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Antenna Arrays for Mobile Communication Systems Practical Considerations & BS Accessories Antennas and Antenna Systems Development : Antennas and Antenna Systems Development Radio antennas couple electromagnetic energy from one medium (space) to another (e.g., wire, coaxial cable, or waveguide). Examples of Antennas Yagi-Antenna Array Horn Antenna Parabolic Dish Slide 5: Omni 2000 360° 11dBi UMTS 741 790 Radiator: Copper and brass Radome: closed self-supporting fiber-glass profile Base: Weather-proof aluminum XXPol A-Panel 900/1800 C 65°/60° 15/17dBi (GSM) 2 x 7-16 female Bottom or Top < 1.5 50 Ohm. +45/-45 > 30 dB 1296 / 262 / 116 mm 741 326 Radome: closed self-supporting fiber-glass profile, (no drill-holes) closed by two end caps with short sealing rings Slide 6: GSM Omni Base Station Panel Antenna HPBW = 65 deg. HPBW = 90 deg. Antenna Mounting : Antenna Mounting Attachment Clamp Down-tilt Bracket Antenna Setting Procedure : Antenna Setting Procedure 1) Set this angle on the scale of the Azimuth Adjustment Tool (AAT) 2) Attach the tool to the antenna 3) Aim at the target through the telescope and twist the antenna accordingly to set the correct radiating direction Why are Dipoles better than Printed Board Solutions at BS? : Why are Dipoles better than Printed Board Solutions at BS? Dipoles Usage advantages: Excellent CPR over azimuth( dB) For 60 degree from the main direction for 65 or 90 degree HPBW Low intermodulation products ( -150 dBc) Low internal losses ( low loss power distribution of cable harness) High isolation between the two polarization inputs of min. > 30 dB (typically 35 dB) Dipole design permits rain, ice and snow have only little effect on the electrical parameters such as VSWR, isolation and cross polar ratio Slide 10: NONE Antenna Systems : Antenna Systems How can an antenna be made more intelligent? Adding more elements. Design to shift signals at each of the successive elements. This basic hardware and software concept is known as the phased array antenna. Slide 12: Coverage Capacity QOS For Non Adaptive BSs For Adaptive BSs Cell Splitting : Cell Splitting Cell Splitting subdivides a congested cell into smaller cells called microcells Advantages: Antenna height & Transmitter Power Reduction Capacity Improvement by decreasing R and Unchanged D/R Disadvantages: Increasing of BSs, Handoffs & Processing Load of subscriber (I) Sectorized Systems : (I) Sectorized Systems Basic Sectorized System Higher-Order Sectorized System Sectorized System based on Cell – Sectoring technique Capacity is improved by reducing the number of cells and, thus, increasing the frequency reuse. while keeping the cell radius unchanged and reducing the D/R ratio Most systems in commercial service today employ 3 sectors, each one with 120? coverage .Operationally, each sector is treated as a different cell in the system Sectorized System (continue) : Sectorized System (continue) 1-Antenna Sector System Sector Base Station 2-Antenna sector System Macro – Cell BS Radius: 1-20 Km Height:15 m Micro – Cell BS, R:100-1000 m, h: 12 m Pico – Cell BS, indoor environment, h: 7 m Slide 16: Basic Sectorized System Sectorized Systems (Continue) HIGH LOW (II) Diversity Systems : (II) Diversity Systems (1) Diversity Concept: Basic idea: Tx: Send same bits over independent fading paths. Rx: Receive multiple i/p signals at Diversity Branches. Aim: To reduce the negative fading effects & multipath fading without increasing Tx power or channel BW. All Diversity Branches outputs are selected or combined before reaching the detector. & Rx is ( a Diversity Rx ) OR ( an Adaptive Rx ) Slide 18: Two Separated Antenna Sites - Two or more Antennas at same site Large-Term fading reduction - Short-Term fading reduction Soft handoff -Frequency hopping of TDMA system ( CDMA ) ( GSM ). RAKE Receiver - Interleaver ( Time Diversity ) (2) Slide 19: Basic Microscopic Diversity Techniques Space diversity : Multiple antenna elements separated by decorrelation distance (horizontal separation of 10 to 20 wavelengths) for low correlation of signal reception prevails between them Angle or direction diversity : One or multiple directional antenna(s), each responds to a narrow direction of arrival (DOA) spread Slide 20: Polarization diversity Two transmit or receive antennas with different polarizations. These (orthogonal) polarizations pose a low correlation and size-wise maximum diversity gain is limited to 2dB. Normally, horizontal polarization is weaker than the Vertical polarization about 6 to 10 dB Time diversity : Transmitting a message two or more times on the same frequency across the radio channel, the probability of good reception is increased. As using in paging systems. 1 0 1 0 1 0 1 Info. 1 0 1 0 1 0 1 Info. Delay time Slide 21: (3) Diversity combining techniques: Selection diversity combiner (SC) It involves a set of M antennas and the (output) signal is acquired from an antenna of this array such that it yields the largest signal-to-noise (SNR) at the output It achieves 3 dB diversity Gain improvement (one antenna is used at a time) Non Coherent Combiner (One antenna is used at a time) It is implemented in BSC or MSC to achieve soft handoff in CDMA System Maximal-ratio combiner (MRC) : Maximal-ratio combiner (MRC) It takes advantage of all the diversity branches of the array It achieves 6 dB diversity Gain Improvement (M antennas are used at a time). So, it is a Coherent combiner All branches are added in phase so as to realize maximum diversity gain. This method is more sophisticated Slide 23: Equal-gain Combining (EGC) Although optimal, MRC is expensive to implement. Also MRC requires an accurate tracking of the complex fading, which is difficult to achieve in practice. A simpler Alternative is given by EGC Slide 24: Selective (Switched) System Diversity Systems (Continue) HIGH LOW (III) Beamforming Systems : (III) Beamforming Systems beamforming: Multiple signals are combined to form an RF beam to the user A Visible Light Beamforming Analogy (1) Phased Array System (Scanning Beamforming System) : (1) Phased Array System (Scanning Beamforming System) What is smart Antenna? : What is smart Antenna? A smart antenna consists of an antenna array, RF hardware, and a controller that changes the array pattern in response to Signal environment to improve the performance of a communication system Slide 28: Finite fixed patterns( nulls & SLL) Low Side lobes are directed to Interferers Infinite (scenario-based) patterns with steered nulls SLL Reduction 40 dB Smart Antenna Systems Comparison : Smart Antenna Systems Comparison Type Limitation Very High EXCELLENT (1) Switched (Fixed) Beam System : (1) Switched (Fixed) Beam System It is the simplest smart antenna technique using fixed BF system It forms multiple fixed beams with heightened sensitivity in particular directions and switches from one beam to another as the cellular phone moves throughout the sector It is an alternative to Higher-Order Sectorized System by dividing the macro-sector into several micro-sectors without Antennas increasing in the BS site. The same beam can be used for UL or DL (i) Concept: (ii) Block Diagram: : (ii) Block Diagram: It Consists of : phase shifting network: forms multiple beams looking in certain directions (i.e. Buttler Matrix or Blass Matrix) RF Switch: actuates the right beam in the desired direction The control logic is governed by an algorithm which scans all the beams and selects the one receiving the strongest signal based on a measurement made by the detector Slide 32: Switched Beam Simulation (3) Fixed Beamforming NW Example : (3) Fixed Beamforming NW Example Buttler Matrix is the most popular switched BF network Inter-element phase shifts is given by: Advantages: * Easy implementation *Small Loss in Hybrids, phase shifters & T.L Disadvantages: * Beamwidths & Beam angles vary with frequency * Complex for Bigger matrix UL & DL Scenario (4) Benefits & Limitations : (4) Benefits & Limitations (I) Benefits: Coverage Extension (from 20% to 200 % Compared to Conventional BS) Compatible with the Systems Low Complexity & Cost (II) Limitations: Susceptibility to interfering signals or multipaths arriving from angles near that of the desired signal Scalloping Lack of path diversity (No Coherent Combining) Slide 35: (5) Whole Implementation (2) Adaptive Beam System : (2) Adaptive Beam System Concept: It is fully smart antenna System It likes a Switched Beam System but with a Signal Processing Controller The Signal processor steers the main beam towards the desired MS, follows it as it moves & the nulls toward the interfering signals The Processing is governed by Complex Computationally intensive Algorithms (ii) Block Diagram : (ii) Block Diagram In this Digital Beamformer, the Adaptive System utilizes base band Adaptive & DOA Algorithms to Continuously distinguish between desired signals, multipath, and interfering signals (SOI & SNOI) There are many adaptive algorithms ( Blind or Non Blind) to update the array Weights, each with its speed of Convergence and required Processing time (i.e CMA & LMS adaptive algorithms) There are many DOA-estimation methods that can calculate the DOA of all incoming signals (i.e. MUSIC Algorithm) (iii) LMS Adaptive Algorithm : (iii) LMS Adaptive Algorithm * it is the most common used adaptive algorithm in the smart antenna implementation It is either Constrained Algorithm (No Knowledge of DOA of the signals) OR Unconstrained Algorithm (which needs a reference signal to update weights) * The Unconstrained LMS Algorithm is the most applicable Slide 39: Constrained LMS Code Simulation: (IV) MUSIC Algorithm : (IV) MUSIC Algorithm MUSIC algorithm is efficient tool for the plot of spatial spectrum for estimate the number of incident signals and the angle of arrivals But it will be only suitable for smaller number of signals The number of incident signals can be calculated by counting the number of Eigen values above the noise floor. (V) Unconstrained LMS Smart Antenna Simulation : (V) Unconstrained LMS Smart Antenna Simulation SDMA (Space Division Multiple access) : SDMA (Space Division Multiple access) SDMA system block diagram SDMA is the most sophisticated utilization of smart antenna technology It is based upon the concept that a signal arriving from a distant source reaches different antennas in an array at different times due to their spatial distribution SDMA concept Example : Example Why smart Antenna? : Why smart Antenna? Range/Coverage Extension Greater Battery Life & Smaller Handset Fewer Base Stations (Nc decrease) Co-Channel Interference Rejection Capacity Improvement Multipath Rejection Without using of Equalizer Higher Bit Rate Using of independent spot beams Reduction in Handoff except only when two beams use the same frequency cross each other DL power efficiency Due to P.G Lower Cost (i.e. Lower Amplifiers Cost) Compatible With Various MA Techniques, any Modulation & any BW. Who can use Smart Antenna Technology? : Who can use Smart Antenna Technology? Cell Phones WiFi Applications for access points and clients WiMax/4G Mobile Applications for tower, base stations and clients Laptops, Palmtops (Mobile personal digital assistant (PDAs)) and Handset Applications 3G Cellular (UMTS) RFID Ultra Wide Band/Bluetooth Example (1): IS-136 TDMA (AT&T Wireless Service Provider) AT&T (American Telephone & Telegraph Company) serves over 14 million subscribers with digital TDMA technology and some remaining analog technology, and provides packet data service with CDPD (Cellular Digital Packet Data) technology.* TDMA parameters:i- 30 KHz channels (like analog & CDPD)ii- 20 msec speech framesiii- 3 time-slots/usersiv- 7.4 kbps ACELP speech codingv- 1/2-rate channel coding on important bits interleaved over 2 bursts in 40 msecvi- Differential pi/4-QPSK modulation : Example (1): IS-136 TDMA (AT&T Wireless Service Provider) AT&T (American Telephone & Telegraph Company) serves over 14 million subscribers with digital TDMA technology and some remaining analog technology, and provides packet data service with CDPD (Cellular Digital Packet Data) technology.* TDMA parameters:i- 30 KHz channels (like analog & CDPD)ii- 20 msec speech framesiii- 3 time-slots/usersiv- 7.4 kbps ACELP speech codingv- 1/2-rate channel coding on important bits interleaved over 2 bursts in 40 msecvi- Differential pi/4-QPSK modulation TDMA Capacity Roadmap : TDMA Capacity Roadmap Reuse N = 7 N = 5 N = 4 Smart Antennas Base station antennas systems that use digital signal processing to cancel interference 2000 2001 2002 * Dual band base Operation at 800 or 1900 MHz. Calls can be set up on either frequency band and handed between them to manage traffic Additional spectrum at 1900 MHz adds directly to capacity of cell Dynamic Channel Assignment Network automatically assigns radio frequencies to cell sites for more efficient utilization of frequencies Base Station Power Control Base stations only transmit power required to reach mobile with adequate signal quality resulting in lower interference Discontinuous Transmission Mobiles transmit only during when user is speaking. Lowers interference in the system and increases talk time Slide 48: IS-136 Smart Antenna Test Bed Reuse of 3/9 to 4/12, instead of 7/21, approximately 2x capacity Two dual polarization uplink antennas, downlink multibeam antenna with 4 - 30° beams Shared linear power amplifier unit with Butler matrices Real-time downlink power control with beam tracking Slide 49: IS-136 Smart Antenna System (TDMA) Slide 50: Example(2) : Smart Antenna Usage in a Mixed CDMA2000 Voice and Data Environment Motorola Global Telecom Solutions Sector (October 1, 2002) The first advanced antenna solution (Beam Switching Overview – Embedded Solution) – Fixed beams technology (from 3 to 4) within existing sectors – Same pilot in one sector illuminates all beams – Compatible with all IS-95A/B, CDMA2000 1X, 1xEV-DV – Voice capacity gains estimated to be between 1.8X and 2.3X (Voice) over a 3 sector site *Block Diagram: Narrow Beam Antenna - (NBA) – Switch/Sum. – Passive RF Beamformer (Butler Network) Slide 51: (II) The second advanced antenna solution (Beam Steering Overview – Embedded Solution) – Adaptive beam per user – Potential impacts on Asics and requires calibration – More sophisticated method – Voice capacity gains 2X to 3X (Voice) over 3 sector sites Slide 52: (III) Smart Antenna Technology for the 1xEV-DO and 1xEV-DV Shared Packet Channels (i) 1xEV-DO Challenges for Implementation of Beam Switching / Beam Steering: * Characteristics: • TDM only • Adaptive Modulation/Coding. • Scheduler uses mobile C/I feedback. * Using Switched Beams • Doubles power received per Walsh Code • Walsh SIR increase: 0 to 3 dB • Depends on mobile geometry and channel • Changes adjacent cell interference. Slide 53: (ii) 1xEV-DV Capacity Benefits from Switched Beams (switched beams exploit 2-user CDM) Assumptions: - N Walsh codes for shared PDCH - a = C/I per Walsh of Beam 1 user - b = C/I per Walsh of Beam 2 user 1- Switched Beams with 2-user CDM: • Schedule 1 user per beam • Equal (or unequal but constant) power per beam • Each packet channel user gets a fraction of the Walsh space • Walsh allocation maximizes capacity • Divide power transmitting equally over Walsh subset • In each beam, only transmit Walsh code allocated to the user in that beam Slide 54: 2- Switched Beam Benefits for 1xEV-DV: • Without CDM – PDCH Capacity = N log (1 + max ( a, b )) • If a=b, Capacity = N log (1+a) • With CDM – PDCH Capacity = N log (1 + a + b) – N x a/ (a+b) Walsh codes for user 1 – N x b/ (a+b) Walsh codes for user 2 • If a = b – PDCH Capacity = N log (1 + 2 a) – A 3 dB increase in SIR per Walsh code Installation Issues of the Antenna System : Installation Issues of the Antenna System Wind Loading & Static weight Feeder Selection Exp. A: 9 m BS , Exp. B: 15 m BS, Unit Area Square 50 Ohm RF Coaxial Cables Slide 56: Feeder issue Development By using (1) Fiber Optic Cable Advantages: *small, Very light & flexible Disadvantages: * Additional Hardware near Antenna Array * Mast top Servicing & maintenance Problems OR (2) Spatial Multiplexing of Local Elements Technique (SMILE) It uses TDM Technique between RF Antennas Advantages: * One feeder is used * Mutual Coupling Reduction Disadvantages: * The MUX Insertion Loss Accessories : Accessories Slide 58: (1) Band-Pass Filter: (i) Usage 1- Input selectivity of receivers and amplifiers Improvement 2- Isolation of Transmitters Improvement whose respective antennas are mounted close together 3- Intermodulation products & noise sidebands Suppression 4- Acting as a Combiner Component (ii) Design and Construction It consists of 2 – capacitively coupled (lamda/4) Coaxial Resonators mounted on a Stable Mounting plate Slide 59: (iii) Filter characteristics Narrow Pass band with low insertion loss, high stop band attenuation outside of the pass band & is centered at with A bandwidth of ( ) (iv) Technical Data f0 f0 ±1.75 MHz Slide 60: (v) Tuning Examples Slide 61: (2) Band Stop Filter: (i) Usage 1- Interfering signals Attenuation 2- Isolation between a transmitted a receiver 3- Intermodulation products Suppression (ii) Design and Construction The band-pass filter consists of two lamda /4 coaxial resonators mounted on a stable mounting plate Slide 62: (iii) Filter characteristics Narrow stop band with high stop band attenuation, low insertion loss outside of the stop band & centered at with a bandwidth of ( ) (iv) Technical Data f0 f0 ±1.75 MHz Slide 63: (v) Tuning Examples You do not have the permission to view this presentation. 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