1. Spatial Reuse Strategies in 60 GHz
January 2010
doc.: IEEE xx/xxx1r0
Spatial Reuse Strategies in 60 GHz
Date:
Authors:
Name
Affiliations
Address
Phone
Ananth
Subramanian
Institute for Infocomm Research (I2R), A*STAR
1 Fusionopolis Way, #21-01 Connexis, Singapore
Xiaoming
Peng
David Wong, I2R

2. Outline Introduction - Spatial reuse and device discovery
Summary of our solution
Details of our solution
Information element (IE) proposed
Caches proposed (extensions to NAV of IEEE )
Device discovery strategies
Spatial reuse strategies
Rules / Addendum / Details 2

3. Spatial Reuse and Device Discovery1 2 3 4 C G F E B D
A device discovery strategy must allow a device to discover the orientation of
each of its neighbors with respect to itself.
Spatial reuse strategy must allow two or more pairs of devices within the
Omni-directional transmission range of each other to communicate
simultaneously.

4. Summary of Our Solution
We propose spatial reuse strategy and device discovery schemes that
work with both sector antennas and phased array antennas,
work with DCF based medium access, PCF based medium access and HCF based medium access,
are backward compatible additions to IEEE ,
do not require location information.
We propose spatial reuse and device discovery strategies based on
Topology Information Element (IE)
Topology Matrix (TM)
Directional Network Allocation Vectors (DNAVs)
IEEE MAC
Proposed device discovery
strategies
Proposed spatial reuse

5. Spatial Reuse and Device Discovery
Every node (device, STA) is supposed to
label its logical sectors
consecutively in clockwise
or anti-clock wise direction.
(At a few places, we will
explain the concept
assuming that each STA
has 4 sectors just for the sake
of brevity) A 1 2 3 4 C G F E B D
We propose that every
STA (device) transmit
Topology IEs,
have DNAVs
and a TM.
We propose that STAs perform
frequent device discovery phases to keep themselves updated of their respective
neighborhood orientations (not necessarily locations).
Figure : Network of STAs

6. Topology IE Format of the Topology IE
Octets :1 1 K 6 ..
Element ID
Length
(= 1+ K+6N)
Number of Sectors
Topology Information Bitmap
STA Address 1
STA Address N
Format of the Topology IE
Element ID 15 16 1
STA Addr. 1
STA Addr. 2
An example format of the Topology IE
STA Address fields are the addresses of the neighbors of STA that is transmitting the element.
The Topology Information Bitmap field consists of N (=K) octets of 8-bit elements to indicate the logical sector usage, that is the logical sector used by a neighbor to communicate with the STA, where N is the total number of addresses included.
The least six significant bits of an element ‘n’ indicate the number of the logical sector which can be any of zero (or 1) to sixty three (or 64) used by the neighbor ‘n’ to communicate with the STA.
The most significant bit and the second most significant bit, both of an element ‘n’ may signify how many sectors on both sides of the logical sector
given by the six least significant bits of the corresponding element are used for communication by the neighbor ‘n’ to communicate with the STA.

7. Topology IE
Topology IEs are transmitted by a STA using discovery data blocks (details are in the following).
Optionally, every device (STA; even PC or HC) shall generate a unique 16 bit address (Dev. Addr.).
Topology IE transmitted by a device may have an additional field called the Transmitting Dev. Addr. field which is the unique 16 bit address generated by the transmitting device (device transmitting the Topology IE) for itself.
In this case then, each of the STA Address fields in a Topology IE would be of two octets length instead of 6 octets if the generated addresses are used.
Conflicts between 16 bit Dev. Addrs. are discovered using Topology IEs.
If a device discovers that its Dev. Addr. is in conflict, it shall generate a new Dev. Addr. applicable from the end of transmission of its next discovery data block (see details that follow).
Optionally, a Topology Control frame may be used to achieve the same functionality of Topology IE using rules given herein.

8. Topology Matrix (TM) Figure : Example of TM at device ‘B’1 2 3 4 C G F E B D
STA Address 1 of Link tab
STA Address 2 of Link tab
STA Address 1’s Logical Sector(s) tab
STA Address 2’s Logical Sector(s) tab H L
Sector number A C 1 :
Figure : Example of TM at device ‘B’
TM is maintained by each device pertaining to itself and its neighbors as to which logical sector the device or its neighbour will use to communicate as a source with another device.
Each row corresponds to a particular link (between STAs) in the network.
Each row contains link information in regards to first STA address of the corresponding link, second STA address of the corresponding link, first STA address’s best logical sector(s) for that link and second STA address’s best logical sector(s) for that link.

9. Topology Matrix (TM)
Each of the eight columns in the “STA Address 1’s Logical Sector(s)” tab or “STA Address 2’s Logical Sector(s)” tab in the TM corresponds to a bit.
The least six significant bits of STA Address 1’s Logical Sector(s) tab indicate the number of the logical sector which can be any of zero (or 1) to sixty three (or 64) used by STA Address 1 to communicate with STA Address 2.
The least six significant bits of STA Address 2’s Logical Sector(s) tab indicate the number of the logical sector which can be any of zero (or 1) to sixty three (or 64) used by STA Address 2 to communicate with STA Address 1.
The most significant bit and the second most significant bit, both of either “STA Address 1’s Logical Sector(s)” tab or “STA Address 2’s Logical Sector(s)” tab
together (as two bits) may signify how many sectors on both sides of the logical sector mentioned by the six least significant bits of the corresponding
tab are used for communication by STA address 1 or STA address 2 respectively.
In this case then, a STA may use up to 7 logical sectors to communicate with another STA.

10. Topology Matrix (TM)
Optionally the two most significant bits of either
“STA Address 1’s Logical Sector(s)” tab or “STA Address 2’s Logical Sector(s)” tab
may inform how many sectors on one apriori known side of the logical sector
given by the six least significant bits of the corresponding tab are used.
This format of the TM is also proposed to be updated frequently by the STA based on device discovery results and Topology IEs received.
The TM of a device may contain device addresses of devices that are up to two hops from the device.
Information from other STAs about other links (where the
STA is not a vertex) that is needed to update the format of the TM is
received through the Topology IEs discussed earlier.

11. Directional Network Allocation Vectors (DNAVs)
A STA that transmits or receives frames shall maintain one Directional Network Allocation Vector (DNAV) for each of its logical sectors that contains the remaining time that the logical sector shall not be used for transmission or reception because of a neighbour STA’s transmission or reception.
Rules for using a DNAV are similar to those for NAV but that DNAV applies only to medium accessible by a particular sector.

12. Device Discovery Strategy (Mandatory Step)
Back off slots O D1 D2 D3 D4
Medium Busy
DIFS
Medium idle
Discovery data block
Management/Control/data:
O -- Omni-directional
D1,D2, D3, D4 -- Directional
Frame ‘O’ is
Device Discovery Request
frame in the discovery data
block
Inter Frame Spacing
Back off slot
Every STA transmits a discovery data-block using contention access of the medium. However, the STA that intends to transmit a discovery data-block has to ensure that the medium is available Omni-directionally based on its TM and its DNAVs.
The above illustration is for DCF. But discovery data block can also be transmitted using CFP or HCCA when HC gives opportunity using QoS-CF-Poll frame.
Note that the order of transmission of the directional frames is from sector 1 of that STA going sequentially up to the last sector of that STA.

13. Device Discovery Strategy (Mandatory Step)1 2 3 4 C G F E B D
Assume ‘C’ is involved in transmission of
discovery data block. Device ‘F’ with the
knowledge of the frame end of the
Omni-directional frame from ‘C’ and with the
reception of 3rd directional frame from ‘C’
can know that STA ‘C’ would use ‘C’s sector
‘3’ to communicate with it.
Note that in the above, every STA in the neighborhood of ‘C’ would be able to
determine at the end of ‘C’s transmission of the discovery data block, which of ‘C’s sector would ‘C’ use to communicate with it.
When STA ‘F’ sends a similar discovery data block, STA ‘C’ can infer in a similar manner that STA ‘F’ would use sector 1 to communicate with ‘C’ and update its TM. With the reception of Topology IEs from ‘C’ and ‘F’, all STAs including
‘C’ and ‘F’ can update their TMs.

14. A Few Rules Concerning Device Discovery and Spatial Reuse
A STA is said to have established orientation (device discovery) information
with a neighbor if the STA has obtained information about the STA’s best
logical sector(s) to communicate with the neighbor and the neighbor’s best
logical sector(s) to communicate with the STA.
Toward this, the STA should have transmitted a Topology IE with the
neighbor’s address included in it and should have also received a Topology IE
from the neighbor with it’s address included in the neighbor’s Topology IE.

15. Spatial Reuse Transmission of RTS frames :
Before any RTS packet is sent, the STA shall determine if it had obtained a
TXOP in the logical sector it intends to send the directional data.
If the STA had obtained a TXOP for Omni-directional transmission,
the STA shall send the RTS packet Omni-directionally (if RTS is sent).
Concerning transmission of RTS - only if the STA has the medium unavailable
for Omni-directional transmission, should the STA send a directional RTS
(using all available sectors) should it decide to send a RTS.
The upper bound on the duration field in the RTS packet that is sent
Omni-directionally is aTXOPLimit (a parameter). The upper bound on the duration
field in the RTS packet that is sent directionally is the value of the least of the
STA’s non-zero DNAVs for its logical sectors minus RTS frame transmission
time.

16. Spatial Reuse Transmission of CTS frames :
If the medium is idle and available in all of its logical sectors, the STA shall send
the CTS packet Omni-directionally with duration field derived from
the duration field in the received RTS packet.
If the medium is not idle in all the logical sectors but available in the
logical sector it intends to receive the directional data, the STA
shall send the CTS packet directionally in the logical sector it intends
to receive directional data (and also in the other available sectors).
In the CTS packet sent directionally by the STA, the upper bound on the
duration field in the CTS packet shall be the minimum of -
the least of the STA’s non-zero DNAVs for its logical sectors minus CTS
frame transmission time.
the duration field (for Omni-directional CTS) as derived from the RTS packet
received by the STA.

17. Spatial Reuse
Concerning sending a directional RTS frame or directional CTS frame or directional initiating frame of a TXOP, the device shall send the frame simultaneously in every logical sector whose DNAV has a zero value and whose medium has been available for more than DIFS/AIFS while sending the frame in the logical sector it intends to transmit or receive data.
This can easily be done using sector antennas or through beamforming with phased array antennas.
A device shall not transmit a directional RTS frame (or initial frame at the start of a TXOP) in a logical sector if the DNAV of any of the other logical sectors is zero and the medium in that other
logical sector whose DNAV is zero has been idle for less than DIFS.
If a device has a sector (numbered S) with non zero DNAV, the device shall not send a CTS frame in a sector that is diametrically and geometrically opposite to that sector S (for the purpose of receiving data in the sector geometrically opposite S).
All control frames transmitted directionally should be with power control to offset the directional transmit antenna gain.

18. Spatial Reuse Using EDCA1 2 3 4 C G F E B D
As an example, if STA ‘A’ sends an
Omni-directional RTS to STA ‘C’,
then upon reception of the above
RTS, all the neighbors of ‘A’ shall
infer from the RTS
received that the intended destination
is STA ‘C’.
Each of the neighbors of ‘A’ shall also
after looking at its TM set it’s DNAVs
after inferring that ‘A’ intends to use its
logical sector 1 to communicate with STA ‘C’s logical sector 4.
Device ‘G’ sets its DNAV for sector 1 as sector 4 of STA ‘C’ is
reachable from its sector 1.
Device ‘F’ sets the DNAV for its logical sector 2 using the duration field
from received RTS packet, STA ‘D’ sets the DNAV for its logical sector
3, and STA ‘B’ sets the DNAV for its logical sector 3.

19. Spatial Reuse Using EDCA1 2 3 4 C G F E B D
Upon reception of the RTS
from ‘A’, STA ‘C’ infers from its
TM that it has to use its logical
sector 4 for receiving packets from
‘A’ and assuming its DNAV for sector
4 is zero along with all of its other
DNAVs (with Omni-directional
medium availability), the STA ‘C’ shall
respond with a CTS packet with duration
derived from duration from RTS.
Device ‘C’ shall also send Omni-directional CTS since the DNAVs of all its sectors
were zero with medium availability (just prior to transmission of CTS).
Upon reception of a CTS from STA ‘C’, each of STAs ‘G’, ‘F’, ‘B’, ‘E’ and ‘D’ with the
use of its own TM needs to update its DNAVs.

20. Spatial Reuse Using EDCA
Now if STA ‘B’ wants to send a RTS
packet to ‘D’ when ‘A’ and ‘C’
communicate, it infers that its DNAV
for sector 3 alone is non zero with
medium availability in other sectors.
Hence should it choose to send a
RTS, it should send RTS directionally
to ‘D’ using sector 2 (as well as sectors 1
and 4; beam pattern such as null in sector 3).
Since ‘D’ has a non-zero DNAV for its
sector 3 alone (because of link ‘A’-‘C’), ‘D’
shall send a CTS directionally
to ‘B’ using sectors 1 and 2 and 4 (assuming medium availability) with duration
field set to a value less than or equal to the DNAV of its sector 3 minus CTS
frame transmission time. A 1 2 3 4 C G F E B D

21. Spatial Reuse Using EDCA
A STA shall not send any RTS or CTS frame or any other frame other than
Device Discovery Request frame if it had not sent even one discovery data block
in past aMaxDiscoveryLatency Time Units (TUs).
A STA shall not send a RTS or CTS frame to a neighbor with which it had not
established orientation (device-discovery) information even once in the past
2 x aMaxDiscoveryLatency TUs.
If a STA receives an Omni-directional RTS or CTS not addressed to itself
from a neighbor or to a neighbor with which it had not established orientation
(device-discovery) information in the past 2 x aMaxDiscoveryLatency TUs, the
STA shall update all its DNAVs of its logical sectors using the duration
mentioned in the received RTS or CTS frame.

22. Spatial Reuse Using EDCA
If a STA receives a directional or Omni-directional RTS addressed to itself from a neighbor with which it had not established orientation (device-discovery) information even once in the past
2 x aMaxDiscoveryLatency TUs, it shall not respond with a CTS frame.
A STA is allowed to send RTS or CTS to a neighbor only if the orientation (device-discovery) information had not changed in its TM concerning that neighbor (for all the links the neighbor is involved with as a vertex) for the past 4 x aMaxDiscoveryLatency TUs.

23. Details / Rules / Addendum

24. Medium Availability
For CP purposes, a device shall consider the medium in a logical sector to be
busy for any of the following conditions:
— When its Clear Channel Assessment (CCA) mechanism indicates that the
medium in this logical sector is busy (though the medium may be directionally
available or idle in other logical sectors);
— When the device’s DNAV for this logical sector is greater than zero;
— When the device is transmitting or receiving a frame on the medium using
this logical sector ;
— When the Duration announced in a previously transmitted frame from or
to a logical sector of a neighbor of the device that is reachable by this
logical sector of the device (inferred using TM) has not yet expired;
At all other times a device may consider the medium in a logical sector to be idle
The medium is considered to be idle by the device Omni-directionally if the
medium is idle for each of its logical sectors.

25. Back-off Procedure and CCA
A STA shall maintain a back off counter for every Access Category (AC) for Omni-directional transmission purposes.
In addition to the above, we propose that a STA shall maintain an independent
back off counter for every AC for every logical sector.
The back off counter for an AC for a logical sector shall be decremented only
if the medium in the corresponding logical sector (whose DNAV is zero) is idle
(similar to that given in IEEE ).
A STA shall be able to independently perform Clear Channel Assessment
in each of its logical sectors.
A STA shall also be able to independently invoke a back off for the medium
in any logical sector.

26. TXOP The device shall consider itself to have obtained a
TXOP in a logical sector if it meets the following conditions:
— The device has one or more newly arrived frames or newly generated frames;
— The device had a backoff counter corresponding to that logical sector of zero
value and had no frames prior to the arrival or generation of the new frames; and
— The device determines that the medium in that logical sector has been idle for
DIFS/AIFS or longer;
The device shall also consider itself to have obtained a TXOP in a logical sector
if it meets the following conditions:
— The device has one or more frames buffered for transmission, including retry; and
— The device decremented its backoff counter corresponding to that logical sector
from one to zero and no frame was transmitted by the device in that logical sector
(with medium in that logical sector having remained idle (for DIFS/AIFS or longer))
since then;
Similar rules as above apply concerning Omni-directional TXOP and
TXOPs for ACs.

27. Conclusion We have proposed spatial reuse strategies based on
Topology Information Element (IE)
Topology Matrix (TM)
Directional Network Allocation Vectors (DNAVs)

28. Straw Poll
Do you support inclusion of the technique,     - Spatial Reuse Strategies as described in 10/0250r0 in the TGad draft amendment? Y: N: A:
Slide 28