Last Updated: 31/08/2005
What does the abbreviation 3G (or UMTS or XXX) stand for?
Please see Vocabulary Section for the abbreviation you are looking for.
I am looking for a particular definition related to 3G/UMTS, where can i find it?
Please see Terms and Definitions section for the definitions you are looking
I am looking for UMTS/3G related job, what are good places to look for them?
Please see Jobs Section for the job you are looking. If you know of any other good links, please let us know so we can add it.
What are these 1G, 2G, 2.5G, 3G and 4G
All these terms specified are the Generations of the mobile networks.
What is TDD and FDD?
TDD stands for Time Division Duplex and FDD stands for Frequency Division Duplex. They are different modes of CDMA. In FDD mode of transmission both the Transmitter and the Receiver transmit simultaneously. This simultaneous transmission is possible because they are both on different frequencies. In TDD mode of operation either Transmitter or Receiver can transmit at one time. This is because they use the same frequency for the transmission.
Which mode is more common, TDD or FDD?
At present all the major 3G Networks are using FDD mode of operation. As far as i am aware there are no commercial TDD networks at the moment. Recently T-Mobile announced that they wil install TDD Network in Czech Republic. See News Section for more details.
Can you expand on the FDD mode of operation?
In the FDD mode of operation, the uplink and downlink use separate frequency bands. These carriers have a bandwidth of 5 MHz. Each carrier is divided into 10-ms radio frames, and each frame further into 15 time slots. The frequency allocation consists of one frequency band at 1920-1980 MHz and one at 2110-2170 MHz. These frequency bands are used in FDD mode both by the UE and the Network. The lower frequency band is used for the Uplink (UL) transmission and the upper frequency band is used for the Downlink (DL) transmission. The frequency separation is specified with 190 MHz for the fixed frequency duplex mode and with 134.8MHz to 245.8MHz for the variable frequency duplex mode.
Can you expand on the TDD mode of operation?
The TDD mode differs from the FDD mode in that both the uplink and the downlink use the same frequency carrier. There are 15 time slots in a radio frame that can be dynamically allocated between uplink and downlink directions. Thus the channel capacity of these links can be different which is very advantageous especially when people are downloading stuff on their mobiles. The chip rate of the normal TDD mode is also 3.84 Mcps, but there exists also a “narrowband” version of TDD known as TD-SCDMA. The carrier bandwidth of TD-SCDMA is 1.6 MHz and the chip rate 1.28 Mcps. TD-SCDMA has been proposed by China and potentially has a large market share in China if implemented.
What is TDD HCR and TDD LCR?
HCR stands for "High Chip Rate" and is same as 3.84Mcps TDD described above. LCR stands for "Low Chip Rate" ans is the same as TD-SCDMA described above.
Can you expand on the unequal bandwidth concept in TDD?
The HCR TDD uses 10ms radio frame that is divided into 15 time slots each being able to carry a chip sequence of 2560 complex valued chips. At least one slot has to be reserved for Downlink (DL) transmission to allow for broadcast information and one for Uplink (UL) transmission in order to realize customer’s access to the system. The remaining slots can be arbitrarily distributed to either direction in order to adapt to the asymmetry of requested services. The LCR option, a 10 ms radio frame is divided into two sub-frames of 5 ms duration. Each of the sub-frames contains seven time slots. Transmission bursts fitting into a single slot contain 864 complex valued chips. The first time slot is always used for DL transmission, the latter six can be divided into UL and DL transmission adaptively, starting with the time slots used for UL. Unlike transmission in the HCR mode, the time slots used for LCR transmission in a certain direction have to be grouped together. Between the first two slots in each sub-frame special synchronization and pilot signals are included.
If FDD is so popular why would people use TDD mode of operation?
Juha Korhonen in his book Introduction to 3G Mobile Communications has summarised the reasons for TDD mode being used. They are:
All the advantages above make TDD look better option than FDD. Why not use only TDD mode? Are there any problems?
The following are the problems that make TDD unpopular:
How is UMTS subscriber differentiated from a GSM subscriber?
UMTS subscriber differentiated from a GSM subscriber based on SIM card. For UMTS and GSM subscriiber the SIM is different. UMTS subscriber uses USIM while GSM one uses SIM.
Can 2G SIM be used to access 3G Services?
Section 13.1 of 22.101 says: For access to services, provided by PS or CS CN domains, a valid USIM shall be required. Optionally, SIM according to GSM phase 2, GSM phase 2+, 3GPP release 99, 3GPP release 4 specifications may be supported. I guess its upto the network to allow or disallow 2G SIM accessing 3G services.