Single-satellite geolocation achieves effective localization of ground electromagnetic interference (EMI) signals with a low cost compared to the multi-satellite counterparts. In such systems, the Doppler and Doppler rate are commonly exploited to extract the information of the ground EMI sources and the constrained Unscented Kalman filter (cUKF) is found effective to provide instantaneous EMI locations over time. In this letter, we address the benefit of exploiting Doppler acceleration in the underlying single-satellite geolocation problem, and point out that exploiting additional constraint on the altitude of the ground emitter provides enhanced EMI tracking performance. The importance of such constraint is more pronounced in the beginning of the tracking process, whereas removing such constraint after a short period of time does not compromise the performance. The effect of sampling rates on performance and the required time to converge are investigated.

This paper presents mobile-to-mobile (M-to-M) channel measurements and models at 1.85 GHz in dense-scattering suburban areas. Three test scenarios were considered for different transmitter (Tx) and receiver (Rx) antenna placements. Scenario 1: inside-vehicle-to-inside-vehicle (IV2IV), where both Tx and Rx antennas were placed inside the test vehicles; Scenario 2: inside-vehicle-to-walk (IV2W), where the Tx antenna was placed inside the vehicle and the Rx antenna was inside the pocket or next to the face of the tester; and Scenario 3: walk-to-walk (W2W), where the Tx and Rx were moving at walking speeds, the Tx antenna was placed on a test cart, and the Rx was inside the pocket or next to the face of the tester. To mimic more typical M-to-M channels in practice, eight sub-scenarios were configured under the availability of the line-of-sight (LoS) between the Tx and Rx. Detailed channel models are proposed for path loss, shadowing, small scale, and multi-scale fading based on the collected measurements. The level crossing rate (LCR) and average fading duration (AFD) are studied from the measurements and compared with the theoretical expressions.

In this paper, we investigate several relay selection strategies for cooperative Single-Carrier Frequency-Domain Equalization (SC-FDE) with the amplify-and-forward protocol. We consider both maximum likelihood (ML)-SC-FDE and minimum mean square error (MMSE)-SC-FDE receivers. We provide a novel pairwise error probability (PEP)-based selection criterion (SHARM) for frequency selective channels. We further present several selection strategies for cooperative (C) MMSE-SC-FDE receivers, which are motivated by minimizing the instantaneous error rate. These are, norm-based relay selection (NBRS), instantaneous mutual information-based relay selection (CBRS), singular value based relay selection (SVRS), and equalizer output signal quality-based relay selection (EQRS) strategies. We further propose a novel relay selection strategy, selective-to-flat fading relay selection (SFRS), in which from the effective frequency selective source-relay-destination channel link associated with the selected relay, only the channel tab with highest power is passed to the destination terminal. Additionally, to tackle the multiple relay selection problem considering generic mobile scenarios with moderately fast fading channels, in order to select the near best relay subset within the minimum processing time, we apply estimation of distribution algorithm (EDA) and formulate a modified EDA for the relay selection problem. Our results show promising performance of EDA with comparable computational complexity.

This paper considers the blind detection for a two-way relay system in which two source nodes exchange information via a relay node by amplify-and-forward relaying. An efficient transmission scheme is first proposed to achieve unique identifications of both the transmitted symbols and channel coefficients at a noise-free receiver using the M-ary phase shift keying modulation. Blind receivers based on the generalized likelihood ratio test are then derived for both the reciprocal and nonreciprocal channels with additive Gaussian noise. The least square error-based receiver is also studied for the case without prior knowledge of the noise power for detection. Moreover, constellation selection algorithms are proposed to achieve a uniform transmission bit rate for the ease of implementation. Finally, numerical results are provided to validate the proposed schemes.

In this paper, a cooperative system with two users and one relay is considered. An amplify-and-forward relaying protocol is applied in a half duplex mode. To make the transmission delay as short as possible, the relay forwards for both users simultaneously. We consider transmission schemes with symbol rates 2/3 to demonstrate the tradeoff among performance, delay, and symbol rate. Based on the analysis for the pairwise error probability (PEP), an optimal precoder is proposed to achieve the full diversity and best coding gain. Simulations show that the proposed precoder can provide about one dB improvement over some conventional space-time block codes at bit error rate 10-4.

In this paper, the ergodic channel capacities are established for the amplify-and-forward (AF) half-duplex cooperative systems, which consist of a source node, a destination, and multiple-relay nodes. The relay nodes assist the transmission from the source node to the destination. Since the channel matrices for the cooperative systems involve product of Gaussian random variables, which are no longer Gaussian, the approach in obtaining the ergodic channel capacity for conventional multiple-input-multiple-output (MIMO) Gaussian channels (Telatar, 1999) is not applicable. By using a novel approach, we have arrived at the following conclusions about the ergodic channel capacities for the AF cooperative systems. For the single antenna AF relay systems in which all nodes are equipped with one antenna, the optimal covariance matrix of the input signals to achieve the ergodic channel capacity is diagonal, and the diagonal elements are obtained by solving optimization problems of multidimensional integrals. These diagonal entries are not all equal even if all the channel gains in the cooperative systems are independent and identically distributed (i.i.d.) Gaussian with unit variance. Therefore, a white input signal for the AF cooperative system may not achieve the ergodic channel capacity of the system. This is in direct contrast to the case of conventional multiple-input-single-output (MISO) systems having i.i.d. Gaussian channel gains of unit variance, in which case, the ergodic capacity is achieved if the input covariance matrix is a scaled identity matrix. For the MIMO relay system in which the nodes have multiple antennas, the input covariance matrix to achieve the ergodic capacity is block diagonal and each block diagonalizes the autocorrelation of channel matrix from the source to the destination. This is different from the case of conventional MIMO systems, where the input covariance matrix to achieve the ergodic channel capacity diagonalizes the channel autocorrelation matrix of the MIMO system (Tulina, Lozano, and Verdu, 2006). If the channel gains in conventional MIMO systems are correlated Gaussian random variables, the input covariance matrix is a full matrix, not block diagonal; and if the channel gains are i.i.d. Gaussians, the optimal input covariance matrix is a scaled identity. The observations obtained in this paper reveal useful insights of how the AF cooperative systems ldquomimicrdquo the conventional MISO and MIMO systems from the ergodic channel capacity perspective.

In this paper, we investigate a cooperative system with multiple relays and amplify-and-forward relaying over frequency-selective channels. To extract the available multipath diversity, we employ orthogonal frequency division multiplexing (OFDM) with precoding. Through the derivation of pairwise error probability (PEP), we demonstrate that PEP is not a simple exponential function of the signal-to-noise ratio (SNR), but it includes a term that involves some power of logarithm of the SNR. If that term is ignored, the diversity order is given by the summation of the channel length in the direct link and the minimum of channel lengths in each relaying link confirmed by simulation results. Based on the PEP expression, we also propose two relay selection strategies; one is on a per-subcarrier basis and the other is on an all-subcarrier basis. Our simulation results indicate that both strategies result in performance improvements although the per-subcarrier method performs better.

In this paper, an optimal unitary precoder is designed for an amplify-and-forward (AF) half-duplex relay system to obtain the maximum coding gain while the original ergodic channel capacity for the relay system is kept unchanged. A closed-form design is derived for quadrature amplitude modulation (QAM) signals by employing the properties of Farey sequence in number theory. Simulation results indicate that the proposed design greatly improves the bit error rate (BER) performance for the relay system.

In this paper, we design an optimal precoder for the amplify-and-forward (AF) half-duplex cooperative system. We first present asymptotic pairwise error probability (PEP) expression and identify the corresponding terms for diversity and coding gains. By employing the properties of the Farey sequence in number theory, we obtain a closed form optimal precoder to achieve both full diversity as well as maximum coding gain for square quadrature amplitude modulation (QAM) signals. Simulation results indicate that the proposed design significantly improves the BER performance of the relay system.

Two strategies for improving the (uncoded) bit error rate (BER) performance of practical rate-adaptive block-by-block communication schemes, such as discrete multitone modulation (DMT) is proposed. Our strategies are inspired by some recent work which showed that for uniformly bit-loaded schemes, the transmission strategy which minimizes the BER for a linear receiver involves allocating power to the subchannels that are implicit in the block-by-block framework in a minimum mean square error (MMSE) fashion and linearly combining these subchannels using a normalized discrete Fourier transform (DFT) matrix. This combining equalizes the decision point signal-to-noise ratios (SNRs) of the subchannels. Given a nonuniformly bit-loaded scheme, our first design strategy simply performs a DFT-based linear combination within the groups of subchannels which share the same constellation. Our second strategy provides further reduction in the BER by reallocating power within these groups in a MMSE fashion prior to DFT combining. Our examples indicate that our design strategies can provide significant reductions in the BER, and give rise to substantial SNR gains (of the order of several decibels).

In this paper we derive an analytic expression for the linear precoder which minimizes the bit error rate (BER) for block transmission systems with zero-forcing equalization and threshold detection. The design is developed for the two standard schemes for eliminating inter-block interference; viz, zero padding (ZP) and cyclic prefix (CP). The CP minimum BER precoder has a structure similar to that of the conventional water-filling discrete multitone (DMT) modulation scheme, but the diagonal water-filling power loading matrix is replaced by a full matrix consisting of a diagonal minimum mean square error (MMSE) power loading matrix post-multiplied by a Discrete Fourier Transform (DFT) matrix. The ZP minimum BER precoder has a corresponding structure. Performance evaluations indicate that the signal-to-noise ratio (SNR) gain of the ZP and CP minimum BER precoders over conventional water-filling DMT, MMSE, and orthogonal frequency division multiplexing (OFDM) schemes can be as much as several decibels.