Search

We observe that in a multichannel wireless system, an opportunistic channel/spectrum access scheme that solely focuses on channel quality sensing measured by received SNR may induce users to use channels that, while providing better signals, are more congested. Ultimately the notion of channel quality should include both the signal quality and the level of congestion, and a good multichannel access scheme should take both into account in deciding which channel to use and when. Motivated by this, we focus on the congestion aspect and examine what type of dynamic channel switching schemes may result in the best system throughput performance. Specifically, we derive the stability region of a multiuser multichannel WLAN system and determine the throughput optimal channel switching scheme within a certain class of schemes. We also empirically examine the impact of considering congestion in addition to signal quality in making channel selection decisions. [ABSTRACT FROM AUTHOR]

Given the multilevel internal SSD parallelism at the different four levels: channel-level, chip-level, die-level, and plane-level, how to exploit these levels of parallelism will directly and significantly impact the performance and endurance of SSDs, which is in turn primarily determined by three internal factors, namely, advanced commands, allocation schemes, and the priority order of exploiting the four levels of parallelism. In this paper, we analyze these internal factors to characterize their impacts, interplay, and parallelism for the purpose of performance and endurance enhancement of SSDs through an in-depth experimental study. We come to the following key conclusions: 1) Different advanced commands provided by Flash manufacturers exploit different levels of parallelism inside SSDs, where they can either improve or degrade the SSD performance and endurance depending on how they are used; 2) Different physical-page allocation schemes employ different advanced commands and exploit different levels of parallelism inside SSDs, giving rise to different performance and endurance impacts; 3) The priority order of using the four levels of parallelism has the most significant performance and endurance impact among the three internal factors. The optimal priority order of using the four levels of parallelism in SSDs is found to be: 1) the channel-level parallelism; 2) the die-level parallelism; 3) the plane-level parallelism; and 4) the chip-level parallelism. [ABSTRACT FROM PUBLISHER]

This paper studies relay selection schemes for two-way amplify-and-forward (AF) relay networks. For a network with two users that exchange information via multiple AF relays, we first consider a single-relay selection (SRS) scheme based on the maximization of the worse signal-to-noise ratio (SNR) of the two end users. The cumulative distribution function (CDF) of the worse SNR of the two users and its approximations are obtained, based on which the block error rate (BLER), the diversity order, the outage probability, and the sum-rate of the two-way network are derived. Then, with the help of a relay ordering, a multiple-relay selection (MRS) scheme is developed. The training overhead and feedback requirement for the implementation of the relay selection schemes are discussed. Numerical and simulation results are provided to corroborate the analytical results. [ABSTRACT FROM AUTHOR]

Inner and outer bounds are derived on the optimal performance of fixed-length block codes on discrete memoryless channels with feedback and errors-and-erasures decoding. First, an inner bound is derived using a two-phase encoding scheme with communication and control phases together with the optimal decoding rule for the given encoding scheme, among decoding rules that can be represented in terms of pairwise comparisons between the messages. Then, an outer bound is derived using a generalization of the straight-line bound to errors-and-erasures decoders and the optimal error-exponent tradeoff of a feedback encoder with two messages. In addition, upper and lower bounds are derived, for the optimal erasure exponent of error-free block codes in terms of the rate. Finally, a proof is provided for the fact that the optimal tradeoff between error exponents of a two-message code does not improve with feedback on discrete memoryless channels (DMCs). [ABSTRACT FROM PUBLISHER]

Based on superposition of signals in the time domain, we propose a new low-complexity scheme for the reduction of the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme first generates signal candidates by combining an OFDM signal and its cyclically delayed versions with different delays and phases, and then selects the candidate signal with minimum PAPR. It is shown that the complexity of the proposed scheme is significantly lower than that of the selective mapping (SLM) at the cost of some degradation in the bit error rate (BER) performance and, at similar PAPR and coded BER performance, is lower than that of the low-complexity SLM proposed recently. [ABSTRACT FROM AUTHOR]

Delay-tolerant networks (DTNs) provide a promising solution to support wide-ranging applications in the regions where end-to-end network connectivity is not available. In -DTNs, the intermediate nodes on a communication path are expected to store, carry, and forward the in-transit messages (or bundles) in an opportunistic way, which is called opportunistic data forwarding. Such a forwarding niethod depends on the hypothesis that each individual node is ready to forward packets for others. This assumption, however, might easily be violated due to the existence of selfish or even malicious nodes, which may be unwilling to waste their precious wireless resources to serve as bundle relays. To address this problem, we propose a secure multilayer credit-based incentive scheme to stimulate bundle forwarding cooperation among DTN nodes. The proposed scheme can be implemented in a fully distributed manner to thwart various attacks without relying on any tamperproof hardware. In addition, we introduce several efficiency optimization techniques to improve the overall efficiency by exploiting the unique characteristics of DTNs. Extensive simulations demonstrate the efficacy and efficiency of the proposed scheme. [ABSTRACT FROM AUTHOR]

We study the information brokerage schemes in wireless sensor networks, which allow consumers to obtain data from producers by replicating and retrieving data in a certain set of sensors, and propose a novel information brokerage scheme, termed RDRIB. Unlike existing information brokerage schemes, RDRIB guarantees successful data retrieval without using any boundary detection algorithm and the geographic location information acquired by the global positioning system (GPS). In RDRIB, the double-ruling technique is used to replicate and retrieve the data within a constructed virtual boundary, and simulations show that RDRIB has good performance in terms of the replication memory overhead, the replication message overhead, the retrieval message overhead, the retrieval latency, and the construction message overhead. [ABSTRACT FROM PUBLISHER]

This paper introduces a video coding scheme called Realistic Multi-view Scalable Video Coding (RMSVC), which is designed for the future ubiquitous environment. Unlike most video coding schemes that support only 2D or 3D displays, the proposed RMSVC coding scheme can support realistic services, such as 3D television, stereoscopic display, variablesized 2D displays, etc., and can efficiently deliver realistic video data in the ubiquitous environment that mixes various terminals and networks. In this paper, the proposed RMSVC scheme is designed and implemented by integrating the structures of Multi-view Video Coding (MVC) and Scalable Video Coding (SVC) schemes, and then shows in a simulation the possibility of realizing RMSVC. In addition, this paper proposes a layered prediction structure for the proposed RMSVC scheme. The simulation results show that the proposed structure remarkably improves the performance of random access while maintaining very similar coding efficiency. [ABSTRACT FROM PUBLISHER]

In this paper, we study the performance of non-cooperative multiple access systems with noisy separated channels, where correlated sources communicate to an access point (AP) through block-faded links. In the considered scenario, perfect channel state information (CSI) is assumed at the receiver while no CSI is available at the transmitters. We first consider uncoded transmissions from the sources to the AP, which exploits the source correlation to carry out joint channel detection (JCD). In this scenario, we propose an analytical approach to evaluate the achievable performance in terms of average bit error rate (BER). We then investigate the impact of coding, considering the same fixed coding scheme at each source. Then, we consider an extrinsic information transfer (EXIT) chart-based framework to optimize the design of concatenated and low-density parity-check (LDPC) codes for JCD schemes. [ABSTRACT FROM PUBLISHER]