CDMA Interview Preparation Guide

EDGE is an acronym for Enhanced Data GSM Environment
An improved wireless technology over GSM
A 2nd generation cell phone technology
EDGE is used for wireless data transfer via mobile phone connection
Data transfer rates up to 4 times more than GSM networks
With the advent of Blackberry and iPhone, faster data transfer is sought
Using more sophisticated coding, usually without high end hardware, wireless carrier’s base stations are supported for data transfer speeds up to 384 KBPS
EDGE is an alternative to replacing wireless technology, such as GPRS
EDGE will eventually be replaced by 3G technology such as WCDMA.

EVDO stands for Evolution Data Optimized
EVDO is a 3G broadband technology used by Verizon, Spring, Alltel
It provides typical download speeds of 600 to 1400 KBPS
A personal broadband service for wide range of customers
It is always On
EVDO utilizes CDMA signals
Users can be connected remotely for using email, downloading large files, spreadsheets etc.
EVDO is relatively low cost with high capacity
Allows rich web browsing and application usage
Seamless roaming, internal internet connectivity without relying on other’s connection, accessibility to the corporate Virtual Private Network by customers are some of the advantages over WiFi .

CDMA stands for Code Division Multiple Access
CDMA is a wireless technology used in transmission of signal from places with high Security and noise reduction.
The principle of Spread Spectrum is used to work with CDMA.
Spread signal is below the noise level noise and has no effect on the signal.
CDMA does not frequency specific to each user. Instead, every channel uses the full available spectrum.
Individual conversations are encoded with a pseudo-random digital sequence.
CDMA always provides better capacity for voice and data communications
CDMA is a common platform for 3G technologies
Analog radio transmission technologies like Advanced Mobile Phone System were used in CDMA at the time of its inception
A unique code is received by all mobile network users and is allowed continuous network access instead of intermittent and timed access.

CDMA one refers original ITU IS-95 CDMA wireless interface protocol. It is considered as a 2G mobile wireless technology
The version IS-95A protocol employs a 1.25 Mhz carrier and data speeds up to 14.4 Kbps
The version IS-95B support data speeds up to 115 kbps by employing 800 MHz / 1.9 GHz.

CDMA2000 is a Multi-carrier code-division multiple access version of IMT-2000 standard
CDMA2000 is a 3G wireless technology.
World’s first 3G commercial system was launched by SK Telecom of South Korea using CDMA2000 1X
CDMA 2000 supports mobile data communications at speeds from 144KBPS to 3MBPS
The versions of CDMA2000 have been developed by Qualcomm and Ericsson
There were 250,300,000 subscribes world for CDMA by March 2006.

DECT is one of the wireless technologies, originated in Europe
DECT was designed to interwork with various networks such as PSTN, ISDN, GSM etc.
The initial standard. of DECT focused on developing air interface which is a radio link between cordless telephone and the base stations
This standard plugged into the telephone socket and the standard protocols for handover between several base stations
All these are connected to the same office switchboard, typically a PABX
The first product of its kind was from Olivetti, was a wireless LAN type product, known as NET3..

HSPA is a combination of 2 mobile telephony protocols – High Speed Downlink Packet Access and High Speed Uplink Packet Access
HSPA improves the performance of existing WCDMA protocols.
HSPA provide increased performance by utilizing schemes of modulation and refining the protocols, through which the base stations and handsets communicate
HSPA is used for better usage of the available bandwidth provided by WCDMA
HSPA supports data rates of up to 14 MBit / s in the downlink
HSPA supports data rates of up to 5.8 MBit / s in the uplink
HSPA reduces the latency and increases up to 5 times more system capacity during downlink and twice more system capacity during uplink
HSPA uses 16QAM for yielding higher bit rates
HSPA rollouts are achieved by implementing software upgrades to existing 3G networks. This gives HSPA a head start over WiMax.

CDMA

Same frequency is used by every user and simultaneous transmission occurs
Every narrowband signal is multiplied by wideband spreading signal, usually known as codeword
Every user has a separate pseudo-codeword, i.e., orthogonal to others
Only the desired codeword is detected by the receivers and others appear as noise
It is mandatory for the receivers to know about the transmitter’s codeword

FDMA

When the channel is not in use, it sits simply idle
Bandwidth of Channel is relatively narrow (30 KHz), known as narrowband system
Little or no equalization is needed for spreading symbol time
Analog links are suitable for FDMA
Framing or synchronization bits are not needed for continuous transmission
Tight filtering is needed to minimize interference
Combined with FDD for duplexing

CDMA

Power limited system
While people talking, random noise band playing occurs
Conversation need to be extracted from the background din
GP is high when people speak different languages, which is easier to distinguish individual speakers
It is difficult for distinguishing individuals, when GP is low.
The system performance will be degraded for every user when the number of users increases.
Fading would be reduced with wide frequency spectrum
Need to have separate multipath signals with different delays by “chip” unit.

TDMA

Receiving or transmission is allowed for only one user in a given slot
All slots are assigned cyclically
The transmission is non-continuous
It is essential to use digital data and modulation
Data rate overhead is between 20% – 30%
Overhead tradeoffs are size of data payload and latency
Multiple users are shared with single carrier frequency
Handoff is made simpler by using non-continuous transmission
All slots are assigned on demand
Due to reduced inter user interference, the power control is less stringent

Data Transfer Speed:

CDMA is faster than GSM.
CDMA2000 downstream rate is 2 megabits / second, through EVDO, where GSM downstream rate is up to 384 kilobits / second, through EDGE technology

Subscriber Identity Module (SIM) cards:

SIM is tied to the network, rather than the actual phone. Phones with card-enabled can be used with any carrier of GSM
Proprietary handsets are linked to one carrier only and not card-enabled in CDMA

Roaming:

GSM carriers have wider coverage of more rural areas, where as CDMA may not cover rural areas compared to GSM carriers

International Roaming:

GSM has facility to offer more international roaming, as the number of connections in world market dominate GSM network.
CDMA phones do not have the capacity; however, there are more countries that use CDMA networks.