Outline

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

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

BS BSBS

BSBSBS

Backbone Network

Organization of Cellular Networks

BS (base station)- modulation, antenna

MSC (mobile switching center)

HLR (home locationregister)– information

VLR (visitorlocation register)– information

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 whi

ch 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

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

Traffic-Driven Power Saving in Operational 3G Cellular Networks

ACM Mobicom 2011Las Vegas, Nevada, USA

Chunyi Peng1, Suk-Bok Lee1, Songwu Lu1, Haiyun Luo , Hewu Li∗ 2

1University of California, Los Angeles2Tsinghua University

Surging Energy Consumption in 2G/3G 0.5% of world-wide electricity by cellular netw

orks 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

Mobicom 2011 19C Peng (UCLA)

[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.

Energy Consumption in Cellular Networks

0.1w X 5B = 0.5GW

1~3kw X 4M = 8GW

10kw X 10K = 0.1GW

>90% (~99%)Cellular

Infrastructure

>90% (~99%)Cellular

Infrastructure

<10% (~1%)Mobile

Terminals

<10% (~1%)Mobile

Terminals ~80% by BSes

The key to green 3G is on BS network

Mobicom 2011 20C Peng (UCLA)Source: Nokia Siemens Networks (NSN)

Case Study in a Regional 3G Network

Non-energy-proportionality (Non-EP) to traffic loadMobicom 2011 21C Peng (UCLA)

Load: (#link in 15min)

Ideal

Current

Power-load curve in a big city with 177 BSes (3G UMTS)

Root Cause for Energy Inefficiency Traffic is highly dynamic

Fluctuate over time Be uneven at BSes

Mobicom 2011 C Peng (UCLA) 23

Large energy overhead at light traffic => non-EP. Turn off BS completely to save more energy!

Low usage at night

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. tr

affic Virtual BS Grids


turn on/off BSes s.t. cap >= load

ji ri + d(i,j) < Ri

rj + d(i,j) < Rj✔✗

✗✗✗

✗

✗

✗✗✗

✗

✔✔✔

Recall the Case Study

Ideal

Current

GreenBS


Power-load curve in a big city with 177 BSes (3G UMTS)

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 breaks down the base station into two parts Baseband Unit (BBU) – a digital unit the implements th

e MAC phy and Antenna array system (AAS) Remote Radio Head (RRH) that obtains the digital signa

ls, 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

C-RAN: Cloud Paradigm for Wireless Networks

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