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Slot Time Synchronization for Coexistence of 5 MHz, 10 MHz and 20 MHz Systems

Slot Time Synchronization for Coexistence of 5 MHz, 10 MHz and 20 MHz Systems. Date: 2010-05-11. Authors:. Outline. Problem Description Proposed Solutions Conclusions References. Problem Description.

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Slot Time Synchronization for Coexistence of 5 MHz, 10 MHz and 20 MHz Systems

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  1. Slot Time Synchronization for Coexistence of 5 MHz, 10 MHz and 20 MHz Systems Date: 2010-05-11 Authors:

  2. Outline • Problem Description • Proposed Solutions • Conclusions • References

  3. Problem Description • Three channel bandwidths, 5 MHz, 10 MHz and 20 MHz, are considered to use in TVWS for 1, 2 and 4 contiguous available channels. • Networks with different bandwidth may overlap in space and frequency, e.g., a 10 MHz network operates in Ch 20, 21 and a 5 MHz network operates in Ch 20. • According to Table 17-15 in [1], the parameters of aSlotTime and aSIFSTime are different for different channel bandwidth. • The network with longer slot time will get much less medium access opportunity.

  4. Proposed Solutions • All 802.11af devices use longest slot times • aSlotTime = 21 μs, aSIFSTime = 64 μs • Simple implementation • Worse throughput performance • Dynamic slot time adaptation • Explore the slot times used by other networks and modify to a larger one • Require Radio Measurement • Better throughput performance

  5. Dynamic Slot Time Adaption • STAs shall change slot times based on one passive and one active mechanisms: • Passive mechanism – Set slot times according to slot time information contained in Beacon, Probe Response, Association Response, and Reassociation Response from other networks. • Active mechanism – Set slot times according to radio measurement results.

  6. Passive Mechanism – (1) • B10 – Short Slot Time is not required in TVWS. • Use B10 and B12 to indicate slot times: (B10 B12) • (0 0): aSlotTime= 21 μs, aSIFSTime=64 μs • (0 1): aSlotTime= 13 μs, aSIFSTime=32 μs • (1 0): aSlotTime= 9 μs, aSIFSTime=16 μs • (1 1): Reserved

  7. Passive Mechanism – (2) • MIB attributes should also include the slot time information • Current 802.11 • dot11ShortSlotTimeOptionImplemented (1 bit) • dot11ShortSlotTimeOptionEnabled (1 bit) • 802.11af • dot11SlotTimeOptionSelection (2 bit) • 00: aSlotTime= 21 μs, aSIFSTime=64 μs • 01: aSlotTime= 13 μs, aSIFSTime=32 μs • 10: aSlotTime= 9 μs, aSIFSTime=16 μs • 11: Reserved

  8. Passive Mechanism – (3) • STAs shall set the MAC variable aSlotTime and aSIFSTime to the corresponding values indicated in Capability Information field (B10 and B12) upon reception of Beacon, Probe Response, Association Response, and Reassociation Response from other 802.11 networks.

  9. Radio Measurement – (1) • Utilize dot11 radio measurement service to identify if there are other networks of different bandwidth. • Include detection of dot11 networks with different bandwidth in the Basic request. Table 7-30—Measurement Type definitions for measurement reports [1]

  10. Radio Measurement – (2) • The 5 MHz network does not need to perform measurement since it cannot change its slot times. • The 10 MHz network should measure if there is a 5 MHz network and adjust its slot times. • The 20 MHz network should measure if there is a 10 MHz network or a 5 MHz network and adjust its slot times to the one used by a network with smallest bandwidth. • Utilize 2 of the 3 reserved bits in the Map field of the basic measurement report to indicate existence of dot11 networks of different channel bandwidth.

  11. Radio Measurement – (3) Map field format of the basic measurement report

  12. Conclusions • Two parallel mechanisms are proposed to synchronize slot times for dot11 networks which are overlapped in frequency and space. • Slot time information is included in Capability information field and MIB to support dynamic slot time selection. • The measurement of other dot11 networks with different bandwidth is proposed to be included in the basic request of the dot11 radio measurement service. • The reserved bits of the Map field of the basic measurement report are used to indicate the existence of other dot11 networks with different bandwidth. • All overlapping dot11 networks will use the same slot times and fairly access the wireless medium.

  13. References • IEEE Standard, "IEEE Standard for Information Technology-Telecommunications and Information Exchange Between Systems-Local and Metropolitan Area Networks-Specific Requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications," IEEE, New York, NY, June 2007.

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