Wireless/SDR Archives | Page 18 of 21

Computing noise power within a specified bandwidth

August 15, 2016 Wireless/SDR

Additive White Gaussian Noise (AWGN)

The performance of a digital communication system is quantified by the probability of bit detection errors in the presence of thermal noise. In the context of wireless communications, the main source of thermal noise is addition of random signals arising from the vibration of atoms in the receiver electronics. You can also watch the video below. The term additive white Gaussian noise (AWGN) originates due to the following reasons: [Additive] The noise is additive, i.e., the received signal is equal to the transmitted signal plus noise. This gives the most widely used equality in communication systems. \begin{equation}\label{eqIntroductionAWGNadditive} r(t) = s(t)

Coverage and throughput in different bands

December 20, 2021 Wireless/SDR

Channel Propagation Effects in mmWave Systems

In a previous article, we have discussed in detail the free space propagation in mmWave systems. We saw that the received power at any distance is independent of the carrier frequency as long as the effective antenna aperture is taken into account. Today, we describe the role of atmospheric effects such as water vapors, oxygen, rain and penetration loss in materials that impact the signal propagation at higher carrier frequencies. Important parameters of small-scale fading in a wireless channel such as delay spread and Doppler spread are also explained in the context of mmWave systems. Atmospheric Effects In realistic channels,

August 14, 2016 Wireless/SDR

Modulation – From Numbers to Signals

The purpose of digital communications is to send digital data across a channel which can be wireless telephone lines coaxial cable optical fiber Ethernet USB chips on a printed circuit board Considering the examples shown in Figure above, clearly neither a bit sequence nor a symbol sequence can be transmitted on their own through these channels — as they are nothing more than a set of numbers. Therefore, a signal waveform is an appropriate tool that can travel down the channel and carry the required information — just like a train running on its track and carrying the load. For

An illustration of wiping off the modulation process without any training information

August 11, 2016 Wireless/SDR

Non-Data-Aided Carrier Phase Estimation

A carrier phase offset rotates the Rx constellation causing decision errors even in a perfectly noiseless environment. One of the techniques used to overcome this problem is to insert a known sequence at the start of the transmission known as a preamble. Then, the Rx can utilize these known symbols in the arriving signal to estimate the carrier phase and de-rotate the constellation. However, inserting a known sequence within the message decreases the spectral efficiency of the system. To avoid this cost, a phase estimator (as well as estimators for other distortions) can be derived in a non-data-aided fashion. One

Square-Root Raised Cosine (SR-RC) spectrum with different excess bandwidths

August 7, 2016 Wireless/SDR

Modulation Bandwidths

From the article on pulse shaping, we can correctly determine the occupied bandwidth for each modulation scheme where the Square-Root Raised Cosine spectrum shows the bandwidth of a Square-Root Raised Cosine pulse shape as $0.5(1+\alpha)R_M$. Also, we have discussed earlier that the spectrum approximately remains the same, provided that there is enough randomness in bit stream and the resulting symbols are equally likely and independent from each other. Therefore, the bandwidth for a PAM modulated signal can be given as \begin{equation}\label{eqCommSystemBWPAM} BW_{\text{PAM}} = 0.5\left(1+\alpha\right)R_M \end{equation} QAM is basically a similar modulation scheme except that it is modulated on a carrier.