Communication – SYMON MUTHEMBA

FPGAs for Innovating Digital Communication Interfaces

symonmk — Mon, 28 May 2018 19:26:46 +0000

It’s 11th May, and we just arrived at a client’s studio at 11:45pm. I assure my colleague that we’ll get it right this time. Our job that night was to link two studios over an Ethernet connection. Simple enough despite the fact that neither of us had done it before. We had gone through the manuals over and over again, 4 different manuals in fact, that’s why I felt certain, at least 80% certain it would be possible. In the end, we achieved connecting two LAWO audio engines over a VLAN network that could send and receive digital audio channels over MADI (AES 10). More on that later. After our 5 hour stint, I couldn’t help wonder how even such an interface was achieved. In this post I cover what it takes for hardware and communications engineers to prototype, test and innovate such interfaces using FPGAs. Field Programmable Gate Arrays (FPGAs) FPGAs, Figure 1, are re-programmable silicon integrated circuits developed by Xilinx in 1984. FPGAs are what exist between ASICs (application specific integrated circuits) and general purpose processors. This means that FPGAs can be programmed to perform one complex task and later be fully reprogrammed to perform another. This flexibility is why FPGAs have become increasingly popular for prototyping and deploying custom functionality. Programming for FPGAs can be done with low level (digital design) or high level (C code) programming environments. These software then compile the code into a bitstream or configuration file that reconfigures the internal circuitry of the FPGA. Some advantages of using FPGA technology over the common microprocessor include: High performance. As FPGAs are custom programmed chips for a specific functionality, data (signal) processing performance is high as applications have full control of processing cycles as well as inputs and outputs. Rapid prototyping. With the recent improvements in high level design, engineers spend less time developing and prototyping FPGA functionalities. Also, since FPGAs are re-programmable iteration is faster as compared to ASICs. Low costs. Consider ASICs, they’re manufactured once to handle specific tasks. If a customer’s requirements change they have to obtain a new chip (often a new device altogether) with more functionality. FPGAs recognize the need to change the functionality of the chip as the user’s requirements change. Can be used long-term. In this post we are about to discuss FPGA use in digital communication interface design. However, we know that standards are ever changing with the market. Luckily, with FPGAs you can perform field updates years after the initial installation. FPGA use in Digital Communications Applications for FPGAs span across different industries like medical electronics, aerospace and defense, broadcast and pro A/V, consumer electronics, wired and wireless communication and manufacturing. I take a special interest in communications and will cover that. You may be wondering, what was I dealing with that night? Who’s MADI? MADI is Multichannel Audio Digital Interface (AES 10) which you can read more about here. In summary, MADI is an interface that can carry multiple channels of digital audio (one interface port can carry 64 mono channels!) over coaxial or optical fiber up to 2km! What the exclamation points signify in the last sentence is that MADI is a capable system for large pro A/V and broadcast applications. Its scalability has made it increasingly attractive in such applications. We carried the MADI channels over the RAVENNA (AES67) media-over-IP standard. RAVENNA is an open standard for carrying real-time media over an IP network. With this in mind, we see how such an interface and a network can be made possible with FPGA boards and a can-do attitude. Implementation To understand how this can be implemented, we start with the understanding what is going on inside FPGAs. A single chip has three parts to it: input/output blocks, logic blocks and programmable routes. During development cycles, you are in full control of these 3 segments to configure to your specific application. Then comes the interesting bit of (re)programming. In the not so distant past, FPGAs were mostly programmed using hardware description languages (HDL) such as VHDL and Verilog. That was much harder and not so friendly to most programmers. Only recently have development being made easier with the SDAccel development environment. With this, applications can be built in C/C++. A popular programming and design suite is the Xilinx ISE. Now back to our work today. To start developing for a particular protocol, you need to identify all the technical specifications with that protocol. For MADI you are required to know the electrical characteristics and data organisation, Figure 3, of the protocol. Additional circuitry should also be accounted in design as the final system will be a combination of input and output ports. Then reference the timing diagram to define the logical signal flow. This simple tutorial shows how one can program an FPGA board to accept audio signals and transmit them over a MADI channel. Your Future with FPGA As we develop more complex systems, we’ll paradoxically need simpler communication interfaces. FPGA based solutions work best when ideas are still experimental and budgets are limited. They provide a simple solution to the interface I described in the first chapter. (FPGAs are just one way they made it possible, in reality it could be with ASICs or DSPs) In the IoT industry, FPGAs are popular in interface design. Even in processing, FPGAs are currently being used to replace power hungry GPUs and inflexible ASICs. This leads to smaller, power efficient and future-proofed systems. (The IoT industry is shrouded in uncertainty due to continuous development of telecommunication technologies as I discussed before.) When doing this research, I was humbled by the vast information that already existed on this topic. I’ll be sure to dive deeper and experiment with this. The learning curve seems pretty steep, but that’s why I always carry my harness. Badum tss! Thank you if you have made it this far. I’ll be happy to know more about this topic from you so let’s […]

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Off-Grid Communications For The Masses: Smart Metering

symonmk — Mon, 30 Apr 2018 20:50:28 +0000

In East Africa, a large percent of the population still does not have access to electrical energy and its benefits. To address this, several companies have developed micro-grids to provide AC power to rural East Africa. In order to sustain these grids, a remote, robust communication system has to be developed for purposes of metering and billing. In this post, I propose several efficient designs of a communication system that could be used to monitor and manage off-grid customers. Specifically, it proposes the technologies that can be used, the hardware and software implementation of such as system and how it can make business sense addressing equipment and operation costs. This post proposes a communications system that tackles the stated situation within the boundaries of the limitations set by a real-world scenario, i.e. budget, energy supply and manpower. A comprehensive approach to systems design is valuable to ensure the sustainability of such a project. Sections in this post will cover the hardware, communications channels and protocols, remote monitoring systems and software that can be used to solve the stated design issue. The goal is to provide micro-grid providers with a trustworthy system for off-grid power management as well as help the locals with a solution that sufficiently caters to their needs. Hardware Implementation A reliable remote metering system has to have a few basic characteristics: A smart metering system that connects every household, enabling 2-way data transfer between the customer and utility provider A network technology to enable the 2-way communication (fixed wired or wireless) A software system that actively manages the billing system and analyses usage data With a system defined as in Figure 1, we can start to see how we can bring together the hardware components. Smart Metering Smart meters are already in the market, such as Hexing Electric HXE 110-KP single phase prepayment smart meter and ZTE ZX E211, Figure 2, single phase prepayment smart meter. These meters meet Standard Transfer Specification (STS) standards and are fit for our application. The ZX E211 is the preferred choice here as its supports a variety of communication protocols (RS485, M-BUS, ZIGBEE, RF-MESH, PLC and GPRS). We will see how these communication protocols will be used in this post. ZTE ZX E211 LoRa based meter is particularly useful in long distance communication and allows us to adjust several parameters such as the transmission rate and frequency. The main feature is its low power consumption with a transmit current of less than 90mA@ 17dBm, receive current less than 13mA and standby current less than 0.7 uA. Since data communication may occur only few times a day, a majority of the consumption will be the standby current. Depending on the data that is provided by this meter, or a comparable one in the market, we may choose to consider meters that do not conform to STS standards. This may help us with communication protocols unavailable to us but may limit us in scaling and future upgrades with the national grid. Fabrication of a communications device alongside the meter may be required to send more usage statistics and deliver the desired data. This can be used for analysis to improve the overall system. This can be covered in a future post with AVR, PIC or FPGA as the processing IC in our DIY smart meter. Communication System This post will discuss two concepts of a smart meter communications in a rural area based on two assumptions: Location size – Are the residents physically close to each other or spread out? Terrain – Is the area flat or hilly? Dense vegetation cover or dry grassland? To meet the requirements of the location, I propose two systems that can be established. They are the RF-MESH network and RF-STAR network. Both networks rely on wireless channels to carry data. RF-MESH Network This type of network allows for data transmission via other wireless devices via a mesh (chain) network using a low power transceiver radio. This network is suitable for close-knit residential areas with few obstacles and is cheap to implement and scale. The architecture consists of low power transceiver radios per every meter box and data concentrators as in Figure 3. A proposed transceiver is the Silicon Labs Si4463 chip that facilitates the RF communications link. This is a transceiver I’ve worked with before on a previous project. Schematics of the full transceiver system is covered here. It is a low power transceiver with up to 20dBm (100mW) transmitting output power and a receiving sensitivity of -117dBm. Its wireless frequency band is 433.4 – 473.0MHz, and up to 100 channels can be set up with a channel stepping of 400 kHz. A serial port baud rate of 2400bps allows for a baud rate in air of 5000bps and a wireless receiving sensitivity of -117dBm. This gives an operating range of 1000m at clear line of sight between modules under ideal conditions. A concentrator can then be installed somewhere central in the village to aggregate the data of multiple smart meters and one concentrator may support hundreds of smart meters. This system is immune to sudden channel blocking as communication can flow using alternative paths. The DRF1110N20-C concentrator works well with DRF1110N20-N network nodes on a sub 1GHz channel. The concentrator can then upload the received data to micro-grid databases at different times of the day depending on the availability of the data network. RF-STAR Network This network type is of a point to multi-point (PtMP) configuration. This communication system is admittedly more expensive than the RF-MESH network but is suitable in hilly terrains with thick vegetation and obstacles. The architecture consists of high-power radio transceivers with a line-of-sight to an omni-directional antenna radio as in Figure 4. To implement this system, a 2.4GHz ISM channel may be used. A clear line of sight from a transmitter antenna to the receiver should be established, I recently talked about the art of obtaining strong microwave links. The smart meter information […]

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Simplification in Design of Wireless Systems: 5 Useful Steps

symonmk — Fri, 20 Apr 2018 08:02:26 +0000

As we all know, wireless is the preferred method of connectivity between most of our devices. This is going to take more precedence in coming years. The number of connected devices per person and the demand for fast, reliable content delivery within a network is rapidly increasing. Add that to the already ongoing craze of developing IoT devices and the super-scaling of server farms to support them. In my view, RF, DSP and embedded systems engineers will have a lot going on. This shift is largely dependent on the wireless systems we build. In this post, I try to figure out the best way forward in design of wireless systems. The RF spectrum houses a number of wireless standards and medium in use today, these include WiFi, Bluetooth, FM broadcast, DVB-T, DAB, GSM, UTMS, LTE, WLAN, radar. The upcoming 5G standards are yet to be agreed upon as I illustrated here, but we can consider some technologies already in use today such as MIMO and MU-MIMO. Engineers responsible for the development of these systems are aware of the standards involved, however, they are required to understand a vast number of fields during the design phase that implementation takes a lot of time. This, of course, is uneconomical in the fast paced world we live in. Fortunately, engineers have figured out that the design process could be simplified into 5 major blocks: Modelling and simulation of digital, RF and antenna systems Optimization of design algorithms Automatic HDL and C code for hardware and software implementation Prototype design and testing with SDR hardware Iterative verification using model as a reference Modelling and Simulation There are a number of softwares in use for modelling. In today’s case, we will consider MATLAB (free alternative GNU Octave). MATLAB is a renowned development kit for engineers and scientists. It is rare that you find something you can’t do with this software and its additional toolboxes. Must be why it costs a kidney, but it’s a good place to start. Simulink is an environment within MATLAB that you use to perform model-based design. I’ve developed a simple communications link, Figure 1, that I can use as a basis of further developments. The model in Figure 1 is initiated by the following script: The model above used the DSP System Toolbox and Communication System Toolbox. This model can be useful in the following ways: a starting point of system level design and verification a test-bench of design algorithms written in C language a point of generation of C or HDL code for use in DSP/FPGA implementation This model also allows us to simulate the results of our input and process variables to ensure we are getting the desired outputs. Algorithm Design and Optimization Algorithms are the coded processes within a process block of a program. It defines what steps are in between the START and STOP operations of a process. Simple well known algorithms are flow control loops, error handling and on higher level languages we have object oriented programming (OOP). A while back I wrote an article touching on FFT algorithms. Many programming environments are set up with debugging features for your code. They analyze and give warnings of bad syntax and compile errors. This is particularly useful before running bad code into your hardware that may bring firmware failure. The best environments go a step further and allow you to optimize your code. You can set break points to see what happens when your program reaches a certain step, allowing you to tweak your variables accordingly. Very useful in precise calculations, characteristic of antenna design. A feature of MATLAB called Profiler allows you to run your algorithm while measuring its performance. It then generates a profile with details of the areas of your code that could use some improvement. This is based on the time the section took to run and how much of the processing resources it required. HDL and C code Generation Hardware Description Language (HDL) and C/C++ language are pretty similar languages used in design and implementation of integrated circuits on supported microcontrollers, microprocessors or FPGA devices. They are the core of every embedded system, like in Figure 2, a Xilinx FPGA board. While developing complex wireless systems involving several devices, it is inefficient to separate simulated algorithms and IC programming. A software like MATLAB enables the automatic generation of HDL and C code using MATLAB Coder. To illustrate, we will generate C code from a Kalman filter algorithm. A Kalman filter is an optimal estimation algorithm used for parameter prediction. It is quite popular and used in the fields of vehicle navigation and guidance, computer vision and wireless systems design. MathWorks provides a write up of the example in use. In that example kalmanfilter.m is my function file and ObjTrack.m is my algorithm which defines inputs, runs the Kalman filter and plots it in a graph, Figure 3. Conversion involves using the MATLAB Coder. Add the function on the entry point file and define its inputs types after which go ahead and build the C code, Figure 4. The generated C code can be obtained from your MATLAB code directory. SDR Hardware Prototypes Software-defined radios (SDRs) deserve a post of their own and thus will be briefly covered here. Basically these are computers whose components, traditionally implemented in hardware, are implemented through software. This means that the filters, amplifiers, modulators/demodulators are implemented using programming languages. In the previous section we discussed how to perform code generation. What SDRs offer is the flexibility to test and implement wireless designs and architecture with the provision to add more features in future. SDRs are used in conjunction with FPGA, GPP (general purpose processors), DSP or ASIC (application specific ICs) to implement various wireless architectures. It is a low cost method that is becoming increasingly popular in wireless systems design. Verification Finally, the system is rigorously verified using simulated and on-field test parameters to ensure the best product […]

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Easy Ways to Simulate the Strongest Microwave Links

symonmk — Tue, 27 Feb 2018 20:47:15 +0000

Having recently been involved with several microwave link installations and servicing, I have gathered several best practices to installing digital IP microwaves and obtaining the best PtP (point-to-point) links from them. A PtP link is simply a directional link between microwave antennas with a clear line of sight. During installation, several prior calculations have to be made to ensure the best possible link as well as mitigate the chances of link failure. With the recent development of online geographical maps, these calculations have been even more simplified and in this post we will dive into using these tools. In my field of work we apply microwave links in providing distribution links and contribution links. Distribution links are mainly the links between a studio and a transmitting site, such a link is mentioned here. Contribution links are the links between an OB (outside broadcast) site and their studio. Path Profiles A path profile refers to a straight line cross-section of two points on the earth’s surface. This can be used in obtaining the clearance characteristics of two points. From secondary school geography, for those who can remember, this was obtained by drawing a straight line between two points on a topographical map (scale of 1:50000 for example), obtaining the altitudes of all the points on the line then drawing an altitude versus distance graph. Joining the points on the graph smoothly gives you the path profile required for your point to point connection. Beyond this an earth bulge calculation has to be performed on points on your profile close to the straight line of sight. This is to compensate for atmospheric refraction which causes variations of the atmospheric refractive index caused by the effective earth radius , these variations lead to bending of microwave rays. A value of 4/3 is usually taken to denote the change in atmospheric index with height due to the earth’s radius which may cause the microwave ray to bend downwards. Other changes in atmospheric refraction may cause the value of to drop to about 2/3 which may cause an upward bending of the ray. The earth bulge constraint helps you better plan the height to set your antennas with the calculation as: where and are distances between the particular point on the path and the each end on the path in kilometers. After this we obtain the radius of the first Fresnel Zone which to put in technically is the locus of all points surrounding a radio beam from which reflected rays would have a path length one half-wavelength greater than the direct ray but may be simply understood as the region where a direct line of sight is achieved with the strongest signal link. The first Fresnel zone may be calculated as follows: where where and are the distances to each end of the path in kilometers, and F is the frequency in gigahertz. A minimum 60% clearance criterion is also required. This is normally a clearance of 60% (0.6) over obstacles of the first Fresnel zone calculated above with equal to 2/3 . With this, we can now use the manufacturer’s data of our radios and antennas to determine the final parameters in our planning. These include: Antenna gain Branching losses at both ends of the link Feeder equipment losses Alternatively… With all these in place you should be fine to gather your equipment and start right away. However, the process discussed may be too lengthy and prone to errors depending on your math skills. At the time of writing this post technology has made more complicated areas in life such as dating as simple as swiping right, so why not this too? Thankfully, a lot of manufacturers offer proprietary simulators to determine a clear PtP or even PtMP (point-to-multipoint) link from the comfort of your computer. One such manufacturer is Ubiquiti with their popular link simulator. Using Ubiquiti’s tool is fairly simple. I did a simulation of two points, Figure 1, between Chiromo area in Nairobi area and Limuru where transmitter sites for broadcast are usually found. To start off, obtain the coordinates of the two points. During site surveys I find it very useful using My GPS Coordinates which is a simple, free Android app which gives you your current coordinates. Having the coordinates of your access point (AP) and station (STA) we can now simulate link of the two sites. Here I have -1.275106,36.807504 as my access point and -1.127295,36.635714 as my station. In a previous installation, we used the Rocket M5 radios operating at 5GHz frequency using RocketDish antennas with a gain of 34dBi. Antennas with gains of 30dBi would also have sufficed but the higher gain antennas gave us better signal strengths. This information is filled on the section in Figure 2 together with the channel width. At this point you leave it up to the simulator to perform the calculations that give you details on the signal strength. If one has not been achieved between the two points the simulator will state that the link is obstructed. This can be rectified by adjusting the antenna height (to as high as is reasonable) or changing the station area by moving the antenna position to get a clear LoS. If this is still not achievable, consider setting up repeater stations to navigate around the obstructions. With a clear line of sight the next step is to check if the signal strengths are satisfactory. The higher the better. According to my simulation, Figure 3, -90dBm is weak while -60dBm is good. Aim for the strongest link possible to counter effects of fog, precipitation and changes in atmospheric gases. The same steps defined can be used for PtMP links. Conclusion This is a helpful skill I gathered from setting up microwave links and troubleshooting when failure occurs. To ensure the highest levels of availability in a year, the strongest possible links should be set at your client site. Understanding the important parameters helps you in prior planning before installation and the performance […]

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5G and the War for Supremacy: The 4 Key Technologies Involved

symonmk — Wed, 31 Jan 2018 07:00:19 +0000

Fifty years from now, when you’re aged and wrinkled (assuming we won’t have discovered the cure for aging) you’ll be sure to tell your grand-kids of the war for the rise of the 5G cellular network from 2016 – 2020. You’ll explain to them how the differences in spectrum efficiency, power efficiency and performance in connectivity were used to decide the ultimate victor. The challengers being MU-MIMO, D2D, NOMA and mmWave technologies. How the battles were fought, not on the ground or sea, but through the electromagnetic spectrum led by top research scientists all over the globe. You’ll remember to tell them that the puppet-masters were the telcos giants while us, the wee subscribers, could only hope for the best outcome. Better yet, direct them here for a simplified description of the technologies currently involved in the 5G revolution. Silly intros aside. I recently attended a lecture on Key Wireless Access Technologies in 5G and IoT Systems held on 15th January 2018 at Strathmore University’s Transcentury Auditorium. The event was organized by IEEE ComSoc in conjunction with the university. The IEEE Distinguished Prof. Rose Qingyang Hu, Figure 1, delivered the lecture on her ongoing research on the next generation of wireless communication. Her research focuses on the network design and optimization schemes, the Internet of Things, cloud and fog computing, multimedia QoS/QoE, wireless system modelling and performance analysis. In this post I share my insights on what I learned. Just as in the previous fourth generation, 4G, the search for a stable standard to be used for cellular communication involves a conflict between newly discovered or improved technologies. 4G technologies included LTE (Long Term Evolution), WiMAX (Worldwide Inter-operability for Microwave Access) and UMB (Ultra Mobile Broadband). As we now know, LTE has become the preferred 4G technology and has been widely implemented and accepted. In Nairobi, increased 4G coverage has been going on for about 2 years now. However, as user requirements have increased, a new standard of communication needs to be established. 5G promises to be the answer to the limitations with the current modes of communication. The 5G model of communication especially focuses on handling IoT (Internet of Things) devices. IoT devices broadly refer to the increasingly ubiquitous devices connected to the internet for general (smartphones, tablets) or specific (autonomous cars, wearables) applications. A quick example would be a smart stapler that connects to an app on your phone to tell you how many staples are left, an extremely useful device in my opinion. Let’s explore these competing technologies in 5G. MU-MIMO This stands for multi-user – multiple input, multiple output. MIMO systems are communication systems involving signal transmission with multiple antennas at the source and multiple antennas at the destination. MIMO systems have been in use in existing 4G networks, however to handle the requirements of 5G, MU-MIMO has been proposed to bring additional improvements. In MU-MIMO, MIMO is performed simultaneously on n number of user equipment (UEs) as in Figure 2. In MIMO we have a channel matrix H for M transmit antennas and N receivers. In order for this to be possible, beamforming, which involves space division beam direction, separates the receivers. In 4G this exists but its performance is limited. 5G will be set to push this to its limit, however it is only easy said as some factors make it challenging to even consider. The factors include: Number of transmitting and receiving antennas Coverage and the number of UEs to be supported per antenna Precoding scheme to be used Precoding schemes involve a matrix ‘code’ that are sent with the message so that the receiver can achieve ‘pre-knowledge’ of the channel. Useful especially in MU-MIMO systems to reduce corruption as well as optimize message reception by the receivers. Such schemes include matched filter precoding, zero-forcing (ZF) precoding, and transmit Wiener precoding. The Signal to Interference plus Noise ratio for the ith user served by one MU-MIMO base transceiver is: where: is the precoding vector for the ith user is the channel vector for the ith user is the variance of the complex circular zero mean white Gaussian noise at the nth user There’s a great YouTube lecture on MIMO and MU-MIMO calculus. D2D Device-to-Device communication is another technology associated with the rise of 5G networks. It basically means the direct communication of devices with each other. UEs involved in D2D will have to be at close proximity so as radio communication can be sustained. This will greatly reduce the load on the base station transceivers or access points. Existing technologies already enhance this form of communication such as Bluetooth and WiFi-Direct. It is up to cellular networks to leverage such concepts for the increasing number of communicating devices. Devices use existing cellular infrastructure while switching to D2D when location proximity is sufficient as in Figure 3. Researchers have deduced that there are several advantages to this scheme including: Ultra-low latency in communication as the signal path is greatly minimized Load on core network is reduced, increasing spectral efficiency Supports a variety of emerging applications such as Machine-to-Machine (M2M) and context aware applications D2D communication has already been established as part of the 4G-LTE standard defined by the Third Generation Partnership Project (3GPP) Release 12. D2D looks very promising as some of its features have been in use for quite a while now. Some challenges, especially in security and pricing for service providers are yet to be fully solved. NOMA Non-orthogonal multiple access (NOMA) schemes have become recently popular in achieving spectral efficiency, becoming attractive for the 5G networks. Currently up to 4G, cellular networks have been using orthogonal multiple access (OMA) schemes. They include the frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA). NOMA has been recently proposed as it meets the requirements of 5G networks unattainable using OMA. NOMA can be achieved by two techniques of power-domain and code-domain. In the power-domain NOMA scheme, superposition coding at the transmitter and successive interference […]

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Quick Guide To Radio Broadcast Transmission

symonmk — Thu, 18 Jan 2018 04:22:05 +0000

Your studio is already set up and it’s now time to go LIVE! Right? Well, there is the issue of how to get that audio to your audience. In Kenya, FM radio is the most common, and profitable, form of broadcast. This is why most of the infrastructure to support it has been set up across the country. Installation might be a grueling task for a small team (such as ours about a month ago), but the outcome becomes far more rewarding than I expected. In this post I go over the technologies that make radio broadcast transmission possible. With a new studio seeking to have their first broadcast transmission or an existing one seeking to expand to other regions, the requirements to be installed remain largely the same as they have been for decades, only this time, we have IP on our side, making things much easier. Audio Link Now starting from your studio, that fresh audio has been captured by your state of the art audio console and you need the people to hear. Transmitting audio over IP is as simple as installing a PtP (point-to-point) microwave link to your transmitting site. Usually the studio site and transmitting site are not in the same location as the transmitting sites are commonly in isolated highland regions. The audio over IP network can be achieved using audio IP-STL (Internet Protocol – Studio Transmitter Link). In our use case, Sigmacom’s Digital IP-STL encoder/decoder system. We set up them using their first recommended configuration as in Figure 1. In our previous installation, the IP link was of about 35 kilometers from the studio to the transmission site. The link was achieved through a PtP microwave link using Ubiquiti’s Rocket M5 radios (TX and RX) attached to RocketDish antennas that we mounted on masts at the TX and RX sites. After the signal has been captured and decoded, it is fed to the exciter. In our example the EuroCaster DS2000 FM Transmitter can power an RF signal up to 2kW of power. This transmitter power (TPO) is adjustable as is the frequency range of transmission, in Kenya it ranges from 87.5 MHz to 108.0 MHz. From this point, the signal can be sent to the broadcast antenna system. Filters, Feeders and Splitters Try saying that three times. The signal from the transmitter has to be propagated to the antenna system somehow. In between comes in a connection of transmission line components. The filter is a factory calibrated FM band-pass filter, which is set to the exact desired frequency, example 98.00MHz. The filter is connected to the antenna system through a coaxial feeder cable. A large feeder cable, like in Figure 2 that can go up to 170mm diameter, carries the large amount of energy from the filter with minimum attenuation to a splitter which splits the signal, in our example 8 times, to the low power antenna elements. The low power antennas may be fed with smaller feeder cables of 20mm. At every connection point with the feeder cable, for example, connection with the filter and splitter, a waveguide rotary joint is used in connecting the RF waveguides. The feeder cable is also grounded to the mast tower. The signal has now reached the antenna system. Transmission Antenna For this application, a circularly polarized antenna was used to achieve omni-directional signal transmission. Figure 3 shows one bay of the antenna. The antenna achieves circular polarization by having the radiating components perpendicular to one another, thereby propagation of horizontal and vertical components occur simultaneously. A singular antenna as in Figure 3 has the following features: Impedance of 50 Ohm Omni-directional pattern, approx. +/- 3dB Band start 87.5MHz, band stop 108.0Mhz Lightning protected, all metal parts DC grounded The antenna is combined with 7 other antennas producing an 8-bay antenna as in Figure 4. Increasing the antenna bays improves several performance parameters such as the directionality and gain. How? Circular polarization splits the effective radiated power (ERP) between the horizontal and vertical components, adding antenna bays on top of each other leads to addition in gain per bay. ERP is used to calculate the range of the signal, mathematically defined as: ERP = [Antenna Power] X [Antenna Power Gain] A 2-bay system has a gain of approximately 4.1dBd/6.25dBi while an 8-bay system has a gain of 10.1dBd/12.25dBi. Since the gain is higher and losses minimized, the system requires less TPO. Additional bays, however, increase overall system weight as the main trade-off. These are the basic components one would require to achieve broadcast, in our example, a radiating diameter of 100km could be achieved with the above discussed configuration. When setting up such a system, it is important to capture the necessary requirements so as not to have conflicting components during set up. Hopefully this guide will bring you closer to understanding what goes on before you tune in to your favorite FM channel.

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Working as a Broadcast Systems Engineer

symonmk — Tue, 22 Aug 2017 16:32:54 +0000

It is mid-August 2017 and I have been working as a broadcast engineering intern at Byce Broadcast and Technologies Kenya Limited, a system integrator company that offers turn-key solutions for TV and radio broadcasting. This business has a steep learning curve and I am required to learn real fast. Thankfully, the work is interesting and the fast changing technologies in this industry means that I’ll never stop learning. This post is just to simply provide an overview of the skills and competencies that are required in broadcast engineering and the work involved as a systems integrator. Broadcast Stations TV and Radio stations require solutions that facilitate their ability to deliver content to their audience. Satellite uplink – This refers to setting up a signal link from a TV/radio station to a satellite uplink provider who will send the signal to a satellite in space that will perform a broadcast downlink to users. You can read more about this on my previous post here. Teleport services – This is connecting a link from a TV/radio to a center that offers regional transmission of signals from the stations and has gateways to national networks. Budget – TV and radio stations are required to pay certain fees in order to access infrastructure for transmission and broadcast. Also, licensing of an allocation of the frequency spectrum to the Communications Authority of Kenya, CA. An understanding of satellite communication with reference to broadcast is required to provide the solutions stated above. In the last few decades, a set of international standards for digital television has popular. This is the Digital Video Broadcasting (DVB) standards. They are internationally recognized and supported by over 270 members. DVB standards are implemented for a variety of modes, the two of most importance are: Satellite: DVB-S, DVB-S2 Television: DVB-T, DVB-T2 Another way of broadcasting media that has been rapidly rising in adoption is the OTT (Over-the-top) distribution which allows for transmission of audio and video content straight to the Internet without any requirement of a satellite operator. Users can access this content directly on the Internet without the need to subscribe to a satellite TV provider. TV and Radio Studios Although TV and radio studios have different equipment set up in them, much of the underlying principles of design and setup is largely similar. Some of the technical considerations that are handled here are: Studio size and design Sound acoustics and material considerations Room temperature and air conditioning Choice of studio equipment Lighting considerations Choice of transmitting equipment Desk size and design Inventory Safety measures These considerations and equipment may be detailed further in later posts. Roles and Responsibilities Some of the organizational key activities include understanding client needs and budget, design of the proposed solutions, configuring, supplying and installing equipment at client site. For most clients, the four major initial service processes are to supply, install, commission and train users on the equipment. Thereafter, a SLA (service-level agreement) is defined between the system integrator company and the client to agree on terms of after-sales support such as troubleshooting and repairs. This is handled through official phone calls or email ticketing and could be handled either remotely or on site. So far I am involved in two ongoing projects for major clients in the country, as well as having successfully performed a small project involving the coverage of a recent graduation ceremony in the biggest university in Kenya. This is only the beginning and I anticipate exciting times ahead. Broadcast is a field of electrical engineering I formerly was not much aware of but my experience in the past few weeks has opened me up to a broader world.

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Understanding Satellite Earth Stations

symonmk — Mon, 17 Jul 2017 13:43:13 +0000

Satellite earth stations are ground sites that are designed for extraterrestrial telecommunication with orbiting satellites. They often have large antennas for this purpose and we further dive in to what they are and how they are used. Introduction Satellite earth stations form a section of satellite communications systems. A satellite communications system consists of an earth station and a satellite in space. The satellite in space acts as a relay station to communicate to another earth station. Such a system may be subdivided into two segments: Space segment: This segment consists of orbiting satellites and the earth-based satellite control subsystem on the ground, such as the TT&C station, that is used to operate and maintain satellites in orbit. This infrastructure is owned by the satellite operators who may be private companies or government parastatals. Ground segment: This section consists of service provider infrastructure such as gateways and hubs as well as user terminals owned by companies and individuals. The TT&C station provides functions of tracking, telemetry and command and often is equipped to receive various types of sensor information. This station determines a satellite’s orbital position and provides commands to adjust its altitude, orientation and trajectory. The station also relays information regarding the health and operational status of the satellite devices and equipment. In the ground segment, gateways and hubs communicate with the user terminals using the satellite as a relay for the signals. Gateways connect to other terrestrial networks such as the Public Switched Telephone Network (PSTN), cellular networks and the Internet. Hubs connect different elements of the network by exchange of messages with the user terminals and can also relay messages between the terminals. Figure 1 shows the Longonot Earth Station, a typical earth station found in Rift Valley, Kenya. The large antenna equipment offers a scenic view of the area. Communication configurations A satellite communication system communicates using microwave frequencies forming a microwave relay station. A satellite in space is used to link two or more microwave transmitters/receivers (transceivers) found in the earth stations. Basically, one earth station sends a transmission to the satellite via an uplink that is in a certain frequency band. The satellite transponder receives this transmission, coverts and amplifies the signal and sends it to another earth station via a downlink. Transponder may be transparent or regenerative. A single satellite will operate in a number of frequency bands called transponder channels. Most satellites providing point-to-point service today use a frequency bandwidth in the range 5.925 to 6.425 GHz for transmission from earth to satellite (uplink) and a bandwidth in the range 3.7 to 4.2 GHz for transmission from satellite to earth (downlink). This combination is referred to as the 4/6-GHz band. The two common communication configurations are: Point-to-point: This is communication between two earth stations using one satellite as a relay between them. Point-to-multipoint: This is communication between one earth station transmitter and a number of earth station receivers. This configuration is also called broadcast link. A great application of point-to-multipoint is the Direct-to-Home (DTH) television systems. Earth Station Elements and Design Major earth stations differ in size and complexity according to their functions which may be one of the following: Gateways, for telephone, cellular or Internet networks. They allow user terminals access a larger public or private network. Broadcasting uplink to originate various non-interactive forms of content such as video, audio (radio) programming and data. Hubs connecting remote user terminals back to a central location to access a host computer, servers, telephone switching equipment and private video transmission. Network control, a center to process requests from remote terminals for service and satellite bandwidth and to manage the overall satellite communication network. A generic block diagram of a typical earth station is shown in the Figure 3. From figure 3, we see that a typical earth station has a RF terminal which comprises of at least one transmitter channel and one receiver channel. The transmitter receives multiple data streams from the users and a multiplexer routes this signals to the appropriate modulator. The modulator may produce a modulated IF operating at 70 MHz with a channel bandwidth of 40 MHz or an IF of 140 MHz with a channel bandwidth of 80 MHz. The multiple channels are added together and upconverted to the RF carrier which includes frequencies in the L, C, X, Ku, K and Ka bands. The up-converters convert the signal to the desired carrier frequency. The signal is then amplified and transmitted out the earth station via a large antenna pointed to the satellite. The antenna may have a single, dual or circular polarization. A single antenna may be used for transmitting the uplink and receiving the downlink. A frequency duplexer is used to route the signals between the transmitter and receiver to the shared antenna (think switch). The duplexer is designed with a high isolation between transmit and receive channels. The receiving block is similar to that of the transmit section but in reverse. The downlink received is filtered and amplified. A pre-select filter rejects out of band RF interference. The signal is then block down-converted to the lower IF making it easier for the demodulation process. Most downlinks use an L band IF (950 MHz to 1450 or 2150 MHz), so most validation and troubleshooting measurements are made in this range. If multiple data channels are required by the system, a signal divider and output multiplexer will route the signals to the appropriate output port. This is only an introductory overview of satellite earth stations. Further understanding can be facilitated using a site visit or from engagement with an RF systems engineer. REFERENCES Keysight Technologies, “Precision Validation, Maintenance and Repair of Satellite Earth Stations FieldFox Handheld Analyzers”, August 24, 2015. Bruce R. Elbert, “The Satellite Communication Ground Segment and Earth Station Handbook”, Artech House, 2001. William Stallings, “Data and Computer Communications”, 8th Edition, Pearson Education, Inc, 2007

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Final Year School Project: Introduction to the Project

symonmk — Wed, 05 Apr 2017 16:07:48 +0000

For my 5th and final year in EEE at JKUAT, I was required to do a school project that accounted for two class units spread out over the two semesters of 2016/2017. The project I came up with is called OFFGRID MOBILE COMMUNICATION which the name suggests that communication can happen without a service provider network. Brief Abstract As communication is becoming widespread in Kenya, many people are opting for high-end smartphones that can do more than simple communication and support a variety of features. However, communication obstacles may arise due to several factors such as network congestion, deadzones within urban centers and extreme weather conditions. Let’s also not forget the dips in cell reception when we go to the rural countryside to visit our grandfolks on Christmas. A way to mitigate this constraint in communication is completely abandoning the dependency to the service providers and creating a small network based on two available technologies Bluetooth 4.0 modules and RF Transceiver modules. Together these are enough to create a small area network (radius 1 – 1.8km). Objectives My objectives for this project include: Design and implement the internal circuitry of the device including the Bluetooth, microcontroller and RF transceiver modules which will allow the device to transmit, process and receive data. Design and implement the code to configure the Bluetooth, microcontroller and RF transceiver modules to perform as intended. Design and implement an android application user interface to allow users to connect and work with the off-grid communication device as intended. Resources My project will involve the use of an ATmega1284P microcontroller, a HM-10 Serial Bluetooth 4.0 module and a HC-12 RF Transceiver module. I am using Atmel Studio to program my microcontroller (Newbiehack.com has great tutorials on this), KiCad, discussed here, to draw my schematics and eventually my PCB and Android Studio to write the mobile interface to use with the device. As of now in my final semester already made strides with this project more posts on its progress will follow. References Some references I used in researching for this project including the communication industry in Kenya, other solutions, wireless technologies (Bluetooth, RF), antennas, microcontrollers, mobile app development can be found below: [1] CA, “Quarterly Sector Statistics Report Fourth Quarter for The Financial Year 2015-2016 (April-June 2016)”, page 5. [2] CA, “Quarterly Sector Statistics Report Fourth Quarter for The Financial Year 2015-2016 (April-June 2016)”, page 9. [3] CA, “Quality of Service,”. [4] CA, “Mobile operators Fail to Meet Quality of Service targets for the third year running,”. [5] Abdiwahid Biriq. (2014, May. 16). “Is Safaricom short-changing its customers?”. [6] Dave Aiello. (2004, Aug 13). “Mobile Carriers Ready “Cells on Wheels” in Case of Outages or Network Overloads.”. [7] Chris Woodford. (2016, March 9). “Walkie-talkies.”. [8] AARL. “What is Ham Radio?”. [9] Chris Woodford. (2016, June 13). “How Does Bluetooth Work”. [10] ATHLOS. “Bluetooth™”. [11] Robin Heydon. “Bluetooth Low Energy: The Developer’s Handbook”. Prentice Hall, 2012, pp 1-7 [12] Tarun Agarwal “Block Diagram and Explanation of RF Transceivers.”. 33 [13] antenna-theory.com. (2011) “The Monopole Antenna”. [14] Louis E. Frenzel. (2005, Mar 31). “Printed-Circuit-Board Antennas”. [15] Freescale Semiconductor, Inc. “Compact Integrated Antennas”. Freescale Semiconductor, Inc, 2015 pp 8-9 [16] CA. “Kenya Table of Frequency Allocations”. CA, 2008 pp 37-186 [17] Frank Duignan. “An Overview of Microcontrollers.”. [18] Android Developers. “Bluetooth Low Energy”.

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