Implementation of a WAP model to evaluate Capacity in 3G radio access networks. Henrik Fållby

Transcription

1 Implementation of a WAP model to evaluate Capacity in 3G radio access networks Henrik Fållby

2 Outline Scoop of this thesis Packet switched vs. circuit switched networks Packet Data in GSM radio networks Wireless Application Protocol WAP traffic model Petra System Simulator Evaluation results for WAP over EGPRS Comparing EGPRS with GPRS with WAP traffic Comparing WAP vs. WWW over EGPRS Summary

3 Scoop of the Thesis Development of a WAP model Evaluation of WAP traffic over GPRS and EGPRS RAN Comparison of WAP vs. WWW performance

4 Packet switched contra Circuit switched networks Packet Switched Several users can chare the same channel (Time Slot) Channel only used when needed Suitable for non real-time applications, i.e WAP/WWW Circuit Switched Only one user per channel Channel occupied until the session is closed Suitable for real-time applications, i.e. voice

5 Packet Data in GSM radio networks: GSM radio network Traffic and signaling information Switching System Signaling information AUC Base Station System EIR HLR MS BTS BSC MSC/VLR GMSC ISDN/PSTN GPRS nodes SGSN External IP Network Other PLMN IP-Backbone NetWork GGSN External X.25 Network

6 Packet Data in GSM radio networks: Modulation and Coding Schemes for EGPRS and GPRS GMSK 8PSK φ 1 1 φ 1 (0,1,0) (0,0,0) (0,1,1) 0 (0,0,1) (1,1,1) φ 2 φ 2 Coding Schemes Max no of info bits per radio block Max data rate per TS (kbps) CS CS CS CS (1,0,1) (1,1,0) (1,1,0) Coding Schemes Modulation Max no of info bits per radio block Max data rate per TS (kbps) MCS-1 GMSK MCS-2 GMSK MCS-3 GMSK MCS-4 GMSK MCS-5 8PSK MCS-6 8PSK MCS-7 8PSK MCS-8 8PSK MCS-9 8PSK GPRS Coding Schemes EGPRS Modulation and Coding Schemes

7 Packet data in GSM networks: GPRS multiframe structure User data Application layer Packet Header User data Network layer ~1.6 kbytes LLC PDU Header User data Tail LLC layer <1.5 kbytes RLC/MAC blocks USF RLC Header RLC Information BCS USF RLC Header RLC Information RLC BCS RLC/MAC layer bytes Radio blocks Normal Burst Normal Burst 8PSK Normal Burst Normal Burst By EGPRS effected layers Physical layer 4 x 114 bits B0 B1 B2 X B3 B4 B5 X B6 B7 B8 X B9 B10 B11 X 52 TDMA frames

8 Wireless Application Protocol: Properties of a mobile terminal Narrowband Access Small Display Limited Keyboard Limited Memory and Computing Power

9 Wireless Application Protocol: WAP architecture Client WAP Gateway/ Proxy Origin Server WAP User Agents WSP request (URL) Encoders HTTP request (URL) CGI Scripts, etc. WAP Protocol Stack WSP Resp. (WAP binary WML) Protocol Conversion HTTP Response (WML) WML WMLScript WIRELESS DOMAIN: WAP Protocols INTERNET DOMAIN: Internet Protocols

10 Traffic model: Building a WAP traffic model Session interarrival time Session length Packet size Packet interarrival time Measurements Analysis Choice of model structure Parameterisation

11 Traffic model: Distributions and parameters for the WAP model Session interarrival time Session length Packet size Packet interarrival time Session interarrival time [s] Number of Packets within a session Packet interarrival time [s] Packet size [Byte] Distribution Exponential Geometric Negative exponential Lognormal Minimum value Maximum value Mean 1/λ Standard deviation 1/λ

12 PETRA System Simulator: Overview Multiple cell simulator Equally sized 3-sector macro cells 4/12 frequency reuse TU3 no frequency hoping Downlink 20 ms iterations EGPRS MCS9 with IR GPRS CS2 without LA Multislot allocation not modeled BSS MS

13 PETRA system simulator: Simulation environment Application IP / X.25 SNDCP SNDCP Relay GTP IP / X.25 GTP LLC RLC* MAC GSM RF MS Traffic model RLC* MAC GSM RF Relay BSSGP Network Service L1bis LLC BSSGP Network Service L1bis UDP/TCP IP L2 L1 UDP/TCP Um BSS Gb Gn Gi SGSN GGSN Header data Detailed simulation IP L2 L1 *TBF setup not included Packet Emulator Tool for Radio network Application (PETRA) used to simulate the RAN

14 PETRA system simulator: Packet handling Data Traffic model Headers present in PETRA Application Payload Application layer Headers not present in PETRA Header User Data IP +WDP/ TCP Header User Data Network layer LLC header byte User Data 1500 byte LLC layer USF RLC header RLC Information BCS USF RLC header RLC Information byte BCS RLC/MAC layer

15 Simulation results WAP over EGPRS: CDF of packet throughput The 10th percentile of packet throughput states that 90% of the packets will have throughput equal to or higher than the plotted values Note if assuming even packet distribution over cell area the probability can be seen as cell area C.D.F. [%] WAP users per cell 350 " 700 " CDF (cumulative distribution function) Definition: x F( x) = f ( i) = P( X x) = α i= Average packet throughput per timeslot [kbps]

16 Simulation results WAP over EGPRS: 10 th percentile of packet throughput for WAP QoS target/reference point: Definition: 90% of the packets shall have a throughput higher or equal to 10 kbps/timeslot The reference point is defined to be able to compare results and estimate capacity. QoS target/ref point Capacity estimate At the reference point an average of 700 parallell WAP sessions per sector can reside befort the quality limit is reached 10 th percentile of packet throughput per timeslot [kbps] 35 (25) (50) (100) (200) (300) (350) (400) (500) (600) (700) (800) 5 (In parenthesis average number of users per cell) Average offered load [kbps]

17 Simulation results WAP over EGPRS: Average packet throughput for WAP At the reference point, where 90% of the packets have at least 10 kbps/timeslot (700 parallel users) an average throughput of 31 kbps/timeslot can be seen With lower loads a higher average throughput is reached Average packet throughput per timeslot [kbps] (25) (50) (100) (200) (300) (350) (400) (500) (600) (700) (800) 5 (In parenthesis average number of users per cell) Average offered load [kbps]

18 Simulation results WAP over EGPRS: Queuing and transmission delays The transfer time for WAP increases with higher load due to more retransmissions The major part of the total delay for higher loads is due to queuing time Average normalised delay per packet [s/kbit] total queuing transmission Average offered load [kbps]

19 Comparing EGPRS vs. GPRS with WAP traffic: Major conclusions EGPRS can handle 4.7 times as many users as GPRS Average amount of users and Spectral efficency Average Download time for WAP 0,40 0,35 EGPRS is 4.5 times more spectral efficient than GPRS ,30 0,25 0,20 0,15 The time it takes to download a WAP packet is very small (0.18s for EGPRS and 0.36 s for GPRS) EGPRS GPRS Average number of parallell WAP sessions/sector Spectral efficiency [kbps/mhz/site] 0,10 0,05 0,00 EGPRS GPRS The WAP end user will not perceive major differences in quality The system performance increase for the operators are significant

20 Comparing WAP vs. WWW over EGPRS: Model differences WWW have ~19 times larger packets than WAP Session interarrival time Session length WWW is a state based model with 3 traffic intensities compared to WAP that isn t state base WWW models have in average 10 packets per session compared to 5 for WAP Packet interarrival time Packet size WAP WWW Max packet size [Byte] 1600 N/A Mean packet size [Byte] Standard deviation [Byte] Average interarrival time [seconds] /3.6/28.4 Average session time [seconds] Model constants

21 Comparing WAP vs. WWW over EGPRS: Capacity for two types of Internet browsing In the defined reference point an EGPRS carrier can handle ~18 times as many WAP users as WWW users in the system At the reference point, where 90% of the packets have a throughput of at least 10 kbps/timeslot, the system can host 700 WAP users per sector compared to 40 WWW users 10% percentile of packet throughput per timeslot [kbps] WAP WWW Average number of users per sector

22 Comparing WAP vs. WWW over EGPRS: Spectral efficiency for WAP and WWW The spectral efficiency is higher for WWW than for WAP Note that even though WAP have 700 user compared to 40 WWW users the WWW service uses the available bandwidth more efficiently Reason: WAP is more effected by final ACK and the small WAP packets leave up to 20 percent empty space in the RLC blocks 10 th percentile of packet throughput per timeslot [kbps] WAP WWW System load [kbps/mhz/site]

23 Comparing WAP vs. WWW over EGPRS: Average download time The average time to download a WWW packet is 3.5 seconds compared to 0.2 seconds for WAP 4,00 3,50 3,00 2,50 2,00 Average download time [s] 1,50 1,00 0,50 0,00 WAP WWW WAP is a service that the have very short waiting periods for the user compared to WWW

24 Summary WAP over EGPRS and GPRS have similar download performance WAP over EGPRS can handle 700 WAP users WAP is a service with good performance over both carriers WAP can host many more users than WWW (18 times) WWW is more spectral efficient than WAP Huge difference in download times for WAP and WWW (19 times)