Optimal Packet Scheduling in a Multiple Access Channel with Energy Harvesting Transmitters

Yang, Jing,Ulukus, Sennur The Korea Institute of Information and Commucation 2012 Journal of communications and networks Vol.14 No.2

In this paper, we investigate the optimal packet scheduling problem in a two-user multiple access communication system, where the transmitters are able to harvest energy from the nature. Under a deterministic system setting, we assume that the energy harvesting times and harvested energy amounts are known before the transmission starts. For the packet arrivals, we assume that packets have already arrived and are ready to be transmitted at the transmitter before the transmission starts. Our goal is to minimize the time by which all packets from both users are delivered to the destination through controlling the transmission powers and transmission rates of both users. We first develop a generalized iterative backward waterfilling algorithm to characterize the maximum departure region of the transmitters for any given deadline T. Then, based on the sequence of maximum departure regions at energy arrival instants, we decompose the transmission completion time minimization problem into convex optimization problems and solve the overall problem efficiently.

Secure Broadcasting Using Multiple Antennas

Ekrem, Ersen,Ulukus, Sennur The Korea Institute of Information and Commucation 2010 Journal of communications and networks Vol.12 No.5

We consider three different secure broadcasting scenarios: i) Broadcast channels with common and confidential messages (BCC), ii) multi-receiver wiretap channels with public and confidential messages, and iii) compound wiretap channels. The BCC is a broadcast channel with two users, where in addition to the common message sent to both users, a private message, which needs to be kept hidden as much as possible from the other user, is sent to each user. In this model, each user treats the other user as an eavesdropper. The multi-receiver wiretap channel is a broadcast channel with two legitimate users and an external eavesdropper, where the transmitter sends a pair of public and confidential messages to each legitimate user. Although there is no secrecy concern about the public messages, the confidential messages need to be kept perfectly secret from the eavesdropper. The compound wiretap channel is a compound broadcast channel with a group of legitimate users and a group of eavesdroppers. In this model, the transmitter sends a common confidential message to the legitimate users, and this confidential message needs to be kept perfectly secret from all eavesdroppers. In this paper, we provide a survey of the existing information-theoretic results for these three forms of secure broadcasting problems, with a closer look at the Gaussian multiple-input multiple-output (MIMO) channel models. We also present the existing results for the more general discrete memoryless channel models, as they are often the first step in obtaining the capacity results for the corresponding Gaussian MIMO channel models.

Age of Information Games Between Power Constrained Schedulers and Adversaries

Banerjee, Subhankar,Ulukus, Sennur,Ephremides, Anthony 한국통신학회 2023 Journal of communications and networks Vol.25 No.5

We consider a time slotted communication network consisting of a base station (BS), an adversary, $N$ users and $N_{s}$ communication channels. In the first part of the paper, we consider the setting where $N_{s}$ communication channels $\mathcal{N}_{s}$ are heterogeneously divided among $N$ users. The BS transmits an update to the $i$th user on a subset of the communication channels $\mathcal{N}_{s,i}$ where $\mathcal{N}_{s,i}\cap \mathcal{N}_{s,j}$ is not necessarily an empty set. At each time slot, the BS transmits an update packet to a user through a communication channel and the adversary aims to block the update packet sent by the BS by blocking a communication channel. The BS has $n$ discrete transmission power levels to communicate with the users and the adversary has $m$ discrete blocking power levels to block the communication channels. The probability of successful transmission of an update packet depends on these power levels. The BS and the adversary have a transmission and blocking average power constraint, respectively. We provide a universal lower bound for the average age of information for this communication network. We prove that the uniform user choosing policy, the uniform communication channel choosing policy with any arbitrary feasible transmission power choosing policy is $4$ optimal; and the max-age user choosing policy, the uniform communication channel choosing policy with any arbitrary feasible transmission power choosing policy is $2$ optimal. In the second part of the paper, we consider the setting where the BS chooses a transmission policy and the adversary chooses a blocking policy from the set of randomized stationary policies and $\mathcal{N}_{s,i}=\mathcal{N}_{s}$ for all $i$, i.e., all users can receive updates on all channels. We show that a Nash equilibrium may or may not exist for this communication network, and identify special cases where a Nash equilibrium always exists.

Secure Communication in Multiple Relay Networks Through Decode-and-Forward Strategies

Bassily, Raef,Ulukus, Sennur The Korea Institute of Information and Commucation 2012 Journal of communications and networks Vol.14 No.4

In this paper, we study the role of cooperative relays to provide and improve secure communication rates through decodeand-forward (DF) strategies in a full-duplex multiple relay network with an eavesdropper. We consider the DF scheme as a basis for cooperation and propose several strategies that implement different versions of this scheme suited for cooperation with multiple relays. Our goal is to give an efficient cooperation paradigm based on the DF scheme to provide and improve secrecy in a multiple relay network. We first study the DF strategy for secrecy in a single relay network. We propose a suboptimal DF with zero forcing (DF/ZF) strategy for which we obtain the optimal power control policy. Next, we consider the multiple relay problem. We propose three different strategies based on DF/ZF and obtain their achievable secrecy rates. The first strategy is a single hop strategy whereas the other two strategies are multiple hop strategies. In the first strategy, we show that it is possible to eliminate all the relays' signals from the eavesdropper's observation (full ZF), however, the achievable secrecy rate is limited by the worst source-relay channel. Our second strategy overcomes the drawback of the first strategy, however, with the disadvantage of enabling partial ZF only. Our third strategy provides a reasonable compromise between the first two strategies. That is, in this strategy, full ZF is possible and the rate achieved does not suffer from the drawback of the first strategy. We conclude our study by a set of numerical results to illustrate the performance of each of the proposed strategies in terms of the achievable rates in different practical scenarios.

Optimal Packet Scheduling in a Multiple Access Channel with Energy Harvesting Transmitters

Jing Yang,Sennur Ulukus 한국통신학회 2012 Journal of communications and networks Vol.14 No.2

In this paper, we investigate the optimal packet scheduling problem in a two-user multiple access communication system,where the transmitters are able to harvest energy from the nature. Under a deterministic system setting, we assume that the energy harvesting times and harvested energy amounts are known before the transmission starts. For the packet arrivals, we assume that packets have already arrived and are ready to be transmitted at the transmitter before the transmission starts. Our goal is to minimize the time by which all packets from both users are delivered to the destination through controlling the transmission powers and transmission rates of both users. We first develop a generalized iterative backward waterfilling algorithm to characterize the maximum departure region of the transmitters for any given deadline T . Then, based on the sequence of maximum departure regions at energy arrival instants, we decompose the transmission completion time minimization problem into convex optimization problems and solve the overall problem efficiently.

Secure Communication in Multiple Relay Networks Through Decode-and-Forward Strategies

Raef Bassily,Sennur Ulukus,최진영 한국통신학회 2012 Journal of communications and networks Vol.14 No.4

In this paper, we study the role of cooperative relays to provide and improve secure communication rates through decodeand-forward (DF) strategies in a full-duplex multiple relay network with an eavesdropper. We consider the DF scheme as a basis for cooperation and propose several strategies that implement different versions of this scheme suited for cooperation with multiple relays. Our goal is to give an efficient cooperation paradigm based on the DF scheme to provide and improve secrecy in a multiple relay network. We first study the DF strategy for secrecy in a single relay network. We propose a suboptimal DF with zero forcing (DF/ZF) strategy for which we obtain the optimal power control policy. Next, we consider the multiple relay problem. We propose three different strategies based on DF/ZF and obtain their achievable secrecy rates. The first strategy is a single hop strategy whereas the other two strategies are multiple hop strategies. In the first strategy, we show that it is possible to eliminate all the relays’signals from the eavesdropper’s observation (full ZF), however,the achievable secrecy rate is limited by the worst sourcerelay channel. Our second strategy overcomes the drawback of the first strategy, however, with the disadvantage of enabling partial ZF only. Our third strategy provides a reasonable compromise between the first two strategies. That is, in this strategy, full ZF is possible and the rate achieved does not suffer from the drawback of the first strategy. We conclude our study by a set of numerical results to illustrate the performance of each of the proposed strategies in terms of the achievable rates in different practical scenarios.

Minimizing Age of Information with Soft Updates

Melih Bastopcu,Sennur Ulukus 한국통신학회 2019 Journal of communications and networks Vol.21 No.3

We consider an information updating system where aninformation provider and an information receiver engage in an updateprocess over time. Different from the existing literature whereupdates are countable (hard) and take effect either immediatelyor after a delay, but instantaneously in both cases, here updatesstart taking effect right away but gradually over time. We cointhis setting soft updates. When the updating process starts, theage decreases until the soft update period ends. We constrain thenumber of times the information provider and the information receivermeet (number of update periods) and the total duration ofthe update periods. We consider two models for the decrease of ageduring an update period: In the first model, the rate of decrease ofage is proportional to the current age, and in the second model, therate of decrease of age is constant. The first model results in an exponentiallydecaying age, and the second model results in a linearlydecaying age. In both cases, we determine the optimum updatingschemes, by determining the optimum start times and optimum durationsof the updates, subject to the constraints on the number ofupdate periods and the total update duration.

Secure Broadcasting Using Multiple Antennas

Ersen Ekrem,Sennur Ulukus 한국통신학회 2010 Journal of communications and networks Vol.12 No.5

We consider three different secure broadcasting scenarios:i) Broadcast channels with common and confidential messages (BCC), ii) multi-receiver wiretap channels with public and confidential messages, and iii) compound wiretap channels. The BCC is a broadcast channel with two users, where in addition to the common message sent to both users, a private message, which needs to be kept hidden as much as possible from the other user, is sent to each user. In this model, each user treats the other user as an eavesdropper. The multi-receiver wiretap channel is a broadcast channel with two legitimate users and an external eavesdropper,where the transmitter sends a pair of public and confidential messages to each legitimate user. Although there is no secrecy concern about the public messages, the confidential messages need to be kept perfectly secret from the eavesdropper. The compound wiretap channel is a compound broadcast channel with a group of legitimate users and a group of eavesdroppers. In this model, the transmitter sends a common confidential message to the legitimate users, and this confidential message needs to be kept perfectly secret from all eavesdroppers. In this paper, we provide a survey of the existing information-theoretic results for these three forms of secure broadcasting problems, with a closer look at the Gaussian multiple-input multiple-output (MIMO) channel models. We also present the existing results for the more general discrete memoryless channel models, as they are often the first step in obtaining the capacity results for the corresponding Gaussian MIMO channel models.

Age of Information in Multihop Multicast Networks

Baturalp Buyukates,Alkan Soysal,Sennur Ulukus 한국통신학회 2019 Journal of communications and networks Vol.21 No.3

We consider the age of information in a multihop multicastnetwork where there is a single source node sending timesensitiveupdates to nL end nodes, and L denotes the number ofhops. In the first hop, the source node sends updates to n first-hopreceiver nodes, and in the second hop each first-hop receiver noderelays the update packets that it has received to n further usersthat are connected to it. This network architecture continues infurther hops such that each receiver node in hop ` is connected ton further receiver nodes in hop ` + 1. We study the age of informationexperienced by the end nodes, and in particular, its scalingas a function of n. We show that, using an earliest k transmissionscheme in each hop, the age of information at the end nodes can bemade a constant independent of n. In particular, the source nodetransmits each update packet to the earliest k1 of the n first-hopnodes, and each first-hop node that receives the update relays it tothe earliest k2 out of n second-hop nodes that are connected to itand so on. We determine the optimum k` stopping value for eachhop ` for arbitrary shifted exponential link delays.

Expression of matrix metalloproteinase-2 and survivin in endometrioid and nonendometrioid endometrial cancers and clinicopathologic significance

Evren Yilmaz,Meral Koyuncuoglu,İlknur Bilkay Görken,Emre Okyay,Bahadir Saatli,Emine Cagnur Ulukus,Ugur Saygili 대한부인종양학회 2011 Journal of Gynecologic Oncology Vol.22 No.2

Objective: To determine matrix metalloproteinase-2 and survivin expressions in endometrial cancers, their relation to clinical and histologic parameters and to investigate any difference in the expression of these markers between endometrioid and nonendometrioid cancers. Methods: Ninety-five patients with endometrial cancer, were included. Matrix metalloproteinase-2 and survivin expressions were analyzed immunohistochemically from paraffin-embedded tissues by using specific monoclonal antibodies. Results: Survivin nuclear expression was higher in endometrioid cancer as compared to nonendometrioid cancer (p=0.040), but there was no difference for cytoplasmic survivin and matrix metalloproteinase-2 expressions between type I and type II carcinomas. Survivin cytoplasmic staining was significantly lower in patients with deep myometrial invasion (p=0.038). Nuclear expression of survivin is decreased in histologic grade 3 tumors compared to grade 1 and 2 tumors (p=0.013), but there is no difference between grade 1 and 2. We did not find any statistically significant difference between survivin or matrix metalloproteinase-2 expressions and survival. Conclusion: Survivin and matrix metalloproteinase-2 are present in endometrioid and nonendometrioid cancers. Grade 1 and 2 tumors and carcinomas having myometrial invasion less than 50% have higher survivin expression. These results supports that, survivin may play an important role in early stage tumors and early phases of tumor development. We did not find any association between matrix metalloproteinase-2 expression and classical prognostic factors in endometrial cancer and both proteins were not associated with survival. Objective: To determine matrix metalloproteinase-2 and survivin expressions in endometrial cancers, their relation to clinical and histologic parameters and to investigate any difference in the expression of these markers between endometrioid and nonendometrioid cancers. Methods: Ninety-five patients with endometrial cancer, were included. Matrix metalloproteinase-2 and survivin expressions were analyzed immunohistochemically from paraffin-embedded tissues by using specific monoclonal antibodies. Results: Survivin nuclear expression was higher in endometrioid cancer as compared to nonendometrioid cancer (p=0.040), but there was no difference for cytoplasmic survivin and matrix metalloproteinase-2 expressions between type I and type II carcinomas. Survivin cytoplasmic staining was significantly lower in patients with deep myometrial invasion (p=0.038). Nuclear expression of survivin is decreased in histologic grade 3 tumors compared to grade 1 and 2 tumors (p=0.013), but there is no difference between grade 1 and 2. We did not find any statistically significant difference between survivin or matrix metalloproteinase-2 expressions and survival. Conclusion: Survivin and matrix metalloproteinase-2 are present in endometrioid and nonendometrioid cancers. Grade 1 and 2 tumors and carcinomas having myometrial invasion less than 50% have higher survivin expression. These results supports that, survivin may play an important role in early stage tumors and early phases of tumor development. We did not find any association between matrix metalloproteinase-2 expression and classical prognostic factors in endometrial cancer and both proteins were not associated with survival.