C802.20-03/29
Smart Antenna and MC-SCDMA
Next Generation Technologies for Wireless Broadband
Guanghan Xu, CTO
Navini Networks
July 26, 2016
April, 12 2001
1
C802.20-03/29
Outline
• Comparative Analysis of CDMA, OFDM, and MC-SCDMA
• Comparative Analysis of Smart Antennas vs Conventional
Antennas
• Comparative Analysis of TDD vs. FDD
• Optimal Integration of Technologies to Create a Broadband
Solution
• Field Trial Results of the Integrated Technologies
C802.20-03/29
Wireless Broadband Challenges
Path Loss (Link Budget)
14.4Kbps to 1Mbps
= 69 times or 18dB more power
Multipath Fading
Intercell Interference
F1
F1
Suburban
F1
F1
t
F1
F1
F1
Free space
Time Domain
F1
City
Rural
Mixture of Broadband
& Narrowband (voice)
f
Frequency Domain
0.1
1
2
3 5
10 20 km
F1
C802.20-03/29
OFDM Multiple Access
• OFDM offers very good immunity to
multipath issues.
• FFT is very efficient in channelization NlogN
instead of O(N2).
• OFDM needs much higher fade margin
requiring higher signal levels and complex
coding.
• OFDM has high peak to average ratio that
impacts link budget due to large PA backoff.
• OFDMA is difficult to reliably transmitting
narrowband data or voice due to the
spectrum nulls. Frequency hopping does
smooth out the probability of hitting the nulls.
• OFDM is susceptive to intercell interference
in the N=1 deployment while all the
neighboring cells are fully loaded.
Transmitted OFDM Spectrum
f
Received OFDM Spectrum
Signal Threshold
f
C802.20-03/29
Conventional CDMA
+
+
+
Received CDMA
Spectrum
Transmitted CDMA
Spectrum
Interference
Signal
f
f
Frequency Domain
Frequency Domain
Code 1 Code 2 Code 3 Code 4
• CDMA (1XEVDO, EVDV & WCDMA) all have asynchronous CDMA uplink.
• Due to high spreading gain, CDMA (1X and WCDMA) signals are more resistant
to intercell interference which enables N=1 deployment.
• Since each code has sufficient bandwidth, signal fading is marginal.
• Due to high intercode or intracell interference, the link budget is adversely
impacted leading to the cell breathing effect.
• The high intracell interference also considerably reduces the capacity or
throughput of the system.
C802.20-03/29
Synchronous CDMA (SCDMA)
Symbol Period
+
+
+
Code 1
Code 2
Code 3
Code 4
• Synchronous CDMA (SCDMA) can maintain code orthogonality and its
multipath interference or intercode interference is minimized.
• Due to the spreading gain, the SCDMA signals are also more resistant to
intercell interference which enables N=1 deployment.
• Since each code has sufficient bandwidth, signal fading is marginal.
C802.20-03/29
Multipath Effect to SCDMA
Multipath Channel of User 1
+
+
+
+
+
Multipath Channel of User 2
+
+
+
+
Symbol Period
Other User Interference
Self Interference
User 1 Signal
User 2 Signal
Code 1
Code 2
Code 3
Code 4
C802.20-03/29
Joint Detection for SCDMA
• Joint detection is the solution to effectively handle the multipath in multiuser CDMA systems.
• Joint detection is computationally expensive and its complexity is O(N2L),
where N is the spreading factor and L is the channel length.
• Increasing N leads to more resistence to signal fading and the ability to
assign lower data rates to handle the mixture of narrowband and broad
applications
• Increase N does increase the complexity of joint detection quadratically.
• Wide bandwidth (1.2288Mcps for IS-95 or 1X, 3.84Mbps for WCDMA)
also leads to small chip periods or relatively increases L which will
increase the complexity and degrade the performance.
C802.20-03/29
Optimal Tradeoff: MC-SCDMA
f
f
f
WCDMA
OFDM
Best on multipath interference
Bad on intercell interference
Worst on signal fading
Best on signal fading
Worst on multipath interference
Good on intercell interference
f
MC-SCDMA
Optimal tradeoff among multipath
interference, intercell interference,
and signal fading
f
f
C802.20-03/29
Subcarrier Arrangement
5MHz
•Subcarrier spacing =500KHz
•Chip rate = 400kcps
•Chip period = 2.5us
C802.20-03/29
Maintain Sync in Mobility
• Mobile speed 250KM/hour
• Worst case movement distance in 10ms is 0.69M
• Time of arrival change = 0.69/3x108 = 2.3ns.
• Time of arrival change for one second is 200ns
• For chip period of 2.5us, the time of arrival change is only 1/12.5 chip.
C802.20-03/29
Competitive Analysis
SUI Propagation Model (IEEE802.16)
SUI Channel
model index
1
2
3
4
5
6
Tap 1
Tap 2
Tap3
0 ms, 0 dB
0.4 ms, -15 dB
0.8 ms, -20 dB
0 ms, 0 dB
0.5 ms, -12 dB
1 ms, -15 dB
0 ms, 0 dB
0.5 ms, -5 dB
1 ms, -10 dB
0 ms, 0 dB
2 ms, -4 dB
4 ms,
0 ms, 0 dB
5 ms, -5 dB
10 ms, -10 dB
0 ms, 0 dB
14 ms, -10 dB
20 ms, -14 dB
-8 dB
C802.20-03/29
Downlink Performance of WCDMA, 1X, MC-SCDMA
WCDMA
1X
MC-SCDMA
100% loaded w/ JD
MC-SCDMA has at least 4 times improvement in performance.
25%W/O
loaded
100% loaded
JD
25% loaded
50% loaded
50% loaded
100% loaded
100% loaded
Sprint Model Index
C802.20-03/29
Simulations of Uplink Performance of Best Case
WCDMA, 1X, SCDMA Technologies
WCDMA
1X
MC-SCDMA
100% loaded w/ JD
MC-SCDMA has at least 4 times improvement in performance.
25%W/O
loaded
100% loaded
JD
25% loaded
50% loaded
50% loaded
100% loaded
100% loaded
SUI Model Index
C802.20-03/29
Fade Margins of OFDM vs MC-SCDMA
32 tones or 32 codes in 500KHz bandwidth
for SUI model 4
95% reliability
Reliability
OFD
M
SCDMA
SCDMA
Joint
Detection
95%
13dB
7dB
8dB
99%
20dB
9dB
11dB
99% reliability
The fade margin for OFDM with 99% reliability is about 10dB
more than MC-SCDMA.
C802.20-03/29
Comparison among WCDMA/1X, OFDM, & MC-SCDMA
• With respect to intercell interference, MC-SCDMA has similar
performance as WCDMA/1X and outperforms OFDM significantly due to
spreading gain.
• With respect to intercode interference, MC-SCDMA with low
complexity joint detection has similar performance as OFDM and
outperforms WCDMA/1X significantly in the presence of multipath.
• With respect to signal fading, MC-SCDMA with low complexity joint
detection has similar performance as WCDMA/1X and outperforms
OFDM significantly in the presence of multipath.
• With respect to mixture of narrowband and broadband, the MCSCDMA performs similarly as WCDMA and has the similar low
complexity as OFDM (leveraging FFT).
C802.20-03/29
Adaptive Antenna Array
Conventional
Smart
Antenna
Power Distribution
Legacy
RF System
Patented
Smart Antenna
Software
Power
Distribution
Low Capacity
High Capacity
Signal
Interference from other users
High Complexity
Signal
128W
Interference from other users
Low Complexity
2W
Power Level
Power Amplifier Module
Power Level
Power Amplifier
C802.20-03/29
Link Budget Advantages
Conventional
2 Watts + 0 dB Gain
Adaptive Phased Array
2 Watts + 18 dB Gain
Same scale, same terrain, same clutter, same location
C802.20-03/29
Interference Nulling
Desired Signal 1
Desired Signal 2
C802.20-03/29
Interference Nulling
I/C=18dB
Desired Signal 1 Lost
I/C=15dB
Desired Signal 2 Lost
C802.20-03/29
Interference Nulling
Simple CDMA with a Single Antenna
C802.20-03/29
Interference Nulling
Simple Beamforming
Interference Nulling
Interference Nulling
C802.20-03/29
C802.20-03/29
Interference Nulling Example
Signal Without Interference
BTS Receive
Period
BTS Transmit
Period
Actual Signal Measured at 2.4GHz
C802.20-03/29
Interference Nulling for N=1 Deployment
Simulation Assumptions:
• 3 sectors linear array with 8 elements
• Each sector has 10 simultaneous users each has the same data rate
C802.20-03/29
FDD vs TDD
Frequency division duplex (FDD) requires at least 30-40 MHz guard band
between up and down streams to make the duplexer feasible.
>30MHz
Unusable
Spectrum
Up/down
stream
Down/up
stream
Duplexer filtering
Profiles
C802.20-03/29
FDD vs TDD
Summary of FDD Advantages:
1.
Guard time of TDD fundamentally limits the communication distance while FDD
does not have such a restriction.
2.
TDD may not be backward compatible to existing FDD wireless communication
systems such as cellular phones.
3.
FDD has 3dB more link budget than TDD in uplink link budget for symmetric
separation.
Summary of TDD Advantages:
1.
Flexibility of selecting a carrier for providing services.
2.
Flexibility of providing dynamic asymmetric services for both uplink and downlink.
3.
Exploitation of full benefits of smart antenna technologies leading to high capacity,
high performance, and low cost.
C802.20-03/29
Optimal Integration of Smart Antennas,
MC-SCDMA, and TDD
•
Smart Antennas with TDD
• Smart uplink and smart downlink (same carrier frequencies)
•
Smart Antennas with MC-SCDMA
• Simple smart antenna algorithms and robust performance
• Low complexity joint detection algorithms
•
TDD and MC-SCDMA
• Simple open-loop power control scheme for mobile communications
•
Smart Antennas + TDD + MC-SCDMA
• Require simple signaling protocol
• Multiple antennas lead to high redundancy
• Can localize the terminal and predict handoff
C802.20-03/29
Baton Handoff
• Determine distance from uplink synchronization
Downlink
Uplink
Downlink
•
Uplink
Close to base station
Far from base station
Determine direction-of-arrival (DOA) from smart antennas Determine the
terminal location from DOA and distance
q
Handset
Antenna Array
• Location based handoff
Baton handoff
C802.20-03/29
Base Station
• Antenna installation on 30m PCS
tower
• Outdoor cabinet
C802.20-03/29
Frequency Planning
F2
E2
F2
F2
E3
E2: 2608-2614MHz
F2: 2614-2620MHz
E3: 2620-2626MHz
Frequency Reuse
E2
C802.20-03/29
Outdoor Tests
Omni antenna used for drive test, CPE located inside car
C802.20-03/29
Indoor Tests
C802.20-03/29
Test Items in the Trials
–
Technology
1) Beamforming Gain Stability (Up and Down Link)
2) C/I Comparative Performance (Up and Down Link)
3) Effectiveness of Interference Rejection Technology
–
Product and Network Deployment
1) Data Rates vs Distance
2) Coverage Prediction Accuracy
3) Service Level Agreement Stability Across System Load Levels
4) System Stability with Large Number of Simultaneous Users
5) System Stability with under High User Contention Load
6) CPE Portability (Roaming) Between Cells
7) System Recovery Speeds
8) Cell Coverage Stability Across System Loads
9) Quality of Service/Grade of Service
10) Indoor Penetration Loss
C802.20-03/29
Beam Pattern
• Many beam patterns suggests high levels of multipath
during data rate tests
• This multipath is exploited by adaptive antennas.
• This multipath would severely degrade conventional
systems.
C802.20-03/29
Beamforming Results
Distribution of CPE Results During Drive Testing
Navini Beamforming Results from Drive Test
40%
35%
1 Average per Drive Site
1 Sample per Sec at each site
25%
20%
15%
10%
5%
27
<=
x
<
26
26
25
<=
x
<
25
<=
x
<
24
24
23
<=
x
<
23
<=
x
<
22
22
21
<=
x
<
21
<=
x
<
20
20
19
<=
x
<
19
18
<=
x
<
18
<
x
17
<=
x
<
17
0%
<=
% of samples
30%
16
16 <= x < 17
17 <= x < 18
18 <= x < 19
19 <= x < 20
20 <= x < 21
21 <= x < 22
22 <= x < 23
23 <= x < 24
24 <= x < 25
25 <= x < 26
26 <= x < 27
Total
Samples
Average
1 Average per
1 Sample per
Drive Site Sec at each site
0%
1%
0%
4%
5%
10%
18%
20%
14%
18%
41%
24%
18%
10%
5%
6%
0%
2%
0%
1%
0%
1%
100%
97%
22
3908
21.1
21.1
45%
• Average Downlink beamforming gain was 21 dB
• 92% of Non Line Of Site (NLOS) locations had a downlink beamforming
gain of 18dB or better
C802.20-03/29
Drive Test Result of One of Six BTS Sectors
C802.20-03/29
Prediction vs Field Measurement
C802.20-03/29
FTP Raw Downlink Data Rates
FTP Downlink Data Rates
(Raw bit throughput in upto 2 MHz @ 50% Duty Cyle)
(Site with SLA Coverage, Single BTS)
4000
3500
kb/s (Raw Data Rate)
3000
1A
2A
3A
4A
5A
6A
Avg Front of Home
Avg Inside Good
Avg Inside Worst
2500
2000
1500
1000
500
0
-
1.0
2.0
3.0
Distance (km)
4.0
5.0
6.0