Technical Writing

GSM vs CDMA

Global Competition between GSM and CDMA in Providing The Best Service to The Publics in Indonesia

It's probably the understatement of the decade to say that cell phones have become the single greatest tool in business. In today’s world the ability to communicate with business associates while on the go is not just an advantage, it’s a necessity. And because of that, the choices people make when choosing their handheld devices matter more than ever.

When it comes time to select a cell phone or smart phone, the major part of the evaluation people make focuses on the features and benefits of the handset. People may choose a device with the best features but in other way they spend money as few as possible. A device with features such as access to the Internet and email, an organizer that will sync with Outlook will be selected. This features can take the owner scheduler, contacts, and information on the road. And most importantly, the body and size of the phone cell, the slick one is better.

But if people conduct a lot of their business on the road or internationally, the most important decision they make regarding their service may not have anything at all to do with the features they usually consider important for handhelds. They choice of carrier and the technology it uses for its network might make the difference between being productive or ending up out of area.

By now, people have probably heard all of the acronyms in the alphabet soup of carrier technologies. The two major terms that pertain to cellular phone communication that people are likely to run into GSM and CDMA, the two major technologies service providers use to carry voice signals across the network. But what are they and why do they matter? There are our focuses now, so in this paper we will reveal some things in other to make clear the problem about this case, such as:

1. Here are two major methods for wireless communication. They are CDMA (Code Division Multiple Access) and GSM (Global System for Mobile Communications). Those two methods, which have different protocol and standards, have different process for providing wireless communication. How those two methods exactly work?
2. Those different processes explained above, will lead to the difference of their advantages. Futhermore, current-marketing-scope of those two methods will differ their advantages too. What are advantages and disadvantages of those two methods?
3. Those two methods have the same business action. Futhermore, those methods may exploit the same network coverage too. Hence, how far exactly those two methods interferes each other?

GSM Overview

GSM, The Global System for Mobile Communications, which is the original acronym Groupe Spécial Mobile. This service as standard for mobile phones has been used by over 12 million people across more than 212 countries and territories. GSM is a cellular network, which means that mobile phones connect to it by searching for cells in the immediate vicinity. GSM networks operate in four different frequency ranges. Most GSM networks operate in the 900 MHz or 1800 MHz bands. Some countries use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency bands were already allocated.

In the 900 MHz band the uplink frequency band is 890-915 MHz, and the downlink frequency band is 935-960 MHz. This 25 MHz bandwidth is subdivided into 124 carrier frequency channels, each spaced 200 kHz apart. Time division multiplexing is used to allow eight full-rate or sixteen half-rate speech channels per radio frequency channel. There are eight radio timeslots (giving eight burst periods) grouped into what is called a TDMA frame. Half rate channels use alternate frames in the same timeslot. The channel data rate is 270.833 kbit/s, and the frame duration is 4.615 ms. The transmission power in the handset is limited to a maximum of 2 watts in GSM850/900 and 1 watt in GSM1800/1900.

GSM has used a variety of voice codecs to squeeze 3.1kHz audio into between 6 and 13kbps. Originally, two codecs, named after the types of data channel they were allocated, were used, called "Full Rate" (13kbps) and "Half Rate" (6kbps). These used a system based upon linear predictive coding (LPC). In addition to being efficient with bitrates, these codecs also made it easier to identify more important parts of the audio, allowing the air interface layer to prioritize and better protect these parts of the signal.

GSM Signal Transferring Process

The network behind the GSM system seen by the customer is large and complicated in order to provide all of the services which are required. But actually, it is divided into a number of sections such as.

1. The Base Station Subsystem (the base stations and their controllers).
2. The Network and Switching Subsystem (the part of the network most similar to a fixed network). This is sometimes also just called the core network.
3. The GPRS Core Network (the optional part which allows packet based Internet connections).
4. All of the elements in the system combine to produce many GSM services such as voice calls and SMS.
   

The process can be described that the phone signal from PSTN (Public Service Telecommunication Network) come into MSC (mobile services switching center) and VLR (visitor location register). The MSC performs the telephony switching functions of the system. It controls calls to and from other telephone and data systems. It also performs such functions as toll ticketing, network interfacing, common channel signaling, and others. The VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time.

After that there are HLR (home location register), AUC (authentication center) and EIR (equipment identity register) which give additional process to the signal. The HLR is a database used for storage and management of subscriptions. The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. When an individual buys a subscription from one of the PCS operators, he or she is registered in the HLR of that operator. A unit called the AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network operators from different types of fraud found in today's cellular world. The EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR node. The output is joined into SS7 Network (Switching System 7 Network), from here the signal will be sent to the SGSN receiver. All that part of process is done in the Switching System mode.

In other way different from PSTN group, the signal from mobile phone is received firstly by BTS (Base Transceiver Stations) which as function is to handles the radio interface to the mobile station. The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network. A group of BTSs are controlled by a BSC. And then the signal is continued into BSC (Base Station Controllers). The signal from here is sent to the MSC and VLR and then has the same treatment as the PSTN signal. But there are PCU that BSC is associated with to make signal can pass the switching system process, and the signal will directly come onto GPRS core Network and received by SGSN (System GPRS Service Node). After that, signal will be sent to the server in order to process client’s request. Knowing the clients needs, the server will connect it to phone number destination with reversed process, so the call will be made.

Reference:

http://www.gsmworld.com , accessed at December 4^th, 2006

http://www.protocols.com/pbook/, accessed at December 4^th, 2006

Authors :

Made Harta Dwijaksara (13504137)

Hadi Saloko (13504157)

posted by made harta @ 9:12 AM