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US Channelization

US Channelization. Authors:. Date: 2011-11-07. From 2011-11-1329r1/1296-r3 (Rolf de Vegt , Qualcomm) . US Channelization (902 – 928MHz). 902 MHz. 928 MHz. 1 MHz. 2 MHz. 4 MHz. 8 MHz. 16 MHz.

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US Channelization

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  1. US Channelization Authors: Date: 2011-11-07 Raja Banerjea, et. Al.

  2. From 2011-11-1329r1/1296-r3 (Rolf de Vegt, Qualcomm) US Channelization (902 – 928MHz) 902MHz 928MHz 1 MHz 2 MHz 4 MHz 8 MHz 16 MHz Note:Devices operating in the 1 MHz PHY mode are expected to operate in the lower 1 MHz of each 2 MHz wide channel Channels >= 4 MHz are right aligned to prevent interference on the 1 and 2 MHz channels at the lower edge of spectrum. Raja Banerjea, et. Al.

  3. Use Case 1 : Sensors and meters Use Case 2 : Backhaul Sensor and meter data Use Case 3 : Extended range Wi-Fi TGah Use Cases Raja Banerjea, et. Al.

  4. Use Case 3a : Outdoor Extended Range Hot Spot : Requirements (11/0457) Raja Banerjea, et. Al.

  5. November 2011 Cellular Offload Use case • US allows 26 MHz of spectrum from 902 – 928 MHz for unlicensed transmission • Maximum EIRP = 1W • IEEE 802.11ah includes • <= 4 Spatial stream MIMO • Transmit beamforming • DL-MU MIMO • 1/2/4/8/16 MHz channel BW • TGah could provide cellular offload with adequate coexistence to low power sensor devices Raja Banerjea, et. al.

  6. Scenario • AP transmits 1/2/4 MHz BW PPDU • Transmit power for all bandwidth and modulation is the same • STA receives 1 MHz PPDU with one higher MCS than 2 MHz • STA receives 2 MHz PPDU with one higher MCS than 4 MHz • DBPS number are based on 11 ac 20 MHz 1 spatial stream • The throughput calculation considers a single frame exchange with medium access, IFS, Ack overhead • Parameters used Raja Banerjea, et. Al.

  7. Modulation Parameters used • 11ac 20/40/80 down clocked by 10 for 2/4/8 MHz • PHY parameters as defined in TGac • 1 MHz with 24 data tones • 1MHz Rep 2 with 12 effective data tones DBPS Values used Raja Banerjea, et. Al.

  8. Throughput comparison • 2MHz transmission is more efficient than 1 MHz Throughput comparison for 200 Byte (Mbps) Raja Banerjea, et. Al.

  9. Power consumption comparison • Sensors which can receive 2 MHz transmission achieve ~20% improvement in battery life Transmission duration for 200 Byte (us) Raja Banerjea, et. Al.

  10. Support of extended range with 2 MHz BSS • In a 2 MHz BSS an AP could transmit both 1 MHz and 2 MHz Beacon • If all sensors in the BSS can receive a 2 MHz BW beacon then the network overhead of supporting longer range is limited • 3.5 ms ever 100 ms (64 Byte beacon) • If some sensors can receive only the 1MHz repetition coded beacon then they would operate at the most robust MCS of the BSS. • As sensors transmit limited amount of data, the network performance is not adversely affected Raja Banerjea, et. Al.

  11. Overhead Comparison • Fixed overhead include • ACK packets 50% of the packets are ACK packets • Beacon (255 byte) • TIM for large number of STA (255 byte) • 2 MHz BSS 44% more efficient than a 1 MHz BSS Overhead in 100 ms [1] Assumption 10 data packets transmitted every 100ms, so 10 ACKs are required. Raja Banerjea, et. Al.

  12. Offload use case • 1 MHz PPDU transmission may not support offload • PPDU duration beyond maximum PPDU duration of packet for lower MCS • PPDU duration beyond channel coherence time for lower MCS • Long PPDU duration causes sensor devices to stay awake for longer time for medium to be free • Higher bandwidth required for Offload use case Transmission time for 1500 Byte (us) Effective Throughput for 1500 Byte (Mbps) Raja Banerjea, et. Al.

  13. 2MHz Channelization is Preferred • 11ah STAs support both 1MHz and 2MHz PHYs • It is NOT recommended that a 11ah STA (either a sensor STA or a 3G offloading STA) uses 1MHz PHY mode unless it has difficulty to reach the peer STA by 2MHz/MCS0 • 1MHz PHY suffers large overhead and very low throughput due to long preamble (2x rep) and narrow bandwidth • 2MHz PHY is much more efficient from both throughput and power saving aspects • Allowing 1MHz BSS may increase sensor power consumption – since 2MHz is mandatory it doesn’t make sense for BSS to limit communication to 1MHz • Sensor applications have higher priority to access a shared channel and will not suffer from low availability of 2MHz channels • Allowing 1MHz only BSS will eventually fragment the bulk bandwidth available and downgrade most BSSs to 1MHz BSS • Any sophisticated and mandatory coexistence rules to prevent such fragmentation are, in reality, hard to be enforced (11ac is facing the same problem now) Raja Banerjea, et. Al.

  14. Conclusion • 1 MHz channelization has the following issues • Long PPDU duration can’t support offload use case • Longer transmission time at 1 MHz causes lower battery life for sensors • Less efficient than larger bandwidth transmission • Higher overhead • 1MHz channelization should only be a result of regulatory requirements or very limited spectrum (e.g. only two 2MHz channels in Europe) Raja Banerjea, et. Al.

  15. Straw Poll:US Channelization (902 – 928MHz) 902MHz 928MHz 2 MHz 4 MHz 8 MHz 16 MHz Note:2MHz BSS allows 1MHz transmission in the TBD (lower/higher) 1MHz for improved range by 6dB [1] Yes: No: Abstain: Raja Banerjea, et. Al.

  16. Reference • [1] IEEE 802.11/1484r0 “11ah PHY Transmission flow” Raja Banerjea, et. Al.

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