Mohamed Hadi Habaebi

Circular polarized active microstrip antenna for commercial GPS application

A circularly polarized microstrip antenna was investigated for a commercial land-based GPS application mainly due to its polarization potential and attractive physical properties. Both a circular and square patch design were fabricated and analyzed to investigate the design and fabrication sensitivity to geometry. The effect of smaller patch size on performance was also investigated. The inherently low gain characteristic of the patch antenna was improved by integrating an active circuit with the patch. At 1575.42 MHz, a gain of 16 dB and input return loss, S/sub 11/>-30 dB was obtained with the active patch. Measured performance of several patch designs and GPS satellite acquisition data are presented.

Performance evaluation of OFDM schemes over multipath fading channels

This paper discusses the transmission of the orthogonal frequency division multiplexing (OFDM) signal through the multipath fading indoor channel and its capability to combat the intersymbol interference (ISI) as well as its effective implementation with the discrete Fourier transform is described. The channel model used was based on Saleh-Valenzuela model with lognormal fading distribution of gain amplitudes. Simulation modules were developed and the effect of the multipath on the OFDM system performance with BPSK, QPSK, 16PSK, 64PSK, 16QAM, 64QAM, and 128QAM modulations was evaluated in terms of the bit error rate (BER) as a function of the energy per bit-to-noise ratio (EBNR). The influence of the number of carriers as well as the guard interval duration on the performance was also investigated. Simulations showed that the EBNR required to achieve a certain BER is significantly increased by 8-10 dB for dense multipath fading channels over that required in AWGN channels. These performance measures are useful for the design and assessment of high speed indoor wireless communication systems.

Aggregate History of User Mobility Pattern for QoS Provisioning in Multimedia Wireless Networks

Multimedia traffic is expected to be included in the next generation of wireless networks. As in wireline networks, the wireless network must also be capable of providing guaranteed quality-of-service (QoS) over the lifetime of mobile connections. In this paper, a bandwidth reservation scheme incorporating a user mobility prediction is proposed to manage the QoS of the networks. The mobility prediction scheme is developed based on the aggregate history of mobile users. Based on the mobility prediction, bandwidth is reserved to guarantee the uninterrupted handoff process. Simulation results demonstrate that the proposed scheme can guarantee the required QoS requirements in terms of handoff call dropping probability and new call blocking probability while maintaining efficient bandwidth utilization.

A new MAC protocol for wireless ATM networks

We study the performance of a new-framed pseudo-Bayesian Aloha algorithm with prioritized adaptive assignment algorithm. This algorithm provides to high priority control packets to the uplink frame of the reservation-TDMA wireless ATM MAC protocols with minimum effect on the access time of the low priority control packets. The protocol is analyzed with the wireless channel effect and results show that wireless channel improves access time performance for all priority classes.

A new multicast-based architecture to support host mobility in IPv6

A new multicast group join/leave mechanism for mobile nodes (MNs) is proposed. The mechanism is based on hash algorithm. This paper explains the construction of a dynamic delivery tree of the mobile node movement for a multicast-based mobile IPv6 network, such that the branches of the tree constitute the shortest paths from the packet source to each of the visited locations. The branches of the tree grow and shrink to reach the mobile node when necessary. The mobile node is assigned a multicast address and the correspondent nodes (CNs) send packets to the multicast group. As the mobile node moves to a new location, it joins the multicast group through the new location and prunes through the old location. The performance of the proposed mechanism was evaluated through a simulation model built for this purpose. Simulation results show that the dynamics of joining and leaving the group directly affect handoff latency and smoothness, as a result it conserve radio frequency (RF) bandwidth.

Dynamic channel allocation scheme for mobile satellite systems

A new dynamic channel allocation scheme (DCAS) has been proposed for mobile satellite systems with the aim of improving the utilization of the network resources by reducing the handoff call dropping probability (HODP) while guaranteeing a certain quality of service for the new call blocking probability (NCBP). The arriving calls are given channels based on their priority. The handoff calls have higher priority compared to the new calls, and real time traffic calls have higher priority over non real rime calls. The DCAS is then combined with the shortest path routing for a adaptive channel management scheme.