Mona Shokair

Proposed relay selection scheme for physical layer security in cognitive radio networks

In this study, the physical layer security for cognitive radio network (CRN) will be investigated in which a secondary user transmitter (SU-Tx) sends confidential information to a SU receiver (SU-Rx) on the same frequency band of a primary user (PU) in the presence of an eavesdropper receiver. Moreover, relay selection scheme is proposed for the security constrained CRNs with single eavesdropper, multiple eavesdroppers and PUs. The proposed scheme selects a trusted decode and forward relay to assist the SU-Tx and maximise the achievable secrecy rate that is subjected to the interference power constraints at the PUs for the different number of eavesdroppers and PUs under available channel knowledge. The SU cooperates with relays only when a high secrecy rate is achieved. Secrecy rate and secrecy outage probability are the two performance metrics that are used to verify the effectiveness of the proposed scheme although asymptotic approximations of the secrecy outage probability are also derived. Simulation and analytical results demonstrate that the performance improvement of the proposed scheme reaches to the double relative to the conventional scheme for the secrecy capacity.

Hard and softened combination for cooperative spectrum sensing over imperfect channels in cognitive radio networks

Recently, cognitive radio (CR) access has received much attention to overcome spectrum scarcity problem. Spectrum sensing methods are often used for finding free channels to be used by CR. In this paper, the problem of cooperative spectrum sensing will be investigated in CR networks over realistic channels. This problem is not clarified until now by taking into account the error effect on the decision reporting. The analytical expressions of the hard and softened one bit and two bits hard combination scheme for cooperative spectrum sensing will be derived. These expressions are investigated to compare with simulation results. The analysis and simulation results show that the performance of cooperative spectrum sensing is limited by the probability of reporting errors. Moreover, it is shown that there is a significant performance loss when a final decision regarding to primary user’s (PU) state made at the fusion depends on a set of local spectrum sensing information that are distorted by imperfect reporting channels during transmission. The probability of detection is degraded due to imperfect reporting channel by 16.5% and 12.2% with one bit hard combination and softened two bits hard combination, respectively. To reduce this performance loss, Amplify and Forward (AAF) relying mechanism will be proposed. The probability of detection is improved by 8% and 9.3% with one bit hard combination and softened two bits hard combination, respectively using AAF relaying mechanism.

PROPOSED MAC PROTOCOL VERSUS IEEE 802.15.3A FOR MULTIMEDIA TRANSMISSION OVER UWB NETWORKS

In this paper, a Medium Access Control (MAC) protocol is proposed to investigate Quality of Service (QoS) for multimedia traffic transmitted over Ultra Wide-Band (UWB) networks and increase the system capacity. This enhancement comes from using Wise Algorithm for Link Admission Control (WALAC) which has three suggested versions. The QoS of multimedia transmission is determined in terms of average delay, admission ratio, loss probability, utilization, and the network capacity. In addition, a new parameter is aroused for the network performance. Comparisons between the IEEE 802.15.3a protocol and the proposed one are done. The proposed protocol shows better results in both sparse and dense networks for real time traffic transmission.

COMBINED INTERLEAVING AND COMPANDING FOR PAPR REDUCTION IN OFDM SYSTEMS

Peak to Average Power Ratio (PAPR) is one of the serious problems in any wireless communication systems using multicarrier modulation technique as OFDM, which reduces the efficiency of transmit high power amplifier. In this paper, proposed scheme will be introduced, which combines interleaving technique and companding technique to reduce PAPR. This scheme will be compared with the system that uses other technique for reduction which is the clipping technique. By using proposed scheme, the PAPRof OFDM signal can be reduced by 6.8 dB over the original system, i.e., without PAPR reduction. Also, SNRdecreases by more than 5 dB for Bit Error Rate (BER) of 10 −3 over the original system. Moreover, the proposed scheme gives improvement more than 4.5 dB for BERof 10 −3 over the system that uses clipping. All these systems will be evaluated in the presence of nonlinear power amplifier.

C42. PAPR reduction for LFDMA using a reduced complexity PTS scheme

Three subcarrier mapping schemes are used for single carrier frequency division multiple access (SC-FDMA) system: interleaved (IFDMA), distributed (DFDMA) and localized (LFDMA) subcarrier mapping. Comparison between these schemes showed that the peak to average power ratio (PAPR) for both IFDMA and DFDMA systems is less than that of LFDMA system. In this paper, a low complexity Partial Transmit Sequence (PTS) technique is proposed for the reduction of PAPR in LFDMA system by generating the candidates using the time domain cyclical shift of each sub-block sequence and combining them in a recursive manner. This enables the detector to recover the original signal without needing side information. In this paper, mathematical analysis is explained in details for both the conventional PTS (C-PTS) scheme and the proposed PTS (P-PTS) scheme. Also, computational complexity comparison is performed between the C-PTS and P-PTS schemes.

An Efficient Adaptive Technique with Low Complexity for Reducing PAPR in OFDM-Based Cognitive Radio

Cognitive radio (CR) is considered nowadays as a strong candidate solution for the spectrum scarcity problem. On standards level, many cognitive radio standards have chosen Non-Contiguous Orthogonal Frequency Division Multiplexing (NC-OFDM) as their modulation scheme. Similar to OFDM, NC-OFDM suffers from the problem of having a high Peak to Average Power Ratio (PAPR). If not solved, either the transmitted signal will be distorted, which will cause interference to primary (licensed) users, or the effeciency of the power amplifier will be seriously degraded. The effect of the PAPR problem in NC-OFDM based cognitive radio networks is worse than normal OFDM systems. In this paper, we propose enhanced techniques to reduce the PAPR in NC-OFDM systems. We start by showing that combining two standard PAPR reduction techniques (interleaver-based and selective mapping) results in a lower PAPR than using them individually. Then, an “adaptive number of interleavers” will be proposed that achieves the same performance of conventional interleaver-based PAPR reduction while reducing the CPU time by 41.3%. Finally, adaptive joint interleaver with selective mapping is presented, and we show that it gives the same performance as conventional interleaver-based technique, with reduction in CPU time by a factor of 50.1%.

Three bits softened decision scheme in cooperative spectrum sensing among cognitive radio networks

Recently, cognitive radio (CR) access has received much attention to overcome spectrum scarcity problem. Spectrum sensing methods are often used for finding free channels to be used by CR. In this paper, one of spectrum sensing method will be investigated. This method is cooperative spectrum sensing which is based on energy detection in CR networks in order to overcome fading, noise and shadowing effects on individual CR user and increase the reliability and efficiency of spectrum sensing. The sensing information from CR users combines at the Fusion center (common receiver) by soft combination or conventional hard combination techniques. Soft combination has excellent performance but, it requires a lot of overhead for feedback observation. In contrast, the conventional hard combination scheme requires only one bit of overhead, but it has worst performance because of loss of information caused by local hard decisions. In this paper, the detection performance improves by increasing the levels of local observations by proposing three-bit softened decision scheme which is not clarified until now. Analytical Expressions of proposed three bits scheme will be derived. Design parameters are optimized to find the detection performance with a given false alarm probability. The simulation results show that, at 90% detection probability, the cooperative signal detection improves by 1.75 dB of signal to noise ratio over conventional hard combination (i.e., one bit scheme). Moreover, comparisons between proposed scheme, one bit and two bits schemes will be made.

Optimal Power Allocation for Sensing-Based Spectrum Sharing in MIMO Cognitive Relay Networks

With most of the radio spectrum already allocated, cognitive radio acts as a promising solution to the spectrum scarcity problem. Increasing the secondary throughput without making interference to the primary user (PU) is a major challenge. In this paper, the secondary throughput is maximized under power constraints by obtaining an optimum value of the relay amplification factor. Comparison between using single antenna, double antennas at all the nodes of the cognitive relay network (CRN), and double antennas at the relay node only is performed. The mathematical analysis of the system is investigated for two cases: (1) The opportunistic access case, where the secondary user (SU) can transmit data only in the vacant bands of the allocated spectrum to the PU; and (2) The sensing-based spectrum sharing case, where the SU can transmit data all the time but with different transmit powers depending on the sensing information. Simulation results show that the achieved secondary throughput can be maximized at a given value of the relay amplification factor. Moreover, using double antennas at all the nodes of the CRN increases the maximum achievable throughput and improves the detection capabilities compared with using single antenna or using double antennas at the relay node only. Finally, results show that the SU can achieve more throughput under the sensing-based spectrum sharing case compared with that achieved under the opportunistic access case.

Profit of Price with Supermodular Game for Spectrum Sharing in Cognitive Radio Using Genetic Algorithm

Cognitive radio is wireless communication system used for higher spectrum utilization for spectrum holes that are shared between primary (or licensed) users and secondary (or unlicensed) users. Primary service provider can sell unused holes for secondary service provider in which pricing is interested factor for market equilibrium. This process called spectrum trading. Pricing in spectrum sharing depends on spectrum demand from unlicensed users and requirements of primary users to gain payoff. In this paper, supermodular competitive game will be investigated considering Bertrand competition model among primary service providers, which is not clarified until now. In the competitive Bertrand game, the aim of spectrum trading process is to maximize the individual payoff or profit for each primary service provider. Moreover, genetic algorithm will be applied to demonstrate the effect of pricing in profit gained by primary service provider with optimizing profit function from abrupt changing in pricing and achieving market equilibrium.

An efficient technique for reducing PAPR of OFDM system in the presence of nonlinear high power amplifier

Peak to average power ratio (PAPR) is one of the serious problems in any wireless communication system using multicarrier modulation technique like OFDM, which reduces the efficiency of the transmit high power amplifier. In this paper, proposed scheme will be introduced that combines interleaving method with peak windowing method. With the proposed scheme, the simulation results show that, the PAPR is reduced by 3.5 dB. Moreover Eb/N0, is decreased more than 3 dB at bit error rate (BER)=10mnplus3 in the presence of nonlinear power amplifier.