Simulation study of IEEE 802.16a broadband wireless access network

2006:045 CIV

M A S T E R ' S T H E S I S

Simulation Study of IEEE 802.16a Broadband Wireless Access Network

Fadi Dak Elbab Johan Fornander

Luleå University of Technology MSc Programmes in Engineering Computer Science and Engineering

Department of Computer Science and Electrical Engineering Division of Computer Science

2006:045 CIV - ISSN: 1402-1617 - ISRN: LTU-EX--06/045--SE

Simulation Study of IEEE 802.16a Broadband Wireless Access Network

Mhd Fadi Dak Elbab Johan Fornander

Luleå University of Technology

Dept. of Computer Science and Electrical Engineering

December 5, 2005

R ^{ESUMEN EN} E ^SPAÑOL S PANISH SUMMARY

PFC

Luleå Tekniska Universitet, Suecia Tutor del proyecto: Kaustubh Phanse 5 de Diciembre de 2005

Simulación del Estándar 802.16a Acceso a los Redes Inalámbricas de banda ancha

Introducción

La arquitectura inalámbrica de la banda ancha está siendo estandartizada por el grupo de trabajo IEEE 802.16 y sistemas WiMAX World Interoperability for the Microwave Access". El grupo de trabajo de 802.16a desarrolla estándar para las capas física PHY y la capa MAC, así como para el sistema de seguridad y el modulo de la capa red. El desarrollo de estos estándares para el Acceso Inalámbrico de la Banda Ancha BWA" de los sistemas punto-multipunto es encima de 10 GHz, después de eso desarrollaron para el 802.16 la banda autorizada entre 2 -11 GHz incluyendo las bandas no autorizadas alrededor 5.8GHz. Un sistema de IEEE 802.16 consiste en una Estación Base BS y una o varias Estaciones de Suscriptor SS. En la link de bajada downlink" (desde la BS hacia SS) el sistema opera con múltiplexación división del tiempo TDM, y en la subida uplink"

todos los SSs comparten la capacidad del link a base de la demanda. El nuevo estándar puede ofrecernos alta velocidad de acceso a Internet in nuestras casas, ocinas de trabajo con sistemas inalámbricos, donde la estación base BS puede manejar a miles de estaciones subscritores soportándoles los siguientes servicios:

• Sistemas de voz

• Voz sobre IP

• TCP/IP

• Usos con exigencias diferentes QoS

Objetivo del Proyecto

El objetivo del proyecto es simular el estándar 802.16 versión (a) en GloMoSim el sim- ulador de redes inalámbricas, sabiendo que existe solo una primera simulación de este estándar en Irlanda, nuestro trabajo era validar y estudia esta existente versión y luego extenderla añadiendo mas funciones que cubren el funcionamiento del estándar e imple- mentar el modo GPSS que veremos a continuación y así tendremos una nueva versión, la simulación está basada en tres partes:

• Estudio teórico del estándar 802.16a

• Implementar el estándar en GloMoSim

 Programando en C

• Simulación y resultados

Estándar 802.16a

El protocolo 802.16 esta enfocado a las dos capas de PHY y la MAC, con lo que vamos a explicar a continuación:

La Capa MAC

Es la interfase entre la capa superior que es la capa de red y la capa inferior que es la física. El estándar está diseñado para suportar servicio entre la estación base BS y las estaciones subscritoras SS.

El protocolo de MAC es conexión orientada. Todas las transmisiones de información ocurren en el contexto de conexiones. Cada ujo de servicio está asociado a una conexión y la conexión está asociada con un nivel de QoS. Las conexiones son unidireccionales y son identicadas por el código de identicación CID de 16 bites.

Las conexiones en la dirección (downlink) son unicast o multicast mientras las conex- iones en la dirección uplink son siempre unicast. Durante la inicialización de un SS, tres conexiones particulares son establecidas en ambas direcciones.

• Conexión Básica se usa para los mensajes críticos iv

• La Conexión de Dirección Primaria

• La Conexión de Dirección Secundaria se usa para mensajes de dirección de las capas más altas y datos de conguración del SS

Los mensajes sobre la Conexión de Dirección Secundaria viajan en paquetes IP, donde cada SS viene con una dirección de MAC única de 48 bits. Esto simplemente sirve como un identicador de una maquina, durante la inicialización cada SS también es asignado como IP la dirección por el medio DHCP. En nuestro proyecto nos concentramos en la capa MAC y en la Calidad de Servicio (QoS) la ventaja que ofrece el estándar IEEE 802.16a.

Subcapas de la MAC Mac tiene tres subcapas:

• La primera es Convergence Sublayer que es la interface entre las capas de arriba y de abajo hacienda conexión a través de CS-SAP convergente sublayer service access point".

• La segunda es MAC Common part Sublayer la que nos da las funciones vitales de la capa MAC.

• La tercera es Privacy Sublayer la que se ocupa del sistema de seguridad y autenti- cación y encriptación.

La subcapa de convergencia de paquete ofrece 3 modos básicos:

• IP especico: Este se usa para llevar IP, suporta IPV4, IPv6 y las variantes IP móviles

• IEEE Std 802.3/Ethernet Parte Especica: Esto se usa para llevar 802.3 de Ether- net a través 802.16a

• IEEE Std 802.1Q-1998 VLAN parte especica: Esto se usa para llevar 802.1Q VLAN

Clases de Servicio de Planificación

El IEEE 802.16 MAC dene varias clases de servicio de planicación, las estaciones de suscriptor pueden establecer conexiones que usan la clase de servicio de planicación el que es más conveniente para las aplicaciones. Cada SS negocia sus acuerdos de servicio con el ancho de banda durante la conexión del sistema. El ancho de banda se asigna en el mapa de uplink para los SSs.

Varias clases de servicio de planicación denidas enIEEE 802.16 son:

• Unsolicited Grant Service (UGS):

UGS es la clase de servicio ideal para usos como E1/T1 y aquellos usos que generan el traco constante CBR como VoIP.

• Real Time Polling Service (rtPS):

El servicio que sondea en tiempo real asegura que el SS consigue oportunidades de petición de ancho de banda periódicas. El SS entonces puede solicitar BW. Es ideal para usos que de vez en cuando generan paquetes variables. Ejemplos es MPEG.

• Non-Real Time Polling Service (nrtPS):

Está diseñado para los usos que necesitan altas conexiones de BW y no tienen retrasos sensibles, por ejemplo, la transferencia de archivo FTP.

• Best eort (BE):

En este servicio ningún rendimiento o garantías de retraso son necesarios, ejemplos HTTP.

Asignación del BW Hay dos modos para SS:

• Conceder por Conexión (GPC):

La estación base concede el BW a una conexión, sobre todo conveniente para pocos usuarios por estación de suscriptor, permite a la estación de suscriptor mas simple.

• Conceder por Estación de Suscriptor (GPSS):

La estación base concede BW a la estación de suscriptor, SS que redistribuya la BW a sus conexiones, con "Algoritmos y planicación" el mantenimiento QoS, es conveniente para muchas conexiones por terminal. Este modo esta implementado en nuestro proyecto.

Capa Física (PHY)

En Los sistemas de IEEE 802.16 el objetivo que PHY funciona en la gama de 2 - 11 GHz, está diseñado para Non line of Sight, la tasa de bits es 1.0 a 75 Mbps. Las modulaciones que podemos usar son:

• QPSK, 16QAM, 64QAM, (256QAM)

• Solo portadora

• OFDM 256 Subportadores

vi

Global Mobile Information System Simulator GloMoSim

Este simulador fue diseñado para ser extensible, los protocolos de comunicación de redes inalámbricos están divididos en capas cada una con su propio API (access point interface).

Con sólo estos API'S los modelos de protocolos en una capa actuaran recíprocamente con la capa mas abajo o mas alta. En el ambiente militar y comercial los problemas de diseño de alto nivel de la infraestructura de comunicación digital son muchos:

• La escala es grande.

• El tráco de Red es una mezcla de voz(voto), datos e imágenes.

• La Conectividad puede cambiarse dinámicamente de modos imprevisibles y las calidades de exigencias de servicio son a menudo severas.

Es un simulador de base de biblioteca secuencial y paralela para redes inalámbricas, está diseñado como módulos de bibliotecas, cada uno simula un protocolo inalámbrico de comunicación especíco. La biblioteca ha sido desarrollada usando PARSEC, una lengua de simulación basada en C-parallel.

Uno de los objetivos de este proyecto es estudiar la biblioteca GloMoSim (el Simulador de sistema Global Móvil) con la adopción de un protocolo recién escrito para el estándar 802.16a.

Es relativamente fácil poner en práctica nuevos protocolos para añadir al los protoco- los existentes. El problema principal con GloMoSim es que este carece de documentación, y entonces la codicación y la programación del estándar están hechas sobre la base de error y una prueba.

En Dublín el estándar fue desarrollado, usando esta versión y después de validarla se hizo una extensión del código existente principalmente en el directorio de la capa MAC.

Todos los protocolos usan los mismos métodos de comunicarse con las capas de Internet de encima y debajo. Esto es lo que hace el diseño de simulador cuando esto viene a la agregación de protocolos en una base modular. Este nuevo código debía ser mejorado y añadido la funcionalidad suplementaria en la conformidad al IEEE 802.16-2003 (802.16a).

Simulación y Resultados

Haciendo escenarios de redes inalámbricas muy simples podemos notar que el estándar 802.16 funciona en Glomosim, y mirando a nuestros resultados que vienen al nal pode- mos notar que la nueva versión del estándar 802.16a funciona correctamente y extendida como ya hemos mencionado antes, para mas detalles pueden consultar el capitulo 5.

Limitaciones

Las simulaciones fueron controladas con algunas limitaciones, ante todo dieron al archivo de conguración que analiza la función las opciones de QoS. Con esto, el simulador

compensaba la posibilidad para cada nodo para tener un uso de BW de 40, 60, y el 80 por ciento. Estos eran las limitaciones de las simulaciones que los autores establecen ellos mismo. Otras limitaciones vinieron de las diferencias de arquitecturas entre el documento 802.16a-2001 y su correspondencia del módulo GloMoSim.

viii

A ^BSTRACT

This master's thesis focuses on the part of the IEEE 802.16 standard which has the title Air Interface for Fixed Broadband Wireless Access Systems". This part, the IEEE 802.16a amendment, is only one of many amendments to the 802.16 standard, and this one presents a set of rules for how a wireless network with xed nodes behaves.

The aim of the project is to simulate the use of Quality of Service" (QoS) ows in a 802.16a network using the Global Mobile Information Systems Simulation Library"

(GloMoSim) environment. Based on a previous master's thesis [1], the work presented here tries to extend the existing code structures to implement QoS ows inside the ex- isting 802.16a GloMoSim module derived from the earlier thesis.

P ^REFACE

We would like to express our deepest gratitude to our supervisor Dr. Kaustubh Phanse, and thank him for his invaluable guidance, support, and his patience.

Mhd Fadi Dak Elbab Johan Fornander

C ONTENTS

Chapter 1: Introduction 1

1.1 Introduction . . . 1

1.2 802.16 standards . . . 2

Chapter 2: Thesis background 3 2.1 Broadband Wireless Access . . . 3

2.2 The IEEE 802.16 Wireless MAN Standard . . . 3

Chapter 3: The 802.16a standard 5 3.1 The 802.16a standard . . . 5

3.2 MAC layer . . . 5

Chapter 4: Methodology 23 4.1 Introduction . . . 23

4.2 Global Mobile Information System Simulator (GloMoSim 2.03) . . . 23

4.3 Layer architecture . . . 24

4.4 Simple APIs . . . 24

4.5 Installing GloMoSim on Slackware 10.2 . . . 27

4.6 Extended implementation of GloMoSim . . . 30

4.7 The Irish model . . . 30

4.8 The authors' model . . . 30

Chapter 5: Results 33 5.1 Overview of the 802.16a GloMoSim module . . . 33

5.2 Simulation results . . . 34

5.3 Interpreting the simulation output . . . 37

Chapter 6: Conclusions and discussion 41 6.1 Achievements . . . 42

6.2 Areas of discussion . . . 43

Chapter 7: Future work 45 7.1 Physical layer, frame implementation in 802.16a . . . 45

7.2 GloMoSim Application layer extension . . . 45

7.3 Documentation of critical GloMoSim parts . . . 46

7.4 Security models . . . 46

List of abbreviations : 47

Appendix A:Application layer configuration 51

Appendix B:The work flow of the QoS mechanism 53

xiv

L IST OF F IGURES

1.1 Example of an 802.16a implementation . . . 2

3.1 802.16a Reference model. . . 7

3.2 MAC PDU . . . 7

3.3 Generic MAC header for the generic MPDU. . . 8

3.4 The bandwidth request header. . . 9

3.5 The grant management subheader for UGS. . . 9

3.6 Management sub-header format used for connections using the rtPS, nrtPS, or BE scheduling service. . . 10

3.7 A fragment subheader is added at the start of a payload. . . 10

3.8 Typical fragment sub-header. . . 10

3.9 Diagram of the packet sub-header. . . 11

3.10 Range of Connections Supported With 802.16a. . . 12

3.11 Various frame formats with 802.16a. . . 13

3.12 Extended fragmentation sub-header that is used when ARQ is enabled. . 13

3.13 ARQ feedback structured. . . 14

3.14 GPC mode. . . 15

3.15 GPSS mode. . . 16

3.16 GPSS requests handling. . . 16

3.17 Bandwidth request message. . . 17

3.18 Synchronization scheme for a typical subscriber station. . . 18

3.19 Adaptive PHY. . . 19

3.20 FDD Downlink subframe. . . 20

3.21 TDD downlink subframe. . . 20

3.22 Time division duplexing TDD. . . 21

5.1 The simple layout of the simulation scenario. . . 35

5.2 Typical initial output lines when running a 802.16a simulation. . . 37

5.3 output showing the BS preparing to send a control message. . . 38

5.4 Simulation output showing packet arriving from network layer and being classied as coming from the CBR client/server. . . 38

5.5 Simulation output showing packet arriving from network layer and being classied as coming from the FTP client/server. . . 39

5.6 Simulation output showing the sending of packets. . . 39

6.1 The relationship between the standard and the implementation of it in GloMoSim. . . 41

B.1 Flow chart describing the QoS mechanism. . . 54

2

C ^HAPTER 1 Introduction

1.1 Introduction

The broadband wireless architecture is being standardized by the IEEE 802.16 Working Group (WG) and the World Interoperability for the Microwave Access (WiMAX) forum.

The 802.16a WG is developing standards for the Physical (PHY) and MAC layers. The new standard 802.16a provides services for metropolitan area network (MAN). Standards development for broadband wireless access (BWA) point to multi-point systems above 10 GHz, after that they develops amendments to 802.16 for operation on the licensed band 2GHz - 11GHz including the unlicensed bands around 5.8GHz. This amendment is known as IEEE 802.16a. An IEEE 802.16 system consists of a Base Station (BS) and one or more Subscriber Stations (SS). In the downlink direction (from the BS to SS) the system operates in a Time Division Multiplexing TDM. In the uplink all SSs share the link capacity on a demand basis. Figure 1.1 shows us an example in which we can see exactly where the standard 802.16a is implemented.

The new standard can provide us a high speed Internet access for our homes, building and oces, with wireless systems; the base station can handle thousands of subscriber stations supporting the following services:

• Legacy voice systems

• Voice over IP

• TCP/IP

• Applications with dierent Quality of Service (QoS) requirements

2 Introduction

Point-to-point Point-to-point

12345672789 12345672789

Phone line Phone line

63 845672789

802.16 Standard

63 845672789 63 845672789

802.16 Standard

Point-to-Multipoint

Ethernet Wi-Fi

Ethernet

Access point

Home, bussines, or hot spot

Point-to-Multipoint

Ethernet Wi-Fi

Ethernet

Access point

Home, bussines, or hot spot Ethernet Wi-Fi

Ethernet

Access point

Home, bussines, or hot spot

Internet

Fiber Network Internet

Fiber Network

Figure 1.1: Example of an 802.16a implementation

1.2 802.16 standards

• 802.16.1 (10-66 GHz, line-of-sight, up to 134Mbit/s)

• 802.16.2 (minimizing interference between coexisting Wireless Metropolitan Area Networks (WMANs).)

• 802.16a (2-11 Ghz, Mesh, non-line-of sigth)

• 802.16b (5-6 Ghz)

• 802.16c (detailed system proles)

• 802.16e (Mobile Wireless MAN)

C HAPTER 2 Thesis background

2.1 Broadband Wireless Access

Broadband wireless access (BWA) has become the best way as alternative to wired so- lutions oering lower cost of ownership and more exibility, also a high speed Internet connection also voice and video services. BWA oer more capacity in compare with systems installed with cable networks or digital subscriber lines (DSL) also can extend

ber optic networks. One of the most obligation aspects of BWA technology is that networks can be created in just few weeks by deploying a small number of base stations on buildings to create high-capacity wireless access systems.

BWA has had limited scope till now, in part because of the unfound need for a universal standard. While providing such a standard is important for developed countries, it is even more important for the developing world where wired infrastructures are limited.

2.2 The IEEE 802.16 Wireless MAN Standard

The Institute of Electrical and Electronics Engineers Standards Association (IEEE-SA) planed to do that BWA be more extensively available with the new Standard 802.16, which species the Wireless MAN Air Interface for wireless metropolitan area networks.

This standard had been published in April 2002, the standard was created during tow years, by hundreds of engineers from the world's leading operators and companies.

The standard 802.16 addresses the connection in wireless MAN metropolitan area net- works. It focuses to be able to provide using on the bandwidth 10 - 66 GHz and denes a medium access control (MAC) layer that supports multiple physical layer specications adapted for the frequency band in which we want to use.

4 Thesis background

The standard for the bandwidth between 10 - 66 GHz supports trac levels in various licensed frequencies as (10.5, 25, 26, 31, 38 and 39 GHz). It can provide interoperability through devices, and in this way, carriers has the possibility to use products from nu- merous vendors and it could be the availability of lower cost equipment. The plan for the change to 2 to 11 GHz region will support both unlicensed and licensed bands.

C HAPTER 3 The 802.16a standard

3.1 The 802.16a standard

In this chapter the details of the MAC and PHY layer will be discussed.

3.2 MAC layer

3.2.1 Introduction

Media Access Control (MAC) layer is a common interface that interprets data between the upper Data Link layer and the lower Physical layer. 80216a standard employs Time Division Multiplexing (TDM) for downlink communication. Since 802.16a is designed to handle the communication between hundreds of SSs and BS, the ecient use of bandwidth is demanded. The on-demand bandwidth request (from SS) and bandwidth allocation (from BS) makes ecient use of the spectrum. 802.16a MAC also provides high QoS mechanism to support the dierent applications. For applications like video and voice transmission requires low latency but can tolerate some error rate, but for most data transmission zero error rates is necessary while latency is not so critical. The support of multi-PHY layers also gives the vendors large exibility.

The MAC protocol is connection oriented. All data transmissions take place in the context of connections. Every service ow is mapped to a connection and the connection is associated with the level of QoS. Connections are unidirectional and are identied using a 16-bit CID. Connections in the downlink direction are either unicast or multicast while uplink connections are always unicast. During initialization of an SS, three particular connections are established in both directions.

• The Basic Connection is used for short time critical messages.

6 The 802.16a standard

• The Primary Management Connection is used to exchange longer, more delay tol- erant messages.

• Secondary Management Connection is intended for higher layer management mes- sages and SS conguration data.

The messages on the Secondary Management Connection are carried in IP packets.

Each SS comes with an unique 48-bit MAC address. It merely serves as an equipment identier. During the initialization each SS is also assigned as IP address by means of dynamic host conguration protocol (DHCP).

The MAC layer consist of the three sub-layers Convergence Sublayer (CS), Mac Com- mon Part Sublayer (MAC CPS) and Privacy Sublayer.

In this thesis the authors will concentrate on the MAC layer and the QoS support that is provided by IEEE 802.16 standard.

3.2.2 MAC Sublayers

As mentioned before the Mac layer has three sublayers, shown in the reference model Figure 3.1, packets are transmitted through service access point (SAP).

• Convergence Sublayer (CS) This sublayer provides receive and classify PDUs from the higher layer, all mapping of the external data coming from the Common sublayer through its SAP into MAC SDU then classies them with their CID and service ow. Also a payload header suppression it function as can be seen in the standard [2]. There are two CSs: the asynchronous transfer mode (ATM) CS and the packet CS. The rst one provides an interface for ATM services, and the second one provides the classication of the higher layer PDU, mapping and transport all packets like Internet protocol IP, point to point protocol PPP, IEEE 802.3 Ethernet.

• Common Part Sublayer (CPS) This Sublayer provides the core functions of MAC layer using MAC SAP, such as bandwidth allocation, connections and pro- vides high quality of services (QoS) to support transmission of voice and video as VoIP.

• Privacy Sublayer This sublayer provides authentication, encryption of data and security system.

3.2.3 MAC PDU formats and Headers

MAC Protocol Data Units are shown in Figure 3.2, all PDUs should have the same structure, the rst part is Generic MAC Header, then the following is Payload of the MAC PDU, as seen in Figure 3.2, and is optional. MAC PDU headers have two parts;

the rst one is Generic MAC header and the second is the Bandwidth Request Header, this is to request additional BW.

3.2. MAC layer 7

Figure 3.1: 802.16a Reference model.

Generic MAC Header Payload (Optional) CRC (Optional)

msb lsb

Generic MAC Header Payload (Optional) CRC (Optional) Generic MAC Header Payload (Optional) CRC (Optional)

msbmsb lsb

Figure 3.2: MAC PDU

8 The 802.16a standard

3.2.4 Generic MPDU Header

Generic MPDU carry management information and CS data, dependent on which con- nection the CID in the header indicated. The Generic MPDU shown in Figure 3.3.

CI

Type

CID MSB

LEN LSB

CID LSB

HCS

LEN MSB (3 bits) EKS

(2bits)

EC

HT = 0

Byte#

1

2,3

4,5

6

reserved reserved

CI

Type

CID MSB

LEN LSB

CID LSB

HCS

LEN MSB (3 bits) EKS

(2bits)

EC

HT = 0

Byte#

1

2,3

4,5

6

Type

CID MSB

LEN LSB

CID LSB

HCS

LEN MSB (3 bits) EKS

(2bits)

ECECEC

HT = 0

Byte#

1

2,3

4,5

6 Byte#

1

2,3

4,5

6

reserved reserved

Figure 3.3: Generic MAC header for the generic MPDU.

If the bit Header Type HT = 0 it means that we have Generic MAC Header If the bit Header Type HT = 1 it means that we have BW Request Header The EC indicates that the frame is encrypted while the CRC indicator (CI) indicates the presence of the optional CRC at the end of the MPDU. To know which key was used to encrypt the frame it will be indicates by EKS Encryption Key Sequence. The rest of eld is dened in the standard [2]. The sub headers are used to implement the signaling necessary for the fragmentation, packing, ARQ and mesh features of the MAC.

3.2.5 Bandwidth Request Header

Each connection has dierent characteristics, depending of these characteristics the PDU can change; in Figure 3.4 we can see the contents of bandwidth request header.

When HT = 1 this indicate that the header is a bandwidth request header as it is shown in Figure 3.4

The CID eld to identify and indicates the connection for which the bandwidth request is made. Thus the bandwidth request does not need to be only for a connection that is specied in the GMH. It can apply to any connection specic to the requesting SS. The other elds are dened according to the standard [3].

3.2.6 MAC SUB-Headers

There are three MAC subheaders: Grant Management subheader, Fragmentation sub- header and Packing Subheader.

3.2. MAC layer 9

Type

CID MSB

LEN LSB

CID LSB

HCS BR MSB

EC = 0

HT = 1

Byte#

1

2,3

4,5

6

Type

CID MSB

LEN LSB

CID LSB

HCS BR MSB

EC = 0

HT = 1

Byte#

1

2,3

4,5

6

Figure 3.4: The bandwidth request header.

3.2.7 Grant Management Subheader

Is used by the SS to convey bandwidth management needs to the BS. Each connection has its class of scheduling service and this subheader will be encoded depending of this type of the UL scheduling service. For example we will suppose that we have a channel that use UGS then the grant subheader format used is shown in Figure 3.5.

………..

bit 7

SI PM

recerved (14bits)

bit 7 bit 6 bit 5 bit 0 ……….. bit 0………..

bit 7

SI PM

recerved (14bits)

bit 7 bit 6 bit 5 bit 0 ……….. bit 0

bit 7

SI PM

recerved (14bits)

bit 7 bit 6 bit 5 bit 0 ………..

SI PM

SI PM

recerved (14bits)

bit 7 bit 6 bit 5 bit 0 ……….. bit 0

Figure 3.5: The grant management subheader for UGS.

Bit 7 Slip Indicator (SI) is used by the SS to inform the BS that the uplink buer servicing a ow has lled up.

Bit 6 Poll Me (PM=1) is used to request that the BS sends a bandwidth poll. In Figure 3.6 we show the format of grant management subheader in case of scheduling services (rtPS, nrtPS or BE):

The piggyback request (16-bit) is number of bytes of uplink bandwidth requested by the SS. The bandwidth request is for the CID [2]. This means that the piggyback request indicate the amount of uplink bandwidth that the SS want to be granted to it.

10 The 802.16a standard

………..

bit 7

piggyback request (16bits)

bit 7 bit 6 bit 5 bit 0

………..

………..

bit 7

piggyback request (16bits)

bit 7 bit 6 bit 5 bit 0

………..

………..

bit 7

piggyback request (16bits)

bit 7 bit 6 bit 5 bit 0

……….. ………..

bit 7

piggyback request (16bits)

bit 7 bit 6 bit 5 bit 0

………..

Figure 3.6: Management sub-header format used for connections using the rtPS, nrtPS, or BE scheduling service.

3.2.8 Fragmentation Subheader

Fragmentation means that we can divide an MSDU in fragments and then transmit them separately. For this a fragment sub-header (FSH) tells the system to divide the MSDU into Fragments. And these fragments subheaders are included at the start of the payload, as shown in Figure 3.7

MSDU Fragment GMH

(6 bytes) FSH

Payload

Optional CRC (4 bytes) MSDU Fragment

GMH (6 bytes) FSH

Payload

Optional CRC (4 bytes)

Figure 3.7: A fragment subheader is added at the start of a payload.

The FSH provides a fragment of an MSDU. The typical FSH is shown in Figure 3.8:

FC (2 bits)

FSN

(3 bits) Reserved

(3 bits) Byte #

1

FC (2 bits)

FSN

(3 bits) Reserved

(3 bits) Byte #

1

Figure 3.8: Typical fragment sub-header.

The Fragment Control (FC) bits indicate the fragmentation state of the payload: 00

= No fragmentation of MSDU 01 = the last fragment of the MSDU 10 = First fragment of an MSDU 11 = Fragment somewhere in the middle of MSDU

The Fragment Sequence Number (FSN) denes the sequence number of the current SDU fragment and it is increases by 1 for each fragment of an MSDU.

3.2. MAC layer 11

3.2.9 Packing Subheader

The MAC layer can combine multiple MAC SDUs into a single MAC PDU. We have tow situations the rst one is if we have on a connection with variable-length MAC SDUs packed PDU contains a subheader for each packed SDU and the second one if we have on connections with xed length MAC SDUs then we do not need packing subheader.

A packing sub-header is shown in Figure 3.9 an MPDU can contain multiple packing sub-headers:

Length (3 bits) FC

(2 bits) FSN (3 bits) Byte #

1,2

Length (3 bits) FC

(2 bits) FSN (3 bits) Byte #

1,2

FC (2 bits)

FSN (3 bits) Byte #

1,2

Figure 3.9: Diagram of the packet sub-header.

Since an MSDU can be divided into many fragments and then transmitted in packed frames, this will make enable the BS to provide a better use of the available slots and the channel.

The eld of the packing subheader is the same as for fragmentation as such; the Fragment Control (FC) bits indicate the fragmentation state of the payload:

00 = No fragmentation of MSDU 01 = the last fragment of the MSDU 10 = First fragment of an MSDU 11 = Fragment somewhere in the middle of MSDU

The Fragment Sequence Number (FSN) denes the sequence number of the current SDU fragment and it is increased by 1 for each fragment of an MSDU.

3.2.10 MAC Connections

First of all we have to know that the service of Mac layer is connection oriented, the idea in which the connection will be received is that each connection has its QoS parameters and this connection will be serviced by a scheduling service (here we have our four scheduling services). Each connection has its own CID, code identier of the connection; this CID will be assigned by the BS when the connections will be established. All connections are unidirectional and identied by its CID.

Mac connections could be classied by Management and Transport connections, the

rst type Management connection is where all management messages will be carried and these connections will be established before the transport connections when a SS wants to establish connexion with the BS for the rst time in the registration phase, the second

12 The 802.16a standard

type Transport connections is where all others trac messages will be carried like data messages.

In the setup phase when SS wants establish the connection with the BS primary and secondary management connections are setup, here BS assign the CIDs to the connections and its numbers (m). Now SS can set up its transport connections and these transport connections will be able to carry all Service Flows.

Figure 3.10 shows the connections range

Name CID Comment

Initial Ranging 0x0000 This CID is used by a station performing initial ranging. Its use in a RNG-REQ message informs the BS that it initial ranging being performed, rather than periodic ranging of an already attached station.

Basic 0x0001 -m Each SS is assigned a basic CID, it is used for low level delay intolerant management messages such a ranging or burst profile updates.

Primary Management

m+1 – 2m Each SS is assigned a primary management CID. This connection carries most of the remaining delay tolerant management messages.

Transport and Secondary management

2m+1 – 0xFEFE

Each SS is assigned a Secondary management CID. This really a special transport channel that is used to carry IP traffic used for device management. The management IP stack used only for device management and is separate from the typical user IP stack that might reside above the MAC layer in the main data path of the system. Other transport connections are allocated is this space. They are created and destroyed as result of

“MAC_CREAT_CONNECTION” and “MAC_TERMINATE_CONNECTION” messages at the MAC service interface.

AAS Initial Ranging

0xFEFF This initial ranging CID is used when as AAS (Advanced Antenna System) capable SS is ranging.

Multicast polling CIDs

0xFF00- 0xFFFD

Bandwidth access for uplink multicast connections is generated via polls sent on these CIDs. Each multicast group is assigned one of these CIDs as the place to listen for polls that grant uplink access.

Padding CID 0xFFFE This CID is used when sending padding data

Broadcast CID 0xFFFF This CID is used to transmit broadcast data to all the SSs in a system. Downlink information including DL_MAPs, UL_MAPs, burst profiles and beacon information is transmitted on this CID.

Figure 3.10: Range of Connections Supported With 802.16a.

Some frame formats are shown in Figure 3.11, these frame formats could be contained in a payload in a transport connection like Mac service data unit (MSDU), fragments of MSDUs, packing and ARQ, bandwidth requests or retransmission requests according to the MAC rules on bandwidth requesting, fragmentation [4].

3.2.11 Automatic Retransmission Request ARQ

ARQ is not enabling with 802.16 operating with the 10-66 GHZ frequency band. In sys- tems with ARQ enabled (in which operate with 2-11GHz) If an ARQ request is happened to retransmit blocks by identifying with BSN then:

• The BSN will indicate the rst block in the fragment this is in the extended FSH.

• A fragment is built from an integral number of blocks of an MSDU so the rst block in a fragment will align with the start of a fragment.

3.2. MAC layer 13

Figure 3.11: Various frame formats with 802.16a.

• The PSH is extended when used in an ARQ capable connection so that an 11-bit BSN is used in place of the 3-bit FSN (Figure 3.12). Also we can see through Figure 3.13, a block sequence number (BSN) is used in steed of FSN [4].

BSN (11 bits) FSN

(2 bits) Byte #

1,2

Length MSB (3 bits)

Length LSB (8 bits) 3

BSN (11 bits) FSN

(2 bits) Byte #

1,2

Length MSB (3 bits)

Length LSB (8 bits) 3

Figure 3.12: Extended fragmentation sub-header that is used when ARQ is enabled.

ARQ feedback information can be transmitted as MAC management messages, and these messages can not be fragmented. In Figure 3.13 the ARQ feedback payload is structured is shown:

The ACK maps are a bitmap in which indicate that we have a successful received blocks.

Like this we can know which blocks are received and which we have to retransmit.

3.2.12 Scheduling Service Classes

The IEEE 802.16 MAC was designed with four scheduling services classes. Which we will explain a continuation; this classes are designed to provides us through the subscriber station connections that can use this four classes for our applications. In our thesis

14 The 802.16a standard

BSN (11 bits)

CID (16 bits)

ACK Type (2bits)

number of ACK Type (2bits)

ACK Map (16 bits) Byte #

LAST Only when ACK type != 01

1,2

3,4

5,6

7,8 etc

Repet up to a total of 4 ACK maps as defined in ”number of ACK maps” field BSN

(11 bits) CID (16 bits)

ACK Type (2bits)

number of ACK Type (2bits)

ACK Map (16 bits) Byte #

LAST Only when ACK type != 01

1,2

3,4

5,6

7,8 etc

Repet up to a total of 4 ACK maps as defined in ”number of ACK maps” field

Figure 3.13: ARQ feedback structured.

we implement both them; the idea is that the SS negotiates with the BS. These four scheduling service classes are:

• Unsolicited Grant Service (UGS): This scheduling service class was designed for real time service ows for applications that use a x size of data packets periodically.

This scheduling service class is use for E1/T1 and all applications of voice and video in real time, for example VoIP this is CBR constant bit rate trac, in which it eliminates the overhead and latency of SS requests. UGS was implemented in our thesis.

• Real Time Polling Service (rtPS): This scheduling service class was designed for real time service ows for applications that use a variable size of data packets periodically. The service provides unicast request opportunities to the SS, this service class has more overheads then UGS and is perfect to applications as MPEG.

• Non-Real Time Polling Service(nrtPS): This scheduling service class was designed for designed for non real time service ows for applications that use a variable size data grant burst types. The service provides unicast polls. The application that use this service is FTP.

• Best Eort (BE): This scheduling service class was designed to provide best eort trac, the delay and latency is not specied for application such as Http. BE was implemented in this thesis .

3.2.13 Bandwidth Allocations

There are two modes for SSs:

Grant per Connection (GPC): basically the idea of this mode is that the base station grants bandwidth directly to a connection, this means to individual CIDs, it will

3.2. MAC layer 15

provide a few users per subscriber station; it has higher overhead then GPSS, but allows simpler subscriber station then GPSS. In Figure 3.14 shows us GPC mode.

BS

C1

C2 C3

QoS Schedule

r

SS1

Figure 3.14: GPC mode.

Grant per Subscriber Station(GPSS): In this mode Base station grants bandwidth directly to a subscriber station, and then each SS will re-distribute allocating the bandwidth requested to each connection, this allocating from SS to the connections is done using a scheduling algorithms (which is not present in the standard 802.11a), maintaining QoS and service-level agreements; GPSS allows use too much users per SS in compare with GPC mode but with more complexes and intelligent SSs, also it has less overhead , GPSS was implemented in our thesis as a principal goal. Figure 3.15 shows us GPSS mode and Figure 3.16 shows GPSS requests handling.

Bandwidth Request messages come from the connection, and there are several kinds of requests:

• implicit requests (UGS), negotiated at connection setup

• BW request messages which uses the especial BW request header, requests up to 32 KB with a single message and incremental or aggregate as indicated by MAC header

16 The 802.16a standard

BS SS1

C1

C2

C3

QoS Scheduler

Figure 3.15: GPSS mode.

1

122334455554433667755338855995544664433883355 7733556633

1122334455667788997755776677 7766 227733445533446677

773344775566774444554477 557755 7777222244556677

7766 33227755 77889977334477

5 5 77444455446677 8877665577335577337766 4477 332255 77



 334466773344777733557777

77445577557755 77889977

Figure 3.16: GPSS requests handling.

3.2. MAC layer 17

• Piggybacked request (for non-UGS services only), presented in GM sub-header and always incremental, and it is up to 32 KB per request for the CID

• Poll-Me bit (for UGS services only), used by the SS to request a bandwidth poll for non-UGS services

Figure 3.17 shows the Bandwidth request messages.

Type (6) BR msb (8)

CID msb (8)

HCS (8) BR lsb (8)

CID lsb (8) HT = 1(1) EC = 0(1)

lsb msb

Type (6) BR msb (8)

CID msb (8)

HCS (8) BR lsb (8)

CID lsb (8) HT = 1(1) EC = 0(1)

lsb msb

Figure 3.17: Bandwidth request message.

3.2.14 Request Mechanisms of 802.16a

The SS has to synchronize the BS doing tow mechanism, the rst one is to register and the second one is ranging. Figure 3.18 shows the steps in which the SS synchronizes a BS using the 802.16a.

3.2.15 Registration and Ranging

Registration is a form of capability negotiation, SS sends a list of capabilities and parts of the conguration le to the BS in the REG-REQ message, after that the BS replies with the REG-RSP message BS replies with the REG-RSP message (tells which capabilities are supported/allowed tells which capabilities are supported/allowed). SS acknowledges the REG-RSP with REG-ACK message.

During registration, a new SS registers using the random access channel, and if suc- cessful, is entered into a ranging process under control of the base station. The ranging process is cyclic in nature where default time and power parameters are used to initiate

18 The 802.16a standard

S

SSS SSyynncchhrroonniizzeess BBSS

R

Reeggiissttrraattiioonn RaRannggiinngg

BBSS rreesseerrvveess BBWW

FoForr nneeww SSSS DDeetteerrmmininee RRTTDD ffoorr FoForr eeaacchh SSSS MiMinnii--sslloottss aallllooccaatteedd

aanndd sseenndd ttoo j

jooiinn tthhee nneettwwoorrkk SSSS

SSSS kknnoowwss tthhee ttiimmee ttoo bbee CoCorrrreecctteedd ttoo kkeeeepp iinn S

Syynncchhrroonniizzaattiioonn wwiitthh BBSS

Figure 3.18: Synchronization scheme for a typical subscriber station.

the process followed by cycles where (re)calculated parameters are used in succession until parameters meet acceptance criteria for the new subscriber. These parameters are monitored, measured, and stored at the base station, and transmitted to the subscriber unit for use during normal exchange of data. During normal exchange of data, the stored parameters are updated in a periodic manner based on congurable update intervals to ensure changes in the channel can be accommodated. The update intervals shall vary in a controlled manner on a subscriber unit by subscriber unit basis. Ranging on re- registration follows the same process as new registration.

Contention Slot Allocator (CSA): Decides the usage of each mini-slots in the uplink channel. Used by the BS to dynamically adjust the ratio of the BW allocated to the contention slots and reservation slots, too few contention slots: increase the chances of BW request collision so reduce the amount of data that can be TX, and too many contention slots: reduce BW left for data transmission the output of the CSA denes the BW resources allocated to the CRA and BS
s uplink grants scheduler for collision resolution and scheduling.

Contention Resolution Algorithm (CRA): Denes the utilization of contention slots and the rules used to resolve contention, simple algorithm can be used, because con- tention slots are used for nrt-PS and BE ows. The actual QoS mechanisms such as packet scheduling algorithms for these service ows are left undened in this standard, and we have many of proposes to use.

3.2. MAC layer 19

3.2.16 Physical Layer (PHY)

The IEEE 802.16 PHY targets systems operating in the range of 2 - 11 GHz, is designed for Non Line of Sight, the raw bit rate is 1.0 to 75 Mbps. The modulations are:

• QPSK, 16QAM, 64QAM, (256QAM).

• Single Carrier.

• OFDM 256 Sub-carriers.

In Figure 3.19 the adaptive PHY can be seen:

QPSK

Sub #4 Base Station

Sub #3 QAM 16

Sub #2 QAM 64

Sub #1

QPSK

Sub #4 Base Station

Sub #3 QAM 16

Sub #2 QAM 64

Sub #1

QPSK

Sub #4

QPSK

Sub #4 Base Station

Sub #3 QAM 16

Sub #2

Sub #3 QAM 16

Sub #2 QAM 64

Sub #1

Figure 3.19: Adaptive PHY.

PHY allows use of directional antennas and tow dierent duplexing schemes:

• Frequency Division Duplexing (FDD)

• Time Division Duplexing (TDD)

Figure 3.20 shows the FDD downlink subframe, Figure 3.21 shows the TDD downlink subframe and nally Figure 3.22 shows the time division duplixing TDD frames.

20 The 802.16a standard

Figure 3.20: FDD Downlink subframe.

Figure 3.21: TDD downlink subframe.

3.2. MAC layer 21

Frame j Frame j+1 Frame j+2 Frame j-1

Frame j-2

Downlink Subframe Uplink Subframe

Adaptive

PS 0 PS n-1

.... _{Frame j-2 Frame j-1 Frame j Frame j+1 Frame j+2} ....

Downlink Subframe Uplink Subframe

Adaptive

PS 0 PS n-1

.... ....

Figure 3.22: Time division duplexing TDD.

C HAPTER 4 Methodology

4.1 Introduction

This simulator was designed to be extensible, the wireless networks communication pro- tocols is divided into a set of layers every one with its own application programming interface (API). With only these APIs the models of protocols at one layer will interact with the lower or higher layer. In military and commercial environment a high-level design problems for the digital communication infrastructure are very challenging in a number of dimensions:

• The scale is large

• Network trac is a mix of voice, data and imagery

• Connectivity can change dynamically in unpredictable ways and the qualities of service requirements are often severe

4.2 Global Mobile Information System Simulator (Glo- MoSim 2.03)

Is a library-based sequential and parallel simulator for wireless networks, It is designed as a set of library modules, each of which simulates a specic wireless communication protocol in the protocol stack. The library has been developed using PARSEC, a C-based parallel simulation language [5].

24 Methodology

4.3 Layer architecture

GloMoSim use a layered approach which is similar to OSI, a seven layers network archi- tecture, like the most network systems and standard APIs will be used between these layers:

Application layer: Here there are four class services available:

• CBR (constant bit rate): Class of service dened by ATM, where is need a specic amount of bandwidth such as voice and video also timing is important, it has a high priority level.

• FTP (le transfer protocol): the protocol for exchanging les over internet, works is the same way like http, and it use TCP/IP network trac (tcplib).

• Http (hypertext transfer protocol): the simulation for this application is used to provide the low priority, BE data trac.

• Talent: Is a terminal emulation program for TCP/IP networks such as the internet; it runs on our machine and connects our PC to a server on network.

It will not be simulated.

Transport layer: The transport layer provides two transport protocols:

• UDP (User Datagram Protocol): a connectionless protocol, runs on top of IP networks. It is just used by CBR.

• TCP (Transmission Control Protocol): enables two hosts to establish a con- nection and exchange streams of data, it is used by the rest of applications.

Network layer: This layer implements routing protocols, AODV DSR ODMRP and ZRP, and also in this layer only the protocol supported is Internet Protocol (IP).

MAC layer: This layer has the protocol 802.11, we will explain more about it in our implementation. Also several protocols for the simulation, CSMA, TSMA, MACA, 802.11.

4.4 Simple APIs

Simple APIs between every two neighbouring models on protocol stacks is predened to support their composition. These APIs specify parameter exchanges and services between neighbouring layers. The simplicity of the APIs allows developers to model their protocols rapidly in an independent fashion. The APIs currently dened [6] in GloMoSim are presented:

Channel Layer - Radio Layer APIs :

4.4. Simple APIs 25

• Data packet from Channel to Radio:

 Fields: payload, packetSize. These elds refer to the actual data and size of data being received. They have similar meanings when used subsequently for the reception or transmission of packets.

• Data packet from Radio to Channel:

 Fields: payload, packetSize.

Radio Layer - MAC Layer APIs :

• Data packet from Radio to MAC:

 Fields: payload, packetSize.

• Data packet from MAC to Radio:

 Fields: payload, packetSize.

• Request Channel Status from MAC to Radio:

 Fields: (none). This message is used by the MAC layer to request infor- mation about the current channel status.

• Report Channel Status from Radio to MAC:

 Fields: status, ag. This message is used by the radio layer to return the current status of the channel as well as the method by which the information is being reported (passively or actively based on the request message sent by the MAC layer).

MAC Layer - Network Layer APIs :

• Data packet from MAC to Network:

 Fields: payload, packetSize, sourceId. The sourceId refers to the previous hop from which the packet arrived.

• Data packet from Network to MAC:

 Fields: payload, packetSize, destId. The destId refers to the next hop where the packet will travel.

Network Layer - Transport Layer APIs :

• Data packet from Transport to Network:

 Fields: payload, packetSize. The IP header should be a part of the packet that is sent from the transport to the network layer.

• Data packet from Network to Transport:

 Fields: payload, packetSize, sourceId. The sourceId refers to the original source where the packet originated. For the packet sent from the network to the transport layer, the IP header is no longer a part of the packet.

26 Methodology

Network Layer - Application Layer APIs :

• Data packet from Network to Application:

 Fields: payload, packetSize, sourceId.

• Data packet from Application to Network:

 Fields: payload, packetSize. These APIs, which are similar to the APIs used between the network and transport layers, are used for communica- tion between routing daemons (such as OSPF) that are running at the application layer and need to communicate directly with the network layer.

UDP Transport Layer - Application Layer APIs :

• Data packet from UDP to Application:

 Fields: payload, packetSize, sourceAddr, sourcePort, destAddr, destPort.

• Data packet from Application to UDP:

 Fields: payload, packetSize, sourceAddr, sourcePort, destAddr, destPort.

In these APIs, the sourceAddr and sourcePort refer to the source address and port number where the packet originates. The destAddr and destPort refer to the destination address and port number where the packet is going.

TCP Transport Layer - Application Layer APIs :

• Open Listen Socket from Application to TCP:

 Fields: appType, localPort. This API is used by an application type (such as telnet server) to open a listen connection on the given port number.

• Connection Open from Application to TCP:

 Fields: appType, localPort, remoteAddr, remotePort. This API is used by an application to inform TCP to try to setup a connection from the given local port number to the given remote address and port number.

• Data packet to send from Application to TCP:

 Fields: payload, packetSize, connectionId. This API is used by an appli- cation to send a packet using on the given connectionId.

• Connection Close from Application to TCP:

 Fields: connectionId. This API is used by an application to close a par- ticular connection.

• Listen Socket Open Result from TCP to Application:

 Fields: localPort, connectionId. This API is used by TCP to inform the application about the result of trying to open a listen connection.