1. ARQ Proxy for Cross-Layer Error Control Optimization in 3G LTE
26-30 November 2007
Washington, DC, USA
ARQ Proxy for Cross-Layer Error Control Optimization in 3G LTE
Dzmitry Kliazovich
Fabrizio Granelli
University of Trento, Italy
Simone Redana
Nicola Riato
Nokia Siemens Networks S.p.A

2. Fabrizio Granelli (granelli@dit.unitn.it)
Outline
3G Long-Term Evolution
Background and features
TCP over 3G LTE
ARQ Proxy
Multi-layer ARQ optimization
Packet identification techniques
Operation in WiFi and WiMAX
Conclusions
November 2007
Fabrizio Granelli

3. Fabrizio Granelli (granelli@dit.unitn.it)
3G LTE background
3G LTE (Long-Term Evolution) - an attempt to bring 4G technology into 3G spectrum
Reason: challenge other advanced technologies (like WiMAX) meeting high data rate service demands
November 2007
Fabrizio Granelli

4. 3G LTE: Targeted features
High data rates
100 Mbps in DL (for 20 MHz band) – Efficiency 5 bps/Hz
50 Mbps in UL (for 20 MHz band) – Efficiency 3.5 bps/Hz
Low Latency
Between terminal and Radio control device (RAN): < 10 ms
Recovery from idle mode: < 50 ms
From standby mode: < 100 ms
Mobility
15 km/h – optimized performance
120 km/h – high performance
350 km/h (or 500 km/h) – establish communication
Flexible Channel Bandwidth
1.25 MHz, 5MHz, 10 MHz, 15 MHz and 20 MHz
November 2007
Fabrizio Granelli

5. 3G LTE: Key Technologies
Evolved Architecture
Reduced number of nodes
Low delay
Evolved Radio Access
OFDM for spectrum efficiency
Multiple Antenna Techniques
Evolved Link Layer
One TCP/IP datagram mapped into one RCL packet
ARQ + HARQ for error recovery
November 2007
Fabrizio Granelli

6. Fabrizio Granelli (granelli@dit.unitn.it)
TCP over 3G LTE
Evolved Packet
Core
File Server
Enhanced Node B
User Equipment
(eNB)
(UE) IP
TCP Data
Header
PHY/LL IP
TCP Data
TCP data packet
Headers
Header
HARQ
ACK
TCP ACK
Uplink Scheduling Request
Unlink Grant
HARQ
ACK IP
Header
TCP
PHY/LL
Headers
November 2007
Fabrizio Granelli

7. Fabrizio Granelli (granelli@dit.unitn.it)
ARQ Proxy - Approach
Idea: Substitute the transmission of TCP ACK packets with a short MAC layer request on the radio link
November 2007
Fabrizio Granelli

8. Fabrizio Granelli (granelli@dit.unitn.it)
ARQ Proxy - Approach
Enhanced Node B
(eNB)
Evolved Packet
Core
User Equipment
(UE)
File Server
TCP
ARQ
Proxy
MAC
MAC
ARQ
Client
TCP
TCP Data
TCP
Data
PHY / LL
Headers
TCP Data
Access TCP header
Get IP addr, port, etc.
Generate TCP ACK & store
Generate
TCP ACK
TCP ACK
Index
TCP ACK
Index
HARQ
ACK +
TCP
Index
Compute TCP ACK identification index
TCP
ACK
November 2007
Fabrizio Granelli

9. ARQ Proxy – Packet Identification
3G LTE: Hash values
WiFi: Frame Sequence Numbers
PHY
Header LL
TCP data
Sequence
Control
Address 3
Address 4
Fragment
Number B3 B4
Bits: 4 12
B15 B0
Sequence Number
Hybrid ARQ (HARQ-ACK)
Enhanced Node B
(eNB) or
User Equipment
(UE)
HARQ
ACK
November 2007
Fabrizio Granelli

10. Fabrizio Granelli (granelli@dit.unitn.it)
ARQ Proxy - Benefits
Performance and System Capacity Increase
Evolved Packet
Core
File Server
Enhanced Node B
User Equipment
(eNB)
(UE) IP
TCP Data
Header
PHY/LL IP
TCP Data
Headers
Header
HARQ
ACK
Overhead reduction
PHY/LL IP
TCP IP
TCP
Headers
Header
ACK
Header
ACK
HARQ
ACK
November 2007
Fabrizio Granelli

11. Scheduling + TCP ACK Transmission over radio channel
ARQ Proxy - Benefits
Reduced RTT (Round Trip Time)
TCP Data
File Server
Evolved Packet
Core
Enhanced Node B
User Equipment
(eNB)
(UE)
TCP
ACK
Scheduling + TCP ACK Transmission over radio channel
November 2007
Fabrizio Granelli

12. Fabrizio Granelli (granelli@dit.unitn.it)
ARQ Proxy - Benefits
End-to-end TCP semantics are maintained
TCP Data
File Server
Evolved Packet
Core
User Equipment
(UE)
Enhanced Node B
(eNB)
TCP
ACK
Hash value
November 2007
Fabrizio Granelli

13. ARQ Proxy - Benefits Higher channel error rates tolerance
Wired channel (BER = 10-6 to 10-8)
Wireless channel (BER = 10-3 to 10-1)
File Server
Evolved Packet
Core
User Equipment
(UE)
Enhanced Node B
(eNB)
TCP
ACK
Hash value is smaller than TCP ACK
November 2007
Fabrizio Granelli

14. No TCP state related information is maintained
ARQ Proxy - Benefits
Mobility & Incremental deployment
No TCP state related information is maintained
File Server
Evolved Packet
Core
User Equipment
(UE)
Enhanced Node B
(eNB)
November 2007
Fabrizio Granelli

15. Fabrizio Granelli (granelli@dit.unitn.it)
ARQ Proxy - Benefits
Performance and system capacity increase
Reduced RTT (Round Trip Time)
End-to-end TCP semantics are maintained
Higher channel error rates tolerance
Full mobility support
Incremental deployment & Co-existence
November 2007
Fabrizio Granelli

16. ARQ Proxy - Limitations
TCP ACKs are not substituted:
During connection establishment and connection termination packets (identified by SIN and FIN flags)
For TCP ACK encapsulated into TCP data packet in case of bidirectional data transfer
For Duplicate TCP ACKs
TCP ACK advertising exhausted receive buffer resources (rwnd field)
November 2007
Fabrizio Granelli

17. Fabrizio Granelli (granelli@dit.unitn.it)
Evaluation Results
Simulation Setup
Enhanced UMTS Radio Access Extensions (EURAE) for Ns2 simulator
To make it look like 3G LTE
Node B and RNC are combined
Modified link layer
One-to-one mapping of IP packets into RLC PDUs
Physical layer
HSDPA with trace data for UE within 300 meters from eNB
Header overhead: TCP (20 bytes), IP (20 bytes), PDCP (1 byte), RLC (2 bytes)
File Server
Evolved Packet
Core
User Equipment
(UE)
Enhanced Node B
November 2007
Fabrizio Granelli
(eNB)

18. Fabrizio Granelli (granelli@dit.unitn.it)
Evaluation Results
Round Trip Time (RTT) improvement
Order of milliseconds
November 2007
Fabrizio Granelli

19. Fabrizio Granelli (granelli@dit.unitn.it)
Evaluation Results
No need to introduce additional error recovery for hash values
November 2007
Fabrizio Granelli

20. Motivation for Scenario Choice
Why link layer ARQ/HARQ as a feedback channel?
Why TCP?
Accounts for more than 85% of Internet traffic*
Why cellular network scenario?
Over 95% of wireless links are on the last mile
[*] C. Fraleigh at el. “Packet-level traffic measurements from the Sprint IP backbone,” IEEE Network, vol. 17, no. 6, pp. 6 – 16, Nov.-Dec
November 2007
Fabrizio Granelli

21. Other Operation Scenarios
ARQ Proxy
ARQ Proxy
. . .
Single-hop Ad hoc network
Multi-hop network
ARQ Proxy
Fixed Source
Fixed Network
Infrastructure
Cellular network with relays
November 2007
Fabrizio Granelli

22. Fabrizio Granelli (granelli@dit.unitn.it)
ARQ Proxy for WiFi
Simulation Setup
Ns2 simulator with ARQ proxy extensions
IEEE b physical layer, no RTS/CTS
Bottleneck buffer: 700 packets
TCP NewReno flows
Results averaged over 10 runs
IEEE 11 Mb/s
100 Mb/s, 15 ms
Fixed Host
Base Station
Mobile Node
ARQ
Proxy
Client
November 2007
Fabrizio Granelli

23. VoIP and Multimedia Applications TCP file transfer, Ethernet MTU
Evaluation Results
Throughput performance
Improvement: 20%
Improvement: up to 100%
VoIP and Multimedia Applications
TCP file transfer, Ethernet MTU
November 2007
Fabrizio Granelli

24. Fabrizio Granelli (granelli@dit.unitn.it)
Evaluation Results
Round Trip Time (RTT)
Error rate tolerance
November 2007
Fabrizio Granelli

25. Current Activities and Future Work
ARQ proxy material (Available)
ARQ proxy for 3G LTE (Super-3G)
ARQ proxy for WiFi (IEEE )
EU patent
D. Kliazovich, N. Ben Halima, and F. Granelli, “Cross-Layer Error Recovery Optimization in WiFi Networks,” Tyrrhenian International Workshop on Digital Communication (TIWDC), Ischia island, Naples, Italy, September, 2007.
D. Kliazovich, F. Granelli, S. Redana, and N. Riato, “Cross-Layer Error Recovery Optimization for 3G LTE Systems,” EP
November 2007
Fabrizio Granelli

26. Current Activities and Future Work
ARQ proxy material (Coming soon…)
ARQ proxy for WiMAX (IEEE )
Adaptation and system level simulations
Proposal to 3GPP standardization group
Under consideration for next generation equipment produced by Nokia Siemens Network (NSN)
November 2007
Fabrizio Granelli

27. Fabrizio Granelli (granelli@dit.unitn.it)
Thank you!
November 2007
Fabrizio Granelli