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

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Ad Hoc Networks: Technologies and Protocols

The enhancements in Internet technology and mobile access technology over the last decade, can be leveraged effectively to build Wireless in Local Loop (WiLL) systems, which can enable rapid expansion of telecom and Internet access in developing countries. However, the design of a WiLL system requires one to understand some fundamentals concerning the Access Network and its connectivity to backbone network as well as the traffic requirement for a voice and Internet connection. The requirements of WiLL, in contrast to that of a Mobile cellular system need to be clearly understood. Equally important is the concern for capacity and spectral efficiency, especially as higher bit-rate Internet systems become a must for developing countries to get a fair share of the economic advantages that telecom technologies provide. This paper looks at these fundamental issues in context of GSM, IS-95 and DECT Technologies. This paper further takes a brief look at some recent technological developments, which are likely to ...

Wireless in Local Loop—Some Fundamentals

Design of robust test statistics which mitigate the channel and noise uncertainties are the essential requirement of detection applications. Covariance absolute value (CAV) detection is one of the non-parametric detection methods which claims robustness [1]. Achieving the theoretical probability of detection performance depends on the accuracy in calculating the thresholding parameter, which in turn depends on the distribution of the test statistic under the null hypothesis. Since the exact analysis of distribution is cumbersome, approximation techniques are used. We present approximation techniques which achieve performance very close to the one obtained from exact distribution of the test statistic (using Monte-Carlo simulation). Further, an equivalent test statistic compared to CAV is proposed which uses the Bartlett decomposition of the sample covariance matrix and its performance is compared with CAV. The robustness of the proposed test statistic is verified for the noise uncertainty model assumed [2].

Almost exact threshold calculations for covariance absolute value detection algorithm

Linear dispersion codes (LDC) designed for multiple input multiple output (MIMO) wireless systems are examples of space-time codes which try to maximize the mutual information between the transmitter and receiver. However, such codes are typically designed for flat fading channels. It is possible to extend LDC designs for frequency selective fading channels using orthogonal frequency division multiplexing (OFDM). Additionally, the multipath diversity available as frequency diversity could be potentially exploited by properly designed space-frequency LDC codes for MIMO-OFDM systems. In this paper, the design criteria to obtain such space-frequency LDC along with the error-rate performance of such codes in frequency selective fading channels are provided.

Exploiting multipath diversity using space-frequency linear dispersion codes in MIMO-OFDM systems

The advent of location based services has increased the need for accurate positioning of mobile stations (MS). Global Positioning Systems (GPS) is not reliable in indoor and urban environments. Cellular wireless communication systems like the OFDM based 3GPP-LTE provide an alternative via Time Difference of Arrival (TDoA) measurements. Typical Extended Kalman Filter (EKF) algorithms using TDoA make certain assumptions about the mobility model and associated noise statistics of the MS. In this paper, we develop an alternate formulation of the TDoA localization problem and adaptive EKF algorithm that does not make the assumptions made by traditional EKF algorithms. We demonstrate that the proposed algorithm gives better position estimates than a static positioning estimator.

TDoA based EKF localization for LTE

Cochannel interference affects not only the signal quality, but also the capacity of most wireless cellular networks. Unlike in spread spectrum communications, in systems employing nonspread signals, cochannel signal suppression is expensive. Moreover, at the portable station, joint estimation rather than suppression of the cochannel signal(s) may be a cheaper alternative and may often-times also provide a better signal quality. In this work we propose a novel two-stage joint Viterbi algorithm with full feedback. This technique, which is sub-optimal to the ideal joint maximum likelihood sequence estimator, provides an excellent way to trade complexity for performance, and is amenable for single-input mobile and hand-held receiver implementations.

Devendra Jalihal

Papers

Wireless in Local Loop—Some Fundamentals

Almost exact threshold calculations for covariance absolute value detection algorithm

Exploiting multipath diversity using space-frequency linear dispersion codes in MIMO-OFDM systems

TDoA based EKF localization for LTE

Near-optimal low complexity joint estimation of cochannel ISI signals for mobile receivers