RF Planning for In-Building
Systems
IBTUF 8
Austin, TX
Scott Townley
Corporate Technology
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
Why have in-building systems?
• Provide strategic coverage
– Sales/Marketing input to Network
– Network reacts
• Capacity solution
– Same as sector splits, new builds, small cells…
– Network proactively addresses
• But they’re really expensive!
– So why not solve in-building issues from the macro network?
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
2
Building Penetration Loss
• Penetration Loss into a building is significant
• One survey1 found 14.2dB/13.4dB/12.8dB at 900/1800/2300 MHz
• Why not cover from the outside (macro network)?
– The 13 dB (or so) penetration loss is equivalent to halving the cell radius
• Which is 4x cell count—very expensive
– While adequate coverage may be achieved indoors, the cell overlap ruins onstreet signal quality (high interference–low SINR)
• In-Building coverage is best accomplished in the direct fashion—by inbuilding systems
Turkmani and Parsons, “Estimating Coverage of Radio Transmission into and within Buildings at 900, 1800, and
2300 MHz”, IEEE Personal Communications Magazine, April 1998
1Toledo,
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
3
Did you notice?
• Penetration loss into a building generally decreases with increasing
frequency
– A consolidation of surveys2 (next slide) showed -8 dB per decade trend
– Don’t confuse this result with the general result of increasing pathloss with
frequency!
• Why is this?
– Signal penetration is due to openings (windows, doors, etc.)
– Openings get electrically larger with increasing frequency
2Davidson
and Hill, “Measurement of Building Penetration Into Medium Buildings at 900 and 1500 MHz”, IEEE Trans.
Vehicular Technology, Feburary 1997
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
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Davidson and Hill
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
5
Required Metrics
• Once an in-building system has been decided upon, what should it look
like?
• Downlink
– RSRP (coverage)
– SINR (quality and achievable throughput)
• More on next slide
– MIMO*
• Uplink
– UE TX power (coverage)
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
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“Sufficient” signal quality
• “Sufficient” signal quality depends on the technology and service offered
• With CDMA voice, all users have the same signal quality requirement
– 1x Ec/Io >= -14 dB (equivalent to SINR of -14 dB)
– Managed with power control (14 dB) and rate control (9 dB)
• Data services are different. Adaptive modulation translates different
values of SINR to different burst rates (instantaneous throughputs)
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
7
Signal Quality Ranges for Wireless Data
Service Technologies
EV-DO
LTE
Minimum SINR (dB)
-12
-10
Maximum SINR (dB)
13
26 (TxD)
34 (SM)
Minimum TP (kbps)
38.4
500
Maximum TP (kbps)
3072
38800 (TxD)
67400 (SM)
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
8
Implication for LTE Systems
• To achieve the promise of LTE throughputs, you must strive for very high
SINR levels!
– “Good Enough”, isn’t. LTE sets the bar MUCH higher!
– Managing overlap and isolation from the exterior macro network becomes
critical
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
9
Terminology Check
• Lowest implementation level is “SIMO”
– 1 TX, 2 RX (at UE)
– What we use for 1x and EV-DO
• “MIMO” is a general term for multiple antennas at each end
– Any 2 TX, 2 RX system is “MIMO”
• LTE always uses some form of “MIMO”…either
– Transmit Diversity, where every transmitter sends the same information
• Resulting in a similar effect as Receive Diversity: an increase in average SINR
– Spatial Multiplexing, where each transmitter sends different information
• In theory, throughput can scale with the number of T/R pairs used
• When most people say “MIMO”, what they really mean is “Spatial Multiplexing”
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
10
Spectral Efficiency of a SISO channel
• Spectral Efficiency (SE) measures how densely a channel can be packed
– Bits per Second per Hertz (bps/Hz)
• SE = log2(1+S/N) Shannon’s Law
– Log(1+x)~x for x~0. At low S/N, SE increases linearly with S/N
• SE doubles for each doubling of S/N
– Log2(1+x)~log2(x) for x>>1. At high S/N, SE increases much more slowly
• SE increases exactly 1 bps/Hz for each doubling of S/N
• Diminishing returns with increasing S/N
• Note that diversity techniques (SIMO, TxD) work by increasing the timeaverage value of S/N
– And so suffer from the same diminishing returns
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A very simple MIMO channel illustration
Receivers R can uniquely determine
(separate) transmitters T if H is known
and invertible
H has attributes of amplitude, phase,
and polarization
H is estimated from measurements on
the cell-specific Reference Signal
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Super-Simplified Spatial Multiplexing,
along with some familiar terminology
• Multiple transmitters and
receivers modify the equation for
SE as shown to the right
“Rank” of H
• The “Condition Number” (CN) of
H is simply (σmax2 / σmin2)
𝑛
𝑆𝐸 =
• If the singular values are equal,
the resultant SE is the SE of a
single channel, multiplied by the
rank of H
– SE increases with Rank(H)
regardless of S/N!
𝑙𝑜𝑔2
𝑖=1
𝑆𝐸 = 𝑙𝑜𝑔2 (1+
𝑆𝐸 = 2𝑙𝑜𝑔2
“Singular values”
of H
𝑆𝑖
1 + 𝜎𝑖
𝑁
2
𝑆1
𝜎
)
𝑁 1
2
𝐻
+ 𝑙𝑜𝑔2 (1+
2
𝑆2
𝜎
)
𝑁 2
𝑆
1+
𝑁
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
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Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
14
Notes on Statistical Spectral Efficiency
• Spectral Efficiency as shown is optimistic
– In reality, all curves are more to the right (require higher SINR)
• SIMO and TxD have the same first derivative
– Note that TxD(10)=SIMO(50) and TxD(50)=SIMO(90)
– In plainer English: TxD improves the reliability of achievable throughput
• Spatial Multiplexing has a larger first derivative as SINR increases
– More incremental gain (linear vs logarithmic)
– Higher achievable maximum Spectral Efficiency: K times SIMO or TxD
• But this requires higher SINRs to realize the benefits
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
15
Some Capacity Distributions
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Just say YES to MIMO
• If
– You can realize a high SINR environment, AND
– Support multiple TX (SM)
• Then
– You have a smoking fast wireless data system
• In-building systems are well-positioned to achieve both these
requirements
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
17
PIM
• Is passive intermodulation (PIM) an issue for in-building systems?
• For Verizon Wireless-only systems, the same rules for the macro network
apply
• For neutral-host/multi-carrier systems,
– The PIM problem is much larger and more difficult
– Don’t assume the DAS provider understands this
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Gain and Noise Distribution in a DAS
• DAS ideal objective:
– “Appropriate” noise figure at each node
• Maintains proper UE transmit power and uplink throughput
– Minimum noise rise at the eNB receiver input
• eNB receiver has a finite dynamic range
• Too much noise rise ultimately limits the achievable UL throughput
• Two calculations required
– Cascaded noise figure: gives F and sensitivity at node
– Total noise power (input to receiver): gives noise rise at eNB
•
•
•
•
Convert DAS NF to noise power (dBm)
Add cascaded gain to noise power = noise power input to receiver
Convert eNB NF to noise power (dBm)
Compare noise power input to eNB noise power
Confidential and proprietary materials for authorized Verizon personnel and outside agencies only. Use, disclosure or distribution of this material is not permitted to any unauthorized persons or third parties except by written agreement.
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Example Calculation
𝑇 = 288 ∙ (10𝑁𝐹
10
− 1)
𝑁𝑃𝑆𝐷 = 10 ∙ log10 𝑇 − 198.6
𝑁𝑃,𝑖𝑛 = 𝑁𝑃𝑆𝐷 + 10 ∙ log10 𝐵𝐻𝑧 + 𝐺𝑐𝑎𝑠𝑐𝑎𝑑𝑒
𝑁𝑃,𝑒𝑁𝐵 = 𝑁𝑃𝑆𝐷 + 10 ∙ log10 𝐵𝐻𝑧
Bandwidth
You do not need a lot of gain!
69.5
69.5 dB-Hz
Noise figure of DAS (referenced to preamp input)
Cascade gain of DAS
noise temperature of DAS (referenced to preamp input)
Noise PSD (referenced to preamp input)
Noise power at eNB input
2.5
3.5 dB
20.0
0.0 dB
224.1 356.8 K
-175.1 -173.1 dBm/Hz
-85.6 -103.5 dBm
Noise figure of eNB
noise temperature of eNB
Noise PSD of eNB
Noise power of eNB
2.7
2.7 dB
248.3 248.3 K
-174.7 -174.7 dBm/Hz
-105.1 -105.1 dBm
Noise rise
19.6
1.6 dB
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Noise vs Gain
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