We analyze the performance of underwater acoustic ad-hoc networks in the presence of interference. We assume a uniform distribution of nodes over a finite area, and focus for simplicity on a two-dimensional network. The node-to-node channel is modeled using frequency dependent path loss and Ricean fading. We adopt a communication theoretic approach and study the sustainable number of hops through the network as an indicator of the network connectivity, as well as power and bandwidth requirements. The network operation is highly dependent on the node density with two distinct regions of limited performance: the coverage-limited region, where the number of nodes in the network is small, and the interference-limited region, where the number of nodes is large. We show that a desired level of connectivity can be achieved through a judicious selection of the operating frequency, power and bandwidth. Numerical examples illustrate the results of the analysis. These results motivate us to propose a hierarchical underwater acoustic sensor network architecture in which the sensors and the collector stations operate in distinct layers. The hierarchical architecture is supported by the property of the acoustic underwater transmission medium that for each transmission distance there exists an operating frequency for which the narrow-band signal-to-noise ratio is maximized. The sensors and the collector stations are consequently allocated different operating frequencies. We assume a uniform distribution of both sensors and collector stations over the finite area of the sensing field, and model the channel accordingly. The analysis is performed under the assumption that there is interference from other nodes within the same layer of the hierarchy. Numerical examples illustrate the network performance and demonstrate that the preferred operating frequencies ensure network operation without any cross-interference between the collector network and the sensor network.

We consider the performance of underwater acoustic ad-hoc networks. We assume a uniform distribution of the nodes over a finite area. The node-to-node channel is modeled through the Ricean fading model. We adopt a communication theoretic approach and study the interdependence of the sustainable number of hops through the network, end-to-end frame error probability, power and bandwidth allocation and operating frequency. We find that the network connectivity, given by the sustainable number of hops, exhibits a bimodal behavior. We present numerical examples that illustrate the results of the analysis.

In this paper, we consider the general design criteria, properties and explicit code design procedures for cooperative multiple trellis coded modulation (CMTCM) schemes over Rayleigh fading channels. The cooperative system of interest utilizes the decode and forward protocol based on orthogonal transmissions from the cooperating terminals to the destination. We design full diversity cooperative multiple trellis codes using asymmetric constellations that at a frame error probability of 10-3provide around 10-12 dB gains over non-cooperative coded modulation without sacrificing the data rate and/or bandwidth efficiency. This is achieved by expanding the baseline constellation used in the non-cooperative transmission, designing the signal constellation to be asymmetric, and adopting multiple mappings among users. The consistent performance gains due to coding, asymmetry, and mappings of symbols onto the constellation are evaluated in terms of the frame error probability. We present simulation results that support the theoretical designs and illustrate the viability of the proposed cooperative MTCM technique.

We introduce general design criteria and study the properties of cooperative multiple trellis coded modulation (MTCM) systems, in the context of the decode and forward protocol based on orthogonal transmissions from the cooperating terminals to the destination. We present simulation results illustrating the performance of the proposed cooperative MTCM codes.

In this paper, we derive the exact pairwise error probability (PEP) expression for MIMO block Rayleigh fading OFDM systems. We begin with the quasi-static fading OFDM system, and derive the PEP expression for MIMO quasi-static fading OFDM system. The exact PEP expression for MIMO block fading OFDM system can then be determined using the general quasi-static fading result.

In this paper, we derive the exact pairwise error probability (PEP) expression for Rayleigh fading OFDM systems. We begin with the quasi-static fading OFDM system, and derive the PEP expression for both the case when the eigenvalues of the channel code are all the same, as well as the more general case when they could be different. The exact PEP expression for the block Rayleigh fading OFDM system can then be determined using the general quasi-static fading result

User cooperation is an efficient approach to obtain diversity in both centralized and distributed wireless networks. In this paper, we consider a coded cooperative system under quasi-static Rayleigh fading and investigate the partner-choice problem. We find conditions on the interuser and user-to-destination channel qualities for cooperation to be beneficial. Using frame-error rate (FER) as a metric, we define the user cooperation gain (G) for evaluating the relative performance improvement of cooperative over direct transmissions when a particular channel code is used. We introduce the cooperation decision parameter (CDP), which is a function of user-to-destination average received signal-to-noise ratios (SNRs), and demonstrate that whether cooperation is useful or not ($G≫1$or$G≪1$) depends only on the CDP, not the interuser link quality. We use an analytical formulation of the CDP to investigate user cooperation gain and provide insights on how a user can choose among possible partners to maximize cooperation gain. We first consider the asymptotic performance when one or both partners have high average received SNR at the destination. We then provide conditions on user and destination locations for cooperation to be beneficial for arbitrary SNRs. We illustrate these cooperative regions and study geometric conditions for the best partner choice. We also define the system cooperation gain and illustrate cooperation benefit for both users. All of our theoretical results are verified through numerical examples.

User cooperation is an efficient approach to obtain diversity in both centralized and distributed wireless networks. In this paper, we consider a coded cooperative system under quasi-static Rayleigh fading and investigate the partner-choice problem. We find conditions on the interuser and user-to-destination channel qualities for cooperation to be beneficial. Using frame-error rate as a metric, we define the user cooperation gain (G) for evaluating the relative performance improvement of cooperative over direct transmission when a particular channel code is used. We introduce the cooperation decision parameter (CDP), which is a function of user-to-destination average received signal-to-noise ratios (SNRs), and demonstrate that whether cooperation is useful or not (G>1 or G<1) depends only on the CDP, not the interuser link quality. We use an analytical formulation of the CDP to investigate user cooperation gain and provide insights on how a user can choose among possible partners to maximize cooperation gain. We first consider the asymptotic performance when one or both partners have high average received SNR at the destination. We then provide conditions on user and destination locations for cooperation to be beneficial for arbitrary SNRs. We illustrate these cooperative regions, and study geometric conditions for the best partner choice. We also define the system cooperation gain and illustrate cooperation benefits for both users. All of our theoretical results are verified through numerical examples

We consider a cooperative transmission scheme in which the collaborating nodes may have multiple antennas. We present the performance analysis and design of space-time codes that are capable of achieving the full diversity provided by user cooperation. Our codes use the principle of overlays in time and space, and ensure that cooperation takes place as often as possible. We show how cooperation among nodes with different numbers of antennas can be accomplished, and how the quality of the interuser link affects the cooperative performance. We illustrate that space-time cooperation can greatly reduce the error rates of all the nodes involved, even for poor interuser channel quality.

Cooperation of mobiles provides signal diversity in wireless networks. We consider a coded cooperative system under Rayleigh fading and path loss. For an arbitrary signal to noise ratio, we find conditions on the user geometry for two-user cooperation to be beneficial. We find that whether cooperation is useful or not is only determined by the cooperation decision parameter (CDP). We illustrate regions for which cooperation results in a gain in frame error rate (FER) for individual users and use the analytical formulation of the CDP to investigate how locations of the user and the partner affect the user cooperation gain. Our analytical results also provide insights on how a user can choose among many partners to maximize cooperation gain. All of our theoretical results are verified by numerical simulations of the FER.

User cooperation represents an effective way of introducing diversity in wireless networks. Spatial diversity gains are obtained through the cooperative use of antennas belonging to several nodes. We design and analyze the performance of channel codes that are capable of achieving the full diversity provided by user cooperation, with the constraint that they also provide the best possible performance in the interuser link. We show that even though the interuser channel is noisy, the codes provide substantial diversity and coding gains over the noncooperative case.

We consider a cooperative system in which the partnering mobiles are equipped with multiple antennas. We present space-time codes that have the capability of providing full cooperation diversity, while achieving maximum possible diversity and best performance in the inter-user channel. Our codes also perform well when cooperation does not take place. We illustrate that cooperative space-time coding offers significant performance improvement over direct transmission even when the inter-user channel is noisy. We also consider code design for users with different numbers of antennas.

Cooperative coding is a way to exploit the diversity provided by user cooperation in wireless networks. In this paper, we provide performance analysis of cooperative space-time coding, which arises when mobiles have multiple antennas. We perform an asymptotic analysis in order to determine the achieved diversity order through cooperative space-time coding for various inter-user channel qualities. In addition, we derive tight bounds on the performance of cooperative space-time codes. Numerical examples are presented to demonstrate the results.

We derive performance bounds for turbo-coded systems with transmit and receive antenna diversity. The bounds are derived by limiting the conditional union bound before averaging over the fading process. It is demonstrated that this approach provides a tight upper bound on the error probability of the turbo-coded multiple antenna systems. We also describe a method for deriving the weight-enumerating function of turbo-coded multiple antenna systems in order to take into account the presence of transmit and receive antenna diversity. Examples of the bounds are presented to illustrate their usefulness.

We consider the design of space-time overlays to upgrade single-antenna wireless communication systems to accommodate multiple transmit antennas efficiently. We define the overlay constraint such that the signal transmitted from the first antenna in the upgraded system is the same as that in the single-antenna system. The signals transmitted from the remaining antennas are designed according to space-time coding principles to achieve full spatial diversity in quasi-static flat fading channels. For both binary phase-shift keying (BPSK) and quaternary phase-shift keying modulation systems, we develop an algebraic design framework that exploits the structure of existing single-dimensional convolutional codes in designing overlays that achieve full spatial diversity with minimum additional decoding complexity at the receiver. We also investigate a concatenated coding approach for a BPSK overlay design in which the inner code is an orthogonal block code. This approach is shown to yield near optimal asymptotic performance for quasi-static fading channels. We conclude by offering a brief discussion outlining the extension of the proposed techniques to time-varying block fading channels.

We derive the union bound for space-time trellis codes over quasi-static fading channels. We first observe that the standard approach for evaluating the union bound yields very loose, in fact divergent, bounds over the quasi-static fading channel. We then develop a method for obtaining a tight bound on the error probability. We derive the union bound by performing expurgation of the standard union bound. In addition, we limit the conditional union bound before averaging over the fading process. We demonstrate that this approach provides a tight bound on the error probability of space-time codes. The bounds can be used for the case when the fading coefficients among different transmit/receive antenna pairs are correlated as well. We present several examples of the bounds to illustrate their usefulness.

We consider the design of space-time overlays to upgrade single antenna wireless communication systems to efficiently accommodate multiple transmit antennas. We define the overlay constraint such that the signal transmitted from the first antenna in the upgraded system is the same as that in the single antenna system. The signals transmitted from the remaining antennas are designed according to space-time coding principles to achieve full spatial diversity in quasi-static flat fading channels. For both BPSK and QPSK modulated systems, we develop an algebraic design framework that exploits the structure of existing single dimensional convolutional codes in designing overlays that achieve full spatial diversity with minimum additional decoding complexity at the receiver. We also investigate a concatenated coding approach for BPSK overlay design in which the inner code is an orthogonal block code. This approach is shown to yield near optimal asymptotic performance for quasi-static fading channels.

In this paper, we consider the design of space-time overlays to upgrade single antenna wireless communication systems to accommodate multiple transmit antennas efficiently. We define the overlay constraint such that the signal transmitted from the first antenna in the upgraded system is the same as that in the single antenna system. The signals transmitted from the remaining antenna's are designed according to space-time coding principles to achieve full spatial diversity in quasi-static flat fading channels. For both BPSK and QPSK modulated systems, we develop an algebraic design framework that exploits the structure of existing single dimensional convolutional codes in designing overlays that achieve full spatial diversity with minimum additional decoding complexity at the receiver.

Previous results have demonstrated excellent performance of turbo coded modulation with iterative demodulation-decoding for systems with antenna diversity. However, the computational complexity at the receiver is exponential in the number of transmit antennas; hence it is too high for the case of large number of transmit and receive antennas. We present a new iterative-greedy demodulation-decoding algorithm for turbo codes for multiple antenna systems. The decoding algorithm is based on a novel greedy detection method for multiuser communications. The iterative-greedy demodulation-decoding algorithm is characterized by the exchange of soft information between the demodulator and the decoder, and the significant decrease in computational complexity, as compared to the standard method of iterative demodulation-decoding, with a slight degradation in performance. This is due to the novel, greedy method of calculating the log-likelihoods to be used in the iterative decoding process, where only a small subset of the possible received vectors is considered, resulting in a receiver with only polynomial complexity in the number of transmit antennas.

We study the use of turbo-coded modulation for wireless communication systems with multiple transmit and receive antennas over block Rayleigh fading channels. We describe an effective way of applying turbo-coded modulation as an alternative to the current space-time codes with appropriate interleaving. We study the performance with the standard iterative turbo decoding algorithm, as well as the iterative demodulation-decoding algorithm. In addition to the introduction of the turbo-coded modulation scheme, we consider a variety of practical issues including the case of large number of antennas, the effects of estimated channel state information, and correlation among subchannels between different transmit-receive antenna pairs. We present examples to illustrate the performance of the turbo-coded modulation scheme and observe significant performance gains over the appropriately interleaved space-time trellis codes.