ANALISIS KINERJA SISTEM AKSES JAMAK PADA ORTHOGONAL FREKUENSI DIVISION MULTIPLEXING (OFDM) MENGGUNAKAN TEKNIK CODE DIVISION MULTIPLE ACCESS (CDMA)

Problems in the current telecommunications system is how to send data with a very high speed but limited in the frequency allocation. One of the solution of this problems that is used a OFDM (Orthogonal Frequency Division Multiplexing)system which is a multicarrier communication scheme where the inter-frequency subcarriers orthogonal to each other andoverlapping each other so it can save the frequency allocation. To serve more than one user, OFDM systems have combined witha multiple access techniques like CDMA. A simulation of the OFDM system created using Matlab 7.6 by applying the CDMA system for the multiple access technique in the OFDM system and known as CDMA-OFDM. Combination of these two techniques will increase the speed of data transmission and it can serve many users at one time. This final project aims to determine the influence of the number ofusers in the system, the long PN code, the number of subcarrier and the value of Eb/No CDMA-OFDM system in Additive White Gaussian Noise (AWGN) transmission channel. The performance of the system was known from the value of Bit Error Rate (BER)at receiver. For PN code length variation 32, 64 and 128, the simulation CDMA-OFDM system with 32 users showed that the longer PN code is used, the system will show a better performance. It can be seen from the value of the BER system is decreases. For PN code length 32, the system will show the value of BER 0 in the level of Eb/No 9 dB. For PN code length 64, the system will show the value of BER 0 in the level of Eb/No 7 dB and for PN code length 128, the system will show the value of BER 0 in the level of Eb/No 3 dB. Keywords: CDMA, OFDM, PN code, Subcarrier, multiuser

Performance Optimization of Peak to Average Power Ratio in FBMC Waveforms

High spectral efficiency and low computational complexity are the requirements of 5G wireless communication systems. They must also offer low PAPR (peak to average power ratio), low latency, and high throughput. In 5G it is not possible to realise all of these requirements through a single technique. One of the efforts is to look for a suitable technique for 5G. So, a suitable technique emerges whose name is Filter Bank Multicarrier (FBMC). But it has a high complexity, high Peak to Average Power (PAPR) and high out of band (OOB) leakage which results in inter-carrier interference and inter-channel interference. Also, due to high PAPR, mobile batteries are depleted more rapidly. So, a PAPR reduced method is needed. In this paper, a method of Pruned DFT Precoded FBMC to optimize the PAPR for different number of subcarriers. The performance evaluation in terms of bit error rate (BER) and spectral efficiency of OFDM, FBMC and Pruned DFT Precoded FBMC has been done in this paper.  In DFT Precoded FBMC, a DFT spreading matrix is multiplied with FBMC waveform and transmit only some part especially half of the DFT precoded matrix and rest remain zero by us. Monte Carlo simulation with one tap equalizer is used to validate our results

The Alamouti Scheme with CDMA-OFDM/OQAM

This paper deals with the combination of OFDM/OQAM with the Alamouti scheme. After a brief presentation of the OFDM/OQAM modulation scheme, we introduce the fact that the well-known Alamouti decoding scheme cannot be simply applied to this modulation. Indeed, the Alamouti coding scheme requires a complex orthogonality property; whereas OFDM/OQAM only provides real orthogonality. However, as we have recently shown, under some conditions, a transmission scheme combining CDMA and OFDM/OQAM can satisfy the complex orthogonality condition. Adding a CDMA component can thus be seen as a solution to apply the Alamouti scheme in combination with OFDM/OQAM. However, our analysis shows that the CDMA-OFDM/OQAM combination has to be built taking into account particular features of the transmission channel. Our simulation results illustrate the 2×1 Alamouti coding scheme for which CDMA-OFDM/OQAM and CP-OFDM are compared in two different scenarios: (i) CDMA is performed in the frequency domain, (ii) CDMA is performed in time domain

An enhanced multicarrier modulation system for mobile communications

PhD ThesisThe recent revolution in mobile communications and the increased demand on more efficient transmission systems influence the research to enhance and invent new modulation techniques. Orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM) is one of the multicarrier modulations techniques that overcomes some of the weaknesses of the conventional OFDM in term of bandwidth and power efficiencies. This thesis presents a novel multicarrier modulation scheme with improved performance in mobile communications context. Initially, the theoretical principles behind OFDM and OFDM/OQAM are discussed and the advantages of OFDM/OQAM over OFDM are highlighted. The time-frequency localization of pulse shapes is examined over different types of pulses. The effect of the localization and the pulse choice on OFDM/OQAM performance is demonstrated. The first contribution is introducing a new variant of multicarrier modulation system based on the integration of the Walsh-Hadamard transform with the OFDM/OQAM modulator. The full analytical transmission model of the system is derived over flat fading and frequency selective channels. Next, because of the critical requirement of low implementation complexity in mobile systems, a new fast algorithm transform is developed to reduce the implementation complexity of the system. The introduced fast algorithm has demonstrated a remarkable 60 percent decrease in the hardware requirement compared to the cascaded configuration. Although, the problem of high peak to average power ratio (PAPR) is one of the main drawbacks that associated with most multicarrier modulation techniques, the new system achieved lower values compared to the conventional systems. Subsequently, three new algorithms to reduce PAPR named Walsh overlapped selective mapping (WOSLM) for a high PAPR reduction, simplified selective mapping (SSLM) for a very low implementation complexity and Walsh partial transmit sequence (WPTS), are developed. Finally, in order to assess the reliability of the presented system in this thesis at imperfect environments, the performance of the system is investigated in the presence of high power amplifier, channel estimation errors, and carrier frequency offset (CFO). Two channel estimations algorithms named enhanced pair of pilots (EPOP) and averaged enhanced pair of pilots (AEPOP), and one CFO estimator technique called frequency domain (FD) CFO estimator, are suggested to provide reliable performance.Ministry of Higher Education and Scientific Research (MOHSR) of Ira

CDMA transmission with complex OFDM/OQAM

CDMA transmission with complex OFDM/OQA