On the Asymptotic Performance of Bit-Wise Decoders for Coded Modulation

Two decoder structures for coded modulation over the Gaussian and flat fading channels are studied: the maximum likelihood symbol-wise decoder, and the (suboptimal) bit-wise decoder based on the bit-interleaved coded modulation paradigm. We consider a 16-ary quadrature amplitude constellation labeled by a Gray labeling. It is shown that the asymptotic loss in terms of pairwise error probability, for any two codewords caused by the bit-wise decoder, is bounded by 1.25 dB. The analysis also shows that for the Gaussian channel the asymptotic loss is zero for a wide range of linear codes, including all rate-1/2 convolutional codes

General BER Expression for One-Dimensional Constellations

A novel general ready-to-use bit-error rate (BER) expression for one-dimensional constellations is developed. The BER analysis is performed for bit patterns that form a labeling. The number of patterns for equally spaced M-PAM constellations with different BER is analyzed.Comment: To appear in the Proceedings of the IEEE Global Communications Conference (GLOBECOM) 2012. Remark 3 modifie

On the Exact BER of Bit-Wise Demodulators for One-Dimensional Constellations

The optimal bit-wise demodulator for M-ary pulse amplitude modulation (PAM) over the additive white Gaussian noise channel is analyzed in terms of uncoded bit-error rate (BER). New closed-form BER expressions for 4-PAM with any labeling are developed. Moreover, closed-form BER expressions for 11 out of 23 possible bit patterns for 8-PAM are presented, which enable us to obtain the BER for 8-PAM with some of the most popular labelings, including the binary reflected Gray code and the natural binary code. Numerical results show that, regardless of the labeling, there is no difference between the optimal demodulator and the symbol-wise demodulator for any BER of practical interest (below 0.1)

On the Information Loss of the Max-Log Approximation in BICM Systems

We present a comprehensive study of the information rate loss of the max-log approximation for $M$-ary pulse-amplitude modulation (PAM) in a bit-interleaved coded modulation (BICM) system. It is widely assumed that the calculation of L-values using the max-log approximation leads to an information loss. We prove that this assumption is correct for all $M$-PAM constellations and labelings with the exception of a symmetric 4-PAM constellation labeled with a Gray code. We also show that for max-log L-values, the BICM generalized mutual information (GMI), which is an achievable rate for a standard BICM decoder, is too pessimistic. In particular, it is proved that the so-called "harmonized" GMI, which can be seen as the sum of bit-level GMIs, is achievable without any modifications to the decoder. We then study how bit-level channel symmetrization and mixing affect the mutual information (MI) and the GMI for max-log L-values. Our results show that these operations, which are often used when analyzing BICM systems, preserve the GMI. However, this is not necessarily the case when the MI is considered. Necessary and sufficient conditions under which these operations preserve the MI are provided

Website Design and Mobility: Culture, Gender, and Age Comparisons

Anytime/anywhere services offered through mobile commerce hold great potential to serve customers in wireless environments. However, there is limited understanding of how to best tailor mobile interaction and design for individual differences. This paper seeks to explore the influence of individual differences (namely culture, gender and age) on the design (namely information design, navigation design and visual design) and satisfaction of mobile devices. Sixty subjects who differ on cultural, gender and age dimensions were tested in a controlled laboratory experiment on a mobile product, an Internet enabled phone. The results of this exploratory analysis were inconclusive in terms of cultural and gender differences, but significant differences were found between older and younger subject groups. Consistent with findings in the stationary Internet domain, design elements were found to impact satisfaction with mobile services. Implications and limitations of this research are presented, emphasizing the importance of additional investigations

Perceived Interactivity Leading to E-Loyalty: An Empirical Investigation of Web-Poll Design

With the growth of e-commerce, novel applications of website interactivity are important to attract and retain online users. In this empirical study five levels of interactivity are examined using different web-poll applications. A model is created to validate the relationship of perceived interactivity to efficiency, effectiveness, enjoyment, and trust of the website. Further, specific elements of interactivity including control and user connectedness are examined for their relationship to trust. In turn, efficiency, effectiveness, enjoyment and trust are tested for their impact on e-loyalty. All relationships in the model are supported. In addition, qualitative comments from users regarding the various web-poll treatments were analyzed with subtle differences detected between treatments. The research advances knowledge on the consequences of perceived interactivity. It has additional merit in that the treatments employed and their outcomes will be of interest to web designers and online marketers for how to enhance interactive online web applications

Coherently coupled photonic-crystal surface-emitting laser array

The realization of a 1 × 2 coherently coupled photonic crystal surface emitting laser array is reported. New routes to power scaling are discussed and the electronic control of coherence is demonstrated