1. 1 Interference Aware Medium Access for Dynamic Spectrum Sharing Advisor Advisor ： Wei-Yeh Chen Student Student ：楊 于 世 Reference G. Auer, H. Haas and P. Omiyi, “Interference Aware Medium Access for Dynamic Spectrum Sharing,” in DySPAN Ireland Dublin, pp. 399 - 402, April 2007.

2. 2 Outline Introduction DSA principle Dynamic channel assignment Busy-tone concept Dynamic spectrum assignment using busy bursts Delay-throughput performance Simulation Conclusion

3. 3 Introduction Dynamic spectrum sharing for future mobile communication systems where multiple operators share license exempt( 免除 ) spectrum. We propose dynamic spectrum assignment (DSA) based on busy burst (BB) signaling.

4. 4 DSA principle Its basic principle is that receivers upon data reception transmit a busy signal in an adjacent( 鄰近的 ) time multiplexed minislot. Through exploitation( 利用 ) of channel reciprocity( 相互作用 ), other potential( 潛在的 ) transmitters are prevented( 阻止 ) from interfering by first listening to the busy signal.

5. 5 Dynamic channel assignment The implementation of an efficient medium access in distributed self-organized networks is inevitably( 不可避免的 ) tied( 出租 ) with the ability to deal with the hidden and exposed node problems. The exposed node problem occurs( 發生 ) when a transmitter, refrain( 抑制 ) from access due to strong interference from a nearby transmissions.

6. 6 Example of inter-cellular interference scenario.

7. 7 Protocol All potential( 潛在的 ; 可能的 ) transmitters must sense the minislot prior to transmission. Transmitters that sense a strong busy burst are prohibited( 禁止 ) to use this slot.

8. 8 Busy-tone concept Busy-tone concept: The key principle of the busy-tone concept is that the receiver sends out a busy-signal on a time- multiplexed( 多路傳輸 ) channel when it has successfully received a data packet. A busy-tone is detected as “strong” by an intending transmitter when the condition

9. 9 Dynamic spectrum assignment using busy bursts Orthogonal( 矩形 ) frequency division multiplexing (OFDM) is considered a strong candidate as a wireless data transmission technology in broadband( 多頻的 ) cellular networks. In the considered busy-tone concept, a number of time/frequency resource units (slots) are grouped into fixed-duration frames, and associated with each slot is a minislot.

10. 10 MAC frame structure including in-band minislots for busy signaling.

11. 11 Delay-throughput performance(1) The performance of BB-DSA is analyzed by evaluation( 估計 ) of the throughput-delay performance of a certain user. For BB-DSA, only the first packet of a burst is transmitted in contention (i.e., without busy burst protection),which may cause outage( 中斷 ) due to high interference in contention mode.

12. 12 Delay-throughput performance(2) When this occurs, repeated transmission attempts( 企圖 ) of the packet are made in contention mode until the packet is successfully received. Once a packet burst has been granted access to the channel, it is protected by the receiver busy burst, effectively reserving the slot for subsequent( 後來的 ) packets, and so every packet in the burst can be received without error.

13. 13 Simulation System Model: An OFDM system with 256 subcarriers and 10 OFDM symbols per frame is used for a numerical ( 數值的 ) example. Results: The BB-DSA is compared with a fixed spectrum assignment (FSA) algorithm, without any interference protection mechanism.

14. 14 Delay-throughput results for cell size Rcell = 1 km.

15. 15 Conclusion (1) 了解 DSA principle (2) 了解 Busy-tone concept (3) 了解 minislot 的運用