1. RF Propagation Basic Track Phil Ziegler Principal Consultant APRIL 4, 2016 4/4/16Copyright © 2016 | CIBET | All rights reserved1

2. Agenda RF Propagation Fundamentals Coupling Loss and Antennas Quick review of dB Math Other Phenomena Effecting Propagation 2Copyright © 2016 | CIBET | All rights reserved4/4/16

3. Wavelengths & Frequencies Where: =  x   m/s = 300 m/  s = 1 ft/ns Remember this number ! Propagation in the atmosphere (snow, rain, …) is slightly slower (through glass, 1/3 slower) due to optical density of medium As we will see, RF Propagation is strongly dependent on Wavelength 3Copyright © 2016 | CIBET | All rights reserved4/4/16

4. Radio Transmission in Free Space F = Power Flux Density Energy decay (dispersion) as surface area expands, inversely with the square of the distance Power is energy applied over time distributed over space P R is radiated power To go twice as far requires 4x the power To go three times as far requires 9x the power Etc, … 4Copyright © 2016 | CIBET | All rights reserved4/4/16

5. Friis Equation for Received Power (not pathloss) Friis Transmission Equation 5 Copyright © 2016 | CIBET | All rights reserved 4/4/16

6. Free-Space & d n Model of Path Loss (not Rx Power) The path loss equation is characterized by a constant term, frequency term and a distance term. When the distance is 0 only coupling loss [….] remains. in dB: When the environment is not free space, the rate of decay is other than it is in free space and the distance term 20 log(d) becomes Nx10Log(d). Where n is the rate of decay relative to free space. Where: n = Propagation Constant; d = distance in meters; f = frequency in MHz 6Copyright © 2016 | CIBET | All rights reserved4/4/16

7. Large-Scale Path Loss Measurements Various Environments Will signals propagate farther indoors or outdoors? 7Copyright © 2016 | CIBET | All rights reserved4/4/16

8. Review of RF Mathematics Basics 8Copyright © 2016 | CIBET | All rights reserved4/4/16

9. dB’s The Units of Choice for RF Engineers Typical Power amps provide 1 watt of power. Typical Receivers can receive.00000000001 watts of power. The difference in these numbers require us to use a system of mathematics that keeps track of orders of magnitude (groups of 10) rather than linear units dB math uses logarithmic units of Bels to measure power » The relationship between watts and bels is given by Bels = Log (Watts) » One decibel is one tenth of a bel, 1B = 10 dB » One watt is 1000 milliwatts = 30 dBm We use milliwatts not watts and deciBels not Bels as our units of choice for discussions Path loss is a ratio -> dB, Signal strength is an amount of power -> dBm dB ± dB = dB dBm ± dB = dBm; dBm – dBm = dB 9Copyright © 2016 | CIBET | All rights reserved4/4/16

10. Free-Space & d n Model of Path Loss (not Rx Power) The path loss equation is characterized by a constant term, frequency term and a distance term. When the distance is 0 only coupling loss [….] remains. in dB: When the environment is not free space, the rate of decay is other than it is in free space and the distance term 20 log(d) becomes Nx10Log(d). Where n is the rate of decay relative to free space. Where: n = Propagation Constant; d = distance in meters; f = frequency in MHz 10Copyright © 2016 | CIBET | All rights reserved4/4/16

11. 11 Power Decay Distance In Free Space it takes about 4 times the amount of power to double the distance covered. 100-200 m 6dB 2 km - 4 km Initial Power In Linear Units of Distance Copyright © 2016 | CIBET | All rights reserved4/4/16

12. 12 Log(Distance in Meters) 1-10 10 -100 100-1000 1,000-10,000 700 MHz 0m 800 MHz 1900 MHz ~ dB CL Slope of these lines is the propagation decay coefficient or “n” In Logrithmic Units of Distance Copyright © 2016 | CIBET | All rights reserved4/4/16

13. Antenna Overview 13Copyright © 2016 | CIBET | All rights reserved4/4/16

14. Isotropic Antennas An isotropic antenna is a hypothetical reference, to which all other antennas may be compared Radiation pattern is uniform in all directions Used to calculate gain or directivity, usually expressed in dBi dB(isotropic) – is defined as the forward gain of an antenna compared with the hypothetical isotropic antenna which uniformly distributes energy in all directions 14 Copyright © 2016 | CIBET | All rights reserved4/4/16

15. Understanding Gain Geometrically Example – a perfect antenna with a 60 degree horizontal beam width and 10 degree vertical beam width vs.an isotropic antenna radiating at the same power would have antenna gain in dBi equal to the ratio of the surface area of the sphere divided by the surface area of the covered by the directionality of the antenna Geometrically, the antenna gain would be 20.33 dBi = 10log(2 * 6 * 9); -Factor of 1/2 for bottom half of sphere -Factor of 1/6 for 60 degree beam width -Factor of 1/9 for 10 degrees In reality the energy radiated from a directional antenna is not restricted to the main beam, side lobes and back lobes reduce the gain from the geometrically calculated conceptual solution. 154/4/16 Copyright © 2016 | CIBET | All rights reserved

16. Isotropic Antenna in Free Space Transmitted power is amplifier output power less cable loss, plus antenna gain.  Outdoors = BTS Power – Cable Loss + Antenna Gain  Indoors = BTS Power +DAS Impacts to the Remote Amplifier- Cable Loss + Antenna Gain EIRP (Effective Isotropic Radiated Power) EIRP = P t – Losses + Antenna Gain Note – ERP is sometimes used when antenna gain is measured in dBd or referenced from a dipole instead of an isotropic point source. Think of this as a different choice of units such as Fahrenheit vs. Centigrade 164/4/16 Copyright © 2016 | CIBET | All rights reserved

17. Radiated Power ERP or EiRP 17 Gain dBd +2.15dB Gain dBi X One More Confusing Item Antenna Gain Units Copyright © 2016 | CIBET | All rights reserved4/4/16

18. Dipole or OMNI Antenna in Free Space Three-Dimensional Radiation Pattern Position the 2 vertical elements in the “hole” of the doughnut 18Copyright © 2016 | CIBET | All rights reserved4/4/16

19. Directional Antennas Directional Antennas have radiation patterns described by horizontal and vertical beam width and GAIN. The pattern and the associated gain are driven by antenna size. Here we see that the antenna gain is a function of the Area of the antenna element and the wavelength of the radiation. Higher frequencies can use smaller antennas. Gain is simply the ratio of input power to output power and is usually expressed in dB. 19Copyright © 2016 | CIBET | All rights reserved4/4/16

20. Other Conditions that make up the RF Environment 20Copyright © 2016 | CIBET | All rights reserved4/4/16

21. Multipath Concepts Direct path Multipath 1 Multipath 2 21Copyright © 2016 | CIBET | All rights reserved4/4/16

22. Multipath & Fading Large-Scale and Small-Scale Statistical Accounting for Fading determines Design Confidence Multipath fading is due to constructive and destructive interference of the transmitted waves (in air) 6-14dB of variance indoors Channel varies when mobile moves a distance on the order of the carrier wavelength. This is about 0.3 m for 850 MHz cellular. (fades may occur every ½ wavelength) For vehicular speeds, this translates to channel variation of the order of 100 Hz. Pedestrian speeds see this variation on the order of 10 Hz or less. Primary driver behind wireless communications system design, especially coding and power control Channel varies due to two fading effects: - Rayleigh non-LOS lots of obstructions - Rician LOS self interfering 22Copyright © 2016 | CIBET | All rights reserved4/4/16

23. Multipath Rich Environments Allow For MIMO Channel Conditions 23Copyright © 2016 | CIBET | All rights reserved4/4/16

24. SISO SIMO MISO MIMO Communication Schemes FACTS: 1. Current baseline ”1-TX-1-RX-antenna” wireless communications are running out of improvement possibilities (we are indeed close to the theoretical capacity bounds as defined by Shannon) 2. Multi-stream/MIMO based transmission schemes redefine those bounds! 3. Multi-stream/MIMO transmission schemes are realizable in cellular systems & frequencies 4. Interference can be managed better in future/evolved wireless systems This becomes increasingly critical as an increased utilization of Mobile Broadband increases network density 24Copyright © 2016 | CIBET | All rights reserved4/4/16

25. 25 The basic Shannon Formula demonstrates that the main factors governing channel capacity (a.k.a throughput) are channel bandwidth and the signal to noise plus interference ratio. C = B*log 2 (1 + SNR) Where C is the channel capacity in bits per second; B is the bandwidth of the channel in hertz; SNR is the signal to noise ratio expressed as a unitless linear power ratio Capacity increases linearly with Bandwidth but as the FCC mostly controls bandwidth allocations, the only available parameters available for different vendors to increase the information capacity (or quality) of the channel is to use:  physics (by managing the physical radio isolation) and  communications coding theory to virtually and substantially enhance the Signal to Noise ratio of the channel. Review: Shannon-Hartley Capacity Formula Copyright © 2016 | CIBET | All rights reserved4/4/1625

26. Theoretical Shannon Capacity Formula 26Copyright © 2016 | CIBET | All rights reserved4/4/1626

27. MIMO Receive Side Spatial Diversity Gain In a fast fading (Raleigh) environment, independent fading characteristics at each of the Receive antennas in a MIMO system are exploited to improve the signal quality. Datastream A -> Datastream B -> In a 2 x 2 MIMO system, -Multi-path effects are used to separate and extract the two data streams, A and B, at each receiver. -SNR power gain is realized from multiple copies received (since SNR is additive) and combined using various combining techniques such as Maximal Ratio Combining (MRC) -Diversity Gain is calculated by the product of N T x N R. For a 2 x 2 MIMO system, the maximum diversity gain achievable is 4. 27 TxRx h 11 h 21 h 12 h 22 1212 1212 Copyright © 2016 | CIBET | All rights reserved4/4/1627

28. The basic idea of how MIMO increases data throughput to extend the Shannon limit is to view the MIMO channel as a set of uncorrelated data streams in the downlink direction. This technique, known as spatial multiplexing, increases the bandwidth by using multiple channels. Spatial multiplexing uses multipath fading as an asset by taking advantage of how the fading environment changes the signal at each receiver to use the delay spread across multiple antennas to create unique channels. The environment in effect becomes the “code” which spreads the signal in the frequency. Using the knowledge of the communications channel, a receiver recovers independent streams from each of the transmitter's antennas. The overall capacity increase can then be viewed as the sum of the individual capacities. Spatial Multiplexing Gain is the min(N T, N R ). For a 2 x 2 MIMO system, the maximum SMG achievable is 2. 28 MIMO Spatial Multiplexing Techniques Copyright © 2016 | CIBET | All rights reserved4/4/1628

29. The MIMO Channel – How Does it Work? 29 To illustrate how the MIMO channel uses multi-path to be able to discriminate among differing data streams and improve signal throughput, consider a 2 x 2 MIMO channel. Let’s use the analogy of a piano player striking (and sustaining) playing a chord consisting of 5 notes with the left hand and another chord consisting of another 5 different notes with the right hand at the same time. Think of the individual notes as resource elements and each chord as a symbol. The chord played by the left hand is transmitted from transmit antenna A. The chord played by the left hand is transmitted from transmit antenna B. Assume that the propagation path from transmit antenna A results in 3 multi-paths Assume that the propagation path from transmit antenna B results in 4 multi-paths The following animation illustrates how the arrival of each multi-path results in a detectable power change for either symbol through constructive or destructive interference Copyright © 2016 | CIBET | All rights reserved4/4/1629

30. Multi-Path Animation 30 Frequency Relative signal strength F1 F10F8F6F3 F2F9F7F5F4 T 1 direct path T 2 Multi-path A 1 arrives T 3 Multi-path B 1 arrives T 4 Multi-path A 2 arrives T 5 Multi-path B 2 arrives T 6 Multi-path B 3 arrives (deconstr.) T 7 Multi-path A 3 arrives T 8 Multi-path B 4 arrives F2F7F6F5F4F3F8F9F10 F1 Initially, each receiver hears all the notes and is unable to determine which chord (symbol) each belongs to Based on the changes to the signal strength of the notes, the receiver is able to separate out the notes into individual chords (symbols) F1, F3, F6, F8 and F10 are parts of symbol 1 F2, F4, F5, F7 and F9 are parts of symbol 2 Copyright © 2016 | CIBET | All rights reserved4/4/1630

31. 31 Conclusions Shannon’s law still applies, even for MIMO; MIMO extends Shannon due to channel gain characteristics which support multiple uncorrelated spatial transmission modes by exploiting transmission environments rich in fading, multipath and scattering. Transmission environments rich in fading, multipath and scattering offer the most channel gain whereas environments with a strong line-of-sight (direct) path will exhibit limited MIMO channel gains. MIMO systems offer a combination of both diversity and spatial multiplexing gains to increase system reliability and data throughput. MIMO is unique in that it can support multiple uncorrelated data streams. Spatial Multiplexing Gains offer a linear increase (ignoring channel overhead) in the transmission rate based on the min(N T, N R ) for the same bandwidth and with no additional power. In particular, a 2 x 2 MIMO system produces two spatial streams to effectively double the maximum data rate of what might be achieved in a traditional SISO communications channel Copyright © 2016 | CIBET | All rights reserved4/4/1631

32. Radio Wave Reflection & Scattering Reflection occurs when radio waves hit an object with large dimensions compared to size of one wavelength – Similar to optical reflection from a mirror – Typical examples are reflections from the earth’s surface, buildings and walls Scattering occurs when the area through which a radio wave travels contains objects whose dimensions are small compared to the size of a wavelength – Caused by rough surfaces and small objects – Examples are foliage, street signs, lamp posts – Scattering may be caused by non-metallic objects Penetration Loss occurs when a signal passes through a medium other than air. Loss through many solid materials as well as apertures are very frequency dependent. 32Copyright © 2016 | CIBET | All rights reserved4/4/16

33. Radio Wave Diffraction May occur when an object with sharp edges obstructs the radio path between a transmitter and receiver Causes bending of the waves around the obstruction 33Copyright © 2016 | CIBET | All rights reserved4/4/16

34. In the real world path loss curves are not strictly decreasing function. Diffraction and the emergence from a shadow will sometimes cause signal levels to rise as distance grows. Obstruction Diffraction Line of Site 34Copyright © 2016 | CIBET | All rights reserved4/4/16