1. IEEE P802.22 Wireless RANs Date: 2008-03-15
July 2007
doc.: IEEE yy/xxxxr0
March 2008
Defects of BCH
IEEE P Wireless RANs Date:
Authors:
Notice: This document has been prepared to assist IEEE 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 grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE
Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair
Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE Working Group. If you have questions, contact the IEEE Patent Committee Administrator at
>
Cheng Shan, Samsung Electronics

2. March 2008
Introduction
The BCH is designed to carry the MAC addresses of BS and CPE in each US burst, so that a transmitting CPE as well as its associated BS could be quickly identified from its US burst.
As of WDv0.4.8,
BCH contains 104bits for each burst; (6.6.3)
BCH is transmitted at the same data rate as the rest of the payload symbols. ( )
Cheng Shan, Samsung Electronics

3. Overhead Cost of BCH An exemplary calculation:
March 2008
Overhead Cost of BCH
An exemplary calculation:
Assuming 10 OFDM in US frame, equivalently, useful sub-carriers are available;
If the average modulation and coding rate is QPSK-rate-3/4
10 bursts in US frame: BCH = 4.2% overall US throughput
60 bursts in US frame: BCH = 25% overall US throughput
If the average modulation and coding rate is 16QAM-rate-3/4
10 bursts in US frame: BCH = 2.1% overall US throughput
60 bursts in US frame: BCH = 12.5% overall US throughput
Cheng Shan, Samsung Electronics

4. Detection Complexity of BCH
March 2008
Detection Complexity of BCH
For any detector to decode BCH, it must
first synchronize to the associated BS,
decode at least the US-MAP for US burst allocation,
try to decode the BCH parts for all US bursts, and
obtain those BCH bits with correct CRC check bits.
Cheng Shan, Samsung Electronics

5. March 2008
US Burst Alignment
Cheng Shan, Samsung Electronics

6. How Robust Should a BCH be?
March 2008
How Robust Should a BCH be?
As of section 6.6.3, the BCH is designed so that when a CPE is causing interference to incumbents or other WRAN systems, it could be pinpointed out by the MAC addresses BCH carries;
In other words, it is required a BCH shall be detectable when its related burst is causing interference to incumbents.
Cheng Shan, Samsung Electronics

7. How Likely Is the BCH to Be Detected?
March 2008
How Likely Is the BCH to Be Detected?
Assuming a CPE is causing interference to a TV receiver which is at the edge of TV service area:
ATSC signal level to be protected: -92dBm
Protection D/U ratio: 23dB
Maximum allowed interference power from WRAN: -115dBm
Noise level at room temperature: -95.2dBm
To detect WRAN signal, the SINR=-24.7dB
i.e., when a WRAN device starts to cause interference to a TV receiver, the detection SINR for WRAN could be as low as -24.7dB
WRAN Detection Thresholds: CDMA code: 3dB; QPSK ½: 6dB; …
It is quite likely that when a CPE is causing interference to incumbent systems, its payload is un-decodable for any interference detector.
Cheng Shan, Samsung Electronics

8. March 2008
References
IEEE P802.22™/ WDv0.4.8, Draft Standard for Wireless Regional Area Networks Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Policies and procedures for operation in the TV Bands
Doc. IEEE /007r47 “Functional Requirements for the WRAN Standard”
Doc. IEEE /0103r3 “WRAN Sensing Receiver Characteristics”
Cheng Shan, Samsung Electronics