Transcript Wireless Networks

Outline
• Wireless introduction
• Wireless cellular (GSM, CDMA, 3G, 4G)
• 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
Access techniques for mobile
communications
FDMA (TACS)
P
F
T
TDMA (GSM, DECT)
ATDMA (UMTS)
P
F
T
P - Power
T - Time
F - Frequency
CDMA (UMTS)
P
F
T
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
inner-product S . T =
1
m
m
S
Si.Ti
i=1
C4,1 = (1,1,1,1)
C = (1,1)
2,1
C4,2 = (1,1,-1,-1)
C
C = (1,-1)
= (1,-1,1,-1)
4,3
2,2
C
4,4
= (1,-1,-1,1)
= 0 S .S = 1
Spread Spectrum
•
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)
• WCDMA, CDMA 2000, TD-SCDMA, WiMAX
•
3+G, 4G systems
– OFDM, Software radio, Array antennas
– WiMAX, LTE (Long Term Evolution) ?
Multiple Migration Paths Are Available
•
•
2G
•
PDC
•
GSM
TDMA
(IS-136)
•
CDMA
(IS95A/B)
3G
WCDMA
•
•
3+G
•
HSPDA
GPRS
•
•
•
•
2.5G
EDGE
•
4G
•
OFDM
•
Software
radio
Array
antennas
•
•
•
CDMA •
One
•
1xRTT
1XEVDO/HDR
1 xtreme • CDMA2000
•
•
•
•
TD-SCDMA
WiMAX
WiMAX
LTE
Architecture
•
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
Cellular Concept
BS
BS
BS
Backbone Network
BS
BS
• Geographical separation
• Capacity (frequency) reuse
• Backbone connectivity
BS
1G: AMPS (Advanced Mobile Phone System)
---- FDMA
B
B
A
C
G
A
D
F
E
D
F
C
G
E
B
C
G
A
D
F
E
• 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
Channels are divided into 4 categories:
1. Control (base to mobile) to manage the system
2. Paging (base to mobile) to alert mobile users to incoming
calls
3. Access (bidirectional) for call set up and channel
assignment
4. Data (bidirectional) for voice, FAX, or data
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
HLR (home location
register)
– information
MSC (mobile
switching center)
VLR (visitor
location register)
– information
BS (base station)
- modulation, antenna
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 Division
Duplex)
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
Frame
1944 bits in 40 ms( 48600 b/s)
SLOT 1
SLOT 2
G R DATA11 SYNC2
28
6 6
6
SLOT 3
SLOT 4
DATA11
22
SACCH1 DVCC
G:GUARD TIME R:RAMP TIME
DVCC: DIGITAL VERIFFICATION COLOR CODE
RSVD: RESERVE FOR FUTURE USE
SYNC2
28
SACCH
12
DATA1
130
12
SLOT 5
12
SLOT 6
DATA11
22
MOBILE TO BASE
DVCC
12
BASE TO MOBILE
DATA1
130
RSVD
12
2G: European GSM (Group Special Mobile)
• Second Generation: Digital voice
• FDMA / TDMA
• Frequency Division duplex (890-915 MHz Up; 935960 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
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
video
conference
remote
medical
service
384K
16K
internet
video
on
demand
mobile
TV
electronic
newspaper ISDN
64K
32K
video
catalogue
shopping
telephone
conference
voice
mail
pager
distribution
services (voice)
electronic
publishing
9.6K
telephone
FAX
2.4K
mobile
radio
distribution
services
(data)
1.2K
bidirectional
unidirectional
point to point
multicast
multipoint
Third generation bandwidth assignment
-- high frequency 2 GHz, wideband 150 MHz
ITU
IMT-2000
1885
1920
IMT-2000
MSS
1980
2010 2025
2110
MSS
2170
2200 MHz
EUROPE
DECT
1880
IMT-2000
1900
MSS
1980
2010 2025
IMT-2000
2110
MSS
2170
2200 MHz
JAPAN
PHS
1885 1895 1918.1
IMT-2000
MSS
1980
2010 2025
IMT-2000
2110
MSS
2170
2200 MHz
UTRAN Architecture
(UMTS Terrestrial Radio Access Net)
Core Network
Iu
Iu
UTRAN
RNS
Iu
RNC
RNS
r
I
Iub
Site Contr
Site Contr
Site Contr
Site Contr
BTS BTS BTS
BTS BTS BTS
BTS BTS BTS
BTS BTS BTS
B-nodeub
B-node
I
B-node ub
RNC
Iub
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
Radio Interface - protocol architecture
C-plane
U-plane
L3
RRC
L2/LAC
LAC
LAC
LAC
Logical
channels
L2/MAC
RLC
RLC
RLC
RLC
MAC
Transport
channels
L1
Physical Layer
Layer 1 - up link physical channels
(W-CDMA example)
Dedicated Physical
Data Channel
Data
0.667 ms
Pilot
Feedback
indicator
Slot#1 Slot#2
Slot#i
Frame#1Frame#2
Transport Dedicated Physical
Transmit
power control format ind. Control Channel
Slot#15
Frame#i
10 ms
Frame#72
frame
superframe
Layer 1 - down link physical channels
(W-CDMA example)
DPCCH
Pilot
TPC
DPDCH
Data
TFI
0.667 ms
Slot#1Slot#2
Frame#1 Frame#2
Slot#i
Slot#15
Frame#i
10 ms
Frame#72
frame
superframe
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
WMAN (wireless metropolitan area networks)
WMAN 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
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-bylink 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, BWrequest, 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
New Physical Layer
• 正交频分复用OFDM (Orthogonal Frequency Division
Multiplexing) ：将信道分成许多正交子信道，并在每个子
信道上进行窄带调制和传输，各个子信道的载波相互正交
以减少子信道间的相互干扰。
• 多入多出MIMO (Multiple Input Multiple Output)：MIMO
的主要任务是将资料经过多重切割之后，经由多重天线并
行同步传送。在传送的过程中，切割过的数据经由不同的
天线、不同的路径反射或穿透障碍物，到达多重天线的接
收端，再由相关算法重新计算后进行重组。
经由多支面向不同方向的天线进行收发，一来可以减少遇
到障碍物或干扰源的骚扰；二来就算遇到障碍物或干扰源
也只需要重传遗失的数据而不需要全部重传。在MIMO技
术的辅助下，数据流由一条变成了多条，如果其中一条遇
到障碍，另外几条仍可正常传送与接收数据，重传时也只
需要重新传送遗失的那一小部分数据即可。
• 智能天线 (Smart Antena)：其实这是一个由多组独立天线
组成的天线阵列，天线阵列以调整相位差的方式动态地调
整波束的方向，就如同加装了一支定向天线，将波束指向
接收数据的目标区，以扩大无线网络的最大覆盖范围。
New Physical Layer
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