1. Cooperative Diversity Scheme Based on MIMO-OFDM in Small Cell Network Dong-Hyun Ha hadong_zzang@naver.com Sejong University

2. Contents Introduction System Model Proposed Scheme Simulation Results Conclusions - 2 -

3. Introduction (1) Transmit diversity scheme Multiple antennas are used in a transmitter A signal is transmitted to the receiver through the multiple channels. In the receiver, the received signal obtains the diversity gain by the multiple channels But, the use of multiple antennas generates the problems of complexity, cost and size Cooperative scheme Providing a diversity gain without the multiple antennas in the transmitter But, having the weakness of rate loss by the time delay between a source and a relay - 3 -

4. Introduction (2) MIMO (multiple-input multiple-output) detection scheme The multiple reception antennas can detect the multiple received signals by multiple independent channels V-BLAST (vertical-Bell laboratories layered space-time) is a typical MIMO detection scheme V-BLAST can provide the multiplexing gain Linear detection scheme ZF, MMSE Repetitive detection scheme OSIC, DFE, QRD-M, ML - 4 -

5. System Model (1) The proposed system model is composed of the BS (base station), relay nodes and mobile user The mobile user can receive the signals having more reliability from the relay when the channel is a bad and mobile user is located in the cell edge - 5 -

6. System Model (2) Assumptions The relay nodes and the mobile user have the two antennas The channel between relay nodes and the mobile user is independent The conventional 2 X 2 MIMO system The 2 X 2 MIMO system has the 4 channels between Tx and Rx - 6 -

7. Proposed Scheme (1) Transmission signal configuration in the relay nodes The proposed scheme applies the cooperative scheme using two relay nodes Therefore, the mobile user receives the signals from the four channels In order to obtain the improved diversity gain, Relay node 2 uses the CDD (cyclic delay diversity) scheme - 7 -

8. Proposed Scheme (2) - 8 -

9. Proposed Scheme (3) - 9 -

10. Simulation results (1) The simulation parameters FFT size: 256 CP (cyclic prefix): 64 Convolutional code is used Modulation order: BPSK - 10 -

11. Simulation results (2) BER performance Scenario (a), (b) and (c) are the conventional schemes with the application of the cooperative scheme Scenario (b) and (c) mean that the channel between BS and mobile user is bad by the influence of the high fading and bad location - 11 -

12. Simulation results (2) - 12 -

13. Conclusion The cooperative scheme using the small cell network is proposed to obtain the improved reliability in the MIMO- OFDM system The new transmission signal configuration applying the CDD scheme provides the high reliability in the MIMO detection process The mobile user obtains the high performance without additional effort Therefore, the proposed scheme is useful in wireless communication system compared with the conventional schemes - 13 -

14. - 14 - Q & A