A Tutorial on Multiple Access Technologies for Beyond 3G Mobile Networks

1
A Tutorial on Multiple Access Technologies for
Beyond 3G Mobile Networks

• Speaker Chen-Nien Tsai
• Authors A. Jamalipour et al.
• IEEE Communications Magazine, February 2005

2
Outline

• Introduction
• A Review of Multiple Access Technologies
• Key Features of 3G Multiple Access Technologies
• Multiple Access Technologies For B3G Systems
• Conclusions

3
Introduction (1/3)

• Beyond third-generation (B3G) wireless cellular
  systems...
• can achieve high-data-rate transmission.
• are capable of delivering multiple services to
  users.
• should provide services comparable to those
  offered by wired networks.
• Multimedia, VoIP, network games, etc.

4
Introduction (2/3)

• One of the main issues involved in the
  development of B3G systems is the choice of
  multiple access (MA) technology.
• The choice of MA technique could significantly
  enhance or lower the service quality.

5
Introduction (3/3)

• The existing MA techniques used in 2G/3G systems
  are basically suitable for voice communications
  but not for burst data traffic.
• Therefore, the need to develop new MA techniques
  for B3G becomes imperative.

6
Outline

• Introduction
• A Review of Multiple Access Technologies
• Key Features of 3G Multiple Access Technologies
• Multiple Access Technologies For B3G Systems
• Conclusions

7
A Review of Multiple Access Technologies

• A telecommunications network has finite resources
  (bandwidth).
• More than one user will access such limited
  bandwidth.
• An MA scheme must to control the share of
  bandwidth among multiple users
• Everyone can use services.
• No single user spends all available resources.

8
What is Multiple Access?

• The techniques that enable multiple users to
  share limited network resources efficiently.
• Four basic MA schemes
• FDMA (Frequency-Division MA)
• TDMA (Time-Division MA)
• CDMA (Code-Division MA)
• SDMA (Space-Division MA)

9
A Review of Multiple Access TechnologiesFDMA
(1/2)

• Dividing the available frequency spectrum into
  some frequency channels.
• Each channel occupies a portion of total
  available bandwidth and is given to a single
  user.
• Multiple users using separate frequency channels
  could access the same system.

10
A Review of Multiple Access TechnologiesFDMA
(2/2)
11
A Review of Multiple Access TechnologiesTDMA
(1/3)

• Dividing the time axis into portions or time
  slots, each assigned to a single user to transmit
  data information.
• Frame and multiframe concept
• A user could send a large data file within time
  slots of periodical frames.
• Data from a single user always sits in the same
  time slot position of a frame.

12
A Review of Multiple Access TechnologiesTDMA
(2/3)
13
A Review of Multiple Access TechnologiesTDMA
(3/3)

• TDMA has kept its dominance in wired and wireless
  systems for many years.
• 2G (GSM) and 2.5G (GPRS) adopted TDMA as their MA
  scheme.
• In a TDMA system, the used system bandwidth is
  usually divided in to smaller frequency channels.
• Hybrid FDMA/TDMA system

14
A Review of Multiple Access TechnologiesHybrid
FDMA/TDMA
15
A Review of Multiple Access TechnologiesCDMA
(1/3)

• In both FDMA and TDMA techniques the number of
  channels or time slots is fixed.
• By increasing the number of services from simple
  voice to more burst data transmissions, it lack
  of efficiency in utilizing the scarce spectrum.
• Hence, CDMA schemes started to come into
  commercial systems.

16
A Review of Multiple Access TechnologiesCDMA
(2/3)

• In a CDMA system
• Each user is assigned a spreading code.
• Users information is spread into a much wider
  spectrum using a high clock (chip) rate.
• It is possible to send multiple users
  information on the same frequency spectrum.
• CDMA is an MA scheme that has no fixed maximum
  number of users. (in theory)

17
A Review of Multiple Access TechnologiesCDMA
(3/3)
18
A Review of Multiple Access TechnologiesSDMA
(1/2)

• In SDMA, users are separated in a spatial way.
• Generally an adaptive array antenna technique is
  adopted.
• One disadvantage is the difficulty of separating
  two users who are placed near the base station.

19
A Review of Multiple Access TechnologiesSDMA
(2/2)
Space
Time
Frequency
20
Outline

• Introduction
• A Review of Multiple Access Technologies
• Key Features of 3G Multiple Access Technologies
• Multiple Access Technologies For B3G Systems
• Conclusions

21
Key Features of 3G Multiple Access Technologies
(1/3)

• International Mobile Telecommunications-2000
  (IMT-2000) is the umbrella specification of all
  3G systems.
• IMT Direct Spread (DS-CDMA, aka UTRA-FDD)
• IMT Time Code (TD-CDMA, aka UTRA-TDD)
• IMT Multicarrier (MC-CDMA, aka CDMA 2000)
• IMT Single Carrier (SC-CDMA, aka UWC-136)
• IMT Frequency Time (IMT-FT, aka DECT)

22
Key Features of 3G Multiple Access
TechnologiesIMT-2000 Family
23
Key Features of 3G Multiple Access Technologies
(2/3)

• IMT-2000 has five standard, four of which are
  based on CDMA.
• CDMA is a promising access technology for
  high-data-rate wireless communications.
• The advantages of CDMA
• Tolerance to the effects of channel fading.
• Efficient frequency reuse.
• Soft handover among cells is achievable.

24
Key Features of 3G Multiple Access Technologies
(3/3)

• Near-far problem
• A signal transmitted by a user who is far from
  the base station can easily be blocked by a
  signal from a nearby user.
• Calls for a power control technique.

25
Key Features of 3G Multiple Access
TechnologiesUMTS

• Stands for Universal Mobile Telecommunication
  System.
• Its the most important one of the 3G
  telecommunications systems
• Two modes of operation in the UMTS terrestrial
  radio access (UTRA)
• Time-division duplex (UTRA-TDD)
• Frequency-division duplex (UTRA-FDD)

26
Key Features of 3G Multiple Access
TechnologiesIMT Direct Spread

• The most important IMT-2000 system.
• Its being developed by 3GPP consortium
• UTRA-FDD
• UTRA-FDD is purely a CDMA-base system, but can be
  considered a combination of CDMA with FDMA.
• UTRA-FDD separating frequency spectrum for
  downlink and uplink.

27
Key Features of 3G Multiple Access
TechnologiesIMT Time Code (1/4)

• Its also being developed by 3GPP consortium
• UTRA-TDD
• Can be considered a combination of CDMA with
  TDMA.
• UTRA-TDD using the same spectrum for both uplink
  and downlink channels.

28
Key Features of 3G Multiple Access
TechnologiesIMT Time Code (2/4)

• For both UTRA-TDD and UTRA-FDD
• Each carrier has a bandwidth of 5MHz.
• Chip rate is 3.84 Mcps
• Each carrier is divided into 10-ms radio frames,
  and each frame further into 15 time slots.

29
Key Features of 3G Multiple Access
TechnologiesIMT Time Code (3/4)
30
Key Features of 3G Multiple Access
TechnologiesIMT Time Code (4/4)

• Advantages
• Its possible to flexibly arrange different
  numbers of time slots on uplink and downlink.
• It can change the ratio of uplink and downlink
  capacity dynamically.
• This concept would be necessary for B3G systems
  where burst data traffic becomes the dominant
  part.
• Appropriate to share power control information.

31
Key Features of 3G Multiple Access
TechnologiesIMT Multicarrier (1/4)

• The 3GPP2 promotes the CDMA2000 system.
• In the world or IMT-2000, this proposal is known
  as IMT-MC.
• CDMA2000 is backward compatible with IS-95
  systems, which is a standard for 2G system.

32
Key Features of 3G Multiple Access
TechnologiesIMT Multicarrier (2/4)

• The chip rate in CDMA2000 will be a multiple of
  1.2288 Mcps.
• The maximum rate will be 3x (3.6864 Mcps) in the
  first phase.
• The original goal was to have a system with three
  narrowband (1.25 MHz) carriers.
• Same bandwidth as an IS-95 carrier

33
Key Features of 3G Multiple Access
TechnologiesIMT Multicarrier (3/4)
34
Key Features of 3G Multiple Access
TechnologiesIMT Multicarrier (4/4)

• Advantages over DS-CDMA
• Suitable for frequency-selective fading channels.
• Low interference and less outband radiation.
• The disadvantages
• Require a high linear amplifier that causes
  inefficient power consumption.

35
Outline

• Introduction
• A Review of Multiple Access Technologies
• Key Features of 3G Multiple Access Technologies
• Multiple Access Technologies For B3G Systems
• Conclusions

36
Multiple Access Technologies For B3G Systems

• Main feature required in B3G systems
• High-data-rate transmission. (10 Mbps or more)
• It is difficult to introduce an actual
  compensation method for the fading effect of
  every user and every subchannel.
• The current CDMA schemes unfortunately do not
  satisfy the requirement of B3G.

37
Multiple Access Technologies for B3G
systemsAdvanced MA Schemes (1/3)

• Multicarrier DS-CDMA (MC/DS-CDMA)
• Combination of MC-CDMA and DS-CDMA
• Can achieve very-high-data-rate transmission with
  the advantages of both schemes.
• Requires an amplifier with high linearity, which
  results in power inefficiency. (similar to
  MC-CDMA)

38
Multiple Access Technologies for B3G
systemsAdvanced MA Schemes (2/3)

• TDD-CDMA
• A modified version of TD-CDMA.
• Better frequency efficiency than UTRA-FDD.
• Can easily achieve asymmetric transmissions.
• Will become a major MA scheme for B3G system.

39
Multiple Access Technologies for B3G
systemsAdvanced MA Schemes (3/3)

• Orthogonal frequency-division MA (OFDMA)
• Has attracted much attention in the IEEE 802.16
  standard.
• The concept is essentially the same as FDMA, but
  it has some advantages.
• Transmission with different rates among users is
  available according to each users requirement.

40
Outline

• Introduction
• A Review of Multiple Access Technologies
• Key Features of 3G Multiple Access Technologies
• Multiple Access Technologies For B3G Systems
• Conclusions

41
Conclusions

• The technologies for MA schemes that have been
  adopted in 3G systems are examined.
• None of the existing MA techniques would be able
  to satisfy the transmission criteria in B3G
  system.

42
Conclusions

• Next-generation networks will be developed
  through good management and a combination of the
  advanced MA technologies, rather than the
  development of new schemes.

43
References

• A. Jamalipour, T. Wada, and T. Yamazato, "A
  Tutorial on Multiple Access Technologies for
  Beyond 3G Mobile Networks," IEEE Communications
  Magazine, vol. 43, no. 2, Feb. 2005, pp. 110-117.
• Juha Korhonen, Introduction to 3G Mobile
  Communications 2nd ed., Artech House, 2003.

44
B3G MA schemes

• L.-L. Yang and L. Hanzo, Multicarrier DS-CDMA A
  Multiple Access Scheme for Ubiquitous Broadband
  Wireless Communications, IEEE Communications
  Magazine, vol. 41, no. 10, Oct. 2003, pp.
  116-124.
• R. Esmailzadeh and M. Nakagawa, TDD-CDMA for the
  4th Generation of Wireless Communications, IEEE
  Communications Magazine, vol. 41, no. 8, Aug.
  2003, pp. 8-15.
• P. Xia, S. Zhou, and G. B. Giannakis, Bandwidth-
  and power-Efficient Multicarrier Multiple
  Access, IEEE Trans. Commun., vol. 51, no.11,
  Nov. 2003, pp. 1828-37.