator circuit, and FIG. 8 is a block diagram of the configuration of the attenuator control circuit which is the core of the present invention. 20...data burst, 40...carrier wave,
32...Earth station device, 34...Communication terminal device, 3
6... Terrestrial line connection device, 102... Terrestrial line,
110...Control information, 202...Storage circuit, 20
4... Frame period counter, 210... Attenuator, 212... Oscillator, 216... Attenuator control circuit, 606... Burst separation circuit, 608...
Demodulator.

Claims

[Claims] 1. In a TDMA satellite communication device that is used for the TDMA method using multiple carrier waves within the band of one satellite repeater and operates based on burst time plan information stored within the device, The vessel and
It has an attenuator that controls the input level of the demodulator and an attenuator control circuit that controls the attenuator, and the amount of attenuation provided by the attenuator is determined directly or indirectly by burst time plan information. A variable TDMA satellite communication device characterized in that carrier power is changed at a TDMA frame period according to a specific pattern. 2 The attenuator control circuit has a memory circuit that stores the correspondence between the communication partner station and the attenuator control information, and the pattern of change in the attenuation amount of the attenuator within the TDMA frame is determined during the burst time plan. The variable carrier wave power according to claim 1 is controlled by information read out from the storage circuit in response to information regarding the communication partner station.
TDMA satellite communication equipment. 3. The attenuator control circuit has a memory circuit that stores the correspondence between the identification code or number of the received burst and the attenuator control information, and the attenuation amount of the attenuator is
The pattern of changes within the TDMA frame is controlled by information read out from this storage circuit in correspondence with information regarding the identification code or number of the received burst in the burst time plan. A variable carrier power TDMA satellite communication device according to claim 1. 4. The attenuator control circuit has a memory circuit that stores the correspondence between the carrier wave selection information in frequency hopping and the attenuator control information, and the attenuation amount of the attenuator is
Claim 1, characterized in that the pattern of changes within a TDMA frame is controlled by information read out from this storage circuit in response to selection information of a receiving carrier in a burst time plan. The variable carrier power TDMA satellite communication device according to item 1. [Claims] [Industrial Application Field] The present invention relates to a TDMA satellite communication system using a plurality of carrier waves within the band of one satellite repeater, and particularly to a TDMA satellite communication device used for business satellite communication. be. [Prior Art] TDMA (Time Division Multiple Access) satellite communication system is a system in which multiple earth stations use all or part of the frequency band of a satellite transponder in a time-division manner. It is. In this case, each earth station sends the signal to be transmitted in the form of an intermittent signal, that is, a burst, at a specific period.
In other words, it needs to be transmitted at the TDMA frame cycle, but it is known as an efficient communication method because it not only can handle a variety of digital signals in an integrated manner, but also allows for the construction of highly flexible networks. . In particular, the low-speed TDMA system, which uses a portion of the transponder's band and operates at a relatively low transmission speed, is economical in equipment, and can be expanded to a TDMA system using multiple carrier waves using frequency hopping technology, which will be described later. Therefore, it is suitable for so-called business satellite communications where earth stations are installed on the rooftops of buildings in urban areas or near offices. In a TDMA system, one or two earth stations are usually selected as reference stations from among multiple participating earth stations, and are responsible for transmitting reference timing signals necessary for TDMA synchronization within the system and for other control and monitoring purposes. It is normal to perform a function. One way to make the TDMA system more flexible is to define the TDMA operation using a burst time plan and control it using software data rather than hardware. That is, the number of bursts transmitted by each earth station is
The position and width within the TDMA frame, the destinations of the various types of traffic included in the frame, etc. are given in the form of data to control the transmitting side, while the received bursts and the processing method of their contents are also given in the form of data. It is. These data can be stored in the memory circuit, so by separately storing the data for the new plan in each station and switching from the old plan to the new plan all at once on the entire system, it is possible to connect to the network without affecting the traffic being transmitted. It is also possible to instantly change the configuration of the workpiece. Typically, a new burst time plan is transmitted from the reference station via satellite to each earth station using special data lines and downloaded into storage circuitry. Next, we will discuss system expansion using the low-speed TDMA method. Since the TDMA system is a system in which multiple stations use a common carrier wave in a time-division manner,
Each station transmits signals only intermittently. This means that the transmission equipment is used only intermittently. Furthermore, since the signal to be received usually corresponds to the transmitted signal, even if the receiving equipment appears to be receiving signals continuously, it is actually only used intermittently. . Therefore,
When transmitting/receiving equipment is not used for a certain carrier within a TDMA frame period, the transmission capacity of the equipment can be expanded if another carrier with a different frequency can be used successfully. When such an operation is performed between a plurality of carrier waves selected within the same transponder, this is called frequency hopping. Figures 2a and 2b illustrate the principle of a multi-carrier TDMA system using frequency hopping.
Here, it is assumed that there are three carrier waves 40, f1, f2, and f3, in the frequency band of the satellite transponder. In Figure a, three stations A, B, and C are respectively transmitting using specific carrier waves. here
Bursts for synchronization and control accompanying the operation of the TDMA system are omitted, and only the bursts (data bursts) 20 that carry the original traffic are shown.
However, for the sake of explanation, bursts for different stations are shown as independent bursts. On the receiving side, on the other hand, the burst destined for the local station is received while switching reception carrier waves using frequency hopping technology. Assuming that one earth station has only one communication device, it cannot transmit on more than one carrier at the same time, nor can it receive on more than one carrier at the same time. Therefore, when creating a burst time plan, the positions of the bursts to be transmitted by each station and the destinations of the bursts must be determined with consideration given to avoiding inconsistencies. In FIG. 1B, the frequency of the received carrier wave is assigned to each station, and the transmitting side transmits using the corresponding carrier wave depending on the destination of the traffic to be sent. That is, this is the case when carrier hopping technology is used on the transmitting side. Although these diagrams are simplified, an actual system would be complicated because there are many earth stations and each station has a different transmission capacity. Furthermore, frequency hopping is often required to be performed not only on either the transmitting side or the receiving side, but on both sides. [Problems to be solved by the invention] Conventionally, however, when constructing such a TDMA system, the line design was done with consideration given to passing one carrier wave through the entire transponder band or a part of the allocated band. Therefore, the maximum power level on the satellite that is allowed for that carrier is specified. On the other hand, each earth station using that carrier transmits bursts at a power corresponding to its maximum power level to make effective use of its power, so the power level of each burst passing through the transponder depends on its content and destination. It remains constant regardless. As a result,
Earth stations participating in a TDMA system each require equipment of approximately the same size, regardless of the transmission capacity required, resulting in a large initial investment and narrowing the range of application from an economic point of view. was. The present invention solves this problem and enables TDMA operation even between earth stations of different scales.
This allows the system to be constructed more economically. Furthermore, the present invention provides a system that can flexibly respond to requests for different transmission quality, and also solves the problem of rain attenuation peculiar to the K band (14/1 GHz, 30/20 GHz band) used for business satellite communications. It is also useful. [Means for Solving the Problems] One of the features of the system to which the present invention is applied in order to solve the above problems is that although it is a TDMA system,
The power level of the transmitted burst is changed depending on the conditions of the destination earth station and the content to be transmitted. Originally, the transmission power level of each burst or carrier wave is constant and should be determined at the line design stage, but in the present invention, the bandwidth allowed within the satellite transponder as a whole of multiple carrier waves used in the system, It is assumed that the available power allocation conditions are met, and the number of carrier waves and the power level of bursts transmitted on individual carrier waves can be changed flexibly according to the network situation, and this can be changed based on the burst time plan. This is something we try to thoroughly implement in our work. In other words, the maximum (N≧
2) Can use carrier waves up to
In a TDMA satellite communication system, there are multiple earth stations operating on mutually compatible burst time plans, and at least some of the earth stations transmit multiple carrier waves in a time-sharing manner by frequency hopping. or for reception or both, while for a particular value indicating the total carrier power level available within the system, the sum of the carrier power levels within N waves at any instant is The method is to use M-wave carrier waves (N≧M≧1) within a range not exceeding a specific value, and to individually set the power level of each burst transmitted using each carrier wave. The value of N is the number of carriers possible if the width of the frequency band allowed in the transponder and the available power are used to transmit traffic with normal quality between large earth stations in the network during clear weather. It is considered to be the maximum value of If small-scale earth stations coexist in the system, each earth station can operate within the same network by appropriately increasing the transmit power level of the bursts that the small-scale earth stations should receive. .
In this case, the power distribution naturally changes and the number of carrier waves in the system must decrease. If higher quality traffic transmission is required, the higher quality transmission can also be achieved by increasing the transmission power level of the bursts carrying that traffic. In this case as well, this is a factor that reduces the number of carrier waves in the entire system. Further, as will be described later, if a margin is provided in power distribution in consideration of rain attenuation, the number of carrier waves may be reduced. One way to set the power level of each burst is to set it permanently or on an ad hoc basis depending on the reception conditions of the earth station receiving the carrier. A permanent power level setting condition is the size of the receiving earth station, that is, the signal receiving ability. The rainfall characteristics of the region may also be taken into consideration. These conditions are taken into account when creating burst time plan data, so once the data burst containing the traffic that a certain earth station should receive is determined, the transmission power level of the corresponding burst for each earth station is determined. Become. When the transmission quality requirements for the traffic to be transmitted are specified in the burst time plan, this also becomes a condition for setting the power level. When the content of traffic is not managed by the burst time plan, each earth station monitors the transmission quality requirements of the traffic that each earth station accepts, and the results are used as the requirements of each earth station for creating a burst time plan. It is possible to allocate the necessary power by having the power submitted. Setting the power level at any time is mainly a rain attenuation countermeasure. Transmission power control technology that compensates for rain attenuation in uplinks from earth stations to satellites is already in practical use. The problem is compensation for rain attenuation in the downlink. Two methods are possible here. One method is for each earth station to monitor the quality of its received signal, i.e., the bit error rate, and to broadcast an alarm signal within the network when an earth station detects that the quality of its received signal has deteriorated beyond a standard. , each earth station receiving the burst autonomously changes the power level of the burst it is receiving according to a prescribed procedure. Another method involves a reference station intervening, the reference station receives the alarm signal,
This is to change the transmission power of each station as a command. In this case, by utilizing the monitoring function of the reference station, the above-mentioned transmission power control function can also be executed in the form of a command from that station, and the related equipment of each station is simplified. The premise that this method is possible is that burst
When creating a time plan, it is necessary to take into account power margins for rainfall. However, this power margin can be applied to any of the multiple bursts simultaneously present on the transponder. Therefore, if this method is adopted, it is possible to eliminate the waste of securing extra power for all lines during clear weather, and it is possible to achieve a remarkable effect in terms of effective use of satellite power. FIG. 3 shows the principle of one method to which the present invention is applied. In the figure, four carrier waves f1, f2, and f3 are included in the available frequency band of the satellite transponder.
0, and is assigned as a transmission carrier wave for three stations, A station, B station, and C station. That is,
f3 is for A station transmission, f2 is for B station transmission, f1 is for A station
This is for transmission by station C, which is smaller in size than station B or has worse reception conditions such as rain. The power level of each carrier wave is appropriately set depending on its purpose, that is, whether it is for voice transmission, data transmission requiring high transmission quality, or for an earth station with poor reception conditions. Of course, the total power of the entire carrier must be within the power level assigned to this system at the satellite transponder. Among the bursts transmitted by station A, the bursts labeled "broadcast" distribute data in broadcast mode, which is a characteristic of satellite communications. In this case, station B or C
If all stations other than station A receive this burst, this time slot will not be available for transmission by any station other than station A. However, it is possible to set the power level of broadcasting bursts higher by that amount, making it possible to distribute data with sufficiently high transmission quality even to stations under the worst reception conditions due to rain, etc. . In this case, it can be considered that the number of carrier waves is reduced from three to one during this time slot. The present invention realizes a specific TDMA satellite communication device to enable the above method.
In order to make the effects of the above system a reality, the receiving side of the communication device also needs a function for efficiently demodulating by dealing with fluctuations in carrier wave power for each burst. The present invention realizes this function on the receiving side. Most of the reception performance of a communication device depends on the performance of the demodulator. In TDMA communication systems, a receiver demodulator must receive and demodulate multiple bursts transmitted from different earth stations within a TDMA frame. However, because they contain carrier and clock signal components that are asynchronous to each other, the demodulator must extract the carrier and clock signals for each burst before demodulating the traffic data contained in the burst. This type of operation is called "burst operation," and requires more advanced technology than a demodulator that receives and demodulates continuous signals, and in order to effectively utilize its function, each input burst must be It is necessary to keep the power level as constant as possible.
That is, in a TDMA system where the carrier power level of each burst is intentionally changed,
The purpose is to keep the power level input to the demodulator as constant as possible. Of course, a simple method would be to use a circuit such as a limiter, but in recent digital signal transmission,
Since spectrum shaping is strictly performed using a Nyquist filter or the like to improve transmission characteristics, intentionally inserting a circuit with non-linear characteristics is undesirable as it will cause deterioration of the characteristics. Therefore, the present invention attempts to achieve the objective by applying transmission power control technology to the receiving side. That is, a feature of the present invention is that the device operates based on burst time plan information stored within the device. The device includes a demodulator, an attenuator that controls the input level of the demodulator, and an attenuator control circuit that controls the attenuator, and the amount of attenuation provided by the attenuator is determined based on burst time plan information. It is configured to change at the TDMA frame period according to a specific pattern determined directly or indirectly. Furthermore, specifically, the attenuator control circuit has a memory circuit, and this memory circuit stores the correspondence between the communication partner station and the control information of the attenuator, and the attenuation amount of the attenuator.
The pattern of changes within the TDMA frame is controlled by the information read out by this storage circuit, corresponding to the information about the correspondent station in the burst time plan. In this case, the attenuator control information stored in correspondence with the communication partner station may be data given from the outside as a system parameter, or may be the result of measurement by the own station at any time. Alternatively, a storage circuit in the attenuator control circuit stores the correspondence between the identification code or number of the received burst and the attenuator control information,
The pattern of changes within the TDMA frame is controlled by this storage circuit based on information regarding the identification code or number of the received burst in the burst time plan. Alternatively, a storage circuit in the attenuator control circuit stores the correspondence between the carrier wave selection information in frequency hopping and the attenuator control information, and stores the correspondence between the carrier wave selection information in frequency hopping and the attenuator control information, and
The pattern of changes within the TDMA frame is controlled by the information read by this storage circuit with respect to the selection information of the receive carrier in the burst time plan. [Example] Next, the present invention will be described with reference to the drawings. FIG. 1 shows an example of a control circuit configuration used in the present invention. Here, the signal from the satellite is sent to the earth station device 32.
After being received by the communication terminal equipment 34 and subjected to demodulation and other processing, it is sent to the terrestrial line connection equipment 3.
6 to the land line 102. The circuit of the present invention is normally included in the communication terminal device 34, but of course equivalent functions may be distributed and included in several devices, and in that case, the scope including the circuit of the present invention shall be included in the scope of the present invention. Think of it as a communication device. In the figure, a frame period counter 204 is a counter that determines the reference timing on the receiving side,
It generates various timing signals at the cycle of the TDMA frame and controls the operation of various circuits inside the communication terminal equipment. The burst time plan downloaded from the reference station via the satellite is processed by the supervisory control device 38, for example, and then loaded into the storage circuit 202. The contents of the storage circuit 202 are sequentially read out according to the count number of the frame period counter 204, and are used in the received data/burst separation processing in the burst separation circuit 606, as well as being applied to the attenuator control circuit 216. Oscillator 212 includes up to N frequency synthesizers, one output of which is selected in any suitable manner and is applied to demodulator 608 to define the carrier frequency of the demodulator input. The received carrier wave is sent to earth station equipment 3.
After being appropriately frequency-converted by 2, it is normally supplied to a demodulator 608 in the communication terminal equipment 34 and demodulated, and a burst separation circuit 606 extracts the traffic required by the earth station from among each data burst. After only the data portion is extracted, it is added to the terrestrial line connection device 36. In the present invention, an attenuator 210 is provided at the input of the demodulator 608, and the amount of attenuation is controlled by the output of the attenuator control circuit 216, thereby controlling the input power level of the received carrier wave from the earth station device 32. Note that the attenuator control circuit converts the attenuator control information included in the burst time plan data into a signal that directly controls the attenuator, but this signal is generated using separately given control information. 110
can also be taken into account. Figure 4 is an example of a circuit that utilizes the burst time plan, and although this circuit itself is publicly known,
This is one of the important components of the present invention, so it will be explained. The figure shows the storage circuit 202 and frame period counter 204 of FIG. The frame period counter includes a K-digit binary counter 302 driven by a symbol clock 350 and a frame period decoder 304, and a reset pulse 352, which is the output of the decoder 304, resets the K-digit binary counter 302 to an initial state. This realizes a frame period counter. The main components of storage circuit 202 are RAM circuit 308, address counter 310, and comparator 312. The RAM circuit 308 stores the supplied burst time plan in an easily available form. In this example, the stored burst time
The plan has been translated into a set of code words consisting of timing information, control information, and control information. Each code word corresponds to one event and is arranged in order of occurrence within the TDMA frame. Timing information, which is the content of the code word, is the number of counts in a binary counter at which the event should occur, control information is the meaning of the event, information about the circuit to be controlled, etc. The operating states up to this point are shown below. The contents of RAM circuit 308, i.e. the code word, are transferred to address counter 310 at its address terminals.
By supplying the contents of , they appear one by one at the output terminal, and the timing information therein is supplied to the comparator 312 as a K-bit parallel signal. On the other hand, since the contents of the K-digit binary counter are also supplied to the comparator 312 as a K-bit parallel signal, when the two match, a match pulse 356 is generated. This match pulse 356 is applied as a clock signal to the address counter and advances the contents of the address counter by one. As a result, the RAM circuit 30
New content or code words also appear at the output of 8. When one frame period ends and the frame period decoder 304 generates a reset pulse 352, this pulse is also provided as a reset pulse to the address counter, returning the address counter to its initial state. Therefore, during one period of the frame period counter 204, code words corresponding to each event are read out one after another. Meanwhile, the control information of the code word is applied to the control content decoder 314 to translate the content and cause one of the AND gates 316 to be "open". When a match pulse occurs, it passes through an open AND gate 316 and is provided as an event pulse 358 to the relevant circuitry. The control information is also latched into latch circuit 330 by match pulse 356 and held until the next match pulse occurs. The output of this latch circuit is also supplied to each part of the apparatus as is or via a decoder 239 or the like. FIG. 5 shows another example of a burst time plan utilization circuit. In this case, each event within a TDMA frame is designed to occur every 2 ^L counts of symbol clock 350 or an integer multiple thereof. Therefore, the K-digit binary counter 30
The content of the last L digit of 2 is the timing decoder 30.
5 to generate a timing pulse 357 every 2 ^L counts, resulting in an event pulse 358 when any of the AND gates 316 are open. On the other hand, the contents of the upper (K-L) digits of the counter 302 are
It is used as an address signal for the RAM circuit 308. Therefore, this circuit does not require address counter 310 or code word timing information as shown in FIG. FIG. 6 shows an attenuator circuit 210 used in the present invention.
This is an example. Attenuators are 1dB, 2dB, and
Fixed attenuator 4 with attenuation of 4dB, 8dB, ...
02, 404, 406, 408 are connected in series, and each attenuator has a switch S0, S
A bypass circuit that is opened and closed by 1, S2, S3, and so on is attached. Each switch is a high speed diode switch and is individually controlled by bypass switch control circuit 410. Control circuit 41
0 is controlled by an attenuator control signal 116 provided from an attenuator control circuit. If the control signal 116 is a binary number representing the amount of attenuation in dB, the control circuit 410 is simply a decoder that connects the terminal equipment input 115 and the demodulator input 113 by appropriately opening and closing the bypass switch. Between,
Any attenuation can be created from 0dB to 15dB in 1dB steps. FIG. 7 shows another example of the attenuator circuit. A PIN diode attenuator 412 is used here. Normally, one stage of PIN diode can provide attenuation of about 20 dB, so if more attenuation is required, another PIN diode attenuator 414 is used in series. As a method of obtaining the bias voltage to be applied to the PIN diode, in the figure, the output of the ROM circuit 432, which is read out using the attenuator control signal 116 as an address signal, is sent to the D/A converter 4.
22 (and 424) is shown. FIG. 8 shows an example of the configuration of an attenuator control circuit which is the core of the configuration of the present invention. Here, the output of the latch circuit 330 of FIG. 4 or 5, that is, the control information in the burst time plan data, is used as the control information. When the attenuation amount of the attenuator 210 is uniquely controlled by the burst time plan, the code corresponding to the attenuation amount is directly included in the burst time plan,
It is supplied as attenuator direct control information 126. However, in such applications, the attenuation is usually 3 dB,
Since the control information 126 is chosen in large steps, such as 5 dB, it will be represented in 2 to 3 bits and converted by converter 508 into an attenuator control signal 116 representing the actual amount of attenuation. The RAM circuit 506 is used when the setting of the attenuation amount is not fixed but determined based on operational conditions. The RAM circuit 506 is supplied with one or more of the communication partner station identification code, reception burst identification code, or burst number, reception carrier selection information in frequency hopping, etc. included in the control information, and is used as an address signal. Ru. The attenuation amount is stored in the RAM circuit in correspondence with the address signal, and the information on the read out attenuation amount becomes the attenuator control signal 116 via the converter 508. When the attenuator direct control information 126 is simultaneously supplied to the transducer, addition is performed in the transducer and the result is output as the control signal 116. The RAM circuit 506 is normally used for read-only purposes, but if there is a change in operating conditions, for example, there is heavy rain near a certain earth station and it is necessary to amplify the transmission power only for bursts destined for that earth station. For example, the attenuation amount setting processor 502 having a microprocessor decodes and calculates information supplied as data line information 122, and with the help of the RAM control circuit 504, the TDMA
The corresponding data is rewritten, aiming at the period when the RAM circuit is not being read within the frame.
It can be adapted to new conditions. The control information 110 in FIG. 1 corresponds to information related to such changes in operating conditions. [Effects of the Invention] As explained above, in a TDMA satellite communication system that uses multiple carrier waves, the present invention can individually adjust the power level of the burst to be transmitted depending on the size of the receiving station, the receiving condition, the content of the traffic to be transmitted, etc. It solves many problems in business communications, makes it possible to efficiently use the available power of the satellite, and has a great effect on reducing the overall cost of satellite communications.