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

Motivation  IEEE 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 (no networking, just information sharing) and ECMA- 392 MAC and TV operation in the White Spaces  IEEE af group has submitted its Project Authorization Request for new standard: IEEE in the TV white spaces There seem to be no papers that would analyze this network in detail  Whenever IEEE 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), 2010 Bi-Weekly Cores Lab Meeting

Question Given 1.Realistic activity of Primary Users (channel bandwidths, signal levels, activity patterns) 2.In the area with densely populated Primary Users 3.Detailed implementation of IEEE (traffic types, admission strategies, frame structure, modulation and coding types, bandwidth, subcarrier allocation and channel sizes and channel numbers) 2010 Bi-Weekly Cores Lab Meeting What is the average throughput and delay of IEEE network user experience?

Approach Investigation is composed of two parts 1.Analysis of steady state system behavior (throughput only) for a simplified network (more in system model) for tractability reasons 2.Further investigation (throughput and delay) via extensive NS-2 simulations with presumably first in the world implementation of IEEE 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 2010 Bi-Weekly Cores Lab Meeting

Illustration

Preliminaries  IEEE has tons of similarities with existing IEEE e IEEE IEEE e OFDMA channel profile (MHz) 6,7,820,28,17.5,14,10,8.75,7,3.5, 1.25 Air interfaceOFDMAOFDMA, OFDM, Single Carrier Burst allocationLinearTwo dimensional Subcarrier permutationDistributed (with enhanced interleaver) Adjacent/distributed MIMONoSTC, beamforming Frame size10 ms, superframe: 16 frames No superframe, multipme frame sizes: 2, 5, 10, 20 ms 2010 Bi-Weekly Cores Lab Meeting

Preliminaries: superframe structure 2010 Bi-Weekly Cores Lab Meeting

Preliminaries: frame structure 2010 Bi-Weekly Cores Lab Meeting

Preliminaries: frame structure 2010 Bi-Weekly Cores Lab Meeting

Preliminaries: frame structure 2010 Bi-Weekly Cores Lab Meeting

Analytical Model: Assumptions 2010 Bi-Weekly Cores Lab Meeting A bandwidth B of one TV channel is fully available to IEEE 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) One base station only (no spectrum sharing among multiple IEEE base stations)  Spectrum sensing process is assumed to be non-perfect  False alarm probability affects the throughput of IEEE  Note that mis-detection does not, as given in the standard (detection is done per frame basis)

Analytical Model: Assumptions 2010 Bi-Weekly Cores Lab Meeting 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 IEEE 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

Analytical Model: Limitations 2010 Bi-Weekly Cores Lab Meeting  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 base stations  Example: what to do when in one location only two full TV channels are present with three base stations?  No adaptive modulation features considered (yet)  No two-stage spectrum sensing considered (yet)  No co-channel interference (should we?)  Infinite number of users

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

Analysis, cont. Recursive solution is needed to compute departure probability 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 –num 100 –conf 0.9

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 –num 100 –conf 0.9

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 –num 100 –conf 0.9

2010 Bi-Weekly Cores Lab Meeting 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 –num 100 –conf 0.9 Analysis results and model verification

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

2010 Bi-Weekly Cores Lab Meeting Two stage spectrum sensing

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

2010 Bi-Weekly Cores Lab Meeting Two stage spectrum sensing

2010 Bi-Weekly Cores Lab Meeting NS-2 Model

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

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