In wireless Broadcasting System, users in different locations of wireless link quality is very different, some users and the channel between the transmitter conditions are better, while others are very poor. To ensure service to all users of the service quality area, the system is usually in the worst case according to still guarantee the quality of service conditions of the design of transmission parameters, which makes it multi-channel users with better conditions and channel conditions can only be bad Users get the same data rate, resulting in lower overall system's transmission rate. In addition, the broadcast system in the future will have a variety of different types of receiving equipment, they use different terms, receive very different capacity. For example, high-quality indoor receiver should be able to receive high-speed data, and the small portable device just to receive the lower rate data. To fully utilize the transmission capacity of the channel and meet the different users and different receiving equipment requirements, to design a multi-level transmission systems. The concept of multi-stage transfer was first proposed by Cover [1] proposed, he pointed out that the program can take into account the grade transmission channel conditions, user needs, to achieve higher transmission efficiency. Europe Digital TV Broadcast standards ( DVB -T) proposed a two-stage coding modulation scheme [2]. [3] discusses multi-level modulation and coding technologies such as multi-level decoding errors caused by different protection features, [4] analyzed the coding system is not multi-level modulation scheme performance. Recent years, with Communicate Technology, efficient encoding and decoding methods emerging for the design of programs to better the conditions for radio transmission. This paper, a digital radio broadcast system for multi-level transfer program, which uses low-density parity check codes (LDPC) codes of broadcasting data classification and coding combined with multi-resolution multi-level modulation technique for different priority of data provide different error protection, so that each user can own the quality of transmission channel, or the ability to receive equipment, access to different data transmission rate and improve the whole system of transmission efficiency.
Multi-level transmission system Multi-stage transmission system refers to the data to be transferred or content according to the importance of different into different priority, the transmitter modulation coding process the data of each separate priority treatment, so different priority data by different error protection, high-priority data, low threshold decoding, decoding is relatively easy to decode the low priority data, the higher the threshold, decoding is relatively difficult. In the receiver, the user, or according to received signal quality receiving equipment capacity selection demodulation only high-priority data, or all the data demodulation. This will not only ensure basic coverage of the network, they can make a good channel condition or the reception of the stronger user access to more data, thus improving the system, the average transfer rate.
Transmission system mainly consists of multi-level coded modulation, channel transmission, demodulation, decoding three parts. Figure 1 shows the block diagram of multi-stage transmission system, data to be transferred in accordance with the priorities were divided into multiple parallel data streams into the multi-stage encoder. Different encoder data were independently coded on separate ways, encoding the first symbol after the code constellation for set partitioning and mapping, and then into the wireless channel after OFDM modulation. In the receiver, first the received signal, channel estimation, further demodulation and decoding are all priority classification data.
Figure 1 multi-stage transmission system I am an expert from China Chemicals Products, usually analyzes all kind of industries situation, such as wish pearl jewelry , paua shell jewelry.
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