At the very outset, we would like to take this opportunity to thank our lecturer Mr. Vishal Kaushik, who has been a constant guide throughout this project. Without his help and support, the completion of this project would have been the next impossible thing. We are grateful to him because his motivation and support has inspired us to dedicate ourselves completely towards this project.
We would also like to extend our heart-felt thanks and gratitude towards APIIT SD INDIA, Panipat and our director, Prof. R. K. Choudhury for providing us an excellent learning environment in the form of a well-stocked library, well-equipped labs and ever-helping faculty members.
Lastly, we would like to mention the support provided to us by our peers and seniors, whose contribution towards the completion of this project is note-worthy.
Aaditya Kumar (Group Leader)
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Telecommunication is a general term for a vast array of technologies that send information over distances. Mobile phones, land lines,satellitephones andvoice over Internet protocol (VoIP)are alltelephonytechnologies -- just one field of telecommunications.
Data is conveyed in a telecommunications circuit by means of an electrical signal called thecarrieror carrier wave. In order for a carrier to convey information, some form ofmodulationis required. The mode of modulation can be broadly categorized as eitheranalogordigital.
GSM (Global System for Mobile communication) is a digital mobile telephone system that is widely used in Europe and other parts of the world. It uses a variation of Time Division Multiple Access (TDMA) and is the most widely used of the three digital wireless telephone technologies (TDMA, GSM, and CDMA). It digitizes and compresses data, then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1,800 MHz frequency band.
Code Division Multiple Access (CDMA) is a digital air interface standard, claiming eight to fifteen times the capacity of traditional analog cellular systems. It employs a commercial adaptation of a military spread-spectrum technology. Based on spread spectrum theory, it gives essentially the same services and qualities as wire line service. Though CDMA's application in cellular telephony is relatively new, it is not a new technology. CDMA has been used in many military applications, such as: Anti-jamming, Ranging, Secure communications. The technology is used in ultra-high-frequency (UHF)cellular telephonesystems in the 800-MHzand 1.9-GHzbands.
Reasons for preferring CDMA technology:-
- CDMA offers EDVO technology which provides best data transfer speed (maximum download speed is about 2mbps) than any other technology (GSM provides EDGE technology which provides maximum download speed 384kbps).
- It provides extreme security than any other technology. CDMA send data packet by code division process, meaning that it cannot be hacked.
- Its chipset is far smaller than GSM, thus you can put a lot more multimedia functions, from ringtones to better screens and super cameras, and it weighs less than GSM.
- It provides better coverage than GSM in rural areas.
cdmaOne: It refers to the original ITU IS-95 (CDMA) wireless interface protocol that was first standardized in 1993. It is considered a second-generation (2G) mobile wireless technology.
Today, there are two versions of IS-95, called IS-95A and IS-95B.
IS-95A: The IS-95 specification was first published in 1993 and the first revision (IS-95A) in 1995. This specification forms the basis of many commercial cellular operations around the world, and describes the structure and operation of a 1.25-MHz CDMA radio system. This specification supported basic voice services and "dial-up" data connections at speeds up to 14.4 kbps. The first operational IS-95 system was operated by Hutchison in Hong Kong in 1995.
IS-95B: The second revision, IS-95B, combines a number of standards into one and addresses some interworking issues between IS-95 systems and others. IS-95B can also support higher data rates, with some operators offering 64-kbps connections. It also offers the greater efficiency of packet data, making it a 2.5G system. cdmaOne IS-95B was first deployed in September 1999 in Korea and has since been adopted by operators all over the world. There are nearly 300 million cdmaOne subscribers in 400 networks worldwide, the majority of these being in North America and the Asia Pacific regions (Figure 1.43).
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cdma2000 1 X: 1 X is an evolution technology bringing further efficiency and higher data rates to existing 2G deployments. This technology can double the voice capacity in a network and support packet data rates of up to 307 kbps.
The world's first cdma2000 1X commercial system was launched by SK Telecom (Korea) in October 2000. Since then, cdma2000 1X has been deployed in Asia, North and South America, and Europe. There are now 126 operators in 57 countries around the world, with an estimated subscriber base of 200 million; subscriber figures are growing at a rate of 7 million users per month.
Hand off Techniques: -
Hand off occurs when a call has to be passed from one cell to another as the user moves between cells.
In hard hand off, the connection to the current cell is broken, and then the connection to the new cell is made and is also known as a "break-before-make" hand off.
Since all cells in CDMA use the same frequency, it is possible to make the connection to the new cell before leaving the current cell. This is known as a "make-before-break" or "soft" hand off which requires less power, which reduces interference and increases capacity.
CDMA codes are not required to provide call security, but create a uniqueness to enable call identification. Codes should not correlate to other codes or time shifted version of itself. Spreading codes are noise like pseudo-random codes, channel codes are designed for maximum separation from each other and cell identification codes are balanced not to correlate to other codes of it.
IMPORTANCE OF CDMA
The CDMA technology is used by more than 100 million subscribers in India so it has many importance humans social and work life. They are as follows:
Coverage: In older days we have coverage for CDMA technology in Metropolitan areas. But now a days CDMA technology enable us to use its services in rural areas also. So the people in rural area without any knowledge of mobile are also start to use mobiles and become so much literate about the use of mobile.
Calls: The mobile phones act like a necessity of human's daily life. In the time of emergency when the thief broke out into house or any medical emergency we can use our phone with CDMA technology to contact our friends, police or doctor. In case the person is a doctor but he is at leave and a patient came with a disease which needs immediate operation else the person will die then what the hospital staff will do they call the doctor rather than go and find the doctor.
SMS: SMS are used if the person want to send important information to his friend who is presently not available for any cause he can send him a SMS , so whenever the person become available he get that information.
Roaming: When we out of our state we have to face heavy STD (Subscribed Truck Dialling) call rates but CDMA technology provide peoples with rooming facility so that they can use CDMA technology facility at low rates as compare to STD booth.
Wireless Internet: The CDMA technology provide wireless high speed internet at reasonable cost. Today everybody want to use the internet while travelling or moving in the work place .The CDMA technology enables peoples to use Internet in their mobile phones or PC with the help of which a human can do most of his task perfectly. If you want to book a ticket of train, airplane or any other ticket you can book it in seconds if that is available on internet. The normal persons can use their credit card or any other card to pay his bills.
Soft Hand off: In the CDMA technology it is possible to connect to the next BTS before leaving the present one. So the call does not break in between. So the person can still make a call when he travelling through any fast moving vehicle.
MODULATION TECHNIQUE USED
CDMA uses a special type of digital modulation called spread spectrum which spreads the voice data over a very wide channel in pseudorandom fashion. The receiver undoes the randomization to collect the bits together and produce the sound.
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Spread Spectrum uses wide band, noise-like signals. Because Spread Spectrum signals are noise-like, they are hard to detect. Spread Spectrum signals are also hard to Intercept or demodulate.
It uses fast codes that run many times the information bandwidth or data rate. These special "Spreading" codes are called "Pseudo Random" or "Pseudo Noise" codes.
Because Spread Spectrum signals are so wide, they transmit at a much lower spectral power density, measured in Watts per Hertz, than narrowband transmitters. This lower transmitted power density characteristic gives spread signals a big plus. Spread and narrow band signals can occupy the same band, with little or no interference.
Key elements of spread-spectrum techniques:-
- The signal occupies a bandwidth much greater than that which is necessary to send the information. This results in many benefits, such as immunity to interference and jamming and multi-user access.
- The bandwidth is spread by means of a code which is independent of the data.
- The receiver synchronizes to the code to recover the data. The use of an independent code and synchronous reception allows multiple users to access the same frequency band at the same time.
Types of spread-spectrum techniques:-
Frequency hopping: -
The signal is rapidly switched between different frequencies within the hopping bandwidth pseudo-randomly.
Time hopping: -
The signal is transmitted in short bursts pseudo-randomly, and the receiver knows beforehand when to expect the burst.
Direct sequence: -
The digital data is directly coded at a much higher frequency. The code is generated pseudo-randomly, the receiver knows how to generate the same code, and correlates the received signal with that code to extract the data.
CDMA is a Direct Sequence Spread Spectrum system. The CDMA system works directly on 64 Kbit/sec digital signals.
A complete spread-spectrum communication link requires various advanced and up-to-date technologies and devices like an RF antenna, a powerful and efficient PA, a low-noise and highly linear LNA, compact transceivers, high-resolution ADCs and DACs, rapid low-power digital signal processing (DSP) etc.
SECURITY ISSUES WITH CDMA
The CDMA technology is generally known as powerful security during communication. However, the communication data might be eavesdropped and forged, because the mobile communication sends data through wireless communication channel. So it is essentially necessary to setup the entire system securely. For the sake of this following steps are taken:-
- CDMA uses a greater spectrum range, which means that a much greater range of frequencies must be evaluated. This also makes jamming a CDMA signal much harder than TDMA- or FDMA-based systems.
- CDMA handsets utilize a 64-bit symmetric key (called the A-Key) for authentication. This key is programmed into the handset at the retail outlet and is also saved by the network provider. Software in the handset calculates a simple checksum to verify that the A-Key value has been properly entered.
- CDMA's spread spectrum techniques and random codes were widely considered harder to crack than GSM-based TDMA signals.
- To minimize the risk of intercepting an individual A-Key in the air, CDMA derive a dynamic value for authentication based on the A-Key. This dynamic value is called the shared secret data (SSD) and is calculated using three values:
- The individual subscriber's A-Key
- the ESN of the individual's handset
- A random number
This operation generates two 64-bit values, SSD_A and SSD_B. SSD_A is designated for authentication, while SSD_B is designated for encryption algorithms.
Key or authentication key is a 64 bit permanent number stored in permanent storage of mobile phones. The ESN is the 32 bit electronic serial number of the mobile phone.
IMPLEMENTATION AREAS OF CDMA
As a matter of fact is implementation of CDMA technology depends of willingness of users towards this technology. Earlier it was more popular in America in the age of Second World War. Right now this technology is used in US, Canada and some Asian Country (India). CDMA uses spread spectrum technique to increase spectrum efficiency over current FDMA and TDMA systems. Many military applications used Spread spectrum, such as ranging (measuring the distance of the transmission to determine when it will be received), anti-jamming (because of the spread signal, it is difficult to interfere with or jam), and secure communications (the spread spectrum signal is very hard to detect).
This technology can be implemented in those areas where Population density is too low. We know CDMA technology provide signal in high range. So implementing CDMA technology, we can save cost in order to stand this technology. This covers high range and delivers secure communication. So there is a chance of CDMA in Military and marines areas. CDMA provide fast and secure communication, it cannot be hacked easily due to its nature. So it can be implemented in security area where secure communication is required.
It saves costs of calls so it can be implemented in those area and locality where people are too poor and unable to bear out so many expanses on mobile phones. CDMA covers large geographical area so it can be implemented in Desert areas, hill Areas, Seas etc. In this area CDMA will save costs as well as provide a clear communication to the users.
CDMA technology is best suited in Developing Country, where people are not economically well and those localities where people are not more literate. They have a single purpose to use mobile phones that is Communication.
The most feasible scenario in case of CDMA is it costs less for phone calls, and create and a Competitive platform with other corresponding technology in their call rates. This will help to keep low call rate in order to use another technology.
ADVANTAGES AND DISADVANTAGES OF CDMA
Advantages of CDMA:
- Soft Handoff: - Since all cells in CDMA use the same frequency, it is possible to make the connection to the new cell before leaving the current cell. This is known as a "make-before-break" or "soft" handover. Soft handovers require less power, which reduces interference and increases capacity.
- Stupendous Voice and Call Excellency: CDMA does not allow background sound, disturbance, cross-talk, and interference. So User may enjoy crystal-clear voice quality, highly privacy, and enhanced call Features by this technology.
- Greatest Coverage at Lower Cost: CDMA disperse spectrum signal provides the widely coverage in the wireless industry through the Globe, allowing networks to be made with far fewer cell sites than other wireless technologies. Fewer cell sites translate to reduced functioning costs, which grades in savings to both Company and consumers money.
- Packet Data: CDMA Technology is built with standard IP packet data protocols. Other Technology requires expensive upgrades to append new data tools in the network and will require new data phones.
- Long Talk Time, Longer Battery Life and Smaller Phones: CDMA handsets usually broadcast at the least power levels in the trade. It allowing for longer battery life which results in longer talk time. CDMA handsets can also slot in smaller batteries, resulting in smaller and lighter-weight phones. So these are easier to carry and easier to use.
- Smaller number of Dropped Calls: CDMA technology use "soft handoff" method of passing calls between cells rapidly reduces the menace of interruption or dropped calls during a handoff. The progression of soft handoff leads to less dropped calls because 2 or 3 cells are monitoring call at that time.
- Enhanced protection and Privacy: it's digitally encoded extend spectrum transmissions prevent to attic dropping. CDMA practically eliminates cloning and other deceit.
- Greater capability: CDMA covers the largest number of subscribers to allocate the similar radio frequencies; serving service providers amplify their profitability. CDMA uses spread spectrum technology which can offer up to 10-20 time the capability of analogue equipment and more than three times the capability of other digital platforms. In case of dual-mode phones, CDMA is well-suited with other technologies for faultless widespread roaming exposure.
- Compact Background Noise and Interference: It mixed up multiple signals and improves signal strength. It eliminates the interference and fading it also exclude electrical sound (computer noise) and acoustic sound (background conversations) by filtered out using narrow bandwidth which relative to the frequency of the human voice
- Rapid Deployment: This technology can be deployed and extended quicker and more cost effectively than most wire line networks. Because of they involve fewer cell sites, so it can be deployed faster than another wireless Technology.
- Wide Product Selection: QUALCOMM has accredited CDMA technology to over 65 leading communication manufacturer's globally, offering service vendors and customers to prefer from a wide range of highly sophisticated, cost-competitive, CDMA-based products and Commodities.
- Continuing Advances: this technology offers users to access a broad variety of new services, including caller identification, short messaging services and Internet connections. Instantaneous voice and data calls are also possible using CDMA technology.
Disadvantage of CDMA:
- Self-jamming: arriving transmissions from multiple users not aligned on chip boundaries unless users are perfectly synchronized.
- Near-far problem: signals closer to the receiver are received with less attenuation than signals farther away.
- One major problem in CDMA technology is channel pollution, the quality of the audio degrades when this situation arises. Where signals from too many cell sites are present in the subscriber's phone but none of them is dominant.
- CDMA has the lack of international roaming capabilities. This technology does not give chance to upgrade or change to another handset because the network service information for the phone is put in the actual phone unlike GSM which uses SIM card for this.
- There is limited availability in variation of CDMA mobile Handsets.
- These CDMA Handsets are not compatible with GSM Handsets. We don't change SIM Card in case of CDMA Mobile Handsets. But GSM handsets provide some more leniencies in this case. GSM Handsets are flexible with respect of CDMA Mobiles.
- Extra Features like Instant Messaging, web services, web browsing etc. slightly difficult to implement in case of Mobile handsets in CDMA technology.
- Batteries Power consumption is highs in CDMA handsets.
PROBLEMS IN IMPLEMENTATION OF CDMA
- A big problem faced by CDMA systems ischannel pollution. It occurs when signals from too many base stations are present at the user's phone, but none are dominant. When this situation occurs the audio quality degrades rapidly, even when the signal seems otherwise very strong. It occurs frequently in densely populated urban environments where service providers must build many sites in close proximity. It can also result from massive multipath problems caused by many tall buildings.
- Sometimes the exact site location chosen for the plantation of antenna is not utilised due to some government property or any private area located at that place.
- The signals of one particular technology can get affected by the signals of other technologies by interference or any other reason.
- The size of the cell should not be too big and the location of the base-station should at the centre, so that a user is not likely to be overshadowed by the nearer users and suffers extreme battery power.
- The load on a particular base-station should not be high because CDMA is a Soft Accommodation feature, that is, when the number of users of the network goes up, the voice quality progressively gets poorer.
- Signal deterioration inside buildings is also a big problem faced by the CDMA.
- If the neighbouring cells are not included interference cancellation, then efficiency is greatly reduced.
IMPLEMENTATION OF CDMA
Before the implementation the market survey is done which tells weather it is beneficial or not, weather the area have any other signal which are affected by CDMA signals or CDMA signal are affected by any other signal.
Continues Wave test:
A continues wane is sent from where the tower is to be implemented. The clear graph is drawn which tell the strength of frequency in each area.
After the CW test the budget is calculated for the proposed site. This will be based on the CW test which tell what height of the antenna should be and various other aspects.
After all these step the tower is get implemented. After implementation several post-test and maintenance is done.
SCOPE AND LIMITATIONS
- When the cell is situated in a highly populated area then this technology can be utilised because it can handle more users than any other technology.
- When a user is suffering from bad call quality then he can switch to CDMA technology which provides an improved call quality.
- When a user is handling any secured data then he utilise this technology.
- Simplified system planning.
- When a user lives in any rural area then in that case he can utilize CDMA technology because it has an improved coverage area.
- When a user is far away from the base-station, then it is likely that his signal will be overshadowed by the nearer users.
- Users at the far end of the cell usually consume large amount of power which will shorten the battery life and damage the amplifiers.
- Being the standard for mobile communication in very few countries, it lacks the international roaming capabilities.
CDMA provides an advanced technology for cellular applications and a radically new concept in wireless communication. It provides high-quality service to a large number of users. It is a system that has been extensively tested. It has gained widespread international acceptance by cellular radio system operators as an upgrade that will dramatically increase both their systems capacity and the service quality. Moreover it spread spectrum technology is both more secure , less probable to intercept and jam, highly private and offer higher transmission quality than any other technology because of its increase resistance to multipath distortion.