Search

In this paper, a novel demapper for 2-D non-uniform constellations (2D-NUCs) is proposed, exploiting the characteristics of these constellations. It represents the combination of two underlying demapping techniques targeting the ATSC 3.0 compliant OFDM transceiver. On the one hand, for low code rates, we define a metric to perform condensed demapping. On the other hand, for high code rates, adaptive sub-region demapping is proposed. In this paper, a combination of both demapping methods is designed showing comparable performance to the classical ML demapper. The gap does not exceed 0.1 dB for all code rates of the ATSC 3.0 standard. Higher complexity reduction, from 79.2% to 95.4%, than state of art 2D-NUC demappers is obtained for 2D-256NUCs. These results are validated for ideal and non-ideal channel state information over additive white noise Gaussian and Rayleigh independently and identically distributed channels. Results are extended to 2D-1kNUCs and 2D-4kNUCs showing demapping complexity reduction from 96% to 99.7% with a negligible impact on performance. [ABSTRACT FROM AUTHOR]

This paper presents a modified partial transmit sequence (PTS) algorithm for peak-to-average power ratio (PAPR) reduction of M-QAM orthogonal frequency division multiplexing (OFDM) signals by partitioning an OFDM block into non-disjoint OFDM sub-blocks. Since an M-QAM constellation can be written as sum of several QPSK constellations, we can then apply different disjoint partitions on the QPSK OFDM blocks, which result in an equivalent non-disjoint partition on the M-QAM OFDM block. Compared to a disjoint sub-block partition in conventional PTS, simulation results show that the modified PTS with a non-disjoint partition achieves better PAPR reduction in adjacent, interleaved, and random partitioning schemes. [ABSTRACT FROM PUBLISHER]

In this paper, spatial modulation (SM) is introduced to layered division multiplexing (LDM) systems for enlarging the spectral efficiency (SE) over broadcasting transmission. First, the SM aided LDM (SM-LDM) system is proposed, in which different layered services utilize SM for terrestrial broadcasting transmission with different power levels. Then a SE analysis framework for SM-LDM systems is proposed, which is suitable for the SM-LDM systems with linear combining. Moreover, the closed-form SE lower bound of SM-LDM systems with maximum ratio combining (MRC) is derived, which is based on this framework. Since the theoretical SE analysis of single transmit antenna (TA) LDM systems with MRC and spatial multiplexing (SMX) aided LDM systems with MRC lacks a closed-form expression, the closed-form SE is also derived for these systems. Monte Carlo simulations are provided to verify the tightness of our proposed SE lower bound. Furthermore, it can be shown via simulations that our proposed SM-LDM systems always have a better SE performance than single-TA LDM systems, which can even outperform the SE of SMX aided LDM (SMX-LDM) systems. [ABSTRACT FROM AUTHOR]

The paper presents an admission approach for IPTV service providers that is designed to minimize QoS violations whilst effectively utilizing available bandwidth. Central to the approach is an empirical method of estimating the effective bandwidth required to satisfy QoS targets for admitted traffic flows. The paper describes this method and specifies two admission control algorithms based on the use of effective bandwidth estimates. The first algorithm employs a simple evaluation of whether there is sufficient bandwidth available to ensure, with an appropriate degree of confidence, that QoS targets will not be violated if a requested flow is admitted. The second algorithm utilizes information relating to the cost, duration and request frequency of specific IPTV content to prioritize higher revenue flows within the admission control process. Results of a simulation study (employing real traffic traces of long-lived flows) indicate that the proposed algorithms ensure that an adequate, but not overly generous, amount of bandwidth is allocated to ensure that QoS targets for accepted flows are met. Furthermore, they demonstrate the potential advantage of using content specific information in the admission control process to maximize generated revenue. [ABSTRACT FROM AUTHOR]

Although patching has shown to be a simple and efficient technique for immediate media on-demand delivery, there is still much scope for further improvement compared with the lower bound of the server network-I/O bandwidth requirement. In this paper, a new technique of two-level patching scheme is proposed for the first time, in which patching channels are rearranged through merging and further patching. Simulation results show that the proposed two-level patching scheme outperforms the conventional patching technique by a significant margin. It even performs better than the dynamic skyscraper algorithm over a wide range of client request rates. Furthermore, it is reasonably competitive with hierarchical multicast stream merging (HMSM) at low to modest client request rates. Most importantly, the implementation complexity of our algorithm is much lower than the skyscraper and HMSM. [ABSTRACT FROM AUTHOR]

Spectral efficiency improvement is essential for mobile systems development in the light of growing demand for high data transmission rate. The Time-domain synchronous OFDM transmission system increases bandwidth utilization by time-domain channel estimation without any support from frequency-domain pilot signals. Channel identification methods use a training sequence, added at the beginning of every OFDM symbol. Sparse nature of the channel impulse response, which manifests itself during wireless broadband transmission, enables one to implement compressed sensing techniques for channel identification. Channel sparsity reduces the number of measurement samples required in channel reconstruction procedure, but they should be taken from the inter-block interference (IBI) free part of the received training sequence. If maximum delay spread of the channel is comparable with the length of the training sequence, the number of measurements within the IBI-free region may be insufficient for accurate channel identification. This paper discusses a new iterative approach to sparse channels estimation, which uses the measurements from outside the IBI-free region. The proposed solution is examined for simulated transmission over randomly generated doubly-selective channels when compared with the conventional CS technique and perfect channel state information condition. The experiments reveal an enhancement of the transmission quality in terms of SER for slow-time selective channels when both delays and gains of the channel impulse response are estimated with the orthogonal matching pursuit algorithm. Further improvement, also for transmission over moderate varying channels, is observed when the path delays are found in advance. A suitable frame structure is proposed to do so. [ABSTRACT FROM PUBLISHER]

The DVB standard does not mandate the use of authentication and integrity protection for transport streams. This allows malicious third parties to replace legitimate broadcasts by overpowering terrestrial transmissions. The rogue signal can then deliver a malicious broadcast stream to exploit security vulnerabilities on Smart TVs (STVs) in range. We implemented a proof-of-concept attack based on a malicious Hybrid Broadcast Broadband TV app, able to acquire permanent system-level access to an STV over the air, in less than 10 s. These attacks, however, are severely limited in range due to required co-channel protection ratios (CCPRs), which is in direct contradiction to previous publications. We present evidence for these limitations in form of laboratory experiments, extensive simulations, and field measurements. To this end, we developed an automated, low-cost method for CCPR determination, as well as a method for non-disruptive attack range measurements based on a gap filler and the resulting channel impulse response. [ABSTRACT FROM PUBLISHER]

Video transmission over unreliable channels may suffer from the data loss or corruption. To facilitate the transmission, video content is compressed to save the bandwidth. The compression algorithms remove the redundancies in the video signal, meanwhile increasing the dependencies among symbols in the compressed bit-stream. Thus, when errors occur, they may propagate in both space and time. Among various error control techniques, error concealment (EC) is an effective method that is performed at the decoder to mitigate the influence of errors on the quality of reconstructed images. In this paper, a joint spatial and temporal EC algorithm (JSTEC) is presented. First, several existing temporal EC algorithms are combined in an appropriate order. Then, the spatial correlation in the video is exploited in an iterative form to improve the performance of the temporal EC. Experimental results show that JSTEC performs better both in peak signal-to-noise ratio and subjective quality of images than the existing algorithms. [ABSTRACT FROM AUTHOR]

It is well known that HPAs (High Power Amplifiers) are inherently nonlinear devices and many researches have focused on the predistortion for memoryless HPAs. However, memory effects of HPAs can no longer be ignored when communication systems have wider bandwidth. Memoryless predistortion techniques proposed previously seldom have satisfactory effectiveness for typical wideband applications such as OFDM (Orthogonal Frequency Division Multiplexing) systems. In this paper, an improved adaptive predistortion method called 2D LUT (2-dimension look-up table) with different accuracy levels is presented to linearize HPAs with memory effects. Simulation and experimental results show that 2D LUT implements excellent performance in mitigating the signal deterioration caused by memory effects, both rectifies the signal constellation distortion and suppresses the spectrum emission. Large scale matrix computation is also avoidable in these adaptive algorithms, which makes them feasible when a real-time system is necessary. [ABSTRACT FROM AUTHOR]

Transmit diversity can be applied to OFDM systems by adopting space time code. Since the received signal is the overlapped signals transmitted from different transmit antennas, channel estimation is a rather challenging task for space time coded OFDM (ST-OFDM) systems. Pilot structure can help the receiver to effectively separate the overlapped signals and perform accurate channel estimation. In this paper, we propose three different channel estimation algorithms based on specially designed comb type pilots inserted in frequency domain. One of our proposed algorithms is performed in frequency domain and the other two are performed in time domain. Such comb type pilot based algorithms can provide higher bandwidth efficiency than common significant-tap-catching algorithm using training block pilots. Numerical analyzes and computational simulation show that our proposed estimation schemes have the same good performance while the time domain methods have relatively simple structure. [ABSTRACT FROM AUTHOR]

In this paper, an arbitrary frame rate transcoding joint considering temporal and spatial complexity of frames in the adaptive length sliding window is proposed. The length of a sliding window can be adjusted according to bandwidth variation in order to decide the number of skipped frames. The proposed method preserves significant frames and drops non-significant ones using the complexity measurements. Moreover, the motion vector composition algorithm is proposed to reduce the computations of motion estimation process by adopting the coding feature of variable block sizes in H.264/AVC video transcoder. Experimental results show that the proposed method achieves higher visual quality compared to other existing methods. After combining with the proposed fast motion composition algorithm, our proposed algorithm reduces encoding time significantly with slight visual quality degradation. [ABSTRACT FROM AUTHOR]

Quality Oriented Adaptation Scheme (QOAS) is compared against other adaptive schemes such as TCP Friendly Rate Control Protocol (TFRCP), Loss-Delay-based Adaptation Algorithm (LDA+), and a nonadaptive (NoAd) solution when streaming multiple multimedia clips with various characteristics over broadband networks. Streaming efficiency is assessed in terms of loss rate, bandwidth utilization, number of concurrent clients and end-user perceived quality. Simulation results show that using QOAS a significantly higher number of simultaneous clients can be served than when using the other schemes given a target average end-user quality. This is while having higher bandwidth utilization. Testing results also indicate that higher performance is achieved when streaming to the same number of clients using QOAS than when other solutions are used. [ABSTRACT FROM AUTHOR]

One of the primary objectives for media-on-demand systems is the reduction of bandwidth requirements. In this article we show a way how some bandwidth can be saved at the beginning of a media stream transmission. This saving is accomplished by omitting segments at their first transmission if the second transmission is in due time. To increase the number of omissions we propose an algorithm which optimizes the transmission schedule for this aim without modifying its maximum bandwidth requirement. [ABSTRACT FROM AUTHOR]

Describes an algorithm which was used to assign upstream bandwidth of hybrid fiber-coax (HFC) networks. Bases of the algorithm; Development of techniques of bidirectional communication in HFC networks; Implementation of simple algorithm of assigning bandwidth.