Detecting anomalies and attacks in smart cyber-physical systems are of paramount importance owing to their growing prominence in controlling critical systems. However, this is a challenging task due to the heterogeneity and variety of components of a CPS, and the complex relationships between sensed values and potential attacks or anomalies. Such complex relationships are results of physical constraints and domain norms which exist in many CPS domains. In this article, we proposeABATe, anAutomaticBehavioralAbstractionTechnique based on neural networks for detecting anomalies in smart cyber-physical systems. Unlike traditional techniques which abstract the statistical properties of different sensor values,ABATelearns complex relationships between event vectors from normal operational data available in abundance with smart CPS and uses this abstracted model to detect anomalies.ABATedetected more than 88 percent of attacks in the publicly available SWaT dataset featuring data from a scaled down sewage water treatment plant with a very low false positive rate of 1 percent. We also evaluated our technique's ability to capture domain semantics and multi-domain adaptability using a real-world automotive dataset, as well as a synthetic dataset.

Secure communication with low computational resources is a critical issue in the Internet-of-Things (IoT) implementations. It is more challenging in the presence of hybrid adversary enabled with full-duplex (FD) capability to perform eavesdropping and jamming simultaneously. In this work we aim to address this issue through optimal subcarrier allocation towards combating the FD hybrid attacker. We begin with secrecy performance analysis in a multi-user IoT system considering statistical channel state information only of all attacker links. Novel analytical expression for the exact intercept probability is derived and a closed-form approximation is also provided. We further propose an optimisation framework for fair subcarrier allocation with a novel objective of minimising maximum intercept probability among multiple users. Considering the proposed optimisation framework as a non-convex combinatorial, we propose a low-complexity sub-optimal solution by leveraging the integer linear program (ILP) structure of the problem. To reduce the complexity further, the original problem is mapped to the assignment model and solved by exploiting its special structure with graph theory tools providing an optimal solution in polynomial time. Comprehensive investigations, conducted to verify the analysis and quantify the secrecy performance, demonstrate that proposed optimal solutions yield significant enhancement in secrecy performance over relevant schemes.

To address the growing concern of security in advance communication networks like Internet of things (IoT), this work aims to propose an optimisation framework for fair subcarrier allocation to encounter a full duplex (FD) attacker. We first analyse the performance of secure communication in a multi-user IoT system against an FD hybrid attacker possessing the capability of concurrent eavesdropping and jamming. Specifically, a novel analytical expression has been derived for the exact intercept probability considering incomplete information of all ungoverned communication links that include self-interference link along with eavesdropping and jamming ones. The optimisation problem of subcarrier allocation is then formulated as an integer linear program. Finally, a low-complexity suboptimal solution is proposed to circumvent the need for high computational resources for finding the optimal solution to the problem in practice. Numerical results, validating the analytical framework, report the average improvement of more than 25% in secrecy performance over relevant benchmarks. This establishes that the proposed scheme has a potential to mitigate the secrecy outage efficiently for secure and reliable communication in IoT networks.

Securing wireless communication, being inherently vulnerable to eavesdropping and jamming attacks, becomes more challenging in resource‐constrained networks such as internet‐of‐things. Towards this, physical layer security (PLS) has gained significant attention due to its low complexity. The authors address the issue of random inter‐node distances in secrecy analysis and develop a comprehensive quality‐of‐service (QoS) aware PLS framework for the analysis of both eavesdropping and jamming capabilities of the attacker. The proposed solution covers the spatially stochastic deployment of nodes. The secrecy performance is characterised against both attacks using inter‐node distance‐based probabilistic distribution functions. The model takes into account the practical limits arising out of underlying QoS requirements, which include the maximum distance between legitimate users driven by transmit power and receiver sensitivity. A novel concept of eavesdropping zone is introduced, and the relative impact of jamming power is investigated. Closed‐form expressions for asymptotic secrecy outage probability are derived offering insights into the design of optimal system parameters for desired security level against the attacker's capability of both attacks. The analytical framework, validated by numerical results, establishes that the proposed solution offers a potentially accurate characterisation of the PLS performance and key design perspective from point‐of‐view of both legitimate user and attacker.

Integrating the Internet-of-Things (IoT) paradigm with industrial wireless sensor networks (IWSNs) has led to a technological evolution known as Industrial IoT (IIoT). To ensure reliable, secure, and low-latency communication in IIoT applications like healthcare, we use rateless codes (RCs) for forward error correction (FEC) at the physical layer (PHY) in a cooperative delay-constrainted environment. Probability of violation (Prvio) is used as a performance metric which consists of: 1) reliability outage probability, i.e., the probability with which the information cannot be successfully decoded within the time constraint T and 2) information intercept probability, which reflects the secrecy performance. Since RC can adjust the rate on the fly, we analyze the performance when relay transmits a fraction of the message and the receiver does energy accumulation (EA). We derive a closed-form expression of Prvio in a single-relay system at a high signal-to-noise ratio (SNR) when the receiver either accumulates energy or mutual information (MI) from the received signals. Furthermore, Prvioof various relay selection schemes is evaluated in a multirelay system. Such kind of analysis in which relay selection is done using RC for PHY-FEC is first of its kind and it is compared to fixed-rate codes. Overall, results show the significant benefits of PHY-RC for guaranteeing the Quality-of-Service (QoS) requirements essential in IIoT applications.

In this paper, we consider a two-tier downlink scenario, where femtocell users are interested in receiving both macrocell and femtocell information simultaneously at a single frequency (joint two-tier downlink reception). Unlike in conventional handsets, which use orthogonal schemes for accommodating two-tier downlink reception, we propose two non-orthogonal schemes based on precoding-aided spatial modulation (PSM) for handling cross-tier downlink interference. In both the proposed schemes, the femtocell information is conveyed as an active antenna index at the user (spatial symbol), while the macrocell information is conveyed as a phase shift keyed (PSK) symbol on the activated antenna. Appropriate precoders are designed at femtocell base station (FBS) and macrocell base station (MBS) to manage the cross-tier interference. We derive average transmit powers at the MBS and all FBSs for both the schemes. We also optimize the transmit powers of both the schemes at a given target signal-to-noise ratio (SNR). Further, we exploit the existing cross-tier interference as a source of artificial interference for enhancing the physical layer security of femtocell users. We derive secrecy rates of the proposed schemes, and corroborate the analytical expressions derived throughout the paper with simulation results.

Physical layer security (PLS) in wireless communication has gained recent attention due to the emergence of new technological breakthroughs in this space. Since the internode distances have been noted to play a key role in the desired security performance, we propose a novel quality-of-service-aware PLS model that incorporates the random spatial deployment of the legitimate users and a potential attacker. This proposed model considers practical constraints like maximum separation between legitimate users and eavesdropping capability of attacker. In this regard, a novel concept of eavesdropping zone is also introduced. Eventually, closed-form expressions are derived for secrecy outage probability using the probabilistic inter-node distance distributions between the legitimate users and attacker to shed key analytical insights like optimal parameter designing to achieve a desired secrecy performance. Lastly, specific simulation results, presented to validate the analytical claims and provide key secured system designing perspectives, corroborate the potential of the proposed framework for more accurately characterizing the desired PLS performance from both the legitimate users' and attackers point-of-view.

Rateless codes (RCs) have the ability of successfully recovering the message from any subset of the fixed number of encoded symbols, making them a good candidate for delay‐tolerant systems. However, most of the applications are delay‐constrained. In this study, quality of violation probability (QVP) is used as the performance metric which includes reliability, secrecy, considering delay‐constraint conditions. The performance of the RC in the presence of an eavesdropper is studied, and a relay selection technique is used to minimise the QVP in a system with regenerative relays. The authors derive an expression for the QVP when adequate mutual information (MI) is obtained at the receiver, and compares it to the energy accumulation (EA) receiver. Further, based on the direct link channel state information available, relay selection scheme is analysed. They observe that MI accumulation reduces QVP significantly in comparison to the EA. It is also observed that initially on increasing the maximum number of allowed channel usages, the QVP gets reduced and later gets saturated. They observe an improvement in outage probability and intercept probability due to diversity gain. A closed‐form expression of QVP for relay selection is determined for the EA and the MI accumulation receiver.

Application of Internet of Things (IoT) in health, defense, banking, and other confidential information transfer urges the need for secure IoT. As most of the IoT devices are resource-limited (antennas, bandwidth, energy), securing the information transfer has always been a challenge. Looking at a solution for enhancing the security of single antenna, single carrier, energy efficient devices, we propose a novel scheme, channel-based mapping diversity. This scheme uses the inherent randomness of the wireless channel and multiple mappings available for an M-ary phase shift keying constellation in confusing an eavesdropper. When the legitimate and the eavesdropper channels are independent of each other, it is shown that a symbol error rate (SER) of (M-1)/ M is induced at the eavesdropper. Whereas, when the channels are correlated, optimal and suboptimal strategies at source and eavesdropper are derived for their respective optimal performances. Further, a closed-form expression for a lower-bound on the SER at the eavesdropper is derived. Simulation results show that for the correlated case, as SNR at the eavesdropper increases, SER initially decreases, later saturates to a relatively high SER, hence making the job of the eavesdropper difficult in getting the legitimate data. Furthermore, the effect of the correlation is more pronounced on SER at higher levels of correlation. This indicates that for practical correlation scenarios, SER is high enough to confuse the eavesdropper.

In this paper, we investigate the secrecy outage performance of a dual-hop decode-and-forward (DF) threshold-based cooperative relay network, both with and without the direct links between source-eavesdropper and source-destination. Without assuming that all the relays can always perfectly decode, here we consider that only those relays who satisfy predetermined threshold can correctly decode the message. We have investigated the outage probability of optimal relay selection scheme, when either full instantaneous channel state information (ICSI) or statistical channel state information (SCSI) of all the links is available. We have shown that CSI knowledge at the transmitter can improve secrecy, and the amount of improvement for the outage probability is more when the required rate is low and for low operating SNR. Asymptotic and diversity gain analysis of the secrecy outage for both the single relay and multi-relay system is obtained, when average SNRs of source-relay and relay-destination links are equal or unequal. We have shown that the improvement in predetermined threshold, eavesdropper channel quality, direct links, and required secrecy rate significantly affects the secrecy performance of the system.

For reliable operation and control of smart grid, estimating the correct states is of utmost importance to the system operator. With recent incorporation of information technology and advanced metering infrastructure, the futuristic grid is more prone to cyber-threats. The false data injection (FDI) attack is one of the most thoroughly researched cyber-attacks. Intelligently crafted, it can cause false estimation of states, which further seriously affects the entire power system operation. In this paper, we propose joint-transformation-based scheme to detect FDI attacks in real time. The proposed method is built on the dynamics of measurement variations. Kullback–Leibler distance is used to find out the difference between probability distributions obtained from measurement variations. The proposed method is tested using IEEE 14 bus system considering attack on different state variables. The results shows that the proposed scheme detects FDI attacks with high detection probability.

Demand of minimal hardware requirement and low energy consumption for internet of things (IoT) has gained the importance of techniques enhancing the physical layer security. Looking at this, we propose a channel-based mapping diversity (CBMD) scheme for a source (S), destination (D) pair to increase the average bit error rate (ABER) at an eavesdropper (E). CBMD leads to an ABER of 0.5 at E when the channels between S - D and S - E are independent. In the case where S - D and S - E are correlated (due to the proximity of E at D), we derive an optimal strategy at E which leads to the best performance at E. We also derive an optimal strategy at S, assuming E uses its optimal strategy, thereby, considering the worst case scenario. A sub-optimal strategy is also proposed at S which does not require any statistical information about the link S - E and hence, has low implementation complexity. We analyze the variation of ABER at E with the signal to noise ratio (SNR) and the channel correlation coefficient. Our simulation results demonstrate that CBMD indeed leads to significant performance degradation at E even at moderate channel correlation for a properly chosen strategy.

This study evaluates the intercept and outage probability of a decode‐and‐forward (DF) underlay cognitive radio network. The secondary users are subject to interference limitations from the primary network, with an eavesdropper tapping the second hop of cognitive network, when all the links undergo Rayleigh fading. For this threshold‐based system, without assuming that the DF relays can always decode the message correctly, here the authors consider that only a set of relays whose SNR satisfies a predetermined threshold can decode the message successfully. The authors have obtained asymptotic analysis for both cases, when average SNRs of secondary source‐relay and relay‐destination links are balanced or unbalanced. The authors have shown that the desired secrecy rate, predetermined threshold, eavesdropper channel quality and interference power limitations significantly affects the secrecy performance of the cognitive radio system. They have investigated the outage and intercept probability of relay selection scheme, when either full instantaneous channel state information or statistical channel state information of all the links is available. They have shown that the optimal relay selection improves the performance of the multi‐relay cognitive system, when the number of relays is increased.

This paper investigates the relay assignment and power allocation problem for two different network power management policies: group lifetime maximization (GLM) and minimum weighted total power (MWTP), with the aim of lifetime maximization in symbol error rate (SER) constrained multiple-user cooperative network. With optimal power allocation solution obtained for each policy, we show that the optimal relay assignment can be obtained using bottleneck matching (BM) algorithm and minimum weighted matching (MWM) algorithm for GLM and MWTP policies, respectively. Since relay assignment with BM algorithm is not power efficient, we propose a novel minimum bottleneck matching (MBM) algorithm to solve the relay assignment problem optimally for GLM policy. To further reduce the complexity of the relay assignment, we propose suboptimal relay selection (SRS) algorithm which has linear complexity in number of source and relay nodes. Simulation results demonstrate that the proposed relay selection and power allocation strategies based on GLM policy have better network lifetime performance over the strategies based on MWTP policy. Compared to the MBM and SRS algorithm, relay assignment based on BM algorithm for GLM policy has inferior network lifetime performance at low update interval. We show that relay assignment based on MBM algorithm achieves maximum network lifetime performance and relay assignment with SRS algorithm has performance very close to it.

We have considered a dual‐hop wireless network consisting of a decode‐and‐forward (DF) relay in presence of an eavesdropper. Relay can correctly decode and retransmit only if the received signal‐to‐noise ratio (SNR) meets a particular threshold. The eavesdropper can tap signals both from the relay and the source. The performance of the maximal ratio combining (MRC) and selection combining (SC) diversity at the eavesdropper is investigated. Whether knowledge of channel state information (CSI) at the transmitter is available or not is considered for the performance evaluation in secrecy outage probability and ergodic secrecy rate. Asymptotic analyses of performances are provided. We show that direct link has a significant impact on system secrecy. It is found that secrecy performances are the best if the relay is always able to decode correctly. We also found that knowledge of CSI helps to achieve better secrecy at lower rate. It is observed that unbalance created due to constraint on either of the source‐relay link average SNR or relay‐destination link average SNR does not yield similar secrecy outage performance but both can limit the secrecy outage performance. On the contrary, it is found that only source‐relay link quality can limit the ergodic secrecy rate performance.

Energy efficiency is a major issue in the energy‐constrained wireless sensor network to ensure longer battery life. In this study, minimisation of total energy per bit for multi‐hop decode‐and‐forward network employing M‐ary quadrature amplitude modulation is considered. An average bit error rate (ABER) requirement at the destination over an independent Rayleigh fading channel is assumed. A realistic energy model is considered. The authors have proposed joint optimisation of constellation size, energy allocation per bit and relay location assuming fixed end‐to‐end distance. The authors have considered two scenarios: one, that each hop employs the same constellation size per hop and two, it adapts independently to take different constellation size. A novel solution is implemented following least square method to find the approximate closed‐form solution of the optimal constellation size, which otherwise would not have been possible. It is observed that joint optimisation technique where the constellation size adapts independently per hop outperforms the one where the constellation size is same. Least amount of total energy is consumed per bit for balanced link. Finally, the analysis shows that for a realistic energy model, the dual hop network provides significant energy saving of 58% at 10 − 4 ABER over multi‐hop network with four hops.

Energy efficiency is a crucial design issue in energy‐constrained wireless networks to ensure uninterrupted information exchange. With the requirement of average end‐to‐end bit error rate (BER), the problem of joint routing and power allocation optimisation in multihop wireless network is studied here for two network power management policies: one is to minimise overall transmit power and the other is to maximise network lifetime. The proposed minimum total power strategy is optimal for minimising the overall transmit power consumption in the network and is preferable in network with tethered energy resources. To maximise the lifetime of a network with battery‐operated nodes, the authors have developed two residual energy‐aware joint routing and power allocation strategies: path lifetime maximisation (PLM) strategy and minimum weighted total power (MWTP) strategy. A distributed implementation for these strategies is also presented. Simulation results demonstrate that the proposed strategies achieve significant power saving and prolong network lifetime considerably over traditional routing algorithm with individual link BER constraint. It has also been shown that at reasonably low route refresh interval, the MWTP strategy performs best in terms of network lifetime, whereas at very high route refresh interval, the PLM strategy is optimal for network lifetime maximisation.

A joint optimisation of power allocation (PA) and relay location is proposed for decode‐and‐forward relaying over multi‐hop, independent, log‐normal fading channels. Optimisation is carried out at high signal‐to‐noise ratio (SNR) and low SNR scenarios to minimise the outage probability with a constraint on total transmit power and end‐to‐end relaying distance. End‐to‐end average bit error rate is also minimised assuming the same constraints. Optimisation is carried out to find optimal PA (OPA) for a given relay location, optimal relay location (ORL) for a given PA and joint OPA and relay location. All the optimisation problems reformulated from the original problems are shown to be convex except relay location optimisation minimising outage probability at low SNR scenario. It is then solved using properties of concave minimisation. Optimal allocation factors do not depend on the instantaneous channel state information. It also does not depend on total available power in the system except allocation factors evaluated by optimising outage at high SNR. It is observed that OPA allocates more power to weaker links and ORL allocates less distance to weaker links. It is also observed that performance improvement increases with increase in link unbalance and distance‐based allocation is most effective.

Relay selection is considered to enhance the secrecy of a dual-hop regenerative multi-relay system with an eavesdropper. Without assuming perfect decoding at the relays, the secrecy outage probability of a single relay system is obtained first. Secrecy outage of optimal, traditional, and suboptimal relay selection schemes is then evaluated. To reduce the power consumption, partial relay selection schemes based only on either of the source-relay or relay-destination instantaneous channel state information (ICSI) are introduced. The secrecy outage is evaluated and compared with the other schemes. Secrecy outage of all the selection schemes are obtained in closed-form. An optimal relay selection scheme is proposed using secrecy outage, which does not require any ICSI. Asymptotic and diversity gain analysis of the secrecy outage is presented when source-relay and relay-destination average SNRs are the same or different. We observe that the improvement in eavesdropper link quality affects the secrecy outage more when required secrecy rate is low as compared to the case when rate is high. We also observe that relay selection improves performance more when number of relays are more. It is important to note that either of the source-relay or the relay-destination link quality can equally limit the secrecy outage performance even if the other link quality is infinitely good.

We evaluate the bounds on the secrecy outage probability of a dual hop Amplify-and-forward (AF) system with an eavesdropper tapping the second hop, when all the links undergo Rayleigh fading. An approximate expression of outage is also obtained when the signal-to-noise ratio of the first hop is high. Based on the developed outage expressions we evaluate the bounds and the approximate outage for optimal relay selection when full instantaneous channel state information (FCSI) i.e. of all the links is available. We also propose a novel relay selection scheme when only statistical channel state information (SCSI) of all the links is available. The proposed scheme can be used in networks where feedback of FCSI to the decision making node is power intensive and CSI of the eavesdropper cannot be obtained at all instants. In the results section we show that the approximate expression follows the simulations exactly and the outage for relay selection in FCSI decreases with an increase in the number of relays.

Efficient power management is a crucial design issue in energy constrained wireless networks to ensure uninterrupted information exchange. With the requirement of end-to-end outage probability constraint, we study the problem of joint routing and power allocation optimization in multihop wireless network for two network power management policies: one is to minimize overall transmit power for which we propose minimum total power (MTP) strategy and the other is to maximize network lifetime for which we have developed energy aware minimum total power (EA-MTP) strategy. The proposed strategies only depend on channel statistics and node energy information and can be implemented distributedly. Simulation results demonstrate that compared to traditional routing algorithm with individual link outage probability constraint, MTP and EA-MTP strategies achieve significant improvement in power saving and network lifetime performances respectively. Also it has been shown that MTP strategy performs well in terms of network lifetime although it does not require periodic route updation and can be implemented efficiently in large networks.

In this paper, a joint optimization of power allocation (PA) and relay location is proposed for Amplify-and-Forward (AF) multihop relaying over independent lognormal fading channels. The proposed optimization method maximizes the end-to-end (e2e) average signal-to- noise ratio (ASNR) having constraints on total transmit power with no per terminal maximum limit and assuming fixed e2e distance. Optimal parameters do not depend on instantaneous channel state information (ICSI) and can reduce complexity and power consumption. Optimal PA for maximizing e2e instantaneous SNR (ISNR) is also derived considering same constraints. Outage performance of joint optimization method based on ASNR and optimization method based on ISNR is compared. It is observed that joint optimization not only performs better than equal allocation, it can also outperform PA based on ISNR when link unbalance is large.

For sensor nodes deployed at small distances, computation energy along with radio energy determines the battery life. We have proposed a system-level design space exploration methodology in [1] for searching an energy-efficient error-correcting code (ECC). This methodology takes into account the computation and the radio energy in an integrated manner. In this paper, we validate this methodology by deploying the Imote2 nodes and measuring energy values under different operating modes, e.g., with and without ECC. In this process, we propose a validation framework and node energy model. Experimental results validate the methodology and show that with ECC we can save up to 14% transmitter energy under a certain set of conditions. The main contribution of this paper is that it establishes experimentally that our methodology is effective in exploration of various node configurations and finding an energy-efficient solution.

In This paper we have addressed the problem of direction of arrival (DOA) estimation algorithm and beamforming for Impulse Radio (IR) Ultra-wideband (UWB) communication systems in additive white Gaussian noise. The multi user UWB pulse-position modulation (PPM) signals are received by smart antenna(Uniform linear array) are Fourier transformed to split the array output into multiple frequency channels, and the corresponding indexed bin data arranged in the form of polynomial model. On this Iterative quadratic maximum likelihood (IQML) algorithm is applied to yield DOA estimates. These DOA estimates at different frequencies are combined into a single estimate in an averaging manner. After obtaining a frame work for DOA estimation we turn our attention to beamforming. Interference-plus-noise subspace characterized and DOA's of the interference signals are exploited to estimate signal free covariance matrix and weight vector is developed to maximize the signal -to- interference-plus noise ratio (SINR) at the output of the beamformer. The performance of the proposed method is studied via extensive computer simulations.

For closely deployed sensor nodes, computation energy along with radio energy determines the battery life. We have proposed a system level design space exploration methodology [1] for searching an energy efficient error correcting code (ECC). This methodology takes into account the computation and the radio energy in an integrated manner. In this paper we validate this methodology by deploying Imote2 nodes and measuring energy values under different operating modes, e.g., with and without ECC. Experimental results validate the methodology and show that with ECC we can save upto 13% transmitter energy for certain set of conditions. This paper validates experimentally that our methodology is effective in exploration of various node configurations and finding an energy efficient solution.

Physical layer security is an emerging security field that explores the possibilities of achieving perfect secrecy data transmission between the intended network nodes, while possible malicious nodes that eavesdrop the communication obtain zero information. In this paper, we observe how node cooperation improves the physical layer security of a simple wireless network by reducing the surface of the geographical area in which the malicious nodes can listen to the transmitted data from the source to the destination. Our analysis and simulation results show a dramatic improvement even by cooperation with only one relay node. The improvement gets better by adding more cooperating nodes. We also observe that if cooperating nodes are closer to the line that connects the source and the destination node, the region in which the malicious node can profit from the eavesdropping gets smaller.

In this paper, we first establish that, in wireless sensor networks, operating over ldquosmallrdquo distances, both computation energy and radio energy influence the battery life. In such a scenario, to evaluate the utility of error-correcting codes (ECCs) from an energy perspective, one has to consider the energy consumed in encoding-decoding and transmitting additional ldquoredundantrdquo bits vis-a-vis the energy saved due to coding gain. This paper presents a framework for evaluating various ECCs based on a comprehensive energy model of a sensor node. The framework supports exploration of sensor node design space with application- and deployment-related parameters, like distance, bit error rate, path loss exponent, as well as the modulation scheme and ECC parameters. The exploration results show that, as compared to the uncoded-data transmission, the energy-optimal ECC saves 15%-60% node energy for the given parameters.

Optimizing energy consumption is a key objective in designing wireless sensor nodes. It has been shown earlier that the node energy is strongly influenced by the modulation and the error correcting code (ECC) used. The utility of using ECC from an energy perspective is determined by the energy saving due to the ECC coding gain vis-a-vis the energy overhead of "redundant" bits and of energy saving. Furthermore, the node energy varies with the change in errorcorrecting capability and code word length of a particular ECC as well as the modulation constellation size. The ECC coding gain is influenced by the constellation size. In this paper, the node energy variations with ECC and modulation parameters are analyzed for an energy optimal node design for the nodes operating in the additive white Gaussian noise channel. Based on this analysis, we compute the per information bit node energy and this is used to select an "optimal" ECC and modulation scheme pair. Our results show that the energy optimal ECC-modulation pair selected for some specific operating conditions could save as much as 50% energy. In nutshell, our work is targeted towards reducing the search space and finding an energy optimal ECC modulation pair for the given environment and application.

In this paper, we consider the effect of carrier offsets in arbitrarily correlated flat-fading multiple-input multiple-output (MIMO) Rayleigh channels. We propose a double-differential coding for square orthogonal space-time block code (OSTBC) with non-unitary constellations over flat-fading MIMO channels with carrier offsets. In order to improve the performance of the proposed double-differential orthogonal space-time block code (DDOSTBC) over arbitrarily correlated Rayleigh channel we introduce a full memoryless precoder matrix in the transmitter. For the proposed precoded DDOSTBC, a pair-wise error performance (PEP) analysis is conducted. Then we propose a precoder design based on the PEP upper bound. The proposed DDOSTBC differs from the previously proposed DDOSTBC by: 1) The previously proposed DDOSTBC is aplicable to only a specific class of OSTBC which follows diagonal group property, whereas, the proposed DDOSTBC is applicable to any square OSTBC. 2) The previously proposed DDOSTBC can work withM-PSK constelation only, whereas, the proposed DDOSTBC is applicable toM-QAM,M-PAM, orM-PSK constellations. The proposed DDOSTBC provides higher performance gain as compared to the same rate previously proposed DDOSTBC. In addition, the proposed precoded DDOSTBC is able to perform better than the unprecoded DDOSTBC over arbitrarily correlated Rayleigh channels.

In wireless sensor networks due to the small transmission distances involved, the computation energy along with the radio energy determines the battery life. Energy consumption of error control codes (ECCs) is a complex function of the energy consumption in computing encoding-decoding, transmitting "redundant" bits and energy saved by coding gain. This paper presents a methodology, which integrates computation and radio energy for searching an energy optimal ECC. Based on this methodology, a design space exploration framework and the energy model of sensor node have been developed. Exploration results show that the energy optimal ECC saves 15-58% node energy for given parameters.

The design of pulse position modulated (PPM) space–time trellis codes (STTC) for ultra-wideband impulse radio (UWB-IR) multiple-input multiple-output (MIMO) communication systems over slow and fast fading multipath channels is considered. First, A probability of error analysis is carried out to derive upper bounds on pairwise symbol error probability at high and low signal-to-noise ratios (SNRs). From the upper bounds, A new distance notion is introduced and novel design criteria for optimal (in error rate performance) M-ary PPM STTC are deduced for UWB. An optimal binary-PPM STTC is designed for two transmit antennas. Finally, simulation results of the UWB-IR MIMO system, using the optimal STTC, confirm significant improvement in bit-error-rate performance over the uncoded UWB-IR single-input single-output system and also over previously proposed space–time coding scheme for UWB, at higher SNR.

Multiple-input multiple-output (MIMO) systems with space–time (ST) coding are desirable in ultra-wideband (UWB) communication systems to improve the error-rate performance of the UWB link. The authors have considered the design of optimal (in error-rate performance) M-ary pulse-amplitude modulated (M-PAM) ST trellis codes (STTC) for a pulse-based UWB MIMO communication system. Following the approach by Vucetic et al. for narrowband systems, the authors carry out a probability of error analysis to derive upper bounds on pairwise symbol error probability for a UWB communication system for slow fading and fast fading at both low and high signal-to-noise ratios (SNRs). The authors deduce the design criteria from the upper bounds. Based on these criteria, an optimal four-state binary-PAM STTC, for two transmit antennas, is designed by hand. Finally, simulation results of the optimal binary-PAM STTC in a UWB communication system confirm significant improvement in bit error-rate performance over previously proposed ST coding scheme for UWB, at higher transmit SNR.

We introduce a new distance notion and develop novel design criteria for optimal MN-ary pulse position amplitude modulation (PPAM) space-time trellis codes (STTC) for ultrawideband multiple-input multiple-output systems for slow and fast fading at both low and high SNR. Simulation results of the 2,2-ary PPAM STTC, constructed through set partitioning, confirm significant reduction in bit error rate.

We present a novel method for constructing trellis codes, based on recursive nonlinear equations. Using this method, trellis codes having good code rates (R = k/n) can be constructed. At the same time, the method allows the code-designer to construct a trellis with a large free distance, d/sub free/, at the cost of a larger number of states in the trellis. It has been shown in this paper that for the code rate, R, less than a critical rate, R/sub c/ the free distance can be made as large as desired for large n. This design methodology provides the freedom to play with the code performance and the code rate of the trellis code. Using this method, a rate 3/4 trellis code has been constructed with d/sub free/ =12.