Effect of Slow Fading and Adaptive Modulation on TCP/UDP Performance of High-Speed Packet Wireless Networks

Xuanming Dong

EECS Department, University of California, Berkeley

Technical Report No. UCB/EECS-2006-109

August 25, 2006

http://www2.eecs.berkeley.edu/Pubs/TechRpts/2006/EECS-2006-109.pdf

High speed data wireless networks in multipath environments suffer channel impairment from many sources such as thermal noise, path loss, shadowing, and fading. In particular, short-term fading caused by mobility imposes irreducible error floor bounds on system performance. We study the effect of fading on the performance of the widely used TCP/UDP protocol, and investigate how to improve TCP performance over fading channels. Our solutions target upcoming mobile wireless systems such as IEEE 802.16e wireless MANs (Metropolitan Area Networks) where adaptive modulation is enabled and the underlying medium access scheme is On-Demand Time Division Multiple Access (On-Demand TDMA).

Adaptive modulation is used in the new generation of wireless systems to increase the system throughput and significantly improve spectral efficiency by matching parameters of the physical layer to the time-varying fading channels. Most high-rate applications for such wireless systems rely on the reliable service provided by TCP protocol. The effect of adaptive modulation on TCP throughput is investigated. A semi-Markov chain model for TCP congestion/flow control behavior and a multi-state Markov chain model for Rayleigh fading channels are used together to derive the steady state throughput of TCP Tahoe and Reno. The theoretical prediction based on our analysis is consistent with simulation results using the network simulator NS2. The analytical and simulation results triggered the idea of cross-layer TCP protocol design for single-user scenarios. The fading parameters of wireless channels detected in the physical layer can be used to dynamically tune the parameters (such as packet length and advertised receiver window size) of the TCP protocol in the transport layer so that TCP throughput is improved.

For multi-user scenarios, we study how multi-user diversity can be used to improve the aggregate TCP throughput of base stations in fading channels. Since TCP performance involves complex interactions among layers of the networking protocol stack, the cross-layer design approach is adopted to tackle the problem. The performance improvement is achieved through channel-aware packet scheduling algorithms and active delay of TCP ACK packets in the buffer. Based on the adaptive modulation information from the physical layer, the advertised receive window size of TCP ACK packets is dynamically changed to accommodate the rate changes resulting from adaptive modulation. Our simulation results show that the new cross-layer approach increases TCP throughput.

Advisors: Pravin Varaiya

BibTeX citation:

@phdthesis{Dong:EECS-2006-109,
    Author= {Dong, Xuanming},
    Title= {Effect of Slow Fading and Adaptive Modulation on TCP/UDP Performance of High-Speed Packet Wireless Networks},
    School= {EECS Department, University of California, Berkeley},
    Year= {2006},
    Month= {Aug},
    Url= {http://www2.eecs.berkeley.edu/Pubs/TechRpts/2006/EECS-2006-109.html},
    Number= {UCB/EECS-2006-109},
    Abstract= {High speed data wireless networks in multipath environments suffer channel impairment 
from many sources such as thermal noise, path loss, shadowing, and fading. In particular, 
short-term fading caused by mobility imposes irreducible error floor bounds on system 
performance. We study the effect of fading on the performance of the widely used TCP/UDP 
protocol, and investigate how to improve TCP performance over fading channels. Our 
solutions target upcoming mobile wireless systems such as IEEE 802.16e wireless MANs 
(Metropolitan Area Networks) where adaptive modulation is enabled and the underlying 
medium access scheme is On-Demand Time Division Multiple Access (On-Demand TDMA).


Adaptive modulation is used in the new generation of wireless systems to increase the 
system throughput and significantly improve spectral efficiency by matching parameters 
of the physical layer to the time-varying fading channels. Most high-rate applications 
for such wireless systems rely on the reliable service provided by TCP protocol. The 
effect of adaptive modulation on TCP throughput is investigated. A semi-Markov chain 
model for TCP congestion/flow control behavior and a multi-state Markov chain model 
for Rayleigh fading channels are used together to derive the steady state throughput 
of TCP Tahoe and Reno. The theoretical prediction based on our analysis is consistent 
with simulation results using the network simulator NS2. The analytical and simulation 
results triggered the idea of cross-layer TCP protocol design for single-user scenarios. 
The fading parameters of wireless channels detected in the physical layer can be used 
to dynamically tune the parameters (such as packet length and advertised receiver window 
size) of the TCP protocol in the transport layer so that TCP throughput is improved.


For multi-user scenarios, we study how multi-user diversity can be used to improve the 
aggregate TCP throughput of base stations in fading channels. Since TCP performance 
involves complex interactions among layers of the networking protocol stack, the 
cross-layer design approach is adopted to tackle the problem. The performance improvement 
is achieved through channel-aware packet scheduling algorithms and active delay of TCP 
ACK packets in the buffer. Based on the adaptive modulation information from the physical 
layer, the advertised receive window size of TCP ACK packets is dynamically changed to 
accommodate the rate changes resulting from adaptive modulation. Our simulation results 
show that the new cross-layer approach increases TCP throughput.},
}

EndNote citation:

%0 Thesis
%A Dong, Xuanming 
%T Effect of Slow Fading and Adaptive Modulation on TCP/UDP Performance of High-Speed Packet Wireless Networks
%I EECS Department, University of California, Berkeley
%D 2006
%8 August 25
%@ UCB/EECS-2006-109
%U http://www2.eecs.berkeley.edu/Pubs/TechRpts/2006/EECS-2006-109.html
%F Dong:EECS-2006-109