Space time block coded multi-carrier CDMA with minimum total squared correlation signatures and multiuser detection

• Main Author: Mohammad Sigit Arifianto
• Format: Thesis
• Language: English; English
• Published: 2010
• Subjects: TK5101-6720 Telecommunication Including telegraphy, telephone, radio, radar, television
• Online Access: https://eprints.ums.edu.my/id/eprint/10285/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/10285/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/10285/
• Institution: Universiti Malaysia Sabah

The merging of multimedia based applications with mobile communications in areas such as telemedicine, military, business, and entertainment implies that wireless communication systems have to provide high-speed broadband multiple-access solution to meet the demand. One approach to achieve the required solution is by combining Space Time Coding (STC) and Multi-Carrier Code Division Multiple Access (CDMA). The uncovering of the limits and capacity of Multiple Input Multiple Output (MIMO) system has placed STC, applied on MIMO system, as the answer for high-speed wireless communications. While Multi-Carrier COMA, with its ability to combat frequency selective channel experienced by broadband Signals, has been adopted as the enabling technology behind 3G communication systems and widely considered for the future 4G systems. This work focuses on the combination of a variant of STC, namely Space Time Block Codes (STBC) with the frequency domain spreading variant of Multi-Carrier CDMA, namely MC-CDMA. The thesis proposes the enhancement of STBC MC-COMA through two new designs. Firstly, a Pilot Aided STBC MC-CDMA scheme based on overloaded Minimum Total Squared Correlation (TSC) signature set was introduced for the first time. Since overloaded signatures were utilized as the spreading codes, a number of sub-channels in STBC MC-COMA were not used for data transmission. These sub-channels were exploited for comb-type pilot signaling. To maintain low system complexity, for the pilot sub-channels Least Square Estimation (LS) method was employed, and for interpolating the characteristics of the data sub-channels linear interpolator was applied. The validity of the scheme was confirmed by comparing its performance with that of the Walsh-Hadamard based STBC MC-COMA with block-type pilot. The result showed that although the spreading codes of interest are not fully orthogonal codes, for a low number of users, e.g. less than 7 users in a system with a capacity of 32, the system under investigation performed better than its Walsh-Hadamard based counterpart with the same capacity. This will be valuable for Wireless Personal Area Network (PAN) where the number of users is typically low. Secondly, a multiuser detector (MUD) using Genetic Algorithm (GA) was devised specifically for the STBC MC-CDMA. Basically, optimum detection for CDMA based systems using conventional MUD has a high computational complexity. For K number of users for instance, the computational complexity grows exponentially with K. The problem presents even more impact for the more complicated CDMA derivation such as STBC MC-CDMA that requires more processing time. Although suboptimum detection methods with less complexity are available, they are less powerful than MUD. To achieve the optimality of MUD while avoiding the computational complexity, GA is included in the detector design. Furthermore, the STBC MC-CDMA system was simulated over a frequency selective rayleigh fading channel with the receiver employing the GA assisted MUO. The result showed that the system under investigation performed better than STBC MC-COMA using Equal Gain Combining (EGC). For instance, at the BER value of 0.01, the required level of Eb/Nâ‚€ for 2x2 STBC MC-CDMA using GA assisted MUO was dropped by 3 dB compared to the 2x2 scheme using EGC.