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28 GHz and 73 GHz Millimeter-Wave Indoor Propagation Measurements and Path Loss Models

Sijia Deng, Mathew K. Samimi, Theodore S. Rappaport

arXiv:1509.00395v1cs.ITmath.IT

TL;DR

Limited propagation evidence at millimeter-wave frequencies motivates indoor measurements for channel modeling. This paper measures 28 and 73 GHz office channels with directional sounders, finding distinct path-loss exponents and delay-spread statistics across frequencies and propagation conditions.

  • Problem

    Indoor channel measurements are needed to characterize path loss and temporal and spatial properties for system-capacity and throughput simulations, while E-band propagation had received little research attention.

    Source: §I · p. 1

  • Method

    The study used broadband sliding-correlator sounders and steerable directional antennas to measure 28 and 73 GHz propagation in an office across locations and antenna configurations.

    Source: A. Propagation Measurements and… · p. 1, C. Measurement Procedure · p. 2

  • Results

    Omnidirectional path-loss exponents were 1.1 and 2.7 in LOS and NLOS at 28 GHz, and 1.3 and 3.2 at 73 GHz; mean RMS delay spreads were 18.4 ns and 13.3 ns, respectively.

    Source: §V · p. 6

  • Takeaways & Limitations

    The measured values can help implement beamforming or beam-finding algorithms to search for transmitter and receiver pointing angles with the lowest path loss or link attenuation.

    Source: §IV · p. 6

Abstract

from arXiv · show

This paper presents 28 GHz and 73 GHz millimeter- wave propagation measurements performed in a typical office environment using a 400 Megachip-per-second broadband sliding correlator channel sounder and highly directional steerable 15 dBi (30 degrees beamwidth) and 20 dBi (15 degrees beamwidth) horn antennas. Power delay profiles were acquired for 48 transmitter-receiver location combinations over distances ranging from 3.9 m to 45.9 m with maximum transmit powers of 24 dBm and 12.3 dBm at 28 GHz and 73 GHz, respectively. Directional and omnidirectional path loss models and RMS delay spread statistics are presented for line-of-sight and non-line-of-sight environments for both co- and cross-polarized antenna configurations. The LOS omnidirectional path loss exponents were 1.1 and 1.3 at 28 GHz and 73 GHz, and 2.7 and 3.2 in NLOS at 28 GHz and 73 GHz, respectively, for vertically-polarized antennas. The mean directional RMS delay spreads were 18.4 ns and 13.3 ns, with maximum values of 193 ns and 288 ns at 28 GHz and 73 GHz, respectively.

I. INTRODUCTION

Demand for high-throughput wireless communications motivates mmWave research, but indoor propagation evidence at 28 and 73 GHz is needed to characterize path loss and time dispersion. This paper presents indoor measurements to support channel modeling for system design.

I. INTRODUCTION

  • Indoor channel measurements characterize path loss with distance and temporal and spatial properties needed for system-capacity and throughput simulations.Source: §I · p. 1
  • The E-band offers substantial spectrum but had received little research attention, motivating study of its propagation characteristics.The introduction identifies 71–76, 81–86, and 92–95 GHz as E-band frequencies.Source: §I · p. 1
  • Indoor measurements at 28 and 73 GHz provide path-loss models and time-dispersion characteristics for mmWave system design.The paper presents extensive measurements for indoor environments.Source: §I · p. 1
  • At 60 GHz, reported indoor path-loss exponents were 1.3–2.2 in LOS and 3.0–3.8 in NLOS office environments.Average RMS delay spreads reported for 60 GHz were 12.3 ns in LOS and 14.6 ns in NLOS.Source: §I · p. 1

A. Propagation Measurements and Environment Description

The study measures indoor propagation in a typical office using steerable directional antennas across multiple transmitter-receiver locations and polarization configurations. It distinguishes LOS and NLOS differently for omnidirectional and directional models.

A. Propagation Measurements and Environment Description

  • Measurements covered five transmitter and 33 receiver locations at 3.9–45.9 m in a modern office with common furnishings and partitions.The transmitter and receiver antennas were 2.5 m and 1.5 m above ground, respectively.Source: A. Propagation Measurements and… · p. 1
  • Two pairs of 15 dBi and 20 dBi directional antennas were rotated in azimuth and elevation to collect departure and arrival angle statistics.Their half-power beamwidths were 30° and 15°, respectively.Source: A. Propagation Measurements and… · p. 1
  • Power delay profiles were acquired at unique pointing angles in V-V and V-H configurations to study depolarization effects.The pointing-angle steps were 15° or 30°, depending on carrier frequency.Source: A. Propagation Measurements and… · p. 2
  • For omnidirectional models, LOS means an unobstructed path and NLOS means obstructions; directional LOS additionally requires boresight alignment.Directional NLOS includes misaligned antennas whether or not the LOS path is obstructed.Source: A. Propagation Measurements and… · p. 2

B. Measurement Equipment

Two broadband sliding-correlator sounders measured propagation at 28 and 73 GHz. Their signal chains generated and correlated pseudorandom sequences to produce power delay profiles.

B. Measurement Equipment

  • Two 400 Mcps broadband sliding-correlator sounders with similar architectures and interchangeable RF conversion front ends served the 28 and 73 GHz measurements.The sounders differed in intermediate-frequency and local-oscillator frequencies.Source: B. Measurement Equipment · p. 2
  • A 2047-chip pseudorandom noise sequence clocked at 400 MHz was upconverted and transmitted through a high-gain directional horn antenna.The stated carrier frequencies were 28 GHz and 73.5 GHz.Source: B. Measurement Equipment · p. 2
  • The receiver cross-correlated the downconverted signal with an identical sequence clocked at 399.95 MHz, using a slide factor of 8,000.Recorded profiles were formed by summing squared I/Q components and averaging 20 instantaneous profiles aligned to the strongest measured multipath component.Source: B. Measurement Equipment · p. 2

C. Measurement Procedure

The measurement procedure used eight azimuth sweeps at each transmitter-receiver location to sample arrival and departure directions under varied antenna alignments. Sweeps were repeated for co- and cross-polarized configurations.

C. Measurement Procedure

  • Eight azimuth sweeps sampled arrival and departure directions at each location, with antenna steps of 15° or 30° depending on carrier frequency.A power delay profile was acquired for fixed transmitter and receiver positions.Source: C. Measurement Procedure · p. 2
  • The first two sweeps measured arrival and departure directions with transmitter and receiver antennas aligned on boresight in elevation.They were designated M1 and M2, respectively.Source: C. Measurement Procedure · p. 2
  • Sweeps M3–M6 tilted one antenna by one beamwidth, M7 used the second-strongest departure direction, and M8 tilted the transmitter in the strongest received-power elevation plane.These sweeps were conducted in both V-V and V-H polarization configurations.Source: C. Measurement Procedure · p. 2

A. Directional 28 GHz and 73 GHz Path Loss Models

Directional path loss is estimated from received power summed across multipath components, with transmit power and antenna gains removed. Strongest-angle NLOS links have lower path loss exponents than arbitrary-angle NLOS fits at both frequencies.

A. Directional 28 GHz and 73 GHz Path Loss Models

  • Directional path loss is recovered by summing multipath-component powers, then subtracting transmit power and removing transmit and receive antenna gains.The resulting measurements support estimates at arbitrary unique pointing angles.Source: A. Directional 28 GHz and 73 GHz Path… · p. 2
  • The indoor map covers 48 TX-RX location combinations in a 65.5 m × 35 m × 2.7 m office.The building includes drywall, glass and metal doors, elevator doors, and soft office partitions.Source: Figure 1 · p. 3
  • Strongest-angle link PLEs are 3.0 at 28 GHz and 3.4 at 73 GHz, indicating the benefit of handset beamforming.These use the strongest TX-RX antenna pointing angle at each location combination.Source: A. Directional 28 GHz and 73 GHz Path… · p. 3
  • Arbitrary-angle NLOS PLEs are 4.5 at 28 GHz and 5.3 at 73 GHz, with shadowing factors of 11.6 dB and 15.6 dB, respectively.The authors report faster signal-level degradation over distance in NLOS.Source: A. Directional 28 GHz and 73 GHz Path… · p. 3
  • Arbitrary-angle LOS PLE is 1.7 at both frequencies, with shadowing factors of 2.6 dB and 2.1 dB.The authors attribute the below-free-space PLE to a likely waveguide effect from indoor hallways and partitions.Source: A. Directional 28 GHz and 73 GHz Path… · p. 3
  • In NLOS with V-H polarization, PLEs are 5.1 at 28 GHz and 6.4 at 73 GHz, with shadowing factors of 10.9 dB and 15.8 dB, respectively.Source: A. Directional 28 GHz and 73 GHz Path… · p. 3

B. Omnidirectional Close-in Reference Path Loss Models

The section derives omnidirectional close-in path-loss models by summing directional received powers and fitting a 1 m-reference model. Co-polarized LOS exponents are below free-space at both bands, while NLOS exponents are higher than LOS.

B. Omnidirectional Close-in Reference Path Loss Models

IV. MILLIMETER-WAVE CHANNEL TIME DISPERSION PROPERTIES

Directional RMS delay spreads were generally lower in LOS V-V than NLOS V-V, with reported distributions varying by frequency and polarization. The paper also relates delay spread to propagation conditions and points to beam selection as a way to balance spread and path loss.

IV. MILLIMETER-WAVE CHANNEL TIME DISPERSION PROPERTIES

  • RMS delay spread is the square root of the power delay profile's second central moment, characterizing multipath time dispersion and coherence bandwidth.It can be used to estimate data rates and bandwidth limitations; each delay-bin power P(τk) is measured in mW.Source: §IV · p. 5
  • Directional RMS delay spread showed little correlation with T-R separation distance across co- and cross-polarized scenarios.Source: §IV · p. 5
  • LOS V-V mean RMS delay spreads were 4.1 ns at 28 GHz and 3.3 ns at 73 GHz, versus 18.4 ns and 13.3 ns in NLOS.Short-delay LOS components reduce spread, while strong, long-delay reflections contribute to larger NLOS spread.Source: §IV · pp. 5–6
  • At 73 GHz, 90% of arriving angles were within about 5.1 ns and 37.8 ns in LOS, and 33.2 ns and 26.0 ns in NLOS, for co- and cross-polarization, respectively.Source: §IV · p. 5
  • At 73 GHz, V-H mean RMS delay spread was 21.2 ns in LOS versus 10.3 ns in NLOS; polarization mismatch weakens LOS while reflections can enhance reflected components.Source: §IV · p. 6
  • Selecting beam directions with both low RMS delay spread and path loss can provide relatively high received power without complicated equalization.The cited algorithm seeks beam directions that also support maximum SNR and simple equalization.Source: §IV · p. 6

V. CONCLUSION

The conclusion reports indoor 28 and 73 GHz path-loss models and RMS delay-spread statistics. LOS and NLOS path-loss exponents differ, and strongest-angle pointing lowers the reported directional exponents relative to arbitrary pointing.

V. CONCLUSION

  • Omnidirectional PLEs were 1.1 and 1.3 in LOS and 2.7 and 3.2 in NLOS at 28 and 73 GHz, respectively, for vertically polarized antennas.Source: §V · p. 6
  • Directional PLEs were 4.5 and 5.1 for arbitrary pointing angles, decreasing to 3.0 and 4.3 when selecting the strongest TX-RX pointing link at each RX location.The conclusion identifies beamforming at the base station and handset as valuable for SNR enhancement and increased coverage.Source: §V · p. 6
  • Mean and maximum RMS delay spreads were 18.4 ns and 193.0 ns at 28 GHz, and 13.3 ns and 287.5 ns at 73 GHz.The paper says strong multipath components can arrive at large time delays and that the channel models can support indoor system simulations and radio-system design.Source: §V · p. 6
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