1. OFDM Concepts for Future Communication Systems School of Info. Sci. & Eng. Shandong Univ.

2. Outline of Course Ch 1 Introduction Ch 2 Channel Modeling Ch 3 Link-Level Aspects Ch 4 System Level Aspects for Single Cell Scenarios Ch 5 System Level Aspects for Multiple Cell Scenarios Ch 6 OFDM/DMT for Wireline Communications

3. Chapter 1: Introduction 1.1 Radio Channel Behavior 1.2 Basics of the OFDM Transmission Technique 1.3 OFDM Combined with Multiple Access Schemes

4. 1.1 Radio Channel Behavior Multi-path propagation Figure 1.1: Multi-path propagation scenario

5. Time-variant Frequency-selective behavior Figure 1.2: Frequency-selective and time-variant radio channel transfer function

6. The maximum multipath delay The maximum Doppler frequency The coherence time and the coherence bandwidth : Two important system parameters

7. Relationships among a single OFDM symbol duration, The coherence time,the coherence bandwidth, and the distance between two adjacent subcarriers is OFDM feature and superiority

8. OFDM can effciently deal with all these ISI effects, the OFDM transmission technique needs much less computational complexity in the equalization process inside each receiver.

9. 1.2 Basics of the OFDM Transmission Technique The general idea of the OFDM transmission technique is to split the total available bandwidth B into many narrowband sub-channels at equidistant frequencies. The sub-channel spectra overlap each other but the subcarrier signals are still orthogonal. The single high-rate data stream is subdivided into many low- rate data streams for the sub-channels. Each sub-channel is modulated individually and will be transmitted simultaneously in a superimposed and parallel form.

10. Figure 1.3: OFDM spectrum which consists of N equidistant sinc functions

11. Figure 1.4 : OFDM system structure in a block diagram

12. 1.3 OFDM Combined with Multiple Access Schemes Figure 1.5: OFDM transmission technique and some multiple access schemes

13. OFDM-FDMA OFDM-TDMA OFDM-CDMA OFDM-SDMA