It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

Underwater wireless information transfer is of great interest to the military, industry, and the scientific community, as it plays an important role in tactical surveillance, pollution monitoring, oil control and maintenance, offshore explorations, climate change monitoring, and oceanography research. In order to facilitate all these activities, there is an increase in the number of unmanned vehicles or devices deployed underwater, which require high bandwidth and high capacity for information transfer underwater. Although tremendous progress has been made in the field of acoustic communication underwater, however, it is limited by bandwidth. All this has led to the proliferation of underwater optical wireless communication (UOWC), as it provides higher data rates than the traditional acoustic communication systems with significantly lower power consumption and simpler computational complexities for short-range wireless links. UOWC has many potential applications ranging from deep oceans to coastal waters. However, the biggest challenge for underwater wireless communication originates from the fundamental characteristics of ocean or sea water; addressing these challenges requires a thorough understanding of complex physio-chemical biological systems. In this paper, the main focus is to understand the feasibility and the reliability of high data rate underwater optical links due to various propagation phenomena that impact the performance of the system. This paper provides an exhaustive overview of recent advances in UOWC. Channel characterization, modulation schemes, coding techniques, and various sources of noise which are specific to UOWC are discussed. This paper not only provides exhaustive research in underwater optical communication but also aims to provide the development of new ideas that would help in the growth of future underwater communication. A hybrid approach to an acousto-optic communication system is presented that complements the existing acoustic system, resulting in high data rates, low latency, and an energy-efficient system.

Underwater Optical Wireless Communication

This chapter contains sections titled: Introduction Overview of Multicarrier CDMA Systems Channel Model Performance of MC-CDMA System Performance of Overlapping Multicarrier DS-CDMA Systems Performance of Multicarrier DS-CDMA-I Systems Performance of AMC DS-CDMA Systems Performance of SFH/MC DS-CDMA Systems Chapter Summary and Conclusion 
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Overview of Multicarrier CDMA

We consider the problem of estimating sparse communication channels in the MIMO context. In small to medium bandwidth communications, as in the current standards for OFDM and CDMA communication systems (with bandwidth up to 20 MHz), such channels are individually sparse and at the same time share a common support set. Since the underlying physical channels are inherently continuous-time, we propose a parametric sparse estimation technique based on finite rate of innovation (FRI) principles. Parametric estimation is especially relevant to MIMO communications as it allows for a robust estimation and concise description of the channels. The core of the algorithm is a generalization of conventional spectral estimation methods to multiple input signals with common support. We show the application of our technique for channel estimation in OFDM (uniformly/contiguous DFT pilots) and CDMA downlink (Walsh-Hadamard coded schemes). In the presence of additive white Gaussian noise, theoretical lower bounds on the estimation of sparse common support (SCS) channel parameters in Rayleigh fading conditions are derived. Finally, an analytical spatial channel model is derived, and simulations on this model in the OFDM setting show the symbol error rate (SER) is reduced by a factor 2 (0 dB of SNR) to 5 (high SNR) compared to standard non-parametric methods - e.g. lowpass interpolation.

Estimation of Sparse MIMO Channels with Common Support

/pdf/ad-hoc-networks-technologies-and-protocols-mahkhtf0hu.pdf

Ad Hoc Networks: Technologies and Protocols

In \cite{Chandar2008}, Chandar et al studied a problem of sequential frame
synchronization for a frame transmitted randomly and Uniformly in an interval
of size $A$ slots. For a discrete memory-less channel, they showed that the
frame length $N$ must scale as $e^{\alpha(Q) N} > A$ for the frame detection
error to go to zero (asymptotically with $A$). $\alpha(Q)$ is defined as the
synchronization threshold for the discrete memory-less channel and depends on
the channel transition probabilities $Q$. In our paper, we study the sequential
frame synchronization problem for a fading channel and additive noise and seek
to characterize the effect of fading. For a discrete ON-OFF fading channel
(with ON probability $p$) and additive noise (with channel transition
probabilities $Q_n$), we characterise the synchronisation threshold of the
composite channel $\alpha(Q)$ and show that $\alpha(Q) \leq \alpha(Q_n) \times
p$. We then characterize the synchronization threshold for Rayleigh fading and
AWGN channel as a function of the fading and noise parameters. The asynchronous
communication framework permits a trade-off between sync frame length, $N$, and
channel, $Q$, to support asynchronism. This allows us to characterize the
synchronization threshold with sync frame energy for the wireless channel.

Optimal Sequential Frame Synchronization for Fading Channel

Video caching provides an effective solution to the problem of increasing power consumption due to Internet infrastructure. The present work is the extension of [1] where we provided an approximate solution for optimal caching size. In this paper, we classify videos in N sets based on estimated arrival rate and analyze the power consumption of the video service. We analytically obtain the value of threshold for arrival rate to decide which videos to cache. We derive lower and upper bounds for caching size and show that the optimal caching size lies between these bounds. Further, we obtain a condition for the existence of lower and upper bounds. We perform simulations to analyze the performance of these bounds with optimal caching size.

Energy optimized caching decision and size for IP-TV services based on estimated arrival rate

The Diversity Multiplexing Tradeoff (DMT) (1) is a compact, yet elegant framework to capture the performance of wireless communication systems at asymptotically high signal to noise ratios (SNR). Recent application of DMT at finite SNR (2) makes the DMT a versatile framework. We have analyzed the DMT for the rate-adaptive SIMO maximal-ratio combining (SIMO-MRC) for asymptotic and non-asymptotic signal to noise ratios. This has resulted in arriving at closed form expression of the diversity gain. The DMT arrived by analysis using the non-asymptotic finite SNR framework is found to be consistent with the known interpretations arrived through the asymptotic high-SNR framework (1). The results of this analysis have been presented in this paper.

http://www.ncc.org.in/download.php?f=NCC2009/file7.pdf

Diversity Multiplexing Tradeoff of SIMO Maximal-Ratio Combining Scheme

In many reconstruction problems decision making is the primary goal Signal detection theory is applied to the problem of processing of finite noisy projections The problem is formulated as a two hypotheses problem Optimal processors based on the likelihood ratio approach are presented for two cases- (i) direct processing of the projection data and (ii) processing of the reconstructed image from convolution backpre jection (CBP) followed by optimal decision making Results for a simple imaging scenario are presented in the form of receiver operating characteristic (ROC) curves to show how direct optimal processing yields a considerable gain in the decision-making performance over that obtained when first using image reconstruction Results for the second case can be interpreted as providing an upper bound on the decisionperformance of all postprocessing algorithms that use CBP

Optimal Detection Theory And Image Reconstruction- Comparison Of Performance In The Presence Of Noise

In \cite{Chandar2008}, Chandar et al studied a problem of sequential frame synchronization for a frame transmitted randomly and uniformly among $A$ slots. For a discrete memory-less channel (DMC), they showed that the frame length $N$ must scale as $e^{\alpha(Q)N}>A$ for the frame detection error to go to zero asymptotically with $A$. $\alpha(Q)$ is the synchronization threshold and $Q$ is channel transition probability. We study the sequential frame synchronisation problem for a fading channel and additive noise and seek to characterise the effect of fading. For a discrete ON-OFF fading channel (with ON probability $p$) and additive noise (with channel transition probabilities $Q_n$), we characterise the synchronisation threshold of the composite channel $\alpha(Q)$ and show that $\alpha(Q)\leq p\,\alpha(Q_n)$. We then characterize the synchronization threshold for Rayleigh fading and AWGN channel as a function of channel parameters. The asynchronous framework permits a trade-off between sync frame length, $N$, and channel, $Q$, to support asynchronism. This allows us to characterize the synchronization threshold with sync frame energy instead of sync frame length.

Devendra Jalihal

Papers

Optimal Sequential Frame Synchronization for Fading Channel

Energy optimized caching decision and size for IP-TV services based on estimated arrival rate

Diversity Multiplexing Tradeoff of SIMO Maximal-Ratio Combining Scheme

Optimal Detection Theory And Image Reconstruction- Comparison Of Performance In The Presence Of Noise

Asynchronous Communication over a Fading Channel and Additive Noise.