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IEEE 802.16 d/e standards aim to attain high rate data for nomadic/mobile users having access to notebooks, handheld PC, PDA and smart phones etc. To evaluate the performance of the system under various propagation environments and system parameters, an easy to use and time-efficient simulator is required. MTRL (Mobile Telecommunications Research Lab) of Inha University in Korea created simulators by using C/C++ based S-Functions using MATLAB Simulink. In the simulator, DL/UL traffic channels, Synchronization & cell searching, DFE (AGC, AFC, and DC-offset compensator), CINR estimator, and UL ranging are implemented. In addition, the DL/UL Fixed-Point (FXP) models are also implemented where less than 0.5 dB of performance degradation is achieved compared to the performance of FLP model.
Figure 1. DL FLP traffic channel.
Fig. 1 shows the DL traffic channel FLP simulator where the simulation parameters can be easily modified. The hybrid encoder block implements the CTC & convolutional encoder, and the subcarrier allocator block implements the five standardized sub-channelizations. Fig. 2 describes the traffic channel performance for various code rates, sub-channelization and modulation schemes.
Figure 3. DC offset compensator.
Fig. 3 shows the structure and the performance of the DC offset compensator using the average of the preamble. If DC offset is not removed, decision error probability increases because signal level is clipped towards one side. Fig. 4 shows the structure and the performance of the automatic frequency controller (AFC) by using phase shift between samples. Frequency offset is brought by the difference of local oscillator between tx & Rx and Doppler effect. Frequency offset destroys orthogonality among neighbour subcarriers in OFDM systems.
KyungHi Chang received the B.S. and M.S. degrees in electronics engineering from Yonsei University, Seoul, Korea, in 1985 and 1987, respectively. He received his Ph.D. degree in electrical engineering from Texas A&M University, College Station, Texas, in 1992. From 1989 to 1990, he was with the Samsung Advanced Institute of Technology (SAIT) as a Research Staff, and involved in the digital signal processing system design. From 1992 to 2003, he was with the Electronics and Telecommunications Research Institute (ETRI) as a Principal Member of Technical Staff. During this period, he leaded the team of WCDMA UE modem design and 4G radio transmission technology (RTT). He is currently with the Graduate School of Information Technology & Telecommunications, Inha University, where he is an Associate Professor since 2003. His current research interests include RTT design for IMT-Advanced & 3GPP LTE systems, WMAN system design, cognitive radio, cross-layer design and cooperative relaying system. Dr. Chang has been served as a Senior Member of IEEE since 1998. Currently he is an Editor in Chief for the Korean Institute of Communication Sciences (KICS) Proceedings. He has also been served as an Editor of ITU-R TG8/1 IMT.MOD, and he is currently an International IT Standardization Expert of Telecommunications Technology Association (TTA).
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