2.1 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Mobile Communications Chapter 2: Wireless Transmission Frequencies Signals, antennas, signal propagation Multiplexing, Cognitive Radio Spread spectrum, modulation Cellular systems

2.2 Wireless communications The physical media – Radio Spectrum – There is one finite range of frequencies over which radio waves can exist – this is the Radio Spectrum – Spectrum is divided into bands for use in different systems, so Wi-Fi uses a different band to GSM, etc. – Spectrum is (mostly) regulated to ensure fair access Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC

2.3 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Frequencies for communication VLF = Very Low FrequencyUHF = Ultra High Frequency LF = Low Frequency SHF = Super High Frequency MF = Medium Frequency EHF = Extra High Frequency HF = High Frequency UV = Ultraviolet Light VHF = Very High Frequency Frequency and wave length  = c/f wave length, speed of light c  3x10 8 m/s, frequency f 1 Mm 300 Hz 10 km 30 kHz 100 m 3 MHz 1 m 300 MHz 10 mm 30 GHz 100  m 3 THz 1  m 300 THz visible light VLFLFMFHFVHFUHFSHFEHFinfraredUV optical transmission coax cabletwisted pair

2.4 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Example frequencies for mobile communication VHF-/UHF-ranges for mobile radio simple, small antenna for cars deterministic propagation characteristics, reliable connections SHF and higher for directed radio links, satellite communication small antenna, beam forming large bandwidth available Wireless LANs use frequencies in UHF to SHF range some systems planned up to EHF limitations due to absorption by water and oxygen molecules (resonance frequencies) weather dependent fading, signal loss caused by heavy rainfall etc.

2.5 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Frequencies and regulations In general: ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences) ExamplesEuropeUSAJapan Cellular networks GSM , , , UMTS , LTE , , AMPS, TDMA, CDMA, GSM , TDMA, CDMA, GSM, UMTS , PDC, FOMA , PDC , FOMA , Cordless phones CT , CT DECT PACS , PACS-UB PHS JCT Wireless LANs b/g b/g b g Other RF systems 27, 128, 418, 433, , , 868

2.6 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Signals I physical representation of data function of time and location signal parameters: parameters representing the value of data classification continuous time/discrete time continuous values/discrete values analog signal = continuous time and continuous values digital signal = discrete time and discrete values

2.7 Signals I signal parameters of periodic signals:  period T: time to complete a wave.  frequency f=1/T :no of waves generated per second  amplitude A : strength of the signal  phase shift  :where the wave starts and stops sine wave as special periodic signal for a carrier: s(t) = A t sin(2  f t t +  t ) These factors are transformed into the exactly required signal by Fourier transforms. Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC

2.8 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Fourier representation of periodic signals tt ideal periodic signal real composition (based on harmonics) It is easy to isolate/ separate signals with different frequencies using filters

2.9 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Signals II Different representations of signals amplitude (amplitude domain) frequency spectrum (frequency domain) phase state diagram (amplitude M and phase  in polar coordinates) Composed signals transferred into frequency domain using Fourier transformation Digital signals need infinite frequencies for perfect transmission modulation with a carrier frequency for transmission (analog signal!) f [Hz] A [V]  I= M cos  Q = M sin   A [V] t[s]

2.10 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Antennas: isotropic radiator Radiation and reception of electromagnetic waves, coupling of wires to space for radio transmission Isotropic radiator: equal radiation in all directions (three dimensional) - only a theoretical reference antenna Real antennas do not produce radiate signals in equal power in all directions. They always have directive effects (vertically and/or horizontally) Radiation pattern: measurement of radiation around an antenna zy x z yx ideal isotropic radiator

2.11 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Antennas: simple dipoles Real antennas are not isotropic radiators but, e.g., dipoles with lengths /4 on car roofs or /2 as Hertzian dipole  shape of antenna proportional to wavelength Example: Radiation pattern of a simple Hertzian dipole Omni-Directional Antennas are wasteful in areas where obstacles occur (e.g. valleys) side view (xy-plane) x y side view (yz-plane) z y top view (xz-plane) x z simple dipole /4 /2

2.12 Directional antennas reshape the signal to point towards a target, e.g. an open street Placing directional antennas together can be used to form cellular reuse patterns Gain: maximum power in the direction of the main lobe compared to the power of an isotropic radiator (with the same average power) Often used for microwave connections or base stations for mobile phones (e.g., radio coverage of a valley) Directed antennas are typically used in cellular systems, several directed antennas combined on a single pole to construct Sectorized antennas. Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC

2.13 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Antennas: directed and sectorized side view (xy-plane) x y side view (yz-plane) z y top view (xz-plane) x z top view, 3 sector x z top view, 6 sector x z directed antenna sectorized antenna

2.14 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Antennas: diversity Multi-element antenna arrays: Grouping of 2 or more antennas multi-element antenna arrays Antenna diversity switched diversity, selection diversity receiver chooses antenna with largest output diversity combining combine output power to produce gain cophasing needed to avoid cancellation + /4 /2 /4 ground plane /2 +

2.15 Smart antennas use signal processing software to adapt to conditions –e.g. following a moving receiver (known as beam forming), these are some way off commercially E.g. wireless devices direct the electro magnetic radiation away from human body toward a base station to reduce the absorbed radiation. Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC

2.16 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Signal propagation ranges Transmission range communication possible low error rate Detection range detection of the signal possible no communication possible Interference range signal may not be detected signal adds to the background noise Wireless is less predictable since it has to travel in unpredictable substances – air, dust, rain, bricks distance sender transmission detection interference

2.17 Signal propagation: Path loss (attenuation) In free space signals propagate as light in a straight line (independently of their frequency). If a straight line exists between a sender and a receiver it is called line-of-sight (LOS) Receiving power proportional to 1/d² in vacuum (free space loss) – much more in real environments (d = distance between sender and receiver) Situation becomes worse if there is any matter between sender and receiver especially for long distances Atmosphere heavily influences satellite transmission Mobile phone systems are influenced by weather condition as heavy rain which can absorb much of the radiated energy Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC

2.18 Signal propagation: Path loss (attenuation) Radio waves can penetrate objects depending on frequency. The lower the frequency, the better the penetration Low frequencies perform better in denser materials High frequencies can get blocked by, e.g. Trees Radio waves can exhibit three fundamental propagation behaviours depending on their frequencies: Ground wave (<2 MHz): follow the earth surface and can propagate long distances – submarine communication Sky wave (2-30 MHz): These short waves are reflected at the ionosphere. Waves can bounce back and forth between the earth surface and the ionosphere, travelling around the world – International broadcast and amateur radio Line-of-sight (>30 MHz): These waves follow a straight line of sight – mobile phone systems, satellite systems Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC

2.19 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Signal propagation Propagation in free space always like light (straight line) Receiving power proportional to 1/d² in vacuum – much more in real environments, e.g., d 3.5 …d 4 (d = distance between sender and receiver) Receiving power additionally influenced by fading (frequency dependent) shadowing reflection at large obstacles refraction depending on the density of a medium scattering at small obstacles diffraction at edges reflectionscatteringdiffractionshadowing refraction

2.20 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Multipath propagation Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction Time dispersion: signal is dispersed over time interference with “neighbor” symbols, Inter Symbol Interference (ISI) The signal reaches a receiver directly and phase shifted distorted signal depending on the phases of the different parts signal at sender signal at receiver LOS pulses multipath pulses LOS (line-of-sight)

2.21 Thanks to Prof. Dr.-Ing. Jochen H. Schiller for the slides MC Effects of mobility Channel characteristics change over time and location signal paths change different delay variations of different signal parts different phases of signal parts  quick changes in the power received (short term fading) Additional changes in distance to sender obstacles further away  slow changes in the average power received (long term fading) short term fading long term fading t power