As digital mobile TVs continue to transfer, applications and system engineers, applications and system engineers are facing various challenges, such as miniaturization, lower power consumption, and signal integrity. Research on existing mobile TV standards will be placed on DVB-H. This article will discuss the opportunities and challenges faced by the DVB-H receiver design from the perspective of the system, and focus on the radio front end.
Mobile TV standard
Table 1 lists the existing and upcoming mobile TV standards and systems (excluding honeycombs such as MBMS and BCMCs).
DVB-H is built on a DVB-T based and keeps compatible, allowing DVB-H signals to be sent on an existing DVB-T channel. The maximum change is to increase 4KFFT mode, deep interleaving of 2K and 4KOFDM, another forward error correction layer (MPE-FEC) for multi-protocol package data, and time interpretation intended to save power consumption. Italy has started commercial services of DVB-H, and many other countries will invest commercially in 2007/2008.
QUALCOMM has developed a FLO (forward link) technology based on Mediaflotm, and will be put into use in North America. Similar to DVB-H, FLO effectively reduces power consumption by using a time interval.
T-DMB is developed based on Eureka147DAB standard and has been widely used in South Korea. South Korea's mobile satellite system S-DMB is one of the few systems that do not use OFDM. S-DMB uses a code division multiple access (CDM) technology, working on a 25MHz wide S-band channel.
Japan starts with ISDB-T standard from 2006 to provide mobile TV services. This standard provides mobile services with a 6MHz channel.
Table 1: Comparison list of various mobile TV standards
China has recently promulgated its mobile phone broadcast service standard, named CMMB (China Multimedia Mobile Broadcast). The critical part of CMMB is STIMI (satellite ground interaction multi-service infrastructure), which is based on OFDM technology. China also announced the use of DMB-TH (Digital Multimedia Ground Broadcast / Mobile Phone) digital TV standards available for mobile phones.
Not long ago, the DVB decision-making body (SteeringBoard) approved the DVB-SH (Mobile Satellite Service) specification. DVB-SH provides a service to mobile devices via satellite and ground hybrid networks, which connect satellites directly to mobile transmitting devices and ground relay devices. DVB-SH can be subtracted into two standards, namely SH-A and SH-B. In SH-A, satellite and ground links use COFDM technology. In SH-B, the satellite link uses TDM, and the ground link adopts COFDM. DVB-SH made a demonstration at the 3GSM global meeting in Barcelona this year.
RF interface requirements for DVB-H
At present, DVB-H is recognized as the dominant standard for global mobile TV. This article will later introduce the DVB-H standard, although other standards have a certain market. Many key parameters associated with the analog and radio portion of the mobile terminal receiver are summarized in Table 2.
For DVB-H, the zero intermediate frequency direct conversion receiver shown in Figure 1 has become a mainstream architecture because they can meet the specification requirements given in Table 2, and the number of external components is minimized, power consumption is also Low.
Figure 1: DVB-H front end embedded in a honeycomb environment
Table 2: Keyic indicators of DVB-H mobile terminal RF interface
Another low intermediate frequency architecture is trapped around the strict image suppression requirements caused by the N +/- 1 barrier (Blocker). Due to the use of advanced CMOS technology, various mixed signal corrections and circuit technologies can be utilized to overcome some significant disadvantages of zero intermediate frequency direct conversion architecture, such as DC bias. DVB-T and DVB-H use high bandwidth and large quantity sub-carrier frequencies can reduce the spectrum in the KHz range near DC signals without significantly affecting performance.
In addition, just as the new product TUA9000 is displayed, although the input frequency required for DVB-H is wider, low noise amplifiers (LNAs) may still be integrated on the pure CMOS tuner. Since the system noise value at the RF reference point is less than 3.5 to 4 dB, the desired sensitivity can be obtained.
Mobility
The mobile characteristics of the terminal can cause rapidly changing channels and Doppler frequency shifts for receiving signals and their echoes. The receiver performance under these conditions is largely dependent on the standard modulation and protection methods employed and the performance of the signal processing algorithm. DVB-H has strong immunity to these signal damage, which can meet the actual requirements by a large number of different configuration adjustments. Due to the use of excellent AGC concepts and sufficient C / N margin, the impact of the simulated tuner part is generally quite small.
System realization
The recovery of mobile TV signals in the mobile environment often encounters various signal damage issues including specific system integration.
Taking into account the high bandwidth of the UHF receiver and the limited length of mobile terminal antenna, the antenna design is very challenging. If the antenna is designed as a broadband antenna, the achieved gain is naturally low, thereby seriously affecting the link budget. Although the low noise receiver design can alleviate this problem to a certain extent, the antenna is still the best "low noise amplifier" in the system. It is therefore best to find alternative antenna schemes. Tuning or resonant antennas can provide better performance. However, nonlinear tuning elements such as contam diodes reduce useful signal quality when there is a strong GSM emission signal in the environment because the isolation between the honeycomb antenna and the DVB-H antenna is only 10-20 dB. Read more
Our other product:
