1. Cellular Industry Landscape
Suresh Kalyanasundaram
Global Telecom Solutions Sector
Motorola
Arlington Heights
Illinois, USA

2. Outline Cellular industry overview Role of standards
Generations of cellular technologies
Sketchy details of GSM air interface
Enhancements to GSM air interface for GPRS/EDGE
Wireless link and interactions with TCP
Where to next? (3G vision, WLANs, etc.)

3. How the industry is organized?
Chip manufacturers
Texas Instruments, Qualcomm, Motorola, etc.
Equipment manufacturers
Motorola, Nokia, Ericsson, Siemens, Lucent, etc.
Operators
In India: Hutch, Bharti Cellular, Reliance, Airtel, etc.
In US: Cingular, AT&T, Nextel, Vodafone

4. Equipment manufacturers
Handset manufacturers
Motorola, Nokia, etc.
LG, Samsung,
SonyEricsson
etc.
Infrastructure equipment manufacturers
Motorola, Nokia, etc.
Lucent, Nortel, etc.

5. Typical Voice Network Architecture (GSM, 2G)
PSTN
MS- Mobile Station
BTS - Base transceiver station
BSC - Basestation controller
MSC - Mobile switching center
PSTN - Public switched telephone network
MSC
BSC
BTS
BTS MS MS MS

6. Interfaces
Standardized open interfaces between different network elements
Example: BTS to MS interface is called the air interface
BTS from one manufacturer should be able to operate with MS from another manufacturer
Standards bodies define messages exchanged across open interfaces
Encourages competition

7. Role of standards bodies
Define network architecture
Apportion tasks to different network elements
Define open interfaces and messages exchanged across those interfaces
Define protocols across open interfaces
Set expected performance standards from different network elements
Example: ETSI (European Telecommunications Standardization Institute) defined the GSM (Global system for mobile communications) standards

8. Families of Standards
Currently two main families of standards: GSM and CDMA
GSM — GPRS — EDGE — UMTS — HSDPA
IS-95 — CDMA 1X — CDMA 1X EV-DO/DV
3GPP (Third generation partnership project): Handles GSM family of standards
3GPP2: Handles CDMA family of standards

9. How manufacturers distinguish their products
Is everything standardized?
If everything is standardized, how do manufacturers distinguish their products?
No, not everything is standardized.
Manufacturers have a lot of freedom to decide what proprietary algorithms go in the different network elements within the constraints imposed by the standards

10. Generations of cellular technologies
1G: Analog cellular voice
Examples: AMPS (American mobile phone system), NMT (Nordic mobile telephony)
2G: Digital cellular voice
Examples: GSM, IS-95, PDC, US-TDMA (IS-136)
Provided significant capacity increase and voice quality improvement over 1G

11. Generations of cellular technologies (Cont’d)
2.5G: Digital cellular voice + low-speed packet switched data
Examples: GPRS (General packet radio service), EDGE (Enhanced data rates for GSM evolution), CDMA 1X
3G: Fully integrated voice + high-speed packet data (upto 2 Mbps)
Examples: UMTS (Universal mobile telecommunications system), CDMA 1X EV-DO/DV

12. Cellular Packet Data (2.5G/3G)
Enables wireless web browsing, access to , FTP, etc.
Provides the same ubiquitous coverage provided by cellular voice.
Packet-switching technology over the air interface
Enables charging only for times when the user has data to transmit
Efficient use of air interface resources to suit bursty data traffic

13. Some details of GSM air interface
The spectrum allocated to GSM is divided into 200 KHz carriers. (FDMA, Frequency division multiple access)
Each carrier is divided into frames with 8 timeslots (TDMA, Time division multiple access)
Hybrid FDMA/TDMA multiple access scheme

14. Enhancements to GSM air interface for GPRS/EDGE
Adaptive modulation and coding (AMC):
For voice, a single modulation and coding scheme (MCS) is chosen to give reasonable performance for users at the cell edge.
Other users closer to the cell center have better channel conditions, but cannot exploit it.
With AMC, users with better channel conditions reduce the coding to get more useful bits across.

15. Adaptive Modulation and Coding (Cont’d)
Multiple modulation and coding schemes to make use of better radio conditions
CS 1-4, provides rates of 8-20 kbps per timeslot in GPRS
MCS 1-9 provides rates of kbps per timeslot in EDGE
Dynamic MCS selection

16. Enhancements to GSM air interface (Cont’d)
Timeslot allocation
Each user can be allocated multiple timeslots (for voice, a user is allocated only a single timeslot)
Multiple users can be allocated the same timeslot
Each user can be allocated a maximum of 8 timeslots (according to standards, but there are no handsets available yet).

17. Enhancements to GSM air interface (Cont’d)
Assuming good channel conditions => CS-4 usage, a user can get upto 160 kbps in GPRS
Assuming MCS 9 a user can get upto kbps in EDGE
Allowing multiple users to share a timeslot enables usage of air interface resources by other users when a certain user is idle

18. Enhancements to GSM air interface (Cont’d)
“Always on” connection -- Similar to PCs connected to LANs
Unlike “dial-up” connections that require elaborate procedure to get a session going
Allows operators to charge only for the traffic that a user generates

19. New Network Elements for GPRS/EDGE
PSTN
Internet
GGSN
SGSN
MSC
PCU
BSC
Combined voice
and data path
BTS
Data path
BTS
Voice path MS MS MS

20. New Network Elements (Cont’d)
PCU – Packet control unit
SGSN – Serving GPRS support node
GGSN – Gateway GPRS support node

21. Wireless Link and TCP
Transmission Control Protocol (TCP) runs end-to-end between the mobile terminal and the server
Errors on wireless links much higher than that on wired links
TCP is designed for wired networks, and TCP running at the sender reduces transmission rate when it sees errors occurring on wireless links
TCP interprets packet losses as indication of congestion

22. Wireless Link and TCP (Cont’d)
However, these errors are due to error-prone wireless medium
Radio link control (RLC) protocol tries to hide the wireless link from TCP
RLC performs hybrid ARQ (automatic repeat request) protocol
Hybrid of forward error correction (FEC) and local retransmissions

23. Simplified protocol stack
Application
Application
TCP
TCP IP IP
RLC
RLC
MAC
MAC
GSM RF
PCU
Server MS

24. The 3G vision (UMTS)
A user can get upto 2 Mbps, under good channel conditions, if they get exclusive access to a carrier
Even under poor channel conditions, users can get 384 kbps, if they get exclusive access to a carrier
Based on WCDMA (wideband code division multiple access) technology
5 MHz carriers instead of 200 KHz narrowband carriers

25. The 3G vision (Cont’d) Support for multimedia
Capability to meet the different Quality of Service (QoS) requirements of different traffic types
Four different traffic classes identified
Conversational (conversational voice, video telephony, etc.)
Streaming (Streaming audio and video)
Interactive (Interactive web browsing, telnet, etc.)
Background (Background download of s, FTP, etc.)

26. Challenges today’s cellular industry
Over capacity and falling prices
Heavy recruitment in anticipation of unrealistic future growth expectations
Huge license fees to obtain 3G licenses
Requirement to entirely replace existing equipment to move to UMTS from GSM/GPRS/EDGE.
Competition from WLANs (Wireless local area networks)

27. Wireless Local Area Networks
Smaller coverage area, but higher bitrates (up to 10 Mbps)
Cheap access points and WLAN cards
Unlicensed spectrum
Ubiquity may not be needed for data
People drive a lot in the west, but will not be browsing the Internet while driving.
Only need wireless data at airports, highway rest areas, coffee shops, etc.
In Japan, wireless data has become more popular because Japanese use trains

28. Conclusions
Huge scope for cell phone penetration in developing nations, such as, India.
Low telephone density
Can be used as an alternative to non-existent landline connections
In developed nations, very high penetration rates already
Need wireless data to take off
Wireless data will become popular eventually
Question is if it will be the WLAN variety or the cellular variety