The aggregation of Wi-Fi links has been identified as one way of taking advantage of available channels to achieve higher speed data transmission in future cognitive radio networks. However variations in link quality make it difficult to achieve stable performance from aggregated Wi-Fi links. In this paper we present a method for controlling aggregation of Wi-Fi links based on monitoring of link status. We first discuss the requirements for detecting bad-links which degrade the performance of aggregated Wi-Fi links. We then describe the implementation of an enhanced link-status detection algorithm based on monitoring of signal strength and number of retransmissions. In particular, we address the problems of monitoring and recovering links after they have been dropped from use, and adjusting decision thresholds to adapt to changing wireless conditions. Finally, we report the results of tests which demonstrate the effectiveness for attaining efficient aggregation of Wi-Fi links for high throughput under varying wireless conditions.

Cognitive Radio is an advanced enabling technology for efficient utilization of vacant spectrum due to its ability to sense the spectrum environment. Various detection methods have been proposed for spectrum sensing, which is the key function in implementing cognitive radio. However most of the existing methods put their interests in detecting TV signal and wireless microphone signals. In this paper, we explore the periodicity of the equally spaced pilot subcarriers in OFDM signal. Simulations in various fading environments show that the proposed cyclostationarity based detection method works well for OFDM signal.

We propose a neurodynamical approach to a large-scale optimization problem in Cognitive Wireless Clouds, in which a huge number of mobile terminals with multiple different air interfaces autonomously utilize the most appropriate infrastructure wireless networks, by sensing available wireless networks, selecting the most appropriate one, and reconfiguring themselves with seamless handover to the target networks. To deal with such a cognitive radio network, game theory has been applied in order to analyze the stability of the dynamical systems consisting of the mobile terminals' distributed behaviors, but it is not a tool for globally optimizing the state of the network. As a natural optimization dynamical system model suitable for large-scale complex systems, we introduce the neural network dynamics which converges to an optimal state since its property is to continually decrease its energy function. In this paper, we apply such neurodynamics to the optimization problem of radio access technology selection. We compose a neural network that solves the problem, and we show that it is possible to improve total average throughput simply by using distributed and autonomous neuron updates on the terminal side.

Cognitive Radios (CR) can recognize the communication environment and switch its communication scheme to more efficiently and flexibly utilize the radio spectrum. The performance of ultra wideband (UWB) degrades if interference is not suppressed properly. We propose here a series of adaptive chirp waveforms in UWB systems. By designing waveform shaping of both linear chirp and non-linear cases, we avoid the estimated spectrum of the on-going applications without the necessity of notch filters, and thus reduce the system complexity. We evaluate system performance of the proposed scheme by simulations and verify that the proposed scheme is a candidate for cognitive UWB systems.

A technique for suppressing the clipping noise of an analogue-to-digital converter (ADC) is proposed to realize a cognitive radio transceiver that offers high sensitivity carrier-sensing. When a large bandwidth cognitive radio transceiver performs carrier-sensing, it must receive a radio wave that includes many primary user transmissions. The radio wave may have high peak-to-average power ratio (PAPR) and clipping noise may be generated. Clipping noise becomes an obstacle to the achievement of high-sensitivity carrier-sensing. In the proposed technique, the original values of the samples clipped by an ADC are estimated by interpolation. Polynomial spline interpolation to the clipped signal is performed in the first step, and then SINC function interpolation is applied to the spline interpolated signal. The performance was evaluated using the signals with various PAPR. It has been found that suppression performance has a dependency on the number of samples clipped at once rather than on PAPR. Although there is an upper limit for the number of samples clipped at once that can be compensated with high accuracy, about 20 dB suppression of clipping noise was achieved with the medium degree of clipping.

In this paper, we propose a soft decision based cooperative sensing method for cognitive radio (CR) networks for opportunistic frequency usage. To identify unused frequency, CR should exploit sensing technique to detect presence or absence of primary user and use this information to opportunistically provide communication among secondary users while performance of primary user should not be deteriorated by the secondary users. Because of multipath fading or shadowing, the detection of primary users may be significantly difficult. For this problem, cooperative sensing (CS), where gathered observations obtained by multiple secondary users is utilized to achieve higher performance of detection, has been investigated. We design a soft decision based CS analytically and analyze the detector in several situations, i.e., signal model where single-carrier case and multi-carrier case are assumed and two scenarios; in the first scenario, SNR values of secondary users are totally equal and in the second scenario, a certain SNR difference between secondary users is assumed. We present numerical results as follows. The first scenario shows that there is little difference between the signal models in terms of detection performance. The second scenario shows that CS is superior to non-cooperative sensing. In addition, we presents that detection performance of soft decision based CS outperform detection performance of hard decision based CS.

Cognitive radio and/or SDR (Software Defined Radio) inherently requires multi-band and multi standard wireless circuit. The circuit is implemented based on Si CMOS technology. In this article, the recent progress of Si RF CMOS is described and the reconfigurable RF CMOS circuit which was proposed by the authors is introduced. At the present and in the future, several kind of Si CMOS technology can be used for RF CMOS circuit implementation. The realistic RF CMOS circuit implementation toward cognitive and/or SDR is discussed.

Cognitive radio, which utilizes the radio frequency spectrum efficiently by recognizing radio resource availability, is an attractive technology for overcoming the shortage of radio frequency. From the perspective of networking, cognitive radio technologies are also useful since they allow flexible network construction. This paper proposes base station networks using cognitive radio technologies. In order to achieve efficient utilization of the radio frequency spectrum and flexible network construction, we also propose a topology management and route control method for our proposed base station network. Our method shares the status of the wireless links along with topology information and establishes routes by using this information. Through simulation, we evaluate that our method significantly improves the throughput by efficient utilization of the radio frequency spectrum. Moreover, we demonstrate that our method works well when the size of the network gets larger.

Outage performance of cognitive radios is analyzed in this paper. The scenario under consideration requires the cognitive radio to sense whether the primary user (PU) link is free (i.e. a spectrum hole exists) before making an active transmission using that link. Multiple antennas are available at the cognitive radio link to provide array gains at the sensing stage. We derive a closed-form expression of the outage probability for cognitive transmission by classifying it into several cases. A sensing threshold is deduced according to the PU arrival model illustrated in this paper. Simulation results verify our analysis.

The Project Authorization Request (PAR) for the IEEE P1900.4 Working Group (WG), under the IEEE Standards Coordinating Committee 41 (SCC41) was approved in December 2006, leading to this WG being officially launched in February 2007 [1]. The scope of this standard is to devise a functional architecture comprising building blocks to enable coordinated network-device distributed decision making, with the goal of aiding the optimization of radio resource usage, including spectrum access control, in heterogeneous wireless access networks. This paper introduces the activities and work under progress in IEEE P1900.4, including its scope and purpose in Sects. 1 and 2, the reference usage scenarios where the standard would be applicable in Sect. 4, and its current system architecture in Sect. 5.

In this paper, sampling rate selection diversity (SRSD) scheme for Direct-Sequence/Spread-Spectrum (DS/SS) is proposed. In DS/SS communication systems, oversampling may be employed to increase the signal-to-noise ratio (SNR). However, oversampling enlarges the power consumption because signal processing of the receiver has to be carried out at a higher clock rate. Higher sampling rate does not always maximize the SNR. In the proposed SRSD scheme, the power consumption can be reduced by selecting the optimum sampling rate depending on the characteristics of the channel. The proposed SRSD scheme can also reduce the BER more than the conventional oversampling scheme under certain channel conditions.

Reliable detection of other radio systems is crucial for systems that share the same frequency band. In wireless communication channels, there is uncertainty in the received signal level due to multipath fading and shadowing. Cooperative sensing techniques in which radio stations share their sensing information can improve the detection probability of other systems. In this paper, a new cooperative sensing scheme that reduces the false detection probability while maintaining the outage probability of other systems is investigated. In the proposed system, sensing information is collected using multi-hop transmission from all sensing stations that detect other systems, and transmission decisions are based on the received sensing information. The proposed system also controls the transmit power based on the received CINRs from the sensing stations. Simulation results reveal that the proposed system can reduce the outage probability of other systems, or improve its link success probability.

CR (Cognitive Radio) is a technology that can realize more intensive and efficient spectrum use through spatial and temporal utilization. In the context of mesh networks where each base station consists of heterogeneous multi-radio interfaces, packet switch in L2/L3 of each base station selects each radio interface and channel adaptively in order to take full advantage of all multiple heterogeneous interfaces. At first, this paper examines the achievable performance of the new packet switch schemes in mesh topology. Secondly, we investigate the potentiality of dynamic base station relocation approach in order to cope with the change of terminal traffic distribution, and show the impact of packet switch policy on dynamic base station relocation.

Cognitive Radios (CRs) are expected to perform more significant role in the view of efficient utilization of the spectrum resources in the future wireless communication networks. In this paper, a cognitive radio coexisting with cellular systems is proposed. In the case that a cellular system adopts Frequency Division Duplex (FDD) as a multiplexing scheme, the proposed CR terminals communicate in local area on uplink channels of the cellular system with transmission powers that don't interfere with base stations of the cellular system. Alternatively, in the case that a cellular system adopts Time Division Duplex (TDD), the CR terminals communicate on uplink slots of the cellular system. However if mobile terminals in the cellular system are near the CR network, uplink signals from the mobile terminals may interfere with the CR communications. In order to avoid interference from the mobile terminals, the CR terminal performs carrier sense during a beginning part of uplink slot, and only when the level of detected signal is below a threshold, then the CR terminal transmits a signal during the remained period of the uplink slot. In this paper, both the single carrier CR network that uses one frequency channel of the cellular system and the multicarrier CR network that uses multiple frequency channels of the cellular system are considered. The probabilities of successful CR communications, the average throughputs of the CR communications according to the positions of the CR network, and the interference levels from cognitive radio network to base stations of the cellular system are evaluated in the computer simulation then the effectiveness of the proposed network is clarified.

In a Cognitive Radio system, it is essential to recognize and avoid sources of interference signals. This paper describes a study on a location sensing scheme for interference signals, which utilizes multi-beam phased array antenna for cognitive wireless networks. This paper also elucidates its estimation accuracy of the interference location for the radio communication link using an OFDM signal such as WiMAX. Furthermore, we use the frequency spectrum of the received OFDM interference signal, to create a method that can estimate the propagation status. This spectrum can be monitored by using a software defined radio receiver.

The cognitive radio system consists of multiple wireless access systems that cover overlapping areas and cognitive terminals that use one or more of the wireless accesses simultaneously. In this paper, we describe the architecture of the cognitive radio system and the inter-system handover protocols. In the architecture, each cognitive terminal, which can access multiple radio systems, operates with a single local IP address. The control sequence and packet format are designed to achieve fast handover among the radio systems. Based on the architecture, we have developed a testbed system. On this system, we demonstrate that data can be delivered continuously and radio systems can be switched correctly without any packet loss. In addition, we present the result of the evaluation of the end-to-end latency on the testbed system. These testbed results demonstrate the system architecture described in the paper can achieve a cognitive radio system.

The present paper proposes two novel and practical schemes for distributed and asynchronous power control in wireless ad hoc networks, in which users dynamically share several frequency bands as in "cognitive radio" networks. These schemes iteratively adjust transmit powers of individual network transmitters with respect to mutually caused interference in the shared bands. Their most attractive feature is that they find network-wide acceptable trade-offs to diverse signal-to-noise and interference (SINR) requirements and efficiently use techniques of stochastic approximation and time-averaging to guarantee a robust performance in random channels. Advantageously, both proposed algorithms do not assume any particular modulation, coding, QoS measure definition or network architecture, which assures their high applicability in the industry and research. Moreover, the broad definition and non-linear nature of these schemes mathematically generalize and thus encompass as a special case many widely deployed power control schemes such as e.g. those for achieving fixed SINR targets or using game-theoretic utility maximization. Simulations are provided to illustrate our approach and its better performance compared to standard algorithms.

RF system and circuit approaches for cognitive radios, based on software defined radio technology, are discussed. The increasing use of digital techniques, combined with wideband data converters and tunable front-end technologies, will enable these systems to become cost effective in the coming years.

"Cognitive radio" and "software-defined radio" (SDR) are today an important consideration in major spectrum debates in the United States. The U.S. drafted its first SDR rules in 2001, and since has continued efforts to resolve potential regulatory concerns and facilitate the benefits of the technology. At the same time, Japan has had a very rich experience in the lab with SDR, with significant achievements on many engineering topics. However, the regulatory state of SDR in Japan has not kept pace with the United States. Likewise cognitive radio, while a topic of inquiry, betrays a different focus. The paper explores why the paths for these technologies have diverged in the U.S. and Japan.