Wireless Multimedia Communications and Networking Based on JPEG 2000
Max Agueh · Sciyo eBooks · 2010
4.1 On JPEG 2000 codestreams interleaving In this section, we discuss and evaluate the impact of data interleaving in the effectiveness of the FEC rate allocation scheme. Thanks to the interleaving matrix presented in Figure 9, protected JPEG 2000 data are decorrelated before being sent through the wireless channel. Hence, the impact of consecutive channel errors sequences on the transmitted codestreams is reduced. In Figure 9 the protected JPEG 2000 codestream is divided into Px packets of length N . Then, the interleaving process consists in storing M consecutive packets into a M × N matrix and to read the columns of this matrix so that two initially consecutive symbols are separated by a distance of I = M (symbols). We refer to I as the interleaving degree. The considered channel is a real mobile ad-hoc network channel experiencing PER = 3.88 × 10 −2 and the interleaving degrees are 1, 2, 4, 8, 16, 32, 64 and 128. Table 1 shows the PSNR evolution as function of interleaving degree I . The considered image is speedway_0.j2k protected with the optimal packet-oriented JPWL compliant scheme. The interest of interleaving is shown in table 1 in the sense that the PSNR and the successful decoding rate increase with the interleaving degree I . The results in table 1 are valid for a Gilbert channel with a specific error correlation factor and are no longer the same when this factor changes. For the considered channel, we observe that for I ≤ 8 , interleaving has no noticeable impact because the interleaving degree I is smaller than the average error burst length. In fact, we show in (Agueh et al, 2008) that the upper bound of the mean error burst length is Lmax = 10 bytes. Hence, in order to be efficient, the interleaving degree should be B higher than 10 bytes. When I is increased to 16 or more, we notice an improvement of both the PSNR and the successful decoding rate. However, we observe that higher values of I