Readings related to the subject • General readings – WCDMA for UMTS – Harri Holma, Antti Toskala – HSDPA/HSUPA for UMTS – Harri Holma, Antti Toskala • Network planning oriented – Radio Network Planning and Optimisation for UMTS – Janna Laiho, Achim Wacker, Tomás Novosad – UMTS Radio Network Planning, Optimization and QoS Management For Practical Engineering Tasks – Jukka Lempiäinen, Matti Manninen
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Readings related to the subject
• General readings
– WCDMA for UMTS – Harri Holma, Antti Toskala
– HSDPA/HSUPA for UMTS – Harri Holma, Antti Toskala
• Network planning oriented
– Radio Network Planning and Optimisation for UMTS – Janna Laiho, Achim
Wacker, Tomás Novosad
– UMTS Radio Network Planning, Optimization and QoS Management For
Practical Engineering Tasks – Jukka Lempiäinen, Matti Manninen
Outline
• Background
• Key concepts
– Code multiplexing
– Spreading
• Introduction to Wideband Code Division Multiple Access (WCDMA)
• WCDMA Performance Enhancements
– High Speed Packet Access (HSDPA/HSUPA)
– Advanced features for HSDPA
Why new radio access system
• Need for universal standard (Universal Mobile Telecommunication System)
• Support for packet data services – IP data in core network
– Wireless IP
• New services in mobile multimedia need faster data transmission and flexible utilization of the spectrum
• FDMA and TDMA are not efficient enough– TDMA wastes time resources
– FDMA wastes frequency resources
• CDMA can exploit the whole bandwidth constantly
• Wideband CDMA was selected for a radio access system for UMTS (1997)– (Actually the superiority of OFDM was not fully understood by then)
Frequency allocations for UMTS
• Frequency plans of Europe, Japan and Korea are harmonized
• US plan is incompatible, the spectrum reserved for 3G elsewhere is
currently used for the US 2G standards
• IMT-2000 band in Europe:
– FDD 2x60MHz
Expected air interfaces and spectrums, source: “WCDMA for UMTS”
Standardization
• WCDMA was studied in various research programs in the industry and
universities
• WCDMA was chosen besides ETSI also in other forums like ARIB
(Japan) as 3G technology in late 1997/early 1998.
• During 1998 parallel work proceeded in ETSI and ARIB (mainly), with
commonalities but also differences
– Work was also on-going in USA and Korea
Standardization
• At end of 1998 different standardization organizations got together and created 3GPP, 3rd Generation Partnership Project.
• Different companies are members through their respective standardization organization.
ETSI Members
ETSI
ARIB Members
ARIB
TTA Members
TTA
T1P1 Members
T1P1
TTC Members
TTC
CWTS Members
CWTS
3GPP
WCDMA Background and Evolution
• First major milestone was Release ‘99, 12/99– Full set of specifications by 3GPP– Targeted mainly on access part of the network
• Release 4, 03/01 – Core network was extended– markets jumped over Rel 4
• Release 5, 03/02– High Speed Downlink Packet Access (HSDPA)
• Release 6, end of 04/beginning of 05– High Speed Uplink Packet Access (HSUPA)
• Release 7, 06/07– Continuous Packet connectivity (improvement for e.g. VoIP), advanced features for HSDPA
(MIMO, higher order modulation)
WCDMA Background and Evolution
2000 2002 2004 2006 2007200520032001
3GPP Rel -9912/99
3GPP Rel 4
03/01
3GPP Rel 5 (HSDPA)
03/02
3GPP Rel 6(HSUPA)
2H/04
3GPP Rel 7
HSPA+
06/07Further Releases
JapanEurope
(pre-commercial)Europe
(commercial)
HSDPA (commercial)
HSUPA (commercial)
Evolution of Mobile standards
EDGE
GPRSGSM
HSCSD
cdmaOne(IS-95)
WCDMA FDD
HSDPA/HSUPA
cdma2000
TD-SCDMA TDD LCR
cdma20001XEV - DO
cdma20001XEV - DV
TD-CDMATDD HCR
HSDPA/HSUPA
LTE
Current WCDMA markets• Graph of the technologies adopted by the wireless users worldwide:
• Over 3.5 billion wireless users worldwide
• GSM+WCDMA share currently over 88 % (www.umts-forum.org)
• CDMA share is decreasing every year
GSM (80.9%)
CDMA (12%)
WCDMA (4.6%)
iDEN (0.9%)
PDC (0.8%)
US TDMA (0.8%)
Current WCDMA markets
• Over 200 million WCDMA subscribers globally (04/08) (www.umts-forum.org)
– 10 % HSDPA/HSUPA users
• Number of subscribers is constantly increasing
Mil
lio
n s
ub
scri
bers
Key concepts
• CDMA
• Spread Spectrum
• Direct Sequence spreading
• Spreading and Processing gain
Multiple Access Schemes
• Frequency Division Multiple Access (FDMA), different frequencies for different users– example Nordic Mobile Terminal (NMT) systems
• Time Division Multiple Access (TDMA), same frequency but different timeslots for different users, – example Global System for Mobile Communication (GSM)– GSM also uses FDMA
• Code Division Multiple Access (CDMA), same frequency and time but users are separated from each other with orthogonal codes
Code
Frequency
Time
1
2
N
…
TDMAFDMA CDMA
Spread Spectrum
• Means that the transmission bandwidth is much larger than the information
bandwidth i.e. transmitted signal is spread to a wider bandwidth
– Bandwidth is not dependent on the information signal
• Benefits
– More secure communication
– Reduces the impact of interference (and jamming) due to processing gain
• Classification
– Direct Sequence (spreading with pseudo noise (PN) sequence)
– Frequency hopping (rapidly changing frequency)
– Time Hopping (large frequency, short transmission bursts)
• Direct Sequence is currently commercially most viable
Spread Spectrum
• Where does spread spectrum come from
– First publications, late 40s
– First applications: Military from the 50s
– Rake receiver patent 1956
– Cellular applications proposed late 70s
– Investigations for cellular use 80s
– IS-95 standard 1993 (2G)
– 1997/1998 3G technology choice
– 2001/2002 Commercial launch of WCDMA technology
Direct Sequence
• In direct sequence (DS) user bits are coded with unique binary
sequence i.e. with spreading/channelization code
– The bits of the channelization code are called chips
– Chip rate (W) is typically much higher than bit rate (R)
– Codes need to be in some respect orthogonal to each other (cocktail party
effect)
• Length of a channelization code
– defines how many chips are used to spread a single information bit and thus
determines the end bit rate
– Shorter code equals to higher bit rate but better Signal to Interference and
Noise Ratio (SINR) is required
• Also the shorter the code, the fewer number of codes are available
– Different bit rates have different geographical areas covered based on the
interference levels
Direct Sequence
• Transmission (Tx) side with DS
– Information signal is multiplied with channelization code => spread signal
• Receiving (Rx) side with DS
– Spread signal is multiplied with channelization code
– Multiplied signal (spread signal x code) is then integrated (i.e. summed
together)
• If the integration results in adequately high (or low) values, the signal is meant for the receiver
Direct Sequence
Direct Sequence
Processing gain and Spreading
Frequency
Despread narrowband signal
Spread wideband signal
W
R
Po
we
r d
en
sit
y (
Wa
tts
/Hz)
Po
we
r d
en
sit
y (
Wa
tts
/Hz)
Frequency
Transmitted signalbefore spreading
Received signalbefore despreading
Interference for the part we are interested in
Processing gain and Spreading
Frequency
Po
we
r d
en
sit
y (
Wa
tts
/Hz)
Po
we
r d
en
sit
y (
Wa
tts
/Hz)
Frequency
Received signalafter despreading butbefore filtering
Received signalafter despreading andafter filtering
Transmitted signal
Interference
Processing gain and Spreading
• Spread spectrum systems reduce the effect of interference due to processing gain
• Processing gain is generally defined as follows:
– G[dB]=10*log10(W/R), where ’W’ is the chip rate and ’R’ is the user bit rate
• The number of users takes negative effect on the processing gain. The loss is defined as:
– Lp = 10*log10k, where ’k’ is the amount of users
• Processing gain when the processing loss is taken into account is
– Gtot=10*log10(W/kR)
• High bit rate means lower processing gain and higher power OR smaller coverage
• The processing gain is different for different services over 3G mobile network (voice, web browsing, videophone) due to different bit rates
– Thus, the coverage area and capacity might be different for different services depending on the radio network planning issues
Processing gain and Spreading
• Processing gain is what gives CDMA systems the robustness against
self-interference that is necessary in order to reuse the available 5
MHz carrier frequency over geographically close distances.
• Examples: Speech service with a bit rate of 12.2 kbps
– processing gain 10 log10(3.84e6/12.2e3) = 25 dB
– For speech service the required SINR is typically in the order of 5.0 dB, so
the required wideband signal-to-interference ratio (also called “carrier-to-
interference ratio, C/I ) is therefore “5.0 dB minus the processing” = -20.0
dB.
– In other words, the signal power can be 20 dB under the interference or
thermal noise power, and the WCDMA receiver can still detect the signal.
– Notice: in GSM, a good quality speech connection requires C/I = 9–12 dB.
Introduction to Wideband Code Division Multiple Access (WCDMA)
• Overview
• Codes in WCDMA
• QoS support
• Network Architecture
• Radio propagation and fading
• RAKE receiver
• Power Control in WCDMA
• Diversity
• Capacity and coverage
WCDMA System
• WCDMA is the most common radio interface for UMTS systems
• Wide bandwidth, 3.84 Mcps (Megachips per second)
– Maps to 5 MHz due to pulse shaping and small guard bands between the
carriers
• Users share the same 5 MHz frequency band and time
– UL and DL have separate 5 MHz frequency bands
• High bit rates
– With Release ’99 theoretically 2 Mbps both UL and DL
– 384 kbps highest implemented
• Fast power control (PC)
=> Reduces the impact of channel fading and minimizes the interference
WCDMA System
• Soft handover
– Improves coverage, decreases interference
• Robust and low complexity RAKE receiver
– Introduces multipath diversity
• Variable spreading factor
– Support for flexible bit rates
• Multiplexing of different services on a single physical connection
– Simultaneous support of services with different QoS requirements:• real-time
– E.g. voice, video telephony
• streaming
– streaming video and audio
• interactive
– web-browsing
• background
– e-mail download
Codes in WCDMA
• Channelization Codes (=short code)
– Codes from different branches of the code tree are orthogonal
– Length is dependent on the spreading factor
– Used for
• channel separation from the single source in downlink
• separation of data and control channels from each other in the uplink
– Same channelization codes in every cell / mobiles and therefore the additional scrambling code is needed
• Scrambling codes (=long code)
– Very long (38400 chips = 10 ms =1 radio frame), many codes available
– Does not spread the signal
– Uplink: to separate different mobiles
– Downlink: to separate different cells
– The correlation between two codes (two mobiles/NodeBs) is low
• Not fully orthogonal
Codes in WCDMA
• For instance, the relation between downlink physical layer bit rates and codes