Research On Error Control Technologies For Next Generation Mobile Communication System

Communication is the art of error control, error control technologies is the key of the communication. Enduring time-variant and frequency-selection fading channel, the mobile channel is quite complicated and thus a qualified and reliable error control mechanism is required for communication reliability. Error control technologies in mobile communication system mainly include two different kinds of technologies:hybrid automatic retransmission query (HARQ) and channel coding. HARQ achieves both energy and time-diversity gains by retransmission and channel coding offers error detection and correction abilities by introducing redundancy information.In next generation mobile communication system, it's a highlighted issue how to combine MIMO, OFDM and relay with error control technologies effectively. HARQ has been widely applied due to its simple but effective principle and easy to be implemented. Among all schemes, incremental redundancy is mostly deployed, in which different coding version is repeated. However different repeat packet selection schemes lead different gain due to different code's property and channel condition. As a result, how to design an effective repeat packet selection method is the key challanege for HARQ design.In last decady, low density parity check (LDPC) code is the hottest topic in channel coding area. With simple coding structure, significant coding gain and low decoding dealy LDPC has been widely implemented in mobile TV and communication systems. Recognized as different column weight (a.k.a. degree) LDPC is divided into two categories:regular and irregular LDPC code. As the column weight is well optimized and different in a check martrix, irregular LDPC code outperforms regular code. Bits in a code block with different degree have different performance and those with large degree perform better due to larger protection. Known as unequal protection (UEP) of LDPC code bits with larger degrees are often used to protect important information. The system is optimized with UEP property and higher power efficiency would thus be achieved.In this paper the performance of HARQ and LDPC codes is studied. Topics including the error control scheme of MIMO, OFDM and relay system are studied based on the UEP property. Besides, the performance of repeat partner selection scheme in relay network is also investigated. By leveraging the space diversity of MIMO, frequency selection scheduling of OFDM, repeat packet selection of HARQ and time-space diversity of relay, transmission schemes for next generation mobile network are designed for high transmission power efficiency.Work in this paper could be summarized as:1. A LDPC coded MIMO scheme (DDB-MIMO) is proposed. In this scheme, important bits (with large degrees) are mapped to the transmission diversity (TD) symbols for better protection and bits with small degrees are mapped to spatial multiplexing (SM) symbols for higher transmission rate. By offering better protection to important bits the scheme achieves significant gain.2. A LDPC coded OFDM scheme (DD&R LDPC-COFDM) is proposed by taking both first transmission and repeat packet selection method into consideration. By combining LDPC UEP property and different reliability of OFDM subcarriers together the important bits are mapped to reliable subcarriers (with large receiving SNR) and for retransmission the bits on less reliable subcarriers are prior to be repeated.3. The frame error probability (FEP) based on pairwise error probability (PEP) for relay network is analyzed and it is found that:in order to achieve both diversity and coding gain a good channel code is required in broadcast (BC) mode and for MAC mode different redundancy version is important. A LDPC based relay transmission scheme is proposed. In the scheme a good LDPC code is required and then divided into several sub code blocks by mean column weight (MCW). In BC mode the sub block with large MCW is employed and the rest blocks are transmitted in MAC mode. The scheme provides reliable transmission in BC mode and thus the diversity gain is guaranteed. In MAC mode by combining different redundancy version the decoding at destination node is more reliable.4. A HARQ repeat partner selection scheme is proposed. In the partner candidate region where every partner could provide enough power for retransmission the partner with less forwarding power is chosen and thus the higher repeat power efficiency is achieved.