f6]
`
`TRANSPERFECT
`
`City of New York, State of New York, County of New York
`
`1, Connie Wong, hereby certify that the following is, to the best of my
`knowledge and belief, within the given parameters, a true and accurate
`translation, of the following document “Diplomarbeit Hettich” from German
`into English.
`
`
`
`
`Connie Wong
`
`Sworn to bef e me this
`
`Thursday, December 08, 2011
`
`
`Signature, Notary P
`
`
`
`/?
`
`vb
`
`
`KEVIN M KELLEY JR
`-
`‘ Notary Public - State of New York
`'
`No. O1-KE-6229266
`Qualified in Queens Count:
`"’Enmmission Expires October
`
`
`tamp, Notary Public
`
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`BROADC'OM 1 0 0 7
`
`

`

`Department of Communication Networks
`Aachen Technical University (RWTH)
`Prof. Dr.-Ing. B. Walkc
`
`Diploma Paper
`
`Development and performance evaluation of a
`Selective Repeat-Automatic Repeat Request
`(SR-ARQ) protocol for transparent, mobile
`ATM Access
`
`by
`
`Andreas Hettich
`
`Student ID NO. 181475
`
`Aachen, April I7, 1996
`
`Mentors:
`
`Prof, Dr.-lng, B. Walke, Associate Professor
`DipI.-Ing. D. Petras
`
`This paper is for internal use only. All copyrights reserved by the mentoring department. We
`give no warranty for its content. Reproduction and publication of any kind are subject to the
`Department’s permission.
`
`

`

`I hereby confirm that I have conducted this work independently without the assistance from third
`parties — except for the official mentoring by the department. All literature used for this paper is
`listed completely in the Bibliography section.
`
`Aachen, April 17, 1996
`
`(Andreas Hettich)
`
`

`

`TABLE OF CONTENTS
`
`
`Introduction
`
`Broadband [SDN (B-ISDN)
`
`4
`
`6
`
`2.1
`
`Services in broadband ISDN ........................................................................... 6
`
`2.2
`
`Switching in B-ISDN:
`Asynchronous Transfer Mode (ATM) ............................................................ 6
`
`2.2.1
`
`Structure of an ATM cell .................................................................... 7
`
`2.2.2 ATM switching .................................................................................. 8
`
`2.2.3 ATM reference model ......................................................................... 9
`
`2.2.4 ATM service classes ......................................................................... 10
`
`Mobile broadband system
`
`11
`
`3.1 Overview ....................................................................................................... 11
`
`3.2 Bit transfer layer in an MBS ......................................................................... 14
`
`3.3 Cell structure of an M38 .............................................................................. 15
`
`Logical link control (LLC) in an MES
`
`17
`
`4.1
`
`Tasks and requirements................................................................................. 17
`
`4.1.1
`
`End-to—end error correction in an AAL ............................................ 17
`
`4.2 Requirements for an ARQ protocol .............................................................. 19
`
`4.3
`
`LLC and MAC layer interaction ...................................................................21
`
`4.4 Structure of the MAC layer........................................................................... 22
`
`4.5
`
`Structure of the LLC layer ............................................................................22
`
`Link access protocols
`
`25
`
`5.] Conventional ARQ protocols ........................................................................ 25
`
`5.1.1
`
`Stop-and-wait ARQ .......................................................................... 26
`
`5.1.2 Go back 1? (continuous) ARQ ........................................................... 27
`
`5.1.3
`
`Selective Repeat (SR) ARQ .............................................................. 28
`
`5.2 Adaptive Selective Repeat (ASR) ARQ protocol ........................................ 29
`
`5.2.1 Elements of ARQ in the ISO 8802-2 standard .................................. 30
`
`

`

`2
`
`Table ofComems
`
`5.2.2 The Ignore timer ............................................................................... 31
`
`5.2.3 Treatment of time-critical ATM cells ............................................... 34
`
`5.2.4 The Delay PDU................................................................................. 34
`
`5 .25
`
`Parallel ARQ instances ..................................................................... 36
`
`5.2.6 Acknowledge methods ...................................................................... 37
`
`6
`
`Implementation of the ASR ARQ protocol
`
`40
`
`6.1 The Connection Handler ............................................................................... 42
`
`6.2
`
`Send_Data .....................................................................................................43
`
`6.2. 1
`
`Send_Data_Obj ect ............................................................................44
`
`6.3 Receive_Data ................................................................................................47
`
`6 . 3. l Receive_Data_0bj ect .......................................................................48
`
`7 The SlMCOBH/MBS simulator
`
`50
`
`7.1 Overview ....................................................................................................... 50
`
`7.2 The stat_APP application layer..................................................................... 52
`
`7.3
`
`Sources .......................................................................................................... 54
`
`7.3.1
`
`Poisson source ................................................................................... 54
`
`7.3.2 LAN source ....................................................................................... 54
`
`7.3.3 Video source ..................................................................................... 55
`
`7.3.4 CBR source ....................................................................................... 56
`
`7.4 The MAC_Test_LCC MAC layer ................................................................ 57
`
`7.5 The .sim_defaults configuration file ............................................................. 58
`
`7.6 The graphic debugger ................................................................................... 59
`
`8 Simulation results
`
`62
`
`8.1
`
`Introduction ................................................................................................... 62
`
`8.1.1 Measured variables and performance parameters .............................62
`
`8.1.2
`
`Statistical power ................................................................................ 63
`
`8.1.3
`
`Simulation parameters of the ASR ARQ .......................................... 64
`
`8.2 Optimization of the ARQ Timer Delay and A ck_ Threshold parameters .......65
`
`8.2.1 ARQ Timer Delay .............................................................................65
`
`8.2.2 Ack_Threshold66
`
`8.3 Examining the causes for cell delays ............................................................ 68
`
`8.3.1
`
`Influence of the Ignore timer ............................................................ 68
`
`

`

`Table ofcomems
`
`8.3.2
`
`Influence of the error model ............................................................. 71
`
`8.4 Examining the effort required for discarding cells ....................................... 72
`
`8.5
`
`Separation of acknowledgments and user data ............................................. 74
`
`8.6 Asymmetric traffic ........................................................................................ 75
`
`9 Summary and outlook
`
`79
`
`A List of abbreviations ............................................................................................81
`
`List of figures ..............................................................................................................84
`
`List of tables ................................................................................................................85
`
`Bibliography ...............................................................................................................86
`
`

`

`CHAPTER 1
`
`
`Introduction
`
`The telecommunications industry has been able to increase its sales despite a recession in the
`past few years. In Germany, sales rose from DM 11 billion to DM 23 billion in the period from
`1990 to 1995 [25]. Another significant
`increase in sales is expected with the fall of the
`telecommunications monopolies in Europe in 1998. This illustrates the growing importance of
`telecommunications networks and services.
`
`Many additional new services in the field of telecommunications became possible due to digital
`telecommunications systems. ISBN (Integrated Services Digitai Network) deserves mentioning
`in this context. [SDN eliminates the variety of different network-user interfaces and offers all
`voice,
`text, and data services via a uniform network interface.
`In addition to digital fixed
`networks, new digital mobile networks became established based on the GSM (Gfobal System
`for Mobile Communication) and DCS 1800 (Digital Cellular System 1800) standards.
`In
`Germany, the DI network of Deutsche Telekom and the D2 network by Mannesmann Mobilfunk
`are based on the GSM standard. The E network by E-Plus was build according to the DCS
`standard.
`
`The fixed bandwidth assignment from 64 kbit/s in the ISDN network and 22.8 kbit/s (gross) in
`the GSM system is designed for narrowband voice transmission (cutoff frequency 4 kHz) and
`cannot provide the high variable data rates that future broadband services such as video
`communication, data transmission in computer networks, and multimedia will require in general.
`This is why the ATM transmission method (Asynchronous Transfer Mode) was developed that
`is used in broadband ISDN (B-ISDN) and can provide a variable bit rate of 622 Mbit/s and more.
`
`Since the need for higher data rates is beginning to show in mobile telephone networks,
`development of the UMTS system (Universal Mode Telecommunication System) was launched.
`It provides data rates of up to 2 Mbitt’s when service-specific protocols are used.
`
`An alternative approach is pursued under the M85 project (Mobile Broadband System). A
`system is to be designed that comes as close as possible to the functionality of broadband ISDN
`in landline networks. The targeted maximum gross data rate is 155 Mbitt’s.
`
`These very high data rates for a mobile telephone system can only be achieved by using
`accordingly high carrier frequencies in the ranges of 1?, 40, or 60 GHz. There are unutilized
`bandwidths in these ranges. New powerful signal processing components will have to be
`developed for this purpose. Silicon technology can be used for 17 and 40 GHz, while 60 GHz
`require the use of gallium arsenide which is much more expensive.
`
`A high subscriber density can be reached by small cell sizes with radii from 100 to 200 m. Small
`cell sizes can be achieved by using high carrier frequencies because there is additional resonance
`damping of the air in this range. This damping is around
`
`

`

`2.2 Switching technology in B-ISDN.‘ Asynchronous transfer mode (A I'M}
`
`5
`
`l4 dB/km and can increase by another 10 dB/km when it rains. This high damping ensures that
`the frequencies can be reused at a close distance-
`
`The data is transmitted service neutral, and only the 003 (quality of service) parameters as
`defined in the ATM standards and the defined ATM service classes are specified. CAC
`(Connection Admission Control) analyzes the (203 parameters and traffic characteristics prior to
`setting up the connection. A connection that has been set up has to be monitored for compliance
`with the traffic characteristics agreed during setup, otherwise the quality of other connections
`may be impaired.
`
`A physical channel in the MBS can carry 34 Mbitx’s as gross data rate. If a virtual channel has a
`data rate of more than 34 Mbit/s, it will have to be split up over multiple frequency channels
`(multi-link transfer).
`
`The protocols of the link layer have to meet special requirements; new concepts have to be
`implemented. A mobile ATM terminal is to be integrated into a landline ATM network while
`retaining the end-to—end relationship of the ATM adaptation layer. Poor transmission quality on
`the radio interface represents a special problem because does not allow the bit error rate required
`by ATM without additional measures. This can be remedied using forward error correction
`(FEC) in combination with a protocol for repeated transmission of ATM cells (Automatic Repeat
`ReQuest (ARQ)).
`
`It is the purpose of this paper to design a new link access protocol and to assess it using a
`simulation. The protocol
`is based on known ARQ protocols and is adjusted to the special
`requirements of MBS.
`
`the paper gives an overview of broadband ISBN (Chapter 2) and the Mobile
`At the outset,
`Broadband System (Chapter 3). Chapter 4 presents the logic link control (LLC) layer designed
`for mobile transparent ATM access and describes the special requirements of MBS. After an
`introduction to conventional ARQ protocols, Chapter 5 outlines the ASR ARQ protocol
`developed and implemented in this paper. Chapter 6 describes the implementation of the protocol
`in the system simulator. Chapter 7 presents the SIMCO3++KMBS simulator used for simulative
`performance assessment. Chapter 8 evaluates the capabilities of the protocol elements based on
`simulations. Chapter 9 concludes this paper with a summary and outlook.
`
`

`

`CHAPTER 2
`
`
`Broadband ISDN (B-ISDN)
`
`2.1
`
`Services in broadband ISDN
`
`The integration of new broadband applications into the Integrated Services Digital Network
`(ISDN) requires data rates of up to 155 Mbiti’s on the local loop. Some of these applications are
`services with a continuous data volume, others are cluster-type interactive services. The
`applications that generate continuous bit
`streams
`include voice transmission and video
`conferencing. Interactive services are characterized by varying bit rate requirements. A short
`query in a database, for example, can result in a reply with a very high data rate.
`
`0
`
`Interactive services
`
`0 Data communication
`
`— telephony
`— image telephony
`— broadband video conference
`
`:- Retrieval services
`— access to databases
`
`— radio, TV, HDTV, video on
`demand
`
`— electronic newspaper
`— video mail
`
`— LAN connections
`— file transfer
`— CAM connections
`
`— high-resolution image
`transmission
`
`The very diverse requirements of the broadband services can be met with difficulty only by using
`synchronous transmission methods (STDM). While over dimensioning the transmission capacity
`of synchronous channels reduces wait times, the capacity of the transmission medium is utilized
`poorly. The asynchronous transfer mode (ATM) can handle these requirements better.
`
`2.2
`
`Switching technology in B-ISDN:
`Asynchronous transfer mode (ATM)
`
`The asynchronous transfer mode is the connection-related packet switching mode of B-ISDN. It
`combines the advantages of connection- and packet-oriented switching. The data streams to be
`transmitted are divided into blocks of a fixed length, the so-called ATM cells. The cells of
`various connections are transmitted in a time-interleaved manner via a physical channel.
`Different amounts of transmission capacity are assigned dynamically depending on the data rates
`of these connections. The cells are transmitted in the order of their arrival.
`
`

`

`2.2 Switching technologz in B-ISDN.‘ Asynchronous transfer mode (A TM)
`
`7
`
`connection A
`
`
`
`
`
`
`conneclinn C
`
`l:lEl
`
`
`
`
`
`
`
`connection I]
`
`
`
`
`
`
`
`cell slrcam behind the multiplexer
`connection A
`connection 13
`connection L‘
`idle cell
`
`Figure 2.1: Statistical multiplex in the ATM method
`
`The ATM multiplexer inserts “idle cells” into the joint data stream if none of the connections
`needs transmission capacity. This method is called statistical multiplexing and is particularly
`well suited for adapting to the dynamic communication behavior of very different connections.
`
`2.2.1 Structure of an ATM cell
`
`An ATM cell includes 53 bytes and is composed of a 5—byte header and a 48-byte information
`field that contains payload data. The connection of the cells is connection-oriented. All cells of
`one virtual connection take the same transmission path that is determined during setup by
`defining virtual channels. The network controls the cells based on the routing information stored
`in their headers. The header field contains the following parameters:
`
`B-ISDN UNI
`
`B-ISDN NNI
`
`GFC
`Um
`
`UPI
`Wit
`
`
`1
`
`2
`
`3
`
`‘
`
`5
`
`Byte
`
`
`
`VCI
`
`PT
`
`(3 LP
`
`V61
`
`HEC
`
`HEC
`
`C LP
`GFC
`HEC
`NNI
`
`Cell loss priority
`Genetic flow control
`Header error GorIlI-Dl
`Nelwnrt-nnde Interface
`
`PT
`VCl
`VPl
`UNI
`
`Payload type
`Vltlual channel idenliller
`Vlllual path Identifier
`User-network meflace
`
`Figure 2.2: Header of an ATM cell
`
`VCI
`
`Virluaf Channel Identifier, 2 bytes
`Identification of the virtual channel is used to distinguish among different simultaneous
`connections and the assignment of cells to these connections. The virtual channel
`identifier is assigned to one connection section only.
`
`VPI
`
`Virruaf Path Identifier, S or [2 bits
`The VPI identifies a channel bundle. Multiple bundles can be distinguished that go in the
`same direction and each contain multiple virtual channels.
`
`

`

`2. Broadband ISDN (B-ISDN)
`
`The switching network will be able to identify and forward cells from channels of the
`same bundle faster.
`
`PT
`
`Payload Type, 3 bits
`This identification of the type of information field for distinguishing payload and
`signaling information. The latter may contain information needed to update the routing
`tables that are kept in the switches. A switch has to analyze both the header and the
`payload data field of an ATM cell. If payload data is transmitted in the information field
`of an ATM cell, its contents is ignored.
`HEC Header Error Control, 1 byte
`Since the header of an ATM cell contains data that is of particular significance for the
`transport of the cells, it is protected by a special check sequence. It is used for detecting
`and clearing errors.
`CLP Celt Loss Priority, 1 bit
`This parameter identifies low-priority cells that are discarded in the event of a queue
`overflow condition in the ATM switches.
`
`2.2.2 ATM switching
`
`VC swllch
`
`VCI 2
`
`
`
`VC' 4
`
`VC' 3
`YO! 1
`
`
`
`
`
`VCI 3
`VCI 4
`van 5
`VCI 6
`VC! 1
`W21 2
`
`VCI 1
`mm 2
`VCI 1
`VCI 2
`
`V6! 1
`vcn 2
`von 3
`we: a
`V6! 5
`VC' 6
`
`Figure 2.3: Virtual path switching and virtual channel switching
`
`Like other packet switching methods, ATM cells are switched based on the routing information
`contained in their headers. Only the complete origin and destination addresses are sent during
`connection setup to keep this information as concise as possible for increased throughput. Other
`identifications of logical channels (VCI, VPI) are assigned for the various sections of the
`connection. The ATM switches establish routing tables based on the incoming control
`information. These tables contain an origin and destination identifier (line + virtual channel
`identifier). The cells are switched based on these tables as follows: The switch extracts the
`virtual channel identifiers from the incoming cells. It then enters the identifier of the next link
`based on the information contained in its routing table and routes the cell to the respective output
`of the switching network.
`
`Figure 2.3 shows the switching elements used in the switches. There are VP and VC switches. A
`VP switch only analyzes the VPI values of the cells, which allows fast switching of the cells. The
`entries of the VCI fields remain unchanged. The VCI
`
`

`

`2.2 Switching technology in B-ISDN: Asynchronous transfer mode (AIM)
`
`9
`
`identifiers are changed by VC switches only.
`
`2.3.3 ATM reference model
`
`Based on the recommendations of the OSI reference model, a four-layer reference model can be
`defined for ATM. These include the physical layer, the ATM layer, the ATM adaptation layer
`(AAL), and a layer that represents the functions of higher-order layers. Three different planes are
`also defined: the user plane, the control plane, and the management plane. The management plan
`includes the functions for plane management and the functions for layer management. The plane
`management is responsible for managing the entire system while the layer management controls
`each layer.
`
`Management Plane
`
`
`
`
` Control Plane
`User Plane
`
`
`
`
`
`
`Higher Layers
`
`
`
`Higher Layers
`
`ATM Adaptation Layer
`
`Physical Layer
`
`Plane Management
`
`Layer Management
`
`l45
`
`
`
`
`
`
`ATM Layer
`
`
`
`Figure 2.4: ATM reference model
`
`The physical layer depends on the transmission medium and is to provide the functions for
`assembling and transmitting the cells via the physical medium. The tasks of the ATM layer
`include:
`
`Multiplexing and demultiplexing of cells from various connections
`Control of VCI- and VPl-oriented functions
`
`Generation and extraction of header information
`
`Generic flow control at the user-network interface (UNI) for setting up the connection.
`
`The ATM adaptation layer (AAL) is used by the higher-order layers for adapting to the ATM
`layer, It performs the required segmenting of data streams and ensures a secure transmission. The
`AAL layer is divided into two sub layers:
`
`1. The segmentation and reassembly (SAR) layer that maps the protocol data units of the
`higher-order layers to the ATM cells and vice versa.
`
`

`

`10
`
`2. Broadband ISDN (B-LS'DN)
`
`2, The Convergence Sub layer (CS) that corrects undesired effects through cell transfer
`delay variations of different services.
`
`For instance, the short data bursts generated during voice transfer are collected for a certain
`period of time in order to utilize the capacity of an ATM cell to the fullest. The receiver
`generates a continuous data stream again from the incoming ATM cells.
`
`Transfer delay variations of the cells through the network are corrected by the ATM adaptation
`layer at the receiver. This is achieved by adding a constant time delay.
`
`2.2.4 ATM classes of service
`
`In order to keep the number of the required protocols for the ATM layer at a minimum, the
`services are subdivided into four different classes according to the parameters “time reference
`between source and drain”, bit rate and connection type, and are shown in fig. 2.5.
`
`
`Class 4
`Class 3
`Class 2
`Class 1
`
`
`Time
`
`Real time
`
`Non-real time
`
`variable Connection
`
`reference
`
`
`Bit rate
`
`Constant
`
`Connecti on—oriented
`
`type
`
`Fig. 2.5: Classification of the services in ATM adaptation layer
`
`Control data is also added to the content information depending on the service class used. The
`control data are used for restoring content information that is distributed into multiple cells. The
`control data is generated by the SAR sub layer during the distribution of the data in the cells. In
`the receiver, the respective SAR sub layer must join the data together again in the right sequence
`based on the control data.
`
`I.
`
`In order to identify the individual cells, they are assigned sequence numbers. Based
`on this, it is possible for the receiver to detect any dropped cells. While the sequence
`number is present in all classes of service, additional back-up data and different
`segment types are only included in some classes. Due to the different proportions of
`control data,
`the resulting proportion of control data is 44-48 bytes
`[36].
`
`

`

`CHAPTER 3
`
`
`Mobile Broadband System
`
`3. I
`
`Overview
`
`The RACE 11 research program (Research and Technoiogy Development in Advanced
`Communications feelinologies in Europe) advanced the development of third generation mobile
`radio systems from 1992 to 1995, which was supposed to enable the merger of systems such as
`GSM, DECT (Digitai European Cordless Telecommunications) and trunked radio systems and
`their different areas of application, into a universal mobile radio system (Universai Mobiie
`Telecommunications System UMTS) with data rates of up to 2Mbitts. At the same time, they
`strived to develop uniform end devices and expand the service to broadband services with high
`data rates [8].
`
`
`
`fast
`
`User
`
`mobility
`
`medium
`
`movable
`
`fixed
`
`I
`Q 8
`km u’ 5
`
`I
`2
`
`
`
`
`
`I
`20
`
`Mbit a 5
`
`I
`155
`
`-—
`
`Available data rates
`
`Fig. 3.] : M88 and other data networks
`The MBS project that is being sponsored within the framework of RACE II deals with the
`connection of mobile users to stationary broadband networks (Integrated Broadband
`Communication Network
`iBCN) at data rates of up to 155 Mbitt’s. Apart from that, narrow band
`services still continue to be available. One of MBS’ goals in particular is the provision of
`broadband ISDN services for mobile users and ATM transfer support.
`
`Apart from the connection to broadband ISDN, MBS concept also includes possible
`collaboration with other systems such as UMTS. At the same time, the network type and the
`level of integration can vary
`
`

`

`12
`
`3. Mobile Broadband System
`
`from a privately-operated MBS system with low service integration and mobility to a public
`MBS system with high integration, wide-range mobility and large coverage area [3]. In Fig. 3.1,
`MBS is linked with other data networks. It is evident that through MBS, the broad service
`spectrum of broadband [SDN is combined with the mobility of the mobile radio networks.
`
`Due to the flexibility of M83 and the availability of B-ISDN services, a variety of different
`applications is possible. They are distinguished by the required data rates and the mobility of
`their users as shown graphically in Fig. 3.2.
`
`
`
`Smilance
`of property
`
`‘
`Access In
`331W 59"”?5
`
`(est mobile
`
`.
`5‘0" mobile
`
`5
`g
`g
`
`mable
`
`
`
`
`Interactive
`
`“quasi real time"
`
`
`Services
`
`Special needs
`GAD inter-comedian
`
`
`{2.9. health)
`
`Teleomsmh'ng
`
`
`
`required animate. Int-ii” 5
`
`Fig. 3.2.: MBS applications and services
`
`Specific conditions are required at the air interface during the integration of broadband services
`in mobile radio systems. They are a result of the mobility of the users and the utilization of a
`joint physical transfer medium- There are basically two different possibilities of implementation
`of mobile connection to fixed ATM network:
`
`1. Provision of service—specific protocols for communication via air interface, whereby ATM
`transfer takes place only between the base station and the fixed network.
`2. Transfer of ATM cells via the air interface whereby the mobile stations can transparently
`access the ATM network.
`
`

`

`3. I
`
`Overview
`
`13
`
`Mobile Station
`
`Base Station
`
` Mobile Station
`
`Physical layer
`Li"
`fibre link of
`ATM—Net
`
`lower layers
`
`_
`_
`.
`.
`air Interface
`
`Fig. 3.3: Service-specific ATM transfer
`
`The first process is used for example in UMTS and does not require any features for ATM
`transfer via the air interface. As a result, no channel access procedures that support the static
`multiplexes of the ATM are necessary and existing protocols can be adapted to the standards of
`different services. The disadvantages of this procedure are the need for different complex
`channel access procedures, lack of transparent ATM access and non—flexibility with regard to
`integration of new services (Fig. 3.3)
`
`
` BBS radio access
`
`fixed ATM
`new
`
`system
`
`AAL
`
`“cal Law:
`M—PHY MES
`ATM Adaptation Layer
`roadbanizl Tammation
`A.
`humus Transfer Mode Lay,er MBT
`Mobile
`alL'ui: Control Lrer
`UNI
`User to Netwmk Interface
`Access Comm]
`yer
`
`M—LLC
`M—MAC‘ MES
`
`Fig. 3.4: Transparent, mobile ATM access
`
`Transparent access means that the ATM adaptation layer must not be changed and can access the
`MBS-PHY layer like that of the ATM-PHY layer of a conventional ATM network. That is why
`the second approach only requires a service-independent MAC scheme (Medium Access Control)
`to transfer in asynchronous transfer mode. ATM services to be added in the future will also be
`supported by this universal solution. However, channel access procedures that support static
`multiplexes of the ATM are necessary. This procedure can provide the same functionality but not
`the same quality of service like in
`B-ISDN. This approach was selected in the MBS system (Fig. 3.4) [15].
`
`

`

`14
`
`3. Mobile Broadband System
`
`3.2
`
`Bit transfer layer in M33
`
`The bit transfer layer (Physical layer) represents the lowest layer in lSO-OSI reference model and
`specifies the protocols for transferring the bits to the physical channel. The transfer of high data rates that
`require large broadband is included in MBS. As a result, frequencies in the 60 GHz frequency range were
`selected as carriers. On the one hand, these frequencies are otherwise available, and on the other hand, the
`atmospheric oxygen attenuation is very high. In addition to the parameters just mentioned above, the
`radius ofa radio cell depends mainly on the noise factor, the required signal to noise power ration in the
`receiver, the bandwidth and the channel characteristics. Taking these factors into account results in cell
`radii in the scale if R = 100 to 200m. Due to damping, the rcusability intervals of a frequency are very
`short. This allows high user densities to be achieved. Cell planning as is required for operating second
`generation mobile communication networks can no longer be carried out due to the microccllular
`structure in MBS.
`
`It requires the use of procedures for dynamic channel allocation.
`
`For synchronization, the mobile station establishes the time interval on the downlink that it receives
`delayed around the signal propagation time. This leads in uplink to maximum asynchronizations between
`mobile stations near the base station and those at a large distance of Tamra = 2.Rfc : 0.666145 to 1.33us (c
`is the velocity of light) because the transmit signal of the mobile station arrives in the base station delayed
`at an equivalent run time. A measurement of the order Tasy‘nch by the base station, which is also called loop
`delay, as occurs e.g. in GSM networks is not included in MBS.
`
`
`62 to 63 GHZ
`Freuuenc rane for the downlink
`65 to 66 GHZ
`Freuenc rane for the ulink
`32
`Number of frequency channels
`30 MHZ
`Bandwidth er freuenc channel
`
`2 FDD
`Du IlCX s Mlittin
`
`Multiplex procedure
`FDMA f TDMA (hybrid)
`21.33
`s
`Slot len th
`
`Guard time
`1.33 #5
`
`QPSK x 16 QAM
`Modulation procedure
`Data rate
`20 M S mbolsfs (Tsmtm. =50 as)
`1 (2 424 bits)
`
`ATM cells E slot
`
` 100 -200 m
`
`
`Asynchronization
`T mm: 0.666 to 1.33m
`
`(t 13 to 26 symbols)
`
`Radio cell radius
`
`Table 3.1: System parameter of MBS system
`
`The system basically represents a hybrid FDMA f TDMA channel structure (FrequencyTime Division
`Multiple Access). The frequency range is subdivided into 32 channels for each 30 MHz bandwidth that
`are separated from each other by guard bands. The time range is split into time slots. The length of a slot
`is Tslol = (20 + 1.33) [15. It consists of a guard time Tguard = 1.33 as on the uplink, which is supposed to
`prevent time overlapping of the packets that are sent on the same carrier in succession from different
`mobile stations. The length of the guard time is
`
`

`

`3.3 Cell structure in MES
`
`15
`
`equivalent to the maximum asynchronization Tasy'nch such that irrespective of the position of a mobile
`station within a cell, the sum of the delay and length of a packet dies not exceed the length of the slot.
`The] .33us correspond to the signal propagation of base to mobile station and back again, if the mobile
`station assumes largest distance possible from the base station. On the downlink, guard time is required to
`adjust the transmitter when using the power control method.
`The allocation ofa slot is shown in Fig. 3.5. In addition to the actual data (2 x 168 symbols), each slot
`contains a [mining sequence (15 symbols) in the center, which serves to assess the channel step response
`of the equalizer as well as synchronization. Three different slot lengths are shown in Fig. 3.5 but only
`normal and very short slots are deployed. Normal slots serve for transferring data while very short slots
`are used for transferring dynamic parameters and collision resolution.
`If QPSK (Quaternary Phase Shifi Keying) is used, a symbol is equal to two bits and in the case of the 16
`QAM (Quadrature Amplitude Modification) a Symbol would be equal to four bits. The cost as well as the
`error susceptibility of the second modulation procedure is clearly on a higher scale and as such, QPSK
`should be deployed in the first level of implementation.
`QPSK is also taken as the modulation procedure so that 168 - 2 - 2 bits = 672 bits = 84 bytes is available
`in the case of a normal slot, out of which an ATM cell generally needs 53 bytes, and as overhead, MAC
`and LLC layer split up the remaining 53 bytes. A slot of very short length which will now be called
`subslot, has 24 - 2 - 2 bits = 96 bits = 12 bytes [15].
`
`I Guard Tlme (23 symbols)
`
`|:l Tail (5 symbols}
`Data
`
`D Train‘ng Sequence {15 symbols}
`
`Fig. 3.5 Layout ofa slot
`
`3.3
`
`M38 cell structure
`
`The MBS cell structure is similar to