OFDM

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Symbol Error rate for QAM (16, 64, 256,.., M-QAM)

by Krishna Sankar on January 1, 2012

plot_symbol_error_rate_16qam_64qam_256qam_ofdm_awgn

In May 2008, we derived the theoretical symbol error rate for a general M-QAM modulation (in  Embedded.com, DSPDesignLine.com and dsplog.com) under Additive White Gaussian Noise. While re-reading that post, felt that the article is nice and warrants a [...]

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Quiz on IEEE 802.11a specifications

by Krishna Sankar on October 7, 2009

The IEEE 802.11a specifications are used by many to understand a wireless communication link built using OFDM. In this post, I have put together a set of 10 multiple choice questions based on 802.11a specifications. [...]

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Inter Carrier Interference (ICI) in OFDM due to frequency offset

by Krishna Sankar on August 8, 2009

Plot of the magnitude of error vs frequency offset in OFDM

In this post, let us evaluate the impact of frequency offset resulting in Inter Carrier Interference (ICI) while receiving an OFDM modulated symbol. We will first discuss the OFDM transmission and reception, the effect of [...]

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BER for BPSK in OFDM with Rayleigh multipath channel

by Krishna Sankar on August 26, 2008

BER plot for BPSK with OFDM modulation in a 10-tap Rayleigh fading channel

Mr. Lealem Tamirat, in a comment on BER for BPSK in Rayleigh channel, wondered about the performance of an OFDM modulated system in a frequency selective Rayeligh fading channel. My response was that, Though the [...]

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Negative Frequency

by Krishna Sankar on August 8, 2008

Negative Frequency Real Complex Sinusoidal

Last week, I received an email from Mr. Kishore. He was wondering about the physical significance of negative frequency. Does negative frequency really exist? Though I have seen conflicting views on the net (thread in [...]

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Trying out PAPR reduction for OFDM by multiplication with j

by Krishna Sankar on July 2, 2008

OFDM PAPR for BPSK/QPSK with j rotation

In this post, we will explore a probable way of reducing PAPR (peak to average power ratio) in OFDM by changing the phase of some of the subcarriers. This is in response to the comment [...]

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BPSK BER with OFDM modulation

by Krishna Sankar on June 10, 2008

BER plot for BPSK using OFDM modulation

Oflate, I am getting frequent requests for bit error rate simulations using OFDM (Orthogonal Frequency Division Multiplexing) modulation. In this post, we will discuss a simple OFDM transmitter and receiver, find the relation between Eb/No [...]

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Frequency offset estimation using 802.11a short preamble

by Krishna Sankar on March 3, 2008

plot of frequency offset estimate using 802.11a short preamble

From the previous post on OFDM (here), we have understood that an OFDM waveform is made of sum of multiple sinusoidals (also called subcarriers) each modulated independently. In this post, let us try to understand [...]

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Peak to Average Power Ratio for OFDM

by Krishna Sankar on February 24, 2008

cdf_papr_ofdm_bpsk

Let us try to understand peak to average power ratio (PAPR) and its typical value in an OFDM system specified per IEEE 802.11a specifications. What is PAPR? The peak to average power ratio for a [...]

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Cylcic prefix in Orthogonal Frequency Division Multiplexing

by Krishna Sankar on February 17, 2008

ofdm symbol with multipath

In a previous post (here), we discussed in brief, Orthogonal Frequency Division Multiplexing (OFDM) transmission. Let us know probe bit more into the motivation of cyclic prefix (aka guard interval) associated with each OFDM symbol. [...]

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Understanding an OFDM transmission

by Krishna Sankar on February 3, 2008

spectrum of an OFDM transmit waveform

Let us try to understand simulation of a typical Orthogonal Frequency Division Multiplexing (OFDM) transmission defined per IEEE 802.11a specification. Orthogonal pulses In a previous post (here ), we have understood that the minimum frequency [...]

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