Abstract
Wireless video multicast has become one of the key technologies in wireless applications. But the main challenge of conventional wireless video multicast, i.e., the cliff effect, remains unsolved. To overcome the cliff effect, a hybrid digital-analog (HDA) video transmission framework based on SoftCast, which transmits the digital bitstream with the quantization residuals, is proposed. With an effective power allocation algorithm and appropriate parameter settings, the residual gains can be maximized; meanwhile, the digital bitstream can assure transmission of a basic video to the multicast receiver group. In the multiple-input multiple-output (MIMO) system, since nonuniform noise interference on different antennas can be regarded as the cliff effect problem, ParCast, which is a variation of SoftCast, is also applied to video transmission to solve it. The HDA scheme with corresponding power allocation algorithms is also applied to improve video performance. Simulations show that the proposed HDA scheme can overcome the cliff effect completely with the transmission of residuals. What is more, it outperforms the compared WSVC scheme by more than 2 dB when transmitting under the same bandwidth, and it can further improve performance by nearly 8 dB in MIMO when compared with the ParCast scheme.
Highlights
With the boom of wireless digital facilities and the development of wireless video communication technology, wireless video multicast has become one of the key technologies in wireless local area networks
The proposed hybrid digital-analog (HDA) schemes consist of three parts: a digital part coded by H.264/AVC,[4,5] an analog part coded by SoftCast in multicast or ParCast in multiple-input multiple-output (MIMO), and an HDA mapping scheme that superimposes the digital signals with analog signals
Since only the low-frequency layers of discrete wavelet transform (DWT) coefficients in WSVC are encoded by H.264/AVC, peak signal-to-noise ratio (PSNR) performance of WSVC may be worse than the pure H.264/AVC digital transmission scheme with the same quantization parameter (QP) at some bad channels
Summary
With the boom of wireless digital facilities (e.g., smart phone, laptop, and tablet PC) and the development of wireless video communication technology, wireless video multicast has become one of the key technologies in wireless local area networks. SoftCast broadcasts one video to all the receivers without allocating different bit-rates to different receivers, and, at the same time, the decoded video on each receiver matches up to their channel It can completely solve the existing cliff effect problem in traditional digital video multicast schemes. When it comes to video performance, SoftCast does not behave well at low channel qualities. The H.264/AVC stream is encoded by forward error correction (FEC), and both the compression ratio of H.264/AVC and bit error rate (BER) are taken into account to guarantee effective and trustworthy digital transmission.[4,5] It is crucial that residuals of H.264/AVC are coded by SoftCast in video multicast and by ParCast in MIMO-OFDM video transmission.
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