This document discusses CDMA technology, including its key attributes and components. It describes CDMA's high system capacity which is enabled by features like soft handoff and RAKE receivers that handle multipath signals. It also discusses power control in CDMA systems, which helps maximize capacity by adjusting mobile transmit power levels. The document outlines CDMA handoff methods and the sets of pilot channels used. It provides an overview of the CDMA2000 standard and its protocol stack.

1. CDMA
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15-6-2013

2. • FDMA
• TDMA
• CDMA
– Direct sequence
– Frequency hopping

3. Attributes of CDMA systems
• System Capacity:
• QoS:
– Soft Handoff
– RAKE receiver for multipath signals
– Ping pong effect elimination
– Hand off noise elimination
– Make before break handoff
• Economies:
– Lower average mobile power – longer battery life

4. RAKE receiver

5. Direct Sequence Spread spectrum
• The user data is multiplied by a PN code with
higher rate and spread.
• spreading factor is the ratio of the chip rate to
the data rate,
• At the receiver end by multiplying the received
baseband signal with a phase-coherent copy of
that PN code

6. Power control in CDMA
• Most important requirements in a CDMA
system
• Far-near problem
• With out power control – Difficult for BS to
detect signal with lower SIR
• To over come this power control commands
sent by BS to
– Increase power of remote MS
– Decrease power of nearby MS

7. Power control
• One key advantage is design of compact MS
with longer battery life.
• The system capacity is maximum when the
transmitter power of each mobile station is
adjusted such that the received SIR from each
mobile is just about enough to maintain the
desired quality.

8. Power control
• Works in both forward and reverse link
directions.
• MS requests BS to adjust it transmit power
• Closed loop power control is based upon direct
measurements of the desired signal
• Open loop power control where For example, the
mobile station could measure the signal received
from the base station, estimate the path loss on
the forward channel, and accordingly adjust the
transmit power of the reverse channel

9. Handoff in CDMA systems
• In GSM MS changes its frequency from one
cell to other, called Hard handoff
– Break before make
• Soft handoff in CDMA
– Make before break

10. Handoff in CDMA
• Handoffs Supported in IS-95
– Soft handoff
– Hard handoff
– CDMA to analog cellular system handoff

11. Handoff in CDMA
• MS continuously monitors pilot channels
• It send pilot channel information to BS for
initiation of handoff
• For the purpose of handoff, a mobile station
maintains four sets of pilots:
– Active set
– Candidate set
– Neighbor set
– Remaining set

12. CDMA2000
• Traffic types
– Traditional Voice and voice over IP
– Data traffic- IP based traffic
– Circuit-emulated broadband data(Fax etc. dialup
etc, circuit emulated audio, video)
– SMS

13. CDMA2000
• Bandwidth:
– 1.25 and 5 MHz(WCDMA also uses 5MHz)
• Quality of service:
– MS can request QoS if multiple services are being
used
• Packet Mode Data Services
– if there is a packet to send, the user attempts to
establish the dedicated and common control channels
using the multiple-access slotted Aloha scheme

14. CDMA2000
• Transmit Diversity
• With a 5 MHz, direct-spread CDMA system,
the user data may be divided into two or
more streams, each spread with an
orthogonal code, and then transmitted to
mobile stations. Because of multipath
diversity, the forward channel performance
may improve significantly ,

15. CDMA2000 protocol stack
• The link layer consists of the link access
control (LAC) and media access control (MAC)
layers.
• The MAC layer is divided into two sub layers:
– the physical layer-independent convergence
function (PLICF)
– and physical layer-dependent convergence
function (PLDCF)

16. CDMA2000 protocol stack
• Each traffic type coming from the higher layer
has a different QoS requirement in terms of
delays, delay variations, and error rates. The
function of the LAC is to ensure that various
types of traffic are transferred over the air
interface according to their QoS requirements.

17. CDMA2000 protocol stack

18. MAC sublayer
• A MAC sub layer performs the following functions
1. It controls user access to the physical layer (that
is, the medium) by resolving, if necessary,
contention among multiple applications from
the same user or among multiple users, and
scheduling its resources so as to ensure efficient
utilization of bandwidth. Resources include
buffers, spreading codes and so on.

19. MAC sublayer
2- User data and signaling information from the
upper layers (that is, the LAC layer and the
higher layers) are multiplexed, mapped into
different physical channels, and delivered to
the physical layer on a best-effort basis,
providing a basic level of transmission
reliability.

20. Contd..
• PLCIF: Functions that are independent of the
physical layer, such as controlling access to the
medium so as transmit packets, are performed by
the sub layer called PLICF.
• PLDCF: Functions performed at this sub layer
when transmitting over the air interface include
multiplexing logical channels coming from PLICF,
mapping them into physical channels, assigning
proper priorities to each according to its QoS
requirement, and delivering them to the physical
layer.

21. 17-05-2013

22. CDMA 2000(IS-2000)
• IS-95 -CDMAone
• IxRTT(One time Radio Txn tech.) 1.25 MHz
FDD pair
• Migration path for next G
• Multi carrier vs single carrier
• CDMA2000 logical extension of CDMAone
• Packet handling capability added to existing
architecture.(Packet data serving node)

23. CDMA evolution

24. Spectrum for CDMA evolution

25. Spectrum
• CDMA2000 and WCDMA are both based on
CDMA technology
• Unlike WCDMA(5MHz) spectrum, CDMA2000
can utilize Wide and narrow channels
• World wide uniform spectrum allocation
• LTE spectrum allocation? Next slide

26. LTE spectrum 2011-2015

27. Capacity of CDMA systems
• Eb/No (energy per bit/noise power per bit)
relation to capacity of system
• Processing gain(ratio of the spread bandwidth
to the un spread (or baseband) bandwidth)
• Number of Walsh codes
• Number of carriers aggregated
• Voice activity detection, Saves BW

28. CDMA capacity
• Offsets have to be different for different
sectors in a cellular system, their allocation
must be managed and coordinated in much
the same way as the channels for cellular and
TDMA systems.