The aim of this research context is to develop the WiMAX OFDM physical layer defined in IEEE 802.16 using matlab simulink software. Taking into consideration various MIMO scenarios we will analyze the performance of the system. For combining the diversity scheme we will also define, a maximum ratio which will be present at the receiver side for the same purpose. In order to maximize the throughput and improve the BER performance, multiple modulation and coding schemes will settle in to the variations that exist in the channel SNR, thus maximizing the system throughput and improving BER performance. The System performance with transmitter and receiver part will be studied in order to estimate the performance gains of some optional features, for e.g. the MIMO extension will be studied and analyzed. We will monitor the performance of the system in great detail by analyzing the simulation results and computing the BER and SNR influence on the system.
WiMAX happens to be a fast growing wireless communication system which is expected to give a comprehensively high data rate communications in the metropolitan area networks(MANs).Basically it takes into account the very physical layer and the MAC layer. At the physical layer, there are some five types of dissimilar modulating methods: Wireless-SCa Wireless-OFDMA, Wireless-SC and Wireless HUMAN and Wireless-OFDM. In that, the OFDM is the compulsive item; requires every equipment which matches IEEE802.16 standard to do. OFDM technology is the main technology to give the operators an effective way to counter the challenges of the non-line-of-sight (NLOS) travel in the WiMAX. Also its robustness and high transmission capability for the effects of frequency-selective multipath channels makes it the important for wireless communications.
The physical layer of WiMAX has OFDM for downlink uplink with a time split duplex (TDD) frame structure in time 5ms which is common between the DL and UL. The coding and adaptive modulation are used on both the DL and UL for WiMAX. This research doesn't consider the enhancement because of the hybrid automatic repeat request (H-ARQ). WiMAX tells the use of two antennas for the receiver's end.
Due to the features of this WiMAX and the shortcomings of OFDM system which happens to be very time sensitive. The OFDM system in WiMAX takes any deliver mode, With High data rate being achieved in between the transmitter and the receiver in case there is any synchronization between them. But, they generally exists a small timing and frequency offset whose exists will dramatically degrade the performance of the whole OFDM systems. Therefore, before the desired signals are demodulated, OFDM symbols are to be time-synchronized compensated. This goes to show that a very high request to the node the synchronization system, In order to get this synchronization, we should take synchronization algorithm for less smaller calculations.
Comparison Existing System
Wimax technology based on IEEE 802.16 specifically designed for MAN is configurable in the same as compared to traditional cellular networks involving base stations and which support point to multipoint architectures. The range and NLOS (Non line of sight) features of wimax makes it attractive among users
The basic aim of any Wimax system is to provide wireless broadband access services to users, with the help of base stations with distance measures in terms of miles. Earlier wimax system services were restricted to only fixed links, but due to the increasing popularity among people, wimax was extended to include portable devices for e.g. phones, Laptops, personal digital assistants. Support to mobility was also added in Wimax systems, to enable connection flexibility to moving devices such as mobile. Wimax systems support transmission frequencies upto 2.66 Ghz. But there were also some factors that hampered the performance of WiMAX systems such as channel capacity, interference, these factors degraded the performances of wimax system, Therefore there is need to address these issues in order to improve the performance of the system.
There are a lot of techniques used for computing the performance of WiMAX system, based on different factors, one such technique is based on convolutional coding, and convolutional product code. In CPC technique the bits carrying information with them are usually stored in 2D matrix, every row and column of the matrix are encrypted independently by making use of recursive convolutional encoders, but the drawback involved in this scheme is that recursive encoders consists of feedback mechanism which needs to be terminated, which increases the complexity, also generator polynomial's are used in recursive encoders, which requires additional zeroes to terminate the encoder which is also increases the difficulty. Therefore we use a different technique altogether, for computing the performance of Wimax system based on Signal to nose ratio and bit error rate which is easy to estimate than convolutional product code based wimax system.
The main components required in any wireless communications system are outlined in the in Figure (1) these include the transmitter, a path for data transmission, and the receiver who is the intended receiver of the message. Initially transmitter takes an arbitrary data in the form of signal it then processes that input signal or message to be sent and generates an appropriate signal called as transmitted signal suitable for transmission.
The next step is then called signal processing which involves modulation, coding and demodulation for a signal. The process of modulation signifies an encrypted signal which can be safely sent on the transmission medium towards the destination. The demodulation process takes place at the receiver side where the encrypted carrier wave is converted and transformed in to the original message or signal again. Coding comes under the operation process which makes the communication between the transmitter and receiver more robust. Modulation and coding techniques help protect the desired signal in maintaining its integrity by keeping it away from noise to a large extent.
Our main aim in this research work is to simulate a WIMAX system and study its performance on the basis of two parameters.
- BER (Bit error Rate).
- SNR (Signal to noise ratio)
In a wireless or telecommunication system BER bit error ratio is defined as the number of bits that got corrupted while travelling through the transmission medium, to the total no of bits that were sent within a specific time interval.
In simple terms it can be defined as the ratio of no. bits in error to the total no. of transmitted bits.
SNR (Signal to Noise ratio) is defined as the difference between the noise level and the actual reference level.
Where P is the average power, if the ratio is higher than 1:1 then we can say that less noise is present in the signal.
There have been a lot of advancements in the field of computer technologies in recent years. One such popular technology existing today is WiMAX, Which is one of the most important wireless technologies that exist today. These systems are designed to provide access services related to broadband technology specially designed taking in to consideration residential and enterprise customers in a cost-effective way.
In other words we can say that, WiMax is a standardized wireless version of Ethernet designed with a basic aim of providing an alternative to wire technologies for instance Cable Modems, DSL and T1/E1 links to provide wireless access service in customer's surroundings. To be more specific we can consider wimax as an industrial trade organization developed by popular communication component and equipment companies to aid and certify interoperability and compatibility of wireless broadband access service that agrees with that of the IEEE 802.16 and ETSI HIPERMAN standards.
Working of Wimax is pretty similar to WiFi but based on certain conditions such as higher speeds, greater distances and for greater number of users. Wimax is equipped with the feature of providing service even in areas that are difficult to reach for wired infrastructures. At the same time it also has the ability to overcome the physical limitations associated with traditional wired infrastructure.
Wimax was invented in April 2001, in expectation with respect to the publication of original 10-66 GHz IEEE 802.16 specifications.
What is 802.16a?
Wimax is a simple term that people often use for the 802.16 standards and technologies themselves, but however it firmly applies to systems that can satisfy the particular criteria defined in the Wimax Forum.
The 802.16a standard for internet is nothing but (MAN) metropolitan area network technology whose basic job is to provide broadband wireless connectivity to a variety of Fixed, Portable and Nomadic devices. It can be also used for connecting 802.11 hot spots to the internet, or setup connectivity for a campus. It is a standard basically designed to prove as alternative to DSL cable or wired networks.
THE WIMAX OFDM SIGNAL
The 802.16-2004 standard gives a physical layer which uses 256 sub-carriers and these are modulated using 16-QAM, BPSK or 64-QAM and QPSK constellations. Numerous of boosted sub-carriers are reserved for pilot signals. These Pilots are taken for the estimation of the channel and frequency synchronization because these are known at the receivers. These Null values indeed provide implementation of the previously known frequency bands of guard. The shape of the WiMAX OFDM signal for the frequency domain is as follows
The WiMAX standard
The standard of IEEE 802.16 was initially designed for solving the address communications using direct visibility seen in frequency band of 10 to 66 GHz. As the non-line-of-sight transmissions happen to be tough in high frequency communication, the change of 802.16a was given for working in the less frequency band of and between 2 and 11 GHz. The IEEE specification of 802.16d is a difference of the fixed standard of IEEE 802.16a having the main advantage of regulating the power consumption in the mobile devices.
While in other case, the IEEE 802.16e standard is a change in the 802.16-2004 base specification in order to regulate mobile domain by adding the portability feature.
The WiMAX based various products are developed to work with IEEE 802.16e and IEEE 802.16-2004 specifications. The IEEE 802.16-2004 is basically used static transmissions, deployments of mobile and the IEEE 802.16e is formulated for both the statics.
This considered WiMAX specification has the interface to air required IEEE 802.16-2004 specification for the functions for the considered frequency band 2-11 GHz. This interface for the mobile ha the physical (PHY) layers as well as the mobile medium access control (MAC) properly defined.
Medium Access Control (MAC) layer
Few functionalities are concerned with the provision of the service to subscribers. These have the data transmission in frames as well as the control of the access to the valuable shared wireless medium. The medium access control (MAC) layer is always residing above the physical one, takes together the functions mentioned. Actual MAC is updated to take numerous physical layer data and works, making the needs for different work atmosphere. Basically it is developed for doing the mentioned network topology of point-to-multipoint, having the base station to control various independent sectors together. Access allocation and bandwidth algorithms should accommodate thousands of terminals in every channel, with computers that can be shared by numerous users. Hence, the protocol of MAC tells what and at what time can begin initiates the transmission of data through the channel. The direction of downstream consists only a single transmitter. But, in the upstream direction, in which various SSs struggle to access the medium, the protocol of MAC puts a time division multiple access (TDMA) way, thereby giving an efficient bandwidth use.
The main features of the mentioned fixed WiMAX are detailed next:
- Use of an OFDM modulation scheme, which allows the transmission of multiple signals using different subcarriers simultaneously. In order to localize the selective fading to carrier division, we can utilize the OFDM waveform which consists of multiple narrowband orthogonal carriers which are relatively easy to equalize.
- Wimax also makes easier the work of developing an adaptive modulation and coding mechanism, which relies on behavioral channel and interference conditions. It makes efficient use of bandwidth in the most efficient way by making adjustments in the modulation method on a regular basis in order to achieve optimum data transfer.
- Robust FEC9 techniques, used to detect and correct errors in order to improve throughput. In order to implement an FEC scheme we require a Reed-Solomon encoder merged with a traditional version, followed by an interleave. If required optional support of (BTC) block turbo coding and convolutional turbo coding (CTC) can also be embedded.
- Use of flexible channel bandwidths, comprised from 1.25 to 20 MHz, thus providing the necessary flexibility to operate in many different frequency bands with varying channel requirements around the world. Due to this feature, it has become possible to perform flexible transmissions at longer ranges and with the help of different types of subscriber platforms. Besides this, it is also important for cell planning, specifically taking in to consideration the licensed spectrum.
- To enhance the performance in fading environments by the use of spatial diversity both the entities i.e. transceiver and receiver can take help of optional support in order to increase capacity of the system. To provide with freedom of transmit source independence, at the same time focusing on reducing the fade margin requirement, and combating interference, the transmitter in WiMAX makes use of STC's Space Time Codes. In order to improve the performance of the system in terms of availability, the receiver can make use of (MRC) maximum ratio combining techniques.
- In order to cut short or minimize the interference, WiMAX provides support for the design of dynamic frequency selection (DFS) mechanism.
- Wimax provides support for smart optional antennas which if deployed, can instantly focus on specific directions which might be always pointing at the receiver, and thus also simultaneously, evading interference present in adjacent channels. It also focuses improving the overall spectral density and SNR. There exist two fundamental types of smart antennas, the one that contains several beam antennas which are directional and second also known as adaptive antenna systems (AAS). The first ones can use either a fixed number of beams choosing the most suitable for the transmission or an steering beam to the desired antenna. Whereas second type of antenna operates usually with multi-element antennas that support different beam pattern. These types of smart antennas are proving to be a better alternative for BWA10 deployments.
WiMax Speed and Range:
WiMAX provides an initial speed of up to 40 Mbps for both fixed and portable applications, based on the specific technical configuration chosen, which can correctly support hundreds of businesses with T-1 speed type of connectivity and with DSL speed connectivity for thousands of residencies. WiMAX has support for variety of data including voice, video and Internet data.
The whole and sole responsibility of Wimax is to provide wireless access services to buildings, which can be considered as competition if there are existing wired networks present or serving entirely alone in current rural or thinly populated area which is yet to be served with connectivity. It can also be used to setup WLAN hotspots connections with the public networks such as the Internet. It is also developed to extend its connectivity services to mobile devices. Mobile connectivity services will not be fast as in case of fixed applications, but we can expect speed of upto15 Mbps spanning about 3 km cell coverage area. Using WiMAX it has become possible for users to cutoff free from existing Internet access environments and it has also given users ability to go online at broadband speeds, almost from many different places they wish to go from within a Metro Zone. WiMAX proves to be potential solution that can be used in a variety of spectrum or color bands: for e.g. 2.3GHz, 2.5GHz, 3.5GHz, and 5.8GHz.
Need of Wimax
- WiMAX can fully meet the requirements of many different access services. Possible applications consist of expanding broadband capabilities in order to bring them closer to subscribers, DSL and T1 services, filling gaps in cable, Wi-Fi and cellular backhaul, giving service providers another economic option for encouraging broadband services.
- WiMAX supports very high bandwidth connectivity where we can expect large spectrum deployments using existing infrastructure with minimal costs at the same time allocating the bandwidth required to support high-value, multimedia services.
- WiMAX has helped internet service providers to meet many challenges they have to face as a result of increasing customer demands without disturbing their current investments already spent in the infrastructure. This has become possible due the scalability of wimax to seamlessly interoperate across wide range of networks.
- It is an IP-based wireless technology, which has made it possible to integrate both (3G) wide-area third-generation mobile and wireless and wire line networks, which has enabled it to become seamless anytime, anywhere access solution.
Wimax has proved itself as an efficient a reliable solution in terms of overcoming a lot of barriers such as interoperability, and deployment or setup cost. It will also help in improving the wireless MAN community to a lot of extent. The technology developed in wimax has made it possible to provide excellent non line of sight coverage as compared with traditional line of sight coverage.
Wimax OFDM falls in the category of transmission schemes called as multicarrier modulation, whose basic idea is to divide high-bit-rate data stream under consideration into various parallel data streams with lower bit-rate. At the same time it also modulates every stream on separate carrier's or channels often called subcarriers, or tones.
The main task in any multicarrier modulation schemes is to remove or minimize inter symbol interference (ISI). In order to achieve this it simply increases symbol time to a extent so that the channels will start inducing delays. The spread of these Delays spread prove to be good measure for wireless channels. Delays are sometimes considered as an insignificant fraction of the symbol duration.
Therefore, taking into consideration systems which support high data transmission rates, the symbol duration in such systems is small, being inversely proportional to the data rate, therefore dividing the data stream into several parallel streams results into increase in the symbol duration of each stream in such a way that the delay spread's for only a small fraction of the total symbol duration.
OFDMis an efficient and reliable version of multicarrier modulation, In OFDM subcarriers used for data transmission are selected based on the criteria that all the subcarriers that are chosen will be orthogonal to each other with respect to the symbol duration, which also helps in ignoring the requirement of selecting non overlapping subcarrier channels In order to eliminate inter carrier interference. Guard intervals are defined between OFDM symbols in order to completely get rid of ISI. This is generally achieved by making the guard interval greater than the expected multipath delay spread. However addition of guard interval results in power wastage and also decreases the bandwidth efficiency. OFDM (orthogonal frequency division multiplexing) proves to be an competent solution to prevail the challenges posed by NLOS. The advantage of using WiMAX OFDM is that allows operators to work with larger delay spread of the NLOS environment; OFDM is also successful in eliminating Inter symbol interference. This ability of OFDM to overcome delay, multipath and ISI efficiently increases the data throughput.
The IEEE 802.16 standards were invented in order to provide wireless broadband technology over a long-range connection starting from the service provider. These standards are also known as WiMAX as they are supported by the WiMAX Forum. It was the year January 2006, when WiMAX Forum produced the first products specially designed for IEEE 802.16-2004-compliant certification. These IEEE standard guarantees interoperability and compatibility between wireless access components that rely on broadband communication service.
IEEE 802.16 technology supports speeds that can be compared with wired systems, for e.g. cable and (DSL) digital subscriber line links. Using these links end users can setup connection it to either internal wired Ethernet or wireless LANs. The business community has been already affected in a positive way with the invention of Wireless technology with some inexpensive wireless products available in the marketplace.
This chapter describes the different steps the transmitter performs before transmitting the data. The overall functional blocks that together constitute the transmitter architecture of the WiMAX simulators are shown in figure.
Firstly, the data is randomizes as of the sources and thereafter, coded as well as mapped to the QAM1symbols. The simulators designed in the work for the WirelessMAN OFDM physical layers of WiMAX. PHY layer thus mentioned makes use of orthogonal frequency division multiplexing (OFDM) with the help of 256 subcarriers.
Every OFDM2 symbols is collected of 192 data sub carrier, 1 zero DC sub carrier, 8 pilots sub carrier, and 55 guards carrier. So, a process of assembling the zero DC sub carriers, data, and pilots is required to built the symbol. In addition, preambles containing of training sequences are appended at the starting of every bursts. These training sequences are used for performing an estimation of the channel coefficients at the receiver.
Subsequent to the assembling process, a zero padding is done. The signals are converted to the time area with the help of inverse fast fourier transform (IFFT) algorithm, and finally, a cyclic prefix (CP) with the target of preventing inter symbol interference is added.
As describe in figure bellow, the encoding process have a concatenations of an outer Reed-Solomon (RS) code and an inner convolutional code (CC) same as a FEC schemes. That means that first data passes in block format through the RS encoder, and then, it goes across the convolutional encoder. It is a flexible coding process due to the puncturing of the signal, and allows different coding rates. Finally the end block of the encoder, does the process of interleaving in order to eliminate long error bursts.
A variable rate code schemes that dependent on the channels conditions is intended to offer finest errors protection level to the user. The FEC options are paired with a number of modulation schemes to form burst profiles of unstable robustness and efficiency.
The following Table illustrates about the block sizes and code rates that are generally used for the different modulations.
The users report the current channel condition to the base station (BS) and, based on this report, a specific coding rate is selected for the downlink data transmissions. Thus, users who experience a "bad" channel condition, i.e. low SNR, at a given time, will be provided with better error correction than those users experiencing "good" channel conditions at the same time. This process is known as adaptive modulation and coding.
OFDM is thought of as a type of frequency division multiplexing (FDM) that has a unique property, that every tone is orthogonal with respect to all other tones, but it is not similar exactly to FDM in many ways. In one case, FDM needs, usually, the survival of frequency guard band among the frequency so that they don't interfere with each other. In the other case, OFDM let the spectrums of every tone to overlaps, and as they are orthogonal, they don't obstruct with each other. Also, generally amount of needed spectrum is reduced because of the overlapping of the tone.
Within a solo carrier modulations system the data is send serially on the channels by modulating one sole carrier at a baud rate of R symbol per seconds, being the data symbol period Tsym = 1/R.
The essential plan of the multi carrier modulation is, nonetheless, that the accessible bandwidth, W, is separated into a number Nc of sub band, commonly called subcarriers. As defined in Figure, every one of these subcarrier have a width, which is ?f = W/Nc. Instead of transmitting the data symbol in a serial ways at a baud rate of R, a multicarrier transmitter separation of the data flow into blocks of Nc data symbol and those are transmits in analogous by modulating the Nc subcarriers.
The symbols period for a multi carrier system is then tsym = Nc/R. One of the main advantages of using a multicarrier modulation is that inter-symbol interference can be reduced when the number of subcarriers, Nc, increases. ISI can sometimes appear in multipath fading channel, because of the fact, that the dispersion of time is significant as compared to the symbol period. If a single carrier modulation is used, a complex equalizer for compensating the channel distortion is needed. However, the multicarrier modulation simplifies the equalization into single multiplications in the frequency domain.
In order to guarantee a high spectral efficiency the sub channels wave forms must have overlapping send out spectra. On the other hand, to allow simple partition of these overlapped sub channels at the receiver they require being orthogonal. Orthogonality is a concept that permits the signals to be completely transmits over an ordinary channel and detected lacking interference. However, loss of orthogonality results in blurring between these information signals and degradation in communication.
Caring the signal during a time dispersive channels is responsible ISI. Within an OFDMsystem, a losses of the orthogonality occurred because of ISI, ensuing in ICI2.
For a given system bandwidth the symbol rate for an OFDM signal is much lower than a single carrier transmission scheme. It was due to the OFDM systems bandwidth is breaks up into Nc subcarrier producing in a symbol rate that is Nc times lesser. This little symbols rate makes OFDM naturally opposed to to effects of ISI due to the multipath transmission. The several signals that come out because of the multipath propagation arrives at the recipient at different time, spreading, this ways, the symbols boundaries and causing energy leakage between the OFDM symbols. Furthermore, in an OFDM signal the amplitude and phase of the subcarrier must remain constant over a period of the symbol in order to maintain the orthogonality of the subcarriers. In case there are no constants, the spectral form will not have nulls at the accurate frequency, producing in ICI.
As a result, the benefit gained for the Consequently, the benefit gained for the summation of a cyclic prefix is twofold. First, it keep away from ISI performing as a security band among two successive symbol. Second, it translates the linear convolution by means of the channel impulse reply into a cyclic difficulty of a cyclic prefix is twofold.
The OFDM system model
OFDM signals are usually created digitally because of the difficulty in forming huge bank of phase lock recipient and oscillator within the analog system. Figure 3 contains the diagram of a such an OFDM system.
Within the transmitter, the arriving stream of data is clustered in blocks of Nc data symbols, which are nothing but the OFDM symbols, and can be shown by a xm vector. Next, an IFFT is performed on each data symbol block and a cyclic prefix of length Ng is added. The coming signal is, generally, the addition of a linear difficulty with the distinct channel impulse reaction, h(n), and an additive white Gaussians noise, w(n). It is absolutely assumed that the channel fading is very slow to think it steady during single symbol, and both, receivers and transmitters, are completely synchronized. At the receiver, the cyclic prefix is removed, and then, the data symbol yk,m (frequency index k, OFDM symbol m) is obtained by performing the FFT operation.
Moreover, the data symbol which are transmitted, x k, m, can be expected from the usual data symbol, y k, m, by means of a sole tap equalizer go after by a slicer. This estimated symbol is obtained by dividing each received data symbol by its corresponding channel coefficient.
WiMAX Transceiver simulation
The system level simulation model of the WiMAX transceiver will include the following subcomponents:
- Data generation
- Forward error correction using Reed Solomon (RS) coder/decoder
- Convolution coder and Viterbi decoder
- Channel model.
- OFDM symbol creation
The WiMAX system model for mobile is developed on the basis of Simulink behavioral modeling; the system consists of the modulation and demodulation based on the OFDM simulation, also there will be one behavioral transmitter and a receiver, and a channel model for transmitting data. To carry out proper transmitter modeling additional components are required. Firstly, the OFDM carriers that we will be using must be inverse-Fourier Transformed followed by a pretended cyclic prefix to OFDM Symbol. Also, there is need to predefine the OFDM burst structure by using proper preamble and data sequences. Modeling is required for all these extra elements.
IEEE 802.16 broadband and mobile based wireless access service is likely to become an important component in the next-generation i.e. 3rd generation wireless systems. 802.16 standard for IEEE, includes many different advanced technologies of radio transmission such as (OFDM) orthogonal frequency-division multiplexing, (AMC) adaptive modulation and coding and adaptive forward error correction (FEC), is developed with an aim to distribute broadband wireless services using clearly defined (QoS) quality of service framework. Therefore, this is a trusted technology that will distribute wireless services based on high data transmission rates. Generally it is observed that technical requirements of many communication standards are based on pure mathematics, therefore simulation tools such as MATLAB and Simulink are well suited to the task of creating such executable specification.
SYSTEM PERFORMANCE ANALYSIS
We will analyze the following parameters:
- Final outcome of signal spectrum
- QAM constellation
- Spectrum of signal source
- Transmitted signal
- Received signal.
- System throughput.
It is already declared that WiMAX will soon provide as a strong alternative for other existing broadband technologies challenging in the same sector. It will also become an efficient solution for the deployment of the well-known wireless services in places where it is very hard to install the services involving other technologies, e.g. cable or DSL, and also in scenarios where the cost of deploying and maintaining such technologies is not affordable. WiMAX will also serve as a bridge in connecting rural areas of developing countries also including all the metropolitan areas that are underserved. WiMAX can also perform the role of delivery agent which will deliver backhaul required for enterprise campus, carrier structures and hot-spots involving WIFI. WiMAX is gaining popularity in the above mentioned scenarios because its ability to provide cost effective, and rapidly deployable solution .
In addition, it is forecasted that WiMAX will also become a serious competitor to all 3G (Third Generation) cellular systems as high speed data applications for mobile will be satisfied with the 802.16e specification.
Physical (PHY) layer
The IEEE 802.16-2004 standard has declared 3 different PHYs that can be used in parallel with the MAC layer in order to provide a reliable end-to-end deliver of packets using a stable link. These specifications of PHY consists of the following:
- SC (single carrier) modulated air interface.
- A 256-point FFT OFDM7 multiplexing scheme.
- A 2048-point FFT OFDMA8 scheme.
The SC air interface mentioned above is specially designed for (LOS) line-of-sight transmission; whereas the other two OFDM-based systems are more adaptable to (NLOS) non line-of-sight operations the equalization process for multicarrier signals in such systems is pretty simple. Profiles in fixed WiMAX standard are specified using the 256 point FFT OFDM PHY layer specification. In addition, fixed WiMAX systems cover up to 5 km of service area supporting data transmissions with max data rate of up to 70 Mbps using bandwidth of 20 Mhz, It also provides people with broadband capability which eliminates the need of direct line-of-sight form the base station.
The mobile standard of WiMAX (IEEE 802.16e) specifically designed for mobile application utilizes the fixed 2048-point FFT OFDMA PHY specification. It covers a service area up to 1.6 to 5 km range, this helps in supporting transmission rates upto 5 Mbps using 5 MHz channel In terms of bandwidth, and with a user access speed which is below 100 km/h. The IEEE 802.16e wimax exhibits the same features as that in the case for fixed WiMAX specification that has been previously specified. However, in order to achieve reliable communication other features for e.g. handoffs, power-saving mechanisms are also added. When it comes to mobile computing generally two issues of concern which need to be focused are the handoff that takes place and also the battery life of the device. If one wishes to achieve max battery life, he needs to sacrifice or restrict the power consumption of the mobile station (MS). Whereas taking in to consideration any mobile network, we find that it is extremely essential to support handoff and handovers in order to enable the Mobile station to move from one (BS) base station to another at faster speeds without disturbing the connection link.
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