Volume 10, Issue 1, August 2011

Modeling of Opportunistic Spectrum Sharing with Sub-banding in Cognitive Radio Networks [Full Text]

Samira Homayouni, Seyed Ali Ghorashi

Cognitive radio  is a  technology  to solve  the problem  of  spectrum under-utilization in some  licensed bands.  In  this paper,  we  propose  a  model  for  opportunistic  spectrum  sharing  in  cognitive  radio  networks  for  a  special  case  in  which,  two secondary users are allowed to coexist in a channel (sub-banding). The proposed model is such that, when all the channels are occupied by the primary and secondary users, then the secondary users’ channels can be divided into two sub-bands, and two secondary users may use a sub-band, simultaneously. The state equations of the system are derived based on two-dimensional Markov chain model. Next, the system performance is evaluated by some metrics such as blocking and dropping probability as well as channel utilization. Furthermore, the results for the cases of using and not using sub-banding for the secondary users have been compared. The  results demonstrate  that in  a spectrum  sharing system,  channel  sub-banding significantly  reduces the blocking and dropping probabilities of the secondary users, with the cost of lower quality channels in comparison with state without using sub-bands.


Simulation Study on Performance Analysis of Decoding Algorithms in Turbo Codes
[Full Text]

Mohd Kasim N.S and Ab.Rashid S.R
Abstract – Turbo codes are a new class of forward error correcting codes that have proved to give a performance close to the Shannon’s Limit. Its encoder  is  formed  by  the  constituent  concatenation  of  identical  recursive  convolutional  encoders  and  interleaver  while  the  decoder  utilizes cascaded decoding components to share a priori information. The decoding algorithms have the benefit to work iteratively such that the overall performance can be improved. The performance of Turbo codes depends on its architectural components and the decoding algorithms. In this paper, the performance of Turbo codes is analyzed in terms of bit error rate (BER) and bit energy to noise ratio spectral density (Eb/No). This paper focuses on comparison of decoding algorithm such as Log-Maximum A Posteriori (Log-MAP) and Soft Output Viterbi Algorithm (SOVA) which is applied in Turbo codes iterative decoding. Finally, the parameters that influenced the Turbo codes performance are investigated. The number of iterations, frame size, puncturing effects and generator matrices are varied in MATLAB simulations to determine the effects in performance of Turbo Codes.


Modelling of Carrier-Phase Offsets in Digital Pass Band Communication Systems using Simulink
[Full Text]

Ojo F.K and Ogunti E.O
In this study, the performance of a SIMULINK-based communication phase models with numerical integration (NI) approximate method and Low density parity check (LDPC) coding for the estimation of carrier-phase offsets in digital passband communication systems using  Quadrature  Phase  Shift  Keying  (QPSK)  modulation technique was  investigated. The  models  considered were the  constant-phase  and the  random-walk  phase  models.  The  optimum  performances  of  the  two  models  were  determined  from  simulation  graphs  in  SIMULINK where the Frame Error Rate (FER) and the Minimum Mean Square Error (MMSE) were plotted against Signal to Noise Ratio (SNR) at the receiver. The previous research do not provide information on which of the models is better for the estimation of the carrier-phase offsets in digital passband communication systems. The lower the FER and the MMSE values at a particular SNR, the better the performance of the model.  The  results  show  that  the  performance  of  the  SIMULINK-based  phase  estimator  using  the  constant-phase  model  gives  a  better performance over the random-walk phase model in terms of FER and MMSE.


Speaker Identification using Discrete Wavelet Transform and Daubechies Wavelets based Decomposition
[Full Text]

H.B.Kekre and Vaishali Kulkarni 

In  this  paper  we  present  Speaker  Identification  using  Discrete  Wavelet  Transform.  The  speech  signal  has  been decomposed upto seven levels using Discrete Wavelet Transform (DWT) by using different Daubechies mother wavelets. The mean of the approximate and exact coefiiecents of every level have ben taken as the feature vector. This technique has been applied for text dependent identification for the four different sentences in the database. The accuracy of identification obtained for all the sentences has been compared. It is observed that longer the sentence better is the accuracy.


Reduction of ICI Effect in MIMO-OFDM System using Self-Cancellation [Full Text]
S. R. Sabuj, M. S. Islam and R. Khan

Abstract-  Multiple  inputs  and  multiple  outputs  (MIMO)  OFDM  provides  high  spectral  efficiency.  One  of  the  main  disadvantages  of  MIMO-OFDM  is  its  sensitivity  against  carrier  frequency  offset  and  phase  noise  which  causes  intercarrier  interference  (ICI).  Our  main  goal  in  this paper  is  to  suppress  the  ICI  effect  significantly  in MIMO-OFDM  system  using  self-cancellation  with  data  conjugate.  In  this  paper  we  have analytically derived expression for common phase error (CPE), ICI, carrier to interference (CIR) and Symbol Error Rate (SER) of the system. Results show that at SER of 10-8, data conjugate SC in MIMO-OFDM system has been reduced about 5.6 dB than MIMO-OFDM system. 


Recent Trends in Protection of Data for Intelligent Wireless Network [Full Text]

Ravneet Kaur

Abstract—Frontier of computer science and technology is intended to facilitate effective communication and exchanges all over the world. It will not only reflect the significant advances that are currently being made in computer science but also will represent a powerful and unique forum for discussing innovative, cutting-edge advances in high performance computing, networking, storage and analysis from stakeholders in academia, government and corporate institutions around the globe. The present paper deals with the recent trends in protection of Data for intelligent Wireless Network.