Power saving and interference reduction with TPC under DCF Joonsuk Kim and Christopher J. Hansen

1. Power saving and interference reduction with TPC under DCF Joonsuk Kim and Christopher J. Hansen Broadcom Corporation Kim and Hansen, Broadcom Corporation

2. Outline • Background • Objectives • TPC under DCF • Scenario • Simulations • Analysis • Comments and Summary Kim and Hansen, Broadcom Corporation

3. Background • Spectrum Management of the 5 GHz band for coexistence with other WLAN (or RLAN) and alien services. • The merged proposal for TPC/DFS by Philips/Nokia/Cisco/Broadcom was accepted in TGh. • Current draft allows TPC under PCF/HCF only. Kim and Hansen, Broadcom Corporation

4. Background • IEEE Std 802.11h/D0.1 states “a recommended default transmit power for an STA operating under DCF is a constant transmit power …. ” • IEEE 802.11-01/227 states “Throughput is decreased when large variations of power are used by STAs in BSS.” Kim and Hansen, Broadcom Corporation

5. Objectives • Goal of this presentation • to provide an example of TPC under DCF mode • to present an advantage of TPC under DCF • to suggest “Default Max TxPower for all STAs under DCF” to be an option, or to eliminate the sentence. • To allow to use TPC under DCF if necessary. Kim and Hansen, Broadcom Corporation

6. TPC under DCF in BSS • Allows different power level to each STA • May have less collision • Saves power for equivalent performance • May need efficient power information exchange method • Link margin • MAC frame Kim and Hansen, Broadcom Corporation

7. A Scenario under DCF mode Kim and Hansen, Broadcom Corporation

8. Simulation environment • MaxTxPower in BSS is set to 100mW • The range of TxPower of STA_50 is 0 to 100mW • Poisson arrival for traffic, uniformly distributed packet size [128, 1024] bytes • 6 Mbps transmission Kim and Hansen, Broadcom Corporation

9. Parameters for PHY modeling • STA_50 is located 50 meters from AP, and the other four STAs are located around 200~250 meters from AP. • At 5.2 GHz with bandwidth of 20 MHz • Path loss • Noise figure: 10 dB • Coding gain: 3 dB Kim and Hansen, Broadcom Corporation

10. Analysis of the performance • Path loss • Ld=200 – Ld=50 = 12 dB • TxPower of STA_50 for fair access • 20 dBm – 12 dB = 8 dBm = 6.3 mW • More collision is expected at fair access • Better performance, e.g. in throughput, may be achieved not at fair point but at near point. Kim and Hansen, Broadcom Corporation

11. Throughput with TPC under DCF • Global Throughput and Data rate under which packets are sent by each STA Kim and Hansen, Broadcom Corporation

12. Media Access Delay under DCF • Global media access delay and media access delay for each STA under DCF. Kim and Hansen, Broadcom Corporation

13. Dropped Packets under DCF • Packets are dropped due to failure of media access. Kim and Hansen, Broadcom Corporation

14. TPC under DCF to reduce interference BSS1 BSS2 • Another reason to use TPC under DCF • Without performance penalty, BSS2 can reduce interference to BSS1 by choosing less power on STA2 STA3 STA2 AP STA4 AP STA1 Kim and Hansen, Broadcom Corporation

15. Benefits of TPC under DCF • Battery can be saved without degrading the performance. • TPC can be used to avoid collision. • TPC would allow more efficient interference avoidance under DCF to other system. Kim and Hansen, Broadcom Corporation

16. Summary • The system can achieve similar performance with lower power if TPC under DCF is allowed. • IEEE 802-11h should not prevent implementers from achieving better solution. • IEEE 802-11h may need to provide efficient mechanism for power information, e.g., link margin. • The real system performance under TPC is algorithm-dependant. Kim and Hansen, Broadcom Corporation