Multiple access techniques are essential for allowing multiple users to share the same communication resources effectively and efficiently. Here are the primary types of multiple access techniques used in wireless communication:
Time Division Multiple Access (TDMA):
Description: In TDMA, the available bandwidth is divided into time slots. Each user is assigned a specific time slot during which they can transmit or receive data. This ensures that multiple users can share the same frequency channel without interference by transmitting in different time intervals.
Applications: TDMA is used in various systems, including 2G GSM cellular networks and certain satellite communications.
Frequency Division Multiple Access (FDMA):
Description: FDMA allocates separate frequency bands to each user. Each user operates on a distinct frequency channel, minimizing interference between users. The total available bandwidth is divided into multiple frequency bands, each assigned to a different user.
Applications: FDMA is commonly used in analog cellular systems, traditional broadcast radio, and television.
Code Division Multiple Access (CDMA):
Description: In CDMA, each user is assigned a unique code that is used to modulate their signal. Multiple users can transmit simultaneously over the same frequency band, and the receiver uses the unique code to distinguish between different signals. This technique allows efficient use of the available bandwidth and provides resistance to interference and eavesdropping.
Applications: CDMA is widely used in 3G cellular networks (such as CDMA2000 and WCDMA) and in GPS systems.
Orthogonal Frequency Division Multiple Access (OFDMA):
Description: OFDMA is an extension of Orthogonal Frequency Division Multiplexing (OFDM). In OFDMA, the available frequency spectrum is divided into orthogonal subcarriers, and users are assigned different subcarriers. This technique allows simultaneous transmission by multiple users with minimal interference.
Applications: OFDMA is used in 4G LTE, WiMAX, and some modern Wi-Fi standards (such as Wi-Fi 6).
Space Division Multiple Access (SDMA):
Description: SDMA uses spatial separation to allocate resources to users. It leverages multiple antennas (MIMO technology) to direct signals towards specific users, allowing multiple users to share the same frequency channel simultaneously. By focusing signals in different spatial directions, SDMA minimizes interference.
Applications: SDMA is utilized in advanced MIMO systems, 5G networks, and satellite communications.
Non-Orthogonal Multiple Access (NOMA):
Description: NOMA allows multiple users to share the same time and frequency resources by assigning different power levels to each user. Signals are superimposed, and advanced signal processing techniques are used to separate the signals at the receiver. This technique improves spectral efficiency and user fairness.Multiple access techniques are essential for allowing multiple users to share the same
Design and Implementation of Digital PLL using Self Correcting DCO SystemIJERA Editor
The mainstay of the paper is to use a PLL using self healing pre-scalar. When a CMOS technology approaches to a nanometer scale, the non-idealities like variability and leakage current may affect the circuit performances. The process variability leads to the large variations to degrade the device matching and performances. The leakage current is highly dependent upon the process variations. In the existing method the key parameter is to be change the modulus value of the pre- scalar. By changing the value of the pre-scalar the PLL frequency range will be extended. In the proposed design we are planning to implement the digital PLL technique with self correcting DCO. The structure utilizes the DDR synthesizer as a base for generating the DCO frequency, so many methods are there to correct the DCO errors , here we detect the error or delay and correct it by using smooth jumping method. The DPLL varies from minimum system clock frequency 60 to 1489 MHZ (Minimum) maximum of GHZ frequency of any range we can generate, since our design act as a general platform for any kind of application.
GSM Based Device Controlling and Fault DetectionIJCERT
The mobile communication has expanded to a great extent such that it can be applied for controlling of electrical devices. These projects make use of this capability of mobile phone to control three electrical devices with some use of embedded technology which can be extended up to eight devices. Apart from controlling it also does the sensing of the devices. Thus a user can be able to know of the status of the devices and in addition to that the user get notified if any fault is detected. Here in the project controlling and sensing is done for three electrical devices only. According to the user need both of this can be expanded.
Design and Implementation of Digital PLL using Self Correcting DCO SystemIJERA Editor
The mainstay of the paper is to use a PLL using self healing pre-scalar. When a CMOS technology approaches to a nanometer scale, the non-idealities like variability and leakage current may affect the circuit performances. The process variability leads to the large variations to degrade the device matching and performances. The leakage current is highly dependent upon the process variations. In the existing method the key parameter is to be change the modulus value of the pre- scalar. By changing the value of the pre-scalar the PLL frequency range will be extended. In the proposed design we are planning to implement the digital PLL technique with self correcting DCO. The structure utilizes the DDR synthesizer as a base for generating the DCO frequency, so many methods are there to correct the DCO errors , here we detect the error or delay and correct it by using smooth jumping method. The DPLL varies from minimum system clock frequency 60 to 1489 MHZ (Minimum) maximum of GHZ frequency of any range we can generate, since our design act as a general platform for any kind of application.
GSM Based Device Controlling and Fault DetectionIJCERT
The mobile communication has expanded to a great extent such that it can be applied for controlling of electrical devices. These projects make use of this capability of mobile phone to control three electrical devices with some use of embedded technology which can be extended up to eight devices. Apart from controlling it also does the sensing of the devices. Thus a user can be able to know of the status of the devices and in addition to that the user get notified if any fault is detected. Here in the project controlling and sensing is done for three electrical devices only. According to the user need both of this can be expanded.
Periodic impulsive noise reduction in ofdm based power line communicationeSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Detection of heart murmurs using phonocardiographic signalseSAT Journals
Abstract The realization of cardio vascular diseases is low due to which most of the rural people were expired. The early recognisation of heart diseases is done by using phonocardiogram. This paper presents a non invasive technique to estimate the beat-to-beat information, phases and its durations, detection of heart diseases. Phonocardiogram is a representation of heart sounds done by means of ultrasonic transducer probe, LM386L which is the low voltage audio power amplifier and 8 ohms speaker. The real time and cost effective system for the heart auscultation monitoring and detection. During the cardiac cycle the heart normally produces repeatable heart sounds. However, under pathological conditions, such as with heart valves stenosis, ventricular septal defect, blood flow, turbulence may leads to the production of additional sounds called murmurs. These are random in nature, while the underlying heart sounds are being deterministic. The heart sound signal has much more information that can be assessed by the human ear are by visual inspection of the signal tracing as currently practiced. The system designed comprises of a phonocardiographic low voltage audio power amplifier circuit with LM386L and it is consist of an ultrasonic transducer probe which is used to pickup electrical signals into sound signals which is used as input for the circuit. The systolic and diastolic heart sounds are heard in the speaker. The designed circuit board is interfaced with arduino to record the analog values. These analog values are programmed in MATLAB and graphical is shown. Keywords:-Phonocardiogram, Auscultations, stenosis, Ventricular septal defect, murmurs, Arduino, Matlab
Noise Immune Convolutional Encoder Design and Its Implementation in Tanner ijcisjournal
With the rapid advances in integrated circuit(IC) technologies, number of functions on a chip was
increasing at a very fast rate, with which interconnect density is increasing especially in functional logic
chips. The on-chip noise affects are increasing and needs to be addressed. In this paper we have
implemented a convolution encoder using a technique that provides higher noise immunity. The encoder
circuit is simulated in Tanner 15.0 with data rate of 25Mbps and a clock frequency of 250MHz
NOISE IMMUNE CONVOLUTIONAL ENCODER DESIGN AND ITS IMPLEMENTATIONIN TANNERIJCI JOURNAL
With the rapid advances in integrated circuit(IC) technologies, number of functions on a chip was increasing at a very fast rate, with which interconnect density is increasing especially in functional logic chips. The on-chip noise affects are increasing and needs to be addressed. In this paper we have implemented a convolution encoder using a technique that provides higher noise immunity. The encoder circuit is simulated in Tanner 15.0 with data rate of 25Mbps and a clock frequency of 250MHz
Using EMI Analyst™ to Perform Method CS114 Analyses for MIL-STD-461EMI Software LLC
CS114 is a conducted susceptibility test method imposed on nearly all military and space electronics. EMI Analyst manages its conditional injection levels effortlessly.
Microcontroller Based Obstacle Detection Device Using Voice Signal for the V...IJMER
This paper aims in helping the visually impaired people through an electronic aid, which
senses any obstacle in the path and alarms the user of the obstacle. The device uses a simple principle of
transmitting an ultrasonic signal in the path generated by a wave generator. The signal gets reflected by
the obstacle (if any) in the path. The reflected signal is sensed by a sensor and produces a sound signal in
the form of voice. This voice signal directs the visually impaired person to identify the obstacles in front
of them
Codec Scheme for Power Optimization in VLSI InterconnectsIJEEE
This paper presents a codec scheme for optimizing power in VLSI Interconnects. It is based on the traditional bus encoding method which is considered to be one of the most effective ways of power and delay reduction. The work done aims at optimizing power by designing the scheme using Full-Custom design approach. The model has been designed and implemented using Cadence Virtuoso Analog Design Suite in 0.18µm CMOS technology. Power has been computed for different possible combinations of input data. Delay has been reckoned for the maximum power consuming input combination. Layout editor has been used to generate the physical description of the circuit. The 4 bit input data combination consuming maximum dynamic power of 6.44µW and propagation delay of 722.7ps is “1000” with previously transmitted 4 bit data being “0111”. A significant power reduction of 38.89% has been observed by designing the scheme using Full-Custom approach as compared to the conventional Semi-Custom approach of design.
Biomedical Parameter Transfer Using Wireless Communicationijsrd.com
In spite of the improvement of communication link and despite all progress in advanced communication technologies, there are still very few functioning commercial wireless monitoring systems, which are most off-line, and there are still a number of issues to deal with. Therefore, there is a strong need for investigating the possibility of design and implementation of an interactive real-time wireless communication system. In this paper, a generic real-time wireless communication system was designed and developed for short and long term remote patient-monitoring applying wireless protocol. The primary function of this system is to monitor the temperature and Heart Beat of the Patient and the Data collected by the sensors are sent to the Microcontroller. The Microcontroller transmits the data over the air. At the receiving end a receiver is used to receive the data and it is decoded and fed to Microcontroller, which is then displayed over the LCD display. If there is a dangerous change in patient's status an alarm is also sounded. The paper deals with the design and development of hardware and software for temperature and heartbeat measurement of a patient over LCD.
Communications Mining Series - Zero to Hero - Session 1DianaGray10
This session provides introduction to UiPath Communication Mining, importance and platform overview. You will acquire a good understand of the phases in Communication Mining as we go over the platform with you. Topics covered:
• Communication Mining Overview
• Why is it important?
• How can it help today’s business and the benefits
• Phases in Communication Mining
• Demo on Platform overview
• Q/A
Securing your Kubernetes cluster_ a step-by-step guide to success !KatiaHIMEUR1
Today, after several years of existence, an extremely active community and an ultra-dynamic ecosystem, Kubernetes has established itself as the de facto standard in container orchestration. Thanks to a wide range of managed services, it has never been so easy to set up a ready-to-use Kubernetes cluster.
However, this ease of use means that the subject of security in Kubernetes is often left for later, or even neglected. This exposes companies to significant risks.
In this talk, I'll show you step-by-step how to secure your Kubernetes cluster for greater peace of mind and reliability.
Contenu connexe
Similaire à Chap# 2-Multiple Access Techniques explained
Periodic impulsive noise reduction in ofdm based power line communicationeSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Detection of heart murmurs using phonocardiographic signalseSAT Journals
Abstract The realization of cardio vascular diseases is low due to which most of the rural people were expired. The early recognisation of heart diseases is done by using phonocardiogram. This paper presents a non invasive technique to estimate the beat-to-beat information, phases and its durations, detection of heart diseases. Phonocardiogram is a representation of heart sounds done by means of ultrasonic transducer probe, LM386L which is the low voltage audio power amplifier and 8 ohms speaker. The real time and cost effective system for the heart auscultation monitoring and detection. During the cardiac cycle the heart normally produces repeatable heart sounds. However, under pathological conditions, such as with heart valves stenosis, ventricular septal defect, blood flow, turbulence may leads to the production of additional sounds called murmurs. These are random in nature, while the underlying heart sounds are being deterministic. The heart sound signal has much more information that can be assessed by the human ear are by visual inspection of the signal tracing as currently practiced. The system designed comprises of a phonocardiographic low voltage audio power amplifier circuit with LM386L and it is consist of an ultrasonic transducer probe which is used to pickup electrical signals into sound signals which is used as input for the circuit. The systolic and diastolic heart sounds are heard in the speaker. The designed circuit board is interfaced with arduino to record the analog values. These analog values are programmed in MATLAB and graphical is shown. Keywords:-Phonocardiogram, Auscultations, stenosis, Ventricular septal defect, murmurs, Arduino, Matlab
Noise Immune Convolutional Encoder Design and Its Implementation in Tanner ijcisjournal
With the rapid advances in integrated circuit(IC) technologies, number of functions on a chip was
increasing at a very fast rate, with which interconnect density is increasing especially in functional logic
chips. The on-chip noise affects are increasing and needs to be addressed. In this paper we have
implemented a convolution encoder using a technique that provides higher noise immunity. The encoder
circuit is simulated in Tanner 15.0 with data rate of 25Mbps and a clock frequency of 250MHz
NOISE IMMUNE CONVOLUTIONAL ENCODER DESIGN AND ITS IMPLEMENTATIONIN TANNERIJCI JOURNAL
With the rapid advances in integrated circuit(IC) technologies, number of functions on a chip was increasing at a very fast rate, with which interconnect density is increasing especially in functional logic chips. The on-chip noise affects are increasing and needs to be addressed. In this paper we have implemented a convolution encoder using a technique that provides higher noise immunity. The encoder circuit is simulated in Tanner 15.0 with data rate of 25Mbps and a clock frequency of 250MHz
Using EMI Analyst™ to Perform Method CS114 Analyses for MIL-STD-461EMI Software LLC
CS114 is a conducted susceptibility test method imposed on nearly all military and space electronics. EMI Analyst manages its conditional injection levels effortlessly.
Microcontroller Based Obstacle Detection Device Using Voice Signal for the V...IJMER
This paper aims in helping the visually impaired people through an electronic aid, which
senses any obstacle in the path and alarms the user of the obstacle. The device uses a simple principle of
transmitting an ultrasonic signal in the path generated by a wave generator. The signal gets reflected by
the obstacle (if any) in the path. The reflected signal is sensed by a sensor and produces a sound signal in
the form of voice. This voice signal directs the visually impaired person to identify the obstacles in front
of them
Codec Scheme for Power Optimization in VLSI InterconnectsIJEEE
This paper presents a codec scheme for optimizing power in VLSI Interconnects. It is based on the traditional bus encoding method which is considered to be one of the most effective ways of power and delay reduction. The work done aims at optimizing power by designing the scheme using Full-Custom design approach. The model has been designed and implemented using Cadence Virtuoso Analog Design Suite in 0.18µm CMOS technology. Power has been computed for different possible combinations of input data. Delay has been reckoned for the maximum power consuming input combination. Layout editor has been used to generate the physical description of the circuit. The 4 bit input data combination consuming maximum dynamic power of 6.44µW and propagation delay of 722.7ps is “1000” with previously transmitted 4 bit data being “0111”. A significant power reduction of 38.89% has been observed by designing the scheme using Full-Custom approach as compared to the conventional Semi-Custom approach of design.
Biomedical Parameter Transfer Using Wireless Communicationijsrd.com
In spite of the improvement of communication link and despite all progress in advanced communication technologies, there are still very few functioning commercial wireless monitoring systems, which are most off-line, and there are still a number of issues to deal with. Therefore, there is a strong need for investigating the possibility of design and implementation of an interactive real-time wireless communication system. In this paper, a generic real-time wireless communication system was designed and developed for short and long term remote patient-monitoring applying wireless protocol. The primary function of this system is to monitor the temperature and Heart Beat of the Patient and the Data collected by the sensors are sent to the Microcontroller. The Microcontroller transmits the data over the air. At the receiving end a receiver is used to receive the data and it is decoded and fed to Microcontroller, which is then displayed over the LCD display. If there is a dangerous change in patient's status an alarm is also sounded. The paper deals with the design and development of hardware and software for temperature and heartbeat measurement of a patient over LCD.
Communications Mining Series - Zero to Hero - Session 1DianaGray10
This session provides introduction to UiPath Communication Mining, importance and platform overview. You will acquire a good understand of the phases in Communication Mining as we go over the platform with you. Topics covered:
• Communication Mining Overview
• Why is it important?
• How can it help today’s business and the benefits
• Phases in Communication Mining
• Demo on Platform overview
• Q/A
Securing your Kubernetes cluster_ a step-by-step guide to success !KatiaHIMEUR1
Today, after several years of existence, an extremely active community and an ultra-dynamic ecosystem, Kubernetes has established itself as the de facto standard in container orchestration. Thanks to a wide range of managed services, it has never been so easy to set up a ready-to-use Kubernetes cluster.
However, this ease of use means that the subject of security in Kubernetes is often left for later, or even neglected. This exposes companies to significant risks.
In this talk, I'll show you step-by-step how to secure your Kubernetes cluster for greater peace of mind and reliability.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Pushing the limits of ePRTC: 100ns holdover for 100 daysAdtran
At WSTS 2024, Alon Stern explored the topic of parametric holdover and explained how recent research findings can be implemented in real-world PNT networks to achieve 100 nanoseconds of accuracy for up to 100 days.
Why You Should Replace Windows 11 with Nitrux Linux 3.5.0 for enhanced perfor...SOFTTECHHUB
The choice of an operating system plays a pivotal role in shaping our computing experience. For decades, Microsoft's Windows has dominated the market, offering a familiar and widely adopted platform for personal and professional use. However, as technological advancements continue to push the boundaries of innovation, alternative operating systems have emerged, challenging the status quo and offering users a fresh perspective on computing.
One such alternative that has garnered significant attention and acclaim is Nitrux Linux 3.5.0, a sleek, powerful, and user-friendly Linux distribution that promises to redefine the way we interact with our devices. With its focus on performance, security, and customization, Nitrux Linux presents a compelling case for those seeking to break free from the constraints of proprietary software and embrace the freedom and flexibility of open-source computing.
Unlock the Future of Search with MongoDB Atlas_ Vector Search Unleashed.pdfMalak Abu Hammad
Discover how MongoDB Atlas and vector search technology can revolutionize your application's search capabilities. This comprehensive presentation covers:
* What is Vector Search?
* Importance and benefits of vector search
* Practical use cases across various industries
* Step-by-step implementation guide
* Live demos with code snippets
* Enhancing LLM capabilities with vector search
* Best practices and optimization strategies
Perfect for developers, AI enthusiasts, and tech leaders. Learn how to leverage MongoDB Atlas to deliver highly relevant, context-aware search results, transforming your data retrieval process. Stay ahead in tech innovation and maximize the potential of your applications.
#MongoDB #VectorSearch #AI #SemanticSearch #TechInnovation #DataScience #LLM #MachineLearning #SearchTechnology
Unlocking Productivity: Leveraging the Potential of Copilot in Microsoft 365, a presentation by Christoforos Vlachos, Senior Solutions Manager – Modern Workplace, Uni Systems
In his public lecture, Christian Timmerer provides insights into the fascinating history of video streaming, starting from its humble beginnings before YouTube to the groundbreaking technologies that now dominate platforms like Netflix and ORF ON. Timmerer also presents provocative contributions of his own that have significantly influenced the industry. He concludes by looking at future challenges and invites the audience to join in a discussion.
UiPath Test Automation using UiPath Test Suite series, part 6DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 6. In this session, we will cover Test Automation with generative AI and Open AI.
UiPath Test Automation with generative AI and Open AI webinar offers an in-depth exploration of leveraging cutting-edge technologies for test automation within the UiPath platform. Attendees will delve into the integration of generative AI, a test automation solution, with Open AI advanced natural language processing capabilities.
Throughout the session, participants will discover how this synergy empowers testers to automate repetitive tasks, enhance testing accuracy, and expedite the software testing life cycle. Topics covered include the seamless integration process, practical use cases, and the benefits of harnessing AI-driven automation for UiPath testing initiatives. By attending this webinar, testers, and automation professionals can gain valuable insights into harnessing the power of AI to optimize their test automation workflows within the UiPath ecosystem, ultimately driving efficiency and quality in software development processes.
What will you get from this session?
1. Insights into integrating generative AI.
2. Understanding how this integration enhances test automation within the UiPath platform
3. Practical demonstrations
4. Exploration of real-world use cases illustrating the benefits of AI-driven test automation for UiPath
Topics covered:
What is generative AI
Test Automation with generative AI and Open AI.
UiPath integration with generative AI
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Building RAG with self-deployed Milvus vector database and Snowpark Container...Zilliz
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Threats to mobile devices are more prevalent and increasing in scope and complexity. Users of mobile devices desire to take full advantage of the features
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Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
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PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
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The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
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39. For each channel the base station generates a unique code
that changes for every connection.
The base station adds together all the coded transmissions
for every subscriber.
The subscriber unit correctly generates its own matching
code and uses it to extract the appropriate signals.
EE-494 Wireless communication
Dr. Ibrar Ullah
40. It must be deterministic. The subscriber station must be able to
independently generate the code that matches the base station
code.
It must appear random to a listener without prior knowledge of
the code (i.e. it has the statistical properties of sampled white
noise).
The cross-correlation between any two codes must be small
The code must have a long period (i.e. a long time before the
code repeats itself).
EE-494 Wireless communication
Dr. Ibrar Ullah
41. The FEC coded Information data modulates the pseudo-random code.
Chipping Frequency (fc): the bit rate of the PN code.
Information rate (fi): the bit rate of the digital data.
Chip: One bit of the PN code.
Epoch: The length of time before the code starts repeating itself (the period of the
code). The epoch/duration must be longer than the round trip propagation delay
(The epoch is on the order of several seconds).
EE-494 Wireless communication
Dr. Ibrar Ullah
42. the bandwidth of a digital signal is twice its bit rate. The bandwidths of the information
data (fi) and the PN code are shown together. The bandwidth of the combination of the
two, for fc>fi, can be approximated by the bandwidth of the PN code.
EE-494 Wireless communication
Dr. Ibrar Ullah
43. This is a theoretical system gain that reflects the relative
advantage that frequency spreading provides. The processing
gain is equal to the ratio of the chipping frequency to the data
frequency:
There are two major benefits from high processing gain:
Interference rejection: the ability of the system to reject interference is directly
proportional to Gp.
System capacity: the capacity of the system is directly proportional to Gp.
So the higher the PN code bit rate (the wider the CDMA bandwidth), the better the
system performance.
EE-494 Wireless communication
Dr. Ibrar Ullah
44. 44
A PN generator is typically made of N cascaded flip-flop circuits and a
specially selected feedback arrangement as shown in figure below:
The flip-flop circuits when used in this way are called a shift register,
since each clock pulse applied to the flip-flops causes the contents of each
flip-flop to be shifted to the right.
The period of the PN sequence is:
PN Sequence Generation
EE-494 Wireless communication
Dr. Ibrar Ullah
45. 45
Example:
Starting with the register in state 001
the next 7 states are :
100, 010, 101, 110, 111, 011
and then 001 again and the states
repeats
The output taken from the right-most flip-flop is 1001011 and then
continue to repeat.
The three-stage shift register shown, the period is
PN Sequence Generation
EE-494 Wireless communication
Dr. Ibrar Ullah
46. 46
The tap connections are based on primitive polynomials on the order of the
number of registrars.
The polynomial should be irreducible for the sequence to be an m-sequence
and have the desired properties.
PN Sequence Generation
For example, IS-95 specifies the in-phase PN generator shall be built
based on the characteristic polynomial:
EE-494 Wireless communication
Dr. Ibrar Ullah
47. 47
IS-95 and IS-2000 use two types of m-sequences but have special names
and uses and are called:
Long codes and Short codes
Long codes and Short codes
Long code
The long PN code is generated by a 42-stage linear shift register.
The length of the Long code is
This code runs at the chip frequency of 1.2288 Mc/s
The time it takes to recycle this length of code at this speed is 41.2 days
EE-494 Wireless communication
Dr. Ibrar Ullah
48. 48
It is used to both spread the signal and to encrypt it.
A cyclically shifted version of the long code is generated by the cell phone
during call setup.
The shift is called the Long Code Mask and is unique to each phone call
Long codes and Short codes
Long Codes
EE-494 Wireless communication
Dr. Ibrar Ullah
49. Short code
The short code used in CDMA system is based on a m-sequence created
from a LFSR of 15 registers.
The code Length is L =
Long codes and Short codes
The short code repeats every 26.666 milliseconds. The sequences repeat
exactly 75 times in every 2 seconds.
These codes are used for synchronization in the forward and reverse
links and for cell/base station identification in the forward link.
EE-494 Wireless communication
Dr. Ibrar Ullah
50. 50
During call setup, the mobile looks for a short code and needs to be able
find it fairly quickly as two seconds is the maximum time that a mobile will
need to find a base station.
If one is present because in 2 seconds the mobile has checked each of
the allowed base stations in its database against the network signal it is
receiving.
Each base-station is assigned one of these codes.
Since short code is only one sequence, each station gets the same
sequence but cyclically shifted.
Long codes and Short codes
EE-494 Wireless communication
Dr. Ibrar Ullah
51. 51
PN Offset and PN Roll
Different cells and cell sectors all use the same short code, but use
different phases or shifts, which is how the mobile differentiates one base
station from another.
The phase shift is known as the PN Offset
For short code there can be 32,768 PN offsets.
The moment when the Short code wraps around and begins again is called
a PN Roll
There are actually two short codes per base station. One for each I and Q
channels to be used in the quadrature spreading and despreading of
CDMA signals.
EE-494 Wireless communication
Dr. Ibrar Ullah
52. 52
From properties of the m-sequences, the shifted version of a m-sequences
has a very small cross correlation and so each shifted code is an
independent code.
if two adjacent offsets are used, a multi-path of the leading sequence
(delayed by exactly one chip) would look identical to the lagging sequence.
In IS-95, a 64 chip separation is recommended for each adjacent station.
This gives 512 different short PN offsets used for different cells and cell
sectors, that is how the mobile differentiates one base station from another.
PN Offset and PN Roll
EE-494 Wireless communication
Dr. Ibrar Ullah