UMTS Cell Search and WCDMA Architecture Components
English with a size of 355.61 KBQ18. UMTS Cell Search Importance and Procedure
Importance of Cell Search
Cell Search allows the User Equipment (UE) to find and synchronize with a nearby UMTS cell before communication begins. It ensures correct timing, frequency, and scrambling code detection.
Steps in Cell Search
Step 1 – Slot Synchronization:
- UE detects the Primary Synchronization Channel (P-SCH) to identify slot boundaries (10 ms slots).
Step 2 – Frame Synchronization:
- UE detects the Secondary Synchronization Channel (S-SCH) to determine frame start and scrambling code group.
Step 3 – Scrambling Code Identification:
- UE reads the Common Pilot Channel (CPICH) to determine the exact scrambling code of the cell.
Diagram: Cell Search Flow
+-------------------------------+
| CELL SEARCH PROCEDURE |
+-------------------------------+
| Step 1: Slot Sync (P-SCH) |
| Step 2: Frame Sync (S-SCH) |
| Step 3: Scrambling Code ID |
+-------------------------------+
Outcome
- UE identifies the strongest cell.
- Enables proper decoding of the Broadcast Channel (BCH) and system information.
- Essential for network registration and call setup.
Q19. WCDMA Architecture Component Functions
Main Components:
User Equipment (UE):
- Performs call setup, authentication, and mobility.
- Contains the SIM (USIM) with subscriber identity.
Node-B (Base Station):
- Transmits/receives radio signals.
- Handles spreading/despreading, modulation/demodulation.
- Implements power control and measurement reporting.
Radio Network Controller (RNC):
- Controls multiple Node-Bs.
- Responsible for call admission, resource management, and handover control.
- Handles ciphering and load balancing.
Core Network (CN):
- Circuit Switched (CS) domain: For voice and video calls.
- Packet Switched (PS) domain: For Internet/data services.
- Includes MSC, SGSN, GGSN, and HLR.
| Component | Function |
|---|---|
| UE | Access & communication |
| Node-B | Radio transmission |
| RNC | Control & resource management |
| CN | Switching & routing services |
Q20. WCDMA vs. IS-95 Power Control Differences
Power control in WCDMA (UMTS) is significantly more sophisticated than in IS-95 (CDMA) due to the need to manage interference in a wideband system and support higher data rates.
| Feature | IS-95 (CDMA) | WCDMA (UMTS) |
|---|---|---|
| Frequency Division | FDD only | FDD + TDD |
| Rate | 800 Hz (1.25 ms) | 1500 Hz (0.667 ms) |
| Channels Controlled | Reverse (mainly) | Both uplink and downlink |
| Purpose | Maintain equal received power at BS | Maintain signal quality and reduce interference |
| Mechanism | Open & closed loop | Inner, Outer, and Open loop |
| Resolution | 1 dB steps | 0.5 dB steps |
Types of Power Control in WCDMA:
Open Loop:
- MS adjusts initial power based on received signal strength from the Node-B.
Inner Loop (Fast Power Control):
- Adjusts power 1500 times per second based on the Signal-to-Interference Ratio (SIR) target.
- Ensures fast correction of rapid fading effects.
Outer Loop:
- Node-B updates the SIR target according to the required Quality of Service (QoS) and error rate.
Conclusion:
WCDMA uses a three-level power control system (Open, Inner, Outer) to effectively manage fast fading and interference, resulting in superior link quality compared to IS-95.
Q21. Justification for CS and PS Domains in UMTS
UMTS Core Network Structure:
UMTS divides its core network into two logical domains to handle different types of traffic efficiently, optimizing both real-time services and data throughput.
Circuit Switched Domain (CS):
- Used primarily for voice and video calls (real-time services).
- Establishes a dedicated, end-to-end physical path for the duration of the connection.
- Key Components: Mobile Switching Center (MSC), Gateway MSC (GMSC), Home Location Register (HLR).
- Characteristics: Guarantees constant delay and reserved bandwidth.
Packet Switched Domain (PS):
- Used for Internet access, email, and file transfers (bursty data).
- Data is divided into packets sent via Internet Protocol (IP).
- Key Components: Serving GPRS Support Node (SGSN), Gateway GPRS Support Node (GGSN).
- Characteristics: Highly efficient for non-real-time traffic using shared resources.
Justification for Dual Domains:
- The CS domain ensures reliable voice calls by dedicating resources, minimizing jitter and delay.
- The PS domain enables efficient data transmission by sharing network resources dynamically, maximizing spectral efficiency for data.
- This dual-domain design allows UMTS to support simultaneous voice and data services effectively within the same network infrastructure.
