STATE OF THE ART IN OPPORTUNISTIC SPECTRUM ACCESS MEDIUM ACCESS CONTROL DESIGN

Pawelczak, P.; Pollin, S.; So, H.-S.W.; Motamedi, A.; Bahai, A.; Prasad, R.V.; Hekmat, R.;Department of EEMCS, Delft University of Technology, The NetherlandsCognitive Radio Oriented Wireless Networks and Communications, 2008.

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Presenter: Han-Tien ChangAdvisor: Professor Dr. Yeali S. Sun

Outline Introduction Survey of Opportunistic Spectrum

Access MACs The essential features (functionalities) of

OSA MAC Measurements of Licensee Channel

Occupancy Conclusion Comments

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Introduction3

Opportunistic Spectrum Access (OSA) A promising new spectrum management

approach Allow co-existence of both licensed and

opportunistic users in each spectrum band Potentially decreasing the spectrum

licensing costs for both classes of users Boost the throughput of the networks

Introduction (cont’d)4

Exclusive: exclusive channel use to each user

Spectrum commons: everybody competes to use the spectrum

Hierarchical: give PU more rights to use the spectrum Overlay: only one user can use a frequency

band in particular time and space Underlay: SU can transmit in an occupied

channel with PU, but it cannot increase the interference to PU over than a threshold

Modern spectrum management: classification with the application examples

Extensively discuss in this paper

[Ref] Przemyslaw Pawelczak ; et. al, “Quality of Service Assessment of Opportunistic Spectrum Access: A Medium Access Control Approach” , IEEE Wireless Communications, Oct. 2008

Introduction (cont’d)5

In this paper survey, Catalogue the features about the deign of

OSA MAC in the literature Focus on the distributed channel access

OSA MAC protocol The OSA nodes locally decide on, where and

how to access the channel Comparing different design choices

Introduction (cont’d)6

Many different coexistent scenarios for OSA networks and licensed users But it’s still unclear what are the most

realistic or useful scenarios Thus, in this paper

performing some measurements of licensed bands get an idea of the expected licensed channel

use

Survey of OSA MACs7

Catalogue the features of 20 OSA MACs explain the features later

Survey of OSA MACs8

Bootstrapping A pre-process during which an OSA node decides

which PU channels are allowed for opportunistic spectrum communication Consult such an external entity (spectrum regulator)

Radio Front Ends (RFEs) The number of RFEs significantly affects the operation

of an OSA node Increasing RFEs higher reliability, lower delay (channel

switch), but increasing the total cost Channel Joining (6/20)

Combine the together to increase the throughput Variable bandwidth

Survey of OSA MACs (cont’d)9 Multiple Channel Management

Dedicated (Common) Control Channel (DCC) One SU channel is dedicated solely to the transport

of control messages Drawback

When a PU is active on the control channel, all communication is obstructed.

Need extra dedicated RFE Hopping Control Channel (HCC)

All nodes hop between all channels following a predefined hopping pattern

HCC doesn’t require a particular single channel to be free from PU activity

Survey of OSA MACs (cont’d)10

Split Phase Control Channel (SPCC) Time is divided into control and data phases During the control phase

1. All nodes switch their RFEs to the dedicated control channel

2. Decide on the channels to use for the upcoming data transfers

Need no extra RFE, but need stronger synchronization Multiple Rendezvous Control Channel (MRCC)

Multiple nodes can exchange control information at the same time, using all available channels

Also need a stringent synchronization

Survey of OSA MACs (cont’d)11 Discuss the performance about these

multichannel management mechanism Offer different primary users’ load in all

channel Observe the average delay and throughput

Survey of OSA MACs (cont’d)12

Dashed lines: the shorter PU packet sizeSolid lines: the longer PU packet sizes

MRCC and HCC are better

MRCC doesn’t suffer a lot from PU packet sizeMRCC randomizes the channel access maximally among all PU channels

PU Load vs. average packet delay

PU Load vs. average throughput

Survey of OSA MACs (cont’d) Scanning Process

Since an SU cannot use the channel when a PU is present, it should obtain information about PU activities on each channel Via PU detector or broadcast by a central device

Scanning increases the overhead since nodes cannot transmit when they are scanning

It’s hard to distinguish SU and PU signals, the whole SU network has to be quiet during sensing.

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Survey of OSA MACs (cont’d)

Quiet period management Let all SU network be quiet during sensing The approach can be done periodically or before

each transmission attempt The more tolerant the PU to interference, the

less often sensing should be done. Scanning performance is measured in terms

of the probability of detecting a PU when present, and the probability of falsely detecting a PU. The measurement of protecting PU’s QoS

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Survey of OSA MACs (cont’d)15 Policies

The operation of every OSA network has to be governed by the radio regulator policies. Time based

Define time frame during which the OSA node is allowed to transmit on the occupied PU channel

Power based Define certain power regimes that the OSA nodes

needs to fulfill to be able to use certain PU channels

Collision based Define the probability that OSA traffic will collide

with the PU packets

Survey of OSA MACs (cont’d)16 Multi-hop Communications

Depending on the targeted infrastructure Interaction Between Licensed and

Opportunistic Users The SU may know a priori of the

transmission feature from the other party But the ultimate scenario OSA network

shall be deployed into a completely unknown radio environment

Survey of OSA MACs (cont’d)17 Negotiated Parameter

Between the transmitter and receiver in the secondary users tune to the best channel Channel Number Queuing parameters: queue size and packet length Channel history: collision prob. and PU occupancy

distribution Physical properties of the channel

ARQ level, link adaptation strategy Traffic Estimation

A good prediction of the PU traffic can result in significant performance

Measurement of licensee channel occupancy

18 Objective of this measurement [22]

Get some information on what type of channel occupancy distributions that can expect while observing the PU channels

Measurement setup Using Rhode&Schwartz ESPI07 spectrum analyzer

(SA) Time: on March 13 2007, between 11 AM and 8

PM. Frequency band: between 446.04 and 467.82 MHz.

Measure the On/Off period[22] P. Pawełczak, S. Pollin, H.-S. W. So, A. Bahai, R. V. Prasad, and R. Hekmat, “Performance analysis of multichannel medium access control algorithms for opportunistic spectrum access,” IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 58, NO. 6, JULY 2009

Measurement of licensee channel occupancy

19 Statistical analysis of the measured data

Using the Kolmogorov-Smirnov test (K-S test) To determine which continuous distribution fits

the obtained data best Result

The majority of traces had no identified type of distribution

The exponential distribution usually assumed in the analysis of OSA MACs has only a reflection in a handful of the identified

activities.

Conclusion20

Identified different MAC designs proposed so far in the literature different designs have been classified and

assesses in systematic manner Performance analysis of the multichannel

MAC design feature (channel access) spreading the communication across channels

enables to optimally avoid PU activity

Comments Know the features of the OSA MAC

Protocols With the importance and the functionality

The channel access management mechanism is very important to both the PU and SU QoS

The realistic whitespace usage is not considered here

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