Guided By Presented byDr.David solamon Reshma Ravi.kAssociate Professor Roll.no:4Dept of ECE S1 Mtech ECE

COOPERATIVE CARRIER SIGNALING:HARMONIZING
COEXISTING WPAN AND WLAN DEVICES

Wireless communication networks are receiving increasing interest compared to wired networks

Most of them are operating in 2.4 Ghz ISM band which causes interference

Zigbee and WiFi interference problem

Existing methods are ineffective

New method CCS

INTRODUCTION

Both Zigbee and WiFi operate in 2.4Ghz ISM band and ZigBee networks experience a packet loss rate from 0% to 85% under varying WiFi traffic load

ZIGBEE-WIFI COEXISTENCE IN THE ISM BAND

1) Static & dynamic channel allocation2) Wifi white space utilization(WISE)Arrival of wifi frame is bursty and clustered

Zigbee can transmit in this inter cluster interval(white space) to improve the channel utilization

Zigbee packets are divided into subframes if its packet length is higher than that of white space

Subframes will transmit in a session

Session ID assignment

Session initialization and subframe transmission

APPROACHES TO REDUCE INTERFERENCE

3)Adaptive radio channel allocation scheme

Basic idea of the adaptive scheme is to make the interference affected nodes to switch to a new clean channel

Interference detection

Group formation

Tear down

4)CSMA based signalingSence before transmit or listen before talk

Zigbee Versus WiFi: Mac/Phy LayersEach ZigBee WPAN assigns a unique coordinator to perform association control and beacon scheduling for clients.

The coordinator schedules a mixture of TDMA and CSMA frames periodically. Each scheduling period is called a superframe

EXISTING PROBLEMS FOR COEXISTENCE

In the CAP slot zigbee and WiFi differs from each other

Due to long backoff time(640s) and rx/tx switching time(192s) zigbee get low priority when WiFi is transmitting

Since WiFi CCA duration is much shorter ,WiFi can preempt zigbee in the middle of a Rx/Tx switching gap even though both can perfectly sense each others presence

Maximum transmit power of zigbee is 0dbm and that of WiFi is 15-20 dBm hence WiFi cannot sense zigbee

IEEE 802.15.4IEEE802.11b/g

TRANSMIT POWER0 dBm20 dBm

BANDWIDTH2 Mhz22 Mhz

TRANSMIT RATE250 Kb/s11/6 mbps

BACKOFF UNIT320 s20/9 s

RX/TX SWITCHING TIME192 s

10 s

CCA128 s

N/A

It was found that the ZigBee packet loss rate strongly depends on WiFis airtime usage w1)Spatial Collision Hazards Asymmetric Interference

Hidden terminal

CAUSE AND EFFECT OF CONFLICTING COEXISTENCE

2)Temporal Collision HazardsPartial Carrier Sensing

WiFi Preemption

Use of a signaler

This establishes the key motivation and rationale behind CCS (cooperative carrier signaling).CCS makes WiFi better aware of ZigBees presence, and hence achieving better channel sharing.

CCS assigns a separate ZigBee node called signaler as a proxy to perform the carrier signaling.

The busy tone persists throughout the data and ACK round trip, thus preventing the WiFis preemption in the rx/ tx switching gap

Signal classifier

Coexistence manager

Busy tone is scheduled jointly by the coordinator , clients and the signaler

CCS ARCHITECTURE

Signaler must emit the busy tone concurrently with the data transmission and the signaler must not interrupt the ongoing or forthcoming transmission from the desired transmitter.

temporary channel hopper uses the spectrum features of ZigBee and WiFi

TEMPORARY CHANNEL HOPPING

Each WiFi channel overlaps with four ZigBee channels.

When running the temporary channel hopper, a ZigBee signaler switches to a nearby channel before its scheduled signaling and returns to the original channel immediately after the busy tone is sent

CCS must decide on hopping to the left or right side of the channel

It should schedule the busy tone at an appropriate time

CSMA schedulerRTS/CTS exchange and channel hopping

Busy tone duration

Since the signaler does not perform backoff it tends to send the busy tone before the data transmission

So the busy tone is extended by a guard period

SIGNALING SCHEDULER

TDMA schedulerGTS mechanism is used

Slot allocation information is carried in the coordinators beacon message

After slot allocation , the signaler will send the busy tone when a scheduled TDMA slot fires

Presignaling time

TDMA scheduler will protect beacon message also

A single signaler is placed near the coordinator

To find the signaling power needed for the signaler an impirical propagation model is used

At distance d, the signals path loss in db is

L db(d) =40.2+20log10(d), d8m=58.5+33log10(d), d>8mFor uplink transmission WiFi interferer can cause packet loss if

PW [L (M wr)]-1(2/22) = PZ[L (Dm) ]-1Ca-1 (1)To make the busy tone sensible by WiFi, the signalers transmit power Ps must satisfy

Ps[L(M wr)]-1 W cs (2)

SIGNALER CONFIGURATION

From (1) and (2) minimum signaler power for protecting entire WPAN is

Ps Pw/5Pz (W cs L (D m) C a (3)For downlink traffic the required signaler power for protecting zigbee is

Ps ( Pw/5Pz) Wcs L(D m+ M wr)C a (4) Required signaler power when pw=15dBm,pz=0dBm, ca=10dBm at

Wcs=-81dBm and -62 dBm for uplink and downlink

Signaler needs a signal classifier to differentiate WiFi interference

Three different modes of CCA(Energy sensing mode, feature detection, mixed mode)

CCS uses mode 3

After classifying WiFi interference, the clients periodically report the mean RSSI reading to the coordinator

The coordinator triggers the carrier signaling if the interference level exceeds the RSS of any link by the capture threshold .

SIGNAL CLASSIFIER

CCS can be used when two coexisting networks have heterogeneous transmit power, scheduling mode

To enable the temporary channel hopping, these networks must be able to tune to different bands

Bluetooth has been a popular means of establishing WPANs. It has a similar level of transmit power as ZigBee, but it must runs frequency hopping based on a TDMA schedule

CCS can be used as a complementary approach to allow Bluetooth and WiFi to share the same spectrum via a dedicated Bluetooth- compatible signaler.

APPLICATION TO OTHER HETEROGENIOUS NETWORK

Zigbees performance is degraded in the presence of WiFi traffic even if WiFi leaves sufficient idle time

Spatial and temporal hazards fails the CSMA

CCS to enhance CSMA and enable zigbee WiFi coexistence

Use of a separate signaler

Scheduler

Signal classifier

CCS can be deployed for real time application

Decoupling carrier signaling from data transmission can be used to facilitate the coexistence of other heterogeneous networks

CONCLUSION

J. Huang, G. Xing, G. Zhou, and R. Zhou, Beyond co-existence: Exploiting WiFi white space for ZigBee performance assurance, in Proc. IEEE ICNP, 2010, pp. 305314

C. Won, J.- H. Youn, H. Ali, H. Sharif, and J. Deogun, Adaptive radio channel allocation for supporting coexistence of 802.15.4 and 802.11b, in Proc. IEEE VTC, 2005, vol. 4, pp. 25222526.

K.Shuaib,M.Boulmalf,F.Sallabi and A. Lakas ,College of Information Technology,UAE University, Co-existence of Zigbee and WLAN, A Performance Study.

Anucha U. Sylvester, Asagba O. Prince, Ogheneovo E. Edward ,Department Of Computer Science, University Of Port Harcourt, Carrier Sensing Mechanisms: The Impact On Throughput Performance Of Ieee 802.11 Wlans.

REFERENCES

Thank you

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