Loay D. Khalaf

On enhancing reputation management using Peer-to-Peer interaction history

Cooperation incentive mechanisms are an essential ingredient to the success of Peer-to-Peer (P2P) systems as they restraint the phenomenon of free-riding. We introduce an enhancement on reputation-based cooperation incentives used by the eDonkey2000 (ED2K) P2P file sharing network. This enhancement, called History-based Reputation System (HRS), can achieve better detection and control of free-riders, and by doing so enhances the scalability and fairness of the P2P system. HRS does not need the help of dedicated servers and/or central authorities, thus avoiding a single-point of failure. In addition, simulation results show that HRS achieves higher average download rate and smaller average download time for altruistic peers in a file sharing P2P system.

Design and laboratory testing of 802.15.4 2.4 GHz baseband modem

The 802.15.4 was chosen by Zigbee as the physical layer due to its characteristics; low power and low hardware complexity. This will make it available in a large number of devices ranging from remote controls to wireless sensors. We present a design for the Baseband section of the PHY and a laboratory testing environment where the real world impairments are simulated and controlled by the user to test the hardware implementation in real time. The Modem was implemented on a field programmable gate array (FPGA) software defined radio (SDR).

UWB antenna and LNA receiver simultaneous matching

This paper describes a method used to design an ultra wideband (UWB) receiver antenna and low noise amplifier (LNA) simultaneously using optimization methods. In narrow band (NB) design, the impedance of the LNA or antenna is almost constant, usually matched to 50 or 75 Ohms. Thus, the antenna and LNA are designed independently. In UWB, the antenna impedance is a function of frequency, and varies greatly. Thus, the designers option of designing each subsystem independently is difficult.

B5. Ultra wideband patch antenna and power amplifier transmitter front end

An ultra wideband (UWB) transmitter front end (RFE) consisting of UWB circular patch antenna and an UWB GaAs common source (CS) power amplifier (PA) for the frequency range 3 to 10 GHz is presented. The patch antenna covers most of the UWB range and has an area of 30×30 squared mm. The UWB patch antenna has a return loss below 10 dB from 3 to 9 GHz, simulated with a port of 50 Ohm impedance. Since the PA and antenna both have variable impedance, the matching is performed simultaneously. The antenna impedance is directly matched to the PA using optimization algorithms. The transmitted power from the antenna is simulated with a variation around 2 dB over the entire frequency range. The PA has a gain varying from 15 to 30 dB to compensate for the antenna impedance variation.

Performance of only-phase equalization in OFDM with soft decoding in indoor environment

In this paper, we investigate the performance of frequency domain equalization in conjunction with Soft Decision (SD) Viterbi decoding in the Orthogonal Frequency Division Multiplexing (OFDM) systems. Specifically, we compare the performance of two frequency domain equalization methods, one using complete phase and magnitude equalization of complex Quadrature Amplitude Modulated (QAM) symbols, while the other using only-phase equalization, or constellation rotation. Our investigation shows that the OFDM system using only-phase equalization in conjunction with soft decision decoding for convolutional codes has a better performance of about 2.5–4 dB in multipath environment than the system implementing complete equalization with the same soft decision decoding at 10−4 BER level.