RFIRAT Measurements: GSM, WCDMA, LTE, and TD-SCDMA
This page covers the fundamentals of Inter-RAT (IRAT) measurements. It’s designed to be helpful for those involved in multimode modem design, covering GSM, WCDMA, LTE, and TD-SCDMA IRATs.
This page explains common measurements performed for Inter-RAT (IRAT) scenarios when a User Equipment (UE) is actively using one Radio Access Technology (RAT). The UE, or mobile device, performs measurements in both IDLE and CONNECTED modes. This ensures the UE remains connected to the best available cell. To achieve this, the UE monitors cells on frequencies different from the serving or camped-on cell, encompassing both inter-frequency and inter-RAT neighboring cells. This is made possible by multi-mode or multi-RAT UEs/mobiles.
Multi-RAT mobiles support multiple RATs depending on the manufacturer. These can include GSM, WCDMA, LTE, or TD-SCDMA, among others. In many RATs, specific locations aren’t provided within the frame for measurements. In these cases, measurement gaps are necessary.
GSM Measurement Parameters
- RSSI (Received Signal Strength Indicator)
- BSIC (Base Station Identity Code) Identification
- BSIC Re-confirmation
These measurements are performed during idle mode and connected mode, utilizing idle frame time slots within the 51-frame multi-frame structure.
WCDMA Measurement Parameters
- Scrambling code
- RSCP (Received Signal Code Power)
- DL channel (Downlink Channel)
- RSSI
- Ec/No (Energy per chip over Noise power spectral density)
- Path loss
Since WCDMA has a continuous frame structure without dedicated slots for measurements, compressed mode is used to insert gaps into the mobile phone’s transmit and receive signals. There are various ways to achieve this.
LTE Measurement Parameters
- EARFCN (E-UTRA Absolute Radio Frequency Channel Number)
- Cell ID (Cell Identity)
- RSRP (Reference Signal Received Power)
- RSRP decode
- RSRQ (Reference Signal Received Quality)
- RSRQ decode
In LTE, different algorithms are designed to determine how long to spend on BSIC identification of cells and when to perform it. In LTE Connected mode, BSIC Identification requirements are specific to the DRX (Discontinuous Reception) configuration and periodicity of the UE.
The following table outlines specifications defined in 3GPP for publishing gaps and measurement durations for different RATs based on controlling and non-controlling modes. These specifications are critical for IRAT measurements.
| Requirement | Standard Reference |
|---|---|
| GSM Idle Mode RSSI measurement requirement | 3GPP TS 45.008, Section 6.6.1 |
| GSM Idle Mode BSIC Reconfirmation Measurement Requirement | 3GPP TS 45.008, Section 6.6.1 |
| GSM Non Controlling Mode, active RAT in Idle Mode RSSI Measurement Requirement | 3GPP TS 25.133, Section 4.2.2.5 / 3GPP TS 36.133 section 4.2.2.5.3 |
| GSM Non Controlling Mode, active RAT in Idle Mode BSIC Identification Measurement Requirement | When GSM stack is in Non-Controlling mode, the maximum time to identify a new GSM cell is defined to be 3*TmeasureGSM. Finding FCCH-SCH should not exceed 3 times TmeasureGSM |
| GSM Non Controlling Mode, active RAT in Idle Mode BSIC reconfirmation Measurement Requirement | 3GPP TS 25.133, Section 4.2.2.5 / 3GPP TS 36.133 section 4.2.2.5.3 |
| GSM Connected Mode, BSIC reconfirmation Measurement Requirement | 3GPP TS 45.008 Section 7.2, 10.1.1.2 |
| GSM Connected Mode, BSIC identification Measurement Requirement | 3GPP TS 45.008 Section 7.2, 10.1.1.2 |
| GSM Connected Mode, Sync Measurement Requirement | 3GPP TS 45.008 Section 7.2, 10.1.1.2 |
| GSM Connected Mode, RSSI Measurement Requirement | 3GPP TS 45.008 Section 7.2, 10.1.1.2 |
| GSM in non Controlling Mode, LTE in connected, RSSI Measurement Requirement | 3GPP TS 36.133, Section 8.1.2.4.5.1.1 |
| GSM in non Controlling Mode, LTE in connected Non-DRX, Sync Measurement Requirement | 3GPP TS 36.133, section 8.1.2.4.5.1.2 |
| GSM in non Controlling Mode, LTE in connected DRX, Sync Measurement Requirement | 3GPP TS 36.133, section 8.1.2.4.5.1.2 |
| Neighbour Cell RSSI Measurements In WCDMA FACH State | 3GPP TS 25.133, section 8.4.2.5.1 |
| BSIC validation & reconfirmation for 9eighbor cells In In WCDMA FACH State | 3GPP TS 25.133, Section 8.4.2.5.2.1 |
| BSIC validation & reconfirmation for 10 neighbor cells In In WCDMA DCH State | 3GPP TS 25.133, Section 8.4.2.5.2.2 |
| Scheduling of Gaps | 3GPP TS 25.133, Section 8.4.2.5 |
| Neighbour Cell RSSI Measurements In WCDMA DCH State | 3GPP TS 25.133, section 8.1.2.5.1 |
| BSIC validation & reconfirmation for neighbour cells In In WCDMA DCH State | 3GPP TS 25.133, Section 8.1.2.5.2 |
| BSIC validation & reconfirmation for neighbour cells In In WCDMA DCH State | 3GPP TS 25.133, Section 8.1.2.5.2 |
