Cognitive Transmission Research Articles

Efficient secondary access with intelligent spectrum sensing in cognitive radio networks

SUMMARYIn cognitive radio networks, cooperative sensing can significantly improve the performance in detection of a primary user via secondary users (SUs) sharing their detection results. However, a large number of cooperative SUs may induce great sensing delay, which degrades the performance of secondary transmissions. In this paper, we jointly consider cooperative sensing and cognitive transmission in cognitive radio networks, aiming to achieve efficient secondary access with low sensing overhead under both the sensing time and reporting power limitations, where primary users are guaranteed to be sufficiently protected. We first propose an adaptive sensing scheme to lower the detection time while not degrading the detection probability. Then, based on the proposed adaptive sensing scheme, an efficient cognitive transmission protocol is well designed, which improves the throughput of secondary transmissions while ensuring the QoS of primary transmissions. We analyze the performance for the proposed secondary access framework in terms of misdetection probability, average detection time and normalized secondary throughput, respectively, and derive their closed‐form expressions over Rayleigh fading channels with considering the reporting errors accordingly. We also study the problems of optimizing the number of cooperative SUs to minimize the misdetection probability and average detection time, and maximize the normalized secondary throughput for proposed framework. Simulation results reveal that the proposed framework outperforms the traditional case significantly. Copyright © 2013 John Wiley & Sons, Ltd.

A Phase Adjustment Approach for Interference Reduction in OFDM-Based Cognitive Radios

The problem of cross-band interference in single-antenna and multi-antenna OFDM cognitive transmitters is considered. Cross-band interference, which is caused by large OFDM signal sidelobes, is a major drawback of OFDM, especially in cognitive radio applications where it is crucial to protect primary licensed users from the secondary user's interference. In this paper, we propose a novel low complexity technique, referred to as a phase adjustment technique, to tackle this problem in single-antenna and multi-antenna OFDM cognitive transmitters. In this technique, the phase of each OFDM symbol is adjusted in an attempt to minimize the interference caused by the secondary user to the primary. Unlike prior methods, this technique does not decrease data throughput and has no impact on the bit-error-rate and peak-to-average power ratio of the OFDM symbols. Furthermore, to calculate the adjustment phases, three heuristics, one of which is very low complexity and achieves near optimal performance in numerical simulations, are also proposed. In addition, the performance of the proposed technique is evaluated analytically in some special cases in single and multi-antenna cognitive transmitters, and is verified by numerical simulations.

On the Throughput and Energy Efficiency of Cognitive MIMO Transmissions

In this paper, throughput and energy efficiency of cognitive multiple-input-multiple-output (MIMO) systems operating under quality-of-service (QoS) constraints, interference limitations, and imperfect channel sensing are studied. It is assumed that transmission power and covariance of the input signal vectors are varied, depending on the sensed activities of primary users (PUs) in the system. Interference constraints are applied on the transmission power levels of cognitive radios (CRs) to provide protection for the PUs, whose activities are modeled as a Markov chain. Considering the reliability of the transmissions and channel sensing results, a state transition model is provided. Throughput is determined by formulating the effective capacity. The first derivative of the effective capacity is derived in the low-power regime, and the minimum bit energy requirements in the presence of QoS limitations and imperfect sensing results are identified. Minimum energy per bit is shown to be achieved by beamforming in the maximal-eigenvalue eigenspace of certain matrices related to the channel matrix. In a special case, wideband slope is determined for a more refined analysis of energy efficiency. Numerical results are provided for the throughput for various levels of buffer constraints and different number of transmit and receive antennas. The impact of interference constraints and benefits of multiple-antenna transmissions are determined. It is shown that increasing the number of antennas when the interference power constraint is stringent is generally beneficial. On the other hand, it is shown that, under relatively loose interference constraints, increasing the number of antennas beyond a certain level does not lead to much increase in throughput.

Cognitive Radio Transmissions Exploiting Multi-User Diversity under Channel and Sensing Uncertainty

In this paper, a cognitive multiple access channel (MAC) in which the secondary transmitters opportunistically communicate with a secondary receiver (i.e., a secondary base station) is considered. It is assumed that the base station first determines the channel availability through channel sensing and then broadcasts a pilot symbol with energy depending on the channel sensing decision in order to facilitate the linear minimum mean-square estimation (LMMSE) of the channel fading coefficient between itself and each secondary user. The user with the largest estimated channel gain is selected opportunistically for data transmission during each frame. In this setting, achievable rates and energy efficiency are studied by exploiting the multi-user diversity in the presence of channel sensing and channel estimation errors. The interactions between number of users, channel sensing parameters and performance (e.g., detection and false-alarm probabilities), achievable rates, and energy efficiency are analyzed. Performance gains due to collaborative sensing and multi-user diversity are investigated.

Optimal Spectrum Sensing Interval to Minimize the Transmission Delay for Cognitive Radio

In this work, we have studied the optimal spectrum sensing interval, which is the time between two consecutive spectrum sensing activities, such that the delay of the cognitive transmission is minimized. The throughput maximization of the cognitive radio is always a common goal of the researchers, which is keenly related to the delay of the cognitive transmission. Whereas the delay is mostly decided by the spectrum sensing interval for a given primary user (PU) channel. Therefore, we have studied the setting of the spectrum sensing interval to minimize the transmission delay of the secondary user (SU). Especially, the retransmission is considered, which deteriorates the delay of the cognitive transmission; however, neglected by the most studies. Finally, we provide both the optimal setting of the spectrum sensing interval and the numerical values.

Energy Efficiency Maximization Based on Cooperative sensing in Cognitive Relay Networks

I n this paper, we investigate the energy efficiency maximization problem of cognitive radio systems. We propose to study energy efficiency of cognitive relay transmission scheme based on cooperative spectrum sensing, since empirical studies have shown that optimal sensing time and transmit power are key factors for energy efficiency maximization. We design a method that simultaneously considers the parameters of spectrum sensing time and transmit power. Finally, we conduct deep experiments which show that our proposed approach can significantly improve the throughput and energy efficiency than the non-cooperative spectrum sensing method. DOI: http://dx.doi.org/10.11591/telkomnika.v11i8.2446

CogTRA: a deployable mechanism for cognitive transmission rate adaptation in IEEE 802.11 networks

Abstract Wireless local area networks have become vastly popular, and IEEE 802.11 is the chosen standard for almost all wireless devices. This standard specifies several modulation and channel coding techniques that must be implemented by all wireless interfaces to adapt to changes in wireless channels. As a result, these interfaces support multiple transmission data rates. However, this standard does not define how to dynamically select the appropriate data rate; instead, manufacturers can design and implement their own algorithms. Although several solutions have been proposed in the literature, only a few are used in practice. Moreover, their performance is still limited to specific conditions, such as highly dynamic environments. To tackle these challenges, this paper introduces CogTRA, which is a deployable mechanism built upon an existing cognitive framework called CogProt. Due to its self-adjustment functionality, CogTRA can work not only in stable but also in dynamic environments. It was implemented in the OpenWrt Linux distribution for embedded devices and evaluated through experiments using real network equipment. The results underline performance benefits with respect to existing data rate adaptation algorithms, with CogTRA exhibiting better performance especially in such dynamic networks.

Joint single transmit and receive antenna selection for MIMO cognitive radios without channel state information

For multiple-input multiple-output cognitive radios, a single transmit and receive antenna selection scheme is proposed for when the channel state information from a cognitive transmitter to a cognitive receiver is unknown to the transmitter. In the proposed scheme, the transmit antenna at the cognitive transmitter that maximises the transmit power and the receive antenna at the cognitive receiver that maximises the signal-to-interference-and-noise ratio are selected. Also derived is the exact closed-form outage probability considering the peak interference power constraint, the peak transmit power constraint, and interference from the primary transmitter to the cognitive receiver.

Interference-Aware Resource Control in Multi-Antenna Cognitive Ad Hoc Networks with Heterogeneous Delay Constraints

In this work, we consider a multi-antenna cognitive ad hoc network (CAHNet) with heterogeneous delay requirements. To fulfill the interference and delay constraints simultaneously, we propose to perform adaptive zero-forcing beamforming (ZFBF) at cognitive transmitters according to interference channel state information (CSI). To assist the CAHNet to obtain the interference CSI, we use a win-win inter-network cooperation strategy, namely quantized interference CSI feedback from the primary network to CAHNet through a feedback link, under the condition that the CAHNet pays a proper price for it. Considering the scarcity of feedback and power resources, we focus on the minimization of the overall resource cost subject to both interference and delay constraints. To solve the problem, we derive a joint feedback and power control algorithm amongst multiple links of CAHNet. Finally, simulation results validate the effectiveness of the proposed algorithm.

Achievable rate region for the multiple-access channel with multiple cognitive transmitters

A scenario where one ‘dumb’ radio and multiple cognitive radios communicating simultaneously with a common receiver is considered. In this paper, we derive an achievable rate region of the multiple-user cognitive multiple-access channel (MUCMAC) under both additive white Gaussian noise (AWGN) channel and rayleigh fading channel, by using a combination of multiple user dirty paper coding (DPC) and superposition coding. Through cognition, it is assumed that the secondary users (SUs) are able to obtain the message of the primary user (PU) non-causally beforehand. Using this side information, the SUs can perform multiple user DPC to avoid the interference from the SU. Besides, the SUs can also allocate part of their transmit power to aid the PU, using superposition coding. Therefore, the capacity region of traditional multiple-access channel (MAC) can be enlarged. Moreover, some asymptotic results are shown as the number of SUs increases. In the AWGN case, it is illustrated that the maximum achievable rate of the PU grows logarithmically with the increase of the number of SUs, whereas in the Rayleigh case, we show that the cognitive gain will increase with the decreasing of the channel signal to noise ratio (SNR).

Green Power Control in Cognitive Wireless Networks

A decentralized network of cognitive and non-cognitive transmitters where each transmitter aims at maximizing his energy-efficiency is considered. The cognitive transmitters are assumed to be able to sense the transmit power of their non-cognitive counterparts and the former have a cost for sensing. The Stackelberg equilibrium analysis of this $2-$level hierarchical game is conducted, which allows us to better understand the effects of cognition on energy-efficiency. In particular, it is proven that the network energy-efficiency is maximized when only a given fraction of terminals are cognitive. Then, we study a sensing game where all the transmitters are assumed to take the decision whether to sense (namely to be cognitive) or not. This game is shown to be a weighted potential game and its set of equilibria is studied. Playing the sensing game in a first phase (e.g., of a time-slot) and then playing the power control game is shown to be more efficient individually for all transmitters than playing a game where a transmitter would jointly optimize whether to sense and his power level, showing the existence of a kind of Braess paradox. The derived results are illustrated by numerical results and provide some insights on how to deploy cognitive radios in heterogeneous networks in terms of sensing capabilities. Keywords: Power Control, Stackelberg Equilibrium, Energy-Efficiency.

Prescient Precoding in Heterogeneous DSA Networks with Both Underlay and Interweave MIMO Cognitive Radios

This work examines a novel heterogeneous dynamic spectrum access network where the primary users (PUs) coexist with both underlay and interweave cognitive transmitters (UCTs and ICTs); all terminals being potentially equipped with multiple antennas. UCTs are allowed to transmit concurrently with PUs subject to interference constraints, while the ICTs employ spectrum sensing and are permitted to access the shared spectrum only when both PUs and UCTs are absent. We investigate the design of MIMO precoding algorithms for the UCT that increase the detection probability at the ICTs, while simultaneously meeting a desired Quality-of-Service target to the underlay cognitive receivers (UCRs) and constraining interference leaked to PUs. The objective of such a proactive approach, referred to as prescient precoding, is to minimize the probability of interference from ICTs to the UCRs and primary receivers due to imperfect spectrum sensing. We begin with downlink prescient precoding algorithms for multiple single-antenna UCRs and multi-antenna PUs/ICTs. We then present prescient block-diagonalization algorithms for the MIMO underlay downlink where spatial multiplexing is performed for a plurality of multi-antenna UCRs. Numerical experiments demonstrate that prescient precoding by UCTs provides a pronounced performance gain compared to conventional underlay precoding strategies.

Outage Probability and SER of Amplify-and-Forward Cognitive Relay Networks

This letter considers amplify-and-forward (AF) cognitive relay networks with interference power constraint and transmit power constraint in a spectrum-sharing context. In particular, we impose the interference power constraint on secondary source node, and impose the interference power constraint and the transmit power constraint on secondary relay node. We derive the exact outage probability and the lower bound on symbol error rate (SER) of cognitive transmission over Rayleigh fading channels. Our results show that the outage probability and SER saturation phenomenons occur when the interference power constraint or the transmit power constraint reaches a specified value. Monte Carlo simulations are shown to validate the accuracy of the analytical results.

Potential bargaining for resource allocation in cognitive relay transmission

Cooperative transmission between cognitive users can effectively decrease interference with primary users in underlay mode. Relay transmission between cognitive user and primary user can not only benefit the primary communications and facilitate the cognitive transmission too. Having obtain considerable profits from the cooperation, the primary user may lease its spectrum dynamically or upgrade the interference temperature timely for the cognitive user as a repayment. In this paper, we first consider a system model under the circumstances of Rayleigh fading channels which are coming close to real conditions. Then, we analyze the incomes of the primary transmitter in underlay mode and raise a rational scheme to compensate the cognitive relay by increasing certain interference temperature. In overlay mode, we propose an appropriate time-division pattern for the cooperative transmission under the deployment of dynamic spectrum leasing. Game theory is used when we resolve the bargaining problem of time division. Simulation tests are further run in MATLAB platform to prove the feasibilities of our proposals. The results demonstrate that both the primary and cognitive users can benefit from the cooperation.

Non-intrusive Cognitive Radio Using Adaptive Nulls-Steering

In this paper, we propose an adaptive non-intrusive cognitive radio network based on smart antenna technologies. The cognitive transmitter (CT), which is equipped with antenna array, first estimates and tracks the composite steering vectors of each primary (licensed) user. In what follows, CT forms transmit beamforming to place nulls to primary receivers based on the estimated spatial signatures. Moreover, we extensively analyze performance degradation caused by spatial signatures mismatch (estimation error) and verify that the proposed robust nulls-steering beamformer can comprehensively alleviate the mismatch effect. Simulation results demonstrate convergence of the proposed gradient-based recursive least squares algorithm. Furthermore, we have shown that outage probability can be kept extremely low under appropriate array size, which ensures the practicability of the proposed scheme.

Interference alignment for spectral coexistence of heterogeneous networks

The coexistence of heterogeneous networks within the same spectrum for enhancing the spectrum efficiency has attracted large interest lately in the research community. Furthermore, the research interest towards the deployment of small cells and multibeam satellites is increasing due to high capacity, easier deployment and higher energy efficiency. However, due to the scarcity of available spectrum and the requirement of additional spectrum for these systems, small cells need to coexist with macrocells and multibeam satellites need to coexist with monobeam satellites within the same spectrum. In this context, this contribution investigates an underlay spectral coexistence mechanism which exploits an interference alignment (IA) technique in order to mitigate the interference of cognitive transmitters towards the primary receivers in a normal uplink mode. More specifically, three types of IA techniques, namely static, uncoordinated and coordinated are investigated. The performance of the IA technique is evaluated and compared with primary only, resource division and no-mitigation techniques in terms of sum-rate capacity, primary to secondary rate ratio and primary rate protection ratio. It is shown that the coordinated IA technique perfectly protects the primary rate in both terrestrial and satellite coexistence scenarios.

Capacity Bounds and Exact Results for the Cognitive Z-Interference Channel

We study the discrete memoryless Z-interference channel (ZIC) where the transmitter of the pair that suffers from interference is cognitive. We first provide an upper bound on the capacity of this channel. We then show that, when the channel of the transmitter-receiver pair that does not experience interference is deterministic, our proposed upper bound matches the known lower bound provided by Cao and Chen in 2008. The obtained results imply that, unlike in the Gaussian cognitive ZIC, in the considered channel superposition encoding at the non-cognitive transmitter as well as Gel'fand-Pinsker encoding at the cognitive transmitter are needed in order to minimize the impact of interference. As a byproduct of the obtained capacity region, we obtain the capacity under the generalized Gel'fand-Pinsker conditions where a transmitter-receiver pair communicates in the presence of interference noncausally known at the encoder.

Cooperative transmissions for secondary spectrum access in cognitive radios

SUMMARYIn cognitive radio networks (CRNs), the primary users (PUs) and secondary users (SUs) will interfere with each other, which may severely degrade the performances of both primary and secondary transmissions. In this paper, we propose a two‐phase cognitive transmission (TCT) protocol for secondary spectrum access in CRNs, aiming at improving the secondary transmission performance while guaranteeing the quality‐of‐service (QoS) of primary transmissions. In TCT protocol, SUs gain the opportunities to access the licensed spectrum through assisting primary transmissions using superposition coding (SC), where SUs limit their transmit power to satisfy a given primary QoS requirement and also employ interference cancelation technique to mitigate the interference from PUs. Under the constraint of satisfying a required primary outage probability, we derive the closed‐form expressions of secondary outage probabilities over Rayleigh fading channels for proposed TCT protocol. Numerical and simulation results reveal that, with a guaranteed primary outage probability, TCT achieves better secondary transmission performance than traditional case. Copyright © 2013 John Wiley & Sons, Ltd.

On the Optimization of the Secondary Transmitter's Strategy in Cognitive Radio Channels with Secrecy

This paper investigates cooperation for secrecy in cognitive radio networks. In particular, we consider a four-node cognitive scenario where the secondary receiver is treated as a potential eavesdropper with respect to the primary transmission. The cognitive transmitter can help the primary transmission, and it should also ensure that the primary message is not leaked to the secondary user. We consider two cognitive scenarios depending on whether the secondary transmitter knows the primary message or not. In the first case, the secondary transmitter is unaware of the primary transmitter's message and acts as a helping interferer to enhance the secrecy of the primary transmission, whereas in the second case, relaying of the primary message is also within its capabilities. First, we find achievable rate regions for these two scenarios in the case of AWGN channels. We then investigate three different optimization problems: the maximization of the primary rate, the maximization of the secondary rate and the minimization of the secondary transmit power. For these optimization problems, we find closed-form expressions in important special cases. Furthermore, we analyze the cooperation between the primary and secondary transmitters from a game-theoretic perspective. We model their interaction as a Stackelberg game, for which we define and find the Stackelberg equilibrium. Finally, we use numerical examples to illustrate the rate regions, the three optimizations, and the impact of the Stackelberg game on the achievable rates and on the transmission strategies of the secondary transmitter.

Evolved Cognition and Cultural Transmission of Honour Concepts

Abstract In many cultures people value the importance of honour and related rules and behaviours. Honour can be seen as concepts and cultural items represented and processed according to evolved cognitive capacities and emotions supported by local social institutional arrangements. Indeed, this article holds that one reasonable way to analyze honour is to model how cognitive processes and transmission biases work in tandem with institutional support and environmental cues to exert selective pressures on the cultural distribution and formation of honour. The scope of this article is theoretical, aiming to address and explain culturally recurrent aspects of widespread honour concepts. What evolved cognitive systems and selection factors underpin the cultural transmission of honour concepts and institutions? It will be argued that the transmission of honour concepts draws upon cognitive systems referring to male formidability, management of reputation, coalitions, costly signals, shame and stigma, concern for protectiveness and parental investments, essentialist understanding and disgust and on the cognition of institutions.