Impact of Highly Active Primary Users on IEEE 802.22 Network: A Single Cell Case

1. 2010 Bi-Weekly Cores Lab Meeting Impact of Highly Active Primary Users on IEEE 802.22 Network: A Single Cell Case Jihoon Park, Pål Grønsund, Przemysław Pawełczak

2. 2010 Bi-Weekly Cores Lab Meeting • Motivation • IEEE 802.22 is a Wireless Regional Access Network standard developed by IEEE since early 2006 • Standard is still in the draft phase (latest version is 2.0, July 2009) • This is one of three currently available standards that focus on TV white spaces • The other two are IEEE 1900.4 (no networking, just information sharing) and ECMA-392 MAC and TV operation in the White Spaces • IEEE 802.11af group has submitted its Project Authorization Request for new standard: IEEE 802.11 in the TV white spaces • There seem to be no papers that would analyze this network in detail • Whenever IEEE 802.22 name appears the system analyzed has actually nothing to do with the real standard • Example of papers: Zhao et al. (Tridentcom’09), Liu et al. (EMC’07), Hu et al. (Comm Mag’07), Song et al. (Chinacom’08),

3. 2010 Bi-Weekly Cores Lab Meeting • Question • Given • Realistic activity of Primary Users (channel bandwidths, signal levels, activity patterns) • In the area with densely populated Primary Users • Detailed implementation of IEEE 802.22 (traffic types, admission strategies, frame structure, modulation and coding types, bandwidth, subcarrier allocation and channel sizes and channel numbers) What is the averagethroughput and delay of IEEE 802.22 network user experience?

4. 2010 Bi-Weekly Cores Lab Meeting Approach Investigation is composed of two parts Analysis of steady state system behavior (throughput only) for a simplified network (more in system model) for tractability reasons Further investigation (throughput and delay) via extensive NS-2 simulations with presumably first in the world implementation of IEEE 802.22 stack NS-2 simulations will be also used to see how severe the simplifications of analytical model were and how well the analysis follow NS-2 traces

5. 2010 Bi-Weekly Cores Lab Meeting Illustration

6. 2010 Bi-Weekly Cores Lab Meeting • Preliminaries • IEEE 802.22 has tons of similarities with existing IEEE 802.16e

7. 2010 Bi-Weekly Cores Lab Meeting Preliminaries: superframe structure

8. 2010 Bi-Weekly Cores Lab Meeting Preliminaries: frame structure

9. 2010 Bi-Weekly Cores Lab Meeting Preliminaries: frame structure

10. 2010 Bi-Weekly Cores Lab Meeting Preliminaries: frame structure

11. 2010 Bi-Weekly Cores Lab Meeting Analytical Model: Assumptions One base station only (no spectrum sharing among multiple IEEE 802.22 base stations) A bandwidth B of one TV channel is fully available to IEEE 802.22 network, provided that no Primary User is actively transmitting • Bandwidth is divided into multiple (logical) sub-channels • Two types of Primary Users are considered • Wireless Microphones (high variation in channel occupancy), occupies Z (currently Z=1) channel; it can appear on any sub channel • Other auxiliary device (low variation in channel occupancy) – tries to resemble a TV transmission, occupies Y (currently Y=2) channels; it can also appear on any sub-channel • Activity of two types of PUS follow a Poisson process • Parameterized by individual arrival and departure rate Transmission is slotted (a parameter of our model – one slot is one frame size) • Spectrum sensing process is assumed to be non-perfect • False alarm probability affects the throughput of IEEE 802.22 • Note that mis-detection does not, as given in the standard (detection is done per frame basis)

12. 2010 Bi-Weekly Cores Lab Meeting Analytical Model: Assumptions • IEEE 802.22 users generate two types of traffic • Elastic traffic (Variable Bit Rate - VBR), occupies X (X is a real number) logical channels • Non-Elastic Traffic (Constant Bit Rate - CBR), occupies Y (at the moment Y=1) logical channels • Both streams are Poisson, described by individual values of arrival and departure • Admission control strategy • Whenever a VBR call occupies a channel and CBR call arrives, VBR must free space for VBR call by “squeezing” the number of occupied channels to allow CBR to access • When any of PU occupies a channel both CBR and VBR must vacate its corresponding sub-channels • CBR: switches to idle channel, if nothing available then connections is being buffered; no requirement on continuous channel availability, Y channels can appear anywhere in the bandwidth B • VBR: tries to squeeze the connection, if no space available then it is being buffered; just like in CBR no requirement on continuous channel availability

13. 2010 Bi-Weekly Cores Lab Meeting Analytical Model: Limitations • No adaptive modulation features considered (yet) • No two-stage spectrum sensing considered (yet) • No co-channel interference (should we?) • Infinite number of users • No other connection strategies considered (in relation to our previous work), like just buffering or switching only • Obviously only one cell considered • The opposite requires designing of channel sharing strategies among many IEEE 802.22 base stations • Example: what to do when in one location only two full TV channels are present with three base stations?

14. 2010 Bi-Weekly Cores Lab Meeting Analysis #PU class 1, #PU class 2, #CBR flows, #VBR flows Transition probability for PU class 1

15. 2010 Bi-Weekly Cores Lab Meeting Analysis, cont. Recursive solution is needed to compute departure probability

16. 2010 Bi-Weekly Cores Lab Meeting Analysis results and model verification • PU: TV and WM • SU: CBR Only • t = 5 /s, t = 3 /s • w = w = 3, 30, 300 /s • c = c = 100 /s • Pf=0.1 • M = 4 • Batch • size 10000 • num 100 • conf 0.9

17. 2010 Bi-Weekly Cores Lab Meeting Analysis results and model verification • PU: TV and WM • SU: CBR Only • t = 5 /s, t = 3 /s • w = w = 3, 30, 300 /s • c = c = 100 /s • Pf=0.9 • M = 4 • Batch • size 10000 • num 100 • conf 0.9

18. 2010 Bi-Weekly Cores Lab Meeting Analysis results and model verification • PU: TV and WM • SU: CBR and VBR • t = 5 /s, t = 3 /s • w = w = 3, 10, 30 /s • c = c = 10 /s • M = 4 (#channels) • Pf=0.9 • Batch • size 10000 • num 100 • conf 0.9

19. 2010 Bi-Weekly Cores Lab Meeting Analysis results and model verification • PU: TV and WM • SU: CBR and VBR • t = 5 /s, t = 3 /s • w = w = 3, 10, 30 /s • c = c = 10 /s • M = 4 (#channels) • Pf=0.1 • Batch • size 10000 • num 100 • conf 0.9

20. 2010 Bi-Weekly Cores Lab Meeting • NS-2 Simulations • Adaptation of existing WiMax forum IEEE 802.16e NS-2 stack • More than 20.000 lines of code • What is currently implemented • Spectrum sensing (single stage) • Bandwidths is changed • Frame size conforms to IEEE 802.22

21. 2010 Bi-Weekly Cores Lab Meeting Two stage spectrum sensing

22. t+1ms t+5ms t 2010 Bi-Weekly Cores Lab Meeting Time DL Subframe UL Subframe DL Subframe UL Subframe Fast Sensing RTG = receive transmit gap TTG = transmit transceive gap Freq This implementations uses some symbols at the end of the UL frame. 802.22 uses quiet periods starting from the end of the frame Two stage spectrum sensing

23. 2010 Bi-Weekly Cores Lab Meeting Time Fine Sensing Freq OFDMA Frame 25 ms (5 OFDMA frames) PS: fine sensing can be set to other values, but it must be a multiply of OFDMA frame length Two stage spectrum sensing

24. 2010 Bi-Weekly Cores Lab Meeting NS-2 Model

25. 2010 Bi-Weekly Cores Lab Meeting NS-2 Model CBR = packetSize_ * pps = packetSize_ * 1/interval_ CBR_802.22= 100 * 1/100 = 10 K = 10 * 8 = 80 Kbps Constant Exponential on/off process: burst (on) = 2 sec idle (off) = 3, 4, 5, 6 sec CBR_WM= 100 * 1/100 = 10 K = 10 * 8 = 80 Kbps Exponential on/off process: burst (on) = 60 sec idle (off) = 60, 120, 180 sec CBR_TV= 1000 * 1/10 = 10 K = 10 * 8 = 80 Kbps

26. 2010 Bi-Weekly Cores Lab Meeting • NS-2 Model • CBR traffic, Wireless microphone only, On time: 2 s, off is a variable