Multiple Input Multiple Output (MIMO) technology offers the possibility of increased throughput in wireless communications, and as such, it is a potential candidate for High Frequency (HF) systems where only small bandwidths are available. However, the increased wavelength and size of antenna elements complicate the implementation of HF multi-antenna transceivers. In this paper, we consider multi-carrier (OFDM) MIMO HF communication systems where the multiple non co-located antennas at each communication end are interconnected through Radio Frequency (RF) links. We consider Minimum-Mean-Squared-Error- (MMSE) pilot-assisted channel estimation at the receiver side in OFDM transmission, and, leveraging results from random matrix theory, we present novel upper and lower bounds on the achievable throughput in the presence of imperfect channel estimation. Our representative numerical results for a 9 × 9 HF MIMO system quantify the achievable rate for realistic HF channel parameters, validating the interest in multi-antenna systems.

This paper focuses on the effect that various co-transmission schemes have on a single receiver's SNR, under a stochastic-geometry setting for the emitters' location. The model includes all standard effects of ground propagation: power law to account for the distance, fast fading, shadowing, plus delay spread (resolvable multipath). The schemes addressed include: the dimension-expanding fully orthogonal case (namely channel-blind transmission on completely orthogonal dimensions); the two extreme co-transmission schemes of fully coherent (perfectly known channel) as well as fully incoherent (purely channel-blind) cases; randomly orthogonalized co-transmission; plus selected transmission schemes such as the strongest signal or the nearest node to the receiver. The emphasis is on outage statistics, but capacity and bit-error-rate are also computed in selective cases. The analysis highlights the role of the various parameters involved, in particular demonstrating the importance of resolvable multipath on the relative performance of the schemes addressed.

The paper investigates the use of Radio Environment Maps (REMs) as a tool for Interference Management (IM) in two-tier cellular networks comprising macro- and femto-cells. The REMs are databases that provide, through different instances distributed over network elements, a variety of network- and user-related context information for improving IM and Radio Resource Management (RRM) procedures. In this context, the focus in this paper is to present the benefit of using REM information on practical power control schemes for the Femtocell downlink transmission in co-channel two-tier deployment.

Bit-Power Loading (BPL) algorithms are proposed based on Effective SINR Mapping (ESM) techniques. The ESM techniques used are the Exponential ESM (EESM) as well as the Mean Mutual Information per Bit (MMIB). The algorithms are based on proper usage and modifications of algorithms already proposed in the literature, applied to ESM compatible link-level performance models. The performance gain when using the proposed algorithms is assessed for an IEEE 802.16 OFDM system.

Barrage relay networks (BRNs) are mobile ad hoc networks designed from the ground up to meet the demands of tactical edge communications. The fundamental building block of BRNs is not a point-to-point wireless link, but rather a rapid and robust broadcast mechanism that employs an autonomous cooperative communications scheme. Following a summary of basic BRN concepts, this paper demonstrates how the efficient barrage broadcast mechanism can be contained for unicast traffic via controlled barrage regions (CBRs). In particular, a protocol for CBR establishment is defined and formally verified.

The estimation of the position of an emitting source is an important aspect of emerging cognitive radio systems. We readdress the known problem of estimating the Direction-of-Arrival (DOA) of an emitting source via passive radio means, namely an antenna array. The challenges in the considered scenarios are (a) time-varying, terrestrial multipath propagation with medium-to-low SNR and (b) very short capture records (single-packet processing). We present a two-stage estimation procedure: first an overall channel estimation stage followed by a DOA extraction method suitable to both blind (no training data employed) as well as training-assisted cases. The performance results presented demonstrate that the DOA estimation performance of this procedure is close to the theoretical Cramer-Rao Lower Bound for a large variety of challenging propagation scenarios.

A low-complexity decision-directed iterative scheme is proposed for the estimation and mitigation of strong phase noise plus frequency offset in OFDM-modulated signals, transmitted over frequency-selective or frequency-flat channels. It is based on a time-domain, windowed least-squares estimation algorithm of the total phase perturbation vector, developed through proper system modeling and optimized so as to minimize the residual inter-carrier interference. An extension of the diagonal-loading technique is also introduced in order to enhance the convergence of the algorithm in high-SNR regimes. The resulting scheme outperforms previously proposed approaches in terms of achievable error rate in the data-detection stage while, in the channel-estimation stage, it attains performance near the Cramer-Rao bound with comparatively smaller computational complexity.

This review article explores the notion of radio flexibility, its various versions (as presented in a brief taxonomy) and its efficient instantiations under various metrics, primary among which is the broad applicability of a parametrically compact, single model or design over a large set of modes and scenarios. The focus is on the algorithmic part of the base-band. It is argued that this systematic approach to the subject yields benefits both in understanding past results as well as charting new research frontiers.

This paper proposes an enhanced receiver (Rx) configuration for multiple-input, multiple-output (MIMO) OFDM systems, operating under the composite effect of phase noise (PHN), residual frequency offset (RFO) and the transmission channel, herein modeled as quasi-static but unknown. The proposed Rx identifies the different impairments by exploiting their different time constants and compensates for each one accordingly. It includes a novel inter-frame fine frequency synchronization (FFS) scheme, which is closely coupled to an intra-frame adaptive phase synchronizer/channel estimator. The proposed scheme is evaluated for a 2 times 2, Alamouti space-time code (STC), and is shown to provide significant performance gain. The theory can be employed with any other STC scheme.

The simultaneous perturbation of an orthogonal frequency-division multiplexing receiver by phase noise plus a residual frequency offset (due to synchronization errors) is modeled here as a combined phase impairment, whose effect is evaluated analytically for the case of a frequency-selective fading channel. A nonpilot-aided (decision-directed) scheme is proposed, which compensates for the common (over all the subcarriers) phase-impairment effect. By representing the resulting intercarrier interference as an uncorrelated, unequal-variance process in the frequency domain, maximum-likelihood (ML) and approximate ML estimators of the complex-vector and phase-only types are derived and analytically evaluated. The present schemes are also compared with other current methods based on individual phase trackers, one per subcarrier. Finally, two suggestions are introduced for increasing the robustness of the algorithms to tentative-decision errors. It is demonstrated through simulations that the analysis is accurate, and that the proposed schemes achieve error-rate performance close to that of ideal compensation.

This paper deals with the analysis of the code-acquisition process performed by a mobile terminal in a code-division multiple-access cellular system. The fundamental contribution is the setting of a theoretical framework for code-acquisition analysis, accounting for the presence of fading and shadowing with specified coherence time. A multidwell architecture is considered, accounting for different verification strategies. The MAX/TC detection criterion is used, and the acquisition performance is analyzed, following both the direct and flow-graph approaches. Expressions for the acquisition time probability density function under different assumptions are given, as well as closed-form expressions for the mean and variance of the acquisition time. Practical applications and numerical results are reported in the Part II companion paper.

It is shown that a random phase noise Wiener process and a fixed but unknown residual (post-FFT) frequency offset, jointly perturbing an OFDM receiver, manifest themselves as a phase-rotation random variable which is common to all subcarriers, provided that their defining values (variance and fixed amount, respectively) are small, in which case the ICI (intercarrier interference) and the per-subcarrier amplitude distortion induced by them are both negligible. Assuming a known arbitrary channel profile, we propose and evaluate by simulations two decision-directed (i.e., non-pilot-based) compensation schemes, one intuitive and the other based on ML theory. The algorithms exhibit robustness despite the lack of pilots, whereas uncompensated performance degrades rapidly.

This paper investigates the effect of large frequency offset induced (FOI) intersymbol interference (ISI) on the performance of a digital receiver and proposes corresponding remedies. General expressions are derived for the exact representation of ISI caused by an arbitrary frequency offset at the output of the receiver matched filter. Specific examples are developed for the case of a square root raised cosine (SQRT-RC) pulse shape. It is shown that when FOI ISI compensation is performed digitally after the matched filtering operation, an equalizer is necessary for efficient data demodulation, even in the case of a non - dispersive channel. Maximum likelihood (ML) frequency offset estimation is revisited to accommodate the case of large FOI ISI. Its performance is assessed via simulation examples and compared to the derived Cramer-Rao bound. A combined equalization-frequency tracking scheme is also explored, in order to cope with residual frequency estimation errors and potential phase noise.

In unknown channels, nonadaptive maximum likelihood sequence detection (NA-MLSD) is far from optimum in the presence of channel-induced uncertainty. To counteract this uncertainty, conventional solutions augment MLSD with external channel estimators. However, for very low SNR values this estimation procedure becomes marginal and the conventional adaptive MLSD (CA-MLSD) approaches perform poorly. We consider joint data decoding and parameter estimation techniques, and in particular per survivor processing (PSP) techniques, as a potentially effective solutions to this problem, at the expense of increased complexity. The performance/complexity tradeoff is addressed for a convolutionally encoded Q-PSK return link of an SHF/EHF satellite system for multimedia services impaired by phase noise and frequency offsets. By contrasting NA-MLSD, CA-MLSD, and PSP, ranges are provided for channel conditions where the tradeoff favors a particular technique. Further, CA-MLSD and PSP are also contrasted in terms of scalar/ vector estimation performance.

The application of per-suvivor processing (PSP) to digital satellite communications at Ka-band and beyond is considered. The PSP approach is used in a convolutionally encoded M-PSK transmission scheme to effectively counteract the degradations caused by phase noise and frequency offsets. Second order tracking loops are considered for per-survivor parameter estimation. A comparison is carried out between conventional adaptive maximum likelihood sequence detection (CA-MLSD) and PSP schemes both in terms of detection and estimation performance. Emphasis is placed on the analysis of the estimation quality one of the most unexplored research areas in the field of PSP-based systems. To this aim, novel definitions for a decision-related tracker and virtual tracker are introduced and their performance analyzed. Monte-Carlo simulations are provided to show the improvement in both estimation and detection quality brought about by PSP with respect to CA-MLSD.

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.

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.

For pt. I see ibid., vol.44, no.7, p.836, 1996. The channel-tracking mode performance of the front-end (FE) processors is determined through approximate analysis and computer simulation. A general model for the FE processing, which encompasses these representative FEs, is assumed. Previous analysis techniques are extended to include the effects of FE processing. The specific system analyzed consists of a Rayleigh-fading, diffuse multipath channel, with several data pulse shapes considered. An adaptive maximum likelihood sequence estimation (MLSE) algorithm based on the per-survivor processing (PSP) technique is analyzed and compared to an algorithm based on correct symbol feedback. The results show that significant performance degradation is suffered when suboptimal FE processing is used. Some of the issues which may complicate matters in practice are examined with an emphasis on application in packet mobile radio systems. The limitations of the results and the models used are discussed.

The design issues and the performance evaluation of packet radio communication systems for automated highway systems (AHS) are presented. The main focus is on the analysis and interaction between the physical and the link-access layers of a packet radio system that can accommodate communication between vehicles and roadside infrastructure as well as between vehicles. We discuss the information flow requirements of AVCS (advanced vehicle control systems) and ATMIS (advanced traffic management and information systems) services and we present preliminary results from the performance evaluation of four multiple access schemes (slotted-ALOHA, reservation-ALOHA, TDMA, and CDMA).

Exact and approximate statistical models (analytical and simulation), based on average- and maximum-likelihood ratio tests, are studied and compared for the purpose of establishing an accurate assessment of the performance of noncoherent SFH M-FSK intercept receivers. Both continuous and discontinuous phase M-FSK cases are considered with important differences between the two.>

Multiple-hop autocorrelation (MHAC) processing is considered as a means of estimating the parameters of frequency-hopping signals in the presence of broadband thermal noise. It is shown that power sampling in the MHAC domain suppresses the dependence on the hopping frequency, carrier phase, and hop timing, while maintaining the hop-rate information. Moreover, when the signal's hop-rate is known a priori or can be estimated reliably, the multiple-hop combining of single-hop autocorrelation (SHAC) estimates can be employed to extract hop-timing information. Taking advantage of these features, we propose and analyze a hop-rate estimator and an epoch estimator, based on maximum-likelihood arguments. The conditional mean and variance of both estimators are derived analytically and confirmed by extensive simulation.>

New algorithms based on the likelihood functional (LF) and approximations thereof are proposed for the problem of classifying MPSK modulations in additive white Gaussian noise. Previously introduced classifiers for this problem are theoretically interpreted as simplified versions of the ones in here. The performance of a single-term approximation to the optimal LF classifier is evaluated analytically and is shown to be very close to that of the optimal. Furthermore, recursive algorithms for the implementation of this new quasi-log-likelihood-ratio (qLLR) classifier are derived which imply no significant increase in classifier complexity. The present method of generating classification algorithms can be generalized to arbitrary two-dimensional signal constellations.>

Per-survivor processing (PSP) provides a general framework for the approximation of maximum likelihood sequence estimation (MLSE) algorithms whenever the presence of unknown quantities prevents the precise use of the classical Viterbi algorithm. This principle stems from the idea that data-aided estimation of unknown parameters may be embedded into the structure of the Viterbi algorithm itself. Among the numerous possible applications, the authors concentrate on (a) adaptive MLSE, (b) simultaneous trellis coded modulation (TCM) decoding and phase synchronization, (c) adaptive reduced state sequence estimation (RSSE). As a matter of fact, PSP is interpretable as a generalization of decision feedback techniques of RSSE to decoding in the presence of unknown parameters. A number of algorithms for the simultaneous estimation of data sequence and unknown channel parameters are presented and compared with "conventional" techniques based on the use of tentative decisions. Results for uncoded modulations over interSymbol interference (ISI) fading channels and joint TCM decoding and carrier synchronization are presented. In all cases, it is found that PSP algorithms are clearly more robust than conventional techniques both in tracking a time-varying channel and acquiring its characteristics without training.>

The optimum hop timing estimator, based on classical likelihood-ratio (LR) theory, is derived for noncoherent slow and fast frequency-hopped M-FSK intercept receivers. Such receivers have no a priori knowledge of the hopping code and thus the solution to this estimation problem differs considerably from the more commonly considered case of the friendly receiver. The implementation and performance of the LR hop timing structures are presented and compared with that of other previously documented suboptimum schemes. In particular, when compared to the multiple-hop autocorrelation (MHAC) approach and the "ping-pong" approach, the average-likelihood ratio (ALR) and maximum-likelihood ratio (MLR) optimum estimators offer an improvement in performance of several dB in input SNR. Robustness issues for the optimal estimator are examined and alternative configurations are proposed that offer enhanced insensitivity to unknown frequency offsets.>

Exact and approximate statistical models (analytical and simulation), based on average-and maximum-likelihood ratio tests, are studies and compared for the purpose of establishing an accurate assessment of the performance of coherent SFH M-FSK intercept receivers.>

Optimum detectors have previously been derived for fast frequency-hopped (FFH) signals with M-ary frequency-shift-keyed (MFSK) data modulation received in additive white Gaussian noise (FFH here implies that a single MFSK tone is transmitted per hop), The present paper extends that work to the more analytically complex category of slow frequency-hopped (SFH) signals with multiple MFSK tones per hop. A special subset of the SFH/MFSK format that receives particular attention in the paper is the case of continuous-phase modulation (CPM) for which the carrier phase is assumed to be constant over the entire hop. A fundamental conclusion is that SFW/CPM modulation is advantageous not only to the communicator but also to a sophisticated noncoherent detector. By applying techniques developed in the paper to exploit the continuous-phase characteristic, an intercept receiver of reasonable complexity will perform appreciably better than traditional channelized detectors.>

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.>

A new lower bound is developed for the error variance of maximum-likelihood time-delay estimation when the received signal is a square pulse, corrupted by additive white Gaussian noise. The bound is generated by combining concepts previously developed for a special class of stochastic processes, induced by the signal model. For moderate signal to noise ratios, the new bound is significantly tighter than previously known ones.>

A general approach is proposed to resolve the wideband detection problem, which utilizes data in the correlation domain via autoregressive modeling. The structures of Gaussian autoregressive processes are reviewed and applied to the modeling of a sinusoid in additive white Gaussian noise (AWGN). Based upon the output sequences of this adopted model, optimal hypothesis-testing tools are employed, leading to a novel scheme, namely the multiple-correlation-coefficient detector. For a properly selected model, this statistic is shown to be competitive to the spectral-maximum detector. This fact is established analytically as well as through extensive simulations. Connections to the other detectors in the correlation domain are also established by means of this model-based approach.>

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.< >

An analysis is presented of a frequency-noncoherent, two-lag autocorrelation statistic for the wideband detection of random binary phase-shift keying (BPSK) signals in noise plus random multitone interference. It is shown that this detector is quite robust to the presence or absence of interference and its specific parameter values contrary to an energy detector. The rule assumes knowledge of the data rate and the active scenario under H/sub 0/. The purpose of the paper is to promote the real-time autocorrelation domain and its samples (lags) as a viable approach for detecting random signals in dense environments.>

Optimal and suboptimal decision rules for the detection of constant-envelope quadrature digital modulations in broadband noise are derived and analyzed. The effect of various stochastic models for the carrier phase is examined in detail, while no epoch or frequency uncertainty is assumed. The delay-and-multiply type of detector is considered. A new binary/quadrature phase shift keying (BPSK/QPSK) classifier is compared to the more traditional ad hoc techniques of a square-law classifier and a phase-based classifier (weighting on the phase histogram). The new classifier is derived by approximating the likelihood-ratio functionals of phase-modulated digital signals in white Gaussian noise, hence is named the quasi-log-likelihood ratio (qLLR) rule. It is shown analytically that its performance is significantly better than that of intuitively designed phase-based rules or the conventional square-law classifier.>

The authors develop approximate methods for performance evaluation of a general class of slotted Aloha-type random-access spread-spectrum networks. Approximation is used in three levels: the diffusion approximation of the process Q(t) (a variant of the number of backlogged users), the approximation of the random-access channel and the existing receivers by a single server with equivalent queue-size-dependent service rate, and the approximation of the state-dependent composite traffic distribution by a Gaussian random variable with equivalent mean and variance. Applications and comparisons with the precise solutions are given.>

An analytic framework is proposed for the study of singlehop spread-spectrum networks using random access and packet switching under various network topologies and channel conditions. The key feature of the theory is the identification of a set of probabilistic parameters, which, based on a symmetry argument, serve to efficiently summarize the effect on performance of various network considerations such as transmitter-receiver configuration, spreadspectrum code allocation, error correction and detection mechanisms, spreading format, jamming conditions, etc. Examples investigating capture effects, coding tradeoffs, and scheduling optimizations are presented. Various previously known results are shown to be special cases of the framework that we describe.

A family of autoregressive (AR) detection statistics is introduced and their potential for enhanced detection of unknown-frequency sinusoids in noise is illustrated. AR models applied to both the time data and the correlation data are addressed and compared. The computational complexity of the resulting decision rules is also incorporated in the analysis.

The performance of sum/difference and reference/difference code tracking loops in direct-sequence spread-spectrum communication systems are fully analyzed and compared for nonwhite interference situations. In particular, symmetric dual-tone interference is considered and the worst case tone spacing and relative tone energies are determined. Parameterized curves of tracking-error variance and mean-time to lose lock are presented as a function of signal-to-interference ratio, dual tone spacing, and early-late gate delay difference.

Interception of frequency-hopping (FH) waveforms is commonly achieved by using a set of radiometers (energy detectors) that individually energy-detect subbands of the total spread bandwidth of the suspected transmission. In this paper, a scheme is analyzed which can improve the detection performance of FH waveforms in wide-band additive Gaussian noise (AWGN) using samples from the autocorrelation domain. It is shown that, under fairly general operational assumptions, an appreciable gain in decision signal-to-noise ratio (SNR) can be achieved over that of the radiometer. This gain is proportional to\gamma_{H}^{2}where\gamma _{H}is the hop SNR. The proposed algorithm, albeit inferior to the optimal likelihood-ratio test, has the advantage of reduced complexity. The overall approach has been motivated by the recent implementational feasibility of large time-bandwidth-product real-time correlators such as surface-acoustic wave devices (SAWD's).

The implementation and performance of wide-band detectors for direct-sequence and time-hopping spread-spectrum waveforms in the presence of additive white Gaussian noise are considered in this paper. Of interest here is the performance penalty incurred when going from optimal to suboptimal detector structures. In both cases, performance is quantified by appropriately defined distance measures and is ultimately compared to that of the simplest hypothesis-discriminating device, namely, the energy detector (radiometer).

The purpose of this paper is to apply the renewal theory approach for analyzing aperiodic finiteS-curve code-tracking loops developed by Meyr [9] to the case of a noncoherent, arbitrary offset, early-late, delay-locked loop ("noncoherent δ-DLL"). The exact (renewal) approach is compared to the approximate (periodic-extension) approach of using the periodicS-curve or phase-locked loop theory, as well as to the linear theory developed herein for the aforementioned codetracking loop. Finally, loop optimization with respect to the offset δ is carried out according to certain performance criteria. The results indicate that, for low SNR, the exact and approximate theories could deviate significantly while, for high SNR, all three theories yield identical performance, as expected. Furthermore, it is shown that the optimal δ for both low and high SNR could differ from the commonly accepted choice\delta = 1/2.

A simple circular state-diagram method has been recently proposed [1], [2] for the modeling, analysis, and optimization of straight serial search code acquisition in spread-spectrum systems. Herein, the approach is generalized to arbitrary serial strategies, such as theZ-search expanding window search, etc., and arbitrary a priori probability distributions for the code phase uncertainty. The basic idea is the construction of equivalent circular state diagrams, wherefrom the transform domain description, i.e., the generating or characteristic function of the stochastic acquisition process is derived. This general method is readily systematized, circumvents the need for complicated time-domain combinatorial arguments, and allows past results [3], [4] to be obtained as particular examples. In principle, the generating function can be used to calculate any moment of the acquisition process; here, however, due to complexity considerations, we restrict our attention to the first moment and its associated performance measure, the mean acquisition time. Based on the derived analytical expressions for the mean acquisition time, an expanding-window single-dwell search strategy has been optimized in terms of the required number of partial windows, parameterized by the prior distribution of the phase uncertainty.

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.

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.

The combined effects of data asymmetry and a noisy carrier phase reference on the bit error rate performance of an unbalanced QPSK system are examined. The results are presented in terms of the SNR loss for a nominal error rate of 10-5, parameterized by the mean and variance of the reference phase error φ at the receiver. The effect of asymmetry on the carrier tracking loop (hence, on φ) is not included. The results show a considerable sensitivity in performance of both channels to asymmetry, the lower data rate channel being, as expected, more prone to degradation.

In this paper the concept of differentially coherent detection of differentially phase-encoded QASK signals (DQASK) is described, and a receiver structure proposed. The remainder of the paper analyzes the performance of DQASK in the presence of a Gaussian noise environment with comparisons made to coherent detection of QASK.

This paper examines the performance of coherent QPSK and QASK systems combined with FH or FH/PN spread spectrum techniques in the presence of partial-band multitone or noise jamming. The worst-case jammer and worst-case performance are determined as functions of the signal-to-background noise ratio (SNR) and signal-to-jammer power ratio (SJR). Asymptotic results for high SNR are shown to have a linear dependence between the jammer's optimal power allocation and the system error probability performance.