Hierarchical Quadrature Amplitude Modulation Research Articles

A low-complexity unequal error protection of H.264/AVC video using adaptive hierarchical QAM

In this paper, a low-complexity unequal error protection (UEP) of H.264/AVC coded video using adaptive hierarchical quadrature amplitude modulation (HQAM), which takes into consideration the non-uniformly distributed importance of intracoded frame (I-frame) and predictive coded frame (P-frame) is proposed. Simulation results show that in terms of average peak signal-to-noise ratio (average PSNR), our proposed (EEP) scheme outperforms the equal error protection (EEP) by up to 5 dB

H.264 Layered Coded Video over Wireless Networks: Channel Coding and Modulation Constraints

This paper considers the prioritised transmission of H.264 layered coded video over wireless channels. For appropriate protection of video data, methods such as prioritised forward error correction coding (FEC) or hierarchical quadrature amplitude modulation (HQAM) can be employed, but each imposes system constraints. FEC provides good protection but at the price of a high overhead and complexity. HQAM is less complex and does not introduce any overhead, but permits only fixed data ratios between the priority layers. Such constraints are analysed and practical solutions are proposed for layered transmission of data-partitioned and SNR-scalable coded video where combinations of HQAM and FEC are used to exploit the advantages of both coding methods. Simulation results show that the flexibility of SNR scalability and absence of picture drift imply that SNR scalability as modelled is superior to data partitioning in such applications.

Combined turbo coding and hierarchical QAM for unequal error protection of H.264 coded video

This paper investigates the unequal error protected (UEP) transmission of scalable H.264 bitstreams with two-priority layers, where differentiated turbo coding provides better protection for the high priority (HP) base layer than for the low priority (LP) enhancement layer. The drawback of such a method is the high overhead introduced by the channel coding, which results in a low source data rate for the HP layer, and hence lowers video quality. To overcome this problem, we introduce an efficient combination of turbo coding and hierarchical quadrature amplitude modulation (HQAM) to provide a high protection for the HP layer and at the same time maintaining the requisite channel coding redundancy. Simulation results show that, over a wide range of channel signal-to-noise ratio (SNR), our combined technique is superior to non-scalable transmission and outperforms UEP with turbo coding alone.

Prioritized transmission of data partitioned H.264 video with hierarchical QAM

In this letter, hierarchical quadrature amplitude modulation (HQAM) is used to provide unequal error protection (UEP) for layered (data partitioned) H.264 coded video. In a conventional HQAM system, the high-priority (HP) and low-priority (LP) capacities have a constant ratio, whereas in H.264 data partitioning, the corresponding parts do not necessarily have this constant ratio. This letter proposes a multilevel HQAM arrangement with adaptive constellation distances that provides a graceful degradation in the quality of the decoded video without requiring feedback from the receiver. The arrangement improves the quality relative to nonhierarchical transmission through poor signal-to-noise ratio (SNR) channels at the price of a modest quality reduction through good SNR channels.

A recursive algorithm for the exact BER computation of generalized hierarchical QAM constellations

Hierarchical constellations offer a different degree of protection to the transmitted messages according to their relative importance. As such, they find interesting application in digital video broadcasting systems as well as wireless multimedia services. Although a great deal of attention has been devoted in the literature to the study of the bit error rate (BER) performance of uniform quadrature amplitude modulation (QAM) constellations, very few results were published on the BER performance of hierarchical QAM constellations. We obtain exact and generic expressions in M for the BER of the generalized hierarchical M-PAM (pulse amplitude modulation) constellations over additive white Gaussian noise (AWGN) and fading channels. We also show how these expressions can be extended to generalized hierarchical M-QAM constellations (square and rectangular). For the AWGN case, these expressions are in the form of a weighted sum of complementary error functions and are solely dependent on the constellation size M, the carrier-to-noise ratio, and a constellation parameter which controls the relative message importance. Because of their generic nature, these new expressions readily allow numerical evaluation for various cases of practical interest.

BER computation of 4/M-QAM hierarchical constellations

Hierarchical constellations offer a different degree of protection to the transmitted messages according to their relative importance. As such they found interesting application in digital video broadcasting systems as well as wireless multimedia services. Although a great deal of attention has been devoted in the literature to the study of the bit error rate (BER) performance of uniform quadrature amplitude modulation (QAM) constellations, very few results were published on the BER performance of hierarchical QAM constellations. Indeed the only available expressions "leading-term" approximate BER expressions for 4/16-QAM and 4/64-QAM. We obtain exact and generic expressions in M for the BER of the 4/M-QAM (square and rectangular) constellations over additive white Gaussian noise (AWGN) and fading channels. For the AWGN case, these expressions are in the form of a weighted sum of complementary error functions and are solely dependent on the constellation size M, the carrier-to-noise ratio, and a constellation parameter which controls the relative message importance. Because of their generic nature, these new expressions readily allow numerical evaluation for various cases of practical interest. In particular numerical results show that the leading-term approximation gives significantly optimistic BER values at low carrier-to-noise ratio (CNR) in particular over Rayleigh fading channels but is quite accurate in the high CNR region.

Hierarchical QAM: a spectrally efficient dc-free modulation scheme

A new spectrally efficient, dc-free modulation scheme called hierarchical quadrature amplitude modulation is proposed. The use of HQAM in high-data-rate digital communication systems opens new possibilities for the practical realization of highly integrated receivers.

Robust mobile image transmission using hierarchical QAM

Abstract This paper proposes a robust hierarchical image transmission system based on the hierarchical quadrature amplitude modulation (QAM) scheme, which gives high-quality image transmission in a band-limited Rayleigh fading channel. Authors examine the selection of Bose–Chaundhuri–Hocquenghem (BCH) error correction codes for two-layer system, and clarified that it is effective to apply forward error correction (FEC) codec to only base significant layer to get higher system performance. By using BCH(63,45,3) code for significant layer, there is about 10 dB improvement of the robustness against channel CNR degradation, with slightly image quality degradation in higher channel CNR region. Authors also analyzed the optimum hierarchical parameter in the Rayleigh fading channel which maximizes the received image quality. Using optimized hierarchical modulation, there is another 2 dB improvement of the robustness against channel CNR degradation.