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Performance Analysis Of Adaptive Modulation For High Mobility Lte System

2014 words - 9 pages

The demand of high data rate and affirmation to the real-time communications (network). LTE is well placed to fulfill the demands of next generation mobile networks. It delivers beneficial features such as high mobility transmission and scalability of bandwidth using both TDD and FDD duplexing methods, for the time varying and frequency selective wireless channel within one OFDM sub-carrier. For the exact estimation of wireless channel, some of OFDM subcarrier used as a reference signal while other subcarrier are either used to transmit data symbols are set as unused. The weighted time-domain interpolation computed from the channel based on the Doppler spread information and Parallel ...view middle of the document...

The technology used for Downlink is OFDMA to attain the peak data rate of 100Mbit/s and Uplink is based on Single Carrier FDMA (SC-FDMA) to attain a peak data rate of 50Mbit/s. LTE provide connected automobiles, which produce a broad reach of broadband services and also facilitate better speed on current as well as new mobile applications

The main methodology in LTE to achieve high data rate, high QOS and bandwidth efficiency is using MIMO [2]. The OFDM is a multicarrier transmission scheme which provides several advantages like eliminating the ISI using CP, efficient use of spectrum by overlapping the subcarriers using the orthogonality principle and provides robustness against Co channel interference. The existing channel estimation methods [2-6], assume an invariant wireless channel within one OFDM symbol which leads to ICI (Inter Carrier Interference) problem in high mobility LTE system by losing the orthogonality between the subcarriers due to the Doppler spread. To suppress the ICI, between OFDM subcarriers, iterative Doppler assisted channel estimation with the PIC-DSC interference cancellation scheme is used [3-6]. The wireless channel is evaluated by the Doppler spread information, pilot symbols, and estimates of the data symbols at the recipient. Each channel coefficient is estimated by using time domain marker, which is expressed as a weighted interpolation between two selected time-domain markers which has maximum correlation. The detected data symbols together with the pilot symbols are used to improve the channel estimation in the next iterations. This existing method of estimation produces low SNR, leading to increased BER and decreased throughput.

In frequency domain estimation of wireless channel the color noise has been determined when there is a variation in the power spectral density. This spectral content variation affects some of the subcarriers of OFDM channel. By regular transmission of training sequences or pilot data the SNR can be estimated and using intermediate signals in channel estimation the color noise variance is calculated. 2-D minimum mean square error (MMSE) is used for noise variance at each subcarrier is estimated. By using statistics, the coefficient of noise can be calculated [7]. These estimates are very useful on adaptive modulation. To measure the average spectral efficiency in imperfect channel estimation, the system performance in the presence of color noise was provided in [8]. Adaptive modulation and coding (AMC) used for the efficient resource allocation technique by changing the system among various modulation coding schemes. By setting the modulation order depending on the quality of fading channel adaptive modulation scheme aims to improve link spectral efficiency, i.e. when the channel quality is good more bits are sent and based on the measured channel conditions additional subcarriers are allocated the different modulation scheme. The spectral efficiency is maximized even though the...

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