OFDMA
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OFDMA is a cellular air interface technology that uses orthogonal frequency division multiplexing to allow multiple users to access the network simultaneously over subsets of subcarriers. It provides superior air interfaces to CDMA and TDMA and is used in networks like WiMAX and LTE. OFDMA assigns subsets of subcarriers to individual users, whereas OFDM allocates users only in the time domain. OFDM uses a large number of subcarrier signals to carry parallel data streams.
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Which system performs better using OFDM to service two different us.pdf
Which system performs better: using OFDM to service two different users simultaneously with
two 20 MHz channels or using OFDMA to service these two users asynchronously using a 40
MHz channel? Can OFDMA achieve better performance than MU-MIMO? Justify your
reasoning in terms of the number of simultaneous users supported, multipath mitigation, and the
achievable data rate or throughput.
Hint: OFDMA may allow all channels of say the 2.4 or 5 GHz bands to be used simultaneously.
Solution
Multiple input, multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) is
the dominant air interface for 4G and 5G broadband wireless communications. It combines
multiple input, multiple output (MIMO) technology, which multiplies capacity by transmitting
different signals over multiple antennas, and orthogonal frequency-division multiplexing
(OFDM), which divides a radio channel into a large number of closely spaced subchannels to
provide more reliable communications at high speeds. Research conducted during the mid-1990s
showed that while MIMO can be used with other popular air interfaces such as time division
multiple access (TDMA) and code division multiple access (CDMA), the combination of MIMO
and OFDM is most practical at higher data rates.
MIMO-OFDM is the foundation for most advanced wireless local area network (wireless LAN)
and mobile broadband network standards because it achieves the greatest spectral efficiency and,
therefore, delivers the highest capacity and data throughput. Greg Raleigh invented MIMO in
1996 when he showed that different data streams could be transmitted at the same time on the
same frequency by taking advantage of the fact that signals transmitted through space bounce off
objects (such as the ground) and take multiple paths to the receiver. That is, by using multiple
antennas and precoding the data, different data streams could be sent over different paths.
Raleigh suggested and later proved that the processing required by MIMO at higher speeds
would be most manageable using OFDM modulation, because OFDM converts a high-speed data
channel into a number of parallel, lower-speed channels.
OFDMA with 40 MHz will perform better.
Which system performs better using OFDM to service two different us.pdf
What is outsourcing?
- When would it make sense based on quantitative factors only for companies like Toyota and
Boeing to outsource?
- What are 3 qualitative factors that companies like Toyota and Boeing should consider before
outsourcing?
Solution
Outsourcing is when one company hires anther company to perform some of its functions on a
contract basis.The main motive is to save costs and increase profits.For eg. A call centre.
It would not make sense for companies like Toyota and Boeing to outsource based only on
quantitative factors
such as costs.
Qualitaive factors they should consider before outsourcing:
1) Employee Morale : outsourcing leads to lay offs , which may have an adverse effect on the
remaining employees
who may fear that they may be the next to be laid off.
2)Quality :The quality of the goods or services supplied by the external company should be good
, other
wise the reputation of these companies is at stake.
3) Stability of the external company: The company should be financially stable , because if it
shuts down,
it will interrupt the activities of the outsoucing company ( ie Boeing and Toyota).
B.I.T , MESRA [M.Tech] Assignment : MULTIPLE ACCESS TECHNIQUES FOR WIRELESS ...
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FDMA-TDMA-CDMA
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.
v unit (1).pptx
The document discusses various multiple access techniques used in wireless communication systems to allow multiple users to access a shared radio channel simultaneously. It describes Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), and Space Division Multiple Access (SDMA). FDMA divides the bandwidth into different frequency channels. TDMA divides the time dimension into different time slots. CDMA uses unique codes to identify users within the same frequency band. SDMA enables spatial separation of users within the same frequency and time. The document provides details on the principles, advantages, and disadvantages of each multiple access technique.
OFDM.ppt
OFDM is a digital multi-carrier modulation technique that encodes data over multiple carrier frequencies. It splits a high-rate data stream into multiple lower-rate streams that are transmitted simultaneously over separate subcarriers. The subcarriers are chosen so they are orthogonal to each other, allowing them to be packed closely together without interference. OFDM provides high spectral efficiency, resilience to radio interference and multipath distortion, and works well for broadband applications including wireless networks, digital television and audio broadcasting.
What is the main difference between single carrier and ofdm yahoo! answers
Single carrier (SC) transmission has a lower peak-to-average power ratio than orthogonal frequency-division multiplexing (OFDM). SC frequency-division multiple access (SC-FDMA) divides the frequency band into subsets, assigning each user a different subset, whereas OFDM divides data into multiple parallel streams and assigns each stream a unique subcarrier. Both SC-FDMA and OFDM use guard intervals and fast Fourier transforms to combat interference, but SC-FDMA applies these on the transmitter side while OFDM applies them on the receiver side. SC-FDMA has a lower peak-to-average power ratio than OFDM, making it more suitable for applications with power constraints like uplink mobile communications.
scribd.vpdfs.com_multiple-access-fdma-cdma-tdma-sdma-dsss-fhss-aloha-packet-r...
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.
Chapter8,,,,,,,multiple access
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.
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TIME DIVISION MULTIPLEXING TECHNIQUE FOR COMMUNICATION SYSTEM
Time Division Multiplexing (TDM) is a method of transmitting multiple signals over a single communication channel by dividing the signal into many segments, each having a very short duration of time. These time slots are then allocated to different data streams, allowing multiple signals to share the same transmission medium efficiently. TDM is widely used in telecommunications and data communication systems.
### How TDM Works
1. **Time Slots Allocation**: The core principle of TDM is to assign distinct time slots to each signal. During each time slot, the respective signal is transmitted, and then the process repeats cyclically. For example, if there are four signals to be transmitted, the TDM cycle will divide time into four slots, each assigned to one signal.
2. **Synchronization**: Synchronization is crucial in TDM systems to ensure that the signals are correctly aligned with their respective time slots. Both the transmitter and receiver must be synchronized to avoid any overlap or loss of data. This synchronization is typically maintained by a clock signal that ensures time slots are accurately aligned.
3. **Frame Structure**: TDM data is organized into frames, where each frame consists of a set of time slots. Each frame is repeated at regular intervals, ensuring continuous transmission of data streams. The frame structure helps in managing the data streams and maintaining the synchronization between the transmitter and receiver.
4. **Multiplexer and Demultiplexer**: At the transmitting end, a multiplexer combines multiple input signals into a single composite signal by assigning each signal to a specific time slot. At the receiving end, a demultiplexer separates the composite signal back into individual signals based on their respective time slots.
### Types of TDM
1. **Synchronous TDM**: In synchronous TDM, time slots are pre-assigned to each signal, regardless of whether the signal has data to transmit or not. This can lead to inefficiencies if some time slots remain empty due to the absence of data.
2. **Asynchronous TDM (or Statistical TDM)**: Asynchronous TDM addresses the inefficiencies of synchronous TDM by allocating time slots dynamically based on the presence of data. Time slots are assigned only when there is data to transmit, which optimizes the use of the communication channel.
### Applications of TDM
- **Telecommunications**: TDM is extensively used in telecommunication systems, such as in T1 and E1 lines, where multiple telephone calls are transmitted over a single line by assigning each call to a specific time slot.
- **Digital Audio and Video Broadcasting**: TDM is used in broadcasting systems to transmit multiple audio or video streams over a single channel, ensuring efficient use of bandwidth.
- **Computer Networks**: TDM is used in network protocols and systems to manage the transmission of data from multiple sources over a single network medium.
### Advantages of TDM
- **Efficient Use of Bandwidth**: TDM all
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OFDMA
- 1. OFDMA • (Orthogonal Frequency Division Multiple Access) A cellular air interface based on OFDM for multiple, simultaneous users used in communications networks such as WiMAX and LTE, OFDMA provides air interfaces that are superior to CDMA and TDMA.
- 2. What does Ofdma do? • Orthogonal frequency-division multiple access (OFDMA) is a multi-user version of the popular orthogonal frequency-division multiplexing (OFDM) digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users.
- 3. What is the difference between OFDM and Ofdma and what is in common? • The main difference between an OFDM and an OFDMA (Orthogonal Frequency Division Multiple Access) system if the fact that in the OFDM the user are allocated on the time domain only while using an OFDMA system the user would be allocated by both time and frequency
- 4. What is OFDM and how it works? • OFDM is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method. A large number of closely spaced orthogonal sub-carrier signals are used to carry data on several parallel data streams or channels.
- 5. Figure 1
- 6. Figure 2