CELLULAR AND MOBILE COMMUNICATIONS DSCDMA full report
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07062010, 12:14 AM
CELLULAR AND MOBILE COMMUNICATIONS DSCDMA.DOC (Size: 256.5 KB / Downloads: 191) CELLULAR AND MOBILE COMMUNICATIONS DSCDMA Presented By: V.VIJAYA KUMAR, IV B.Tech E.C.E SREE VIDYANIKETHAN ENGINEERING COLLEGE ,TIRUPATI ABSTRACT So far transmission errors have been described as evil entity in communication literature. Introducing error intentionally can save power and reduce interference. This has been proved by scientists Jik Dong Kim (South Korea), Sang Wu Kim (USA) and Young Gil Kim (South Korea). It is about combined power and error control in multicarrier DSCDMA systems which are most popular in various indoor and mobile communication systems. This paper explains new scheme devised by them along with performance comparison with older systems to prove it is better than existing systems. This work originally appeared in IEEE transactions on communications in August 2004. I. INTRODUCTION A combined power control and error control coding in multicarrier direct sequence codedivision multipleaccess (DSCDMA) systems is explained in this paper. The transmission power is controlled in such a way that channel fading in each subchannel is compensated for only when the channel gains in all subchannels are above a prescribed cutoff fade depth 0; otherwise, no power is allocated for the corresponding symbols (i.e., power truncation), and erasures are generated at the receiver. The motivation for this technique is that the symbols with low channel gain is likely to be error and yet, if transmitted, consumes the energy resources and generate interference to the other users. Truncating the power for those symbols has the effect of reducing the interference to other users and allocating more power on symbols with high channel gain (there by reducing the error probability). Since block codes can correct twice as many erasures as errors, the coded performance can be improved by properly combining the power control with the errorcontrol coding. II. SYSTEM MODEL We consider a multicarrier DSCDMA system with K active transmitters communicating with a common receiver (base station). The block diagrams of the transmitter and receiver are shown in Fig. below. Each packet of data is encoded by an (n, k) extended ReedSolomon (RS) code over GF (Q), where n is equal to Q and is a power of two. In order to randomize error bursts, an ideal interleaver/deinterleaver is assumed. A code symbol (Qary) is converted into M (= log2 Q) parallel bits, and each bit is spread by a random sequence pk(t). The substreams are modulated on M subcarriers with a carrier spacing that provides nonoverlapping subbands. The subchannels are assumed to experience an independent flat fading. This assumption can be justified by choosing the number of subcarriers and the bandwidth of each subband, such that the carrier spacing between adjacent subcarriers, f, is greater than the coherence bandwidth, Bc, and the delay spread is less than the chip duration of each subchannel. Let k,i be the channel power gain in the ith subchannel for transmitter k. We assume that {k, i} are independent and identically distributed (i.i.d) random variables with probability density function (pdf) given by (1) Where = E [k, i] for all i and k. We also assume that = k,1, k,2Â¦ k,M can be estimated perfectly at the receiver, and fed back to the transmitter k through a reliable feedback channel for power control. The channel state changes at a rate slow enough (slow fading) for the delay on the feedback channel to be negligible. However, the sideinformation error may occur if the receiver fails to identify the correct gain (due to the low SNR of pilot) or the feedback channel is not reliable. The receiver signal r (t) at the base station can be expressed as (2) Where Pi( ) is the transmission power, dk,i(t) and pk(t) are the data and random spreading waveforms, respectively, fi is the carrier frequency, tk is the propagation delay and k,i is the carrier phase, all for transmitter k at the ith subchannel. We will assume a raisedcosine chip waveform with rolloff factor a, n(t) represents the thermal noise and is modeled by a zero mean white Gaussian noise with twosided power spectral density N0/2. If the channel power gains of all M subchannels are greater than a threshold 0 (i.e., k,i = 0, for all i), then the corresponding Qary code symbol is transmitted with a power Pi( ),i = 1, 2,Â¦.,M. Otherwise, it is not transmitted (i.e., (A) TRANSMISSION FOR THE kth USER (B) RECEIVER FOR THE kth USER Pi( ),i = 0, for all i), and an erasure is generated for the corresponding Qary code symbol at the receiver. Thus the probability of symbol erasure is given by (3) The erasure probability is also the activity factor; each user turns off its power with probability . Thus, the power truncation will reduce the average number of interfering users from K1 to (K1) , thereby reducing the symbolerror probability (SEP). Notice that the conventional power control corresponds to a special case of 0 being equal to zero. III. MATHEMATICAL ANALYSIS Because an (n, k) RS code can correct any set of s erasures and t errors provided s+2t = nk, the probability of incorrect decoding PE is given by (4) Where per and pc are the symbol (Qary) erasure probability and the correct symbol (Qary) probability, respectively. Below, we will derive the correct symbol probability pc for two types of power control. A. Power Truncation Only (Scheme B) In this subsection, we consider the following power control: (5) for some constant P. The required feedback information for this type of power control is one bit indicating whether the channel power gains of all M subchannels are greater than a threshold o (i.e., k,i = o, for all i). The special case of 0 = 0 corresponds to the conventional errorsonly decoding without power control. The coherent correlation receiver calculates a decision statistic Zk,i (6) where T is the bit duration, and dk,i is the channel bit in the ith subchannel. The first term in (6) is the desired signal term. The second term (7) represents multiuser interference, where f is a random variable uniformly distributed over [0, 2p). According to the central limit theorem, the distribution of IM is approximately Gaussian with mean zero and variance (8) (9) where is a constant that depends on the chip waveform, N Ã‹ T/Tc is the processing gain, and Tc is the chip duration of each subchannel. For the rectangular chip waveform and raisedcosine chip waveform with a rolloff factor a, is 1/3 and (1 a /4)/2, respectively. The third term in (6) represents the background white Gaussian noise with mean zero and variance N0/2. Thus, Zk,i is a Gaussian random variable with (10) where (11) Therefore, the conditional probability pc( ) of correct symbol (Qary) is (12) where (13) In (12), we assumed that the Qary code symbol is correct only when all log2Q bits constituting the code symbol are correct, i.e., if atleast one bit constituting the code symbol is in error, the probability of correct symbol pc is given by (14)(15). (14) (15) In deriving (14), we assumed that the k,iâ„¢s for i=1,2,Â¦.,M are i.i.d. It follows from (5) and the assumption that the k,iâ„¢s for i=1,2,Â¦.,M are i.i.d. that the average transmission power per channel bit is (16) (17) Therefore, the average received energy per information bit is (18) (19) Where r=k/n is the code rate. B. Truncated Channel Inversion (Scheme A) In this subsection, we consider the following power control: (20) for some constant PR. This type of power control makes the fading channel appear as a timevariant additive white Gaussian noise (AWGN) channel during nontruncation periods. The required feedback information for this type of power control is the channel gains of all subchannels (k,1, k,2,Â¦Â¦,k,M), which is much more than what power truncation only (scheme B) requires. The special case of 0=0 corresponds to the conventional errorsonly decoding with channel inversion. It follows from (8) and (20) that the variance of the multiple access interference is (21) The equivalent noise spectral density Ne/2 can be then obtained form (11) and (21). Therefore, the probability of the correct symbol (Qary) is given by (22). (22) It follows form (16) and (20) that the average channel bit power PT is (23) The average received energy per information bit can be obtained from (18) and (23). IV. NUMERICAL RESULTS AND DISCUSSION Fig. 1 is a plot of the probability of incorrect decoding PE versus the normalized cutoff threshold /Ã‚Â¯. We find that there exists an optimum threshold that minimizes PE , and the optimum choice of for scheme A can reduce PE by almost two orders of magnitude, when compared with the conventional errorsonly decoding with channel inversion (0 = 0). Also, scheme A provides a better performance than scheme B. This can be explained as follows. Scheme A (percarrier adaptation) makes the channel appear as an AWGN channel during nontruncation periods, and thus, provides a better performance over scheme B. However, if the available energy resources is limited (i.e., very low Eb/N0), then the truncation period for scheme A may be too long (i.e., too many erasures to correct), so that its decodingerror probability may become higher than scheme B. Fig. 2 is a plot of the probability of incorrect decoding PE versus Eb/N0 with several erasuregeneration methods, where the simulation results for the proposed scheme are included for the validation of the analysis. We find that the combined power control and errorcontrol coding scheme (A and B) provide a much lower PE over the conventional errorcontrol coding without power control (C, D, and E), particularly at high Eb/No. This is because the proposed scheme suppresses the multiuser interference Fig. 4. Probability of incorrect decoding PE versus Eb/No: (512,170) RS code, N=64, K=30, M=9, a=0.25, A=truncated channel inversion, B= power truncation only, C= convolutional code of rate with an optimum distance profile of the generator polynomial (4 564 754) in octal number and constraint length of seven. and saves the energy resources by truncating the transmission power during unfavorable channels, and allocates the saved energy on symbols on high channel gain. shows that the combined power control and errorcontrol coding provides a significant capacity gain over conventional schemes.shows the characteristic steep slope of the RS code versus the graceful degradation of the convolutional code. We also find that the convolutionalcoded system provides a lower PE than the RScoded system in the low SNR region, but exhibits an error floor and provides a higher PE in the high SNR region(interferencelimited region). V. CONCLUSIONS We explained that the probability of incorrect coding can be significantly reduced by combining the power control with the errorcontrol coding. It is also seen that power can be saved and interference can be reduced. How much power can be saved In reference 4 it has been explained that for a large communication network every one dB saving in power will result in savings of many millions of dollars annually. Will Reliance India mobile which uses CDMA technology save crores of rupees by implementing this technique These two questions will be answered when we meet in ERODE SENGUNTHAR Engg college on 22nd & 23rd of September 2005. REFERENCES : 1. Jik Dong Kim (South Korea), Sang Wu Kim (USA) and Young Gil Kim (South Korea), COMBINED POWER CONTROL AND ERROR CONTROL CODING IN MULTICARRIER DSCDMA SYSTEMS, IEEE TRANSACTIONS ON COMMUNICATIONS VOL. 52, No. 8, AUGUST 2004. 2. Dr. KAMILO FEHER Wireless Digital Communications, PHI 2002 3. WILLIAM C.Y.LEE, Mobile communications engineering, 2Ã‚Â¬Ã‚Â¬Ã‚Â¬nd edition MC GrawHill. 4. K.SAM SHANMUGAM, digital and analog communication systems, John Wiley. Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion



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26102010, 05:00 PM
MohitGargDDPThesisppt.pdf (Size: 914.8 KB / Downloads: 89) Multiuser Signal Processing Techniques for DSCDMA Communication Systems Mohit Garg (00D07015) Guide: Prof. U. B. Desai Introduction Multiuser signal processing techniques can be classified into two broad categories: • Multiuser Detection Receiver based schemes Can be used on the uplink channel Maximum Likelihood Multiuser Detector formulated by Verd´u (1986) • Multiuser Transmission Transmitter based schemes so as to reduce complexity at the receiver Can be used on the downlink channel – Need channel knowledge at the transmitter • The focus of this work has been towards reducing the computational burden at the receiver. We have proposed + A modification to two existing multiuser detection algorithms + Two new multiuser transmission algorithms 


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29102010, 10:54 AM
[b]Design of Secure Mobile Communication using Fingerprint[/b] Seifedine Kadry Aziz Barbar American University of Science and Technology Department of Computer Science [hr\ Abstract Mobile handheld device is a popular device that provides secure, private, authentic, and accurate communication and exchange of confidential information. In this paper we propose a technique to solve the authenticity problem in mobile communication. This technique is mainly based on the usage of the Fingerprint to identify both the speaker and the sender. This technique is simple, requires less calculation than other public/private key techniques, assures more authenticity than digital signature, and eliminates the need for a third party. Moreover, when applied to mobile phones, this technique resists any forge imposed by another party. 1. Introduction A recent survey carried by Interactive Statistics Corporation (IDC) shows that around 90% of mobile users use messaging as their main communication tool disregarding the safety level of such a communication system; if phones are lost or shared, anyone can access the data on the phone. This is known as the AUTHENTICITY in cryptography science. That is why, scientists should come up with a concept that minimizes the risk associated with losing or sharing a phone, thus offering a safe environment for communication. This paper presents a solution for the above mentioned problem. “Fingerprint Identification Technique” is the most effective technique for solving such a problem. This technique works on the Fingerprint basis whereby the phone can be accessed when it identifies the Fingerprint of the user(s). This paper is organized as follows: In section 2, we provide an overview of the secure communication in mobile handheld device. Then, section 3 describes the digital signature scheme and the related algorithm RSA [3]. In section 4, we write the code of the RSA algorithm in JAVA for the performance purpose. Section 5 gives a literature review of fingerprint matching technique. Next in section 6, we describe the proposed design which is based on the fingerprint to authenticate the caller, the performance of our design is given in section 7 and finally section 8 concludes the paper with future work. for more ::> http://eurojournals.com/ejsr_30_1_11.pdf 


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02052011, 12:41 PM
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Sunil Phour Cellular Communication.ppt (Size: 283.5 KB / Downloads: 48) Cellular Communication Cellular Phone System The cellular phone service area is divided into smaller geographical areas called cells. Cellular phone system Each cell has a base station with a tower which receives and transmits signals. All the base stations are connected by phone lines to mobile telephone switching office (MTSO). How does it work? A caller communicates via radio channel to its base station, which sends the signal to MTSO. If the called number is land based, MTSO sends the signal through central telephone office like any other phone call. If the called number is mobile, MTSO sends the signal to the base station of the cell where the called number is. The base station transmits the signal to the called number using the available radio channel. As the caller moves from one cell to another, MTSO automatically switches the user to an available channel in the new cell. Cell Phones Cell phones communicate in the high frequency range: 806890 MHz and 18501990 MHz for the newly allocated ‘PCS’ range. Cells are spaced 12 miles apart. The concept of cells is the key behind the success of cell phones because by spacing many cells fairly close to each other, the cell phones may broadcast at very low power levels (typically 200mW1W, depending on system). Since the cell phones may broadcast at low power levels, they use small transmitters and small batteries. Reuse frequencies at cells that are not adjacent. Encoding and Multiplexing With thousands of cellular phone calls going on at any given time, everyone cannot talk on the same channel at once. Therefore, several different techniques were developed by cell phone manufacturers to split up the available bandwidth into many channels each capable of supporting one conversation. Analog cellular systems use a 3 kHz audio signal to frequency modulate a carrier with transmission bandwidth 30 kHz. FDMA FDMA (Frequency Division Multiple Access): It is used on analog cellular systems. When a FDMA cell phone establishes a call, it reserves the frequency channel for the entire duration of the call. The voice data is modulated into this channel’s frequency band (using FM) and sent over the airwaves. At the receiver, the information is recovered using a bandpass filter. FDMA systems are the least efficient cellular system since each analog channel can only be used by one user at a time. These channels are larger than necessary given modern digital voice compression and are also wasted whenever there is silence during the cell phone conversation. Analog signals are also especially susceptible to noise. Given the nature of the signal, analog cell phones must use higher power (between 1 and 3 watts) to get acceptable call quality. TDMA TDMA (Time Division Multiple Access): TDMA builds on FDMA by dividing conversations by frequency and time. Digital compression allows voice to be sent at well under 10 kilobits per second (equivalent to 10 kHz). TDMA shares the same channel with multiple sessions. While TDMA is a good digital system, it is still somewhat inefficient since it has no flexibility for varying digital data rates (high quality voice, low quality voice, pager traffic) . In other words, once a call is initiated, the channel/timeslot pair belongs to the phone for the duration of the call. TDMA also requires strict signaling and timeslot synchronization. Due to the digital signal, TDMA phones need only broadcast at 600 mW. CDMA CDMA (Code Division Multiple Access): CDMA uses ‘spread spectrum’ techniques. CDMA has been likened to a party: When everyone talks at once, no one can be understood, however, if everyone speaks a different language, then they can be understood. CDMA systems have no channels, but instead encodes each call as a coded sequence across the entire frequency spectrum. Each conversation is modulated, in the digital domain, with a unique code (called a pseudonoise code) that makes it distinguishable from the other calls in the frequency spectrum. Using a correlation calculation and the code the call was encoded with, the digital audio signal can be extracted from the other signals being broadcast by other phones on the network. Since CDMA offers far greater capacity and variable data rates depending on the audio activity, many more users can be fit into a given frequency spectrum and higher audio quality can be provide. The current CDMA systems boast at least three times the capacity of TDMA systems. CDMA technology also allows lower cell phone power levels (200 miliwatts) since the modulation techniques expect to deal with noise and are well suited to weaker signals. The downside to CDMA is the complexity of deciphering and extracting the received signals. Comparison Spread Spectrum CDMA is a form of Direct Sequence Spread Spectrum communications. In general, Spread Spectrum communications is distinguished by three key elements: 1. The signal occupies a bandwidth much greater than that which is necessary to send the information. This results in immunity to interference and jamming and multiuser access. 2. The bandwidth is spread by means of a code which is independent of the data. The independence of the code distinguishes this from standard modulation schemes. 3. 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. In order to protect the signal, the code used is pseudorandom. This pseudorandom code is also called pseudonoise (PN). Direct Sequence Spread Spectrum(DS/SS) CDMA is a DS/SS system. Signal transmission consists of the following steps: A pseudorandom code is generated, different for each channel and each successive connection. The Information data modulates the pseudorandom code (the Information data is “spread”). The resulting signal modulates a carrier. The modulated carrier is amplified and broadcast. Signal reception consists of the following steps: The carrier is received and amplified. The received signal is mixed with a local carrier to recover the spread digital signal. A pseudorandom code is generated, matching the anticipated signal. The receiver acquires the received code and phase locks its own code to it. The received signal is correlated with the generated code, extracting the Information data. Spread Spectrum Generation PseudoNoise Spreading Bit rate of PN is much higher. (chip rate) Spectrum of DS/SS SS modulation is applied on top of a conventional modulation. One can demonstrate that all other signals not receiving the SS code will stay as they are, unspread. Properties of DS/SS Secure Communication The signal can be detected by authorized persons who know the PN code. The signal power is small due to spreading (hide signal inside the noise) Difficult to jam since it is wideband Multiple Access Individual users have independent, uncorrelated spreading codes Advantages of CDMA over TDMA and FDMA Greater capacity TDMA and FDMA have a fixed number of slots Frequencies can be reused in all the cells in CDMA. No hard limit to the number of users. Resistance to multipath fading. Other Applications of Spread Spectrum GPS (Global Positioning System) Determine time, location and velocity of a person Consists of 24 satellites to measure the exact location Each satellite uses the same frequency band with DS/SS. Military Applications 


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02052011, 02:32 PM
ABHI.ppt (Size: 378.5 KB / Downloads: 52) Cellular Technology Introduction MOBILE PHONE…most popular device WHY ‘CELL PHONES’? Cellular Evolution Concept first tested in Chicago in 1978 First operational in Sweden in 1981 In the US, became operational in 1983 Introduced in Canada in 1986 Until 1991, all systems were analogue 1994, PCS were introduced Frequency Bands Operate in the UHF range, either in: 450 MHz: Analogue 800 MHz: Analogue & Digital 900 MHz: Analogue & Digital 1400 MHz: Digital (Japan only) 1800 MHz: Digital PCN 1900 MHz: Digital PCS What does this tell you? how is …EXAT MODEL? Cellular System  Why Limited Spectrum The cellular concept solved the problem by replacing a single, high power transmitter (large cell) with many low power transmitters (small cells). Each providing coverage to only a small portion of the service area. Fundamental Concepts The fundamental idea behind cellular communications is Frequency Reuse. Question: Is this TDMA? CDMA?…. Answer: SDMA (space division multiple access) frequencies used in one area can be reused in another area located some sufficient distance away (to avoid cochannel interference) NOTE: WE CAN USE ANY TYPE OF MA TECHNIQUE Geographic Layout Theoretical 7cell cluster arrangement Real World Cell Shape Each cell has a coverage area which is ~circular (exact shape is subject to distortions from obstacles and ground topology). Cell Frequency Distribution Each subset of frequency pairs are then reused according to a pattern WHAT depends on cell size? Changing the Cell Size Cluster STRUCTURES Sectorization Why sectorize? Results in lower interference due to an increase in D/R ratio (means more freq in a cell) How it works IN DETAIL 4 Channels between BS & MS Where am I Every live cell phone always knows the location area via the location area identity code (transmitted from BS) position is entered in the Home Location Register, and if roaming, in the Visitor Location Register of network BS continually monitors signal strength of all Mobile Stations (MS) in its area. If strength falls below a specified level, cell phone tells the Mobile Switching Centre (via the nearest Base Station), and a new BS is selected Current generation mobile user monitors signal strength of various cells and updates BS of strongest  much faster handoff Handoffs Goal: seamless connectivity from cell to cell without dropping or disrupting calls in progress If required  info is exchanged via FCC & RCC During the handoff, conversation is interrupted for less than 400 ms (not noticeable to the voice user) Two Types of Handoffs: Hard Handoffs new frequency allocated (FDMA & TDMA systems) Soft Handoffs same frequency is retained (CDMA systems) Conclusion…. Whatever………is was basic!!! Applications in…… 1.CDMA 2.FDMA 3.GSM……[2G , 3G ,4G….] 


