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Spatial Reuse and Interference Mitigation in 60 GHz. Authors:. Date: 2009-07-14. Introduction and Goals. As described in [2], channel access in 60GHz will use directional communication

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spatial reuse and interference mitigation in 60 ghz
Spatial Reuse and Interference Mitigation in 60 GHz

Authors:

Date: 2009-07-14

Carlos Cordeiro, Intel

introduction and goals
Introduction and Goals
  • As described in [2], channel access in 60GHz will use directional communication
  • As a result, there is a big potential to exploit spatial reuse in 60GHz and increase the spectrum efficiency
    • This becomes even more important in those regulatory domains with a single 60GHz channel (e.g., Australia)
  • On the flip side spatial reuse may also increase interference, since a higher number of links will operate simultaneously and may interference with each other
  • Therefore, in this presentation we:
    • Introduce spatial reuse and the potential it holds in 60GHz
    • Propose that TGad provides means for spatial reuse and interference mitigation in 60GHz

Carlos Cordeiro, Intel

what is spatial reuse
What is spatial reuse?
  • Spatial (Frequency) Reuse = Two or more links sharing the same frequency channel in the same spatial vicinity at the same time

Example in the office

Example in the home

STA 1

STA 2

PCP

STA 4

STA 3

Spatial reuse

within one BSS/PBSS [1]

Spatial reuse across neighboring BSS/PBSS [1]

Carlos Cordeiro, Intel

example usage models 3 4 which can take advantage of spatial reuse
Example usage models [3][4] which can take advantage of spatial reuse
  • Wireless networking for small office (usage 2d in [3])
  • Multi-media mesh backhaul (usage 4a in [3])
    • Hotspot, enterprise, small Office or home, campus-wide deployments, municipal deployments
  • Enterprise cubicle [4]

The Enterprise Cubicle [4]

Carlos Cordeiro, Intel

recap of 1 the personal bss and high density environments
Recap of [1]: the Personal BSS and high-density environments
  • To support several key TGad usages [3] and cope with directional communication in 60GHz, the Personal BSS (PBSS) was introduced in [1]
    • PBSS is an extension of the IBSS
  • PBSSs are logical and “unmanaged” networks
    • Not defined by physical proximity (e.g., as it is typical in a BSS), and hence there can be multiple PBSSs in the same vicinity
    • Typically not managed by an authority with global information (e.g., IT department)
    • Thus, PBSSs can lead to a highly dense environment
      • Number of interfering links >> the number of available 60GHz channels (e.g., enterprise cubicle [4])
  • Important TGad usages require a high spectrum efficiency and interference mitigation mechanisms

Carlos Cordeiro, Intel

assessing the spatial reuse gain 1
Assessing the spatial reuse gain (1)
  • Goal: compare the potential of spatialreuse with omni and directional communication
  • Topology
    • Enterprise cubicle [4]
    • 9 cubicle office space, each office hasone randomly placed link
  • Simulation parameters
    • Transmit power = 10 dBm
    • Square ant. array (random orientation)
    • No. of ant. elements = 1 (omni) and 16 (directional)
    • NF=8 dB, implementation loss = 2dB
    • 5 reflectors/cube (2 dB reflection loss)
    • Penetration loss of partition wall = 3 dB*
  • Methodology
    • Links are added to the office as long as the SINR of active links do not drop below a prescribed SINR Threshold

* This is based on internal channel measurements, which revealed that the penetration loss of a cubicle wall ranges from -3~-1 dB

Carlos Cordeiro, Intel

assessing the spatial reuse gain 2
Assessing the spatial reuse gain (2)
  • Spatial reuse through directional only communication can provide up to 5 times performance gain over omni communication

SINR Threshold = 20dB

SINR Threshold = 10dB

Spatial reuse gain

Spatial reuse gain

Carlos Cordeiro, Intel

the impact of spatial reuse on interference
The Impact of Spatial Reuse on Interference
  • Spatial reuse provides large gain, but may also lead to increased interference
  • To evaluate this, we have setup a simple MAC simulator in OPNET
    • No “multiple access” (only 2 STAs per link and per PBSS)
  • The Antenna/RF model of this simulator is the same as in [5]
    • The simulator implements the partition-based path loss model [6]

Carlos Cordeiro, Intel

simulation parameters
Simulation parameters
  • PHY:
    • Antennas:
      • PCP [1]: 36 antenna elements
      • STA: 16 antenna elements
    • TX_Power: 10dBm output power
    • PHY_Rate (fixed, no real time link-adaptation)
      • PHY rate of 3.8 Gbps used for directed data transmission
      • PHY rate of 0.9Gbps used for directed control transmissions
      • Beacon is transmitted with an effective rate of 2.5Mbps
  • MAC: 16msec beacon interval
  • Traffic: each PBSS has one flow which sends data at 751 Mbps CBR traffic rate

Carlos Cordeiro, Intel

example spatial reuse 1
Example: Spatial Reuse (1)

PBSS 1 “on” times

PBSS 2

PBSS 1

1m

PBSS 2 “on” times

1m

time

Transmissions on top of each other:

allowing spatial reuse

  • The two PBSSs can achieve spatial reuse with good throughput and no packet drop

CBR=Constant Bit Rate

Carlos Cordeiro, Intel

example interference impact 2
Example: Interference impact (2)

PBSS 1 “on” times

PBSS 2

PBSS 1

1m

1m

PBSS 2 “on” times

1m

time

STA in PBSS 2 moved

to a different location

Transmissions on top of each other:

causing interference

  • PBSS 1 suffers significant throughput degradation due to interference from PBSS 2
    • Also leads to higher power consumption and latency

Carlos Cordeiro, Intel

how to mitigate the interference impact some options
How to mitigate the interference impact? Some options
  • Several mechanisms are possible to mitigate interference such as channel switching and power control
  • In addition, there are options which are access scheme dependent. For example:
    • Random access inherently adapts to the available bandwidth (there are challenges to this in 60GHz though [2])
    • For scheduled access, re-scheduling on the basis of interference may be used
  • Or a combination of an access scheme dependent option with power control and/or channel switching

Carlos Cordeiro, Intel

example interference mitigation in scheduled access
Example: Interference mitigation in scheduled access

PBSS 1 “on” times (after re-scheduling)

PBSS 2

PBSS 1

1m

PBSS 2 “on” times (after re-scheduling)

1m

1m

time

Time-sharing the channel

  • STAs in PBSS 1 detect the interference and re-schedule their links
    • This helps the performance of PBSS 1 to recover
  • If security is not a concern, PBSS 1 and PBSS 2 could also be merged

Carlos Cordeiro, Intel

conclusions
Conclusions
  • Directionality makes spatial reuse a natural characteristic in the 60GHz band
  • TGad should define means to enable interference mitigation and exploit spatial reuse in order to:
    • Take advantage of directionality in 60GHz
    • Satisfy the needs of important usage models (e.g., high-density scenarios such as enterprise cubicle)
    • Better utilize the limited number of channels available in the 60GHz spectrum
    • Substantially increase network capacity

Carlos Cordeiro, Intel

references
References

[1] C. Cordeiro et al., 802.11-09/0391r0

[2] S. Shankar et al., 802.11-09/0572r0

[3] A. Myles and R. de Vegt, 802.11-07/2988r3

[4] E. Perahia, 802.11-09/296r6

[5] M. Park et al., 802.11-09/559r0

[6] C. R. Anderson and T. S. Rappaport, “In-Building Wideband Partition Loss Measurements at 2.5 and 60 GHz,” IEEE Trans. on Wireless Comm., Vol. 3, No. 3, May 2004, pp922-928.

Carlos Cordeiro, Intel

backup
Backup

Carlos Cordeiro, Intel

assessing the spatial reuse gain in terms of aggregate throughput
PHY rate=4Gbps for SINR ≥ 20 dB

PHY rate=2Gbps for 10 dB ≤ SINR < 20dB

PHY rate=6Gbps for SINR ≥ 20 dB

PHY rate=2Gbps for 10 dB ≤ SINR < 20dB

Assessing the spatial reuse gain in terms of aggregate throughput

Carlos Cordeiro, Intel