This band allow data rate of 144 kbps and 384 kbps to be achieved in mobile environment.
Also data rate up to 2 Mbps under limited condition, eg. localize indoor environment.
The chip rate refer to the bit rate of spreading code and is measured in chip per second. In the ordinary WCDAM proposal submitted by ETSI, a modulating chip rate 4.096 Mchips/sec was used in the IMT-2000 standardization process. However as a result of harmonization this rate was reduced to 3.84 Mchips/sec. This allow easier implementation of DS-CDMA and MC-CDMA dual mode terminal.
In order to limit the spectrum of WCDMA carrier, special transmit pulse-sharping filters are employed.
Known as root raised cosine filter. The bandwidth of this filter was determined by its roll out factor.
Although the nominal channel spacing is 5 MHz this can be adjust to optimize performance where necessary.
The spacing between WCDMA carrier is restricted to multiple of 200 KHz with typical carrier spacing in the rang of 4.2 to 5 MHz.
As a part of IMT-2000 standardization process, the ITU-R recommended two frequency band lower 1885-2025MHz and upper band 2110-2200 MHz
However part of this frequency band were already used by others services in different region of the world. Then the spectrum system of 3G can be allocated differently in different region.
These pairs band will support Frequency Division Duplex (FDD) mode in operation. FDD is best suited to symmetrical service such telephony.
Frequency 1900-1920 MHz and 2010-2025 MHz will be available as unpaired band can support Time Division Duplex (TDD). TDD best suited to asymmetrical service such as internet access service.
Both FDD and TDD modes of operation are base upon on standard radio frame length of 10 ms which allow for low speech delay and and fast control signaling.
The radio frame is divided in 15 time-slot (TS) of 0.667 ms (10 ms divided by 15). This duration cor responses to one power control period. In other word, the output power from the mobile station is adjusted every 0.667 ms or 1500 Times in a second. A time-slot corresponds to 2560 chips/slot, at chip rate of 3.84 Mchips/s.
The FDD Mode of operation is intended for use in the pair band. It is best suited to symmetrical service such as telephony.
The TDD Mode of operation is intended to use in the unpaired bands. It is best suited to asymmetrical service such internet.
The TDD mode is base upon TD-CDMA which is a combination of TDMA and CDMA. The TDD share the same frame and time-slot (TS) structure as the FDD mode, except the time-slot can be allocated to eihter the uplink or downlink. It is therefore describe as an asymmetrical service. This means it can adopt more easily to changing the traffic pattern.
