Department of Electrical and Information Technology
3G Evolution
Chapter:8WCDMA evolution: HSPA
and MBMS
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Isael Diaz
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Outline
• Evolution
• HSPA and MBMS
• Multiple Access
• Direct Sequence Spread Spectrum
• Network Architecture
• Protocol Architecture
• Physical Layer
• Channelization Codes
• Asynchronous Operation
• Power Control
• Soft handover
• Packet Data Session
WCDMA: Evolution
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HSDPA -improved downlink packet-data support-Reduced delays- 14Mbits/s peak data rate~3xR99 capacity
Enhanced uplink – improvedUplink packet-data support - Reduced delays - 5.74 Mbps peak data rate - ~2xR99 capacity
- MBMS – Multimedia broadcastMulticast Services - Introduction of improved broadcast servicios ('Mobile TV')
- MIMO and higher-order modulation - 28 Mbps DL peak data rate - 11 Mbps UL peak data rate- Continuous Packet Connectivity - 'Always on' user experience
*Image inspired “3G evolution HSPA and LTE Mobile Broadband”
WCDMA: HSPA and MBMS
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• HSPA (More details in further chapters)– Evolution of WCDMA– 14Mbps in DL– 5.8Mbps in UL
• MBMS (Further explanation in Chapter 12)– Enables broadcasting
services such as TV, radio, traffic reports, etc.
WCDMA: Multiple Access
• CDMA– Multiple users
share physical medium in time and frequency
– Based on interference robustness
– All user have same carrier frequency
– Each user has a unique code
– Benefits from multi path environment
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*Image courtesy of Ericsson AB
WCDMA: DS-SS
• Direct Sequence Spread Spectrum– Same carrier frequency– Looks like noise if correct spreading code is not
used– To recover the transmitter signal the receiver needs
the spreading code
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*Image courtesy of Ericsson AB
WCDMA: Network Architecture
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• An UE communicates with one or more NodeBs
• NodeB is responsible for– FEC– Modulation– Spreading
• RNC in charge of– Control of one or
more NodeBs– Charge of call set
up– QoS– Radio resources
(ARQ)*Image inspired “3G evolution HSPA and LTE Mobile Broadband”
WCDMA: Protocol Architecture
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• PDCP– Performs header
compression• RLC
– IP packet segmentation
– ARQ protocol• MAC
– Interfaces logical channels and transport channels
• PHY– Coding, spreading,
modulation, etc.*Image inspired “3G evolution HSPA and LTE Mobile Broadband”
WCDMA: Physical Layer
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• 3.84Mchip/s• Turbo coder 1/3• QPSK for DL• BPSK for UL• Every specific spreading
codes corresponds to a each physical channel
• CPICH reference channel for DL
*Image inspired “3G evolution HSPA and LTE Mobile Broadband”
WCDMA: Channelization Codes (OVSF)
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• Mutual orthogonality• OVSF must be selected from different branches• Different OVSF provide different spreading factors• Different Spreading factors provide different data-rates• Spreading factor is selected by the MAC layer• Some channelization codes are pre-allocated (CPICH, cell
specific information, etc)
*Image inspired “3G evolution HSPA and LTE Mobile Broadband”
WCDMA: Asynchronous Operation
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• WCDMA does not require inter-base station synchronization (no GPS dependency)
• Advantage– Reduced deployment efforts
• Drawback– BS interference to other BS– More challenging cell-search procedure– Complicated handover implementation
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WCDMA: Power control
• Formally named fast closed/closed loop power control
• Attempts to avoid the near-far problem by:– measuring the UE
signal 1500 times/sec
– Regulating the transmission power of both UE and BS
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WCDMA: Soft handover
• The UE communicates with multiple cells simultaneously (active set)– The RNC determines
based on measurements which cells are part of the active set
– Provides diversity against fast fading in both DL and UL
– Typically a rake receiver is used
– “Or of the downs” ensures that average power is kept low
*Image is courtesy of Ericsson AB
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WCDMA: Packet Data Session
• UE: Cell search (connection request)
• RNC: Channelization codes available
• RNC: Interference level• RNC Connection
established• Transmission power
varies according to traffic pattern
*Image inspired Ove Edfors, lecture on WCDMA
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WCDMA: Summary
• HSPA is the evolution of WCDMA• Spread Spectrum• A major milestone in mobile telecommunication• Flexible radio interface• Transmission power dependent on traffic pattern• Sensitive to inter-cell interference• Sensitive to near-far problem
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• Thank you for your attention