BER PERFORMANCE REVIEW OF WIMAX MIMO SYSTEM

: The demand for high data rate is increasing day-by-day in today’s scenario. With limited bandwidth resources, WiMAX can be viewed as efficient solution to this problem .WiMAX technology is based on IEEE 802.16 standard and is able to support greater number of customers at higher data rates. Although WiMAX standard can support both fixed and mobile applications, but the latter have larger demand. Its performance can be further boost up by utilizing MIMO techniques. This paper reviews the BER performance analysis of WiMAX system with MIMO technique .


INTRODUCTION
WiMAX ,an acronym of Worldwide Interoperability for Microwave Access , is a technology developed to satisfy high data rate requirement for wireless broadband access services. Based on IEEE802.16 standard , it is one of the hottest wireless broadband access technique in today's scenario. Prior to the development of WiMAX system,T1,Digital Subscriber Line(DSL) or cable modem were effective methods to attain wirelesss broadband access. However, these wired infrastructure have high cost associated with them.This limitation instigated the industry to evolve an alternative method to obtain broadband access with wireless medium. In June 2001, a non-profit organization called WiMAX Forum consisting of network operators, component vendors ,equipment manufacturers and system integrator was set up to maintain interoperability among WiMAX products from different manufacturers.The name WiMAX was propounded by WiMAX forum. WiMAX functions in similar way as Wi-Fi but provide higher speed for larger distances and for more no. of users .It is a wireless metropolitan area technology and is able to support high data rate applications requiring variety of quality of serviceS (QoS). Some of the key features of WiMAX systems are: utilization of OFDMA technique , use of any channel width ,time and frequency division duplexing ,modern antenna techniques,various QoS classes ,per user adaptive modulation ,use of advanced codes like space time codes and turbo codes. WiMAX based on IEEE802.16d standard, introduced in 2004, was capable to support only fixed application [1]. It works on frequency range 2-11GHz.The mobile WiMAX variant of the system based on IEEE802.16e [2] ,was added with the feature to support secure seamless handover of ongoing connection from one base station to another. Both techniques MIMO and OFDMA are included in WiMAX 802.16e specification to improve the coverage and multiply the system capacity.
Modern wireless communication systems are moving from SISO and SIMO systems to MIMO systems to attain increase in the channel capacity and to suppress the fading effects. MIMO systems have been greatly employed in several wireless communication standards such as IEEE802.11n standard for local area network and IEEE802.16e-2005standard for portable broadband access. MIMO system uses a number of parallel channels to achieve multiplexing gain [3].Using MIMO systems increased bandwidth efficiency can be attained at the cost of increased computational complexity. This bandwidth efficiency can be used to acquire higher data rates and capacity without requiring any extra bandwidth resources and power. The overlay of this paper is : Section 1 gives brief introduction to WiMAX system , its layer architecture and MIMO techniques .It is followed by section 2 which describes the literature review of WiMAX MIMO system. Conclusion concludes the paper in section 3.  [5,6], sp Siavansh Ala de [10] with w using two tra t it provide receiver term find optimum ]. In [14] both technical and non-technical issues have been explored to evaluate the quality experienced by end user in a WiMAX based system. The test was conducted on WiMAX broadband network configuration in Tanzania. From the study, it is determined that base station with sectorized antennas outperform those with omnidirectional antennas. Also, WiMAX configuration with outdoor CPE outperformed TTCL DSL network. But performance of indoor CPE is similar to that of TTCL network. Thus it can be concluded that in all prevailing environmental conditions, outdoor CPE provides improved performance than indoor CPE.

A. WiMAX LAYER ARCHITECTURE
In [15] capacity of an online,interference based pre-coding algorithm for MU-MIMO system has been evaluated. Also the concerns related to its implementation has been considered. Simulation is done with the help of WiMAX 802. 16-2004 compliant simulator. From the analysis, it is clear that with the selected technique, capacity of the system is improved,but there are many issues associated to its implementation such as number of required iteration increases linearly as number of users multiplexed increases. Such issues are prohibiting the system designer to introduce this technique into the wireless specification.
In [16] MIMO techniques with space time block code modulation scheme is focused upon to increase the overall capacity of the system and to deliver enhanced service to users at cell boundary. Multiple antennas are implemented both at transmitter and receiver terminal. It is seen that for user at boundary of cell the receiver SNR is very low and BER is reduced as no. of antennas are increased at transmit or receive side.
In [17] WiMAX system is tested under various fading channels-Rayleigh, Rician,Nakagami,Lognormal shadowing channels for different modulation schemes to examine BER with respect to SNR. From BER vs SNR plot, it is observe that on increasing SNR ,BER decreases. Among different fading channels, it is found that Nakagami channel shows improved performance at high SNR and also among various modulation schemes , BPSK modulation provide lowest BER. Thus it can be deduced that to attain efficient bandwidth utilization Nakagami channel is best.
In [18] MIMO OFDM physical layer performance with QC LDPC codes using different modulation schemes is evaluated. From the evaluation of BER performance of proposed system, it is clearly evident that higher order modulation provides higher data rates but they are less resilient to noise. Hence, dynamic adaptive modulation schemes along with forward error correction code are used widely.
In [19] WiMAX system with WPM technique has been proposed. The BER performance of proposed system is evaluated in both AWGN and Rayleigh fading condition and compared with conventional WiMAX system based on OFDM. DQPSK modulation scheme is opted for WiMAX based on WPM. From the results found using simulation done with MATLAB software, it is clear that the performance of WiMAX system based on WPM is better than WiMAX system with OFDM technique ,in terms of low BER, in both channel condition by 4dB .The result obtained for Rayleigh frequency selective channel is further enhanced. Also the multicarrier based on wavelet transform gives improved performance than multicarrier based on fourier transform. From the BER performance of the system , it is evident that higher order modulation provides higher data rates but they are less resilient to noise. 2016 Sayali R.Band,Megha S.Dorle ,Dr. S.S.Dorle [19] Analysing BER performance of WiMAX system with WPM BER performance of proposed system is evaluated in both AWGN and Rayleigh fading channel and compared with conventional WiMAX system based on OFDM From the results found using simulation done with MATLAB software, it is clear that BER performance of WiMAX system based on WPM is better than WiMAX system with OFDM technique in both channel condition by 4dB .

III. CONCLUSION
This paper reviews the performance of WiMAX system along with MIMO technique which offers potential advantages such as increased utilization of spectrum bands , increased system capacity and improved coverage. The results of some recent work held on WiMAX -MIMO systems are reported and an ample survey of recent and relevant work published in this field is properly studied and is specified in chronological order.