Outline

• Wireless introduction • Wireless cellular (GSM, CDMA, UMTS, WiMAX)• Wireless LANs, MAC layer• Wireless Ad hoc networks

– routing: proactive routing, on-demand routing, scalable routing, geo-routing – multicast– TCP– QoS, adaptive voice/video apps

• Sensor networks

Cellular Wireless Network Evolution

• First Generation: Analog voice– AMPS: Advance Mobile Phone Systems– Residential cordless phones– FDMA

• Second Generation: Digital voice– GSM: European Digital Cellular - TDMA – IS-54/136: North American - TDMA– IS-95: CDMA (Qualcomm)– DECT: Digital European Cordless

Telephone

Cellular Evolution (cont)• Third Generation: Packet data

– will combine the functions of: cellular, cordless, wireless LANs, paging etc.

– will support multimedia services (data, voice, video, image)

– Requirements• 384 Kbps for full area coverage• 2 Mbps for local area coverage• variable bit rate• packet traffic support• flexibility (eg, multiple, multimedia streams on

a single connection)

Cellular Evolution (cont)• Third Generation: Packet data

– 2.5 G• GPRS (for GSM)

(General Packet Radio Service )• EDGE (for GSM)

(Enhanced Data rates for Global Evolution)• 1xRTT (for CDMA)

– 3G (W-digital CDMA)• IMT-2000/UMTS

(International Mobile Telecommunications) (Universal Mobile Transport Service)• CDMA 2000, WCDMA, TD-CDMA, TD-SCDMA

• 3+G, 4G systems– OFDM, Software radio, Array antennas– WiMAX

• System architecture– networking– addressing

• Physical (PHY) layer– radio band– modulation– error control (FEC/interleaving)– frame structure– multiple access (multi-user, up/down)

• MAC/DLC layer– channel mapping (control/traffic) – medium access techniques– call setup– standby behavior

Architecture

Cellular Concept

• Geographical separation• Capacity (frequency) reuse• Backbone connectivity

BS BSBS

BSBSBS

Backbone Network

1G: AMPS (Advanced Mobile Phone System) ---- FDMA

Channels are divided into 4 categories:1. Control (base to mobile) to manage the system2. Paging (base to mobile) to alert mobile users to incoming

calls3. Access (bidirectional) for call set up and channel

assignment4. Data (bidirectional) for voice, FAX, or data

B

A

ED

C

F

G

B

A

ED

C

F

G

B

A

ED

C

F

G

• Frequencies are not reused in a group of 7 adjacent cells• To add more users, smaller cells can be used• In each cell, 57 channels each for A-side carrier and B-side carrier respectively

Handoff

• Handoff: Transfer of a mobile from one cell to another

• Each base station constantly monitors the received power from each mobile

• When power drops below given threshold, base station asks neighbor station (with stronger received power) to pick up the mobile, on a new channel

• The handoff process takes about 300 ms

Organization of Cellular Networks

BS (base station)- modulation, antenna

MSC (mobile switching center)

HLR (home locationregister)– information

VLR (visitorlocation register)– information

To register and make a phone call

• When phone is switched on , it scans a preprogrammed list of 21 control channels, to find the most powerful signal

• It transmits its ID number on it to the MSC which – informs the local HLR– adds it to VLR and informs the home MSC

which informs the HLR– registration is done every 15 min

• To make a call, user transmits dest Ph # on random access channel; MSC will assign a data channel

• At the same time MSC pages the destination cell for the other party (idle phone listens on all page ch.)

How does a call get to the mobile ?

• Suppose (310) 643 - 1111 is roaming in the (408) area code

• Cell phone registers with the (408) MSC, which adds it to (408) VLR and informs the (310) HLR of the location of the cell phone

• A call comes in for (310) 643 – 1111. Then (310) MSC queries its HLR, and directs the call to the (408) MSC

• The (408) MSC forwards the call to the mobile

(Freq DivisionDuplex)

2G: Digital Cellular: IS-54 TDMA System

• Second generation: digital voice • FDMA / TDMA• Same frequency as AMPS – 416 ch• Each 30 kHz RF channel is used at 48.6 kbps

– 6 TDM slots/RF band (2 slots per user)– 8 kbps voice coding – 16.2 kbps TDM digital channel (3 channels fit in

30kHz)• 4 cell frequency reuse (not 7)• Capacity increase per cell per carrier

– 3 x 416 / 4 = 312 (instead of 57 in AMPS)– Additional factor of two with speech activity

detection.

IS-54 slot and frame structure

BASE TO MOBILE

SLOT 1 SLOT 2 SLOT 3 SLOT 4 SLOT 5 SLOT 6

Frame1944 bits in 40 ms( 48600 b/s)

G6

R6

DATA116

SYNC228

DATA1122

SACCH112

DVCC 12

DATA1122

MOBILE TO BASE

DATA1130

DATA1130

DVCC 12

SACCH 12

SYNC228

RSVD 12

G:GUARD TIME R:RAMP TIMEDVCC: DIGITAL VERIFFICATION COLOR CODERSVD: RESERVE FOR FUTURE USE

2G: European GSM (Group Special Mobile)

• Second Generation: Digital voice• FDMA / TDMA• Frequency Division duplex (890-915 MHz Up; 935-

960 MHz Down)– 125 frequency carriers, Carrier spacing: 200 Khz

• 8 channels per carrier (Narrowband Time Division)• Physical ch 124x8 = 992, reuse factor N = 3 or 4

– Capacity per cell per carrier: 992/ N = 330 or 248 • Speech coder: linear predictive coding (13 Kbps)• Modulation: Frequency Shift Keying (Gaussian

Minimum Shift Keying)• Multilevel, time division frame structure• Slow frequency hopping to overcome multipath fading

Access techniques for mobile communications

P - PowerT - TimeF - Frequency

P

TP

T

F

P

T

F

FDMA (TACS)

TDMA (GSM, DECT)

CDMA (UMTS)

F

ATDMA (UMTS)

Spread Spectrum

•

CDMA (Code Division Multiple Access)

• unique “code” assigned to each user; i.e., code set partitioning

• all users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode data

• Note: chipping rate >> data rate (eg, 64 chips per data bit)

• encoded signal = (original data bit) X (chipping sequence)

• decoding: inner-product of encoded signal and chipping sequence

• allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)

CDMA Encode/Decode

CDMA: two-sender interference

Orthogonal Variable Spreading Factor

C4,1

= (1,1,1,1)

C2,1

= (1,1)

C4,2

= (1,1,-1,-1)

C4,3

= (1,-1,1,-1)

C2,2 = (1,-1)

C4,4

= (1,-1,-1,1)

S S = 1.S T = = 0. Si.Ti

i=1

m

m1 inner-product

CDMA (Code Division Multiple Access): IS-95 QUALCOMM, San Diego

• Based on DS spread spectrum

• Two frequency bands (1.23 Mhz), one for forward channel (cell-site to subscriber) and one for reverse channel (sub to cell-site)

• CDMA allows reuse of same spectrum over all cells. Net capacity improvement:

– 4 to 6 over digital TDMA (eg. GSM)– 20 over analog FM/FDMA (AMPS)

CDMA (cont’d)

• One of 64 PS (Pseudo Random) codes assigned to subscriber at call set up time

• RAKE receiver (to overcome multi path-fading)• Pilot tone inserted in forward link for:

– power control– coherent reference

• Speech activity detection • Voice compression to 8 kbps (16 kbps with FEC)• IS-95: 20 wideband channels, BW=1.25 MHz

Third generation services-- vs 2G

2M

384K

64K

32K

16K

9.6K

2.4K

1.2K

point to point multipoint

bidirectional unidirectional multicast

videoconference

remote medicalservice video

catalogueshopping

videoon

demand

mobileTV

inte

rnet

telephoneconference

telephone

voice mail

electronicnewspaper ISDN

electronicpublishing

FAX

distributionservices(data)

mobile radio

distributionservices (voice)

pager

Third generation bandwidth assignment -- high frequency 2 GHz, wideband 150 MHz

IMT-2000IMT-2000 IMT-2000IMT-2000

18851885 2025202519201920 20102010

MSSMSS

19801980 21102110 22002200

MSSMSS

21702170 MHzMHz

ITUITU

IMT-2000IMT-2000 IMT-2000IMT-2000

18801880 2025202519001900 20102010

MSSMSS

19801980 21102110 22002200

MSSMSS

21702170 MHzMHz

EUROPEEUROPEEUROPEEUROPE

DECTDECT

JAPANJAPANJAPANJAPAN

IMT-2000IMT-2000 IMT-2000IMT-2000

18851885 202520251918.11918.1 20102010

MSSMSS

19801980 21102110 2200220021702170 MHzMHz18951895

MSSMSSPHSPHS

UTRAN Architecture(UMTS Terrestrial Radio Access Net)

Core Network

RNC RNC

Site Contr

BTS BTS BTS

Site Contr

BTS BTS BTS

Site Contr

BTS BTS BTS

Site Contr

BTS BTS BTS

RNS

UTRAN

RNS

Iub IubIub Iub

Iu

r

IuIu

B-node B-node B-node B-node

W-CDMA (Wide Band CDMA)Key features• Improved capacity and coverage (over second

generation); thus, backward compatible– high frequency 2 GHz, wideband 150 MHz

• High degree of service flexibility: multiple, parallel services per connection; efficient packet access

• Operator flexibility: asynchronous interstation operation; hierarchical cell structures (HCS); adaptive antenna arrays (enabled by uplink pilot symbols); TDD (Time Division Duplex) mode for asymmetric traffic & uncoordinated environments

RLCRLC

LACLAC

Radio Interface - protocol architecture

RLC

RRC

LAC

MAC

Physical Layer

L3

L2/LAC

L2/MAC

L1

C-plane U-plane

Logicalchannels

Transportchannels

RLC

Layer 1 - up link physical channels(W-CDMA example)

Data

Pilot

Dedicated PhysicalData Channel

Dedicated PhysicalControl Channel

Transmitpower control

Transportformat ind.

Slot#1Slot#2 Slot#i Slot#15

Frame#1Frame#2 Frame#i Frame#72

0.667 ms

10 ms

Feedbackindicator

frame

superframe

Layer 1 - down link physical channels(W-CDMA example)

Data

Slot#1Slot#2 Slot#i Slot#15

Frame#1Frame#2 Frame#i Frame#72

Pilot TPC TFI

DPCCH DPDCH

frame

superframe

0.667 ms

10 ms

WiMAX - IEEE 802.16a - 3G/4G? • Worldwide Interoperability for Microwave Access

(WiMAX) is an industry trade organization to promote and certify compatibility and interoperability of broadband wireless access equipments that conform to the IEEE 802.16a specified wireless metropolitan area networks (WMAN)

• IEEE 802.16a - support WMAN operating at 2-11 GHz that will provide broadband wireless connectivity to fixed, portable and nomadic devices

• It supports WMAN to connect 802.11 hot spots to the Internet providing a wireless alternative to cable and DSL for last mile broadband access

WAN Configuration

• The core components of a WAN system are the subscriber station (SS) and the base station (BS)

• A BS and one or more SSs can form a cell with a point-to-multipoint (P2MP) structure

• The BS controls activity within the cell including access to the medium by SSs, allocations to achieve QoS and admission to the network

• Multiple BSs can be configured to form a cellular wireless network. The radius of a cell can be 2-40 km while practical one is around 7-8 km with data rate as 70 Mbps per RF channel at a BS

• A point-to-point (P2P) or mesh topology also supported by the IEEE 802.16 standard

WMAN (wireless metropolitan area networks)

Protocol Stack

WiMAX: Physical Layer

• WiMAX can operate in both licensed and unlicensed bands

• The 2.5 and 3.5 GHz licensed bands will be the most common bands for WiMAX applications

• On 2.4 GHz and 5 GHz non-licensed bands, their usage could be limited due to interference, which can degrade QoS services

• The minimum channel bandwidth for WiMAX usage is 1.75MHz per channel, while 10 MHz is considered as an optimum

WiMAX: Physical Layer

• IEEE 802.16a standard featured with 256 OFDM physical layer specification conforms the ETSI HiperMAN standards

• OFDM (Orthogonal Frequency Division Multiplexing) 正交频分复用技术– Multi-Carrier Modulation 多载波调制– 将信道分成若干正交子信道，将高速数据信号转

换成并行的低速子数据流，调制到在每个子信道上进行传输

– 正交信号可以通过在接收端采用相关技术来分开，可以减少子信道之间的相互干扰

WiMAX: Physical Layer

• The transmission time is divided into frames that are divided into slots

• In an FDD system, uplink (SS to BS) and downlink (BS to SS) subframes are time aligned on separate frequency channels

• In a TDD system, each frame is divided into a downlink subframe and an uplink subframe

• In both modes, the length of any frame can vary under the control of the BS scheduler

• In TDD mode, the length of any uplink and downlink subframe can also vary, allowing asymmetric allocation between uplink and downlink

WiMAX: Physical Layer• IEEE 802.16 has specified several physical layers:

– physical layer for 10-66 GHz– physical layer for 2-11 GHz, which can be further

divided into subgroups

WiMAX: MAC Layer Features

• The on-air timing is based on consecutive frames that are divided into slots

• The size of frames and the size of slots within the frames can be varied under the control in the BS

• The 802.16 MAC provides a connection-oriented service to upper layers of the protocol stack

• The QoS parameters for a connection can be varied by the SSs making requests to the BS to change them while a connection is maintained

• While extensive bandwidth allocation and QoS mechanisms are specified, the details of scheduling and reservation management are left unstandardized

WiMAX: MAC Layer Features

• MAC protocal data units (MPDUs) are transmitted in time slots. MPDUs are the packets transferred between the MAC and the PHY layer

• A privacy sublayer performs authentication of network access and connection establishment, key exchange and encryption of MPDUs

• MAC service data units (MSDUs) are the packets transferred between the top of the MAC and the layer above

• A convergence sublayer at the top of the MAC enables Ethernet, ATM, TDM voice and IP services to be offered over the MAC layer

WiMAX: MAC Layer Features

• The MAC is concerned much with performing the mapping from MSDUs to the MPDUs

• Across MPDUs, MSDUs can be fragmented. Within MPDUs, MSDUs can be packed (aggregated).

• Automatic retransmission request (ARQ) is used to request the retransmission of unfragmented MSDUs and fragments of MSDUs

WiMAX: MAC Layer Features

• Each connection in the uplink is mapped to a scheduling service associated with rules for BS to allocate the uplink capacity

• The specification of the rules and the scheduling service for a particular uplink connection is negotiated at setup

• 4 scheduling services defined in the standard• Unsolicited grant service (UGS) carries traffic of

periodical fixed units of data. The BS grants of the size negotiated at setup regularly and preemptively without an SS request.

WiMAX: MAC Layer Features

• Used with UGS, an SS can report status of its transmission queue and request more by the grant management subheader

• The BS can allocate some additional capacity to the SS to allow it recover the normal queue state

• The real-time polling service serves traffic with dynamic nature and offers periodic dedicated request opportunities to meet time requirements

• An SS issues explicit requests and capacity is granted only as the real need. The overhead and latency is more. It is well suited for connections carrying VoIP, streaming video or audio traffic

WiMAX: MAC Layer Features

• The non-real-time polling service is similar to the real-time polling service. But connections send bandwidth requests by random access. The served traffic needs to tolerate longer delays and is insensitive to delay jitter suitable for Internet access with a minimum guaranteed rate;

• A best effort service is defined without throughput and delay guarantees. An SS can send requests for bandwidth by random access or dedicated transmission opportunities if available.

WiMAX: Mesh Networks

• Three types of important nodes in Mesh systems:– The SSs with direct links to a node are the

neighbors of the node. A node’s neighbors are one-hop away from the node.

– Neighbors of an SS form a neighborhood. `– An extended neighborhood contains all the

neighbors of the neighborhood.

WiMAX: Mesh Networks

WiMAX: Mesh Networks --centralized scheduling

• The centralized scheduling is more determined than that in the distributed scheduling mode

• The network connections and topology are the same as in the distributed scheduling mode

• The request and grant process uses the Mesh Centralized Scheduling (MSH-CSCH) message

• The BS determines the flow assignments from the resource requests from the SSs

• Then, the SSs determine the actual schedule from the flow assignments

WiMAX: Mesh Networks -- coordinated distributed scheduling

• In the coordinated distributed scheduling mode, all the nodes shall coordinate their transmissions in their extended two-hop neighborhood

• Control portion of each frame is used to regularly transmit its proposed schedule on a PMP basis to all its neighbors– Within a given channel, all neighbors receive the

same schedule– All stations in a network shall use the same

channel to transmit schedule information in a format of specific resource requests and grants

• Coordinated distributed scheduling ensures that transmissions are scheduled without a BS

WiMAX: Mesh Networks -- Uncoordinated distributed scheduling

• Uncoordinated distributed scheduling can be used for fast, ad-hoc setup of schedules on a link-by-link basis, established by directed requests and grants between two nodes

• Data and control traffic are scheduled to avoid collisions

• Both the coordinated and uncoordinated distributed scheduling employ a three-way handshake with MSH-DSCH message:– Request is sent to seek availabilities indicating potential

slots requested and actual schedule. Grant is sent indicating a subset of the suggested availabilities that fits the request. Grant confirmation is sent back by the requester

WiMAX: Mobility Supports

• Similar to the GSM networks, the standard of IEEE 802.16e introduces “Handover” schemes to migrate a mobile station from the air-interface of one base station to another to provide mobility

• Pre-handover process has been designed• The entire Handover process consists of the

following five stages:• Cell Reselection• Handover Decision and Initiation• Synchronization to Target BS downlink• Ranging• Termination with the Serving BS

• And some special scenarios of Handover process has been defined

Research Issues: QoS Service• IEEE 802.16d has been designed to support multimedia

service with different QoS requirements• The BS can determine the number of time slots that each SS

will be allowed to transmit in an uplink subframe• IEEE 802.16d has defined:

• The framework to support QoS service in the PMP topology

• The signaling mechanism for information exchange between BS and SS such as the connection set-up, BW-request, and UL-MAP

• The uplink scheduling for UGS service flow • IEEE 802.16 has not defined:

• The uplink scheduling algorithms to implement QoS to rtPS, nrtPS, and BE service flow

• The admission control and traffic policing scheme

Research Issues: Mesh Networks• IEEE 802.16d has been designed to support mesh networks

in order to extend the coverage of one BS and serve more SSs with limited resources

• The standard has defined a framework to effectively schedule the traffic among remote SSs, relay SSs, and the BS

• IEEE 802.16d has defined:• The centralized and 2 distributed scheduling mechanisms

for information transmission and the Internet access from remote SSs

• The management messages to deliver the scheduling information

• IEEE 802.16d has not defined: • The detailed scheduling algorithms to implement 3 traffic

scheduling strategies• The QoS issue and the scheduling algorithms to ensure the

QoS in the mesh networking

Research Issues: Mobility Supports

• The IEEE 802.16e standard has defined the procedures to support mobility

• But the standard has not defined any decision algorithm to decide when to perform a handover

• The challenge of the research on mobility support is how to design quick handover decision algorithms to perform fast handover and ensure the QoS during and after the handover

• Another challenge is to how to combine the mobility support with mesh networking to implement an mobile WiMax mesh network

• Another issue is to establish a comprehensive mobility management system to systematically control the mobility support

WiMAX