cdma vs gsm

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CDMA vs GSM-Difference between CDMA and GSM


This page on CDMA vs GSM describes difference between CDMA and GSM technical specifications. It describes about gsm and cdma technologies.
Both the GSM and CDMA are cellular wireless technologies. They have been developed to support voice as well as data communications between various subscribers located across the world. In GSM, GPRS is used to support the data services.
GSM is developed and specified in 3GG as well as ETSI. CDMA is specified in US standard IS95 and also 3GPP.

About GSM

About GSM (Global System for Mobile Communication):
This technology uses TDMA/FDMA access scheme in order to assign channels to the different subscribers to utilize the service from the service operator's base stations. One frequency and one time slot (f1,t1) is needed for one way communication and a pair for two-way communication( (f1,t1) and (f2,t2) ).
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About CDMA

About CDMA (Code Division Multiple Access):
This technology uses PN codes for communication between subscribers and NodeBs. As the PN codes are unique to the users, information is extracted by despreading at the receiver using the same PN code which is used at the transmit side. Pls. note that information is not retrieved using (time,frequency) assignment in CDMA. All the different PN codes will utilize the same frequency/time in order to communicate. CDMA uses 1xEV-DO and EV-DV versions in 3rd generation. CDMA has edge over GSM due to its immunity to interference as well as jamming. 
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In GSM, as the available transmission BW is small and hence leads to compromise in quality of voice transmission. 
In CDMA entire transmission BW is utilized and hence voice quality can be enhanced.
In GSM(i.e. TDMA/FDMA), cell frequency planning is more tedium task as frequency and time planning need to be carried out in CDMA frequency planning is minimal.
GSM (due to TDMA) is a band-limited system. CDMA is a power limited system. Following table mentions difference between CDMA and GSM technologies.

SpecificationsCDMAGSM
Frequency Band(MHz)UL:824-849,DL:869-894 
UL:1850-1910, DL:1930-1990		UL:890-915,DL:935-960,
UL:1710-1785, DL:1805-1885
Carrier Spacing(KHz)1230200
Physical channels per carrierSoft capacity8
AccessCDMAFDMA/TDMA
DuplexFrequencyFrequency
Frame Duration(ms)204.6
Modulation MethodPSKGMSK
Channel rate (Kb/s)1228.8270.833
Modulation Efficiency (b/s/Hz)1.01.35
Maximum Terminal Transmitter Power (watt)6.38
Speech codingQCELPRPE
Speech rate,including channel coding(kb/s)Variable22.8
Cellular Efficiency(conversations/cell/MHz)12.1-45.15.0-6.6
Associated Control Channeldim-and-burstseparate slots in each frame
Out-of-band ACCH rate(b/s)4400-7600(Speech quality reduced when control channel is active)950
Standard versionsCDMA-one(as per IS-95)
,CDMA-2000(as per CDMA2000),
WCDMA(as per UMTS 3G std.)		GSM and GSM Advanced
(supports MUROS,
VAMOS,MSRD,AMR,SAIC)

Related Links on GSM and CDMA

GSM RF planning  CDMA tutorial   GSM basics Tutorial   GSM Measurements 
GSM protocol stack which covers GSM layer 1, layer 2 and layer 3 basics.Read More 
GSM Physical layer or GSM layer 1 modules in depth.READ MORE 
GSM Mobile originated call flow,READ MORE 
GSM Mobile Terminated call flow,READ MORE

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