TECHNOLOGY IN WIRELESS COMMUNICATION
This is to certify that members of this group have submitted the project of "Telecommunication- CDMA Technology in Wireless Communication". They worked on this project from 5th Feb, 2009 to 5th April, 2010.
They were found honest, diligent towards their work during the project work. I wish them all the best for their future accomplishments.
First, we, thank our lecturer and advisor, Mr. VISHAL KAUSHIK, for his continuous support towards the learning the subject matter. He has always been there to listen and to give fruitful advice.
He taught us how to ask questions and express our ideas. He showed us different ways to approach a research problem and the need to be persistent to accomplish any goal.
He is the most responsible person for helping us complete the writing of this report as well as the challenging research that lies behind it. He taught us how to write academic papers and had confidence in us when we doubted ourselves, and brought out the good ideas in us. Without his encouragement and constant guidance, we could not have finished this project.
The beginning of the 21st century saw the advancement and proliferation of wireless communication technologies, specifically in the mobile network categories. The examples of these standards include: GSM (Global System for Mobile Communications), CDMA (Code Division Multiple Access) & TDMA (Time Division Multiple Access). Now in a group of four our lecturer has allotted us the work to explain the following terminologies about CDMA technology, this includes CDMA Service, Soft Hand Off, Hard Hand Off, Spectrum Of CDMA.
It was started in early 1989 after the NA-TDMA standard (IS-54) was established. A CDMA demonstration to test its feasibility for digital cellular system was held in November 1989. The CDMA "Mobile Station -Base Station Compatibility Standard for dual mode wide band spread spectrum cellular system" was issued as IS-95 (PN-3118) on December 9, 1992.
CDMA stands for code division multiple accesses describe the communication channel access principle that employees spread spectrum technology and special coding scheme (where each transmitter is assigned a code). In this technology each conversation transmitted is spread over a 1.25 MHz frequency channel as it is sent. It divides up the air waves by associating a unique code to each call.
The Handoff process is a unique feature that allows cellular system to operate effectively. There are two kinds of Handoffs techniques "Hard handoff" & "Soft handoff". In mobile wireless communication system Soft handoff technology refers to over lapping of repeater coverage zones so that every cell phone is always within a range of at least one repeater. Soft handoff technology is used by CDMA systems where all the repeaters use the same frequency channel for each mobile phone set no matter where the set is located. The Hard handoff process is also known as "brake and make". It is a process in which the connection is briefly broken by one base station (BS) before being re-established by another as mobile station (MS) which moves out of the range of the first and enters into the range of the second.
The word spectrum is referred to the air waves which are composed of different range of frequencies. Frequencies refer to the type of air wave as measured by wavelength. It is also mandatory that efficient ways to carry wireless traffic is crucial. This is called "Spectral Efficiency", the capability by which the same amount of spectrum carries more voice or data services.
CDMA technology has changed the world of mobile wireless communication and is also presently continuing to have a huge effect on our society. While the technological advancements offer many great conveniences and other benefits, there are also some faults to these wireless technologies and we also know that throughout the history of wireless communication the benefits and drawbacks of wireless communication have varied greatly.
CDMA technology was at first originated by the military during World War II. Researchers were spurred into looking at ways of communicating that would be secure and work in the presence of congestion. Some of the properties that have made CDMA useful are:
- Signal thrashing and non-interference with existing systems.
- Anti-jam and interference elimination
- Information security
- Accurate Ranging
- Multiple User Access
- Multipath tolerance
CDMA (Code Division Multiple Access) one of the most widespread 2G air interfaces in the world, as far as the worldwide subscriber use is concerned. CDMA is a "spread spectrum" technology which allows many users to occupy the same time and frequency allocations in a given band or space of the frequency spectrum. It uses a special coding scheme in which a unique code is assigned to each communication to differentiate it from others in the same spectrum. Each conversation by this technology transmitted is spread over a 1.25 MHz frequency channel as it is being sent. Use of this technology gives CDMA more capacity than the other two technologies GSM and TDMA.
CDMA supports more phone calls and data sessions per cell than any other 2G air interface. The CDMA technology was pioneered by a United States based technology company "Qualcomm". In the today's world of finite spectrum resources, CDMA enables many people to simultaneously share the airwaves at the same time than the other alternative technologies. CDMA uses the idea of enduring interference by spread-spectrum modulation. The power control scheme in a CDMA system is a requirement for digital cellular application. However, it was a challenging task and has been solved.
According to CDMA development Group, there are more than 516 million global subscribers worldwide who use CDMA technology. The CDMA air interface is used in both 2G and 3G networks. 2G CDMA standards are branded CDMA One and include IS-95A and IS-95B. CDMA is also the base for 3G services.
An equivalence to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different directions (spatial division). In CDMA they would speak different languages. Generally people speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of user is given a shared code. Many codes occupy the same channel, but not only users associated with a particular code can understand each other. CDMA is also the current name for the cellular technology originally known as IS-95 which was developed by Qualcomm and enhanced by Ericsson, CDMA is characterized by high capacity and small cell radius. CDMA also refers to digital cellular telephony systems that use this multiple access scheme, as originated by Qualcomm, and W-CDMA by the International Telecommunications Unions (ITU), which is also used in GSM's UMTS. CDMA has been used in many communications and navigation systems, including the Global Positioning system and the OmniTRACS satellite system for transportation logistics.
The Three important features of CDMA technologies are as follows-
CDMA is interference limited multiple access system. Because in this technology all the users transmit on the same frequency, internal interference generated by the multiple access system is the most significant factor in determining system capacity and call quality. The transmission power of each user must be reduced to limited interference, hence the power should be enough to maintain the required signal to noise ratio for a satisfactory call quality. Maximum capacity of the system is achieved when signal to noise ratio per no. of every user is at the minimum level as needed for the acceptable channel performance. The advantages of this system are longer mobile battery life and longer life span of BTS (Base Transceiver Station) power amplifiers.
Handover occurs when a call has to be passed from one cell to another as the user moves between cells. In a "hard" handover process, the connection to the current cell is broken and then the connection to the new cell is made. This is known as a "break-before-make" handover. 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. Since, Soft handovers require less power which reduces interference and increases capacity of the system. Thus the mobile can be connected to more than two BTS. "Softer" handover process is where the radio links that are added and removed belongs to the same Node.
CDMA soft handover
MULTIPATH AND RAKE RECEIVERS
One of the main advantages of CDMA systems is the capability of using signals that arrive in the receivers with different time delays, this phenomenon is called multipath. FDMA and TDMA, which are the types of narrow band systems unable to distinguish between the multipath arrivals and help in equalization to mitigate the negative effects of multipath. CDMA subscriber units use rake receivers, a set of several receivers. One of the receivers (fingers) constantly searches for different multipath and feeds the information to the other three fingers. Each finger then demodulates the signal corresponding to a strong multipath. The results are then combined together to make the signal stronger.
IMPORTANCE OF CDMA
In CDMA technology, a unique digital codes (Walsh Codes) rather than separate radio frequencies/ channels are used to differentiate users. The Walsh codes are shared by the mobile phone and the base station which are called "pseudo-Random Code Sequences." All users access the entire spectrum allocation for whole time. That is every user uses the entire block of allocated spectrum space to carry his/her message. A user's unique Walsh Code separates his/her call from all other calls.
CDMA, being a "spread-spectrum" technology, spreads the information contained in a signal over the entire available bandwidth and not simply through one frequency. Due to the wide bandwidth of a spread-spectrum signal, it is very difficult to cause jamming in this spectrum as well as it is difficult to interfere with and is also difficult to identify. It appears as nothing more than a slight rise in the "noise floor" or interference level. Unlike other technologies where the power of the signal is concentrated in a narrower band making it easier to detect. Therefore CDMA systems provide more privacy than FDMA or TDMA systems. These are great advantages over the technologies which are using a narrower bandwidth.
CDMA channels can handle an indefinite number of users. The capacity of the system depends on the quality of current calls. Since more users are added, noise is also added to the wideband frequency and thus decreases the quality of current calls. Each user's transmission power increases the level of the frequency spectrum's "noise floor" and therefore decreases the overall call quality for all users. To abolish the "noise floor," CDMA mobile phones and base stations use the minimum amount of power which required communicating with each other. They use precise power control to decrease users' transmission power. By decreasing a user's transmission power, the mobile phone has been added with more battery life, increased talk time, and smaller batteries.
As CDMA is a spread spectrum technology so it requires less frequency planning. The original spectrum is not divided into separate blocks/channels, like as in FDMA and TDMA systems. Therefore, the requirement of plan for multiple frequency guard bands does not exist. As all the users have access to the entire spectrum all time, frequency planning is only needs to consider one frequency/channel. However, the channel requires relatively wide contiguous bandwidth. With CDMA we have unique digital codes (Walsh Codes) rather than separate radio frequencies/ channels are used to differentiate users. The Walsh codes are shared by the mobile phone and the base station and are called "pseudo-Random Code Sequences." All users access the entire spectrum allocation all of the time. That is, every user uses the entire block of allocated spectrum space to carry his/her message. A user's unique Walsh Code separates the call from all other calls.
In the current scenario of human life CDMA has introduced a new era of communication. CDMA has provided us the base for 3G technology. In India now a day's technology of wireless internet i.e. in the form of USB modem generally called as Data Card is also promoted on the basis of CDMA technology only. As we know that CDMA provides better network coverage than GSM and TDMA technologies therefore it is best performer in terms of mobility which is one of the good reasons for companies to use CDMA technology for the Data Card purpose.
IMPACT ON SOCIETY
One of the largest benefits people get from advances in wireless technology is convenience. Wireless technology has removed a lot of hassle associated with cords and cables. Portable devices can now use wireless technology to transfer data without being physically connected to a computer or any other devices. As far as the CDMA technology is concerned it is new for the many till today, but it's been popularizing day by day and the advancement in the field of CDMA technology will grow by leaps and bound in the upcoming years.
Due to these the number of users will increase which could be easily handled by the CDMA technologies. Wireless networks technology such as CDMA can also be easier and cheaper to install.This is especially important in places where running wires would be prohibited or impossible.Many organizations within large buildings may use CDMA enabled WiFi devices to easily provide internet access to all machines within the building, since it can handle a more number of users at the same time.
Cell phones, laptops and PDAs allow for increased mobility and flexibility. This is a big benefit for both personal and business users.CDMA technology allows cell phone users to talk with contacts while traveling or performing other everyday tasks such as walking the dog. By the help of these technologyPDA's and other portable devices can receive and transmit data wirelessly, allowing people to work even when they are out of the office, also allowing people to be connected practically where ever they go. Cell phones and other portable communication devices allow users to contact emergency services without a landline or power outlet. CDMA Wireless communications offer a great sense of safety and security.
Wireless technology has had and still continues to have a huge effect on society. While the technological advancements offer many great conveniences and other benefits, there are also some faults to the wireless CDMA technology.Throughout history, the benefits and drawbacks of CDMA technology have varied greatly. CDMA technology also opens up many security holes. The main issues arise due to the fundamental functionality of a CDMA i.e. broadcasting a signal out over an area. Many concerns have been stressed about radiofrequency energy emissions.Scientific studies show that high levels of radiofrequency energy can warm spots of the body and lead to tissue damage. It also does not provide international roaming which did not fulfill the customer's needs and makes a negative impact on the customer towards the technology.
Wireless cellular telephony has grown at a faster rate than wired-line telephone networks. The main reason driving this tremendous growth in wireless coverage is that it does not require setting up of expensive infrastructure like copper lines and switching equipment. Code Division Multiple Access (CDMA) has become a popular technology for cellular communications. The other multiple access techniques are Frequency Division Multiple Access (FDMA) and Time-Division Multiple Access (TDMA) which are limited in frequency band and time duration respectively but on the other hand CDMA uses all of the available time-frequency space. One form of CDMA is called Direct Sequence CDMA (DS-CDMA) because it uses a set of unique signature sequence or spreading codes for modulating the data bits of different users. By the knowledge of these spreading codes, the receiver can isolate the data related to each user by the process of channel estimation and detection which provides spreading the bandwidth of the data signal therefore CDMA technique is also named as spread spectrum technique.
MODUALTION TECHNIQUE USED
Various techniques are under concern for the new era of digital phone communication systems, with the intention of improving cell capacity, multipath immunity, and flexibility in the technique such as Code Division Multiple Access (CDMA) and Coded Orthogonal Frequency Division Multiplexing (COFDM). We can apply both of these techniques for providing a fixed wireless system for rural areas. We can use each of this technique for a specific application as in both is having their own special properties.
In CDMA systems, all users are using the same frequency band for transmitting, some specialized codes are used for channelization. The transmitted information is spread throughout the bandwidth by multiplying it by a wide bandwidth pseudo random sequence. Both the base station and the mobile devices know with these PN codes which are used to control the data sent and allowing it to de-scramble the received signal.
The transmission from base station to mobile or downlink transmission are using Quadrature Amplitude modulation (QAM) and Quadrature phase shift keying (QPSK) modulation scheme for transmitting data in W-CDMA system. We can analyze the performance of these modulation techniques when the system is subjected to perform AWGN and multipath Rayleigh fading which are consider in the channel. We will go for analysis of Quadrature phase shift key and 16-ary Quadrature Amplitude modulation technique which are being used in wideband code division multiple access system, so that the system can go for more suitable modulation technique to suit the channel quality, thus we can deliver the finest and proficient data rate to mobile stations.
One of the most important concepts required to understand spread spectrum techniques is the scheme of process gain. The process gain of a system indicates signal to noise improvement demonstrated by a spread spectrum system as it has the nature of the spreading and dispreading process. The process gain of a system is equal to the ratio of the spread spectrum bandwidth used, to the original information bandwidth. Thus, the process gain can be written as:
Where BWRFis the transmitted bandwidth after the data is spread, and BWinfois the bandwidth of the information data being sent.
In the figure below the data to be transmitted (a) is spread before transmission by modulating the data using a PN code. This extends the spectrum as shown in (b). In this example the process gain is 125 as the spread spectrum bandwidth is 125 times greater the data bandwidth. In Part (c) the received signal is shown. This consists of the required signal, plus background noise, and any interference from other CDMA users or radio sources. The received signal is recovered by multiplying the signal by the original spreading code. This process causes the wanted received signal to be despread back to the original transmitted data. However, all other signals that are uncorrelated to the PN spreading code become more spread. The wanted signal in (d) is then filtered removing the wide spread interference and noise signals.
Basic CDMA transmission.
CDMA is achieved by modulating the data signal by a pseudo random noise sequence (PN code), in which the chip rate higher than the bit rate of the data. The PN code sequence is a sequence of ones and zeros (called chips), which alternates in a random manner. Modulating the data with this PN sequence generates the CDMA signal. The modulation is performed by multiplying the data with the PN sequence. In the Figure below a basic CDMA transmitter is showed.
Simple direct sequence modulator
The PN code used to spread the data can be of two types. A short PN code (typically 10-128 chips in length) can be used to modulate each data bit. The short PN code is then repeated for every data bit allowing for quick and simple synchronization of the receiver. Below figure shows the generation of a CDMA signal using a 10-chip length short code. On the other hand a long PN code can be used. These long codes are generally thousands to millions of chips in length and thus they are repeated from time to time. Because of this they are useful for adding security as they are more difficult to decode.
Direct sequence signals
The forward link, from the base station to the mobile, of a CDMA system can use special orthogonal PN codes which are called Walsh codes, it separates multiple users on the same channel. These are based on a Walsh matrix which is a square matrix with binary elements and dimensions that are a power of two. It is generated from the basis that Walsh(1) = W1= 0 and that:
Where Wnis the Walsh matrix of dimension n. For example:
Walsh codes are orthogonal, which means that the dot product of any two rows is zero. This is due to the fact that for any two rows exactly half the number of bits match and half do not.
Each row of a Walsh matrix can be used as the PN code of a user in a CDMA system. By doing this the signals from each user is orthogonal to every other user, resulting in no interference between the signals. Walsh codes works when the transmitted chips from all users are synchronized. If the Walsh code used by one user is shifted in time by 1/10 of chip period, with respect to all the other Walsh codes. It loses its orthogonal nature resulting in inter-user interference. This is not a problem for the forward link as signals for all the users originate from the base station, ensuring that all the signal remain synchronized.
The reverse link is different from the forward link because the signals from each user do not originate from a same source as in the forward link. The transmission from each user will arrive at a different time, due to propagation delay, and synchronization errors. Due to the unavoidable timing errors between the users, there is little point in using Walsh codes as they will no longer be orthogonal. For this reason, simple pseudo random sequences are typically used. These sequences are chosen to have a low cross correlation to minimize interference between users.
The capacity is different for the forward and the reverse links because of the differences in modulation. The reverse link is not orthogonal, resulting in significant inter-user interference. For this reason the reverse channel sets the capacity of the system.
Hardware Requirement and Cost
In the design of a mobile unit, fixed-point hardware is an attractive alternative because of increased speed, reduced power consumption, and reduced hardware cost.
The wireless local loop (WLL) system has been deployed as a new application for wireless communication with fixed subscriber units which impose a fixed propagation and no handoffs compared to the wireless mobile communication systems. The hardware design and the implementation of the code acquisition module and code tracking loop module of the base station receiver for the code division multiple access (CDMA) WLL system are according to the Electronics and Telecommunications Research Institute (ETRI). These modules of the CDMA WLL system are implemented by hardware chips, such as digital signal processors (DSP), erasable programmable logic devices (EPLD), and field programmable gate arrays (FPGA). Timing simulation of the implemented system is operated using the ALTERA MAXPLUS tool. The basic hardware modules of the base station receiver consist of two searchers for antenna diversity and four fingers for multi-path combining. After verifying the operation of the code acquisition and time tracking loop on the call test. The reconstructed voice data show good quality in the reverse link.
Performance of CDMA system is analyzed for different parameters compared with previous analog or digital mobile systems. Receiver design is also given special attention by designing a work optimal RAKE receiver. Reduction of multipath effect can be achieved by this RAKE receiver design .Finally real time implementation of CDMA encoding and decoding using TMS320C50 DSP kit is explored.
Software required for a CDMA network to be fully functional and effective are-
- Sperry Software Distribution Manger List 1.0
- CDMA USB Modem Driver 1.0
- CDMA Mobile 1.0
- SU-6200U CDMA Modem 1.0
- Venus CDMA 20001x 1.0
With the arrival of Wireless Broadband, wireless users are enjoying many rich application and services over the Internet virtually with mobility. These Wireless Broadband services offer a new way of life to people where one can have any information at his fingertips whenever it's needed ultimately reducing the pressure of anticipation. Business transactions are carrying out in real-time resulting in minimizing delay and maximizing productivity. These profits overshadow some of the potential security concerns of doing business over the Internet. Wireless Broadband service providers are facing many problems which include public network risks such as viruses, worms, blended threats, and software vulnerabilities affecting their infrastructure, service offering and their end user experiences with the customers.
Security measures are taken in order to minimize service disruptions, to avoid loss of revenue from theft and to maintain a high level of customer satisfaction. Code Division Multiple Access (CDMA) technology originated from military applications and cryptography, and till today do not have any report of high jacking or eavesdropping on a CDMA call.
CDMA air interface is naturally secure and is clearly superior to first-generation analog and Time Division Multiple Access (TDMA) systems. This form of security in CDMA air interface comes from the use of the most important spread spectrum technology and the use of Walsh codes. CDMA utilizes specific spreading sequences and pseudo-random codes for the forward link (i.e. the path from the base station to the mobile) and on the reverse link (i.e. the path from the mobile to the base station). These spreading techniques forms unique code channels for particular users in both directions of the communication channel. Since the signals of calls in a coverage area are spread over the entire bandwidth creating a noise-like appearance to other mobiles or detectors in the network as a form of disguise and making the signal of any other call difficult to distinguish and decode.
CDMA uses a soft handoff process which allows a user to connect to as many as six radios in the network by the help their own Walsh code. This implies that if someone attempts to eavesdrop on a subscriber's call the person requires several devices connected at exactly the same time in an attempt to synchronize with the intended signal. CDMA also employs a fast power control approximately 800 times per second, to maintain its radio link. Therefore it is difficult for any third party to create a stable link for intercepting a CDMA voice channel though it had a full knowledge of Walsh code. Synchronization process is very critical, as without synchronization, the listener could only hear noise.
Code Division Multiple Access (CDMA) mobile communication system starts from IS-95, called 2nd generation system, to CDMA2000 1x, which is the 3rd generation system. Now a days CDMA2000 1x EV-DO system for high speed packet data is served. CDMA 2000 1xRTT technology makes eavesdropping very complex. It uses 42-bit PN (Pseudo-Random Noise) Sequence called "Long Code" to scramble voice and data. The current CDMA systems uses Cellular Authentication and Voice Encryption (CAVE) algorithm but it only provides unilateral authentication leading to false base station attacks & is also prone to cryptographic attacks. These are the major challenges in the current CDMA systems.
Among all wireless technologies of communications, Code Division Multiple Access (CDMA) offers the best combination as it provides good signal quality, high security, low power consumption, and excellent system reliability. Features added in the IS-95 standard means this impressive list now also includes a Third Generation (3G) data capability which enables CDMA providers to offer many Internet and intranet services for multimedia applications, high-speed business transactions, and telemetry. The upcoming cdma2000 standard will further expand usable bandwidth without sacrificing voice quality or requiring additional spectrum.
CDMA has established itself as the no.1 technology for digital cellular -- and the 3G CDMA 2000 standard makes it an even more compelling wireless technology. This up-to-the-minute guide gives communications professionals all they need to deploy and manage CDMA now -- and to migrate to CDMA 2000 whenever they're ready.
ADANTAGES AND DISADVANTAGES
- The CDMA technology spreads the spectrum using the orthogonal codes.
- All the terminals are active at same moment which is uninterrupted, simultaneous conversation.
- The other advantages of CDMA technology are its flexibility, soft handover and also less planning is enough for it.
- The scheme provides individual codes for each user.
- Unlike TDMA or FDMA, CDMA has a soft capacity that is there is no absolute limit on the number of users in CDMA.
- Selective addressing capability of the CDMA Spread Spectrum.
- The other advantages include message security, interference rejection, and also code division multiplexing is possible for multiple accesses.
- It provides low density-power spectrum for signal hiding, increased cellular communications security.
- CDMA also provides so called soft handoffs from cell site to cell site that makes the transition virtually inaudible to the users.
- Extended reach in case of rural users situated far from cells.
- Precise power control increases talk time and battery size for mobile phone.
- Receivers here in CMDA are complex in nature.
- It needs more complicated power control for senders.
- Self jamming is a problem in CDMA system.
- The near-far problem occurs at a CDMA receiver if an undesired user has a high detected power as compared to the desired user.
- Due to the proprietary nature, engineering community is not aware of all the CDMA flaws.
- CDMA cannot offer international roaming, a large GSM advantage.
- CDMA is relatively new, and the network is not as mature as GSM.
- Your handset can only be used with the provider that you got the phone from.
- Difficult to optimize to maximize performance.
- Low traffic areas lead to inefficient use of spectrum and equipment process.
- Currently, base station equipment is expensive.
PROBLEMS IN IMPLEMENTATION
The problems faced during the implementation of CDMA technology comprises mainly of reception problem, several PC connection issues, complexity, power control, large frequency allocation and most importantly channel pollution.
CDMA reception problems are due to the poor reception or cellular coverage. For this problem we verify that CDMA cellular service is working in the particular location by checking with a cell phone with CDMA cellular service.
To troubleshoot this problem of reception with receiver of CDMA and Cell Sync, the steps are-
- To check that the receiver has power.
- Check the cablingbetween the receiver and the computer is proper and in a good working condition.
- Use the CDMA Test screenin Cell Sync which confirms that the receiver is working and is getting a readable signal.
- Ensure that you are getting CDMA cellular service at the location where the receiver is installed.
- Check whether the indicator light on the receiver. If signals are received the light should be flashing every second and if the light is continuously in "on" state, than it indicates that the receiver is not in the range of the transmitter.
Test screen showing CDMA receiver output
Connection problems which are involved in the connection of the CDMA receiver to the computer can be resolved with the proper setup. This includes joining a special data cable to connect receiver to the computer and double checking the cables.
Data output issues include getting the time from the broadcast and for that the receiver must first of all validate the time signal.
The main problems facing CDMA technology today is channel pollution and deterioration of signal inside the buildings. CDMA comes into its basics when you are out in the countryside with few sites covering large expanses of land. CDMA also has a very high data transmission rate, from 153.6 to 614 kbps. Channel pollution can also result from massive multipath problems caused by many tall buildings. Taming pollution is a tuning and system design issue. It depends on the service provider to reduce this phenomenon.
Power control is one of the main features in 3rd generation cellular CDMA systems. Power control reduces the interference in the system and hence increases the capacity. The problem of errors in the power control commands becomes worse during soft handoff where the terminal communicates with more than one base station simultaneously. Few algorithms are introduced during soft handoff to increase the system capacity like power control rate reduction and the adjustment loop.
FUTURE OF CDMA
Characteristics of CDMA technology have been incorporated into the third-generation IMT-2000 standard, designed to allow interoperability between the different networks and integration with satellite technology. This third-generation technology will allow broadband data access that can be used for voice, video and data communication at speeds of up to 2Mbps.
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