Abstract: In WiMAX networks, the biggest challenge is to overcome the effects of fading especially when nodes are mobile. The multipath nature of channel leads to ISI (Inter Symbol Interference) and the severity of ISI effects increases with bandwidth increase and this might get worse when nodes are moving . The radio link between the Base Station and Service Station/Mobile Station can be a LOS or it can be a NLOS. The environmental objects and features like buildings, weather conditions can severely obstruct NLOS signal. In this paper the effect of pedestrian multipath and node mobility in WiMAX network is studied under different codecs schemes in order to evaluate the effect of multipath channel fading when nodes are moving on the QoS parameters end to end delay, jitter, mean opinion score and throughput of a VoIP application. The obtained results showed that multipath fading with mobile nodes has sever effect on throughput and MOS value for all studied codecs and on the other parameters the effect varies depending on the implemented codecs. arabic 14 English 71
N. Aboalgasm, I. Almerhag , A. Daeri(3-2018)

in wireless networks, mobility is an important issue because Internet connectivity can only be effective if it is available during the movement of a node. To enhance mobility, the IEEE802.16e standard has set procedures to design wireless access systems to operate on the move without any disruption of services. The major difference between mobile WiMAX and fixed WiMAX is mobility support. However, speed and trajectory of nodes are unpredictable and can vary even in identical circumstances. In this paper mobile node trajectory is studied under different codecs schemes in order to evaluate the effect of node movement, towards or away from the base-station, on end to end delay, jitter, mean opinion score and throughput of a VoIP application. The results showed that trajectory inward improves network performance since mobile node gets closer to the base-station and hence signal is improved and less power is required. arabic 12 English 67
I. Almerhag, N. Aboalgasem(5-2017)

DLFSR is promising for enhancing the security of stream ciphers. However, good inviolability and statistical properties of the DLFSR generator are only achievable when the parameters of the switching algorithm are properly selected. This paper describes a new experimental method for choosing suitable parameters for the algorithm of switching the polynomial in DLFSR. This method was used to enhance the Grain-128 stream cipher. The randomness of the modified Grain was evaluated using the NIST suite, and the results are encouraging. The modified Grain was also compared to the original, and the results indicated that the modified algorithm outperforms the original in several tests. arabic 12 English 82
Fayrouz Aljadi, Ibrahim Almerhag, Fardous Eljadi(3-2019)