1. [Proposed Burst Allocation Method Relating to DS/US-MAP]
March 2007
doc.: IEEE xxx
July 2007
[Proposed Burst Allocation Method Relating to DS/US-MAP]
IEEE P Wireless RANs Date:
Authors:
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Chang-Joo Kim, ETRI
Chang-Joo Kim, ETRI

2. July 2007
Abstract
In this presentation, we propose the burst allocation (burst mapping) method for WRAN system, which is related to DS and US MAP design. In order to develop the best burst allocation method, several features should be considered as follows,
Required bit size of DS/US-MAP IE
Time diversity gain
Decoding latency till delivering to MAC
A bundle of 7 OFDMA symbols for US burst
Contention-based burst in US (Ranging/BW Request/UCS notification, CBP)
Chang-Joo Kim, ETRI

3. Required Bit Size of DS/US-MAP IE
July 2007
Required Bit Size of DS/US-MAP IE
The linear allocation only needs to define the length of the burst, on the other hand, the rectangular allocation needs to define the start point and end point of the burst.
Though, in case of linear allocation, a CPE (or a BS) should trace the history of the length for foregoing CPEs, it may not a big burden to each CPE.
In the point of the required bit size, a linear allocation is more fascinating than a rectangular allocation.
Chang-Joo Kim, ETRI

4. July 2007
Time Diversity Gain
If the terminal has a high mobility, such as e, we have to consider the diversity effect in the time direction.
In that case, it is desirable to allocate the burst in the time direction first (i.e., linear-horizontal scheme).
However, in the case of fixed WRAN system, it seems that there is no rationale to follow the allocation method same as e.
For WRAN system, it is possible to allocate the burst in the frequency direction first (i.e., linear-vertical scheme) without any deterioration.
Chang-Joo Kim, ETRI

5. Decoding Latency till Delivering to MAC
July 2007
Decoding Latency till Delivering to MAC
To minimize the decoding latency as much as possible
Allocate the burst using the linear-vertical scheme
Or allocate the burst using the rectangular scheme so that it occupy a reasonable time and frequency area
When the burst is allocated using the linear-horizontal scheme in the time direction first using only length, the decoding latency could be drastically increased, particularly in the downstream in which more OFDM symbols could be allocated.
Chang-Joo Kim, ETRI

6. Worse Case of Decoding Latency
July 2007
Worse Case of Decoding Latency
For Burst 2 of DS sub-frame, though the length of burst is small, the decoding latency is large.
Chang-Joo Kim, ETRI

7. A Bundle of 7 OFDMA Symbols for US Burst
July 2007
A Bundle of 7 OFDMA Symbols for US Burst
In upstream, the number of OFDMA symbols allocated to a CPE needs to be at least 7 to access sufficient pilot carriers for best channel estimation.
Therefore, each row of the subchannels within the burst should include at least 7 OFDMA symbols.
In case that US sub-frame contains 7 to 13 OFDMA symbols, all OFDMA symbols can be included to only one burst.
In case that US sub-frame contains more than 14 OFDMA symbols, the OFDMA symbols can be divided into several burst.
Chang-Joo Kim, ETRI

8. Hybrid Burst Mapping in Upstream
July 2007
Hybrid Burst Mapping in Upstream
To reduce the decoding latency, the burst should be allocated by the bundle of 7 OFDMA symbols.
On the other hand, if a CPE needs to transmit at maximum EIRP, the coverage of CPE will be larger if it uses more OFDMA symbols in time and less subchannels in frequency so that the power per subchannel can be maximized.
So we propose the hybrid burst mapping as follows,
For latency-sensitive burst, the burst will be allocated in terms of at least 7 OFDMA symbols width
For power-sensitive burst, the burst will be allocated in full width of US sub-frame.
In hybrid burst mapping, the type of Diversity subchannel can be identified by using 2 bits in US-MAP IE.
Chang-Joo Kim, ETRI

9. Segmentation for Latency-Sensitive Burst
July 2007
Segmentation for Latency-Sensitive Burst
An US sub-frame can be divided into several segment in terms of at least 7 OFDMA symbols width.
Each burst can be defined within the segment.
If the total OFDMA symbols within US sub-frame excluding CBP packet are not divided into 7, total_OFDMA_symbols % 7 are included to the last segment.
If the total OFDMA symbols within US sub-frame excluding CBP packet are X, then X = 7*Y+Z=7*(Y-1)+(7+Z), here, Z<7. Thus, there are (Y-1) segment with 7 OFDMA symbols width and 1 segment with (7+Z) OFDMA symbols width in the time direction. The segments are sequentially located from left to right in the time direction.
For example, if the total number of OFDMA symbols of US sub-frame excluding CBP packet (X) are 16, there are 1 segment with 7 OFDMA symbols width and 1 segment with 9 OFDMA symbols width in the time direction.
Chang-Joo Kim, ETRI

10. Proposed Modification of US-MAP IE
July 2007
Proposed Modification of US-MAP IE
Chang-Joo Kim, ETRI

11. Contention-Based Burst in US
July 2007
Contention-Based Burst in US
A rectangular burst would be allocated for the function of Ranging, BW Request, and UCS notification
At the end of US sub-frame, the CBP packet would be transmitted for self-coexistence with rectangular shape
Chang-Joo Kim, ETRI

12. Proposed Partition of Subchannel Zone
July 2007
Proposed Partition of Subchannel Zone
AMC and Diversity zones are divided in the frequency domain with the rectangular shape.
After identifying the AMC zone using DS-MAP, the rest excluding the AMC zone is assigned to the Diversity zone.
The AMC subchannel starts from the next OFDMA symbol of the FCH, DS/US-MAP, and DCD/UCD.
The CPE have to know the range of AMC subchannel from the DS-MAP. If AMC subchannel start from the following the preamble symbol, the CPE would not know the information on subcarrier de-allocation of Diversity subchanel, at least for the first frame within superframe.
The rest subchannel(s) in the header field will be allocated to the Diversity subchannel for data transmission.
Chang-Joo Kim, ETRI

13. Proposed Partition of Subchannel Zone (Cont’d)
July 2007
Proposed Partition of Subchannel Zone (Cont’d)
Chang-Joo Kim, ETRI

14. July 2007
Proposed Burst Structure (In case that US sub-frame contains 7 to 13 OFDMA symbols)
Chang-Joo Kim, ETRI

15. July 2007
Proposed Burst Structure (In case that US sub-frame contains more than 14 OFDMA symbols)
Chang-Joo Kim, ETRI

16. July 2007
Proposed Burst Structure (In case that the remains of orange zone is less than 7 OFDMA symbols)
Chang-Joo Kim, ETRI

17. July 2007
Conclusions
We propose to use only length (i.e., linear scheme) for DS and US burst allocation.
Each upstream burst has to contain at least 7 OFDMA symbols at each row of subchannel.
For Diversity subchannel, the DS and US burst are allocated by using linear-vertical scheme and linear-horizontal scheme within burst, respectively.
For AMC subchannel, the DS and US burst are allocated by using linear-vertical scheme within burst.
We propose the hybrid burst mapping to deal efficiently with both latency- and power-sensitive burst.
Chang-Joo Kim, ETRI