LTE – RAYmaps

October 14, 2018December 22, 2018Antennas, BER Performance, Fundamentals, LTE

Massive MIMO Fundamentals and Code

Background Just like different frequency bands and time slots can be used to multiplex users, spatial domain can also be exploited to achieve the same result. It is well known that if there are 4 transmit antennas and 4 receive antennas then four simultaneous data streams can be transmitted over the air. This can be scaled up to 8 x 8 or in the extreme case to 128 x 128. When the number of transmit or receive antennas is greater than 100 we typically call it a Massive MIMO scenario and we need specialized signal processing techniques to handle this […]

February 9, 2018October 20, 2018Antennas, BER Performance, Channel Modeling, LTE

Fundamentals of Linear Array Processing – Receive Beamforming

In the previous two posts we discussed the fundamentals of array processing particularly the concept of beamforming (please check out array processing Part-1 and Part-2). Now we build upon these concepts to introduce some linear estimation techniques that are used in array processing. These are particularly suited to a situation where multiple users are spatially distributed in a cell and they need to be separated based upon their angles of arrival. But first let us introduce the linear model; I am sure you have seen this before. x=Hs+w Here, s is the vector of symbols transmitted by M users, H […]

January 27, 2018September 6, 2019Antennas, Fundamentals, LTE, WiFi

Basics of Beamforming in Wireless Communications

In the previous post we had discussed the fundamentals of a Uniform Linear Array (ULA). We had seen that as the number of array elements increases the Gain or Directivity of the array increases. We also discussed the Half Power Beam Width (HPBW) that can be approximated as 0.89×2/N radians. This is quite an accurate estimate provided that the number of array elements ‘N’ is sufficiently large. But the max Gain is always in a direction perpendicular to the array. What if we want the array to have a high Gain in another direction such as 45 degrees. How can […]

November 24, 2017November 25, 2017Fundamentals, LTE, Network Planning

Open Signal Coverage Maps for Pakistan

Open Signal is a mobile application that collects the data about your wireless network (2G/3G/4G) and generates coverage maps and host of other reports. The data is collected in the background while the user is busy in his daily routines. But data can also be collected on the request of the user. This is much better than drive testing since the data is collected in real life scenarios and on thousands of different devices that are in use. The app works while the user is indoor or outdoor, at rest or in motion, on land or on water, at sea […]

August 24, 2017August 28, 2017BER Performance, Channel Modeling, LTE, WiMAX

BER for BPSK-OFDM in Frequency Selective Channel

As the data rates supported by wireless networks continue to rise the bandwidth requirements also continue to increase (although spectral efficiency has also improved). Remember GSM technology which supported 125 channels of 200KHz each, which was further divided among eight users using TDMA. Move on to LTE where the channel bandwidth could be as high as 20MHz (1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz and 20MHz are standardized). This advancement poses a unique challenge referred to as frequency selective fading. This means that different parts of the signal spectrum would see a different channel (different amplitude and different phase offset). Look at […]

August 22, 2017August 22, 2017Channel Modeling, Fundamentals, LTE

Rayleigh Fading Envelope Generation – Python

When wireless signals travel from a transmitter to a receiver they do so after reflection, refraction, diffraction and scattering from the environment. Very rarely is there a direct line of sight (LOS) between the transmitter and receiver. Thus multiple time delayed copies of the signal reach the receiver that combine constructively and destructively. In a sense the channel acts as an FIR (finite impulse response) filter. Furthermore since the transmitter or receiver may be in motion the amplitude and phase of these replicas varies with time. There are several methods to model the amplitude and phase of each of these […]

Eclipse

Eclipse 1.0 – A Paradigm Shift in RF Planning NEW: Simulation of a Moving Transmitter (such as a car) NEW: Simulation of a Moving Transmitter (such as a pedestrian) Radio frequency planning is an essential component of network planning, roll-out, up-gradation, expansion etc. Several methods can be adopted for this from something as simple as free space models, empirical path loss models to the significantly more complicated, time consuming and expensive drive testing. Drive testing gives very accurate results but these results can be rendered useless by changing the position of an antenna or the tilt or transmit power of […]

Udemy Course

Introduction to Wireless Communications • In this course you will learn the basic principles of wireless communications from 1G to 5G and beyond. You will learn about frequency reuse, capacity, channel coding, modulation and demodulation, OFDM, MIMO, and a host of other topics. • This course is for you if you are a student and have just started learning about wireless communications or if you are a guy in the field who wants to get a better handle on the fundamental concepts of wireless communications. Here is the link to the course.

October 1, 2014October 31, 2014Channel Modeling, Fundamentals, LTE

Modified Young’s Fading Simulator

In the previous posts we had discussed generation of a correlated Rayleigh fading sequence using Smith’s method [1] and Young’s modification of Smith’s method [2]. The main contribution of Young was that he proposed a mechanism where the number of IDFTs was reduced by half. This was achieved by first adding two length N IID zero mean Gaussian sequences filtered by the filter F[k] and then performing the IDFT on the resulting complex sequence. This was different to Smith’s method where the IDFT was performed simultaneously on two branches and then the outputs of these branches were added in quadrature […]