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Wireless 101: Cellular Network Basics © Paul Bedell 2010 Copyright (c) Paul Bedell 2010 Cellular Technology Defined: A communications system which serves users via radio waves (a “radio air interface”) by connecting the user’s mobile terminal to the antennas at the nearest “cell base station”. The cell base station antennas can be tower mounted; rooftop mounted; mounted on water tanks; or hidden from sight for aesthetic purposes. Average base station coverage area today: 2-5 miles radius. The system functions by re-using frequencies at the low- powered cell base stations throughout a cellular market area, and handing off calls in progress from one cell base station to another as users move throughout the market area. Copyright (c) Paul Bedell 2010 Call Base Station Photos Copyright (c) Paul Bedell 2010 Mobile Telephone (Cellular Technology) Wireless service is founded on one key concept known as “frequency re-use” Cellular service launched in Chicago in 1983 Traditionally, to engineer a cell network to support millions of users in a metropolitan area, or thousands in a rural area, markets are broken down into cells. Cells are geographic areas that use their own sets of frequencies (channels) to support dozens of users simultaneously. Frequency re-use is accomplished by breaking down all available frequencies into groups of 7 (N=7). Each cell base station has its own transmission system (antennas) and set of assignable channels. Copyright (c) Paul Bedell 2010 N=7 Frequency Re-Use Cluster. Each hexagon represents a base station with distinct set of frequencies. Note how identical frequency sets are laid out symmetrically. This facilitates design and engineering. This concept isn’t used much anymore, as the majority of system design is now done via complex software programs. Copyright (c) Paul Bedell 2010 Five Key Components To Every (Macro) Wireless Network: Mobile phone, aka “UE” (user equipment) or “mobile terminal” Cell Base Station Fixed network, aka “backhaul network” Mobile Switching Center (MSC) (aka “MTSO”) Interconnection to PSTN and Internet Copyright (c) Paul Bedell 2010 (2) (4) (3) Mobile Switching Center (Location of Switch and System Peripherals (5) (1) (1) The Mobile Unit (2) The Cell Base Station (3) The Backhaul Network (aka “Fixed Network” (4) The Mobile Switching Center (5) Interconnection to PSTN and Internet (“other networks”) Copyright (c) Paul Bedell Internet 2010 PSTN (Landline) Key design and engineering concepts that drive cellular technology: Frequency Re-Use – supports simultaneous use of hundreds or thousands of frequencies (channels) to exponentially increase system capacity Call Handoffs – seamless transfer of a call / transmission in progress from one base station to an adjacent (neighbor) base station Frequency Agility: in handsets / terminals – ability of cell phones to operate on any one of dozens or hundreds of possible frequencies. Call handoff cannot occur without this ability. Working together, these concepts support basic cellular operation. Copyright (c) Paul Bedell 2010 Radio Spectrum: Industry Gold Range Band Code 30 to 300 Hz 300 to 3,000 Hz 3 kHz to 30 kHz 30 kHz to 300 kHz 300 kHz to 3,000 kHz 3 MHz to 30 MHz 30 MHz to 300 MHz 300 MHz to 3,000 MHz Extremely Low Frequency Voice Frequency Very Low Frequency Low Frequency Medium Frequency High Frequency Very High Frequency Ultra High Frequency ELF VF VLF LF MF HF VHF UHF 3 GHz to 30 GHz Super High Frequency SHF 30 GHz to 300 GHz Extremely High Frequency EHF Copyright (c) Paul Bedell 2010 Applications Commercial power transmission Telecommunications speech Sonar, submarine communications WWV, radio navigation AM radio Amateur radio Amateur radio, TV GPS, cellular, PCS, MW, UHF TV, military search radar, ATC transponder, space telemetry, microwave heating Airport search radar, microwave relay, satellite communications, STL microwave relay, police radar (C & K band), airborne FC radar Experimental, military, satellit e communications RF Propagation defines how well a radio wave travels through a given medium, which can be air, water, cable, or optical fiber. Three things can impact RF propagation in the cellular world: Free space loss – any radio signal will fade over distance. This is especially true at higher frequencies. The higher the frequency, the greater the degree of free space loss. Rayleigh Fading – any signal propagating from one point to another will reflect off many objects in its path, which can weaken the signal and cause multiple “reflected” signals. If reflected signals combine with the strongest signal, they can weaken the composite signal entering the antenna. Absorption: all radio signals can be absorbed by objects in the path of propagation. This is especially true of organic entities and anything that is waterbased (i.e. plants, trees) Copyright (c) Paul Bedell 2010 Rayleigh Fading Reflected Signal (Indirect) House ro n nal (St g i S t c D i re gest) Cell Base Station Food Mart Convenience store Reflected Signals (Indirect) Lake Copyright (c) Paul Bedell 2010 Tower Types 1.Monopole: single tubular structure 2.Free Standing, aka “Lattice”: 3 or 4sided structure with cross-arm sections (lattice design). Self sustaining (no guy cables). Looks like an elongated pyramid. Seen at many toll plazas. Red and white. 3.Guyed Towers: tallest tower type. Held up by guyed cables that are 80% of the tower’s height. Can reach heights of 2000 feet !! Copyright (c) Paul Bedell 2010 Free Standing Tower. Note the parabolic reflector microwave radio antennas Copyright (c) Paul Bedell 2010 Guyed Tower Copyright (c) Paul Bedell 2010 Monopole Towers Copyright (c) Paul Bedell 2010 Stealth Cell Sites Copyright (c) Paul Bedell 2010 Cell On Wheels “COW” Copyright (c) Paul Bedell 2010 Free-Standing Tower In Colorado Subjected To “Rime Ice”, which is when fog crystallizes and freezes. Copyright (c) Paul Bedell 2010 Generations Of Wireless Technology Wireless Service(s) Cellular service first launched in 1983 in Chicago, Illinois by Illinois Bell. First generation (1G) service: All analog, more prone to noise, crosstalk, call drops Limited system capacity Used 850 Mhz frequency spectrum 1983 – 1994 KEY DIFFERENTIATOR: first instance of frequency re-use to exponentially increase capacity over previous mobile systems Second generation (2G) service: Also known as “PCS” (Personal Communication Service) Co-existed with analog service for 15 years Used different frequency spectrum (1900 Mhz / 1.9 Ghz) KEY DIFFERENTIATOR: all digital service Copyright (c) Paul Bedell 2010 Generations Of Wireless Technology Wireless Service(s) Continued: Third generation (3G) service: All digital “Always On” Internet access High-speed access and transmission (> 384 Kbps) Technologies: UMTS (GSM-based), CDMA 1X-EVDO KEY DIFFERENTIATOR: supports sustainable multimedia transmissions (i.e. voice, video, text, image, video) Fourth generation (4G) Launching in 2009 with Clearwire WiMax launch Key technologies: WiMax (802.16) and LTE (Long Term Evolution) KEY DIFFERENTIATOR: super-fast access and transmissions – tens of Megabits. Technology built into laptops. Copyright (c) Paul Bedell 2010 RF SIGNAL FLOW THROUGH A CELL SITE: DOWNLINK (Forward Channel) Radio / Transceiver RX 0 antenna RX 1 TX Duplexer: allows for TX and RX over one antenna duplexer Power Amp: Boosts Signal Combiner Combiner: wireless “mux” Copyright (c) Paul Bedell 2010 Incoming Transmission RF SIGNAL FLOW THROUGH A CELL SITE: UPLINK (Reverse Channel) RX-O RX-1 Bandpass Filter Bandpass Filter Low Noise Amp (LNA) DIVERSITY RECEIVE ANTENNAS filters out all frequencies except RCV freq. Low Noise Amp (LNA) Boosts RX signal level for separation Radio / Transceiver Multicoupler (Wireless “Demux” Multicoupler (Wireless “Demux” TX RX 1 RX 0 To Other Transceivers Copyright (c) Paul Bedell 2010 To MTSO / Core Network Two Antenna Types: Omnidirectional: propagates radio signal equally 360 degrees, aka “omni”. Also called “stick” antennas. (Lamp With No Shade) Directional: radio energy is focused in a specific direction at a specific beamwidth, based on a reflector within the antenna housing. (Flashlight) Copyright (c) Paul Bedell 2010 Omni Antenna Copyright (c) Paul Bedell 2010 Directional “Panel” Antennas Copyright (c) Paul Bedell 2010 Why LTE? LTE’s Key Radio Access Network (RAN) Capabilities: Peak Data Rate • Instantaneous downlink peak data rate of 100 Mbps within a 20 MHz downlink spectrum allocation (5 bps/Hz) • Instantaneous uplink peak data rate of 50 Mbps within a 20MHz uplink spectrum allocation (2.5 bps/Hz) Control-Plane Capacity • At least 200 users per cell should be supported in the active state (for spectrum allocations up to 5 MHz). 200 simultaneous transmissions per cell !! User Throughput • Downlink: average user throughput per MHz, 3 to 4 times Release 6 HSDPA • Uplink: average user throughput per MHz, 2 to 3 times Release 6 Enhanced Uplink • Improved cell edge throughput performance – more consistent performance Copyright (c) Paul Bedell 2010 LTE’s Key RAN Capabilities: Spectrum efficiency • Downlink: In a loaded network, target for spectrum efficiency (bits/sec/Hz/site), 3 to 4 times Release 6 HSDPA ) • Uplink: In a loaded network, target for spectrum efficiency (bits/sec/Hz/site), 2 to 3 times Release 6 Enhanced Uplink Spectrum flexibility • E-UTRA (LTE physical layer) shall operate in spectrum allocations of different sizes, including 1.4 MHz, 3 MHz, 5 MHz, 15 MHz, and 20 MHz in both the uplink and downlink. Operation in paired and unpaired spectrum shall be supported • Improved system latency Modulation • Downlink would use Orthogonal Frequency Division Multiplexing (OFDM) and the uplink would use Single Carrier – Frequency Division Multiple Access (SCFDMA). • Supported downlink data-modulation schemes are QPSK, 16QAM, and 64QAM. The possible uplink data-modulation schemes are BPSK, QPSK, 8PSK and 16QAM. • The use of the Multiple Input Multiple Output (MIMO) scheme, with possibly up to four antennas at the mobile side, and four antennas at the Cell site. Copyright (c) Paul Bedell 2010 4G Building Blocks Core Network • • • • IP-Based Core Network Packet Voice Solutions Reduced Cost Scalable Design • Distributed, IP-Based Architecture • Reduced Latency • Scalable Design Access Network • OFDMA • Multiple Antenna Techniques • Very High Radio Efficiency Air Interface Copyright (c) Paul Bedell 2010 High Level LTE Network Architecture E-UTRAN: Evolved Universal Terrestrial Radio Access Network eNodeB Backhaul Network eNodeB EPC: Evolved Packet Core MME S-GW HSS P-GW eNodeB: S-GW: P-GW: MME: HSS: UE (User Equipment) Evolved Node B Serving Gateway Packet Gateway Mobility Management Entity Home Subscriber Server = Main Logical Nodes Copyright (c) Paul Bedell 2010 Mobility Management Entity (MME): • Device Registration and Tracking • Bearer Management EPC Architecture Home Subscriber System (HSS)): • Subscription Data • Security Information EPC MME S-GW HSS P-GW Serving Gateway (SGW): • Packet Data Routing • Mobility Anchor IP Network PDN Gateway (PGW): • Default Gateway • Packet Filtering • QOS Enforcement Copyright (c) Paul Bedell PCRF 2010 Policy Charging and Rules Function (PCRF): • QOS Decisions LTE Downlink Modulation Scheme: OFDM: (Orthogonal Frequency Division Multiplexing) • Orthogonal frequency-division multiplexing (OFDM) is a method of digital modulation in which a signal is split into several narrowband channels at different frequencies. In some respects, OFDM is similar to conventional frequency-division multiplexing (FDM). The difference lies in the way in which the signals are modulated and demodulated. Priority is given to minimizing the interference, or crosstalk, among the channels and symbols comprising the data stream. • The basic principle of OFDM is to split a high-rate data stream into a number of lower rate streams that are transmitted simultaneously, in parallel, over a number of subcarriers. OFDM splits the transmission bandwidth (channel) into many narrow subchannels which are transmitted in parallel. • OFDM is present in: • LTE • Mobile WiMax IEEE 802.16e • xDSL • Wireless LAN IEEE 802.11a,g,n Copyright (c) Paul Bedell 2010 Major Challenges For Wireless Industry: – 1983 – Present: The “NIMBY” phenomenon. “Not In My Backyard”. Wireless subscribers desire – demand – great cellular coverage but protest when base station towers are installed in areas where “ugly towers” are not desired. – 2006 – Present: Backhaul network congestion and bottlenecking due to proliferation and popularity of wireless data technologies and services, based on 3G rollouts. • Traditionally, base station-to-MSC (switch) connections have been one or two DS-1 circuits. This traditional model is quickly becoming outmoded as the backhaul network now has huge potential to become a bottleneck. Adding more and more DS-1 circuits becomes expensive. Solution? Ethernet in the backhaul network: simple, known technology. Ultimately less expensive than multiple DS-1 circuits. – 2010: Radio spectrum is becoming a precious and increasingly scarce commodity. Also, data traffic vs. revenue dichotomy. Copyright (c) Voice Paul Bedell 2010 TDC-425 / Data Network Fundamentals For More Information……… Available On Amazon.com and other fine Internet outlets. Copyright (c) Paul Bedell 2010