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

Transcription

1 Implementation of a model to evaluate Capacity in 3G radio access networks Henrik Fållby Outline Scoop of this thesis switched vs. circuit switched networks Data in GSM radio networks Wireless Application Protocol traffic model Petra System Simulator Evaluation results for over EGPRS Comparing EGPRS with GPRS with traffic Comparing vs. WWW over EGPRS Summary

2 Scoop of the Thesis Development of a model Evaluation of traffic over GPRS and EGPRS RAN Comparison of vs. WWW performance switched contra Circuit switched networks Switched Several users can chare the same channel (Time Slot) Channel only used when needed Suitable for non real-time applications, i.e /WWW Circuit Switched Only one user per channel Channel occupied until the session is closed Suitable for real-time applications, i.e. voice

3 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 Data in GSM radio networks: Modulation and Coding Schemes for EGPRS and GPRS GMSK 8PSK φ 1 1 φ 1 (,1,) (,,) (,1,1) (,,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 GPRS Coding Schemes (1,,1) (1,1,) (1,1,) 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 EGPRS Modulation and Coding Schemes

4 data in GSM networks: GPRS multiframe structure User data Application layer Header User data Network layer ~1.6 kbytes LLC PDU Header User data Tail LLC layer <1.5 kbytes /MAC blocks USF Header Information BCS USF Header Information BCS /MAC layer 2-5 bytes Radio blocks Normal Burst Normal Normal Burst Burst 8PSK Normal Burst By EGPRS effected layers Physical layer 4 x 114 bits B B1 B2 X B3 B4 B5 X B6 B7 B8 X B9 B1 B11 X 52 TDMA frames Wireless Application Protocol: Properties of a mobile terminal Narrowband Access Small Display Limited Keyboard Limited Memory and Computing Power

5 Wireless Application Protocol: architecture Client Gateway/ Proxy Origin Server User Agents WSP request (URL) Encoders HTTP request (URL) CGI Scripts, etc. Protocol Stack WSP Resp. ( binary WML) Protocol Conversion HTTP Response (WML) WML WMLScript WIRELESS DOMAIN: Protocols INTERNET DOMAIN: Internet Protocols Traffic model: Building a traffic model interarrival time length size interarrival time Measurements Analysis Choice of model structure Parameterisation

6 Traffic model: Distributions and parameters for the model interarrival time length size interarrival time interarrival time [s] Number of s within a session interarrival time [s] size [Byte] Distribution Exponential Geometric Negative exponential Lognormal Minimum value Maximum value Mean 1/λ Standard deviation 1/λ PETRA System Simulator: Overview Multiple cell simulator Equally sized 3-sector macro cells 4/12 frequency reuse TU3 no frequency hoping Downlink 2 ms iterations EGPRS MCS9 with IR GPRS CS2 without LA Multislot allocation not modeled BSS MS

7 PETRA system simulator: Simulation environment Application IP / X.25 SNDCP Relay SNDCP GTP IP / X.25 GTP LLC * MAC GSM RF Relay * BSSGP MAC Network Service GSM RF L1bis LLC BSSGP Network Service L1bis UDP/TCP IP L2 L1 UDP/TCP MS Um BSS Gb Gn Gi SGSN GGSN Detailed Traffic model Header data simulation *TBF setup not included Emulator Tool for Radio network Application (PETRA) used to simulate the RAN IP L2 L1 PETRA system simulator: 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 15 byte LLC layer USF header Information BCS USF header Information BCS 2-5 byte /MAC layer

8 Simulation results over EGPRS: CDF of packet throughput The 1th percentile of packet throughput states that 9% 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 CDF (cumulative distribution function) Definition: x F( x) = f ( i) = P( X x) = α i= C.D.F. [%] users per cell 35 " 7 " Average packet throughput per timeslot [kbps] Simulation results over EGPRS: 1 th percentile of packet throughput for QoS target/reference point: Definition: 9% of the packets shall have a throughput higher or equal to 1 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 7 parallell sessions per sector can reside befort the quality limit is reached 1 th percentile of packet throughput per timeslot [kbps] (25) (5) (1) (2) (3) (35) (4) (5) (6) (7) (In parenthesis average number of users per cell) Average offered load [kbps] (8)

9 Simulation results over EGPRS: Average packet throughput for At the reference point, where 9% of the packets have at least 1 kbps/timeslot (7 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] 5 (25) 45 (5) (1) (2) (3) (35) (4) (5) (6) (7) (8) 5 (In parenthesis average number of users per cell) Average offered load [kbps] Simulation results over EGPRS: Queuing and transmission delays The transfer time for 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]

10 Comparing EGPRS vs. GPRS with traffic: Major conclusions EGPRS can handle 4.7 times as many users as GPRS 8 7 Average amount of users and Spectral efficency Average Download time for,4,35 EGPRS is 4.5 times more spectral efficient than GPRS ,3,25,2,15 The time it takes to download a packet is very small (.18s for EGPRS and.36 s for GPRS) 2 1 EGPRS GPRS Average number of parallell sessions/sector Spectral efficiency [kbps/mhz/site],1,5, EGPRS GPRS The end user will not perceive major differences in quality The system performance increase for the operators are significant Comparing vs. WWW over EGPRS: Model differences WWW have ~19 times larger packets than interarrival time length WWW is a state based model with 3 traffic intensities compared to that isn t state base WWW models have in average 1 packets per session compared to 5 for interarrival time size WWW Max packet size [Byte] 16 N/A Mean packet size [Byte] Standard deviation [Byte] Average interarrival time [seconds] /3.6/28.4 Average session time [seconds] 69 1 Model constants

11 Comparing 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 users as WWW users in the system At the reference point, where 9% of the packets have a throughput of at least 1 kbps/timeslot, the system can host 7 users per sector compared to 4 WWW users 1% percentile of packet throughput per timeslot [kbps] WWW Average number of users per sector Comparing vs. WWW over EGPRS: Spectral efficiency for and WWW The spectral efficiency is higher for WWW than for Note that even though have 7 user compared to 4 WWW users the WWW service uses the available bandwidth more efficiently Reason: is more effected by final ACK and the small packets leave up to 2 percent empty space in the blocks 1 th percentile of packet throughput per timeslot [kbps] WWW System load [kbps/mhz/site]

12 Comparing vs. WWW over EGPRS: Average download time The average time to download a WWW packet is 3.5 seconds compared to.2 seconds for 4, 3,5 3, 2,5 2, Average download time [s] 1,5 1,,5, WWW is a service that the have very short waiting periods for the user compared to WWW Summary over EGPRS and GPRS have similar download performance over EGPRS can handle 7 users is a service with good performance over both carriers can host many more users than WWW (18 times) WWW is more spectral efficient than Huge difference in download times for and WWW (19 times)