Abstract—In this paper we investigate the performance of Pilot Aided Space Time Block Codes (STBC) Multi-Carrier Code- Division Multiple-Access (MC-CDMA) using overloaded minimum Total Squared Correlation (TSC) spreading codes in indoor channel environment. Since we employed overloaded spreading codes, a number of MC-CDMA sub-channels in the scheme were not being used for data transmission. These empty sub-channels were utilized as comb-type pilot. For interpolating the channel characteristics of the other sub-channels we applied linear interpolator to maintain low complexity. The validity of the system is confirmed by comparing it with multiple-access STBC systems using the original MC-CDMA method with Walsh- Hadamard spreading codes, employing block-type pilot. All systems use Equal Gain Combining (EGC) or Maximum Ratio Combining (MRC) at the receiver. The simulation result shows that although the spreading codes of interest are not fully orthogonal codes, for a low number of users the system under investigation performed better than Walsh-Hadamard based STBC MC-CDMA using block-type pilot. This will be valuable for Personal Area Network (PAN) where the number of users is typically low. Index Terms—Space time block codes (STBC), Multi-carrier code-division multiple-access (MC-CDMA), minimum total squared correlation (TSC) I. INTRODUCTION PARKED by the uncovering of the limits and capacity of Multiple Input Multiple Output (MIMO) systems [1]-[2], Space Time Coding (STC) emerged as a promising method for wideband wireless communication system. In general, variants of STC can be classified as Space Time Block Codes (STBC) [3]-[5], Space Time Trellis Codes (STTC) [6], Space Time Turbo Trellis Codes [7]-[8], Layered Space Time [9]-[11], and also concatenated versions of Space Time Coding with outer channel codes. Earlier, in a closely related field, hybrid transmission This work was supported in part by The Ministry of Science Technology and Innovation (MOSTI) Malaysia, through the Intensification of Research in Priority Areas (IRPA) Programme, under Grant 04-02-10-0041-EA0039. M. S. Arifianto, L.Barukang, A. Chekima, and M. Y. Hamid are with the School of Engineering and Information Technology, Universiti Malaysia Sabah, Locked Bag No. 2073, 88999 Kota Kinabalu, Sabah, Malaysia (phone: +60-88-320000; fax: +60-88-320348; e-mail: msarif2a@gmail.com, liawas@ums.edu.my, chekima@ums.edu.my, yunus@ums.edu.my) techniques based on code-division multiple-access (CDMA) and Multi-Carrier Modulation (MCM), particularly Orthogonal Frequency Division Multiplexing (OFDM), has gained a lot of attention. The hybrid schemes, commonly known as multi- carrier CDMA, incorporate the benefits of OFDM into CDMA. Multi-carrier CDMA can be divided into two groups, i.e. frequency domain spreading and time domain spreading. The spreading on the frequency domain was first introduced by Yee et al. [12], and named Multi-Carrier CDMA (MC-CDMA). It was also the first published hybrid MCM and CDMA scheme, and since then, the commonly used name for the general idea overlaps with the name for the specific frequency domain spreading case. To differentiate the two, in this paper we use multi-carrier CDMA for the general name of the hybrid schemes, and MC-CDMA for the specific frequency domain spreading case. As for the time domain spreading method, it was introduced in Multi-Carrier DS-CDMA (MC-DS-CDMA) proposed by DaSilva and Sousa [13] and also in Multi-Tone CDMA (MT-CDMA) by Vandendorpe [14]. In another development, Karystinos and Pados provided a tight lower bound of the total squared correlation (TSC) of a binary signature set [15]. They also set up the optimum design of CDMA spreading codes with minimum TSC for almost any number of signatures K and almost any length of signatures L. Based on the concepts of STBC, MC-CDMA, and minimum TSC spreading codes we propose a pilot aided scheme. In this scheme, an STBC system cooperates with MC-CDMA and in the MC-CDMA building block we employ overloaded minimum TSC spreading codes based on Pados-Karystinos design. The term overloaded here means that the system capacity (number of available signatures K) is greater than the processing gain (signatures length L). Naturally, the original MC-CDMA scheme [12] employs orthogonal codes such as Walsh-Hadamard codes, in which L = K equals to the number of sub-channels M. If we maintain the number of sub-channels M to be the same and change the Walsh-Hadamard codes with the overloaded minimum TSC codes, which is shorter, then there will be some sub-channels which are not occupied by data. Those unused sub-channels can be filled with pilot signals. In the overloaded minimum TSC based STBC MC-CDMA, for low Multiple-Access Interference (MAI), i.e. low number of operating user K o , we expected that the advantage of having Pilot Aided STBC MC-CDMA Using Overloaded Minimum TSC Spreading Codes M. S. Arifianto, L. Barukang, A. Chekima, M.Y. Hamid S Proceedings of the 2007 IEEE International Conference on Telecommunications and Malaysia International Conference on Communications, 14-17 May 2007, Penang, Malaysia 1-4244-1094-0/07/$25.00 ©2007 IEEE. 12