CDMA WIRELESS DATA TRANSMITTER

By Vijay kumar kintaliB.tech 7th semesterRegd no:0701222065

CONTENTSNEED FOR WIRED DATA TRANSMITTER

LIMITATION OF WIRED DATA TRANSMITTER

EVOLUTION OF WIRELESS DATA TRANSMITTER

CDMA TECHNIQUE

SPREAD SPECTRUM TECHNIQUE

SIGNAL MODULATION TECHNIQUES

MULTIPLE ACCESS METHODS

ADVANTAGES DISADVANTAGES AND FUTURE SCOPE

APPLICATIONS

CONCLUSION

NEED FOR WIRED DATA TRANSMITTER

For the past decade the state of technology for machine health monitoring has been continuously improving.

Majority of monitoring systems employed at the factory floor still require maintenance engineers to manually collect data and analyze them off-line.

Most of these systems require wired connections for data acquisition and transmission.

LIMITATION OF WIRED DATA TRANSMITTER

Low accessibility

Complex hardware

Space consuming

Power consuming

EVOLUTION OF WIRELESS DATA TRANSMITTER

To overcome the restrictions of wired data connection wireless data transmission for embedded sensing and machine condition monitoring has been developed.

Most of these systems operate on batteries and transmit data over a short distance to a data logging station nearby.

A challenging issue in wireless data transmission is to design for low power, less circuitry complexity, and high reliability.

The paper deals with wireless data transmitter employing code division multiple access schemes.

CDMA TECHNIQUE

CDMA stands for CODE DIVISION MULTIPLE ACCESS.

Developed by US company –QUALACOMM.

Digital technology for delivering mobile telephone services.

Uses spread-spectrum techniques.

CDMA doesn’t design a specific frequency to each user neither it is time-shared.

SPREAD SPECTRUM TECHNIQUE

SIGNAL MODULATION TECHNIQUES:

Amplitude Shift Keying(ASK) The ASK technique modulates the data by assigning each symbol a different amplitude level, e.g.: two levels for binary data.

Frequency Shift Keying(FSK) This technique employs different frequencies for different symbols transmitted.

PHASE SHIFT KEYING(PSK) Here, the carrier wave by itself represent a symbol, whereas all other symbols are defined by phase shift from the phase of carrier.

MULTIPLE ACCESS METHODS :

In order to accommodate multiple transmitters with one data receiver and achieve design flexibility and extensibilitya multiple data access scheme needs to be implemented.

Three design options were considered:

Frequency division multiple access[FDMA] In FDMA, each transmitter has a frequency exclusively assigned to it. This enables transmitter to send data at any time regardless of other transmitters. The frequency ranges can be transmitted simultaneously and should be non-overlapping.

Contd

Time Division Multiple Access [TDMA]

A single carrier frequency can be used by several transmitters, if it is ensured that at no time more than one transmitter sends data simultaneously.

Accordingly, each transmitter is assigned a time slot for signal transmission.

The time slots need to be synchronized between all the transmitters in the system.

This requires that for each transmitter, a separate receiver is implemented, and the receiver must be ON at all times, increasing the power consumption of the circuitry.

contd

Code Division Multiple Access [CDMA]

CDMA is based on coding theory and uses sequences of numbers called chips.

Here the bandwidth of shared through code, the stations use different codes to achieve multiple access.

To generate chip sequences we use Walsh tablesit uses two basic rules

w1=[ +1]

w2N=WN WN

WN WN

Bit 0 Bit 0

Bit 0silent

-1

0 +1

[-1 -1 -1 -1]

[+1 +1 +1 +1] [+1 -1 +1 -1]

[+1 -1 -1 +1] [+1 +1 -1 -1]

[0 0 0 0] [+1 -1 -1 +1]

[-1 +1 -1 +1]

-1

[-1 -1 -3 +1]

DATA

Data bit 0 - 1 Data bit 1 +1 Silence 0

Data Transmitter based on CDMA technique

Flow-chart for data transmission sequence

ADVANTAGES

Power tuning

Voice quality

User density

Cost at a suitable level i.e., less cost

Wireless increases utility and accessibility

Software implementation allows further modification

Increased mobility and scalability: more portable, half the size of credit card.

DISADVANTAGES WCDMA has higher data speed than CDMA

It reported initial difficulty in market introduction.

Reducing clock frequency and transmission speed for reduced power consumption will lead to a prolonged transmission time.

FUTURE SCOPECan be used in mobile communication with a speed up to 2mbps for voice, video data and image transmission with WCDMA.

APPLICATIONS

Machine health monitoring to machine components

Design of a wide range of electronic instruments such as data loggers, data acquisition cards, hand-held metering devices 

Systems that are difficult to access or not suitable for wired sensor data acquisition.

A rice sized chip called Verichip embedded in body ,made of biocompatible materials, stores entire medical history of implantee.

ConclusionCDMA transmitter demonstrates the feasibility of employing a sophisticated transmission scheme in an embedded sensor for machine health monitoring. Focusing on constraints and power efficiency during the design phase.

References:

www.google.com

www.TECHONLINE.com

www.wikipedia.com

Halsall.F,’ “ Wireless Local Area Networks”, Data communications, Computer networks and open systems.

Robert. X . Gao, Philipp Hunerberg- design of a CDMA-Based wireless Data Transmitter for Embedded serving

Thank you

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