In this paper, we propose an energy efficient MAC protocol for wireless sensor networks. In sensor networks, reducing energy consumption is one of the critical issues for extending network lifetime. One good solution to resolve this issue is introducing listen-sleep cycles, allowing sensor nodes to turn their transceiver off during sleep periods, which was adopted by S-MAC [1]. However, in S-MAC, due to the synchronized scheduling, transmission collisions will increase in heavy traffic situations, resulting in energy waste and low throughput. Hence, in this paper, we propose probabilistic scheduled MAC (PS-MAC), in which each node determines ‘listen’ or ‘sleep’ pseudo-randomly based on its own pre-wakeup probability and pre-wakeup probabilities of its neighbor nodes in each time slot. This allows the listen-sleep schedule of nodes in each transmitter and receiver pair to be synchronized, while maintaining those of the rest of nodes to be asynchronous. Therefore, collisions can be reduced even under heavy traffic conditions, resulting in reduced energy waste and high throughput. In addition, by dynamically adjusting the pre-wakeup probabilities of sensor nodes based on the change of the network environment, system throughput and latency can be further improved. Simulation results show that PS-MAC provides significant energy savings, low delay, and high network throughput.

The multiple-access channel (MAC) becomes very popular in various communication systems, because multi-terminal communication systems have been widely used in practical systems, e.g., mobile phones and P2P, etc. For some MACs, it is known that feedback can enlarge the capacity region, where the capacity region is the set of rate pairs such that the error probability can be made arbitrarily small for sufficiently large block length. The capacity region for general MACs, which are not required to satisfy ergodicity and stationarity with perfect feedback was first shown by Tatikonda and Mitter without the proof, where perfect feedback means that the channel output is perfectly fed back to senders. In this paper, we generalize Tatikonda and Mitter's result to the case of deterministic feedback, where the values of deterministic functions of past channel outputs is fed back to senders. We show that the capacity region for general MACs with deterministic feedback can be represented by the information-spectrum formula introduced by Han and Verdu, and directed information introduced by Massey. We also investigate the compound MAC problem, the ε-coding problem, the strong converse property and the cost constraint problem for general MACs with deterministic feedback.

Due to an increase in multimedia content and the acceleration of digital convergence, demand for next-generation IPTV service is rapidly growing. IPTV service seamlessly provides both real-time broadcasting and content sharing services on diverse terminals through complex networks. In this paper, a secure and scalable content sharing framework is proposed for next-generation IPTV service. The proposed framework has an advantage over conventional content protection techniques in producing scalable content with transcodable, adjustable, and perceptual security features. Moreover, it ensures end-to-end security over the entire service range based on a single security mechanism. The suitability of the proposed approach is demonstrated experimentally using a practical service scenario with real-world environments. The experiments show that the proposed approach can provide several different levels of content security, from a perceptual level to an almost unintelligible level, while keeping the additional time overhead low. Consequently, it is expected that use of this security technology alone can have a practical contribution in creating new business opportunities for IPTV services.

We propose frequency-domain optical code-division-multiplexing (CDM) employing quadrature-amplitude-modulation (QAM) using two of multi-level (M-ary) data generated based on electrical-domain spatial code spreading. Its spectral efficiency is enhanced compared to the conventional scheme with amplitude-shift-keying (ASK) using only one of M-ary data. Although it demands the recovery of amplitude and optical phase information, the practicality of the receiver is retained with self-homodyne detection using a phase-shift-keying (PSK) pilot light. Performance is theoretically evaluated and the optimal parameters are derived. Finally, the feasibility of the proposed technique is experimentally confirmed.

Dynamic spectrum access (DSA) has drawn immediate attention recently since it can opportunistically exploit any spectrum holes and thus improve bandwidth utilization. From the perspective of medium access control (MAC) design, the QoS requirement of SU is one of the design issues in DSA network. In this paper, we propose a new admission control scheme referred to as log-based dynamic spectrum access admission control (DSAC) aiming at (1) protection of the primary users and (2) QoS prioritization for the existing secondary users. The DSAC algorithm protects the PU by limiting SUs' access using PU's arrival log or statistics. Furthermore, the DSAC reserves a channel for previously admitted SU to reduce frequent service disruption of the SU. Reservation of channels is carried out without assuming any specific arrival process, and thus the DSAC would be practical for general user arrival patterns unlike the existing admission control techniques. Performance evaluation has shown that the proposed DSAC outperforms existing admission control schemes with respect to the PU blocking rate, SU communication stability, and SU aggregate throughput by about 13%, 26%, and 20%, respectively.

We present a highly integrated quasi-millimeter-wave receiver MMIC that integrates 22 circuits in a 3 2.3 mm area using three-dimensional MMIC (3D-MMIC) technology. The MMIC achieves low noise (3 dB) and high gain (41 dB) at 26 GHz by using an on-chip image reject filter. It integrates a multiply-by-eight (X8) local oscillator (LO) chain with the IF frequency of the 2.4 GHz band and can use low-cost voltage-controlled oscillators (VCOs) and demodulators in a 2–3 GHz frequency band. Multilayer inductors contribute to the miniaturization especially in a 2–12 GHz frequency band. Furthermore, it achieves a high dynamic range by using two step attenuators with a new built-in inverter using an N-channel depression field-effect transistor (FET). The power consumption of the MMIC is only 450 mW.

In this paper, we propose a simple, yet effective, multiuser detection scheme for a two-hop cooperative CDMAs. In phase 1, the minimum mean square error (MMSE) detector at the destination is used to identify reliable decisions of direct transmissions from the sources and return them to the relays. Then, in phase 2, based on the reliable decisions, the relays and the destination successively utilize the maximum likelihood (ML) detectors to estimate the residual symbols. Due to the destination estimating the symbols separately from direct transmissions and the relaying signals, as a result the destination does not need the information about the relays' decision performance for the construction of the ML detector. Hence, the proposed scheme is more feasible than existing approaches for practical implementation. In addition, due to the ML detectors in phase 2 only estimating the residual symbols, the number of computations performed by the ML detectors can be reduced significantly. The results of simulations and complexity analysis demonstrate the efficiency and effectiveness of the proposed scheme.

We propose FuzzyCoop, a cooperative MAC layer protocol employing a fuzzy logic partner selection algorithm. The protocol is based on the Distributed Coordination Function (DCF) protocol used in the IEEE 802.11 standard. There are three inputs to the fuzzy system: the Signal to Noise Ratio (SNR), the error ratio between two neighbors and the time the most recent packet was received from a neighbor. The fuzzy output is the partnership probability of a neighboring terminal. Besides, we introduce a cooperation incentive to the stations by providing them with the right to transmit their own data without contention after a successful cooperation. The protocol is evaluated through extensive simulations in different scenarios and is compared to the DCF protocol and a previously proposed cooperative protocol. Simulation results show that FuzzyCoop improves the performances of a wireless network and provides a more robust partner selection scheme.

In this letter, the reliabilty of the generalized normal-Laplace (GNL) distribution used for modeling the multiple access interference (MAI) plus noise in time-hopping (TH) binary phase-shift keying (BPSK) ultra-wideband (UWB) systems is evaluated in terms of the probability density function and the BER. The multiple access performance of TH-BPSK UWB systems based on GNL model is analyzed. The average BER performance obtained by using GNL approximation well matches with the exact BER results of TH-BPSK UWB systems. The parameter estimates of GNL distribution based on the moments estimation method is also presented.

A 10-Gbit/s-class ac-coupled average-detection-type burst-mode receiver (B-Rx) with an ultra fast response and a high tolerance to the long consecutive identical digits has been developed. Key features of the circuit design are the baseline-wander common-mode rejection technique and the inverted distortion technique adopted in the limiting amplifier to cope with both the fast response and the high tolerance. Our B-Rx with newly developed limiting amplifier IC achieved a settling time of less than 150 ns, a sensitivity of -29.8 dBm, and a dynamic range of 23.8 dB with a 231-1 pseudo random bit sequences. Moreover, we also describe several potential B-Rx applications. We achieved better performance by applying the proposed systems to our B-Rx.

Quadratic congruence code (QCC)-based frequency-hopping and time-spreading (FH/TS) optical orthogonal codes (OOCs), and the corresponding expanded cardinality were recently studied to improve data throughput and code capacity. In this paper, we propose a new FH/TS two-dimensional (2-D) code using the QCC and the cubic congruence code (CCC), named as the QCC/CCC 2-D code. Additionally the expanded CCC-based 2D codes are also considered. In contrast to the conventional QCC-based 1-D and QCC-based FH/TS 2-D optical codes, our analysis indicates that the code capacity of the CCC-based 1-D and CCC-based FH/TS 2-D codes can be improved with the same code weight and length, respectively.

We achieve concurrent access to WiFi and WiMAX networks on a mobile terminal equipped with a common RF subsystem by providing time-interleaved RF access control schemes to both of the MAC layers. We propose cooperative and competitive sharing schemes, neither of which requires any modification to other network components. We implement our schemes on a WiFi/WiMAX dual-mode SoC platform. Experimental results show that these schemes work and have affordable overheads.

Broadcasters transmit TV programs and often need to transmit an individual message, e.g. an individual contract, to each user. The programs have to be encrypted in order to protect the copyright and the individual messages have to be encrypted to preserve the privacy of users. For these purposes, broadcasters transmit not only encrypted content but also encrypted personalized messages to individual users. Current broadcasting services employ an inefficient encryption scheme based on a symmetric key. Recently, several broadcast encryption schemes using a public key have been proposed in which the broadcaster encrypts a message for some subset S of users with a public key and any user in S can decrypt the broadcast with his/her private key. However, it is difficult to encrypt a personalized message and transmit it to every user efficiently. In this paper, we propose a broadcast encryption scheme that has a personalized message encryption function. We show that our scheme is efficient in terms of the ciphertext size.

Recently, global positioning system (GPS)-enabled mobile units have been popular in wireless mobile communications systems, and thus it becomes possible for mobile units to estimate the velocity before a random access for initiating communications. Motivated by this, we propose a new random access scheme establishing two or more access slot groups corresponding to velocity ranges of mobile units, where each mobile unit attempts a random access only at the slot group corresponding to its current velocity. It gives advantages that access slots can be flexibly grouped according to vehicle traffic conditions and detection algorithms can be optimized to each velocity range.

In this letter, we propose a Partially Observable Markov Decision Process (POMDP) based Distributed Adaptive Opportunistic Spectrum Access (DA-OSA) Strategy for Cognitive Ad Hoc Networks (CAHNs). In each slot, the source and destination choose a set of channels to sense and then decide the transmission channels based on the sensing results. In order to maximize the throughput for each link, we use the theories of sequential decision and optimal stopping to determine the optimal sensing channel set. Moreover, we also establish the myopic policy and exploit the monotonicity of the reward function that we use, which can be used to reduce the complexity of the sequential decision.

We propose a new resource prediction method for the Demand Assigned Multiple Access (DAMA) scheme in satellite networks. Inaccurate prediction of future traffic causes degradation of QoS and utilization due to the long delay in satellite networks. The Dynamic Leveling Scheme (DLS) use a leveling method to modify its prediction to a discrete one to change the precision of the prediction result. This new scheme has two features: 1) It enhances the probability of successful prediction and 2) it can be applied to any type of existing prediction method. Simulations show enhanced utilization and performance of the satellite link.

In this paper, we develop linear-programming (LP) decoding for multiple-access channels with binary linear codes. For single-user channels, LP decoding has attracted much attention in recent years as a good approximation to maximum-likelihood (ML) decoding. We demonstrate how the ML decoding problem for multiple-access channels with binary linear codes can be formulated as an LP problem. This is not straightforward, because the objective function of the problem is generally a non-linear function of the codeword symbols. We introduce auxiliary variables such that the objective function is a linear function of these variables. The ML decoding problem then reduces to the LP problem. As in the case for single-user channels, we formulate the relaxed LP problem to reduce the complexity for practical implementation, and as a result propose a decoder that has the desirable property known as the ML certificate property (i.e., if the decoder outputs an integer solution, the solution is guaranteed to be the ML codeword). Although the computational complexity of the proposed algorithm is exponential in the number of users, we can reduce this complexity for Gaussian multiple-access channels. Furthermore, we compare the performance of the proposed decoder with a decoder based on the sum-product algorithm.

Secure access is one of the key concerns of wireless sensor networks (WSNs). In WSNs, because there are many dynamically mutable attributes, continuous access decisions and dynamic attribute updates should be important properties of access control. In addition, WSNs need low-complexity authentication protocols because of the constrained resources. However, the authentication protocols of most current security access schemes have relatively high complexity. More importantly, the access control models of existing schemes cannot provide attribute mutability and continuous decisions dynamically. To address above issues, we propose a dynamic secure access mechanism for WSNs. Firstly, we design a lightweight secure authentication protocol and dynamic access control based on security token and usage control (UCON), respectively. Then, the agent technology is adopted to implement the proposed secure access scheme. Secondly, we analyze the probability of the dynamic attribute update and decisions. Thirdly, we implement an instance of UCON. The implementation results indicate the feasibility of using UCON in WSNs. Finally, by evaluating and comparing with current schemes, the authentication protocol in our scheme presents several advantages including the low expenses in calculation, storage and communication. To our best knowledge, this paper is the first to realize next generation dynamic access control with attribute mutability and continuous decisions in WSNs.

Utilizing available channels to improve the network performance is one of the most important targets for the cognitive MAC protocol design. Using antenna technologies is an efficient way to reach this target. Therefore, in this paper, we propose a novel cognitive MAC protocol, called Polarization-based Long-range Communication Directional MAC Protocol (PLRC-DMAC), for Cognitive Ad Hoc Networks (CAHNs). The proposed protocol uses directional antennas to acquire better spatial reuse and establish long-range communication links, which can support more nodes to access the same channel simultaneously. Moreover, the PLRC-DMAC also uses polarization diversity to allow nodes in the CAHN to share the same channel with Primary Users (PUs). Furthermore, we also propose a Long-range Orientation (LRO) algorithm to orient the long-range nodes. Simulation results show that the LRO algorithm can accurately orient the long-range nodes, and the PLRC-DMAC can significantly increase the network throughput as well as reduce the end-to-end delay.

Mobile operators need to migrate from 2G to 3G networks in a cost-effective manner. Cognitive radio systems are currently being investigated as a promising solution to achieve spectrum efficiency by allowing coexistence of unlicensed (secondary) networks and licensed (primary) networks. However, conventional mechanisms to operate these systems incur additional complexity and fail to maximize network performance. In this paper, we propose a pilot sensing and frequency selection method with low complexity for OFDMA-based cognitive radio systems. Subject to the interference constraints imposed by the primary network, capacity maximization problems involving both up-link and down-link connections are considered for overall network performance improvement. The throughput and outage probability of the proposed method are evaluated by simulations. Our proposed method shows outstanding performance if the channel varies frequently in the primary network and the frequency reuse factor of the primary network is high.