1. January, 2006
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Medium Access Control (MAC) in Wireless PAN using Directional Antennas]
Date Submitted: [16 January, 2006]
Source: [Chun-Ting Chou, Alireza Seyedi and Richard Chen] Company [Philips]
Address [345 Scarborough Rd, Briarcliff Manor, NY 10510]
Voice:[ ], FAX: [ ],
Re: [N/A]
Abstract: [Investigation of required MAC functionalities, given the introduction of directional antennas in c physical layer]
Purpose: [Discuss required MAC functionalities, given the introduction of directional antennas in c physical layer]
Notice: This document has been prepared to assist the IEEE P 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.
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Chun-Ting Chou, Philips

2. Medium Access Control (MAC) in Wireless PAN using Directional Antennas
January, 2006
Medium Access Control (MAC) in Wireless PAN using Directional Antennas
Opportunities and challenges
Chun-Ting Chou, Philips

3. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
January, 2006
Outline
Background
Benefits of Directional Antennas
Challenges at MAC layer
Issues of existing IEEE MAC
Conclusions
Chun-Ting Chou, Philips
<author>, <company>

4. January, 2006
Background
IEEE c Task Group is generating a high rate mm wave (60GHz) alternate PHY for
High frequency results in high path-loss. Hence, exploiting antenna gain is necessary.
High frequency enables us to design small directional antennas and/or antenna arrays.
What functionalities are necessary and/or beneficial for a WPAN MAC with directional antennas.
Is MAC equipped to handle devices with directional antennas?
Chun-Ting Chou, Philips

5. Benefits of Directional Antennas
January, 2006
Benefits of Directional Antennas
Chun-Ting Chou, Philips

6. Omni. vs. Directional Antennas
January, 2006
Omni. vs. Directional Antennas
Abstract model
Advantages of directional antennas
Higher gains, longer transmission range
Directional transmission/reception: spatial reuse Tx Rx Rx Tx
Chun-Ting Chou, Philips

7. Challenges at MAC Layer
January, 2006
Challenges at MAC Layer
Chun-Ting Chou, Philips

8. Challenge #1: Neighbor Discovery
January, 2006
Challenge #1: Neighbor Discovery
Different Tx/Rx antenna modes could be used at PHY layer
Three types of neighbors
Omni-omni neighbors
Directional-omni neighbors
Directional-directional
neighbors
Chun-Ting Chou, Philips

9. Challenge #1: Neighbors Discovery (conti.)
January, 2006
Challenge #1: Neighbors Discovery (conti.)
Mechanisms for neighbor discovery
Discovery of omni-omni neighbors is trivial
New mechanisms are required for discovery of directional-omni and directional-directional neighbors
Location/direction information makes it a lot easier; otherwise,
Intelligent algorithms are needed
Chun-Ting Chou, Philips

10. Challenge #2: New Hidden-node Problems
January, 2006
Challenge #2: New Hidden-node Problems
The Cause: Deafness
Asymmetry in Tx/Rx antenna gains
Directional Transmission/Reception B A
RTS
CTS Rx B
RTS
B does not know
the transmission between A and Rx Rx
DATA A B
Rx2
Many other
Cases !!
A does not know
the transmission of
B and vice versa
Rx1
Chun-Ting Chou, Philips

11. Challenge #3: Spatial Reuse
January, 2006
Challenge #3: Spatial Reuse
A by-product of directional transmission and reception
Advantages: higher spectrum efficiency and user/system throughput (as high as 800% depending on the node density, antenna gain and types [1]-[3], very useful for compensating higher overheard due to high transmission rate) B A
Rx2
Chun-Ting Chou, Philips

12. Challenge #3: Spatial Reuse (conti.)
January, 2006
Challenge #3: Spatial Reuse (conti.)
A non-trivial problem
Hidden node problems (challenge #2)
Longer interference range
Potential Solutions
Use directional network allocation vector (D-NAV) in distributed networks B
RX2 A
RX1 B
Rx2 A
Rx1
(a) Interference-free
concurrent transmissions
(b) Interfering concurrent transmissions
Chun-Ting Chou, Philips

13. Challenge #3: Spatial Reuse (conti.)
January, 2006
Challenge #3: Spatial Reuse (conti.)
Use space-time scheduling in centralized networks
Antenna gain/power control
without control
with control
Receive interference
from B
Rx2 B A
Rx1
directional-directional neighbors
Concurrent directional transmission
Rx2 B A
Rx1
No interference
Chun-Ting Chou, Philips

14. Issues of existing IEEE 802.15.3 MAC
January, 2006
Issues of existing IEEE MAC
Chun-Ting Chou, Philips

15. Contention access period Channel time allocation period
January, 2006
Existing IEEE 15.3 MAC
Omni-omni neighbor is assumed
Contention- and polling-based channel mechanism are both used
Superframe # m-1
Superframe # m
Superframe # m+1
Beacon
# m
Contention access period
Channel time allocation period …
MCTA 1
MCTA 2
CTA 1
CTA 2
CTA n
Piconet controller/devices
association via broadcasting
beacons (neighbor discovery)
CSMA/CA medium access
control to send control messages)
Scheduled transmission in channel time
allocated by piconet controller
Challenge # 1
Challenge # 2
Challenges # 2 and 3
Chun-Ting Chou, Philips

16. Conclusions Directional antennas bring in new opportunities
January, 2006
Conclusions
Directional antennas bring in new opportunities
Longer transmission range, higher spectrum efficiency
Challenges at MAC layer
Neighbor discovery, new hidden node problems, spatial reuse and power control
The next step?
Chun-Ting Chou, Philips

17. January, 2006
References
[1] R. Ramanathan and etc., “Ad Hoc Networking With Directional Antennas: A Complete System Solution,” IEEE Journal on Selected Areas in Communications, vol. 23, No. 3, Mar
[2] R. Ramanathan, “On the Performance of Ad Hoc Networks with Beamforming Antennas”, ACM MobiHoc, 2001.
[3] R. Choudhury and etc., “Using Directional Antennas for Medium Access Control in Ad Hoc Networks,” ACM MOBICOM, 2002.
[4] L. Bao and etc., “Transmission Scheduling in Ad Hoc Networks with Directional Antennas,” ACM MOBICOM, 2002.
[5] T. Korakis and etc., “A MAC Protocol for Full Exploitation of Directional Antennas in Ad Hoc Wireless Networks,” ACM MobiHoc, 2003
Chun-Ting Chou, Philips