doc.: ieee 802.11-11/1539r0 submission dec. 2011 minho cheong, etrislide 1 beam forming for 11ah...

doc.: IEEE 802.11-11/1539r0

Submission

Dec. 2011

Minho Cheong, ETRISlide 1

Beam forming for 11ah

Date: 2011-12-12

Name Affiliations Address Phone email Minho Cheong ETRI Daejeon, Korea +82-42-860-5635 [email protected]

Heejung Yu ETRI Daejeon, Korea +82-42-860-6204 [email protected]

Sok-kyu Lee ETRI Daejeon, Korea +82-42-860-5919 [email protected]

Authors:

doc.: IEEE 802.11-11/1539r0

Submission

Dec. 2011

Minho Cheong, ETRISlide 2

Abstract

This submission proposes beamforming technique for coverage extension in TGah.

doc.: IEEE 802.11-11/1539r0

Submission Minho Cheong, ETRI

Coverage extension in 802.11ah

• Coverage extension is one of key requirements 802.11ah needs to achieve– Coverage extension is highly needed in most of 802.11ah applications

• Smart Grid, Sensor networks which covers over 1km x 1km area• Extended range Wi-Fi as well

– 802.11ah FR-EM specifies the requirement up to 1km with a data rate over 100kbps at PHY SAP

• But, coverage extension is not an easy one to achieve in 802.11ah– Coverage is mainly limited by uplink range because many STAs are likely to be

power saving single antenna devices– Coverage is additionally limited by transmit power regulations across many coun-

tries• It is needed to exploit all the possible techniques to extend the coverage

– Repetition : already introduced for 802.11ah preamble design– Beamforming, STBC et al.

Dec. 2011

Slide 3

doc.: IEEE 802.11-11/1539r0


Beamforming

• Beamforming technique enables – Enhanced throughput for the same distance

• Specifically, quasi-ML detection performance can be achieved with quite reduced receiver complexity by introducing beamforming

– Coverage extension (it is more important feature in 802.11ah)• By focusing transmitting energy on specific direction, signals can be transmitted much

farther than not-beamformed transmission

• Beamforming in 802.11– In 802.11ac (or 11n)

• Main focus is on enhancing throughput at high SNRs rather than coverage extension– In 802.11ad

• Due to 60GHz band characteristics, coverage extension is highly important in 802.11ad. Analog beamforming is used. But, 802.11ad puts up with CSMA/CA-based problems in-cluding hidden node things, because it may be in some sense beneficial in terms of spatial re-use (which could not be neglected in high resolution beam cases such 60GHz)

• 802.11ad seems to prefer its another MAC architecture (TDMA MAC) when coverage ex-tension is really important to take into consideration

Dec. 2011

Slide 4

doc.: IEEE 802.11-11/1539r0


Beamforming in 11ac (or 11n)

• Sounding protocol will be done before actual beamformed data transmission not only for channel sounding but for preventing hidden node problems– Sounding protocol

• (RTS/CTS exchange),• NDPA (NDP Announcement), NDP (Null Data Packet)• VHT CB (Compressed Beamforming Report Feedback)

Dec. 2011

Slide 5

doc.: IEEE 802.11-11/1539r0


Beamforming in 11ac (or 11n) (2)

• If just try to apply 802.11ac-type beamforming to 802.11ah– Control frames (including RTS/CTS exchange, NDPA, NDP et al.) are

not beamformed (omni-directional). Even though beamformed actual data may be transmitted much farther, it may not meaningful because control frames cannot be heard at the extended distance.

– So, there is critical limitation on coverage extension due to range shortage of control frames.

Dec. 2011

Slide 6

송신단수신단

전방향으로 전송되는제어 프레임의 도달거리

빔포밍을 활용하여 전송되는데이터 프레임의 도달거리

transmitterreceiver

Range by omnidirectional transmission

Range by beamformed transmission

doc.: IEEE 802.11-11/1539r0


Range extension of control frames

• To extend range of control frames up to that of beamformed transmission– Beamform control frames as well

• It is not possible to apply beamforming before any channel sounding– Additional power boosting for control frames (when needed)

• It may put a hard burden on hardware implementation– Additional coding option for control frames (when needed)

• e.g.) STBC may need to be considered firstly for control frames – Additional repetition option for control frames (when needed)

• See next slide

Dec. 2011

Slide 7

doc.: IEEE 802.11-11/1539r0


Additional repetition for ctrl frames

• In addition to already-introduced fixed repetition, it needs to have additional repetition option by which range of control frames can be matched to (or larger) that of beamformed data transmission• Additional repetition may be chosen for control frames among multiple options (e.g.

2/4 or 2/4/8 et al.) if it is determined to be really critical for coverage extension

Dec. 2011

Slide 8

송신단수신단

전방향으로 전송되는제어 프레임의 도달거리(반복 전송 없는 경우)

빔포밍을 활용하여 전송되는데이터 프레임의 도달거리

전방향으로 전송되는제어 프레임의 도달거리(반복 전송으로 도달거리 확장)

Range by omnidirectional control frames (with add. repetition)

Range by omnidirectional control frames (without add. repetition)

Range by beamformed data frames

transmitter receiver

doc.: IEEE 802.11-11/1539r0


Additional repetition for ctrl frames (2)

• If introducing additional repetition for control frames– This repetition option needs to be selected considering the number of

(max.) antennas which may be involved in beamformed transmission (mainly in AP’s side), because range extension by beamformed transmis-sion is apparently depending on it

– In this case, length of STF and LTF in the control frames also needs to be adjusted accordingly to enhance other subsequent performances such as channel estimation, synchronization, packet detection and so on.

– Indication of which repetition option is used can be indicated in the SIG field

Dec. 2011

Slide 9

doc.: IEEE 802.11-11/1539r0


Additional repetition for ctrl frames (3)

Dec. 2011

Slide 10

STF LTF SIG LTF LTF data data data

STF LTF SIG LTF LTF data data data

반복의 회수에 따라 data의 길이 증가(OFDM 심볼 단위로 반복 회수만큼 증가)

반복의 회수에 따라 data의 길이 증가 가능(채널 추정 및 동기를 성능 향상을 위해서 조정 가능하지만 반드시 반복회수만큼 증가하지는 않는다.)

반복의 회수에 따라 SIG 심볼(MCS, 길이 정보 등 포함)의 길이 증가(OFDM 심볼 단위로 반복 회수만큼 증가)반복 횟수 검출이 가능하도록 BP나/QBPSK 등의 변조 방식 구분 가능하도록 한다.SIG 정보에 반복회수를 표현하도록 비트 할당도 가능

반복의 회수에 따라 data의 길이 증가 가능(패킷 검출 성능 향상을 위해서 조정 가능하지만 반드시 반복회수만큼 증가하지는 않는다.)

• For preamble and data in that control frame

Data length extension according to additional repetition

SIG length extension according to additional repetitionRepetition option can be indicated in SIG

STF length extension (not necessarily according to additional repetition)

LTF length extension (not necessarily according to additional repetition)

doc.: ieee 802.11-11/1539r0 submission dec. 2011 minho cheong, etrislide 1 beam forming for 11ah...

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