RFGSM vs CDMA: A Detailed Comparison of Mobile Communication Standards
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GSM and CDMA are both digital cellular communication standards, defining how mobile devices communicate and connect to cellular networks. Both have been specified in the 3GPP series of standards and support voice and data transmission, enabling users to make calls, send texts, and use mobile data services. GSM utilizes GPRS for data, and both require cellular network infrastructure with base stations and mobile switching centers. Despite these similarities, key differences exist between GSM and CDMA.
GSM (Global System for Mobile Communications) uses TDMA (Time Division Multiple Access), allowing multiple users to share the same frequency through different time slots. CDMA (Code Division Multiple Access) relies on code division, enabling simultaneous communication by assigning unique codes to users on the same frequency.
Let’s delve into the features of each technology before comparing them in detail.
What is GSM?
GSM, short for Global System for Mobile Communications, is a standard developed to ensure a common platform for mobile devices, facilitating communication across networks and countries. Conceived in the 1980s, GSM has become the dominant mobile communication standard globally.
This technology employs a TDMA/FDMA access scheme to allocate channels to different subscribers, allowing them to utilize services from the operator’s base stations. One frequency and one time slot (f1, t1) are needed for one-way communication, and a pair ((f1, t1) and (f2, t2)) for two-way communication.
Here, different users share the same frequency but at distinct time slots for transmission.
GSM also introduced the use of SIM (Subscriber Identity Module) cards, enabling users to easily switch devices by transferring the SIM. The figure above depicts the GSM network architecture and its elements.
What is CDMA?
CDMA stands for Code Division Multiple Access, a digital cellular technology that allows multiple users to share the same frequency band simultaneously.
CDMA was developed as an alternative to other multiple access technologies, such as TDMA/FDMA. It uses PN codes for communication between subscribers and NodeBs. Information is extracted by despreading at the receiver using the same PN code used at the transmitter.
Note that information isn’t retrieved using (time, frequency) assignment in CDMA. All different PN codes utilize the same frequency/time to communicate. CDMA uses 1xEV-DO and EV-DV versions in 3rd generation.
CDMA has an edge over GSM due to its immunity to interference and jamming.
In CDMA, each user’s signal is spread over a wide frequency band using a unique code. This spreading allows multiple users to transmit and receive data simultaneously without interfering with each other. Unlike GSM, CDMA doesn’t use time slots; instead, it assigns a unique code to each user, allowing all users to communicate at the same time.
Difference between GSM and CDMA
The following table compares these cellular technologies, highlighting the differences between GSM and CDMA.
| Specifications | GSM | CDMA |
|---|---|---|
| Full form | Global System for Mobile Communication | Code Division Multiple Access |
| Frequency Band(MHz) | UL: 890-915, DL: 935-960, UL: 1710-1785, DL: 1805-1885 | UL: 824-849, DL: 869-894, UL: 1850-1910, DL: 1930-1990 |
| Carrier Spacing(KHz) | 200 | 1230 |
| Physical channels per carrier | 8 | Soft capacity |
| Channel access | FDMA/TDMA | CDMA |
| Range | Shorter | Longer |
| Security | Relies on SIM card for security features | Built-in security features including encryption and authentication |
| Frame Duration(ms) | 4.6 | 20 |
| Modulation Method | GMSK | PSK |
| Channel rate (Kb/s) | 270.833 | 1228.8 |
| Modulation Efficiency (b/s/Hz) | 1.35 | 1.0 |
| Maximum Terminal Transmitter Power (watt) | 8 | 6.3 |
| Speech coding | RPE | QCELP |
| Speech rate, including channel coding(kb/s) | 22.8 | Variable |
| Cellular Efficiency(conversations/cell/MHz) | 5.0-6.6 | 12.1-45.1 |
| Associated Control Channel | separate slots in each frame | dim-and-burst |
| Out-of-band ACCH rate(b/s) | 950 | 4400-7600 (Speech quality reduced when control channel is active) |
| Standard versions | GSM and GSM Advanced (supports MUROS, VAMOS, MSRD, AMR, SAIC) | CDMA-one (as per IS-95), CDMA-2000 (as per CDMA2000), WCDMA (as per UMTS 3G std.) |
| Network structure | More widespread globally | Historically more prevalent in North America |
| Handset compatibility | More international compatibility | More region-specific |
| Tutorial for further study |
Some key comparisons include:
- In GSM, the available transmission bandwidth is smaller, potentially compromising voice transmission quality. In CDMA, the entire transmission bandwidth is utilized, potentially enhancing voice quality.
- GSM (TDMA/FDMA) requires more tedious cell frequency planning, while CDMA frequency planning is minimal.
- GSM (due to TDMA) is a band-limited system, while CDMA is a power-limited system.
Conclusion
GSM and CDMA have historically been distinct technologies in mobile communication. Both have significantly contributed to global telecommunications, with GSM’s international adoption and CDMA’s prominence in North America.
The convergence towards technologies like LTE and 5G has diminished the significance of their differences. Today, the choice between GSM and CDMA is less relevant as modern networks and devices often support both standards.
The focus has shifted to delivering advanced features, higher data speeds, and enhanced user experiences, transcending the traditional distinctions between GSM and CDMA.
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