{{Technical, date=September 2010 CPICH stands for ''Common Pilot Channel'' in

UMTS The Universal Mobile Telecommunications System (UMTS) is a 3G mobile cellular system for networks based on the GSM standard. UMTS uses Wideband Code Division Multiple Access, wideband code-division multiple access (W-CDMA) radio access technolog ...

and some other

CDMA Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...

communications systems. In

WCDMA The Universal Mobile Telecommunications System (UMTS) is a 3G mobile cellular system for networks based on the GSM standard. UMTS uses wideband code-division multiple access (W- CDMA) radio access technology to offer greater spectral efficienc ...

FDD cellular systems, CPICH is a

downlink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or shar ...

channel broadcast by

Node B {{Unreferenced, date=May 2019, bot=noref (GreenC bot) Node B is the telecommunications node for mobile communication networks, namely those that adhere to the UMTS standard. The Node B provides the connection between mobile phones (User equipme ...

s with constant power and of a known bit sequence. Its power is usually between 5% and 15% of the total Node B transmit power. Commonly, the CPICH power is 10% of the typical total transmit power of 43 dBm. The Primary Common Pilot Channel is used by the UEs to first complete identification of the Primary Scrambling Code used for scrambling Primary Common Control Physical Channel (P- CCPCH) transmissions from the

. Later CPICH channels provide allow phase and power estimations to be made, as well as aiding discovery of other radio paths. There is one primary CPICH (P-CPICH) for each Cell, which is transmitted using spreading code 0 with a

spreading factor In digital communications, a chip is a pulse of a direct-sequence spread spectrum (DSSS) code, such as a pseudo-random noise (PN) code sequence used in direct-sequence code-division multiple access (CDMA) channel access techniques. In a binary d ...

of 256, notationally written as C_ch,256,0. Optionally a Node B may broadcast one or more secondary common pilot channels (S-CPICH), which use arbitrarily chosen 256 codes, written as C_ch,256,n where

0 .

The CPICH contains 20 bits of data, which are either all zeros, or in the case that Space–Time Transmit Diversity (STTD) is employed, is a pattern of alternating 1's and 0's for transmissions on the Node B's second antenna. 25.211

section 5.3.3.1 "Common Pilot Channel (CPICH)" The first antenna of a base station always transmits all zeros for CPICH. A UE searching for a

Node B will first use the primary and secondary synchronization channels (

P-SCH P-SCH stands for "Primary Synchronisation Channel" in Universal Mobile Telecommunications System.The P-SCH is a pure downlink physical channel broadcast over the entire cell. It is transmitted unscrambled during the first 256 chips of each time ...

and

S-SCH S-SCH stands for "Secondary Synchronization Channel in UMTS" ( Universal Mobile Telecommunications System). S-SCH is a pure downlink physical channel broadcast over the entire cell. It is transmitted unscrambled during the first 256 chips of ea ...

respectively) to determine the slot and frame timing of a candidate P-CCPCH, whether STTD is in use, as well as identifying which one of 64 code groups is being used by the cell. Crucially this allows to UE to reduce the set of possible

Primary Scrambling Codes Primary or primaries may refer to: Arts, entertainment, and media Music Groups and labels * Primary (band), from Australia * Primary (musician), hip hop musician and record producer from South Korea * Primary Music, Israeli record label Work ...

being used for P-CPICH to only 8 from 512 choices. At this point the correct PSC can be determined through the use of a

matched filter In signal processing, the output of the matched filter is given by correlating a known delayed signal, or ''template'', with an unknown signal to detect the presence of the template in the unknown signal. This is equivalent to convolving the unkn ...

, configured with the fixed channelisation code C_ch,256,0, looking for the known CPICH bit sequence, while trying each of the possible 8 PSCs in turn. The results of each run of the matched filter can be compared, the correct PSC being identified by the greatest correlation result. Once the scrambling code for a CPICH is known, the channel can be used for measurements of signal quality, usually with

RSCP In the UMTS cellular communication system, received signal code power (RSCP) denotes the power measured by a receiver on a particular physical communication channel. It is used as an indication of signal strength, as a handover criterion, in down ...

and Ec/No. Timing and

phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform *Phase space, a mathematica ...

estimations can also be made, providing a reference that helps to improve reliability when decoding other channels from the same Node B. Pilot signals are not a requirement of CDMA, however, they do make the UE's receiver simpler and improve the reliability of the system.

References

UMTS

Further reading

References