28-11-2012, 11:48 AM
DESIGN AND IMPLEMENTATION OF AN EFFICIENT OFDM TRANSRECEIVER CHAIN FOR WiMAX
AN EFFICIENT OFDM.docx (Size: 480.32 KB / Downloads: 36)
Abstract
The telecommunication industries are insisting on new standardized technologies with high transmission abilities like in IEEE 802.16 versions, which are also referred as WiMAX. WiMAX is a wireless transmission infrastructure that allows fast deployment as well as low maintenance costs. In this system efficient utilization of bandwidth is possible for a wide range of frequencies and can be used as a last mile solution for broadband internet access. It offers both line of sight and non-line of sight wireless communication.
This paper elucidates all compulsory features of the WiMAX OFDM physical layer specified in IEEE 802.16 standards by simulating the WIMAX models and also this paper will manifest a study on WiMAX system by comparing different modulation schemes such as BPSK, QPSK and QAM (Both 16 and 64). The performance of the designed system is evaluated based on BER and SNR with the aid of MATLAB tools.
INTRODUCTION
WiMAX (Worldwide Interoperability for Microwave Access) is introduced by the Institute of Electrical and Electronic Engineers (IEEE) which is designated by 802.16. There are fixed (802.16d) and mobile (802.16e) WiMAX [1] which offers both line of sight and non-line of sight wireless connectivity. This technology offers a high speed, secure, sophisticate, last mile broadband service, ensuring a flexible and cheap solution to certain rural access zones. In a fixed wireless communication, WiMAX can replace the telephone company's copper wire networks, the cable TV's coaxial cable infrastructure. In its mobile variant it can replace cellular networks. In comparison with Wi-Fi and Cellular technology, Wi-Fi provides a high data rate, but only on a short range of distances and with a slow movement of the user. And Cellular offers larger ranges and vehicular mobility, but it provides lower data rates, and requires high investments for its deployment. WiMAX tries to balance this situation. WiMAX fills the gap between Wi-Fi and Cellular, thus providing vehicular mobility, and high service areas and data rates WiMAX developments have been rapidly moving forward.
SYSTEM INTEGRATION AND
IMPLEMENTATION OF WORK FLOW
In the development and testing of IEEE 802.16 Wireless MAN -OFDM PHY, [2] the specifications of communication transfer have varying systems, which are based on our needs. For our study, we used the standard communication system box with a map provided by Matlab, which contains the following: Internal Communications Block set, Signal processing Block set, and Simulink Block set. These correspond to our use of the hardware development platform. The overall WIMAX PHY system construction is opened in the Simulink interface and Matlab is used to communicate the internal functions. We intend to build a finished system into a module, in accordance with the code of each block. Through this, we can perform the compilation and completion that will be automatically compiled in Matlab.
Modulation/Demodulation:
The bit interleaved data are then passed to the constellation mapper, where depending upon its size the data was modulated using the following four different modulation schemes [6]: BPSK, Gray-mapped QPSK, 16-QAM and 64-QAM. Modulation is done by dividing the incoming bits into groups of i bits to represent a modulated signal. As a result there are 2i points, and the total number of points represents a constellation. The size of i for BPSK, QPSK, 16-QAM and 64-QAM are 1, 2, 4 and 6 respectively. The constellations are presented in the I-Q plane, where I and Q denote the in-phase and quadrature component as shown in below figure 7 where b0 denotes the Least Significant Bit (LSB) for each modulation.
Doppler Frequency Shift
Doppler frequency shift is caused by the motion of relative motion. For a mobile wireless communication, it is assumed that the receiver is movingsuch that the classical Jakes’ spectrum is used. While for a fixedwireless communication, both the transmitter and receiver are stationarybut actually some reflectors in the environment move, therefore therounded Doppler PSD model is proposed.
Besides the above channel factors, coherence distances, co-channelinterference, antenna gain reduction factor should be taken in toconsideration when simulating or multichannel communicationsystem. In this project we only consider SISO and single channeltransmission and the channel for simulation is Multipath Rayleigh fadingchannel.
CONCLUSION
Wireless technologies are currently limited to some restricted services, but by offering high mobility, high data rate and high QoS wireless technologies will offer new alternatives. Offering a trade-off between coverage, data rate, and mobility with generic air interface architecture is the primary goal of the next generation of wireless systems (4G). In this context, WiMAX appears to fulfill cited requirements, providing vehicular mobility and high service areas and data rates. WiMAX Physical layer is based on OFDM techniques with employing adaptive technologies such as different combinations of channel coding and modulation together with power control, we can conclude the performance of WiMAX as, BPSK is more power efficient and needs less bandwidth. During all simulations we got, BPSK has the lowest BER and 64-QAM has the highest BER than other modulation techniques.