Siva D. Muruganathan

A centralized energy-efficient routing protocol for wireless sensor networks

Wireless sensor networks consist of small battery powered devices with limited energy resources. Once deployed, the small sensor nodes are usually inaccessible to the user, and thus replacement of the energy source is not feasible. Hence, energy efficiency is a key design issue that needs to be enhanced in order to improve the life span of the network. Several network layer protocols have been proposed to improve the effective lifetime of a network with a limited energy supply. In this article we propose a centralized routing protocol called base-station controlled dynamic clustering protocol (BCDCP), which distributes the energy dissipation evenly among all sensor nodes to improve network lifetime and average energy savings. The performance of BCDCP is then compared to clustering-based schemes such as low-energy adaptive clustering hierarchy (LEACH), LEACH-centralized (LEACH-C), and power-efficient gathering in sensor information systems (PEGASIS). Simulation results show that BCDCP reduces overall energy consumption and improves network lifetime over its comparatives.

A Hybrid Routing Protocol for Wireless Sensor Networks Based on a Two-Level Clustering Hierarchy with Enhanced Energy Efficiency

A two-level hierarchical clustering based hybrid routing protocol (THCHP) for wireless sensor networks is proposed in this paper. The per frame time average energy dissipation performance of THCHP is analytically evaluated. The accuracy of the derived analytical expression is validated via comparisons with simulation results. Furthermore, we compare the performance of THCHP to the previously proposed APTEEN protocol. Our results show that THCHP achieves significant energy savings when compared to APTEEN. In addition, comparisons between the average query response times of THCHP and APTEEN show that the proposed THCHP scheme achieves a much lower query response time and can operate over a broad range of query arrival rates with minimal increases in response time.

A QRD-RLS-Based Predistortion Scheme for High-Power Amplifier Linearization

A digital baseband predistortion (PD) scheme for high-power amplifier (HPA) linearization is proposed and analyzed in this brief. The proposed approach utilizes the QR-decomposition-based recursive least squares (QRD-RLS) algorithm to estimate the memoryless complex polynomial coefficients that characterize the HPA. The inverse polynomial model coefficients corresponding to the PD are similarly extracted using QRD-RLS. The performance of the proposed PD scheme is analyzed via simulations and compared with previously published techniques. Results show that the QRD-RLS-based solution offers improved performance over its comparatives

Analytical query response time evaluation for a two-level clustering hierarchy based wireless sensor network routing protocol

In this letter, we analytically evaluate the average query response time of the Two-level Hierarchical Clustering based Hybrid-routing Protocol (THCHP) proposed recently for wireless sensor networks (WSNs). The accuracy of the average query response time analysis is verified via numerical simulations. Additionally, average query response time comparisons, between THCHP and a previously proposed Adaptive Periodic Threshold-sensitive Energy Efficient sensor Network (APTEEN) protocol, show that THCHP is better suited than APTEEN for delay sensitive WSN applications.

An Efficient PAPR Reduction Method for Wavelet Packet Modulation Schemes

This paper proposes a novel peak-to-average power ratio (PAPR) reduction method for wavelet packet modulation (WPM) based multi-carrier systems. Orthogonal basis functions that minimize a newly derived PAPR upper bound are designed. The performance of the proposed orthogonal basis functions is compared to those of the conventional Daubechies basis functions and OFDM. Via these comparisons, it is shown that the proposed orthogonal basis functions achieve notable performance improvements over its comparatives.

A Low-Complexity Decision-Directed Channel-Estimation Scheme for OFDM Systems With Space–Frequency Diversity in Doubly Selective Fading Channels

In this paper, we propose a low-complexity decision-directed channel-estimation scheme, which offers improved performance for space-frequency-block-coded orthogonal frequency-division multiplexing (SFBC-OFDM) systems under doubly selective (i.e., frequency selective and fast fading) channels. First, we propose a square-root-free inverse-QR-decomposition-based groupwise recursive (SIQR-GR) channel-estimation algorithm employing sequences of scaled Givens rotations. The proposed SIQR-GR scheme recursively processes data decisions corresponding to the SFBC groups within each OFDM block to improve system performance under doubly selective channels. Furthermore, the avoidance of square roots and the utilization of scaled Givens rotations ensure that the proposed SIQR-GR scheme is computationally efficient. Second, we derive semianalytical expressions for the normalized mean square error (NMSE) performance of SIQR-GR and verify the accuracy of the NMSE analysis via numerical simulations. Finally, we provide performance and complexity comparisons between SIQR-GR and previously proposed schemes. These comparisons show an excellent performance-complexity tradeoff achieved by SIQR-GR over the previous solutions under various channel conditions.

A recursive QR detector for space-frequency block coded OFDM systems with four transmit antennas

The use of orthogonal space-time block coding (O-STBC) across sub-carrier tones is a promising solution for future orthogonal frequency division multiplexing (OFDM) based broadband wireless systems. However, due to high channel gain variation across adjacent sub-carriers, conventional methods for O-STBC decoding yield poor performances. In this paper, we propose a square-root-free recursive QR detector for O-STBC based OFDM systems with four transmit antennas. Theoretical performance bounds are analyzed and compared with results obtained from exact link simulations. The performance gain attained by the proposed detector under multi-path fading environments is confirmed by simulation results.

A Null-Subcarrier-Aided Reference Symbol Mapping Scheme for 3GPP LTE Downlink in High-Mobility Scenarios

In this paper, a new reference symbol (RS) mapping scheme for the Third-Generation Partnership Project (3GPP) long-term evolution (LTE) and LTE-Advanced (LTE-A) downlink is proposed to improve channel estimation performance in high-mobility communication scenarios. The proposed scheme employs null subcarriers to guard RSs, which helps mitigate the effect of intercarrier interference (ICI) on subcarriers carrying RSs. Additionally, the proposed scheme allows the ICI gain parameters to be estimated via a simple frequency-domain estimator. Modified Cramer-Rao bound (MCRB) expressions are derived for the proposed scheme, as well as for the conventional RS mapping scheme defined in the 3GPP LTE and LTE-A standards to compare their performance at high mobile user speeds. These bounds, together with mean square errors obtained from simulations, reveal superior performance achieved by the proposed scheme in high-mobility scenarios. Additionally, at high mobile user speeds, the proposed scheme offers significant bit-error-rate (BER) performance improvement over the standard RS mapping.

Peak-to-Average Power Ratio Reduction for Wavelet Packet Modulation Schemes via Basis Function Design

In this paper, we propose a novel peak-to-average power ratio (PAPR) reduction method based on optimum basis function design for wavelet packet modulation schemes. We first establish a cost function to be optimized by analytically deriving an upper bound for the PAPR. The cost function is then used to design the optimum basis function. Simulation results show that the proposed optimum basis function achieves significant PAPR reductions when compared to the conventional Daubechies basis function. In addition, it is also shown that a superior PAPR- bandwidth tradeoff can be achieved through the proposed basis function over the conventional one.

A Computationally Efficient QR-Successive Interference Cancellation Scheme for Simplified Receiver Implementation in SFBC-OFDM Systems

In this paper, we propose a computationally efficient square-root and division free recursive QR (SDRQR) decomposition based successive interference cancellation (SIC) receiver for space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) transmit diversity schemes. The performance of the proposed SDRQR-SIC receiver is semi- analytically evaluated taking into account the effects of channel estimation errors and error propagation during SIC. In addition, performance and complexity comparisons are drawn with previously proposed approaches. These comparisons show an excellent performance-complexity tradeoff achieved by SDRQR-SIC over the previous solutions under various channel conditions.