The mobile DVB-T receiver uses an antenna diversity technology, but it is at the expense of increasing power consumption and dimensions. The antenna diversity requires the shortest distance between the two antennas, so it is actually difficult to implement on the handheld device.
To this end, DVB organizations have developed DVB-H standards, which are fully known as digital video broadcasts, which is a transmission standard that provides multimedia services to hand-held devices through the ground digital broadcast network. Briefly, the DVB-H standard is to rely on the current DVB-T transport system, by increasing a certain additional function and improvement technology, the handheater can stably receive the broadcast television signal.
The DVB-H standard is an expansion of the DVB-T standard, but in order to support the video reception of the handheld device, it adds the following functions:
Time slice to reduce power consumption.
IP data broadcasting for low resolution video streaming.
MPE-FEC to obtain a stable signal reception.
4K carrier mode, optimize the network.
DVB-H front end
In order to integrate a DVB-H front end, a key issue such as power consumption, performance, and mechanical size is used in hand-held devices, and a new generation of silicon tuner and demodulator are used.
Silicon tuner characteristics
The silicon modulator is the latest form of the cartridge tuner common to the top-top box and the PC peripheral TV tuner. The interface between the tuner and the demodulator is changed from the ratio (DVB-T) to the fundamental frequency (DVB-H). This is likely to be adjacent to the baseband, and the filter is integrated into the tuner, thereby reducing the occupying area of the entire solution. At the same time, the power consumption of such tuner is also reduced to 300MW. DVB-h is usually used in the UHF band, but it can also be used for other frequency bands, such as 1.672GHz.
DVB-H demodulator characteristics
The basic requirements for the demodulator provide good reception performance in the moving environment. For the DVB-H receiver, Doppler compensation requires at least 100 Hz, and the receiver should have the ability to respond to the change of the channel, and the same signal-to-noise ratio obtained when the low Doppler frequency is maintained to obtain the same quality of service ( QoS). This is critical to designers when planning a broadcast network. When the speed of the receiver changes, the coverage of the network must remain constant.
In addition to Doppler effect, the receiver also faces changes in channel characteristics. The various echoes received by the antenna end changes at any time, and the distance between the return wave is not fixed. In order to avoid the loss of synchronization of the transmitter and maintain a good reception state, the receiver must compensate for these changes.
Co-channel interference is another important instantaneous interference, instantaneous interference from various sources, is generated in the working environment, sometimes even from adjacent networks. The receiver should have a strong anti-interference ability, and even maintain a good reception state even when the interference power is higher than the required signal. For example, in a GSM phone, such interference usually comes from the upstream GSM channel.
Sensitivity is an important parameter that provides ideal coverage. The demodulator design should be guaranteed to achieve a 0.5 ~ 1DB safety factor relative to a lower degradation of theoretical value.
Figure 1 is a block diagram of a DVB-H receiver, mainly including two major portions, demodulators, and MAC (media access control) processing. Link layers or Macs are also integrated in the demodulator. This layer is used to handle time slice, IP data extraction, and IP data error correction. Since DVB-H must maintain a high rate, the RS (Reed-Solomon) decoder is implemented with hardware.
Be
Be
Figure 1 block diagram of DVB-H demodulator
Time slice
Time slice uses a burst to transmit data, with a higher instantaneous rate than traditional data flow services. DVB-T Move Image Expert Group (MPEG-2) The speed of up to 10MB / s, which is much higher than that can be processed by the handheld handheld and the quarter video image array (QVGA) display can display s speed. Generally, a data stream below 500kb / s has been able to provide good video resolution on a small screen. Time slice is a data stream with a high rate of low rates. The front end of the receiver operates within the burst time, and the remaining time is closed so that power can be further reduced. For example, a 500kb / s data stream, if the burst frequency is 10 times, theoretically saves 90% of power consumption. The latest DVB-H front end (tuner plus demodulator) is about 500MW of power consumption, and the actual power consumption is only 50 mW.
In addition to saving power, the time slice technology enables the handheld device to scan the adjacent honeycomb, scan other frequency signals, and test signal strength without interrupting its own business. When the mobile user enters a new network, the optimized seamless exchange can be switched in the idle period based on the monitoring situation at any time.
IP data broadcast
In the DVB-H system, DVB-MPE (multi-protocol package) is used as part of the video stream and data transfer specification. The transfer amount of the MPEG-2 IP data packet is based on the Digital Media Instruction and Control (DSMCC) section, which encapsulates the entire IP packet payload in the payload of the DSMCC section, and maps the MAC address to the header in the DSMCC section. And payload. The section format allows the datagram to enter multiple bytes. If the length of the datagram is less than or equal to 4096 bytes, it is sent within one section. In an IP occasion, the maximum transmission unit (MTU) is set to 4096 bytes, so the data newspaper does not form a debris. The MAC address is 6 bytes, divided into two groups, 5 and 6 bytes to map to the Table 裪 D Xtension field in the DSMCC section; and 1, 2, 3, and 4 bytes are mapped to the payload area of the DSMCC section. This mapping is completed by the limited capacity of the first generation demodulator. This IP video stream sent to small screen devices is ideal for low resolution, low rate data transmission. , Reading the full text, the technology area
Low-power Bluetooth wearable devices use heart rate sensors to track and record user health and
I understand: Realize the low phase noise of the radio frequency signal source and the coexistence of high-speed frequency switching
First look: Low phase noise radio frequency signal source new standard for avionics test measurement
high tech! Jia Zhao Technology Releases RECPLAY-32P RF Signal Recording Playback System
High-frequency peripheral and radio frequency signal measurement certification technology and market trend
Our other product:
