6 research outputs found
Performance of hard handoff in 1xev-do rev. a systems
1x Evolution-Data Optimized Revision A (1xEV-DO Rev. A) is a cellular
communications standard that introduces key enhancements to the high data rate packet
switched 1xEV-DO Release 0 standard. The enhancements are driven by the increasing
demand on some applications that are delay sensitive and require symmetric data rates
on the uplink and the downlink. Some examples of such applications being video
telephony and voice over internet protocol (VoIP).
The handoff operation is critical for delay sensitive applications because the
mobile station (MS) is not supposed to lose service for long periods of time. Therefore
seamless server selection is used in Rev. A systems. This research analyzes the
performance of this handoff technique. A theoretical approach is presented to calculate
the slot error probability (SEP). The approach enables evaluating the effects of filtering,
hysteresis as well as the system introduced delay to handoff execution. Unlike previous
works, the model presented in this thesis considers multiple base stations (BS) and
accounts for correlation of shadow fading affecting different signal powers received
from different BSs. The theoretical results are then verified over ranges of parameters of
practical interest using simulations, which are also used to evaluate the packet error rate
(PER) and the number of handoffs per second. Results show that the SEP gives a good indication about the PER. Results also
show that when considering practical handoff delays, moderately large filter constants
are more efficient than smaller ones
Performance of hard handoff in 1xev-do rev. a systems
1x Evolution-Data Optimized Revision A (1xEV-DO Rev. A) is a cellular
communications standard that introduces key enhancements to the high data rate packet
switched 1xEV-DO Release 0 standard. The enhancements are driven by the increasing
demand on some applications that are delay sensitive and require symmetric data rates
on the uplink and the downlink. Some examples of such applications being video
telephony and voice over internet protocol (VoIP).
The handoff operation is critical for delay sensitive applications because the
mobile station (MS) is not supposed to lose service for long periods of time. Therefore
seamless server selection is used in Rev. A systems. This research analyzes the
performance of this handoff technique. A theoretical approach is presented to calculate
the slot error probability (SEP). The approach enables evaluating the effects of filtering,
hysteresis as well as the system introduced delay to handoff execution. Unlike previous
works, the model presented in this thesis considers multiple base stations (BS) and
accounts for correlation of shadow fading affecting different signal powers received
from different BSs. The theoretical results are then verified over ranges of parameters of
practical interest using simulations, which are also used to evaluate the packet error rate
(PER) and the number of handoffs per second. Results show that the SEP gives a good indication about the PER. Results also
show that when considering practical handoff delays, moderately large filter constants
are more efficient than smaller ones
Impact of Mobility and Wireless Channel on the Performance of Wireless Networks
This thesis studies the impact of mobility and wireless channel characteristics, i. e. , variability and high bit-error-rate, on the performance of integrated voice and data wireless systems from network, transport protocol and application perspectives. From the network perspective, we study the impact of user mobility on radio resource allocation. The goal is to design resource allocation mechanisms that provide seamless mobility for voice calls while being fair to data calls. In particular, we develop a distributed admission control for a general integrated voice and data wireless system. We model the number of active calls in a cell of the network as a Gaussian process with time-dependent mean and variance. The Gaussian model is updated periodically using the information obtained from neighboring cells about their load conditions. We show that the proposed scheme guarantees a prespecified dropping probability for voice calls while being fair to data calls. Furthermore, the scheme is stable, insensitive to user mobility process and robust to load variations. From the transport protocol perspective, we study the impact of wireless channel variations and rate scheduling on the performance of elastic data traffic carried by TCP. We explore cross-layer optimization of the rate adaptation feature of cellular networks to optimize TCP throughput. We propose a TCP-aware scheduler that switches between two rates as a function of TCP sending rate. We develop a fluid model of the steady-state TCP behavior for such a system and derive analytical expressions for TCP throughput that explicitly account for rate variability as well as the dependency between the scheduler and TCP. The model is used to choose RF layer parameters that, in conjunction with the TCP-aware scheduler, improve long-term TCP throughput in wireless networks. A distinctive feature of our model is its ability to capture variability of round-trip-time, channel rate and packet error probability inherent to wireless communications. From the application perspective, we study the performance of wireless messaging systems. Two popular wireless applications, the short messaging service and multimedia messaging service are considered. We develop a mathematical model to evaluate the performance of these systems taking into consideration the fact that each message tolerates only a limited amount of waiting time in the system. Using the model, closed-form expressions for critical performance parameters such as message loss, message delay and expiry probability are derived. Furthermore, a simple algorithm is presented to find the optimal temporary storage size that minimizes message delay for a given set of system parameters
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Reverse Link Analysis and Modeling of CDMA based Distributed Antenna Systems
Distributed Antenna Systems (DAS) are gaining widespread popularity in the indoor wireless market. Most of the existing research literature on this subject has focused on comparing the advantages of DAS systems with traditional macro cells. The goal of this thesis is to define a performance platform for CDMA based distributed antenna systems which can serve as essential design guidelines for future DAS deployments. One of the major issues presented by DAS systems is the noise floor rise in the reverse link caused by the DAS noise figure. This noise rise becomes a limiting factor in determining capacity and coverage of the DAS based network. The common practice of adding an attenuator (padding) in front of the Base Station receiver can bring down the noise floor, but at the same time force the mobile units to transmit at higher power. We establish an operating platform for the DAS so that the system can be effectively operated within the limits of mobile transmit power and base station receive power, maximizing the system capacity