Jeong Geun Kim

Bandwidth allocation in wireless networks with guaranteed packet-loss performance

Providing quality-of-service (QoS) guarantees over wireless packet networks poses a host of technical challenges that are not present in wireline networks. One of the key issues is how to account for the characteristics of the time-varying wireless channel and for the impact of link-layer error control in the provisioning of packet-level QoS. We accommodate both aspects in analyzing the packet-loss performance over a wireless link. We consider the cases of a single and multiplexed traffic streams. The link capacity fluctuates according to a fluid version of Gilbert-Elliott channel model. Traffic sources are modeled as on-off fluid processes. For the single-stream case, we derive the exact packet-loss rate (PLR) due to buffer overflow at the sender side of the wireless link. We also obtain a closed-form approximation for the corresponding wireless effective bandwidth. In the case of multiplexed streams, we obtain a good approximation for the PLR using the Chernoff-dominant eigenvalue (CDE) approach. Our analysis is then used to study the optimal forward error correction code rate that guarantees a given PLR while minimizing the allocated bandwidth. Numerical results and simulations are used to verify the adequacy of our analysis and to study the impact of error control on the allocation of bandwidth for guaranteed packet-loss performance.

Fluid analysis of delay and packet discard performance for QoS support in wireless networks

Providing quality-of-service (QoS) guarantees over wireless links requires thorough understanding and quantification of the interactions among the traffic source, the wireless channel, and the underlying link-layer error control mechanisms. We account for such interactions in an analytical model that we use to investigate the delay distribution and the packet discard rate (PDR) over a wireless link. Our analysis accommodates the inherent autocorrelations in both the traffic source as well as the channel error characteristics. An on-off fluid process is used to model the arrival of packets at the transmitter. These packets are temporarily stored in a first-in-first-out (FIFO) buffer before being transmitted over a channel with a time-varying and autocorrelated service rate. Using fluid analysis, we first derive the distribution for the queueing delay at the transmitter. As part of this analysis, we solve a fundamental fluid problem, namely, the probability distribution for the workload generated by a two-state fluid source over a fixed time interval. We then use the delay analysis to derive the PDR at the receiver. A closed-form expression for the effective bandwidth subject to a delay constraint is provided as a function of the source, channel, and error scheme parameters. This expression enables fast assessment of the bandwidth requirement of real-time traffic over QoS-based wireless networks. Numerical results and simulations are used to verify the adequacy of the analysis and to study the interactions among various system parameters.

Effective bandwidth in wireless ATM networks

Wueless ATM aims at -tending ATM services to the wire 1= environment. In contrast to wirehne ATM, which is primarily based on refiable fiber optic, wirel= ATM will have to cope with an unreliable radio channel. ThB POS= a host of technical chdlengw related to the prov~loning of qurdity of service (QoS). Key imttw include incorporating the characteristics of the wirelm channel in the protiloning of cell-level QoS, and improving the perceived qurdity by using error control mechanisms. k this study, we propose a model for anrdyzing the cell IOS statistim due to btier overflow in a wireless ATM environment. This model incorporate the service disruption caused by the unreliable radio channel as well as the impact of error control schema, e.g., automatic repeat requwt (ARQ) and forward error correction (FEC) mechanisms. The main theme of this study is to invatigate the cdl loss behavior of a wireless ATM fink as a finction of the assigned bandwidth and error control schemw. Using fluid analysis, we pr=ent an approximate ar-ion for the cell loss rate (CLR). This ~r-ion is used to derive a closed-form ~ression for the wireless tiective bandwidth. It is *O used to investigate the optirnd FEC code rate that gttarante= a given CLR wtie m_lng the unitization of the wireless bandwidth. The Mldity of our andyticd re sttlts are tested by contrasting them to simulation r=ttlts. Our observations indicate that the proposed qrassion of CLR is quite accurate over a range of moderate bit error rat=.

Quality of service over wireless ATM links

Several technical issues must be resolved before ATM services can be efficiently extended to the wireless environment. Key issues include incorporating the characteristics of the time-varying wireless channel in the provisioning of the cell-level QoS, and improving the transport performance using error control mechanisms. We analyze the cell loss and delay performance over a wireless ATM link. We consider both cases of a single and multiplexed ATM connections. The link capacity fluctuates according to a fluid version of Gilbert-Elliot channel model. Traffic sources are modeled as on-off fluid processes. The analytical framework incorporates the effects of error control schemes (i.e., ARQ and/or FEC), which are used to improve the transport performance over the wireless link. For the single-stream case, we derive the mean delay and the cell loss rate (CLR) due to buffer overflow at the sender side of the wireless link. We also obtain a closed-form approximation for the corresponding wireless effective bandwidth. In the case of multiplexed streams, we obtain a good approximation for the CLR using the Chernoff-dominant eigenvalue (CDE) approach. The expressions for the CLR and effective bandwidth are then used to study the optimal FEC code rate that guarantees the requested QoS while maximizing the utilization of the wireless bandwidth. Numerical results and simulations are used to verify the adequacy of our analysis and to study the impact of error control on the allocation of bandwidth for guaranteed cell loss and delay performance.

Connection admission control for PRMA/DA wireless access protocol

Next generation wireless communication systems will handle a wide range of services such as voice, video, and data. In this multi-service scenario, major technical issues are concerned with the selection of a suitable media access control (MAC) protocol and provision of adequate quality of service (QoS) to network users. We introduce a wireless media access control (MAC) protocol which is capable of transporting broadband traffic and providing seamless connectivity to ATM (asynchronous transfer mode) networks. Our protocol, having an air interface comparable to ATM, adopts a dynamic channel allocation scheme which enables expeditious network access and utilizes bandwidth resource efficiently for a mixed voice/video/data traffic environment. Simulation results presented here show the effectiveness of wireless access scheme, QoS provision, and dynamic channel allocation in terms of key performance metrics such as: throughput, cell loss-rate, call access delay, and cell transmission delay.

Fluid analysis of delay performance for QoS support in wireless networks

Providing quality of service (QoS) guarantees over wireless links requires thorough understanding and quantification of the interactions among the traffic source, the wireless channel, and the underlying error control mechanisms. In this paper, we account for such interactions in a network-layer model that we use to investigate the delay performance for an on/off traffic stream transported over a wireless link. The capacity of this link fluctuates according to a fluid version of Gilbert-Elliots model. We derive the packet delay distribution via two different approaches: uniformization and Laplace transform. Computational aspects of both approaches are discussed. The delay distribution is then used to quantify the wireless effective bandwidth under a given delay guarantee. Numerical results and simulations are used to verify the adequacy of our analysis and to study the impact of error control and bandwidth allocation on the packet delay performance.

Performance aspects of IEEE 802.11 wireless local-area networks

We are on the threshold of witnessing an explosion of portable and mobile terminals capable of sending and receiving multimedia traffic. Currently, the standard being worked out by the IEEE 802.11 committee to support wireless connectivity in the local area network appears to be the most promising one. IEEE 802.11 protocols support both scheduling and random access techniques operating simultaneously, called point coordination function (PCF) and distributed coordination function (DCF), respectively. In this paper, we study the interactions between PCF and DCF when voice and asynchronous data traffic needs to be supported. We investigate the dimensioning problems of various parameters, and provide the general rule of thumb of the default values.

Performance of backward handoff in wireless ATM

One of the key issues in wireless ATM is concerned with an efficient handoff scheme that can provide seamless network connectivity to mobile terminals. The handoff scheme must be fast and reliable so that service disruption is minimized. In this paper, we investigate the performance of a backward handoff scheme, which is currently under active consideration in the ATM Forum. The main objective is to study the impact of critical parameters on end-to-end cell delay and service disruption period during connection rerouting.