Veluppillai Mahinthan

Partner Selection Based on Optimal Power Allocation in Cooperative-Diversity Systems

We study how to appropriately match users for two-user cooperative-diversity (CD) systems deploying an optimal-power-allocation (OPA) strategy, considering both the amplify and forward and the regenerate and forward CD schemes. The OPA strategies, which can minimize the total energy consumption for the cooperating pair, are derived for both CD schemes. Then, we study the location of the optimal partner for a user and develop a novel nonbipartite stable matching algorithm with a performance that is very close to the optimal maximum weighted (MW) matching algorithm. The proposed matching algorithm is simple to implement, and its computational complexity is one order lower than that of the optimal MW matching algorithm. Numerical results show that with the OPA and the proposed matching algorithm, a 9~10 dB CD gain can be achieved, which is equivalent to prolonging the cell-phone-battery recharge time by about ten times.

Maximizing Cooperative Diversity Energy Gain for Wireless Networks

We are concerned with optimally grouping active mobile users in a two-user-based cooperative diversity system to maximize the cooperative diversity energy gain in a radio cell. The optimization problem is formulated as a non-bipartite weighted-matching problem in a static network setting. The weighted-matching problem can be solved using maximum weighted (MW) matching algorithm in polynomial time O(n3). To reduce the implementation and computational complexity, we develop a Worst-Link-First (WLF) matching algorithm, which gives the user with the worse channel condition and the higher energy consumption rate a higher priority to choose its partner. The computational complexity of the proposed WLF algorithm is O(n) while the achieved average energy gain is only slightly lower than that of the optimal maximum weighted- matching algorithm and similar to that of the 1/2-approximation Greedy matching algorithm (with computational complexity of O(n2 log n)) for a static-user network. We further investigate the optimal matching problem in mobile networks. By intelligently applying user mobility information in the matching algorithm, high cooperative diversity energy gain with moderate overhead is possible. In mobile networks, the proposed WLF matching algorithm, being less complex than the MW and the Greedy matching algorithms, yields performance characteristics close to those of the MW matching algorithm and better than the Greedy matching algorithm.

Cross-Layer Performance Study of Cooperative Diversity System With ARQ

In this paper, a cross-layer design of a wireless communication system is proposed by considering a quadrature signaling (QS)-based cooperative diversity (CD) system employing truncated stop-and-wait automatic repeat request (ARQ) for error control. The proposed CD-ARQ scheme employs selection relaying at the partner, and all the transmission channels are assumed to exhibit Nakagami-m fading. To analyze the cross-layer performance of the proposed scheme, a Markov model is developed by capturing the effects of correlated transmission errors of the Nakagami-m fading cooperative channels. Based on the analysis, the effective cooperative channel of QS-CD-ARQ is uncorrelated when the normalized Doppler shift of at least one of the user-to-destination channels is higher than 0.2. Performance metrics (e.g., channel efficiency, packet loss rate, throughput, average delay, and jitter) are taken into account in the study. Our numerical results show that the QS-CD-ARQ scheme outperforms both an incremental-relaying-based CD system and a non-cooperative system if the average of the received signal is higher than the receiver sensitivity and if the channel between users is better than the direct transmission channel. In addition, QS-CD-ARQ provides the lowest packet loss rate with the lowest delay among all the schemes for any number of maximum retry limits. Moreover, compared with a scheme that employs incremental relaying, the proposed QS-CD-ARQ scheme is less complex to implement.

A cooperative diversity scheme based on quadrature signaling

A bandwidth and energy efficient cooperative diversity scheme based on quadrature signaling is proposed. The quadrature signaling is achieved by transmitting in the in-phase and quadrature components of QPSK modulation. The diversity gain and the bit error rate of the proposed cooperative diversity scheme improve with the inter-user channel quality. It is shown that the proposed scheme can achieve a diversity order of two for high inter-user signal-to-noise ratios, if the cooperating users are located within a region that permits successful cooperation. The cooperative region corresponding to a specified bit error rate is defined and derived

Performance analysis and power allocation for M-QAM cooperative diversity systems

An adaptive regenerate and forward cooperative diversity (CD) system using quadrature amplitude modulation (QAM) for a two-user cooperation is proposed. The proposed system can achieve a maximum diversity order of two. The bit error probability (BEP) of a CD system depends primarily on the quality of the inter-user channel and user-to-destination channels, and the transmitted power of the cooperating users. Expressions which characterize the asymptotic behavior of the BEP as a function of the received signal-to-noise ratio (SNR) at the relay and the destination are derived. The transmit power is allocated optimally between the source and the relay according to the channel qualities and the CD system employed to achieve a prescribed BEP. Three power allocation strategies, each for a specific wireless communication scenario, which optimize the power consumption of the proposed CD system are introduced. The cooperative region, corresponding to each power allocation scheme, within which the partners must be located in order to yield a specified cooperative energy gain, is determined.

A simple cooperative diversity scheme based on orthogonal signaling [mobile radio applications]

In this paper, a bandwidth efficient and energy efficient cooperative diversity scheme is proposed based on orthogonal signaling. Orthogonal signaling is achieved by transmitting in the in-phase and quadrature components of a phase shift keying modulation system. The bit error rate performance of the proposed cooperative diversity scheme increases with interuser signal strength. Numerical results show that the proposed cooperative diversity scheme can achieve the diversity order of two for high interuser signal-to-noise ratio.

Performance of Adaptive Relaying Schemes in Cooperative Diversity Systems with ARQ

In this paper, the performance of adaptive relaying schemes in cooperative diversity (CD) systems equipped with automatic repeat request (ARQ) is studied. Both selection relaying and incremental relaying are considered with a regenerate and forward CD system. The performance metrics of the CD-ARQ system such as efficiency, packet drop rate, average delay and jitter are presented. Numerical results show that selection relaying with a good partner outperforms incremental relaying. In addition, selection relaying performs better than incremental relaying without the ARQ scheme.

Matching algorithms for infrastructure-based wireless networks employing cooperative diversity system

We study how to optimally group active users in an infrastructure-based wireless network employing two-user- based cooperative diversity technology in order to maximize the cooperative diversity gain in the network. The optimization problem is formulated as a non-bipartite weighted-matching problem, which can be solved with the state-of-the-art maximum weighted-matching algorithm in polynomial time O(n 3 ) .T o reduce the computational complexity, we develop a Worst-Link- First (WLF) matching algorithm, which gives the user with the worse channel condition and the higher energy consumption rate a higher priority to choose its partner. The computational complexity of the proposed WLF algorithm is O(n 2 ) while the achieved average energy gain is only slightly lower than that with the optimal maximum weighted-matching algorithm. Numerical results demonstrate that, with the WLF matching algorithm, 5 ∼ 7 dB energy gain can be achieved.

WLC41-2: Adaptive Regenerate and Forward Cooperative Diversity System based on Quadrature Signaling

In this paper, an adaptive regenerate and forward cooperative diversity (CD) system based on quadrature signaling is proposed. The bit error probability (BEP) of the proposed CD system is derived in terms of the received signal-to-noise ratio (SNR) at the relay and the destination. The derived upper bound of the BEP is validated by simulations. Further, it is shown that the proposed CD system can achieve maximum diversity order of two and performs better even though the inter-user channel is poor. The power consumption of the CD system is location dependent for given BEP. To optimize the power consumption of the proposed CD system, an optimal power allocation strategy is proposed.

Impact of Developer Choices on Energy Consumption of Software on Servers

Abstract The power cost of running a data center is a significant portion of its total annual operating budget. With the aim of reducing power bills of data centers, “Green Computing” has emerged with the primary goal of making software more energy efficient without compromising the performance. Developers play an important role in controlling the energy cost of data center software while writing code. In this paper, we show how software developers can contribute to energy efficiency of servers by choosing energy efficient APIs (Application Programming Interface) with the optimal choice of parameters while implementing file reading, file copy, file compression and file decompression operations in Java; that are performed extensively on large scale servers in data centers. We performed extensive measurements of energy cost of those operations on a Dell Power Edge 2950 machine running Linux and Windows servers. Measurement results show that energy costs of various APIs for those operations are sensitive to the bu ff er size selection. The choice of a particular Java API for file reading with different buffer sizes has significant impact on the energy cost, giving an opportunity to save up to 76%. To save energy while copying files, it is important to use APIs with tunable buffer sizes, rather than APIs using fixed size buffers. In addition, there is a trade off between compression ratio and energy cost: because of more compression ratio, xz compression API consumes more energy than zip and gzip compression APIs. Finally, we model the energy costs of APIs by polynomial regression to avoid repeated measurements.