A novel unequal error protection scheme for 3-D video transmission over cooperative MIMO-OFDM systems
- Omar Hazim Salim^{1} and
- Wei Xiang^{1}Email author
https://doi.org/10.1186/1687-1499-2012-269
© Salim and Xiang; licensee Springer. 2012
Received: 29 February 2012
Accepted: 28 July 2012
Published: 23 August 2012
Abstract
Currently, there has been intensive research to drive three-dimensional (3-D) video technology over mobile devices. Most recently, multi-input multi-output (MIMO) with orthogonal frequency division multiplexing (OFDM) and cooperative diversity have been major candidates for the fourth-generation mobile TV systems. This article presents a novel unequal error protection (UEP) scheme for 3-D video transmission over cooperative MIMO-OFDM systems. Several 3-D video coding techniques are investigated to find the best method for 3-D video transmission over the error-prone wireless channels. View plus depth (VpD) has been found the best technique over other techniques such as simulcast coding (SC) and mixed-resolution stereo coding (MRSC) in terms of the performance. Various UEP schemes are proposed to protect the VpD signals with different importance levels. Seven video transmission schemes for VpD are proposed depending on partitioning the video packets or sending them directly with different levels of protection. An adaptive technique based on a classified group of pictures (GoP) packets according to their protection priority is adopted in the proposed UEP schemes. The adaptive method depends on dividing GoP to many packet groups (PG’s). Each PG is classified to high-priority (HP) and low-priority (LP) packets. This classification depends on the current signal-to-noise ratio (SNR) in the wireless channels. A concatenating form of the rate-variable low-density parity-check (LDPC) codes and the MIMO system based on diversity of space-time block codes (STBC) is employed for protecting the prioritized video packets unequally with different channel code rates. For channel adaptation, the switching operations between the proposed schemes are employed to achieve a tradeoff between complexity and performance of the proposed system. Finally, three protocols for 3-D video transmission are proposed to achieve high video quality at different SNRs with the lowest possible bandwidth.
Introduction
Three-dimensional (3-D) video applications have recently emerged to offer immersive video content compared to two-dimensional (2-D) services. Currently, there has been intensive research to drive 3-D video technology over mobile devices similar to its applications in 3-D cinema and television [1]. This strong motivation is due to 3-D video environment which makes observers unable to distinguish between real media and an optical illusion [2]. The main challenges to realize this ambition are to design efficient 3-D video representations, coding and transmission methods to overcome the effects of error-prone wireless channels [1]. This article aims to transmit 3-D video signals over wireless communication systems by adopting state-of-the-art communication and signal processing techniques.
Generally, high data-rates are required for video transmission, and even more for 3-D video services. Spatial modulation multiplexing techniques such as multi-input multi-output (MIMO) have been developed to address this issue. Furthermore, due to the size and power constraints with an increased number of antennas in MIMO-mobile devices, the cooperative diversity is proposed to harness the spatial diversity without deploying multiple antennas. In addition, the combination between MIMO with one to three antennas and cooperative communications, improves the video system performance [3].
Orthogonal frequency division multiplexing (OFDM) is one of the powerful spread spectrum techniques to increase the transmission bandwidth efficiency. Furthermore, the subcarriers’ orthogonality is implemented efficiently using the inverse discrete Fourier transform (IDFT) and discrete Fourier transform (DFT) at the transmitter and receiver, respectively. In addition, inter-symbol interference (ISI), caused by multipath propagation, is overcomed with the aid of the cyclic prefix (CP). The CP represents an extension of OFDM symbols in the time domain. Meanwhile, in the frequency domain, OFDM turns a frequency-selective channel into multiple frequency-flat subchannels. Consequently, the detrimental effect of the frequency-selective fading channel is mitigated [4].
According to MIMO and OFDM principles, the combination of MIMO and OFDM is crucial in reducing the effect of frequency selectivity, improving the spectral efficiency and providing high data rates. Therefore, MIMO-OFDM becomes the chosen air interface technology for next generations of wireless networks such as WiMAX IEEE 802.16e standard [5].
Video transmission systems generally use compression techniques such as H.264/AVC based on variable-length codes (VLCs) to overcome the problem of channel bandwidth limitation. The resulting bitstream is usually very sensitive to bit errors. A single-bit error can propagate to many subsequent VLCs. Moreover, error propagation causes a synchronization loss between the encoder and decoder. In worst cases, this can lead to an entire system decoding failure. Therefore, video communication systems should use error-resilient video coding and powerful channel coding techniques to provide reliable video communication over error-prone wireless channels [6].
Many different types of error resilient video and channel coding techniques have been proposed to improve video transmission over wireless communication systems. These schemes mainly are: unequal error protection (UEP) with assistance of forward error correction (FEC) methods and joint source-channel coding (JSCC). UEP involves on partitioning the video data into different fractions of visual importance. The most important part is called the high-priority (HP) stream, while the less important stream is termed the low-priority (LP). In addition, UEP is mostly combined with FEC schemes such as turbo codes [7] or low-density parity-check (LDPC) [8] codes to achieve more robust video bit stream. Furthermore, JSCC algorithms control the encoders of source and channel coding to make the video system adaptive to wireless channels changes [9, 10].
The advantages of exploiting diversity and multiplexing gains of multi-antenna systems promotes the application of MIMO technology in wireless video communications systems. Wu et al. [11] investigated the system performance of a MPEG coding scheme with joint convolutional coding and MIMO-based space-time block codes (STBC) techniques over Rayleigh fading channels. The feedback information from the performance control unit (PCU) was employed to control the assigned rates to MPEG source code and convolutional coding stages. Although this study demonstrated that bit error rate (BER) can be improved using STBC and convolutional coding systems, it did not propose any techniques to mitigate error propagation in video signals at the video decoder. Song and Chen [12] proposed an MIMO system based on the adaptive channel selection (ACS) method. The suggested scheme was to load more important video layers to the MIMO sub-channel that has a high signal-to-noise ratio (SNR). Song and Chen [13] also proposed another method to increase the transmission throughput by reallocating the excess power of certain sub-channel to other sub-channels. Zheng et al. [14] proposed hybrid space-time coding structure to achieve the UEP scheme for multiple description coding (MDC) over MIMO-OFDM system. Besides, several hybrid MIMO systems were proposed in [15, 16]. Although these works have suggested different methods to improve video transmission over wireless channels, they are unable to achieve spatial diversity gains and therefore are ineffective in fading channel environments. Furthermore, they need to be adaptive with channel’s characteristics.
Currently, many existing works for 3-D video delivery over wireless communication channels concentrate on fixed designs such as the one proposed by Hewage et al. [17] which was based on view-plus-depth (VpD). In the article, a UEP method based on unequal power allocation (UPA) was proposed to transmit 3-D video signals over WiMAX communication channels. The VpD map was coded with backward compatibility using the scalable video coding (SVC) architecture. Akar et al. [18] utilized the previous method to transmit 3-D video signals over the Internet. Furthermore, Hewage et al. [19, 20] demonstrated that the depth map information is less important than the colour data in terms of perceived video quality. Because of the above reason, the scheme allocates more protection for the colour image than the depth map. It was also determined based on UPA method. Aksay et al. [2] studied the digital video broadcasting-handheld (DVB-H) system at different coding rates for transmitting left and right views. The study recommended to give more protection to the left than the right view. Tech et al. [21] implemented and integrated JMVC 5.0.5 using the slice interleaving method. Micallef and Debono [22] applied the same idea of the slice interleaving method with different slices size to the JMVC 8.0. Most recently, Hellge et al. [23] proposed a layer-aware FEC method to improve the MVC video performance over the DVB-H system. Moreover, the UEP method in [24] used the repetition codes and depended on partitioning the data in the video block based on VLC priority, whereas the UEP scheme in [25] depended on a restricted scheme because that the HP and LP streams represented the I-frame and the P-frame packets, respectively. It can be concluded, although the slice interleaving method is useful to minimize and isolate effects of error propagation, it is suitable only when the noise level is low. Moreover, an increase in the number of slices per frame leads to a reduction in video compression efficiency. In addition, in [24], the FEC scheme of repetition codes is much simpler than LDPC codes in this article, whereas the LDPC encoding method in [25] is more complex than the encoding method adopted in this article.
- 1.
A new video encoder and transmitter structure is proposed that adopts UEP and EEP schemes for 3-D video transmission. The proposed UEP schemes are implemented by isolating HP and LP streams depending on the current SNR in the wireless channel and the packet type.
- 2.
A new classification method of video packets of GoP for the left and right views as well as color and depth sequences is proposed. The packet categorization depends on classifying GoP packets into distinct groups which each of them then classified further according to its importance and priority protection.
- 3.
Switching operations between the schemes are proposed to achieve an elegant trade-off between 3-D video compression efficiency and the perceptual performance against error propagation.
- 4.
An efficient algorithm called the approximate lower triangular form (ALTF) in [26] for the LDPC with different coding rates is adopted and integrated into the 3-D video system. The adopted LDPC code is adaptive to the channel state according to the proposed JSCC algorithm.
The rest of the article is organized as follows. The cooperative MIMO-OFDM system for 3-D video transmission is described in Section ‘Cooperative MIMO-OFDM design for 3-D video transmission’. The rate-distortion analysis is illustrated in Section ‘Rate-distortion analysis for 3-D video compression’. The performance analysis of the LDPC codes 3-D system is explained in Section ‘Performance analysis of the LDPC codes 3-D system’. The simulation results of the 3-D video transmission over the cooperative MIMO-OFDM system are presented in Section ‘Simulation and results of the 3-D video transmission over cooperative MIMO-OFDM systems’. Finally, Section ‘Conclusion’ concludes the article.
Cooperative MIMO-OFDM design for 3-D video transmission
In this section, the design of the proposed cooperative MIMO-OFDM system for 3-D video transmission is described in detail in the subsequent sections.
3-D video encoding with UEP
Several video representations and coding methods for 3-D video signals have been proposed [27]. The use of these methods is basically determined by underlying 3-D video applications and display techniques. The 3-D video input is generally captured by two cameras representing the left and right views.
Various source coding approaches have been considered in the literature to process the 3-D video signal. In this article, simulcast coding (SC), mixed-resolution stereo coding (MRSC) and view plus depth (VpD) representations are considered due to their suitability for low-rate applications such as mobile services [1, 28]. The MRSC method encodes the left and right views separately using H.264/AVC standard. MRSC is implemented by down-sampling one of the views and up sampling back to the original resolution at the decoder. This operation yields different views with unequal resolution and the overall 3-D video quality is almost retained. This method is similar to SC, which encodes the left and right views separately without down-sampling. The VpD method encodes one of the views such as the right view with auxiliary depth information. At the decoder, the left view can be reconstructed using the depth-image-based rendering (DIBR) technique [29]. It can be concluded that, the SC and MRSC methods decode the left and right views independently, whereas the DIBR technique reconstructs the left view depending on the relationship between the view and depth. Furthermore, this relationship is beneficial in improving the compression efficiency for the 3-D video signal. VpD is less affected by noise than other 3-D video coding techniques as will be demonstrated later in the subsequent sections. This is due to that the depth sequence, which is gray scales ranging from 0 to 255.
PSNR and video distortion with different packet groups
Group | PSNR | Distortion |
---|---|---|
g _{1} | 28.8309 | 85.119 |
g _{2} | 32.7692 | 34.3685 |
g _{3} | 42.5035 | 3.6537 |
Based on the above discussions, seven video transmission schemes are proposed in the presence of a varying channel SNRs. The first scheme is called P-VpD. This scheme employs packet partitioning, where SPS, PPS and I-frame packets in the color and depth sequences are classified as HP packets, while P-frame packets are considered as LP packets. The second scheme, called P-V, which also applies the packet partitioning but on the color sequence only. The HP packets are protected with a high priority in both schemes, since any error in the SPS and PPS packets may lead to entire system decoding failure. Furthermore, any error in the I-frame packets will propagate to the P-frames packets. The third scheme is a direct UEP scheme, called D-VpD. This method sends the right and the depth sequences directly without packet partition. In this scheme, the right view has higher protection than depth, due to the fact that the left view is reconstructed depending on the relationship between the right view and depth. Therefore, any error in the right view will spread to the reconstructed left view. While the previous UEP schemes are static, the other four proposed UEP methods are adaptive in terms of classifying the P-frame packets.
In the adaptive UEP schemes, the P-frame packets are classified to four groups (Ng=4). The partitioner blocks (Partitioner-1 and Partitioner-2) in Figure 1 follow four methods to classify the P-frame packets. The fourth scheme, called P-VpD-1/4, treats g_{1}in the right and depth sequences as the HP packets, while the fifth method, called P-VpD-1/2, considers g_{1} and g_{2} as the HP packets. To evaluate the P-VpD schemes (P-VpD-1, P-VpD-1/4, and P-VpD-1/2) with other possible packet partitioning of view (color) packets, P-V schemes are proposed. The classification of the HP packets for P-V schemes as follows: the SPS, PPS and I-frame packets of the color sequence are considered HP packets in the P-V scheme. Meanwhile, HP packets represent g 1 in the P-V-1/4 scheme, and g_{1}and g_{2}groups in the P-V-1/2 scheme. The SPS, PPS and I-frame packets are also classified as the HP packets for the schemes.
States of switch circuits for each video transmission scheme
Scheme | Switch-1 | Switch-2 | Switch-3 | Switch-4 |
---|---|---|---|---|
D-VpD | connecting I N_{1} | connecting I N_{2} | off | connecting I N_{6} |
with D P_{1} | with D P_{2} | with D P_{3} | ||
P-VpD | connecting I N_{1} | connecting I N_{2} | connecting I N_{3} | |
P-VpD-1/4 | with P P_{1} | with P P_{2} | with P P_{3} | off |
P-VpD-1/2 | ||||
P-V | connecting I N_{1} | connecting I N_{2} | connecting I N_{4} | |
P-V-1/4 | with P P_{1} | with D P_{2} | with P P_{3} | off |
P-V-1/2 |
The difference between direct and packet partitioning schemes is the isolation method of HP and LP packets. The D-VpD scheme is more reliable at low SNRs because it gives more protection for important information (color). In addition, it is simpler compared to the P-VpD schemes. On the other hand, the D-VpD scheme requires more bandwidth compared to other schemes. Therefore, the best method is to strike a trade-off between the complexity of the P-VpD schemes and the simplicity of the D-VpD scheme, which will be explained on more detail later.
It is worth mentioning that SC coding is generally considered more resilient to error propagation compared to other 3-D video techniques. It also provides a good video quality at low SNRs, due to the fact that both views are decoded separately. However, this error resilience comes at the expense of high data rates. In light of this, VpD is more suitable.
Signal and channel models for cooperative MIMO-OFDM systems
where $\left(\right)close="">{\left\{{\mathbf{\text{H}}}_{j}^{\mathrm{sd}}\right\}}_{j=1}^{{N}_{\mathrm{RX}}}$ is the channel frequency response between the source and destination with an independent Rayleigh fading channel, with quasi-static fading coefficients, $\left(\right)close="">\mathbf{\text{F}}\in {\mathbb{C}}^{{N}_{T}N\times {N}_{T}N}$ is the DFT matrix with its (l,m) the element given by $\left(\right)close="">{\mathbf{\text{F}}}_{\mathit{\text{l}},\mathit{\text{m}}}\triangleq (1/\sqrt{N}){e}^{-j(2\mathrm{\Pi ml}/N)}$ with m,l=0,1,…,N_{ T }N−1 and $\left(\right)close="">{\left\{{\mathbf{\text{n}}}_{j}^{\mathrm{sd}}\right\}}_{j=1}^{{N}_{\mathrm{RX}}}\sim \mathcal{C}\mathcal{N}(\mathbf{\text{0}},{\sigma}_{\mathrm{sd}}^{2})$.
where $\left(\right)close="">{\left\{{\mathbf{\text{H}}}_{k}^{\mathrm{sr}}\right\}}_{k=1}^{{N}_{R}}$ is the channel frequency response between the source and relay with an independent Rayleigh fading channel, with quasi-static fading coefficients and $\left(\right)close="">{\left\{{\mathbf{\text{n}}}_{k}^{\mathrm{sr}}\right\}}_{k=1}^{{N}_{R}}\sim \mathcal{C}\mathcal{N}(\mathbf{\text{0}},{\sigma}_{\mathrm{sr}}^{2})$.
The received signal vectors $\left(\right)close="">{\left\{{\mathbf{\text{r}}}_{j}^{\mathrm{sd}}\right\}}_{j=1}^{{N}_{\mathrm{RX}}}$ (2) and $\left(\right)close="">{\left\{{\mathbf{\text{r}}}_{j}^{\mathrm{rd}}\right\}}_{j=1}^{{N}_{\mathrm{RX}}}$ (5) are applied to the DFT operation. Maximal ratio combining (MRC) is utilized in the destination to obtain cooperative diversity gains by adding the decoding samples of the direct and relay links coherently.
Rate-distortion analysis for 3-D video compression
To minimize D_{ T }, two methods are followed. The first method uses a rate-distortion (R-D) model to estimate the source encoding rate that minimize the $\left(\right)close="">{D}_{{s}_{L}}$ and $\left(\right)close="">{D}_{{s}_{R}}$. The second method reduces the $\left(\right)close="">{D}_{{c}_{L}}$ and $\left(\right)close="">{D}_{{c}_{R}}$ by choosing suitable code rates of the LDPC encoder.
where R_{ D } in bps is the encoding rate of the depth encoder.
Distortion factors of left, right and depth encoders
Left view | θ _{ L } | $\left(\right)close="">{R}_{{0}_{L}}$ | $\left(\right)close="">{D}_{{0}_{L}}$ |
5.48×10^{3} | 6.39 | −1.755 | |
Right view | θ _{ R } | $\left(\right)close="">{R}_{{0}_{R}}$ | $\left(\right)close="">{D}_{{0}_{R}}$ |
2.14×10^{3} | 10.85 | −1.38 | |
Depth sequence | θ _{ D } | $\left(\right)close="">{R}_{{0}_{D}}$ | $\left(\right)close="">{D}_{{0}_{D}}$ |
842.69 | 23.09 | −0.11 |
Performance analysis of the LDPC codes 3-D system
The LDPC code, which has variable coding rates is employed to protect the HP and LP streams. $\left(\right)close="">{D}_{{c}_{L}}$, $\left(\right)close="">{D}_{{c}_{R}}$, and $\left(\right)close="">{D}_{{c}_{D}}$ values can be minimized with an appropriate design of LDPC codec. The operations of LDPC encoding and decoding must be efficient and simple. Hence, an encoding algorithm of the approximate lower triangular form (ALTF) and a decoding method of sum-product algorithm (SPA) are utilized to achieve this goal [26, 36].
The ALTF algorithm is based on row and column permutations only. This operation performs as many transformation as possible in order to reduce the gap (g) in the ALTF matrix, where the encoding complexity is proportional to the gap size.
SPA is a soft decision algorithm that calculates the a priori probabilities of the received code bits and uses a posteriori probabilities for decoding operation. These probabilities are known as log-likelihood ratios.
Gap values at various code rates
Coding rates | Column weight (j) | Row weight (k) | Gap (g) |
---|---|---|---|
13/16 | 3 | 16 | 6 |
12/16 | 3 | 12 | 12 |
11/16 | 3 | 10 | 13 |
10/16 | 3 | 8 | 21 |
9/16 | 3 | 7 | 29 |
8/16 | 3 | 6 | 38 |
As can be observed from Figure 9, the decreasing of the code rates improves the BER. In addition, it definitely increases the gap value as shown in Table 4, which leads to increase the computational complexity of channel encoding and decoding. Therefore, the best method to select a suitable rate is to strike a trade-off between the channel codec complexity and video quality. These two factors are determined according to the channel state.
$\left(\right)close="">{R}_{{H}_{1}}$, $\left(\right)close="">{R}_{{L}_{1}}$, $\left(\right)close="">{R}_{{H}_{2}}$, and $\left(\right)close="">{R}_{{L}_{2}}$ (after Partitioner-1 and Partitioner-2) can be calculated by counting the HP and LP packets. For example, if a video packet has fixed length of 150 bytes, and if there are 42 HP packets and 378 LP packets, then $\left(\right)close="">{R}_{{H}_{1}}$ is 50.4 kbps and $\left(\right)close="">{R}_{{L}_{1}}$ is 453.6 kbps.
According to the variables above, two factors must be considered to minimize the end-to-end 3-D video distortion (D_{ T }). Firstly, the required data rate for 3-D video signal must be equal or less than R_{ T }. Secondly, the D_{ T }should be less or equal to 650.25, which represents the maximum tolerable distortion D_{max}[23].
In this equation, MSE_{ l }and MSE_{ r }represent the mean square error between the original and reconstructed left and right sequences, respectively, [37].
From the above discussion, it can be concluded that, the encoding rates and the available SNR in the wireless channel determine the total 3-D video distortion. Moreover, the channel coding rates and the bandwidth are the main factors to minimize the channel distortion.
Simulation and results of the 3-D video transmission over cooperative MIMO-OFDM systems
Simulation configurations
System parameters | Value |
---|---|
Source coding | H.264/AVC |
Tested sequence | Car |
Video sequence dimensions | (432x240) pixels |
Tested video frames | 30 |
Down sampling factor | 2:1 |
GoP | 10 |
Fading channel | Quasi-static Rayleigh fading |
Noise channel | AWGN |
Relay protocol | AF |
No. of antennas for source | 2 |
No. of antennas for relay | 2 |
No. of antennas for destination | 2 |
CRC | 16 |
Code rates | 4/16, 8/16, and 13/16 for UEP |
13/16 for EEP | |
Diversity technique | Alamouti scheme |
Guard period ratio | 1/4 |
OFDM sub-channels | 1024 |
For noisy channels, most VLCs could not be reconstructed, and in some cases, the video decoder reconstructs the wrong coefficients because it lost the synchronization with the video encoder. To overcome this problem, this article proposes two error-resilient video methods. The first method is to resynchronize the video decoder using resynchronization patterns. This method adopted in [25] and is extended to SC and VpD applications in this article. The second method is to make the 3-D video transmitter adaptive with the channel state.
In the first method, special information in the video packet header is exploited by the video decoder to isolate the effect of error propagation. The length of header information is around 20 bytes and in hexadecimal form 00 00 FF FF FF FF 80, which exists in most packets (e.g., SPS, PPS, intra and even inter frames packets). This pattern is utilized to maintain the synchronization with the video encoder by restarting the decoding operation when the error occurs in the video packet. The error propagation could be detected easily by a cyclic redundancy check (CRC) at the decoder side. In this procedure, the decoder depends on the CRC to determine the corrupt packets and discard them. Thus, restarting the video decoder is necessary to minimize the effect of error and isolate the error propagation between the video packets. It is also suitable when the noise level is low.
The second method (which will be explained in more detail later) exploits the CSI signal to achieve adaptive video transmission. In this method, the 3-D video transmitter allocates the coding rates for LDPC encoders corresponding to several UEP schemes or fixed EEP scheme.
Required data rates for 3-D coding methods
Scheme | R _{HP-LDPC} | R _{HP-LDPC} | R_{ T }for | R_{ T }for |
---|---|---|---|---|
UEP | EEP | |||
D-SC | 2.548 | 1.479 | 4.027 | 3.047 |
D-MRSC | 2.548 | 0.794 | 3.342 | 2.362 |
D-VpD | 2.404 | 0.583 | 2.987 | 2.062 |
P-VpD | 0.786 | 1.578 | 2.364 | 2.062 |
P-VpD-1/4 | 1.464 | 1.161 | 2.625 | 2.062 |
P-VpD-1/2 | 2.116 | 0.76 | 2.876 | 2.062 |
P-V | 0.622 | 1.679 | 2.301 | 2.062 |
P-V-1/4 | 1.077 | 1.399 | 2.476 | 2.062 |
P-V-1/2 | 1.536 | 1.117 | 2.653 | 2.062 |
As outlined in Table 6, the D-VpD scheme is better data rates than the D-SC and D-MRSC schemes. In addition, packet partitioning schemes for VpD have lower data rates compared to D-VpD. Moreover, the packet partitioning schemes of VpD compared to the MRSC and SC schemes provide the same quality of the 3-D video signal with lowest bandwidth.
where the values of $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{1}}$ and $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{2}}$ are −6, −3 dB, respectively. These SNRs values are chosen to achieve high video quality with lowest possible bandwidth at moderate-to-high SNRs. Hence, when $\left(\right)close="">\mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{1}}$, the D-VpD-UEP (R_{LDPC-HP}=4/16) scheme is adopted to achieve a PSNR between 31.5 to 41.36 dB at the data rate of 5.3915 Mbps, while the D-VpD-UEP (R_{LDPC-HP}=8/16) and D−VpD−EEP schemes are selected at $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{1}}\le \mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{2}}$ and $\left(\right)close="">\mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{2}}$ to achieve a PSNR = 41.36 dB at the data rate 2.987 and 2.062 Mbps, respectively.
where $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{1}}$ , $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{2}}$, and $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{3}}$ are −6, −4, and −3 dB, respectively. Furthermore, $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{1}}$ represents $\left(\right)close="">{\mathrm{SNR}}_{\mathrm{th}}$ in (13) and (14). These SNRs values are chosen to achieve high video quality with lowest possible bandwidth at moderate-to-high SNRs. Hence, when $\left(\right)close="">\mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{1}}$, the D-VpD-UEP (R_{LDPC-HP}= 4/16) scheme is adopted to achieve a PSNR between 31.5 to 41.36 dB at the data rate of 5.3915 Mbps, while the P-VpD-1/2, P-VpD and D−VpD−EEP schemes are selected at $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{1}}\le \mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{2}}$, $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{2}}\le \mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{3}}$, and $\left(\right)close="">\mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{3}}$ to achieve a PSNR = 41.36 dB at the data rates 2.876, 2.364, and 2.062 Mbps, respectively.
To achieve the above protocol, the switch circuits follow different states as shown in Table 2. In addition, Partitioner-1 and Partitioner-2 change their behavior according to the control unit. It can be concluded that, the proposed 3-D video system exhibits a high level of flexibility to change its behavior for any channel state to achieve reliable video transmission.
where the $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{1}}$, $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{2}}$, $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{3}}$, and $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{4}}$ are −6, −5, −4 and −2.5 dB, respectively. These values are chosen to achieve high video quality with lowest possible bandwidth at moderate-to-high SNRs. Hence, when $\left(\right)close="">\mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{1}}$, the D-VpD-UEP (R_{LDPC-HP}= 4/16) scheme is adopted to achieve a PSNR between 31.5 to 41.36 dB at the data rate of 5.3915 Mbps, while the P-VpD-1/2, P-V-1/2, P-V and D−VpD−EEP schemes are selected at $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{1}}\le \mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{2}}$, $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{t}h}_{2}}\le \mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{3}}$, $\left(\right)close="">{\mathrm{SNR}}_{{\mathrm{th}}_{3}}\le \mathrm{S}\mathrm{NR}{\mathrm{SNR}}_{{\mathrm{th}}_{4}}$, and $\left(\right)close="">\mathrm{SNR}{\mathrm{SNR}}_{{\mathrm{th}}_{4}}$ to achieve a PSNR = 41.36 dB at the data rates 2.876, 2.653, 2.301, and 2.062 Mbps, respectively.
To achieve this protocol, the control unit switch the switch circuits according to Table 2 and change the method of packet partitioning in Partitioner-1 and Partitioner-2 according to the CSI.
Conclusion
In this article, a novel UEP scheme is proposed to transmit a 3-D video signals over the cooperative MIMO-OFDM systems. In the framework, a new video encoder and cooperative MIMO-OFDM architecture for 3-D video transmission are proposed. Specifically, the 3-D video encoder adopts various UEP schemes with two error resilient methods to overcome the effects of error propagation in the 3-D video streams. The first method is proposed using the resynchronization technique, which is useful when SNRs are high. The second method adopts seven UEP schemes based on packet partitioning and direct transmission of video packets. According to the performance of the proposed schemes, three video protocols for 3-D video transmission are proposed to enhance the system performance at different states of wireless channels. They achieve a high video quality at different channel states with lowest possible bandwidth. Switching operations are proposed to achieve these protocols that are adaptive with the variation of the wireless channel. The simulation results have demonstrated the effectiveness of the proposed 3-D video protocols.
Joint source and channel rate optimization of the cooperative MIMO-OFDM system using hybrid AF and DF for 3-D video applications will be considered in the future work of this research.
Declarations
Authors’ Affiliations
References
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