studying the impact of lte-u on wi-fi downlink performance

Amr ABDELFATTAH

Naceur MALOUCH

Studying the Impact of LTE-U on Wi-Fi Downlink Performance

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Why LTE-U is needed?

What are LTE-U’s requirements?

How LTE-U could be achieved?

Duty Cycled LTE (LTE-U) Wi-Fi downlink performance Wi-Fi downlink/uplink performance

Conclusion.

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AGENDA

Opportunistic use of unlicensed spectrum to address the mobile data growth challenges

Unified network compared to WLAN data offloading

Operators are more free to chose between LTE-U and LTE/Wi-Fi interworking

Efficient utilization of unlicensed spectrum resources

Licensed spectrum ensures quality of service and unlicensed spectrum for boosting data speeds

…etc

LTE-U small cell deployment scenario

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(from C. Hoymann, \LTE in unlicensed spectrum|technical and regulatory aspects")

Why LTE-U is needed ?

Effective and fair coexistence with Wi-Fi

Should not impact Wi-Fi services (data, video and voice services) more than an additional Wi-Fi network on the same carrier

Effective and fair coexistence among LTE-U networks deployed by different operators

With/Without coordination among operators

User equipment capability

User equipment supports two technologies (Wi-Fi & LTE-U) in the same spectrum

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What are LTE-U’s requirements?

How LTE-U could be achieved?

1) TDM (USA, China and Korea )

Backward compatibility Based on Rel.10,11 and 12 Time division multiplexing

• Blank subframe Allocation • Scell Activation/Deactivation

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2) LBT (Europe and Japan)

Global solution Based on Rel. 13 Listen Before Talk

• Load Base Equipment (LBE)• Frame Based Equipment (FBE)• …etc

Duty cycled LTE configuration:

A. Duty cycle period Short (1 ̴10 ms) Long (20 ̴100x ms) Long + Short

B. Duty cycle percentage 50%, 30%, ... , depends on Wi-

Fi needs

C. ON/OFF periods distribution M = number of disjoint

transmission periods per duty cycle.

Wi-Fi performance:

A. Throughput Delay Data + Voice or Video

B. 50% duty cycle is not enough to share equally the channel

C. As M , Throughput

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Duty Cycled LTE (LTE-U)

Periodic DTMC with period M = 3 7


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Random Walk / Renewal Process

0


For a given period, N has an upper bound nmax, where With

Similarly, we can compute all other transition probabilities. Now we can deduce the probability of occurrence of each state at multiples of M , ϵ (1,…,M).

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Probability of Collision

Downlink Wi-Fi Throughput

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, ,


Analytical model Vs

Duty Cycled

5x0

3x2

4x1

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5X0 ON/OFF pattern

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Collisions degrade the throughput by a non-marginal amount

Standard behavior of Wi-Fi throughput versus packet size is not valid anymore

For small packet size, the probability of collision has a positive linear relationship

After a specific packet size, the probability of collision shows some ripples

Throughput ripples are so much sharp that may cause loosing up to 26% of throughput compared to the maximum

50% ON/OFFduty cycle is not enough


5X0 ON/OFF pattern

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As Wi-Fi speed increases :

The impact of LTE-U on Wi-Fi performance decreases

Throughput ripples and collision probability stairs start to appear for a larger packet sizes


3X2 ON/OFF pattern

4X1 ON/OFF pattern 14


6Mbps

12 Mbps 15


165X0 ON/OFF pattern with number of Wi-Fi stations = 10


Using our analytical model, we quantify the impact of LTE-U on Wi-Fi performance

The impact of LTE-U on Wi-Fi performance depends on both network configuration parameters:

• LTE-U duty cycle configuration ( M parameter, Duty cycle period and percentage) • Wi-Fi Network (number of station, data rate and packet size )

We tie up between the different TDM schemes of LTE-U and Wi-Fi performance, henceforth, it is possible to find the required compensation that makes the sharing equal between the two systems

We provide a novel Wi-Fi throughput analysis in case of a hidden node (i.e. LTE-U) using a random walk approach

The duty cycled LTE-U traffic (i.e. deterministic traffic ) cannot be approximated by an exponential traffic as the PASTA property does not hold which leads to the need of our model

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Conclusion

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Questions

studying the impact of lte-u on wi-fi downlink performance

Engineering