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 Concept
BS
BS
BS
Backbone Network
BS
BS
• Geographical separation
• Capacity (frequency) reuse
• Backbone connectivity
BS
Organization of Cellular Networks
HLR (home location
register)
– information
MSC (mobile
switching center)
VLR (visitor
location register)
– information
BS (base station)
- modulation, antenna
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
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
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
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
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
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
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
Traffic-Driven Power Saving in
Operational 3G Cellular Networks
Chunyi Peng1, Suk-Bok Lee1, Songwu Lu1, Haiyun Luo∗, Hewu Li2
1University of California, Los Angeles
2Tsinghua University
ACM Mobicom 2011
Las Vegas, Nevada, USA
Surging Energy Consumption in 2G/3G

0.5% of world-wide electricity by cellular networks in
2008 [Fettweis]




~124Twh in 2011 (expected) [ABI]
CO2 emission, comparable to ¼ by cars
Operation cost, e.g., $1.5B by China Mobile in 2009
Rising energy consumption at 16-20%/year

Moore’s law: 2x power every 4~5 years by 2030
[Fettweis]: G. Fettweis and E. Zimmermann, ICT energy consumption-trends and challenges, WPMC’08.
[ABI]: ABI Research. Mobile networks go green–minimizing power consumption and leveraging renewable energy, 2008.
Mobicom 2011
C Peng (UCLA)
19
Energy Consumption in Cellular Networks
0.1w
X 5B = 0.5GW
<10% (~1%)
Mobile
Terminals
1~3kw
X 4M = 8GW
10kw
X 10K = 0.1GW
>90% (~99%)
Cellular Infrastructure
~80% by BSes
The key to green 3G is on BS network
Source: Nokia Siemens Networks (NSN)
Mobicom 2011
C Peng (UCLA)
20
Case Study in a Regional 3G Network
Power (Kw)
Current
Ideal
Load: (#link in 15min)
Power-load curve in a big city with 177 BSes (3G UMTS)
Non-energy-proportionality (Non-EP) to traffic load
Mobicom 2011
C Peng (UCLA)
21
Root Cause for Energy Inefficiency

Traffic is highly dynamic


Fluctuate over time
Be uneven at BSes
Low usage at night
Large energy overhead at light traffic => non-EP.
Turn off BS completely to save more energy!
Mobicom 2011
C Peng (UCLA)
23
Solution I: Building Virtual Grids

Divide into BS virtual grids

BSes within a grid cover each other


Decouple coverage constraint
Location-dependent capacity meets location-dep. traffic
Virtual BS Grids
turn on/off BSes
s.t. cap >= load
✗
✗
✔
✗
Mobicom 2011
✗ ✗
✗
✔
✔ ✗j
✗
✗
i✔
✗
C Peng (UCLA)
ri + d(i,j) < Ri
rj + d(i,j) < Rj
24
Recall the Case Study
Current
GreenBS
Ideal
Power-load curve in a big city with 177 BSes (3G UMTS)
Mobicom 2011
C Peng (UCLA)
25
C-RAN, Cloud Radio Access Network:
Cloud Paradigm for Wireless Networks
中国移动通信公司
Cell Site Map


Dense Cell improve Coverage
Each site includes signal access
and processing
High Energy Consumption, Low Resource
Efficiency, Traffic unbalance.
C-RAN: Cloud Paradigm for Wireless
Networks

通过结合集中化的基带处理、高速的光传输网络和
分布式的远端无线模块，形成绿色清洁、集中化处
理、协作化无线电、云计算化的无线接入网构架
C-RAN: Cloud Paradigm for Wireless
Networks

C-RAN breaks down the base station into two parts





Baseband Unit (BBU) – a digital unit the implements the MAC
phy and Antenna array system (AAS)
Remote Radio Head (RRH) that obtains the digital signals,
coverts digital signals to analog, amplifies the power and sends
the actual transmission.
RRH typically connect using fiber with BU
RRH can support multiple cellular technology (GSM,
3G, LTE ) eliminating the need for multiple antennas.
BBUs are centralized and provides services on the
cloud