Mobile Network Technologies
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 globally.
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 and its uses in communications
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 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.
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 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.
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 filters out background noise, cross-talk, and interference so you can enjoy crystal-clear voice quality, greater privacy, and enhanced call quality. It uses a vocoder EVRC for noise reduction where the background noise is reduced. This is exclusively available in CDMA technology only CDMA combines multiple signals and improves signal strength. This leads to the near elimination of interference and fading. Both computer noise and background conversations are filtered out by using narrow bandwidth which corresponds to the frequency of the human voice. This reduces the background noise and interference out of your conversations.
CDMA's spread spectrum signal provides the greatest coverage in the wireless industry.Because CDMA system require fewer cell sites, CDMA networks can be deployed and expanded faster and more cost effectively than most wireless networks. Fewer cell sites translate to reduced operating expenses, which results in savings to both operators and consumers.
One of the main advantages of CDMA is that network failure occurs only when the phone is at least twice as far from the base station. Thus it is used in the rural areas where GSM cannot cover. This is beneficial to rural users situated far from cells.
CDMA handsets typically transmit at the lowest power levels allowing for longer battery life which results in longer talk time and standby time. Battery power is conserved since the handset only transmits when it actually has something to send. CDMA handsets can also incorporate smaller batteries, resulting in smaller and lighter-weight phones. Easier to carry and use.
CDMA is digitally encoded, Because of spread spectrum technology it uses transmissions resist eaves dropping. Designed with about 4.4 trillion codes, CDMA virtually eliminates cloning and other types of fraud.
CDMA as 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 enables users to access a wide range of new services, including caller identification, short messaging services and Internet connections. Simultaneous voice and data calls are also possible using CDMA technology.
Because of the spread spectrum technology it uses, which has increased resistance to multipath distortion. Various factors such as echoes, call dropping, or voice distortion are almost non-existent in CDMA, whereas in GSM, there is a high probability of errors.
CDMA is harmless among other existing technologies. CDMA technology checks 800 times per second its transmission level. Therefore, radiation level is 10 times less than GSM. Another point 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:
- 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 the major mobile companies use GSM technology since it is not old and simpler as GSM.
- One major disadvantage in this technology CDMA cannot offer international roaming. When compared to GSM. The ability to upgrade or change to another handset is not easy with this technology because the network service information for the phone is put in the actual phone unlike GSM which uses SIM card for this.
- One major problem in CDMA technology is channel pollution, where signals from too many cell sites are present in the subscriber's phone but none of them is dominant. When this situation arises the quality of the audio degrades
- Another problem for CDMA users is of carriers. The law requires CDMA carriers to provide handsets to users, for which the users cannot change their carriers. Whereas, GSM users can change their carriers whenever they want. Also there are limited service providers for CDMA, which restricts the user choice of provider.
- Another problem in CDMA mobile phones is that there is a special number 112 that every GSM compatible device in the world can call in case of an emergency. But in CDMA, this cannot be implemented because of certain technological limitations.
- CDMA mobiles also transmit microwaves while on standby mode, like other technologies do.