View
47
Download
0
Category
Preview:
Citation preview
Performance of WLAN RSS-based SON for LTE/WLAN access network selection
Yu Wang+, Relja Djapicφ, Andreas Bergström+, István Z. Kovács*, Daniela Laselva*, Kathleen Spaeyx, Bart Sasx
+Ericsson Research, Stockholm, Sweden; φTNO, Delft, Netherlands; *Nokia, Aalborg, Denmark; x iMinds/University of Antwerp, Antwerp, Belgium
§ Why SON for LTE/WLAN access selection - Motivation
§ What is it – Access selection rule and SON function
§ If it works – Simulation results in a heterogeneous network scenario
§ How does it work – Load balancing leading to user throughput improvement
§ If it really works – Various traffic model parameters
§ How dose it work in practice – Implementation issues
§ How to make it better – Summary and future work
Introduction
2 SEMAFOUR
§ Operators are using WLAN for offloading – “Carrier grade Wi-Fi”
§ Great interests in integrating cellular and WLAN networks
§ One of the key technology component: access selection / traffic steering
§ SON for access selection – SON: proved working in related areas, e.g. load balancing – A good candidate to address the LTE/WLAN access selection
§ Task: design a SON function and prove if it works (or not) by simulation
Why SON for LTE/WLAN Access Selection?
3 SEMAFOUR
§ Control parameter – Wi-Fi RSS admission threshold
§ RSS-based access selection rule – Connect to WLAN if RSS > RSS_Thr – Access selection at session start
§ Monitoring KPIs – LTE: PRB utilization percentage – Wi-Fi: Channel busyness percentage
– Busy: at least one node is transmitting or attempts to transmit
– Limitation: may not reflect load especially with full buffer users
– Not comparable between them
What Is It – Control Parameters and Monitoring KPIs
4 SEMAFOUR
UEs are served by Wi-Fi in locations with RSS > RSS_thr
LTE macro LTE micro &Wi-Fi
What Is It – SON Algorithm
5 SEMAFOUR
LTE load measurement (period: pL)
Wi-Fi load measurement (period: pW)
Filtering (αW) Filtering (αL)
Yes
Yes
Yes
Yes
No
No
No
No
repeat every pSON seconds
KPI
mon
itor
Off
load
ing
Onl
oadi
ng
RSS threshold regulation
RSS threshold initialization
Decrease RSS threshold
Wi-Fi high load
LTE low load?
LTE high load
Increase RSS threshold
Increase RSS threshold
Decrease RSS threshold
LTE low load
Wi-Fi low load
Yes
No
LTE & Wi-Fi congested
)(L)1(L)1()(L nnn measured∗+−∗−= αα
§ SON function – Overload protection – Offloading – Onloading
§ Important parameters – Filtering factor – SON update period and step size – Congestion/High/low load thresholds
§ Operator policy fulfillment – Utilize LTE network until highly loaded – Balanced LTE/WLAN user
throughput
§ Environment: 1.1 km2 urban area located in city center of Hannover § Deployment: 5 LTE Macros (46 dBm), 28 co-located outdoor LTE Micro (33
dBm) / AP (20 dBm) § 6 dB cell extension offset for Micros § Spatial traffic distribution: Outdoor busy hour traffic + a hotspot with 70%
traffic outdoor § Offered traffic: Fixed size UDP downloading / uploading (DL: 5 MB; UL: 0.8
MB; 12 arrival/sec)
If It Works – Simulation Scenario
6 SEMAFOUR
LTE Macro
LTE Micro & WLAN AP
1 Micro/AP Index
Micro: 20MHz@1.8GHz AP: 20MHz@5GHz
Macro Index
1
1200
1200
0
0
Met
er
Meter
Macro: 20MHz@1.8GHz
User Location
§ Indoor users are located on the ground floor only
§ No external interference § Mobility: Stationary users only
§ Highest average and 5th percentile user throughput
– Fixed RSS threshold = -65 dBm. – User session split:
– WLAN: 42% – LTE Micro: 37% – LTE Macro: 21%
If It Works – Fixed RSS Threshold
-92 -85 -75 -65 -55 -450
20
40
60
80
100
RSS Threshold (dBm)
User
Ses
sion
Per
cent
age
(%)
LTE MacroLTE MicroWi-Fi
-92 -85 -75 -65 -55 -450
20
40
Aver
age
User
Thro
ugph
ut (M
bps)
-92 -85 -75 -65 -55 -450
5
10
RSS Threshold (dBm)
5%-il
e Us
erTh
roug
phut
(Mbp
s)
5%-ile / Avg. user thrp.
(Mbps)
WLAN users (%)
Reference: WLAN if coverage Fixed RSS_Thr = -92 dBm 0.1 / 11 87 Reference: Best Fixed Threshold Fixed RSS_Thr = -65 dBm 7.2 / 31.6 42 SON: reference settings PSON/PL/PW=1s, RSS_Thr_Step=1dB, α=0.9 8.2 / 31.7 41 SON: smooth load filtering PSON/PL/PW=1s, RSS_Thr_Step=1dB, α=0.5 7.5 / 33.1 45 SON: slow RSS_Thr update PSON/PL/PW=2s, RSS_Thr_Step=0.5dB, α=0.9 3.7 / 28.2 54
SON: fast RSS_Thr update PSON/PL/PW=0.5s, RSS_Thr_Step=2dB, α=0.9 7.1 / 31.2 38
If It Works – SON Function to Improve User Throughput
8 SEMAFOUR
0 5 10 15 20 25 30 35 40 450
10
20
30
40
50
60
70
80
90
100
CDF
[%]
User Throughput (Mbps)
All (DL)Macro (DL)Micro (DL)WLAN (DL)All (UL)Macro (UL)Micro (UL)WLAN (UL)
§ 14% gain in 5th percentile user throughput comparing to the best fixed threshold reference case
§ Sensitivity to SON parameter configuration – Not very sensitive to the load filtering factor – Need to be fast enough to capture traffic load variation
§ Balanced DL user throughput among users
§ UL user throughput is not optimized with the DL KPI driven algorithm
§ A more balanced load between the two system – Load was kept in the configured range by the SON function
§ Convergence of the RSS threshold – ‘Warming-up’ and stabilization
How Does It Work – Load Balancing
9 SEMAFOUR
1 2 3 4 5 1 2 3 4 5 6 7 8 9 1011121314151617180
20
40
60
80
100
Cell
load
-80-75-70-65-60-55-50-45-40
RSS
thre
shol
d (d
Bm)
1 2 3 4 5 1 2 3 4 5 6 7 8 9 1011121314151617180
20
40
60
80
100
Cell
load
-80-75-70-65-60-55-50-45-40
RSS
thre
shol
d (d
Bm)
Fixed Threshold = -65 dBm
SON function
20 40 60 80 100 1200
20
40
60
80
100
Load
(%)
-80-75-70-65-60-55-50-45-40
RSS
thre
shol
d (d
Bm)
Time (sec)
RSS thresholdWLAN AP loadLTE cell load
SON with the reference settings RSS_Thr = -65 dBm
[File size: DL/UL, User arrival rate]
5%-ile / Avg. user
thrp. (Mbps)
WLAN users (%)
5%-ile / Avg. user
thrp. (Mbps)
WLAN users (%)
Reference [5 MB/0.8 MB, 12] 8.2/31.7 41 7.2/31.6 42
[2.5 MB/0.4 MB, 24] 7.2/27.8 39 6.6/26.8 42 [1.25 MB/0.2 MB, 48] 5.8/23.1 34 3.9/21.8 42 [10 MB/1.6 MB, 6] 6.6/33.0 40 7.2/35.6 42 [5 MB/0.8 MB, 6] 10.7/38.1 48 8.3/40.1 42
If It Really Works – Various Traffic Parameters
10 SEMAFOUR
§ Smaller file size and higher user arrival rate: More simultaneously active users à Lower WLAN efficiency and higher WLAN load à SON moves more users to LTE
§ Larger file size and lower user arrival rate: Approaching to full buffer traffic à Resource utilization is not a good load measure
§ Lower offered traffic: SON outperforms the fixed RSS threshold in the 5th percentile user throughput
§ The RSS-based SON algorithm is primarily a distributed solution because it may be difficult for the central controller, e.g. ANDSF, to execute an algorithm which updates parameters every few seconds.
§ Implementation of the RSS-based access selection rule – Executed in terminals:
– RSS_Thr is send to terminals via broadcasted or dedicated signalling channels being standardized in 3GPP
– Executed in network: – Uplink RSS is monitored at the network node and the node controls the access
selection
§ Information exchange between LTE and WLAN – Standardization of such an interface is being discussed in 3GPP – Proprietary interfaces – Terminals as relays
§ WLAN RSS measures – RSSI: Received Signal Strength Indicator – RCPI: Received Channel Power Indicator
How it Works in Practice
11 SEMAFOUR
§ Simulation results showed a RSS-based SON algorithm for access network selection between the LTE and WLAN systems successfully
– Balanced the load between the two systems – Optimized user throughput statistics with various traffic parameter settings.
§ Future work – The optimization of the SON parameters with respect to the traffic parameters is
subject to further study. – Better load measure – Evaluate the SON function in more dynamic scenarios: mobility and and/or
mixed traffic types. – More understanding of the coexistence of distributed and centralized SON
functions is needed to achieve a holistic solution and further optimize the performance.
How to Make It Better
12 SEMAFOUR
Recommended