Presentation on CDMA www.ppttopics.com

Multiple access simultaneous use of a transmission medium by multiple users. Advantages : Increased capacity: serve more users. Reduced capital requirements since fewer media can carry the traffic. Decreased per user expense. Easier to manage and administer. www.ppttopics.com

MULTIPLE ACCESS METHODS www.ppttopics.com

MULTIPLE ACCESS METHOD FDMA TDMA CDMA www.ppttopics.com

A comparative study between the above three access technologies with respect to time and frequency is as shown below. www.ppttopics.com

CDMA Concept Cocktail party in same room (same wide band channel) $%&@# CDMA can bring big business This is John Doe CDMA Concept: CDMA concept can be explained with an analogy to a cocktail party with people speaking different languages. Everybody is in the same party room speaking as loudly as possible. Since, different set of people use different languages, they will be able to hear each other over noise (or interference) In CDMA, all users transmit over same wide band channel. Since, each user is identified by a unique digital code. interference resulting from other users in the same channel is rejected. Cocktail party in same room (same wide band channel) Use different languages (different digital codes) www.ppttopics.com

BPSK Modulation Why Choose BPSK? Easy to implement Well suited for CDMA www.ppttopics.com

Spread Spectrum Concept 1800 1850 1910 1930 1990 2000MHz Cell TX m Mobile TX User 1 Code 1 User 2 Code 2 User 3 Code 3 Code n User n Spread spectrum uses much larger slice(1.25MHz) of the available bandwidth. Same slice is used for all user with no time multiplexing but user is assigned www.ppttopics.com

Spread Spectrum Principles Many code channels are individually “spread” and added together to create a “composite” signal. www.ppttopics.com

CDMA SPREADING (Time Domain) www.ppttopics.com

CDMA SPREADING (Frequency Domain) www.ppttopics.com

Types of spread-spectrum Direct sequence spread-spectrum. Frequency hopping spread-spectrum. Multi-carrier cdma system. www.ppttopics.com

DIRECT SEQUENCe SPREAD SPECTRUM www.ppttopics.com

Frequency hopping Frequency occupying order- function of code sequence. Rate of hopping from one carrier to another function of information rate. www.ppttopics.com

PN(pseudo noise) codes PN –CODE is a sequence of high data rate bits(“chips”) ranging from –1 to + 1 (polar) or 0 to 1 (non polar). By “chips” we mean the no. of small data bits in the PN-CODE per single bit of the original signal. They are either linear codes generated by EX-OR gates used in shift register feedback path or otherwise non linear codes. www.ppttopics.com

Spreading a Bit by the means of many chips www.ppttopics.com

Steps evolved for signal transmission A pseudo random code is generated, different for each channel& successive connections. The information data modulates the pseudo random codes. The resulting signal modulates the carrier. The modulated carrier is amplified and broadcast. www.ppttopics.com

Steps evolved for receiving the signals The carrier is received and amplified. The received signal is now demodulated by receiving the codes. The receiver acquires the received code and phase locks its own code to it. The received signal is correlated with the generated code, extracting the information data. www.ppttopics.com

CDMA MODULATION www.ppttopics.com

CDMA DEMODULATION The modulated signal is transmitted over the channel and all users can receive it but only the user which knows the correct code can decode the message. www.ppttopics.com

CDMA System Block Diagram www.ppttopics.com

History of CDMA A method for multiple access (single channel , multiple users). The conventional methods were FDMA. Then after developing synchronization TDMA was developed in early 1980s it was introduced. Its first use was done in military. in early 1990s its first use was done in cellular communication system. www.ppttopics.com

Origination of CDMA www.ppttopics.com

FEATURES OF CDMA FLEXIBLE NETWORK. COMPATIBILITY. NETWORK ACCESs. LINE UTILIZATION. ERROR-FREE TRANSMISSION. VOICE AND CALL QUALITY. www.ppttopics.com

Multipaths www.ppttopics.com

Rake Receiver Mobile station receives multiple attenuated replicas of the original signal. Two signals are resolvable only if their relative delay exceeds the chip period Tc . Amplitudes and phases of multipath components are found by correlating the received waveform with multiple delayed versions of the signal (delay = nTc). Searcher performs the above task for up to 3 different multipath signals. RAKE fingers isolate the multipath components and the RAKE receiver combines them. www.ppttopics.com

CDMA RAKE Receiver www.ppttopics.com

RAKE RECEIVER www.ppttopics.com

CDMA Coding Procedure CDMA is based on Coding Theory. Each station is assigned a code which is a sequence of numbers called CHIPS. In this example we have four stations each has a sequence of chips which designate as A,B,C, and D. www.ppttopics.com

We Adopt the following Rules For Encoding. If a station needs to send a 0 bit it sends -1. If a station needs to send a 1 bit it sends +1. When a Station is idle, it sends no signal which is represented by 0. www.ppttopics.com

CDMA Multiplexer www.ppttopics.com

CDMA Demultiplexer www.ppttopics.com

CDMA Codes Codes in CDMA Orthogonal Codes Pseudo-noise (PN) Codes Walsh Codes Short PN Codes Walsh Codes Long PN Code Short PN Codes www.ppttopics.com

R F OVERVIEW What is cell? A cell is a small area of service within a city, serviced by its own antenna. Frequency Reuse In CDMA- All users use same frequency. Universal frequency reuse applies to the users in the same cell as well as to those in others. Complicated reuse pattern is not necessary. www.ppttopics.com

Frequency reuse AMPS CDMA www.ppttopics.com

CDMA Different Systems IS-95. CDMA-2000 (which is also called WCDMA in Europe). www.ppttopics.com

CDMA Switch Overview CDMA Network Architecture www.ppttopics.com

Comparative network speeds www.ppttopics.com

CDMA channels FORWARD CHANNELS: Pilot channel. Sync channel. Paging channel. Forward traffic channel. REVERSE CHANNELS: Access channels. Reverse traffic channels. www.ppttopics.com

TECHNICAL DATA FREQUENCY OF OPERATION :800MHZTO1900MHZ TRANSMISSION RATE : 9600 KBITS/SEC OPERATION BAND : C-BAND RF SPACING : 1.25 MHZ COVERAGE : 20 KMS. WITH FIXED UNITS GRADE OF SCIENCE : 1% www.ppttopics.com

Forward Link Channels in CDMA On the forward link there are 4 channels used to transmit control and voice data to the mobile. These code channels are: Pilot Channel Synchronize Channel Paging Channel Traffic Channel www.ppttopics.com

Reverse Link Channels in CDMA On the reverse link there are 2 types of channels used to transmit control and voice data to the mobile. These channels are: Access Channel Traffic Channel www.ppttopics.com

Call Processing in CDMA There are 4 Call Processing modes in CDMA: Initializing mode. Idle mode. Access mode. Traffic mode. www.ppttopics.com

ADVANTAGES Increased capacity. Improved voice quality. Enhanced privacy and security Reduced interference to other electronic devices. Co existence with the other technologies. Reduction in the number of calls dropped due to the handoff failures. Improved battery life due to reduced average transmitted power. www.ppttopics.com

Unauthorized systems and network access Auditability and compliance CDMA SECURITY Security becomes key to delivering solutions that meet today’s demand for mobility. Some of today’s top security issues and concerns are: Unauthorized systems and network access Auditability and compliance Customer data breaches Internal and external sabotage www.ppttopics.com

Handoff in CDMA System In GSM hard handoff occurs at the cell boundary Soft Handoff Mobile commences Communication with a new BS without interrupting communication with old BS. same frequency assignment between old and new BS. provides different site selection diversity . Softer Handoff Handoff between sectors in a cell. CDMA to CDMA hard handoff Mobile transmits between two base stations with different frequency assignment. www.ppttopics.com

Soft Handoff- A unique feature of CDMA Mobile Advantages Contact with new base station is made before the call is switched. Diversity combining is used between multiple cell sites If the new cell is loaded to capacity, handoff can still be performed for a small increase in BER Neither the mobile nor the base station is required to change frequency www.ppttopics.com

Handoff: act of transferring a call from one cell to the other www.ppttopics.com

Disadvantages of cdma technology Multi-user interference or multiple-access interference(mai). Multi-path fading. Near-far problem. M-commerce difficult. www.ppttopics.com

The near far problem users may be received with very different powers: Users near the base station are received with high power. Users far from the base station are received with low power. Nearby users will completele swamp far away users. www.ppttopics.com

Processing gain It is the increase in S/N ratio for successful data communication Processing gain (Gp) Gp=(band width of spectrum/message signalbandwidth) www.ppttopics.com

Power Control in CDMA CDMA goal is to maximize the number of simultaneous users. Power transmitted by mobile station must be therefore controlled. www.ppttopics.com

Two factors important for power control Propagation loss due to propagation loss, power variations up to 80 dB a high dynamic range of power control required Channel Fading average rate of fade is one fade per second per mile hour of mobile speed power attenuated by more than 30 dB power control must track the fade www.ppttopics.com

Power control Reverse link open loop power control. Reverse link closed loop power control. Forward link power control. www.ppttopics.com

Services in cdma Voice: In the form of calls made. SMS: It allows subscribers to send and receive short text messages between mobile stations . MMS: It allows for the transmission of images, audio, video, and rich text using WAP Pocket data ( 144 kbps / 2.4 Mbps ) –NIC & EV-DO cards. Prepaid and Postpaid Services VPN(Virtual Private Network) Bank ATM / Branch ATM connectivity www.ppttopics.com

DEPARTMENTS OF CDMA POI NLD/ID MSC R F CDMA OSP FIXED ACCESS TRANSPORT www.ppttopics.com

Current Market 480 million CDMA subscribers world over. 110 million CDMA subscribers in India. 25% of cellular subscribers in India are CDMA users. ARPU Rs 99 for CDMA in India. www.ppttopics.com

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CDMA COMPARED TO GSM Technique Used-CDMA uses code division multiple access whereas GSM uses time division multiple access. Power Consumption and Adjacent Channel Interference. Data Transfer Speed-CDMA has been traditionally faster than GSM. Subscriber Identity Module (SIM) cards and RUIM. www.ppttopics.com

In Technology CDMA Has Plus Point Over GSM, Why? CDMA is faster. CDMA is more secure. Connection on a CDMA network will never get dropped when moving from cell to cell. CDMA base stations cover a large area. www.ppttopics.com

Billing and Customer Care System Prepaid Services: The customer is charged for usage in the prior month. Postpaid Services: It asks customers to add a certain amount to their accounts prior to usage. Customer service-a series of activities to enhance the level of customer satisfaction. Many organizations have implemented feedback loops. www.ppttopics.com

Future Of CDMA CDMA has overcome most cynicism to dominate the worldwide wireless voice market. GSM & CDMA both are moving towards improved technology based on CDMA technique Ongoing research on CDMA Applying CDMA to other applications: optical CDMA, adhoc networks, dense wireless LANs etc. “MultiCDMA”: multiple antenna CDMA, multicarrier CDMA, multicode CDMA etc. www.ppttopics.com

Conclusion CDMA provides more number of users per cell site. A very secure mode of communication encouraging its use in military. It is power efficient and provides extended battery life. Provide better call quality due to soft handoff reducing the number of call drops. www.ppttopics.com

Thank You www.ppttopics.com