1. Coexistence Capacity Allocation Methods
March 2008
doc.: IEEE /0xxxr0
March 2008
IEEE P Wireless RANs Date:
Coexistence Capacity Allocation Methods
Authors:
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Gerald Chouinard, CRC
Gerald Chouinard

2. Coexistence Capacity Allocation Methods
March 2008
doc.: IEEE /0xxxr0
March 2008
Coexistence Capacity Allocation Methods
WRAN standard needs to allow for coexistence of overlapping co-channel cells with proper capacity sharing (avoid system failure caused by interference)
Coexistence algorithms have been proposed at the MAC layer but the PHY layer has not been fully developed to operate in such burst collision environment
Two methods are investigated to share the channel capacity among overlapping co-channel cells:
inter-frame capacity allocation: frame-by-frame basis
intra-frame capacity allocation: using different parts of the same frame
Gerald Chouinard, CRC
Gerald Chouinard

3. RF environment resulting from overlapping co-channel WRAN cells
March 2008
doc.: IEEE /0xxxr0
March 2008
RF environment resulting from overlapping co-channel WRAN cells
Adjacent non-interfering cell
52 km
31 km
Gerald Chouinard, CRC
Gerald Chouinard

4. RF environment resulting from overlapping co-channel WRAN cells
March 2008
doc.: IEEE /0xxxr0
March 2008
RF environment resulting from overlapping co-channel WRAN cells
Grey area is where normal demodulation (QPSK, rate: 1/2) is not possible
Overlapping cell with worst case of negative signal differential
31 km
31 km
Gerald Chouinard, CRC
Gerald Chouinard

5. Inter-frame capacity allocation
March 2008
doc.: IEEE /0xxxr0
March 2008
Inter-frame capacity allocation
TDM of transmission frames
Collision during superframe preamble and SCH
Preamble: do orthogonal PN-sequences need to be used?
SCH: needs more robust modulation than QPSK, rate: 1/2
Need to minimize the size of the SCH payload because of the large overhead in the ruggedized version
This SCH payload needs to be the same for all BSs in the same area: CPE will decode the strongest
SCH to carry information on allocation of the 16 frames to the various BSs, and to the inter-frame quiet periods
SCH MAC section will need to be reviewed
Gerald Chouinard, CRC
Gerald Chouinard

6. Inter-frame capacity allocation (Cont’d)
March 2008
doc.: IEEE /0xxxr0
March 2008
Inter-frame capacity allocation (Cont’d)
Frequency synchronization could be acquired from the superframe but not the timing synchronization due to propagation delays
Timing information will be acquired by CPE from the header of the frame allocated to the associated BS
Minimum pace for frame tranmission:
To keep time sync at the CPE: minimum one per superframe
To provide QoS: every two frames but not practical => compromise on QoS when coexistence
If yes, the MAC coexistence algorithms will end up assigning the 16 frames in a superframe to the local BSs according to their capacity loading
Gerald Chouinard, CRC
Gerald Chouinard

7. Inter-frame capacity allocation (Cont’d)
March 2008
doc.: IEEE /0xxxr0
March 2008
Inter-frame capacity allocation (Cont’d)
Special AGC requirements at BS receiver to deal with widely varying frame amplitude
AGC to keep track of wanted upstream subframe amplitude
AGC to block interfering frames
Special AGC requirements at CPE receiver to deal with widely varying frame amplitude
AGC to keep track of superframe header amplitude
AGC to keep track of wanted downstream subframe amplitude
Should the standard allow for two modes of operation?
Normal mode to keep overhead to minimum
Rugged mode in case of co-channel overlapping cells
How and when would the switch take place?
Gerald Chouinard, CRC
Gerald Chouinard

8. Intra-frame capacity allocation
March 2008
doc.: IEEE /0xxxr0
March 2008
Intra-frame capacity allocation
Share the capacity among co-channel overlapping WRAN cells by allocating parts of a frame
This would more easily preserve the QoS requirement
Both superframe and frame headers will need to be decoded under collision environment
More rugged headers will result in much more overhead (the frame header carries much more information: FCH, DS/US-MAPs, DCD, UCD, etc.)
TDM of portions of frames
Can be accommodated in downstream because of vertical mapping
More difficult to accommodate in upstream because of horizontal mapping: use of 7-symbols columns
will require symbol buffers to absorb the propagation time differences among the BSs and CPEs
Gerald Chouinard, CRC
Gerald Chouinard

9. Intra-frame capacity allocation (Cont’d)
March 2008
Intra-frame capacity allocation (Cont’d)
Time buffers
Gerald Chouinard, CRC

10. Intra-frame capacity allocation (Cont’d)
March 2008
doc.: IEEE /0xxxr0
March 2008
Intra-frame capacity allocation (Cont’d)
Downstream/upstream apportionnement will need to be common to all overlapping cells
If TTG is not common, downstream and upstream bursts will collide, the advantage of TDD is no longer available
Special AGC requirements at CPE receiver to deal with widely varying parts of the downstream bursts
AGC to keep track of superframe and frame header amplitude
AGC to keep track of wanted portion of the downstream bursts
AGC to block interfering portions of the downstream bursts
Special AGC requirements at BS receiver to deal with widely varying parts of the upstream bursts
AGC to keep track of wanted portion of the upstream bursts
AGC to block interfering portions of the uptream bursts
Gerald Chouinard, CRC
Gerald Chouinard

11. March 2008
Conclusion
Inter-frame capacity allocation seems to be the only reasonable alternative for accommodating coexistence at the PHY layer
Need to review the SCH MAC section to re-define and minimize the payload requirement
Need to re-define the modulation and coding of the superframe header (preamble and FCH)
Need to determine minimum CPE time re-sync refresh rate for minimum frame allocation to BSs (one per superframe?)
Need to define MAC coexistence algorithms according to what can be done by the PHY
Need to define two modes of operation? (normal and coexistence operation)
Gerald Chouinard, CRC