1. Comments on LAA EVM Date: 2015-01-14 Authors: January 2015 Month Year
doc.: IEEE yy/xxxxr0
January 2015
Comments on LAA EVM
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.
Alireza Babaei, CableLabs
John Doe, Some Company

2. Month Year
doc.: IEEE yy/xxxxr0
January 2015
Abstract
This document provides recommendations related to Annex A (Evaluation methodology) of the 3GPP draft study item document on Licensed-Assisted Access to Unlicensed Spectrum: 3GPP TR v0.1.0 ( ).
The purpose of this contribution is to include these recommendations in an upcoming liaison from 802 to 3GPP on its ongoing LAA study item
Alireza Babaei, CableLabs
John Doe, Some Company

3. Summary of Recommendations
January 2015
Summary of Recommendations
Incorporate Truncated Exponential Backoff in LBT requirements and simulate its effect.
For a complete understanding of LAA impact on Wi-Fi, a range of load densities should be simulated.
Include VoIP and other traffic types as mandatory traffic models and evaluate corresponding performance metrics.
Consider 256 QAM, LDPC and RTS/CTS mandatory for simulation.
Alireza Babaei, CableLabs

4. Month Year
doc.: IEEE yy/xxxxr0
January 2015
LBT
Listen-Before-Talk (LBT) based on European regulations (ETSI v1.7.1) is mainly considered as a coexistence mechanism in 3GPP contributions.
LBT, as defined in the above ETSI document, has two forms :
Load Based and Frame Based Equipment (LBE and FBE)
3GPP contributions indicate majority opinion is tending towards LBE
Concerns:
Fixed linear backoff window for extended CCA (q is fixed for a given device)
No increase with collision (q is fixed during operation)
Load based equipment (LBE): Equipment where the transmit/receive structure is not fixed in time but demand-driven
Frame based equipment (FBE): equipment where the transmit/receive structure is not directly demand-driven but has fixed timing
CC A
20 µs
Extended CCA
Extended CCA = N * 20 µs
N ∈ {0, 1, … , q} and q ∈ {4, 5, … , 32}
Channel Busy
Slide 4
Alireza Babaei, CableLabs
John Doe, Some Company

5. LBT Simulation Results
January 2015
Transmission Success Rate Gain/Loss 1X
0.23X
1.68X
1.53X
0.12X
Poor fairness with Wi-Fi
Simulation Assumptions: Full buffer traffic, all nodes within CCA range of each other, single 20 MHz channel, co-channel operation, clients and APs/eNBs are stationary, Wi-Fi STAs use EDCA, BE AC (AIFS = 3, CWmin = 15)
Assume Load Based Equipment LBT, q = 32
Tx Success Rate: probability of any client sending successful burst
Steps to Tx Success:
Client must pass CCA
Client must Tx without collision
Results relative to the Tx Success Rate when both operators use Wi-Fi
1X applies to any client count
Conclusion: Version of ESTI LBT rules are not sufficient for fairness between LTE and Wi-Fi
Slide 5
Alireza Babaei, CableLabs

6. What version of LBT to use?
January 2015
What version of LBT to use?
has proven success in enabling sharing between independent systems in a wide variety of use cases an load scenarios.
The basis of this success is EDCA which is based on CSMA/CA; CSMA/CA is an LBT mechanism using truncated exponential backoff.
The use of a similar mechanism by LAA should provide the basis for fair sharing between LAA and Wi-Fi (and also between LAA and LAA)
The Wi-Fi Alliance made a proposal to ETSI BRAN that defines LBT with exponential backoff for LAA (See [3])
Recommendation: Incorporate Truncated Exponential Backoff in LBT requirements and simulate its effect
John Doe, Some Company

7. January 2015
System Load
Section A.1.1 lists the parameters for indoor LAA coexistence evaluation.
Only 10 LAA UEs or Wi-Fi clients is assumed per unlicensed band carrier for DL-only LAA coexistence evaluation.
The impact of LAA (using EU LBT) on Wi-Fi clients is more evident at high system load particularly when number of nodes is large
See the backup slides.
Recommendation: For a complete understanding of LAA impact on Wi-Fi, a range of load densities should be simulated
Alireza Babaei, CableLabs

8. January 2015
Traffic model
Wi-Fi and LAA have to operate in unlicensed spectrum carrying a variety of traffic types including voice, video, FTP, etc.
However, the simulations evaluating the fairness of LAA with Wi-Fi is currently limited to FTP.
Once initial simulations showing basic fairness between Wi-Fi and LAA are complete, further simulations will be required to ensure fairness and functionality are maintained using a variety of traffic types in a diversity of use and load scenarios.
Recommendation: Include VoIP and other traffic types as a mandatory traffic models and evaluate corresponding performance metrics.
Alireza Babaei, CableLabs

9. Assumptions on Wi-Fi Parameters
January 2015
Assumptions on Wi-Fi Parameters
Section A.2.1 lists Wi-Fi system evaluation assumptions.
256 QAM and LDPC are considered optional.
Use of lower order modulation (when SINR is sufficient for 256 QAM) means unnecessarily longer frame duration. Longer frame duration increases the backoff period and decreases the channel utilization for other Wi-Fi clients.
RTS/CTS is considered optional.
The hidden node behavior of two wireless systems is key to coexistence. RTS/CTS is optional but commonly used in congested environments.
Recommendation: Consider 256 QAM, LDPC and RTS/CTS mandatory for simulation
Alireza Babaei, CableLabs

10. January 2015
References
[1] Study on Licensed-Assisted Access to Unlicensed Spectrum, 3GPP TR v0.1.0 ( ) [2] /0082r0: Overview of EU LBT and its Effectiveness for Coexistence of LAA LTE and Wi-Fi [3] ETSI BRAN(14)000102
Alireza Babaei, CableLabs

11. January 2015
Backup
Alireza Babaei, CableLabs

12. Simulation Parameters
Cable Labs
Simulation Parameters
January 2015
Overall Simulation Assumptions:
All nodes are within CCA range of each other
Single channel access scenario
Full buffer traffic
EDCA channel access modeled
Best Effort access category (AIFSN = 3, CWmin = 15)
Stationary nodes
Monte Carlo simulations with 1,000,000 TXOPs evaluated per data point
ETSI LBT Assumptions:
Always use extended CCA
LBE rules Implemented by LAA nodes
Slide 12
Alireza Babaei, CableLabs

13. Successful Packet Transmission
Cable Labs
Successful Packet Transmission
January 2015
ETSI LBT performs poorly compared to Wi-Fi channel access
Lower q value = worse performance
Poor fairness behavior when sharing and >5 clients/operator
LAA clients get significantly higher P(success) compared to Wi-Fi clients i.e. black lines are all above the red lines.
At a certain client count, LAA clients nearly starve Wi-Fi clients i.e. P(success) approaches zero
This value varies with q, best case shown
Slide 13
Alireza Babaei, CableLabs

14. Collisions in the Shared Channel
January 2015
ETSI LBT performs poorly compared to Wi-Fi channel access
Collision rate increases rapidly to 1 for low q values
Even for q = 32, collision rate dominates after 12 transmitting clients per operator
Inefficient channel usage for low q and/or scenarios with ~25 or more transmitting nodes.
Attributed to non-increasing backoff range
Slide 14
Alireza Babaei, CableLabs