RFRSCP vs. Ec/No vs. RSSI: Signal Strength and Quality in WCDMA
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This page explains the differences between RSCP, Ec/No, and RSSI in the context of a WCDMA (Wideband Code Division Multiple Access) system.
Understanding the Key Metrics
Let’s break down each term:
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RSSI (Received Signal Strength Indicator): RSSI is a general measure of the total power received by a device. It’s typically expressed in dBm (decibel-milliwatts). It doesn’t differentiate between the desired signal and interference or noise.
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RSCP (Received Signal Code Power): RSCP, also measured in dBm, specifically refers to the power received from the CPICH (Common Pilot Channel) in a WCDMA system. The CPICH acts as a beacon, continuously transmitted by the WCDMA base station (NodeB). Think of it as similar to the BCCH (Broadcast Control Channel) in a GSM (Global System for Mobile communications) network. It’s your base station’s signal strength.
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Ec/No (Energy per Chip over Noise spectral density): Ec/No is a crucial metric for assessing the quality of the received signal in a WCDMA system. It represents the ratio of the received power of the CPICH (the useful signal) to the total received power, including noise and interference. A higher Ec/No value indicates a better signal quality.
The Relationship Between Them
Ec/No can be derived from RSCP and RSSI using the following formula (in dB):
Alternatively, Ec/No can be expressed as:
This formula highlights that Ec/No represents the proportion of the total transmitted power that’s dedicated to the CPICH signal.
Practical Implications
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RSSI: Gives a general idea of signal strength but isn’t specific to the WCDMA signal.
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RSCP: Provides a more precise measurement of the WCDMA base station’s signal strength, specifically from the CPICH.
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Ec/No: Offers the most important indication of signal quality. A good Ec/No is essential for reliable communication. It tells you how well the signal stands out from the noise.
