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Information about cdma

Published on September 5, 2008

Author: medoia


Slide 1: Prepared By Ibrahim AL-OBIDA 1/16 Outline : Prepared By Ibrahim AL-OBIDA 2/16 Outline Introduction Type of Multiplexing FDMA TDMA CDMA Future Work Introduction : Prepared By Ibrahim AL-OBIDA 3/16 Introduction The multiplexing is used to combined a number of independent signals into a composite signal suitable for transmission over a common channel Type of Multiplexing: : Prepared By Ibrahim AL-OBIDA 4/16 Type of Multiplexing: 1. Frequency-Division Multiple Access (FDMA). 3. Code-division Multiple-Access (CDMA) 2. Time-Division Multiple Access (TDMA). Frequency-Division Multiple Access (FDMA) : Prepared By Ibrahim AL-OBIDA 5/16 Frequency-Division Multiple Access (FDMA) It is a communications technique that divides a communications channel into a number of equally spaced frequency bands Time-Division Multiple Access (TDMA) : Prepared By Ibrahim AL-OBIDA 6/16 Time-Division Multiple Access (TDMA) It is a digital transmission technology that allows a number of users to access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel. Code Division Multiple Access (CDMA) : Prepared By Ibrahim AL-OBIDA 7/16 Code Division Multiple Access (CDMA) is a wireless communications technology that uses the principle of spread spectrum communication. There are three ways to spread the bandwidth of the signal: Frequency hopping Time hopping Direct sequence Code Division Multiple Access (CDMA) : Prepared By Ibrahim AL-OBIDA 8/16 Code Division Multiple Access (CDMA) CDMA Features: All users use same frequency and may transmit simultaneously Narrowband message signal multiplied by wideband spreading signal, or codeword Each user has its own pseudo-codeword (orthogonal to others). Receivers detect only the desired codeword. All others appear as noise. Receivers must know transmitter’s codeword. CDMA is a Direct Sequence Spread Spectrum system Code Division Multiple Access (CDMA) : Prepared By Ibrahim AL-OBIDA 9/16 Code Division Multiple Access (CDMA) Code Division Multiple Access (CDMA) : Prepared By Ibrahim AL-OBIDA 10/16 Code Division Multiple Access (CDMA) Pseudo-Noise Spreading Code Division Multiple Access (CDMA) : Prepared By Ibrahim AL-OBIDA 11/16 Code Division Multiple Access (CDMA) Direct Sequence Spread Spectrum System Code Division Multiple Access (CDMA) : Prepared By Ibrahim AL-OBIDA 12/16 Code Division Multiple Access (CDMA) Processing Gain: is the processing gain is Chipping Frequency (the bit rate of the PN code). is Information Frequency (the bit rate of the digital data). = fc fi Code Division Multiple Access (CDMA) : Prepared By Ibrahim AL-OBIDA 13/16 Code Division Multiple Access (CDMA) System Capacity: The capacity of a system is approximated by : is the maximum number of simultaneous calls is the processing gain is the total signal to noise ratio per bit is the inter-cell interference factor. Code Division Multiple Access (CDMA) : Prepared By Ibrahim AL-OBIDA 14/16 Code Division Multiple Access (CDMA) Advantages: Increased capacity Improved voice quality Eliminating the audible effects of multipath fading Enhanced privacy and security Reduced average transmitted power Reduced interference to other electronic devices Disadvantages: Wide bandwidth per user required Precision code synchronization needed Code Division Multiple Access (CDMA) : Prepared By Ibrahim AL-OBIDA 15/16 Code Division Multiple Access (CDMA) The Future Planning For Next Semester We will evaluate interference and capacity in CDMA system and analysize them using MatLab simulator Study the capacity of CDMA Study the interference rises from the increasing of capacity and how to reduce its effect. Slide 16: Prepared By Ibrahim AL-OBIDA 16/16 Than you for attendance Any question?

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