Advantages And Disadvantages Of 5.1 Ofdm-IDMA Scheme

The market for wireless communications has experienced incredible growth over recent years and wireless LANs have rapidly become a very

4. Please explain frequency division multiple access (FDMA), and time division multiple access (TDMA) multiple access methods. (8 points)

Time Division Multiple Access (TDMA) is a technique that takes advantage of FDMA. The frequency spectrum is first split into

802.11ac is a fifth generation WLAN standard. The transfer speed of this standard is three times higher than the speed of its predecessor and is at the same time much faster than the standard that emerged in 1997. Its security is improved, and both the capacity and the range of this standard are significantly enlarged. Those features play a key role in its quality improvement. Its speed reaches up to 1Gbps, enabling high bandwidth transfer on multiple devices at the same time. The 5GHz channel reduces the number of errors. There is large number of wireless devices that broadcast equivalent omnidirectional signals but when using the 802.11ac standard there is an option to find the location of the broadcasting device in the network. Using this option, the sender can locate and send the packages directly to the device which is connected to the Internet and that is the reason why the signal is stronger, clearer and three times faster. The aim of this research would be to analyze all characteristics mentioned above and their practical implementation in a device that uses 802.11ac standard.

These sub-carriers are orthogonal to each other. It is very much popular scheme used in digital television, audio broadcasting and 4G communications. OFDM has the ability to deal with severe channel fading conditions without complex equalization filters. Due to the longer symbol period and the CP extension, OFDM is more robust against the effect of timing offset and delay spread in multipath fading channels. OFDM also gain higher spectral efficiency due to the overlapping of the subcarrier spectrum which are orthogonal to each other. The major drawback of OFDM is high

The IEEE 802.11 is basically for the denial of service attacks and counter measures in wireless networks. The paper mainly focuses on security of 802.11 wireless networks. In this paper 802.11 standard is discussed with respect to frames types, contention resolution, physical layer convergence protocol (PLCP), Channels and security.

Turbo codes being a capacity approach codes are very popular and these codes are also being used for peak to average power ratio reduction. Three turbo coded OFDM systems for peak to average power ratio reduction were proposed where first using m-sequences for peak to average power ratio reduction and short codes for side information, second uses interleaving and third is combination of first two schemes. A tail-biting turbo coded OFDM system is proposed to generate candidates in a selective mapping scheme, without need of side information protection.

ORTHOGONAL FREQUANCY DIVISION MULTIPLEXING techniques allow the transmission of high data rates over broadband radio channels subject to multipath fading without the need for powerful channel equalization. However it is very sensitive to nonlinear effects due to the high PEAK TO AVERAGE POWER RATIO owned by their transmitted signals. Slimane Ben Slimane (2007) proposed an efficient technique for reducing the PEAK TO AVERAGE POWER RATIO of ORTHOGONAL FREQUANCY DIVISION MULTIPLEXING signals. The proposed technique is data-independent that does not require new processing and optimization for each transmitted ORTHOGONAL FREQUANCY DIVISION MULTIPLEXING block. The reduction in PEAK TO AVERAGE POWER RATIO of the ORTHOGONAL FREQUANCY DIVISION

Meanwhile, to transmit the weighted OFDM signal the required time duration is same as the original OFDM signal 's time duration. Computer simulations will evaluate the effectiveness of the scheme which is proposed now. From the numerical results it is observed that , the weighted OFDM signal has bit error rate (BER) performance that is improved when compared with the C&F method and has PAPR smaller than the clipping and filtering (C&F) method. Here, the proposed method is simpler than the clipping and Filtering method. Keywords: Bit error rate, Convolution, Orthogonal Frequency Division Multiplexing

In the present wireless systems, the demand of proliferation of bandwidth for high data rate and reliable communication requirement is increasing. Multiple-input multiple-output (MIMO) systems are investigated to achieve these requirements. Also, diversity techniques are recommended to increase the reliability of system. Orthogonal space time block codes (OSTBCs) are employed in MIMO systems to achieve the full transmit diversity while allowing a simple maximum likelihood decoding algorithm. This algorithm is based on linear processing of received signals [1-2]. MIMO system uses

The hοme autοmatiοn is cοntrοl οf hοme devices frοm a central cοntrοl pοint, autοmatiοn is tοday’s fact, where mοre things are being cοmpleted every day autοmatically, usually the basic tasks οf turning οn οr οff certain devices and beyοnd, either remοtely οr in clοse prοximity The cοncept οf the RF-based systems is tο use the underlying wireless data netwοrk such as IEEE 802.11 (Wi-Fi). The pοpularity οf wireless netwοrks in hοme has increased in recent years, and the advanced cοmputer technοlοgy has made the persοnal digital device tο cοmmοnly have the capability tο cοmmunicate thrοugh the wireless netwοrk. Hence, it is suitable tο use RF-based lοcatiοn determinatiοn system tο estimate the lοcatiοn οf the persοnal digital device in a hοme envirοnment, with high data rate transmissiοn, suppοrting multimedia applicatiοns may be feasible in WLAN . Οne οf the pοssible applicatiοns are wireless netwοrks fοr hοme autοmatiοn. Imagine a private hοme equipped with mοtiοn, light, temperature and οther sensοrs and actuatοrs fοr οpening the dοοr, dimming the light, cοntrοlling the heating and sο οn . It can be as basic as dimming lights with a remοte cοntrοl οr as cοmplex as setting up a netwοrk οf items in yοur hοme (such as a thermοstat, security system, lighting and appliances) that can be prοgrammed using a main cοntrοller . The basic idea οf hοme autοmatiοn is tο emplοy sensοrs and cοntrοl systems tο mοnitοr a dwelling, and accοrdingly adjust the variοus mechanisms that prοvide

Keywords— Orthogonal frequency division multiplexing (OFDM), Generalized K-fading, binary phase shift keying (BPSK), 16-qardature amplitude modulation (16-QAM), symbol error rate (SER).

Orthogonal Frequency Division Multiplexing is considered as an advanced communication model which has wide range of applications such as 3G, 4G, and Wi-Fi etc. Though orthogonal frequency division multiplexing has lots of advantages over conventional communication models such as FDMA, CDMA still it has some disadvantages in that the major drawback is Peak to Average Power Ratio. In literature several theories are proposed to resolve this issue but none of the algorithm is designed to meet the practical approach. In our work a novel approach is present to resolve the Peak to Average Ratio by introducing the variable slopes parameters K1, K2 and inflexion points A (A>0) and CA (0<C<1) in the probability density function in the Non Linear Companding Transform Technique then based on the inflexion point and variables parameter analysis, the

orthogonal frequency modulation has successfully solved the Inter Symbol Interference problem in frequency selective wireless environment. An interesting application of

Now a day’s communication is an important factor and requirement high data rate for the communication and also require the error free environment. So for these entire requirements we use OFDM. OFDM is used for both wired and wireless communication. OFDM belongs to a broader class of multicarrier modulation (MCM) in which the data information is carried over many lower rate subcarrier [1]. OFDM is a solution of intersymbol interference (ISI). ISI is caused by dispersive channel.