CPICH (common pilot channel)

The Common Pilot Channel (CPICH) is an important channel used in WCDMA (Wideband Code Division Multiple Access) cellular networks. It is a dedicated channel that is continuously transmitted by the base station to provide important timing and synchronization information to mobile devices. In this article, we will explore the details of CPICH, including its purpose, characteristics, and usage in WCDMA networks.

Purpose of CPICH

The main purpose of the CPICH is to provide synchronization and timing information to mobile devices. The CPICH signal is transmitted continuously by the base station, and it provides a reference signal that mobile devices use to synchronize their internal clocks. The CPICH also provides information about the base station's identity and location, which is necessary for proper handover procedures between cells.

Characteristics of CPICH

The CPICH is a common channel that is transmitted by all base stations in a WCDMA network. It is a constant-amplitude, phase-stable signal that is transmitted on a fixed frequency. The CPICH is transmitted at a power level that is higher than most other channels in the network, which ensures that it can be detected by mobile devices even in areas with weak signal strength.

The CPICH uses QPSK (Quadrature Phase Shift Keying) modulation, which means that it modulates two quadrature carriers with two bits of information per symbol. The symbol rate of the CPICH is 30.72 ksymbols/s, which means that it transmits 30,720 symbols per second. Each symbol consists of two bits, so the CPICH has a bit rate of 61.44 kbps.

The CPICH signal is transmitted using a spreading code that is unique to each base station in the network. This spreading code is used to distinguish the CPICH signal from other signals in the network, such as the primary synchronization channel (P-SCH) and the secondary synchronization channel (S-SCH).

Usage of CPICH

The CPICH is used by mobile devices for a variety of purposes, including synchronization, timing, and handover procedures.

Synchronization

One of the most important uses of the CPICH is for synchronization purposes. Mobile devices use the CPICH signal to synchronize their internal clocks with the base station's clock. This is necessary for proper transmission and reception of data over the air interface. Without proper synchronization, data can be lost or corrupted, resulting in poor call quality or dropped calls.

Timing

In addition to synchronization, the CPICH is also used for timing purposes. Mobile devices use the CPICH signal to measure the time delay between the transmission of a signal from the base station and its reception by the mobile device. This time delay is used to calculate the distance between the base station and the mobile device, which is necessary for location-based services and handover procedures.

Handover procedures

Handover procedures are an important aspect of WCDMA networks, as they allow mobile devices to move between cells without interrupting their ongoing calls. The CPICH is used to facilitate handover procedures by providing information about the location and identity of neighboring cells. When a mobile device detects that the signal strength of the current cell is weak, it scans for neighboring cells using the CPICH signal. Once it finds a suitable neighboring cell, it sends a handover request to the base station, which then coordinates the handover process.

Conclusion

The Common Pilot Channel (CPICH) is an important channel in WCDMA networks that provides synchronization, timing, and handover information to mobile devices. It is a dedicated channel that is continuously transmitted by the base station using a unique spreading code. Mobile devices use the CPICH signal for synchronization and timing purposes, as well as for facilitating handover procedures between cells. Understanding the role of the CPICH in WCDMA networks is crucial for ensuring reliable and high-quality communication services for mobile users.