TELECOMMUNICATIONS GROUP ASSIGNMENT
First of all we would like to express our heartfelt thanks to Mr.R.K.Chodhary ,the Director of our esteemed institution APIIT SD INDIA for providing us with such a superb infrastructure. Secondly, we would like to thank our module Lecturer MR.Vishal Kaushik without whom we would not have been able to to complete this project.
We would also like to thank our seniors and friends who always put forward their hands in case of need,such as to find out the shortcomings and resolve the faults in the assignment.
Finally, we would like to thank all our group members for their valuble co-operation and efforts to complete the given task on time.
This is to certify that Kartikeya Rai(PT0882242), Bedanta Borah(PT0882243), Deepanshu Tripathi(PT0882215) and Sanjay Rathore(PT0882226) of Group-29(Computing) Level-1 have completed their Group assignment of the module Telecommunication and submitted the assignment within the stipulated time.
There are two main competing mobile network technologies in cellular service:
- GSM: Global System for Mobile Communications
- CDMA: Code Division Multiple Access
As per given choice between above two technologies we have chosen CDMA for our assignment. On the basis of our research we have found that it is new and more advanced than GSM.
CDMA stands forCode Division Multiple Access. CDMA technology is a wireless technology used in transmission of signal from one place to another with high security and noise reduction.
CDMA is a form ofmultiplexing, which allows numerous signals to occupy a single transmissionchannel, optimizing the use of availablebandwidth. It is a cellular technology that incorporates spread-spectrum techniques. Both data and voice are separated from signals using codes and then transmitted using a wide frequency range. Hence, there is more space available fordatatransfer (this was one of the reasons why CDMA is thepreferred technology for the 3G generation, which is accessing broadband and the use of large multimediamessages). The CDMA system works directly on 64 kb/sec digital signals. These signals can be digitized voice, ISDN channels, modem data, etc.
Basically CDMA is a type of multiple access scheme (which means allotting the given bandwidth to multiple users) and makes use of spread spectrum technique which is essentially increasing the size of spectrum.In CDMA each user is provided a unique code and all the conversation between 2 users are coded.
The importance of the technology for human beings at work and social life:
The best example to show the importance of this technology is that CDMA was developed during Second World War in order to transmit signals in military. High security provides a wide application in military. The military preferred CDMA because signals are coded in a large number of possible combinations which resulted in highly secure transmissions.
CDMA is nowadays the becoming most the most important wireless technology in cellular networks.In India, CDMA mobile services were firstly launched in December 2002. Today, more than 100 million satisfied CDMA subscribers in India that possess the outstanding voice quality and excellent data throughput, justify CDMA services in India.India has now become the world's second-largest CDMA market. Reliance Communications and Tata Teleservices are ranked second and fourth, respectively among the top five CDMA operators in the global market.
As it is more secured and faster than the other present wireless technologies therefore its demand is higher than the other technologies such as GSM, TDMA etc. CDMA mobile broadband is already fulfilling the demand for affordable high-speed wireless data services. Especially after the arrival of 3G, now we are able to make use of the full potential of applications and services provided by CDMAin India.
CDMA started the wireless revolution in India by making mobile communication more affordable to the subscribers and played a key role in bridging the digital divide.
The modulation technique used and basic requirement for successful implementation of the technology:
SPECTRUM OF CDMA
CDMA is a Direct Sequence Spread Spectrum system. In CDMA technology every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence. CDMA which incorporates spread-spectrum technology works by digitizing multiple conversations. It attaches a code known only to the sender and receiver, and then dicing the signals into bits and reassembling them.
There are many devices which use the same spread spectrum (hence multiple access). There is one physical channel, and a special code for every device in the coverage network. Using this code, the signal of the device is multiplexed, and the same physical channel is used to send the signal (the codes may or may not change). CDMA scheme has two concepts, spread spectrum techniques with single user detection and multi user concepts with joint detection of user signals. CDMA gives the user entire spectrum all of the time. CDMA spread spectrum technology in which it uses unique spreading codes to spread the baseband data before transmission. The receiver then dispreads the wanted signal, which is passed through a narrow band pass filter. The unwanted signals are not dispread and will not be passed through the filter. The codes are a sequence of zeros and ones produced at a much higher rate of that of the baseband data. The rate of spreading code is referred to as chip rate.
CDMAuses a special type ofdigital modulationcalledspread spectrumwhich spreads the voice data over a very wide channel inpseudorandomfashion. The receiver undoes the randomization to collect the bits together and produce the sound.
CDMA digitized the multiple conversations. It attaches a unique code which is known only to the sender and receiver, and then gambles the signals into bits and reassembles them.
CDMA supports variable bandwidth connections, with enhanced standards at 13Kbps and 64Kbps for superior quality speech and faster data connections. This 'bandwidth-on-demand' limits the number of simultaneous connections to a particular base station.
Since during the calls most conversations are consists mostly of silence, thus CDMA phones have to transmit less data as they don't have to send silence, like GSM or TDMA phones do. Hence more CDMA calls can be fit into a given amount of frequency spectrum which is more efficient for the network. CDMA uses newer vocoder called EVRC, which suppress the background noise even when the user is talking.
The Concept of signal spreading in CDMA:
Let's take a stright forward binary signal of symbol rate 2.
To modulate this signal, we would multiply this sequence with a sinusoid and its spectrum would look like as In figure 2. The main lobe of its spectrum is 2 Hz wide. The larger the symbol rate the larger the bandwidth of the signal.
Now we take an another binary sequence of data rate 8 times larger than of sequence shown in Fig. 1.
Instead of modulating with a sinusoid, we will modulate the sequence 1 with this new binary sequence which we will call the code sequence for sequence 1. The resulting signal looks like Fig. 4.
Since the bit rate is larger now, we can guess that the spectrum of this sequence will have a larger main lobe.
The spectrum of this signal has now spread over a larger bandwidth. The main lobe bandwidth is 16 Hz instead of 2 Hz it was before spreading. The process of multiplying the information sequence with the code sequence has caused the information sequence to inherit the spectrum of the code sequence (also called the spreading sequence).
The spectrum has spread from 2 Hz to 16 Hz, by a factor of 8. This number is called the spreading factor or the processing gain (in dBs) of the system. This process can also be called a form of binary modulation. Both the Data signal and the modulating sequence in this case are binary signals.
In CDMA we do modulation twice. First time with a binary sequence and second time by a carrier. The binary sequence modulation ahead of the carrier modulation accomplishes two functions
- It spread the signal
- It introduces a form of encryption because the same sequence is needed at the receiver to demodulate the signal.
SOFT HANDOFF AND HARD HANDOFF:
In a traditional hard handoff process the connection to the new cell site is made after breaking a connection to the present cell site. While in the soft handoff process, the connection to the new cell site can be made without breaking the connection of the present cell site. Since CDMA uses the same frequency CDMA uses the soft hand off. Soft handoff requires less power, which reduces interference and increases capacity. The CDMA network chooses one or more alternative sites that it feels are handoff candidates while a call is in progress. It simultaneously broadcasts a copy of the call in each of these sites. It can then choose one of the sites and can move between them whenever it feels like it. This puts the phone in complete control of the handoff process.
A CDMA network consists of the following components:
- Mobile station.The CDMA mobile station (or mobile phone) communicates with other parts of the system through the base-station system.
- Base station (BS).The base station (BS) handles the radio interface to the mobile station. The base station is the radio equipment (transceivers and antennas).
- Base station controller (BSC).The BSC provides the control functions and physical links between the MSC and BTS. It provides functions such as handover, cell configuration data and control of RF power levels in base transceiver stations. A number of BSCs are served by a MSC.
- Mobile switching center (MSC).The MSC performs the telephony switching functions of the system. It also performs such functions as toll ticketing, network interfacing, common channel signalling, and others.
- Home location register (HLR).The HLR database is used for storage and management of subscriptions. The home location register stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status.
- Visitor location register (VLR).The VLR database contains temporary information about subscribers that is needed by the mobile services switching center (MSC) in order to service visiting subscribers. When a mobile station roams into a new mobile services switching center (MSC) area, the visitor location register (VLR) connected to that MSC will request data about the mobile station from the HLR, reducing the need for interrogation of the home location register (HLR).
- Authentication center (AC).The AC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The authentication center (AUC) also protects network operators from fraud.
- Operation and administration (OAM).The OAM is the functional entity from which the network operator monitors and controls the system. The purpose of operation and support system is to offer support for centralized, regional, and local operational and maintenance activities that are required for a CDMA network.
Due to higher bandwidth available in CDMA the number of channels(users) that can be allocated in a given bandwidth is comparatively higher for CDMA than for GSM. CDMA networks are built with standard IP packet data protocols. Other networks require costly upgrades to add new data equipment in the network and will require new data phones. Standard CDMA phones already have TCP/IP and PPP protocols built into them. Thus the cost of setting up a CDMA network is also comparatively less than the GSM network.
Security issues of the CDMA technology:
The CDMA technology is generally known as powerful security during communication. CDMA uses a drastically different approach other than the GSM. It assigns a unique code called "pseudo-random code sequence" to put multiple users on the same bandwidth channel simultaneously. The base station and handset both use these unique codes to differentiate between conversations. This provides user's communication more security and privacy.
Increased privacy is inherent in CDMA technology. CDMA phone calls will be secure from the casual eavesdropper since, unlike an analog conversation, a simple radio receiver will not be able to pick individual digital conversations out of the overall RF radiation in a frequency band.
CDMA air interface is inherently secure and is clearly superior to first-generation analog and (TDMA) systems. The inherent security of CDMA air interface comes from spread spectrum technology. Spreading techniques are used to form unique code channels for individual users in both directions of the communication channel. Because the signals of all calls in a coverage area are spread over the entire bandwidth, it creates a noise-like appearance to other mobiles or detectors in the network as a form of disguise, making the signal of any one call difficult to distinguish and decode.
In CDMA data signal is spread like a noise like signal which is unable to detect by others which provides security. Since the spread signal is below the noise level noise has no effect on the signal which results in noise reduction.
CDMA air interface technology is inherently secure for protection of signalling and bearer traffic with excellent security in service provisioning for handset and parameter distribution.
CDMA employs a fast power control, 800 times per second, to maintain its radio link. It is difficult for a third party to have a stable link for interception of a CDMA voice channel, even with a full knowledge of a Walsh code.
Industry and locality best suited for implementation of CDMA technology:
CDMA technology can be implemented in the area where there is high demand of wireless cellular network for serving the purpose of cellular services. Especially the highly densed urban area is best suited for implementation of CDMA technology as there is more demand of cellular network for using mobile phones and broadband access hence there would be more subscribers. CDMA can play an important role in large organisations which are spread worldwide where transmission of data and information takes place frequently. CDMA can provide assistance in the transmission of data and information of an organization with more security and privacy. In metro cities 3G is becoming very popular nowadays, CDMA is best for providing 3G services in the metro cities. Demand of broadband is also increasing day by day mainly in the urban areas, CDMA can fulfils the needs of wireless network for more fast and advanced broadband access.
Advantages and Strengths of CDMA technology:
- Outstanding Voice and Call Quality
- Greatest Coverage for Lower Cost
- Extended reach:
- Low power requirements and Smaller Phones
- Increased cellular communications security:
- Greater Capacity
- Continuing Advances
- higher data and voice transmission quality
- Most harmless among other technologies:
- Highest data transmission capacity
- CDMA is relatively new technology, and its network is also not as mature as GSM. Therefore all of CDMA's defects are not known to the engineering community. Also limited variety of the handset in CDMA, because at present GSM is use by the major mobile companies since it is not old and simpler as GSM.
- One major disadvantage in this technology CDMA cannot offer international roaming, when compared to GSM. In CDMA the ability to change handset is not easy because the network service information for the phone is put in the actual handset. However now some CDMA carriers are giving facility to upgrade the handset but with the same carriers. Whereas in GSM network information is stored in SIM card.
- Channel pollution is also a main problem in CDMA technology, where signals from too many cell sites are present in the user's mobile but no one among them is dominant. The quality of the audio goes down when this type of situation arises.
- Another problem for CDMA users is of limited service provider. The CDMA carriers have to provide handsets to users, for which the users cannot change their Sims (service provider). While in GSM users can easily change their service provider whenever they want. Also there are limited service providers for CDMA, which restricts the user's choice of service provider.
- Another problem in CDMA mobile phones is that there is an emergency number "112" that every GSM mobile in the world can call anytime in case of any emergency. Because of certain technological limitations this facility is not implemented in CDMA.
- CDMA mobiles also transmit microwaves like other existing wireless technologies do, even in standby mode also.
- The air link
- The cell site tower/antenna and the cable connection to the Base Station Transceiver Subsystem (Um)
- The Base Station Transceiver Subsystem (BTS)
- The communications path from the Base Station Transceiver Subsystem to the base station controller (ABS)
- The Base Station Controller (BSC)
- The Packet Control Function (PCF)
- Our report basically describes all about CDMA, how it works what sort of modulation technique it requires, security issues, implementation of CDMA etc.
- Certain Hardware, software, skills, cost required for successful implementation of CDMA is also described above.
- Later on The security issues, implementation and problems while implementation are also discussed.
- There are certain advantages and disadvantages of CDMA which are also described in our report.
- Our report only discussed these issues regarding CDMA which are importance, security, Implementation, problems in implementation, Advantages and disadvantages of CDMA etc. It could contain some more features of CDMA.
- Our report could contain some more practical aspects of application of CDMA which will make our report more of descriptive.
- Our report could contain more descriptive but due to word limit we have to be more specific towards the topics.
CDMA eliminates the background noise, cross-talk, fading and interference during the conversations so that user can enjoy crystal-clear voice quality and enhanced call quality with greater privacy. It uses a vocoder EVRC for noise reduction where the background noise is reduced. This is exclusively available in CDMA technology only Both computer noise and background sounds are filtered out by using narrow bandwidth which corresponds to the frequency of the human voice.
CDMA's spread spectrum signal provides the greatest coverage at the lower cost in the wireless industry.Because CDMA system require fewer cell sites, CDMA networks can be set up and expanded faster and more cost effectively than the other wireless networks. Moreover the operating expenses are also reduced for operators due to fewer cell sites.
The major advantages of CDMA are that network failure occurs only when the location of phone is at least twice as far from the base station. Thus it can be used in the rural areas where GSM network usually cannot cover. This is favourable to rural users which are situated far from cells.
CDMA handsets generally transmit at the lowest power levels which consumes less battery power resulting in longer talk time and standby time. Battery life is long since the handset transmits data only when it actually has to send. CDMA handsets can also easily incorporate smaller batteries which results in smaller and lighter-weight phones which are easier to carry and use.
CDMA is digitally encoded and designed with trillion of possible frequency-sequencing codes. Because of spread spectrum technology it uses transmissions resist eaves dropping. This enhances the privacy and makes cloning difficult and also eliminates other types of frauds.
CDMA has a very high spectral capacity that it uses spread spectrum technology which can provide up to 10-20 times the capacity of analog equipment and more than three times the capacity of other digital platforms that allows the largest number of subscribers per MHz of bandwidth. With dual-mode phones, CDMA is compatible with other technologies for seamless widespread roaming coverage.
CDMA technology allows users to access a high range of services, including caller identification, short messaging services and Internet connections. Simultaneous conversations can be made using CDMA technology.
Because of the spread spectrum technology it uses, which has increased resistance to multipath distortion. Various issues such as sound echoes, call dropping, or voice distortion are almost non-existent in CDMA, while the possibility of errors is high in GSM.
CDMA is harmless among other existing technologies. CDMA technology checks its transmission level 800 times per second. That's why radiation level in CDMA is 10 times lesser than GSM phones. Another reason is that less radiation is being created from the phone towards the user. In CDMA system user gets the radiation only when the user starts conversation.
Disadvantages of CDMA:
PROBLEMS DURING IMPLEMENTATION OF CDMA TECHNOLOGY:-
INEFFICIENCY IN USER DATA PACKET TRANSMISSION:
Frequently in a cdma2000 network the TCP user-plane packets have a small Window Size. This implies that end-to-end TCP connections are not stable. The more TCP packets lost in the network and not acknowledged, the smaller the Window Size, with the result that more TCP connections are dropped and re-established.
DUPPLICATION OF IP-TRAFFIC:-
PDSN configuration problems can give rise to other types of problems in addition to tunnel loops. One common issue is associating the PDSNs logical IP addresses with more than one physical MAC address. When this occurs, more than one hardware card has the same IP address. All traffic sent to that IP address goes to two different hardware entities and receives responses from both. This effectively doubles the amount of IP traffic associated with that single IP address on that segment.
ROUTING PROBLEMS IN CORE NETWORK:
Sometimes internal problems can cause PDSN routers to go offline and come back online after a period of time. This can happen frequently and continuously in a cdma2000 core data network.When a router first comes online its routing table are not optimized.It takes time for the built-in OSPF (Open Shortest Path First)routing algorithm to learn the best way to route packets depending on adjacent available routers. Until the routing tables are optimized, there will be degradation in quality of service.
3-G NETWORK PROBLEM:-
The focus of most current research is on Wideband CDMA (W-CDMA) or NG (next generation) CDMA. In W-CDMA, the multimedia wireless network will become feasible. Not only voice, but also images, video and data can be transmitted by mobile phones or other portable devices. Achieving a higher data rate and higher capacity are two major goals for W-CDMA, which makes the multi-user interference problem more and more crucial.
Another major problem for CDMA systems is channel pollution. This problem occurs mostly in densely populated area where service providers have built numerous cell sites in a close proximity. Because of this too many signals from the cell sites are present at the subscriber's handset but no one is dominating among them even though the signal are seem to be strong as they are within the cell site's coverage. When subscriber's phone is at such location the quality of sound degrades rapidly. Channel pollution can occurs due to high and large buildings which cause massive multipath problems.
SIMPLE DESIGN OF THE IMPLEMENTATION OF CDMA TECHNOLOGY :-
EXPLANATION OF DIAGRAM:
In a cdma2000 1X network, the mobile stationthe subscriber's handsetfunctions as a mobile IP client.The mobile station interacts with the Access Network to obtain appropriate radio resources for the exchange of packets, and it keeps track of the status of radio resources (e.g. active, stand-by, dormant). It accepts buffer packets from the mobile host when radio resources are not in place or are insufficient to support the flow to the network.
RADIO ACCESS NETWORK:-
It is the mobile subscriber's entry point for communicating either data or voice content. It contains-