impact of highly active primary users on ieee 802.22 network: a single cell case 2010 bi-weekly...

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

2010 Bi-Weekly Cores Lab Meeting

Jihoon Park, Pål Grønsund, Przemysław Pawełczak

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),


Question

Given1. Realistic activity of Primary Users (channel bandwidths, signal levels, activity

patterns)2. In the area with densely populated Primary Users3. 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 average throughput and delay of IEEE 802.22 network user

experience?

Approach

Investigation is composed of two parts1.Analysis of steady state system behavior (throughput only) for a simplified network (more in system model) for tractability reasons2.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



Illustration

Preliminaries

IEEE 802.22 has tons of similarities with existing IEEE 802.16e

IEEE 802.22 IEEE 802.16e

OFDMA channel profile (MHz)

6,7,8 20,28,17.5,14,10,8.75,7,3.5,1.25

Air interface OFDMA OFDMA, OFDM, Single Carrier

Burst allocation Linear Two dimensional

Subcarrier permutation Distributed (with enhanced interleaver)

Adjacent/distributed

MIMO No STC, beamforming

Frame size 10 ms, superframe: 16 frames

No superframe, multipme frame sizes: 2, 5, 10, 20 ms


Preliminaries: superframe structure


frame 0

Superframe n-1 Superframe n Superframe n+1 . . .Time

. . .

SuperframePreamble

SCH

. . .

FramePreamble

FramePreamble

160 ms

frame 1

10 ms

frame 15

FramePreamble

Preliminaries: frame structure


frame n-1 frame n frame n+1 ... Time...

DS PHY PDU

FramePreamble FCH DS burst 1 DS burst 2 DS burst x...

UDC

DCD

MAC PDU 1 ... MAC PDU y Pad

MAC Header MAC Payload CRC

DS subframeRanging

slots

BW

slots

US PHY PDU(CPE m)

US PHY PDU(CPE p)

...

US subframe

US burst

MAC PDU 1 ... MAC PDU k Pad

MAC Header MAC Payload CRC

Self-coexistence

window

UCSNotification

slots

US-MAP

DS-MAP

OptionalbroadcastMAC PDU

TTGRTG

request



frame n-1 frame n frame n+1

Adaptive

N time slots

DownstreamSubframe

UpstreamSubframe

...Time

...

Time slot 0 Time slot N-1Time slot



DS sub-frame

TTG

RTG

US sub-frame(smallest US burst portion on a given subchannel= 7 symbols)

26 to 42 symbols corresponding to bandwidths from 6 MHz to 8 MHz and cyclic prefixes from 1/ 4 to 1/ 32

Fra

me P

ream

ble

FCH

DS-

MAP

Burs

t 1DCD

Burs

t 2 ti

me

buff

er

tim

e bu

ffer

Self-c

oexi

stence

win

dow

(4 o

r 5 s

ymbol

s w

hen

sch

edu

led)

Burst 1

60 s

ubch

anne

ls

Burst 2

Burst 3more than 7 OFDMA symbols

Burst

Burst n

Burst

Burs

t m

Ranging/ BW request/ UCS notification

Burst

Burst

Bursts

Burs

ts

frame n-1 frame n frame n+1... Time...

10 msUS-

MAP

US-

MAP

UCD

Analytical Model: Assumptions


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)

One base station only (no spectrum sharing among multiple IEEE 802.22 base stations)

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)

Analytical Model: Assumptions


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 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

Analytical Model: Limitations


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?

No adaptive modulation features considered (yet) No two-stage spectrum sensing considered (yet) No co-channel interference (should we?) Infinite number of users

Analysis


P(Ut ,Uw ,Uc ,Uv → Ut + kt,Uw + kw,Uc + kc,Uv + kv) =Pt(Ut → Ut + kt)Pw(Uw → Uw + kw |Ut)×Psu(Uc → Uc + kc,Uv → Uv + kv |Ut,Um)

0 ≤Ux ≤Ux,max,0 ≤Ux + kx ≤Ux,max,−Ux ≤kx ≤Ux,max −Ux

Pt (Ut → Ut + kt) = ft(n|Ut, μt,Ts)gt(kt + n|λt,Ts)n=0

Ut

∑ ,0 ≤kt <Ux,max −Ux

Pt(Ut → Ut + kt) = ft(n|Ut, μt,Ts)n=|kt |

Ut

∑ gt(n−|kt ||λt,Ts),−Ut ≤kt < 0

Pt(Ut → Ut + kt) = ft(n|Ut, μt,Ts) gt(kt + m|λt,Ts),Ut,max −Utm=n

∞

∑n=0

Ut

∑

π (nt ,nw ,nc ,nv )

Transition probability for PU class 1

#PU class 1, #PU class 2, #CBR flows, #VBR flows


Analysis results and model verification

•PU: TV and WM•SU: CBR Only•λt = 5 /s, μt = 3 /s•λw = μw = 3, 30, 300 /s•λc = μc = 100 /s•Pf=0.1•M = 4•Batch–size 10000–num 100–conf 0.9

100

101

102

103

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

λw

(/s)

Sys

tem

thr

ough

put

(Mbp

s)



•PU: TV and WM•SU: CBR Only•λt = 5 /s, μt = 3 /s•λw = μw = 3, 30, 300 /s•λc = μc = 100 /s•Pf=0.9•M = 4•Batch–size 10000–num 100–conf 0.9

100

101

102

103

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

λw

(/s)

Sys

tem

thr

ough

put

(Mbp

s)



•PU: TV and WM•SU: CBR and VBR•λt = 5 /s, μt = 3 /s•λw = μw = 3, 10, 30 /s•λc = μc = 10 /s•M = 4 (#channels)•Pf=0.9•Batch–size 10000–num 100–conf 0.9

100

101

102

103

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

λw

(/s)

Sys

tem

thr

ough

put

(Mbp

s)


•PU: TV and WM•SU: CBR and VBR•λt = 5 /s, μt = 3 /s•λw = μw = 3, 10, 30 /s•λc = μc = 10 /s•M = 4 (#channels)•Pf=0.1•Batch–size 10000–num 100–conf 0.9

100

101

102

103

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

λw

(/s)

Sys

tem

thr

ough

put

(Mbp

s)



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


Two stage spectrum sensing



DLSubframe

ULSubframe

Time

Fre

q

t t+5mst+1ms

RTG = receive transmit gapTTG = transmit transceive gap

This implementations uses some symbols at the end of the UL frame.802.22 uses quiet periods starting from the end of the frame

DLSubframe

ULSubframe

Fast

Sen

sing



OFDMA Frame Fine

Sensing

Time

Fre

q

25 ms (5 OFDMA frames)

PS: fine sensing can be set to other values, but it must be a multiply of OFDMA frame length


NS-2 Model


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 secidle (off) = 3, 4, 5, 6 sec

Exponential on/off process:burst (on) = 60 secidle (off) = 60, 120, 180 sec

Constant


NS-2 Model

CBR traffic, Wireless microphone only, On time: 2 s, off is a variable

impact of highly active primary users on ieee 802.22 network: a single cell case 2010 bi-weekly...

Documents

delay of ieee

existing ieee

tv channel

white spaces ieee

world implementation

channel occupancy

channel sizes

sub channel