From the category archives:

Receiver

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

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 frequency offset and later we will define the loss of orthogonality and resulting signal to noise ratio (SNR) loss due [...]

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Softbit for 16QAM

In the post on Soft Input Viterbi decoder, we had discussed BPSK modulation with convolutional coding and soft input Viterbi decoding in AWGN channel. Let us know discuss the derivation of soft bits for 16QAM modulation scheme with Gray coded bit mapping. The channel is assumed to be AWGN alone.

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Gray code to Binary conversion for PSK and PAM

Given that we have discussed Binary to Gray code conversion, let us discuss the Gray to BInary conversion.
Conversion from Gray code to natural Binary
Let be the equivalent Gray code for an bit binary number with representing the index of the bit.
1. For ,
i.e, the most significant bit (MSB) of [...]

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Need for I-Q modulator and demodulator

Post describes about the need for I-Q modulation by comparing the spectral efficiency of passband PAM and passband QAM.

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Frequency offset estimation 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 the estimation of frequency offset in a typical OFDM receiver (using the short preamble specified per IEEE 802.11a specification as [...]

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First order digital PLL for tracking constant phase offset

Considering a typical scenario where there might exist a small phase offset between local oscillator between the transmitter and receiver.

Figure 1 :
Transmitter receiver with constant phase offset
In such cases, it might be desirable to estimate and track the phase offset such that the performance of the receiver does not degrade.

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