Salwa H. El Ramly

PR-LEACH: Approach for balancing energy dissipation of LEACH protocol for wireless sensor networks

Wireless sensor networks are composed of hundreds or even thousands of sensor nodes which have limited energy. Energy consideration is a very critical issue for designing routing protocols. This paper discusses a common clustering protocol, called LEACH, and improves cluster-head selection criteria. LEACH selects cluster-heads based on random probability, while the proposed algorithm considers the sensor nodes residual energy in order to balance energy dissipation among all of the nodes to extend network lifetime as one unit to minimize dead-spots. MATLAB simulation shows that the proposed energy consideration protocol which is called Percentage LEACH (PR-LEACH), provides better performance compared to LEACH protocol.

Novel hybrid soft-hard demodulation schemes for RQD constellation

Rotated constellation with Q-delay (RQD) is a new modulation scheme adopted by some wireless standards including the second generation of the digital video broadcasting for terrestrial (DVB-T2) system. This scheme offers significant improvement over unrotated modulation in terms of bit error rate (BER) performance due to its signal space diversity. In this paper, we present four novel computationally efficient demodulation schemes with hybrid soft-hard outputs used in hard demapping of data. The main idea is to take advantage of the unique projections the rotated cells have in the RQD system. The proposed schemes reduce the number of log likelihood ratio (LLR) computations. One proposed scheme gives the same BER performance as traditional LLR while reducing the computational complexity by 34% at SNR = 20 dB. Another scheme reduces the computations by 25% independent of the SNR level. The other two schemes offer a tradeoff between computational complexity and power efficiency.

Modified MIMO-OFDM Channel Estimation Technique for DVB-T2 Systems

This paper proposes an enhanced pilot-aided channel estimation algorithm for the second generation of the digital video broadcast for terrestrial (DVB-T2) standard. Two channel estimation techniques are discussed, the first is based on the 3-points averaging technique, while the second is based on studying the frequency domain pattern of the channel response. The second technique leads to a 0.5 dB reduction in the SNR needed to guarantee a specific bit error rate (BER) requirement when compared to the conventional estimation technique recommended by the DVB-T2 implementation guide lines.

Improving TCP congestion control for wireless sensor networks

The development of wireless technologies makes it necessary to find a way of improving Transmission Control Protocol (TCP) efficiency with regards to optimal utilization of wireless channel capacity. This paper describes a modification to the TCP congestion control for use in wireless sensor networks. It shows that by slightly modifying the algorithm of the TCP, it can be made to respond better to wireless links, while maintaining its advantages on the wired networks at the same time. This is certainly a very desirable feature as the conventional TCP in most cases contradicts the demands of the wireless links of the network. Our simulation results indicate that the modified TCP gives better performance in terms of higher throughput, delay, retransmission, and energy consumption than conventional TCP protocol.

Adaptive chaotic frequency hopping

Chaotic systems are widely used as robust and secure communication systems in jamming environments. Frequency hopping spread spectrum (FHSS) is an effective mechanism used to mitigate the effects of jamming, fading, and interference. To improve the performance of FHSS many adaptive frequency hopping schemes are used such as matched frequency hopping (MFH), clipped matched frequency hopping (CMFH), and advanced matched frequency hopping (AMFH). These schemes adaptively select the hopping pattern that includes only good sub-channels. Using these schemes result in forcing the system to be vulnerable to smart jammer attack. In this paper we propose a new algorithm that synthesizes one dimensional chaotic map which generates a random code that mostly selects good sub-channels to achieve good bit error rate (BER), good frequency diversity, and secure transmission provided by the high randomness properties of the chaotic systems.

Design of ranging codes for low-earth orbit satellites

In this paper, a satellite pseudorandom ranging code is proposed. The proposed code is a composite code built from a pseudorandom maximum length linear feedback shift register sequence and a nonlinear sequence. The design takes into consideration the requirements for unambiguous maximum range determination, ranging accuracy, security, and fast acquisition of the ranging signal.

Exact Analysis of PCC-OFDM Subjected to Carrier Frequency Offset over Nakagami-m Fading Channel

Orthogonal frequency division multiplexing (OFDM) is sensitive to frequency synchronization errors which results in degradation of system performance. Polynomial cancelation coding (PCC) OFDM is introduced to reduce OFDM sensitivity to carrier frequency offset. In this paper, PCC-OFDM performance modeling is considered. An exact closed form expression for symbol error rate (SER) is evaluated for PCC-OFDM subjected to carrier frequency offset. The performance is evaluated over Nakagami-m fading channel. PCC-OFDM improvement as compared to conventional OFDM is emphasized. It is shown that PCC-OFDM outperforms conventional OFDM by about 4 dB in the QPSK modulation at error rate of 10-2 over fading channels with a normalized carrier frequency offset of 0.1.

Cross-coupled chaotic matched frequency hopping in presence of partial band noise jamming

Frequency hopping spread spectrum (FHSS) is widely used in the communication systems that required anti-jamming protection. Several jamming techniques are used against FHSS such as barrage noise jamming (BNJ), multi-tone noise jamming (MTNJ), follower jamming (FJ) and partial band noise jamming (PBNJ). FJ and PBNJ are the most effective jamming techniques for the FHSS. In this paper, we present cross-coupled matched frequency hopping (CCMFH) model that mitigates the PBNJ effect by exploiting the performance of matched frequency hopping (MFH) technique and secure the frequency hopping pattern using the cross-coupled chaotic maps. The model is slow frequency hopping (SFH) and modulation is binary frequency shift keying (BFSK) non-coherence detection over frequency selective Rayleigh fading channel. Cross-coupled technique and PBNJ probability of error performance analysis in Rayleigh fading channel of PBNJ are illustrated in this paper. The results show that CCMFH maintains the probability of error of MFH technique and improve hopping pattern security by using the cross-coupled chaotic maps.

Effect of PUs Mobility in CRAHNs using an Activity and Mobility Based Routing Protocol

Cognitive Radio (CR) is capable to identify the unused spectrum in order to allow Cognitive users (CUs) to occupy it without interfering the primary users (PUs). Routing in Cognitive Radio Ad-Hoc Networks (CRAHNs) is a very challenging task due to diversity in the available channels. In this paper, Mobility and Activity Based Routing Protocol (MABRP), is proposed. In the proposed protocol, CUs discover next hops based on the collected spectrum and mobility information. In addition, using cooperative communication mechanisms to reveal new routing opportunities, enhance route qualities, and enable true coexistence of primary and secondary networks is investigated. The performance of MABRP and Cognitive Ad-hoc On-demand Distance Vector (CAODV) are evaluated on the basis of packet delivery ratio (PDR), end-to-end delay, routing overhead, and hop count in two different scenarios: mobile PUs scenario, and static PUs scenario. The availability of a routing channel dynamically varies in time due to the changes of the PUs relative positions. The performance evaluation is carried out using NS2 simulator. The simulation results proved that MABRP achieves better performance in terms of average PDR, with a slight increase in overhead and end-to-end delay in low PUs activity compared to CAODV routing protocol.

Interference mitigation in heterogeneous networks using Fractional Frequency Reuse

Femtocells are the rising new technology aiming to enhance the indoor coverage for Long Term Evolution (LTE) Advanced networks. However, the interference between the macrocells and femtocells can be a huge obstacle against deploying the femtocells on a large scale. In this paper, two Fractional Frequency Reuse (FFR) deployment schemes (FFR-3 and FFR-6) are being evaluated for heterogeneous networks (HetNets). Moreover, a new scheme is proposed aiming to minimize the interference on the macro-user (MU) in the cell center. Simulation results show that the proposed scheme reduces the outage probability and improves the throughput of the whole network. Furthermore, in the proposed scheme, higher percentages of users are using higher order modulation which improves the total throughput.