Multiple Antennas: Performance Gains with Channel Measurements May 2003 Multiple Antennas: Performance Gains with Channel Measurements Minnie Ho, Qinghua Li, Sumeet Sandhu Cliff Prettie, David Cheung Minnie Ho, Intel Corporation

Performance Metrics of Interest May 2003 doc.: IEEE 802.11-03/279r0 May 2003 Performance Metrics of Interest Capacity Gain Definition: bits per second per Hz Implication: Efficiency in use of bandwidth Increase in data rate for given bandwidth Diversity Order Definition: slope of BER curve vs. SNR Increase in SNR at a fixed BER Can translate to increase in range Alamouti code (diversity order = 2) Slope is 2 In this talk, we consider two performance metrics of interest. There are many others relevant to multiple antenna systems, such as degrees of freedom, coding gain, array gain, etc. Here, we focus on capacity and diversity order. The plot shows an increase in diversity order using the Alamouti code. Minnie Ho, Intel Corporation Minnie Ho, Intel Corporation

Theoretical Gains are Well-Known May 2003 Theoretical Gains are Well-Known Shannon Capacity [Telatar] Mr receive antennas Mt transmit antennas Capacity is linear with min(Mr, Mt) Diversity Order Maximum diversity order = Mr x Mt ZF receiver [Winters] Mr + Mt receive antennas Mr-1 (users) interferers can be nulled out Mt+1 diversity order Questions: How can we apply these results to real systems? What are the gains with measured channels? Minnie Ho, Intel Corporation

Techniques for Increasing Throughput May 2003 Techniques for Increasing Throughput Point-to-point MIMO Increases maximum data rate between a user and an AP (PHY rate) Improves spectral efficiency (bits/sec/Hz) Point-to-multipoint SDMA Simultaneous transmission from AP to multiple users Increases throughput at the MAC SAP at an AP SDMA MIMO Minnie Ho, Intel Corporation

Techniques for Increasing Diversity May 2003 Techniques for Increasing Diversity Switched diversity (selection between multiple antennas) MRC Alamouti MMSE (minimum mean-squared error) ZF (zero-forcing) ML (maximum likelihood) Minnie Ho, Intel Corporation

Measurement environment: Enterprise (office cubicles) May 2003 Measurement environment: Enterprise (office cubicles) Stationary (night) Automated positions WLAN “AP” WLAN “STA” Minnie Ho, Intel Corporation

May 2003 Measurement Setup At a given tone, the complex channel response from 1 transmit location to 1 receive location is measured RF component responses compensated from measurements Other frequency bands measured (UWB, full UNII, ISM) 750,000+ measurements in searchable database Minnie Ho, Intel Corporation

Propagation Snapshot at 3.5 m May 2003 doc.: IEEE 802.11-03/279r0 May 2003 Propagation Snapshot at 3.5 m The second is the same movie but cut to 17 to 22 ns in time (takes 5 seconds to watch in real-time).   These are probably the most visually appealing movies we have – nice distinctive wavefront arrivals from a few different directions.  Some things you can note as you show the movie: the movies were generated from data collected over 4 STA (desktop) positions and 37x37 AP (ceiling) positions in the 2-8 GHz band at a distance of about 3.5m, in SC12, 3rd floor (cubicle environment).  The 4 STA positions are at the corners of a 6” square.  The 37x37 AP positions are spaced over a grid with 0.5” spacing (total travel of 1.5’x1.5’).  The movie consists of 5476 actual vector network analyzer measurements (4*37*37) taken using an automated system (robotic positioners, etc.).  To generate the movie we took the inverse Fourier transform of each measurement (resulting in the impulse response at each point).  Each frame of the movie is a slice in time of all the impulse responses, the colors representing the intensity of the energy (in volts) at that point on the array.  Minnie Ho, Intel Corporation Minnie Ho, Intel Corporation

Theoretical Capacity Results May 2003 Theoretical Capacity Results SDMA 4 antennas at the AP (Mr = 4) 1 antenna at each STA (Mt = 1) Four “degrees of freedom” AP should be able to support 4 simultaneous users MIMO 2 antennas at the AP (Mr = 2) 2 antennas at the STA (Mt = 2) Link should be able to support 2x the data rate Minnie Ho, Intel Corporation

Measurement Locations and Grid May 2003 Measurement Locations and Grid 12m 5m 7m 9m 3m 25m 14m 18m 13m Minnie Ho, Intel Corporation

Measured Capacity: Downlink May 2003 doc.: IEEE 802.11-03/279r0 May 2003 Measured Capacity: Downlink SDMA increases the capacity of SISO between 3 and 4 times The capacity of zero-forcing is close the maximum (coordination) The capacity of zero-forcing is greater than 275 Mbps with a 90% probability. Three 54 Mbps links with 62% MAC efficiency delivers 100 Mbps network throughput at AP. Minnie Ho, Intel Corporation Minnie Ho, Intel Corporation

Measured Capacity: Uplink May 2003 doc.: IEEE 802.11-03/279r0 May 2003 Measured Capacity: Uplink SDMA increases the capacity of SISO between 3 and 4 times. MMSE technique reduces capacity and suffers from noise amplification and MAI. The capacity of zero-forcing is greater than 275 Mbps with probability 90%. Minnie Ho, Intel Corporation Minnie Ho, Intel Corporation

Theoretical Diversity Gain May 2003 Theoretical Diversity Gain Theoretical Maximum diversity order = Mr x Mt Diversity order for ZF receiver = Mr – Mt + 1 [Winters et al] SDMA 4 antennas at the AP (Mr = 4) 1 antenna at each of 3 STAs (Mt = 3) ZF Diversity order should be 2 for each link MIMO 2 antennas at the AP (Mr = 2) 2 antennas at the STA (Mt = 2) MMSE Diversity order should be about 1 Minnie Ho, Intel Corporation

Measured Diversity: Downlink May 2003 doc.: IEEE 802.11-03/279r0 May 2003 Measured Diversity: Downlink 4-antenna diversity gain compared to SISO is 1.6 5-antenna diversity gain compared to SISO is 2.6 The diversity gain for SDMA with 4 antennas vs SISO is 7.2/4.5 in downlink.  2)       The diversity gain for SDMA with 5 antennas vs SISO is 7.2/2.8 in downlink.  Minnie Ho, Intel Corporation Minnie Ho, Intel Corporation

Measured Diversity: Uplink May 2003 doc.: IEEE 802.11-03/279r0 May 2003 Measured Diversity: Uplink 4-antenna diversity gain compared to SISO is 1.5 5-antenna diversity gain compared to SISO is 2.0 3)       The diversity gain for SDMA with 4 antennas vs SISO is 7.2/4.8 in uplink.  4)       The diversity gain for SDMA with 5 antennas vs SISO is 7.2/3.5 in uplink.  Minnie Ho, Intel Corporation Minnie Ho, Intel Corporation

Theoretical Capacity Results May 2003 Theoretical Capacity Results SDMA 4 antennas at the AP (Mr = 4) 1 antenna at each STA (Mt = 1) AP should be able to support 4 simultaneous users MIMO 2 antennas at the AP (Mr = 2) 2 antennas at the STA (Mt = 2) Link should be able to support 2x the data rate Minnie Ho, Intel Corporation

Measurement Locations and Grid May 2003 Measurement Locations and Grid 12m 5m 7m 9m 3m 25m 14m 18m 13m Minnie Ho, Intel Corporation

May 2003 Measured Capacity Minnie Ho, Intel Corporation

May 2003 Minnie Ho, Intel Corporation

Theoretical Diversity Gain May 2003 Theoretical Diversity Gain Theoretical Maximum diversity order = Mr x Mt ZF Diversity order = Mr – Mt + 1 [Winters et al] SDMA 4 antennas at the AP (Mr = 4) 1 antenna at each of 3 STAs (Mt = 3) ZF Diversity order should be 2 for each link MIMO 2 antennas at the AP (Mr = 2) 2 antennas at the STA (Mt = 2) MMSE Diversity order should be about 1 Minnie Ho, Intel Corporation

Measured Diversity Diversity is of order 1 for uncoded MMSE May 2003 doc.: IEEE 802.11-03/279r0 May 2003 Measured Diversity Diversity is of order 1 for uncoded MMSE Diversity is the same order as SISO Coded gives more diversity (frequency diversity). The code is the standard 802.11a code with interleaving. Minnie Ho, Intel Corporation Minnie Ho, Intel Corporation

Conclusions Measured capacity less than (close to) theoretical May 2003 doc.: IEEE 802.11-03/279r0 May 2003 Conclusions Technique Theoretical Capacity Measured Diversity Measured Diversity Point-to-Point MIMO (w/o channel knowledge) Linear with number of antennas Linear (2x with 2x2 system) Mr-Mt+1 Mr-Mt+1 (order 1 with 2x2 system with MMSE) Point-to-Multipoint SDMA Sub-linear (3 users with 4 antennas) (2 for 4 antennas, 3 users) Down: 1.6 Up: 1.5 Measured capacity less than (close to) theoretical Measured diversity less than (close to) theoretical Practical system design is the challenge Minnie Ho, Intel Corporation Minnie Ho, Intel Corporation

For further information May 2003 doc.: IEEE 802.11-03/279r0 May 2003 For further information Send e-mail to Minnie Ho To: minnie.ho@intel.com Subject: SmantIntel For further information, send e-mail to Minnie Ho. In the subject line, please include the following word: SmantIntel Minnie Ho, Intel Corporation Minnie Ho, Intel Corporation

May 2003 Backup Slides Minnie Ho, Intel Corporation

BER Comparison for SDMA May 2003 Downlink and BER 10-5 SDMA with 4 antennas requires 1ower SNR than SISO and SISO with selection in 86% and 74% of the time respectively. SDMA with 5 antennas requires 1ower SNR than SISO and SISO with selection in 97% and 92% of the time respectively. Uplink and BER 10-5 SDMA with 4 antennas requires 1ower SNR than SISO and SISO with selection in 65% and 50% of the time respectively. SDMA with 5 antennas requires 1ower SNR than SISO and SISO with selection in 81% and 71% of the time respectively. Minnie Ho, Intel Corporation