1. <January 2002>
doc.: IEEE <02/139r0>
May, 2008
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [ Anti-blocking Mechanism by PNC]
Date Submitted: [May 15, 2008]
Source: Hyoungjin Kwon, Jinkyeong Kim, Seungeun Hong, Yongsun Kim, Kyeongpyo Kim, Wooyong Lee
Company: [Electronics and Telecommunications Research Institute (ETRI)]
Address: [ETRI, 161 Gajeong-dong, Yuseong-gu, Daejeon, , Republic of Korea]
Voice: [], FAX: [], ,
Re: []
Abstract: [In order to avoid blocking in line-of-sight, anti-blocking mechanism via PNC is introduced.]
Purpose: [To be considered in IEEE c standard]
Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P
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Chuck Brabenac, Intel Labs

2. Contents Human Blocking Previous Approaches
May, 2008
Contents
Human Blocking
Previous Approaches
Anti-blocking Mechanism by PNC
Link Setup
Normal Data Transmission via PNC
Blocking Detection and Avoidance
Recovery of Blocked Link
Amplify and Forward Operation
Conclusion
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3. Human Blocking In general, a device uses single (direct) link.
May, 2008
Human Blocking
In general, a device uses single (direct) link.
If there is a (human) blocking, the direct link is cut off.
Slide 3
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4. May, 2008
Previous approaches
To overcome the human blocking, there is a beam steering mechanism. However, once the steered signal is reflected, its power is degraded more than 20dBs. In addition, there can be no medium to reflect beams.
DEVs exchange data directly or via the PNC. However, in case of passing through PNC, transmission time will be at least doubled compared to the time via direct link, because the data packet received at PNC should be decoded and then forwarded to destination DEV.
Slide 4
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5. May, 2008
Anti-blocking by PNC
In order to meet delay constraint as well as avoid blocking, we introduce new functionality of PNC. It is the capability to relay packets from one DEV to another DEV.
Assumptions of PNC for anti-blocking mechanism
Amplify and forward (AF) on RF level
Have at least two RF chains for receiving signal and at the same time, sending it
Switch the mode of two RF chains, (Rx->Tx and Tx->Rx)
Beam forming capability is preferable.
ETRI

6. Link setup A pair of devices set up 2 relay links with a Relay-PNC.
May, 2008
Link setup
A pair of devices set up 2 relay links with a Relay-PNC.
If there is a Relay-PNC, a pair of devices request association to Relay-PNC.
If the Relay-PNC grants access to its use, then do beam-forming sequentially with a pair of devices in CAP.
Do beam-forming inbetween a pair of devices in CTA, if necessary.
Then, two DEVs and Relay-PNC move to CTA together for data transmission.
Relay-PNC
Relay link
Relay link
Source
Destination
Direct link
[Configuration of a pair of devices and PNC]
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7. Normal Data Transmission via PNC
May, 2008
Normal Data Transmission via PNC
Then, two devices can use a direct link and relay links via PNC for data transmission.
In this “example”, we assume data transmission uses two links alternatively for easy explanation of our proposed scheme.
The source DEV transmits its data and receives acknowledgment in response to the data.
Then, the a pair of devices switch their transmission path and exchange data again.
Relay links
Direct link
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8. Blocking Detection and Avoidance
May, 2008
Blocking Detection and Avoidance
If there is no acknowledgement frame in response to data frame sent from chosen link, a source device considers the link blocked.
Then, the device should use another link to avoid the blocking.
The pair of devices move to detour link and exchange data via the detour link.
Relay links
Direct link
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9. Recovery of the Blocked Link
May, 2008
Recovery of the Blocked Link
Sometimes later (or periodically), the device can check whether the blocked link is available or not because the human blocking may be temporary.
If it is still impossible to exchange data through the direct link, the device use only the relay links for data transmission and repeat checking the availability of the direct link.
Otherwise, the source device can send data via the recovered direct link.
Relay links
Direct link
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10. AF operation of Relay-PNC
May, 2008
AF operation of Relay-PNC
During beacon period and CAP, the relay-PNC is operating as normal PNC. So, both antennas are being operated in the same Rx mode or Tx mode.
In CTA, the relay-PNC does amplify-and-forward.
Thus, a source-sided antenna is being operated in Rx mode and the other one is in Tx mode first.
Anti-blocking mechanism is based on ACK frame. Therefore, after relaying from source to destination, the antenna mode of relay-PNC should be switched in order to relay ACK frame from destination to source.
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11. May, 2008
Conclusion
Advantages of introduced anti-blocking mechanism based on ACK via PNC
When the human blocking occurs, seamless communication can be achieved by detour link via PNC.
Simple blocking avoidance mechanism
Power efficient solution compared to beam steering technology
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12. May, 2008
Backup slide
Slide 12
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13. Alternating Link vs Single Link Transmission
May, 2008
Alternating Link vs Single Link Transmission
Alternating Link Transmission
When there is a blocking, one of the links is still available and some of the data can be received.
Antennas of the Relay-PNC are already set for the current data transmission and the relay-PNC doesn't require any antenna mode switching time.
Good for AV streaming application
Single Link Transmission
When blocking occurs, the relay-PNC needs to switch the mode of either antenna from RX to Tx which requires switching time and there can be packet loss due to this latency.
Good for file transfer application
Slide 13
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