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Ralink Technology

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Tarng W.,National Hsinchu University of Education | Ou K-L.,National Hsinchu University of Education | Huang K-J.,National Hsinchu University of Education | Deng L-Z.,National Hsinchu University of Education | And 4 more authors.
International Journal of Communication Networks and Information Security | Year: 2011

In recent years, the applications of wireless sensor networks have increased steadily. Sensor nodes are often scattered outdoors and their energy consumption depends heavily on the area of coverage and network topology. Many studies were focused on saving the energy of sensor nodes to maintain their functionality. This work aims at extending the lifetime of a wireless sensor network by using cluster merging and dynamic routing mechanisms. Cluster merging can increase the number of sensor nodes in a cluster to balance its energy consumption; dynamic routing prevents the cluster heads from exhausting electric power by forwarding data through detoured routes. The simulation results show that cluster merging followed by dynamic routing is more efficient in extending network lifetime. The best combination of the above two mechanisms is to set the threshold of the remaining energy to 90% for applying cluster merging and 10% for applying dynamic routing, which results in the lifetime about 9 times that of a wireless sensor network without using the adaptive mechanisms.


Griot M.,Qualcomm | Casado A.I.V.,Mojix Inc | Weng W.-Y.,Ralink Technology | Chan H.,Pharmaco-Kinesis Corporation | And 2 more authors.
IEEE Transactions on Communications | Year: 2012

This paper presents a practical technique that uses Ping's interleave(r)-division multiple access and single-user decoding to provide uncoordinated access for a family of binaryinput binary-output multiple-access channels (MACs) including the OR-MAC where users' binary transmissions are combined with the logical OR operation. Information theoretic calculations provide the achievable sum-rates and optimal ones densities for these MACs. Because the required ones densities are significantly less than 50%, new nonlinear trellis code analysis and design techniques are introduced to provide the needed codes. Union bound techniques that predict the performance of these codes are also presented. Simulation results and a working FPGA implementation verify the performance and feasibility of the proposed nonlinear codes and overall multiple access scheme. © 2012 IEEE.


Lee H.-C.,National Tsing Hua University | Ueng Y.-L.,National Tsing Hua University | Yeh S.-M.,National Tsing Hua University | Weng W.-Y.,Ralink Technology
IEEE Transactions on Communications | Year: 2013

When residual belief-propagation (RBP), which is a kind of informed dynamic scheduling (IDS), is applied to low-density parity-check (LDPC) codes, the convergence speed in error-rate performance can be significantly improved. However, the RBP decoders presented in previous literature suffer from poor convergence error-rate performance due to the two phenomena explored in this paper. The first is the greedy-group phenomenon, which results in a small part of the decoding graph occupying most of the decoding resources. By limiting the number of updates for each edge message in the decoding graph, the proposed Quota-based RBP (Q-RBP) schedule can reduce the probability of greedy groups forming. The other phenomenon is the silent-variable-nodes issue, which is a condition where some variable nodes have no chance of contributing their intrinsic messages to the decoding process. As a result, we propose the Silent-Variable-Node-Free RBP (SVNF-RBP) schedule, which can force all variable nodes to contribute their intrinsic messages to the decoding process equally. Both the Q-RBP and the SVNF-RBP provide appealing convergence speed and convergence error-rate performance compared to previous IDS decoders for both dedicated and punctured LDPC codes. © 1972-2012 IEEE.


Weng L.,Ralink Technology | Anastasopoulos A.,University of Michigan | Pradhan S.S.,University of Michigan
IEEE Transactions on Communications | Year: 2011

In wireless communication systems, users with heterogeneous information content constrain the network by having different reliability requirements. In this paper an information-theoretic framework is proposed to study communication systems which provide heterogeneous reliabilities for the users. This is done by defining individual probabilities of error for the users in the network and obtaining their fundamental tradeoffs. Using this framework, a system can be realized, which can provide a tradeoff of reliabilities among the users for a fixed vector of users' rates. This adds a completely new dimension to the performance tradeoff in such networks, which is beyond what is given by the conventional performance versus rate tradeoff in single-user systems. Although this is a very general concept and can be applied to any multi-terminal communication system, in this paper we consider multiple-input multiple-output (MIMO) fading broadcast channel. In particular, we quantify the reliability tradeoff by introducing the notion of diversity gain region (DGR), which specifies the set of diversity gain vectors that are simultaneously achievable by the users for a fixed vector of users' multiplexing gains. We show the existence of a tradeoff among the users' diversity gains by deriving inner and outer bounds for the DGR. © 2011 IEEE.

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