| 1. |
- Bayley, Todd, et al.
(författare)
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Call Quality Monitoring for VoIP
- 2011
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Konferensbidrag (refereegranskat)abstract
- A method of monitoring the speech quality of a Voice-over-IP call is described in this paper. This method is attractive because it employs the ITU-T standard P.862 for Perceptual Evaluation of Speech Quality which is well-known for its accuracy. In addition, with the proposed method, call quality is monitored without interfering with the call while it is in progress. The results corresponding to an implementation of this method shows call quality can be measured with excellent accuracy under typical network delays.
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| 2. |
- Engelke, Ulrich, et al.
(författare)
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Reduced-reference metric design for objective perceptual quality assessment in wireless imaging
- 2009
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Ingår i: Signal Processing-Image Communication. - : ELSEVIER. - 0923-5965. ; 24:7, s. 525-547
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Tidskriftsartikel (refereegranskat)abstract
- The rapid growth of third and development of future generation mobile systems has led to an increase in the demand for image and video services. However, the hostile nature of the wireless channel makes the deployment of such services much more challenging, as in the case of a wireline system. In this context, the importance of taking care of user satisfaction with service provisioning as a whole has been recognized. The related user-oriented quality concepts cover end-to-end quality of service and subjective factors such as experiences with the service. To monitor quality and adapt system resources, performance indicators that represent service integrity have to be selected and related to objective measures that correlate well with the quality as perceived by humans. Such objective perceptual quality metrics can then be utilized to optimize quality perception associated with applications in technical systems. In this paper, we focus on the design of reduced-reference objective perceptual image quality metrics for use in wireless imaging. Specifically, the Normalized Hybrid Image Quality Metric (NHIQM) and a perceptual relevance weighted L_p-norm are designed. The main idea behind both feature-based metrics relates to the fact that the human visual system (HVS) is trained to extract structural information from the viewing area. Accordingly, NHIQM and L_p-norm are designed to account for different structural artifacts that have been observed in our distortion model of a wireless link. The extent by which individual artifacts are present in a given image is obtained by measuring related image features. The overall quality measure is then computed as a weighting sum of the features with the respective perceptual relevance weight obtained from subjective experiments. The proposed metrics differ mainly in the pooling of the features and amount of reduced-reference produced. While NHIQM performs the pooling at the transmitter of the system to produce a single value as reduced-reference, the L_p-norm requires all involved feature values from the transmitted and received image to perform the pooling on the feature differences at the receiver. In addition, non-linear mapping functions are developed that relate the metric values to predicted mean opinion scores (MOS) and account for saturations in the HVS. The evaluation of prediction performance of NHIQM and the L_p-norm reveals their excellent correlation with human perception in terms of accuracy, monotonicity, and consistency. This holds not only for the prediction performance on images taken for the training of the metrics but also for the generalization to unknown images. In addition, it is shown that the NHIQM approach and the perceptual relevance weighted L_p-norm outperform other prominent objective quality metrics in prediction performance.
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| 3. |
- Griffiths, Wayne, et al.
(författare)
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APP Decoding of Binary Linear Block Codes on Gilbert-Elliott Channels
- 2005
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Konferensbidrag (refereegranskat)abstract
- In this paper, a mathematical framework for APP decoding of binary linear block codes on the Gilbert-Elliott channel (GEC) is developed. For this purpose, the theory of group representations and finite state machines are combined for deriving a `dual APP' algorithm for the GEC. The presented approach belongs to the class of single-sweep algorithms. As such, complexity benefits of the dual approaches are preserved while additional storage savings are obtained over other single-sweep algorithms. The presented APP decoding technique also takes account of the increasing demand for efficient utilization of bandwidth making higher rate codes more desirable.
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| 4. |
- Griffiths, Wayne, et al.
(författare)
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APP Decoding of Block Codes Over Gilbert-Elliott Channels Using Generalized Weight Polynomials
- 2006
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Konferensbidrag (refereegranskat)abstract
- We present an a posteriori probability (APP) decoding algorithm for binary linear block codes over a Gilbert- Elliott channel (GEC) using generalized weight polynomials. The proposed approach is based on a single-sweep APP decoding technique that uses matrix multiplications. By fixing the crossover probability in the ‘bad’ state of the GEC at fifty percent, an APP decoding decision can be reached by evaluating trivariate polynomials without the need for the computationally more expensive matrix multiplications. In this case, the GEC is described by three variables, namely, the average fade to average connection time ratio, the burst factor, and the channel reliability factor. These variables can easily be deduced from error sequence measurements and hence can be related to many practical digital communication scenarios. The polynomial approach is demonstrated using a simple example and results of computer simulations are presented.
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| 5. |
- Griffiths, Wayne, et al.
(författare)
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APP Decoding of Block Codes Over Prime Fields on Non-Binary Gilbert-Elliott Channels
- 2008
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Konferensbidrag (refereegranskat)abstract
- We present an a-posteriori probability (APP) decoding algorithm for linear block codes over prime fields when used on non-binary Gilbert-Elliott channels (GECs). The proposed approach is based on a single-sweep APP decoding technique that uses matrix multiplications. The trellis-based decoding algorithm incorporates the channel-induced error process by modeling it as a stochastic automaton. It is applicable to high rate block codes over prime fields on channels with memory such as the non-binary GEC. It allows simple implementation in the spectral domain.
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| 6. |
- Griffiths, Wayne, et al.
(författare)
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APP Decoding of Non-Binary Block Codes on Gilbert-Elliott Channels Using Generalized Weight Polynomials
- 2008
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present an a-posteriori probability (APP) decoding algorithm for non-binary block codes on non-binary Gilbert-Elliott channels (GECs) using generalized weight polynomials. The proposed approach is based on a single-sweep APP decoding technique that utilizes matrix multiplications. By fixing the crossover probability in the `bad' state of the non-binary GEC such that for a given transmitted symbol, all symbols are equally likely to be received, an APP decoding decision can efficiently be reached by evaluating trivariate polynomials. In this case, the non-binary GEC is described by three variables that are referred to as the average fade to connection time ratio, the burst factor, and the channel reliability factor. The application of the generalized weight polynomial approach is demonstrated with respect to numerical performance results obtained for simple non-binary block codes from computer simulations.
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| 7. |
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| 8. |
- Holland, Ian, et al.
(författare)
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Performance of an Adaptive QAM Scheme over Correlated Rayleigh Fading with Non-zero Delay
- 2004
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Konferensbidrag (refereegranskat)abstract
- Link adaptation techniques have recently been proposed as a spectrally efficient method of obtaining high quality service for mobile communication systems. These schemes aim to better utilise channel capacity compared to fixed transmission schemes, by adapting signal transmission parameters, such as modulation constellation and transmit power. Adaptive modulation schemes, which adapt the modulation constellation, have gained considerable favour for exploiting time-varying channel conditions without increasing the level of co-channel interference. However, the traditional adaptive modulation schemes are designed assuming zero delay between the channel estimation and the modulation mode adaptation. In the case of non-zero delay, the transmitter would update the modulation mode based on outdated channel state information from the receiver. In this paper, we investigate an adaptive quadrature amplitude modulation (AQAM) scheme, which by way of retransmissions, allows a targeted reliability level to be met even in the presence of non-zero delay. The effect of non-zero delay on performance is then investigated. Closed form expressions for the average number of bits per symbol (BPS) throughput and the average bit error rate (BER) of the proposed scheme are derived.
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| 9. |
- Holland, Ian, et al.
(författare)
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Soft Combining for Hybrid ARQ
- 2005
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Ingår i: Electronics Letters. - : IEE. - 0013-5194. ; 41:22, s. 1230-1231
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Tidskriftsartikel (refereegranskat)abstract
- A soft combining approach utilising symbol-by-symbol maximum a posteriori probability decoding is proposed for hybrid automatic repeat request schemes. In comparison to an existing soft combining approach, significant reductions in post-decoding bit error rate can be obtained without sacrificing the throughput efficiency. This is achieved with the proposed method by accumulating the signal-to-noise ratio at the channel output on each additional retransmission, for use in calculating extrinsic log-likelihood ratios on subsequent decoding attempts.
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| 10. |
- Kusuma, Tubagus Maulana, et al.
(författare)
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On the Development of a Reduced-Reference Perceptual Image Quality Metric
- 2005
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Konferensbidrag (refereegranskat)abstract
- User-oriented image quality assessment has be- come a key factor in wireless multimedia commu- nications. In particular, perceptual quality assess- ment methods are required to measure the overall perceived service quality based on the grading given by human subjects. This paper focuses on the de- velopment of a reduced-reference perceptual image quality metric, which can be applied for in-service quality monitoring and link adaptation purposes. In contrast to the conventional image ¯delity metrics such as the peak signal-to-noise ratio (PSNR), the proposed hybrid image quality metric (HIQM) takes the human perception into account. In addition, HIQM does not rely on the availability of the full reference of the original image at the receiver.
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