Wireless and SDR Archives | Page 4 of 23

April 12, 2026 Wireless and SDR

Why OFDM is Used in UAV Links

In a previous article on OFDM, we have seen that single-carrier systems are simpler and less power-hungry. On the other hand, OFDM slices the allocated wireless spectrum, hence making it easier to equalize in high multipath scenarios. This is why it has been the dominant technique in most high data-rate applications such as WiFi and cellular networks. However, multipath problem is relatively less severe for Unmanned Aerial Vehicles (UAVs) in non-urban settings. In this situation, UAV communication links can use both single-carrier and OFDM-based schemes. Yet, modern systems increasingly favor OFDM even though the multipath channel and frequency selectivity are

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

June 13, 2022 Wireless and 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 and 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 and 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.

Synchronization circuit for a Minimum Shift Keying (MSK) modem

April 25, 2022 Wireless and SDR

Carrier and Clock Synchronization in MSK Signals

Minimum Shift Keying (MSK) is a versatile and spectrally efficient digital modulation scheme. On this website, I have previously written a tutorial on MSK in some detail. We saw how MSK is a special case of Continuous-Phase Frequency Shift Keying (CPFSK) which is a special case of Continuous-Phase Modulation (CPM). We also explored how it can also be cast as Offset Quadrature Phase Shift Keying (OQPSK). In designing a real communication system, the design of modulators and demodulators is the easy part. The main difficulty arises from acquiring synchronization with the incoming signal. Today we investigate the carrier and timing