Volume 24, Issue 1, March 2014

Improvements on Athermal All – Fibre DPSK- WDM based on Unbalanced Thermally Expanded Core optical fibres Mach-Zehnder Interferometer [Full Text]

Anouar Rahmouni, Nawfel Azami, Abdi Farid and Driss El idrissi

Abstract—An innovative method to achieve passively temperature-­‐‑independent fibre-­‐‑type Mach-­‐‑Zehnder interferometer design is proposed. In this work, we demonstrate that the temperature dependence of the fundamental mode effective index is linked to the expansion of single-­‐‑mode fiber core. When the thermal dependence (dneff/dT of the thermally diffused optical fiber) decreases, the mode field diameter increases. Using the optical fused biconical technique fabrication (FBT), a passively temperature independent fiber-­‐‑type optical Mach-­‐‑Zehnder interferometer based on thermally expanded core optical fiber in one arm has been developed. The experiment results are in good agreement with the numerical simulation and expectation.  


Review on Measured and Calculated Radio Frequency Radiation Emission From The Base Stations [Full Text]

S. Kaigarula, M.Kisangiri and M.M Nyaruba

Abstract - The nature of communication towers is a constant emission of pulsed radio frequency radiation. The randomly distributed base stations, especially in highly populated areas is caused by cellular operators who are not investing much in radio network planning. Improper planning causes antenna power adjustment during the busy and peak hours to overcome the call blocking and call drops. The power increase tends to increase the radiation emission level around the base station antennas, in which case if it persist for long periods may result into biological effects. Complaints have been raised by residents about the effects that may arise after installation of communication towers near their residences. These include headache, sleepless and lower sense of well-being. It has been proven by different researchers from different countries that there are significant electromagnetic radiation levels from some of the communication towers. However, control of radio frequency radiations requires proper and frequent measurement which is expensive and time consuming. This paper reviews and investigates the creation of national RF level profiles of the radiation emitted from base stations and suggests proper network planning for the determination of national EMF standards in Tanzania. 


Optimizing throughput in HARQ systems using Space - Time to Turbo [Full Text

Hamidreza Fotoohi and Aliakbar Khazae

Abstract- HARQ schemes design with a high utilization of the communication system is proposed. In this scheme, the two ARQ and FEC error correction schemes are used. The HARQ throughput is lower than ARQ. Various methods are used to improve throughput in HARQ scheme that turbo codes space - time is an example of them. In this paper, first, we introduce projects HARQ, features and characteristics of the projects are examined. Using Turbo Codes for space - time, throughput and bit error rate are improved.