JPH1188287A - Relay system by hierarchical transmission, its transmitter and repeater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce missing in real time performance at the receiver by reducing processing time for re-transmission by the repeater in the system where the repeater applies hierarchical multiplex of a signal to be sent again onto a signal received by the receiver directly through hierarchical modulation and transmits the multiplexed signal. SOLUTION: A mapping circuit 6 applies hierarchical modulation multiplexing to a signal for a receiver obtained by an inner interleave circuit 4 without applying inner interleaving to a signal for the repeater obtained by an inner error correction coder 3. Thus, the repeater requires no processing of inner deinterleaving so as to reduce the processing time from the reception by the repeater till the re-transmission and hence to reduce missing in the real time performance by the receiver.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relay system in wireless transmission, and more particularly to a relay system based on hierarchical transmission when an OFDM system is employed, and a transmission device and a relay device thereof.

[0002]

2. Description of the Related Art When performing broadcasting or communication for a mobile unit, the reception environment of the mobile unit is inferior to a fixed reception environment. Need to be configured. When performing multi-stage relay, it is necessary to transmit information transmitted by a transmitting device or a relay device via a wired line or a wireless line.

As described above, when a wired or wireless line for transmitting information is a dedicated line, it is not economical because capital investment and operation costs are required.
On the other hand, when a signal transmitted by another transmitting apparatus or a relay apparatus is received and retransmitted, the economical burden is reduced, but the signal processing time of the error correction circuit including deinterleaving is increased, so that real time processing is required. Sex is impaired.

Therefore, when a signal transmitted by another transmitting apparatus or a relay apparatus is received and retransmitted, the received signal is amplified as a high-frequency signal without demodulation and retransmitted. However, in the case of an SFN (single frequency network) that configures a relay network using the same frequency for effective use of the frequency, transmission / reception separation in the relay device is necessary, and cost is required for transmission / reception separation. The choice must be made whether to multiply or to some extent allow for the degradation of the retransmitted signal caused by wraparound due to insufficient separation. If the received signal has already been deteriorated due to multipath or the like, the deterioration is transmitted to a further relay device or a receiving device by the relay device.

[0005]

In order to solve the above problem, in wireless transmission, information to be relayed may be hierarchically modulated to be directly hierarchically multiplexed with a signal received by a receiving apparatus and transmitted. In this case, since the demodulation and error correction processing is required in the relay device, there is a new problem that a delay time of the demodulation and error correction processing occurs during relaying. For this reason, when configuring an SFN (single frequency network), a delay corresponding to the processing time of demodulation and error correction in the relay device must be given to the information transmitted directly from the transmitting device to the receiving device. As a result,
This is because the real-time property of information transmitted directly from the transmitting device to the receiving device is impaired.

An object of the present invention is to provide a relay system by hierarchical transmission capable of minimizing the loss of the above-described real-time property of information to be transmitted when SFN is performed, and a transmitting apparatus and a relay apparatus used for the method. Is to do.

[0007]

The relay system based on hierarchical transmission according to the present invention for solving the above-mentioned problems is configured as follows.

(1) In a broadcasting or communication system, in which a signal to be retransmitted by a relay device is multiplexed with a signal directly received by a receiving device by hierarchical modulation and transmitted, and the signal is directly received by a hierarchical transmission method. A signal received by the device is interleaved, and a signal to be retransmitted by the relay device is not partially or entirely interleaved.

(2) In the configuration of (1), a transmission system in a system for performing pre-broadcasting or communication is an OFDM (orthogonal frequency division multiplexing) system.

(3) In the configuration of (1) or (2), the signal received by the direct receiving device is applied,
Interleaving that is not performed on a signal to be retransmitted by the relay device is referred to as time interleaving.

[0011] Further, the transmitting device used in the relay system is
It is configured as follows.

(4) A system for performing broadcasting or communication, wherein a signal to be retransmitted by a relay device is hierarchically modulated and multiplexed with a signal received by a direct receiving device by hierarchical modulation and transmitted. The interleaving is performed on the signal received by the relay device, and part or all of the interleaving is not performed on the signal to be retransmitted by the relay device.

(5) In the configuration of (4), the transmission system in the system for performing pre-broadcasting or communication is the OFDM system.

(6) In the configuration of (4), the interleaving that is performed on the signal received by the direct receiving apparatus and not performed on the signal to be retransmitted by the relay apparatus is time interleaving.

(7) A method of performing broadcasting or communication by the OFDM method, wherein a signal to be retransmitted by the relay apparatus is hierarchically modulated and multiplexed with a signal received by the receiving apparatus by hierarchical modulation, and transmitted. When the relay device that received the signal retransmits the signal for retransmission, the signal received by the direct receiving device is interleaved, and the signal to be retransmitted by another relay device is partially or entirely interleaved. Do not give.

(8) In the configuration of (7), the transmission system of the previous broadcast or communication is the OFDM system.

(9) In the configuration of (8), the interleaving that is performed on the signal received by the direct receiving device and not performed on the signal to be retransmitted by the relay device is time interleaving.

That is, in the relaying method based on hierarchical transmission according to the present invention, part or all of interleaving is not performed on relaying information, thereby delaying relaying information transmitted from the transmitting device to the relaying device. The time is reduced, and the delay time added to the information transmitted directly from the transmitting device to the receiving device is reduced.

When information is transmitted to a mobile unit by radio transmission, strong error correction is performed so that reception can be performed in the presence of fading that occurs during reception of the mobile unit, and burst reception is performed. In order to avoid concentration of errors due to a decrease in signal level, it is general to perform time-direction interleaving in addition to frequency-direction interleaving.

On the other hand, when the relay apparatus receives the information to be relayed, unlike the reception at the mobile unit, the reception is within the line of sight. No direction interleaving is required.

[0021] Therefore, by not interleaving the information to be relayed by the relay device in the time direction but by performing the interleaving in the time direction only on the information directly received by the mobile unit, deinterleaving is not required in the relay device. As a result, the processing time from reception to retransmission can be reduced, and the loss of the real-time property of the information transmitted directly from the transmitting device to the receiving device can be reduced.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1A and 1B show a transmission apparatus used in a relay system based on hierarchical transmission according to the present invention. FIG. 1A shows the configuration, FIG. 1B shows a constellation of a transmission signal, and FIG. Shows the relationship.

In the transmitting apparatus shown in FIG. 1A, the input digital input signal is added with redundancy for error correction by an outer error correction encoder 1, and its output is output by an outer interleave circuit 2. The order of the columns is changed under certain rules. This signal is sent to the inner error correction encoder 3
, The redundancy for error correction is added again, and its output is input to the mapping circuit 6 and also to the inner interleave circuit 4.

In the inner interleave circuit 4, the order of the data sequence is changed again under a certain rule, and the output is input to the mapping circuit 6 via the delay circuit 5. The two signals input to the mapping circuit 6 are hierarchically modulated and multiplexed by the mapping circuit 6, and are also allocated to carriers of each frequency constituting OFDM. The output is converted from a signal in the frequency axis direction into a signal in the time axis direction by an IFFT (fast inverse Fourier transform) circuit 7, and the output is input to a quadrature modulator 8. The signal orthogonally modulated by the orthogonal modulator 8 is frequency-converted and amplified in the transmission high-frequency unit 9 and transmitted from the antenna 10.

Next, the operation of the transmitting apparatus having the above configuration will be described.

In the transmitting apparatus shown in FIG. 1A, an input digital input signal is subjected to error correction encoding by a concatenated code by an outer error correction encoder 1 and an inner error correction encoder 3. For example, a Reed-Solomon code with low redundancy is used as the outer error correction code, and a convolutional code with high redundancy is used as the inner error correction code.

The concatenated code reduces errors remaining after error correction by the inner error correction code in the receiver by further performing error correction by the outer error correction code. However, if the error remaining after error correction by the inner error correction code is a burst-like error, the error correction capability of the outer error correction code may be exceeded.

Therefore, in the present embodiment, an outer interleave circuit 2 is inserted between the outer error correction encoder 1 and the inner error correction encoder 3 to change the order of the data sequence under a certain rule. Thus, the presence of a burst-like error in a signal for which the receiver performs error correction using the outer error correction code is avoided.

The outer interleave circuit 2 is inserted for the purpose of avoiding a burst-like error resulting from the limit of the correction capability of the inner error correction code, whereas the inner interleave circuit 4 is inserted.
Is to average the deterioration of a received signal in a receiver due to fading or the like occurring in a transmission line, thereby effectively using the capability of an inner error correction code.

In other words, the fading that occurs at the time of receiving a mobile object involves fading due to a multipath signal due to the necessity of using an omni-directional antenna as an antenna used for mobile object reception, and the mobile object being hidden by a building. And the like.

In the former case, since there is a delay time difference between signals arriving from a plurality of paths, the signals are strengthened by the frequency of each carrier due to the phase relationship between the received signals passing through a plurality of paths. And the carrier whose signal is canceled. Therefore, in the case of fading due to a multipath signal, by performing interleaving between carriers constituting the OFDM signal, that is, frequency interleaving, deterioration of the received signal can be averaged. On the other hand, in the latter case, since the fading occurs depending on the receiving location of the moving object, it is necessary to average the deterioration of the received signal in the time direction, and time interleaving is required.

In the frequency interleaving, the order of the data sequence is changed under a certain rule by a unit for converting a signal on the frequency axis into a signal on the time axis by IFFT, that is, a unit of the number of carriers constituting the OFDM signal. Things. For this reason, a delay time is not essentially generated. On the other hand, the time interleaving causes a delay time of one second when it is desired to average the deterioration of the received signal in the time direction for one second, for example. That is, the time interleaving causes the real-time transmission to be impaired.

In the case of mobile reception, time interleaving is an effective means for averaging the deterioration of the received signal. However, in the case of a relay station, since the reception is generally fixed within the line of sight, the time interleave is used. The reception quality is good due to the use of a directional antenna with low fluctuation and high gain, and time interleaving is not always necessary. On the other hand, also in a relay station, when an error is expected to occur in a carrier of a specific frequency due to interference, it is necessary to perform frequency interleaving.

As described above, time interleaving is required for a signal transmitted directly from a transmitting device to a receiving device of a mobile unit, but time interleaving is not required for a signal transmitted from a transmitting device to a relay device. Absent.

Therefore, in the transmitting apparatus shown in FIG. 1A, the outer error correction encoder 1,
The outer interleave circuit 2 and the inner error correction encoder 3 add redundancy for error correction. The output of the inner error correction encoder 3 is a signal that has not been subjected to time interleaving, and this signal is input to the mapping circuit 6 as a signal directed to the relay device.

The output of the inner error correction encoder 3 is time-interleaved by the inner interleave circuit 4 at the same time, passes through the delay circuit 5, and is input to the mapping circuit 6 as a signal to be directly received by the mobile receiver. Is done. The delay circuit 5 will be described later. In the mapping circuit 6,
A signal, which is output from the delay circuit 5 and is to be received by the receiving device of the direct mobile unit, is subjected to hierarchical modulation multiplexing with a signal that is output from the inner error correction encoder 3 and is directed to the relay device.

FIG. 1B shows an example of a constellation of a hierarchically modulated multiplexed signal. This example shows a case where a signal to be received directly by a mobile receiving apparatus is QPSK-modulated, and a signal intended for a relay apparatus is hierarchically modulated and multiplexed on the signal to obtain non-uniform 16QAM.

In this case, the information of the signal to be received by the receiving device of the direct mobile unit is transmitted depending on which quadrant on the complex plane including the I axis and the Q axis exists.
Therefore, the receiving device receives the received non-uniform 1
The necessary information can be obtained by demodulating the 6QAM signal as a QPSK signal. On the other hand, in the signal directed to the relay device, information is transmitted by a position in each quadrant on a complex plane including the I axis and the Q axis. For this signal, necessary information can be obtained, for example, by demodulating the non-uniform 16QAM signal received by the relay apparatus assuming it as a 64QAM signal.

Due to the difference in the distance between the codes, the required C / N of the repeater is higher than the required C / N of the mobile receiver, but the antenna gain, the antenna height, and the presence or absence of fading. Reception is possible due to the difference between the two. The output of the mapping circuit 6 is input to the IFFT circuit 7 as information to be transmitted by carriers of each frequency constituting the OFDM,
The IFFT circuit 7 converts the signal on the frequency axis into a signal on the time axis. Further, this output is output to the quadrature modulator 8.
At the same time, and becomes a high-frequency OFDM signal.
The OFDM signal is frequency-converted in the transmission high-frequency unit 9 to a frequency to be transmitted, power-amplified, and transmitted from the antenna 10.

By the way, when a single frequency network is constituted by a plurality of transmitting devices and relay devices, at the receiving point,
If there is a delay time difference exceeding the guard interval period between the signals from the transmitting devices and the relay devices, the reception quality is greatly reduced. Therefore, each transmission device and relay device need to adjust the transmission time.

In the present invention, the signal directed to the relay device is the same digital input signal information as the signal transmitted directly to the mobile receiving device, and is a signal whose transmission time is earlier. This difference in transmission time is for compensating for a delay caused by performing processing from reception to retransmission in the relay device, and the longer the number of relay stages, the longer the time. This delay time compensation is performed by the delay circuit 5 in FIG.

FIG. 1C shows the time relationship between a high-layer signal directed to a receiving device of a mobile unit and a low-layer signal directed to a relay device. In the figure, the same information is transmitted in the shaded portions. The fact that the hatched portion of the high-layer signal extends over a plurality of symbols indicates that the information is dispersed into the plurality of symbols by time interleaving. In addition, t1 indicates the time of the time interleave, and t2 indicates the time given by the delay circuit 5.

Next, another embodiment of the present invention will be described.
This will be described in detail with reference to FIGS.

FIG. 2 is a diagram showing a configuration of a relay apparatus used in a relay system by hierarchical transmission according to the present invention. still,
In FIG. 2, the same parts as those in FIG. 1 (A) are denoted by the same reference numerals, and redundant description is omitted here.

In the repeater shown in FIG. 2, the signal for the repeater transmitted from the transmitting station is received by antenna 11, amplified and frequency-converted by reception high-frequency section 12, and then quadrature-demodulated by quadrature demodulator 13. . And
The signal on the time axis is converted into a signal on the frequency axis by the FFT circuit 14, demodulation is performed for each carrier of each frequency by the demodulation circuit 15, error correction is performed by the inner error correction decoder 16, and then the outer deinterleave circuit The error correction is again performed by the outer error correction decoder 18 after the rearrangement of the data sequence by the data 17. The output signal of the outer error correction decoder 18 is processed by the outer error correction encoder 1 and thereafter and transmitted from the antenna 10 as in the case of the transmission device shown in FIG.

Next, the operation of the relay device having the above configuration will be described.

In the repeater shown in FIG.
Is a signal for the relay apparatus transmitted from the transmitting station, for example, the above-mentioned non-uniform 16QAM signal. The signal received by the antenna 11 is amplified and frequency-converted by the reception high-frequency unit 12, converted into an intermediate signal, and then quadrature-demodulated by the quadrature demodulator 13. This quadrature-demodulated signal is supplied to an FFT circuit 1
4 converts the signal on the time axis into a signal on the frequency axis.

The converted signal is a restored signal.
This corresponds to a signal on a complex plane including the I axis and the Q axis shown in FIG. This signal is demodulated by the demodulation circuit 15, and information required in the relay device is information transmitted by a position in each quadrant on a complex plane including the I axis and the Q axis.

In the demodulation circuit 15, for example, when the non-uniform 16QAM signal is a subset of the constellation of 64QAM, the demodulation circuit 15 demodulates the signal by a circuit similar to the demodulation circuit of 64QAM, and transmits information from the transmitting apparatus to the relay apparatus. available. The demodulated signal is subjected to an error correction by an inner error correction decoder 16 and then subjected to an outer deinterleave circuit 17 in which the reverse of the data sequence performed by the outer interleave circuit 2 of the transmission device is performed. Error correction is performed again by the correction decoder 18.

The signal after the error correction is the same as the digital input signal input to the outer error correction encoder 1 of the transmitting apparatus shown in FIG. 1A, and thereafter, the signal shown in FIG. )
As in the case of the transmission device shown in FIG. 1, the data is processed by the outer error correction encoder 1 and subsequent ones and transmitted from the antenna 10. However, the delay circuit 5 is used to adjust the difference between the arrival times of the signals from the transmitting device and the other relay devices constituting the SFN at the receiving point so as to fall within the guard interval.

In FIG. 3, the accumulation of the delay time (processing time) from the transmission of the master station to the transmission of the signal directly to the receiving device of the mobile unit by the second relay station is added to the signal for the relay device. The case where interleaving is added and the case where interleaving is not added are shown in comparison. FIG. 3A shows a delay time when interleaving is added to a signal for the relay device, and FIG. 3B shows a delay time when interleaving is not added to a signal for the relay device. In the figure,
“Sign” indicates error correction coding processing time, “interleave” indicates interleaving processing time, “variable” indicates modulation to transmission processing time, “decoding” indicates reception to demodulation processing time, and “deinterleaving”. "" Indicates a deinterleave processing time, and "correction" indicates an error correction decoding processing time.

As is apparent from FIG. 5, when interleaving is added to a signal for a relay device, a processing time for deinterleaving is required for each relay device to decode an error correction code, and furthermore, a parent time is required. The transmission device and each relay device require an interleaving processing time. On the other hand, when the interleaving is not added to the signal for the relay device, deinterleaving is not required in each relay device, and the processing time for interleaving is required only for the signal directly directed to the receiving device of the mobile unit in the relay device. .

From the above, according to the configuration of the present embodiment, it is clear that the real-time performance of transmission is unlikely to be lost, and that the effect increases as the number of relay stages increases.

It should be noted that performing frequency interleaving without delay does not impair the effects of the present invention, so that frequency interleaving can be performed.
If a certain delay time is allowed, time interleaving with the same level as the higher layer or different interleaving depth is also possible. In addition, by performing the short-time interleaving, it is also possible to avoid the influence such as the flutter disturbance due to the reflected wave of the airplane.

Further, when performing multi-stage relay, it is not necessary to decode the error correction code in all the relay devices, and in some relay devices, the received signal is decoded without decoding the error correction code. It is also possible to retransmit after amplifying and, if necessary, equalizing.

The case where the OFDM system is used has been described above. However, it is apparent that the present invention can be implemented in a relay network using a single carrier.

[0058]

As described above, according to the present invention, SF
It is possible to provide a relay system by hierarchical transmission that can minimize the above-described loss of the real-time property of information to be transmitted at the time of performing N, and a transmission device and a relay device used therein.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a transmission device of a relay system using hierarchical transmission according to the present invention, a diagram showing a constellation of a transmission signal, and a timing diagram showing a time relationship of a transmission signal.

FIG. 2 is a block diagram showing an embodiment of a relay apparatus of a relay system using hierarchical transmission according to the present invention.

FIG. 3 is a diagram showing a comparison of delay times (processing times) in a case where interleaving is added to a signal for a relay device and in a case where interleaving is not added in the embodiment of FIG. 2;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 outer error correction encoder 2 outer interleave circuit 3 inner error correction encoder 4 inner interleave circuit 5 delay circuit 6 mapping circuit 7 IFFT circuit 8 orthogonal modulator 9 transmission high frequency unit 10 Antenna 11 ... Antenna 12 ... Receiving high frequency unit 13 ... Orthogonal demodulator 14 ... FFT circuit 15 ... Demodulation circuit 16 ... Inner error correction decoder 17 ... Outer deinterleave circuit 18 ... Outer error correction decoder

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toru Hoshina 1-10 Nisshinmachi, Fuchu-shi, Tokyo Inside the Fuchu Office of NEC Corporation

Claims (9)

[Claims] A method for performing broadcasting or communication, wherein a signal to be retransmitted by a relay device is multiplexed with a signal received by a direct receiving device by hierarchical modulation and transmitted by hierarchical transmission. The interleaving is performed on the signal received by the relay device, and a part or all of the interleaving is not performed on the signal to be retransmitted by the relay device. 2. The relay system according to claim 1, wherein the transmission system in the system for performing the pre-broadcasting or communication is an OFDM (Orthogonal Frequency Division Multiplexing) system. 3. The layer according to claim 1, wherein the interleaving performed on the signal received by the direct receiving apparatus and not performed on the signal to be retransmitted by the relay apparatus is time interleaving. Relay method by transmission. 4. A transmitting apparatus for performing broadcasting or communication, wherein a signal to be retransmitted by a relay apparatus is hierarchically modulated and multiplexed with a signal received by a receiving apparatus by hierarchical modulation and transmitted. A transmitting apparatus for use in a relay system by hierarchical transmission, wherein interleaving is performed on a signal to be received, and part or all of the interleaving is not performed on a signal to be retransmitted by the relay apparatus. 5. A transmission system in a system for performing pre-broadcasting or communication is an OFDM system.
A transmission device used in the relay system by the hierarchical transmission described in the above. 6. The hierarchy according to claim 4, wherein interleaving that is performed on a signal received by the direct receiving apparatus and not performed on a signal to be retransmitted by a relay apparatus is time interleaving. A transmission device used for a relay system by transmission. 7. A relay apparatus for broadcasting or communicating according to an OFDM method, wherein a signal to be retransmitted by a relay apparatus is hierarchically modulated and multiplexed with a signal received by a receiver directly by hierarchical modulation, and the signal is transmitted. When the relay device that retransmits the signal for retransmission, interleaving is applied to the signal directly received by the receiving device, and part or all of the interleaving is performed for the signal to be retransmitted by another relay device. A relay apparatus used in a relay system based on hierarchical transmission, characterized in that it is not performed. 8. The relay apparatus according to claim 7, wherein the transmission method of the pre-broadcast or communication is the OFDM method. 9. The hierarchy according to claim 7, wherein the interleaving applied to the signal received by the direct receiving apparatus and not applied to the signal to be retransmitted by the relay apparatus is time interleaving. A relay device used for a relay method by transmission.