Basic Concepts of Wcdma
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Transcript of Basic Concepts of Wcdma
BASIC CONCEPTS OF WCDMA
UMTS AIR INTERFACE
UMTS AIR INTERFACE
WCDMA – FDD TECHNOLOGY• Multiple access technology is wideband CDMA
(WCDMA)• All cells at same carrier frequency• Spreading codes used to separate cells and users• Signal bandwidth 3.84 MHz
• Multiple carriers can be used to increase capacity• Inter-Frequency functionality to support mobility between
frequencies
• Compatibility with GSM technology• Inter-System functionality to support mobility between GSM
and UMTS
ACCESS TECHNOLOGY EXPLANATION
• Multiple Access means “Many users share the same medium”
• There are a number of different Multiple Access (MA) strategies :
• Time Division Multiple Access (TDMA)• Frequency Division Multiple Access (FDMA)• Code Division Multiple Access (CDMA)
TDMA
freq
uen
cy
time
User 1 User 1
Timeslot Period Frame Period
Idealised TDMA (with no guard periods)
Available Frequency Band
FDMA
freq
uen
cy
time
User 1
Frame Period (we may still need frames/timeslots for signaling)
Channel Bandwidth
Idealised FDMA (with no guard bands)
CDMA - DIRECT SEQUENCE SPREAD SPECTRUM
freq
uen
cy
time
code
Frame Period (we may still need frames/timeslots for signaling)
WCDMA TECHNOLOGY
5 MHz
3.84 M Hz
f
5+5 MHz in FDD mode5 MHz in TDD mode
Freq
uenc
y
TimeDirect Sequence (DS) CDMA
WCDMA Carrier
WCDMAWCDMA5 MHz, 1 carrier5 MHz, 1 carrier
TDMA (GSM)TDMA (GSM)5 MHz, 25 carriers5 MHz, 25 carriers
Users share same time and frequency
UMTS & GSM NETWORK PLANNING
GSM900/1800: 3G (W CDM A):
SC PLANNING
TRANSMISSION POWER
Frequency
5MHz
Power density
Time
High bit rate user
Low bit rate user
- Radio Frame: 38400 chip = 10ms = 15 Time Slots
- Time Slot: 2560 chip = 666,6 us (Slots are used for periodic functions (e.g. Power Control), they are not used for channel separation)
- Chip Rate: 3.84 Mcps
- Chip Time: 0.2604 us
WCDMA SPREADING OPERATION• In WCDMA two separate codes are used in the spreading
operation– Channelisation code– Scrambling code
Data
Bit rate
Chanelization code (SF)
scrambling code
chip rate chip rate
Chanelization (increases signal BW)- using orthogonal codes
Scrambling (doesn’t affect signal BW)- using pseudo noise code
Downlink Spreading Factor
Uplink Spreading Factor
Channelisation and Scrambling Codes
Scrambling & Channelization Codes
CONCEPTS OF RSCP AND EC/NO
• Two Important Terms
– RSCP– Ec/No, Ec/Io
TOTAL RECEIVED POWER IO• In a WCDMA network the User Equipment (UE) receives signals from
many cells• Io* = The sum total of all of these signals (dBm)• *Note: Sometimes Io is referred to as No, RSSI
RECEIVED POWER OF A CPICH• Using the properties of SCs the UE is able to extract the respective CPICH
levels from the sites received• RSCP = The Received Power of a Particular CPICH (dBm) • Ec = Energy per Chip
Ec2Ec1
THE CPICH QUALITY (EC/IO)• From the previous two measures we can calculate a signal quality for each
CPICH (SC) received• Ec/Io = Ec - Io (dB)• *Note: Sometimes Ec/Io is referred to as Ec/No
Ec1 Ec2
Logical Channels
RLC
MAC
Physical Layer
Logical Channels
Transport Channels
Physical Channels
Dedicated Logical Channels
Dedicated Traffic Channel (DTCH)
Dedicated Control Channel (DCCH)
Common Logical Channels
Broadcast Control Channel (BCCH)
Paging Control Channel (PCCH)
Common Control Channel (CCCH)
Common Traffic Channel (CTCH)
RLC Radio Link Control
MAC Medium Access Control
RNC Radio Network Controller
Logical ChannelsDTCH is a point-to-point channel, dedicated to one UE, for the transfer of user information. DTCH can exist both in the downlink and uplink.
DCCH is a point-to-point bi-directional channel that transmits dedicated control information between an UE and the network. This channel is established through RRC connection setup procedure.
BCCH is a downlink channel for broadcasting system control information.
PCCH is a downlink channel that transfers paging information.This channel is used when the network does not know the location cell of the UE, or the UE is in the cell connected state (utilizing UE sleep mode procedures).
CCCH is a bi-directional channel for transmitting control information between network and UEs. This channel is commonly used by the UEs having no RRC connection with the network, and by the UEs using common transport channels when accessing a new cell after cell reselection.
CTCH is a point to multipoint unidirectional channel for transfer of dedicated user information for all or a group of specified UEs.
Transport Channels
RLC
MAC
Physical Layer
Logical Channels
Transport Channels
Physical Channels
Dedicated Transport Channels
Dedicated Channel (DCH)
Common Transport Channels
Broadcast Channel (BCH)
Paging Channel (PCH)
Forward Access Channel (FACH)
Random Access Channel (RACH)
Downlink Shared Channel (DSCH)
Common Packet Channel (CPCH)
RLC Radio Link Control
MAC Medium Access Control
RNC Radio Network Controller
Transport ChannelsDCH is a channel dedicated to one UE used in uplink or downlink.
BCH is a downlink channel used for broadcast of system information into an entire cell.
PCH is a downlink channel used for broadcast of control information into an entire cell allowing efficient UE sleep mode procedures. Currently identified information types are paging and notification. Another use could be UTRAN notification of change of BCCH information.
FACH is a common downlink channel without closed loop power control used for transmission of relatively small amount of data.
RACH is a contention based uplink channel used for transmission of relatively small amounts of data, e.g., for initial access or non-real time dedicated control or traffic data.
DSCH is a downlink channel shared by several UEs carrying dedicated control or traffic data.
CPCH is a contention based uplink channel used for transmission of bursty data traffic. This channel only exists in FDD mode. CPCH is shared by the UEs in a cell and therefore it is a common resource. It is fast power controlled.
Physical ChannelsRLC
MAC
Physical Layer
Logical Channels
Transport Channels
Physical Channels
Dedicated Physical Channels
Dedicated Physical Channel (DPCH)
- Dedicated Physical Data Channel (DPDCH)
- Dedicated Physical Control Channel (DPCCH)
Common Physical Channels
Common Pilot Channel (CPICH)
Synchronisation Channel (SCH)
Primary Common Control Physical Channel (PCCPCH)
Secondary Common Control Physical Channel (SCCPCH)
Physical Random Access Channel (PRACH)
Physical Downlink Shared Channel (PDSCH)
Physical Common Packet Channel (PCPCH)
Acquisition Indicator Channel (AICH)
Page Indicator Channel (PICH)
Physical ChannelsThe DPCH = DPDCH + DPCCH carries the DCH in the downlink and uplink.
CPICH is a fixed rate (30 Kbps, spreading factor = 256) downlink physical channel that carries a pre-defined bit/symbol sequence
SCH is a downlink signal used for cell search. The SCH consists of two sub-channels, Primary and Secondary SCH.
PCCPCH is a fixed rate (30 Kbps, spreading factor = 256) downlink physical channel used to carry the BCH.
SCCPCH is a downlink physical channel used to carry FACH and PCH.
PRACH is an uplink physical channel used to carry RACH.
PDSCH is a downlink physical channel used to carry the DSCH.
PCPCH is an uplink physical channel used to carry CPCH.
AICH is a downlink physical channel used to carry acquisition indicators. Acquisition indicator AI_s corresponds to signature s on the PRACH or PCPCH.
PICH is a fixed rate (spreading factor = 256) downlink physical channel used to carry the page indicators. The PICH is always associated with a SCCPCH to which a PCH transport channel is mapped.