Performance Enhancement of WiMAX System using Adaptive Equalizer RICHA ANAND *1, PRASHANT BHATI *2 *1 (Prof. of Department, Patel college of science and technology / RGPV University, India) *2(student of EC Department, Patel college of science and technology, Indore, India) prashantbhati@yahoo.com*1, Richa_anand87@yahoo.com*2 ABSTRACT The telecommunication industry has been developing at a very fast rate, but data networking service revenue has continued to rise. This paper presents on performance enhancement of the WiMAX system (Worldwide Interoperability for Microwave Access) by using Adaptive Equalizer. WiMAX is an emerging global broadband wireless system based on IEEE 802.16 standards. It is a new wireless OFDM-based technology that provides high quality broadband services. Mobile WiMAX is a wireless networking system which provides wireless broadband to fixed and mobile terminals. In this paper, firstly performance evaluation of WiMAX system with channel estimation is discussed. Performance evaluation with channel estimation is used because amplitude and phase shift causes error in wireless channel. Performance evaluation of WiMAX system using adaptive equalizer technique is then carried out. Bit error rate performance for different modulation schemes is then compared. Results show that by using adaptive equalization technique, bit error rate for all adaptive modulation techniques are improved. The equalizer mitigates the effect of the wireless channel and allows subsequent symbol demodulation. Keywords: WiMAX, OFDM, Equalizer, LMS, RLS Broadband Access, 3G and 4G. INTRODUCTION Telecommunications has grown at a tremendous rate in the last ten to twenty years. Improved semiconductor and electronics manufacturing technology, and the growth of the internet and mobile telecommunications have been some of the factors which have fueled this growth in telecommunications. The deployment of state of the art telecommunications infrastructure and services has however been restricted to the developed world. The least developed countries have been left in the technological dark ages with few or none of the next generation networks installed. Developed countries now boast high speed connections with a large percentage of homes having access to the internet and broadband services at an affordable fee. The underdeveloped countries are yet to enjoy such facilities. This is referred to as the digital divide. The digital divide has persisted due to the relatively high cost of putting up modern telecommunications infrastructure. This is compounded by the fact that there are a number of different services available and each service requires its own technology and network. Therefore existing technologies such as Wireless Fidelity (WiFi), Digital Subscriber Line (DSL), Global System for Mobile communications (GSM), Integrated Services Digital Network (ISDN), and the relatively new 3G technologies have not been able to provide a total solution to closing the digital divide WiMax earned an important seal of approval recently when the Radio 1
communication sector of the International Telecommunication Union (ITU-R) certified it as a 3G (third-generation) mobile data technology. WiMAX is an industry trade organization formed by leading communications component and equipment companies to promote and certify compatibility and interoperability of broadband wireless access equipment that conforms to the IEEE 802.16 and ETSI HIPERMAN standards. WiMAX is one of the hottest broadband wireless technologies around today. WiMAX systems are expected to deliver broadband access services to residential and enterprise customers in an economical way. WiMAX stands for Worldwide Interoperability for Microwave Access formed by WiMAX forum in 2001. It provides wireless broadband to fixed and mobile terminals in a large geographical area. The 2005 version of WiMAX provides data rate up to 40Mbits/s and 2011 version can support data rate up to 1 Gbit/s for fixed stations [1]. It is one of the latest developments and considered as a 4G (Fourth Generation) technology. Wimax supports data rate up to 75 Mbit/s which is higher than conventional cable modem and digital subscriber line (DSL) connections which are all wired access technologies. The name "WiMAX" was created by the WiMAX Forum, which was formed in June 2001 to promote conformity and interoperability of the standard. The forum describes WiMAX as "a standards-based technology enabling the delivery of last mile wireless access as an alternative to cable and DSL" WiMAX is based on Wireless Metropolitan Area Network (WMAN). IEEE 802.16 group developed WMAN and it is adopted by ETSI (European Telecommunication Standard Institute) in HiperMAN group i.e. High Performance Radio Metropolitan Area. WiMAX scenario is shown in Figure: WiMAX scenario Network. WiMAX system uses OFDM in the physical layer. OFDM is based on the adaptive modulation technique in non-line-of sight (NLOS) environments. Base stations of WiMAX can provide communication without the need of lineof-sight (LOS) connection. WiMAX base station has enough available bandwidth so at a time it can serve large number of subscribers and also cover large area range. WiMAX standard have two versions: IEEE 802.16-2004 and IEEE 802.16e. IEEE 802.16-2004 standard supports for fixed applications so it is called as fixed WiMAX or IEEE 802.16d. It supports OFDM (Orthogonal Frequency Division Multiplexing) in physical layer. WiMAX standard 802.16e uses OFDMA (Orthogonal Frequency Division Multiplexing Access) technique. WiMAX is: Acronym for Worldwide Interoperability for Microwave Access. Based on Wireless MAN technology. 2
A wireless technology optimized for the delivery of IP centric services over a wide area. A scaleable wireless platform for constructing alternative and complementary broadband networks. A certification that denotes interoperability of equipment built to the IEEE 802.16 or compatible standard. The IEEE 802.16 Working Group develops standards that address two types of usage models: o A fixed usage model (IEEE 802.16-2004). o A portable usage model (IEEE 802.16e). Related Work Improvement of PHY layer of WiMAX is one of the various areas of research that is just getting started with 802.16 on developing its performance in variable environments. Hybrid ARQ (Automatic repeat request), interference cancellation and adaptive sub carrier power allocation (increase the range and robustness) had been proposed as the four major techniques to increase the throughput and robustness of future WiMAX systems. The finite-length queuing and AMC were combined by the QoS performance was found to be improved in terms of the reduced packet loss rate, increased average throughput, and the average spectral efficiency (ASE) of AMC by. A cross layer design was also proposed and implemented at the data link layer to minimize the packet loss rate and to maximize the average throughput at physical layer. Some researchers also expanded their work on the existing modulation schemes while some inclined on developing a simulation model of the WiMAX PHY layer to study its behavior and suggest few enhancements on various aspects of it. A novel interleaving approach for multi-quality transmission that can effectively combat different burst errors caused by phase noise and multipath fading without deteriorating the channel capacity was proposed. A top level WiMAX simulink model was developed to focus on channel estimation with different interpolation approaches for fixed/mobile OFDM systems. An impact of Doppler shift on the relative performance between the different channel estimators and interpolation approaches was also observed. The performance of the WiMAX under different data rates, coding schemes and channel conditions has also been evaluated which are based on standards from IEEE. The other advanced features of PHY layer include the channel estimation schemes, advanced antenna systems, transmit diversity and MIMO based systems to support mobility extensions to the physical layer. Lower Density Packed Codes (LDPC) and different equalization techniques were proposed to improve the WiMAX system performance. Further verification was done with the improvement in Bit Error Rate (BER) performance by taking into account the channel behavior in terms of capability to switch the order of the modulation and the coding rate to better match the channel conditions with respect to statistical Modulation and Coding Scheme (MCS) selection techniques. The paper also reports the emergence of new hybrid OFDM system with multiple access technology CDMA known as MCCDMA to provide high suppression against multipath fading, high bandwidth efficiency and high throughput with high data rates i.e. delivering the benefits of both OFDM and CDMA. The work also includes 3
the contributions of the performance of both Direct Sequence (DS-CDMA) and MCCDMA systems in frequency selective Rayleigh faded channels. It also found that MCCDMA proved to be an effective technique in these environments with little complexity in the receiver system. Furthermore implementation of these optional schemes in IEEE 802.16d/e based PHY layer standard are the keen research areas that are being explored are to improve the WiMAX performance. In the present work we intend to implement two schemes, AMC and MCCDMA, at the PHY layer of the Base Station (BS) of WiMAX Systems and observe the performance improvements in terms of BER and spectral efficiency for different applications. complex. Modulation techniques used are BPSK, QPSK, 16QAM, 64QAM in frequency selective fading channel. Then data is trained to adjust the received signal with phase recovery. At receiver side adaptive equalizers like LMS (least mean squares) and RMS (recursive mean squares) are used to combat the effect of ISI. Finally BER for all modulation techniques are plotted. PROPOSED WORK PERFORMANCE ENHANCEMENT USING ADAPTIVE EQUALIZER An adaptive equalizer is an equalizer that automatically adapts to time-varying properties of the communication channel. It is frequently used with coherent modulations such as phase shift keying, mitigating the effects of multipath propagation and Doppler spreading. An adaptive equalizer is a time-varying filter that automatically adapts the properties of communication channel. It reduces the effect of inter-symbol-interference (ISI) in wireless channel. Different equalizer algorithms can be used. System model with adaptive equalizer is shown in Figure 4. Here, data are produced by random data generator. After the source data is produced, pilot data is inserted as the header of each source data at each coherence time. It is used to estimate the random phase shift of the fading channel. Then data is mapped from binary to Figure: System model with adaptive equalizer For simulation a model is choosen where carrier frequency is 2GHz, bandwidth of each channel is 200 KHz. For urban environment delay spread is considered to be 10μs, user is walking at a velocity of 5Km/hr. Symbol period is taken as 5μsec. Now, Coherence time may be given by equation (1) [5] (1) Equation (1) may be written as (2) From equation (2), coherence time Tc is found to be 19.4msec. Now, it is seen that Tc>delay spread>ts. Hence, it is a frequency selective and slow fading channel. In system model LMS equalizer is used. Least mean square equalizer is used to find out filter 4
coefficients. LMS produces least mean square of the error signal. CONCLUSION In this paper, performance enhancement of WiMAX system is done with adaptive equalizer. Firstly, BER for different adaptive modulation techniques are evaluated in slow frequency selective fading channel. performance of WiMAX system is evaluated using adaptive equalizer. Using adaptive equalizer technique bit error rate is improved. Further, results for mobile users show that the fading environments, mobile environments, severely degrade the performance of the system. The proposed combination of OFDM and CDMA, MC-CDMA, provided a better BER performance, high bandwidth efficiency and higher throughput in fading environments encountered by mobile users. The BER performance of WiMAX OFDM based PHY layer is hence improved with MCCDMA in PHY layer. Emerging Trends in Computing and Information Sciences, Vol.3, No.3, March 2012. [6]IEEE 802.16m-07/004r4, IEEE 802.16m Evaluation Methodology Document (EMD), (2008). REFERENCES [1] www.wikipedia.com. [2] Mai Tran, George Zaggoulos, Andrew Nix and Angela Doufexi, Mobile WiMAX: Performance Analysis And Comparison with Experimental Results. [3] Jeffery G. Andrews, Arunabha Ghosh, Rias Muhamed, Fundamentals of WiMAX: Understanding Broadband Wireless Networking, Prentice Hall, 2007. [4]What is WiMAX, http://www.wimax.com/education/wimax/what [5] Anita Garhwal, P.P.Bhattacharya, Fuzzy Logic Based Channel Estimation and Performance Analysis of WiMAX Systems, Journal of 5