OFDM传输中的子带自适应Turbo编码调制
Subband Adaptation Employing Turbo Coded Modulation for OFDM Transmissions
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摘要: 为了在无线数据传输中获得更高的频谱利用率，提出了一种用于正交频分复用(OFDM)的基于容量估计的子带自适应Turbo编码调制方法。其目标是在恒定发送功率和目标误码率(BER)限制下优化系统吞吐。仿真表明，在发端完全信道估计下，此自适应OFDM方法比基于固定门限的自适应Turbo编码调制有2.5-5 dB的信噪比(SNR)增益。然而，时变信道中反馈信息的延时会带来自适应性能的恶化。文中接着通过研究表明，在子带自适应编码调制中，减少选取子带的个数，充分利用OFDM频域上的分集特性是一种可以降低信道时变带来性能恶化的有效途径。Abstract: To improve the spectral efficiency for wireless data transmissions, a subband-by-subband adaptive turbo coded modulation scheme based on capacity evaluation is proposed for Orthogonal Frequency Division Multiplexing (OFDM). The target is to optimize the overall throughput under constant transmit power and target Bit-Error-Rate (BER). Sim-ulation results show that the adaptive OFDM scheme exhibits a 2.5~5 dB Signal to Noise Ratio (SNR) gain relative to fixed threshold adaptive turbo coded modulation when the transmitter knows the perfect channel information. However, the adaptation performance is degraded due to the feedback delay in time-varying channels. Then, the investigation indicates that decreasing the amounts of subbands, and utilizing the diversity characteristic adequately in frequency domain of OFDM is an effective approach to reduce the performance degradation.
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