COGNITIVE RADIO NETWORKS USED ANALYSIS OF THE POWER AMPLIFIER

COGNITIVE RADIO NETWORKS:


             The interference to the primary receiver (PR) is a critical issue in the resource allocation of cognitive radio (CR) networks. For instance, the non linearity of the power amplifier (PA) causes nonlinear interference to the PRs.A nonlinear PA with limited dynamic range and a lower limit on the transmit power is assumed for the secondary transmitter (ST). To control the resulting ACI from the ST to the PRs, the PA needs to be turned off in some fading blocks. To investigate the throughput,  an analytical expression for the probability of data transmission between the secondary users is derived as a function of the interference temperature limits of the PRs.

                                                    Fig:Cognitive radio network
     
 


RAPID growth of wireless communications and conventional fixed spectrum allocation policy have led to the problem of spectrum scarcity. However, according to a survey of spectrum utilization in the licensed spectrum is not used efficiently in both temporal and geographical dimensions. Cognitive radio (CR) which is one of the most promising technologies for the future radio spectrum management, improves spectrum utilization by using these underutilized parts of the spectrum. In CR networks, the secondary users are allowed to communicate, provided that the interferences caused to the primary receivers (PRs) are below a given threshold, called interference temperature limit 

FOR MORE DETAILS:

ANALYSIS OF THE POWER AMPLIFIER NONLINEARITY ON THE POWER ALLOCATION IN COGNITIVE RADIO NETWORKS 





 

OFDM Systems used for Eavesdropping Prevention

OFDM;

            ORTHOGONAL frequency-division multiplexing (OFDM) has been widely employed in modern wireless communications networks. Unfortunately, conventional OFDM signals are vulnerable to malicious eavesdropping due to their distinct time and frequency characteristics.Physical layer security, which targets communications security at the physical layer, is emerging as an effective complement to traditional security strategies in securing wireless OFDM transmission

 

                                       Fig: Eavesdropping prevention
 
these secrecy capacity based security techniques usually require the knowledge of the eavesdropping channel, which is conditioned on a successful detection of eavesdroppers. Also, additional resource may be needed like cooperative terminals and multiple antennas. Simple proactive eavesdropping prevention for OFDM at the physical layer, without significant modifications to off-the-shelf systems, has yet to be developed.




FOR MORE DETAILS:

DYNAMIC SUBCARRIER COORDINATE INTERLEAVING FOR EAVESDROPPING PREVENTION IN OFDM SYSTEMS

Outage Performance of Amplify-and-Forward Relaying

AMPLIFY AND FORWARD RELAY:
 
                      The amplify-and-forward relay protocol is a protocol defined for wireless Cooperative communication.An example of a wireless communication network in which cooperation improves the performance of the system is the relay Network In this case, the relay just amplies its received signal, maintaining a fixed average transmit power. selection amplify-and-forward (AF) relaying scheme which has the lower outage probability than that of a conventional AF relaying scheme in  cooperative relay networks. In real wireless environments, as the channel of source-to-destination (SD) link varies with an increase in time, we can also obtain a diversity gain through the SD link by re transmission in common with a conventional AF relaying scheme. Thus, we can expect a performance enhancement by adaptively determining the transmitting node between the relaying and source nodes

                                                                Fig :amplify and forward Relay


      In cooperative relay networks, relaying nodes can forward information from a single antenna terminal to form a virtual antenna array, and thereby achieving space diversity and improving the system performance, hence cooperative communications have attracted much attention. The relaying nodes essentially operate in either amplify and- forward (AF) and decode-and-forward relaying modes, which are basic for various evolved relaying schemes.the adaptive selective relaying scheme which determines the best among multiple AF relaying nodes having the maximum received SNR through the SR link was proposed, and its performances of outage  channel capacity , symbol error rate were analyzed



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ON THE OUTAGE PERFORMANCE OF SELECTION AMPLIFY-AND-FORWARD RELAYING SCHEME

Channel Model for Satellite Communication Links Above 10GHz Based on Weibull Distribution

SATELLITE COMMUNICATION:


Modern satellite communication networks will employ frequencies above 10GHz. At these frequency bands, rain attenuation is the dominant fading mechanism.channel model, a synthesizer for generating rain attenuation time series for satellite links operating at 10GHz and above is presented. The proposed channel model modifies Maseng- Bakken (M-B) model since it generates rain attenuation time
series that follow the Weibull distribution

                                                   Fig : satellite communication

              THE increasing demand for high data rate services and the scarcity of the spectrum lead to the  employment of high frequency bands such as Ka and Q/V bands for the operation of satellite systems.
At operating frequencies above 10 GHz rainfall is the dominant fading mechanism since it causes the highest attenuation among the other atmospheric effects. Due to the high values of rain attenuation for small time percentage, though still critical for high availability systems, the adoption of a fixed power margin as a countermeasure of rain attenuation is not the optimal solution

          An extended comparative test took place considering experimental data from ITUs database of Study Group 3 (DBSG3)  in order to observe the suitability of Weibull distribution for modeling the rain attenuation exeedance probability. Considering 86 experiments from DBSG3 database it was found that the RMS value of the relative error was 13.47% for Weibull distribution and 13.8% for log normal distribution  This leads to the conclusion that Weibull distribution in many cases may describe better rain attenuation exceed probability than log normal distribution. This is a strong motivation in order to derive a rain attenuation synthesizer based on Weibull distribution

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CHANNEL MODEL FOR SATELLITE COMMUNICATION LINKS ABOVE 10GHZ BASED ON WEIBULL DISTRIBUTION

Throughput Analysis for the Distributed Cognitive Uplink

 Throughput analysis:

COGNITIVE radio technology has recently emerged as an aspirant solution for the problem of spectrum scarcity.Unlike the traditional static command-and-control approach, it provides a more dynamic means for spectrum management and utilization channel state information (CSI) is one of the main requisites
for successful implementation of such dynamic cognitive radio protocols. However, its availability is often sidelined in most previous works  either assuming a centralized band manager or perfect instantaneous CSI feedback between primary and secondary networks

                                               Fig:Throughput analysis of Cognitive radio
the design of optimum distributed power control mechanisms for the cognitive uplink,allowing each SU to adjust its transmission power level  based only on local knowledge of its CSI. It also investigates multiuser diversity gains for the distributed cognitive uplink by deriving tight sum-rate capacity scaling laws under the optimum distributed power control mechanisms.



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POWER CONTROL AND ASYMPTOTIC THROUGHPUT ANALYSIS FOR THE DISTRIBUTED COGNITIVE UPLINK

Outage Analysis of Wireless Networks

COOPERATIVE communication

Has attracted a great amount of interest in the past decade. Following certain coordination protocols, a set of nodes can essentially form a distributed multiple-antenna system and transmit signals to the destination in a cooperative manner. Significant performance gains can thereby be achieved by using the available signal processing techniques developed for conventional multiple antenna systems.

                                       
                                                                    Fig: Cooperative Netwok

                                     






In a wireless network of moderate or large size, however, the situation becomes more complicated because there may exist many concurrent transmissions. Since cooperative communication usually involves multiple-node transmissions, it may generate additional spatial interference to other concurrent data transmissions in the network. The aggregate interference power can easily be strong and cause negative impact on the performance of the network. In other words, although each cooperative transmission has the potential to improve the reception quality of its destination, the overall performance taking into account the increased interference level remains unclear






FOR MORE DETAILS
TO COOPERATE OR NOT TO COOPERATE: AN OUTAGE ANALYSIS OF INTERFERENCE-LIMITED WIRELESS NETWORKS

MIMO OFDM Systems in On-Ship Below-Deck Environments

MIMO:

Multiple-input multiple-output, or MIMO, is a radio communications technology or RF technology that is being mentioned and used in many new technologies these days.Wi-Fi, LTE; Long Term Evolution, and many other radio, wireless and RF technologies are using the new MIMO wireless technology to provide increased link capacity and spectral efficiency combined with improved link reliability using what were previously seen as interference paths.

Even now many there are many MIMO wireless routers on the market, and as this RF technology is becoming more widespread, more MIMO routers and other items of wireless MIMO equipment will be seen.

                                                                Fig: Below Deck Environments

 

 

BELOWDECK 

             There has been increased  interest in characterizing electromagnetic propagation in below-deck environments of naval vessels for the purpose of deploying wireless networks. Below-deck spaces are predominantly metal structures. These spaces constitute multipath-rich environments that introduce distinct challenges for deploying wireless networks. The RF spectrum on ships also introduces active radar and communication signals, emissions from working machinery, and interference by personnel on board  Still, deploying wireless networks in below-deck spaces is desirable as it offers significant potential in augmenting, and in some applications, replacing current wired network infrastructure.

The primary contribution of this letter is the quantification of the improvements in capacity, signal integrity, and throughput that can be observed through the use of OFDM and multi antenna techniques in below-deck environments.

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PERFORMANCE EVALUATION OF MIMO OFDM SYSTEMS IN ON-SHIP BELOW-DECK