Wireless/SDR Archives | Page 3 of 22

Data symbols riding on the subcarriers experience a rotation due to residual carrier frequency offset and sampling frequency offset

August 29, 2022 Wireless/SDR

Effect of a Sampling Clock Offset on an OFDM Waveform

In an earlier article on the impact of a sampling clock offset on a single-carrier waveform, we explained the nature of a Sampling Clock Offset (SCO), i.e., a difference in sampling clock frequency between the Tx and the Rx. This is also known as a symbol timing frequency offset. The meaning of a sampling clock offset for a slow Rx clock that skips some samples within an interval is visually demonstrated in the figure below. In the context of OFDM systems, a previous article describes how the normalized Carrier Frequency Offset (CFO) and the normalized Symbol Timing Offset (STO) affect

Reconfigurable Intelligent Surfaces (RIS) concept

July 25, 2022 DSP / Wireless/SDR

Reconfigurable Intelligent Surfaces (RIS) – A Tutorial

For each generation of cellular networks, there is a significant jump in data rates due to the rising demand and novel use cases from emerging applications and associated ecosystems. Some examples in 6G networks are driverless and collaborative transportation, joint communication, localization and sensing, e-health and tactile Internet. Therefore, at the start of each concept-to-deployment cycle, engineers and researchers propose, evaluate and experiment with new ideas, preferably one or two disruptive technologies that can help them meet their targets. For 5G systems, these technologies appeared in the form of a large number of antennas (massive MIMO) and usage of higher

Computation of the metric involves a correlation sum at a time difference of half symbol duration

June 13, 2022 Wireless/SDR

Timing Synchronization in OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) has been the vehicle driving most high rate wireless communication systems in the world today. Some of the notable examples are our WiFi, 4G and 5G technologies. See the interesting LoRa PHY for modulation techniques based on frequency shift – chirp spread spectrum that utilize many of the concepts from OFDM for algorithm design. As a background, we have also discussed before the impact of a timing error on an OFDM signal. It was observed that an integer timing offset does have affect the performance as long as it within certain boundaries. A fractional timing

September 26, 2022 Wireless/SDR

On TeraHertz (THz) Band for Wireless Communication

Larger bandwidth has been the single most contributing factor in higher data rates throughout the history of wireless communication. In the past decade, this resulted in expansion towards mmWave bands that were adopted in 5G systems. Now the trend is continuing towards Tera Hz (THz) bands where large swathes of bandwidth are available for instantaneous and seamless transfer of huge amounts of information. This is because symbol rate $R_M$ is directly proportional to the bandwidth in digitally modulated signals. $R_M=\frac{1}{T_M} \propto B$ This is shown in the figure below where a high data rate implies a short symbol

$A comparison of the input to a symbol-spaced versus fractionally-spaced equalizer$

May 2, 2022 Wireless/SDR

A Classification of Equalization Techniques

We have seen before how a wireless channel distorts the Rx signal. The main task of DSP/comms engineer is to remove the Inter-Symbol Interference (ISI) from the Rx samples and recover the correct symbols. Equalization refers to any signal processing technique that eliminates or reduces this ISI before symbol detection. The output of an equalizer should be a Nyquist pulse for a single symbol case from which digital data can be recovered. A conceptual block diagram of such a process is shown below. The equalizer performs the bulk of the signal processing operations required at the Rx for proper demodulation.