ccond-and third-gcncration (2G and 3G) wiidcss systcins h a w been dcsigiicd primarily for voicc,... more ccond-and third-gcncration (2G and 3G) wiidcss systcins h a w been dcsigiicd primarily for voicc, a connection-oricntcd, dclny-sciisirivc scrvicc rcquiriiig n spccificd bit ratc. In ccmtrast, data scrviccs arc ofttcn coi~ncctioi~lc.ss, dclay inscnsitivc, and have 1 1 0 spccific bit-raw rcq~iircttici~ts. Thcse ditfcrciiccs suggest that ubiquitous (aiiptimc/aiiywhcrc) covcragc tilay iiot bc ;1 strict rcquircincnt for wirclcss data nctworks and in fact may ~iccdlessly complicate the dcsign. ?'his liiic of tlinught lcads to spstciiis that providc isolated high b i t -r a w "POCICC~S" of cnvcragc closc to basc statinn mteniins tlirongli inulcilcvcl iiiodulation and iiicrciscd spectrum rcusc allowcd by pocket isnlatioii. Spccific issiics that arc rclcvaiit for such tier architcctiircs raiigc from tlic physical layer cxtending to radio rcsuircc it~anagcmciit and cvcii application laycrs. In this article, wc dcscribe s u m issiics for wirclcss data targccing tlic following: transccivcr techniques and radio ~~S O I I L ' C C rrianagciiiciit.
Infostations provide a new way to look at the problem of providing high data rate wireless access... more Infostations provide a new way to look at the problem of providing high data rate wireless access. By allowing delayed message delivery, we can lift the constraint on ubiquitous coverage inherited from voice cellular systems. The reduction of coverage results in significant capacity gains, showing the possibility for low cost broadband wireless data services. We give an overview of ongoing research on the Infostation concept.
We consider the admission problem for the two class M/M/C/C queueing system. The admission policy... more We consider the admission problem for the two class M/M/C/C queueing system. The admission policy is coded as a binary string and strings which produce good policies are found using genetic algorithms. We use three policy coding methods:
We consider a centralized Spectrum Server that coordinates the transmissions of a group of links ... more We consider a centralized Spectrum Server that coordinates the transmissions of a group of links sharing a common spectrum. Links employ on-off modulation with fixed transmit power when active. In the on state, a link obtains a data rate determined by the signal-to-interference ratio on the link. By knowing the link gains in the network, the spectrum server finds an optimal schedule that maximizes the average sum rate subject to a minimum average rate constraint for each link. Using a graph theoretic model for the network and a linear programming formulation, the resulting schedules are a collection of transmission modes (sets of active links) that are time shared in a fashion that is reminiscent of spatial reuse patterns in cellular networks. In the special case when there is no minimum rate constraint, the optimal schedule results in a fixed dominant mode with highest sum rate being operated all the time. In order to offset the inherent unfairness in the above solution, we introduce a minimum rate constraint and characterize the resulting loss in sum rate when compared to the case when there is no minimum rate constraint. We also investigate alternate fairness criteria by designing scheduling algorithms that achieve max-min fairness and proportional fairness. It is shown that the max-min fair rate allocation maximizes the minimum common rate among the links. Simulation results are presented and future work is described.
ICC 2001. IEEE International Conference on Communications. Conference Record (Cat. No.01CH37240), 2000
We characterize the user capacity, i.e., the maximum number of supportable users at a common SIR ... more We characterize the user capacity, i.e., the maximum number of supportable users at a common SIR target level for a fixed processing gain, of a single-cell symbol asynchronous CDMA system. We show that the user capacity of an asynchronous system is the same as the user capacity of a synchronous system; that is there is no loss in user capacity due to asynchrony. Optimum signature sequences are those that minimize the total squared asynchronous correlation (TSAC) among the users, and depend on users' delay profile. Optimum received powers of the users are equal, and the optimum linear receiver filters in any observation window of size M ≥ 1 symbols (i.e., M-shot MMSE filters) are one-shot matched filters. We present iterative and distributed signature adaptation algorithms where, at each iteration, only one user updates its signature sequence to decrease the TSAC of the set.
From the idea of using an array of isolated wireless ports called Infostations, we consider the u... more From the idea of using an array of isolated wireless ports called Infostations, we consider the use of existing cellular infrastructure as the location for these Infostations. The coverage area of Infostations, though, will be smaller than the cell area. We determine the worst-case SIR as a function of the coverage-radius-to-cell-radius ratio and the frequency-reuse cluster size. For specific modulation schemes, we identify desirable operating points and calculate the Infostations' utilization.
In wireless networks, it is often assumed that all nodes cooperate to relay packets for each othe... more In wireless networks, it is often assumed that all nodes cooperate to relay packets for each other. Although this is a plausible model for military or mission based networks, it is unrealistic for commercial networks and future pervasive computing environments. We address the issue of noncooperation between nodes in the context of content distribution in mobile infostation networks. We assume all nodes have common interest in all files cached in the fixed infostations. In addition to downloading files from the fixed infostations, nodes act as mobile infostations and exchange files when they are in proximity. We stipulate a social contract such that an exchange occurs only when each node can obtain something it wants from the exchange. Our social contract enables much higher system efficiency compared to downloading from fixed infostations only while not requiring true cooperation among nodes. We show by analysis and simulations that network performance depends on the node density, mobility and the number of files that are being disseminated. Our results point to the existence of data diversity for mobile infostation networks. The achievable throughput increases as the number of files of interest to all users increases. We have also extended the common interest model to the case where nodes have dissimilar interests. Our simulation results show that as mobile nodes change from having identical interests to mutually exclusive interests, the network performance degrades dramatically. We propose an alternative user strategy when nodes have partially overlapping interests and show that the network capacity can be significantly improved by exploiting multiuser diversity inherent in mobile infostation networks. We conclude that data diversity and multiuser diversity exist in noncooperative mobile infostation networks and can be exploited.
ICC 2001. IEEE International Conference on Communications. Conference Record (Cat. No.01CH37240), 2000
Throughput maximization of an adaptive transmission system with a finite number of transmitted po... more Throughput maximization of an adaptive transmission system with a finite number of transmitted power levels and code rates for communication over slow fading channels is analyzed based on the concept of information outage. Properties of throughput maximizing policies lead to an iterative algorithm which suggests good system designs. Numerical results show that carefully designed discrete adaptive transmission systems with a small number of power levels and code rates can achieve throughput values close to ergodic capacity.
Ieee Transactions on Wireless Communications, Mar 1, 2009
Dynamic allocation of spectrum prior to transmission is an important feature for next generation ... more Dynamic allocation of spectrum prior to transmission is an important feature for next generation wireless networks. In this work, we develop and analyze a model for dynamic spectrum allocation, that is applicable for a broad class of practical systems. We consider multiple service providers (SPs), in the same geographic region, that share a fixed spectrum, on a non-interference basis. This
Ieee Transactions on Wireless Communications, 2009
ABSTRACT Network simulation packages such as NS-2 and OPNET have been shown to be a limited optio... more ABSTRACT Network simulation packages such as NS-2 and OPNET have been shown to be a limited option for cross-layer experimentation in wireless networking because they cannot faithfully capture the propagation and interference characteristics of wireless channels. Recent research on network cross-layer optimizations further raises this concern due to the close interaction between physical layer feedback and higher layer protocols. To overcome this shortcoming, wireless testbeds have been used wherein novel protocols and application concepts can be assessed in a realistic environment under controlled and repeatable conditions. Since average signal-to-noise-ratio (SNR) often determines the performance of a wireless link, our goal is to seek link SNR mapping methods that replicate real-world link SNRs onto an indoor testbed. Specifically, we devise and assess link SNR mapping methodologies for two different applications: hierarchical networks with a fixed access point (AP), and mesh networks. For the AP-based networks, we employ the minimum weight matching algorithm to minimize the root-mean-square (RMS) mapping error between the testbed and real-world SNRs. For the mesh networks, to avoid the technical difficulties inherent in ldquoforward mappingrdquo, we develop a ldquoreverse mappingrdquo method by which we turn a testbed configuration with specified link SNRs into a real-world configuration. By inducing the link gain difference between the testbed and the real-world distance-dependent path loss to have a log-normal distribution, a very close approximation to real-world shadow fading is achieved. We present results for a variety of indoor and outdoor real-world scenarios to demonstrate the generality of our method.
We review the design, selected applications and performance of WiPPET Wireless Propagation and Pr... more We review the design, selected applications and performance of WiPPET Wireless Propagation and Protocol Evaluation Testbed, a general parallel simulation testbed for various types of wireless networks. WiPPET has been written in TeD C++, an object-oriented modeling framework that isolates network modeling from the underlying parallel discrete event simulator. We describe the techniques for modeling radio propagation long and short-scale fading and interference and protocols that promote scalability of parallel simulations at session and packet timescales. We outline two selected applications of WiPPET: i n tegrated radio resource management in a mobile wireless voice network; and packet losses due to mobility and short-scale fading over a radio link. We illustrate the e ciency of the simulator under two partitioning schemes with parallel performance data obtained using the Georgia Time Warp optimistic simulator.
We describe the TeD/C ++ implementation of WiPPET, a parallel simulation testbed for mobile wirel... more We describe the TeD/C ++ implementation of WiPPET, a parallel simulation testbed for mobile wireless networks. In this article we emphasize the techniques for modeling of radio propagation (long{ and short{ scale fading and interference) and protocols for integrated radio resource management in mobile wireless voice networks. The testbed includes the standards{based AMPS, NA{TDMA and GSM protocols, and several research{oriented protocol families.
The process of nding a unit in a mobile communications system is called paging and requires the u... more The process of nding a unit in a mobile communications system is called paging and requires the use of limited network resources. Although it is understood how to minimize the use of network resources and satisfy delay constraints when paging a single unit, optimal policies for paging multiple units are di cult to derive. Here we adapt single unit polling methods to obtain simple ensemble polling schemes for use with multiple units which can greatly increase the rate at which page requests can be processed while maintaining acceptable average delay.
Proceedings of the 2nd Acm International Workshop on Foundations of Wireless Ad Hoc and Sensor Networking and Computing, May 18, 2009
A protocol, dubbed BeSpoken, steers data transmissions along a straight path called a spoke throu... more A protocol, dubbed BeSpoken, steers data transmissions along a straight path called a spoke through a wireless sensor network with many location-unaware nodes. BeSpoken implements a simple, spatially recursive communication process, where a set of control packets and a data packet are exchanged among daisy-chained relays that constitute the spoke. It directs data transmissions by randomly selecting relays from crescent-shaped areas along the spoke axis created by intersecting transmission ranges of control and data packets. To specify design rules for protocol parameters that minimize energy consumption while ensuring that spokes propagate far enough and have a limited wobble with respect to the spoke axis, our model of the spoke propagation matches the protocol parameters to the density of network nodes, assuming that nodes are spatially distributed as a Poisson point process of known uniform intensity. To avoid this requirement, we propose and characterize an adaptive mechanism that ensures desired spoke propagation in a network of arbitrary density. This necessitates a qualitatively new protocol model used to evaluate the spoke propagation under both the basic and the adaptive protocol. The introduced adaptive mechanism repairs the spoke when the crescent-shaped area is empty which may occur in the case of network thinning and as a result of random or arbitrary sensor death. Our analytical and simulation results demonstrate that the adaptive BeSpoken creates longer spokes both in networks with uniform distribution of nodes and in networks with holes. In addition, the adaptive protocol is significantly less sensitive to changes in the distribution of network nodes and their density.
ccond-and third-gcncration (2G and 3G) wiidcss systcins h a w been dcsigiicd primarily for voicc,... more ccond-and third-gcncration (2G and 3G) wiidcss systcins h a w been dcsigiicd primarily for voicc, a connection-oricntcd, dclny-sciisirivc scrvicc rcquiriiig n spccificd bit ratc. In ccmtrast, data scrviccs arc ofttcn coi~ncctioi~lc.ss, dclay inscnsitivc, and have 1 1 0 spccific bit-raw rcq~iircttici~ts. Thcse ditfcrciiccs suggest that ubiquitous (aiiptimc/aiiywhcrc) covcragc tilay iiot bc ;1 strict rcquircincnt for wirclcss data nctworks and in fact may ~iccdlessly complicate the dcsign. ?'his liiic of tlinught lcads to spstciiis that providc isolated high b i t -r a w "POCICC~S" of cnvcragc closc to basc statinn mteniins tlirongli inulcilcvcl iiiodulation and iiicrciscd spectrum rcusc allowcd by pocket isnlatioii. Spccific issiics that arc rclcvaiit for such tier architcctiircs raiigc from tlic physical layer cxtending to radio rcsuircc it~anagcmciit and cvcii application laycrs. In this article, wc dcscribe s u m issiics for wirclcss data targccing tlic following: transccivcr techniques and radio ~~S O I I L ' C C rrianagciiiciit.
Infostations provide a new way to look at the problem of providing high data rate wireless access... more Infostations provide a new way to look at the problem of providing high data rate wireless access. By allowing delayed message delivery, we can lift the constraint on ubiquitous coverage inherited from voice cellular systems. The reduction of coverage results in significant capacity gains, showing the possibility for low cost broadband wireless data services. We give an overview of ongoing research on the Infostation concept.
We consider the admission problem for the two class M/M/C/C queueing system. The admission policy... more We consider the admission problem for the two class M/M/C/C queueing system. The admission policy is coded as a binary string and strings which produce good policies are found using genetic algorithms. We use three policy coding methods:
We consider a centralized Spectrum Server that coordinates the transmissions of a group of links ... more We consider a centralized Spectrum Server that coordinates the transmissions of a group of links sharing a common spectrum. Links employ on-off modulation with fixed transmit power when active. In the on state, a link obtains a data rate determined by the signal-to-interference ratio on the link. By knowing the link gains in the network, the spectrum server finds an optimal schedule that maximizes the average sum rate subject to a minimum average rate constraint for each link. Using a graph theoretic model for the network and a linear programming formulation, the resulting schedules are a collection of transmission modes (sets of active links) that are time shared in a fashion that is reminiscent of spatial reuse patterns in cellular networks. In the special case when there is no minimum rate constraint, the optimal schedule results in a fixed dominant mode with highest sum rate being operated all the time. In order to offset the inherent unfairness in the above solution, we introduce a minimum rate constraint and characterize the resulting loss in sum rate when compared to the case when there is no minimum rate constraint. We also investigate alternate fairness criteria by designing scheduling algorithms that achieve max-min fairness and proportional fairness. It is shown that the max-min fair rate allocation maximizes the minimum common rate among the links. Simulation results are presented and future work is described.
ICC 2001. IEEE International Conference on Communications. Conference Record (Cat. No.01CH37240), 2000
We characterize the user capacity, i.e., the maximum number of supportable users at a common SIR ... more We characterize the user capacity, i.e., the maximum number of supportable users at a common SIR target level for a fixed processing gain, of a single-cell symbol asynchronous CDMA system. We show that the user capacity of an asynchronous system is the same as the user capacity of a synchronous system; that is there is no loss in user capacity due to asynchrony. Optimum signature sequences are those that minimize the total squared asynchronous correlation (TSAC) among the users, and depend on users' delay profile. Optimum received powers of the users are equal, and the optimum linear receiver filters in any observation window of size M ≥ 1 symbols (i.e., M-shot MMSE filters) are one-shot matched filters. We present iterative and distributed signature adaptation algorithms where, at each iteration, only one user updates its signature sequence to decrease the TSAC of the set.
From the idea of using an array of isolated wireless ports called Infostations, we consider the u... more From the idea of using an array of isolated wireless ports called Infostations, we consider the use of existing cellular infrastructure as the location for these Infostations. The coverage area of Infostations, though, will be smaller than the cell area. We determine the worst-case SIR as a function of the coverage-radius-to-cell-radius ratio and the frequency-reuse cluster size. For specific modulation schemes, we identify desirable operating points and calculate the Infostations' utilization.
In wireless networks, it is often assumed that all nodes cooperate to relay packets for each othe... more In wireless networks, it is often assumed that all nodes cooperate to relay packets for each other. Although this is a plausible model for military or mission based networks, it is unrealistic for commercial networks and future pervasive computing environments. We address the issue of noncooperation between nodes in the context of content distribution in mobile infostation networks. We assume all nodes have common interest in all files cached in the fixed infostations. In addition to downloading files from the fixed infostations, nodes act as mobile infostations and exchange files when they are in proximity. We stipulate a social contract such that an exchange occurs only when each node can obtain something it wants from the exchange. Our social contract enables much higher system efficiency compared to downloading from fixed infostations only while not requiring true cooperation among nodes. We show by analysis and simulations that network performance depends on the node density, mobility and the number of files that are being disseminated. Our results point to the existence of data diversity for mobile infostation networks. The achievable throughput increases as the number of files of interest to all users increases. We have also extended the common interest model to the case where nodes have dissimilar interests. Our simulation results show that as mobile nodes change from having identical interests to mutually exclusive interests, the network performance degrades dramatically. We propose an alternative user strategy when nodes have partially overlapping interests and show that the network capacity can be significantly improved by exploiting multiuser diversity inherent in mobile infostation networks. We conclude that data diversity and multiuser diversity exist in noncooperative mobile infostation networks and can be exploited.
ICC 2001. IEEE International Conference on Communications. Conference Record (Cat. No.01CH37240), 2000
Throughput maximization of an adaptive transmission system with a finite number of transmitted po... more Throughput maximization of an adaptive transmission system with a finite number of transmitted power levels and code rates for communication over slow fading channels is analyzed based on the concept of information outage. Properties of throughput maximizing policies lead to an iterative algorithm which suggests good system designs. Numerical results show that carefully designed discrete adaptive transmission systems with a small number of power levels and code rates can achieve throughput values close to ergodic capacity.
Ieee Transactions on Wireless Communications, Mar 1, 2009
Dynamic allocation of spectrum prior to transmission is an important feature for next generation ... more Dynamic allocation of spectrum prior to transmission is an important feature for next generation wireless networks. In this work, we develop and analyze a model for dynamic spectrum allocation, that is applicable for a broad class of practical systems. We consider multiple service providers (SPs), in the same geographic region, that share a fixed spectrum, on a non-interference basis. This
Ieee Transactions on Wireless Communications, 2009
ABSTRACT Network simulation packages such as NS-2 and OPNET have been shown to be a limited optio... more ABSTRACT Network simulation packages such as NS-2 and OPNET have been shown to be a limited option for cross-layer experimentation in wireless networking because they cannot faithfully capture the propagation and interference characteristics of wireless channels. Recent research on network cross-layer optimizations further raises this concern due to the close interaction between physical layer feedback and higher layer protocols. To overcome this shortcoming, wireless testbeds have been used wherein novel protocols and application concepts can be assessed in a realistic environment under controlled and repeatable conditions. Since average signal-to-noise-ratio (SNR) often determines the performance of a wireless link, our goal is to seek link SNR mapping methods that replicate real-world link SNRs onto an indoor testbed. Specifically, we devise and assess link SNR mapping methodologies for two different applications: hierarchical networks with a fixed access point (AP), and mesh networks. For the AP-based networks, we employ the minimum weight matching algorithm to minimize the root-mean-square (RMS) mapping error between the testbed and real-world SNRs. For the mesh networks, to avoid the technical difficulties inherent in ldquoforward mappingrdquo, we develop a ldquoreverse mappingrdquo method by which we turn a testbed configuration with specified link SNRs into a real-world configuration. By inducing the link gain difference between the testbed and the real-world distance-dependent path loss to have a log-normal distribution, a very close approximation to real-world shadow fading is achieved. We present results for a variety of indoor and outdoor real-world scenarios to demonstrate the generality of our method.
We review the design, selected applications and performance of WiPPET Wireless Propagation and Pr... more We review the design, selected applications and performance of WiPPET Wireless Propagation and Protocol Evaluation Testbed, a general parallel simulation testbed for various types of wireless networks. WiPPET has been written in TeD C++, an object-oriented modeling framework that isolates network modeling from the underlying parallel discrete event simulator. We describe the techniques for modeling radio propagation long and short-scale fading and interference and protocols that promote scalability of parallel simulations at session and packet timescales. We outline two selected applications of WiPPET: i n tegrated radio resource management in a mobile wireless voice network; and packet losses due to mobility and short-scale fading over a radio link. We illustrate the e ciency of the simulator under two partitioning schemes with parallel performance data obtained using the Georgia Time Warp optimistic simulator.
We describe the TeD/C ++ implementation of WiPPET, a parallel simulation testbed for mobile wirel... more We describe the TeD/C ++ implementation of WiPPET, a parallel simulation testbed for mobile wireless networks. In this article we emphasize the techniques for modeling of radio propagation (long{ and short{ scale fading and interference) and protocols for integrated radio resource management in mobile wireless voice networks. The testbed includes the standards{based AMPS, NA{TDMA and GSM protocols, and several research{oriented protocol families.
The process of nding a unit in a mobile communications system is called paging and requires the u... more The process of nding a unit in a mobile communications system is called paging and requires the use of limited network resources. Although it is understood how to minimize the use of network resources and satisfy delay constraints when paging a single unit, optimal policies for paging multiple units are di cult to derive. Here we adapt single unit polling methods to obtain simple ensemble polling schemes for use with multiple units which can greatly increase the rate at which page requests can be processed while maintaining acceptable average delay.
Proceedings of the 2nd Acm International Workshop on Foundations of Wireless Ad Hoc and Sensor Networking and Computing, May 18, 2009
A protocol, dubbed BeSpoken, steers data transmissions along a straight path called a spoke throu... more A protocol, dubbed BeSpoken, steers data transmissions along a straight path called a spoke through a wireless sensor network with many location-unaware nodes. BeSpoken implements a simple, spatially recursive communication process, where a set of control packets and a data packet are exchanged among daisy-chained relays that constitute the spoke. It directs data transmissions by randomly selecting relays from crescent-shaped areas along the spoke axis created by intersecting transmission ranges of control and data packets. To specify design rules for protocol parameters that minimize energy consumption while ensuring that spokes propagate far enough and have a limited wobble with respect to the spoke axis, our model of the spoke propagation matches the protocol parameters to the density of network nodes, assuming that nodes are spatially distributed as a Poisson point process of known uniform intensity. To avoid this requirement, we propose and characterize an adaptive mechanism that ensures desired spoke propagation in a network of arbitrary density. This necessitates a qualitatively new protocol model used to evaluate the spoke propagation under both the basic and the adaptive protocol. The introduced adaptive mechanism repairs the spoke when the crescent-shaped area is empty which may occur in the case of network thinning and as a result of random or arbitrary sensor death. Our analytical and simulation results demonstrate that the adaptive BeSpoken creates longer spokes both in networks with uniform distribution of nodes and in networks with holes. In addition, the adaptive protocol is significantly less sensitive to changes in the distribution of network nodes and their density.
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Papers by Roy Yates