worldwide interoperability for microwave access · the ieee802.16 bwa network standard applies to...

WIMAX

WorldWide Interoperability for Microwave Access

Internet de Nueva Generación. Curso 2009-10. ETSIT– UPV. Prof. Vicente Casares 2/41

Wireless Access Networks

WWAN (area of 30-40 Km):Cellular networks (2G, 2.5G, 3G) WiMAX (IEEE802.16e version).

WMAN (area of 10 Km):WiMAX (IEEE802.16-2004 version).

WLAN (area of 1 Km.):WiFi (IEEE802.11 and variants).

WPAN (area of 10 -100 m.):Bluetooth IIEEE802.15.1), UWB, Zigbee.

WLAN

WPAN

WMAN

WWANIEEE 802.20Proposed

IEEE 802.16Wroposed


History of WIMAXThe IEEE802.16 working group for BWA was created in 1999.

IEEE Standards provide only the technologyWIMAX Forum (www.wimaxforum.org) was created in June 2001.Objective: To play the same role for IEEE802.16 as WiFi for 802.11.WIMAX Forum provides certification of

Conformity. Compatibility.Interoperability of IEEE802.16 products.


Protocol layers and topologiesThe IEEE802.16 BWA network standard applies to OSI seven-layer model.In WIMAX IEEE802.16 only the two first layers are defined

WIMAX(Common) MAC Layer

WIMAXPhysical Layer

IEEE802.11Standard Scope

Physical Layer (PHY)

Security (or Privacy) Sublayer

MAC Common Part Sub-layer (MAC CPS)

Service-Specific ConvergenceSub-layer (CS)

Data/Control Plane

External Network,Example: IP, or ATM

Management entityService Specific

Convergence Sub-layr

Management entityMAC Common Part Sub-layer

Privacy sub-layer

Management entityPHY Layer

Management Plane


WiMAX: Spectrum

The IEEE802.16 standard considers the band: 2-66 GHz.

First range: 2 -11 GHz. It is destined for NLOS transmissions, the only rang presently included in WiMAx: 2.5 GHz, 3.5 GHz and 5.7 GHzSecond range: 11 – 66 GHz. It is destined for LOS transmissions, but not used for WiMAX

2 11 66

NLOSLOS

GHz

IEEE, 2001


WiMAX: FDD, TDD duplexing techniques

WIMAXBase Station

Subscriber Station

Downlink frequency band

Uplink frequency band

FDD

WIMAXBase Station

Subscriber Station

Common Uplink and Downlink frequency band

TDD


WiMAX: Physical Layer -FrequenciesWiMAX can operate in both licensed and unlicensed bands.

Minimum channel bandwidth for WiMAX usage is 1.75 MHz.The use of 10 MHz per channel is considered as an optimum.

On 2.4 GHz and 5 GHz (close to IEEE 802.11 a) non-licensed bands. With some possible limitations due to interference.The 2.5 GHz (Bluetooth use the same band) and 3.5 GHz licensed bands will be the most common bands for WiMAXapplications.

3.5

3.5

3.5

3.5

3.5

TDD

TDD

FDD

FDD

TDD

Band GHz Duplexing

7

3.5

3.5

7

10

Channelbandwidth MHz

Profolemane3.5T1

3.5T2

3.5F1

3.5F2

5.8T


In 1966, proposed by Bell Labs .In 1997, the ETSI included OFDM in the DVB-T system.In 1999, The WiFi WLAN variant IEEE 802.11g considered OFDM for its Physical layer.OFDM transmits simultaneously many narrow-band orthogonal frequencies, OFDM sub-carriers, that are orthogonal to each other.Each frequency channel is modulated with a possibly different digital modulation.

WiMAX: OFDM Transmission


OFDM and OFDMA

IEEE 802.16d (fixed service) uses Orthogonal Frequency Division Multiplexing (OFDM). IEEE 802.16e (mobile) uses Orthogonal Frequency Division Multiple Access (OFDMA).So, what’s the difference between the two, and why is there a difference?


OFDM –i-OFDM is sometimes referred to as discrete multi-tone modulationInstead of a single carrier being modulated, a large number of evenly spaced subcarriers are modulated using some m-ary of QAM. It is a spread-spectrum technique that increases the efficiency of data communications by increasing data throughput because there are more carriers to modulate. Problems with multi-path signal cancellation and spectral interference are greatly reduced by selectively modulating the “clear” carriers or ignoring carriers with high bit-rate errors.


OFDM –ii-The OFDM spread-spectrum scheme is used for many broadly used applications:

Digital TV broadcasting in Australia, Japan and Europe; Digital audio broadcasting in Europe; Asynchronous Digital Subscriber Line (ADSL) modems and wireless networking worldwide (IEEE 802.11a/g).

OFDM allows only one user on the channel at any given time.To accommodate multiple users, a strictly OFDM system must employ

Time Division Multiple Access (TDMA) (separate time frames)Frequency Division Multiple Access (FDMA) (separate channels). Neither of these techniques is time or frequency efficient: TDMA is a time hog and FDMA is a bandwidth hog


OFDMA –i-OFDMA is a multi-user OFDM that allows multiple access on the same channel (a channel being a group of evenly spaced subcarriers).WiMAX uses OFDMA, extended OFDM, to accommodate many users in the same channel at the same time.OFDMA distributes subcarriers among users so all users can transmit and receive at the same time within a single channel on what are called subchannels.Subcarrier-group subchannels can be matched to each user to provide the best performance, meaning the least problems with fading and interference based on the location and propagation characteristics of each user.


OFDM and OFDMA –i-The WiMAX forum established that, initially, OFDM-256 will be used for fixed-service 802.16d (2004). It is referred to as the OFDM 256 FFT Mode, which means there are 256 subcarriersavailable for use in a single channel. Multiple access on one channel is accomplished using TDMA. Alternatively, FDMA may be usedOn the other hand, OFDMA 128/512/1024/2048 FFT Modes have been proposed for IEEE 802.16e (mobile service).OFDMA 1024 FFT matches that of Korea’s WiBRO. OFDM 256 also is supported for compatibility with IEEE 802.16d (fixed, 2004).


WiMAX: Frequency Domain OFDM

Data sub-carriers: useful data transmission.Pilot sub-carriers: mainly for channel estimation and synchronization (8 units). Null sub-carriers: Guard bands.DC (Direct Current) It corresponds to the RF center frequency of the transmitting station.

Left guardSub-carriers

Right guardSub-carriers

Pilot sub-carriers Data sub-carriers

DC


WiMAX: Illustration of OFDMA principle

Left guardSub-carriers

Right guardSub-carriers

Data sub-carriers

DC

User 1 User 2 User 3 User 4 User 5

OFDMSymbol n

OFDMSymbol n+1

OFDMSymbol n+2

OFDMSymbol n+3

OFDMSymbol n+4

Time


Comparative between of OFDM and OFDMA


Time

Sub-

carr

iers

OFDM


TimeSub-

chan

nels

=12

Su-b

caar

riers

OFDMA

OFDM allocates users in time domain only.OFDMA allocates users in time and frequency domain


WiMAX: Digital Modulation

Four modulations are supported by the IEEE802.16 standard

BPSKQPSK16-QAM64-QAM

Great advantage:Link adaptation can be used (also used in other GSM/EDGE, UMTS, WiFi, etc.)

I

Q


WiMAX. Modulation and coding schemes

These data rate values, in Mb/s, do not take into account some overheads such as preambles. Hence these data rates, are optimistic values.

Number of sub-carriers: 192Occupied bandwidth: 7 MHzSampling factor: 8/7

G ratio BPSK1/2

QPSK1/2

QPSK3/4

16-QAM2/3

16-QAM3/4

64-QAM2/3

64-QAM3/4

1/32 2.92 5.82 8.73 11.64 17.45 23.27 26.18

1/16 2.82 5.65 8.47 11.29 16.94 22.59 25.41

1/8 2.67 5.33 8.00 10.67 16.00 21.33 24.00

1/4 2.40 4.80 7.20 9.60 14.40 19.20 21.60

duration symbol OFDMsymbol OFDMper bits uncoded ofNumber rate Data =


WiMAX. Ilustration of link adatation

WIMAXBase Station

64-QAM 2/3: 12 Mbps; 2 miles

16-QAM 1/2: 6 Mbps; 4 miles

QPSK 1/2: 3 Mbps; 6 miles

Ensure a steady signal strength over increasing distance by decreasing throughput over range to deliver the best QoSpossible.


WiMAX. OFDM(A) Transmission chain

FEC encoding is concatenated coding RS + CC

ModulationInterleavingRandomizationFEC encoder

(CC, Turbo code,.)

PHYsicalPDU to betransmitted

To OFDM Part

OFDM PHY Transmission chain

OFDMA PHY Traasmission chain

ModulationInterleavingRandomizationFEC encoder

(CC, Turbo code,.)

PHYsicalPDU to betransmitted

To OFDM PartRepetition


WiMAX. Physical layerFrames are divided into slots.In FDD and in TDD, the size of frames and the size of individual slots within the frames can be varied on a frame-by-frame basis under the control of a scheduler in the BSIn TDD mode, it is allowed asymmetric allocation between uplink and downlink.Adaptive modulation allows the system to adjust the signal modulation schemes depending on the signal to noise ratio (SNR) condition of the radio link.It allows the system to overcome time-selective fading


WiMAX. Illustration of FDD mode operations

Three different modes of operation:

DownLink Freq.

UpLink Freq.

Fixed Frame duration, j

Broadcast Full duplex, SS # 1 Half duplex, SS # 2 Half duplex, SS # 3

Fixed Frame duration, j+1 Fixed Frame duration, j+2


WiMAX. Illustration of TDD mode operations

TDD is more suitable when data rates are asymmetrical, e.g. for an Internet transmission.Mesh topology supports only TDD duplexing.

Down andLink Freq.

Down Link Sub-frame Up Link Sub-frame

Adaptive

Fixed Frame duration, j Fixed Frame duration, j+1 Fixed Frame duration, j+2

DL Sub-frames UL Sub-frames

Adaptive Adaptive


WiMAX. OFDM PHY Downlink sub-frame

Preamble Frame ControlHeader DL Burst #1 DL Burst #2 DL Burst #m

DL PHY PDU (DL Sub-frame)

Each burst has its own modulation and coding schemes

DL Frame Prefix Broadcastmessages

Regular MAC PDUs Padding Regular

MAC PDUs Padding

MAC Header(6 bytes)

CRC (optional)(4 bytes)Payload (optional)

General format of a MAC PDU


WiMAX. OFDM PHY Uplink sub-frame

Contention slots for initial ranging

UL PHY PDU (UL Sub-frame)

Each UP PHY PDU has its own modulation and coding schemes

Preamble UL burst

MAC Header(6 bytes)



Contention slots For BW requests

UP PHY PDUComing form SS # 1

UP PHY PDUComing form SS # n

MAC Msg 1(MAC PDU 1)

MAC Msg m(MAC PDU m) Padding


WiMAX. OFDMA PHY frame

Guard Time

FCH

DL-

MA

PU

L-M

AP

UL-

MA

P (c

ontin

.)

DL Burst #1

DL Burst #2

DL Burst #3DL Burst #4

DL

Bur

st #

5

DL Burst #6

DL Burst # 7

OFDM Symbol number

Sub-

chan

nel l

ogic

al n

umbe

rDL sub-frame UL sub-frame

DL Burst #3

DL Burst #4

DL Burst # 7

UL Burst #1

UL Burst # 2

AC

K-C

HR

angi

ngOFDM Symbol number


WiMAX. Protocol layers and topologies

S-S Convergence sub-layer enables ATM, IP, .. services to be offered over the MAC layer.MAC CP sub-layer performs bandwidth allocation, connection and maintenance of the connectionSecurity sub-layer performs authentication of network access and connection establishment, key exchanges and encryption of MPDUs

Physical Layer

Security Sublayer

MAC Common Part Sub-layer (CPS)

Service-Specific ConvergenceSub-layer (CS)

PHY SAP

MAC SAP

CS SAP

WIMAX(Common) MAC Layer

WIMAX Physical Layer

MSDU

MPDU(s)- Generic MPDU- Bandwidth request MPDU


WiMAX. MAC Layer Features

While extensive bandwidth allocation and QoSmechanisms are specified, the details of scheduling and reservation management are left un-standardized

MAC Header(6 bytes)




WiMAX. Fragmentation of an MAC SDU

Fragment # 1 Fragment # mFragment # 2

MAC SDU

Fragment Sub-Header

(1 or 2 bytes)

MAC Header(6 bytes)

MAC SDUFragment # 1

OptionalCRC

(4 bytes)

Fragment Sub-Header

(1 or 2 bytes)

MAC Header(6 bytes)

MAC SDUFragment # n

OptionalCRC

(4 bytes)

Fragment Sub-Header

(1 or 2 bytes)

MAC Header(6 bytes)

MAC SDUFragment # 2

OptionalCRC

(4 bytes)

Fragment # 1 Fragment # 2 Fragment # n

Payload


Fragmentation, packing and concatenation

MAC SDUs

MAC PDUs

Burts

MSDU 1 MSDU 2 MSDU 2

Fragmentation Packing

MPDU 2 MPDU 3 MPDU 4 MPDU 5MPDU 1

Concatention

FEC Block 1 FEC Block 2 FEC Block 3

MPDU 6

Preamble


WiMAX. MAC Layer FeaturesThe IEEE802.16 MAC is designed to support a point-to-multipoint architecture with a BS and mesh architecture.The IEEE802.16 MAC is connection-oriented, 16 bits are used for connection identifiers.Two types of MPDUs:

Generic MPDUBandwidth request header

Each connection, with it own QoS, is served according to 1 of the 5 scheduling services.There are two types of connections:

Management connectionsTransport connection


WiMAX. MAC Layer connectionThere are two types of connections:

Management connectionsBasic connection (time critical management messages)Primary Connection (longer, mode delay tolerant)Secondary Connection (messages such as DHCP, SNMP, TFTP, …

Transport connectionEach connection, with its own QoS, is served according to 1 of the 5 scheduling services.


WiMAX. The 5 QoS ClassesThe standard gives all the details about the different classes of QoS and the methods of bandwidth allocation.Each connection, with its own QoS, is served according to 1 of the 5 scheduling services.

Unsolicited Grant Service (UGS)Real Time polling service (rtPS)Non Real Time polling service (nrtPS)Best Effort Service (BE)Extended Real Time polling service (ertPS)


WiMAX. Unsolicited Grant Service (UGS)It is designed to support real – time data streams consisting of fixed-size data packets issued at periodic intervals.

T1/E1classical PCM, VoIP with no silence detectionIn the UGS service, the BS provides fixed-size data grants at periodic intervals.


WiMAX. Real Time Poling Service (rtPS)It is designed to support real – time data streams consisting of variable -size data packets issued at periodic intervals.

MPEG (Moving Pictures Experts Group) video transmission

In the rtPS, the BS provides periodic unicastrequest opportunities.


WiMAX. Non Real Time Poling Service (nrtPS)It is designed to support delay tolerant data streams consisting of variable -size data packets for which a minimum data rate is required.

FTP transmission.In the rtPS, the BS provides periodic unicastrequest polls on a regular basis, which guarantees that the service flow receives request opportunities even during network congestion.


WiMAX. Best effort (BE)It is designed to support data stream for which no minimum service guarantees are required and therefore may be handled on a best available basis

E-mail.


WiMAX. What about the scheduler?The scheduler is in the BS!HOWEVER, The details of scheduling and reservation management are left un-standardisedand are then left for vendors and operators.Any of the well known scheduling algorithms can be used:

Round robin.Weighted Round RobinWeighted Fair Queueing…..


The scheduler is in the BS!Decisions are transmitted to the SSs through the UL-MAP MAC management message

MAC CS

Scheduler

MAC CPS

PacketReconstruct

Subscriber Station (SS)

MAC CPSMAC CS

PacketClassifier

UGS

rtPS

nrtPS

BE

UGS

rtPS

nrtPS

BE

TDM Voice(T1/E1)

VoIP, Video

TFTP

HTTP

E-mail

TDM Voice(T1/E1)

VoIP, Video

TFTP

HTTP

E-mail

Base Station (BS)

UL-MAP

WiMAX. BS scheduler operation for the uplink


WiMAX. BS scheduler operation for the downlink

The scheduler is in the BS!Decisions are transmitted to the SSs through the UL-MAP MAC management message

MAC CS

Scheduler

MAC CPS

PacketClassifier

Subscriber Station (SS)

MAC CPSMAC CS

PacketReconstruct

UGS

rtPS

nrtPS

BE

UGS

rtPS

nrtPS

BE

TDM Voice(T1/E1)

VoIP, Video

TFTP

HTTP

E-mail

TDM Voice(T1/E1)

VoIP, Video

TFTP

HTTP

E-mail

Base Station (BS)

DL-MAP


ReferencesIEEE 802.16-2004 IEEE Standard for Local and Metropolitan Area Networks, Air Interface for Fixed Broadband Wireless Access Systems, October 2004.IEEE 802.16e IEEE Standard for Local and Metropolitan Area Networks, Air Interface for Fixed Broadband Wireless Access Systems, Amendment 2:Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1, February 2006 (Approved 7 December 2005).WiMAX Forum White papers,Loutfi Nuaymi, WiMAX, Technology for Broadband Wireless Access. John Wiley, 2007

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