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Multiple Access Methods

The problem is each wireless system has to have its bandwidth that needs to be shared among several users. That is the reason that multiple access techniques have been designed.

FDMA - Frequency Division Multiple Access
TDMA - Time Division Multiple Access
CDMA - Code Division Multiple Access

FDMA - Each user has its part of overall frequency band i.e. the whole bandwidth is divided for many users. TDMA - The whole bandwidth is reserved for particular user for only specified period of time.
CDMA - User can use whole bandwidth for all time but has to use different code.
As for explanation of difference between these three multiple access technologies there is an example of room with people talking in pairs. When they would use FDMA the room (whole bandwidth) should be divided into smaller rooms and each room would represent one frequency. Walls would be the separation of these frequencies hence people in pairs would have a chance to talk at the same time without disturbing other pairs. As for TDMA each pair in the room would have some specific time to talk when other people should remain in silence. CDMA would allow to talk for all pairs but each of them would have to use different language (code).

This example as described in "UMTS". Javier Sanchez, Mamadou Thioune ISBN: 978-1-905209-71-2 January 2007, Wiley-ISTE

To increase system capacity it is common to use these technologies together. GSM would use for example TDMA together with FDMA.


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NAS: Non-Access Stratum

This post is to give short description of NAS protocols, procedures and functions.
NAS is a layer for communication between Ue and Core Network (CN). This communication is transparent for underlaying Access Stratum.
NAS protocols:
GMM - GPRS Mobility ManagementMM - Mobility Management SM - Session ManagementCC - Call Control SS - Supplementary Services SMS - Short Message Services SM, SMS, SS and CC form a group of protocols called Connection Management.

Figure - Inter protocols communication MS side [3GPP 24.007]

SM - its functions is to activate, deactivate or modify PDP contexts which are sessions for PS traffic in UMTS/GPRS networks

Figure 1 - Simplified PDP context activation procedure

Figure 2 - Inter protocol communication for PDP context activation - MS side

CC - its functions is to establish, maintain and finally release CS calls in UMTS/GPRS/GSM networks

Figure 3- Simplified CS call proceeding

Figure 4 - Inter protocol communication for CS call setup


3GPPThird Generation Partnership Project
AALATM Adaptation Layer
ADCHAssociated DCH
ADSLAsymetric Digital Subscriber Line
ALCAPAccess Link Control Application Part
ARFCNAbsolute Radio Frequency Channel Number
ARQAutomatic Repeat reQuest
ATMAsynchronous Transfer Mode
BCCHBroadcast Control Channel
BCHBroadcast ChannelBERBit Error RateBICCBearer Independent Call ControlBLERBlock Error RateBPSKBinary Phase Shift KeyingBSCBase Station ControllerBSSBase Station SubsystemBTSBase Transceiver StationCAMELCustomised Applications for Mobile network Enhanced Logic
CCCall Control
CCCHCommon Control Channel
CDMCode Division Multiplexing
CDMACode Division Multiple Access
CNCore Network
CMConnection Management
CPICHCommon Pilot Channel
CQIChannel Quality Indicator
CRCCyclic Redundancy Check
C-RNTICell Radio Network Temporary Identifier
CSCirciut Switch
CRNCControlling Radio Network Controller
DCHDedicated Channel
DNSDomain Name Server
DL-SCHDownlink Shared Channel
DRNCDrift Radio Network Controller

Protocols, interfaces, User Plane and Control Plane

When two devices would like to communicate with each other they would use a defined protocol. Protocol is set of rules describing how those two devices can communicate in way that receiver would understand what sender “had in mind” while sending message. Protocol description is usually description of messages (signals) that can be sent and received, it is also description for particular procedures and functions.
Now, our two devices know “how to talk” to each other, but they need to be connected somehow. For this purpose an Interface would be defined. Interface would be generally another device, with or without dedicated software, that would allow connecting, inter-working and changing messages(signals) between our devices – connected using this interface.
Sometimes when connecting two devices using interface there is a need for two protocols. First protocol would allow first device to control how works the second one. This kind of protocol is part of control plane. Second protocol wo…