1. Random Access Mechanism for WRAN System with Adaptive Antennas
doc.: IEEE /xxxxr0
Dec. 2006
January 2007
Random Access Mechanism for WRAN System with Adaptive Antennas
Authors:
IEEE P Wireless RANs Date:
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Soo-Young Chang, Huawei Technologies
Edward S. Zhang, Huawei Technologies

2. January 2007 Co-Authors: doc.: IEEE 802.22-07/xxxxr0 Dec. 2006
Soo-Young Chang, Huawei Technologies
Edward S. Zhang, Huawei Technologies

3. doc.: IEEE /xxxxr0
Dec. 2006
January 2007
Introduction [1]
AAS-CPE1
AAS-CPE2
Regular coverage
Extended coverage based on AAS
The CPEs may be far away from the BS. Conventional solutions may not be able to detect the signal transmitted by those CPEs.
In Draft v0.1, AAS (Adaptive Antenna System) is used to extend the coverage of WRAN system using beam forming to target CPE.
Soo-Young Chang, Huawei Technologies
Edward S. Zhang, Huawei Technologies

4. doc.: IEEE /xxxxr0
Dec. 2006
January 2007
Introduction [2]
Currently, only polling mechanism is used for the AAS CPE to request uplink bandwidth.
In this proposal, we propose a random access mechanism for uplink bandwidth request of AAS CPEs.
We do not propose to replace the current polling scheme for AAS CPEs in the specification draft. Our proposal can work together with the polling mechanism.
Soo-Young Chang, Huawei Technologies
Edward S. Zhang, Huawei Technologies

5. Polling Mechanism January 2007 Initialization Bandwidth Request
doc.: IEEE /xxxxr0
Dec. 2006
January 2007
Polling Mechanism
Initialization
CPEs synchronize to the preamble of the superframe.
CPEs attempt initial ranging on the pre-defined part of the superframe, namely Alert Window.
BS shapes the beam and transmit downstream parameters to CPEs.
Bandwidth Request
Currently, polling is the only mechanism used for the AAS CPEs to transmit the UL bandwidth request.
CPE uses the dedicated bandwidth specified in US-MAP to request the UL bandwidth.
BS uses the dedicated private US-MAP message to indicate the allocated bandwidth.
Soo-Young Chang, Huawei Technologies
Edward S. Zhang, Huawei Technologies

6. Our Proposed Solution: Random Access Mechanism
January 2007
Our Proposed Solution: Random Access Mechanism
The BS should specify a window for bandwidth contention. This window can even be shared with non-AAS CPEs.
CPE transmits bandwidth request subheader (Table 10) in the contention window.
The BS should try to detect the bandwidth request from each predetermined beam.
If no response received from the BS, CPE shall retransmit the request after a backoff period.
If the request is successfully received and the bandwidth is granted, the BS shall notify the CPE in the dedicated US-MAP.
Soo-Young Chang, Huawei Technologies

7. Message Flow: An Example
January 2007
Message Flow: An Example
Soo-Young Chang, Huawei Technologies

8. Our Proposed Solution: System Structure
January 2007
Our Proposed Solution: System Structure
The BS is equipped with multiple parallel processing units (Say N=4). Each of the processing unit can process correlation for one beam.
Since the number of beams (Say M = 8) may be larger than the number of processing units (due to the hardware complexity and cost), the SA Controller is responsible for selecting appropriate beams for processing.
SA modules stores the pre-designed beamforming vectors. In SA modules, the received signals are multiplied by the beamforming vectors before entering the Baseband Process units. Bandwidth request is detected in the Baseband Process unit.
Beamformer
Soo-Young Chang, Huawei Technologies

9. Simulation Configurations [1]
January 2007
Simulation Configurations [1]
Channel Model
Random Complex Gaussian Part: h
Path Loss Part:
Directional Beamforming Part:
CPE Generation
The distance between CPE and BS is uniform distributed between 33km and 50km.
The angle between CPE and BS is uniform distributed between 0 and 360 degrees.
Soo-Young Chang, Huawei Technologies

10. Simulation Configurations [2]
January 2007
Simulation Configurations [2]
BS mechanism
Polling Scheme
The BS polls the CPEs one by one.
If a CPE has a bandwidth request, the BS will successfully capture the request.
Proposed Scheme
The number of antenna components: N = 4, M = 8
Consider the interference from other CPEs, and the following SINR criterion is used:
where Pi is the received power of the i-th CPE at the BS. If the SINR exceeds the threshold, a bandwidth request is declared success. Otherwise, a loss will be declared.
When the collision happens, the bandwidth requests from CPEs will be retransmitted within the backoff window length equals to WL.
Soo-Young Chang, Huawei Technologies

11. Simulation Configurations [3]
January 2007
Simulation Configurations [3]
Loading model and average access time
Loading model
Defined as the probability of a CPE to generate a new bandwidth request.
More than two bandwidth requests for one CPE is not allowed.
Increasing the probability such that a CPE will have a new bandwidth request more and more frequently
Average access time
Defined as the delay averaged over the number of CPEs and the number of bandwidth requests successfully received by the BS.
Backoff Mechanism
CPE randomly selects one time slot within the backoff window and retransmits the bandwidth request. .
Soo-Young Chang, Huawei Technologies

12. Backoff Window Length = 8, # of CPEs = 40
January 2007
Simulation Results [1]
Backoff Window Length = 8, # of CPEs = 40
Soo-Young Chang, Huawei Technologies

13. Backoff Window Length = 16, # of CPEs = 40
January 2007
Simulation Results [2]
Backoff Window Length = 16, # of CPEs = 40
Soo-Young Chang, Huawei Technologies

14. Backoff Window Length = 32, # of CPEs = 90
January 2007
Simulation Results [3]
Backoff Window Length = 32, # of CPEs = 90
Soo-Young Chang, Huawei Technologies

15. Conclusion Proposed random access mechanism
January 2007
Conclusion
Proposed random access mechanism
When the number of the CPEs is relatively low (e.g. 40), proposed random access mechanism performs better.
When the backoff window is sufficiently long (e.g. 16 or 32), proposed random access mechanism performs better.
Proposed random access mechanism can work together with the existing polling mechanism and it can be a supplementary mechanism for the existing standard
Soo-Young Chang, Huawei Technologies