https://www.um.edu.mt/library/oar/handle/123456789/71342 Sun, 05 Apr 2026 06:23:39 GMT 2026-04-05T06:23:39Z https://www.um.edu.mt/library/oar/handle/123456789/101787 Title: Resilient wireless transmission of H.264/AVC through error localisation and control mechanisms Abstract: Current trends in wireless communications provide for fast and location independent access to multimedia services. Due to its high compression efficiency, H.264/AVC is expected to become the dominant underlying technology in the delivery of future wireless video applications. However, H.264/AVC is susceptible to transmission errors common in wireless environments where even a single corrupted bit may cause visual artefacts that propagate in the spatio-temporal domain. The standard incorporates several error resilient mechanisms to minimize the effect of transmission errors on the perceptual quality of the reconstructed video sequence. However, these mechanisms assume a packet-loss scenario where all macroblocks (MBs) contained within a corrupted slice, including numerous uncorrupted MBs, are discarded and concealed. This implies that the error resilient mechanisms operate at a lower bound and thus further performance gains can be achieved by exploiting the residual redundancies available at the decoder side. During this dissertation, decoder-based techniques aimed to enhance the quality of damaged video sequences were investigated. The first method considered in this work exploits the residual source redundancy left by the standard encoder after compression to derive the most likelihood H.264/AVC feasible bitstream. This method manages to completely recover an average of 30% of the corrupted slices at no additional cost in bandwidth. The second approach considered in this dissertation exploits the redundancy available at pixel level to detect and localise visually distorted regions within the damaged slice that would otherwise be discarded. The experimental results show that machine learning algorithms can be taught to automatically detect the regions affected by transmission errors. This method limits the area to be concealed since only visually impaired regions are concealed. Both these methods provide a significant gain in video quality when compared to the standard when adopted individually. The two methods were combined together in a single solution to form the Hybrid Error Control Artefact Detection (HECAD) method which further boosts the performance of the individual components. This gain in performance is achieved at no additional cost in bandwidth and a moderate increase in complexity of the decoder. Furthermore, this method can be applied in conjunction with other error resilient strategies adopted by the standard decoder and still register considerable performance gains. Description: PH.D. Thu, 01 Jan 2009 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/101787 2009-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/101196 Title: Multicast multimedia transmission over wireless local area networks Abstract: Multicast over IEEE 802.1 la/b/g/n Wireless Local Area Networks (WLANs) is an efficient means of transmission exploiting the broadcast nature of the wireless medium. Moreover the use of the unlicensed 2.4GHz or the 5GHz bands does not incur licensing costs. But IEEE 802.lla/b/g/n Access Points (APs) transmit multicast unreliably, because the receivers do not transmit feedback regarding packet reception. Hence, multicast over IEEE 802.lla/b/g/n WLANs suffers from a high Packet Error Rate (PER) which is inappropriate for multimedia transmission. In 2012, the IEEE 802.llaa standard added reliability to multicast using Directed Multicast Service, Groupcast with Retries (GCR) Unsolicited Retry and GCR Block Acknowledgement. However, packet repetition does not result in an optimal code rate. The work in this thesis first verified, using empirical and semi-analytical analyses, that two antennas of an IEEE 802.1 ln AP can be spatially distributed to mitigate the PER experienced. A main contribution was the proposal of a distributed antennas system (DAS), consisting of seven antennas, which was shown to multicast video over IEEE 802.1 ln WLANs with a Peak Signal-to-Noise Ratio (PSNR) of at least 36dB, with the same power but better code rate than other infrastructures. Even packets are multicast over one set of four transmit antennas with an antenna placed in the centre of the coverage area and three transmit antennas placed equidistantly at the periphery. The centre antenna and three other transmit antennas, also placed equidistantly at the periphery, are then used to multicast odd packets. The proposed DAS can also use antenna switching so that unicast transmission uses a centralized antennas system. The proposed DAS is shown to scale up well using a multi-cell approach. It was shown that packet repetition at the application layer, retransmitting each packet proactively once (code rate 0.5), does not result in the entire multicast group receiving good Quality of Service (QoS) with a legacy infrastructure or a DAS using only one set of four transmit antennas, due to burst erasures on the channel. The proposed seven-antenna DAS does guarantee the required QoS to the entire multicast group, on the other hand. Hence, schemes such as IEEE 802.11 aa GCR Unsolicited Retry should be deployed with the proposed DAS. The best code rate is achieved with Block Erasure Coding (BEC) on the proposed DAS. However, Network Coding, achieved by XORing packets to create parity packets, achieves a higher code rate than packet repetition and a lower delay than BEC, and results in good QoS with a PHY data rate of 58.5Mbps. Another original contribution is the proposal and study of two new MAC layer protocols. The first protocol uses a Binary Search guided by feedback from the receivers to determine the necessary number of R-S encoded parity packets. The second protocol combines Network Coding and packet repetition with feedback from the receivers, resulting in smaller channel occupancy than reactive packet repetition. Although this second protocol results in a larger maximum delay than reactive packet repetition, it is still appropriate for live-video streaming since the maximum delay is less than 8 ms. Finally, an infrastructure using distributed IEEE 802.1 ln APs is shown to perform better than the legacy infrastructure, at a code rate of 1/3. The advantage of using distributed APs is that IEEE 802.1 ln MCSs employing Spatial Division Multiplexing can be used for multicasting. Description: PH.D. Tue, 01 Jan 2013 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/101196 2013-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/100910 Title: Source representation for improved channel code performance in Wyner-Ziv video coding Abstract: The Wyner-Ziv video coding paradigm is a new coding paradigm which exploits most of the source correlation at the decoder. This differs from the traditional predictive video coding schemes, where the source correlations are exploited solely at the encoder. Hence, the new paradigm can enable the implementation of low complexity encoders suitable for various applications such as endoscopy capsules and low-power surveillance systems. Slepian-Wolf (SW) and Wyner-Ziv (WZ) theorems prove that when the complexities, of exploring the source statistics, are shifted from the encoder to the decoder, the coding efficiency should not be affect. Hence, under certain conditions, the coding performance of WZ video coding schemes can theoretically be made arbitrarily close to that of conventional schemes where the sources are jointly encoded and decoded. However, the Rate-Distortion (R-D) performance of practical Wyner-Ziv video coding architectures are still far from the best performance attained with predictive video coding architectures like the H264/AVC or High Efficiency Video Coding (HEVC) video coding scheme. This Thesis investigates several methods to improve the performance of Slepian-Wolf coding, in terms of coding efficiency and reduced decoding delays. It is noticed that the traditional Slepian-Wolf coding approaches encode the bits within the same bit-plane level randomly using Low-Density Parity-Check Accumulate (LDPCA) codes and this leads to a sub-optimal performance. The reliability of the bits can be predicted and used to ensure that the bit nodes receiving low reliability bit-predictions are given better protection. A novel LDPCA code construction, targeted to consider the coding problem at hand, is thus proposed. Furthermore, this work also analyses the performance of the traditional LDPCA codes at different entropy points and studies the best way to distribute the correlation noise amongst bit-planes to improve coding efficiency. This is achieved by accumulating the most unreliable bits within the first decoded bit-planes and correcting the remaining bit-planes, having few bit-errors, using 8-bit or 16-bit Cyclic Redundancy Check (CRC) codes. The careful arrangement of discrepancies amongst bit-planes is used together with the arrangement of bits within each bit-plane and the new LDPCA codes, to obtain performance gains of up to 23 % during Slepian-Wolf coding. In context of Slepian-Wolf coding, the Thesis also addresses a comprehensive analysis of the mismatch present within regions of low motion. This is used to develop a scheme where the quantisation module alters between the floor and the round operator, at different pixel or coefficient locations. The operator which is more likely to avoid the Slepian-Wolf codec from correcting mismatch caused by small variation in light intensity is then chosen to improve R-D performance by up to 0.52 dB. Finally, the long decoding times required for Slepian-Wolf decoding are reduced by considering a new indexing scheme and histogram equalisation technique. For parallel WZ video coding architectures, these techniques ensure that the Slepian-Wolf decoders running on different cores of a multi-core processor can finish decoding at the same time, aiding parallel decoding and reducing decoding times by up to 32 %, with minimal affect on the R-D performance. The obtained reduction in rates and decoding delays helps bridge the gap in performance compared to the traditional video coding systems and pave the pathway for applications based on WZ video coding paradigm. Description: PH.D. Tue, 01 Jan 2013 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/100910 2013-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/100877 Title: Multi-view video-plus-depth coding using depth information Abstract: Multi-view 3D videos are required to provide an enhanced immersive user experience, with the ability to perceive the 3D depth effect and arbitrarily select the desired navigation viewpoint. For an efficient representation, the texture multi-view video data require also the transmission of its aligned depth map multi-view counterpart to help reconstruct arbitrary intermediate virtual viewpoints. Encoding these components within these 3D videos require the Multi-view Video Coding (MVC) standard, which is a very computational intensive task. This process increases drastically the 3D video encoding durations, compared to 2D video encoding, which hinders its use for transmission, such as for real-time or broadcast applications, which respectively need the Low-latency and the Hierarchical bi-Prediction MVC structures. Nevertheless, this new aligned depth map data supplies a Jot of useful geometrical information about the scene, which data together with appropriate geometrical properties can be exploited to achieve multi-view video coding within a shorter coding latency and with higher coding efficiencies. Experimental results demonstrate that this geometrical information can be efficiently utilised to calculate more accurate geometric predictors for the disparity and the motion estimations. As these are geometrically assisted, they become more accurate than the median ones adopted by the standard, thus, they allow a reduction in the estimations' search area, and as a result, in their encoding durations. Such aids obtain an overall MVC speed-up gain of up-to 4.2 times when applied to the Low-latency MVC, and of 3.2 times when applied to the Hierarchical bi-Prediction MVC. Exploiting further inter-view geometric relationships within the multi-view video reduce further the disparity estimation's search range, and improve its final speed-up gain to up-to 20.8 times. Moreover, the motion and the disparity estimations can be also modified to exploit this depth map data to limit their actual mode tested during rate-distortion optimisation. This is because this geometry helps identify better equivalent positions in the encoded viewpoints, and exploit them to determine the potential modes to use for motion estimation. Additionally, the most likely macroblock' s best division for disparity estimation can also be determined and exploited. The former improves the MVC's speed-up gain to about 6 times, while the latter reduces the disparity estimation's time by 26.0 times. All of these fast techniques are Pagev then combined together to form a joint computational reduction in MVC, which improved its coding speed up to 6.7 times for low-latency applications, and up to 3.7 times for broadcast applications. Being more accurate, the geometric predictors allow for smaller residual vector encoding, providing around 8 % bit-rate reduction. Additionally, the SKIP mode can also be extended to select automatically the SKIP mode's compensation vector and direction, from either a temporal or a new viewpoint Reference frame. The latter two techniques provide a joint bit-rate reduction of about 14 % for Low-latency MVC, and of about 13 % for Hierarchical bi-Prediction MVC, which is equivalent to an encoded inter-view quality improvement of about 0.6 dB. By using these two techniques together, a trade-off between a fast and an efficient encoding technique can be achieved. These improvements in coding time and efficiencies were obtained with a negligible to acceptably-small degradation in the decoded video quality, for both the texture and the depth map multi-view videos, while the rendering capability and quality of the compressed 3D videos are almost sustained. Hence, exploiting these improvements allows 3D video coding to adhere better to the stringent low-latency requirements needed for real-time and live broadcast scenarios, while making the encoded bit-stream more adequate for limited bandwidth channels. Description: PH.D. Tue, 01 Jan 2013 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/100877 2013-01-01T00:00:00Z