Volume 4, Issue 2, September 2010

Performance Diversity Techniques for Wireless Communication System [Full Text]

Mohammed Aboud Kadhim, School of Electrical and Electronics Engineering, Universiti Sains Malaysia
Dr Widad Ismail,
School of Electrical and Electronics Engineering, Universiti Sains Malaysia


AbstractDiversity is an influential communication receiver technique that provides wireless link enhancement at a relatively low cost. Diversity techniques are used in wireless communications systems to principally to develop performance over a fading radio channel. In such a system, the receiver is provided with multiple copies of the same information signal which are transmitted over two or more real or practical communication channels. Thus the basic idea of diversity is repetition or redundancy of information. The demands for greater capacity and lower transmitted power have historically motivated research .in this paper describe the different receive diversity and compare between them in BPSK modulation and Rayleigh fading channel.
 
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Wideband Non Linear 3 dB Hybrid Coupler for X-Band Switched Beam Antenna
[Full Text]

Y.K. Ningsih, Department of Electrical Engineering, Universitas Indonesia, Depok, Indonesia
M. Asvial, Department of Electrical Engineering, Universitas Indonesia, Depok, Indonesia
E,T. Rahardjo, Department of Electrical Engineering, Universitas Indonesia, Depok, Indonesia

AbstractThis paper presents a new wideband 3 dB hybrid coupler for X-band.  The proposed wideband 3 dB  hybrid coupler has been designed by using non linear arm with exponential impedance taper to achieve a good performance. The proposed hybrid coupler achieved an impedance bandwidth over 22% with coupling coefficient -3.3 dB, isolation coefficient of below -25 dB and reflection coefficient of below -20 dB. The result shows a good performance. To implement the new hybrid coupler, a switched beam antenna is designed. The propose antenna can produce two radiation patterns that can be changed to different beam for reduce the existing interference. Switched beam antenna using a non linear 3 dB hybrid coupler has been design and realization in a single layer substrate, that it has a wideband characteristic. The simulation and measurement results show that the antenna can generate two beams at 20° and 330° with a beamwidth of around 40° at 9 GHz. The return loss of the switched beam antenna can be achieved below -18 dB over a 20% bandwidth with a center frequency at 9 GHz.


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Performance Transmit and Receive Diversity Techniques for Different Modulation Signal
[Full Text]

Mohammed Aboud Kadhim, School of Electrical and Electronics Engineering, Universiti Sains Malaysia
Dr Widad Ismail, School of Electrical and Electronics Engineering, Universiti Sains Malaysia


Abstract—the use of multiple communication paths or channels to achieve efficiency and error protection. The main types of diversity used in communications system one is transmit diversity and the other is receive diversity to exploit multipath effect. Diversity is usually between two antennas and each antenna has one channel. One antenna is at the base station and the other is at the service station. The base stations keeps record of the transmission and receive signal information with each channel. However, there can be many antennas at the base station and the service station.  In this paper we have simulated the system by using Transmit Diversity (Space Time Coding) and Receiver Diversity (Maximum Ratio Combining) techniques. Based on the mathematical calculations for different modulation signals.