Research Papers Mc Cdma

In [14], multiple-input and multiple-output orthogonal frequency-division multiplexing systems were proposed for downlink transmission using orthogonal variable spreading factor codes to obtain spatial diversity for existing single-input and single-output systems.Different types of gain combining schemes were employed in frequency domain to recover the data symbols of desired code channels.Equal gain combining (EGC) works well only in correlated channel conditions.

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Direct sequence code division multiple access (DS-CDMA) is one of the MA techniques for its improved performance in terms of system capacity and coverage compared to time division multiple access and frequency-division multiple access [1].

In CDMA, each user uses a unique code sequence that allows multiple users to share the system bandwidth.

MC CC-CDMA with equalization has recently gained much attention for its ability to offer an excellent performance than traditional systems in frequency-selective fading channels.

In this paper, the authors present an analytical study and investigation of MC CC-CDMA downlink system using different combining schemes.

Section 3 provides finite summation expressions and the resultant performance analysis of CC-CDMA using different combining schemes.

The analytical and simulation results with discussions are presented in Section 4. In this section, the system model for MC CC-CDMA is discussed. The kth user information symbol after baseband modulation denoted as a represent the complementary code and the corresponding element code, respectively.In [8], a superset of perfect complementary codes was proposed to increase the set size of the OCC to its processing gain.In order to achieve interference-free OCC, the flock size of the signature code must be equal to the set size of the codes.Multicarrier complementary-coded code division Multiple Access (MC CC-CDMA) is becoming an attractive multiple access technique for high data rate transmission in future wireless communication systems.MC CC-CDMA systems transmitting over frequency-selective channels suffer from multiple access interference (MAI) owing to non-ideal correlation properties of complementary codes (CC).The codes used for CDMA should have low or zero cross-correlation in order to overcome multiple access interference and multipath interference, which limits the capacity of the current 3G system to half of its processing gain (PG) [2].The major limitation of existing signature sequences [3], such as Gold codes, M-sequence, Kasami sequence, and Walsh-Hadamard sequence, are that they are no longer orthogonal in real-time scenarios such as uplink transmission, multiple access, and multipath interference which reduces the system capacity, initiating the need for perfect orthogonal codes.Even though channel selectivity reduces orthogonality of CC, the multi-sequence spreading and summation at the receiver of MC CC-CDMA system offers additional diversity gain which cannot be achieved in traditional CDMA systems using single carrier.The combining algorithms play a vital role in enhancing the performance of MC CC-CDMA systems.This problem was addressed in [9] where the code generated was able to support more users compared to complete complementary codes.In a complementary-coded (CC) CDMA, each user data is spread with N element codes of a particular complementary code and transmitted using N independent subcarriers [10] to form a multicarrier CC-CDMA system.


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