WiMAX in OFDM Physical layer

1 Objectives:

The goal of this thesis is to implement and simulate the OFDM Physical layer specification of IEEE 802.16e-2005. Using Adaptive Modulation Techniques we analyze the performance of OFDM physical layer in mobile WiMAX based on the simulation results of Bit-Error-Rate (BER), Signal-to-Noise Ratio (SNR) and Probability of Error (Pe). The performance analysis of OFDMA-PHY is done in MATLAB 7.4 under reference channel model with channel equalizer.

2 Motivation

Some decades ago, we were purely dependent on analog system. Both the sources and transmission system were on analog format but the advancement of technology made it possible to transmit data in digital form. Along with those, the computer was getting faster to the fastest, the data payload capacity and transmission rate increased from kilobit to megabit and megabit to gigabit. From wire to wireless concept emerged and after researching and investing so much money, engineers became successful to invent wireless transmitter to transmit data. Applications like voice, Internet access, instant messaging, SMS, paging, file transferring, video conferencing, gaming and entertainment etc became a part of life. Cellular phone systems, WLAN, wide-area wireless data systems, ad-hoc wireless networks and satellite systems etc are wireless communication. All emerged based on wireless technology to provide higher throughput, immense mobility, longer range, robust backbone to thereat. The vision extended a bit more by the engineers to provide smooth transmission of multimedia anywhere on the globe through variety of applications and devices leading a new concept of wireless communication which is cheap and flexible to implement even in odd environment. This is a fact that, Wireless Broadband Access (WBA) via DSL, T1-line or cable infrastructure is not available especially in rural areas. The DSL can covers only up to near about 18,000 feet (3 miles), this means that many urban, suburban, and rural areas may not served. The Wi-Fi standard broadband connection may solve this problem a bit but not possible in everywhere due to coverage limitations. But the Metropolitan-Area Wireless standard which is called WiMAX can solve these limitations. The wireless broadband connection is much easier to deploy, have long range of coverage, easier to access and more flexible. This connectivity is really important for developing countries and IEEE 802.16 family helps to solve the last mile connectivity problems with BWA connectivity.
Simulation Results Analysis

During our simulation we used cyclic prefix to minimize the Inter Symbol Interference (ISI) on the basis of following adaptive modulation techniques through Matlab.

• Binary Phase Shift Keying (BPSK)
• Quadrature Phase Shift Keying (QPSK)
• 16-Quadrature Amplitude Modulation (16-QAM)
• 64-Quadrature Amplitude Modulation (64-QAM) With the help of above modulation techniques we got the following parameters,
• Scattering Points of QPSK
• Scattering Points of QAM
• Bit Error Rate (BER)
  
• Signal to Noise Ratio (SNR)
• Probability of Error (Pe) This is the simulation environment which we used in our simulation,
• Microsoft Windows XP Professional.
• Matlab 7.4.0.287 (R2007a)
• Microsoft Office 2007
• Mersenne Twister – Random Number Generator ( RNG ) Algorithm
• We used Cyclic Prefix to minimize the Inter Symbol Interference (ISI).
  
• Performance of WiMAX has been done on the basis of BER Vs SNR in all plotting.
• We have used AWGN and Rayleigh fading.

Scatter Plots of QPSK

In this subsection, we investigated the constellation of QPSK, 16-QAM and 64-QAM by using ZERO force and MMSE equalizer when FFT size is 256 and 512. After passing through AWGN channels, we got the figure 1.
















Fig 1: QPSK constellation using ZERO force equalizer for FFT size 256