doc.: ieee 802.22-07/0021r0 submission january 2007 baowei ji, samsungslide 1 revisit cbp and...

January 2007

Baowei Ji, Samsung

Slide 1

doc.: IEEE 802.22-07/0021r0

Submission

Revisit CBP and Synchronization of Overlapping WRAN Cells

IEEE P802.22 Wireless RANs Date: 2007-01-10

Name Company Address Phone email Baowei Ji Samsung

Telecommunications America

U.S.A. 1-972-761-7167 [email protected]

Bill Semper Samsung Telecommunications America

U.S.A. 1-972-761-7996 [email protected]

David Mazzarese Samsung Electronics Co. Ltd.

Korea +82 10 3279 5210 [email protected]

K. Sivanesan Samsung Electronics Co. Ltd.

Korea +82 10 3279 5210 [email protected]

Authors:

Notice: This document has been prepared to assist IEEE 802.22. 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 802.22.

Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf 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 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at [email protected].>

January 2007

Baowei Ji, Samsung

Slide 2

doc.: IEEE 802.22-07/0021r0

Submission

Abstract

The method of synchronization of overlapping BSs in the current 802.22 spec. draft does not address the propagation delays between a CBP transmitter and a CBP receiver. The precision of net synchronization is directly limited by this kind of propagation delay. Some solutions are suggested in this contribution.

January 2007

Baowei Ji, Samsung

Slide 3

doc.: IEEE 802.22-07/0021r0

Submission

Outline

• Introduction of CBP and WRAN synchronization.

• The Precision of Network Timing Synchronization.

• Problem: How to deal with propagation delay?

• Potential solutions– Delay calculation from location information.

– Delay measurement via two-way communication.

– A common timing signal such as GPS.

January 2007

Baowei Ji, Samsung

Slide 4

doc.: IEEE 802.22-07/0021r0

Submission

Introduction

• Copy of slides from “22-06-0005-01-0000_ETRI-FT-Philips-Samsung_Proposal.ppt”

January 2007

Baowei Ji, Samsung

Slide 5

doc.: IEEE 802.22-07/0021r0

Submission

Synchronization of Overlapping BSs

• The problem– Frames of co-channel overlapping BSs are asynchronous, which makes

coexistence even harder

• Numerous benefits to synchronization– Incumbent protection

• Quiet period synchronization of overlapping BSs• Improved detection

– Self-Coexistence• Logical channel amongst overlapping BSs• Efficient sharing of resources

frame 0 frame 1 frame m...

frame 0 frame 1 frame m...

BS1:

BS2:

Time

January 2007

Baowei Ji, Samsung

Slide 6

doc.: IEEE 802.22-07/0021r0

Submission

Synchronization of Overlapping BSs (cont.)

• Two steps in synchronization– Establishment

– Confirmation and maintenance

• Establishment– Done through self-coexistence quiet periods and CBP

Transmission Offset

Reception Offset

Frame n at BS1:

...

...

Frame m at BS2:

Time

January 2007

Baowei Ji, Samsung

Slide 7

doc.: IEEE 802.22-07/0021r0

Submission


• Establishment– The synchronization rule guarantees that the system will converge

– Frame slide messages are defined that allow synchronization to be accomplished

– At the time of synchronization, overlapping quiet periods shall also be synchronized (this depends on the quiet period schedule)

frame n-1Preamble SCH frame 0 ...

Time

frame 1 Preamble SCH

Preamble SCHframe mframe m-1frame m-2frame m-3 frame 0

CBP Packet

Slide Count

Slide Amount

frame 0

Partial frame

January 2007

Baowei Ji, Samsung

Slide 8

doc.: IEEE 802.22-07/0021r0

Submission


• Synchronization is confirmed by receiving a CBP packet during the self-coexistence window

MAC Slot Number

Pre

am

ble

FCHDS-MAP

US-MAP

Se

lf-co

exi

ste

nce

UCS Notification

Burst CPE #4

Burst CPE #2

Burst CPE #1

Burst CPE #5

Burst CPE #3

Burst CPE #1

Burst CPE #2

Burst CPE #4

Burst CPE #3

TTG

k k+1 k+3 k+5 k+7 k+9 k+11 k+13 k+15 k+17 k+20 k+23 k+26 k+29

Lo

gic

al M

AC

Ch

an

ne

l Nu

mb

er

s

s+1

s+2

s+L

BW Request

Frame n at BS1:

Frame m at BS2:

Pre

am

ble

FCH

DS-MAP

US-MAP

Se

lf-co

exi

ste

nce

UCS Notification

Burst CPE #4

Burst CPE #2

Burst CPE #1

Burst CPE #5

Burst CPE #3

Burst CPE #1

Burst CPE #2

Burst CPE #4

Burst CPE #3

TTG

Lo

gic

al M

AC

Ch

an

ne

l Nu

mb

er

s

s+1

s+2

s+L

BW Request

CBP packets

Time

January 2007

Baowei Ji, Samsung

Slide 9

doc.: IEEE 802.22-07/0021r0

Submission

Interpretation (one scenario)• Consider to synchronize BS_a and BS_b.

• BS_a directs CPE_a to send CBP packet, with the mark of ‘the transmission offset’ relative to the beginning of the (super)frame in Cell_a.

• CPE_b detects this CBP packet, and marks ‘the reception offset’ relative to the beginning of the (super)frame in Cell_b.

• CPE_b reports this event to BS_b.

• Assumptions:– The time offsets (both TX and RX) are for cell wide.

– Propagation delay between CPE_a and CPE_b is negligible.

• Synchronization: BS_b knows the two offsets, thus aligning the superframe timing in its cell with that of Cell_a.

CPEbBSbCPEa

12

3

BSa

January 2007

Baowei Ji, Samsung

Slide 10

doc.: IEEE 802.22-07/0021r0

Submission

Discussion on the two Assumptions

• A 1: The time offsets (both TX and RX) are for cell wide.– This is done through ranging process.

• A2: Propagation delay between CPE_a and CPE_b is negligible.– Not always. Note that 1Km distance incurs about 3.3µsec

propagation delay.

– Even worse, BS_b could pick up the CBP packet from CPE_a directly. In which case, the propagation delay could easily be tens of microseconds, e.g., 30Km cell radius could incur 100µsec synchronization error.

January 2007

Baowei Ji, Samsung

Slide 11

doc.: IEEE 802.22-07/0021r0

Submission

The Precision of Network Timing Synchronization

• 8.4.10.1.1 Network synchronization*For TDD and FDD realizations, it is recommended (but not required) that

all BSs be time synchronized to a common timing signal. In the event of the loss of the network timing signal, BSs shall continue to operate and shall automatically resynchronize to the network timing signal when it is recovered. The synchronizing reference shall be a 1 pps timing pulse and a 10 MHz frequency reference. These signals are typically provided by a GPS receiver.

For both FDD and TDD realizations, frequency references derived from the timing reference may be used to control the frequency accuracy of Base-Stations provided that they meet the frequency accuracy requirements of 8.4.14. This applies during normal operation and during loss of timing reference.

* IEEE Std 802.16™-2004, Part 16: Air Interface for Fixed Broadband Wireless Access Systems

January 2007

Baowei Ji, Samsung

Slide 12

doc.: IEEE 802.22-07/0021r0

Submission

The Precision of Network Timing Synchronization (cont.)

** Symmetricom. Inc., Timing and Synchronization in WiMAX Networks, http://ngn.symmetricom.com/pdf/application_notes/AN_NGN_WiMAX_092606wb.pdf

January 2007

Baowei Ji, Samsung

Slide 13

doc.: IEEE 802.22-07/0021r0

Submission


• Why precise net timing synch is essential in general TDD systems?– Interference management for edge users, e.g., the UL transmission

of CEPa could destroy the DL receiving of CPEb.

– To support the followings: Soft-handoff (Macro diversity); Mobility management; Inter-cell communications; Locating.

CPEb BSb

CPEa

BSa

January 2007

Baowei Ji, Samsung

Slide 14

doc.: IEEE 802.22-07/0021r0

Submission


• Plus, why precise net timing synch is essential in 802.22?– For reliable spectrum sensing, it is desirable for neighboring cells to be

quiet at the same time, i.e., system-wide quiet period.

– The more precise the neighboring cells synchronize, the less guard time is needed in order to align system-wide quiet period or coexistence slots.

BS1

BS2

Time

BS3

Fast sensing 802.22 TransmissionFine sensing

Channel Detection TimeFast sensing Fine sensing






January 2007

Baowei Ji, Samsung

Slide 15

doc.: IEEE 802.22-07/0021r0

Submission

Problem Illustration I: How to deal with propagation delay?

• Scenario I: BS_b receives a CBP packet or a SCH transmitted by BS_a. – Using existing method, the synch error could easily be 200µsec if cell

radius is 30Km.– As a general principle, BS_b cannot precisely synchronize its

transmission with BS_a without the knowledge of the propagation delay (i.e., 0) between them.

BSa

BSb

time

Tx offset

Rx offset

)( slide frame offset Rx

)(delay n propagatio offset Tx

Without , cannot calculate

January 2007

Baowei Ji, Samsung

Slide 16

doc.: IEEE 802.22-07/0021r0

Submission

Problem Illustration II: How to deal with propagation delay?

• Scenario II: CPE_a transmits a CBP packet under the direction of BS_a. BS_b picks up the packet. – Using existing method, the synch error could easily be

hundreds of microseconds.– As a general principle, BS_b cannot precisely synchronize its

transmission with BS_a without the knowledge of the propagation delay (2).

BSbCPEa

1 2

BSa

January 2007

Baowei Ji, Samsung

Slide 17

doc.: IEEE 802.22-07/0021r0

Submission

Problem Illustration III: How to deal with propagation delay?

• Scenario II: CPE_a transmits a CBP packet under the direction of BS_a. CPE_b picks up the packet and relays the message to its BS_b.

– Using existing method, the synch error could easily be tens of microseconds.

– As a general principle, BS_b cannot precisely synchronize its transmission with BS_a without the knowledge of the propagation delay (3).

CPEbBSbCPEa

12

3

BSa

January 2007

Baowei Ji, Samsung

Slide 18

doc.: IEEE 802.22-07/0021r0

Submission

Problem with Existing Method

• Propagation delays between two BSs, or between two CPES, or between a BS and a CPE, is an uncertainty in current synch method.

• To precisely synchronize overlapping BSs, those propagation delays need to be measured or calculated, and addressed explicitly.

January 2007

Baowei Ji, Samsung

Slide 19

doc.: IEEE 802.22-07/0021r0

Submission

Enhancement I: To address the delay between BSs.

• Since CBP-based synchronization is mandatory in the current draft, for precise net timing, it shall be mandatory in 802.22 spec. to require a BS to know the locations of its neighbors if they want to support cell synchronization over the air.– This information could be acquired through provisioning during

cell installation.

– An alternative would be to include the message of the BS location at each SCH, so that, a neighbor BS can calculate and cancel out the propagation delay between them if it uses SCH to achieve cell synchronization.

January 2007

Baowei Ji, Samsung

Slide 20

doc.: IEEE 802.22-07/0021r0

Submission

Enhancement II: To address the delay when CBP Packet is used.

• Solution One: CBP packet shall carry the transmitter’s (a CPE) location, so that the CBP receiver (a CPE or a BS) can calculate and cancel out the propagation delay between them.– Note that, this requires all those CPEs involved with CBP need to

have a location solution (say, using GPS).

– Also note that the CPEs that are not involved with CBP do not have to know their locations before the establishing of net synchronization.

January 2007

Baowei Ji, Samsung

Slide 21

doc.: IEEE 802.22-07/0021r0

Submission

Enhancement II: To address the delay when CBP Packet is used.

• Solution Two: Distributed Synchronization Using Two-way Communication.– Design philosophy: measure and report the propagation delays.

• The inter-cell delay (e.g., 2 on Slide 12, 3 on Slide 13) between two CPEs, or between a BS and a CPE, could be measured using two-way communication.

• The information should be carried in the CBP message.

January 2007

Baowei Ji, Samsung

Slide 22

doc.: IEEE 802.22-07/0021r0

Submission

Measurement of Inter-cell Delay

• A new transmission procedure is needed for measuring the inter-cell delay whether it is between two CPEs, or between a BS and a CPE.

• Basically, it requires an immediate follow-up transmission in order to measure the propagation delay.

January 2007

Baowei Ji, Samsung

Slide 23

doc.: IEEE 802.22-07/0021r0

Submission

Measurement of Inter-cell Delay (cont.)

• Take CPE_a and CPE_b for example:– BSa selects some CPEs (e.g., CPEa1-3) for transmitting the CBP packet

in a contention manner (e.g., with the contention window of [0 7]).– BSb selects some CPEs (e.g., CPEb1-3) for receiving any CBP packet.

Whoever have received a CBP packet should send a follow-up message again in a similar contention manner.

– Optional: the first CBP transmitter may want to send another follow-up message.

CBP Packet from CPEa,i

Contention time slot

Maximum one-way delay

Self-coexistence Window

Contention among CPEa

Contention among CPEb

CBP Packet from

CPEb,i

CBP Packet from CPEa,i

Maximum one-way delay

e.g., 100µsec

January 2007

Baowei Ji, Samsung

Slide 24

doc.: IEEE 802.22-07/0021r0

Submission

Measurement of Inter-cell Delay (cont.)

• One example.

CBP Packet from CPEa1Contention

among CPEa1-3

Self-coexistence Window

3

Contention among

CPEb1-3

CBP packet from CPEb2

3 CBP packet from CPEa1

January 2007

Baowei Ji, Samsung

Slide 25

doc.: IEEE 802.22-07/0021r0

Submission

Conclusion

• Propagation delays need to be measured and reported in CBP messages for synchronizing overlapping WRAN cells.

• The self-coexistence window needs to be modified so that inter-cell propagation delays can be measured.

• Intra-cell delay can be measured by the ranging process.

January 2007

Baowei Ji, Samsung

Slide 26

doc.: IEEE 802.22-07/0021r0

Submission

Alternative: to use a common timing signal such as GPS

• One issue is raised during some discussion in TG1 conference calls, namely, it is desirable for neighboring cells to synchronize and set up system-wide quiet period, no matter they use the same TV channel or not.

• GPS is a proved solution in achieving accurate (frequency) and precise (timing) cell synchronization in cdma2000.

• Options for the WG– Mandatory to use GPS.

– Mandatory to use CBP-based synch method with enhancements presented in this contribution.

– Optional for either one.

January 2007

Baowei Ji, Samsung

Slide 27

doc.: IEEE 802.22-07/0021r0

Submission

Issue of Processing Delays

• BSs and CPEs could have a certain processing delay in transmitting and receiving CBP and SCH packets. These kinds of delay should be compensated if they are substantial. Generally speaking, they won’t be in practice.

doc.: ieee 802.22-07/0021r0 submission january 2007 baowei ji, samsungslide 1 revisit cbp and...

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