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1 2 3 4 5 10 −7 10 −6 10 −5 10 −4 10 −3 10 −2 10 −1 E b /N 0 / dB BER Turbo Diversity, ∆SNR = 4 dB, LDPC C. Turbo Diversity, ∆SNR = 4 dB, Turbo C. Turbo Diversity, ∆SNR = 6 dB, LDPC C. LLR −Combining, ∆SNR = 4 dB, LDPC C. LLR −Combining, ∆SNR = 4 dB, Turbo C. LLR −Combining, ∆SNR = 6 dB, LDPC C. Figure 3.16: BER performance of MRC and TD using LDPC codes, turbo codes and RSCC (CC) for a DRM-based scenario. LDPC Code Design Wiener filter The performance analysis was carried out for an OFDM scenario in which the channel profile followed “US Consortium” with path delays (1, 0.7, 1.5, 2.2 ms), path gains (1, 0.7, 0.5, 0.25) and normalized Doppler frequency f D = 0.05. Channel estimation was implemented using the Wiener filter method [11] and LDPC codes of rate 3/4 and block length 9000 were used. EXIT characteristics are depicted for both code design techniques in Fig. 3.17 a), where the corresponding LDPC code parameters are (λ 2 = 0.198, λ 4 = 0.2441, λ 5 = 0.1421, λ 29 = 0.093, λ 30 = 0.151, λ 34 = 0.1715, ρ 19 = 0.1655, ρ 20 = 0.8345) and (λ 2 = 0.441, λ 30 = 0.5589, ρ 16 = 0.2644, ρ 17 = 0.7356), respectively. The resulting EXIT functions of method No. 2, for low SNRs are wider opened than EXIT func- tions of method No. 1, what can be understood as better performance for a lower number of iterations. Despite of another design criterion for method No. 2, the area between resulting EXIT functions is smaller than for method No. 1, which is related to a lower distance to channel capacity. 3.3 Iterative Diversity Reception for Coded OFDM Transmission 59 tải về 7.55 Mb. Chia sẻ với bạn bè của bạn:
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