TWI554111B - Method for rapidly switching between alternative transmission paths - Google Patents

Description

Method of quickly switching between alternate transmission paths

The present invention relates to a method for receiving and reproducing a radio frequency television signal, wherein the received signals are supplied to a tuner and a demodulation transformer, the signals are demodulated and replaced by a demultiplexer Divided into video and audio signals and supplied as data to a video and audio decoder, wherein according to the feature of the precharacterizing clause of the first aspect, the video and audio decoder are in parallel at least two receiving paths in parallel Implemented in .

In the mobile digital television reception, the interruption occurs frequently in the data stream due to the change of the reception condition, which means that one of the picture and the sound signal for the user is interrupted. If these interruptions last for a few seconds or longer, it is important that the information from the currently selected program is not perceived by the viewer and the listener. If there is an alternate transmission path with sufficient reception quality, it is possible to switch to one of these alternative transmission paths. The subject matter of this application is a method that is cost effective to quickly change to one of the alternative transmission paths.

Actual options for alternative transmission paths

Hierarchical modulation

The range of reception can be extended by a stronger transmission method (suitable for modulation parameters, higher redundancy and therefore strong error protection). However, this reduction can achieve a data rate and thus the number of programs that can be transmitted and/or its broadcast picture and sound quality in each case.

In the case of DVB and ISDB-T, hierarchical modulation methods are known, and such methods allow a lower bit rate in addition to one of the high bit rate data streams. However, another data stream with greater robustness. This is used in Japan and is called "12 segments" (high bit rate) and "1 segment" (strong component with lower bit rate). Both are transmitted on the same transponder (same frequency).

In the case of DVB, the high data rate is transmitted, for example, using QAM 64 and the strong component is only modulated using QPSK. In general, programs in the strong component must produce significantly lower resolution and higher compression in order to maintain the maximum data rate.

Ideally, a user wants to see a program with a high data rate. In the case of a poor received signal, it is possible to switch to a strong transmission so that it may continue along the broadcast even in the case of poor picture and sound quality. As long as the reception quality is sufficient for a high data rate, it is possible to switch back to a better picture and sound quality.

Other propagation paths

In China, certain programs can also be obtained simultaneously with the low-quality TV-specific DTMB method via the mobile phone standard CMMB. Here, it is possible to switch to the CMMB in the event that one of the receptions of the DTMB signal collapses. Naturally, the prerequisite is that the receiving device supports two standards.

Change the receiving area

A third scenario occurs for the application of the fast handoff described herein when the receiver changes from the transmission area of one transmitter to the area of another transmitter. Ideally, the control unit of the receiver detects that the other transmitter is simultaneously supplying a better signal (so-called transmitter tracking, for example, known from DE 10 2005 039 507 A1) and without interruption. In this case, the two transmitters typically supply the same picture quality. In subsequent texts, there is therefore no high or low bit rate or quality mentioned by the primary (preferred) and alternative receive paths.

At present, it is basically possible to distinguish between two types of devices for the hardware in the reception of mobile television, in particular by means of a TV tuner in the vehicle.

A) A high-priced device that simultaneously decodes both the primary receive path and the alternate receive path and if necessary to switch the decoded content (picture and sound). The switching program can accurately frame the square The pattern occurs, which is undetectable by the user, that is, there is no side effect.

B) The low cost device has only one video and audio decoder. If the primary signal crashes, you will need to switch to the alternate path. Only then will the video and audio decoders be restarted with alternative data. The total switching time obtained is as follows:

a. The tuner and demodulator must be synchronized to the new receive path. It can be assumed that this has occurred in the current operation before the switch and this time can be set to zero.

b. The data buffer (T _buffer ) for the video and audio decoder must be populated.

c. The video decoder waits for one of the first reference frames (T _ref ) in the data buffer.

d. The video decoder decodes the reference frame and displays it. This time is usually less than the display period of one frame (20 ms in the case of 50 Hz and 16.7 ms in the case of a 60 Hz television system).

Disadvantages:

Solution A):

- Requires two video decoders or one video decoder that can decode two independent video formats in a one-time slot program. Video decoding is part of the SOC (System Single Chip) IC (integrated circuit) that requires most of the computing power. Doubling this resource means significantly higher IC costs.

- Larger wafer area or higher clock rate increases power consumption.

- For a second video decoder, the storage must be available both for buffering and for the decoded reference frame. Storage requirements are in the range of several 10 million bytes. The bus width of the memory must also increase significantly. A second memory chip or a wafer having a wider data bus may be required.

Solution B):

- The switching time determined by T _buffer + T _ref is basically in the range of a few seconds. The information transmitted during this time is not perceptible to the user.

Referring to the prior art as explained above, the term "receiving channel" (equivalent to the transmission path) The path has the following meaning: In variant A), a receiving channel comprises all components or units from the reception of the radio frequency signal (antenna) to the received and processed signals providing the output for reproduction. If two or more receiving channels are provided (i.e., receiving channels that exist in parallel with each other), then all of the units of a receiving channel are twice (in the case of two parallel receiving channels) or more than twice. For example, this means that the signal received by an antenna is supplied to a tuner and a downstream demodulation transformer and is converted from the received radio frequency to an intermediate frequency by the tuner and the downstream demodulation transformer. From such signals, a type of ratio/digital converter can generate a digital data stream (for example, an MPEG-2 data stream), and supply the digital data stream to a demultiplexer, the multiplexer The device divides the data stream into video data, audio data and possibly other data. Supplying video data to a video decoder and supplying the audio data to an audio decoder, before providing the signals (data) processed by the decoders to a unit for reproduction (especially for video and audio signals) Other units can be connected to the output of the decoders. In addition to such receiving channels that are present twice or several times, although the receiving channels mean the best performance, they also mean the maximum expenditure, a receiving channel (more especially with regard to solution B) to make tuning , demodulator and demultiplexer, and analog/digital converters are understood in a way that is several times depending on the number of receiving channels, but one of the demultiplexers from the respective receiving channels is only implemented to a single The video decoder, only a single audio decoder and possibly other units below, but only once. According to variant B), there are thus several (partial) receiving channels up to the input of the video and audio decoder, after which there is only a single receiving channel via which the single receiving channel will In particular, the video and audio data are transported individually or collectively to the playback device.

Accordingly, the present invention is based on the object of providing a method for receiving and reproducing radio frequency television signals, including video signals and audio signals, which is improved over the prior art. In particular, while maintaining one of the sounds and pictures that are as undisturbed as possible, the expenditure on the receiving and signal processing components required for this purpose should be kept as much as possible. low.

This object is achieved by the features of the first technical solution of the patent.

According to the invention, it is provided that a data of a receiving channel is stored by a circular buffer while the data is processed by means of another receiving channel and provided for reproduction, wherein switching from the other receiving channel to the one receiving channel is effected The video decoder then receives the data stored in the circular buffer for further processing.

This method and its corresponding implementation in hardware has the advantage that two (or more) receiving channels are provided on the input side of the video and audio decoder to ensure the best possible quality of reception. This means that the desired transmitter (television transmitter) can be received and reproduced by means of one receiving channel while the transmitter tracking can occur by means of another receiving channel. Switching from a previously used receiving channel to another receiving channel is achieved if it is found that the signal of the desired television transmitter received by means of one receiving channel is preferably received by means of another receiving channel. Since the switching procedure is established by itself but presents a problem during startup of the video decoder with the data newly supplied thereto, it is provided according to the invention that the data of the receiving channel is stored in a circular buffer. After switching the program, the circular buffer can provide the data to the video decoder when it receives the data from the receiving channel. Until then, the receiving channel has received and processed the RF signal in the background for the purpose of transmitter tracking. That is, it has been converted into a digital signal. By this means, the video decoder can be more quickly synchronized with the data signal supplied thereto via the switched receiving channel so that the television image is therefore largely stable to the viewer.

Thus, a circular buffer is provided for buffering the alternate path, which can accommodate at least the amount of data between the two reference frames. This buffer is filled permanently and simultaneously with the primary path.

At the moment of switching, the video decoder is populated with data starting from the most recent reference frame. The video decoder therefore receives the data from "past" and can begin decoding immediately. Therefore, T _buffer +T _{ref is} estimated.

The frame decoded since this time can be used by the user as a better. Three options are available:

1) The video is displayed periodically from the reference frame. The disadvantage is that the user sees the last few seconds of the main path again. When switching back to the primary path, an undesired time jump can occur.

2) The video decoder runs in a "forward fast forward" mode until the main path is interrupted at the frame and continues to play the video from there. One drawback is that fast forward can be seen as an interruption.

3) As in 2), the difference is that the last frame of the main path remains frozen until the video decoder has finished its forward fast forward.

Procedures 2) and 3) audio data with alternative paths do not require the advantage of installing a buffer, since audio decoding does not require access to reference information from the past due to the encoding algorithm.

advantage

● The cost is almost no higher than the cost of solution B). Only one video decoder with a corresponding low storage requirement and storage bandwidth is required. The data buffer holds the compressed data and is therefore significantly smaller than the memory used for a second video decoding.

• Significantly faster switching than solution B) without loss of information and with one of the behaviors sensed as "natural" (frozen frame) in the case of receiving interference.

Having one of the two receiving channels before the video decoder corresponds to the receiving device being configured as follows: In each of the receiving channels preceding the video decoder, there is a separate antenna for receiving one of the radio frequency signals. These RF signals are converted to intermediate frequency signals by means of suitable components and supplied to a tuner and a demodulation transformer. By means of a suitable analog/digital signal converter, a digital data stream is supplied to each of the receiving channels to a demultiplexer, and the demultiplexer divides the digital data stream into video signals and audio signals (and possibly Other signals). These signals are then supplied to the video decoder and the audio decoder (and possibly other units) to one of the switching units. Or stream digital data to each of the receiving channels The receiving channel then divides the data stream into at least a video signal and an audio signal. In connection with the present invention, in particular, the video signal of each receiving channel is supplied to a switching unit such that the video signals provided by the two receiving channels can be supplied to the video decoder after the switching unit. That is, a video signal of one receiving channel or a video signal of another receiving channel is supplied to the video decoder. At this time, a circular storage for storing video signals is provided, which are delivered by a demultiplexer that is not connected to the video decoder. If the switching from one receiving channel to another is achieved by means of certain criteria, the video decoder supplies the data stored in the circular buffer so that it can begin its work immediately. At the same time, it is ensured that after the complete switching procedure, the circular buffer not only delivers the data to the video decoder to which the receiving channel has been assigned, but also after the switching procedure, the circular buffer supply that is no longer connected to the receiving channel of the video decoder has Its data is such that it can store this information for use in the next handover procedure.

In principle, the circular buffer can always be active in both paths (receiving channels). In the case where the video decoder receives the data, the circular buffer will not be completely filled. The read indicator (controlled by the decoder) will closely follow the write indicator (controlled by the demultiplexer). If the decoder does not receive any data (eg, on the alternate path before the switch or after the switch), the read indicator is not moved by the decoder and the buffer will fill up. As long as the write indicator has reached the read indicator, the read indicator must be moved by the solution multiplexer or another control entity. Write metrics must not "follow" the metrics. The buffer has now reached its maximum capacity.

If the decoder is switched to a padding buffer, the circular buffer is again emptied by fast forward rotation, because the occurrence of data from the transmitter is slower than the processing by the decoder in the fast forward mode. many. The initial state restarts.

The speed of data delivery from the circular buffer to the decoder is determined by the processing speed of the decoder.

During periodic reception on a path, the decoder speed corresponds to the transmitter's capital Material rate. The buffer fill levels remain the same on average. In the case of a fast forward, the decoder requests data more quickly than in the case of a normal display speed. It is assumed that the circular buffer itself does not indicate a limitation on the data rate, that is, the processing speed of the decoder is less than the data rate of the circular buffer and the circular buffer does not significantly affect the switching speed between the two paths.

Claims (6)

A method for receiving and reproducing a radio frequency television signal, wherein the received signals are supplied to a tuner and a demodulation transformer, and the signals are demodulated and divided into video and by a demultiplexer. The audio signal is supplied as data to a video and audio decoder, wherein the video and audio decoder are implemented in parallel in at least two receive paths, the method being characterized by storing a receive channel by a circular buffer Data, wherein the data is processed by means of another receiving channel and provided for rendering, wherein the video decoder then receives the circular buffer when the switching from the other receiving channel to the one receiving channel is effected The data is used for further processing, and the last frame of one of the receiving channels remains frozen until the video decoder has finished its forward fast forward. The method of claim 1, wherein the circular buffer permanently stores the material of another receiving channel simultaneously with the data of one receiving channel. The method of claim 1 or 2, wherein the video decoder receives the material following the most recent reference frame at the switching instant. The method of claim 1 or 2, wherein the circular buffer stores at least the material between the two reference frames. The method of claim 1 or 2, wherein the image signal is periodically displayed from a reference frame. The method of claim 1 or 2, wherein the video decoder operates in a fast forward manner until a frame in which the receiving channel has been interrupted and continues to play the video via another receiving channel from this time.