Mobile phone industry and broadcast network operators are willing to provide video content services for mobile receiving terminals including laptops, mobile phones and PDAs. DVB-H (Digital Video Broadcasting - Handheld) overcomes the restrictions of DVB-T (Digital Video Broadcasting-Ground) in the mobile environment, it is ready to transmit television signals for handheld devices. In addition, test technology for DVB-H is under evaluation to ensure circuit, terminal, and network reliability integration.
DVB-H sent to mobile TV is an appropriate technology because it can adapt to two difficulties encountered by mobile TV:
• First, DVB-H is adopted as an additional error correction called MPE-FEC, which is not in DVB-T. MPE-FEC works in the Internet Protocol (IP) layer, which can still be safe when many data packets are lost.
• Second, for the battery life of the mobile pick-up terminal, DVB-H is more than 90% of the DVB-T save. This is obtained by time fragmentation techniques, in place of continuous transmitting, so that the receiving terminal is turned off during non-burst information.
In addition, 4K modulated DVB-H is also better than DVB-T standard (Figure 1). This is compromised in 8K (allowed large single frequency network [sfn], but limited) and 2K (allowing very high speed, but only small single frequency network) to ensure that the stable movement at high speed is received. The size of the SFN here refers to the maximum distance between two transmitters within the SFN. The Transmitting Parameter Signaling (TPS) bit indicates whether the receiver has DVB-H feature. If necessary, the related characteristics should be indicated.
Figure 1 a) 4K modulation scheme is the compromise between 2K and 8K modulation schemes B) TPS signaling points out the characteristics of DVB-H specification
DVB-H network configuration
Since DVB-H is based on DVB-T, their network configuration is similar. The play center (Fig. 2) consists of an MPEG-2 transport stream (TS) as an input multiplexer. The new features of DVB-H have minimal TS from the IP package from DVB-H, such as DIP010 in research, which encapsulates the input IP data to pack it into the transport stream.
Figure 2 is a playing center consisting of multiplexers while providing DVB-H and DVB-T services.
The multiplexer output TS is sent to a modulator / transmitter that follows DVB-H, such as the 7000 series in R & D, which supports 4K modulation mode and the TPS bit specified by DVB-H. Because these technical configurations are similar to DVB-T, the broadcaster can share the DVB-T and DVB-H service portfolio within a network of multiplexers. This can provide DVB-H services with ready-made networks to reduce the cost of operators and reduce the risk of DVB-H technology investment. In particular, the demand network, these are beneficial to operators because they can use ready-made devices without purchasing new systems.
When references new technologies, the main requirements for testing and measurement equipment can be obtained during the development process. For DVB-H, there are two main research and development applications: DVB-H chip development and development of DVB-H compatible phones.
DVB-H test
A configuration in R & D laboratory test follows DVB-H RF chip is shown in Figure 3, which drives the test transmitter by a signal generator generating a baseband signal (DVB-H stream), and then the RF signal is sent to the test. Device DUT. The output signal of the DUT is input to the baseband DVB-H analyzer. In order to test various function blocks in the RF receiver chip, the input signal can change. In principle, the corresponding parameters of the transformed input signal can test all the functions of the chip. For example, the MPE-FEC is turned on and disconnected in the signal generation stage to test the MPE-FEC function of the chip. The test transmitter can change the transmission mode (2K, 4K, 8K) or variation parameters (such as modulation level), insert transmission noise, and introduce signal fading to simulate the receiver in motion. Therefore, the performance of the receiver is easily measured by using the bit error rate BER measurement.
Figure 3 Follow the DVB-H chip test configuration, you can test a variety of functions in the chip with MPE-FEC and decoding.
For the characteristics of the mobile terminal, you need to establish an actual launch environment with a DVB-H test transmitter. In order to simulate the actual environment, the calibrated Gaussian noise (Fig. 4a) is added to the test transmitter, and the synthesis signal is sent to the receiver portion of the mobile terminal. The BER test will obtain the ability to process these noise conditions in the receiver.
For mobile terminal testing, it is necessary to use channel simulation or fading simulation to test the test terminal characteristics in motion. The fading reflects the case where the transmitted signal is reached in the motion of the transmit signal. The receiver must process the signal decline because these signal paths have different levels, phases, and different delays. The test used transmitter also reflects fading.
After detecting the DVB-H execution of the mobile terminal, a closed loop test can be used to evaluate the reverse channel (Fig. 4B). The DVB-H test transmitter and wireless communication tester can provide the desired emission simulation. The circle number in Figure 4b describes the order of the simulation:
1. DVB-H Tester generates an air packet.
2. The RF of the DVB-H mobile terminal will be demodulated by the test signal, and then send the demodulated packet to the mobile terminal's mobile radio.
3. Radio stage transmits packets to the air reverse link.
4. Moving tester checks the error rate of the packet and computing the package.
The DVB-H portion in the mobile phone receives the DVB-H signal from the test transmitter, and the mobile phone runs the application to start the wireless reverse path, for example, the integrated data received by the DVB-H channel is transmitted by the reverse path. The mobile wireless tester receives and analyzes these signals, and the communication established with the DVB-H test transmitter makes the loop closes to calculate the bit error rate of the closed loop packet. Then insert the DVB-H signal into Gaussian noise, the limit characteristics of the receiver are obtained by the test system.
Network operator consideration
When the operator runs the DVB-H network (including booting the network and actual work network), the operator must be able to analyze the transmitted signal. To this end, the DVB-H demodulation can be used using the test receiver. Thus, the output baseband signal is sent to the MPEG-2 analyzer, and the content and structure of the analysis service, and the measurement of the data rate. In addition, MPEG-2 can output DVB-H streams to an IP address. This application can realize the content of the service by the MPEG player or H.264 player.
A question about DVB-H is not yet, who is the real network operator? Because business issues are now more than technical issues and become potential obstacles. A trying to use effective pressing solutions and technical problems that are being carried out or will be carried out will be processed.
Editor in charge: GT, read full text
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