The document discusses various multiple access techniques used in wireless networks. It describes Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiplexing (OFDM), and Space Division Multiple Access (SDMA). It also covers concepts like duplexing methods, power control, modulation techniques, and the near-far problem in CDMA systems.
The document summarizes the evolution of multiple access techniques used in mobile communications systems over time. Early systems used simplex or half duplex frequency modulation. Cellular concepts and frequency division duplexing were developed in the 1950s-1960s. The first US cellular system was AMPS in 1983, using FDMA. Later, digital cellular and CDMA were introduced, using time division multiple access and code division multiple access respectively. Multiple access techniques allow sharing of bandwidth among users and include FDMA, TDMA, CDMA and their variations.
Multiple access techniques for wireless communicationDr.Umadevi V
This document discusses multiple access techniques for wireless communication. It begins with an introduction to how multiple access schemes allow efficient sharing of limited radio spectrum among multiple users. It then provides a brief history of wireless communication and pioneers. The document goes on to explain various multiple access techniques in detail including FDMA, TDMA, CDMA, SDMA, and CSMA. It describes their applications, advantages, and disadvantages. Forward and reverse link power control in CDMA is also summarized.
The document provides background information on various wireless technologies including LTE, UMB, and WiMax. It discusses their origins, standards development organizations, key enhancements over time, and speed capabilities. For example, it explains that LTE evolved from GSM/UMTS standards through 3GPP, while UMB originated from CDMA2000/EVDO standards and WiMax came from IEEE 802.16 standards for wireless metropolitan area networks. It provides timelines of developments and comparisons of download/upload speeds for different generations of each technology.
Presentation on MULTIPLE ACCESS TECHNIQUES FOR WIRELESS COMMUNICATION By SUPRIYA BHARATI (ME/EC/10006/16) and KHUSHBOO KUMARI (ME/EC/10010/16) Under the Guidance of Dr. Sanjay Kumar Department of Electronics & Communication Engg. (ECE) Birla Institute of Technology, Mesra ,Ranchi-835215 , Jharkhand , India
Multiple access techniques allow multiple users to share finite radio spectrum resources simultaneously. They can be categorized as narrowband or wideband. Common techniques include FDMA, TDMA, CDMA, and SDMA. FDMA divides the total bandwidth into narrow channels that are allocated to users. TDMA divides each channel into time slots that are allocated to users. CDMA spreads the signal over a wide bandwidth using pseudo-random codes and allows multiple signals to overlap in both time and frequency.
multiple access techniques for wireless communicationSajid ali
This document discusses multiple access techniques for wireless communication. It describes three main techniques: frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). FDMA allocates different frequency bands to different users. TDMA divides the available bandwidth into time slots and allocates slots to users. CDMA spreads user signals using unique codes and allows simultaneous transmission. Common cellular systems that use these techniques include AMPS (FDMA), GSM (TDMA), and IS-95 (CDMA).
Multiple access techniques allow multiple users to share the same wireless spectrum simultaneously. Common techniques include frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). FDMA assigns each user a different frequency band. TDMA assigns each user time slots on the same frequency. CDMA spreads each user's signal across the entire frequency band using unique codes.
This document discusses multiple access communication techniques. It introduces frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and space/beam division multiple access (SDMA). FDMA assigns each user a pair of frequencies, TDMA divides bandwidth into time slots and assigns users slots, CDMA allows signals to occupy the same channel using unique codes, and SDMA serves different users using concentrated spot beams. The document provides examples of applications and advantages/disadvantages of each technique.
The document summarizes the evolution of multiple access techniques used in mobile communications systems over time. Early systems used simplex or half duplex frequency modulation. Cellular concepts and frequency division duplexing were developed in the 1950s-1960s. The first US cellular system was AMPS in 1983, using FDMA. Later, digital cellular and CDMA were introduced, using time division multiple access and code division multiple access respectively. Multiple access techniques allow sharing of bandwidth among users and include FDMA, TDMA, CDMA and their variations.
Multiple access techniques for wireless communicationDr.Umadevi V
This document discusses multiple access techniques for wireless communication. It begins with an introduction to how multiple access schemes allow efficient sharing of limited radio spectrum among multiple users. It then provides a brief history of wireless communication and pioneers. The document goes on to explain various multiple access techniques in detail including FDMA, TDMA, CDMA, SDMA, and CSMA. It describes their applications, advantages, and disadvantages. Forward and reverse link power control in CDMA is also summarized.
The document provides background information on various wireless technologies including LTE, UMB, and WiMax. It discusses their origins, standards development organizations, key enhancements over time, and speed capabilities. For example, it explains that LTE evolved from GSM/UMTS standards through 3GPP, while UMB originated from CDMA2000/EVDO standards and WiMax came from IEEE 802.16 standards for wireless metropolitan area networks. It provides timelines of developments and comparisons of download/upload speeds for different generations of each technology.
Presentation on MULTIPLE ACCESS TECHNIQUES FOR WIRELESS COMMUNICATION By SUPRIYA BHARATI (ME/EC/10006/16) and KHUSHBOO KUMARI (ME/EC/10010/16) Under the Guidance of Dr. Sanjay Kumar Department of Electronics & Communication Engg. (ECE) Birla Institute of Technology, Mesra ,Ranchi-835215 , Jharkhand , India
Multiple access techniques allow multiple users to share finite radio spectrum resources simultaneously. They can be categorized as narrowband or wideband. Common techniques include FDMA, TDMA, CDMA, and SDMA. FDMA divides the total bandwidth into narrow channels that are allocated to users. TDMA divides each channel into time slots that are allocated to users. CDMA spreads the signal over a wide bandwidth using pseudo-random codes and allows multiple signals to overlap in both time and frequency.
multiple access techniques for wireless communicationSajid ali
This document discusses multiple access techniques for wireless communication. It describes three main techniques: frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). FDMA allocates different frequency bands to different users. TDMA divides the available bandwidth into time slots and allocates slots to users. CDMA spreads user signals using unique codes and allows simultaneous transmission. Common cellular systems that use these techniques include AMPS (FDMA), GSM (TDMA), and IS-95 (CDMA).
Multiple access techniques allow multiple users to share the same wireless spectrum simultaneously. Common techniques include frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). FDMA assigns each user a different frequency band. TDMA assigns each user time slots on the same frequency. CDMA spreads each user's signal across the entire frequency band using unique codes.
This document discusses multiple access communication techniques. It introduces frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and space/beam division multiple access (SDMA). FDMA assigns each user a pair of frequencies, TDMA divides bandwidth into time slots and assigns users slots, CDMA allows signals to occupy the same channel using unique codes, and SDMA serves different users using concentrated spot beams. The document provides examples of applications and advantages/disadvantages of each technique.
This document provides an overview of wireless communication and cellular systems. It discusses key concepts such as frequency reuse, cell footprint, handover, interference, and system capacity. It explains how cellular networks divide a service area into smaller cells served by low-power base stations to improve capacity. Neighboring cells are assigned different frequency groups to reduce interference. The same frequencies can be reused in cells far enough apart. Handover allows calls to be transferred between cells as users move. The document also covers channel assignment strategies and methods for expanding system capacity through cell splitting or reducing the frequency reuse factor.
MULTIPLE ACCESS IN WIRELESS COMMUNICATIONjuhi kumari
Multiple access techniques allow multiple terminals to share access to a transmission medium. The document discusses several techniques: frequency division multiple access (FDMA) allocates different frequencies to different users; time division multiple access (TDMA) divides the time frame into slots and allocates different time slots to different users; code division multiple access (CDMA) allocates different codes to different users; space division multiple access (SDMA) uses directional antennas to spatially separate users. The document also discusses ALOHA, slotted ALOHA, carrier sense multiple access (CSMA), and multiple access collision avoidance (MACA) protocols for wireless networks.
multiple access techniques used in wireless communicationSajid ali
This document discusses multiple access techniques for wireless communication. It describes frequency division duplexing (FDD) and time division duplexing (TDD) for sharing radio spectrum. The main multiple access techniques are described as frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). FDMA allocates different frequency bands to each user, TDMA divides the available time into time slots and allocates one slot per user, and CDMA uses pseudo-random codes to distinguish users transmitting simultaneously on the same frequency. Common cellular systems like AMPS, GSM, and IS-95 are cited as examples.
The document discusses various medium access control (MAC) protocols for wireless networks. It describes challenges with applying carrier sense multiple access with collision detection (CSMA/CD) to wireless networks due to problems like hidden and exposed terminals. It then covers different MAC schemes like space division multiple access (SDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA) that aim to address these challenges. Specific protocols discussed in more detail include Aloha, slotted Aloha, and how TDMA can be used for fixed or dynamic channel allocation.
This document discusses multiple access techniques for wireless communications, including FDMA, TDMA, and CDMA. It provides details on how each technique works and its advantages and disadvantages. FDMA divides the frequency band into channels that can be assigned to individual users. TDMA divides each channel into time slots that can be assigned to users. CDMA allows all users to use the whole available bandwidth simultaneously by using unique codes to distinguish users' signals.
The document discusses multiplexing and multiple access techniques. It describes frequency division multiplexing (FDM), time division multiplexing (TDM), code division multiplexing (CDM), and code division multiple access (CDMA). FDM separates a shared transmission medium into different frequency channels. TDM allows multiple signals to share the same transmission medium by dividing the signal into different time slots. CDM uses unique codes to distinguish between signals transmitted over the same shared band. CDMA is a multiple access scheme that uses spread spectrum technology and pseudo-random codes.
TDMA allows multiple users to share the same frequency channel by dividing the signal into different time slots. Each user transmits in brief bursts at periodic intervals, with the time slots being allocated so as not to interfere with each other. Key advantages include efficient use of spectrum and ability to carry voice and data. TDMA networks provide approximately three times the voice channel capacity of analog networks.
Multiple access techniques allow multiple mobile users to simultaneously share a finite amount of radio spectrum for communication. Common techniques include FDMA, TDMA, CDMA, and SDMA. FDMA allocates different frequency bands to different users. TDMA divides the available bandwidth into time slots that are allocated to users. CDMA spreads user signals over the entire available bandwidth through coding.
Wireless Application Protocol (WAP) allows devices to access the Internet over wireless networks. There are three main categories of protocols for managing shared access to wireless networks: fixed assignment, demand assignment, and random assignment. Fixed assignment divides resources like frequency bands or time slots and allocates them exclusively. Demand assignment allocates resources only to nodes that need them. Random assignment does not preallocate resources and relies on collision detection and retransmission to manage shared access. Common protocols that fall under these categories include FDMA, TDMA, CDMA, ALOHA, and CSMA.
This document summarizes key aspects of second-generation digital wireless systems including TDMA-based IS-136 and GSM as well as CDMA-based IS-95. It describes the basic infrastructure components including base stations, mobile switching centers, home and visitor location registers. It also provides overviews of channel structures and framing in GSM, IS-136 and IS-95 including descriptions of broadcast, traffic and control channels. Mobile registration, authentication and handoff procedures are also summarized.
This document discusses multiplexing techniques used in mobile computing. It describes four types of multiplexing: frequency division multiplexing (FDM), time division multiplexing (TDM), code division multiplexing (CDM), and space division multiplexing (SDM). For each type, it provides details on how the technique works and its advantages and disadvantages. FDM uses different frequencies to transmit multiple signals simultaneously. TDM divides a signal into time slots to share a frequency. CDM assigns unique codes to signals sharing the same frequency. SDM splits a channel across physical locations.
This document discusses multiple access techniques in wireless communication. It describes several techniques including Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), and Space Division Multiple Access (SDMA). It also covers packet radio access methods like ALOHA, slotted ALOHA, and Carrier Sense Multiple Access (CSMA). Each technique allows multiple users to share wireless spectrum resources simultaneously through dividing access in frequency, time, code, or space.
FDMA, TDMA, CDMA, and DAMA are multiple access techniques that allow multiple users to share access to a satellite for communication. FDMA divides the available bandwidth into different frequency channels. TDMA divides the bandwidth into different time slots. CDMA spreads each user's signal over the entire bandwidth using unique codes. DAMA dynamically assigns bandwidth according to demand rather than using pre-assigned blocks of time or frequency. These techniques allow efficient sharing of satellite bandwidth among multiple users.
CDMA is a digital cellular standard that allows multiple users to access the same radio frequency channel simultaneously through the use of unique code sequences. Users are separated by spreading their transmitted signals across the frequency band using pseudo-random codes. CDMA provides advantages over other multiple access techniques like FDMA and TDMA such as increased capacity, soft handoffs between cells, and covert operation due to its noise-like signals. The IS-95 standard introduced CDMA to cellular networks and specified the use of orthogonal codes to separate signals and a 1.25 MHz channel bandwidth to support multiple simultaneous voice calls.
This document discusses multiple access techniques used in wireless communication systems to allow multiple mobile users to share limited spectrum bandwidth efficiently. It describes frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA) as the three major techniques. FDMA assigns different frequency channels to individual users. TDMA assigns each user a unique time slot on a frequency channel. CDMA spreads user signals over a wide bandwidth using pseudo-random codes.
CDMA allows multiple users to share the same channel by assigning each user a unique code. It spreads the user's data signal over a wider bandwidth through multiplication with a pseudo-random code. This allows different signals to be separated at the receiver through correlation with the corresponding code. Major technologies using CDMA include WiFi, Bluetooth, and GPS, which employ techniques like DSSS, FHSS, and long/short codes. Performance of 802.11 networks can be analyzed based on collision probability and throughput calculations under saturated traffic conditions. Later developments expanded CDMA capabilities with techniques like W-CDMA, TD-CDMA, and TD-SCDMA.
Frequency Division Multiple Access (FDMA) is a channel access method where the available bandwidth is divided into multiple non-overlapping frequency bands and each user is assigned a specific frequency band. Each user can transmit or receive independently in its assigned frequency band without interference from other users. FDMA requires expensive bandpass filters for each frequency band and has strict linearity requirements for the transmission medium. The number of channels in an FDMA system is calculated by dividing the total available bandwidth minus the guard bands by the bandwidth of each individual channel.
This presentation based on TDMA technology,How it works,comparison between TDMA,FDMA,CDMA,Advantages and disadvantages of TDMA,Synchronization of TDMA and Evolution of TDMA
In the seven-layer OSI model of computer networking, media access control (MAC) data communication protocol is a sublayer of the data link layer (layer 2). The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium, e.g. an Ethernet network. The hardware that implements the MAC is referred to as a media access controller.
The MAC sublayer acts as an interface between the logical link control (LLC) sublayer and the network's physical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service.
This document discusses multiple access techniques for wireless communications, including FDMA, TDMA, and CDMA. It provides details on how each technique works and its advantages and disadvantages. FDMA divides the frequency band into channels that can be assigned to individual users. TDMA divides each channel into time slots that can be assigned to users. CDMA allows all users to use the whole available bandwidth simultaneously by using unique codes to distinguish users.
This document provides an overview of wireless communication and cellular systems. It discusses key concepts such as frequency reuse, cell footprint, handover, interference, and system capacity. It explains how cellular networks divide a service area into smaller cells served by low-power base stations to improve capacity. Neighboring cells are assigned different frequency groups to reduce interference. The same frequencies can be reused in cells far enough apart. Handover allows calls to be transferred between cells as users move. The document also covers channel assignment strategies and methods for expanding system capacity through cell splitting or reducing the frequency reuse factor.
MULTIPLE ACCESS IN WIRELESS COMMUNICATIONjuhi kumari
Multiple access techniques allow multiple terminals to share access to a transmission medium. The document discusses several techniques: frequency division multiple access (FDMA) allocates different frequencies to different users; time division multiple access (TDMA) divides the time frame into slots and allocates different time slots to different users; code division multiple access (CDMA) allocates different codes to different users; space division multiple access (SDMA) uses directional antennas to spatially separate users. The document also discusses ALOHA, slotted ALOHA, carrier sense multiple access (CSMA), and multiple access collision avoidance (MACA) protocols for wireless networks.
multiple access techniques used in wireless communicationSajid ali
This document discusses multiple access techniques for wireless communication. It describes frequency division duplexing (FDD) and time division duplexing (TDD) for sharing radio spectrum. The main multiple access techniques are described as frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). FDMA allocates different frequency bands to each user, TDMA divides the available time into time slots and allocates one slot per user, and CDMA uses pseudo-random codes to distinguish users transmitting simultaneously on the same frequency. Common cellular systems like AMPS, GSM, and IS-95 are cited as examples.
The document discusses various medium access control (MAC) protocols for wireless networks. It describes challenges with applying carrier sense multiple access with collision detection (CSMA/CD) to wireless networks due to problems like hidden and exposed terminals. It then covers different MAC schemes like space division multiple access (SDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA) that aim to address these challenges. Specific protocols discussed in more detail include Aloha, slotted Aloha, and how TDMA can be used for fixed or dynamic channel allocation.
This document discusses multiple access techniques for wireless communications, including FDMA, TDMA, and CDMA. It provides details on how each technique works and its advantages and disadvantages. FDMA divides the frequency band into channels that can be assigned to individual users. TDMA divides each channel into time slots that can be assigned to users. CDMA allows all users to use the whole available bandwidth simultaneously by using unique codes to distinguish users' signals.
The document discusses multiplexing and multiple access techniques. It describes frequency division multiplexing (FDM), time division multiplexing (TDM), code division multiplexing (CDM), and code division multiple access (CDMA). FDM separates a shared transmission medium into different frequency channels. TDM allows multiple signals to share the same transmission medium by dividing the signal into different time slots. CDM uses unique codes to distinguish between signals transmitted over the same shared band. CDMA is a multiple access scheme that uses spread spectrum technology and pseudo-random codes.
TDMA allows multiple users to share the same frequency channel by dividing the signal into different time slots. Each user transmits in brief bursts at periodic intervals, with the time slots being allocated so as not to interfere with each other. Key advantages include efficient use of spectrum and ability to carry voice and data. TDMA networks provide approximately three times the voice channel capacity of analog networks.
Multiple access techniques allow multiple mobile users to simultaneously share a finite amount of radio spectrum for communication. Common techniques include FDMA, TDMA, CDMA, and SDMA. FDMA allocates different frequency bands to different users. TDMA divides the available bandwidth into time slots that are allocated to users. CDMA spreads user signals over the entire available bandwidth through coding.
Wireless Application Protocol (WAP) allows devices to access the Internet over wireless networks. There are three main categories of protocols for managing shared access to wireless networks: fixed assignment, demand assignment, and random assignment. Fixed assignment divides resources like frequency bands or time slots and allocates them exclusively. Demand assignment allocates resources only to nodes that need them. Random assignment does not preallocate resources and relies on collision detection and retransmission to manage shared access. Common protocols that fall under these categories include FDMA, TDMA, CDMA, ALOHA, and CSMA.
This document summarizes key aspects of second-generation digital wireless systems including TDMA-based IS-136 and GSM as well as CDMA-based IS-95. It describes the basic infrastructure components including base stations, mobile switching centers, home and visitor location registers. It also provides overviews of channel structures and framing in GSM, IS-136 and IS-95 including descriptions of broadcast, traffic and control channels. Mobile registration, authentication and handoff procedures are also summarized.
This document discusses multiplexing techniques used in mobile computing. It describes four types of multiplexing: frequency division multiplexing (FDM), time division multiplexing (TDM), code division multiplexing (CDM), and space division multiplexing (SDM). For each type, it provides details on how the technique works and its advantages and disadvantages. FDM uses different frequencies to transmit multiple signals simultaneously. TDM divides a signal into time slots to share a frequency. CDM assigns unique codes to signals sharing the same frequency. SDM splits a channel across physical locations.
This document discusses multiple access techniques in wireless communication. It describes several techniques including Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), and Space Division Multiple Access (SDMA). It also covers packet radio access methods like ALOHA, slotted ALOHA, and Carrier Sense Multiple Access (CSMA). Each technique allows multiple users to share wireless spectrum resources simultaneously through dividing access in frequency, time, code, or space.
FDMA, TDMA, CDMA, and DAMA are multiple access techniques that allow multiple users to share access to a satellite for communication. FDMA divides the available bandwidth into different frequency channels. TDMA divides the bandwidth into different time slots. CDMA spreads each user's signal over the entire bandwidth using unique codes. DAMA dynamically assigns bandwidth according to demand rather than using pre-assigned blocks of time or frequency. These techniques allow efficient sharing of satellite bandwidth among multiple users.
CDMA is a digital cellular standard that allows multiple users to access the same radio frequency channel simultaneously through the use of unique code sequences. Users are separated by spreading their transmitted signals across the frequency band using pseudo-random codes. CDMA provides advantages over other multiple access techniques like FDMA and TDMA such as increased capacity, soft handoffs between cells, and covert operation due to its noise-like signals. The IS-95 standard introduced CDMA to cellular networks and specified the use of orthogonal codes to separate signals and a 1.25 MHz channel bandwidth to support multiple simultaneous voice calls.
This document discusses multiple access techniques used in wireless communication systems to allow multiple mobile users to share limited spectrum bandwidth efficiently. It describes frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA) as the three major techniques. FDMA assigns different frequency channels to individual users. TDMA assigns each user a unique time slot on a frequency channel. CDMA spreads user signals over a wide bandwidth using pseudo-random codes.
CDMA allows multiple users to share the same channel by assigning each user a unique code. It spreads the user's data signal over a wider bandwidth through multiplication with a pseudo-random code. This allows different signals to be separated at the receiver through correlation with the corresponding code. Major technologies using CDMA include WiFi, Bluetooth, and GPS, which employ techniques like DSSS, FHSS, and long/short codes. Performance of 802.11 networks can be analyzed based on collision probability and throughput calculations under saturated traffic conditions. Later developments expanded CDMA capabilities with techniques like W-CDMA, TD-CDMA, and TD-SCDMA.
Frequency Division Multiple Access (FDMA) is a channel access method where the available bandwidth is divided into multiple non-overlapping frequency bands and each user is assigned a specific frequency band. Each user can transmit or receive independently in its assigned frequency band without interference from other users. FDMA requires expensive bandpass filters for each frequency band and has strict linearity requirements for the transmission medium. The number of channels in an FDMA system is calculated by dividing the total available bandwidth minus the guard bands by the bandwidth of each individual channel.
This presentation based on TDMA technology,How it works,comparison between TDMA,FDMA,CDMA,Advantages and disadvantages of TDMA,Synchronization of TDMA and Evolution of TDMA
In the seven-layer OSI model of computer networking, media access control (MAC) data communication protocol is a sublayer of the data link layer (layer 2). The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium, e.g. an Ethernet network. The hardware that implements the MAC is referred to as a media access controller.
The MAC sublayer acts as an interface between the logical link control (LLC) sublayer and the network's physical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service.
This document discusses multiple access techniques for wireless communications, including FDMA, TDMA, and CDMA. It provides details on how each technique works and its advantages and disadvantages. FDMA divides the frequency band into channels that can be assigned to individual users. TDMA divides each channel into time slots that can be assigned to users. CDMA allows all users to use the whole available bandwidth simultaneously by using unique codes to distinguish users.
This document discusses space division multiplexing (SDM), a new technique for fiber optic communication that increases transmission capacity. SDM utilizes unused space within the core or additional fiber cores to establish independent transmission channels. There are two main SDM strategies: multi-core fiber which has multiple cores embedded in the cladding, and multi-mode fiber which supports propagation of multiple independent modes within a single core. SDM provides significant advantages like high scalability and the ability to achieve terabit per second throughput. When combined with software defined networking, SDM networks also enable efficient infrastructure utilization and flexible bandwidth provisioning. However, SDM also faces challenges like crosstalk between cores and high insertion losses.
Code division multiple access (CDMA) allows all terminals to send signals simultaneously over the same frequency by assigning each terminal a unique spreading code. The receiver can isolate a particular sender's signal by correlating the received signal with the known spreading code. CDMA offers advantages like higher capacity and integration of encryption due to the use of spreading codes, though receivers are more complex.
Fast Ethernet increased the bandwidth of standard Ethernet from 10 Mbps to 100 Mbps. It used the same CSMA/CD access method and frame format as standard Ethernet but with some changes to address the higher speed. Fast Ethernet was implemented over twisted pair cables using 100BASE-TX or over fiber optic cables using 100BASE-FX. The increased speed enabled Fast Ethernet to compete with other high-speed LAN technologies of the time like FDDI.
Medium access control (MAC) is the sublayer of the data link layer that coordinates use of a shared medium in wireless networks. It addresses problems like hidden and exposed terminals through techniques like carrier sense multiple access (CSMA) and time division multiple access (TDMA). TDMA divides time into slots and assigns slots to different users to avoid collisions. Early random access protocols like Aloha and slotted Aloha had low throughput due to many collisions, while later protocols use RTS/CTS handshaking and carrier sensing to reduce collisions and improve throughput.
This document describes a Matlab Simulink simulation of frequency-shift keying (FSK) modulation and demodulation. The simulation implements binary FSK (BFSK) using blocks like a Bernoulli binary generator, switch, charge pump PLL, and scope. It aims to prove and easily implement BFSK modulation and demodulation on hardware. The simulation adds noise to make it more realistic. The conclusion verifies that the simulation demonstrates the phenomenon of BFSK.
This document outlines programs and initiatives at Loyola University Chicago that support historically underrepresented student populations through mentorship, education, resources, and community building. It describes programs like STARS for first generation students and students of color, social justice dinner dialogues, LGBTQI spaces, initiatives for Men of Color, LUCES for Women of Color, a leadership retreat, and provides contact information for the university's diversity department.
It is prepared for simple presentation. Focused on basic optical fiber communication. And contains some important information about Space Division Multiplexing Technique.
This document discusses error detection and correction techniques used at the data link layer. It covers parity checks, cyclic redundancy checks (CRC), checksums, and Hamming codes. Parity checks, CRC, and checksums are used for error detection, while Hamming codes can detect and correct errors. The document provides examples of how these techniques work and compares their abilities to detect single-bit and burst errors.
The document discusses the process of registration and call setup in a mobile network. It describes:
1) Registration allows idle mobiles to notify the network of their presence and updates their location information. This allows efficient paging and delivery of incoming calls.
2) The main states and processes involved in call setup are the idle state, access state, and traffic channel state. The document outlines the signaling flows for mobile terminated and originated calls.
3) For a mobile terminated call, the network pages the mobile on the paging channel. The mobile responds on the access channel and is assigned a traffic channel to receive the call. For a mobile originated call, the mobile requests access to initiate the call and is assigned
The document discusses several advantages of CDMA technology, including frequency reuse, large coverage area, high spectrum capacity, privacy, soft handoff, good voice quality, and smooth migration to 3G. It also provides details on ZTE's involvement with CDMA technology development and key components of a CDMA network such as the BSC, BTS, MSC, VLR, and HLR.
This document discusses Digital Audio Broadcasting (DAB) systems. It provides an introduction to DAB and describes some of its key features like providing CD quality audio, robust reception, and ability to transmit ancillary data. It also discusses different DAB standards and specifications like Eureka 147, IBOC, and OFDM modulation. The document outlines the history of DAB and digital radio broadcasting. It provides block diagrams and descriptions of DAB and IBOC system implementations as well as challenges of radio signal propagation in mobile environments.
The document provides an overview of 3G and WCDMA technology. It discusses the evolution of mobile communications standards from 1G to 3G. It compares the different 3G modes including WCDMA, CDMA2000, and TD-SCDMA. It also outlines ZTE's WCDMA features and their solutions for 3G networks.
Smart antenna arrays use digital signal processing to transmit and receive signals in an adaptive, spatially sensitive manner. They have applications in cellular networks, radar, satellite systems, and electronic warfare for counteracting jamming. Key benefits include higher capacity, coverage, bit rates, link quality and spectral efficiency. Smart antennas contain radiating elements, a combining network, and a control unit to maximize gain towards desired signals and minimize it for interferers. Two main types are switched beam antennas, which switch between predefined beams, and dynamically phased arrays, which continuously track signals using direction of arrival algorithms. Smart antennas allow for space division multiple access by separating multiple users on the same channel based on angle. They provide improved interference rejection compared to conventional or
WIMAX is a wireless technology that provides broadband connectivity over long distances in a variety of ways. It uses towers to transmit high-speed internet access to receivers within a range of up to 50 km. WIMAX has several advantages over existing wireless technologies like WiFi and 3G, such as higher speeds, broader coverage areas, and lower infrastructure costs. While WIMAX adoption is still in early stages, it promises to deliver wireless broadband to more users at lower prices than current options.
1. Digital modulation techniques are used to modulate digital information so that it can be transmitted via different mediums. Common digital modulation methods include binary amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK).
2. FSK conveys information by changing the instantaneous frequency of a carrier wave. It is less susceptible to errors than ASK but has a larger spectrum bandwidth. PSK varies the phase of the transmitted signal. BPSK uses two phases while QPSK uses four phases.
3. The performance of digital modulation techniques can be compared using the energy per bit to noise power spectral density ratio (Eb/N0). Lower Eb/N0 values
1: Direct sequence and frequency hopped spread spectrum, spreading sequence and their correlation functions, Acquisition and tracking of spread spectrum signals.
2: Error probability for DS-CDMA, on AWGN channels, DS-CDMA on frequency selective fading, channels, Performance analysis of cellular CDMA.
3: Capacity estimation, Power control, effect of imperfect power control on DS CDMA performance, Soft Handoffs.
4: Spreading /coding tradeoffs, multi-carrier CDMA, IS-95 CDMA system, third generation CDMA systems, multi-user detection.
Successful interference cancellation with Blind Equalization method for MC-CD...IJTET Journal
Abstract— The increasing demand for wireless services has created the need for cost effective transmission techniques that can exploit scarce spectral resources efficiently. Inorder to achieve the high data rates needed to meet the quality of service requirements of future multimedia applications, MC-CDMA has been considered as good air-interface candidate, especially for the downlink. However, the user capacity of MC-CDMA system is essentially limited by interference. This interference can be mitigated by employing precoding techniques, IB-DFE based receivers and other efficient interference suppression techniques. In the proposed system, combined Iterative IA precoding at the transmitter with IB-DFE based processing at the receiver is suggested for MC-CDMA systems. The matrices for this nonlinear space-frequency equalizer are obtained by minimizing the overall MSE of all data streams at each subcarrier.
Multiple access techniques allow multiple mobile users to share limited spectrum resources simultaneously. The main techniques are frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). In FDMA, each user is assigned a unique pair of frequencies. In TDMA, the total bandwidth is divided into time slots that users transmit in turn. In CDMA, all users transmit over the same frequency but are separated by unique codes. Each technique has advantages and disadvantages regarding complexity, bandwidth utilization, and vulnerability to interference.
Dynamic Power Allocation for Mc-Cdma System Using Iterative Water Filling Alg...inventionjournals
ABSTRACT : Power control in Multi Carrier Code Division Multiple Access ( MCCDMA) based wireless cellular network is of great importance. The power allocation methodology to enhance the performance of the MCCDMA system by limiting interference noise is at the expense of signaling overhead due to sharing of Channel State Information (CSI). The distributed algorithms that manage the power level based on the user’s SINR requirements needs the complete knowledge of Channel State Information (CSI) .Since the CSI is subjected to the errors because of the imperfect channel estimation/measurement due to the time varying nature of the channels, the distributed power control algorithm is not globally optimum. The water filling algorithm is used to allocate proper power for every sub channel in order to improve channel capacity. The water filling algorithm distributes power among all users with the help of SINR that is received by the transmitter instead of getting full Channel State Information (CSI).
This document provides an overview of Orthogonal Frequency Division Multiplexing (OFDM). It discusses how OFDM works by splitting a data stream into multiple parallel sub-carriers that are then modulated and overlapped without interference. The document reviews the history and development of OFDM over decades. It also discusses how OFDM compares to other multiple access techniques like Frequency Division Multiple Access (FDMA) and how OFDM allows for higher spectral efficiency.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Multiplexing is a scheme that sends multiple signals over a single transmission medium. There are four main types: frequency division multiplexing (FDM), wavelength division multiplexing (WDM), time division multiplexing (TDM), and code division multiplexing (CDM). FDM uses different frequency bands to separate signals. WDM uses different wavelengths of light to separate signals on optical fibers. TDM divides time into slots and allocates each signal a time slot.
TDMA, CDMA, FDMA, and SDMA are different multiple access techniques used in mobile communications. TDMA divides each channel into time slots and allocates slots to different users. CDMA encodes each conversation with a pseudo-random sequence and all users share the full spectrum. FDMA divides the bandwidth into individual frequency bands, each assigned to a single user. SDMA uses smart antennas to create spatial pipes between the base station and mobile users to improve performance.
Time division multiplexing (TDM) is a technique used in telecommunications to transmit multiple signals over a shared medium. It involves dividing a signal into multiple time slots and assigning each slot to a different signal. TDM was initially developed for telegraphy in 1870 and is now widely used. It is used in digital networks like TDM telephone networks and synchronous digital hierarchy (SDH) networks to efficiently allocate bandwidth to multiple signals or data streams. Common examples of TDM include digitally transmitting multiple telephone calls over the same cable or interleaving left and right stereo signals in an audio file.
The tutorial is designed for all those readers who are planning or pursuing the CDMA course to make their career in this field. However, it is also meant for the common readers who simply want to understand − what is CDMA Technology?
The document discusses the evolution of wireless communication technologies through generations from 2G to 4G. It describes the key characteristics and speed capabilities of each generation. It also provides details on various wireless networking components and concepts such as channel access schemes, radio signals, BTS, BSC, MSC, HLR, AuC, EIR and SMSC.
The document provides an overview of Multi-Carrier Code Division Multiple Access (MC-CDMA) systems and discusses previous research in this area. It then proposes a new complex orthogonal wavelet packet based MC-CDMA system to investigate its bit error rate performance over different modulation techniques on an AWGN channel. The key aspects covered are:
1) MC-CDMA allows multiple users to transmit simultaneously by spreading user symbols across several subcarriers using different code values.
2) Previous research explored combining MC-CDMA with techniques like space-time coding and discrete wavelet transforms to improve performance.
3) The proposed system uses wavelet packet modulation waveforms instead of sinusoidal ones to eliminate guard intervals
The document provides an overview of Multi-Carrier Code Division Multiple Access (MC-CDMA) systems and discusses previous research in this area. It then proposes a new complex orthogonal wavelet packet based MC-CDMA system to investigate its bit error rate performance over different modulation techniques on an AWGN channel. The key aspects covered are:
1) MC-CDMA allows multiple users to transmit simultaneously by spreading user symbols across several subcarriers using different code values.
2) Previous research explored combining MC-CDMA with techniques like space-time coding and discrete wavelet transforms to improve performance.
3) The proposed system uses wavelet packet modulation waveforms instead of sinusoidal ones to eliminate guard intervals
The document provides an overview of Multi-Carrier Code Division Multiple Access (MC-CDMA) systems and discusses several related research papers. It then summarizes 21 research papers on topics such as: implementing space-time coding and discrete wavelet transforms in MC-CDMA systems to improve performance; using wavelet packets as modulation waveforms to eliminate guard intervals; flexible MC-CDMA system designs; and evaluating the performance of different wavelet transforms in MC-CDMA communications. The document analyzes various techniques for enhancing the spectral efficiency and performance of MC-CDMA systems.
The document discusses multi-user CDMA communication using MATLAB. It introduces multiple access techniques such as FDMA, TDMA, SDMA and CDMA that allow multiple users to utilize the same bandwidth. CDMA uses direct sequence spread spectrum that spreads the message signal over a wider bandwidth using a PN code. The document discusses various spreading codes used in CDMA like maximal length sequences, Gold codes and Walsh codes. It then describes multiple access techniques in detail, including FDMA, TDMA, SDMA and CDMA. The block diagram of a DS-SS system is also presented.
Spread spectrum communication was first described in 1941 by actress Hedy Lamarr and pianist George Antheil in a patent for a secure radio link to control torpedoes. Spread spectrum works by transmitting signals across a wider bandwidth than the minimum needed using a code known by the transmitter and receiver. It provides benefits like immunity to interference and robust multiple access capability, though it is not bandwidth efficient for single users. Some examples of multiple access techniques that use spread spectrum are frequency hopping and direct sequence spread spectrum.
This document provides an overview of multiple access techniques for wireless communications, including FDMA, TDMA, CDMA, and various spread spectrum techniques. It describes the basic principles of each technique, including how they divide up frequency bands, time slots, or code channels to allow multiple users to access a shared channel simultaneously. Examples of wireless networks that use each technique are also provided.
This document discusses multiple access procedures used in wireless networks. It describes four main types: FDMA which divides the frequency band into channels; TDMA which divides the available time into time slots; CDMA which uses orthogonal codes to separate signals that occupy the same frequency; and SDMA which divides the space using directional antennas. The document provides details on how FDMA, TDMA, and CDMA work and notes some variants of TDMA including fixed, dynamic, and packet-based TDMA.
1. The document discusses various topics related to data communication and computer networks including Point to Point Protocol (PPP), media access control, multiplexing techniques like frequency division multiplexing (FDM), wavelength division multiplexing (WDM), and time division multiplexing (TDM), and controlled access methods like reservation, polling, and token passing.
2. It provides details on PPP components, types of multiplexers, uses of FDM and WDM, synchronous and asynchronous TDM, and how reservation, polling, and token passing control access to shared media.
3. Controlled access methods like token passing aim to prevent collisions by allowing only one node to transmit at a time, while random access techniques
This document discusses error detection and correction techniques used at the data link layer. It describes different types of errors that can occur like single-bit and burst errors. Error detection methods like parity checks, cyclic redundancy checks (CRC), and checksums are explained. Forward error correction codes like Hamming codes that allow for error correction are also covered. The document provides examples to illustrate how various error detection and correction schemes work.
The document discusses several existing wireless systems including Advanced Mobile Phone System (AMPS), Global System for Mobile communications (GSM), and IS-41 standard. AMPS was one of the first cellular standards and uses FM to transmit voice and FSK for control signals. It divides coverage areas into cells using different frequency bands. GSM is a second-generation standard that aims for roaming between networks. It uses TDMA and operates between 890-960 MHz. IS-41 allows for roaming and handoffs between mobile switching centers.
The document describes the infrastructure and processes that enable cellular communication systems. Key components include:
- Base stations that transmit and receive signals and connect to a base station controller.
- Authentication centers and equipment registers that verify user identities and equipment.
- Home and visitor location registers that track user locations to route calls and support mobility.
- Registration and handoff processes allow users to move between base stations and be reached on their cell phone number anywhere on the network. Location tracking, signaling between registers, and rerouting enable seamless roaming across large areas.
The document discusses network protocols and the OSI model. It describes the 7 layers of the OSI model from the physical layer to the application layer. It then discusses the TCP/IP protocol suite and its 5 layers. For each layer, it outlines the main responsibilities and protocols that are part of that layer such as IP, ICMP, DHCP, TCP, and others. It also discusses some common routing protocols like RIP, OSPF, and BGP. Finally, it covers issues with using TCP over wireless networks and some proposed solutions to improve its performance.
Mobile stations must share a single channel for communication, which can lead to collisions if multiple stations transmit simultaneously. Several protocols have been developed to manage access to the shared channel, including ALOHA, CSMA, and their variations. CSMA/CA with RTS/CTS is commonly used in wireless networks as it helps avoid collisions and resolve the hidden terminal problem.
This document provides an overview of wireless networks and communication systems. It discusses digital and analog communications, examples of wireless systems, and the differences between wireless and wired networks. It also covers wireless system architecture, multiple access techniques, the evolution of cellular networks from 1G to 4G, and various wireless technologies like WLANs, Bluetooth, ad hoc networks, and more. Key concepts around cellular concepts and the components of communication systems are also summarized.
Executive Directors Chat Leveraging AI for Diversity, Equity, and InclusionTechSoup
Let’s explore the intersection of technology and equity in the final session of our DEI series. Discover how AI tools, like ChatGPT, can be used to support and enhance your nonprofit's DEI initiatives. Participants will gain insights into practical AI applications and get tips for leveraging technology to advance their DEI goals.
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The simplified electron and muon model, Oscillating Spacetime: The Foundation...RitikBhardwaj56
Discover the Simplified Electron and Muon Model: A New Wave-Based Approach to Understanding Particles delves into a groundbreaking theory that presents electrons and muons as rotating soliton waves within oscillating spacetime. Geared towards students, researchers, and science buffs, this book breaks down complex ideas into simple explanations. It covers topics such as electron waves, temporal dynamics, and the implications of this model on particle physics. With clear illustrations and easy-to-follow explanations, readers will gain a new outlook on the universe's fundamental nature.
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বাংলাদেশের অর্থনৈতিক সমীক্ষা ২০২৪ [Bangladesh Economic Review 2024 Bangla.pdf] কম্পিউটার , ট্যাব ও স্মার্ট ফোন ভার্সন সহ সম্পূর্ণ বাংলা ই-বুক বা pdf বই " সুচিপত্র ...বুকমার্ক মেনু 🔖 ও হাইপার লিংক মেনু 📝👆 যুক্ত ..
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তাই একজন নাগরিক হিসাবে এই তথ্য গুলো আপনার জানা প্রয়োজন ...।
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A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
A workshop hosted by the South African Journal of Science aimed at postgraduate students and early career researchers with little or no experience in writing and publishing journal articles.
How to Fix the Import Error in the Odoo 17Celine George
An import error occurs when a program fails to import a module or library, disrupting its execution. In languages like Python, this issue arises when the specified module cannot be found or accessed, hindering the program's functionality. Resolving import errors is crucial for maintaining smooth software operation and uninterrupted development processes.
1. Multiple radio access schemes for wireless networks are primarily used
for exchanging control information between a BS and a MS.
Users can also receive signals transmitted by other users in the system. In
fact, many users access the traffic channels when the reverse (uplink)
path from MS to BS is to be established.
There are three basic ways to have many channels within an allocated
bandwidth: frequency, time, or code. They are addressed by three
multiple division techniques :
(FDMA) - frequency division multiple access.
(TDMA) - time division multiple access.
(CDMA) - code division multiple access.
Two other variants known as :
(OFDM) - orthogonal frequency division multiplexing .
(SDMA) - space division multiple access.
Multiple Division Techniques
for Traffic Channels
2. A MS must distinguish which signal is meant for itself among many signals being
transmitted by other users or BSs, and the BS should be able to recognize the
signal sent by a particular user.
Multiple-access techniques are based on the orthogonalization of signals.
If a system employs different carrier frequencies to transmit the signal for each
user, it is called a FDMA system.
If a system uses distinct time slots to transmit the signal for different users, it is a
TDMA system.
If a system uses different code to transmit the signal for each user, it is a CDMA
system.
To provide simultaneous two-way communications (duplex communications), a
forward channel (downlink) from the BS to the MS and a reverse channel
(uplink) from the MS to the BS are necessary.
Two types of duplex systems are utilized:
frequency division duplexing (FDD) divides the frequency used.
time division duplexing (TDD) divides the same frequency by time.
FDMA mainly uses FDD, while TDMA and CDMA systems use either FDD or TDD.
A number of channels can be simultaneously used to transfer data at a much
higher rate, and such an effective technique is known as OFDM.
Concepts and Models for Multiple
Divisions
3. FDMA is a multiple-access system that has been widely adopted in
existing analog systems for portable and automobile wireless telephones.
The BS dynamically assigns a different carrier frequency to each active
user (MS).
A frequency synthesizer is used to adjust and
maintain the transmission and reception
frequencies.
There is a pair of channels for the communication between the BS and the
MS. The paired channels are called forward channel (downlink) and
reverse channel (uplink). Different frequency bandwidths are assigned to
different users. This implies that there is no frequency overlapping
between the forward and reverse channels.
A protecting bandwidth is used between the forward and reverse
channels, and a guard band Wg between two adjacent channels is used to
minimize adjacent channel interference between them. The frequency
bandwidth for each user is called sub-band Wc. If there are N channels in a
FDMA system, the total bandwidth is equal to N · Wc.
FDMA
5. TDMA splits a single carrier wave into several time slots and distributes the slots
among multiple users, the communication channels essentially consist of many
units, i.e., time slots, over a time cycle, which makes it possible for one frequency
to be efficiently utilized by multiple users, given that each utilizes a different time
slot.
This system is widely used in the field of digital portable and automobile
telephones and mobile satellite communication systems.
A TDMA system may be in either of two modes: FDD (in which the
forward/reverse or uplink/downlink communication frequencies differ) and TDD
(in which the forward/reverse communication frequencies are the same).
For a TDMA system, there is guard time between the slots so that interference
due to propagation delays along different paths can be minimized.
A wideband TDMA enables high-speed digital transmissions, in which selective
frequency fading due to the use of multiple paths can become a problem. This
requires that bandwidth be limited to an extent such that selective fading can be
overcome, or appropriate measures such as adaptive equalization techniques
could be adopted for improvement. A high-precision synchronization circuit also
becomes necessary on the MS side to carry out intermittent burst signal
transmission.
TDMA
8. In a CDMA system, different spread-spectrum codes are selected and assigned to
each user, and multiple users share the same frequency.
A CDMA system is based on spectrum-spread technology, which makes it less
susceptible to the noise and interference by substantially spreading over the
bandwidth range of the modulated signal.
CDMA system, received signals at the BS from a far away MS could be masked by
signals from a close-by MS in the reverse channel.
A CDMA system is usually quantified by the chip rate, which is defined as the
number of bits changed per second.
Two basic types of CDMA implementation methodologies:
1) Direct sequence (DS), and 2) frequency hopping (FH). a FH method, a
pseudorandom sequence is used to change the radio signal frequency across a
broad frequency band in a random fashion.
CDMA
9. Spread Spectrum : is a transmission technique wherein data occupy
a larger bandwidth than necessary. Bandwidth spreading is
accomplished before transmission through the use of a code that is
independent of the transmitted data. The same code is used to
demodulate the data at the receiving end.
Originally designed for military use to avoid jamming (interference
created intentionally to make a communication channel unusable),
spread spectrum modulation is now also used in personal
communication systems due to its superior performance in an
interference dominated environment.
CDMA
10. Direct Sequence Spread Spectrum (DSSS) : the radio signal is multiplied by a
pseudorandom sequence whose bandwidth is much greater than that of the
signal itself, thereby spreading its bandwidth.
a pseudorandom sequence directly phase modulates a (data-modulated) carrier,
thereby increasing the bandwidth of the transmission and lowering the spectral
power density (i.e., the power level at any given frequency). The resulting RF
signal has a noise like spectrum and in fact can be intentionally made to look like
noise to all but the intended radio receiver. The received signal is despread by
correlating it with a local pseudorandom sequence identical to and in
synchronization with the sequence used to spread the carrier at the radio
transmitting end.
CDMA
11. Frequency Hopping Spread Spectrum (FHSS) : A spread spectrum
modulation technique implies that the radio transmitter frequency hops from
channel to channel in a predetermined but pseudorandom manner.
The RF signal is dehopped at the receiver end using a frequency synthesizer
controlled by a pseudorandom sequence generator synchronized to the
transmitter’s pseudorandom sequence generator.
A frequency hopper may be fast hopped, where there are multiple hops per data
bit, or slow hopped, where there are multiple data bits per hop.
Multiple simultaneous transmission from several users is possible using FH, as
long as each uses different frequency hopping sequences and none of them
“collides” (no more than one unit using the same band) at any given instant of
time.
CDMA
12. Walsh Codes : In CDMA, each user is assigned one or many
orthogonal waveforms derived from one orthogonal code. Since
the waveforms are orthogonal, users with different codes do not
interfere with each other.
CDMA requires synchronization among the users, since the
waveforms are orthogonal only if they are aligned in time. An
important set of orthogonal codes is the Walsh set . Walsh
functions are generated using an iterative process of constructing a
Hadamard matrix
starting with H0 = [0].
The Hadamard matrix
is built by using the
function :
CDMA
13. Near-Far Problem : The near-far problem stems from a wide range
of signal levels received in wireless and mobile communication
systems.
Out-of-band radiation of the signal from the MS1 interferes with the
signal from the MS2 in the adjacent channel. This effect, called
adjacent channel interference, becomes serious when the
difference in the received signal strength is high. For this reason,
the out-of-band radiation must be kept small.
The tolerable relative adjacent channel interference level can be
different depending on the system characteristics. If power control
technique is used, the system can tolerate higher relative adjacent
channel interference levels. The near-far problem becomes more
important for CDMA systems where spread spectrum signals are
multiplexed on the same frequency using low cross correlation
codes.
CDMA
15. Power Control : Power control is simply the technique of
controlling the transmit power in the traffic channel so as to affect
the received power and hence the CIR.
While power control can often be effective for traffic channels,
there are some disadvantages :
a) Since battery power at a MS is a limited resource that needs to be
conserved, it may not be possible or desirable to set transmission
powers to higher values.
b) Second, increasing the transmitted power on one channel,
irrespective of the power levels used on other channels, can
cause inequality of transmission over other channels.
c) As a result, there is also the possibility that a set of connections
using a pure power control scheme can suffer from unstable
behavior, requiring increasingly higher transmission powers.
d) Finally, power control techniques are restricted by the physical
limitations on the transmitter power levels.
CDMA
16. The basic strategy in OFDM is to split high-rate radio channels into
multiple lower rate sub-channels that are then simultaneously
transmitted over multiple orthogonal carrier frequencies.
The transmitter of OFDM converts high-speed data streams into n
parallel low-speed bit streams, which are then modulated and
mixed with inverse discrete Fourier transform (IDFT); then guard
time is inserted to reduce inter-symbol interferences (ISI). The
reverse actions are taken at the receiver side.
In all these systems, the information is first modulated before
being transmitted over a channel.
Figure 7.21 illustrates the modulation operation of the OFDM
transmitter.
Figure 7.22 shows the demodulation steps of the OFDM receiver,
with explicit use of the discrete Fourier transform (DFT).
OFDM
18. In SDMA, the omni-directional communication space is divided into
spatially separable sectors. This is possible by having a BS use smart
antennas, allowing multiple MSs to use the same channel simultaneously.
The communication characterized by time slot, carrier frequency, or
spreading code can be used as shown in Figure 7.23.
Use of a smart antenna maximizes the antenna gain in the desired
direction, and directing antenna gain in a particular direction leads to
range extension, which reduces the number of cells required to cover a
given area. Moreover, such focused transmission reduces the
interference from undesired directions by placing minimum radiation
patterns in the direction of interferers.
As the BS forms different beams for each spatially separable MS on the
forward and reverse channels, noise and interference for each MS and BS
is minimized. This enhances the quality of the communication link
significantly and increases overall system capacity. Also, by creating
separate spatial channels in each cell intra-cell reuse of conventional
channels can be easily exploited. Currently, this technology is still being
explored and its future looks quite promising.
SDMA
21. AM : Amplitude modulation (AM) is the first method ever used to transfer
voice information from one place to another. The amplitude of a carrier
signal with a constant frequency is as varied as the information signal
required to transmit.
The total power of the transmitted wave varies in amplitude in
accordance with the power of the modulating signal.
The bandwidth of an AM scheme—that is, the amount of space that it
occupies in the Fourier domain—is twice that of the modulating signal.
This double sideband nature of AM halves the number of independent
signals that can be sent using a given range of transmission frequencies.
By suppressing one sideband before transmission, single sideband (SSB)
modulation doubles the number of transmissions that can fit into a given
transmission band.
At the receiver end, the carrier signal is filtered out, rebuilding the
information signal (speech, data, etc.). When a carrier is amplitude
modulated with a pure sine wave, up to one-third (33.3%) of the overall
signal power is contained in the sidebands.
The other two-thirds of the signal power are contained in the carrier,
which does not contribute to the transfer of data. This makes AM an
inefficient mode of communication.
Modulation Techniques
23. FM : Frequency modulation (FM) is a method of integrating the
information signal with an alternating current (ac) wave by varying
the instantaneous frequency of the wave.
The carrier is stretched or squeezed by the information signal, and
the frequency of the carrier is changed according to the value of
the modulating voltage.
In FM, the total wave power does not change when the frequency
alters. To recover the signal, the receiver rebuilds the information
wave by checking how the known carrier signal has modified the
information.
An FM system provides a better signal-to-noise ratio (SNR) than an
AM system, which implies that it has less noise content. Another
advantage is that it needs less radiated power. However, it does
require a larger bandwidth than AM.
Modulation Techniques ( FM )
25. FSK : Frequency shift keying (FSK) is used for modulating a digital
signal over two carriers by using a different frequency for a “1” or a
“0”. The difference between the carriers is known as the frequency
shift.
One obvious way to generate a FSK signal is to switch between two
independent oscillators according to whether the data bit is a “1”
or a “0.” This type of FSK is called discontinuous FSK since the
waveform generated is discontinuous at the switching time.
The phase discontinuity poses several problems, such as spectral
spreading and spurious transmissions. A common method of
generating an FSK signal is to frequency modulate a single-carrier
oscillator using the message waveform.
This type of modulation is similar to FM generation, except that the
modulating signal is in binary.
FSK has high signal-to-noise ratio (SNR) but low spectral efficiency.
It was used in all early low bit-rate modems.
Modulation Techniques ( FSK )
27. PSK : Phase shift keying (PSK) is a method of transmitting and
receiving digital signals in which the phase of a transmitted signal is
varied to convey information.
In digital transmission, the phase of the carrier is discretely varied
with respect to a reference phase and according to the data being
transmitted.
when encoding, the phase shift could be 0◦ for encoding a “0” and
180◦ for encoding a “1,” thus making the representations for “0”
and “1” apart by a total of 180◦.
This kind of PSK is also called binary phase shift keying (BPSK) since
1 bit is transmitted in a single modulation symbol.
PSK has a perfect SNR but must be demodulated synchronously,
which means a reference carrier signal is required to be received at
the receiver to compare with the phase of the received signal,
which makes the demodulation circuit complex.
Modulation Techniques ( PSK )
29. QPSK : Quadrature phase shift keying (QPSK) takes the concept of
PSK a step further as it assumes that the number of phase shifts is
not limited to only two states.
The transmitted carrier can undergo any number of phase changes.
This is indeed the case in quadrature phase shift keying. With QPSK,
the carrier undergoes four changes in phase and can thus represent
four binary bit patterns of data, effectively doubling the bandwidth
of the carrier. The following are the phase shifts with the four
different combinations of input bits .
Normally, QPSK is implemented using I/Q modulation with I (in-
phase) and Q (quadrature) signals summarized with respect to the
same reference carrier signal (in other words, from the same local
oscillator). A 90◦ phase offset is placed in one of the carriers.
Modulation Techniques ( QPSK )
30. We can consider each of the two binary sequences to be a BPSK
signal. The two binary sequences are separately modulated by the
two quadrate signals. The summation of the two modulated
waveforms is the QPSK waveform, and the phase shift also has four
states corresponding to every two adjacent input bits. Figure 7.29
shows the constellations of BPSK and QPSK.
Modulation Techniques ( QPSK )
Figure 7.29
Signal constellations of
BPSK and QPSK.
31. π/4QPSK : In π/4QPSK, the input sequence is encoded by the
changes in the amplitude and direction of the phase shift and not in
the absolute position in the constellation.
In QPSK and BPSK, the input sequence is encoded in the absolute
position in the constellation.
π/4QPSK uses two QPSK constellations offset by ±π/4. Signaling
elements are selected in turn from the two QPSK constellations.
Transitions must occur from one constellation to the other one.
This ensures that there will always be a phase change for each
symbol. Therefore, π/4QPSK can be non-coherently demodulated,
which simplifies the design of the demodulator.
π/4QPSK is popular in most second-generation systems, such as
North American Digital Cellular (IS-54) and Japanese Digital Cellular
(JDC).
Modulation Techniques ( π/4QPSK )
33. QAM : Quadrature amplitude modulation (QAM) is simply a combination
of AM and PSK, in which two carriers out of phase by 90◦ are amplitude
modulated. If the baud rate is 1200 Hz, 3 bits per baud, a signal can be
transmitted at 3600 bps. We modulate the signal by using two measures
of amplitude and four possible phase shifts. Combining the two, we have
eight possible waves (Table 7.2).
Mathematically, there is no limit
to the data rate that may be
Supported by a given baud rate in
a perfectly stable, noiseless
transmission environment.
In practice, the governing factors
are the amplitude (and,
consequently, phase) stability, and
the amount of noise present, in
both the terminal equipment and
the transmission medium
(carrier frequency, or communication channel) involved.
Modulation Techniques (QAM )
34. 16QAM : 16QAM involves splitting the signal into 12 different phases
and 3 different amplitudes for a total of 16 different possible
values, each encoding 4 bits.
16QAM is used in applications including microwave digital radio,
DVB-C (digital video broadcasting—cable), and modems. 16QAM or
other higher-order QAMs (64QAM, 256QAM) are more bandwidth
efficient than BPSK, QPSK, or 8PSK and are used to gain high-speed
transmission. However, there is a tradeoff, and the radio becomes
more complex and is more susceptible to errors caused by noise
and distortion.
Error rates of higher-order QAM systems degrade more rapidly
than QPSK as noise or interference is introduced. A measure of this
degradation would be a higher BER (Bit Error Rate).
Modulation Techniques (16QAM )