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The Cyclic prefixed OFDM systems are very robust to multipath, provided that the delay spread of the transmission channel is less than the length of the CP inserted between transmitted symbols. Moreover, appending CP to each OFDM symbol decreases the bandwidth efficiency of the OFDM system, since the CP does not carry useful information.To maintain bandwidth efficiency, a time-domain equalizer (TEQ) and frequency-domain equalizer (FEQ) is used in the OFDM system to mitigate ISI and ICI when the CIR interval is larger than the CP interval. However, the performances of these two equalizers aredegraded under severe channel condition. So a proposed hybrid equalizer structure is suggested in this paper. The hybrid equalizer gives about 10dB, 5dB and 3dB advantages at 10-4 BER compared with OT-FEQ, TEQ and PTEQ respectively. This comparison at fd=50Hz with sufficient length of CP. Also, for this case but with an insufficient length ofCP, the hybrid equalizer gives about 8dB and 7dB advantage compared with both TEQ and PTEQ respectively. Moreover, at fd=100Hz with sufficient CP length, the hybrid equalizer gives about 6dB, 3.5dB and 3dB advantage at 10-4 BER compared with OT-FEQ, TEQ andPTEQ respectively. Also, for this case but with an insufficient length of CP, the hybrid equalizer gives about 6dB and 4dB advantage compared with both TEQ and PTEQ respectively.

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The combination of multiple-input multiple-output (MIMO) system with OFDM techniques is regarded as a promising solution for enhancing the data rates of next-generation wireless communication systems. SDM is implemented to transmitted different signals simultaneously at the same carrier frequency and to detect the transmitted signals using many techniques such as zero frequency, minimum mean square error with and without decision feedback and maximum likelihood decoding.Furthermore, orthogonal frequency division multiplexing technique included in the simulation process using the parameters of the IEEE 802.11a standard. The fading channel is modeled by exponentially – decayed Rayleigh fading channel which is based on the indoor WLAN, Least Square (LS) method is used to estimate the channel for each subcarrier. Keyword: WCDMA, MIMO-OFDM.

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n this paper a new proposed structure for the Orthogonal Frequency Division Multiplexing (OFDM) system will be studied, which will be based on a different approach, an OFDM system was modeled using MATLAB to allow various parameters of the system to be varied and tested. The aim of doing that simulation is to measure the performance of OFDM under different channel conditions.

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Multicarrier Code Division Multiple Access (MC-CDMA) is attractive technique for high speed wireless data transmission; it's a combination of Orthogonal Frequency Division Multiplexing (OFDM) and Code Division Multiple Access (CDMA). OFDM employs a number of orthogonal subcarriers, this increases the symbol duration while the CDMA technique provides high capacity over other conventional multiple access schemes. In this paper discusses implementation of base band MC-CDMA system using the FPGA technique, all modules are designed using VHDL programming language. The electronic functional performance of designed circuits is tested by simulations using VHDL programming language on XILINX ISE 9.2i. The proposed model is designed using (Fast Fourier Transform/ Inverse Fast Fourier Transform) and the spreading code used is the gold code, the implementation of the proposed model using Spartan-3A/3AN, XC3S700N-3FGG484 FPGA of Xilinx family.

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In this paper, we optimization of the Code division multiple access (CDMA) transceiver by using Adaptive Antenna System (AAS) at the receiver it has been shown that receivers based on successive AAS provide an effective reduction of multiuser access interference at an affordable complexity. The aim of this work is to minimize the bit error rate. An AAS has been deployed at the receiver module to reduce the fading effects signal caused by proposed SUI channels model. AAS uses beamforming technique to focus the wireless beam between the base station and the subscriber station. The Least Mean Square (LMS) algorithm is used at the receiver to direct the main beam towards the desired LOS signal and nulls to the multipath signals. It has been proved through this idea by MATLAB simulations that the performance of the system significantly improves by AAS, where beamforming is implemented in the direction of desired user. The performance of the system can more improve by increasing the number of antennas at receiver.

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The Ultra Wide Band (UWB) scheme faces main challenges in attaining wide coverage without affecting the scheme performance. In current generation communication scheme, Frequency Division Multiplexing (OFDM) is used to cater for increased data rate of wireless medium with good performance. Diversity methods play a significant role in attaining higher performance level under imperfect channel condition. This work studies the performance of Wavelet based OFDM in UWB schemes and a comparison is made with traditional fast Fourier transform (FFT) system based OFDM UWB scheme. Wavelet analysis has some robust benefits over Fourier analysis, as it permits a time-frequency domain operation, permitting optimal resolution and flexibility. Wavelets have been acceptably applied in almost all the fields of wireless communication schemes including OFDM which is a robust applicant for next generation of wireless communication scheme. Lately DWT (Discrete Wavelet Transform) is adopted in lieu of FFT (Fast Fourier Transform) for frequency transform. This paper suggests a DWT-OFDM over UWB scheme to attain improved performance in terms of signal to noise (SNR) and bit error rate (BER) for improved SV model based UWB channel. The performance of discrete wavelets are analyzed and compared with FFT based OFDM. The result indicates better BER performance of wavelet system than FFT system

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AbstractSingle-carrier techniques are vulnerable for fading and multipath propagation. Recently, multicarrier modulation (MCM) or OFDM have received considerable attentions andhave made a great deal of progress in world. Also spread spectrum techniques are robust against fading and interference. In this paper a non-coherent FH-OFDM system is proposed to improve the performance of OFDM system in multiuser interference. This system is examined using two differentschemes of hopping pattern, namely, Random FH (RA-FH) &Revolver FH (RE-FH).The comparison indicates that RA-FH is more efficient than RE-FH and conventional OFDM for multiuser interference.When compared with previous works that depend on Cluster hopping (CH) Diversity System (DS), the proposed system possesses BER of less than (0.001)for six interferes with high SNR.Keywords: Orthogonal Frequency Division Multiplexing (OFDM), Frequency Hopping OFDM (FH-OFDM), Random FH (RA-FH) and Revolver FH (RE-FH).

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In this paper, a proposed structure was suggested by replacing the blocks of the fast Haar Wavelet Transform (WT) with a two dimensional wavelet transform at the transmitter and the receiver sides in the Orthogonal Frequency Division Multiplexing (OFDM) model. This can be done by converting a 1-Dimensional vector into a 2-Dimensional matrix and process it by 2-Dimensional Wavelet Transform (2D-WT). The proposed method was applied on the OFDM in Additive White Gaussian Noise (AWGN) and flat fading channel. It was concluded that the proposed method gives much better Bit Error Rate (BER) performance than the conventional OFDM model based on WT. The simulation results showed that the proposd structure outperforms the other scheme in the carried tests at the AWGN and flat fading channels.

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In this paper, a proposed model based on In-Place Wavelet Transform (IP-WT) was suggested to improve the performance of the Orthogonal Frequency Division Multiplexing (OFDM) under the Additive White Gaussian Noise (AWGN), and flat fading channel. The proposed model does not require additional arrays at each sweep such as in the ordered Haar wavelet transform; this ensures fast processing time with minimum memory size. The results extracted by a computer simulation and compared with the performance of the conventional model based on Fast Fourier Transform (FFT). As a result, it can be seen that the proposed technique has high performance improvement over the conventional OFDM system based FFT, where the Bit Error Rate (BER) is widely reduced under these models of channels.

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