3. Radio & spreadspectrum technologies :– Wireless local area networks use a high-frequency radio technology similar to digital cellular & a low-frequency radio technology. Wireless LANs use spreadspectrum technology to enable communication between multiple devices in a limited area. IEEE 802.11 defines a common flavor of open-standards wireless radio-wave technology known as Wifi.
Energy detection technique has few limitations like, at low SNR does not perform well, cannot distinguish between signal and interference and does not work for the spreadSpectrum techniques. Further, the performance of energy detection suffers in the case when power of the noise is unknown decided the value of threshold based on noise power which varies continuously depending upon the temperature, obstruction and other special effects so unchanging threshold is the problem . During the probability of false alarm input signal x (n) will be,
signal was added into the transmit signal from each transmit- ter in the Advanced Television Systems Committee (ATSC) terrestrial digital television (DTV) system. The injection level of the spreadspectrum signal is significantly lower than the DTV signal, so the performance loss of the DTV signal is small. A watermarking technique is developed to embed cryptography encoded authorship signatures into data acquired by a wireless sensor network in . The signature can be embedded into the data-sensing process or during data processing. The hidden information can be retrieved during extraction, and the original data are not required. An ID Modulation method to embed a bit-stream sensed in the RFID(Radio Frequency Identification) channel was proposed in  and used to authenticate sensor nodes. Watermarking to the physical layer of the wireless modulation waveform by Orthogonal Frequency Division Multiplexing (OFDM) was applied in , which can be used for copyright protection, distribution tracing, and authentication in wireless networks. In , the authentication information was embedded into the transmitted waveform by inserting an intentional frequency offset, which is a practically viable approach and notably robust to harsh channel conditions. In , the inherent redun- dancy in pulse shaping was used to embed the authentication signal into the message signal, which uses the controlled Inter Symbol Interference (ISI) to embed the authentication bits. In , the physical layer watermarking was added into
Conventional sensing methods usually relate to sensing the spectrum in three dimensions only – frequency, time and space. However, there are other dimensions that need to be explored further for spectrum opportunity. For example, the code dimension of the spectrum space has not been explored well in the literature. Therefore, the conventional spectrum sensing algorithms do not know how to deal with signals that use spreadspectrum, time or frequency hopping codes. As a result, these types of signals constitute a major problem in sensing the spectrum. If the code dimension is interpreted as part of the spectrum space, this problem can be avoided and new opportunities for spectrum usage can be created. Naturally, this brings about new challenges for detection and estimation of this new opportunity. Similarly, the angle dimension has not been exploited well enough for spectrum opportunity. It is assumed that the primary users and/or the secondary users transmit in all the directions. However, with the recent advances in multi- antenna technologies, e.g. beam forming, multiple users can be multiplexed into the same channel at the same time in the same geographical area. In other words, an additional dimension of spectral space can be created as opportunity. This new dimension also creates new opportunities for spectral estimation where not only the frequency spectrum but also the angle of arrivals (AoAs) needs to be estimated. With these new dimensions, sensing only the frequency spectrum usage falls short. The radio space with the introduced dimensions can be defined as “a theoretical hyperspace occupied by radio signals, which has dimensions of location, angle of arrival, frequency, time, and possibly others”. This hyperspace is called electro space, transmission hyperspace, radiospectrum space, or simply spectrum space by various authors, and it can be used to describe how the radio environment can be shared among multiple (primary and/or secondary) systems ,.It is of crucial importance to define such an n-dimensional space for spectrum sensing. Spectrum sensing should include the process of identifying occupancy in all dimensions of the spectrum space and finding spectrum holes, or more precisely spectrum space holes. For example a certain frequency can be occupied for a given time, but it might be empty in another time. Hence, temporal dimension is as important as frequency dimension.
Cognitive radionetworks (CRNs) are emerging as a promising technology for the efficient use of radiospectrum. In these networks, there are two levels of networks on each channel, primary and secondary, and secondary users can use the channel whenever the primary is not using it. Spectrum allocation in CRNs poses several challenges not present in traditional wireless networks; the goal of this dissertation is to address some of the economic aspects thereof. Broadly, spectrum allocation in CRNs can be done in two ways- (i) one-step allocation in which the spectrum regulator simultaneously allocates spectrum to primary and secondary users in a single allocation and (ii) two-step allocation in which the spectrum regulator first allocates spectrum to primary users, who in turn, allocate unused portions on their channels to secondary users. For the two-step allocation scheme, we consider a spectrum market in which trading of bandwidth among primaries and secondaries is done. When the number of primaries and secondaries is small, we analyze price competition among the primaries using the framework of game theory and seek to find Nash equilibria. We analyze the cases both when all the players are located in a single small location and when they are spread over a large region and spatial reuse of spectrum is done. When the number of primaries and secondaries is large, we consider different types of spectrum contracts derived from raw spectrum and analyze the problem of optimal dynamic selection of a portfolio of long-term and short-term contracts to sell or buy from the points of view of primary and secondary users. For the one-step allocation scheme, we design an auction framework using which the spectrum regulator can simultaneously allocate spectrum to primary and secondary users with the objective of either maximizing its own revenue or maximizing the social welfare. We design different bidding languages, which the users can use to compactly express their bids in the auction, and polynomial-time algorithms for choosing the allocation of channels to the bidders.
The spectrum management includes time, frequency and transmit-power controls and dynamic spectrum management allowing the radio terminals to operate in the best available frequency spectrum. SDR provides a software control for a variety of modulation method, filtering, wideband or narrowband operations, spreadspectrum techniques and wave form requirements etc. For SDR reconfigurability; a cognitive radio looks naturally to a software-defined radio to perform its task (Fig. 4 ) The method based on cryptography is highly effective against untrusted users in cognitive radio network.The raw packet is modulated first before it is transmitted at a specific frequency. Fig. 5 shows a modulation of a packet and it transmission over an USRP2. In the USRP2 we can control center frequency, transmit power, and interpolation/decimation factor. The range for the center frequency and the power are dependent on the attached daughterboard (RFX2400). The interpolation factor in the transmit path and decimation factor in the receive path must be properly configured. Interpolation (also known as up sampling) increases the sampling rate and requires that we somehow produce values between the samples of the signal. The interpolation by a factor q is accomplished by inserting q-1 zeros in between each sample of x[n] and then discrete time low-pass filtering.The proposed method based on eigen values is highly effective against untrusted users in cognitive radio network. Q d and Q f denote the cooperative probability of detection and false alarm, a graph(figure 6) has been obtained.
2) Survey 2: In this stage, we carried out an extensive search in surveys in Cognitive Radio context to identify research problems. We found that the existing surveys are concerned with: a) A particular QoS objective; b) technical development in one CRNs component; c) A function of a CRN component; d) Investigating various security challenges; e) Security challenges; f) Developments in a CR based application; and j) PHY or MAC layers. Based on these categories, we decided to obtain the QoS provisioning approaches of CRN components. Therefore, we presented in  an up-to- date comprehensive survey of recent improvements in these approaches. To avoid confusing the reader with our main research problem, and due to the extensive nature of the topic, the main part of the survey is presented in Chapter 2. However, we would encourage readers to go through the survey to understand the issues and future directions in the CRNs context. From the survey, we found that to enable efficient communications, CRNs need to address two types of coexistence issues: Incumbent-coexistence, and Self- coexistence. We also found that while Incumbent coexistence has been effectively addressed in the literature, critical issues are still open in self-coexistence.
Cognitive Radio (CR) has been widely adopted as a promising technology to overcome the spectrum scarcity by authorizing CR users to operate opportunistically in the free space of the licensed frequency bands in co-existence of the Primary Users (PUs) . Spectrum sensing, with the aim of finding the idle frequency bands (spectrum holes), is the main function of CR networks [2, 3]. Collaborative Spectrum Sensing (CSS) is known as an effective approach to improve the detection performance . Unfortunately, spectrum sensing process is vulnerable to Primary User Emulation Attack (PUEA) . In PUEA, some malicious users send signal similar to that of PU transmitter and causes the CR users to immediately relinquish the desired frequency band . To mitigate the problem of PUEA, many approaches have been proposed.
a preset minimum number of resources is achieved) to increase the probability of having available resource to be used when needed. In this strategy, a channel is leased in advanced when certain events are detected (i.e., whenever a SU or a PU arrives to the PS). The rationale behind this strategy consists in the reduction of the interruption of SU sessions through the enabling of resources that have been leased in advance, thus mitigating the high interruption rates when the PS is in high occupancy. In this way, this strategy seeks to prevent the full usage of resources by the RUs by renting a channel in advance for each arrival event and thus increase the probability of finding available resources when requests are made by the SUs in the RS sub-network. It can be seen that the extra leased channel is not used immediately. Hence, this strategy is subject to resource wastage. The aim of this mechanism is to reduce the dropping probability of a SU call caused by the arrival of a PU. This dynamic spectrum leasing strategy is called practical anticipated spectrum leasing strategy. With respect to this strategy, we are interested in the minimization of the resource wastage (due to the anticipated lease of channels). In this sense, we consider that the minimum resource wastage occurs when a RU of the RS sub-network is about to use a channel and, an instant before this happens, the SS rents a channel. In a real system, it is not possible to achieve the minimum resource wastage because it cannot be predicted when a RU will make use of the resource in the RS sub-network. This limit case is called ideal anticipated leasing approach and is evaluated only for comparison purposes.
In the present work, a direction of arrival estimator, under spreadspectrum reference of signal-assisted radio operating in a Rayleigh fading channel, is proposed. The analysis, which is applied to general receiver antenna array configura- tions, demonstrates the high performance of the estimator which is due to the double dispreading (code word and refer- ence signal). The probability distribution function of the estimator is extracted and the system’s robustness in regard to large number of interferers is demonstrated.
Abstract—In this paper, the throughput maximization of millimeter-wave (mm-Wave) ultra-dense networks (UDN) using dynamic spectrum sharing (DSS) is considered. Most of the existing works only allow temporal-domain access and admit at most one user at each time slot, resulting in significant under- utilization of spectrum resource, which will be less attractive to mm-wave UDN applications. A generalized temporal-spatial shar- ing scheme is proposed in this paper for UDN by exploiting the location information of incumbent devices, where multiple users are allowed to access each channel simultaneously via spatial separations. For distributed applications, the global information exchange among secondary users (SU) tends to be impractical, given the unaffordable signaling overhead and latency. Thus, a non-cooperative game with fine-grained two-dimensional reuse is formulated, which leads to a more efficient access strategy. It is then proved to be an exact potential game (EPG), which has at least one pure strategy Nash equilibrium (NE). Finally, an improved decentralized reinforcement learning algorithm is designed, with which SUs can learn from wireless environments and adapt towards to a NE point, relying on the individual observation and the historical action-reward (rather than the global information exchanging). The convergence efficiency of the new scheme is also rigorously proved. Numerical simulations are provided to validate the performances of the proposed schemes.
The wireless communication link of a node at high altitude with a node at the ground is often encountered in various different scenarios. The applications of such air-to-ground (A2G) and ground-to-air (G2A) communication links include the provision of navigation services for aeroplanes, airborne Internet access for passengers in aeroplanes and communication links to unmanned air vehicles (UAVs) for military applications, cargo delivery, industrial inspection, weather monitoring, emergency humanitarian missions, law enforcement, border control and remote sensing. Moreover, high altitude platforms (HAP) to assist the land mobile radio cellular networks are expected to play a vital role [1,2] in emerging fifth generation (5G) communication systems for delivering high speed, large volume, power efficiency, low latency and global coverage of the data networks. In delivering the dynamic demands of A2G/G2A communication links, it is essential to have a reliable understanding of the propagation channel. Therefore, various studies to characterize the behaviour
In this paper it is shown that cyclostationary spectrum sensing for Cognitive Radionetworks, applying mul- tiple cyclic frequencies for single user detection can be interpreted (with some assumptions) in terms of op- timal incoherent diversity addition for “virtual diversity branches” or SIMO radar. This approach allows proposing, by analogy to diversity combining, suboptimal algorithms which can provide near optimal cha- racteristics for the Neyman-Pearson Test (NPT) for single user detection. The analysis is based on the Gene- ralized Gaussian (Klovsky-Middleton) Channel Model, which allows obtaining the NPT noise immunity characteristics: probability of misdetection error (P M ) and probability of false alarm (P fa ) or Receiver Opera-
While SDR platforms are not strictly necessary to create CRs, the flexibility of an SDR is one motivation for pursuing the study of CR algorithms. The ability to change the func- tionality of the radio in response to dynamic conditions requires both intelligent algorithms and capable radio plat- forms. In particular, satisfying the demands of DSA re- quires frequency agile radio hardware. For example, mobile communications are an essential component of public safety operations, with systems in many frequency bands, including high frequency (HF) (25–30 MHz), very HF (VHF) (30–50, 138–174, and 220–222 MHz), ultra-HF (UHF) (406–512 MHz), and the 700 MHz, 800 MHz, and 4.9 GHz bands . This profusion of operating frequen- cies and associated modes complicates interoperability and thereby impacts the effectiveness of public safety personnel . Military users are in a similar situation. To effectively exploit frequency-agile CR techniques in applications such as these, it is necessary for radios to operate over large fractional bandwidths and even multiple bands simulta- neously. For example, we may wish to use one (or more) RF chains to search for spectrum Bwhite space[ simulta- neously with ongoing communications, or we may wish to bridge communications taking place in different bands. The ability of the radio platform to adapt dynamically and nearly instantaneously during operation is particularly valuable and novel V until recently, most work on SDR focused on static reconfigurability. Thus, research in CRs and CNs both drives and is driven by research into flexible radio platforms.
Wireless networks are regulated today by using a static spectrum allocation policy. However, an outsized portion of the spectrum is used sporadically and the utilization of the assigned spectrum ranges from 15 to 85%, as illu- strated in Figure 1 . The growing number of wireless technologies and new applications are considerably in- creasing the demand for more bandwidth. Such stringent requirements cannot be met with the conventional infle- xible spectrum management approaches in which each operator is granted an exclusive license to operate. As most of the useful radiospectrum has already been assigned, vacant spaces are difficult to find for setting up new services or add to existing services .
The inefficient mistreatment of allotted spectrum to primary licensed users may be a quite common development, and CR technology has been thought-about as a key answer for that. It permits unauthorized or secondary users WHO square measure referred as CR users to access spectrum bands that are allotted to be licensed. To get the aim of accessing spectrum bands, CR users sense the spectrum so that they will sight the standing through a primary transmitter signal. Thus, spectrum sensing is one in every of the foremost vital problems in CR networks .
Abstract— Cognitive Radio Network (CRN) is a promising network that aims to improve the utilization of the wireless spectrum by enabling unlicensed (secondary) users to reuse the underutilized bands. CRN utilization of residual spectrum bands of Primary (licensed) Networks (PNs) must avoid harmful interference to the users of PNs and other overlapping CRNs. Numerous Internetwork spectrum sharing frameworks have been proposed in the literature; however, spectrum sharing among overlapping CRNs presents significant challenges. This paper comprises two major contributions; firstly, it proposes a novel CRNs management framework, CogMnet, which regulates the operation of centralized CRNs. CogMnet aims to ensure the reliability of CRNs' spectrum sharing by tackling the Primary User Emulation Attack (PUEA) issue and avoiding an overcrowded CRNs scenario. Secondly, it proposes CRN Admission Control (CRNAC) algorithm capable of determining the maximum number of CRNs allowed in any location. To the best of our knowledge CogMnet is the first Internetwork framework able to distinguish an attacker CRN that may perform PUEA. Furthermore, CRNAC is the first network admission decision making algorithm in the CRNs literature. Analytical results are presented to demonstrate the performance of the algorithm. Assigning the number of CRNs is very important to avoid saturated spectrum situation.
SUs attempted to reach a joint decision on the PU presence via interchange of their individual measurements, which were received undistorted at each node. In this paper, in contrast to the absolute majority of previous works on CSS, we consider a distributed CSS scheme where the SUs try to reach the agreement on the PU presence by interchanging their personal binary opinions (yes/no) via an unreliable propagation medium, and a dedicated control channel can be provided for this purpose. Such scenarios are typical, for example, in wireless networks where the nodes have also social ties . Moreover, in this work, we take into account a possible loss of connections in the network because of poor propagation conditions. This scenario diﬀers from that analyzed in our conference paper . Trying to agree, the SUs update their personal opinions (states) based on the “K- out-of-N” rule. But each SU changes the opinion based on only local observations of the network state, which are diﬀerent for diﬀerent users since the wireless medium distorts the transmitted binary signals in a random manner. Therefore the above distributed procedure may result in a disorder (divergence).
unused radiospectrum from primary licensed networks (users). The research in cognitive radio has been encouraged by the measurements of the Federal Communications Commission (FCC), which have revealed that there is a significant amount of licensed spectrum which is largely underutilized in vast temporal and geographic dimensions . The FCC recognizing that there is a significant amount of available spectrum that is currently not being used under the current fixed spectrum allocation policy, has recently allowed the access of unlicensed (secondary) users to the broadcast television spectrum at locations where that spectrum is not being used by licensed services . This unused broadcast television spectrum is often termed as “white spaces” and has been the focus of the IEEE 802.22 WRAN standard that aims to provide broadband wireless internet access to rural areas .