3G Evolution Outline Chapter: 6 p 6 •Introduction •Multi-antenna configurations g •Multi-antenna techniques Multi-antenna techniques M lti t t h i •Multiple receiver antennas, SIMO •Multiple transmitter antennas, MISO •Multiple transmitter antennas MISO Vanja Plicanic •Multiple antennas at both RX and TX, MIMO vanja.plicanic@eit.lth.se vanja plicanic@eit lth se Department of Electrical and Information Technology 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 1 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 2 Introduction Multi-antenna configurations Base station (BS) User Equipment (UE), ex. Mobile station (MS) Multi-antenna systems Multi-antenna techniques Single-input single-output Smart antennas Single-input multiple-output Multiple-input single-output Multiple antennas at the receiver and/or transmitter + + Multiple-input single-output Smart signal processing 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 4
Antenna configurations cont. Antenna configurations cont. - Configuration of the antennas is decided by the requirement on the antenna g y q - However, the case of MS at low frequencies < 900 MHz q mutual coupling and correlation (low/high) => 0.5 wavelengths is large distance for low frequencies - Thus, configuration decided by choice of Common phone size allows for Common phone size allows for ~0.25 wavelengths distance at 850 MHz! 0 25 wavelengths distance at 850 MHz! - spatial distance between the antennas Low mutual coupling and correlation when: p g BS: >10 wavelengths (due to small AoA in macro cell, shorter distance in micro cells) MS: >0.5 wavelengths (due to wide AoA) MS: >0 5 wavelengths (due to wide AoA) - polarization directions of the antennas Antennas with different polarizations for both BS and MS gives lower mutual A t ith diff t l i ti f b th BS d MS i l t l => Polarization diversity hard to implement due to antenna + chassis radiation, coupling and correlation. difficult to rotate chassis wave-mode 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband Multi-antenna techniques cont. Multi-antenna techniques cont. How ? Why? DIVERSITY - Antennas at receiver and/or transmitter - To improve system capacity (more users per cell), - Mitigates fading in the radio channel DIVERSITY better link reliability - Low mutual coupling required Low mutual coupling required BEAM-FORMING - Antennas at receiver and/or transmitter Antennas at receiver and/or transmitter BEAM-FORMING - Shaping of antenna beams to maximize gain - To improve coverage (possibility for larger cells) in certain direction or suppress specific interferer - Low or high mutual coupling required SPATIAL MULTIPLEXING - Antennas at both receiver and transmitter - To achieve higher data rates per user, - Sending several data streams on multiple parallel SPATIAL MULTIPLEXING higher spectral efficiency channels - Low mutual coupling required p g q Figures above Courtesy of Ericsson Figures above Courtesy of Ericsson 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 7 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 8
Multiple receiver antennas, SIMO Multiple receiver antennas, SIMO RX diversity - aims to: aims to: • mitigate fading • suppress specific interferer Linear receiver antenna combining - All information is exploited by combining copies of the signal from all the antennas (in All information is exploited by combining copies of the signal from all the antennas (in comparison to switched/selection diversity) - Assumes non-time variant channel Smart signal processing techniques: - Weights the signal copies with corresponding amplitude - RX diversity RX di i and phase correction - Noise limited system: - Receive beam-forming - Maximum Ratio Combining (MRC) - Adaptive space time processing Adaptive space time processing - Interference limited system: Interference limited system: - Maximum Ratio Combining (MRC) - Interference Rejection Combining (IRC) - Minimum Mean Square Error (MMSE) 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband Multiple receiver antennas, SIMO Multiple receiver antennas, SIMO RX diversity RX diversity Linear receiver antenna combining in: Maximum Ratio Combining (MRC) - Noise limited case: N i li it d - Amplitude and phase weighting A lit d d h i hti - Phase weights- adjustment to assure that signals from two antennas are aligned - Amplitude weights- adjustment of the received signals to correspond to the channels gain, higher weight for stronger signals. g g g - Diversity gain and array gain - For noise limited environments - Maximum Ratio Combining (MRC) - Interference limited system: I t f li it d t - Maximum Ratio Combining (MRC) - Interference Rejection Combining (IRC) Interference Rejection Combining (IRC) - Minimum Mean Square Error (MMSE ) 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
Multiple receiver antennas, SIMO Multiple receiver antennas, SIMO RX diversity RX diversity Adaptive space-time processing Interference Rejection Combining (IRC) Interference Rejection Combining (IRC) - Frequency selective channel - Linear time domain filtering/equalization, linear processing to signals received at different times (MRC Zero forcing MMSE) times (MRC, Zero-forcing, MMSE) - - For interference limited environment For interference limited environment For interference limited environment For interference limited environment - - Uplink intra-cell interference suppression, Spatial Division Multiple Access (SDMA) Uplink intra-cell interference suppression, Spatial Division Multiple Access (SDMA) - Linear receive antenna combining, linear processing to signals received at different antennas - - Able to suppress N R -1 interferers, however large noise increment after combining Able to suppress Nr-1 interferers, however large noise increment after combining Minimum Mean Square Error (MMSE ) Minimum Mean Square Error (MMSE ) - - Weights to minimize the difference between the estimated and transmitted signal. Weights to minimize the difference between the estimated and transmitted signal. 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband Multiple receiver antennas, SIMO Multiple receiver antennas, SIMO Receive beam-forming Receive beam-forming - Switched beam antennas - Antenna array that can form pattern beams pointing in certain discrete direction Switched antenna array Switched antenna array Adaptive antenna array Adaptive antenna array - switching selects the “best” beam for down conversion and post processing, goal to i hi l h “b ” b f d i d i l maximize the SNR - simple implementation, since only one signal to post process - limited flexibility, since only fixed directions y, y - Amplitude and phase weights MRC => a receiver beam with maximum gain N R in the direction of the target signal IRC > a receiver beam with high attenuation in the direction of the IRC => a receiver beam with high attenuation in the direction of the target signal Figures above Courtesy of jackwinters.com 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
Multiple transmit antennas Multiple transmit antennas TX diversity - Does not require channel knowledge at the receiver - Techniques: Techniques: - Delay/Temporal diversity - Cyclic-delay diversity - Space time/frequency coding (STBC/STFC) Smart signal processing techniques: - TX diversity - Transmit beam-forming 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband Multiple transmit antennas Multiple transmit antennas TX diversity TX diversity Delay/Temporal diversity Cyclic-delay diversity - - Time variant channel Time variant channel - Applies cyclic shift instead of linear delays A li li hift i t d f li d l => signals received at different times are uncorrelated => delay diversity already there and can be extracted in advanced receivers (ex. GRAKE) (ex GRAKE) - Time in-variant channel => create artificial time dispersion (frequency selectivity) => transmit identical signals with different delays from different antennas - Delay diversity usually implemented by forward error correction, ARQ, repetition coding etc. - Delay diversity invisible to mobile terminal since it is just additional time dispersion handled by the receiver 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
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