Radio Front End for
Enhanced Data Rate at Cell Edges
Nadim Khlat, Marcus Granger-Jones, Ruediger Bauder, Andy Folkman
What this presentation is addressing ?
3G HSDPA/HSUPA Data rate at the edge of the cells are dropping
much faster than expected versus the simulation done at the network
planning side.
What RF Front End architectures can be considered to help improve
the data rate that a mobile user can experience at the edge (border)
of the cellular network cells ?
Data Rate Drops at the Edge of Cells example
Edge of a
cell, Lower
data rate
x-y axis in meters
Source:Tommi Heikkilä , PG Course in Radio Communications
First understand the system issue:
Inter-cell and Intra-cell interferences
Serving Cell
Inter-Cell Interference is coming from other eNodeB
from other cells, referred as Ioc.
The further the mobile is at the edge of the cell,
the higher is Ioc.
Isc
Ioc
MS
noise
Intra-Cell Interference is coming within the serving cell eNodeB due the
reduced orthogonality created by the multipath of the various spreading Codes
for others Mobile Station (MS) in the cell, referred as Isc
Link Budget and SNIR
• SNIR = (ß.Ior) / ( Ioc + Isc + MS receiver noise )
SNIR is the signal to noise and interference ratio
• Eb/N0 = W/R *SNIR
( where R is the data rate, W is the channel bandwidth)
Ioc is the inter-cell interference.
Isc is the intra-cell interference
MS receiver noise is the noise generated within the Mobile unit.
Ior is the total received signal level and ß.Ior is the received signal level of the traffic
channels only (i.e. we exclude the power level of the pilot channels)
(G=^Ior/Ioc refers to Geometry factor , ^Ior contains Ioc and Ior)
(1-α = Isc/Ior where α refers to Downlink orthogonality )
For a given Eb/N0 , increase the data rate R require increasing the SNIR
Link Budget & SNIR improvements
• SNIR = (ßIor) / ( Ioc + Isc + MS receiver noise )
In several reports, it is stated that at the Edge of the cells, Ioc interference
source is dominating versus other noise sources thus limiting the data rate
performances.
Ioc is something Radio Front End have little to impact directly as it is related
to the network planning and frequency reuse and SOH use and use of antenna
diversity. Also CPC shall help reducing this.
Isc is something that is improved via Modem BB IC processing (enhanced
equalizers).
MS receiver noise can be reduced by appropriate Front End design, however a
1dB of improvement on this noise do not translate into 1dB in SNIR since it is
limited to Ioc , but it can degrades very rapidly under VSWR !
FDD Radio FEM degradation
main sources
Main sources of receiver degradation within FEM for
Duplex systems
TX/RX Isolation, dB (narrow band)
-35
dB(vswr_duplexer_FEM_nominal..S(2,3))
dB(S(2,3))
m17
freq= 2.110GHz
dB(vswr_duplexer_FEM_nominal..S(2,3))= -48.761
-40
-45
m16
m27
f req=1.920GHz
nothing= <inv alid>
dB(v swr_duplexer_FEM_nominal..S(2,3))=-59.122 dB(S(2,3))=<inv alid>
m24
nothing=<inv alid>
dB(S(2,3))=<inv alid>
m26
nothing=<inv alid>
dB(S(2,3))=<inv alid>
m17
-50
m25
nothing= <inv alid>
dB(S(2,3))=<inv alid>
-55
m16
-60
m27
m26
m25
m24
dB(vswr_duplexer_FEM_nominal..S(3,1))
dB(S(3,1))
-65
1.900
1.975
2.050
f req, GHz
2.125
2.200
RX Gt , dB (narrowband)
m10
0
-5
-10
-15
-20
-25
-30
-35
-40
-45
m11
m10
f req=2.110GHz
-50
dB(v swr_duplexer_FEM_nominal..S(3,1))=-3.062
-55
-60
m14
-65
nothing=<inv alid>
-70
dB(S(3,1))=<inv alid>
m11
-75
f req=1.730GHz
-80
dB(v swr_duplexer_FEM_nominal..S(3,1))=-48.415
-85
m15
nothing=<inv alid>
-90
dB(S(3,1))=<inv alid>
-95
-100
-105
-110m14
m15
-115
1.70
1.80
1.90
2.00
2.10
2.20
2.25
f req, GHz
Typical Duplexer Isolation & TX Return Loss
Over VSWR (3:1 case)
Theory
Measurement
Isolation (dB)
Reverse Transmission, dB
-30
-40
-40
-50
-50
-60
-60
-70
-70
-80
1.83
TX Return Loss (dB)
Reverse Transmission, dB
-30
1.93
2.03
2.13
2.23
-80
1.83
0
0
-5
-5
-10
-10
-15
-15
-20
1.83
1.93
2.03
freq, GHz
2.13
2.23
-20
1.83
Nominal (50‐ohm ANT)
1.93
2.03
2.13
2.23
Over VSWR
in 15° increments
1.93
2.03
freq, GHz
2.13
2.23
Typical Duplexer Isolation & TX Return Loss
Over VSWR (6:1 case)
Theory
Measurement
Isolation (dB)
Reverse Transmission, dB
-30
-40
-40
-50
-50
-60
-60
-70
-70
-80
1.83
TX Return Loss (dB)
Reverse Transmission, dB
-30
1.93
2.03
2.13
2.23
-80
1.83
0
0
-5
-5
-10
-10
-15
-15
-20
1.83
1.93
2.03
freq, GHz
2.13
2.23
-20
1.83
Nominal (50‐ohm ANT)
1.93
2.03
2.13
2.23
Over VSWR
in 15° increments
1.93
2.03
freq, GHz
2.13
2.23
Data Rate Drops at Cell Edges:
FE Impairments in RX chain
Typical Duplexer Band 1 degradation over VSWR : reference to 1:1 VSWR
VSWR Antenna
3:1
4:1
6:1
TX to RX noise Isolation degradation
2.9dB
3.3dB
3.9dB … 5.0dB
TX Leakage degradation
3.3dB
3.8dB
4.3dB … 5.0dB
RX blocker attenuation degradation
3.5dB
3.6dB
4.7dB
1dB … 2.7dB
1.7dB … 3.7dB
3dB … 5dB
RX signal path degradation
Assume TX port is matched to 50ohm
Typical Chain (Antenna / Switch /Duplexer Band 1) degradation over VSWR
VSWR Antenna
3:1
4:1
6:1
3:1 & PA(2:1)
TX to RX noise Isolation degradation
2.4dB
2.7dB
3.0dB
3.7dB
TX Leakage degradation
2.1dB
2.5dB
2.7dB
3.0dB
RX blocker attenuation degradation
2.3dB
2.5dB
2.4dB
3.8dB
0.1dB …3.1dB
0.5dB … 4.5dB
1.5dB … 6.5dB
0.1dB…3.1dB
RX signal path degradation
Reference for performance
Quadrature PA can provide this match to the duplexer (1.6:1 VSWR)
Single ended PA’s can have up to 4:1 VSWR causing up to another 3dB degradation
Data Rate Drops at Cell Edges:
Overall Performance
3 GPP Target reference sensitivity
Overall SNIR
DPCH_Ec/Ior
S = DPCH_Ec
Ior
UE TX
Service Data Rate Rb
coding gain
Eb/N0 target
SNIR target >
noise + interference floor target max
1.00
0.50
dBm
dB
0.00
‐0.50
Network= (1)
(1) & Thermal noise = (2)
(2) & TX noise in RX band= (3)
(3) & OOBlocker 2* fduplex = (4)
(4) & IM2 effects = (5)
(5) & OOBlocker 1/2* fduplex = (6)
‐1.00
‐1.50
‐2.00
‐2.50
1
2
3
3:1 VSWR
4
5
6
1:1 VSWR
We have ~1.4dB of minimum link budget degradation
for 3:1 VSWR versus 1:1 case.
-89.0 dBm
-5.5 dB
-94.5 dBm
-89.0 dBm
23.0 dBm
384000.0
10.0 dB
9.4 dB
-0.6 dB
-93.9 dBm
Data Rate Drops at Cell Edges:
Overall Performance
Overall SNIR
1.00
0.50
dBm
0.00
‐0.50
‐1.00
‐1.50
‐2.00
‐2.50
1
2
3
3:1 VSWR
4
1:1 VSWR
5
6
Network= (1)
(1) & Thermal noise = (2)
(2) & TX noise in RX band= (3)
(3) & OOBlocker 2* fduplex = (4)
(4) & IM2 effects = (5)
(5) & OOBlocker 1/2* fduplex = (6)
1.
RX Signal level degradation under VSWR seems the biggest contributor to SNIR
reduction.
2.
Out-Of-Band blocker mixing with TX signal under VSWR changes seems the
second contributor to SNIR degradation
3.
TX-RX Band noise change with VSWR seems the third contributor to SNIR drop
Ways to improve
TX Noise in RX band degradation
Increase Duplexer Isolation ( higher orders)
X Impact IL loss
Tuner usage to reduce VSWR
X Added Cost
X Require smart adaptive tuning
( simultaneous TX and RX matching)
 Pre-filter TRX noise using Tunable notch in PA
X Require some calibration
…
RX Signal Level
Use of Tuner to improve matching
X Added Cost due to need to handle high power
Use of RX Tuner only
Lower switch and Duplexer IL
…
Ways to improve
TX Leakage and RX blocking degradation
Increase Duplexer Isolation ( higher orders)
X Impact IL loss
Tuner usage to reduce VSWR
X Added Cost
X Require smart adaptive tuning
( simultaneous TX and RX matching)
 Better Switch linearity under VSWR
 Better Transceiver linearity and Phase noise
 Use of Quadrature PA for better source match to
duplexers
…
Front End Improvements
Use of Antenna Tuners
 TX/RX tuner (but add cost and complexity for adaptive modes)
 RX only tuner (very small added cost)
Quadrature Power Amplifier versus Single Ended P.A.
 Better source match to duplexer, thus less TX-RX degradation under VSWR.
 Better ACLR under VSWR.
 Lower PA Gain variation under VSWR resulting into less transceiver output power back-off and
thus less noise increase from transceiver (saw-less).
 No phase jump variation versus VSWR as compared to Single Ended Power Amplifiers
Power Amplifier with Reduced Interference
 Reduce Transceiver noise impact on sensitivity for saw-less designs
 Provide compensation to Duplexer TX/RX isolation degradation over VSWR
( via budget reallocation)
Antenna Tuner:TX versus RX tuning
for FDD systems
Issues related to duplex operation
 Is tuning done versus TX frequency or versus RX frequency ?
Using TX Delivered power
Using TX/RX Combined Delivered powers
Tuner Broadband Matching challenge for FDD
systems with large duplex offset

wb
 ln |
wa
1

| d  w0 /( R0.C1.w0)  w0 / Q   .w
The higher the bandwidth or offset between TX and RX ,
the less low reflection can be achieved for a given antenna Qload
Example of Tuner Topology suitable for FDD
Use only 1 series resonance
Tunable element to resonate
with the antenna inductance
The series resonance is set such
fc~= (fTX+fRX)/2
Degrade reflection between fTX and fRX to allow to reduce
Further the reflection at fTX and fRX
0
-2
m3
freq= 1.920GHz
dB(S(1,1))=-9.398
dB(S(1,1))
-4
m4
freq= 2.110GHz
dB(S(1,1))=-9.054
-6
-8
m4
m3
-10
-12
1.5
1.6
1.7
1.8
1.9
2.0
freq, GHz
2.1
2.2
2.3
2.4
2.5
Antenna tuners interaction with Inner Loop Power
Control
Issue with Antenna tuners interaction with Inner Loop Power Control

Most antenna tuning algorithm assumed independent closed control loop , which
In the case of 3G/4G , this can affect the Inner Loop Power control even that the
two loops are operating at different rates ( Antenna tuning operates at 1Hz
resolution while the Inner loop operates at 1.5-2KHz rate) . E.g. the granularity of
antenna tuning power steps changes is near the accuracy of the Inner Loop ( ~ +0.5dB) can create a step change in delivered power to Node-B different from the
last TPC command send.
Antenna tuners interaction with Inner Loop Power
Control
Proposed Solution to Antenna tuners interaction with Inner Loop Power Control



Antenna tuning control commands are synchronized to the TX slot boundary.
Power control is split into two control commands:
Tuning Control to Antenna tuner ( first )
Estimate new delivered power ( incl. the granularity of the tuner )
Tuning Control of remaining power via PA forward power drive
Another possibility is to include “Algorithm4” in the standardization of 3GPP(see next)
Adjacent user interference
switcher
Vcc
UE
Antenna
Transceiver
Output Power
Adjust
RF
FEM
(Switch+
Duplexers)
RFPA input
Directional Coupler
rev_cp
Uplink
eNodeB
Antenna
Antenna
Tuning
Unit
eNodeB
receiver
fwd_cp
Downlink (TPC, each slot)
Envelope
Detector
Envelope
Detector
Prev_fd
Pfwd_fd
Fwd_Adjust[]
Reverse
Correction
+
Prevc_fd
+
Limit
detection
Delivered
Power
Controller
Pdel_fd
Pdel_newtarget
Rev_Adjust[]
N.K,June 08,rev0.1
Suggested “Algorithm 4”
(assume standard adoption to enable Adaptive Antenna tuners)
eNodeB recognizes that UE has an adaptive tuner at registration
UE Power control adjusts two knobs:
- Forward power of TRX/PA
- Antenna tuners settings
When TX power control reach a maximum limit
via adjusting Forward power of TRX/PA , then TX power control can switch to Antenna tuner control
 No need for directional coupler and controller, the antenna tuning is controlled indirectly via the eNodeB
PAPA
stage2
stage2
PAPA
1stage
1stage
RX only Tuner
Low cost overhead adder to
include a RX only tuner with the
Diversity/MIMO Antenna switch
Diversity antenna can
Have different S11 versus
Main antenna
Diversity path indirect benefits
If a terminal has already a Diversity path , the diversity RF path
offers some indirect benefits (other than the diversity gain benefits)





Reduce TX noise in RX band by the antenna’s coupling factor
Reduce TX leakage by the antenna’s coupling factor
Reduced Inter-modulation due to antenna’s isolation
Reduced Reverse-Intermodulation due to antenna’s isolation
Lower cost RX only tuner to improve FEM to Antenna matching
“Tornado” Rx Tuner: Key Features
•
•
•
Architecture
• SP5T + RX tuner integrated into single die on CX50
laminate
• Used with RX diversity or MIMO 2nd antenna
• No external components required
Covers Low-band 700-960MHz and High-band 17002600MHz
RX1
LB
Laminate
CX50
C1-Array LB
RX2
LB
C1-Array LB
1.6x1.6 mm2 module size
Lh
Ll
B
A
ESD
RF input
C3-Array LB
•
Direct battery connection
•
Programming:
• Single GPIO control via pulse counting
• Or MIPI RFFE interface control
RX3
HB
C2-Array HB
RX4
HB
C1-Array HB
•
Stacked Switches
• Maximum Input power ~ +20dBm to handle TX leakage
from main antenna
ISO
RX5
HB
LDO
Switch + RX Tuner die
•
Self ESD Protecting
Simulated IL matching to 50 ohms at 2GHz ~ 0.6dB
•
Capable to tune up to 10:1 VSWR
Vbatt
Enable
Driver +2.5V/0V
•
Vdd
2 Wire MIPI
Or
1 Wire GPIO
SCLK
SDATA/GPI
RX diversity/MIMO
Example of RX tuner+switch
simulation performances (High-Band)
Based on SOI process
(*) Tuner only IL ~ -0.30dB
Frequency sim @ 2.170GHz
VSWR
VSWR
VSWR
VSWR
VSWR
VSWR
VSWR
1:1
2:1
3:1
4:1
5:1
6:1
7:1
–> IL = -0.60dB (*)
(Blue)
(Green)
(Black)
(Cyan)
(Yellow)
(Pink)
Example of RX tuner+switch
simulation performances (Low-Band)
Frequency sim @ 960MHz
VSWR
VSWR
VSWR
VSWR
VSWR
VSWR
VSWR
1:1
2:1
3:1
4:1
5:1
6:1
7:1
–> IL=-0.40dB
(blue)
(green)
(black)
(cyan)
(yellow)
(magnenta)
PARIS: PA Reduced Interference System
a.k.a. A Filter !
Slide 28
Traditional Solutions
Interstage Tx SAW filters
Unsuitable for multi-band
High Performance Duplexers
Trend is for small size& cheaper
rather than better isolation.
Low Noise transmit paths
High current even at low
Pout due to VCO & LO path
Risk of spurs & spurious noise
Separate Tx & Rx antennas
Cost penalty
Level plan tradeoffs
Nothing left to trade !
Trend is for lower power consumption,
improved TRP and better sensitivity.
The PARIS Approach
Add a PA driver with Tunable Notch Filter to the PA
subsystem for FDD systems
• Tunable over entire HB or LB frequency range
• Attenuate Rx band Noise by at least 8dB
• Add ~4dB of power gain to the PA subsystem.
• New level Plan allows new specification trade-off
Duplexer spec vs. PA spec vs. tcvr spec vs sensitivity vs VSWR compensation
• DC-HSDPA require to watch out TX ACLRx leakage in RX band for lower
frequency offsets, thus adding an extra constraint
WCDMA PA Module Large Signal S21
w & w/o PARIS filter
L1 bond wire loop height
S/N
475_2um_20mA
m1
m2
m3
30
dB(f1(2,1))
dB(no_filter(2,1))
20
10
m1
freq=1.75GHz
dB(f1(2,1))=25.71
Peak
m2
ind Delta=0.00
dep Delta=-1.39
Delta Mode ON
0
-10
-20
m4
m5
m6
30
m3
ind Delta=8.00E7
dep Delta=-5.12
Delta Mode ON
20
dB(f2(2,1))
dB(no_filter(2,1))
4
-30
10
m4
freq=1.85GHz
dB(f2(2,1))=26.96
Peak
0
-10
m5
ind Delta=0.00
dep Delta=-1.82
Delta Mode ON
-20
-30
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.5
1.0
1.5
freq, GHz
10
m7
freq=1.91GHz
dB(f3(2,1))=27.86
Peak
-10
m8
ind Delta=0.00
dep Delta=-2.35
Delta Mode ON
-20
-30
0.5
1.0
1.5
2.0
2.5
freq, GHz
m11
20
dB(f4(2,1))
dB(no_filter(2,1))
m9
ind Delta=8.00E7
dep Delta=-9.63
Delta Mode ON
m9
0
2.5
3.0
3.5
4.0
m10
30
m8
20
2.0
freq, GHz
m7
30
dB(f3(2,1))
dB(no_filter(2,1))
m6
ind Delta=8.00E7
dep Delta=-7.39
Delta Mode ON
m12
10
m10
freq=1.98GHz
dB(f4(2,1))=27.99
Peak
0
-10
m11
ind Delta=0.00
dep Delta=-2.86
Delta Mode ON
-20
-30
3.0
3.5
4.0
m12
ind Delta=8.00E7
dep Delta=-10.96
Delta Mode ON
0.5
1.0
1.5
2.0
2.5
freq, GHz
3.0
3.5
4.0
Attenuation at +80MHz &190MHz offsets
PARIS Tunable Filter
Attenuation Vs F_maxima, Max atten & atten at +80MHz offset and at +190MHz offset
E1D0871 Board #735 TO 12381
0
64
48
-10
32
-15
16
-20
-25
0
1.65
1.7
1.75
1.8
1.85
1.9
F_maxima (GHz)
Maximum Atten dB
Atten at Fmax+190M dB
Atten at Fmax+80M dB
Ctune
1.95
Ctune (decimal)
Attenuation (dB)
-5
Simulation of next version of PARIS
S21
Duplexer RX Band Isolation relaxation using PARIS
dB
Duplex TX/RX Isolation RX band ( for same sensitivity )
0
‐5
‐10
‐15
‐20
‐25
‐30
‐35
‐40
‐45
‐50
‐55
Band 1
Band 2
Band 3
Band 4
Transceiver Output Noise floor = -157dBm/Hz
PA Output Thermal Noise floor = -138dBm/Hz
Band 5
Band 8
without "PARIS"
with "PARIS"
P.A.R.I.S Advantages
Allows to trade:
Receiver improved sensitivity under VSWR w/o increasing
Complexity on the duplexers or requiring to add a TX/RX
Tuner
Transceiver current drain reduction
Provides also:
Lower level interface drive
SOC interface compatible
Spurious reduction
Can help also:
New bands with tight duplexer TX-RX gap (e.g. Band 3)
LTE low-bands
PARIS is integrated inside the Multi-Band Power Amplifier
and/or in standalone LTE Power amplifier
Quadrature PA ( VSWR tolerant PA)
For Linear PA:
Immunity from post-PA mismatch for improved ACLR, EVM, Imax
over VSWR
Minimizes sensitivity of the PA to Duplexer interface
Single Ended PA could degrade filter response and cause degradation of
ACLR, EVM and filter rejection if not presenting a good source match < 2:1
Conclusion
 Front End performances degrades rapidly with VSWR
Especially for FDD systems
 Any typical antenna under Free-Space can present 3:1
VSWR
A typical minimum link budget loss of 1.4dB can be expected due to FEM performances
degradation and gained back. For higher VSWR this gain be in the range of 3dB
 Few simple approaches can be considered to improve the performances
-Tunable filter within the multi-band power amplifier driver
-Multi-band Quadrature power amplifier
-RX only tuner when possible or RX/TX tuner
-Continuous improvements on switch and duplexer
design and technologies
Thank you !
Email for any further questions: nkhlat@rfmd.com
Backup
Data Rate Improvements (SISO and MIMO)
Solid lines represent measured data’s
Dash lines represent simulated data’s
2.5dB of improvements can increase by 70% the data rate if we operate a low SNR ( ~ 0dB)
But only provides 20% increase of data rate for higher SNR if we used measured results
Source:IEEE VTC 2009- MIMO HSDPA Throughput Measurement Results in an Urban Scenario
Example of Noise figure degradation versus TX leakage
and Out-of-band blocker
This assume only 30dB of RX attenuation is provided by the duplexer
However duplexers RX attenuation for OOB are improving ( typical ~ 46dB for -380MHz and -38dB for -95MHz))
Source: ISCC, MDK Single-Chip Tri-Band WCDMA/HSDPA Transceiver