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We consider an RFID network that consists of a single reader and multiple tags sojourning in the vicinity of the reader. In such an RFID network, collisions occur among the packets which are simultaneously sent by two or more tags. In order to support the reader to cognize tags while resolving the collision problem, we consider a static naive MAC scheme that employs a collision arbitration method rooted in framed slotted ALOHA. A basic mission of a reader in an RFID network is to cognize every neighboring tag in a prescribed time. Thus, it is of necessity to analyze the cognition completion time, e.g., the time elapsed until the reader cognized all the tags. In this paper, we first mathematically describe the cognition completion time as a hitting time of a homogeneous non-decreasing Markov chain on a finite state space. Next, we construct a fast converging Markov chain on the same state space by using a sequence of random variables that have stochastic dominance. Finally, we propose a numerically efficient method in which the cognition completion time is approximated by a hitting time of the fast converging Markov chain. Numerical examples confirm that the approximate expected value of the cognition completion time provides a lower bound on the exact expected value.

In a wireless passive sensor network, RF sources wirelessly supply energy to sensor nodes. Against theoretical expectations for an abundance of energy, a wireless passive sensor network suffers from a scarcity of energy in practice. By such a scarcity, a wireless passive sensor network is obliged to adopt a contending-type MAC scheme, which inevitably brings about packet collision and hence capture phenomenon. Unfortunately, the capture phenomenon places a sensor node which is far off from the sink node at a distinct disadvantage. In this paper, we propose a MAC scheme, rooted in framed and slotted ALOHA, which provides every sensor node with an equal opportunity for succeeding in packet delivery. In a case study, we prove the existence of an equal opportunity MAC scheme and construct such a MAC scheme explicitly. In addition, we develop an exact expression of the throughput attained by the proposed scheme in a closed form. Using the throughput formula, we then demonstrate that the proposed scheme is able to achieve a higher total throughput than a conventional scheme.

Random coding bounds are obtained for multiple-input multiple-output (MIMO) fading channels. To derive the result in a compact and easy-to-evaluate form, a series of combinatorial codeword enumeration problems are solved for input-constrained MIMO fading channels. The bounds obtained in this paper are shown useful as performance prediction measures for MIMO systems which employ turbo-like block codes as the outer code to derive the space-time inner code. The error exponents for MIMO channels are also derived from the bounds, and then compared with the classical Gallager error exponents as well as the channel capacities. The random coding bounds associated with the maximum likelihood receiver exhibit good match with the extensive system simulation results obtained with a turbo-iterative receiver.

A wireless sensor network is a network of compact micro-sensors equipped with wireless communication capability. In a wireless sensor network, saving energy is a critical issue. Furthermore, a sensor node is expected to face many difficulties in signaling and computing. As a MAC scheme for a wireless sensor network, we thus propose an energy-aware version of pure ALOHA scheme, where rather than sacrificing the simplicity of pure ALOHA, we take a straightforward approach in saving energy by trading off throughput performance. First, we add a step of deciding between stop and continuation prior to each delivery attempt for a MAC PDU. Secondly, we find an optimal stopping rule for such a decision in consideration of the losses reflecting energy consumption as well as throughput degradation. In particular, we note that the results of delivery attempts are hardly predictable in the environment that sensor nodes contend for the error-prone wireless resource. Thus, presuming that only partial information about such results is available to sensor nodes, we explicitly draw an optimal stopping rule. Finally, numerical examples are given to demonstrate the expected losses incurred by optimal stopping rules with full and partial information.

IEEE 802.16 wireless MAN standard specifies the air interface of broadband wireless access systems providing multiple services. In the wireless MAN, the best effort service class is ranked on the lowest position in priority and is assisted by a MAC scheme based on reservation ALOHA. In such a MAC scheme, a collision of resource requests is unavoidable so that the wireless MAN standard adopted a truncated binary exponential back-off scheme to arbitrate request attempts. While an exponential back-off scheme is simple to implement, its capture or starvation effect was revealed to deteriorate the fairness in short-term throughput and delay variance in the long term. Aiming at improving the throughput and delay performance, we thus propose the unisource and multisource m-ary tree schemes as alternatives for resolving request collisions in a wireless MAN. For the unisource tree scheme, we first develop an analytical method to exactly calculate the throughput in the saturated environment. Using the analytical method and simulation method as well, we then evaluate the saturated throughput, mean of MAC PDU delay and variance of MAC PDU delay in each proposed scheme. From the numerical examples, we confirm that the unisource and multisource m-ary tree schemes invoke superior throughput and delay performance to a truncated binary exponential back-off scheme.

In this letter, we propose an approximate symbol error probability (SEP) of M-ary pulse amplitude modulation (PAM) under a noisy carrier phase in a closed form when the carrier phase is governed by Tikhonov probability density function. The approximate results are desirable to evaluate the behavior of the system. The accuracy of the approximation is verified with respect to the numerical integration.

We consider connection-oriented wireless cellular networks. Such second generation systems are circuit-switched digital networks which employ dedicated radio channels for the transmission of signaling information. A forward signaling channel is a common signaling channel assigned to carry the multiplexed stream of paging and channel-allocation packets from a base station to the mobile stations. Similarly, for ATM wireless networks, paging and virtual-circuit-allocation packets are multiplexed across the forward signaling channels as part of the virtual-circuit set-up phase. The delay levels experienced by paging and channel-allocation packets are critical factors in determining the efficient utilization of the limited radio channel capacity. A multiplexing scheme operating in a "slotted mode" can lead to reduced power consumption at the handsets, but may in turn induce an increase in packet delays. Focusing on forward signaling channels, we present schemes for multiplexing paging and channel-allocation packets across these channels, based on channelization plans, access priority assignments and paging group arrangements. For such multiplexing schemes, we develop analytical methods for the calculation of the delay characteristics exhibited by paging and channel-allocation packets. The resulting models and formulas provide for the design and analysis of forward signaling channels for wireless network systems.

In the IEEE 802.16 Wireless MAN standard, the best effort service class is ranked on the lowest position in priority and is assisted by a MAC scheme based on reservation ALOHA. The details of the MAC scheme, however, are not specified in the standard. In this paper, we present the rules for deciding the amount of resource to demand as well as the rules for deciding the amount of resource to grant. Combining these rules, we then construct candidate MAC schemes for the best effort service. In designing a MAC scheme for the best effort service, the throughput and delay performance must be considered since only scarce resource may be available after resource is preferably granted to other service classes. For the performance evaluation, we thus develop a numerical method to approximately calculate the throughput in the saturated environment. Using the approximation and simulation methods, we then investigate the throughput and delay performance exhibited by each candidate MAC scheme. From the numerical results, we observe that the exhaustive demand rule paired with the full grant rule shows superior performance.

In provisioning packet data service on wireless cellular networks, a scheme of altering connection status between mobile and base stations appeared intending to efficiently utilize resource during idle periods. In such a scheme, connection components are sequentially released as an idle period persists, while a transmission activity is resumed as a prescribed amount of traffic load is accumulated at the transmitting station. Before a transmission resume, however, latency depending on previous idle period is unavoidable to retrieve the lost connection components, which also produces a chain reaction in forthcoming idle period and connection retrieval time. An issue arising in design of the scheme is to determine a threshold value for load accumulation in conjunction with packet delay properties. A high threshold apparently incurs along stand-by to gather the prescribed traffic load before resuming transmission. On the other hand, such high threshold may shorten the length of upcoming idle period and reduce the consequent connection retrieval time by suppressing the release of connection components. In this paper, we thus investigate the antithetical effects of load threshold on packet delay performance. First, we generalize the connection retrieval time in consideration of the number of states and maximum sojourn times. Secondly, for general packet arrivals, we estimate average length of idle period and mean packet delay. In addition, we present an approximation method to calculate the moments of packet delay time for Poisson arrivals. Finally, we construct and solve a problem to find an optimal value for load threshold minimizing mean packet delay. From numerical examples, we find non-trivial optimal thresholds in the environments characterized by relatively long connection retrieval time and heavy traffic load.

3GPP RLC protocol specification adopted an error control scheme based on selective-repeat ARQ. In the 3GPP's ARQ, distinctive windows are installed at the transmitting and receiving stations so that each station is prohibited to send or receive a data PDU out of its window. As in a general selective-repeat ARQ, a classical problem of reordering is inherent in the 3GPP's ARQ. While a decrease in window size reduces the occupancy at the reordering buffer, such a decrease incurs degradation in delay and throughput performance. First, for the purpose of investigating the effect of window size on throughput performance, we develop an approximation method to calculate the maximum throughput of the 3GPP's ARQ. Secondly, aiming at reducing the occupancy at the reordering buffer as well as suppressing a deterioration of delay and throughput performance, we propose a scheme of regulating the occupancy at the reordering buffer as an additive to the 3GPP's ARQ. In the occupancy regulation scheme, a threshold is created in the receiving station's window and a data PDU out of the threshold (but within the window) is treated according to a go-back-N ARQ. For judging the effectiveness of the occupancy regulation scheme, we investigate peak occupancy, mean delay time and maximum throughput exhibited by the proposed scheme in various environments. From numerical examples, we confirm the validity of our approximation method and conclude that the occupancy regulation scheme is able to improve the delay and throughput performance of the 3GPP's ARQ without inflating the occupancy at the reordering buffer.

In provisioning packet data service on wireless cellular networks, a scheme of altering connection status between mobile and base stations appeared with an effort to utilize resource during idle periods. A critical issue in such scheme of sojourn and transition on the connection states is to determine a maximum time to sojourn at each state. An excessive sojourn time leads to resource invasion by inactive stations, while a high cost of re-establishing connection components is imposed by an insufficient sojourn. Thus, the maximum sojourn times must be optimized in consideration of the two conflicting arguments. In this paper, we consider a generic scheme of connection status transitions and formulate a decision problem to determine maximum sojourn times by introducing a loss function which reflects the conflicting arguments. From the decision problem, we derive an optimal value for maximum sojourn time, identified as Bayes rule, by observing the delay time of last packet to have posterior information about the length of upcoming idle period. From the analytical results, we show the optimal sojourn time is trivial under a constraint on loss coefficients when packet arrivals follow a Poisson process.

A demand priority network is a high speed local area network. Compared with a fast Ethernet, it is known to have advantages in transmission of delay-sensitive traffic. However, in a demand priority network, the packet delay time is unbounded and the delay levels experienced at stations are unfair. In this paper, we consider Round Robin and FCFS schemes for scheduling packet transmission. Under each scheme, we develop an analytical approximation method for mean delay calculation, and investigate the mean and standard deviation of the packet delay time by the approximation and simulation methods. By introducing a degree of delay fairness, the Round Robin and FCFS schemes are evaluated in delay fairness.

We consider second generation wireless cellular networks such as IS-54, IS-95 and GSM. These are circuit-switched digital networks which employ dedicated radio channels for the transmission of signaling information. A forward signaling channel is a common signaling channel assigned to carry the multiplexed stream of paging and connection allocation packets from a base station to mobile stations. A reverse signaling channel, which employs a contention-oriented medium access algorithm, is used by mobile stations to send connection request packets (requesting the allocation of a call circuit). A location area includes a specified set of adjacent cells. Mobile units must re-register as they cross the boundary of a location area. The connection set-up time and the paging response delay are critical factors in the design of the signaling system. A location area structure must be optimally selected to ensure that acceptable levels of connection set-up time and paging response delay are achieved. In this paper, combining the operation of forward and reverse signaling channels, we present an analytical method for calculating the distribution functions of connection set-up time and paging response delay. We subsequently investigate the impact of the location area architecture on the performance of signaling channels. The resulting model and formulas provide an important basis for the selection of the location area structure.

We consider connection-oriented packet-switched wireless cellular networks such as wireless ATM networks. At a cell's base station, packets destined to mobiles are stored and sent to the cell's mobile stations across forward wireless channels. When a handover occurs, backlogged packets which are destined to the mobile station and which have not yet been delivered remain at the buffer of the old base station. For applications which are sensitive to delay fluctuations but are relatively tolerable to packet losses, (e.g., packetized voice and video streams), it is not effective to forward these packets to the new base station. We thus consider a backlogged packet discard scheme under which all backlogged packets are discarded. In this manner, we eliminate additional packet delays caused by inter-cell rerouting of backlogged packets. In turn, this scheme leads to an increase of the packet loss level due to its dropping of the backlogged packets. To guarantee a pre-negotiated quality-of-service level, the incurred packet loss value must be limited. We develop an analytical method for characterizing the statistics of the number of backlogged packets per handover, and derive an estimate for the probability of handover-induced packet loss. Using the analytical method, we investigate the effect of network parameters on the packet loss probability.