Processing gain and Spreading Frequency Despread narrowband signal Spread wideband signal W R Power density (Watts/Hz) Power density (Watts/Hz) Frequency Transmitted signal before spreading Received signal before despreading Interference for the part we are interested in
Processing gain and Spreading Frequency Power density (Watts/Hz) Power density (Watts/Hz) Frequency Received signal after despreading but before filtering Received signal after despreading and after filtering Transmitted signal Interference
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 log 10 (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)
Simultaneous support of services with different QoS requirements:
up to 2 10 Transport Format Combinations, selectable individually for every radio frame (10 ms)
going towards IP core networks greatly increases the usage of simultaneous applications requiring different quality, e.g. real time vs. non-real time
Optimized usage of different transport channels for supporting different QoS
QoS support Example: D ownlink S hared Ch annel D ownlink D edicated Ch annels .... 10 ms Data Rate 2 Mbps Code 5 Code 4 Code 3 Code 2 Code 1 USER 1 USER 2 USER 3 USER 4 Time USER 1 USER 2 USER 3 USER 1 USER 1 USER 4 USER 2
UMTS Terrestrial Radio Access Network (UTRAN) Architecture
New Radio Access network needed mainly due to new radio access technology
Core Network (CN) is based on GSM/GPRS
Radio Network Controller (RNC) corresponds roughly to the Base Station Controller (BSC) in GSM
Node B corresponds roughly to the Base Station in GSM
Term “Node B” is a relic from the first 3GPP releases
Outer loop PC (running in the MS) defines SIR target for the MS
If the measured SIR at the MS is lower than the SIR-target, the BS is commanded to increases its transmit power for that MS. Otherwise, BS is commanded to decrease its power.
Power control rate 1500 Hz
Power control dynamics is dependent on the service
There’s no near-far problem in DL due to one-to-many scenario. However, it is desirable to provide a marginal amount of additional power to mobile stations at the cell edge, as they suffer from increased other-cell interference.
Active set (AS), represents the Node Bs to which the UE is in soft handover
Neighbor set (NS), represents the links that UE monitors but which are not already in active set
Received signal strength BS1 BS2 Threshold_1 Triggering time_1 Threshold_2 Triggering time_2 BS2 from the NS reaches the threshold to be added to the AS BS2 is still after the triggering time above threshold and thus added to the AS BS1 from the AS reaches the threshold to be dropped from the AS BS1 dropped from the AS
Peak data rates increased to significantly higher than 2 Mbps; Theoretically reaching 5.8 Mbps
Packet data throughput increased, though not as high throughput as with HSDPA
Reduced delay from retransmissions.
Layer1 hybrid ARQ
NodeB based scheduling for uplink
Frame sizes 2ms & 10 ms
Schedule in 3GPP
Part of Release 6
First specifications version completed 12/04
In 3GPP specs with the name Enhanced uplink DCH (E-DCH)
HSPA Peak Data Rates 5 codes QPSK # of codes Modulation 5 codes 16-QAM 10 codes 16-QAM 15 codes 16-QAM 15 codes 16-QAM 1.8 Mbps Max data rate 3.6 Mbps 7.2 Mbps 10.1 Mbps 14.4 Mbps 2 x SF4 2 ms 10 ms # of codes TTI 2 x SF2 10 ms 2 x SF2 2 ms 2 x SF2 + 2 x SF4 2 ms 1.46 Mbps Max data rate 2.0 Mbps 2.9 Mbps 5.76 Mbps
More and more consumers want to use their mobile devices at home, even when there’s a fixed line available
Providing full or even adequate mobile residential coverage is a significant challenge for operators
Mobile operators need to seize residential minutes from fixed line providers, and compete with fixed and emerging VoIP and WiFi services
=> There is trend in discussing very small indoor, home and campus NodeB layouts
Femtocells are cellular access points (for limited access group) that connect to a mobile operator’s network using residential DSL or cable broadband connections
Femtocells enable capacity equivalent to a full 3G network sector at very low transmit powers, dramatically increasing battery life of existing phones, without needing to introduce WiFi enabled handsets