A Realization of Cognitive Pilot Channels

through Wireless Billboard Channel Infrastructure

for Cognitive Radio

Ivan Ganchev Telecommunications Research Centre,

University of Limerick,

Limerick, Ireland.

Zhanlin Ji Beijing University of Science and

Technology, and Hebei United

University, P.R. China.

Máirtín O’Droma Telecommunications Research Centre,

University of Limerick,

Limerick, Ireland.

Abstract—This paper proposes an out-band cognitive pilot channel

(CPC) solution for cognitive radio systems and networks. The

solution exploits wireless billboard channel (WBC) technology

which was originated to play a key role in a ubiquitous consumer

wireless world (UCWW) environment [1, 2]. The paper shows how

the WBC technology and variety of potential WBC downlink

platforms match the requirements of the CPC scheme, with their

main goal of enabling the transfer to mobile terminals (MTs) of

available knowledge of the wireless operational and geographical

environment, established policies and internal state of any usable

and accessible ‘cognitive spectrum’. The paper sets out the three-

layer WBC/CPC system architecture, with specific emphasis on the

top service layer and the CPC ‘service descriptions’, and includes

also details on the link and physical layers for a ‘WBC/CPC over DVB-H’ platform.

Keywords-cognitive radio system (CRS); cognitive pilot channel

(CPC); wireless billboard channel (WBC); advertisement, discovery

and association (ADA); digital video broadcasting-handheld (DVB-H)

I. INTRODUCTION

A cognitive radio system (CRS) employs technology that allows it: “to obtain knowledge of its operational and

geographical environment, established policies and its internal

state; to dynamically and autonomously adjust its operational

parameters and protocols according to its obtained knowledge in

order to achieve predefined objectives; and to learn from the

results obtained”, [3]. CRS can use the following approaches [4]:

Collecting information from component radio systems;

Geolocation;

Spectrum sensing;

White space database access;

Using a cognitive pilot channel (CPC) as a means to exchange information between CRS components.

The CPC concept was developed in order to provide

collaboration between networks and mobile terminals (MTs) for

better support of different radio resource management (RRM)

optimization procedures and for optional dynamic spectrum

access and flexible spectrum management [5]. CPC can be used

to exchange sensing information between MTs, as well as

between MTs and base stations in order to perform

collaborative/cooperative sensing, which could greatly improve

spectrum sensing characteristics, e.g., increase detection

probability, reduce detection time, etc. CPC can also convey the

necessary information to let MTs know the status of radio channel occupancy, which could considerably decrease time and

power consumption [5].

CPC may be used during one or both of the following phases

[5]:

• Start-up phase: after turning on, MT retrieves from CPC

information about a candidate network to camp on. MT first

detects the CPC available in the current area and synchronizes

with it. Then CPC delivers relevant information with regard to

operators, frequency bands, and radio access technologies

(RATs) in the MT location. MT uses this information to initiate

a communication session optimized to time, situation and location.

• Ongoing phase: after MT is registered to (or "camped on") a

network, a periodic check of the information forwarded by CPC

may be useful to rapidly detect changes in the environment due

to either variations of the MT position or network

reconfigurations. The same information as in the start-up phase

could be delivered here by CPC with additional data, such as

services, load situation, etc.

There are two CPC deployment options [5]: (1) out-band

CPC, which considers that a channel outside the bands assigned

to component RATs provides the CPC service, and (2) in-band CPC, which uses a transmission mechanism (e.g., a logical

channel) within RATs of the heterogeneous radio environment

to provide the CPC service.

This paper studies the use of a wireless billboard channel

(WBC) as a downlink, out-band CPC for providing relevant

information to MTs, allowing them to switch to the most

appropriate technology and frequency for the required service in

a cognitive networking environment. First some background is

presented to show how WBC technology is suited to the

requirements of a CPC and then a WBC/CPC system

architecture is set out in some detail. This is followed by a

description of a testbed or prototype platform implementation based on the digital video broadcasting-handheld (DVB-H) link

2012 2nd Baltic Congress on Future Internet Communications

978-1-4673-1671-2/12/$31.00 ©2012 IEEE 19

and physical layers together with the presentation of some

extracted results. Finally, the conclusion lists the main

WBC/CPC research achievements deriving from this work.

II. WBC AS A COGNITIVE PILOT CHANNEL ENABLER

The WBC concept [6] is based on a novel infrastructural idea,

particularly matched to maximizing the efficient and economic use of the massive, and ever-growing, range of wireless

communication interfaces and services. It is in harmony with

realizing the user-driven ‘always best connected and best

served’ (ABC&S) communication paradigm, in which the

mobile user (MU) is not constrained to any particular access

network provider (ANP) and may use any available service

through any available access network. In this regard, the users

are turned into consumers as they are free to choose what is

'best' for them, i.e., the service and the access network they

consider as best match to their needs at any time and/or place.

Taking into account the large number of wireless services

available to MUs, an efficient and flexible mechanism is needed for: (i) service providers (xSPs) to advertize their wireless

services, (ii) MUs to discover favorite services and their updates,

and (iii) MTs to associate with access networks and servers. The

WBC is a novel solution for the above tasks, i.e., for services’

advertisement, discovery, and association (ADA) [7, 8].

WBCs are defined as narrowband, unidirectional (downlink),

and point-to-multipoint (P2MP) broadcasting channels, operated

by non-ANP WBC service providers (WBC-SPs) and used to

push wireless service advertisements simultaneously to a large

number of MTs [6]. This ‘pushing’ is a wireless background

action, normally transparent to the mobile user; in that sense very different from (usually unsolicited) SMS service and

product advertisements. A MT background WBC application,

filtering through received service descriptions (SDs) following

policies based on the user profile, terminal profile, and user

location, will create effectively user-profile-driven priority

choice lists of “best” service and service providers for the user’s

teleservice needs. In a live cognitive network environment, participating

cognitive radio service providers (xSPs) –e.g., spectrum brokers– register their SDs, which comprise a list of service attributes, with the relevant WBC central registries via a web portal alike. The registry operated by any WBC-SP broadcasts all collected SDs in turn, repeatedly and according to agreed transparent structures, on their WBCs to MTs.

Details on the SD structure –format, encoding and service templates– are elaborated in [6]. Services are split in two main categories – access network communications services (including cognitive network services) and teleservices (e.g., information services, entertainment services, education services, m-commerce services, location-based services, etc).

Broadcast technologies, both terrestrial and satellite, are potential candidate carrier platforms for WBCs. Among these,

the DVB-H –a digital standard for broadcasting video, audio,

and multimedia datasets to portable and battery-limited MTs by

employing the IP-datacasting (IPDC) technique– has a great

potential to be exploited effectively in creating a WBC system.

To check the feasibility of using a ‘WBC over DVB-H’ system

as a CPC enabler, a prototype architecture was designed and

evaluated by means of a hybrid software/hardware testbed. This

is the subject of this paper.

III. ‘WBC/CPC OVER DVB-H’ SYSTEM ARCHITECTURE

The designed system prototype was developed along three

layers [8-11]: a service layer, a link layer, and a physical layer

(Fig. 1).

ADP Server

OFDM 2K 4K 8K

DVB-H Modulator

Construct MPE-FEC

frame

4K OFDM 2K 4K 8K

Extract data from

MPE-FEC frame

4K

MT

Middleware

ADP APIs

DVB-H Demodulator

Publish/Submit SDs

Fixed-size segment objects

(JSR 272)

Add UDP and IP headers

TS TS

SDs

Fixed-size segment objects

(JSR 272)

Service Providers

(xSPs)

Mobile Users

(MUs)

Physical Layer

Link Layer

Service Layer

Service Enabler

Sublayer

Application Enabler

Sublayer

WBC/CPC SP MT

Multi-Agent

Middleware for

collecting, clustering,

scheduling, indexing

of SDs

Remove UDP and IP headers

Figure 1. The ‘WBC/CPC over DVB-H’ layered architecture.

On the WBC/CPC service provider (WBC/CPC SP) side, the

service descriptions (SDs) are processed as follows. At the

service layer, the SDs submitted by the corresponding service

provider are first collected, clustered, scheduled, and indexed by

a content server, and the output is captured by a advertisements

delivery protocol (ADP) [9] server for subsequent UDP/IP

packets generation. At the link and physical layers, the IP

packets are encapsulated into transport streams (TSs) and

broadcasted on the channel by a DVB-H modulator.

On the mobile terminal (MT) side, the SDs are processed in

reversed order, as shown in Fig. 1. A generic consumer mobile

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application for receiving and processing of SDs on MTs was

designed as described in [8]. Through this application, the

cognitive network service advertisements –sent as part of the

access network communications service advertisements–

become a background activity. That is, the data is captured,

filtered, analyzed and processed according to individual user’s/MT’s policies.

IV. SERVICE LAYER

This layer is concerned with the organization of service

advertisement data and IPDC, and consists of an application

enabler and service enabler sublayers [10].

A. Application Enabler Sublayer

A heterogeneous software architecture combining an

enterprise application environment and an agent execution

environment [11] is used for facilitating the service descriptions’

collection, clustering, scheduling, indexing, and broadcasting.

1) Service Description Model

Each SD consists of a set of attributes, such as service type,

scope list, length, QoS, and attribute list. In [6], the abstract

syntax notation's packet encoding rules (ASN.1-PER) were

adopted as most suitable to describe the SDs [7].

To integrate the ASN.1-PER scheme into the service layer, an

ASN.1-PER encoder/decoder was developed and used for

transforming the SD Java objects into PER octets (and vice

versa).

2) SD Collecting, Clustering, Scheduling, and Indexing

Schemes

SDs are grouped into fixed-size segments for broadcasting

over the channel. Each segment is made up of a number of SDs

of same type; this facilitates the efficient filtering, caching,

comparison and selection of favorite services (e.g., access

networks, spectrum vacancy, RAT occupancy in the area, etc)

by MTs/users (these actions are performed transparently to the

user by software agents installed on the mobile terminal based

on information stored in the user profile). For optimizing the

access time, the time scheduling of segments/SDs broadcasts

should follow the client access pattern.

B. Service Enabler Sublayer

The IPDC technology plays an important role in P2MP IP broadcasting systems. Several reliable and unidirectional packet-level forward error correction (FEC) schemes have been developed recently such as the file delivery over unidirectional transport (FLUTE), FCAST, etc. However in addition to being complex, these schemes use extra meta-data and produce a significant overhead; thus they were considered unsuitable. To facilitate the IPDC in WBC/CPC, a lightweight advertisement delivery protocol (ADP) [9] was developed, based on the asynchronous layered coding (ALC).

Each data segment is split into a number of ADP messages,

which are subsequently encapsulated into UDP/IP datagrams.

Thanks to the efficient ASN.1 formatting used for ADP

messages, the size of the ADP header is only 8B compared to

the 44B header in FLUTE and the 60B header in FCAST. Thus

our protocol, ADP, was found as more efficient also in

minimizing the associated overhead [10].

C. Service Layer Implementation

A set of open-source tools/APIs has been used for the

implementation of this layer [11]. The resultant Java 2

Enterprise Edition (J2EE) / MAS architecture is depicted in Fig.

2 and described in [10].

V. LINK LAYER

The core elements here are the multi-protocol encapsulation – FEC (MPE-FEC) encoder, the MPE encapsulator, the transport stream (TS) generator, and the time slicer [9]. Each MPE-FEC frame carries a number of data segments.

To improve decoding efficiency, we use an 8-byte smart

correct segment index table (CSIT) inserted at the end of the IP

section of the MPE-FEC frame. In addition, a novel MPE-FEC

cross-layer smart decoding technique was elaborated and

successfully implemented, whereby the MPE-FEC interacts with

the ADP protocol for improving the decoding efficiency.

HTML / WML / Applet

WEB MVC

Service Discovery and Maintenance Tier

WEB Application

Context

O/R Mapping DAOMail

Remote / Local Service Builder

Local/Remote

POJO APIs

Portlet API

(JSR-168)

Business Logic

APIs

Common

APIs

Shared

Ontology

APIs

WBC AOP

Application Tier

WBC Rule

Engine

IoC Container

MAS Container Tier

Shared

Blackboard

..

....

Collecting

Container

.....

....

Clustering

Container

.....

....

Scheduling

Container

.....

....

Indexing

Container

...

Yellow Page

Services

Main WBC

Container

MC

Gateway Agent

DB

WEB Service

Rule

Engine

APIs

IPDC

APIs

Collecting APIs

Scheduling APIs

Indexing APIs

Clustering APIs

RulesBroadcasting

APIs

Figure 2. The J2EE/MAS service layer’s architecture.

21

A. Hardware Implementation

A UDcast real-time DVB-H encapsulator (IPE-10) and a DVB-

H analyzer (GOLDENEAGLE) were chosen for the hardware

implementation of the link layer. IPE-10 includes all standard

DVB-H link layer’s functionalities and in addition provides a

novel solution for IP encapsulation management, bandwidth

allocation, QoS enforcement, and statistical channels

multiplexing. GOLDENEAGLE is a DVB-H reception

equipment, which provides real-time MPE-FEC frame analysis

and monitoring the non-nominal behavior of the DVB-H system

to help find potential problems.

B. Software Implementation

GOLDENEAGLE only supports the standard DVB-H section

erasure (SE) decoding algorithm. Thus, we implemented our

own cross-layer smart decoding algorithm (in software) in order

to be able to conduct performance simulation experiments. The

link layer software testbed was designed and implemented in

C++. The functional model of the encoder/decoder is presented in [9].

VI. PHYSICAL LAYER

This layer is based on the DVB-T standard with the following

three additional DVB-H features:

Transmission parameter signaling – used to enhance and

speed up the service discovery;

4K mode – offering an additional trade-off between the

single-frequency network cell size and mobile reception

performance;

In-depth symbol interleaving – for improving the

robustness in mobile environments and impulse noise conditions.

A. Hardware Implementation

An Audemat DVB-H transmitter (EMAA) and Teamcast

DVB-H portable demodulator (POD-1100) were used for the

physical layer’s hardware implementation. EMAA is a fully

DVB-T/DVB-H compliant modulator, which supports ASI and USB TS stream input, and RF and intermediate frequency

signals output. POD-1100 is a potable USB DVB-H

demodulator, which uses a new generation DIBCOM DVB-H

chipset and supports 5-MHz, 6-MHz, 7-MHz, and 8-MHz RF

channels.

B. Software Implementation

The transport stream packet error rate (TSPER) in real

dispersive wireless environments is an important criterion to

define the system parameters, such as the optimal IP packet

length, the segment size, and the SDs data organization scheme.

A software physical layer testbed was built based on the ETSI-

EN-300-744 standard by using Matlab on Linux platform, as

described in [11].

VII. RESULTS

The development of the ‘WBC/CPC over DVB-H’ system prototype followed the personal software process methodology.

An experience repository database was used to store all

development experiences. A test-driven development and feature

driven development methods were employed to plot the three-

layer system architecture into a set of unit functional models

(features), such as the login model, the SDs encode/decode

model, the SDs organization model, the history log viewer

model, and the DVB-H broadcast/receive model. For each unit

model, unified modeling language (UML) diagrams for

corresponding interfaces were first elaborated. Then each

interface was fully implemented and a unit testing was

performed.

A. WBC/CPC SP Node

Fig. 3a shows the hardware equipment rack of the

WBC/CPC SP node consisting (top-down) of: an UDcast IPE-10,

an ADP server (IBM ThinkPad), a SHUNRA Internet simulator,

an UDcast GOLDENEAGLE, an Audemat ETAA modulator,

and a WBC/CPC content server. Fig. 3b and Fig. 3c show the WBC/CPC portal’s web pages with the following tabs (only the

last two are shown in these figures): (i) a MAS tab for

maintaining the JADE environment, (ii) a portal tab used for

starting/stopping the Java EE distributed environment and

recording log-information for the entire system, (iii) an APP tab

as an entrance to the WBC/CPC portal, and (iv) a send tab with

a remote control panel to control the ADP server to broadcast

data segments/SDs in a carousel way.

B. Mobile Terminal (MT)

Fig. 3d shows the user’s WPAN hardware equipment

including (top-down): a WBC/CPC center, a HTC mobile phone,

an Android Google phone, and a POD-1100 receiver. Fig. 3e

shows the WPAN server-side application with two tabs: (i) a

receive tab, which controls remotely POD-1100 to receive the

broadcasting dataset via the channel; (ii) an APP tab for the

lightweight WBC/CPC server (developed with GWT). Fig. 3f

depicts the developed Android mobile application. An Android-JADE gateway facilitates communication between the Android

Google phone and the WPAN.

C. Performance Simulation Results

The system performance was evaluated by means of a

software testbed. The simulation runs in offline mode. On the WBC/CPC SP node, the output of the service layer (resp. link

layer) is first saved in a binary file, which then serves as an input

to the link layer (resp. physical layer). On the terminal side, the

physical layer’s (resp. link layer’s) output is saved in a binary

file as an input to the link layer (resp. service layer).

22

(a) (b)

(c) (d)

(e) (f)

Figure 3. The ‘WBC/CPC over DVB-H’ system and GUI: (a) WBC/CPC SP’s rack; (b) WBC/CPC portal’s web page for traffic monitoring;

(c) WBC/CPC portal’s web page for broadcasting; (d) mobile user’s WPAN; (e) WPAN service-side GWT application; (f) Android mobile application.

23

(a) (b)

(c) (d)

Figure 4. Performance simulation results: (a) TSPER; (b) IPER; (c) SER; (d) Mean segment access time.

The physical layer’s TSPER, the link layer’s IP packet

error rate (IPER) and segment error rate (SER), and the

service layer’s mean segment tuning time and access time

were the main criteria used for performance evaluation of the

system [10].

1) Physical Layer The obtained simulation results in Fig. 4a illustrate how the

TSPER performance degrades with increasing the Doppler

frequency (fD) and decreasing the signal-to-noise ratio (SNR).

24

2) Link Layer The IPER and SER simulation results are shown in Fig. 4b

and Fig. 4c, respectively. The following observations could be

made:

Doppler effect: IPER and SER increase with increasing

the Doppler frequency. Thus, in order to achieve IPER

(resp. SER) less than 1% for fD=80Hz, the received SNR should be about 1.2-2.5 dB higher than that for

fD=10Hz.

Cross-layer smart decoding effect: Our cross-layer

smart MPE-FEC decoding algorithm works with smart

section erasure (SSE) decoding and ADP (packet

erasure) to improve error protection in the link layer.

The results show that, for IPER (resp. SER) less than

1%, the gain is about 0.6-1dB if using our SSE scheme

instead of the standard SE scheme for fD=10Hz, and

about 1-2dB for fD=80Hz.

3) Service Layer

Packet erasure with byte error decoding effect: For IPER (resp. SER) less than 1%, the gain is about 0.5-

1dB comparing to SSE in the link layer.

Access time: The simulation results in Fig. 4d prove

that our data organization algorithm is more efficient

than the classic broadcast disks algorithm [13].

VIII. CONCLUSION

The real possibility of realizing an out-band cognitive pilot channel (CPC) through use of wireless billboard channels (WBCs) has been proposed and presented in this paper. The prototype testbed WBC/CPC example utilizes a digital video broadcasting – handheld (DVB-H) carrier. The design and development of the corresponding experimental testbed have been described. The main research achievements could be summarized as follows:

A foundational WBC/CPC infrastructure was developed;

A WBC/CPC three-layer system architecture was

designed, implemented, tested and verified;

A WBC/CPC multi-tier service-layer software

framework was designed and implemented;

A potential WBC/CPC carrier (i.e. DVB-H) was studied,

and successfully simulated and demonstrated. A new cross-layer smart decoding algorithm was developed

and evaluated;

Novel schemes for SD encoding/decoding, collecting,

clustering, scheduling, indexing, and IPDC broadcasting,

along with discovery and association algorithms were

elaborated;

The end-to-end advertisement, discovery and

association (ADA) processing has been successfully

tested for different type of services.

Next step is to integrate and test the ‘WBC/CPC over DVB-

H’ system prototype in a fully operational cognitive networking

environment.

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