UMTS multiple access types
UMTS (Universal Mobile Telecommunications System) is a 3G mobile communication technology that uses multiple access techniques to support a high number of users and provide efficient spectrum usage. Multiple access types define how users share the same frequency spectrum and communicate simultaneously. UMTS primarily uses the following multiple access techniques covering WCDMA,TD-CDMA,TD-SCDMA and FDMA. Also we will compare UMTS vs CDMA to understand differences between them.
1. WCDMA (Wideband Code Division Multiple Access)
• WCDMA is the primary multiple access technique used in UMTS. It allows multiple users to share the same
frequency band by assigning unique spreading codes to each user.
• Each user's data signal is multiplied by a unique code (spreading code) that
spreads the signal over a broader frequency band. At the receiver, the same code is used
to extract the user's signal from the combined signals.
• The key features are as follows.
-Supports simultaneous transmission and reception.
-Provides resistance to interference and multipath fading.
-Offers high data rates, enabling better voice and multimedia services.
• Application: WCDMA is used for both voice and data services in UMTS networks.
2. TD-CDMA (Time Division - Code Division Multiple Access)
• TD-CDMA combines Time Division Multiple Access (TDMA) and CDMA techniques.
It divides the available bandwidth into time slots and uses CDMA within each time slot.
• The bandwidth is split into time slots, and within each slot, multiple users
are distinguished by unique spreading codes.
• The key features are as follows.
-Efficient utilization of resources in asymmetric data applications.
-Suitable for applications requiring different uplink and downlink data rates.
• Application: Primarily used for uplink/downlink transmission balancing and capacity optimization.
3. TD-SCDMA (Time Division Synchronous Code Division Multiple Access)
• TD-SCDMA is a unique variant of CDMA, developed in China, that integrates TDMA and CDMA
with synchronous transmission.
• It uses time slots to separate uplink and downlink transmissions and employs a
synchronous method to minimize interference.
• The key features are as follows.
-Higher spectral efficiency and better management of synchronization.
-Reduces the effect of multipath interference using smart antenna techniques.
• Application: Used in China as a part of their 3G network standard.
4. FDMA (Frequency Division Multiple Access)
• In UMTS, FDMA is not used as a primary multiple access method but rather
as a frequency allocation scheme within the WCDMA framework. It assigns different frequency
bands to different operators or services.
• Each operator or service is allocated a separate frequency band, and within that
band, WCDMA is applied to allow multiple users.
• The key features are as follows.
-Allows coexistence of multiple operators in the same geographical area.
-Facilitates better bandwidth allocation.
• Application: Mainly used at the operator level for spectrum allocation.
Compare UMTS vs CDMA
UMTS and CDMA are both technologies used in mobile communication systems, but they have significant differences in terms of access methods, technology generations and capabilities. The following table mentions the same.
| Features | UMTS | CDMA |
|---|---|---|
| Technology Generation | 3G (Third Generation) | 2G (cdmaOne), 3G (CDMA2000) |
| Primary Access Technique | WCDMA (Wideband Code Division Multiple Access) | CDMA (Code Division Multiple Access) |
| Frequency Band | Typically 5 MHz | Typically 1.25 MHz |
| Typical Frequency Bands | 2100 MHz, 900 MHz, 850 MHz, 1900 MHz | 850 MHz, 1900 MHz |
| Data Rate | Up to 2 Mbps (initial UMTS) | Up to 144 kbps (1xRTT); up to 3.1 Mbps (EV-DO) |
| Enhanced Data Rate | Up to 42 Mbps (HSPA+) | Up to 14.7 Mbps (EV-DO Rev B) |
| Network Architecture | RNC (Radio Network Controller), Node B (Base Station) | BSC (Base Station Controller), BTS (Base Transceiver) |
| Core Network | IP-based services and support | Legacy circuit-switched core |
| Backward Compatibility | Compatible with GSM networks | Compatible with cdmaOne (2G) networks |
| Evolution Path | Evolves to HSPA, HSPA+, and LTE | Evolves to EV-DO and LTE |
| Global Adoption | Widely adopted worldwide, especially in Europe, Asia | Primarily used in North America, South Korea, parts of Latin America |
| Voice and Data Services | Better support for simultaneous voice and data | Simpler voice services, data support with EV-DO |
| Roaming Capability | Extensive global roaming support | Limited global roaming due to fewer CDMA networks |
| Spectral Efficiency | Higher spectral efficiency and capacity | Lower spectral efficiency compared to WCDMA |
| Deployment | Commonly used by GSM operators upgrading to 3G | Used by CDMA operators (Verizon, Sprint) |
| Transition to 4G | Smooth transition to 4G LTE | Requires dual-mode phones for GSM/UMTS compatibility |
Summary
UMTS relies mainly on WCDMA as its core multiple access technique, with TD-CDMA and TD-SCDMA used in specific cases. These techniques enable high capacity, efficient spectrum utilization and support for various services, making UMTS a versatile 3G technology.
Useful Links on Multiple Access Types
TDMA
Advantages and disadvantages of TDMA and FDMA
Difference between GSM and CDMA