Cooperative schemes for path establishment in mobile ad-hoc networks under shadow-fading

The performance of routing protocols for multi-hop path-establishment in Mobile Ad-hoc NETworks (MANET) is examined when the individual radio links undergo shadow fading of parameterized severity. Such propagation modeling is typical of ground-level networking along with node mobility. The metrics of main interest are the probability of having a reliable multi-hop path plus the temporal statistics of such availability under a Markovian model. Such availability is an indicator for the suitability of the network to carry delay-sensitive applications (push-to-talk voice, streaming video) in uninterrupted manner. It is shown that high levels of diversity are necessary in such adverse environments, as obtained either by multiple independent paths or via concurrent cooperative transmission. Analytical and simulation comparisons of typical routing options are presented on the above metrics, plus on the required nodal engagement for supporting such diversity.     

Hop-timing estimation for FH signals using a coarsely channelizedreceiver

This paper addresses new hop-timing (epoch) estimation schemes which employ a coarsely channelized preprocessor in order to suppress the frequency and phase dependence in random frequency-hopping (FH) signals. Coarse channelization implies a bank of filters, covering the total spread bandwidth of the FH signal, whose number is much smaller than the size of the candidate hop frequency set. Linear and nonlinear combinations of preprocessor outputs are explored and compared. It is found that post-processing, rather than the size of the filter bank alone, is the determining factor on estimation performance. Performance evaluation is presented via both extensive computer simulations and analytical lower bounds. Comparisons with existing optimal and suboptimal systems are also provided     

A Unified Approach to Serial Search Spread-Spectrum Code Acquisition--Part I: General Theory

The purpose of this two-part paper is threefold: 1) Part I discusses the code-acquistion problem in some depth and 2) also provides a general extension to the approach of analyzing serial-search acquisition techniques via transform-domain flow graphs; 3) Part II illustrates the applicability of the proposed theoretical framework by evaluating a matchedfilter (fast-decision rate) noncoherent acquisition receiver as an example. The theory is formulated in a general manner which allows for significant freedom in the receiver modeling. The statistics of the acquisition time for the single-dwell [2], [3] andN-dwell [5] systems are shown to be special cases of this unified approach.     

A Unified Approach to Serial Search Spread-Spectrum Code Acquisition--Part II: A Matched-Filter Receiver

The unified theory developed in Part I [1] is employed here in the analysis of a noncoherent, matched-filter (fast-decision-rate) code acquisition receiver in a direct-sequence spread-spectrum system. The results illustrate the dynamic dependence of the mean acquisition time on system parameters, such as the predetection signal-to-noise ratio (SNR), the decision threshold settings, and the ratio of the decision rate to the code rate.     

MLSE for an unknown channel .I. Optimality considerations

The problem of performing joint maximum-likelihood (ML) estimation of a digital sequence and unknown dispersive channel impulse response is considered starting from a continuous-time (CT) model. Previous investigations of this problem have not considered the front-end (FE) processing in detail; rather, a discrete-time signal model has been assumed. We show that a fractionally-spaced whitened matched filter, matched to the known data pulse, provides a set of sufficient statistics when a tapped delay line channel model is assumed, and that the problem is ill-posed when the channel impulse response is generalized to a CT, finite-length model. Practical approximations are considered that circumvent this ill-posed condition. Recursive computation of the joint-ML metric is developed. Together, the FE processing and metric recursion provide a receiver structure which may be interpreted as the theoretical foundation for the previously introduced technique of per-survivor processing, and they lead directly to generalizations. Several FE processors representative of those suggested in the literature are developed and related to the practically optimal FE     

Satellite radio interface and radio resource management strategy for the delivery of multicast/broadcast services via an integrated satellite-terrestrial system

A variety of hybrid systems combining third-generation mobile communication networks with broadcast systems have been proposed for the delivery of multimedia broadcast multicast services (MBMS) to mobile users. The article discusses one of these alternatives, which involves the use of a geostationary satellite component for MBMS delivery. In particular, it proposes a radio access scheme for the satellite component of the system that features maximum commonalities with the standardized T-UMTS WCDMA-based interface. The ultimate advantages of this approach are more efficient delivery of MBMS as far as the mobile network operator is concerned. The required adaptations at the interface layers are described, and the radio resource management strategy that fulfills the particular requirements of the satellite system is presented.     

On sampling rate, analog prefiltering, and sufficient statisticsfor digital receivers

We consider the joint sequence estimation, timing and phase recovery for linear modulation. The paper differs from the classical ones in the sense that time-discrete algorithms suitable for fully digital receivers are discussed. Sufficient conditions are given such that the signal samples represent sufficient statistics. These conditions involve signal bandwidth, sampling/symbol rate and the analog prefilter characteristics. It is shown that the sampling rate need not be an exact multiple of the symbol rate, i.e., the samples can be taken from a free-running oscillator. All subsequent signal processing operations in the receiver then operate with the clock of this free-running oscillator. Timing recovery is then performed by a time-variant linear digital interpolator and a decimator. Carrier recovery and sequence estimation are performed at an average rate of one symbol per sample. The digital matched filter for this case is derived for an arbitrary colored noise spectrum     

On the power spectral density of certain digitally modulatedsignals with applications to code despreading

Techniques for deriving the power spectral density (PSD) of certain digitally modulated signals that are more general and easier to use than other similar methods are developed. These techniques are especially well suited for deriving the PSD of signal-product waveforms with arbitrary modulating pulse shapes. This is done by decomposing the PSD expression into two factors, one depending solely on the underlying sequences and the other depending only on the pulse shapes. General formulas are derived and, for some cases, they are expressed in terms of the discrete Fourier transform of appropriately defined sequences and the Fourier transform of the modulating pulse shape. Applications where these expressions would be useful include bit and code synchronizers, delay-and-multiply-type of detectors, and spread-spectrum and code-division multiple-access systems, either at radio or at optical frequencies